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**Sound energy density** or **sound density** is the sound energy per unit volume. The SI unit of sound energy density is the pascal (Pa), which is 1 kg⋅m^{−1}⋅s^{−2} in SI base units or 1 joule per cubic metre (J/m^{3}).^{[1]}^{: Section 2.3.4: Derived units, Table 4 }

Sound measurements | |
---|---|

Characteristic | Symbols |

Sound pressure | p, SPL, L_{PA} |

Particle velocity | v, SVL |

Particle displacement | δ |

Sound intensity | I, SIL |

Sound power | P, SWL, L_{WA} |

Sound energy | W |

Sound energy density | w |

Sound exposure | E, SEL |

Acoustic impedance | Z |

Audio frequency | AF |

Transmission loss | TL |

Sound energy density, denoted *w*, is defined by

where

*p*is the sound pressure;*v*is the particle velocity in the direction of propagation;*c*is the speed of sound.

The terms instantaneous energy density, maximum energy density, and peak energy density have meanings analogous to the related terms used for sound pressure. In speaking of average energy density, it is necessary to distinguish between the space average (at a given instant) and the time average (at a given point).

The **sound energy density level** gives the ratio of a sound incidence as a sound energy value in comparison to the reference level of 1 pPa (= 10^{−12} pascals).^{[2]} It is a logarithmic measure of the ratio of two sound energy densities. The unit of the sound energy density level is the decibel (dB), a non-SI unit accepted for use with the SI Units.^{[1]}^{: Chapter 4: Non-SI units that are accepted for use with the SI, Table 8 }

The sound energy density level, *L*(*E*), for a given sound energy density, *E*_{1}, in pascals, is

- ,

where *E*_{0} is the standard reference sound energy density^{[3]}

- .

- ^
^{a}^{b}Newell, David B; Tiesinga, Eite, eds. (2019). The international system of units (SI) (PDF) (Report). Gaithersburg, MD: National Institute of Standards and Technology. doi:10.6028/nist.sp.330-2019. **^**Deutsches Institut für Normung,*Grundlagen der Schallmessung; Physikalische & subjektive Größen von Schall, Physical & subjective magnitudes of sound*, Norm, Standard, № DIN 45630‑1:1971‑12 (Berlin: Beuth, 1971‑12).**^**Deutsches Institut für Normung,*Akustik—Begriffe, Acoustics—Terminology*, Norm, Standard, № DIN 1320:2009-12 (Berlin: Beuth, 2009‑12).

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