Abstract
The acoustic behavior of micro-perforated panels (MPP) is studied theoretically and experimentally at high level of pressure excitation. A model based on Forchheimer’s regime of flow velocity in the perforations is proposed. This model is valid at relatively high Reynolds numbers and low Mach numbers. The experimental method consists in measuring the acoustical pressure at three different positions in an impedance tube, the two measurement positions usually considered in an impedance tube and one measurement in the vicinity of the rear surface of the MPP. The impedance tube is equipped with a pressure driver instead of the usual loudspeaker and capable of delivering a high sound pressure level up to 160 dB. MPP specimens made out of steel, dural and polypropylene were tested. Measurements using random noise or sinusoidal excitation in a frequency range between 200 and 1600 Hz were carried out on MPPs backed by air cavities. It was observed that the maximum of absorption can be a positive or a negative function of the flow velocity in the perforations. This suggests the existence of a maximum of absorption as a function of flow velocity. This behavior was predicted by the model and confirmed experimentally.
Highlights
Micro‐perforated panels, when associated with air cavities, are of great interest in noise reduction applications such as Helmholtz resonators
The aim of this work is to propose a model for micro‐perforated panels backed by an air cavity involving parameters that are easier to estimate than the discharge coefficient
The experiments and the present model are in good agreement for the high excitation levels. This result points out the fact that for high sound pressure levels, the dependency of the resistance and the Mach number is linear
Summary
Micro‐perforated panels (referred to as MPPs), when associated with air cavities, are of great interest in noise reduction applications such as Helmholtz resonators. Kraft et al.[5,6] used a fixed discharge coefficient of 0.76 in their model assuming constant nonlinear behavior regardless of the flow conditions. Their resistive and reactive part of the plate impedance are independent of frequency essentially assuming constant orifice mass. Maa[8] showed that the acoustic non‐linearity of apertures is an external phenomenon i.e. the internal impedance is independent of the sound intensity He suggested a nonlinear impedance term expression for MPP with small open area ratio. The discharge coefficient and some other parameters of the model were determined empirically
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