How many watts you need depends on the speaker's sensitivity, how loud you want it, how far away the listener sits, and how much headroom you leave for peaks. Enter the values below for the amplifier power required.
How to calculate amplifier power
First find the SPL you need at one meter: add 20 times the log of the distance in meters to your target SPL. Then the power equals 10 raised to (SPL needed minus sensitivity plus headroom) divided by 10. Because 3 dB doubles power, small changes in loudness, distance, or headroom move the wattage a lot.
Power vs level (88 dB speaker at 4 m)
| Target SPL | Watts (with 3 dB headroom) |
|---|---|
| 82 dB | ~8 W |
| 85 dB | ~16 W |
| 88 dB | ~32 W |
| 91 dB | ~64 W |
Frequently asked questions
How do I calculate the amplifier power I need?
Add 20 times the log of the distance to your target SPL for the level needed at 1 m. Then watts = 10 ^ ((SPL needed - sensitivity + headroom) / 10).
How much headroom should I add?
About 3 dB doubles the requirement; many use 6 dB or more for dynamic music so the amp never clips on peaks.
Why does distance need more power?
Level falls about 6 dB per doubling of distance. To keep the same SPL farther away, each 3 dB needs double the watts.
Does a more sensitive speaker save power?
Yes. Every 3 dB more sensitivity halves the power for the same SPL. A 94 dB speaker needs a quarter of the power of an 88 dB one.
Is this the amplifier I should buy?
This is the power to reach your target SPL. Also check the speaker's continuous rating and impedance. To match an amp to a speaker's power handling, use the speaker wattage calculator.
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