Damping Material (Fibergalss)

[stevem]

What is the best damping material for ported woofer cabinets? I have read that fiberglass has superior properties for this application. So far I have used R19 unbacked 4 inch for my projects, but I am wondering if it is too thick. Is 2 inch acoustical (denser) material better? What differences in sound are noticed if you "overstuff" a cabinet? If you don't block the ports, and there is a cavity behind the woofer, can you still have too much stuffing? Thanks!

[Donald]

Giskard,

Is that stuff pink or yellow?

I would like to keep the insides of my L300s yellow.

[DavidF]

Yes, you can have too much stuffing, especially in a vented box. The goal is to minimize reflected sound within the box to prevent unwanted resonance (standing waves) but not so much that the damping will restrict the fluid action of the air in the box. Over damped vented boxes may gain some detail in the midrange with minimal bounce back to the woofer cone, but the bass will sound constipated, for lack of a better word. The bass loses the punch and dynamics. Fiberglass is the simple solution for vented boxes and works well in absorbing the sound waves. Two inches seems standard, applied to the back and at least two of the four sides.



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[stevem]

Thanks. By the way, I use Johns-Mansfield insulation, which is white (I can't bring myself to use the pink stuff!).

Do you think 4 inch (R-19) is too thick? Is the 2 inch "standard" a denser material?

[GordonW]

I've used 4" thick with good results in larger enclosures. As long as the enclosure has "free space" through the majority of the internal volume, 4" on the walls isn't going to restrict bass output. Just don't pack it in there to where there's no space left, unless you intentionally (like I've done sometimes, to "tighten up" a system response) want to re-shape the bass response...

Regards,
Gordon.

[stevem]

Thanks all, I appreciate the input!

[Mr. Widget]

Giskard,

Is that stuff pink or yellow?

I would like to keep the insides of my L300s yellow.

I use Wrap-on fiberglass insulation. It is virtually identical to the stuff used in the classic JBLs. It is 1" non shedding, and yes it is yellow. You can get a 24" wide by 50' roll in a box (part number 16550) shipped to you for around $30. Contact http://www.wrap-on.com/ and they will give you the name of a near by stocking distributor or as in my case a distributor willing to ship it to you.

I have used this stuff for years and it is by far my favorite. Unlike house insulation it doesn't sag with time and since it is non shedding it is much nicer to work with. If you need two inch, you can double it up.

Egg crate foam is my next favorite choice but it is quite costly.

Widget

[sonofagun]

Thought I heard at one time that long fiber wool was the best, but maybe (?) that was in TL (transmission line) cabinets.

Obviously would have other problems ("bugs"), but again remember reading how superior it was.

[Donald]

Thanks, Widget.

For others: The Wrap-On folks will send you to a vendor. B E Atlas in Chicago. 800-305-4393. It is $26.88 plus shipping. Drop shipped from the mfgr. Delivery time about 2 weeks. Mine is ordered!

[Donald]

Forget the 2 weeks. Mine arrived Wednesday. Only 6 days.

[Val]

I just orders some Wrap-On insulation as suggested. What is the best method of attaching?

[Mr. Widget]

I just orders some Wrap-On insulation as suggested. What is the best method of attaching?

I use staples... just a few per panel and have never had a problem. You might want to wear gloves though... the stuff will make your knuckles itch.


Widget

[Val]

great, thanks.

[Steve Schell]

Lately I have been building sound absorbing panels from rigid fiberglass to tame the demo rooms where my partner and I set up our horn system. So far I have built 24 2' by 8' panels from 1.5" thick rigid 'glass, and have materials for another dozen or so. While researching this project I came across this site, where this fellow has measured the absorption coefficients of a large variety of products.

http://www.bobgolds.com/AbsorptionCoefficients.htm

[4313B]

Nice! Thanks.