What is the sound pressure level at 1 meter from a source that emits 90 dBSPL and is measured at 3 meters away?

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Multiple Choice

What is the sound pressure level at 1 meter from a source that emits 90 dBSPL and is measured at 3 meters away?

The important idea here is how sound level changes with distance from a point source in free space. For a point source, the sound pressure level drops by 20 log10 of the distance ratio when you move from one distance to another: L2 = L1 − 20 log10(r2/r1). If the source is 90 dB at 1 meter and you measure at 3 meters, the drop is 20 log10(3/1) ≈ 20 × 0.4771 ≈ 9.54 dB. So the level at 3 meters would be 90 − 9.54 ≈ 80.5 dB, i.e., about 80 dB.

The important idea here is how sound level changes with distance from a point source in free space. For a point source, the sound pressure level drops by 20 log10 of the distance ratio when you move from one distance to another: L2 = L1 − 20 log10(r2/r1).

If the source is 90 dB at 1 meter and you measure at 3 meters, the drop is 20 log10(3/1) ≈ 20 × 0.4771 ≈ 9.54 dB. So the level at 3 meters would be 90 − 9.54 ≈ 80.5 dB, i.e., about 80 dB.

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