Expansion Chamber  The expansion chamber can be considered as a simple low pass filter. The transmission loss performance is determined by the cross-sectional area ratio between the inlet and outlet ducts and the volume. With the single expansion chamber the transmission loss falls to zero when a half wavelength or multiple thereof equates to the length of the chamber.
Extending the inlet and outlet pipes into the volume will give a more abrupt impedance change and hence a larger transmission loss.
The transmission loss is given by:
 - where
- f = frequency [Hz]
- fn = resonant frequency [Hz]
 - c = speed of sound [ms-1]
- S = cross-sectional area of inlet and outlet ducts [m2]
- Sc = cross-sectional area of expansion chamber [m2]
- Lc = length of expansion chamber [m]
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See also: Acoustic Filter Elements, Helmholtz Resonator, Quarter Wave Tube.
  
Subjects:- Noise & Vibration
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