A concert venue example shows that at 20 meters from the stage the average SPL is 65 dB. If you move to 10 meters, the SPL will average which value?

A concert venue example shows that at 20 meters from the stage the average SPL is 65 dB. If you move to 10 meters, the SPL will average which value?

• A. 59 dB SPL
• B. 62 dB SPL
• C. 65 dB SPL
• D. 71 dB SPL

Answer: (D)

Sound pressure level changes with distance from a source according to the inverse-square behavior of a free-field point source. Halving the distance doubles the sound pressure, and SPL scales with 20 log10 of pressure. So moving from 20 meters to 10 meters increases SPL by 20 log10(2) ≈ 6 dB. Starting at 65 dB at 20 m, the level at 10 m is about 65 + 6 ≈ 71 dB SPL. In a real venue, reflections can tweak this a bit, but the straightforward calculation gives ~71 dB.

Sound pressure level changes with distance from a source according to the inverse-square behavior of a free-field point source. Halving the distance doubles the sound pressure, and SPL scales with 20 log10 of pressure. So moving from 20 meters to 10 meters increases SPL by 20 log10(2) ≈ 6 dB. Starting at 65 dB at 20 m, the level at 10 m is about 65 + 6 ≈ 71 dB SPL. In a real venue, reflections can tweak this a bit, but the straightforward calculation gives ~71 dB.