## Sound Power Terms and Definitions ...

**Sound Power**is the total sound energy radiated by a sound source and measured in watts (W).

Sound Power Definition (ASA 2.71) for a specified sound source, is the sound energy radiated per unit of time.

**Sound Power** is the product of sound pressure and volume velocity.

**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 the surface area

**Sound Power** is also known as acoustic power : LPac : Pac : PWL : PWR : SWL.

See also power quantity • root power (field) quantity

**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** in decibels is ten times the logarithm of the ratio of the sound power (W) to the reference sound power (Wo) of 1 picowatt

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

Sound Power Level Calculations.

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 Levels

**LW**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 absorption coefficient* is also known as statistical sound power absorption coefficient.

**Sound Power Density (I),** is the average sound energy flowing through a specified point and the SI units are W/m^{2} (watts per metre-squared) .

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.

*Sound power density* is also known as sound intensity and sound energy flux density.

Sound Power of a Source Definition (IEC 801-21-36) 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 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 Spectrum Level**, the power per unit frequency may be measured for broadband sound, SI units W/Hz (watt/hertz)

**Sound Power Through a Surface Element** (J), the rate of flow of sound energy through a specified area, the SI Unit is the watt (W).

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

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.

**Other Sound Power Related Terms** :
power spectral density •
power spectrum •
power spectrum averaging •
power spectrum level •
sound energy •
sound intensity