Sound pressure level starts from a speaker's sensitivity, rises with amplifier power, and falls with distance. Enter the three values below to get the SPL at the listener and the maximum level at one meter.
How to calculate SPL
Take the speaker sensitivity, add 10 times the log of the power for the level at one meter, then subtract 20 times the log of the distance in meters. Every doubling of distance costs about 6 dB in free field. Note that doubling amplifier power adds only about 3 dB, so an efficient speaker often buys more level than a bigger amplifier.
SPL loss with distance (free field)
| Distance | Level vs 1 m |
|---|---|
| 1 m | reference |
| 2 m | -6 dB |
| 4 m | -12 dB |
| 8 m | -18 dB |
Frequently asked questions
How do I calculate SPL?
Start from sensitivity (dB at 1 W / 1 m). Add 10 times the log of the power for the level at 1 m, then subtract 20 times the log of the distance in meters.
How much SPL is lost with distance?
About 6 dB per doubling of distance in free field (the inverse-square law). Indoors, reflections reduce the loss, so rooms read a little louder at distance.
What is speaker sensitivity?
The SPL a speaker makes with 1 W at 1 m, in dB. Higher sensitivity plays louder for the same power. Typical values are about 84 to 96 dB.
Does doubling power double the volume?
No. Doubling power adds only about 3 dB. A perceived doubling of loudness needs about 10 dB, or ten times the power.
Is this indoor or outdoor SPL?
It uses the free-field inverse-square law, closest to outdoor or absorptive spaces. Reverberant rooms read somewhat higher at distance.
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