Amplitude Attenuation with Distance Sound originating from a small point source will spread spherically in all directions, absent any
Distance from Source (ft)
SPL Loss Relative to 10 ft
SPL (dBA)
10 20 40 80
90 84 78 72 66 60
6
12 18 24 30
160 320
Table A2.1. Decrease of SPL with Distance Due to Spherical Spreading
nearby surfaces. The conservation of energy requires the sound pressure spreading out from such a source to decrease by half with each doubling of distance. This is known as the inverse square law and is demonstrated in 2.1 and 2.3.
r
2 r
9 0 d B A
4 r
8 4 d B A
7 8 d B A
Figure A2.3. Decrease of SPL with Distance Due to Spherical Spreading
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12/15/2019
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