Speaker panel deadening mix of particles + hardener ?

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stephend1714

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Joined 2014
#1
Posts about this might already be on the Forum so, please steer me to them.

If not, here we go: for those of us who build cabinets with MDF or PLY and avoid thickness walls above 1 inch, there are resonances -- even with bracing / foam sheets / fluffy fill.

So, it seems to me that an emulsion of some goopy liquid -- either fast cure epoxy or slow cure glue -- containing ultra-clean sand or other minute particles -- could be poured onto interior sides of the cabinet one by one as each lays flat on a worktable.

Then cured slowly at the right speed to prevent "checking" + minimum shrinkage. Has anyone found the emulsion and particles -- with how to go about doing the cure process ??

Thanks muchly in advance . . . Steve
 
#2
Wont help much. You will just add some mass, and perhaps a tiny bit of damping. This will just lower the resonant frequencies of the panel.

Making the panel very thick both increases mass and stiffness.

I have always fantasized about ways to DIY honeycomb out of resin coated cardboard tubes (lots and lots of short sections) and 1/4" thick hardboard. Never had the guts to try it!
 
#3
stephend1714 said:
Posts about this might already be on the Forum so, please steer me to them.

If not, here we go: for those of us who build cabinets with MDF or PLY and avoid thickness walls above 1 inch, there are resonances -- even with bracing / foam sheets / fluffy fill.
Click to expand...

Cross bracing works.

Use wood braces glued to the centers of each pair of panels on opposite sides of the box.
 
#5
Some years ago I had read about a commercially available sound deadening compound (Quietcote???) that included, essentially, the components of joint compound (limestone etc.) and magnesium sulfate (epsom salt) mixed in with a polymer. So figured I would combine joint compound, epsom salt and tacky glue and spread it on the interior of a mini monitor cabinet (about a 1/4 inch thick coating) that I was building. According to some crude measurements I made with an accelerometer it did make a small but measurable difference. I am not sure it made an audible difference but I can say it didn't seem to hurt, since after several years of living with them I am still surprised that my mini monitors sound pretty good.

To give credit where credit is due, I think I first read about combining joint compound with tacky glue in a North Creek Audio brochure. Also, there appears to be some scientific support for the use of magnesium sulfate since there are numerous papers that show that much of the sound absorption at certain frequencies in sea water is due to magnesium sulfate. Whether that has any applicability to its use in non aqueous uses or when the absorbing volume is very small, is, I think, open for debate.

In any event, joint compound, epsom salts and tacky glue are all pretty cheap. So it doesn't cost much to experiment. Speaker builders have, for ages, sworn by lining their cabinets with roofing or bituminous felt. So I am at least open to consider that a coating of equivalent thickness could be made to work.
 
#9
#13
Cal Weldon said:
Hi Terry,
I believe that would be for the internal standing waves not panel damping.
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Cal,

You may well be right, but Dickason makes this statement in my admittedly out-of-date 6th edition of the LDC, page 102, under Section 5.30 entitled "Box Damping," subsection B, entitled "Wall Resonance Damping Materials." Thus you can see why I stated what I did. Dickason, in fact covers standing waves in the immediately preceding section, 5.20.

I have never tried the method, and likely never will, but I am more than willing to concede that Mr. Dickason, as well as you, are considerably more knowledgeable about this then I am.
 
#15
Hi,

Confusion on terms here. Bitumised felt panels as used by the BBC
I haven't seen available for a long time. Roofing felt is basically
bitumen sheeting of various types and can be used for wall damping.

Use of roofing felt has nothing to do with internal standing waves.

rgds, sreten.
 
#17
Just do what Tannoy have been doing for quite a few years, brace top, bottom, back and both sides of the box all together so that the bracing finishes about 5mm behind the back of the woofer back plate and in that 5mm gap put in some "Blue tack"
Arthur.
 
#18
sreten said:
Hi,
Confusion on terms here.
Click to expand...
I'll say.
Bitumised felt panels as used by the BBC
Click to expand...
All roofing felt is bitumized, that's what makes it a roofing felt.
Roofing felt is basically bitumen sheeting of various types and can be used for wall damping.
Click to expand...
Felt is a loose term now used to describe, felt, fiberglass and polyester reinforcements. What you are referring to is self adhering asphalt roof membrane, a far cry from anything related to roofing felt.
Use of roofing felt has nothing to do with internal standing waves.
Click to expand...
Again, you are mixing up your products and what they can be used for in loudspeakers.

If I seem pedantic, I have to be, I'm in the business.
 
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