ToolsSound, propagation & hearing
Sound power vs. sound pressure
From a source's sound power level to SPL at a distance, or back from a measurement.
Sound power → sound pressure at a distance
dB re 1 pW
m
Q = 1 free space, 2 on a floor or wall, 4 in an edge, 8 in a corner.
- Sound pressure level at that distance
- 89.0079dB SPL
- Acoustic power
- 0.01W
Measured sound pressure → sound power
dB SPL
m
Q = 1 free space, 2 on a floor or wall, 4 in an edge, 8 in a corner.
- Sound power level Lw
- 99.0024dB re 1 pW
- Acoustic power
- 0.00794767W
Free-field relations. Sound power is a property of the source (cause); sound pressure depends on distance and room (effect).
How it works
Sound power describes how much acoustic energy a source emits, regardless of where you listen. Sound pressure level depends on the distance and the surroundings. A source on a hard floor radiates into half space (Q = 2), which raises the level by 3 dB.
Formulas
- Lp = Lw + 10 · log₁₀( Q / (4π r²) )
- P = 1 pW · 10^(Lw / 10)
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