Effect of Panel Damping on Loudspeaker Enclosure Vibration
The paper reports the results of an experimental study where nine enclosures of similar dimensions and material thickness but with different materials were measured. The parameters measured included vibration, far-field sound radiation, and near-field sound radiation. The internal standing waves of the enclosure were damped as much as possible. The enclosures consisted of flat panels glued to each other with no additional support structures. The materials included particle board, plywood, MDF, and plywood with different vibration-damping sheets made of different viscoelastic materials and lead. Among the common enclosure materials (MDF, plywood, particle board), there were rather small differences between the enclosures at the lowest resonances, although both plywood and MDF exhibited small damping also at higher modes. The lowest mode is usually the only mode that needs serious attention, since it is both the most difficult to control using the internal damping and radiates more efficiently than the higher modes because all the points of a given surface vibrate in phase. Only the application of an effective damping material produced so significant a reduction in the resonances that the coloration due to the resonance was removed. As expected, the vibration level well below the lowest resonance is almost unaffected by the choice of enclosure material, with the exception of the enclosure where a lead sheet was used which had a mass significantly larger than the others.
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