The insertion loss of perforated porous plates in a duct without and with mean air flow

Measurements of the acoustic insertion loss of poroelastic plates with different perforation ratios, mounted transversely across a flow duct, without and with flow have been made at various locations in the duct. For the lower perforation ratio the insertion loss is found to be approximately 3 dB higher with air flow than without over the frequency range of the measurements. A parallel impedance model has been formulated to predict the effects of perforation on the insertion loss without flow. Measurements and predictions without flow have been found to be in reasonable agreement.