Acoustic Glossary


Sound Power : Definitions, Terms, Units, Measurements..

Sound Power

is the total sound energy radiated and measured in all directions in watts.


Sound Power

is the sound intensity multiplied by the surface area.


Sound Power

is the sound energy flow per unit of time.


Sound Power

is also known as Acoustic Power : LPac : Pac : PWL : PWR : SWL.


The range of human hearing, 0.000000000001 watts to 100 watts or more, means using absolute sound power values is not practical for everyday use. A neat solution is the Sound Power Level decibel descriptor.

Sound Power Level IEC Definition,

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
Sound Power Reference Level : Wo = 1 pW = 10-12 W ≡ 0dB

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

LW 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

Apparent Sound Power Level IEC Definition,

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.

Sound Power Absorption Coefficient IEC Definition,

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 IEC Definition,

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 Equivalent Absorption Area of an Object or of a Surface IEC Definition,

area of a surface having a sound power absorption coefficient of unity that would absorb the same amount of sound power in a reverberant room with a diffuse sound field as the object or the surface. In the саsе of a surface, the equivalent absorption area is the product of the area of the surface and its sound power absorption coefficient

Sound Power of a Source IEC Definition,

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 : IEC Definition,

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

Statistical Sound Power Absorption Coefficient IEC Definition,

sound power absorption coefficient measured or calculated with plane waves at randomly distributed angles of incidence

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