By optimally placing lumped masses on vibrating shells, it is shown that big reductions in sound power levels are achievable. The lumped masses, which weigh less than 10% of that of the structure, change the mode shapes of vibration such that the radiated noise is reduced. An example showing the mode shapes before and after optimization are included in this paper. What is interesting is that a perfectly symmetric vibrating structure admits a non-symmetric optimal mass placement. Total power from first four modes is reduced by over 13 dB.

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