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Never read about this and was curious if someone had tried it, but to limit sound from passing through enclosure walls, would using a second layer of MDF (inside of the external layer) glued in place only using Green Glue help to isolate sounds and dampen internal standing waves better?

Then one other idea, though a little more challenging, is there a reason other than the technical challenge that enclosure walls are usually made in parallel (seeing as this promotes standing waves). Or are there glaring disadvantages from doing this with an enclosure design?

Thanks,
 

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Never read about this and was curious if someone had tried it, but to limit sound from passing through enclosure walls, would using a second layer of MDF (inside of the external layer) glued in place only using Green Glue help to isolate sounds and dampen internal standing waves better?
Well, it will not isolate the sound from the exterior. It will convert the vibration to low level heat. This is a classic constrained layer cabinet construction, and it is highly effective. The inner and outer walls act as sheer plates, producing maximum molecular friction in the dampening layer/channel. You still must use very heavy/dense bracing on every axis if you want maximum effectivness, thus resulting in very little to no audible cabinet talk.

It will not dampen internal standing waves to any substantial degree.


Then one other idea, though a little more challenging, is there a reason other than the technical challenge that enclosure walls are usually made in parallel (seeing as this promotes standing waves). Or are there glaring disadvantages from doing this with an enclosure design?

Thanks,
You can use non-parallel walls to reduce inherent resonant modes, acoustically, inside the enclosure space. But it is secondary to the acoustical fill material you use. Materials like polyfill and low density fiberglass are not sufficient on most cases to remove all problems. However, if you use a high density fiberglass board or high density rock/mineral wool board, in the range of 4-8lb/ft^3, it can remove all internal acoustical resonant modes. This material has an extremely high acoustical co-efficient; this is why these materials are used in the best quality room treatments and in anechoic chambers. Use the appropriate thickness on each wall according to the frequency bands that require absorption. You should cover this fiber based insulation with a thin cloth or thin open cell foam to prevent the fibers from possibly entering the driver vent, possibly lodging between the driver voice coil and to prevent breach of fibers into a room from ports.

-Chris
 
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