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

**Sound Power** is the **total** sound energy radiated by a source, in all directions and measured in watts. **Sound Power** is the product of the sound pressure and the sound particle 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 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 chambers.

**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 sound power values in watts is not practical for everyday use. However 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 to the 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.

Source | Sound Power W | Lw re 1 pW |
---|---|---|

Jet Engine | 10,000 W | 160 dB |

Loudspeaker Rock | 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 |

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

**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.Related Terms - listed alphabetically

**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.**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.

**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 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 Density units** are watts per square metre.

**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 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 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.

See also • sound power absorption coefficient

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