Page 63 - Master Handbook of Acoustics
P. 63
illustrates the basis for the inverse distance law: when the distance from the source is doubled, the
sound-pressure level decreases by 6 dB. This applies only for a free field. This law provides the
basis for estimating the sound-pressure level in many practical circumstances.
FIGURE 3-2 The inverse square law for sound intensity equates to the inverse distance law for
sound pressure. This means that sound-pressure level is reduced 6 dB for each doubling of the
distance.
Free-Field Sound Divergence
When the sound-pressure level L at distance r from a point source is known, the sound-pressure
1
1
level L at another distance r can be calculated:
2
2
In other words, the difference in sound-pressure level between two points that are distances r and
1
r from the source is:
2
