The Sound intensity reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Sound intensity

The sound intensity is defined as the sound power P_ac per unit area A. The usual context is the measurement of sound intensity in the air at a listener's location. The basic units are watts/m².

For a spherical sound source, the intensity as a function of distance r is:

P_ac is the acoustic power.

The sound intensity J in W/m² is:

Sound pressure p in N/m² = Pa
Sound velocity (particle velocity) v in m/s
Acoustic impedance Z in N·s/m³
Area A in m²

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 is a different measure used in acoustics. Unlike sound intensity, sound intensity level is logarithmic. Neither ear drums nor microphones can convert sound intensity to voltage modulation.

Notice: Do not misuse the word "intensity", if you do not mean watts per area.
Use "magnitude" "strength", "amplitude", or "level" instead.

External links

• Conversion: sound intensity to sound intensity level
  
• Ohm's law of the acoustics - calculations

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