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This paper describes an experimental modal synthesis method for determining the noise characteristics of coupled acoustic-structural systems. This method was developed to provide an essential tool for analyzing passenger compartment noise levels. With this method, it is possible to obtain the coupled acoustic-structural parameters directly from experimental measurements of noise and vibration. The resulting modal parameters provide the basis for predicting how structural modifications will affect interior noise characteristics. This paper presents the theory on which the method is based and gives examples of its application to passenger compartment noise analyses.

An acoustic control technique for reducing booming noise caused by road surface roughness is described. This noise, mainly in the frequency range between 25 and 40Hz and accompanied by a pressure sensation, is closely related to suspension vibration characteristics and the acoustic response of the vehicle compartment. A reduction method which separates the highest acoustic response from suspension resonance in this frequency region is proposed. An acoustic simulation model is used to estimate the effects of the luggage compartment on this noise and of trunk lid vibration characteristics in optimizing acoustic properties of the compartment. As a result, a frequency region for trunk lid resonance which lowers booming noise is obtained. Estimated booming noise reduction is experimentally confirmed in road tests. A study of human auditory characteristics is also conducted to ascertain the frequency range and booming noise level which produce uncomfortable sensations.