A detailed experimental comparison between active and passive approaches for the reduction of total far-field radiated sound power from a point-driven simply support plate

Abstract

Passive and active control of sound radiation from plates has been a challenging problem for a number of years where numerous surface treatments have been examined. The two most viable active surface treatments are active constrained layer damping (ACLD) and modal restructuring (MR). ACLD minimizes the total radiated power through a combination passive/active damping mechanisms as well as by applying restoring forces/moments. MR, on the other hand, achieves far-field attenuation by reducing the plates radiation efficiency through a restructuring of its mode shape. These active approaches show considerably more performance when compared to an optimized (Ross–Kerwin–Ungar) passive constraint layer damping design. The performance is evaluated by scanning near-field acoustic holography (NAH) measurements at several mode frequencies associated with strong radiation. The quantities determined via NAH include the power radiated in the half space as well as spatially dense surface motions of the plate. Both ACLD and MR show ∼50 dB reductions of total far-field radiated sound power (per unit input power). These experimental results will be discussed with particular emphasis placed on the tradeoffs between the passive and active surface treatments as well as the level of performance that can be obtained through other control approaches.