Was out looking for locally available speaker stuffing materials, having been warned off of using fiberglass in a ported application. Came across Poly-Fil brand Nu-Foam at Jo-Ann fabrics....
It's not foam at all, its more like a cross between thick scotchbrite and semi-rigid fiberglass. Best thing is that it comes in 1", 2" and 4" thickness. I picked up a 40"x27"x2" peice for about $18 after their 40% discount coupon (see their web page), enough for two speaker cabs.
Has anyone used this? Online searches yield a few results but no measurements or comparisons. It looks like it should be pretty effective.....
(not my pic, two types of batting, 1" nufoam is on the left)
http://revlimiter.net/mods/armrest.php
It's not foam at all, its more like a cross between thick scotchbrite and semi-rigid fiberglass. Best thing is that it comes in 1", 2" and 4" thickness. I picked up a 40"x27"x2" peice for about $18 after their 40% discount coupon (see their web page), enough for two speaker cabs.
Has anyone used this? Online searches yield a few results but no measurements or comparisons. It looks like it should be pretty effective.....
(not my pic, two types of batting, 1" nufoam is on the left)
http://revlimiter.net/mods/armrest.php
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Hi turbodawg,
Agree, I've been using this type of damping material for more than ten Years:
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There are no measurements or comparisons because these pillw stuffing materials have no acoustical properties. I have measured them a few times and they have almost no effect on standing waves in the box.
Placebo stuffing.
Hard to beat fiberglass. If you are concerned about it blowing out the port then line the box and cover the FG with a layer of porous cloth. In truth, if you cut it neatly there won't be any loose chunks to blow out.
David
David, what about the fibers? There's a lot of contradictory info available about whether or not small particles will be blown into the room and whether or not those particles are dangerous to ones health. Fiberglass is relatively cheap and very effective, but many manufacturers don't use it. Why would that be?
Fiberglass is not carcinogenic by all reports. I do know some factories refuse to use it but that is primarily when the labor force balks. It is itchy stuff and some are more bothered by it than others. I've never been too bothered by it if I keep it off my forearms out of it.
I can't imagine a building contractor refusing to touch the stuff.
I can understand others not wanting it blowing around the room, on principle, but again I think a cloth covering would minimize that. Most of the loose stuff, if present, blows out in the first weeks. Perhaps a break in period in the garage?
Anyhow, what is the point of using itch free BAF wadding or polyester, if it doesn't absorb sound?
David
Dave, this seems to be a bit different than regular loose polyfill - it's denser and the fibers are thicker. Have you tested this specific material in a large thickness like 2" or 4".....?
The PA speakers I'm modding actually have a nearly identical stuffing in them already, but it's about 1/2" thick and less dense.
No accoustic tests, but I can blow into it on one side and feel no air on the other. Can someone suggest tests that can be done at home with a PC based tone generator and radio shack SPL meter......lol?
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Why not just cover the inside end of a port with the porous cloth? That is, if none of the drivers have exposed voice coils.
The stuff on the left looks like standard dacron, but you are right that the other looks a little denser, so who knows.
The best test I have found is to take any woofer cabinet and drill a hole in the corner just large enough to get a test microphone inside. Start with the cabinet empty and run a response curve and you will see the modes in all their glory.
Put any sample in and see how much each mode drops (both Q and height will fall). You can stuff the box as you intend to use it, or for material comparisons just put in, say, 1 square foot of each sample.
In tests like that fiberglass, rockwool and some acoustical foams will do well. The bonded acetate fiber (BAF wading) or standard polyfill (polyester) will do very little.
It would be more tedious, but you could do it with a radio shack meter. Maybe pick one mode and figure out peak level and relative bandwidth (-3dB from peak). That would be a direct measure of Q (Q= bandwidth/center frequency, with bandwidth being the span from the -3dB points).
Regards,
David S.
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