kinetic energy/unit volume: .

The potential energy in compressed gas is an average of 0, to first order. To second order it is . so the kinetic and potential energy terms are the same.

Energy is propagated at the group velocity, . Energy flux = where Z is the acoustic impedance.

microphones detect pressure variation rather than power variation.

The pressure fluctation is where P is the power.

A decibal is .

- 120dB = pain. (737 taking off).
- In the front row of an orchestra, about 100dB = . displacement:
- conversation: 60dB . displacement of
- An empty church, = 30dB.
- For a whisper at 3' .
- Human hearing is around 0-5 dB.

source psfile jl@crush.caltech.edu index