Sound Pressure and related terms, definitions, units etc.,
Sound Pressure Level (SPL or Lp) in decibels is 20 x the logarithm of the effective sound pressure divided by the reference sound pressure (20 μPa).
Sound Pressure Level = 20 log (p/po) dB, where p is the sound pressure in pascals and po is the reference sound pressure of 0.00002 pascals = 0 dB in air ≡ to the threshold of hearing at 1KHz
Some typical Sound Pressure and Sound Pressure Levels
|Sources at 1 m || Sound Pressure || SPL re 20 μPa|
| Rifle || 200 Pa || 140 dB |
| Threshold of pain || 20 Pa || 120 dB |
| Pneumatic hammer || 2 Pa || 100 dB |
| 6 dB = twice or half the pressure || 1 Pa || 94 dB |
| Street traffic || 0.2 Pa|| 80 dB |
| Talking || 0.02 Pa|| 60 dB |
| Library || 0.002 Pa|| 40 dB |
| TV Studio || 0.0002 Pa|| 20 dB |
|Reference Sound Pressure || 0.00002 Pa || 0 dB |
Sound Pressure Level is a sound field quantity and uses the 20 log factor so, as a rule of thumb:
6 dB = a factor of 2 in sound pressure (double or half the sound pressure)
10 dB = a factor of 3 in sound pressure
20 dB = a factor of 10 in sound pressure
Sound Pressure Level Definition IEC 801-22-07, logarithm of the ratio of a given sound pressure to the reference sound pressure in decibels is 20 times the logarithm to the base ten of the ratio.
● Note 1: unless otherwise specified, the reference sound pressure is 20 μP for airborne sound and 1 μPa for sound in media other than air.
● Note 2: unless otherwise specified, the sound pressures are understood to be expressed in root-mean-square values.
Related Terms - listed alphabetically
Average Sound Pressure
see the effective sound pressure
Band Sound Pressure Level Definition IEC 801-22-12, level of the sound pressure produced within a specified frequency band.
● Note: the band may be specified by its lower and upper cut-off frequencies, or by its geometric centre frequency and bandwidth. The width of the band may be indicated by a modifier such as one octave band (sound pressure) level, one-half octave band level, one-third octave band level.
Equivalent Continuous Sound Pressure Level Definition IEC 801-22-11, logarithm of the ratio of a given root-mean-square sound pressure, during a stated time interval, to the reference sound pressure. Average sound pressure level in decibels is 20 times the logarithm to the base ten of that ratio.
● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa.
Equivalent Continuous Sound Pressure Level is also known as the Time-average sound pressure level and should Not be confused with the Equivalent continuous sound level definition IEC 801-22-16.
To compare these definitions directly click here
Impact Sound Pressure Level
under Sound Insulation
See also • sound exposure action values and limit values.
See also • other standard reference levels.
Time-average Sound Pressure Level
under equivalent continuous sound pressure level
See also • Sound Levels •
LA • LAF • LAFmax • LAFmin • LCpeak etc. and the IEC Definition of Level
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