# Sound Energy : Definitions, Terms, Units and Measurements

## The SI units of Sound Energy are joules = watt seconds.

**Energy : J : ** = Force x Distance = Work, a quantity equivalent to the capacity of a physical system to do work; the SI unit of energy is the same as the unit of work - the Joule J and is a Scalar quantity.

## 1 J = 1 N·m = 1 kg·m^{2}/s^{2} = 1 W·s = 10^{7} ergs

**Energy Flux Density** : sometimes known as Intensity

**Energy Spectral Density : ESD** : describes how the energy of a signal or a time series is distributed with frequency.

**Sound Energy : W** : is the energy present in a sound field.

## W = Wo · 10^{LW/10} J .... the units are Joules = Watt seconds

**Sound Energy Level : Lw** = 10 lg W/Wo dB re 1 pJ or 10^{-12} Joule.

**Sound Energy Density : E** : is the
Time-Averaged **Sound Energy** per unit volume, the units are J/m^{3} or W·s/m^{3}

Once again because of the wide range of the human ear the absolute values of Sound Energy Density are enormous. The decibel ratio to a threshold level produces manageable values - hence the

**Sound Energy Density Level : LE** = 10 lg (E/Eo) dB re 10^{-12} J/m^{3} or W·s/m^{3}

Standard Reference Sound Energy Density Level = 1 x 10

^{-12} J/m

^{3}
0 dB = 1 x 10

^{-12} J/m

^{3}
20 dB = 1 x 10

^{-10} J/m

^{3}
40 dB = 1 x 10

^{-8} J/m

^{3}

20 dB is a factor of 100

40 dB is a factor of 10000

**Kinetic Sound Energy Density** : half the product of the Density of the medium and the square of the Particle Velocity in the said medium.

**Total Sound Energy Density** : sum of instantaneous potential and kinetic energy densities.

**Sound Energy Flux : q** : SI units : W/m^{2} = J s/m^{2}

is the 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 power through a surface element**.

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

**Sound Energy Flux Density Level** : is the logarithm of the ratio of a given Sound Intensity in a stated direction to the reference sound intensity.

**Specific Energy** : is the energy per unit mass : joule per kilogram - J/kg

**See also : **
Noise Dose l

Sound Exposure

**Related Terms :**
Leq l

Sound Intensity l

Sound Power l

Sound Pressure