Helmholtz Number

The cut-off frequency of a duct is generally described in terms of the Helmholtz Number.

where
Hn = helmholtz number
k = wavenumber [m-1]
a = duct radius [m]

The plane wave cut-off frequency is when the Helmholtz Number is of the order of 1.84

See also: Cutoff Frequency, Wavenumber.

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Subjects: Noise & Vibration