Sound System Engineering.pdf

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Sound System Engineering

Fourth Edition

Don Davis

Eugene Patronis, Jr.

Pat Brown

Edited by

Glen Ballou

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First published 1975

by Howard W. Sams & Co., Inc.

Indianapolis, Indiana 46268

This edition published 2013

by Focal Press

70 Blanchard Road, Suite 402, Burlington, MA 01803

Simultaneously published in the UK

by Focal Press

2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN

Focal Press is an imprint of the Taylor & Francis Group, an informa business

© 2013 Don Davis, Eugene Patronis, Jr. and Pat Brown

The right of Don Davis, Eugene Patronis, Jr. and Pat Brown to be identified as the authors of

this work has been asserted by them in accordance with sections 77 and 78 of the Copyright,

Designs and Patents Act 1988.

All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form

or by any electronic, mechanical, or other means, now known or hereafter invented, including

photocopying and recording, or in any information storage or retrieval system, without

permission in writing from the publishers.

Notices

Knowledge and best practice in this field are constantly changing. As new research and

experience broaden our understanding, changes in research methods, professional practices,

or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in

evaluating and using any information, methods, compounds, or experiments described herein.

In using such information or methods they should be mindful of their own safety and the

safety of others, including parties for whom they have a professional responsibility.

Product or corporate names may be trademarks or registered trademarks, and are used only

for identification and explanation without intent to infringe.

Library of Congress Cataloging in Publication Data

CIP data has been applied for

ISBN: 978-0-240-81846-7 (hbk)

ISBN: 978-0-240-81847-4 (ebk)

Typeset in Times New Roman and Optimum

by Glen Ballou

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The fourth edition of Sound System Engineering is dedicated to

Carolyn Davis

who is the catalyst that made it happen

and is the glue that held it all together.

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Preface

vii

There are two worlds in audio—one of wave equations, Fourier, Hilbert, and Laplace transforms, and the other of Ohm’s Law, Sabine and Hopkins Stryker. Eugene Patronis, Jr., straddles both like a colossus, as he is able to theorize in Quantum Mechanics and design, build, and service, with his own hands, all components used in audio.

Pat Brown is our new co-author and brings to this volume unique tools he has developed in the course of his loudspeaker testing, particularly directivity measurements, into the twenty-first century. He has taught Syn-Aud-Con seminars all over the world in person as well as through his internet training programs. He is a longtime friend of both Dr. Patronis and Don Davis, and like them, a man who delights in fully sharing his knowledge of sound system engineering with others. We welcome his participation in this volume.

The authors come from two quite different backgrounds: one is academic, the others are industrial and field oriented. “The lion is known by his claw” was said of Newton, whereas the technician approach uses a broad brush to get a workable, if not elegant, answer. Therefore, we have identified each author’s contribution sepa-rately. It’s your privilege to select the approach most applicable to your need. With today’s generation of com-puter users and the wealth of available software it’s you, the reader, who chooses the boundaries of your interests and academic skills. It is our wish that whatever background you bring to the subject you will find new tools for that level and hints of the next.

Sound System Engineering is a widely sold, widely used text on sound system design. The first editions

were oriented toward those planning systems from components available in the existing marketplace, i.e., they were treated as boxes on a diagram. The first editions ignored component design and analysis other than their interconnecting parameters.

When Don and Carolyn Davis, the authors of the first two editions, sought specific advice on component design and in-depth analysis of given components they turned to their long time friend and mentor, Eugene Patronis, Jr. to provide the in-depth analysis he excels in. You will find in this edition both approaches, allow-ing newcomers to operate efficiently while providallow-ing the more experienced an opportunity to achieve a more advanced viewpoint. We know that one can start reading on one level, but as our experience and expertise develops, we are grateful for the more advanced approach. What we read as our learning process starts is much different years later and we become very grateful for the more advanced material.

Those who have benefited from a rigorous and thorough academic background will find that Eugene Patronis’ work is a succinct summary of all you should have absorbed intellectually whereas the less sophisti-cated approach may contain useful nuggets that have surmounted “gray” areas in system compromises. This dual approach provides some seemingly uneven interconnects but benefits from the diverse experience of the authors.

The authors have retained their own mental images of who they are writing for, often a combination of both approaches. We hope that you will find this volume useful in pursuit of our mutual goal of truly engineered rather than merely assembled sound systems.

Thanks to Glen Ballou

Our special thanks to Glen Ballou, who transcribed our material into a publishable format. These simple words can’t begin to describe the agony he has endured.

Pat Brown, Don Davis, Eugene Patronis, Jr.

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Chapter

1

Why Sound System Engineering?

by Don Davis

1

1.1 Prerequisites . . . .3

1.2 Basic Electrical Training . . . .3

1.3 Mathematics . . . .3

1.4 Hearing Versus Listening . . . .3

1.5 Craftsmanship . . . .4

1.6 Rigging . . . .4

1.7 Literacy . . . .4

1.8 The Art, Philosophy, and Science of Sound. . . . .4

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Why Sound System Engineering? 3

“Sound” has over the centuries been associated with human hearing (i.e.: “Is there a sound if a tree falls in the forest without a listener present?”) According to Webster, “The sensation perceived by the sense of hearing.” Also from Webster: “Audio, on the other hand, has largely been associated with electrical communication circuits.”

“System” is a word we use to describe any “experience cluster” that we can map as a set of interacting elements over time. Typically a system is mapped by identifying the pathways of information flow, as well as possibly the flow of energy, matter, and other variables. But the flow of information is special; because only information can go from A to B while also staying at A. (Consider: photocopy machines would be useless if one didn’t get to keep the original). Digital systems, analog systems, acoustic systems, etc. should be regarded by a system engineer as so many “black boxes” that need to be matched, interconnected, and adjusted. The internal circuitry should be the interest of the component designer/manufacturer.

1.1 Prerequisites

What kind of background should an aspiring sound system engineer possess is an often asked question. A list of desirable experiences would include: 1. Some basic electrical training.

2. An interest in mathematics.

3. A good ear (a love of quality sound and acute aural senses).

4. Skill with basic tools.

5. Some appreciation of the perils of rigging. 6. Good reading and writing skills.

7. A genuine appreciation for the art, philosophy, and science of sound.

1.2 Basic Electrical Training

Time spent as an apprentice electrician is not wasted. In many cases, large sound systems deal with separate power systems, and safety springs from knowledge of the power circuits that are involved. Conduits, cable sizes, and types of grounding and shielding can be complex even at power frequencies. Knowledge of the electrical codes is a necessary fundamental tool.

1.3 Mathematics

From Ohm’s law to the bidding process, an ability to quickly learn new algorithms both speeds up processes and ensure profits. In today’s markets “cut and try” is too expensive of both time and money to allow avoidance of basic computer skills; the use of programs such as Mathcad for both technical and financial calculations is important. Knowing what the formulae actually used are doing is essential. In order to trust any computer program, having done it first on paper the hard way, provides knowledge and confidence in the fast way and leaves you capable of detecting unexpected anomalies that might occur. Yes! You do need more than arithmetic.

1.4 Hearing Versus Listening

We all hear. But what we listen to depends to a large degree on our previous listening experiences. I have often stood in the center of an acoustic anomaly such as a reflection from an undesirable angle, distance, and level, that was destroying speech intel-ligibility, and watched the startled expression on the face of a person sitting in the pew as a piece of acoustical material is passed between his ears and the reflection, which restored intelligibility.

Once experienced, your eyes, ears, and brain, can recognize such problems by simply walking through them. Sensitive listening is a great plus in sound system work, and it is a sufficient reason to hear as many venues as possible under normal usage condi-tions. I am always surprised when I see engineers trying to design a church sound system from a set of drawings without ever having attended a service to see what their actual needs are versus what they’d like to provide them.

Because all sound system design starts in the acoustic environment and works back from there to the input, failure to experience the normal use of the space can be fatal to the ultimate end result. On one occasion I was listening in a mammoth cathedral from a position behind the altar, when asked by the administrator, if our design could solve their intelli-gibility problem. The priest about to conduct the service spoke to me, and because of a combination of a speech defect and in a foreign accent, I was unable to understand him to sufficiently compre-hend his message. I had to tell the administrator that our system could only raise the priest’s audio level, not his intelligibility.

Watching successful ministers, politicians, and other public figures use microphones reveals a world of problems unaddressed by the most

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compe-4 Chapter 1

tent engineer. In one case the engineer was asked if he could “put more soul in the monitor.”

1.5 Craftsmanship

Possession of a guitar does not make one a musician nor do tools make a craftsman. Skill with basic tools manifests itself in clean solder joints, orderly cabling, careful labeling on panels and terminals. Construction of successful loudspeaker arrays is a challenge to both artistry and craftsmanship. In my experience craftsmanship is a direct expression of character.

1.6 Rigging

Rigging, in itself, is a business as complex and diffi-cult as engineering the sound system and often behooves sound contractors to seek out professional assistance when required to hang large, heavy, and expensive loudspeaker arrays.

I was involved in a consulting job for a major public arena venue where the owner intended to hang the new array from the previous array’s rigging. (A complicated system of cables and drums for raising and lowering the arrays). I insisted on their hiring a notable rigging authority who went up into the rigging with a camera and came down with a dozen photographs of impending disasters, such as grooves worn in the drums by the cables, frayed cables, unsafe connectors, and a lack of safety cables, to cite but a few of the problems. There are recorded fatalities from falling arrays. It is not a business for amateurs.

1.7 Literacy

This would seem obvious, but is often a weak link in an otherwise successful background experience. Sales presentations, bid offers, instruction manuals for the operators of your systems, all require reading and writing skills. Communications with customers, suppliers, and consultants needs to be thoughtfully and concisely written. For example, the contractor should be on record telling the customer that the design will function properly only if the HVAC contractor meets the specified noise criteria that is provided in the Specification. Failure to do so can be disastrous. A memo on file with the owner can save the sound contractor and/or consultant from having to take the blame.

1.8 The Art, Philosophy, and Science of Sound

The design of well-engineered sound systems stands on the shoulders of the giants who created the communication industry. “Art precedes science” is an axiom that is eternally true. Prof. Higgins as portrayed in the film, “My Fair Lady,” exemplified the majesty of language, the science of studying its proper sounds, and meanings, and the engineering systems used in that earlier day. Even today the most difficult sound systems to design, build, and operate are those used in the reinforcement of live speech. Systems that are notoriously poor at speech rein-forcement often pass reinforcing music with flying colors. Mega churches find that the music reproduc-tion and reinforcement systems are often best sepa-rated into two systems

1.9 Fields

From my first view of the rainbow depiction of the electromagnetic spectrum from dc to gamma ray I have striven to gain a conceptual mental view of various fields, Fig. 1-1. Physical science, during the past century, has come to the conclusion that the Universe is some sort of field. The nature of this universal field remains controversial—is it matter which has mass? Or something more ethereal such as information?

Michael Faraday, 1831, said “Perhaps some

force is emanating from the wire.”

A Cambridge man said “Faraday, let me assure

you, at Cambridge our electricity flows through the wire.”

Oliver Heaviside, 1882, from his book, Electrical

Papers, Vol. 1:

Had we not better give up the idea that energy is transmitted through the wire altogether? That is the plain course. The energy from the battery neither goes through the wire one way nor the other. Nor is it standing still, the transmission takes place entirely through the dielectric. What, then, is the wire? It is the sink into which the energy is poured from the dielectric and there wasted, passing from the electrical system altogether.

John Ambrose Fleming in 1898 wrote:

It is important that the student should bear in mind that, although we are accustomed to speak of current as flowing through the wire in one direc-tion or the other, this is a mere form of

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Why Sound System Engineering? 5

words. What we call the current in the wire is, to a large extent, a process going on in the space or material outside the wire….

Ernst Guillmin, Communications Networks, Vol. II, 1935

Heaviside is the only one who considers the nature of the sources as well as the boundary effects both for the initial buildup or transient behavior and for the steady-state condition. He is the first also, to consider the leakage through the insulation, in view of which the true significance of the inductance parameter may be appreciated…. His work is a first approximation only as compared with other, more rigorous treatments. For the engineer, however, this first approximation is usually suffi-cient….

Further,

The concept of guided waves, before Maxwell, the physical picture of the propagation of electricity through a long circuit was more or less that which is frequently presented in elementary textbooks, where the hydraulic analogy to an electric circuit is given for purposes of visualization. That is, the seat of the phenomenon was taken to be within the conductor. What occurred outside the conductor could be neither definitely formulated nor described. The electrical energy was thought of as being transmitted through the conductor which, therefore, became of prime importance. In fact, if we accept this point of view altogether, it becomes impossible to conceive of a flow of elec-trical energy from one point to another without the aid of an intervening conductor of some sort. It has been the writer’s experience that many students are quite wedded to this point of view, so much so, in fact, that to them the propa-gation of energy without wires (wireless transmission) becomes a thing alto-gether apart from other forms of trans-mission involving an intervening conducting medium.

An appreciation of Maxwell’s theory of electro-magnetic wave propagation brings the so-called wireless and wired forms of transmission under the

same roof, so to speak. They merely appear as special cases of the same fundamental phenom-enon…. The presence of a conductor merely causes the field be broken up into various components, some of which are assigned to the conductor itself, others to the surrounding medium, and still others to the surface separating the two media.

From the Standard Handbook for Electrical

Engineers by Donald G. Fink and H. Wayne

Beaty…. There is a section entitled, “Electromag-netic Wave Propagation Phenomenon.”

The usually accepted view that the conductor current produces a magnetic field surrounding it must be displaced by the more appropriate one that the electromagnetic field surrounding the conductor produces, through a small drain on the energy supply, the current in the conductor. Although the value of the latter may be used in computing trans-mitted energy, one should clearly recognize that physically this current produces only a loss and in no way has a direct part in the phenomenon of power transmission.

Ralph Morrison’s website has some comments on electromagnetic laws.

The laws I want to talk about are the basic laws of electricity. I’m not referring to circuit theory laws as described by Kirchhoff or Ohm but the laws governing the electric and magnetic fields. These fields are fundamental to all electrical activity whether the phenomenon is lightning, electrostatic display, radar, antennas, sunlight, and power gener-ation, analog or digital circuitry. These laws are often called Maxwell’s equations. Light energy can be directed by lenses, radar energy can be directed by waveguides and the energy and power frequen-cies can be directed by copper conductors. Thus we direct energy flow at different frequencies by using different materials. For utility power the energy travels in the space between conductors not in the conductors. In digital circuits the signals and energy travel in the spaces between traces or between the traces and the conducting surfaces. Buildings have halls and walls. People move in the halls not the walls. Circuits have traces and spaces, signals and energy moves in the spaces not in the traces.

Scanning the Electromagnetic Spectrum Chart from dc through radio waves, light itself, out to gamma rays we can see that electromagnetic fields play a key part in our lives, Fig. 1-1.

Researchers studying human consciousness are finding electromagnetic phenomenon in addition to the previously known electrical phenomena. When EMI (electromagnetic interference) occurs in audio systems RF spectrum analyzers can be useful tools.

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6 Chapter 1

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Chapter

2

Voices Out of the Past

by Don Davis

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2.1 Significant Figures in the History of Audio and Acoustics . . . 9

2.2 1893—The Magic Year . . . .11

2.3 Bell laboratories and Western Electric . . . .11

2.4 Harvey Fletcher (1884–1981) . . . .12

2.5 Harry Nyquist (1889–1976) . . . .12

2.6 The dB, dBm, and the VI . . . .12

2.7 Sound System Equalization . . . .13

2.8 Acoustic Measurements—Richard C. Heyser (1931–1987) . . . .13

2.9 Calculators and Computers . . . .14

2.10 The Meaning of Communication . . . .14

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Voices Out of the Past 9

During the fall of 1978, we stopped in Williams-burg, Virginia. As is our habit, we explored the old-bookstores and asked whether they had any books on acoustics. We were told they had just one, an old one. They brought out a vellum bound first edition dated 1657, Magiae Universalis by Gaspare P. Schotto (1608–1666).

He was a colleague of Athanasius Kircher (1602–1680) whose work was discussed in Fred-erick Vinton Hunt’s valuable book Origins in

Acoustics. The book, written in Latin, was published

at Herbipoli, the modern Wurzburg, Germany. Some of the plates from it are shown in Figs. 2-1 through

2-6.

In researching the history of this book we found that it was mentioned in the Edinburgh magazine (volume 12, page 322) in 1790, as well as in Hunt’s,

Origins in Acoustics, regarding Boyle and Hooke’s

work. Magiae Universalis was used by Robert Boyle (1627–1691) and his assistant Robert Hooke (1635–1703) as they worked to improve air pumps and experiment with ticking watches in vacuums.

This book described Otto Von Guericke’s work with air pumps.

An erudite discussion of Athanasius Kircher’s book, Phonurgia Nova by Lamberto Tronchin in January 2009 edition of Acoustics Today, provides one of the best surveys of the period under

discus-sion. Richard C. Heyser put it best when he said, “You don’t really own that book, you are its

tempo-rary custodian.”

These men were Galileo’s contemporaries and were representative of the desire for scientific knowledge, as well as the collectors of all the myths of their age.

2.1 Significant Figures in the History of Audio and Acoustics*

Often, in the modern scheme of things, history is not mandatory in engineering classes taught at the university level. Significant historical figures are encountered as Faraday’s ice-pail experiment, Maxwell’s equations, Ohms’ law etc., but not studied in depth.

Electrical engineers encounter the SI terms, poten-tial difference in volts (Alessandro Volta), current in amperes (Andre Marie Ampere), capacitance in farads (Michael Faraday), and thermodynamic temperature in Kelvin (Lord Kelvin), as units of measurement. These were living breathing men who had occasion to interact with each other and inter-mingle their ideas to the benefit of science. Great seminal ideas belong to the individual, but the

inter-Figure 2-1. Frontpiece of a book published in 1857 at

Herbipoli, the modern Wurzburg, Germany.

Figure 2-2. Water-powered musical instrument that

fascinated our forefathers as much as computers interest us today. From Magiae Universalis.

*. Significant Figures in the History of Audio and Acoustics is an edited version of the chapter, “Audio & Acoustic DNA—Do you

Know Your Audio and Acoustic Ancestors?” in

the 4th_{Edition of the Handbook for Sound}

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10 Chapter 2

mingling of them leads industries. Their predeces-sors and contemporaries such as Joule (work, energy, heat), Charles Coulomb (electric charge), Isaac

Newton (force), Hertz (frequency), Watt (power, radiant flux), Weber (magnetic flux), Tesla (magnetic flux density), Henry (inductance), and Siemens

Figure 2-3. The first bugging system. Horns such as

these were used by Athanasius Kircher, a contempo-rary of Kasper Schott, to speak to the gatekeeper from his quarters and to eavesdrop on the conversation taking place in the courtyard. His experimental horn was 22 palms long. (A palm is about 8.7 inches, so his horn was about 16 feet long). From Magiae Universalis.

Figure 2-4. The basic rules for sound reflection as a

geometric problem. From Magiae Universalis.

Figure 2-5. How oracles talk or music can be

trans-mitted from one space to another. From Magiae Univer-salis.

Figure 2-6. Illustrations of reflections, focusing,

diffu-sion, time delay, and creeping. From Magiae Univer-salis.

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(conductance), are immortalized as international SI derived units. Kelvin and Ampere alone have names inscribed as SI base units. Kirchhoff diagrams define the use of these units in circuit theory.

What the study of these men’s lives provides, to the genuinely interested reader, is the often unique way the great ideas came to these men, the persistent pursuit of the first glimmer, and the serendipity that comes from sharing ideas with other talented minds. As all of this worked its way into the organized thinking of mankind, one of the most important innovations was the development of technical soci-eties formed around the time of Newton, where ideas could be heard by a large receptive audience.

Some of the world’s best mathematicians strug-gled to quantify sound in air, in enclosures and in all manner of confining pathways. Since the time of Euler (1707–1783), Lagrange (1736–1813), and d’Alembert (1717–1783), mathematical tools existed to analyze wave motion and develop field theory.

By the birth of the twentieth century, workers in the telephone industry comprised the most talented mathematicians and experimenters in both what was to become electronics and in acoustics. At MIT, the replacement of Oliver Heaviside’s operational calculus by Laplace transforms gave them an envi-able technical lead in education.

2.2 1893—The Magic Year

At the April 18, 1893 meeting of the American Insti-tute of Electrical Engineers in New York City, Arthur Edwin Kennelly (1861–1939) gave a paper entitled “Impedance.”

That same year General Electric, at the insistence of Edwin W. Rice, purchased Rudolph Eicke-meyer’s company for his transformer patents. The genius, Charles Proteus Steinmetz (1865–1923), worked for Eickemeyer. In the saga of great ideas, I have always been as intrigued by the managers of great men, as much as the great men themselves. E. W. Rice of General Electric personified true leader-ship when he looked past the misshaped dwarf that was Steinmetz, to the mind present in the man. General Electric’s engineering preeminence, in those years, proceeded directly from Rice’s extraor-dinary hiring of Steinmetz.

Dr. Michael I. Pupin of Columbia University was present at the Kennelly paper. Pupin mentioned Oliver Heaviside’s use of the word impedance in 1887. This meeting established the correct definition of the word and established its use within the elec-tric industry. Kennelly’s paper, along with the groundwork laid by Oliver Heaviside in 1887, was

instrumental in introducing the terms being estab-lished in the minds of Kennelly’s peers.

The truly extraordinary Arthur Edwin Kennelly, (1861–1939) left school at the age of thirteen and taught himself physics while working as a telegra-pher. He is said to “have planned and used his time with great efficiency,” which is evidenced by his becoming a member of the faculty of Harvard in 1902 while also holding a joint appointment at MIT from 1913–1924. He was the author of ten books and the co-author of eighteen more, as well as writing more than 350 technical papers. Edison had employed A. E. Kennelly to provide physics and mathematics to Edison’s intuition and “cut and try” experimentation. The reflecting ionosphere theory is jointly credited to Kennelly and Heaviside, and known as the Kennelly-Heaviside layer. One of Kennelly’s PhD students was Vannevar Bush, who ran America’s WWII scientific endeavors.

Steinmetz was not at the April 18, 1893 meeting, but sent in a letter-of-comment which included:

It is however, the first instance here, so far as I know, that the attention is drawn by Mr. Kennelly to the corre-spondence between the electrical term ‘impedance’ and the complex numbers. The importance hereof lies in the following: the analysis of the complex plane is very well worked out, hence by reducing the technical problems to the analysis of complex quantities they are brought within the scope of a known and well understood science.

Nikola Tesla (1856–1943) working with West-inghouse designed the ac generator that was chosen in 1893 to power the Chicago World’s Fair.

2.3 Bell laboratories and Western Electric

The University of Chicago, at the end of the Nine-teenth Century and the beginning of the Twentieth Century, had Robert Millikan, America’s foremost physicist. Frank Jewett, who had a doctorate in physics from MIT, and now worked for Western Electric, was able to recruit Millikan’s top students. George A. Campbell (1870–1954) had by 1899 devel-oped successful “loading coils” capable of extending the range and quality of the, at that time, unamplified telephone circuits. Unfortunately, Prof. Michael Pupin had also conceived the idea and beat him to the patent office. Bell telephone paid Pupin $435,000 for the patent and by 1925, the Campbell designed loading coils had saved Bell Telephone Company $100,000,000 in the cost of copper wire alone.

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12 Chapter 2

To sense the ability of loading coils to extend the range of unamplified telephone circuits, Bell had reached New York to Denver by their means alone. Until Thomas B. Doolittle evolved a method in 1877 for the manufacture of hard drawn copper, the metal had been unusable for telephony due to its inability to support its own weight over usable distances. Copper wire went from a tensile strength of 28,000 pounds per square inch with an elongation of 37%, to a tensile strength of 65,000 pounds per square inch and a elongation of 1%.

H. D. Arnold, with the advent of usable copper wire, the vacuum tube amplifier, 130,000 telephone poles, and 25 tons of copper wire was able to estab-lish transcontinental telephony in the year 1915. There was also a public address system at those ceremonies celebrating this accomplishment.

2.4 Harvey Fletcher (1884–1981)

In 1933, Harvey Fletcher, Steinberg and Snow, Wente and Thuras and a host of other Bell Labs engineers gave birth to “Audio Perspective” demon-strations of three channel stereophonic sound capable of exceeding the dynamic range of the live orchestra. Their exhaustive study led to the conclu-sion that to reproduce the sound field would require an infinite number of sources and that the best compromise lay in three channels. They also demonstrated that two channels were sufficient over headphones for binaural recordings. They under-stood that for stereophonic reproduction each of the three channels had to cover all of the audience, a fact many contemporaries are unaware of. Early in my career at Altec, I had the privilege of working with William Snow and having full discussions of their 1933 system.

Edward C. Wente and Albert L.Thuras were responsible for the full range, low distortion, high-powered sound reproduction using condenser microphones, compression drivers, multicellular exponential horns, and horn loaded low-frequency enclosures, all of which were their original designs. The Fletcher loudspeaker, as designed by Wente and Thuras, was a three-way unit consisting of an 18 inch low-frequency driver horn loaded woofer, the incomparable W. E. 555 as a mid range, and the W. E. 597A high-frequency unit.

The power amplifiers and transmission lines were capable of full dynamic range from 30 Hz to 15,000Hz, capabilities often claimed today but seldom realized.

In 1959, Carolyn and I repeated the original geometry tests of the 1933 experiments while working for Klipsch and Associates. Mr Klipsch and

I then traveled to Bell Telephone Laboratories in New Jersey, where we made a demonstration of our results using Klipsch horns in the Arnold Audito-rium. After our demonstration we were shown one of the original Fletcher loudspeakers.

A perspective can be gained, compared to today’s products, when it is realized that Western Electric components like the 555 and the 597 are to be found today in Japan, where originals sell for up to five figures. It is estimated that 99% of the existing units are in Japan. It is of interest to note that many of today’s seekers of quality sound repro-duction are still building tube-type amplifiers employing the W. E. 300 B vacuum tubes.

2.5 Harry Nyquist (1889–1976)

The word inspired means “to have been touched by the hand of God.” Harry Nyquist’s thirty-seven years and 138 US patents while at Bell Telephone Laboratories personifies “inspired.” In acoustics the Nyquist plot is, by far, my favorite for a first look at an environment driven by unknown source. Nyquist also worked out the mathematics that allowed amplifier stability to be calculated leaving us the Nyquist plot which is one of the most useful audio and acoustic analysis tools ever developed. His cohort, Hendrik Bodie, gave us the frequency and phase plots as separate measurements.

Karl Kupfmuller (1897–1977) was a German engineer who paralleled Nyquist work, indepen-dently deriving fundamental results in information transmission, in closed loop modeling, including a stability criterion. Kupfmuller as early as 1928 used block diagrams to represent closed loop linear circuits. He is believed to be the first to do so.

Today’s computers, as well as digital audio devices, were first envisioned in the mid-1800s by Charles Babbage. The mathematics discussed by Lady Lovelace, the only legitimate daughter of Lord Byron, even predicted the use of a computer to generate musical tones.

Claude Shannon went from Nyquist’s paper on the mathematical limit of communication to develop “Information Theory,” which is so important to today’s communication channels.

2.6 The dB, dBm, and the VI

The development of the dB from the mile of stan-dard cable by Bell Labs, their development and sharing of the decibel, the dBm, and the VU via the

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design of VI devices, changed system design into an engineering design.

The first motion pictures were silent. Fortunes were made by actors who could convey visual emotion. When motion pictures acquired sound in 1928, again via Western Electric’s efforts, a large number of these well-known personalities failed to make the transition from silent to sound. The faces and figures failed to match the voices the minds of the silent movie viewers had assigned them. Later, when radio became television almost all the radio talent was able to make the transition because the familiar voices predominated over any mental visual image the radio listener had assigned to that performer. Often, at the opera, the great voices will not look the part, but just a few notes nullify any negative visual impression for the true lover of opera, whereas appearance will not compensate for a really bad voice.

In 1928, a group of Western Electric engineers became the Electrical Research Products, Inc. (ERPI), in order to service the motion picture theaters using Western Electric sound equipment. At the termination of World War II, the standard for the best bass reproduction was the loudspeakers installed in the better motion picture theaters. The goal of the designers of consumer component audio reproduction was to approach the motion picture theater quality. Western Electric had decimated their competition, RCA, in the theater business, so RCA went to court and obtained a consent decree which restricted Western Electric in the field of motion picture sound. At this point some of the engineers involved formed All Technical Services (Altec), which is why it is pronounced all tech, not al-tect. One of the pioneer engineers told me, “Those days were the equivalent of one ohm across Fort Knox.” They bought the Western Electric theater inventory for pennies on the dollar.They also bought the Lansing Manufacturing Company and Peerless Manufacturing which brought James B. Lansing, Ercel Harrison and Bill Martin (Jim Lansing’s brother) into Altec.

2.7 Sound System Equalization

Dr. Wayne Rudmose was the earliest researcher to perform meaningful sound system equalization. Dr. Rudmose published a truly remarkable paper in

Noise Control (a supplementary Journal of the

Acoustical Society of America) in July 1958. At the AES session in the fall of 1967, I gave the first paper on the one-third of an octave contiguous equalizer, which Altec named Acousta-Voicing. Dr. Rudmose was chairman of that AES session.

The control these equalizers allowed over acoustic feedback in live sound systems quickly led to much more powerful sound reinforcement systems.

I introduced variable system equalization in special sessions at the screening facilities in August 1969 to the head sound men, Fred Wilson at MGM, Herb Taylor at Disney, and Al Green at Warner Bros. Seven Arts. These demonstrations were prior to my leaving Altec to start Synergetic Audio Concepts and others reaped the benefits of this work.

Some early workers in equalization imagined they were equalizing the room; equalization is elec-trical, not acoustical, and what it always adjusts is the input to the loudspeaker terminals. It allowed feedback in a reinforcement system, containing a highly efficient, but uneven amplitude response loudspeaker, to be controlled, while increasing the acoustic energy in the room.

2.8 Acoustic Measurements—Richard C. Heyser (1931–1987)

Plato said, “God ever geometrizes.” Richard Heyser, the geometer, should feel at ease with God. To those whose minds respond to the visual, Heyser ’s measurements shed a bright light on difficult mathe-matical concepts. Working from Dennis Gabor’s (1900–1979) analytic signal theory, the Heyser spiral displays the concept of the complex plane in a single visual flash. Heyser was a scientist in the purest sense of the word, employed by NASA, and audio was his hobby. When I first met Richard C Heyser in the mid-1960s, Richard worked for Jet Propulsion Laboratory as a senior scientist. He invited me to his home to see his personal laboratory. The first thing he showed me on his Time Delay Spectrometry (TDS) equipment was the Nyquist plot of a crossover network he was examining.

I gave the display a quick look and said, “That

looks like a Nyquist plot!”

He replied, “It is.”

“But,” I said, “no one makes a Nyquist analyzer.” “That’s right,” he replied.

At this point I entered the modern age of audio analysis. It was a revelation to watch Dick tuning in the signal delay between his microphone and the loudspeaker he was testing until the correct band-pass filter Nyquist display appeared on the screen. Seeing the epicycles caused by resonances in the loudspeaker, and the passage of non-minimum phase responses back through all quadrants, opened up a million questions.

Heyser’s work led to loudspeakers with vastly improved spatial response, something totally unrec-ognized in the amplitude-only days. Arrays became

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14 Chapter 2

predictable and coherent. Signal alignment entered the thought of system designers. Heyser’s Envelope Time Curve (ETC) technology resulted in the chance to meaningfully study loudspeaker–room interactions.

Because the most widely taught mathematical tools proceed from impulse responses, Heyser’s transform is perceived “through a glass darkly.” It is left in the hands of practitioners to further research into the transient behavior of loudspeakers. The decades-long lag of academia will eventually apply the lessons of the Heyser transform to transducer signal delay and signal delay interactions.

I hold Harry Olson of RCA in high regard because, as the editor of the Journal of the Audio

Engineering Society in 1969, he found Richard C.

Heyser’s original paper in the wastebasket; it had been rejected by means of that society’s inadequate, at that time, peer review system.

2.9 Calculators and Computers

Richard C. Heyser gave us the instrumentation and Tom Osborne of Hewlett-Packard gave us the mathe-matical tools to begin to understand what we were actually doing in both electronics and acoustics as applied to sound reinforcement systems. Back in the 1 9 6 0 s , w e u t i l i z e d t e s t e q u i p m e n t f r o m Hewlett-Packard, General Radio,Tektronics, and Bruel and Kjaer. I purchased one of the very first Hewlett-Packard 9100 computer calculators designed by Tom Osborne. The 9100’s transcen-dental functions, memory, and print out facilities led to lengthy acoustic design algorithms. Many of these same algorithms are still used in today’s computers.

When the HP 35 handheld calculator, so named for its thirty-five keys, appeared we immediately put it to use in our teaching. The proliferation of easy-to-use, accurate software such as Mathcad, Matlab, and Mathematica in today’s computers encourages engineers to explore more precise avenues of design. It was of interest to me that a correspondent, to the best Listserv in the business, stated to his peers that he had entered the audio industry via digital equipment and its operation, and was at a loss to understand analog audio.

I first explored the magic of communication via a crystal radio, then the vacuum tube technology, followed by transistors, integrated circuits, and now fully digital equipment electronically; it is comforting to turn to the acoustic side of sound rein-forcement as an old familiar friend. When, as I expect in the not too distant future, the reinforce-ment system reaches the human brain sans passage via air the cycle will be complete.

2.10 The Meaning of Communication

The future of audio and acoustics stands on the Shoulders of the Giants that we have discussed, and numerous ones that we have inadvertently over-looked. The discoverers of new and better ways to generate, distribute, and control sound will be measured consciously or unconsciously by their predecessor’s standards. Fad and fundamentals will be judged eventually, and put into their proper place. Age councils that “the ancients are stealing our inventions.” Understanding an old idea that is new to you can be as thrilling as it was to the first person to make the discovery.

The history of audio and acoustics is the saga of the mathematical understanding of fundamental physical laws. Hearing and seeing are illusionary, restricted by the inadequacy of our physical senses.

That the human brain processes music and art in a different hemisphere from speech and mathe-matics suggests the difference between information, that can be mathematically defined, and communi-cation that cannot. A message is the flawless trans-mission of the text. Drama, music, and great oratory cannot be flawlessly transmitted by known physical systems. For example, the spatial integrity of a great orchestra in a remarkable acoustic space is today, even with our astounding technological strides, only realizable by attending the live performance. The complexity of the auditory senses defies efforts to record or transmit it faithfully.

The devilish power that telecommunications has provided demagogues is frightening, but shared communication has revealed to a much larger audi-ence the prosperity of certain ideas over others, and one can hope that the metaphysics behind progress will penetrate a majority of the minds out there.

That the audio industry’s history has barely begun is evidenced every time one attends a live performance. We will, one day, look back on the neglect of the metaphysical element, perhaps after we have uncovered the parameters, at present easily heard but unmeasurable, by our present sciences. History awaits the ability to generate the sound field rather than a sound field. When a computer is finally offered to us that are capable of such generation, the question it must answer is, “how does it feel?”

2.11 Historical Notes

When I first ventured into audio in 1951 with nothing more than a background in amateur radio (Ham) and some exposure to engineering in general, at the university level, it was interest in classical music and its reproduction that led the way.

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Fortunately, the postwar revolution in audio was at its height and our operation of a small but eclectic “hi-fi” shop, The Golden Ear, led to personally meeting many of the pioneers of that movement. Paul Klipsch, Rudy Bozak, Avery Fisher, Frank McIntosh, Herman Hosmer Scott, Saul Marantz and others, literally came to our little shop to help us sell the products they had designed and manufactured. Purdue University faculty and students were among our customers; listening to the conversations between these customers and the manufacturers participating soon made us aware of the names and fame of the communication industry’s giants, as well as the early acoustic giants such as Rayleigh, Sabine, and Helmholtz.

In 1951, there was no such thing as the Internet and the only way to get to know these giants was to haunt old bookstores and gradually collect their written works. Our book collecting continued and gradually grew to over 750 volumes on audio and acoustics.

In late 1958, I joined Klipsch & Associates as vice president which gave me the chance to travel nationally and internationally, including sound demonstrations at the Brussels World’s Fair, and at the American National Exhibition in Moscow, where we spent two-and-half months during the summer of 1959.

In late 1959, I joined Altec Lansing where I was privileged to work with three unique innovators in audio technology: John Hilliard, Art Davis, Jim

Noble, and a host of employees that had originally been part of ERPI, the motion picture service divi-sion of Western Electric. These were men who had known Wente and Thuras, Harvey Fletcher, Black, Bode, Nyquist, and Jim Lansing prior to his tragic early death. I was a vice president of Altec when I left in December 1972 to start Synergetic Audio Concepts (Syn Aud Con).

The next twenty-three years were spent teaching classes in the basics of audio and acoustics, consulting and writing texts including Sound System

Engineering, Acoustic Tests and Measurements and How to Build Loudspeaker Enclosures, plus many

papers for the Journal of the Audio Engineering

Society, Audio Magazine, and other popular

publica-tions, in addition to hundreds of articles in the Syn-Aud-Con Newsletters.

I have been led to these reminiscences because of the usefulness of knowing how we got here, as the only sure guide to where we might be going. There-fore, I hope you will not ignore our attempts to share these underlying concepts with you to encourage you to become a professional in the communication industry. Many of the best of tomorrow’s innova-tions will be found by studying the best of the old, combined with the new materials and techniques of the present. “The ancients are still stealing our inventions” is all too true and many papers written at the turn of the Twentieth Century have ideas not able to be implemented when the article was written, but are now possible.

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Chapter

3

Sound and Our Brain

by Don Davis

17

3.1 The Human Brain . . . .19

3.2 The Current Era . . . .19

3.3 Unexpected Validation . . . .22

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Sound and Our Brain 19 3.1 The Human Brain

Over the course of my lifetime my audio experi-ences ran from using a tickler on a crystal in order to hear audio from a local radio station, to the vacuum tube era, transistors, integrated circuits, to today’s digital wizardry. Back in the early 1970s, it was clear that digital circuitry would prevail. It took forty years for that insight to come to full fruition. I truly believe that now mental control of such systems will come to full fruition in the next 10 years. There are already in existence neuron chips, axon chips and synapse chips from the scientists at IBM working to understand the brain.

In this chapter it is pointed out the interweaving of some of the most useful audio engineering tools such as the Fourier transform, Gabor wavelets, and quantum research to the holographic behavior of human consciousness. For those of you young enough and well-educated enough to want to pursue this insight, this chapter provides guidance for the scientist, the engineer, and the technician. It leaves one free to choose the level of your study while still providing future material that is challenging, hence this chapter about the thinkers behind this revolution. As it is reinforced several times in this book, “Sharing an idea is communication, understanding

the idea is metaphysical.” Buckminster Fuller.

The earliest evidence we can find where man first recognized that the brain was associated with consciousness was Alkmaion of Kroton (500 BC) who discerned, based on anatomical evidence, that the brain was essential for perception. The Hippo-cratic School preserved his view regarding the mental primacy of the brain to vision. Nothing in early medical systems claimed any intellectual capacity for the brain. The Egyptians, normally so fastidious in their care for the afterlife, heedlessly discarded the brain in funerary practices. Most early civilizations thought of the heart as primary to understanding.

In the early sixteenth century George Berkeley, Bishop of Cloyne, published a book in 1710 enti-tled, “Treatise concerning the principle of human

knowledge.” In this work he clearly pointed out the

unreality of the external world by demonstrating the illusions of the senses as witnesses in this case. Over 100 years later Ernst Mach (1838–1916) carried Berkeley’s “Du Motu” into Mach’s principle which then led Albert Einstein’s thought to dwell on relativity.

Whether space is an independent entity of its own, a number of relations between material objects or a mere subjective notion superimposed on the world is a question of long tradition and probably rooted in our common impression of the distinct

differences between objects and the empty space between them.

If you truly enjoy “mind-bending” reading Newton, Euler, Kant and Helmholtz’s views of objects, space, and relativity are there for the taking. Mach insists that absolute motion and absolute space, i.e. motion and space in them selves, reside only in our minds and cannot be revealed by experi-ence, hence they are meaningless, idle metaphysical concepts and must not be used in a scientific context. In quantum mechanics, mass and spin are both measures of inertia. Therefore, there are inertial affects proportional to Planck’s constant, such as spin–rotation coupling, which is due to the inertia of intrinsic spin.

3.2 The Current Era

We are currently afloat in “field” theories of the human brain and its distinction from mind and Mind. Francis Crick (of DNA fame), E. Roy John (brain research laboratories NYU school of medi-cine), and Johnjoe McFadden (University of Surrey) have all made significant contributions to the elec-tromagnetic fields in human beings, as well as providing support for wider sweeps of these fields into conjunction with the universe’s field such as suggested by K. H. Pribram in “Proposal for a

quantum physical basis for selective learning.”

What has all this to do with audio? Fourier, Gabor, Shannon et al. have had an immeasurable effect on audio. Pribram writes,

Ga bor wa ve lets are windo we d Fourier transforms that convert complex spatial (and temporal) patterns into component waves whose amplitude at their intersections become reinforced or diminished.

Fourier processes are the basis of holography. Holograms can correlate and store a huge amount of information and have the advantage that the inverse transform returns the results of correlation into the spectral and temporal patterns that provide guid-ance in navigating our universe.

Let me share with you some of the jewels and lumps present in the papers of these researchers with the hope that you, too, possess ideas that might be triggered by these suggestions. One materialistic view by Richard Amoroso written as a criticism of John Bell (of Cern fame),

He mistakenly thought that mind was immaterial; it has only seemed this way for the last 300 years because the material aspects of the normal nounenon of consciousness have been hidden behind the

Sound System Engineering.pdf

Sound System Engineering

Fourth Edition

Don Davis

Eugene Patronis, Jr.

Pat Brown

Edited by

Glen Ballou

First published 1975

by Howard W. Sams & Co., Inc.

Indianapolis, Indiana 46268

This edition published 2013

by Focal Press

70 Blanchard Road, Suite 402, Burlington, MA 01803

Simultaneously published in the UK

by Focal Press

2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN

Focal Press is an imprint of the Taylor & Francis Group, an informa business

© 2013 Don Davis, Eugene Patronis, Jr. and Pat Brown

The right of Don Davis, Eugene Patronis, Jr. and Pat Brown to be identified as the authors of

this work has been asserted by them in accordance with sections 77 and 78 of the Copyright,

Designs and Patents Act 1988.

All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form

or by any electronic, mechanical, or other means, now known or hereafter invented, including

photocopying and recording, or in any information storage or retrieval system, without

permission in writing from the publishers.

Notices

Knowledge and best practice in this field are constantly changing. As new research and

experience broaden our understanding, changes in research methods, professional practices,

or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in

evaluating and using any information, methods, compounds, or experiments described herein.

In using such information or methods they should be mindful of their own safety and the

safety of others, including parties for whom they have a professional responsibility.

Product or corporate names may be trademarks or registered trademarks, and are used only

for identification and explanation without intent to infringe.

Library of Congress Cataloging in Publication Data

CIP data has been applied for

ISBN: 978-0-240-81846-7 (hbk)

ISBN: 978-0-240-81847-4 (ebk)

Typeset in Times New Roman and Optimum

by Glen Ballou

The fourth edition of Sound System Engineering is dedicated to

Carolyn Davis

who is the catalyst that made it happen

and is the glue that held it all together.

Contents

Preface

Chapter 1 Why Sound System Engineering?

Chapter 2 Voices Out of the Past

Chapter 3 Sound and Our Brain

Chapter 4 Psychoacoustics

Chapter 5 Digital Theory

Chapter 6 Mathematics for Audio Systems

Chapter 7 Using the Decibel

Chapter 8 Interfacing Electrical and Acoustic Systems

Chapter 9 Loudspeaker Directivity and Coverage

Chapter 10 The Acoustic Environment

Chapter 11 Audio and Acoustic Measurements

Chapter 12 Large Room Acoustics

Chapter 13 Small Room Acoustics

Chapter 14 Designing for Acoustic Gain

Chapter 15 Designing for Speech Intelligibility

Chapter 16 What is Waving and Why

Chapter 17 Microphones

Chapter 18 Loudspeakers and Loudspeaker Arrays

Chapter 19 Power Ratings for Amplifiers and Loudspeakers

Chapter 20 Computer-Aided System Design

Chapter 21 Signal Delay and Signal Synchronization

Chapter 22 Signal Processing

Chapter 23 Digital Audio Formats and Transports

Chapter 24 Sound System Equalization

Chapter 25 Putting It All Together

Appendix

Preface

Chapter

1

Why Sound System Engineering?

by Don Davis

Chapter