Sound Systems: Design and Optimization: Modern Techniques and Tools for Sound System Design and Alignment

526 Pages·2007·31.76 MB·English

Sound Systems:
Design and Optimization
Modern techniques and tools for
sound system design and alignment
Bob McCarthy
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Focal Press is an imprint of Elsevier
III
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First edition 2007
Copyright © 2007, Bob McCarthy. Published by Elsevier Ltd. All rights reserved
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British Library Cataloguing in Publication Data
McCarthy, Bob
Sound systems design and optimization modern techniques
and tools for sound system design and alignment
1. Sound - Recording and reproducing
I Title
6213'893
Library of Congress Control Number: 2006933362
ISBN-13: 978-0-240-52020-9
ISBN-10: 0-240-52020-3
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IV
C o n t e n t s
Preface ix Acoustic Transmission 44
Acknowledgements xvi Power, Pressure and Surface Area 44
Environmental Effects: Humidity and
SECTION 1: SOUND SYSTEMS 1 Temperature 46
Acoustic Transmitters: Loudspeakers 47
1. Transmission 3
Reference 59
Transmission Goals 3
Audio Transmission Defined 4 2. Summation 60
Time and Frequency 4 Overview 60
Wavelength 5 Properties of Audio Summation 61
The Waveform 8 Audio Summation Defined 61
Transmission Quantified 10 Summation Criteria 61
Decibels 10 Summation Quantity 63
Power 16 Electrical vs. Acoustical Summation 63
Frequency Response 17 Acoustical Source Direction 64
Polarity 19 Summation Math 64
Latency 19 Summation Amplitude 65
Analog Audio Transmission 19 Summation Phase 66
Line Level Devices 20 Response Ripple 70
Line Level Interconnection 32 Summation Zones 71
Speaker Level Devices — Power Amplifiers 35 Comb Filtering: Linear vs. Log 78
Speaker Level Interconnection — Speaker Cables 40 Summation Geometry 79
Digital Audio Transmission 42 Acoustical Crossovers 87
Digital Audio Devices 42 Acoustic Crossover Defined 87
Digital Audio Interconnection 43 Crossover Classes 88
V
Spectral Dividers and Spectral Crossovers 89 Comparing Microphones to Our Ears 178
Spatial Dividers and Spatial Crossovers 101 Measurement Microphones 179
Speaker Arrays 112 References 180
Introduction 112
Speaker Array Types 112 SECTION 2: DESIGN 181
Coupled Arrays 115
4. Evaluation 183
Uncoupled Arrays 125
Introduction 183
Speaker/Room Summation 140
Natural Sound vs. Amplified Sound 184
Analogous Functions 140
Contrasting Emission, Transmission and
Speaker/Room Summation Types 143
Reception Models 185
Absorption Effects 147
Transmission Path Differences 186
Environmental Effects 147
Relating the Worlds of Acousticians and
3. Reception 150 Audio Engineers 191
Introduction 150 Comparing Our Goals 191
Loudness 151 The Middle Ground 198
Loudness and dB SPL 151 Moving Forward 201
The Equal Loudness Contours 152 Reference 205
Localization 153
5. Prediction 206
Introduction 153
Introduction 206
Sonic Image 153
Drawings 207
Vertical Localization 154
2-D Drawing Types 207
Front/Back Localization 157
3-D Drawing Types 208
Horizontal Localization 157
2-D Drawings in a 3-D World 208
Tonal, Spatial and Echo Perception 164
Scale 212
Introduction 164
Acoustic Modeling Programs 212
Tonal Perception 165
Introduction 212
Echo Perception 167
A Very Brief History 213
Spatial Perception 168
Speaker Data Files 214
Perception Zone Detection 169
Acoustic Transmission Properties 220
Stereo Perception 169
Material Absorption Properties 225
Introduction 169
Characterizing Summations 226
Panoramic Field 170
Applications 229
Stereo Scaling 171
Conclusions 230
Stereo Side-Effects 175
Amplified Sound Detection 176 6. Variation 232
Distortion 176 Introduction 232
Compression 176 The Minimum Variance Principles 235
Frequency Response Coloration 176 Variation Defined 235
False Perspective 176 Causes and Standard Progressions of
Microphone Reception 178 Variance 235
Introduction 178 Minimum Variance vs. Maximum SPL 242
VI
The Speaker/Room Link: Aspect Ratio 242 Main Systems 325
Protractors and Pizza 242 Sidefill 327
Maximum Acceptable Variance 243 Infill 327
Asymmetric Coverage Considerations 243 Downfill 328
The Coverage Bow Method 244 Frontfill 328
The Forward Aspect Ratio 244 Delays 328
The Proximity Ratio 246 The Scalable Design 330
Minimum Level Variance 247 Scaling for Power 330
Single Speakers 248 Overlapping for Power 330
Coupled Speaker Arrays 253 Scaling the Shape 331
Uncoupled Speaker Arrays 260 Array Design Procedures 331
Minimum Spectral Variance 265 Main System Design 331
Relating Aspect Ratio, Beamwidth and Symmetric Coupled Point Source 332
Speaker Order 265 Asymmetric Coupled Point Source 333
Speaker Array Methods 274 Asymmetric-Composite Coupled Point Source 337
Minimum Ripple Variance 303 Symmetric Uncoupled Line Source 341
Subwoofer Arrays 303 Asymmetric Uncoupled Line Source 342
End Fire 304 Symmetric Uncoupled Point Source 342
Two-Element In-Line Technique 305 Asymmetric Uncoupled Point Source 342
Inverted Stack 305 Symmetric Uncoupled Point Destination 342
Coupled and Uncoupled Line Source 306 Asymmetric Uncoupled Point Destination 343
Coupled and Uncoupled Point Source 308 The Diagonal Plane 343
Conclusion 309 Balcony Battles 346
Speaker Order and Beamwidth 309 Multichannel Sound 350
Maximum Power vs. Minimum Variance 310
Minimum Variance Coverage Shapes 310
SECTION 3: OPTIMIZATION 353
7. Specification 314
Introduction 314 8. Examination 355
The Principles of Specification 314 Examination Defined 355
Specification Defined 314 Physical Measurement Tools 356
Goals and Challenges 315 Inclinometer 356
Specific Questions 315 Protractor 356
Specific Answers 318 Origami Angle Finder 356
Compromise 319 Laser Pointer 357
Channel/System Types 320 Thermometer 358
Mono 321 Hygrometer 358
Stereo 321 Simple Audio Measurement Tools 358
Surround 322 Volt/ohm meter (VOM) 358
Source Effects 324 Polarity Tester 359
System Subdivision 324 Listen Box 359
Subsystem Types 325 Impedance Tester 359
VII
Oscilloscope 360 Approaches to Calibration 426
Sound Level Meter 360 Anarchy 426
Real-Time Analyzer (RTA) 360 Monarchy 427
Complex Audio Measurement Tools 362 Capitalism 427
The Fourier Transform 363 Democracy 427
Analyzer Basics 363 TANSTAAFL and Triage 428
Signal Averaging 370 Access to Information 428
Single-Channel Spectrum Applications 372 Calibration Subdivision 428
Transfer Function Measurement 374 Physical Access 430
Other Complex Signal Analyzers 397 Electronic Access 430
Analysis Systems 399 Acoustic Access 432
Reference 400 Microphone Position Strategies 445
Procedures 452
9. Verification 401
Acoustic Evaluation 452
Introduction 401
Level Setting 453
Test Structure 401
Speaker Position Adjustment 455
Testing Stages 402
Equalization 458
Access Points 403
Delay Setting 463
Test Setup 403
Order of Operations 467
Procedures 406
Practical Applications 473
Noise Over Frequency 406
Finishing the Process 473
Total Harmonic Distortion + Noise (THD + n) 408
Listening 473
Maximum Input/Output Capability Over
Ongoing Optimization 474
Frequency 409
Using Program Material as the Source 474
Latency 412
Audience Presence 475
Polarity 415
Temperature and Humidity 476
Frequency Response 415
Stage Leakage 476
Phase Response over Frequency 417
Stage Microphone Summation 477
Compression 418
Feedback 478
Microphone Verification 419
Multichannel Program Material 478
Microphone Match 420
Show Mic Positions 479
Microphone Response 420
Subwoofers as a Program Channel 480
Post-Calibration Verification 421
Final Word 480
Additional Considerations 423
Afterword 481
10. Calibration 424
Glossary 482
Calibration Defined 424
Bibliography 492
Goals 425
Index 493
Challenges 425
Strategies 425
Techniques 426
VIII
P r e f a c e
This book is about a journey. On the one hand, the sub- University. This was no simple matter since there was no
ject is the journey of sound as it travels through a sound such thing as a degree in audio. I soon discovered the Inde-
system, then through the air, and inevitably to a listener. pendent Learning Program. Under the auspices of that
On the other hand, it is a journey which concerns my own department, I assembled together a mix of relevant courses
quest to understand the complicated nature of this sound from different disciplines and graduated with a college level
transmission. The body of this text will detail the strictly degree in my self-created program of audio engineering.
technical side of things. First, however, I offer you some of
the personal side.
I was supposed to build buildings. Unbeknownst to
me at the time, this calling was derailed on February 9,
1964 by the appearance of the Beatles on the Ed Sullivan
show. Like so many of my generation, this landmark event
brought popular music and an electric guitar into my life. I
became a great enthusiast of live concerts which I regularly
attended throughout my youth at any chance presented.
For years, it remained my expectation that I would enter
the family construction business. This vision ended on a
racetrack in Des Moines, Iowa on June 16,1974. The experi-
ence of hearing the massive sound system at this Grateful
Figure 0.1 Ticketstub from the June 16,1974 Grateful Dead concert in Des
Dead concert set my life in a new direction. On that day I
Moines, Iowa
made the decision that I was going to work in live concert
sound. I wanted to help create this type of experience for By 1980,I had a few years of touring experience under
others. I would be a mix engineer and my dream was to my belt and had moved to San Francisco. There I forged
one day operate the mix console for big shows. I set my relationships with John Meyer, Alexander Yuill-Thornton II
sights on preparing for such a career while at Indiana (Thorny), and Don Pearson. These would become the key
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relationships in my professional development. Each of us mixed another show, resetting my vision to the task of
was destined to stake our reputations on the same piece of helping mix engineers to practice their art. For Don, John,
equipment: the dual channel FFT analyzer. Thorny and many others, the idea of setting up a system
without the presence of the FFT analyzer was unthinkable.
I would like to say that I was involved in live concert
The bell could not be unrung. From the very beginning,
measurement with a dual channel FFT analyzer from day
we saw its importance and its practical implications. Our
one, but this is not the case. The process was pioneered by
excitement was palpable, with each concert resulting in an
John Meyer on a Saturday night in May of 1984. John took
exponential growth in knowledge. We all saw it as a break-
the analyzer, an analog delay line and some gator clips to
through at the time and we introduced it to every one who
a Rush concert in Phoenix, Arizona. There he performed
had an open mind to listen. The first product to come from
the first measurements of a concert sound system using
the FFT analysis process was a parametric equalizer. A
music as the source while the audience was in place. I was
fortuitous coincidence of timing resulted in my having
not destined to become involved in the project until the
etched the circuit boards for the equalizer on my back
following Monday morning.
porch over the weekend that John was in Phoenix with
From that day forward, I have never been involved in a
Rush. This side project (a bass guitar preamp) for my friend
concert or a sound system installation without the use of a
Rob Wenig was already 6 months late, and was destined to
dual channel FFT analyzer. Also from that day I have never
be even later. The EQ was immediately pressed into service
when John nearly fell over when he saw that it could cre-
ate the complementary response (in both amplitude and
phase) to what he had measured in Phoenix. The CP-10
Figure 0.3 November, 1984 Photo of Luciano Pavarotti, Roger Gans and the
Figure 0.2 July 14,1984, Grateful Dead, Greek Theater, Berkeley, California. author (back row), Drew Serb, Alexander Yuill-Thornton II, and James Locke
The author with the primordial version of SIMlm (photo Clayton Call) (front row) (photo Drew Serb)
X
was born into more controversy than one might imagine. This gave way to a more challenging and interesting
Equalization has always been an emotional "hot button" direction for us: the quest beyond the mix position. Moving
but the proposition that the equalizer was capable of coun- the mic out into the space left us with a terrible dilemma:
teracting the summation properties of the speaker/room the new positions revealed conclusively that the one-size-
interaction was radical enough that we obtained the sup- fits-all version of system equalization was utter fantasy.
port of Stanford's Dr. Julius Smith to make sure that the The precision tuning of parametric filters carried out with
theory would hold up. great care for the mix position had no justification at other
locations. The interaction of the miscellaneous parts of the
The first one outside of our company to really take the
speaker system created a highly variable response through-
concept of in-concert analysis on in the field was Don
out the room. The goal for us shifted from finding a perfect
Pearson, who was then touring as the system engineer for
equalization to the quest for uniformity over the space.
the Grateful Dead. Don and the band immediately saw the
benefit and, lacking patience to wait for the development This would require the subdivision of the sound system
of what would become the Meyer Sound SIM System, into defined and separately adjustable subsystems, each
obtained their own FFT analyzer and never looked back. with individual level, equalization and delay capability.
Soon thereafter Luciano Pavarotti followed under the The subsystems were then combined into a unified whole.
guidance of Roger Gans, sound designer in charge of the The rock and roll community was resistant to the idea, pri-
arena-scale performances given by that artist. We figured marily because it involved turning some of the speakers
it was a matter of months before this became standard down in level. The SPL Preservation Society staunchly
operating procedure throughout the industry. We had opposed anything that might detract from the maximum
no idea it would take closer to 20 years! The journey, like power capability. Uniformity by subdivision was not worth
that of sound transmission, was far more complex than pursuing if it cost power. Without subdivision, the analy-
we ever expected. There were powerful forces lined up sis was pretty much stuck at the mix position. If we are not
against us in various forms: the massive general resistance going to change anything, why bother to look further?
of the audio community to sound analyzers and the pow-
There were other genres that were open to the idea. The
erful political forces advocating for alternate measure-
process required the movement of a microphone around
ment platforms, to name a few.
the room and a systematic approach to deconstructing and
In general, the live sound community was massively reconstructing the sound system. We began developing
opposed to what they conceptualized as an analyzer dic- this methodology with the Pavarotti tours. Pavarotti was
tating policy to the creative forces involved in the music using approximately ten subsystems. When we moved into
side of the experience. Most live concert systems of the day the musical theater world with Andrew Bruce, Abe Jacob,
lacked complexity beyond piles of speakers with left and Tony Meola, Tom Clark and other such sound designers,
right channels. This meant that the process of alignment our process had to be honed to take on even more complex-
consisted of little more than equalization. Since all of the ity. Our emphasis changed from providing a scientifically
system calibration was being carried out at a single loca- derived tonal response to instead providing consistency
tion, the mix position, the scientific and artistic positions of sound throughout the listening space, leaving the tonal
were weighing in on the exact same question at the same character in the hands of the mix engineer. Our tenure as
point in space. Endless adversarial debate about what was the "EQ police" was over as our emphasis changed from
the "correct" equalization ensued since the tonal balancing tonal quality to tonal equality. The process was thus trans-
formed into optimization, emphasizing spatial uniformity
of a sound system is, and always has been, an artistic
while encompassing equalization, level setting, delay set-
endeavor. It was an absurd construct. Which is better — by
ting, speaker positioning and a host of verifications on the
ear or by analyzer?
XI