Acoustics

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Acoustic intensity and decibel

The acoustic intensity represents the acoustic energy flux associated with the wave propagation:

\underline i (t) = p\underline v

We can then define the average intensity:

\underline I = < \underline i >

However, acoustic intensity does not give a good idea of the sound level, since the sensitivity of our ears is logarithmic. Therefore we define decibels, either using acoustic over-pressure or acoustic average intensity:

p^{dB} = 20\log (\frac{p}{{p_{ref} }})  ; L_I = 10\log (\frac{I}{{I_{ref} }})

where pref = 2.10 ? 5Pa for air, or pref = 10 ? 6Pa for any other media, and Iref = 10 ? 12 W/mē.