Theatre sound

A model sound system

In its simplest form, a sound system operates by converting sound waves (physical energy propagated 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.

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 analogue 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 that 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.


Here are some examples of input transducers:

  • microphones:
    convert sound waves travelling in the air into an electrical signal, which travels over, say, a microphone cable. A diaphragm, usually made of some very fine metal, vibrates within a magnetic field which results in an electrical current.
  • Contact pickups:
    convert sound waves travelling in a medium (wood, metal, skin) into an audio signal. Commonly found on instruments such as acoustic guitars, concert basses, violins, mandolins; sometimes found on pianos;
  • Magnetic pickups
    convert fluctuating waves of induced magnetism into an audio signal, such as found on an electric guitar.


Here are some examples of output transducers:

  • Loudspeakers: woofers:
    designed to reproduce low frequencies. A cylindrical magnetic surrounds a cone made of paper (usually anywhere from four to eighteen inches in diameter); the paper is charged with the audio signal, and due to difference in magnetic fields, the paper moves in and out. A woofer loudspeaker works exactly in the same fashion that a dynamic microphone works, but backwards. Subwoofers are loudspeakers specifically designed to reproduce very low frequencies.
  • Loudspeakers: midrange:
    designed specifically to reproduce middle frequencies. Probably looks a lot like a small woofer.
  • Loudspeakers: tweeters:
    designed to reproduce the highest frequencies. There are several types of tweeters, including dome tweeters and compression-drivers.
  • Headphones:
    full-range transducers designed to fit in or on the ears.

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.


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:

  • Mixing Console, Mixing Desk, Mixer, Console, whatever:
    Whatever name you use, it's still basically the same thing. In its simplest form, a mixing desk takes more than one input (in its electrical form) and sums the signals together into more than one output (still in electrical form). The mixing desk is your central control station; this is where you make the vocalists louder than the band, or the violinist softer than the cellist.
  • Signal processors process part or all of the signal to introduce special effects or make the signal clearer, more crisp or in any other way enhance the sound
  • Amplifiers are a basic building block of electrical engineering. In its theoretical form, an amplifier takes an electrical signal and increases its power in a linear fashion- that is to say, the output waveform matches the input waveform, only it's more powerful. While the linearity of common power amplifiers is not necessarily perfect, that is essentially what a common power amplifier does. Power amplifiers are units designed to take an audio signal and make it powerful enough to drive a loudspeaker; due to the loudspeaker construction and its inherent inefficiency, a lot of power is required to produce sound. Other types of amplifiers used in audio include preamplifiers, which are small amplifiers that take an audio signal from a microphone and increase its power so that it can be better manipulated.

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,  there are very few objects that will reflect the sound- trees, grass, and the occasional cow, 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, we are less concerned about intelligibility as the padding will tend to absorb sound rather than reflect it; rooms that are rather non-reverberant 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.