The structure that introducing mechanical impedance plate and
Helmholtz resonators into the traditional MPP is proposed to
enhance sound absorption performance at low frequencies. The
two methods of acoustic electric analogy and impedance transfer
method are adopted to derive the acoustic impedance and the
sound absorption coefficient of the whole composite structure is
calculated. The sound absorption mechanism is the interaction
result of mechanical resonance and cavity resonance. The
mechanical resonant frequency and Helmholtz resonant frequency
are set in low frequencies. Low frequency sound penetrates the
micro perforated plate and energy is absorbed effectively.
The experimental results exhibit good agreement with the theoretical
calculation. In addition, it has revealed that the resonance
frequency of the Helmholtz resonator moves to low frequency
easily by changing the length of the intubation and increasing
the number of Helmholtz resonator appropriately can enhance
the low frequency sound absorption coefficient. It is proved that
the combination of the cavity resonance and mechanical resonance
absorption mechanism can broaden the sound absorption bandwidth
effectively. The sound absorption coefficient can be moved
to lower frequency by adjusting the other parameters of CSA
almost without increasing the need length of the structure.