Acoustic Glossary


 

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 in decibels 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

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
 

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 DensityPower SpectrumPower Spectrum AveragingPower Spectrum LevelSound EnergySound Intensity

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