Sound Power is also known as acoustic power : LPac : Pac : PWL : PWR : SWL.
The Sound Power Unit is the watt. However the range of human hearing is 0.000000000001 watts to 100 watts or more, so sound power values in watts are not practical for everyday use. The sound power level in decibels, discussed below, neatly solves this problem.
Sound Power Level Definition (IEC 801-22-05) logarithm of the ratio of a given sound power to the reference sound power. Such power level in decibels is ten times the logarithm to the base ten of the ratio.
Note : unless otherwise specified, the reference sound power is 1 pW.
Sound Power Level (Lw) = 10 lg (W/Wo) dB - i.e. more manageable numbers
|Source||Sound Power W||Lw re 1 pW|
|Jet Engine||10,000 W||160 dB|
|Loudspeaker rock music||100 W||140 dB|
|2 Pneumatic hammers||2 W||123 dB|
|Pneumatic hammer||1 W||120 dB|
|Outboard motor||0.01 W||100 dB|
|Dishwasher||0.0001 W||80 dB|
|Office||0.000001 W||60 dB|
|Fridge||0.00000001 W||40 dB|
|Whisper||0.0000000001 W||20 dB|
|Threshold||10-12 W||0 dB|
See other Standard Reference LevelsLW uses the 10 lg factor so, as a rule of thumb:
10 dB = a factor of 10 in sound power
20 dB = a factor of 100 in sound power
30 dB is a factor of 1000
40 dB is a factor of 10000
See also apparent sound power level
Sound Power related terms - listed alphabetically
Apparent Sound Power Level Definition (IEC 415-06-03), A-weighted sound power level referred to 1 pW of a point source at the rotor center with the same emission in the downwind direction as the wind turbine being measured as determined at the acoustic reference wind speed.
Note : the apparent sound power level is generally expressed in decibels.
See also sound power level
Reference Sound Power (Wo) = 1 pW = 10-12 W ≡ 0 dB = the threshold of hearing at 1Khz
Sound Power Absorption Coefficient Definition (IEC 801-31-02), at a given frequency and for specified conditions, of a surface, fraction of incident sound power not reflected from the surface.
Note : unless otherwise specified, a diffuse sound field is to be understood.
Sound Power Density (I), is the average sound energy flowing through a specified point.
Sound Power Density Definition (IEC 801-21-38), sound energy flux in a specified direction and sense through an area perpendicular to that direction, divided by the area. Also known as sound intensity and sound energy flux density.
Sound power density units are watts per metre-squared (W/m2).
Sound Power Reflection Coefficient Definition (IEC 801-31-04) at a given frequency and for specified conditions of a surface, fraction of incident sound power reflected from the surface.
Note : unless otherwise specified, random incidence is presumed.
Sound Power Through A Surface Element Definition (IEC 801-21-37) time average product of the in-phase components of the instantaneous sound pressure and the volume velocity through the surface element considered, and is also known as the sound energy flux