Sound intensity
Encyclopedia : S : SO : SOU : Sound intensity
| Sound measurements |
|---|
| Sound pressure p |
| Sound pressure level (SPL) |
| Particle velocity v |
| Particle velocity level (SVL) |
| (Sound velocity level) |
| Particle displacement ξ |
| Sound intensity I |
| Sound intensity level (SIL) |
| Sound power Pac |
| Sound power level (SWL) |
| Sound energy density E |
| Sound energy flux q |
| Acoustic impedance Z |
| Speed of sound c |
The sound intensity, I, (acoustic intensity) is defined as the sound power Pac per unit area A. The usual context is the noise measurement of sound intensity in the air at a listener's location[#endnote_note]. The SI units are W/m2 (watts per square metre).
- [I = \frac \int_^p(t) \cdot v(t)\,dt]
- [I_r = \frac} = \frac}]
- [I = p \cdot v = \frac = Z \cdot v^2 = \xi^2 \cdot \omega^2 \cdot Z = \frac = E \cdot c = \frac} ]
| 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.
- [L_I=10 \log_ \frac ] (dB-SIL),
Note 1↑ : 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]. In stereo the level differences have been called "intensity" differences, but sound intensity is a specifically defined quantity and cannot be sensed by a simple microphone, nor would it be valuable in music recording if it could.
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 waves]
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.