Speaker SPL calculator
Predict sound pressure level at any distance from a speaker's sensitivity spec and the power driving it, with boundary placement gain and a full distance ladder.
2.83 V into 8 Ω is 1 W — that's why most published sensitivity specs use 2.83 V/1 m: it stays comparable across speakers of different impedance without needing a wattmeter.
| Distance | SPL | Δ vs 1 m |
|---|
How this is calculated
Power above the sensitivity reference adds 10·log₁₀(P / Pref) dB. Distance beyond 1 m subtracts 20·log₁₀(d) dB — the inverse-square law, −6 dB every time distance doubles. Placement against room boundaries reflects energy back into the listening space instead of letting it radiate into a full sphere, adding up to +3 dB per boundary (free space → half-space → quarter-space → eighth-space).
SPL(d) = sensitivity + 10·log₁₀(P/Pref) − 20·log₁₀(d) + placement gain
Reading the result
The two top numbers are SPL at 1 m and at your chosen distance; the third is how far you'd need to move back for the level to drop 10 dB — roughly half as loud to the ear, since human loudness perception tracks close to a 10 dB halving, not the 3 dB that halves raw acoustic power. The table below extends the same curve out to 32 m/ft so you can read off any position in the room.
FAQ
Why do some spec sheets use 2.83 V/1 m and others 1 W/1 m?
They're identical only at 8 Ω, since P = V²/Z and 2.83² / 8 = 1. For a 4 Ω speaker, 2.83 V is actually 2 W, so its 2.83 V/1 m sensitivity number reads about 3 dB higher than its true 1 W/1 m figure would. Pick the reference that matches your spec sheet and the impedance field converts it correctly.
Does the inverse-square law hold indoors?
Close to the speaker (the "direct field") yes, closely. Farther out, reflected sound from walls and furnishings stops the level from falling further — a room's critical distance, set by its live-ness. A room with a long RT60 reaches that floor sooner, so in a very reflective room the real drop-off will be gentler than this calculator's free-field prediction once you're several meters out.
Why does power need to double for only +3 dB?
Decibels are logarithmic: every +3 dB needs roughly double the power, and every +10 dB needs 10× the power, which is why going from "loud" to "twice as loud" costs so much more amplifier headroom than it sounds like it should.
What placement should I pick for a subwoofer in a room corner?
Floor-loaded in a corner is eighth-space (+9 dB) — three boundaries (floor plus two walls) reinforcing the same low frequencies a sub produces. It's the loudest placement for a given power, at the cost of the boomiest, least even bass; see the room mode calculator for what that reinforcement does to specific frequencies in your room.