1998-02-23

Booming Noise Analysis Method Based On Acoustic Excitation Test 980588

A method for analyzing and decreasing booming noise in the cabin of a minivan using acoustic excitation tests has been developed. To ensure a pleasant ride for passengers of minivans equipped with four-cylinder engines, decreasing cabin noise from secondary components of engine revolution has become a priority. “Booming noise” in the cabin originates from engine vibration that passes through engine mounts to shake the body structure and body panels. To decrease the level of sound pressure resulting from this shaking, one effective approach is to reduce the level of the mechanical-acoustical transfer function (MATF) in the interval from engine mounts to passengers' ears. This paper reports on a specific method for reducing the level of MATF. In this method, a speaker is positioned near a passenger's ear to measure the vibration-response level at the points where engine mounts are installed when exciting the body structure, and the level is reduced by modifying the body structure. This method makes use of the relationship between MATF and vibration response during acoustic excitation, which can be considered equivalent according to the reciprocity principle. The following conclusions were reached when applying this method to decreasing 60- to 120-Hz booming noise in minivans that mount the engine under the driver's seat. The pattern of vibration distribution measured when exciting body structure by a shaker is generally different from that measured by acoustic excitation, and the proposed method that modifies body structure to suppress the latter vibration can improve MATF levels in a relatively short time. In other words, when exciting body structure by a shaker or when running the vehicle, the vibration components of body structure that excite the cabin resonance mode and generate booming noise are normally hidden by vibration components that do not result in sound.

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