SPL Calculator
Predict sound pressure level from sensitivity, amplifier power, number of subs, distance, boundaries and room gain.
Inputs
Subwoofer driver sensitivity at low frequencies.
Subs placed together add coherently (+6 dB per doubling).
Rooms: 3–6 dB at 40 Hz. Cars: 8–15 dB at 40 Hz.
Voice coils heat up and lose 1–3 dB at high power.
Loudness meter
How it works
Sound pressure level (SPL) in decibels grows with the logarithm of power and shrinks with the logarithm of distance. The classic estimate starts from the driver’s sensitivity, the SPL produced at 1 m with 1 watt, and applies each effect in turn.
SPL = Sens + 10·log₁₀(P) + 20·log₁₀(N)
− 20·log₁₀(d) + boundary + room − compressionPower: doubling power adds only +3 dB; you need 10× the power for +10 dB (which sounds “twice as loud”). Count: subs close together couple their output so each doubling adds +6 dB for the same power per sub (that’s +3 dB from double the total power and +3 dB from the extra acoustic coupling). Distance: free-field sound loses 6 dB per doubling of distance, indoors, long wavelengths bring that closer to 3 dB or less because of reflections.
Boundaries: bass energy that would spread in all directions is focused when you place the sub against a wall (+6 dB) or in a corner (+12 dB). Check whether your sensitivity figure was already measured on the floor (half-space, which is very common for subs).
Remember that this is a low-frequency, steady-state estimate. Real maximum output is also limited by cone excursion, use the Max SPL from Displacement calculator to see which limit hits first.