Wayne Parham Messages: 18831 Registered: January 2001
Illuminati (33rd Degree)
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I've used various insulation materials and I've used constrained-layer panels, with PVC as the damping layer.
I haven't found any damping material that works as well as fiberglass-based R11. And while constrained layer panels definitely damp panel resonance, it didn't give any measurable improvement on my speakers. The bracing that is used is sufficient.