## Sound Power Terms ...

### Sound Power

**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

**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** (Lw) = 10 lg (W/Wo) dB - i.e. more manageable numbers

**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.

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 and our sound power calculation section.

Sound Power related terms - listed alphabetically

### Apparent Sound Power Level

**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 Level

**Reference Sound Power Level** (Wo) = 1 pW = 10^{-12} W ≡ 0 dB = the threshold of hearing at 1Khz

### Sound Power Absorption Coefficient

**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.

See also statistical sound power absorption coefficient.

### Sound Power Density

**Sound Power Density (I),**is the average sound energy flowing through a specified point.

**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 metre-squared (W/m^{2}).

### Sound Power of a Source

**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

**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

**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

**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

**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