Acoustic Glossary


Sound Power : Definitions, Terms, Units and Measurement.

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.

Sound Power is the total sound energy radiated and measured in all directions in Watts.

Sound Power Measurement

Introduction : The immense 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 : LW : is the Logarithmic ratio of sound power to the Threshold of Hearing and makes the values more manageable i.e. 0 to 160 dB and the symbol is Lw - see the table below.

Lw = 10 lg (W/Wo) dB re 1 pW = 10-12 W

Other sound power terms in current use include LPac, Pac, PWL, PWR, SWL and Acoustic Power
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

* Sound Power Reference Level = 1 x 10-12 W = 1 pW = 1 picowatt

LW uses the 10 lg equation 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

see also : other Standard Reference Levels

Sound Power Level IEC Definition : logarithm of the ratio of a given sound power to the reference sound power. Sound power level in decibels is 20 times the logarithm to the base ten of the ratio.
♦ Note 1 unless otherwise specified the reference sound power is 1 pW.

Sound Power Density IEC Definition : is the Sound Energy Flux in a specified direction and sense through an area perpendicular to that direction, divided by the area.

see also : Sound Intensity and Sound Energy Flux Density

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

Related Terms :

Power Spectral Density
Power Spectrum
Power Spectrum Averaging
Power Spectrum Level
Sound Energy
Sound Intensity


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