Sound Pressure Relationships:Sound pressure = sound intensity ÷ particle velocity
Sound pressure = √(sound intensity × acoustic impedance)
Sound Pressure = particle velocity × acoustic impedance
Sound Pressure SI unit is the pascal, symbol Pa,, however the immense range of human hearing, 0.00002 pascals up to 200 pascals, means the pascal is not practical for everyday use. Fortunately the sound pressure level in decibels, discussed below, neatly solves this problem.
|Sources at 1 m||Sound Pressure||SPL re 20 μPa|
|Rifle||200 Pa||140 dB|
|Threshold of pain||20 Pa||120 dB|
|2 Power Mowers||2 Pa||100 dB|
|1 Power Mower||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|
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
● 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.
See also our sound pressure level calculations article
Related Terms - listed alphabetically
Average Sound Pressure see effective sound pressure
● 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.
See also the Effective Value Definition IEC 103-02-03
● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa. Also known as the time-average sound pressure level.
Equivalent continuous sound pressure level should not be confused with
Equivalent continuous sound level, to compare these two different definitions directly click here
Impact Sound Pressure Level under sound insulation
● Note: if frequency weighting is not specified, the A-frequency weighting is understood.
See also other standard reference levels.
For example if the sound pressure level at 1 metre from the source is 2 pascals (100 dB) then the sound pressure level at 2 metres will be 1 pascal (94 dB) and at 4 metres distance the SPL will be 0.5 pascals (88 dB). Often referred to as the inverse square law, but 'strictly speaking' complies with inverse proportionality and the inverse distance law
● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa.
● Note 1 : standard frequency weightings A, B and C and standard exponential time weightings fast (F), slow (S) and impulse (I) are given in IEC 651 sound level meters.
● Note 2 : time and frequency weightings employed should be specified, but if not stated explicitly, Fast (F) exponential time weighting and A-frequency weighting are understood