Page 53 - Master Handbook of Acoustics

FIGURE 2-2 An appreciation of the relative magnitude of a sound pressure of 1 Pa can be gained by
comparison to known sounds. The standard reference pressure for sound in air is 20 μPa, which
corresponds closely to the minimum audible pressure.

The 194-dB sound-pressure level of a Saturn rocket launch is considerable. (For perspective,
detonating 50 lb of TNT 10 ft away would generate a similar SPL.) That sound-pressure level
approaches the atmospheric pressure and hence is a disturbance on the order of magnitude of

atmospheric pressure. The 194-dB sound pressure is an RMS (root-mean-square) value. A peak
sound pressure 1.4 times as great would modulate the atmospheric pressure completely.

Using Decibels

As we have seen, a sound level is expressed as a logarithm of a ratio of two powerlike quantities.
When levels are computed from other than power ratios, certain conventions are observed. The
convention for Eq. (2-4) is that sound power is proportional to sound-pressure squared. The voltage-