Sound levels to combine
dB
dB
Combined Level
88.0 dB
2 sources combined using power summation: 10 × log₁₀(Σ 10^(Lᵢ/10))
Combine sound levels, calculate distance attenuation, and estimate SPL from your amplifier and speakers.
Sound levels to combine
Combined Level
88.0 dB
2 sources combined using power summation: 10 × log₁₀(Σ 10^(Lᵢ/10))
Want full room modeling, measurement, and optimization?
Try the Atuund WorkstationThe decibel scale is logarithmic because human hearing is logarithmic. We perceive a 10 dB increase as roughly "twice as loud," not 10 times louder. This means two identical 85 dB sources don't produce 170 dB — they produce about 88 dB. The power summation formula accounts for this: L_total = 10 × log₁₀(Σ 10^(Lᵢ/10)).
Sound intensity decreases with the square of distance from the source. In practical terms: every time you double the distance from a speaker, SPL drops by about 6 dB. This is the inverse square law, and it applies to any point source in open space. In a room, reflections modify this, but it's a useful starting point.
You can't simply add dB values because the scale is logarithmic. Instead, convert each level to power (10^(dB/10)), add the powers, and convert back: L = 10 × log₁₀(Σ 10^(Lᵢ/10)). Two equal sources produce about +3 dB, not double.
In free space, SPL drops 6 dB each time you double the distance (inverse square law). Use the formula: ΔdB = −20 × log₁₀(d₂/d₁). Indoors, room reflections reduce this drop, especially at bass frequencies.
Atuund uses finite element method (FEM) modal analysis to model room acoustics. Built for hi-fi enthusiasts, home theater builders, and anyone who wants better sound from their speakers.