RoyC

John, I have only seen (deteriorated) foam surrounds on original AR-12 mids. If the surrounds were made of cloth there would be need to replace them. Your source for new foam would be of interest. The repaired AR-12 mids I've been seeing on Ebay these days have new foam surrounds which have been cut and pieced together to fit. Roy

The AR-12 was marketed as an 8 ohm speaker. Dcr of the midrange is around 6 ohms. The last time I checked, there was no replacment available for the midrange foam. Roy

Carl, There is concern that 20oz may not be more "correct" than 28oz. It is not within the scope of the restoration guide to make that determination, or to decide how AR should have designed the speaker. All stuffing amounts between 20oz and 32oz seem to "work", but 28oz to 32oz is the original specification for the cloth surround woofer. There has never been any indication that 28oz provides excessive damping, and no restoration will be compromised by using this amount. While I agree 32oz seems like alot to jam into the cabinet, it always meets the fc specification. As I mentioned above, there are aspects of the upper bass and lower midrange response which are influenced by increased or decreased amounts of stuffing. The big AR-3a woofer reaches much farther into the midrange than modern designs will typically allow for a 12 inch woofer. Varying amounts of stuffing in the 3a affects the sonic character of the speaker, regardless of fc measurements. Q measurements tell some of the story, but not all of it. I have personal preferences, but they are not necessarily "correct" from an authentic restoration point of view. ...which leads to your question. Your guess is as good as mine. We have speculated that Q was raised in the 70's to enable AR to better compete with more bass "boom" in audio show rooms, which had become crowded with competitors demonstrating popular music. Maybe it was a change in design philosophy along the lines of our discussion above. Both types of 3a woofers seem to have the same low bass response with some differences apparent at higher frequencies. Most folks who replace the original stuffing do not have the means to weigh new fiberglass. As I mentioned above, my preference generally agrees with yours in that 3 utility bags (see photo below) of fiberglass per cabinet, or around 24oz, will likely provide satisfactory results across the board for all iterations of the AR-3,3a,2,2a,2x,2ax and 5. Carl, Your point about using the term "required" is well taken, and I'm confident any revisions to the restoration document will include some discussion and clarification along the lines of our conversation. (As always, your input is very appreciated.) Comments could also be added regarding "yellow" fiberglass, which has become difficult to find, and appears to have been replaced by a white type (see photo). The yellow fiberglass was recommended in the document because it was denser and seemed more like the original AR fiberglass, even though we knew the pink stuff would work adequately. BTW, it is somewhat easier to cram 28oz to 32oz of the new, softer, white fg into a cabinet than it is to do so with the pink. Roy

Carl, I've conversed with Tom and John, and have been been looking over the data we used for the AR-3a restoration document cabinet stuffing recommendations. The average amount of original stuffing found in all AR-3a cabinets with cloth surround woofers was around 30 oz, ranging from 28oz to 32oz. The statement regarding using this amount of stuffing for the cloth surround woofer was based on what was found to be in the original cabinets for the purposes of authenticity, *and possible unmeasured differences in upper bass and midrange response between the two types types of woofers*. In other words it was safer to state the original specification for cabinets equipped with cloth surround woofers. It was *not* based on our measurements. If it had been, and fc and Q were our only considerations, we would have recommended 20oz across the board, as our measurements agree with yours. In fact, I found fc remained within specification at amounts less than 20oz as well as over 32oz with most of the 3a woofers I measured. Some other things need to be taken into consideration when discussing the AR-3a woofer and cabinet stuffing. -Cloth surround woofers and very early foam surround 3a woofers were at the lower end of the 18 hz+/- 15% fs specification, and the later, foam surround versions were at the higher end. -There are response differences between the two types of woofers, which is the most likely reason for the change from #7 (1.88mh) to #9 (2.85mh) woofer inductor. -Q was raised closer to 1 in all AR speakers around 1970, when the foam surround woofer was introduced. The cloth surround 3a woofer has lower Q, in and out of cabinet, regardless of stuffing amounts. -We did not find significant differences between the behavior of fiberglass vs rock wool. Cabinets with 32oz of either material were stuffed VERY tightly, and had similar test results. -AR speakers were designed around fiberglass stuffing. Rock wool was used for a two year period when fiberglass was in short supply, and was inserted at the same weight as fiberglass. -According to John, fiberglass fibers are 3-5 um in diameter then, and today. There is no difference between the number of fibers when stuffed with the same density then or now. It is probable that just one amount of stuffing, whether it be 20oz or 28oz or 32oz, is not "optimal" for ALL 3a woofers, but we all seem to agree that a range from 20oz to 32oz will preserve the fc specification. This certainly provides wiggle room for the restorer with regard to the fc parameter. (I personally find 3 small 8 oz utility bags/24oz of unfaced fiberglass per cabinet to work to my satisfaction for most 10 and 12 inch AR woofers of the 70's, and subjectively find 20oz to be a bit too little.) OTOH, the document simply states what was there in the first place, as it relates to an authentic restoration. Roy

Welcome to CSP, 3abill! Did you purchase the replacement woofer from ABT recently? If so, I would return all of the items, as ABT's current woofer replacement does not meet original specs. The l-pad/25 ohm resistor combo works well, but you can purchase the same l-pads for more than 50% less than ABT's price elsewhere. When you say "reconing", do you mean replacing the deteriorated foam surrounds? Regardless, your original woofers are repairable, and your very best bet. ...sent you a Personal Message. Roy

Their primary value has more to do with being good speakers. In terms of re-sale however, they are not worth much (at present). Roy

It sounds like your woofers may have been connected out phase with each other (connected in opposite polarity), and canceling each other out.....if not at the cabinet terminals, then internally at the crossover. If you are sure you had your speakers connected properly (+ to + and - to -), I would check the crossover you removed for proper polarity. Roy

Hi Steve! Thanks for the compliment....but I'm probably more of a relic than any kind of treasure! Anyway, always glad to help out. It's one of those things that makes a hobby worthwhile. KLH caps were generally crappy, so there is every reason to undertake that task without delay. Examine the switches, which appear to be similar to the KLH 5 switches, and use a liberal amount of Deoxit on them. I'm still having some problems with the switches in a pair of 5's, and I have run across similar switches in KLH 23's that could not be adequately cleaned. The lesser KLH models, like the 17 and 20, actually have simpler, more reliable switches. Roy

Hey Kent, You are very welcome! I'm still hearing rave reviews from the folks who I have performed this modification for. IMO, late 70's Avid systems are the hidden gems of the "classic" speaker world. Nice work...They look great! Roy

Nice drawing... John O'Hanlon and I compiled data for literally dozens of 4xs a few years ago. The era indicated by your serial numbers was well represented, and I have seen many 4xs since. I'm convinced AR never installed a 1mh inductor in a 4x on purpose. Attached is the AR coil chart posted by Tom Tyson awhile back. Your 4x should have a #4 or #5 coil. excel_coil_chart.zip Roy

Hi Guys, As Kent mentioned, the HiVi Q1R http://www.parts-express.com/pe/showdetl.c...tnumber=297-417, with an added small inductor in parallel (.05mh to .1mh), seems to be working out for a number of forum members. Madisound also sells the tweeter and inductor. Ebay's "Vintage AR" is selling them already assembled, and drilled for the original screw holes, as a drop-in replacement for the original tweeter. You can check out his listing to see some photos. Feel free to send me a PM if you have any questions. Roy

Hello goldeneye57, On behalf of myself and the rest of the AR-3a Restoration gang, welcome to the CSP forum. To answer you're question, plywood or other materials could be used for the grille frame and not affect the sound. Plywood may be more prone to warping. The original 3a grille frame was constructed of a masonite type of material. Whatever you use, make sure it is a full 1/4" in thickness, so your staples don't pop through the other side when you attach the grille cloth. More importantly, be aware that the current AB Tech replacement drivers are not the same as the originals. You would be better off finding used original midrange units. Of the original 3a drivers, they have held up the best over the years. Roy

Carl has an earlier version of the formula, which I sent to him for evaluation. The current version can best be described as becoming tacky, rather than sticky, though it may still be effective for gnat control . The stuff works well to fill the pores of previously treated cloth surrounds without affecting other parameters of the driver (concluded after much out-of-cabinet testing using the Woofer Tester (WT2) software). Feedback from others has all been very positive so far. It should be noted that many cone and surround treatments are tacky to the touch. Some of the original treatments used by AR and Allison were quite sticky. Virtually all of the materials I have tested that "dry", even those that remain flexible, negatively affects the driver's measurements. Roy

I resurrected this thread to provide an update on the surround sealant I have been experimenting with. In short, I am quite convinced it is effective and safe for use on cloth surrounds. There have been no changes in any of the KLH or AR woofers I have treated over the past 6 months. In every case fs has remained constant, and the surround has remained sealed. The stuff remains very tacky with no signs of "drying". Best of all, it is thin enough not to negatively effect a woofer that may not need re-treatment....so, at worst, performance should be unchanged. It is chemically similar to Permatex gasket sealant (as well as the original AR sealant), but it is thinner, and remains much more tacky. It, like Permatex, is solvent based (toluene) and should be applied in a ventilated area. Although I have had some success, I cannot recommend it for use on foam surrounds, as the solvent can have a negative impact on some types of foam. If anyone would like to give it a try, PM me... Roy

Yes, they were treated (and very sticky) into the 70's sometime. Tom Tyson has posted info in the past about the butyl based stuff that was used. Of course the necessity of treating replacement AR foam surrounds today is open to debate. The most common 12" surround, as well as the preferred JBL surrounds for the 8 and 10 inch woofers, are very compliant and relatively non-porous. A number of the generic replacement surrounds are more porous, and presumably could benefit from a sealant. At the moment I'm just following up on a hunch regarding the duplication of an AR material, which I believe was used for a number of purposes. Roy

I was wondering about that as well. I'm guessing AR really had no idea how long such things would last, or that we would be dissecting and using them 40 years later. The company, however, was apparently confident enough in their materials to offer and make good on a very liberal warranty policy. We have seen AR's QC testing mentioned, but never any mention of "break-in" periods. Attached is a pic showing some of my experimental butyl compound applied to a test foam surround. The surround appears to be OK so far, but when I was experimenting with Permatex I found some foam surrounds react differently than others to solvents. I have applied it to installed cloth surround woofers, and it has not negatively affected compliance or performance, and it remains extremely tacky. I am becoming increasingly convinced that (depending on viscosity) it is very close to the material AR used on surrounds, cones, and early tweeter suspensions. Roy

Agreed...time probably takes its toll on any of the materials used as sealants, but this seemed a bit premature....So, after noticing the surrounds were more flexible after being at room temperature for awhile, I decided to run more measurements at different temperatures . Sure enough, the fs averaged 3.5 hz less at 80 degrees F than at 60F. The increase in fs since first applying the Permatex is not as great as I thought (maybe 1 to 2 hz). I first measured the woofers in my previous post soon after removing them from a very cool storage area. Mike, I have not tried the glue you mentioned, but if it "dries" (even if it remains flexible) it is probably too thick. I am currently experimenting with some stuff that, like Permatex, is butyl rubber based. This material, however, remains very sticky, like the original butyl based material AR used. I am hoping it can be used on foam surrounds as well....stay tuned:-). Roy

Hi Guys, I recently re-tested (out of cabinet) a few woofers treated with Permatex last year, and it appears that fs has risen on the average of 3 to 4 hz. The Permatex has lost its tacky nature, and seems to have stiffened a bit. While still better than anything else I have used in the past, the rise in fs is a little disconcerting. Carl, I was wondering if you still have any of your test woofers around to check out. Roy

I think you used the wrong stuff...4 ounces of the Permatex High Tack Gasket Sealer costs around $5. It is reddish in color, and does not really "dry", as it remains sticky. It is easily thinned with lacquer thinner, and should be used very sparingly. Permatex manufactures many products. Roy

Thanks for the info, Minh... I just double checked with John O'Hanlon to be sure, and it appears Roy Allison mistakenly reversed the 2 ohm and the 14 ohm (pot replacement) fixed tweeter resistors in the AR-3a drawing. The 2 ohm resistor should be in series, and the 14 ohm resistor should be in parallel with the tweeter. The drawing shows it the other way around. Given the typical condition of original 3a tweeters these days, a 15 or 16 ohm parallel resistor with little or no series resistance is probably more appropriate for the tweeter anyway. Roy

Hi Kent, I've heard some good things said about the 12, but have never had the opportunity to hear them myself. The deeper bass response and more elaborate tone controls of the 12 should be advantages over the 5. Anyway, it all looks very nice! I'll be interested in your audition of the new crossovers! Roy

The AR-3a restoration document is pinned for easy access at the top of the Acoustic Research area of this (discussion) section of the forum. Roy

This is one of the most sensible capacitor discussions I have read in a long time (other than the "guru" part...thanks Kent :-)! If you guys want to split the difference, you can try low value mylar caps on the tweeters (maybe even the mids) and electrolytics for high values. Many commercial speaker companies have done this. Mylars, like electrolytics, but less so, appear to have a bit more esr than polys do, so don't feel compelled to tweak the circuit if you are not in the mood to do so. They are relatively inexpensive, and easily obtained from Madisound (Carli branded and "surplus"..the 3uf surplus caps are very good!). The main advantage of this approach is that film caps are very stable for the long term, and that degradation issues are more likely to be bothersome in the upper frequencies. Madisound also sells Bennic electrolytic caps, which have a good reputation. Roy

As a guest at a small gathering back in the 70's, I remember being impressed to the point of asking the host what speakers were being used in the system playing in the background. They turned out to be Avid 103's. I had several brief opportunities to listen to Avids again, and always came away thinking they were quite good (AR speakers being my personal reference standard.) I would have purchased a pair if I had liked their appearance more. Recently I was able to acquire the guts of a pair of 1977 vintage Avid 100's. The drivers are VERY similar to the AR-4x, are physically, and very nearly electrically, drop in replacements for the 4x drivers...in fact MUCH more so than any currently sold AR "replacement" driver. Both the woofer and tweeter are actually better constructed than either 4x counterpart (but they are almost 10 years newer). The Avid crossover is simpler, with no woofer inductor, and a much lower value cap on the tweeter, which is controlled by a 3 position switch. Below are 3 photos comparing the Avid 100 and AR-4x drivers. Roy

Hi Vern, The solvents in the Permatex stuff seem to have a negative effect on the foam surrounds that I've tried to seal with it, so I doubt it would make a good glue for re-foaming. It really is a "sealant" rather than a glue or adhesive, which is a good thing. Roy