How much polyfill is too much?

I'm working with a .7ft^3 fiberglass enclosure for a single 12, and I am using polyfill to try and make up for the small amount of volume. A larger enclosure is just not feasible, and .7ft^3 is the largest it can be physically. I am using 1.2 lbs of polyfill, and the polyfill is so dense in the enclosure that I am wondering if it is not doing more harm than good. I've read that up to 1.5lbs of polyfill per cubic foot can be used successfully on larger enclosures, but I'm not sure about the small volume I am working with. Any thoughts?

When you add polyfill, you are actually INCREASING the size of the box, acoustically. If you box is too large, you must fill in the space with solid objects, NOT polyfill.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Polyfill really doesn't "do" that much. (see comparison graphs in The Loudspeaker Cookbook). Don't get me wrong, it helps, but an extra 0.3 lbs isn't going to affect much of anything. So, work on the safe side and use whatever fits comfortably. If 0.7ft^3 is still far too small for your subwoofer, time to pick a different sub. New Project: 2003 Pathfinder

haemphyst wrote: When you add polyfill, you are actually INCREASING the size of the box, acoustically. If you box is too large, you must fill in the space with solid objects, NOT polyfill.

Sorry... misread your post. You ARE trying to make it larger. Yeah, as kfr01 sez, if .7 is still far too small, time for a different woofer.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

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Thanks guys. The amount of polyfill I am using actually ended up being fine and from my calculations makes the enclosure respond similar to a .9ft^3 enclosure (which is what I need). Turns out the phase was wrong and once that was corrected everything sounds great. The low output initially made me think it was the polyfill because I have never used that much before.

In my experience, any is too much.  You can't really compensate for a poorly built box.

austincustoms wrote: In my experience, any is too much.  You can't really compensate for a poorly built box.

I have to disagree...subwoofers are imperfect. Even a well built (to manufacturers specs) box cannot necessarily compensate for what a subwoofer doesn't recreate correctly. A little polyfill can sometimes be just what is needed. This may be getting into picking nits regarding sound quality from the sub. I WILL agree that for most, a well built box will satisfy most without the polyfill.

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austincustoms wrote: In my experience, any is too much. You can't really compensate for a poorly built box.

I also disagree. Just because a user wants to dampen the box a bit more, doesn't mean the box is poorly built. New Project: 2003 Pathfinder