Cabinet stuff (stuffing)

[Earl K]

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.

regards <> Earl K

[4313B]

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.

[Doctor_Electron]

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]

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]

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" . 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]

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.

[4313B]

"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.

[dderat]

What category does the 1" Radio Shack stuff belong in?

[Robh3606]

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.

Rob

[Earl K]

Hi
- 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

[GordonW]

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...

Regards,
Gordon.

[martinleewin]

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

[martinleewin]

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

[boputnam]

"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.

Thanks.

[martinleewin]

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".
MW