Effect of machining error on accuracy of Maa's theory for micro-perforated panel absorbing constructions with ultra-micro orifices

The effect of machining error on accuracy of Maa's theory for micro-perforated panel (MPP) with ultramicro orifices is discussed theoretically and experimentally in this article. The theoretical analysis model of MPP on considering the effect of machining error is built and a series of MPPs with ultra-micro orifices are fabricated based on the MEMS technology, but the deviation of 10%~20% is made between the actual orifice diameter and the designed orifice diameter due to the machining error. Their normal absorption coefficients were tested in impedance tube. Results show that the measurements and the predictions calculated by the theoretical analysis model on considering the effect of machining error compare well with the calculations based on Maa's theory with the maximum error being less than 6%, which indicates that Maa's theory is still available on considering the effect of machining error. In addition, the limitation of Maa's theory for machining error is discussed through simulation, results reveal that it depends on the pore size of MPPs with ultra-micro orifices.