Although geometric stiffeners (ribs, beads, dimples, etc.) may initially appear to reduce the low frequency (<300 Hz) sound radiation capacity of otherwise flat panels, when sensitivity to treatment and automobile excitation mechanisms are considered, no significant acoustic or vibration benefits are apparent. Testing does reveal that stiffeners reduce the number of low frequency resonance modes, but add on vibration treatments are unavoidable since not all of the resonance modes can practically be raised to frequencies above primary engine excitation. Further, after even relatively Light treatments are added, flat panels exhibit lower
Intuition might suggest that since increased panel stiffness can effectively reduce the overall surface velocities of untreated panels, add on treatments can be reduced and current sound levels will be maintained. However, this is not the case. Although initial reductions have been made, resulting in an initial decrease in sound radiation, evidence suggests that the sound radiation from a beaded panel (treated or untreated) is seldom as low as that from a treated flat panel.