What is the speed of sound?

The approximate rule of thumb for the speed of sound is 1,125 feet/second (1125 fps) at sea level. Sound waves can be transmitted through nearly any substance, and it's propogation is faster with increasing density. There are classical and modern formulas which can closer determine the exact speed depending upon the situation, but since this is a website devoted to audio and music, we'll stick to the rule of thumb.

The speed of sound is different from the wavelength, referred to as frequency. This is the distance between crests of the sine wave, and can be affected by movement of the source relative to the listener. When moving closer, the waveforms pile up on each other, the distances between wave crests is shorter, and the resulting pitch is higher. The opposite happens when the sound source moves away, and the resulting pitch is lower. The well known effect is called the 'Doppler Effect' and can be heard in the wailing of a firetruck. However, the overall speed of sound is not greatly affected.

We can use the this standard speed model to help us in many ways. For example, if we are getting a specific spike of feedback at 1Khz, then we can calculate that the length of a single wave is:

wavelength = speed/frequency

which works out to about 1.125 feet. Using this number we can position the monitors a half-wave offset from a nodal position. Or, we can provide baffles cut to 1.125 feet behind the stage.

Remember, the speed of sound will shift based upon altitude, barometric pressure, temperature, etc.

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