Experimental investigation of coupling effects of passenger compartment and trunk of a car on coupled system natural frequencies using noise transfer function

Abstract The parcel shelf of a car has several holes for speakers and electrical devices. In addition, air ventilation holes are installed on the trim that covers the parcel shelf. The effect of the holes between the two cavities, passenger compartment and the trunk, and the natural frequencies of double cavities connected by the neck (parcel shelf) are very vital and useful to noise–vibration–harshness engineers, as the low frequency resonances contribute to the booming noise inside the car. In the present study, the coupling effect of the passenger compartment and the trunk connected through the holes on the parcel shelf in between, has been investigated experimentally using noise transfer function. The first and second coupled system modes are measured at around 40 Hz and 70–80 Hz respectively. By increasing the effective size of the holes on the parcel shelf, the first and second natural frequencies of coupled modes can be shifted to higher values. The current study has verified that holes act as point sources in the low frequency ranges. It was concluded that the coupled acoustic modes, in the low frequency range, are strongly controlled by fluid–structure interaction as well as changes in the panels mass and stiffness in the car interior space. The shift in the natural frequencies of connected cavities can be useful in the prediction of the interior noise in an automobile as well as provide a verification tool for conventional numerical techniques such as finite element methods.