Sound System Engineering 4e

Don Davis, Eugene Patronis, Pat Brown

• Editore: Routledge
• Anno: 2013
• ISBN:
  9781136111419
• Edizione: 4
• Argomento: Technology & Engineering
• Categoria: Acoustical Engineering

Long considered the only book an audio engineer needs on their shelf, Sound System Engineering provides an accurate, complete and concise tool for all those involved in sound system engineering. Fully updated on the design, implementation and testing of sound reinforcement systems this great reference is a necessary addition to any audio engineering library.Packed with revised material, numerous illustrations and useful appendices, this is a concentrated capsule of knowledge and industry standard that runs the complete range of sound system design from the simplest all-analog paging systems to the largest multipurpose digital systems.

Why Sound System Engineering?

by Don Davis

DOI: 10.4324/9780240818474-1

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
1.9 Fields	4

“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 intelligibility, 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 conditions. 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 intelligibility 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 comprehend 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 competent 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 difficult 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 reinforcement often pass reinforcing music with flying colors. Mega churches find that the music reproduction and reinforcement systems are often best separated 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?

Figure 1-1 Electromagnetic spectrum chart.

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 direction or the other, this is a mere form of 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 sufficient….

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 electrical 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 propagation of energy without wires (wireless transmission) becomes a thing altogether apart from other forms of transmission involving an intervening conducting medium.

An appreciation of Maxwell’s theory of electromagnetic 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 phenomenon…. 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, “Electromagnetic Wave Propagation Phenomenon.”

The usually accepted view that the conductor current produces a magnetic fie...