Knowledge summary
Summary (3)
In the case of a waveguide whose length is superior to the wavelength, the phenomena of internia and compressibility exist at every point of the waveguide. Thus, the lumped element hypothesis is no longer valid.
The relation between the pressure and volume velocity at two points is given by the transmission matrix. This matrix allows the joining of the impedances between these two points.
The nature of the duct endings determine the eigenfrequencies of the waveguide. The usual cases are:
Open-open: the eigenfrequencies are given by the expression
where
is the length of the guide. We speak about half-wavelenght (
) resonance.Open-closed: the natural frequencies are given by the exression
where
is the length of the guide. We speak about quarter-wavelenght
resonance.
