Dampening internal speaker walls

[Hisatugo]

Hi, guys...

Have anyone got hard work on this matter?

I 'd been read so few experiences with damping walls of the cabinets, I'm think you don't do it at all.

I 'm applying a thick 4 mm layer of 3M underseal and still not be sure about its efectiveness. The knocking test reveal a small shift in frequency of ressonance of the board, but not that brick wall sound... I have some braces installed but I still don't know...

any opinions or ideas?

[zygibajt]

You might find this helpful.

http://www.bonavolta.ch/hobby/en/audio/lo_damp.htm


Bartek

[Hisatugo]

oh... that's really weights. I thought to use double box but my floorstanding towers have a very thin front panel and no space to get elaborate solution as that.

But it gave me an idea... I think I can mix the sand and the Underseal ... it will be heavy and could work...

thanks anyway...

Hisatugo

[Colin]

A technique I've heard of but not used myself - laminate plasterboard to the inside wall of the cabinets.

BBC system was to use thin walls (usually birch ply) with bitumin pads to lower resonance. An even earlier BBC technique (early 60s, I believe), used by Russ Andrews Ltd in the UK, is to laminate insulation board to the inside walls of fairly thin wall enclosures. This is the light and rigid school of enclosure design. My sealed box speakers are built this way and the sound fine to me (though I've never tried building a heavy enclosure to the same spec to compare directly).

Colin

[Kittle]

I found that lining the walls of my center channel with carpet padding got rid of a lot of boomyness, and in general made the vocals easier to understand.

I tried the same with my crappy sub and only heard a little improvement -- so your results will vary.

The nice thing is that carpet padding is CHEAP.

[thoriated]

To keep weight down, what I've found helpful is to laminate my own exterior panels with two sheets of 3/8" plywood (I'd use the thinply baltic birch here) glued together with 1/32" - 1/16" of viscoelastic material between them. I used a high solids industrial contact cement for the center layer but asphalty gunk might work here also if it's also a good adhesive. The result is 3/4" thick and acoustically more absorptive than any mdf or regular plywood I've seen while still having plywood's strength and relatively lighter weight.

I've found internal ribbed bracing every foot or so (for a larger cabinet) on all sides & top & bottom works well, keeping the depth of the bracing much higher than the width for maximum stiffness, say 3" deep by 3/4" wide. Gluing and screwing in a strong hardwood such as oak, not a softwood, for this bracing really seems to help here. I've also had good results by using 3/4" baltic birch plywood pieces cut with a large hole in its center & horizontally rabbetted 1/4" deep & well glued to all four of the side panels around the entire inside perimeter of the cabinet at two or three vertically spaced locations. If you want to take it even further (although I haven't done this as of yet), you could screw some 1/8" thick flat or U shaped steel strips at several points along the interior length of each brace away from its panel for additional stiffening.

This is a good deal of work but the result is a much stiffer and more acoustically absorptive (in the midrange & above) cabinet that is lighter than a basic mdf construction and there are still the options available of adding lead and internal stuffing & damping as needed.

[Hisatugo]

uhmmm.. good ideas... maybe I can mix them up, as my enclousures are almost ready, MDF made. I liked the hard wood bracing stuff, I think I do not have pieces of bracing enough.

The walls are very thick, they are 35 mm MDF and internal divisions are 18 mm. It is a D`Apolito configuration and the midrange subenclosure is my focus on dampening. I think the bass volume has longer wavelenghs than could resonate with any wall. Internal volume is only 35 lts(bass volume).

Those shelf type bracing are intalled already, as some divisions was made this way.

Thanks a lot.

Hisatugo

[Ap]

If your walls are 35mm you are going to need to dampen with a layer of something as heavy as the wall itself.
Plasterboard bonded to the walls would be a good start.
I use ply bonded with sound insulation material (barium loaded rubber) topped off with casting plaster & finally bitumous paint.