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Stuffing speaker box -- will foam work?

 
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WildIowa



Joined: 06 Mar 2004
Posts: 490
Location: Henderson IA

PostPosted: Wed Jan 11, 2017 11:02 pm    Post subject: Stuffing speaker box -- will foam work? Reply with quote

I am re-building a couple vintage JBL hifi speakers and ready to seal them back up. I tore out the old fiberglass, and have both fiberglass or foam on hand to stuff the box. I can use either, although the foam is cleaner...is there a difference, or preference? I have a feeling the answer is yes, as I have seen no boxes with foam and almost all with fiberglass...unless it's a cost issue. Again, the foam is cleaner but does not absorb as well as the fiberglass perhaps? What do you guys think?
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BluesmanDave



Joined: 17 Nov 2008
Posts: 2816
Location: Sacramento CA

PostPosted: Thu Jan 12, 2017 10:21 am    Post subject: Reply with quote

I'm speaking from only a tiny bit of knowledge, which is more dangerous than pure ignorance - what I've read is that fiberglass has specific acoustic properties that foam does not, and the physics of air movement works better with fiberglass, in that it 'tricks' the speaker into behaving as though it has as bigger box.

DISCLAIMER: I may be completely, 100% wrong.
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BrightKJ



Joined: 13 Sep 2008
Posts: 342
Location: Midlothian, VA

PostPosted: Thu Jan 12, 2017 12:50 pm    Post subject: Reply with quote

If I'm not mistaken, the whole purpose of the stuffing material is to knock down standing waves created between the 90 degree surfaces of the cabinet. A more solid material like foam could take up too much volume and not allow the speaker cone to flex inward as much as it needs to, creating a pressure imbalance and prematurely reducing the life of your speaker (who knows by how much). Because fiberglass is a much more "open" and random material, it serves this purpose quite well because of all the random surfaces and does so without coloring the sound. The preference for most speaker builders is insulation.
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RolandR



Joined: 03 Sep 2003
Posts: 8908
Location: Coastal Calif.

PostPosted: Thu Jan 12, 2017 1:46 pm    Post subject: Reply with quote

I agree with BluesmanDave. Shocked So we both could be wrong.

WildIowa, is the fiberglass salvageable? I hate that stuff. Just fiberglass insulated our rental home and I have the whole Haze masks, googles overall on.

I'd go to Parts Express and get what they have. Acoustic insulation or acoustic foam, might be health friendly than fiberglass stuff. Yeah, I know, more expense into this project. Confused
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Kregg



Joined: 22 Apr 2008
Posts: 3334
Location: Atlanta

PostPosted: Thu Jan 12, 2017 2:56 pm    Post subject: Reply with quote

Closed cell foams are fine.
Just remember that rubber degrades over time.
For fiberglass I use yellow backed ceiling tile (peel off the facing of course), or duct insulation (the stiff type).
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WildIowa



Joined: 06 Mar 2004
Posts: 490
Location: Henderson IA

PostPosted: Thu Jan 12, 2017 10:14 pm    Post subject: Reply with quote

Fiberglass it is! It didn't take much I had some here. The old stuff was seriously musty and smelled funky so it had to go. Did full rebuild including sealing inside of cabs to contain funky smell, new tweeters, crossover caps and glass. Also took a stab at reconing woofers with good success, sanded cabs and five costs of satin lacquer. Fired them up today and they are solid. Put about $300 in them probably could have bought something good for that price but these are old JBLs and it was a great post Christmas project on cold winter days a treat to bring them back to life.
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rhardman



Joined: 11 Sep 2008
Posts: 4422
Location: Chicago, not ready for reform, yet

PostPosted: Thu Jan 26, 2017 11:59 am    Post subject: Reply with quote

I have used poly blanket insulation...with success. Allergic to fiberglass here
from my job exposure to it. Nasty stuff. Wear a mask. I wish I did.
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BeauZeau



Joined: 26 Dec 2015
Posts: 21
Location: Durham, NC USA

PostPosted: Sun Nov 19, 2017 6:55 pm    Post subject: Reply with quote

Fiberglass sounds and works the best. Foam works but sounds the worst. Polyester fill doesn't work so it doesn't have a sound.
.
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