MEASUREMENT AND PREDICTION OF THE ACOUSTIC PERFORMANCE OF POROELASTIC FOAM FILLED MUFFLERS FOR SLEEP APNOEA DEVICES

Mufflers are incorporated into continuous positive airway pressure (CPAP) devices to reduce noise in the air paths to and from the flow generating fan. The mufflers are very small, irregularly shaped and are required to attenuate noise up to 10 kHz. The acoustic performance of these predominantly reactive mufflers can be enhanced with the inclusion of dissipative materials. It is important that the acoustic performance of these mufflers is reliably predicted and optimised, in order to improve the user experience and maximise compliance with the CPAP therapy. In this study, the acoustic properties of two polyurethane foams were determined using a two-cavity method. Acoustic models of two muffler designs, having dimensions similar to those used in CPAP devices and incorporating foam-filled regions, have been developed using a commercial finite element analysis software package. Experimental results for the mufflers have been obtained using the two-microphone acoustic pulse method. Results of the transmission loss of the muffler designs obtained from the finite element models are presented and validation of the computational results is discussed.