Tools
SPL calculator
Calculate SPL at a given distance from loudspeaker sensitivity and amplifier power. Based on the inverse square law in free field — results are approximate and assume a point source with no room reflections.
Manufacturer-specified sensitivity: dB SPL at 1 W, 1 m (on-axis, anechoic or quasi-anechoic)
Continuous power delivered to the loudspeaker
Distance from the acoustic centre of the loudspeaker to the listener
SPL at 1 m
109.0 dB SPL
89.0 + 10·log₁₀(100.0) − 20·log₁₀(1.0) = 109.0 dB
SPL at distance — 100.0 W
Required power for target SPL
At the distance specified above (1 m)
Required power
125.89 W
SPL addition
Combine incoherent sources (e.g. multiple loudspeakers, independent noise sources). Uses 10·log₁₀(Σ 10^(SPLᵢ/10)).
Incoherent
Independent sources — adds power
10·log₁₀(Σ 10^(SPLᵢ/10))
93.0 dB SPL
+3.0 dB above the loudest source
Coherent
Same-phase sources — adds pressure
20·log₁₀(Σ 10^(SPLᵢ/20))
96.0 dB SPL
+6.0 dB above the loudest source
Free field assumption. This calculation assumes an anechoic environment. In a real room, reflections add energy at the listening position — typically 3–6 dB at distances beyond the critical distance. Results are a lower bound on actual SPL.
Sensitivity variation. Manufacturer sensitivity figures are often measured at a single frequency or averaged over a limited band. Real-world sensitivity varies with frequency; treat the result as an approximation.
Power compression. At high drive levels, voice coil heating increases resistance and reduces efficiency, lowering actual SPL below the calculated value. Thermal power compression of 2–4 dB is common at continuous high power.