OC703 used as box lining

[jk@home]

Quick newbie question...I need to build a couple of sealed subwoofer boxes, the drivers require a 2 cu.ft. internal area.

If I were to use 2" OC703 fiberglass, instead of polyfil, as wall lining, will the drivers "see" a larger box? If so, what could/should I downsize the cu.ft. dimension to?

Thanks
John

[ThomasW]

Build the box per the instructions. Add the OC to taste afterwards

[jk@home]

Thanks Thomas. Guess it doesn't make that big of a difference. I was hoping that by using the OC stuff instead of polyfil, I could slightly reduce the cabinet size, allowing a thicker cabinet wall, equally to a box with the same external dimensions as a standard 3/4" wall cabinet.

[ThomasW]

In theory one can trade off up to 30% of the box volume by using very heavy fill damping. Personally I don't think it's a good way to go...

http://web.archive.org/web/20041027051204/http://www.integracaraudio.com/caraudio/resources/fiberfill/

[Deward Hastings]

I agree with Thomas . . . using fill to control low frequency box acoustics is not the best idea. The best function of fill is preventing (by absorbtion) any re-radiation of the back wave at mid frequencies, either reflected through the cone or through the box walls (augmented by panel resonances). OC703 is excellent for that, but it works better if it is *not* directly on the walls. The most effective mounting is to cut the pieces a bit oversize so they bow in from the walls toward the center of the box. Panel damping, on the other hand, is better accomplished with something like weighted vinyl applied (glued) directly to the panel, or simple bracing.

[jk@home]

Thanks guys, I go with that. Not sure how much I will be able to bend the 703 in a 2 cu.ft. box though, but worth a try.

[thadman]

It works on the principle of velocity damping, if you place it at the position of the walls (ie nodes) where pressure is maximum and velocity is low the resulting damping provided by the fiberglass will be little.

[JonW]

jk,

In case it helps any... I also lined the insides of my speakers with OC703. I started with a more typical amount, on the rear, sides, top and bottom. But it seemed to make things a little bit less lively, maybe deader, or definitely less airy. So I then ripped out the OC703 from the sides and top. And then it definitely sounded better.

You can see a few of the details here. In post #2, under "Stuffing/acoustic absorption" Note the edit note below the second photo:

http://www.htguide.com/forum/showthread.php4?t=25031

So, basically, I think you need to experiment to find how much is best for your given situation.

[jk@home]

So, basically, I think you need to experiment to find how much is best for your given situation.

I probably should quit trying to reinvent the wheel, and just use polyfill.

Gorgeous speakers BTW!