Sound radiation from perforated plates

A practical engineering noise control measure that can often be used for plate-like structures is to construct them from perforates. This can dramatically reduce the sound radiation from such structures. Here, a prediction model is developed to quantify this effect. It is an extension of Laulagnet's model for the radiation from an unbaffled plate, which expresses the surface pressure difference as well as the plate velocity as a sum over plate modes. The perforation is included in terms of a continuously distributed surface impedance, which for moderately sized holes is predominantly inertial. Results show that the radiation efficiency reduces, not only as the perforation ratio increases but also as the hole size reduces for a given perforation ratio. Experimental validation is given which shows a good agreement with the predictions. An approximate formula is also proposed for the effect of perforation which corresponds well with the analytical calculations up to half the critical frequency and could be used for an engineering application to predict the noise reduction due to perforation. A model for the case of a perforated plate embedded in an equally perforated baffle is also discussed for comparison.