Glossary
Sound pressure level
Also: Sound level
Definition
The sound pressure level states the sound pressure logarithmically in decibels, relative to 20 µPa – approximately the threshold of hearing at 1 kHz.
Unit: dB
Formula
Link to section “Formula”- – RMS value of the sound pressure
Distance
Link to section “Distance”For a point source in the free field, the level drops by about 6 dB per doubling of distance. Large arrays and rooms deviate from this.
Adding levels
Link to section “Adding levels”Levels in decibels cannot simply be added. Two equally loud, independent sources give +3 dB, not double. The level calculator covers both cases – independent and in-phase sources.
Further reading
Link to section “Further reading”- Knowledge Decibels and Levels: Calculating with dB in Sound Reinforcement
- Calculator Adding levels – dB incoherent and in phase Adds up to four levels – once for independent sources (incoherent) and once for in-phase sources such as closely stacked subwoofers.
- Glossary Decibel (dB) The decibel is a logarithmic measure of the ratio of two quantities. For power quantities 10·lg applies, for field quantities such as pressure and voltage 20·lg.
- Glossary Sensitivity Sensitivity is the sound pressure level a loudspeaker produces at 1 W or 2.83 V at a distance of 1 m. Into 8 Ω, 2.83 V is exactly 1 W.
- Glossary Half space Half space (2π) means that a sound source stands on a large reflecting surface, such as the floor. Compared with full space (4π), the level rises by 3 dB in theory for the same sound power.
Sources
Link to section “Sources”-
Tier B · secondary source
Wikipedia · accessed on 14 September 2026
Definition Lp = 20·lg(p/p0) with p0 = 20 µPa, inverse distance law (−6 dB per doubling of distance for point sources in the free field), level addition.
-
Tier B · secondary source
Summenpegel von inkohärenten Schallquellen – Pegeladdition
Eberhard Sengpiel · sengpielaudio · accessed on 14 September 2026
Level addition of incoherent sources (+3.01 dB for two equal levels, 10·lg n for n sources) and coherent sources (+6 dB).
Updated: 14 September 2026