# Acoustic Glossary

## Sound Energy and related terms ...

### Sound Energy

Sound Energy is transmitted by vibrating the particles of the various media the sound waves pass through. The resistance to the flow of sound energy through a medium is known as the acoustic impedance.

Sound Energy Definition (ASA 2.67) total energy in a given part of a medium minus the energy that would exist at that same part of the medium with no sound waves present.

The Sound Energy Unit is the joule (J), however the range of human hearing, 0.000000000001 joules up to 10 joules or more, means the joule is not practical for everyday use. The sound energy level in decibels, neatly solves this problem.

### Reference Sound Energy

Reference Sound Energy (Wo) = 1pJ = 10-12 joule ≡ 0 dB

### Sound Energy Level

Sound Energy Level is the logarithmic ratio of the sound energy to the reference sound energy.

Sound Energy Level Formula (Lw) = 10 lg (w/wo) dB, where w is the sound energy and wo is the reference sound energy of 10-12 joule ≡ 0 dB and therefore 1 joule = 120 dB

3 dB is a factor of 2, twice or half the energy.
10 dB is a factor of 10 increase or decrease in the sound energy.
20 dB is a factor of 100
40 dB is a factor of 10000 etc.,

See also our sound level calculations article

Sound Energy related terms - listed alphabetically

### Sound Energy Density

Sound Energy Density (E) is the time-averaged sound energy per unit volume. The SI unit of sound energy density is the Pascal.

Sound Energy Density Definition (IEC 801-21-41) sum of the instantaneous potential and kinetic energy densities and is also known as the total energy density.

Instantaneous Kinetic Sound Energy Density Definition (IEC 801-21-40) half the product of the density of the medium and the square of the velocity of a particle in the said medium.

Instantaneous Potential Sound Energy Density Definition (IEC 801-21-39) half the quotient of the square of the instantaneous sound pressure by the modulus of elasticity of the medium.

### Reference Sound Energy Density

Reference Sound Energy Density (Eo) = 1 pJ/m3 = 10-12 J/m3 ≡ 0 dB

### Sound Energy Density Level

Sound Energy Density Level is the logarithmic ratio of the sound energy density to the reference sound energy density

Sound Energy Density Level (LE) = 10 lg (E/Eo) dB, where E is the sound energy density
and Eo is the reference sound energy density level = 10-12 J/m3 ≡ 0 dB

20 dB is a factor of 100
40 dB is a factor of 10000 etc.,

### Sound Energy Flux

Sound Energy Flux (J) the rate of flow of sound energy through a specified area. The sound energy flux SI unit is the watt (W) and is also known as the sound power through a surface element.

Sound Energy Flux 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.

### Sound Energy Flux Density

Sound Energy Flux Density (I) is the average sound energy flowing through a specified point and the SI units are watts per square metre (W/m²).

Sound Energy Flux 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, and is also known as the sound intensity and the sound power density

### Sound Energy Flux Density Level

Sound Energy Flux Density Level Definition (IEC 801-22-06) logarithm of the ratio of a given intensity of sound in a stated direction to the reference sound intensity. Such intensity level in decibels is ten times the logarithm to the base ten of the ratio. and is also known as the sound intensity level.

Note : unless otherwise specified, the reference sound intensity is 1 pW/m2

See also the IEC Definition of Level

See also noise dosesound exposure

Other related terms, Leqsound intensitysound powersound pressure

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