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Variable reverberation in performance spaces: Passive and active acoustic systems
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Variable reverberation in performance spaces: Passive and active acoustic systems
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Content
VARIABLE REVERBERATION IN PERFORMANCE SPACES:
PASSIVE AND ACTIVE ACOUSTIC SYSTEMS
by
Elizabeth Valmont
____________________________________________________________
A Thesis Presented to the
FACULTY OF THE SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the Requirements of the Degree
MASTER OF BUILDING SCIENCE
December 2005
Copyright 2005 Elizabeth Valmont
UMI Number: 1435121
1435121
2006
UMI Microform
Copyright
All rights reserved. This microform edition is protected against
unauthorized copying under Title 17, United States Code.
ProQuest Information and Learning Company
300 North Zeeb Road
P.O. Box 1346
Ann Arbor, MI 48106-1346
by ProQuest Information and Learning Company.
ii
ACKNOWLEDGEMENTS
It is difficult to explain in words how grateful I am to my invaluable and brilliant committee
members for their guidance and patience through the duration of my thesis process. I am so
honored to have been able to work so closely with all of you.
I would like to thank Professor Marc Schiler for his counsel, encouragement and wisdom. I owe a
great deal to Dr. Douglas Noble for his constant inspiration, profound criticism and unrelenting
confidence in me. Professor Schiler and Dr. Noble presented me with challenges and
opportunities beyond the breadth of building science.
I would like to especially thank Jerry Christoff for his direction, motivation and ability of helping
me understand difficult concepts very easily. You were always there when I needed you most.
I would like to thank Anthony Hoover for his advice and knowledge from the other coast. Thanks
are also due to Jack Hayback and Kevin Goold for their technical guidance and support.
I thank my brother and sisters for their patience putting up with me and their support.
Lastly, I thank my father and mother who made me take piano lessons, always believed in me
with so much pride and encouraged my ambition.
iii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ............................................................................................. ii
LIST OF TABLES ........................................................................................................... vi
LIST OF FIGURES ........................................................................................................ vii
ABSTRACT .................................................................................................................... xi
Chapter 1 Multipurpose Auditorium............................................................................ 1
1.1.0 Introduction..............................................................................................................1
1.2.0 Optimal Acoustic Environment ..............................................................................2
1.2.2 Extending the Perceptual Experiences of Sight and Sound .............................4
1.2.3 Tuning Spaces ......................................................................................................5
Chapter 2 Historical Background of Performance Spaces ......................................... 7
2.1.0 Spatial Impact on the Quality of Musical or Lyric Sound ...................................7
2.2.0 History of Performance Spaces...............................................................................8
2.3.0 Development of the Multipurpose Auditoria.......................................................11
2.4.0 Performance Space Typologies .............................................................................13
Chapter 3 Physical Characteristics of Acoustical Parameters ................................. 15
3.1.0 Acoustic Impression of Space by an Audience ....................................................15
3.2.0 Acoustic Impression of Space by Performers ......................................................19
3.3.0 Acoustical Faults ....................................................................................................20
3.4.0 Architectural Importance of Reverberance.........................................................21
3.4.1 Optimum Reverberation Time for Performance Categories.........................21
3.4.2 Impulse Response...............................................................................................24
3.5.0 Variable Acoustic Methods ...................................................................................25
Chapter 4 Passive Variability ...................................................................................... 27
4.1.0 Passive Variability in Performance Spaces..........................................................27
4.2.0 Advantages and Disadvantages of Passive Techniques.......................................34
4.3.0 Case Studies: Architectural/Physical Variability................................................36
4.3.1 Lucerne Culture and Congress Center (KKL) ...............................................36
4.3.2 Verizon Hall .......................................................................................................39
4.3.3 Segerstrom Hall..................................................................................................41
4.3.4 Meyerson Symphony Center.............................................................................43
4.3.5 Symphony Hall...................................................................................................45
4.4.0 Summary of Passive Case Studies.........................................................................46
Chapter 5 Active Variability........................................................................................ 48
5.1.0 Electronic Variability in Performance Spaces.....................................................48
iv
5.2.0 The Functions of Active Variability .....................................................................49
5.3.0 Types of Active Systems.........................................................................................51
5.4.0 Advantages and Disadvantages of Active Techniques ........................................54
5.5.0 Case Studies: Electronic Variability ................................................................55
5.5.1 Royal Festival Hall.............................................................................................55
5.5.2 Tokyo International Forum ..............................................................................56
5.5.3 Adelaide Festival Center Theatre.....................................................................57
5.5.4 The Prague Congress Center ............................................................................58
5.6.0 Summary of Active Case Studies ..........................................................................59
Chapter 6 Quantifying Variable Acoustic Methods .................................................. 61
6.1.0 Selecting a Method: Vary Reverberation Time...................................................61
6.2.0 Objective and Approach........................................................................................61
6.3.0 Quantitative Process ..............................................................................................62
6.3.1 Acoustical Measurements of Existing Performance Space ............................62
6.3.2 Simulated Computerized Prediction................................................................62
6.3.3 Analytic Calculation Using the Eyring Equation............................................63
Chapter 7 Acoustical Measurements of an Existing Performance Space................ 64
7.1.0 Case Study Selection ..............................................................................................64
7.2.0 Objective .................................................................................................................69
7.3.0 Acoustical Measurements......................................................................................69
7.3.1 Test Equipment..................................................................................................70
7.3.2 Measuring Conditions and Setup .....................................................................71
7.4.0 Results – Reverberation Time Measurements.....................................................73
7.5.0 Summary.................................................................................................................74
Chapter 8 Simulated Computer Predictions .............................................................. 75
8.1.0 Objective .................................................................................................................75
8.2.0 Components and Conditions .................................................................................75
8.3.0 Results .....................................................................................................................76
8.4.0 Summary.................................................................................................................87
Chapter 9 Analytic Calculation Using the Eyring Equation..................................... 88
9.1.0 Objective .................................................................................................................88
9.2.0 Component and Results.........................................................................................88
9.3.0 Summary.................................................................................................................89
Chapter 10 Comparison of Quantitative Methods....................................................... 90
10.1.0 Comparing Reverberation Times .........................................................................90
10.2.0 Unexpected Results ................................................................................................90
10.3.0 Summary.................................................................................................................92
Chapter 11 Conclusion and Future Research .............................................................. 93
11.1.0 Conclusions .............................................................................................................93
11.2.0 Future Research .....................................................................................................94
v
BIBLIOGRAPHY........................................................................................................... 95
GLOSSARY ...............................................................................................................99
APPENDIX A Variable Passive Methods ................................................................ 100
APPENDIX B Variable Active Methods.................................................................. 101
APPENDIX C Analytic Eyring Calculation Spreadsheets ..................................... 103
vi
LIST OF TABLES
Table 1: Acoustical Parameters affecting the audience area............................................................3
Table 2: Acoustical Parameters affecting the performance area......................................................4
Table 3: Preferred values of acoustical parameters in concert halls, opera houses and chamber
music halls...............................................................................................................................6
Table 4 Zwicky Box - morphology for performance space types..................................................14
Table 5: Recommended occupied reverberation times ..................................................................22
Table 6: Appropriate Reverberation Time.....................................................................................22
Table 7: Passive Case Studies........................................................................................................47
Table 8: In-Line Systems...............................................................................................................51
Table 9: Non-In-Line Systems.......................................................................................................52
Table 10: Active Case Studies .......................................................................................................60
Table 11: Measured RT
60
of Cerritos Center Configurations ........................................................73
Table 12: Simulated CATT Acoustical Results.............................................................................76
Table 13: Analytic RT Results.......................................................................................................89
Table 14 Reverberation Time Summary of all Quantification Methods........................................90
vii
LIST OF FIGURES
Figure 1: Impulse Response Diagram............................................................................................24
Figure 2: Drawings of moveable curtains/ louvers/ panels............................................................28
Figure 3: Drawings of moveable curtains/ louvers/ panels............................................................28
Figure 4: Orchestral ceiling panels adjusted for a concert performance (McCain Auditorium,
Kansas State University, Manhattan, Kansas).......................................................................29
Figure 5: Orchestral ceiling panels removed for an opera performance (McCain Auditorium,
Kansas State University, Manhattan, Kansas).......................................................................30
Figure 6: Ceiling over audience adjusted for a concert performance (Auditorium, Fine Arts
Center, Viterbo College, La Crosse, Wisconsin) ..................................................................31
Figure 7: Ceiling over audience adjusted for a drama/theatre performance (Auditorium, Fine Arts
Center, Viterbo College, La Crosse, Wisconsin) ..................................................................32
Figure 8: Use of electro-acoustic coupling for stage-to-hall transfer of reverberant sound for
adjustable reverberance.........................................................................................................33
Figure 9: Reverberant chamber diagram of Meyerson Hall...........................................................34
Figure 10: KKL House Interior......................................................................................................36
Figure 11 (a-c): KKL, Views of concert hall towards the reverberation chambers and moveable
wall panels of concert hall.....................................................................................................37
Figure 12: KKL, plan view, reverberant chambers.......................................................................38
Figure 13: Verizon Hall, interior view...........................................................................................39
Figure 14: Verizon Hall , orchestral view .....................................................................................39
Figure 15: Verizon Hall, plan view, reverberant chambers around the perimeter of the audience
chamber ................................................................................................................................40
Figure 16: Segerstrom Hall, view towards stage ...........................................................................41
viii
Figure 17: Segerstrom Hall, detailed section.................................................................................42
Figure 18: Segerstrom Hall, plan view .........................................................................................42
Figure 19: Eugene McDermott Concert Hall, interior view ..........................................................43
Figure 20: Meyerson Hall, sections and axonometric....................................................................44
Figure 21: Meyerson Hall, plan view ............................................................................................ 44
Figure 22: Symphony Hall, interior view ......................................................................................45
Figure 23: Symphony Hall, plan....................................................................................................46
Figure 24: Symphony Hall, section ...............................................................................................46
Figure 25: Simple Digital Signal Processing audio system ...........................................................48
Figure 26: Electro-acoustic reverberation system..........................................................................50
Figure 28: Auditorium Synthesis - a research tool or a device for studying the influence of direct,
envelopment and reverberant sound on music and speech....................................................53
Figure 29: Royal Festival Hall, interior view ................................................................................55
Figure 30: Tokyo International Forum, proscenum view ..............................................................56
Figure 31: Tokyo International Forum, view of seating ................................................................56
Figure 32: Adelaide Festival Center Theatre .................................................................................57
Figure 33: Adelaide Festival Center Theatre .................................................................................57
Figure 34: Prague Congress Center ...............................................................................................58
Figure 35: Prague Congress Center ...............................................................................................58
Figure 36 (a-f): Six seating configurations at the Cerritos Center .................................................65
Figure 37: Cerritos Center, Plan view of variable configuration mechanics .................................66
Figure 38: Cerritos Center, Axonometric model of variable configuration mechanics .................67
Figure 39: Axonometric model of the Cerritos Center of Performing Arts (CCPA 2005)............68
Figure 40: Cabaret Configuration ..................................................................................................69
Figure 41: Lyric Configuration......................................................................................................69
ix
Figure 42: White curtains drawn and exposed behind balconies of side seating tower.................70
Figure 43: Audio Toolbox
TM
..........................................................................................................70
Figure 44: Acoustic measuring setup, Receiver 80 feet from Source............................................70
Figure 45: Cabaret unoccupied ......................................................................................................71
Figure 46: Diagram of source and receiver locations, Cabaret configuration in section (top) and
plan (below) ..........................................................................................................................71
Figure 47: Lyric unoccupied..........................................................................................................72
Figure 48: Diagram of source and receiver locations, Lyric configuration in section (top) and
plan (below) ..........................................................................................................................72
Figure 49: AutoCAD wireframe models for (a) Cabaret (top) and (b) Lyric (bottom)
configurations........................................................................................................................75
Figure 50: Geometry without curtains (left) ..................................................................................78
Figure 51: Geometry with curtains (right) .....................................................................................78
Figure 52: Echogram without curtains (left)..................................................................................79
Figure 53: Echogram with curtains (right).....................................................................................79
Figure 54: RT without curtains (left) .............................................................................................79
Figure 55: RT with curtains (right)................................................................................................79
Figure 56: Impulse Response without curtains (left) .....................................................................80
Figure 57: Impulse Response with curtains (right)........................................................................80
Figure 58: SPL in audience area without curtains (left) ................................................................80
Figure 59: SPL in audience area with curtains (right) ...................................................................80
Figure 60: LEF without curtains (left) ...........................................................................................81
Figure 61: LEF with curtains (right)..............................................................................................81
Figure 62: C-80, SPL, D-50 without curtains (left) .......................................................................81
Figure 63: C-80, SPL, D-50 with curtains (right)..........................................................................81
x
Figure 64: LF, G RT without curtains (left)...................................................................................82
Figure 65: LF, G RT with curtains (right) .....................................................................................82
Figure 66: Geometry without curtains (left) ..................................................................................83
Figure 67: Geometry with curtains (right) .....................................................................................83
Figure 68: Echogram without curtains (left)..................................................................................83
Figure 69: Echogram with curtains (right).....................................................................................83
Figure 70: RT without curtains (left) .............................................................................................84
Figure 71: RT with curtains (right)................................................................................................84
Figure 72: Impulse Response without curtains (left) .....................................................................84
Figure 73: Impulse Response with curtains (right)........................................................................84
Figure 74: SPL in audience area without curtains (left) ................................................................85
Figure 75: SPL in audience area with curtains (right) ...................................................................85
Figure 76: LEF without curtains (left) ...........................................................................................85
Figure 77: LEF with curtains (right)..............................................................................................85
Figure 78: C-80, SPL, D-50 without curtains (left) .......................................................................86
Figure 79: C-80, SPL, D-50 with curtains (right)..........................................................................86
Figure 80: LF, G RT without curtains (left)...................................................................................86
Figure 81: LF, G RT with curtains (right) .....................................................................................86
xi
ABSTRACT
Architectural acoustical design impacts the sonic and architectural environment. Historically,
architects and acousticians concentrated their efforts in satisfying the acoustic parameters for
performance spaces with single functions; thus building single spaces for single functions. It
would be less expensive and wasteful to provide excellent acoustics for all purposes, ranging
from speech to music, in a single space. Therefore, the advent of multipurpose spaces has created
design challenges for professionals to develop a range of acoustical environments in one static
room and has advanced the acoustical technology of architectural (passive) and electronic (active)
components to suit various performances. A variable acoustical ambience, appropriate to the
event, can be accomplished through purely architectural means, electronic enhancement or a
combination of both, to satisfy the acoustical requirements of most functions. This thesis
addresses the variable acoustic technology available to satisfy most performance functions in a
multipurpose space and its affect on reverberation time.
1
Chapter 1 Multipurpose Auditorium
1.1.0 Introduction
This season La Traviata is playing at the Dorothy Chandler Pavilion in Los Angeles. I usually
race to buy tickets for my family to our favorite operas in order to get the best seats in the house
before they sell out. However, my father is an ‘opera buff’ who will go to the performance under
the stubborn condition he gets the best seats in the house. For him and many other music
aficionados, the “best seat in the house” implies the reception of the “best” musical experience in
the house. In most cases, different seating locations in typical opera houses and concert halls can
have very different acoustical impressions. The “best” sound experience is part of the subjective
acoustical impression of a space that is, of course, in the ear of the beholder.
Creating the perfect acoustic in a performance space is a subjective phenomena no matter how
much science is involved since every individual’s ear perceives sound differently. However,
combining hundred year old acoustical methods which have satisfied the masses combined with
the latest acoustic technology seems to satisfy most architects, acousticians, musicians, music
critics and audience members.
In the brief existence of the formal science of performance space acoustical design,
multifunctional auditoriums are becoming more popular and consequently new acoustical
challenges have surfaced. A multifunctional space means that various programmatic events occur
in a single room at different times. When a range of functions, from lectures to symphonic
recitals, occupy a performance space, there is significant variability in what is acoustically
required. Therefore, the type of science applied to these spaces is referred to as “variable
acoustics,” where one can alter the acoustical environment by architectural or electronic means.
However, there lies the challenge in designing an auditorium space for many sound
2
environments. The acoustician and architect can not optimize the hall for only a single function
but instead must design to meet satisfactory conditions for all sound environments.
What we hear in room acoustics is a combination of direct sound and indirect sound reflections
from the materials and objects in a space. One of the challenges in architectural acoustics is how
to go about manipulating the sound reflections in a room. The fundamental understanding of
room acoustics begins with the surfaces of a space. When sound strikes a receiving surface it is
absorbed, transmitted or reflected. The reflected sound can be “attenuated by a sound absorbing
surface, re-directed by a reflecting surface or scattered by a diffusing surface.”
1
In order to
achieve great sound for every seat in the house sound reflections need to be designed to give
everyone “clear and intelligible speech and music with good tonal balance that has impact
liveliness and a rich enveloping sound field.”
2
1.2.0 Optimal Acoustic Environment
Most lay persons know the difference between “good” sound (speech, music, nature) and “bad”
sound (engines, fans, sirens). Acousticians and most architects can determine the sound quality of
a given architectural environment based on the program use of the space. A symphony hall is a
poor environment for amplified popular entertainment and a Gothic cathedral is a poor
environment for the spoken word.
3
The successful design or tuning of a performance space is
based on “the psycho-acoustic response of human beings, particularly those who might be defined
as experienced or trained listeners.”
4
To design optimal conditions of a performance space,
importance is given to two groups of listeners: the audience and the musicians. An acoustical
balance between the two types of occupants is necessary for optimal communication of sound.
1
RPG Diffusor Systems, Inc. 2000
2
Barbar 2005
3
Jaffe et al. 1999, p.7
4
Jaffe et al. 1999, p.1
3
For example, Jaffe Holden Scarborough Acoustics, acoustical consultants, refined a chart (see
Tables 1 and 2) which explains how subjective musical terms correlate with physical acoustical
criteria. Their research was taken from an initial chart composed by an expert of concert hall
acoustics, Leo Beranek.
Table 1 and Table 2 (shown below) translate musical vocabulary like liveliness, clarity, intimacy,
warmth, loudness, brilliance diffusion, ensemble, balance and blend
5
into architectural
vocabulary. The definition of these terms and their impact on architecture will be further
explained in succeeding chapters, but the charts below clarify the translations between musical
language, scientific language and architectural language. Table 1 caters to the acoustical
impressions received by the audience like liveliness or clarity which are directly related to the
acoustical parameter, reverberance. Presence and brilliance are related to the strength of the early
or first sound reflections which arrive at the audience. Warmth or bass sounds are controlled by
the arrival time of the lower frequencies.
Table 1: Acoustical Parameters affecting the audience area (Jaffe et al. 1999, p.2)
5
Jaffe et al. 1999, p.1
4
The acoustical parameters for the orchestral platform, Table 2, are equally important as those in
the audience area and deeply influence the overall experience of the audience’s impression.
Musicians should hear the instruments from one end of the stage to the other which influences the
sense of ensemble. Orchestral balance also influences the sense of ensemble, but also affects how
loud the audience perceives different parts of an orchestra; the architecture of the stage can
balance the strength of the soloists against the percussion section of the orchestra.
Table 2: Acoustical Parameters affecting the performance area (Jaffe et al. 1999, p.3)
The challenge is to increase the listener’s awareness of these aural parameters so they may have
the “best” performance experience.
1.2.2 Extending the Perceptual Experiences of Sight and Sound
Sound is a part of every space, but architects give most importance to their sense of sight. Unlike
most other building programs, the fundamental nature of a performance space gives importance to
the sense of sound and our ears become a major design tool as oppose to our sight. Variable
acoustics is one way to extend the sensory scope of auditorium spaces since it not only entails the
manipulation of sound but also the composition of the architectural configurations. Ultimately,
the audience member is receiving a single aesthetic experience when enjoying a performance
since their sight and sound is being stimulated at the same time.
5
1.2.3 Tuning Spaces
Every sound has an ideal space; therefore every space must be tuned for that sound. One way to
tune a space is by measuring if it has an appropriate reverberant field. Architects can physically
alter the reverberant field and other acoustic requirements for functions like effective speech
intelligibility to rich symphonic music.
For example, to achieve effective speech one needs:
6
• to reduce the distance between the sound source and the audience
• favor reflections that come from the direction of the sound source
• use surface treatments to reduce reflections and reverberation that detract from
intelligibility
• minimize noise intrusion, e.g. mechanical systems
For symphonic music one provides:
7
• early reflections that increase impact and blend sound sources
• contour the later reflected energy from the sides and rear
• incorporate of surface treatments that produce reverberation that envelops the listener.
6
Barbar, Steven, Acoustic Environment
7
Barbar 2005
6
The recommended acoustic for the preceding examples requires opposing acoustical conditions
and is well known by sound designers. However, these same methods of tuning a space for a
function can also be induced artificially though digital sound processing (DSP) methods.
Leo Beranek composed a table (Table 3) which suggests appropriate values of acoustical
parameters (defined in section 3.0.0) for a given performance condition. Referencing tables such
as these allows one to know what range of acoustical values should be achieved in their designs.
The succeeding sections will further explain both passive and active methods of tuning spaces,
how architectural features influence the sound environment and how developments in digital
signal processing have led to the evolution of electronic acoustical enhancement. The analysis of
how the advancement of these systems affect the important acoustical factor of reverberation time
will also be reviewed.
Table 3: Preferred values of acoustical parameters in concert halls, opera houses and chamber music
halls. (Beranek 2004, p.536)
Reverberation Time Source Strength
Clarity Initial Time
Delay Gap
7
Chapter 2 Historical Background of Performance Spaces
The science of architectural acoustics formally developed only within the last one hundred years.
Before this advanced knowledge, performance spaces were designed through a process of trial
and error, and precedent. If a concert hall was successful in creating a desirable impression upon
its patrons then it was emulated; thus, the “shoebox” geometry for example.
2.1.0 Spatial Impact on the Quality of Musical or Lyric Sound
Different instruments are influenced by the performance space. Depending on the desired
dynamic, a violinist appreciates some reverberation from an auditorium because it can potentially
give notes a robust quality or elongates notes to give a seamless sound. A pianist has more
control of their performance than a violinist since the “soft pedal” can dampen their notes, and the
instrument itself is reverberant and can create a range of dynamics. On the other hand, the pipe
organ cannot control reverberation and very much depends on the architecture of the space to
create reverberance. Throughout history, performances spaces were often shaped by the
prevailing music of the time
8
and the music was influenced by the popular instrument of the time.
Sound behaves differently with respect to the spatial volume. Early composers were limited in
performance spaces available to them and therefore designed the music to suit the space.
Baroque music was played in small auditoria; followed by music of the Classical era where the
performance spaces were larger in cubic volume; and lastly music of the Romantic era was
performed in spaces much larger than the predecessors. The larger the space the more
reverberant, however, to prevent a loss of articulation, speech and amplified music require
improved acoustic qualities such as shorter reverberation times, an absence of echoes and strong
8
Beranek 2004, Ch.1
8
early frontal reflections for loudness. Symphony orchestras need to have a longer reverberation
times in order to create smoother elongated sounds to blend with other voices of the orchestral
instruments; lateral reflections are more important to give the audience a sense of envelopment
and spaciousness.
The reverberation appropriate for an orchestra in a concert hall would not be appropriate for
opera performances where excellent speech intelligibility is needed. Although opera does need
strong early frontal reflections for voices to be audible it also requires the orchestra to blend the
sounds from the pit to not overpower the singer, so the reverberation time encompass short and
long reverberation times.
9
2.2.0 History of Performance Spaces
The four periods of music which shaped music halls forever are Baroque, Classical, Romantic,
and Contemporary. Each period possesses a musical style shaped by the instruments of the age
and on the size and type of space it was performed. Before the first of the musical eras which
defined music history, Gregorian chant was a form of monophonic music developed by the
Catholic Church around 800 – 1000. This music was traditionally sung in religious spaces, most
commonly Cathedrals, where the reverberation time is very long because of the hard, sound
reflecting surfaces.
Baroque Period (1600 - 1750)
Baroque music is classified as “highly rhythmic, harmonic-thematic balance in which voice and
instrument [are] frequently combined and the parts were not all of equal melodic interest.”
10
This
style of music was called contrapuntal because it combines different independent melodic voices
9
Matheson 1999
10
Beranek 2004, p.8
9
in a single harmonic composition which would require shorter reverberation times in order to hear
the harmonic relationship of the lines.
Well known composers of the Baroque period such as Handel, Bach, and Vivaldi composed
music in this contrapuntal style. At the time, the church and court usually commissioned musical
works to be performed in their respective cathedrals or royal courts. These spaces were
acoustically divergent from each other: one highly reverberant and the other with high definition
and low fullness of tone. Baroque orchestral music was usually performed in dry acoustic spaces
like rectangular ballrooms.
Classical Period (1750 - 1820)
The most famous composers of this time were Mozart, Beethoven and Haydn. This period
developed classical symphonies and sonatas, but did not have a contrapuntal emphasis. Instead
the music followed a theory of melody and harmony, an operatic idea of where a tune is
supported by an accompaniment. Halls built in the latter part of the 18
th
century still reflected
court halls instead of the orchestral halls since most were rectangular, held a small capacity of
people (i.e. 400) and had short reverberation times. Not until the middle of the 19
th
century did
the construction of the first large concert hall occur. They were still rectangular in shape with an
influence of court halls, but had longer reverberation times and held a greater capacity of people,
such as Boston Music Hall, which opened in 1863.
11
Romantic Period (1820 – 1900)
Unlike the music of the Baroque and Classical eras, different voices in a musical composition did
not have distinct clear and linear melodies. Larger performance spaces were needed in this era of
music as a result of larger audiences in contrast to chamber music which was performed in small
11
Beranek 2004, p.10-11
10
spaces only for the aristocracy. Furthermore, orchestras also became larger and required a
performance hall that would support music with a high fullness of tone and a lower definition;
therefore a longer reverberation time (RT) was required between 1.9 to 2.1 seconds. Wagner and
Berlioz were famous composers of this time. Halls like the Grosser Musikvereinsaal were built
specifically for concert performance to achieve an acoustical ambiance with high fullness of tone
and less clarity.
12
Contemporary Period (1900 – present)
Currently, the surge in performance culture is well established in Europe and the Americas,
however Japan has recently excelled in concert music. Today, new buildings and renovated
buildings are trying to accommodate the earlier styles of music as well as the development of
more contemporary compositions. Composers of the 20
th
century compose with a wide range of
variety: size, sound, new instruments and new effects. New experiments with sound are not
composed with conventional instruments but with an electronics laboratory, tape machine, and
computer. To meet the needs of most modern music, a modern hall needs to accommodate a
variety of styles.
13
European Opera
One interesting note is that the European opera house design has remained consistent for quite a
while, the classic horseshoe shape, like in Milan’s La Scala. It is probable that the form was based
upon the need for the aristocracy to see each other from the box seating. This sort of hall needs to
have a relatively short reverberation time for speech intelligibility even though it is also meant for
orchestral performance. The design for the auditorium also requires certain programmatic
requirement like the areas for props and changes of scene, like the fly space.
12
Beranek 2004, p.12
13
Beranek 2004, p.13-14
11
Usually composers produced work according to the zeitgeist, “the spirit of the age.” Therefore,
music has reflected the time in which it was written because it followed the acoustical ambience
in the available performance spaces. However, with the advancement of acoustical technology,
musical compositions do not need to follow acoustics. Instead, performance spaces can now be
designed to cater to the music; e.g. the Walt Disney Concert Hall of Los Angeles was specifically
designed to house the Los Angeles Philharmonic. But a space built for a single purpose is also
limited to this type of performance. In an effort to achieve the perfect acoustical environment for
many types of compositions, multipurpose auditorium design has moved forward especially with
the advent of variable acoustic methods.
2.3.0 Development of the Multipurpose Auditoria
The evolution of the multipurpose auditoria is mostly fiscally driven. Prior to the 19
th
century,
musical venues were funded and housed typically by the church or royalty. At the advent of the
contemporary era, the industry of music extensively commercialized so that great seating
capacities and the demand for performance diversity became capitally driven. Therefore, the
surge of greater revenue necessitates variations of seating geometries, audience capacities and
acoustical characteristics which consequently, affect the architecture.
The notion of a multipurpose space is nothing new because at every era a performance space has
been used for different purposes other than those for which they were specifically designed, such
as opera houses that were used as ballrooms or banquet halls in the past. Most of the reasons to
reuse a facility, whether in the past or currently, have been economically driven. Izenour lists
three motives:
14
1. Expenditure of capital funds required to get a building designed and built
2. Use factor
14
1977, p.307
12
3. Maintenance costs, once it is operating.
However, architects are conscious that the reuse of a space, depending on its function, requires
acoustical adjustments or at least electronic enhancement to create any necessary changes in
sound. Spaces used for opera have less resonance than spaces designed for a symphony because
of the need for speech intelligibility. Cathedrals are appropriate spaces for Gregorian chant
because of their reflective surfaces properties which provide for a longer reverberation time.
The major problem with multipurpose performing arts facilities is that the reverberation that
enhances the sound of music is what makes speech intelligibility difficult. The classic “shoebox”
configuration, a rectangular plan with proportions similar to a shoebox, is desirable for music
because it generates more early lateral reflections compared to the fan-shaped configuration. But
this shoebox shape is not ideal for drama or theatre because it pushes the audience further from
the stage.
15
Reverberation has an important role in the quality of music and speech; and through observations
and research, acousticians have selected “optimal” values of reverberation times for various types
of performance spaces and performance categories. When a space has many highly reflective hard
surfaces the reverberation time will be very long and the space is considered “live.” If a space
has a long reverberation time, “music clarity and speech intelligibility will generally suffer unless
the ratio of direct to reverberant sound level can be increased.”
16
Therefore in a multi-functional
space it is difficult to assign a single optimal reverberation time since different uses require
different times; there needs to be some design flexibility.
15
Prissen and Antonio, p.2
16
Christoff 2005, personal communication
13
“A widely held conviction is that a multi-purpose design cannot serve any one performance type
well. I am convinced this is a myth. In fact, I have come to the belief that the best concert hall
can be achieved in the opera-stage house configuration.”
17
2.4.0 Performance Space Typologies
Architects play a pivotal role when attempting to design a single or multipurpose performing arts
facility with or without an acoustical consultant because they are chiefly responsible for its
design. Recognizing the various performance functions and controlling the various architectural
attributes which go in them can be confusing, if not overwhelming.
Approaching a morphological box
18
seemed a technique useful in exploring potential
performance space typologies. The tool defines all possible performance spaces that exist. This
method does not reduce the number of possible types an architect could use in his/her design, but
instead eliminates illogical variations explored.
17
Veneklasen 1974, p.23
18
Fritz Zwicky developer of morphology systems and applications.
14
Table 4 Zwicky Box - morphology for performance space types
15
Chapter 3 Physical Characteristics of Acoustical Parameters
Architectural characteristics of an auditorium influence its acoustic properties. These acoustic
properties can be designed per program function and dictate the subjective audible experience for
the listener. The subjective experience is a response to the acoustic condition and therefore must
be quantified to dictate architectural characteristics.
3.1.0 Acoustic Impression of Space by an Audience
A number of acoustical parameters contribute to the classification of sound and music. However,
the acoustic parameters are translated objectively for architects and acoustic consultants and
subjectively for patrons and musicians of the performing arts. The means of understanding an
acoustical impression may be different but the design and experience is same.
The following acoustical parameters are used to design the appropriate space for the optimum
audience impression: Reverberance, Warmth, Clarity, Intimacy, Sound Level, Diffusion,
Apparent Source Width, Envelopment and Texture.
Reverberence is recognized when sound persistently lingers. Running reverberation is
experienced when there is no complete reverberant decay and few long pauses occur in the
music.
19
Reverberation time (RT
60
) in seconds is calculated acoustically with the Sabine Formula [RT
60
=
0.49 V / A ], (definition page 29). This acoustical attribute can be designed architecturally in a
performance space with consideration to the cubic volume and total surface area absorption
19
Polletti 2005
16
characteristics. “Assuming that sound absorbing materials are kept to a minimum, the design
volume per person for a modern concert hall should be approximately 300 ft
3
/person for
rectangular halls and higher for in-the-round halls.”
20
The geometry of the auditorium will also
affect of the resultant reverberation time since the shape and proportions of surfaces may have
different sound absorption coefficients. Any furnishings and/or surface finishes may also induce
sound reflections depending on their absorptive attributes. Audience capacity and seat spacing are
also important in calculating reverberation time since an auditorium measured while occupied
versus unoccupied will create a difference in sound quality.
Warmth is recognized by the audience when bass sound (or lower frequencies) is louder than
treble sound (or higher frequencies).
21
As a caveat, the reverberation time of different frequencies
vary per room, however it normally decreases at higher frequencies due to sound absorption of
the air and lasts a bit longer at lower frequencies. Therefore the RT
60
is usually larger at bass
frequencies creating that sense of warmth.
This attribute is measured acoustically with bass ratio (BR) between the absorption of low
frequencies to mid-frequencies. A bass ratio more than 1.2 is typically preferred.
Normally, creating a greater sense of warmth architecturally requires thick and heavy enclosing
surfaces. The geometry of the space is recommended to have a height to width ratio greater than
0.7 and size and shape of the side walls should be sound-reflecting. Adding coupled spaces to the
stage-house and perhaps an under-stage moat also contribute to warmth.
Clarity (C
80
) is recognized by the audience when notes are clearly distinct from each other at the
beginning of musical lines or when speech is easy to understand. Early reflections that arrive soon
20
Christoff 2005, personal communication
21
Egan 1988, p.147
17
after the direct sound tend to be integrated with the direct sound by the listener, and therefore
contribute to intelligibility.
22,23
Intimacy is recognized when the source of musical sound seems as though it’s being played in a
small room regardless of the size.
Both clarity and intimacy depend upon sound that reaches the audience’s ears a short time after
the direct sound. They are measured acoustically when the initial-time-delay gap between the
direct sound and the initially reflected sound is less than 20ms; the impulse response of a space
will have a larger early energy component than the later energy component. Impulse response
will be explained in further detail in succeeding sections Clarity can be analytically measured
based upon the logarithmic ratio of the early to late sound energy and intelligibility can be
measured with other calculations as the transmission index or articulation loss.
24,25
A greater sense of intimacy or clarity can be achieved architecturally when the length-to-width
ratio of the room is less than 2 or suspended sound-reflecting canopies or panels are used near the
platforms or stage. In addition, deep under-balconies may also be used to improve clarity because
the seats are shielded from the reverberant sound.
Dynamic range or sound level (G) is important for dramatic effect.
26
It is appreciated when direct
and reverberant sounds are comfortable at louder passages yet audible at weaker ones. The sound
22
Egan 1988, p.147
23
Poletti 2005, p.2
24
Egan 1988, p.147
25
Poletti 2005, p.2
26
Orlowski 1999, p. 238
18
level depends upon the sound source, the distance to the listener and the room sound
absorption.
27, 28
Sound level is measured acoustically in decibel units. It can be increased architecturally with a
strategic distribution of sound-reflecting finishes and the avoidance of excess sound absorption.
An orchestral enclosure utilized in a multi-purpose auditorium with a stage house and sound-
reflecting surfaces at the front end of the hall usually in the form of a canopy, also increases
sound level.
Diffusion is recognized by the performance occupant when enveloped by the ending sounds of
music, the total immersion of sound.
Diffusion has been acoustically quantified only recently with the high correlation demonstrated
between surface diffusivity and acoustical quality. The impression of diffusion can be augmented
architecturally by designing large-scale wall and ceiling irregularities. The shape and proportion
of the room create greater diffusion when they geometrically have narrower widths and greater
height-to-width ratios. The reflections from finishes and furnishings will also create a greater
sense of diffusion. These irregularities cause incident sound to be scattered in different directions,
thereby increasing diffusivity in the sound field.
29, 30
Envelopment is recognized when musical sound is surrounding you; the impression of being
enveloped.
27
Egan 1988, p.147
28
Poletti 2005, p.2
29
Egan 1988, p.151
30
Poletti 2005, p.3
19
Envelopment is acoustically quantified with an impulse response measuring the amount of lateral
energy arriving at the latter part of the response. This impression can be augmented
architecturally by surfaces on the sidewalls that reflect sound across the audience; thereby
creating a reasonably high reverberation time and a greater sound field of diffusion.
31
Texture is recognized when a single reflection after the direct sound creates a different subjective
impression as compared to other smaller reflections of the same sound intensity. Greater texture
creates a smooth image of sound quality which can be achieved architecturally by increasing
early reflections.
32
3.2.0 Acoustic Impression of Space by Performers
Everyone in performance auditoria are affected by the sound exerted from the source, including
performers, who create the source of sound. But unlike most of the audience, the trained ears of
musicians understand tonality; therefore many of the acoustical attributes described above apply
to them as well. However, there are other acoustical attributes designers and acousticians need to
consider that are specific to the performers and most of those parameters are strongly affected by
the early reflections generated from the sound incidence of the stage area dimensions, orchestral
shells and reflective panels.
The following acoustical parameters are used to design the appropriate space and stage for the
optimum impression of the performers: Reverberation Time, Blend, Balance, Ensemble and
Attack.
31
Poletti 2005, p.3
32
Poletti 2005, p.3
20
Reverberation time is important to the musical comprehension of the performers when there is
some liveliness in the space rather than a dry hall.
Blend describes the extent to which different instruments are perceived as being coupled.
Balance is recognized when different sections of the orchestra including soloists have relative
quality and strength from each other; and most of the instruments are treated equally. This
impression is required between stage sound and pit sound for as many listeners as possible
throughout the auditorium.
33
A sense of balance can designed architecturally by the appropriate size of the stage enclosure,
especially with the use of risers for musicians or a choir and also by the position of instruments
on the stage. The shape of the sound-reflecting canopy or panels near the orchestra influence
balance as well as create an aesthetic opportunity for stage enclosure design for multi-purpose
auditoriums with a stage house. Sound-absorbing panels may also be used on stage to change the
balance between instruments.
Ensemble describes the degree to which the musicians can hear each other.
Attack is the immediacy of the hall response.
3.3.0 Acoustical Faults
Although an emphasis on finishes and surface shaping control the acoustic character of a space,
background noise and echoes can interfere with the subjective impressions of a musical
performance as well.
33
Orlowski 1999, p.238
21
Background noise is recognized when source of sound is not the music or audience and usually
heard over faint orchestral notes or when the hall is empty. It may include noise from the HVAC
system: ductwork, mechanical equipment, penetrations connecting vibrations from the structure
to the hall. Sound isolation may be necessary from other architecturally adjacent interior spaces
or from environmental noise due to exterior noise sources such as vehicular traffic and aircrafts.
Echoes are noticed when strong directional long-delayed sound reflections are distinct. Echoes
occur late after direct sound and reduce clarity as well as speech intelligibility.
In summary, optimizing and tuning a performance space to the desired acoustic qualities that are
appropriate to the performance are caused by architectural modifications or by electronic
enhancement.
3.4.0 Architectural Importance of Reverberance
Reverberation is the primary indicator of architectural enclosure
34
and therefore important in
understanding spatial dimensions. The value of reverberation is affected by the physics of its
enclosed environment.
3.4.1 Optimum Reverberation Time for Performance Categories
Reverberation time indicates the global quantitative measure of the sound environment in a room
and must be in a proper range depending on the room’s programmatic function.
35
The table below
illustrates the optimum reverberation time versus performance type. (Table 2) This information
was developed by acousticians based upon observations during performances and preferences
from trained observers in a laboratory environment. From this table speech for lectures requires a
reverberation time which ranges from 0.2 seconds to 1.0 second, whereas a function such as
34
Marshall 2004, p.3
35
VRAS 2005
22
symphonic or romantic classical music would be more appropriate at a range of 1.8 to 2.2
seconds. Below are recommended reverberation times for a few styles of music typical in
performance space design according to Michael Barron:
36
Recommended occupied reverberation times (sec):
Organ music > 2.5
Romantic classical music 1.8 - 2.2
Early classical music 1.6 - 1.8
Opera 1.3 - 1.8
Chamber music 1.4 - 1.7
Drama Theatre 0.7 - 1.0
Table 5: Recommended occupied reverberation times
36
1993, p.29.
Table 6: Appropriate Reverberation Time (Egan 1988, p.64)
23
A physicist named Wallace Clement Sabine (1868-1919) is considered to have begun the modern
science of acoustics. He developed the relationship between the volume of a space and the
amount of absorptive material within it and ultimately formulated a quantity he called
Reverberation Time (RT
60
).
RT
60
= 0.049 V / A
37
RT
60
, reverberation time is the amount of seconds it takes for a sound in a space to decay 60 dB
after it has stopped.
Where:
V = Volume of Room [cubic feet]
A = Total room sound absorption [Sabins]
A = ā x S
ā = Average sound absorption coefficient for the room surfaces
S = Total room surface area
Changing the physics of an enclosed environment will change the variable values of the Sabine
equation which not only changes the reverberation, but other acoustical characters discussed in
the previous sections as well. Today Sabine’s theory of reverberation has been developed further
since the Sabine formula does not take into account complex geometries, coupled volumes and
uneven distributions of absorption.
Understanding the limitation of the Sabine formula has led acousticians to develop more
parameters in which to assess qualitative and quantitative impressions of room acoustics.
37
Sabine 1922, p.124
24
3.4.2 Impulse Response
An impulse response is a physical measurement of an impulsive sound, e.g. a single hand clap, a
single musical note or a single syllable of speech in a room, recording information of direct sound
and all subsequent sound reflections from the room surfaces. Impulse responses are a quantitative
method of measuring qualitative acoustic impressions. This is intended to represent the effects of
sound reflections from the room on a single musical note or a single syllable of speech. The
sound level, frequency content, arrival time and direction of the sound reflections can be
identified from an impulse response with the proper use of directional microphones and digital
signal processing. Furthermore the impulse response is unique to every seat location in an
auditorium.
38
Impulse response measurements indicate that direct sound and subsequent reflected
sounds follow different paths before they reach various locations in an auditorium. This
demonstrates that there are better seats in the house than others, or at least perceived as such. In
order to obtain the mean measurement from a space, measurements of different receiver locations
need to be acquired and the results are generally averaged.
38
Siebein 1999, p.6-7
Figure 1: Impulse Response Diagram
25
There are three fundamental areas of the impulse response measurement to understand. (Figure 2,
shown above) Time on the horizontal axis is measured in milliseconds (ms) and records direct
sound, early reflected sound and reverberant sound; every timed impulse has a sound level
recorded in decibels along the vertical axis. Direct sound is the sound wave heard directly from
the source to the receiver without the obstruction from other surfaces. It is the first impulse
recorded and contributes to the sensations of loudness, clarity and direction. Early sound
reflections are the impulses recorded after the direct sound and are the waves that are reflected
from surfaces local to the source. In the case of a concert hall these reflections typically come
from the orchestra shell or reflecting panels at the front of the room. On the impulse response
diagram, early sound reflections are identified which arrive less than 80 ms after direct sound. If
these reflections arrive less than 20 ms after the direct sound then they contribute to acoustic
clarity and intimacy. The area of the impulse response which records the reverberant sound field
are the incident waves which have reflected from several surfaces before arriving to the listener.
These reflections travel longer distances and depreciate in loudness as compared to direct sound
and early reflections by the time the listener is reached. The reverberance contributes to the
impression of spaciousness in a room if the reverberant sounds are arriving from many directions.
The reverberant sound field also contributes to the impression of warmth or the impression of
brilliance depending on the strength of the bass or treble frequencies respectively. We usually
classify reverberant sounds as those that occur 80 ms or more after the direct sound.
3.5.0 Variable Acoustic Methods
There are many acoustic impressions to consider and more importantly different methods of
objectifying subjective acoustic responses. Architectural characteristics of performance spaces
play a large part in materializing these subjective impressions which can then be quantified.
However, multipurpose performance spaces require more acoustical characteristics than a single
26
static performance space. Therefore variable acoustic methods are used to appropriately alter the
architectural make-up of a single space for multiple functions. However, with the advent of
Digital Signal Processing (DSP), architectural changes are not the only means of changing the
acoustic character of a space. Electronic enhancement systems have advanced so much as to
change an acoustical attribute, such as reverberation time, warmth, envelopment, etc., at the touch
of a button, literally. Further understanding of these systems will follow in the succeeding
sections as well as how they affect the architect and acousticians who use them. For the purposes
of this paper, acoustic variability which uses physical architectural changes are called passive
systems and acoustic variability which uses purely digital means are called active systems.
27
Chapter 4 Passive Variability
4.1.0 Passive Variability in Performance Spaces
Passive variable acoustic technology physically changes architectural characteristics of a
performance space to produce an acoustical ambiance satisfying its performance function.
Altering surface geometries, material absorptions and/or spatial volumes changes critical acoustic
values of the space like the reverberation time.
The difference between “hard” and “soft” architecture, which compose the physical
characteristics of a space, affect the acoustical design. “Hard” surfaces, like concrete or wood,
enhance sound reflections and increase reverberation time. “Soft” surfaces, like fiberglass panels,
drapery and carpet increase the sound absorption characteristics of the room diminishing sound
reflections and reverberation time.
A typical example of passive variability is mechanically installed curtains; exposed against the
walls of a space to utilize their sound absorptive characteristic or retracted into a pocket to expose
the sound reflecting surface behind. These moveable acoustical curtains, such as sound absorbent
panels or curtains, are primary methods of variability used in performance spaces and can usually
extend to cover most of the wall surfaces in a room. This additional absorption will give an
acoustically dryer ambience for musical rehearsals or speaking venues which require the
reduction of loudness and reverberance in the space. Other types of functions requiring more
clarity instead of fullness of tone like chamber or renaissance music use smaller parts of the
banner treatment. As mentioned earlier acoustical banners or curtains can retract to their housings
28
behind walls where the sound waves from the orchestra will not be reached
39
or protracted during
lectures to make full use of their absorptive qualities.
Figure 2: Drawings of moveable curtains/ louvers/ panels (Jaffe 1999)
Figure 3: Drawings of moveable curtains/ louvers/ panels (Jaffe 1999)
Although a moveable heavy curtain is a common example of varying the acoustical qualities in a
performance space, there are other passive variable elements which create greater and more
specific ranges of acoustic possibilities. These include adjustable orchestral ceiling panels,
39
Siebein 1999, p.17
29
moveable ceilings and coupled reverberant chambers. The orchestral ceiling panels are a passive
element that are part of the orchestral shell; usually located above the orchestral or near the front
rows of seats. Adjustment of these panels can alter the balance of the musical ensemble as well
as permit coupling between the stage and the stage house in a multipurpose auditorium.
Early sound reflections from the orchestra will strike the canopy and arrive at the audience
shortly after the direct sound; therefore creating an enhanced sense of intimacy, loudness and
clarity in the room. There are also adjustments made to the orchestral canopy which can provide
support in the form of early reflections to the musicians laterally across the stage increasing the
sense of ensemble. Lastly, this type of canopy cuts off acoustic volume of the fly tower which can
serve as a reverberant chamber.
Figure 4: Orchestral ceiling panels adjusted for a concert performance (McCain Auditorium, Kansas State
University, Manhattan, Kansas) (Izenour 1977, p.390)
30
Figure 5: Orchestral ceiling panels removed for an opera performance (McCain Auditorium, Kansas State
University, Manhattan, Kansas) (Izenour 1977, p.391)
The rule of thumb in designing performance or assembly spaces is that the greater the spatial
volume (ft
3
) the longer the reverberation time (sec). Therefore when a motor-operated ceiling
over the audience is raised or lowered over the main house, the reverberation time is immediately
influenced. For example, when the ceiling is raised to its highest level in a performance space,
longer reverberation times will result; best for a romantic symphony or perhaps Gregorian chant.
For smaller ensembles, like a chamber orchestra, the ceiling can be lowered to provide stronger,
more immediate, sound reflections enhancing the sensation of intimacy and clarity.
40
Just like the
orchestral ceiling panels, the audience ceiling may not just be a single surface, but instead a
composition of several ceiling panels which can be adjusted to direct sound reflections best suited
for the respective performance venue. Furthermore, when a ceiling is raised to its highest position
more surface area of the walls are revealed as well as further access to the possibility of sound
access to reverberant chambers which can assist in achieving even longer reverberation times.
40
Siebein 1999, p.15
31
Figure 6: Ceiling over audience adjusted for a concert performance (Auditorium, Fine Arts Center, Viterbo
College, La Crosse, Wisconsin)
(Izenour 1977, p.398)
32
Figure 7: Ceiling over audience adjusted for a drama/theatre performance (Auditorium, Fine Arts Center,
Viterbo College, La Crosse, Wisconsin)
(Izenour 1977, p.399)
Another form of architectural variability which was first conceived in the 1960s and used with
other halls is the reverberant chamber. These hollow reflective chambers with large cubic
volumes are acoustically coupled to the main room volume and usually surround the perimeter of
the main house. Depending on the aperture size and shape which connects the chamber to the
main house, acoustic qualities will be affected such as warmth, spaciousness and most
importantly the sense of reverberance increases. The aperture of the chambers can be opened or
closed by heavy motorized doors or in some cases louvers, allowing more or less sound to enter.
The sound will then reflect off the “hard” surfaces within the chamber (usually concrete) and then
33
move back into the main room volume.
41
As mentioned earlier, the reverberation time gets longer
proportionally to a greater volume. The overall cubic volume of reverberation chambers can be
greater than or equal to half of the volume of the main house. One of the problems of
reverberation chambers is that higher frequencies which have shorter wavelengths have difficulty
entering and exiting the openings. In general, the use of reverberant chambers with controlled
acoustic coupling has been successful to many halls since it is “highly flexible and adaptable for
the full range of musical repertory of the past, for the music of our time and expected for [the]
future.”
42
Figure 8: Use of electro-acoustic coupling for stage-to-hall transfer of reverberant sound for adjustable
reverberance. (Veneklasen 1974, p.36)
41
Siebein 1999, pp.15 -16
42
Johnson and Kahle 1999, p.3
34
Figure 9: Reverberant chamber diagram of Meyerson Hall.
(Cavanaugh and Wilkes 1999 cited ARTEC Consulting Inc., p.287)
4.2.0 Advantages and Disadvantages of Passive Techniques
Even though passive systems of variability create an opportunity for architects to design and
acousticians to vary the qualities of a performance space, the approaches may be costly and
limited in terms of their range. Exposing drapes, banners or employing reverberant chambers on
the sidewalls may significantly reduce envelopment since the wall surfaces responsible for early
lateral reflections are covered or missing.
43
43
Christoff 2005, personal communication
35
In using passive techniques, attention should also be made to variable sound levels. When there is
too much variable absorption, especially from operable curtains or louvers, the possibility of
loudness reduction and diminished lateral reflections and diffuseness exists.
44
Adjusting the cubic volume of the room using operable ceilings over the audience can potentially
create changes for the large ranges of reverberation times according to the Sabine formula.
However, this approach is very expensive and a moveable ceiling may not be practical in some
auditoria. Using the void created above the ceiling could be coupled to the main auditorium.
45
Coupled volumes located on the sidewalls also create useful increases in room reverberation.
However, the extra volume can cause listeners to perceive reverberant sound as originating from
outside the room creating an impression for a lack of diffusion in musical presence.
46
Most
importantly adequate distribution around the auditoria of coupled space designs must be ensured.
Furthermore, in all cases of passive variable techniques, the initial capital expenditure and
operational costs can be very high.
44
Poletti 2005, p.3
45
Poletti 2005, p.3
46
Poletti 2005, p.3
36
4.3.0 Case Studies: Architectural/Physical Variability
4.3.1 Lucerne Culture and Congress Center (KKL)
Figure 10: KKL House Interior (Futagawa 1999, p.28-29)
The stunning Culture and Congress Center by architect Jean Nouvel is located on the edge of
Lake Lucerne. He with Russell Johnson of ARTEC Consultants, acoustical consultants in New
York, acoustically engineered a space to house Lucerne’s orchestral festival and congresses.
Based on the classic ‘shoebox’ shape, it is considered a pure concert hall with no electronic
amplification, therefore not intended for lyric or theatrical venues. The mostly white colored
interiors of the audience space, seating 1840, are wrapped with three tiers of balconies. However,
accents of wood at the stage, floor, seat backs and organ pipes add warmth to the stark space.
Another compelling design element are the hidden red painted walls of the reverberation
chambers which envelop the moveable perimeter walls.
37
There are fifty-two of these curved white
reverberation doors distributed throughout the three
levels behind the balconies. These heavy doors and
adjoining walls are covered with white plaster
sound diffusing tiles. The doors measure 8 feet wide
and vary in height from 10’ to 20’ tall and operate
using a special motorized hinge which movement
was engineered by Ernst Schultzheiss of the Theatre
Planning AB, a German company.
47
The
reverberant chambers have a volume of 7000 m
3
and are designed to maximize reverberation by
allowing the sound to bounce around inside the
chamber before returning to the audience area. The
curved doors open to the reverberant chamber at
any angle up to 90 degrees. When the doors are
completely shut the chamber the reverberation time
of the room achieves 2.2 seconds and can range up
to six seconds with the doors at its maximum opening.
48
The surface area of the plastered doors
and walls can be covered tier by tier with heavy cotton fabric which can deploy or retract into
curtain pockets.
Figure 11 (a-c): KKL, Views of concert hall towards the reverberation chambers and moveable wall panels
of concert hall. (a)top left (b) middle left (c) bottom left (Yoshida 1998, p. 70)
47
Lampert-Greaux 1999, p.2
48
Lampert-Greaux 1999, p.3
38
These curtains are computer-controlled and used to deaden the space for rehearsals of congress
meetings. The space also includes a two-part moveable ceiling reflectors made of cherrywood
located at the front of the hall which regulates the acoustics at the concert platform and audience
chamber. Raising or lowering the reflectors of this ceiling canopy changes the acoustic volume of
the room. There is further movement at the stage with motorized gliders and podiums to suit the
venue. Furthermore, there is a “tonemeister” on staff to tune the acoustic of the room to suit the
type of performance.
Figure 12: KKL, plan view, reverberant chambers (Beranek 2004, p.467)
39
4.3.2 Verizon Hall
The Verizon Hall in the Kimmel Center of Performing
Arts is the home of Philadelphia’s Symphony Orchestra,
which opened in December 2001. Rafael Viñoly is the
architect and the acoustics designed by ARTEC
Consultants, Inc. The hall seats 2,298 and has a modified
“shoebox” shape similar to the shape of a cello.
Just like the Lucerne, the Verizon Hall also consists of a
reverberation chamber whose apertures are controlled by
100 doors at all balcony tiers, which can reach a
reverberation time up to 1.7 seconds. When the symphony
hall is used for conferences, the reverberation time is
reduced by motor-operated velour curtains drawn over the
walls of the hall. Lastly, the hall also contains the passive
acoustic feature of an orchestral canopy divided into three
sections of adjustable heights.
The hall also includes a mechanized concert platform
extension which has the flexibility of changing the
acoustic environment by a turntable which occupies most
of the floor area of the stage house. Mounted on half of the
turntable is a concert shell, to be used for recitals, choral concerts and performances by small
chamber orchestras.
49
49
Fischer 2003
Figure 13: Verizon Hall, interior view
(Fischer 2003)
Figure 14: Verizon Hall , orchestral
view (http://www.musicweb-
international.com/SandH/2002/Feb02/p
hiladelphia.htm)
40
Figure 15: Verizon Hall, plan view, reverberant chambers around the perimeter of the audience chamber
(Beranek 2004, p.125)
41
4.3.3 Segerstrom Hall
The Orange County Performing Arts Center, Segerstrom Hall opened in 1986 is located in Costa
Mesa, CA and is also a multipurpose auditorium. The architect was Charles Lawrence and
acoustical consultants were Paoletti/Lewitz Associates, Jerald R. Hyde and Marshall/Day
Associates. According to Beranek’s
description of the hall the acoustic design
called for early, laterally reflected sound
to all seating areas. These reflected
sounds are created by tilted panels at the
front and rear of the hall as well as by the
edges of the four seating sections of the
hall. Some of these panels are quadratic
residue diffusers. Since shorter
reverberation times would be more
appropriate during rehearsals or events demanding speech intelligibility, “curtains can be drawn
at various lengths from their storage units in the ceiling and from behind large panel reflectors.”
50
The proscenium stage area can be adjusted to 2400 ft
2
for symphony concerts, 3060 ft
2
for choral
works and 500 ft
2
for soloists. Three removable reflecting panels are located at the stage overhead
to provide the players with cross-stage communication. Soon to be added to the Orange County
Performing Arts Center is the Renée and Henry Segerstrom Concert Hall by Cesar Pelli, acoustics
by Russell Johnson.
50
Beranek 2004, p.67
Figure 16: Segerstrom Hall, view towards stage
(http://www.ocregister.com/newsimages/show/2005/
03/20ocpac.jpg)
42
Figure 17: Segerstrom Hall, detailed section
(Beranek 2004, p.70)
Figure 18: Segerstrom Hall, plan view (Beranek
2004, p.69)
43
4.3.4 Meyerson Symphony Center
The Eugene McDermott Concert Hall in Morton H. Meyerson Symphony Center is a
multipurpose performance space located in Dallas, Texas which opened in 1989. It hall has a
classic “shoebox” shape at the front
two-thirds and the classic opera
“horseshoe” shape at its remaining end.
This hall seats 2,065 and was designed
by Pei Cobb Freed & Partners, the
acoustician, ARTEC Consultants,
Inc.The reverberation time is primarily
controlled by the 254,000 ft
3
reverberant chamber located at the
perimeter of the highest audience level.
The apertures to the chamber are opened and close by 74 concrete motor-operated door. The hall
also contains a four-part moveable audience ceiling canopy which can also be controlled to vary
reverberation.
Figure 19: Eugene McDermott Concert Hall, interior view
(http://boerger.org/)
44
Figure 20: Meyerson Hall, sections and
axonometric (Beranek 2004, p.77)
Figure 21: Meyerson Hall, plan view
(Beranek 2004, p.76)
45
4.3.5 Symphony Hall
The Birmingham Symphony Orchestra in England is housed by Symphony Hall, which opened
in1991, and also used as a convention center. The hall is shaped similar to the Meyerson Hall, the
classic rectangle shape with a multi-tiered opera “horseshoe” shape at the rear, seating 2,211. The
hall also provides a choir area behind the orchestra and a pipe organ centerpiece as a focal point
at the front.
Symphony Hall’s main variable acoustic feature
is the reverberant chamber controlled by concrete
doors and located around the organ as well as the
upper side walls of the main house. An
adjustable large wooden canopy above the
orchestra and front audience provides greater
clarity of sound when lowered appropriately. The
reverberation time can also be varied by the 3”
deep sound-absorbing panels, mounted on rails
which can be moved in and out of the hall. The
hall typically achieves a reverberation time at mid-
frequencies of 1.85 sec.
51
51
Beranek 2004, p.219
Figure 22: Symphony Hall, interior view
(http://pipedreams.publicradio.org/gallery/united
_kingdom/birmingham_hallklais.shtml)
46
4.4.0 Summary of Passive Case Studies
Passive variable acoustical strategies achieve a great range of reverberation times in the preceding
case studies. The most common and effective technique used to vary the reverberation time is the
application of sound absorbing curtains. Although the use of reverberant chambers also affects
reverberation time, it is not as critical as the curtains; the Segerstrom Hall achieves as great a
range as the other performance spaces without employing coupled volume strategies. The
adjustable orchestral ceiling is also a commonly used passive strategy since it is an effective way
to reinforce early lateral reflections and create a sense of intimacy for the audience.
Figure 23: Symphony Hall, plan (Beranek
2004, p.221)
Figure 24: Symphony Hall, section (Beranek
2004, p.220)
47
Table 7: Passive Case Studies
48
Chapter 5 Active Variability
5.1.0 Electronic Variability in Performance Spaces
Electronic enhancement systems alter the sound field in a space like passive acoustic variability,
however through digital, not architectural means. Using strategically placed microphones and
loudspeakers in conjunction with signal processing units, reverberation time and other acoustic
parameters can be manipulated though digital operation.
Active acoustic variability can
only improve sound quality by
providing extra sound energy in
the form or reverberation or
reflections; e.g. reverberation time
can only be increased in seconds, not
decreased. The sound field can only
be induced with more sound pressure, more reverberance or create a greater sense of warmth or
brilliance (low or high frequencies) or envelopment, etc.
Some electronic enhancement systems can create a nearly perfect impression of a desired
acoustical environment completely different from the acoustical environment of the physically
existing space. These systems can work with traditional sound systems or in natural acoustic
environments. It is important to note that enhancement systems do not generate audio signals on
their own but rather pick up sounds already within a space, process them and feed them back into
the acoustic environment.”
52
52
Berkow 2002
Figure 25: Simple Digital Signal Processing audio system
(Bocchiaro 2004)
49
Achieving the “best” acoustic atmosphere or ambience required for a given function not only
depends on the quality of the system’s alignment but relies heavily on the basic acoustic
properties of the physical space;
53
i.e. the digitally enhanced sound systems are limited by the
acoustics of the space for which they are installed. For example, if the original condition of a
room is inherently reverberant, an active system will not be able reduce sound reflections to
achieve a greater sense of clarity, speech intelligibility or texture, if required. If the architect and
acoustician designed the performance space to have minimum reverberation and most of the
surfaces were sound absorbing, then the integration of an active system would be most ideal to
achieve most desired acoustic impression.
Acoustical enhancement systems have improved in their quality of components and advanced in
digital signal processing (DSP) units over time, thereby solving sound challenges that traditional
architecture can not. The integration of an active acoustic system should be intended to ‘enhance’
its enhancement system and can provide tremendous results by a space with already good
acoustic conditions.
5.2.0 The Functions of Active Variability
Active variable systems enhance the natural acoustics of the space. This electronic enhancement
method not only tunes the space for the appropriate style of music function but is also used to
correct deficiencies in the architecture. Active systems are especially useful in cases when the
architectural integrity of a space can not be altered, such as in historic theatres or concert halls.
These systems are based on providing the acoustic impulse response of concert halls by a
combination of architectural and electronic “reflecting” sources.“ A series of microphones pick
up sound from the orchestra or sound source at specific locations. Instead of amplifying the
53
Noack 2005
50
source directly through loudspeaker arrays, the sounds are delayed, filtered, transformed and then
played through a series of loudspeakers at strategic “locations and arrival times to enhance or
subtly augment the “natural“ acoustic impulse response of the room.”
54
The systems have the
capacity of supplying missing directional reflections and can even go as far as superimposing the
sound signature of a totally different space and output the signature into its respective space.
Assisted resonant systems are the earliest form of electronic enhancement which were used for
increasing the reverberation time. In the diagram below microphones pick up music signals from
the stage then turns it into an electrical signal which is fed into a reverberator. After the electrical
signal is modified it is returned to the original room by loudspeakers. Delaying devices are
usually inserted into the electrical circuit so that the sound from the loud speaker doesn’t reach
the listener before the direct sound from the natural source. In the early 1960s, Parking and
Morgan introduced Assisted Resonance (AR) as a system with multiple channels each tuned as a
certain frequency.
55
Figure 26: Electro-acoustic reverberation system (Kuttruff 1973, p.279)
54
Siebein 1999, p.17-18
55
Mulder 2005
51
5.3.0 Types of Active Systems
More sophisticated applications of DSP technology has only recently evolved in the past 20 years
and is utilized primarily for large multipurpose performance spaces. The many types of electronic
enhancement which have since developed usually falls into one of two categories, in-line and
non-in-line systems:
In-line Systems (non regenerative)
These systems only pick up the direct sound energy from the stage as well as some early stage
reflections from the performers and convolve the sound with electronically generated early
reflections and reverberation. Therefore they can be independent from the reverberation of the
hall.
56
These systems mostly affect communication from the performers to the audience and can
not change reverberation properties from sources in the room to enhance sounds like audience
applause.
IN-LINE SYSTEMS DEVELOPER
SIAP
System for Improved Acoustic
Performance
SIAP B.V. at Uden, the Netherlands
ACS Acoustic Control System Delft University, the Netherlands
LARES
Lexicon Acoustic Reinforcement
and Enhancement Sytem
Lares Associates
AAS Assisted Acoustic System Yamaha
CARMEN CSTB, France
Table 8: In-Line Systems
Non-In-line Systems (regenerative)
These systems have a microphone sections that pick up the reverberant sound energy throughout
the hall itself, for recirculation through acoustic feedback. The microphones are not placed to
56
Poletti 2005, p.4
52
detect direct sound. Therefore, these systems are dependent of the sound energy in the acoustical
environment in order to apply some sort of enhancement.
57
A controlled regeneration of sound
communicates between the loudspeaker and microphones to distribute reverberant properties
throughout the sound field of the room.
NON-IN-LINE SYSTEMS DEVELOPER
VRAS
Variable Room Enhancement
System
Marc Poletti of Industrial Research
Limited, New Zealand
MCR Multi-Channel Reverberation Franssen, Philips
ERES Early Reflected Energy System Jaffe Holden Acoustics
Table 9: Non-In-Line Systems
Each of the applications in both in-line and non-in-line systems represents a technique utilizing
reverberant field sampling microphones, DSP processing and loudspeaker arrays within the
space. “Control over routing, reverberation, gating and other parameters allows electronic
acousticians to “tune” the space as desired.”
58
The components and capacities of additional active
systems are tabulated in Appendix B.
Paul Veneklasen
59
was among the first to recognize that early lateral reflection (envelopment)
was even more important than reverberation. Auditorium synthesis was first used as a “tool” to
evaluate the relative importance of direct, envelopment and reverberation in a laboratory
environment. It was used in a few performance spaces to augment the acoustical environment.
Some problems were acoustical feedback, maintenance of the systems, and setup time (refer to
figure 27).
57
Poletti 2005, p.4
58
Bocchiaro 2004
59
Paul Veneklasen, established Veneklasen Associates, consultants in acoustics and founded the Paul S.
Veneklasen Reseach Foudation.
53
Figure 27: Auditorium Synthesis - a research tool or a device for studying the influence of direct,
envelopment and reverberant sound on music and speech. (Veneklasen 1974, p.37)
54
5.4.0 Advantages and Disadvantages of Active Techniques
Electronic enhancement systems are a cost effective way of providing variable and corrective
acoustics to existing performance spaces. Active systems are meant to be integrated into the
architecture; therefore its functions are limited by the space in which it is installed.
Electronic enhancement can ensure optimum acoustic quality for multipurpose auditoria where
traditional architecture and passive enhancement alone cannot. Although, the high cost of passive
variability provides a very wide range of acoustic variability, the comparatively low cost of active
provides an almost infinite range. Furthermore, electronic enhancement is capable of providing
acoustic enhancement with no change in the appearance of the performance space.
Opposition of electronic enhancement strategies usually resonates from musicians or music
patrons who reserve prejudices for this sort of technology for purist reasons; or fear the
possibility of audible electronic artifacts which would not occur in passive systems otherwise. In
addition, as with any electronic device, caution against performance malfunctions with a specific
component from the system equipment should be maintained.
55
5.5.0 Case Studies: Electronic Variability
5.5.1 Royal Festival Hall
The Royal Festival Hall in London is well
known for its musical events and
architecture, however, it is acoustically
considered too “dry” and with a weak bass
tone. The hall, seating 2,901, opened in
1951 and became the test site for concert
hall acoustics since modern acoustic
measuring equipment was not available
for the first half of the 20
th
century.
Therefore, as a result from the lack of
technological information regarding audience sound absorption, the reverberation time at 500 Hz
was 1.5 seconds when the design goal was 2.2 seconds.
60
In addition, acoustical problems began
when the original specifications for room surfaces determined by the acoustic consultants were
ignored in the building process. Therefore an Assisted Resonance (AR) system was installed in
1964 so that the hall could provide a more effective sound for Classical and Romantic period
venues; at 500 Hz the hall has measures an RT of about 2.0 seconds with Assisted Resonance.
Prior to the AR, the hall was effective for piano, chamber and modern music. The acoustic
modification of the Royal Festival Hall set a precedent for architects to begin building
multipurpose halls for speech and then add an Assisted Resonance system.
60
Beranek 2004, p.245
Figure 28: Royal Festival Hall, interior view
(http://www.coxt.freeserve.co.uk/shape.html)
56
5.5.2 Tokyo International Forum
The competition won by architect Rafael Viñoly in
1989 for the Tokyo International Forum has
become an iconic symbol of culture and urbanism
in Tokyo. The project was completed 1996 and
holds a capacity 5,012 seats. Using the latest audio
technology “concert hall shaper” acoustic baffles
and an Active Field Control (AFC) system of
enhancement, the multipurpose hall can provide
for venues from classical concerts to international
conferences. The Active Field Control system
naturally enhances the acoustic characteristics of a
room and secures an ideal sound field for any
space needing acoustic optimization. The
Reverberation Time with the AFC system off
achieves 2.0 seconds, whereas the system on
achieves 2.6 – 2.9 seconds. The AFC has controls
early reflections as well as reinforces loudness, spaciousness and warmth.
Figure 29: Tokyo International Forum,
proscenum view (http://www.yamaha-
afc.com/example/tif/)
Figure 30: Tokyo International Forum, view
of seating (http://www.yamaha-
afc.com/example/tif/)
57
5.5.3 Adelaide Festival Center Theatre
The Adelaide Festival Center Theatre, opened in 1973,
was considered innovational for its variable acoustic
features, such as retractable acoustic curtains along the
rear wall and a moveable ceiling. The hall is primarily
used as an opera house and seats 2800. When used for
multipurpose events, the acoustics normally provides
even coverage for speech, contemporary music
concerts and musical. The natural reverberation time
of the hall is 1.3 seconds, however, it produced
unbalanced low frequency resonance; the
reverberation time was too long at lower frequencies
and too short at higher frequencies. (Matheson 1999,
p.2) When the theatre began to be regarded as having
poor acoustic qualities for opera and especially
symphony orchestra venues, the problem were
acoustically assessed and implementing an electronic
enhancement system was decided. Compared to the
cost of architecturally changing the hall to improve the sound field, the electronic enhancement
was more economic even with the addition of a few passive changes. The acoustical consultants
installed a Lexicon Acoustic Reinforcement and Enhancement System (LARES) which overcame
the halls deficiencies and prevents problems of coloration from feedback.
Figure 31: Adelaide Festival Center Theatre
(http://www.lares-
lexicon.com/pdfs/adelaidereviews.pdf)
Figure 32: Adelaide Festival Center Theatre
(Matheson 1999, p.1)
58
5.5.4 The Prague Congress Center
The Prague Congress Center is one of the largest
conference facilities in Central Europe with six
halls for a total capacity of 4,770 seats. The
Congress Hall is the main multipurpose hall seating
2,766 and was constructed for programs ranging
from congresses to symphonic concerts, but the
controlling political administration required
achieving perfect speech intelligibility first.
61
Therefore, the natural reverberation time of the hall
is about 1.5 seconds. To tune the hall for other
events, it contains a five-section moveable ceiling
system varying ceiling heights and an Assisted
Resonance electro-acoustic system. However, the
combination of the passive ceiling and active
electronic system did not accomplish the acoustic
expectations for the other performance venues and are no longer in use. Instead, Variable Room
Acoustics System (VRAS) by Level Control Systems (LCS) was integrated into the hall in 2001
to accommodate for the classical concerts. The system provided enhanced natural reverberation
appropriate to the event and increased reflected energy diffusion.
61
Noack 2002
Figure 33: Prague Congress Center
(http://www.kcp.cz/index.php?lng=AN)
Figure 34: Prague Congress Center (Noack
2002)
59
5.6.0 Summary of Active Case Studies
In the past 25 years, many electronic enhancement systems have evolved to augment the natural
acoustics of performance spaces. When applied correctly, the four electronic enhancement
systems in the preceding case studies, AR, AFC, LARES and VRAS, solved sound problems that
the acoustical architecture alone could not. However, since these systems are integrated with the
architecture of the space, some physical adjustments to auditoria is common to provide the most
effective conditions for the electronic architecture.
60
Table 10: Active Case Studies
61
Chapter 6 Quantifying Variable Acoustic Methods
6.1.0 Selecting a Method: Vary Reverberation Time
If combinations of passive and active variable acoustic methods achieve a great range of
reverberation time for most multipurpose auditorium conditions, architects need to consider
variable acoustics in their design. Architectural design can be a subjective endeavor, but
recognizing the dynamics and sound characteristics of acoustical parameters is also inherently
subjective. However, we now know what components of a space should be emphasized to achieve
a desired acoustical attribute.
Reverberation time is not the only important acoustic parameter to consider in room acoustics,
but most acousticians would agree that “an appropriate RT is a necessary if not a sufficient
condition for good room acoustics.”
62
The quantification method employed in this thesis involves
analyzing reverberation time in a variable acoustic condition and its impact on other acoustic
parameters and architecture.
6.2.0 Objective and Approach
The objective of the method is for architects to recognize what range of acoustic impressions can
be achieved in designing multipurpose spaces. Although the following quantification process
focuses on a single acoustical parameter, reverberation time, strategies of variable acoustic
techniques will aid architects to exercise other acoustic parameters appropriately with an
acoustical consultant.
62
Dalenback
62
Initially, reverberation time was measured in an existing performance space and then compared a
computerized prediction and finally correlated with analytic calculations of the same simulated
model. This analysis validates the impression variable acoustics provides in a given multipurpose
performance design.
6.3.0 Quantitative Process
The quantification methodology employed consists of three acoustical measuring analyses:
acoustical measurements of an existing performance space, simulated computerized prediction,
and analytic calculations using the Eyring
63
equation.
As a consequence of exploring the different types of variable acoustic techniques in this thesis, a
morphological system of aggregation called a Zwicky Tree
64
was attempted in order to suggest
acoustical recommendations for any design condition of a performance space. However, the
method resulted in over branching and therefore not a useful tool for the purposes of this thesis.
6.3.1 Acoustical Measurements of Existing Performance Space
Reverberation time (RT
60
) measurements were taken at the Cerritos Center for the Performing
Arts. Since this performance space has passive variable acoustic capacities, measurements were
obtained for the hall’s longest and shortest reverberation times.
6.3.2 Simulated Computerized Prediction
Computer simulations were run on a simplified model of the Cerritos Center in CATT-Acoustic
software. The resultant RT
60
data from the computer prediction validates the RT
60
measurements
taken on site and provides empirical conclusions.
63
See Eyring definition on page 80.
64
Fritz Zwicky developer of morphology systems and applications.
63
6.3.3 Analytic Calculation Using the Eyring Equation
Calculated reverberation times from the CATT-Acoustic Cerritos model using an Excel
spreadsheet formatted with the Eyring equation were obtained to validate the computerized
prediction results.
64
Chapter 7 Acoustical Measurements of an Existing Performance Space
7.1.0 Case Study Selection
The Cerritos Center for the Performing Arts located in Cerritos, California is a local auditorium
space where it is possible to architecturally manipulate its geometry and seating configuration for
the appropriate performance. The Cerritos Center of the Performing Arts opened in 1993 and was
considered one of the most technologically innovative theatre spaces on the continent. The
architect, Barton Myers, and the acoustical consultant, Kirkegaard Associates designed the 6390
ft
2
auditorium using hydraulic lifts and air casters to compose six different seating and
configuration arrangements as indicated in Figure 23: Arena, In-The-Round, Lyric, Cabaret,
Concert and Drama. The seating configuration changes take 8 hours or less to arrange.
65
Figure 35 (a-f): Six seating configurations at the Cerritos Center (CCPA 2005)
(a) In-the- Round (1,845 to 1,934 seats)
The in-the-round configuration is used for popular music, comedy and
jazz performances.
(b) Lyric or Lyric with Orchestra Pit (1,311 to 1,391 seats)
This proscenium theater configuration is used for musical theater, dance
and popular music performances.
(c) Drama/Lyric with Shell (921 to 1,083-seats)
The proscenium configuration is used for plays, recitals and chamber
music performances; and an upstage acoustical shell is available.
(d) Concert (1,493 to 1,629 seats)
This configuration has in-the-round seating and acoustic concert ceiling
panels for orchestras, recitals and acoustic performances.
(e) Arena (1,691 to 1,721 seats)
The configuration has 500 floor seats surrounded by box seats and
balconies on one side for popular music, comedy and jazz performances.
(f) Cabaret (1,324 to 1,504 seats)
The configuration can use up to 67 tables and 412 chairs on a flat floor,
surrounded by box seats and balconies, for jazz and other music
performances; Exhibitions and conventions are other available venues.
66
Figure 36: Cerritos Center, Plan view of variable configuration mechanics (CCPA 2005)
67
Figure 37: Cerritos Center, Axonometric model of variable configuration mechanics (CCPA 2005)
68
The floor seating is adjustable on wagons with air casters, enabling them to be raised, lowered or
even removed. The geometry of the ceiling also changes for the appropriate acoustical position
via three 27,000 pound panels hung overhead. For an opera house configuration including a fly
tower, seating 1450 seats will host film, dance musicals, and large scale dramas. If the stage is
moved forward for a proscenium configuration a more intimate space is created for drama with
950 seats. The auditorium will also adjust to a concert hall configuration of 1950 seats. The
orchestra pit can be raised flush to the auditorium floor for banquets, dinner dances and
exhibitions. Finally for an arena configuration 1780 seats are used suitable for sporting events,
pop music concerts and fashion shows.
Figure 38: Axonometric model of the Cerritos Center of Performing Arts (CCPA 2005)
69
7.2.0 Objective
The six different seating configurations provide different geometries and sound absorption which
will yield a range of reverberations times. I wanted to know the shortest and the longest
reverberation times an auditorium of this capacity could achieve. There were no previously
recorded RT
60
values available for the six seating configurations, so on-site testing would have to
be approached to obtain data of the most extreme cases.
7.3.0 Acoustical Measurements
Jack Hayback, the chief sound engineer at the Cerritos
Center, made it possible for me to obtain measurements of
configurations with the greatest and lowest seating capacities,
the Cabaret configuration and the Lyric configuration,
respectively.
Changing the seating configuration passively changes the
cubic volume of the auditorium, however, its typical form of
passive variability are the retractable curtains behind the side
seating towers. Once the auditorium is arranged with the
appropriate configuration, there is also the option of exposing
the curtain to utilize its sound absorptive qualities or retract it
to expose the void behind the side seating towers which acts
like a reverberant chamber. Therefore, it was necessary to test these two configurations with and
then without its greatest sound absorption, the retractable curtains (Figure 29).
Figure 39: Cabaret Configuration
(CCPA 2005)
Figure 40: Lyric Configuration
(CCPA 2005)
70
7.3.1 Test Equipment
Jack Hayback and I not only discovered that the
Cerritos Center did not possess the RT
60
data from
Kirkegaard, but no one at the Cerritos Center had
produced the test data either, until now. Jack and I
measured the Cerritos with an Audio Toolbox™ by
TerraSonde has an audio testing and measurement
platform. It can simultaneously measure audio,
generate pink noise and analyze the data.
Audio Toolbox™ Specifications:
240 x 320 LCD Screen
Onboard USB Audio Preamp
Dual 48v Microphone/Line Level Inputs
Built-In SD Card Slot for Audio Recording/ Playback
Built-In Real Time Clock
T.A.O. DSP Audio Engine
SP/Dif, Toslink Digital Audio Output
Long-Lasting Lithium-Ion Battery System
New Powerful Audio Analysis Tools
Figure 41: White curtains drawn and exposed
behind balconies of side seating tower
Figure 42: Audio Toolbox
TM
Figure 43: Acoustic measuring setup,
Receiver 80 feet from Source
source
receiver
71
7.3.2 Measuring Conditions and Setup
Cabaret Configuration
The first series of measurements were conducted on
April 23, 2005 in the Cabaret configuration (Figure
31). From the drawings (Figure 32) the source of
sound, pink noise, came from the two loud speakers
located at the edge of the stage (indicated in red). The
Audio Toolbox™ microphone measured the sound
80 feet from the source and translated it
into reverberation time in seconds
(Figure 32). The choice of location for
the source and the receiver equipment in
the hall were considered as the most
typical seating. In addition, the location
of testing equipment was most
convenient in the short period of time
allowed to run measurements.
Unfortunately, the measurements were
taken at a time that the Cerritos
configuration-staff needed to set up for
a performance that evening, needless to
say, it was difficult to have pure silence
in the auditorium. Even though this
would be considered an unoccupied space in terms of the absorption, there is probably a slight
discrepancy with the noise.
Figure 44: Cabaret unoccupied
Figure 45: Diagram of source and receiver locations, Cabaret
configuration in section (top) and plan (below)
(CCPA 2005)
72
Lyric Configuration
The second set of measurements were taken on April 23,
2005 in the Lyric configuration (Figure 33). The
conditions for measuring were the same as the cabaret
configuration. As diagrammed in Figure 34, the same pair
of loudspeakers were located on the edge of the stage and
the Audio Toolbox™ was located adjacent to the mixing
platform 80 feet away. Unlike the measurements taken in
the cabaret configuration, there
were no noise discrepancies in our
measurements. With both Cabaret
and Lyric configurations, we took
over 10 measurements with the
curtains retracted into their
housings and then fully exposed
against the side walls the main
house.
Figure 47: Diagram of source and receiver locations, Lyric configuration in section (top) and plan (below)
(CCPA 2005)
Figure 46: Lyric unoccupied
73
7.4.0 Results – Reverberation Time Measurements
At the Cerritos Center we set up the measuring equipment to test the reverberation time at a
controlled location in the auditorium. Since this was a test for RT
60
it wasn’t as critical to place
the microphone at different locations, unlike the testing for early-decay-time (EDT) where the
location for the early reflections makes the difference in the quality of sound. When a burst of
pink noise is projected from the loudspeakers on stage, the Audio Toolbox™ computes the decay
by 25-60 dB and extrapolates to RT
60
. The frequency and bandwidth at which these
measurements were made is not clear, presumed to average broadband.
REVERBERATION TIME OF THE CERRITOS CENTER
CABARET LYRIC
w/ Curtains w/o Curtains w/ Curtains w/o Curtains
1 1.36 1.37 1.19 2.07
2 1.48 1.45 1.38 1.70
3 1.30 1.41 1.35 1.80
4 1.23 1.48 1.40 1.69
5 1.21 1.33 1.33 1.79
6 1.18 1.39 1.28 1.67
7 1.08 1.32 1.20 1.68
8 1.23 1.45 1.26 1.60
9 1.28 1.47 1.27 1.80
10 1.16 1.33 1.13 1.64
11 1.34 2.00
12 1.23 1.88
13 1.10 1.88
Average (sec) 1.25 1.39 1.26 1.78
Table 11: Measured RT
60
of Cerritos Center Configurations
The Cabaret configuration with the curtain fully exposed yielded an average RT
60
of 1.3 seconds
and with the curtains retracted back into their housings, 1.4 seconds. The Lyric configuration with
the curtain fully exposed also yielded an RT
60
of 1.3 seconds and with no curtain, 1.8 seconds.
Since the Cabaret configuration has a greater cubic volume than the Lyric configuration, the
difference between the curtains retracted in or out of the main house is greater for a space with a
74
smaller cubic volume. There was no significant difference in the varying the sound absorption
with retractable curtains in the cabaret configuration since the difference in RT
60
was only one
tenth of a second.
7.5.0 Summary
The Cerritos Center for the Performing Arts was chosen as a case study because of its passive
variable acoustic capacity to vary its cubic volume and sound absorption through six possible
performance configurations. Reverberation time measurements were taken of the most extreme
geometric and surface absorption conditions in order to find the greatest reverberant range that
the auditorium could offer through passive strategies alone. I found the shortest RT
60
achieved
was 1.3 seconds and the longest was 1.8 seconds.
The variation due to different passive acoustic configurations is smaller than what was expected.
However, this may be attributed in part to the minimal exposure of the curtains behind the side
seating towers which are architecturally articulated to receive the majority of reflections before
the curtains. There is also the possibility that the reverberation time is affected by the diffuse
reflections from the architectural articulation of the hall’s surface and material irregularities.
Furthermore, due to the limited capacity of the measuring equipment and the uncontrolled site
conditions, there could also be other discrepancies in the data.
75
Chapter 8 Simulated Computer Predictions
8.1.0 Objective
The following method of testing uses computer simulations through CATT-Acoustic™
65
software. CATT-Acoustic™ is computer software for room acoustic prediction, auralization and
surround reverberation. It can simulate and calculate acoustical characteristics of a space based
solely on the CATT-Acoustic™ model. Therefore, two abstracted models of the Cerritos Center’s
cabaret and lyric configuration were constructed in the CATT software to compare RT
60
results
obtained from the on-site measurements. This validates quantifying future acoustical data if the
measured RT
60
results of the existing auditorium are proportional to the RT
60
results from the
computer simulated auditorium.
8.2.0 Components and Conditions
I used AutoCAD software to build abstract models of the
Cerritos Center auditorium. This was only useful to set up
my coordinate system required to input data in CATT-
Acoustic™ software. Simplified geometries were composed
for both Cabaret and Lyric configurations (Figure 36).
AutoCAD allowed for quick identification of coordinates
and surface materials for the HTML interface of CATT.
The cabaret geometry has a volume of about 570,000 ft
3
and
the lyric geometry has a volume of 500,000 ft
3
.
65
Bengt-Inge Dalenback is the developer of © CATT-Acoustic v8.0 software, Gothenburg, Sweden.
Figure 48: AutoCAD wireframe
models for (a) Cabaret (top) and (b)
Lyric (bottom) configurations
76
8.3.0 Results
After running one set of computerized predictions for both cabaret and lyric geometries without
variable absorption and then a second set of predictions with variable absorption, four sets of data
were produced as tabulated in the Table 4 below.
CATT - Acoustic™ Results
Cabaret Configuration
571,742 cf
Lyric Configuration
504,785 cf
Global
Reverberation Time
@ 500Hz
without drapery with drapery without drapery with drapery
EYR T (sec) 2.18 1.44 2.68 1.91
EYR Tg
(sec)
2.18 1.44 2.64 1.87
SAB T (sec) 2.54 1.79 2.91 2.15
T-15 (sec) 2.72 1.68 3.29 2.40
T-30 (sec) 2.77 1.84 3.41 2.45
AbsC 22.73% 32.57% 17.75% 24.17%
AbsCg 22.66% 32.51% 18.02% 24.64%
MFP 14.44m 14.43m 13.57m 13.56m
Diffs 32.25% 27.19% 26.63% 26.64%
Complete Echogram
EDT 2.49 s 1.11 s 2.74 s 1.71s
T-15 2.49 s 1.37 s 3.27s 1.95s
T-30 2.67 s 1.46 s 3.39s 2.24s
D-50 27.1% 63.8% 27.3% 39.0%
C-80 (-)2.0dB 4.1 dB (-)1.6 dB 1 dB
LFC 36.1% 19.0% 39.0% 25.5%
LF 23.3% 11.4% 25.1% 14.4%
Ts 172.1 ms 66.9 ms 186.4 ms 114.6 ms
SPL 76.9 dB 72.1 dB 78.8 dB 75.5 dB
G 3.0 dB (-)1.8 dB 4.8 dB 1.5 dB
Table 12: Simulated CATT Acoustical Results
77
The first parameter from the chart is labeled EYR T, which is an abbreviation of the Eyring
Formula for reverberation time.
66
The figures calculated in CATT for this specific formula are
significant because they will be used as a means of comparison in the following quantitative
method used in section 9.0.0. The Eyring has calculated a reverberation time for the Lyric
configuration about 20% greater than the Cabaret in both scenarios: without curtains, 2.68 sec and
with curtains, 1.91 sec. Although the Cabaret geometry has a greater cubic volume, it does not
achieve as great a reverberation time as one would think according to the Sabine formula
discussed in section 3.4.1.
The following illustrated data is information provided by CATT-Acoustic™ software as a result
of the four simulated models. The first series of data is from the Cabaret configuration and the
second from the Lyric.
66
See Eyring definition on page 80.
78
Cabaret Geometry
The simplified geometry for the cabaret configuration was abstracted to basically a rectangle with
the proportions similar to the Cerritos Center. An image to the left shows the yellow side wall
(indicated by the black arrow) as wood and the same wall on the right, now cyan, has been
changed to the absorption equal to heavy drapery.
Figure 49: Geometry without curtains (left)
Figure 50: Geometry with curtains (right)
Cabaret - Complete Echogram
Computer processing involves the integration of echogram data which surveys many acoustical
parameter data. The most obvious difference is in decayed reflections which linger longer when
the hall has less absorption on the left than that on the right. This echogram also gives data on
other parameters such as early decay time, RT
15
, RT
30
, definition, clarity, sound pressure level,
and loudness, etc.
79
Figure 51: Echogram without curtains (left)
Figure 52: Echogram with curtains (right)
Cabaret Statistics: Reverberation Time and Mean Absorption
The following graphs give data on the global reverberation time and and mean absorption for all
octave band frequencies. The black arrows indicate the significant drop of reverberation time
when absorption is added. The red arrows compare the rise in the absorption coefficient plot
when the curtains are added.
Figure 53: RT without curtains (left)
Figure 54: RT with curtains (right)
80
Cabaret - Impulse Response Graph
Figure 55: Impulse Response without curtains (left)
Figure 56: Impulse Response with curtains (right)
The following four images are audience area maps which produce color colded energy plots of
different acoustical parameters such as sound pressure levels, lateral energy fraction, Clarity,
Definition, and Reverberation Time.
Cabaret - SPL In Four Time Intervals (Spatial Uniformity)
Figure 57: SPL in audience area without curtains (left)
Figure 58: SPL in audience area with curtains (right)
81
Cabaret - Lateral Energy Fraction In Four Time Intervals
The lateral energy fraction reduces from 39% without curtains to 25% with curtains.
Figure 59: LEF without curtains (left)
Figure 60: LEF with curtains (right)
Cabaret - C-80, SPL, D-50
The C
80
before curtains are introduced into the theatre was -2.0dB versus after the curtains
extended was 4.1 dB.
Figure 61: C-80, SPL, D-50 without curtains (left)
Figure 62: C-80, SPL, D-50 with curtains (right)
82
Cabaret - LF,G, RT’
The loudness factor reduced from 3.0dB to -1.8dB.
Figure 63: LF, G RT without curtains (left)
Figure 64: LF, G RT with curtains (right)
83
Lyric Geometry
The simplified geometry for the lyric configuration is smaller in volume with a sloped floor and
fan shaped seating. An image to the left shows the magenta side wall (indicated by the black
arrow) as plaster and the same wall on the right, now cyan, has been changed to the absorption
equal to heavy drapery.
Figure 65: Geometry without curtains (left)
Figure 66: Geometry with curtains (right)
Lyric - Complete Echogram
Reflections achieving a greater Early Decay Time are again longer when the hall has less
absorption than when it has more.
Figure 67: Echogram without curtains (left)
Figure 68: Echogram with curtains (right)
84
Lyric Statistics: Reverberation Time and Mean Absorption
Figure 69: RT without curtains (left)
Figure 70: RT with curtains (right)
Lyric - Impulse Response Graph
Figure 71: Impulse Response without curtains (left)
Figure 72: Impulse Response with curtains (right)
85
Lyric - SPL In Four Time Intervals (Spatial Uniformity)
Figure 73: SPL in audience area without curtains (left)
Figure 74: SPL in audience area with curtains (right)
Lyric - Lateral Energy Fraction In Four Time Intervals
The lateral energy fraction reduces from 36% without curtains to 19% with curtains.
Figure 75: LEF without curtains (left)
Figure 76: LEF with curtains (right)
86
Lyric - C-80, SPL, D-50
As the reverberation time gets longer, lower values are obtained for clarity, C
80
and definition,
D
50
, attributes which contribute to intimacy and envelopment. The C
80
before curtains are
introduced into the theatre was -1.6dB versus after the curtains extended was 1.0 dB.
Figure 77: C-80, SPL, D-50 without curtains (left)
Figure 78: C-80, SPL, D-50 with curtains (right)
Lyric - LF,G, RT’
The loudness factor reduced from 4.8dB to -1.5dB.
Figure 79: LF, G RT without curtains (left)
Figure 80: LF, G RT with curtains (right)
87
8.4.0 Summary
Abstracted models of the Cerritos Center were simulated in CATT-Acoustic software to compare
the measured reverberation in the existing space with the computer predicted reverberation time
of the simulations. The CATT prediction for the cabaret configuration resulted in a reverberation
time of 2.18 seconds with the curtains retracted to 1.44 seconds with the curtains fully exposed.
The Lyric configuration prediction of reverberation time ranged from 2.68 sec to 1.91 sec under
the same conditions. Detailed analysis of these figures indicates that not only the reverberation
time changes with the introduction of variable sound absorption, but the qualities of other
acoustical parameters, such as clarity and definition, change as well. In conclusion, the
reverberation time results from CATT were 70% greater in value than the measured reverberation
time of the existing auditorium. It was not clear why this discrepancy is so large; additional
measurements at Cerritos that would yield RT
60
versus frequency would be required to be certain.
88
Chapter 9 Analytic Calculation Using the Eyring Equation
9.1.0 Objective
Calculating the reverberation time analytically using the Eyring equation allows an additional
method to validate and compare the abstract models of the Cerritos Center from CATT acoustic
software
9.2.0 Component and Results
I used an Excel spreadsheet developed by Veneklasen Associates, acoustical consultants, which
computes the reverberation time at all frequencies quickly and simply by entering data of the
room characteristics: i.e. the overall volume, surface area and sound absorptive materials of a
space. It is programmed to quickly output the RT
60
at all octave band frequencies. However, the
calculation uses the Eyring formula because it is more accurate than the Sabine equation. The
Sabine is meant for high reverberant fields and assumes air absorption as a constant; i.e. air can
cause excessive absorption at higher frequencies. Furthermore, the Eyring equation takes into
account the exponential affect of added absorption whereas the Sabine assumes a linear addition
of absorption. The difficulty with the Sabine formula for reverberation time is that even if the
room boundaries were 100% sound absorbing, the formula predicts a finite reverberation time,
which is impossible; it should be zero. The Eyring formula eliminates this difficulty.
Sabine Formula:
67
T
60
= 0.049 V / A
Eyring Formula:
68
T
60
= 0.049 V / [- 2.3 S log
10
(1 - ā) + 4mV]
67
Sabine, W., Collected Papers on Acoustics. 124
68
Eyring, C.F., Reverberation Time in ‘Dead’ Rooms. 217
89
Where:
V = Volume of Room [cubic feet]
A = Total room sound absorption [Sabins]
A = ā * S
ā = Average sound absorption coefficient for the room surfaces
S = Total room surface area
m = Attenuation Coefficient at each frequency (depends on humidity)
The appropriate volume, surface areas and absorption coefficients were entered into the Excel
spreadsheet for the Cerritos Cabaret Configuration. The first calculation of the cabaret
configuration with the curtains retracted achieved an RT
60
of 2.22 seconds at 500 Hz. The second
calculation with the draped fully extended achieved an RT
60
of 1.45 seconds at 500Hz. The Lyric
configuration achieved reverberation times of 2.71 seconds and 1.98 seconds respectfully and
under the same conditions. The specifications and further reverberation time results of all octave
band frequencies are in Appendix D and Appendix E.
Eyring Results
Cabaret Configuration Lyric Configuration
without drapery with drapery without drapery with drapery
Reverberation Time
@ 500Hz
2.22 1.45 2.71 1.98
Table 13: Analytic RT Results
9.3.0 Summary
The third phase in the process of quantifying variable acoustic methods, Eyring calculations, was
used to validate the accuracy of the CATT acoustic predications. The results from the analytical
calculations obtained 95% accuracy against the Eyring results for reverberation time in CATT-
Acoustic software.
90
Chapter 10 Comparison of Quantitative Methods
10.1.0 Comparing Reverberation Times
Table 6 below tabulates the resultant reverberation times from the measured existing space, the
computer predicted models and from the analytic calculations of the computer models. The
results from the CATT models (method 2 in Table 6) on average achieved values 70% greater
than those measured at the existing Cerritos Center. The results from the analytic Eyring equation
(method 3 in Table 6 below) achieved values that were on average 95% accurate against the
computer predicted CATT models. Although the reverberation times are not identical in all
instances of the three methods, the results are mostly proportional to each other, implying
consistency in the measurements.
Reverberation Time Results Summary
Cabaret Configuration
571,742 ft
3
Lyric Configuration
504,785 ft
3 Quantification
Methods
without drapery with drapery without drapery with drapery
1 Measured - T
60
1.39 1.25 1.78 1.26
2
Simulated
EYR T
60 500Hz
2.18 1.44 2.68 1.91
3
Calculated
EYR T
60 500Hz
2.22 1.45 2.71 1.98
Table 14 Reverberation Time Summary of all Quantification Methods
10.2.0 Unexpected Results
The Lyric configuration achieves the longest reverberation time even though considered to have
the lower cubic volume of the two performance configurations. This is an unexpected result
according to the Sabine Equation (section 3.4.1) because the lower the cubic volume of a space
the shorter the RT
60
. Therefore, although the Lyric results are consistent for all three acoustical
91
measuring processes, after a critical review of the input data, the reasons for this anomaly are not
consistent.
There are three possible causes for the longer reverberation time in the lyric configuration:
1. Coupled volume: The volume above the stage house (fly space) was open to the main
house causing an unexpected coupled volume. In the Cabaret configuration the stage
house is not coupled with the main house because the moveable ceiling closed off the
stage house opening of the fly space.
2. Vertical surface absorption: The Lyric configuration has less absorptive surfaces
compared to the Cabaret model.
3. Audience area: The audience area had the greatest assigned absorption coefficient
and the cabaret configuration had over 30% more audience surface area than the
Lyric.
Two possible causes apply to the measurements of the existing space: (1) the coupled volume and
(2) the vertical surface absorption. When the CATT models were simulated there were only two
possible causes for a longer reverberation time: (2) the vertical surface absorption or (3) the
audience area. In the analytic calculation, the same possible reasons for the CATT results apply.
Therefore, the cause for a longer reverberation time must either result from (2) inconsistent
vertical surface absorption or (3) the smaller surface area for audience absorption; the fly space is
an eliminated possible cause since it was not simulated in the CATT computer prediction nor
considered in the analytic Eyring calculation.
However, there are other potential causes for the unexpected results:
1. Operator error
2. Computer error
92
Firstly, operator error, one should not assume rules of thumb absolute. According to reverberation
time equations it becomes fundamental acoustic knowledge that spaces with greater cubic
volumes have longer reverberation time. This statement does not always apply if one overlooks
the geometry of the space which could influence the results. Secondly, the computer output could
have been incorrect due to the programmer or the program itself. I could have incorrectly or
inconsistently input the data for the acoustical characteristics of the Cerritos Center space. The
possibility also exists that the software could be in error which would require simulating the same
model in another acoustic program to validate any flaws.
10.3.0 Summary
Although unexpected results were generated from the three quantification methods, it is not an
impossible prediction. The results have confirmed that the sound absorptive curtains provide a
broad range reverberation times. But the unexpected results also provided an empirical
observation that the careful balance between audience absorption, coupled volumes and the lack
of assigned scattering coefficients also make serious reverberant impressions. Changing any of
these physical attributes also changes acoustical characteristics, such as clarity and loudness,
confirming that two spaces with the same reverberation time can sound completely different.
93
Chapter 11 Conclusion and Future Research
11.1.0 Conclusions
Variable reverberation using passive architectural methods and active electronic variable acoustic
strategies have been extensively introduced in this thesis to understand their impact and
possibilities with architectural design. Three quantitative strategies were used to measure and
analyze a multipurpose performance space. The architectural and electronic variability employed
generated considerable impacts on the acoustical characteristics of the space.
As one prime acoustical indicator of a spatial enclosure, reverberation time was critically
evaluated to narrow the investigation for variable impacts. As a result, passive acoustical
techniques provided a very effective range, albeit expensive, of reverberation times for a
multipurpose performance spaces. The combination of passive and active acoustical strategies
provides an almost universally effective range of reverberation time for performance spaces.
However, architectural methods of variability are narrower in acoustic range than electronic
methods. Electronic variation is capable of adding reverberation but cannot reduce it, thus it is
most effective when the initial reverberation time for a space is short.
The sole application of active variability in a performance space is very flexible, economical and
used to overcome the physical limitations that the architectural characteristics of a space cannot.
However, this does not eliminate the need for good architectural acoustical design because the
beginning of the design process is the room itself whose governing architectural characteristics
determine the integration of an active electronic system.
94
11.2.0 Future Research
In addition to the Zwicky Box (section 2.4.0) provided by this thesis, it would be useful to make a
decision matrix in the form of a Zwicky Tree to guide architects in the design process. The
objective of the guideline would produce acoustical recommendations for individual performance
space designs aggregated from the morphological Tree.
A cost comparison of passive and active variable acoustic systems could be developed to provide
architects with knowledge of methods for variability as well as the financial impact of
architectural changes per technique. Estimates for both architectural alterations and electronic
enhancement for the same space could be provided and compared.
95
BIBLIOGRAPHY
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REFERENCES
CHRISTOFF, J. P., 2005. Principal, Veneklasen Associates. Santa Monica, CA. (Email:
jchristoff@veneklasen.com
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Sweden. (Email: bengt@catt.se)
GOOLD, KEVIN. 2005. Sound Engineer. CALARTS (Email: kgoold@verizon.net)
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99
GLOSSARY
BASS RATIO (BR) is the measure of absolute strength of sound in low frequencies bands also
known as warmth. [Beranek]
BRILLIANCE is the persistence of sound at low frequencies or extended low frequency
reverberation. [Siebein] It’s the treble frequencies which decay slowly.
CLARITY (C
80
, C
50
) is the degree to which a listener can distinguish sounds in a performance.
[Beranek] It relates to clarity in music and intelligibility for speech. It is the physical sound
reflections that arrive shortly after the direct sound. [Siebein] It is the ratio of the sound energy in
the first 50 or so milliseconds to the following.
EARLY DECAY TIME (EDT) is a reverberation time derived from the initial 10 dB of decay. It
is the length of time that it takes for the sound to decay 10 dB after the sound source is turned off.
EDT more closely corresponds to subjective evaluation of the reverberation time then RT. It
affects principally the hall's support to the voice and adds definition to the higher tones of music.
The measurement is multiplied by the factor of 6 to make it comparable with RT60. [ProAV]
ECHOES are delayed reflections sufficiently loud enough to annoy the musicians on stage or the
listeners in the hall. [Beranek]
ENSEMBLE is the sound reflection that allows the musicians across stage to be heard. [Siebein]
ENVELOPMENT, LATERAL ENERGY FRACTION (LEF) is degree to which reverberant
sound seems to surround the listener in all directions. [Beranek] It is physically the early sound
reflections arriving at the listener up to 80 msec after the direct sound. [Siebein]
INITIAL TIME DELAY GAP (ITDG) refers to musical intimacy. It is the arrival of the first
sound reflection from a building surface shortly after the direct sound. [Siebein] If the time
difference between the direct sound and the first reflection is short, the hall sounds intimate.
[Beranek] Some of the best halls have an ITDG of 25msec whereas a poor hall may have an
ITDG of over 60 msec.
INTERAURAL CROSS CORRELATION COEFFICIENT (IACC) defines the feeling of
spaciousness. It is the late sound energy arriving from the sides after 80 – 100 msec. [Siebein]
The IACC measure the Binaural Quality Index (BQI) which are the sound waves which arrive at
the listeners ears from lateral directions measured in frequency range of 350 Hz to 2850 Hz.
[Beranek]
REVERBERATION TIME (RT) is the amount of time it takes for a sound in a space to be
reduced by 60 decibels after it has stopped. It is measured in seconds.
STAGE SUPPORT (S
t
) Absorption from the seating area of the audience and the orchestra.
STRENGTH (G) is the loudness of sound measured in decibels (dB). It is the physical sound
reflections from the ceiling and walls shortly after the direct sound. [Siebein]
100
APPENDIX A Variable Passive Methods
101
APPENDIX B Variable Active Methods
102
APPENDIX B Variable Active Methods Continued
103
APPENDIX C Analytic Eyring Calculation Spreadsheets
Cabaret Configuration without Drapery
104
Cabaret Configuration with Drapery
105
Lyric Configuration without Drapery
106
Lyric Configuration with Drapery
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University of Southern California Dissertations and Theses
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Asset Metadata
Creator
Valmont, Elizabeth
(author)
Core Title
Variable reverberation in performance spaces: Passive and active acoustic systems
Degree
Master of Building Science / Master in Biomedical Sciences
Degree Program
Building Science
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
Architecture,OAI-PMH Harvest,Physics, Acoustics
Language
English
Contributor
Digitized by ProQuest
(provenance)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c16-50756
Unique identifier
UC11338115
Identifier
1435121.pdf (filename),usctheses-c16-50756 (legacy record id)
Legacy Identifier
1435121.pdf
Dmrecord
50756
Document Type
Thesis
Rights
Valmont, Elizabeth
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
Physics, Acoustics