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A perforated plate with air
layer between the end face and the ceiling, even if the material
has poor sound absorption function, the layout also has the
function of sound absorption, such as perforated gypsum board,
wood board, metal plate, slit sound absorbing brick and so on.
This kind of sound absorption is called the cavity resonance
sound absorption or Helmholtz (German physicist, von Helmholtz
Ilermmann, 1821hz~1894hz) resonance sound absorption. The
acoustic resonance absorption principle is similar to the
thermos bottle, external space and internal cavity through the
bottleneck link narrow, acoustic wave incident at the resonance
frequency, the energy loss effect of intense resonance occurs
between the air and the inner space of the neck. Helmholtz
resonance sound absorption is characterized as long as the
resonance frequency has a larger sound absorption coefficient.
Cavity resonance sound absorption is the center of the layout
layout, there must be closed volume of the cavity, and through
holes have certain depth and sound spatial connectivity, the
sound absorption mechanism can be used to explain the Helmholtz
resonator. When the depth of the hole T and the aperture D is
much smaller than the acoustic wavelength, the elastic
deformation of the air column in the hole is small and can be
regarded as the mass block. Close the cavity volume ratio of V
hole Jingda much, the whole system of similar spring oscillator.
When the external incident frequency and natural frequency of Fo
to f system usually air column hole in the neck because of
resonance oscillation, the oscillation in the air column and
neck side wall and the cost of energy conflict.
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