Abstract
Micro perforated panel (MPP) absorber is a new form of acoustic absorbing material in comparison
with porous ones. These absorbers are considered as next generation ones and the best alternative for
traditional porous materials like foams. MPP combined with a uniform air gap constructs an absorber
which has high absorption but in a narrow bandwidth of frequency. This characteristic makes MPPAs
insufficient for practical purposes in comparison with porous materials. In this study instead of using
a uniform air gap behind the MPP, the cavity is divided into several partitions with different depth
arrangement which have parallel faces. This method improves the absorption bandwidth to reach the
looked for goal. To achieve theoretical absorption of this absorber, equivalent electro-acoustic circuit and
Maa’s theory (Maa, 1998) are employed. Maa suggested formulas to calculate MPP’s impedance which
show good match with experimental results carried out in previous studies. Electro-acoustic analogy is
used to combine MPP’s impedance with acoustic impedances of complex partitioned cavity. To verify
the theoretical analyses, constructed samples are experimentally tested via impedance tube. To establish
the test, a multi-depth setup facing a MPP is inserted into impedance tube and the absorption
coefficient is examined in the 63–1600 Hz frequency range. Theoretical results show good agreement compared
to measured data, by which a conclusion can be made that partitioning the cavity behind MPP into
different depths will improve absorption bandwidth and the electro-acoustic analogy is an appropriate
theoretical method for absorption enhancement research, although an optimisation process is needed to
achieve best results to prove the capability of this absorber. The optimisation process provides maximum
possible absorption in a desired frequency range for a specified cavity configuration by giving the proper
cavity depths. In this article numerical optimisation has been done to find cavity depths for a unique
MPP.
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