The Sound System Explained
In my days as the rental manager for a large sound company, I often dealt with customers who wanted to rent gear without knowing the slightest idea how to use it. I'd often get calls asking about wireless microphones from people thinking that was all they needed. They had no idea that they also needed a mixer, equalizer, amplifier, and speakers to cover the audience area. I guess they figured the microphones would be enough.
There can be many parts to a sound system, and putting them all together can get complicated and confusing. There are speakers, microphones, CD players, amplifiers, mixers, amplified mixers, amplified speakers; and what is the difference between a graphic equalizer and a parametric eq, anyway? Relax. It's not really that hard. Remember the old slogan for the board game Othello? It takes a minute to learn and a lifetime to master. A public address system is not at all like that.
What's a Sound System For, Anyway?
A sound system has one purpose only: to deliver the sound to the listener in a deliberate way.
A reinforcement system will amplify whatever the microphone picks up and deliver it to the audience through speakers. In this case, the goal of the engineer would be to make the sound in the back of the house about as loud as it would sound up close. One might also use a reinforcement system for artistic reasons. For example, a cabaret singer may use a microphone to energize her performance and musical impact, even if no reinforcement needed for her to fill the room.
A remote delivery system enables people to hear each other over distances. A telephone or teleconferencing systems are remote delivery systems. Speakers placed in the overflow rooms of a large event would also be considered a remote delivery system.
A car stereo system delivers the signal from the CD to your ears via the amp and speakers. A guitar amp delivers the sound from the guitar to your ears via...you guessed it, the big ol’ speaker driver in the cabinet.
So What Is It?
Let's start with the term "Sound System". Accent the word "system" - a group of elements working together for a single purpose. More terms: P.A. system, stereo system, talkback system, surround sound system, monitor system. Notice a trend? Now, before we dive into exactly what those elements are, let's talk about the concept of signal flow.
Signal
Sound travels. To be more specific, sound energy travels. If it didn't travel, well, it wouldn't be sound. One air molecule excites another air molecule, which passes the energy forward. When the sound is picked up by a microphone, that acoustical energy is changed into electrical energy. That's called transduction. Transduction is when one form of energy is turned into another form of energy. A microphone is a transducer that converts sound energy into electrical energy. When the energy is acoustical it's called sound, but when the energy is converted to electrical energy, it's called signal.
Like sound, signal also travels, flowing through the circuits of the latest high-tech thingamabobs or through the wires that connect them. You might think of signal as water flowing through the pipes of a P.A. system, if that helps, but I like thinking of it as electrical current. That's just me.
The basic concept of signal flow is one of the most important tools you'll have when assembling or operating a sound system. Picture in your mind the paths that the signal can take through the microphone, the cable, the mixer, and so on. If you do that, you can get to a point where you’ll be able to tell where a problem is just by listening.
Elements Of a Sound System
All sound systems contain three basic elements. Your son's rock band, the Congressional press conference, the surround system in your local movie theatre, even the huge sound system in Redskin's stadium all break down to three basic components. They are: Input, Processing, Output. The signal flows in, gets messed with, and flows out.
Input - The Signal Flows In
The first time I worked with Donna Migliaccio, I strapped a mic to her head. Sheri Edelen was in the show and I put a microphone on her. Michael Sharpe also wore a mic, as did everyone else in the cast. The tiny house sat 230 people. Those 230 people got a dose of input they'll not soon forget. Microphones are one source of input. They're used for live input. If you ever work with Donna Migliaccio, Sheri Edelen, or Michael Sharpe, make a note. They almost never need one.
Other types of transducers would be contact pickups, often used on guitars or other acoustic instruments, or the magnetic pickups of an electric guitar. Other types include tape heads, phonograph cartridges; even the laser in a compact disc player is a transducer. Such recorded input is generally referred to as playback.
Then there are electronic instruments like synths, electric pianos, electric drums, etc.
Processing - The Sound Gets Messed With
Once the signal is in the system it gets processed. You want to change it in some way, right? After all, that is the whole purpose of the sound system in the first place. These include equalizers, effects processors that add reverb, delay, etc., dynamic processors like compressors, expanders, and limiters. Then there are toys like aural exciters (ugh), tube warmers, digital delays, and feedback eliminators (ugh again), to name a few.
While all of the above are good tools to have when used for the right purpose, there is really only one processor that must be included in all sound systems somewhere in the signal chain. Somewhere down the line there's got to be an amplifier to make the signal loud enough to hear. Most sound systems include many amplifiers, since each piece of gear usually has at least one built in somewhere.
Output - Signal Flows Out
The final step in this transonic triad converts the signal into acoustical energy with, what else? Speakers. They come in all shapes and sizes, from the ear-bud plugged into your cell phone to huge line arrays hanging from the ceiling, juxtaposed between you and Erika Badu. Tweeters, mid-range speakers, and subwoofers are all transducers.
In Conclusion
The three components that make up a sound system are input transducer, processor, and output transducer. If you remember that, you're golden.