SPL Calculator — Sound Pressure Level at Distance

In free-field conditions, SPL drops by 6 dB for every doubling of distance (inverse square law). So if a speaker produces 100 dB at 1 metre, it produces 94 dB at 2 metres, 88 dB at 4 metres, and so on. Indoors, reflections reduce this loss.

Doubling the power adds +3 dB. So to increase SPL by 10 dB (perceived as twice as loud), you need 10× the power. Going from 10W to 100W adds 10 dB; going from 100W to 1000W adds another 10 dB.

Background music: 70-80 dB. Small gig/bar: 90-100 dB. Concert: 100-110 dB. Festival front of house: 105-115 dB. Under the UK Control of Noise at Work Regulations 2005, the upper exposure action value is 85 dB(A) averaged over 8 hours (daily average) — above this, hearing protection is mandatory and health surveillance applies. The absolute exposure limit value is 87 dB(A).

The inverse square law states that sound intensity decreases proportionally to the square of the distance from the source. In dB terms: SPL loss = 20 × log10(distance). This assumes free-field conditions with no reflections.