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OBC115 - What should I use for damping material?

Quilt batting, mattress pad foam or any type of insulation, though that stuff is itchy.

One layer of the mattress pad foam will do it, or layer up the quilt batting to somewhere between 1" and 2" thick.

If you use matrress pad, make sure it's the regular cheap stuff you can easily blow through, like an air filter. Not memory foam or any other type of "closed cell" material. If it can't pass air easily, it loses it's damping properties and actually takes up space, effectively shrinking the size of the box inside.
 
If you're going to line it, be sure to keep the lining at least an inch or two away from the inside mouth of the port. Otherwise, you'll mess up the port performance.

Try huffing through the foam that you're thinking of using. If it passes air freely (like a microphone windscreen), then you can use it. If you can't, then it's closed-cell foam, and it won't work correctly.

Fiberfill is generally easier to work with than glass or eggcrate foam. Don't forget to glue or staple here and there, so it stays put.
 
Since I'm not sure if it's going to be an improvement (not to discredit anyone's opinions I've seen on the issue... just not sure for me), I want to be able to remove it easily if I don't like it. I was thinking of using some spray adhesive to attach velcro to the material and then velcro it to the cab. There won't be 100% surface attachment in that case though. Any concern? I'll go huff some foam and if not I'll go get a mattress pad.
 
The difference would be smoother midrange and a less boxy or boomy sound. You may percieve it to be slightly less loud after the lining, but what it's really doing is smoothing off peaks and dips in the response.

All speakers should have some amount of damping, at least on the back wall. You can however experiment with more or less on the other surfaces for slighter changes in tone. Don't put any lining where it could get in the way of the port opening inside the cab. Also don't put any over any crossovers or circuit boards that may be in there as those need to dissipate heat.
 
Any of this lining is really lightweight stuff. You don't have to smear the whole thing full of glue or use a ton of staples...doesn't take that much to hold it up.

I've used staples in all mine and never had a problem....not saying it couldn't happen though.
 
I think I'll try staples and if it sounds good, I'll go back through with glue. The egg crate I had isn't closed cell but it is around 3.5 inches thick so I'm going to pass on it. I got a roll of Morning Glory High Loft Batting from gov-mart for $8. I'm going to do up my 410 as well if the 115 sounds better.

Thanks for all the tips everyone... much appreciated.