Plastiline as a damping material in vented boxes?

[fjhuerta]

Yesterday night, I was considering using a couple of huge old calendars we have at the office (made out of chipboard) as a basis for some real Recession Buster cabinets.

Unfortunately, I realized the baffle would be around 4 mm. thick. Pretty useless.

My boss asked "hey, maybe you could use something to add rigidity to the board. How about some foam? Or plastiline clay?

Hmm. Plastiline clay.

I began wondering - would plastiline clay be a good idea as a damping material on a vented box? I can imagine that if I heated it and applied it to the walls, it would make a killer, cheap damping compound.

Am I on the right track?

[fjhuerta]

Can't I have an original idea?

http://www.audiocircle.com/circles/index.php?topic=28885.msg390717

http://www.audiocircle.com/circles/index.php?topic=13419.msg115332#msg115332

When I last did this (something like 20 years ago) I used a combination of Plastilina and Plast-I-Clay, and it worked just fine, and they were reasonably comparable. In any case, I did have an issue with it falling off the inside of the enclosure in hot (over 100 degree) weather, but neither seemed to be superior in that regard.

Of course, it does EXACTLY what Frank claims, and had quite remarkable effects on the overall "coloration" of the sound, i.e., the "boxy" sound and many stray resonances completely went away. If speaker manufacturers were really smart, they would use it at the factory. It would be trivial to build a double-walled enclosure with standoffs between the parts, and cast the clay in place. That way it would stay forever. I think it would be far more effective than wooden internal bracing - the panels themselves would be dead, instead of taking "ringy" panels and trying to restrain them.

Apparently, Von Schweikert (sp?) uses plastiline of some sort on their boxes, too.


My next box will have plastiline inside it, no doubt about it.

[BigguyZ]

How exactly would that work? You just mold it to the inside of the box? How thick, and would you have to adjust volume of the box?

[bluewizard]

I don't know if it can be trusted, but here is a supposed recipe for Plastiline -

10 lbs microcrystalline wax
1/2 gal. #10wt oil
4 lbs plain automotive grease
25 lbs dry clay powder (such as Kentucky ball clay)

http://users.lmi.net/drewid/plastilene_recipe.html

That seems like a lot of petroleum products. I wonder if you could substitute mineral oil and petroleum jelly for common oil and grease?

While mineral oil and petroleum jelly are still petroleum products they are mostly inert and safe to ingest. Also, it is possible to get vegetable based petroleum jelly.

It would be nice to find a way to roll the plastiline into nice uniform thin sheets. How thick would this substance have to be, in order to be effective; 1/8th inch, 1/4 inch, a 1/2 inch?

Next, I wonder if you could embed some common plastic window screen into the surface of the clay, then staple the screen to the speaker frame to prevent the Plastiline from pulling away?

Just curious.

Steve/bluewizard

[ThomasW]

This isn't going to stiffen the cabinet walls, it will of course add mass lowering the Fs...

[bluewizard]

I agree stiffening is not the issue. I assumed the benefit was from a soft dense mass between the drivers and the outside world. The clay prevents sound vibrations from penetrating the cabinet walls, but by shear density and mass rather than absorption or rigidity.

This is like lining the walls of the speakers with lead, or some type of sound proofing membrane.

Am I on the right track, or is there something I'm not seeing

Steve/bluewizard

[ThomasW]

Am I on the right track, or is there something I'm not seeing

You're correct, my statement was in reference to the OP's original post

[bluewizard]

Am I also right in thinking that even with walls lined with Plastiline clay, you still need sound absorption material like fiberglass, felt, Poly-fill, acoutic foam, etc...?

[ThomasW]

Yes, both forms of damping are needed.

[fjhuerta]

You're correct, my statement was in reference to the OP's original post

Hi Thomas,

Maybe I wasn't clear. My boss' idea was to use plastiline as a stiffening agent. My idea was to use plastiline as damping instead.

So, if I understand correctly, a box lined with plastiline and a layer of acoustic foam would help lower Fs and remove resonances?

[fjhuerta]

Yeah, I can't have an original idea.

http://www.avahifi.com/root/audio_basics/ab_pdf/ab1982.pdf