![]() ![]() Since bending waves create motion normal to the panel surface, it is the bending waves which are dominant in radiating noise.ġ5.25. Vibration waves traverse across the panel in bending waves and longitudinal waves. The resonant portion of panel noise radiation is governed by the bending (flexural) resonances of the panel. This will be covered in detail in the following section. However, great care should be taken when increasing panel thickness, since this not only increases the mass but also increases the stiffness (and therefore the resonant portion) of the panel radiated noise. This can be done by adding heavy asphaltic or bitumen patches to the panel, or by increasing the panel thickness. Therefore, one way to increase the ability of a body panel to block airborne noise is to increase its mass. 15.12, it can be seen that by doubling the mass of the panel, the mass-law portion of STL is increased by 6 dB. Where m is mass per unit area (kg/m 2) and f is frequency.įrom eq. In some cases a combination of frequency shifting and damping will be required to achieve the best result. In other words, body panel resonances in the structure-borne noise range can be either managed by shifting their frequencies using mass and stiffness or damped using various types of damping treatments. Damping affects the amplitude of the resonance, but also the frequency (to a lesser degree). Mass and stiffness affect the resonant frequency directly, but also affect the amplitude of the resonance (to a lesser degree). Managing panel resonant energy to reduce unwanted radiated noise can be accomplished with various combinations of mass, stiffness and damping in the panel. ![]() Reducing the rigid or forced vibration of the panel is achieved by addressing the upstream areas of the body structure, namely the body attachments and the global body stiffness (covered in Sections 15.3 and 15.4). These resonances have unique mode shapes, which in turn determine how strongly coupled the panel vibrations are to the acoustic medium (passenger space air cavity). Resonant vibration is the result of the same forces acting on the attachment boundaries, but which also excite the various resonances of a panel. This is analogous to the noise radiated by a moving rigid piston. Forced vibration is simply the ‘rigid’ response of the panel to forces acting on it from its attachment boundaries. 15.6.1 Structure-borne noise mechanismsīody panels radiate noise in the structure-borne noise range due to a combination of forced vibration and resonant vibration. ![]() Body panel radiated noise will be broken down into three sections: 1.īody panel structure-borne noise mechanisms 2.īasic design principles. ![]()
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