Sound Transmission Through Primary Bulb Rubber Sealing Systems

Structural sound transmission through primary bulb (PB) sealing systems was investigated. A two-degrees-of-freedom analytical model was developed to predict the sound transmission characteristics of a PB seal assembly. Detailed sound transmission measurements were made for two different random excitations: acoustic and aerodynamic. A reverberation room method was first used, whereby a seal sample installed within a test fixture was excited by a diffuse sound field. A quiet flow facility was then used to create aerodynamic pressure fluctuations which acted as the excitation. The space-averaged input pressure within the pseudo door gap cavity and the sound pressure transmitted on the quiescent side of the seal were obtained in each case for different cavity dimensions, seal compression, and seal designs. The sound transmission predictions obtained from the lumped element model were found to be in reasonable agreement with measured values. The measured noise reduction was found to be very similar for both types of excitation. This confirmed that an acoustic excitation may be used instead of aerodynamic pressure fluctuations for sound transmission measurements, and that the barrier performance of the PB seal was not significantly affected by the presence of a static pressure gradient associated with the mean flow. The wind tunnel method was also found to yield a better signal-to-noise ratio than the reverberation room method.