Resonances in the body of a musical instrument are an essential part of defining its nature and quality. The opposite is true of a loudspeaker. Cabinet panel resonances are a significant cause of sound coloration. Heavy bracing of a typical MDF enclosure can help reduce enclosure flex but at the cost of increased energy storage and damping factor. Although a welcome attribute for midrange outout, over damping is detrimental to bass performance (high energy storage, low wide Q and low resonances).
The graphs here show the spectral decay data across the range of typical enclosure construction methods. No singular material can satisfy all of the properties desirable in a loudspeaker enclosure. As stiffness increases, moving from MDF to phenolic resin to aluminum, cabinet vibrations are drastically reduced, although a sharpened Q of the resonance results in an audible ring. By damping the high Q resonance via elaborate constrained layer damping we have eliminated all energy storage and audible resonance from our enclosure.