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Any thoughts on cabinet stuffing?


owlsplace

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In the process of restoring some cabinets and would like to substitute modern materials for the original rock wool, etc.

Here are some readily available box store items:

Soft-touch fiberglass http://www.homedepot.com/p/Owens-Corning-R-13-Unfaced-Insulation-All-Purpose-Roll-15-in-x-32-ft-RU10/205610783?N=5yc1vZbay7

post-173498-0-05948700-1428764679_thumb.

Ultra-touch denim http://www.lowes.com/pd_409395-42995-10002-01315_4294524376__?productId=3731875&Ns=p_product_price|0&pl=1&currentURL=%3FNs%3Dp_product_price|0%26page%3D1&facetInfo=

post-173498-0-59202600-1428764667_thumb.

Would like to avoid the hazards of fiberglass but it has been considered the best option in the past. Not sure if the "soft-touch" version has the same acoustic properties as the earlier long-strand versions.

Any preferences or comments regarding best material and equivalent weights to use would be appreciated.

Roger

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Along these lines, is there a resource that tells us what the appropriate amount (weight) that should be in the various speakers from AR? I've seen random references to say the 4x amount, but not a list as it were.

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Along these lines, is there a resource that tells us what the appropriate amount (weight) that should be in the various speakers from AR? I've seen random references to say the 4x amount, but not a list as it were.

There is no list, but it is posted for various models around the forum. AR reduced the amount of fibeglass stuffing in all models around 1970, so it depends on the era of the speaker in question.

Generally speaking, the 8 inch woofer cabinets need around 8 oz, and the 10 and 12 inch woofer cabinets need around 20 oz.

Roy

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My rule of thumb is to use 1 lb/cu. ft of volume of OCFG.

Had to look up what OCFG is which took me down a winding road.

Looks like the AR-4x is a bit of an anomaly and used two stuffing densities depending on coil version. There was also an earlier version crossover with 265 turn coil that wasn't mentioned and I'm not sure where that fits into the coil series numbers but I presume it used eighteen ounces of fiberglass.

Here is the scoop on that from a previous thread:

*** IMO, the stuffing was reduced from 18 oz to 12 oz for the purpose of increasing the cabinet Q from about 0.7 to about 1.0 I belive these two changes to be independent and unrelated, but I could be wrong. Have no date for change from 18 oz to 12 oz FG.

*** After swapping data with three of you, a list of 25 serial numbers ranging from 84,xxx to 364,xxx was generated. All cabinets with serial numbers below 174,068 (14 July 1968 parts date) contained a #4 inductor; all those with serial numbers greater than 227,334 (Jan. 1969 parts date) contained a #5 coil. Perhaps other speaker nuts, I mean enthusiasts, can narrow this range.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2080&p=62423

More from Carl on how much FG will go into the AR-4x cabinets:

Both speakers were opened and the rock wool removed and weighed in at 9.6 and 7.8 oz. This was suprisingly low based on my previous work and also what John O'Hanlon has published in the past. http://www.classicsp...cabinet damping

I found the rock wool had been installed mostly around the inside edges with very little located behind the woofer.

Both speakers had inductors marked with the number '200'. This indicated 200 turns or, a #4 coil which is expected for ser. no's as low as these.

Following John's recommendation on stuffing 4x's with #4 coils with 18 oz. of FG, I weight out 18 oz of OCFG removed from a roll of st'd R-13 paper backed insulation. Of course, I removed the backing paper prior to weighing. When I stuffed the cabinet with the OCFG I found I could only put in 12 oz without jamming more in with excessive force.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=5360&p=80147

Roger

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The internal volume of the AR4x is 0.65 cu. ft. Thus somewhere in the range of 10-12 oz. of OCFG should be optimal. Cabinet stuffing is not an exact science. It's not just how much stuffing is used but also where it is stuffed. P. Basel has commented a number of times in this forum about the location of stuffing right behind the woofer and the effects it can have.

The coil changes for the AR4x and 3a speakers where (to my understanding) for the purpose of altering the crossover point of the woofer. How and why that may have been tied to changes in stuffing remains a mystery to me.

IMO, the change from higher wgt to lower was really the result of a change in the stuffing from rockwool with it's relatively higher inherent density vs the yellow FG that was much more fluffy and thus had a lower inherent density (i.e. g/cc). The logic here is it will take less lower density FG to fill a cabinet than a higher density FG. The same holds true regarding stuffing with polyester fiber. It's density is much lower than FG and thus only about 8-10 oz. of PET will fill a 4x cabinet.

I don't agree with the 28 oz. recommendation for Alnico woofer 3a's noted in the restoration document. I've had equal success with 20 oz. of OCFG in speakers with the Alnico woofer and #7 coils. Cabinet resonance of around 40 hz (target) can be obtained with 20 oz. I'll probably catch some flack for this, but so be it.

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I placed quite a bit of stuffing behind my woofers the last time I had the systems apart for recapping. Not sure I did the right thing but I attempted to restuff them as I had found them but that can be tough to replicate. There has to be some measure of shifting and settling that takes place over the years. (decades)

der

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I have never addressed this specific issue with any rigorous approach whatsoever, but I certainly do adhere to Carl's maxim that "Cabinet stuffing is not an exact science". And while Carl is taking flack from artillery shells, you can also throw darts at me for admitting that I have sometimes simply re-used the original mineral wool stuffing when putting things back together. But guess what? The speakers sound just fine, fine, fine, and I doubt that the re-freshed pots are corroding any worse than if I had used new FG stuffing.

Having said that, Carl, I'm confused about one thing you are saying. It seems to me that your comments in posts #5 and #8 are somewhat contradictory. With the AR-3a cabinet having 1.7 cu. ft, applying your formula from post 5 would result in about 27 ounces of FG, but in post 8 you are defending your experience with the use of only 20 ounces. Despite our agreement on there being no exactness to this, that seems to me to be a rather significant difference.

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Yes, the difference is somewhat significant, but I can't explain it either. Too much time has passed since I did all that stuffing work.

The bottom line is I check to see if the 40 hz Fc has been achieved with whatever amount I used and, if so, left it at that. B)

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Looks like the AR-4x is a bit of an anomaly and used two stuffing densities depending on coil version. There was also an earlier version crossover with 265 turn coil that wasn't mentioned and I'm not sure where that fits into the coil series numbers but I presume it used eighteen ounces of fiberglass.

Roger

Actually woofer inductor coil size was increased in all models beginning around 1970. It seems to correlate with decreased stuffing and type of fiberglass, but whether these changes were separate decisions or somehow connected to changes in the woofers themselves (such as the move to foam surrounds and ferrite magnets) is unknown.

In the case of the AR-3a, woofer fs varies from as low as 14hz for the earliest alnico/cloth surround version carried over from the AR-3 to as high as 23hz for later Tonegen versions. Technically the "optimal" amount of stuffing would vary with different versions of this woofer. With that said, extensive meaurements by John O'Hanlon and myself while working on the 3a document correlate with Carl's suggestion that variations do not result in significant (subjective or measured) differences. We decided to simply document the amount of stuffing in the 3a restoration guide for each version. Since then, I have found AR-3's and some early 3a's to have over 30 ounces of very dense stuffing in each cabinet! Interestingly, when the AR-11 went to poly fill, the amount of stuffing was reduced to around 11oz using the same woofer (in approx the same size cabinet) as the later AR-3a.

A more interesting and puzzling aspect of the AR-4x is the "aperiodic" design of many of them, with an apparent allowable amount of air leakage through the alnico magnet/voice coil/dust cap and surround. This, in theory, should have affected other aspects of the design, such as stuffing and woofer fs.

Assuming the original stuffing is not damaged by water/moldy odors, the best bet for purists is to transfer it into separate bags for each cabinet and re-use it. The early tan/brown chunky stuff is very nasty, so do the work outside and wear a dust mask. The later clumpy yellow stuff is much easier to handle, and seems to correlate with the reduced amounts found in 1970+ versions.

Roy

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Yes, the difference is somewhat significant, but I can't explain it either. Too much time has passed since I did all that stuffing work.

The bottom line is I check to see if the 40 hz Qtc has been achieved with whatever amount I used and, if so, left it at that. B)

Carl...I think you mean fc for the AR-3a, the specs of which are in the neighborhood of 40hz.

Qtc is also affected by stuffing type and amount, which accounts for subtle subjective differences in the character of the bass response. Otoh, room placement always seems to trump these differences in my experience.

Roy

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Carl...I think you mean fc for the AR-3a, the specs of which are in the neighborhood of 40hz.

Qtc is also affected by stuffing type and amount, which accounts for subtle subjective differences in the character of the bass response. Otoh, room placement always seems to trump these differences in my experience.

Roy

Thanks for the catch Roy. Correction made on box resonance designation.

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....

A more interesting and puzzling aspect of the AR-4x is the "aperiodic" design of many of them, with an apparent allowable amount of air leakage through the alnico magnet/voice coil/dust cap and surround. This, in theory, should have affected other aspects of the design, such as stuffing and woofer fs.

Assuming the original stuffing is not damaged by water/moldy odors, the best bet for purists is to transfer it into separate bags for each cabinet and re-use it. The early tan/brown chunky stuff is very nasty, so do the work outside and wear a dust mask. The later clumpy yellow stuff is much easier to handle, and seems to correlate with the reduced amounts found in 1970+ versions.

Roy

Roy,

Yes, the 4's design is intriguing not to mention its success in the sales department. I imagine a lot of them ended up in dumpsters over the years and many more are still doing yeoman duty due to the longevity of their cloth-surround woofers even with the A-P pots going south. I can see an old codger sitting there listening to his tube receiver that has been on the same station for the last 50 years complaining about how his hearing is getting bad and how great the AR-4 still sounds after all these years :)

I don't have a problem with the 70s fluffy FG but the rock wool is going bye-bye. Also, I ran across a cabinet where the Kimpac(?) didn't stay in place either because the stuffing density was insufficient or it became compacted. Not all woofers had screens to keep the FG out of the spider area either.

It seems from the comments that the AR-4 cabinets can be stuffed to the max without worrying about putting in too much. I'll weigh the original stuffing for reference and give Lowe's JMFG a try. The link suggests you have to order in bulk but I presume it is available as single packs in the store.

Carl, you did your homework so you won't get any flak from me. Reading through some of the old posts you mentioned running across AR-3 woofer spider(s) that were out-of-spec allowing the vc to bottom out. Another reason to avoid over-driving the classics or doing a total rebuild beforehand including testing and spider replacement if necessary.

Roger

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I use the R-13 pink stuff for fiberglass applications and I believe that it works best and is the

closest to the original stuffing.

The denim is good but not as good as fiberglass.

I usually layer it in pushing it to the back if you like the most bass, add another

layer or pull it closer to the woofer if you want tighter but less bass (lower Qtc).

Both Villchur and Kloss said at various times that a highish, Qtc of about 1 is best.

Advent moved to foam fill in the New Large Advent and when I first saw it thought

it could not possibly work well, but after measuring it found it to be quite good. It

might even suppress (or block) standing waves better than other materials - I've not

seen any testing in this area so just something I'm curious about for now.

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I'd guess that the ceramic magnet woofers had slightly stronger magnets (ceramic magnets are cheap)

and they offset it by using less stuffing.

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The idea is that they had some target Qtc, the later literature provided a figure around .7 for

the big systems. A larger magnet lowers Qec which in turn lowers Qtc, and more acoustical

damping lowers Qmc which also lowers Qtc.

From memory Qtc = (Qmc * Qec)/(Qmc + Qec)

it is like parallel resistors.

So if Qec is lower due to a stronger magnet, one would raise Qmc with less stuffing to maintain

the same Qtc. This is the optimal way to design a system since the stronger magnet also

results in more passband sensitivity. In this case probably very slight, probably less than a

dB as an educated guess.

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I just found some AR-3a measurement notes from way back when...

The alnico magnet/cloth surround version of the 3/3a woofer consistenty produced Qtc around .7 or less. The early ceramic magnet/foam surround 3a woofer (1970/71) with the odd shaped ceramic/ferrite magnet produced highest Qtc of around .9 to 1. (I believe this version of the woofer to have the weakest magnet.) The later iteration of this woofer (1972+) with the perfectly round magnet resulted in Qtc of around .8, which remained pretty much the same through the AR-9 era.

Stuffing type and amount was varied considerably along the way, and while this could move Qtc one way or the other by a small amount, the trend for each type of woofer was very clear and consistent. Out-of-cabinet measurements of these woofers reflected the same Q characteristics as in cabinet testing, with the alnico magnet woofer measuring the lowest, and the early ceramic magnet woofer measuring highest.

The early alnico magnet 3a woofer cones are thin and rigid with foam damping rings around the dust cap and (the earliest) around the edge of the cone. The ceramic magnet version has a heavier soft cone, and with the exception of the earliest iteration, no damping ring.

Roy

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