Basics of Sound Systems

A MODEL OF A SOUND SYSTEM

In its simplest form, a sound system operates by converting sound waves (physical energy propogated by air or in some sort of medium) into electrical energy, increasing the power of the electrical energy using electronic circuitry, and then converting this resultant electrical energy back into physical energy in the form of sound waves.

If you have no idea of what we speak, go pick up a physics textbook and read the parts about sound and waves and air pressure and why it is more difficult to hear when you're in an airplane.

Devices that convert energy from one form into another are called transducers. Some examples of common transducers are loudspeakers, microphones, contact pickups, and headphones. Microphones and contact pickups (types of input transducers) convert fluctuating sound waves (physical energy in the air or in some other medium) into an electrical current that is an analog representation of the original sound wave. That is to say, if a large mass of air produced by a kick drum is picked up by a microphone, a large electrical current will represent that mass of air. Loudspeakers and headphones (which are mini-loudspeakers, essentially), converts the electrical signal back into physical energy.

Devices the actually amplify and change the characteristics of the electrical audio signal are called signal processors. In its simplest form, a signal processor increases the power of the electrical signal (coming out of the microphone and going into the loudspeaker). This sort of signal processor is an amplifier. Sound systems often include many more types of signal processors, which are used to effect change on any number of different audio signals.

GOES-INTA

Here are some examples of input transducers:

GOES-OUTTA

Here are some examples of output transducers:

While this is by no means a complete list of transducers, it gives you an idea of what we speak. There are advances in loudspeaker technology, and developments such as a planar, or flat, loudspeaker, have come into use; however, the basic way in which the loudspeaker works has not changed.

GOES-SOMEWHERE-IN-THE-MIDDLE-A

Here are some examples of signal processors, and what they do. It should be noted, however, that the technical definition of "signal processor" is a device which alters the audio signal in a non-linear fashion; thus a simple level control or amplifier is technically not a signal processor:

A BASIC SOUND SYSTEM

A very basic sound system

The illustration above illustrates a simple, practical sound system.

Note the three sections- input transducers, signal processing, and output transducers. The three microphones are connected to separate inputs on the mixing desk. On each input the mixing desk provides preamplification, which amplify the microphone level signals to line level; equalization, which provides the means to contour the tonal balance of each microphone; and level control, which allows the operator to adjust the relative level of each microphone individual. The mixing desk then sums the inputs to a single line-level output. The output of the console is connected to a power amplifier, which boosts the console's line level output to a level suitable to drive the loudspeaker (line levels typically run from 0.1 to 100 mW, whilst loudspeakers require 0.5 to 1kW, approximately). The loudspeaker converts the power amplifier output signal into sound pressure waves. The level of the sound is much higher than that of the three orators speaking unaided.

Every sound system is merely an extension of this basic model. The principles that apply to this simple model also apply to large-scale concert reinforcement systems.

THINGS TO REMEMBER

The environment in which the sound system is used can alter, both positively and detrimentally, the output of the system. In a free-field environment, such as on a field-hockey field, there are very few objects that will reflect the sound- trees, grass, and girls in field-hockey garb will tend to absorb sound, rather than reflect it. We can eke more level out of the sound system because we do not have to worry about reflected sound waves getting back into the microphone, causing a rather unpleasant ringing sound known as acoustic feedback. In a small room with wooden walls, we have to worry about reflections caused by the amplified sound bouncing off the walls and affecting the overall intelligibility of the system; we are concerned with the amount of gain we can get out of the system before the unpleasant feedback sound. In a small room with padded walls (heh heh), we are less concerned about intelligibility as the padding will tend to absorb sound rather than reflect it; rooms that are rather nonreverberant are usually termed "dead."

There are other factors to consider when designing and installing a system, including proper speaker selection and positioning, proper microphone selection and positioning, and proper tuning or equalization of a system in a given room. And of course there are issues on ease-of-operation and the system's intended use-- whether for music, speech, theatre, or playback. With this handbook, we'll try to provide you with enough knowledge to make an educated decision about your sound system.


Return to the Sound Index. Continue with Input Devices.

Comments, Questions, and Additions should be addressed via e-mail to Kai Harada. Not responsible for typographical errors.
http://www.harada-sound.com/sound/handbook/basics.html - © 2002 Kai Harada. 30.09.02.

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