Perspectives of a Writer and Musician

Issues related to writing, publishing and playing jazz music: One man's muse.
by Al Stevens

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Location: Florida, United States

Saturday, May 20, 2006

Audio and Sound Systems

This article is the first in a series that explains how sound systems work. Entertainers need to know more about sound systems than simply that they make your voice louder so folks in the back row can hear. The more you know about the subject, the better equipped you are to deal with sound problems when they come up in your work.

This article explains the basics of sound amplification. Subsequent articles address problems common to the operation and use of a sound system and specific sound system equipment that an entertainer uses. The next two articles are about distortion and audio feedback.

What is Sound?

When you speak or when anything makes what we call a “sound,” the source of the sound—your vocal cords, for example—vibrate. Those vibrations move air near the source. The air moves back and forth replicating the vibrations of the source. When those air movements reach a person's ears, the eardrums vibrate with the air, and the auditory system sends signals to the brain, which interprets the signals into perceived sound. Our intelligence takes over and translates the perceived sound into information, which our brains interpret and process as words, music, bird calls, train whistles, and so on.

The farther away a listener is from the source of the sound, the less distance the air moves back and forth. The air movements are less intense and the listener hears the sound at a lower volume. Get far enough away from listeners and they don't hear your voice at all because the air movements are too small. That's why you need a sound system.

What is a Waveform?

When your vocal cords vibrate, they move back and forth. The louder you speak, the further they move back and forth. The higher pitched your speech, the faster they move back and forth. When you hear speech, your eardrums move back and forth in the same pattern as the source of the sound. These back and forth movements are represented graphically as a waveform as shown here.

In the waveform graph, the horizontal axis is time. The vertical axis is the amplitude, or volume, of the sound (how loud it is). The red line in the center represents zero volume, or when the speaker's vocal cords are at their rested position. As the vocal cords stretch one way, the waveform goes above the center line. As the vocal cords stretch the other way, the waveform goes below the center line.

What is Sound Amplification?

When you speak into a microphone, the air movements created by your speech vibrate a small diaphragm inside the microphone. The microphone converts those vibrations into a small electrical current that flows back and forth replicating the vibrations. The microphone sends these current fluctuations to the amplifier through a cable.

The amplifier takes the small current fluctuations and produces large current fluctuations by producing a signal with an identical waveform but at a higher voltage, which is a higher amplification. Then the amp sends these larger current fluctuations to a loudspeaker through another cable. The current fluctuations cause the loudspeaker to move its coil back and forth, and the coil vibrates the loudspeaker's cone. These movements move the air in front of the loudspeaker. The vibrating air reaches the listener's ear resulting in a louder perceived sound than the listener would have heard without the amplifier.


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