Foam/Polyfill Question

[Cj Kumz]

Hey Guys. I have a few questions regarding filling the inside of a box with foam.

1. They say it makes the sub act like its in a larger enclosure. How much bigger is this?

2. How much foam should be used? Obviously too much of everything is bad lol.

3. What are the downfalls of stuffing the inside of a box.

4. How does the tuning get affected be filling the box.

Any info will be great

[Kyblack76]

[SQL50]

So it's proven in sealed, which makes sense. The real question is does it effect the ported tuning? Physically you may have a box tuned to 30 hz but does dropping poly or insulation change that? That's something I always wanted to know. For example, I've seen Kicker prefabed ported enclosures with polyfill in them. If they wanted to achieve a certain tuning, why not just build the box to that spec instead of using polyfill as a crutch to get lower and then lose output on top of it? Maybe I'm having a misconception about it. Only way I see using it is in space limited applications to where you can't physically achieve what you want to hear. But maybe someone with more experience with it will chime in on polyfill in ported enclosures.

[Cj Kumz]

Hey guys I just bumped into a space limited situ so I'm reviving an old topic just to see if there have been any new discoverys lol. Has anyone got any info or tests done on the effect polyfill stuffing has on the tuning of a ported box. Thanks

[Triticum Agricolam]

To say that stuffing a box makes it perform like it is larger than it really is is a bit of an oversimplification of what's going on. In regards to sealed boxes, when you stuff the box it lowers the resonant frequency and the QTC of the box. When you make a box larger it also lowers the resonant frequency and the QTC. The difference is when you make a box larger it also increases the efficiency of the box, when you stuff a box you do not get that efficiency increase, if anything you will lose efficiency.

With a ported box, things aren't much different. If you stuff a ported box that stuffing is going to absorb energy inside the box and you are going to lose output around tuning frequency. While I have never stuffed a ported box myself, for the above reason, everything I've read on the topic says it is going to cost you efficiency. I also read that it will lower your tuning, I wish I could remember where I read that so I could give you the link, but can't seem to find it.

What I have done with ported boxes is to line some of the interior walls with foam or felt. This is done for sound quality reasons though to absorb above band noises. If you want to try stuffing just to see for yourself what it will do you want to use polyfil stuffing, you can get it at Walmart. Open cell foam won't do what you are trying to do.

ETA: Found the link: http://techtalk.parts-express.com/showthread.php?184022-Questions-on-stuffing-a-Ported-Subwoofer-box

[Joe X]

Sq bixes are usually stuffed, effects of damping are modeled by some softwares so these are not really a secret.

[Cj Kumz]

Great link. I'm building a box soon for 2 hdc3 15s and I only have around 9.5ft3 gross volume. I was thinking of giving them 3-3.5ft3 per sub then tuning to 38hz and hoping after lining u with form I end up with a ruff lower tuning of around 33-35hz and a bigger box.

[Triticum Agricolam]

Great link. I'm building a box soon for 2 hdc3 15s and I only have around 9.5ft3 gross volume. I was thinking of giving them 3-3.5ft3 per sub then tuning to 38hz and hoping after lining u with form I end up with a ruff lower tuning of around 33-35hz and a bigger box.

You would be better served by just building the box as big as you can to fit your space and tuning where you want it to be and leave out the stuffing.

[Cj Kumz]

Ok thanks. Better to be sure of what I'm doing than hoping for figures lol. Plus all that dampening and slowing of air just gave me a head ache haha