Sound intensity
From Free net encyclopedia
The sound intensity, I, (acoustic intensity) is defined as the sound power Pac per unit area A. The usual context is the measurement of sound intensity in the air at a listener's locationTemplate:Ref. The SI units are W/m2 (watts per square metre).
- <math>
I = \frac{1}{T} \int_{0}^{T}p(t) \cdot v(t)\,dt </math>
For a spherical sound source, the intensity as a function of distance r is:
- <math>
I_r = \frac{P_{ac}}{A} = \frac{P_{ac}}{4 \pi r^2} </math>
The sound intensity I in W/m2 of a plane progressive wave is:
- <math>
I = p \cdot v = \frac{p^2}{Z} = Z \cdot v^2 = \xi^2 \cdot \omega^2 \cdot Z = \frac{a^2 \cdot Z}{\omega^2} = E \cdot c = \frac{P_{ac}}{A} </math>
where:
Symbol | Units | Meaning |
---|---|---|
p | pascals | sound pressure |
f | hertz | frequency |
ξ | m, meters | particle displacement |
c | m/s | speed of sound |
v | m/s | particle velocity |
ω = 2πf | radians/s | angular frequency |
ρ | kg/m3 | density of air |
Z = c · ρ | N·s/m³ | acoustic impedance |
a | m/s² | particle acceleration |
I | W/m² | sound intensity |
E | W·s/m³ | sound energy density |
Pac | W, watts | sound power or acoustic power |
A | m² | area |
The amplitude of sound intensity (not sound pressure!) decreases in the free field (direct field) with 1/r2 of the distance of a point source.
Sound intensity level, LI, is the sound intensity, expressed in logarithmic units.
- <math>L_I=10 \log_{10} \frac {I}{I_o}</math> (dB-SIL),
where Io is the reference intensity, 10-12 W/m2
Note 1Template:Note: The term "intensity" is used exclusively for the measurement of sound in watts per unit area. To describe the strength of sound in terms other than strict intensity, one can use "magnitude" "strength", "amplitude", or "level" instead.
Sound intensity is not the same physical quantity as sound pressure. Hearing is directly sensitive to sound pressure which is related to sound intensity.
See also
External links
- Conversion: sound intensity to sound intensity level
- Ohm's law of the acoustics - calculations
- Connection of acoustic sizes for even progressive acoustic wavesde:Schallintensität
es:Intensidad de sonido nl:Geluidsintensiteit pl:Natężenie dźwięku sl:Jakost zvoka