View Full Version : Cabinet stuff (stuffing)

John Y.
05-30-2003, 12:16 PM
Does anyone know what sound deadening material is used in JBL cabinets, such as the 4648A? Appears to be fiberglass insulation coated with some resin. Is this commercially available?

Thanks, John

05-30-2003, 01:36 PM

Mr. Widget
05-30-2003, 02:00 PM
JBL is using a "non-sheading" fiberglas insulation material. The brand that I buy is "Wrap-on" it comes in roll that is 1" thick by 24" wide. I usually buy it by the box, but many hardware stores carry it by the foot.

05-30-2003, 05:54 PM
I'll second Mr. Widget. But locally, I've only been able to find batting in the desired reasonably small quantities (versus pickup truck sized bundles) as the pipe wrap for plumbing. Rolls are something like 7-in wide, at least 3/4-in thick and 17-ft long.

I cut lenths double the needed size, fold in half and spot-attach with a staple-gun. As with JBL craftsmanship, I line the entire cabinet (not the baffle). Easy enough and works great.

Wear gloves.

Mr. Widget
05-30-2003, 06:45 PM
Wear Gloves!!!!!!!

I wear a respirator too!

The stuff may be called non-shedding, but that is a relative term. It is not much fun to work with, but it is sonically superior to dacron, foam, even that old wool stuff that was popular pre 60's.

Tom Loizeaux
05-30-2003, 08:14 PM
All of my vintage JBL studio monitors had 1" fiberglass insulation in them. JBL glued these to the interior walls and then spray painted the front baffles, getting a fair amount of paint on the fiberglass around the cutouts.
I actually replaced a few of the panels of fiberglass today in my pair of 4343s as they were getting frayed.
Some people suggest spraying a dusting of clear lacquer on the fiberglass to hold down shedding.


Charley Rummel
05-31-2003, 07:58 AM
Has anyone ever heard of using the material (whatever it's called) available from fabric shops that's used for stuffing cushions and pillows? This was recomended in a DIY websight I came across once.

Also, how about going over exposed fibreglass insulation in a cabinet with a spray adhesive? I've never done it, but are there any thoughts to share?

Charley Rummel

05-31-2003, 08:12 AM
"Has anyone ever heard of using the material (whatever it's called) available from fabric shops that's used for stuffing cushions and pillows? This was recomended in a DIY websight I came across once."

If you're referring to polyfill that's fine but I wouldn't retrofit it into existing JBL enclosures as it doesn't add virtual volume which JBL designs depend upon. Fiberglass is a real pain but if you use gloves and a respirator it is manageable. Hitting it with a very light coat of clear spray paint helps. I asked G.T. last year during a "Citation 7.4" conversation if he had ever found anything better than fiberglass and his response was "nope".

John Y.
05-31-2003, 10:22 AM
I am planning to restore a C37 as a subwoof - more later in a separate posting.

Looking at my JBL (official) drawing of the C37 enclosure, which I built in 1956, I see that they recommended cheese cloth stapled over the 1" fiberglass, and I did just that. I recently opened up this cabinet after almost fifty years and found that the fiberglass was intact, but not as fluffy as I remembered.

I plan to reline with fiberglass and I appreciate the help in determining how to go about it. The insulation in my 4648A's look like they are sprayed - probably after installation. Could be lacquer. Seems to be quite a heavy application. Maybe I should call JBL to find out exactly what they use.

Mr. Widget, I shall try to find some "Wrap-On." Thanks.


05-31-2003, 11:00 AM
Yeah, I'd call them at see what they are spraying on it.

In your case, since you are starting from scratch, you will have to tune the volume anyway so use whatever fill you want. Be aware though that only fiberglass adds virtual volume. So, if you measure the net physical volume and come up with 4.5 cubic feet but want 5.0 cubic feet add 1" of fiberglass on every panel except the baffle. If you want 5.5 cubic feet then add something like 2" of fiberglass. When you tune the volume you will see just what effect no fiberglass, and then adding fiberglass, has.

Mr. Widget
06-02-2003, 12:16 AM
Hi Charley,

The white filler material used in pillows is frequently called Dacron. That is the trademark of the fiber patented by Dupont. There are many speaker companies that use it, even some of the high end brands. It does not have the same sonic properties as fiberglas. In my opinion it does not sound as good. It will not absorb the midrange that can reflect back through the woofer cone as well as fiberglas.

I sometimes spray hair spray inside the cabinet to augment the non shedding fiberglass.

You can contact the folks at Wrap-on through their web site.


Mr. Widget

06-02-2003, 05:51 AM
"In my opinion it does not sound as good. It will not absorb the midrange that can reflect back through the woofer cone as well as fiberglass."

I've got two LE14H-1 subs that prove you right Mr. Widget. The original Citation 7.4 came lined with polyfill. I built two LE14H-1 subs and tried one with polyfill and the other with fiberglass. When using higher crossover frequencies, and no crossover at all, the fiberglass lined system sounded significantly better.

Hair spray is a good idea, never thought of that :)

Thanks for the link :)

Earl K
06-03-2003, 06:22 PM
Hi All
You know, I'm just not sure that Dacron info (having no effect ) is accurate. I was just inside one of my test boxes (S99/ le14a), & added a pile of the white stuff ( local version of Dacron ) and lowered the Fb of the box about 4 or 5 hz.
I don't doubt that it's a lot less effective than good old fiberglass. I think it's about half as effective for virtual volume increase.
Now mind-you, we have a change in weather about to occur ( with / maybe thunderstorms ) and this does effect these types of measurements. But , the other untreated/stuffed box still measures where it has all winter ( low 40's Fb ) . When I finally build permanent boxes for my Vertical Twin project , I'll probably start with a 1" lining of the high density fiberglass ( like a stiff wafer board used in insulating skyscrappers ) / cheese-cloth to seal in those pesky glassfibers and finish up with a second layer of something loose like Dacron . Also just tried silicon winter/boot/no-salt spray on the exposed fiberglass - worked quite nicely ( left a slippery film instead of the dreaded itch ) . Thanks for the suggestion !

Regards <. Earl K

John Y.
06-05-2003, 02:38 PM
Well, after looking through the construction drawings of the 4648A, the JBL Pro guy told me that the only thing that he could see was a parts list containing 1" fiberglas with nothing said about coatings. I suspect one would have to contact a shop person to find out what they do. It's possible that this is all done by an outside contractor, at least on the production cabinets.

I like the idea of spraying with lacquer. Hair spray is a form of lacquer, so it should do.

06-05-2003, 02:46 PM
"You know, I'm just not sure that Dacron info (having no effect ) is accurate. I was just inside one of my test boxes (S99/ le14a), & added a pile of the white stuff ( local version of Dacron ) and lowered the Fb of the box about 4 or 5 hz."

Well that's a lot of hertz ;)

I was going to take some measurements with a test box but now I will just wait until I finish a new pair of subs since I have to measure them anyway.

Earl K
06-05-2003, 05:02 PM
Hi Rob
Yes, it is a lot of hertz. And that number is suspicious. That's why I thought I'd mention some of the existing weather conditions / circumstances . ( maybe it was the silicon boot spray ). Today the numbers had bounced up a couple of hertz before the removal of the polyester. With the polyester gone ( original 1" fiberglass still in place ), the Fb has gone right back up to about 44hz ( it was down to just below 40 hz ). I double-check the Loftech/GoldLine that I'm using against "the oscilloscope method". The two results do correlate to each other. The amount of polyester added was about 615 cu inches.
Now I live on a busy street and the truck traffic can play havoc with these measurements. I made the measurements at night when the street was quiet. ( though, even waving my hand around the area will alter these AC impedance readings ) .
Certainly the topic is worth of a more " controlled" study. :D

regards <> Earl K:)

06-05-2003, 05:21 PM
Was it the kind of stuff Parts Express sells in a bag? The loose stuff and not the "sheets" like fiberglass from Radio Shack for instance? It didn't block the port(s) or the vent on the driver right? If it is like the Parts Express stuff then I will buy some, the only non-fiberglass stuff I have to test right now is some polyfill stuff that is in a "sheet" like fiberglass. It's real scratchy and not real dense. I'll post pictures during my testing and that will show what I'm talking about. Just an FYI, my tests won't be the epitome of perfection either.

06-07-2003, 12:23 AM
When I built two ported 5 cu. ft. sub cabs (dimensions corrected for internal bracing, etc.), I wound up using two layers of paper-backed, standard insulation fiberglass. Most likely it is R-18 rated or thereabouts.
The drivers are 2235's, rolled off at 6 db/oct, -3 db @ 125 Hz, and when driven by a 50W/CH. Borbely mosfet amp, the subs put out very clean & detailed bass. Very warm & musical in tone.
The double layer is not per JBL's strict theory / recommendations, but the (no pun intended) bottom line is...it worked, and quite well. Sometimes ya git lucky!
BTW, if you get similar "glass" packaged in a sealed plastic bag, remove it from the plastic and let it air out for several days. Most of the annoying itchy dust and chemical stench "outdusts / outgases" heavily when the package is first opened, and the effects taper off fairly quickly. Two days airing and it should be hardly annoying at all.
BTW2: Drew Daniels recommends plain old 1" fiberglass...if there is a better material, he isn't hawking its use.

Mr. Widget
06-07-2003, 12:36 AM
For my 2235s I have 5 cu ft boxes tuned to 30Hz with a single layer of 1" fiber glass and it works very well too. I put it on and around the cross bracing as well. I have essentially covered every surface excluding the baffle.

The "Wrap-On" fiber glass that I use is essentially the same as the paper backed wall insulation but since it is designed to be used around heating ducts etc. it has been made to shed/tear a heck of a lot less. It is still a pain to work with, but less so than the wall insulation type and it does seem to be an exact duplicate of the 1" material that JBL uses.

Earl K
06-07-2003, 06:13 AM
Hi Rob

Originally posted by Giskard
Was it the kind of stuff Parts Express sells in a bag? The loose stuff and not the "sheets" like fiberglass from Radio Shack for instance?

I'll post a picture of the stuff when I next take it out of the enclosure. ( this weekend ) I bought it in a large roll / bail from a furniture refurbisher. I asked for his most dense stuff. The bagged stuff you might be referring to could be "Acousta-Stuff". I've never seen or used that. I do use this polyester stuff in some small .6 cu' enclosures that have either 2012 or 2123 transducers in them. I wasn't after a virtual volume increase at the time, just some midrange dampening.

It didn't block the port(s) or the vent on the driver right?

Certainly didn't block the port but the driver vent might have been compromised.

It's real scratchy and not real dense.
Scratchy ?? mmm, this stuff has thicker fibers compared to fiberglass and I wouldn't call my stuff real dense.

Just an FYI, my tests won't be the epitome of perfection either.
Well, my next tests are going to be in a different room. The LF loading in my living room gives very "usable" response on these S/L-99 enclosures down to 40 hz. Quite surprising for the actual size of box is ( @ 1.4 cu' before virtual volume is added back ). This room loading effect has made me completely reconsider the sizes of the final enclosures for my "vertical twin" project. All the plans I had drawn up for my le14a woofs seem overly large now.
- Any LF present in the general area of the livingroom couples to the woofer/port and creates wild swings on the "collapsed ellipse" or the AC impedance meter.
- With this white stuff back in the enclosure, the Fb has dropped (max) about 1.5 to 2 hz. Those first "suspicious" readings ( I speculate ) might have been caused by the wetting of the fiberglass with the " silicone boot-spray" . :eek: Need an embarrassed Smilie here.
- Since this polyester is nice to work with, I am going to explore whether or not it'll effectively work in tandem with the high-density 1" fiberglass ( I previously mentioned ). I was first introduced to that HD stuff when I bought some W151/W460 ( JBL 18" horn-loaded ) bass bins back in 1980. The "smallish" sized compression chambers were lined with this stuff. It's dense enough that an exacto knife blade will slice it rather than pull at the fibers. But, I need to see if the HD fiberglass adds or subtracts volume when in an enclosure before commenting more on it.

regards <. Earl K

Paul Joppa
06-19-2003, 03:05 PM
Just a note here on this thread. I would expect that JBL used acoustical fiberglas, which has been available since (I think) the late fifties. It is significantly different from thermal insulatipon, the fibers are much smaller (1.5 microns vs 10 microns, if my aging brain remembers right). Acoustical fiberglas has become pretty hard to find in DIY quantities or at Lowe's Depot type places. But it works much better to absorb sound.

06-19-2003, 03:24 PM
"I would expect that JBL used acoustical fiberglas"

True, and it is quite hard to find just anywhere :(
I have one 30 gallon bag left and then I'm out.

06-21-2003, 10:55 AM
What category does the 1" Radio Shack stuff belong in?

06-21-2003, 11:03 AM
I use 3/4 inch fiberglass ceiling tiles with the back against the cabinet. Seems to work well. Easy to cut and size into panels. Don't khow how it compares to regular glass as it is denser.


Earl K
06-21-2003, 03:52 PM
- My "quasi-sealed" .5 cu' test enclosure for my le10a mid/bass is about 50% full of that white polyester/Dacron stuff. I took it out ( fully sealed the "test port" in this test box ) and measured Fb using the oscilloscope method. Restored the stuffing and measured again under the same conditions; The addition of this stuff dropped Fb by 2 Hz . ( Also forgot to take the picture I promised of the stuff ).

- Also, I ripped out the 1" original fiberglass that JBL installed in my Lancer - S99 "test box" #2 , the one that perennially gives a Fb of @ 44Hz. After installing the 1" thick , High Density "skyscraper-grade" fiberglass insulation,,, the Fb dropped to 42 hz ( just like it's mate - I was concerned , thinking maybe the stuff actually subtracted volume ). I can't make out any midrange tonality difference compared to the box with the original JBL stuff, but then the le14a cone is sooo thick it's probably less suseptable to internal reflections. As I said before , I'd pursue using a 2 part stuffing system using what I have on hand when dealing with regular weight cones ( 100 grams ). I like this HD stuff because an exacto knife slices through it very cleanly with no pulling or tearing .

- Will "Acoustical Insulaton" be labelled as such ? or does it have a more obscure/coded designation ?

regards <. Earl K

06-21-2003, 09:45 PM
Some interesting things about fiberglass/dacron:

- From Dr. Wm. Marshall Leach of Georgia Tech- apparently, in his tests, no other single material has exceeded the effectiveness of just plain old Owens-Corning (or equivalent) pink fiberglass, as far as lining or filling enclosures. He's definitely not a particular fan of Dacron/polyfill...

- From personal experience: it appears that Dacron and fiberglass MAY act in slightly DIFFERENT ways in an enclosure. IME, I've had cases where a COMBINATION of dacron AND fiberglass, was more effective than either alone. Not a BIG difference, we're talking a few percent here and there, but enough to notice repeatedly! As a result, I have taken to doing fiberglass first, topped with a layer of dacron OVER the fiberglass. Takes care of the shedding fiber thing, and gets me the benefits of having both...


07-23-2003, 04:39 AM
Just bought some "New" "Non-Itch" Owens-Corning MIRAFLEX (P/N 195238, R13, 3-1/2" thick x 16" wide 39' long roll for $18) for use as midrange damping material. I won't have before/after test data but will let you know what sound change occurs. Will do that before I lowpass the woofer and some other basics this (non-Lansing) system was lacking.
I would not exactly say it is "no itch", but is much less so than the pink stuff. It is white and cushy (like cottony pillow stuffing) underneath the thin perforated plastic covering. I removed the face covering for the rear wall, but that may not be necessary, given its very thin perforated nature (left it on for a side near the woofer to lessen shedding). The other side of the material has a tough plastic backing which which holds in place well when stapled.
It can be compressed to about half depth if desired and comes in ultra compact roll form. The price is right and it feels absorbent enough. Very easy to cut and does not shed much.
It may not be available in all areas because insulation (material & backing/ vapor barrier type) varies by climate and building codes. I think the birds will love the little scraps left out for them. Makes wonderful nesting liner material.
Martin W.
Wizard Labs

07-23-2003, 05:22 PM
RG; I get the hint... you want test data on this insulation material.
I could not do any tests before I filled the cab cuz I did not trust my Fluke ACVM across much BW. I scored an HP 403B True RMS VM (along w/ a 204C Osc & 343A Atten in an Air Force test set on eBay for $50) but it took 3 days to charge the batteries and it is still out of cal. (Anybody got an HP 403B service manual out there?) It did confirm the Fluke BW to about 2kHz, though. Now I know what to trust.
I just now measured the Fs & Fc of my test specimen.
Now... how do I measure the Qtc and Motional Impedance?
I will pull the stuffing out to get the before data if you give me a reason to.
Martin W.
Wizard Labs

07-23-2003, 05:50 PM
"I had said I would run quite some time ago. I finished it recently and thought I'd post it. "

And I for one, am glad you did - not to "check" on JBL lore, just to show the fact data. And it is real interesting. The impact of the batting is quite astounding.


07-23-2003, 10:07 PM
RG; I am all set up to run the tests with this insulation material if it is feasible to do so with what I have on hand. This material has a different feel to to it. Wonder how that affects its scattering effect or if it is more absorptive. I would really be curious if it is really that beneficial or necessary to remove the perforated facing that makes it "no-itch".