Page 58 - The Master Handbook Of Acoustics
P. 58
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SOUND LEVELS AND THE DECIBEL
Sound-pressure Sound pressure
level-dB Pascal
Riveter 110
100
1 Pa
90
80
0.1 Pa
70
Noise near 60
freeway 0.01 Pa
50
40
0.001 Pa
30
Background noise 20
in studio 0.0001 Pa
10 Standard reference
{ pressure: 20 10 6 Pa
0 20 Pa
(Approximate
threshold of hearing)
FIGURE 2-1
An appreciation of the relative magnitude of a sound pressure of 1 Pascal can be gained
by comparison to known sounds. The standard reference pressure for sound in air is
20 Pa, which corresponds closely to the minimum audible pressure.
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
A level is a logarithm of a ratio of two powerlike quantities. When lev-
els are computed from other than power ratios, certain conventions are
