tysontom

>I've got a pair of AR 11/12" woofers out of AR-11s from the >late 70s, both part #200003.... > >The date codes suggest that these were manufactured in the >30th and 38th weeks of 1978. > >The only thing that does not seem to agree with your findings >is that the spider is so loose that the weight of the cone >causes it to drop when the magnet is face down. I thought the >spider had sagged and lost center until I flipped the woofer >over magnet up and now it sagged the other way. It just seems >that the spider is so loose that it will not return the cone >to center without help from the foam edge. I've not seen this >in most woofers with deteriorated edges. I also note that >there does not seem to be much clearance around the voice coil >and it easily rubs with the edge missing. I'm thinking that >it is probably important to shim the voice coil when refoaming >these drivers, do others agree? The loose-spider phenomenon is completely normal for the AR woofer; the older the woofer, the less mechanical restoring-force the spider would provide. For example, the earliest ceramic-ferrite AR-3a woofers (with the wide masonite flange) were considerably looser than the woofers you describe from 1978. It is also normal for the woofer cone to sag if the woofer is stored or left for any period in the magnet-down or magnet-up position. There is not enough spring to hold the weight of the cone when the speaker is in that position. This is also the reason that AR used to warn against storing any of the older AR speakers in the woofer-up or woofer-down position for prolonged periods. The cones would settle to one position or another, and eventually cause permanent sagging. The voice-coil clearance on the 200003 woofer is actually pretty wide, and rubbing is unusual once the cone is in the approximate center position. With a deteriorated surround, rubbing is common and to be expected, as the cone is never properly supported on the edges, and the cone will move at an oblique angle. It is absolutely unnecessary to shim the voice coil on this woofer when replacing the surround; in fact, it is usually better *not* to shim it, because you can cause a slight deformation of the spider if the coil is perfectly centered with shims and then the surround is glued in place. Rarely is the voice coil perfectly centered even when manufactured. The spider can bind slightly, and eventually it might tear. It is much better to leave the dust cap alone, and to use your fingers close to the apex of the cone to "bounce" the cone back and forth for centering as you let the slow-drying, water-based glue dry. Avoid the fast-drying glues as this makes cone-alignment more difficult. > >Does anyone know if the glue is water soluble to remove the >dust cap, and also the spider outer edge? Does Miller use new >dust caps when he refoams? > I don't believe that any of the original glues were water-soluble compounds, but that might have changed somewhere in the process. You don't need a new dustcap if you avoid using shims. Thanks, --Tom Tyson Pete and Roy: have either of you found examples of the 200003-woofers in which you have noted different Bl or magnet structures? I know the Bl varies a bit from woofer-to-woofer, but I still have not seen (or are aware of) a different magnet structure for this woofer series. Can you provide pictures?

> >Minh, what was Victor Campos' connection to the 10 Pi and 11? >Was he a designer or engineer for the systems? >I know that he was with Adcom in the '80s, but I'm unfamiliar >with his contributions to AR. ar_pro, Victor Campos, now close to 70, actually started at AR before going to work for KLH, to the best of my knowledge. He worked at AR during two periods: (1) from 1960-1963 and (2) from 1974-1979. For awhile in the first period he worked in the AR Music Room under Gerald Landau, Marketing Director, and subsequently in the customer-services area. Campos also was quite involved with an FM broadcast series in Boston public radio (WGHB Boston I believe), and many original master recordings were aired during some of these broadcasts. I am not sure when this occurred, but I have some of the tapes and could probably check them. Although I don't think he was an engineer, he contributed a great deal to the design of several of AR products, especially during the second period. By this time he had a more active marketing role in product development than in the first period. He had a lot to do with the AR-10Pi/AR-11/AR-MST development, and he also had a lot to do with the product development of the AR-9. Incidentally, one version of the AR-9 was going to be "powered," but the design of that speaker never made it into production. Campos was heavily involved in that design. --Tom Tyson

>AR was "this close" to marketing the 3a Improved in the US in >the spring of 1974, but had a change of heart at the last >minute. With the 10Pi and 11 less than a year away, there >would have been no valid reason to try to re-introduce a 3a >variant at that time. >The same holds true for the 2xa, although as far as I know, >that model was never even contemplated for the US market. > >Steve F. Steve and Minh, I know that the AR-3a Improved had a two-position toggle switch in lieu of the two level controls. There was an "A" position and "B" position on a single toggle switch. Did this represent two different settings for both the midrange and tweeter, or just the tweeter, or what? How did the AR-2xa differ from the AR-2ax of that vintage? Thanks, --Tom Tyson

>Thanks Tom...Were the "European" versions ever sold in Canada >by any chance? I've seen some sold on Ebay that were located >there, not to mention a number of them here in NY. > >Roy Roy, I have no idea where those models were marketed, but probably some did come into Canada, as well as in the US. Bitburg in Germany, among other European military stores, also sold zillions of AR speakers to servicemen over the years, but most were the standard US models that were shipped to Europe (Germany) to be sold there to servicemen. I think that most of the "European" versions were made in AR's two European plants, and were distributed mainly overseas. I am sure that some came back to the states, but I don't know the situation other than servicemen and others returning to the states with their speakers. I do know that the AR-3a-Improved and other models of this type were not sold in the US. Steve F might have some insight into these models as well. --Tom Tyson

>I just came upon grills for AR-2xa's. There is no mention of >this model in the library. Can we assume they were sold about >the same time as the 4xa, following the 4x and 2ax era? The >grills are slightly too large to fit the 2ax cabinet. Anyone >have info on this model?...Tom, Steve? > >Roy Roy, The AR-2xa was apparently the European "Improved" version of the AR-2ax, never sold in the US, and it had the thin-molding cabinet similar to the AR-3a-Improved, shown below. Ironically, the AR-2ax was also available in an European version, with the same grill. The grill panel is larger and the grill material is a dark weave, quite similar to the 40-year earlier AR-2 grill color. http://www.classicspeakerpages.net/dc/user_files/498.jpg AR-3a-Improved with European-preferred thin-grill molding. --Tom Tyson

>Tom, > >I noticed on your photo showing the front of the woofer cone, >and on my photo as well, that the cone appears to have a >smooth texture. All of the woofers that have the standard >mounting seem to have a rougher texture (see my attachment). I >don't know if it is just due to the picture resolution of the >older photos, or if the older ones were really smooth. > >If they did indeed have a different texture, could that >indicate that KLH may have slighty changed the cone >formulation and/or the way that they made them? > >(The surround is also has a dark rubber sealant on the later >ones, although I'm assuming that this is just a different >choice of sealer. I don't think this would have any noticeable >effect on the sound.) > >Thank you. > >Gary > Do you think that the dark surround in your image might be a re-foam job or dark butyl-rubber substance put on the surround? I can't tell, but it doesn't appear to be standard, as I think the surround treatment KLH used was a latex substance that dried to a clear texture. But I don't know what KLH actually used on the later surrounds. As far as the cone texture itself, I think that KLH went from a hand-made felting process in the early ones to a production-line process in the latter ones, and this would probably account for differences in cone texture. Sometimes the back of the cone has the rough texture and the front side shows the smooth side of a mold. Both methods are probably viable -- different ways to get the same basic results. Later versions were likely pressed from both sides, with ridges or texture to help the woofer's response both at the low end in long excursions, and at the high end in the prevention of cone "break-up." You are probably right in your assessment of sound differences in the early vs. late woofers. I am sure that KLH engineers attempted to replicate or even improve performance of the earlier woofer, but at greatly reduced manufacturing costs. The early ones had to be expensive to produce. Whether or not they succeded is something that would have to be measured. --Tom Tyson

>Once again this shows the strange dichotomy between the >accuracy of AR speakers reproducing recordings made under the >most carefully controlled conditions and the seemingly more >natural sounding and accurate reproduction of KLH speakers >playing recordings made commercially. I don't follow you here: do you mean that you believe that the live-vs.-recorded sessions were recorded under more carefully controlled conditions than commercial recordings? The AR live-vs.-recorded tapes were made with the same Ampex recorders/Neumann/Sony microphones used in most recording studios, and the setup was very similar except for AR's recording in a more anechoic environment to avoid double-reverberation. Why do you feel that the playback reproduction through KLH speakers played with commercial recordings is more natural-sounding and accurate? What can you use for a reference in this type judgement? Without a reference to live music, how can you know it is more accurate or natural-sounding? Do you think it might be due to the KLH's tendancy to be more forward-sounding than the ARs? >AR4x was absolutely amazing reproducing that 1905 nickelodeon at >the trade show almost keeping up with AR3 at a fraction of AR3s >price. But in the showrooms with almost any recordings, the KLHs >just sounded more like live music. Again, I don't follow you here. Without an instant reference to a live performance, how can you make this judgement? Could this be personal preference? --Tom Tyson

>As far as I know the tweeters for the model 6 and 17 (mid to >late 60s version of the model 6)are the same. The model 6 >woofer had a bigger magnet, a longer voice coil >winding.....this, along with bigger cabinet volume gave them >deeper bass then the model 17, but not by much if you listen >to them side by side. The 17 came out in 1965 for $69. each >and it was a great buy at that price, especially considering >the model 6 cost twice as much at about $135 each.! I think >KLH sold 2:1 more units of the 17 then 6 during this time. It >must ghave been a bit of a thorn in the side of Kloss' old >company Acoustic research since it's price was about the same >as the AR-4x, many folks thought the 17 put out nicer sound >then the 4x, plus it had a 10" woofer compared to the 4x >having a 8" woofer. I think this is true that the tweeter used in the later KLH-6 and the KLH-17 were the same, but the speakers had different crossovers. The bass response was better in the Model Six, but as you comment, not by much. This points out the exponential differences in product engineering that have to occur when you seek to go just slightly lower in bass: the AR-3a over the AR-2ax is a good example, in that the AR-3a speaker cost twice what the AR-2ax cost, yet had only a one-third-octave lower bass response. The AR-3a had lower distortion and deeper bass output, but it was not readily noticeable on most music. To get this, the woofer had to have a lower-resonance, heavier moving system, more voice-coil overhang and a larger, beefier cabinet. All this costs a lot of money. I don't recall the KLH-17 ultimately outselling the AR-4x, but I know that it was close. The 17 could go lower in bass than the 4x and was a bit more forward-sounding, but the 4x was smoother and had better off-axis response. I think that *Consumer Reports* and others generally concluded that the AR-4x was at the top level in accuracy for speakers in this price range. Side-by-side comparisons, however, and the KLH-17 generally came off sounding better than the AR-4x, and this certainly hurt AR's sales somewhat. --Tom Tyson

>Tom, > >You mentioned that you've heard that the early KLH's might >have sounded better. I saw a photo of an old KLH 6 with the >epoxied woofer, and it showed the tweeter with no protective >screen. (The grill must have either been ripped off, or it was >a photo from KLH before the grill was glued on.) If available, >it is at the following website: > >http://fisherdoctor.com/pictures/other/Speakers/KLH6.jpg > >I hadn't gotten an answer in another post, but this seemed >like a good time to ask again. Could the addition of a >protective screen over the tweeter have been a factor in the >difference? I know that the screen changes the sound somewhat >(I have newer KLH 6's that I removed the screens from - they >now sound a bit more open and less conjested), but I didn't >know if KLH made changes to the crossover and/or tweeter to at >least try to compensate somewhat for the change. The original KLH Model Sixes didn't have a protective screen on the tweeter. That was added after the system was changed to the conventional mounting methods. The Alnico magnets went away, also, such that the newer ones had ceramic magnets. The protective screen might have slightly affected the sound of the tweeter, but not by much. If you were to do a "double-blindfold" test of speakers with and without the screen, it might be difficult to detect the differences, even though they probably do exist to some slight extent. The screen was very open, so not too much sound is blocked. The biggest differences seem to be in the change in the magnets on both the tweeter and woofer, and perhaps other changes to the crossover in the later versions. To lower costs, I believe that the crossover was simplified toward the end of production, but I'm not sure of what the changes were. These changes were made long after Henry Kloss sold KLH. Some others may have additional information on the differences in the original Model Six and the later versions. --Tom Tyson

>Was there any noteable change in the sound of the KLH-6s when >they switched to the standard, removable woofer basket? > >Gary I think that the KLH people at the time would say that there was no difference, but I have heard that the original versions were better. For one thing, the epoxied-in woofer insured a perfect acoustic seal, so gaskets were not a concern, and speaker-to-speaker consistency could be assured. But the real issue now is with collectors of these old KLHs: if a woofer, tweeter or crossover is damaged for whatever reason, repair is virtually impossible, and the speaker is literally rendered junk. It is possible, as soundminded suggested, to literally take a Sawzall (Milwaukee trademark) and cut into the back of the cabinet to try to work on the crossover, but if the woofer voice coil is damaged, the cone has to be literally ripped out of the front of the speaker and a new one put in its place. http://www.classicspeakerpages.net/dc/user_files/393.jpg KLH Model Six crossover with oil-filled capacitor http://www.classicspeakerpages.net/dc/user_files/394.jpg KLH Six Woofer (inverted surround) For quite some time a fellow in Massachusetts repaired KLHs, and had extra cones and crossover components and so forth with the capability of repairing these components. He was a former plant manager at the old KLH. I had an old number for him, but it no longer is current: Dominic DeAngelis Abington, Massachusetts 617-878-4425 Incidentally, the early KLH Model One, Model Two, Model Three, Model Four (the early Model Five was a tweeter-only box), Model Six and Model Seven all had this epoxy construction. By the mid-1960s KLH did away with this method, but only the Model Six survived out of that original group, and the woofer was changed to the conventional mounting. An updated version of the Model Seven was the KLH Model Five-derived Model Twelve. --Tom Tyson

A low-resolution image of an early, epoxied-in KLH-Six woofer: http://www.classicspeakerpages.net/dc/user_files/391.jpg Note the Alnico woofer encapsulated in epoxy, with aluminum legs extending to the front baffle, and epoxied into that surface. Note, too, that the front baffle is MDF, not plywood, as the latter is less well suited for this type of installation. There was some hoopla regarding the 15-layer marine plywood used for the early cabinets, but the front baffle had to be MDF, as it is denser, harder and more stable than plywood. Henry Kloss got a patent for this method of mounting a driver, and the patent involved the method of alignment and installation details. This method of woofer installation insured that the speaker voice coil and suspension were properly aligned, and the production-line QC was apparently improved over the conventional method. Note that the treated linen surround was inverted, which helped protect the surround once the speaker was mounted, and allowed the baffle to be placed on a flat surface for work (before completion) without mashing in the half-roll cloth surround material. There is an oil-filled capacitor in the rear of the image; most early KLHs, as well as ARs, used these war-surplus capacitors well into the early 1960s. --Tom Tyson

>Could someone please go over the evolution of the AR 11/12" >woofer from the AR1, AR3, 9, 10, 11, and any drop in >replacements that were offered over the years? > >What's currently available new, is there a new AB tech 11/12", >is it identical to any of the production units? > >I would think that the AR303a woofer will not fit the other >designs because it does not have the side cuts, correct? > >There are some T&S measurements on this site I believe? I'll >try to find that thread. > > The AR-1 (incidentally, AR always used a hyphen separating alpha-numeric characters) was the first product built by Acoustic Research, and the first commercial acoustic-suspension loudspeaker. The woofer was a 4-ohm 12-inch driver with flat sides (always measure a woofer by the frame diameter, not diaphragm diameter as in the case of a midrange or tweeter). The flat sides allowed easy installation in the relatively narrow AR-1, AR-3 and AR-3a front baffle. The acoustic-suspension woofer was designed and patented by Edgar Villchur, who with Henry Kloss co-founded Acoustic Research in 1954. Kloss did most of the mechanical design of the speaker enclosure and woofer magnet, basket and so forth based on the specifications and direction of Villchur. It was Kloss’ idea, for example, to build the drivers in-house to save money, something he would go on to do at his other companies (KLH and Advent). The AR-1 woofer was built with a cast-aluminum frame and Alnico-5 magnet (9.3 lb. magnetic circuit), a 2-inch heavy-copper voice coil, double-wound on a bronze bobbin, with approximately one-half inch overhang in the gap. The free-air resonance of the early woofers was approximately 14-15 Hz, and later ones were closer to 17 Hz. Mounted in the 1.7 cu. ft. AR-1/AR-3 enclosure, the system resonance rose to the optimum 43 Hz, +/- 3 Hz. This woofer was used in the AR-1 and then was added to the AR-3 in 1959, and during that year an improved version of the woofer with a ribbed cone and damping rings was added. This greatly improved the internal damping of the cone, especially considering the crossover frequency of 1000 Hz. The cone ribs strengthened the cone against flexing at higher frequencies, and the damping rings close to the apex and outer surround dampened the cone against unwanted spurious wave propagation -- a problem of all woofers to some degree. The end result was a mounted-woofer system that was measurably flat on axis within 1-1/2 dB from 38 to 1000 Hz -- good by any standard. The AR-3 woofer went through some minor changes on-and-off up through the 1960s, such as elimination of the outer damping ring, and this woofer was then used in the 1967 AR-3a. In 1968, AR had developed and introduced a new vacuum-formed “lossy” cone material and the now-famous urethane-foam surround material. This new combination was first used on the 1968 AR-5, and in 1969 a new 4-ohm woofer was developed for the AR-3a with this new cone material, the urethane surround and a stamped-steel basket with ceramic-ferrite magnet. This woofer had a 2-inch voice coil, but this copper coil was now wound on a high-temperature Nomex former. The moving system was approximately the same weight and had nearly identical parameters as the original woofer. This first version of this woofer had a clear, butyl-latex-coated urethane surround, and was by far the most compliant of any of the AR woofers. AR found that many raw woofers that were being shipped out to service centers were damaged on arrival, and it was found that this very compliant woofer was bottoming against the back plate during transit. A shorting strap was placed across the terminals, and this internal damping stopped the damage. In 1975 AR developed for the new AR-10Pi and AR-11 a new version of this same 4-ohm AR-3a ceramic-ferrite woofer, and the new version had an improved surround material, slightly changed cone material, and higher compliance at excursion extremes to protect the woofer against bottoming. This woofer never had the “bumped” back plate, so excursions greater than 1-1/4-inch or so could result in the voice coil hitting the back plate. Tightening-up the spider in the newer woofers would help protect the speaker against over-excursion. The new woofer retained the same parameters of the early woofers with only slight differences. The voice coil was still 2 inches with one-half inch overhang. The enclosure size was the same, etc. By the late 1970s AR introduced the AR-9 and other versions of the 12-inch speaker such as the AR-58, AR-78 and so forth. However, the woofer used in all of these still had the same basic parameters as the original 1954 AR-1 woofer. Basically, all these flat-side woofers are interchangeable, and have almost identical characteristics with only minor differences. Power-handling is much greater on the later woofers, but the distortion, frequency response and so forth (when mounted identically) are all very close. The Tonegen flat-side woofer, built as a service-replacement item in the early 90s, is also very close in every respect to the original woofer, and is interchangeable in all AR speakers using the flat-side 12-inch woofer. It has a slightly higher resonance due to its relatively low compliance, but the trade off is significantly higher power-handling capability. It is not quite as “warm” sounding as the earlier speakers, but works well as a replacement woofer. The AR-303 woofer does not have the flat sides, and uses a different magnet and so forth, but is very close in performance to the AR-3a. It measures very closely to the the AR-3a/AR-10Pi, but has improved power-handling and minutely lower distortion than the earlier speakers. The resonance is the same. This woofer is not interchangeable with any of the other systems. --Tom Tyson

It is great to have the contributions of Steve F in this forum. He is extremely knowledgeable about the history of Acoustic Research, Advent and related products of this era. He is also current on today's audio technology and marketing strategy -- important in the understanding of audio history. Steve will contribute a great deal to this subject. My apologies on misspelling Andy Kotsatos name -- a typo. --Tom Tyson

The ADC-303ax's were similar in performance and price to the AR-2ax and KLH-6, and were highly rated ("check-rated," I think) in Consumer Reports during their test of mid-priced speakers. I have some technical data on them somewhere, and I can check further if you wish. --Tom Tyson

I'm not as educated on Advents as on ARs, but I think what you might be describing is the original "The Advent Loudspeaker," introduced in late-1969, early-1970, and continued on well into the 1970s. There was a walnut-veneer version that had an outward-facing solid-walnut front cabinet molding (vs. the concave look of the AR-3 and AR-3a molding). The plastic molding strip between the grill cloth and the molding was square at the corners. Advent also offered another version of the same speaker, with a walnut-finish, vinyl-clad utility cabinet. This cabinet resembled the AR-2ax, AR-5 and older KLH-6-style cabinets. In mid-to-late 1970s, Advent brought out an improved version of The Advent Loudspeaker called "The New Advent Loudspeaker," and I think it was designed (or the improvements were engineered) by Andy Kotsados (currently CEO of Boston Acoustics). It, too, was a superb speaker for the price, and was available in walnut veneer or in a vinyl-clad utility cabinet. "The New Advent Loudspeaker" had a more rounded outward-facing molding, and the plastic insert between the grill and the walnut molding was more rounded at the corners. --Tom Tyson

In a post in the "Advent" section, one respondent wrote the following about the The Advent Loudspeaker. He sited an opinion that many people had during the early 70s regarding the performance and value of the AR-3a vs. The Advent Loudspeaker. His comments are below: "Your comparison is set too late in time. The Advent entered the market in '70 or '71 and was pitted against the AR 3a, 5, and 2aX & KLH 5, 6, & 17 line up at that time. The Advent was more than a match for these, and just about stopped sales of those models. At $125 for the veneer cabinet model, and the AR-3a at $225, it was no contest. The Advent sounded better, and was half the price." This comment regarding the Advent being more than a match for the AR-3a, etc., is right off the Advent sales floor fresh from the early-1970s. It's totally untrue, and unfounded. The original Advent was designed in 1969. What is true is that the Advent sold for about one-half the list price of the AR-3a, was an excellent value, and resembled the AR-3a in having a low 43-45 Hz. bass resonance. On the other hand, the Advent had a great deal more output in the midrange and treble (read "brightness"), relative to bass, than the 3a, and this gave the illusion that it was superior in the midrange and treble. Nothing could be further from the truth. The AR-3a had better midrange and treble dispersion, which resulted in smoother and flatter acoustic-power response. In the bass, the Advent woofer was no match for the AR-3a woofer once the volumn was cranked up, or if a lot of organ or bass-drum music was present. At high levels, the Advent had significantly higher bass harmonic distortion. At moderate levels, the two were similar. The Advent, being a two-way, had to cross the largish woofer well up in the midrange, and this created roughness in the response and diminished off-axis response in the lower midrange. The Advent's otherwise excellent tweeter was also taxed pretty heavily in the lower midrange as well. It had to be large enough to handle the midrange, yet still be small enough to have decent extension and dispersion -- a difficult compromise for any tweeter, no matter how good. In the end, The Advent Loudspeaker was a better value than the AR-3a, but it was not a better speaker.