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Old 24th June 2002, 11:22 PM   #1
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Join Date: Oct 2001
Location: New Zealand
Question Function of foam inside speakers and panel resonance

Does the foam damping material inside speakers serve any other purpose other than to:
(a) reduce sound wave reflections within the cabinet, and
(b) increase the apparent volume of the box that the woofer
"sees", via adiabatic compression/heat absorbtion?

Also, am I correct in thinking that if two boards of different bending moduli etc. are laminated together then this will reduce the resonance of that board to less than of a single MDF board? I realise that question depends on the materials being used. What I'm getting at is instead of laminating a thin wood veneer (ie. 1mm) onto 18mm MDF, why not laminate 9mm thick wood onto 10mm MDF. The end result would be the same thickness (19mm) but would the thicker wood dampen the MDF resonance and vice versa, thus producing less resonance overall than the 18mm MDF + 1mm veneer?

Thanks for any input,
joseph.
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Old 25th June 2002, 12:30 AM   #2
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You are completly right what concerns the foame.
I do not think that it has any more purposes than the ones You mentioned already.

You are also right about the advantage of different bending moduli but I would suggest to combine more different materials.
I guess the bending moduli for MDF and wood veneer does not differ so much.
Better to combine a rigid outer enclosure with something really soft and heavy inside.
About 15 years ago I had the idea melting tar and pour it on to the surfaces inside the enclosure. Thickness of the tar I choose about one third or more of the enclosure walls. This gave great results and I always use this since on quality enclosures.
This also has some beneficial effects aside:
This way You can fix perfectly the foam or whatever while putting it on the still liquid tar (before it get dried harder).
You get perfectly air tight enclosures - no hard to find leakages.
disadvantage:
After this treatment You cannot proceed working with the enclosure for about one or two weeks until the gases of the tar disappeared.
Vented enclosures need even more time until the bad smell out of the vent is completly gone.
Time consuming work and ..... You can badly burn Your fingers with this stuff.
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