Sound Power : Definitions, Terms, Units, Measurements ...
Sound Power is the total sound energy radiated by a source in all directions and measured in watts.
Sound Power is the sound intensity multiplied by the surface area = p·v·A : where p is the sound pressure, v the particle velocity and A is the surface area
Sound Power measurements are therefore not straight forward, requiring sound intensity measuring equipment or sound level meter measurements in a Reverberant or Anechoic Chamber
Sound Power is also known as Acoustic Power : LPac : Pac : PWL : PWR : SWL.
The range of human hearing is 0.000000000001 watts to 100 watts or more, so absolute sound power values are not practical for everyday use. However a neat solution is the Sound Power Level decibel descriptor - discussed below.
Sound Power Level
is ten times the logarithm
of the ratio of the sound power
to a sound power reference level
of 1 pico Watt
Sound Power Level : Lw
= 10 lg (W/Wo) dB
Sound Power Reference Level : Wo
= 1 pW = 10-12
W ≡ 0 dB
The table below shows practical examples of the Sound Power Levels versus Watts
See also the official IEC Sound Power Level Definition below.
Some Typical Sound Power Levels
| Source || Sound Power W || Lw re 1 pW|
| Jet Engine ||10,000 W || 160 dB|
| Loudspeaker Rock ||100 W || 140 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 |
Other Standard Reference Levels
uses the 10 lg factor so, as a rule of thumb:
3 dB = a factor of 2 in sound power
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
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
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.
Acoustic Reference Wind Speed Definition IEC 415-06-06, wind speed of 8 m/s at reference conditions (10 m height, roughness length equal to 0,05 m) used in the calculation of the apparent sound power level to provide a uniform basis for the comparison of apparent sound power levels from different wind turbine generator system.
● Note : the acoustic reference speed is generally expressed in meters per second.
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
Equivalent Absorption Area of an Object or of a Surface Definition
Statistical Sound Power Absorption Coefficient Definition IEC 801-31-03, sound power absorption coefficient measured or calculated with plane waves at randomly distributed angles of incidence
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 of a Source Definition IEC 801-22-36, is the total sound energy radiated by the source in a specified frequency band over a certain time interval, divided by the interval.
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
Also known as Sound Energy Flux
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.
Other Sound Power Related Terms :
Power Spectral Density •
Power Spectrum •
Power Spectrum Averaging •
Power Spectrum Level •
Sound Energy •
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