Building A New Box

[NoSweat83]

I need to build a 2cubic foot sealed box for a sub but, before I do so I want to know the advantages/disadvantages of poly-fill.

1. How does it work?
2. When using it how much volume can be removed a certian amount of it?
3. What sq/spl differences are there if you used a regular 2cubic ft box verses what ever would be done with poly-fill?

Any help would be appreciated. Thanks

[violentrapture]

1. Using it causes the thermal expansion to be lowered, effectively tricking the sub to think it's in a larger enclosure - used to absorb standing waves.

2. Not quite sure of the question, but generally you use 1/2 lb. per cu. ft.

3. It can help low end response some, get rid of "boomyness" and tighten up the sound some. Generally you notice that the recommended sealed box dimensions are big - hence the advantage of having the sub think it's in a bigger box.

~vR

[NoSweat83]

Originally posted by violentrapture@May 8 2006, 02:04 PM
2. Not quite sure of the question, but generally you use 1/2 lb. per cu. ft.

Quoted post

So, I could build a 1 cu/ft box instead of a 2 cu/ft box with 1/2 lb. of poly-fill?

[eag182]

You do not change the dimensions of the box when adding polyfil. If you want to know more, register at diyaudio.com and ask this question. The majority of users there are engineers so you'll be getting expert advice.

[violentrapture]

You can change the dimensions - for sealed there's usually a minimum and maximum (recommended) enclosure size.

For example, for the S15L7 I had, the recommended sealed box size was 5ft.^3 if I remember correctly. The minimum sealed size was 1ft.^3. I did a 2ft.^3 with about 1 1/4lb. of polyfill. As long as you stay within the manufacturer's size range, you can build a box on the smaller end and use polyfill.

~vR

[eag182]

You don't have to stay in their size range. You can design an optimum box for your preference with a lot of different programs. Nothing against you violent hah.

[violentrapture]

Of course (and not taken as anything against me) - but the manufacturers have put thousands of hours of R&D time into their woofers and I'd venture a guess they know them pretty well.

~vR

[mikegett]

I have to agree. I am going to trust the engineers specifications any day over someone with no more experience than a box program. Besides, polyfill only works with sealed enclosures. You can't engineer a more efficient sealed enclosure. The only thing you can improve upon is the structural integrity of the box to lower resonance.