Evolution of and Replacements for the AR 11/12" Woofer

[Pete B]

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.

[RoyC]

I have a number of these woofers from different eras. They are all similar electrically (2.8ohms+/- and .75mh+/-) and identical in dimensions. In 69 or 70(?) it was redesigned from the cloth surround, old style magnet, and damping ring (used in the AR1/AR3/ earlyAR3a/) to the current day foam surround, magnet and cone. The suspension seems to have gotten stiffer, and the sensitivity higher, over the years.

Tonegen in Japan built the only replacement drivers currently available. Tonegen also built the NHT1259 and the full 12" AR303 (6ohm) woofer...and is no longer operating as Tonegen, if at all...

ABTech, Simply Speakers are both selling the same replacement woofer.

Not an easy driver to replace...and probably not wise given the collector status these old speakers have achieved.

Roy

[soundminded]

"Not an easy driver to replace...and probably not wise given the collector status these old speakers have achieved"

Are there comparable alternatives for the experimenter and tinkerer who wants to build something comparable with currently available parts? It seems to me that achieving an F3 of 42 hz and a Q of 0.5 in a 1 1/2 cu ft sealed box is something other manufacturers can't or don't want to do. Even the Tonegen 1259 requires twice the volume. That's rather disappointing from an industry which has had fifty years to plagerize and build on this design. Is it that they just don't like it?

Do you consider the relatively low sensitivity of this woofer to be an advantage? My first thought is that given how relatively inexpensive high powered amplifiers are today, it is because it gives you so much leeway to match it to other drivers of varying sensitivities and still maintain overall balance without bi amping tri amping to achieve the right level match. What are your thoughts?

[RoyC]

I agree lower sensitivity shouldn't be an issue these days. Matching the newer woofer to the old drivers is an issue.

Maybe the current AR replacement woofer works better with some of the later models than the AR3a...although there was at least one AR9 owner on this board who was not impressed and went back to the old one. As the competition heated up and power handling and sensitivity became more important, the designs changed accordingly. By the time of the AR11, the tweeter was completely different with ferro fluid, the midrange was tweaked to match the new tweeter, and the woofer was becoming "stiffer". We now have the "one (odd) size fits all" woofer as the only "authentic" alternative for all the models that used it..

In spite of its reputation as power hungry speakers, the vast majority of the AR1/AR3/AR3a era speakers were used with low power amps by today's standards, and not typically played at very loud volumes. They sound great (as did many of that era's acoustic suspension speakers) at low to moderate volumes, and is a big favorite of tube amp owners accordingly....Maybe that original "floppy" woofer would not stand up to the home theater and bass thumping high power applications that drives the "subwoofer" market of today.

In a world of brute force amps and a sea of "subwoofers" its probably not necessary to accomodate us. You would think, however, that one of the many manufacturers out there would make a variety of replacement drivers to make some very nice acoustic suspension cabinets sound good again.

Roy

[soundminded]

"In spite of its reputation as power hungry speakers, the vast majority of the AR1/AR3/AR3a era speakers were used with low power amps by today's standards, and not typically played at very loud volumes."

It's hard to remember that in the 1950s and 1960s a true 60 watt rms per channel amplifier was by the standards of the day a very powerful amplifier and only a handful of the most expensive models engineered for use as high fidelity even existed. 25 wpc was still a fairly expensive amplifier. For audiophiles on a budget, the logical solution to unaffordable McIntosh and Marantz amplifiers was Dyanco whose circuits were simple, straightforward, reliable, and easliy reproducible. Further savings were possible by constructing them as kits, something you don't see much of today anymore. There were others which were satisfactory although many considered them a notch or two down such as HH Scott, Fisher, Harman Kardon, Sherwood, Pilot, Bogen, Eico, Heathkit, and even Lafayette Radio (don't laugh, in 1960 they had a large 60 wpc power amplifier and a stereo preamp with about one million knobs and switches on it.)

There is a major difference between the kinds of music and applications for most home audio sound systems of today and those of that era. Audio equipment then had a very specific goal and that was to accurately reproduce the sound of what is now refered to as acoustic instruments, principly and most demanding were instruments used to play "classical" music and serious jazz. Subtle differences in timbre between a Stradivarius and a Guarnari violin or between a one particular Steinway piano and another were very important. Audio playback equipment was part of a chain which could be considered analagous to a camera requiring a high degree of "photographic" accuracy. Also by today's standards, much of that music was not loud most of the time, the only truely loud music reserved for climactic crecendos. By those standards, much of today's music is vulgar and synthetic and as unpopular as it is, I personally can't give those standars up entirely. Today we live in a different world where most home sound systems have to do double duty as HT reproducing the experience of bombs exploding all around you, jet planes flying 20 feet over your head, 100 car railroad trains roaring between your legs as you watch the best excuse industry can devise at an affordable price as a home substitute for a theater movie screen. Music, or most of what is called music today is often in part or wholey synthesized from purely electronic circuits or if any of it ever had any origins in the real "acoustical" world has been so electronically manipulated as to have little recognizable resemblance to its origins. (Ever hear a "celebrity vocalist" on TV sing on say a Christmas show live without his reverb unit, his sound engineer at a mixing board, his 100 piece orchestra? You hear just how pathetic they really are when they are acoustically naked.)

My best system's speakers are AR9 and I believe that the suspensions are stiffer than the older drivers. They are certainly stiffer than the original cloth surrounds and probably stiffer than AR3a, 10pi, and LST surrounds. I can't say if this makes them less true to the original acoustic suspension principle but they perform very very well IMO judged by their intended use and they can reproduce jet planes with the best of them when they are called upon. They can certainly shake my room and rattle my windows with my 60 wpc MosFet amp I built as a kit from Sound Values of Ohio (also known as Sound Valves) for $200 10 years ago (why didn't I buy several?) And who was Sound Valves? They were the last known source for spare parts for Dynaco whose inventory they had bought out. Alas, like the rest, they are gone forever.

[RoyC]

I purchased an Advent 350 Receiver (rare bird!) and some Dynaco stuff from Sound Values in those days. Of course I sold it all and regret it.

I agree, the AR9's are wonderful speakers! Many believe its the pinnacle of AR as we knew it...I had just found it interesting, and not surprising, that the AR9 owner posted that he went back to his original re-foamed woofers after being disappointed with the AR9 replacement woofers.

AR was probably tweaking as needed all along....hang on to those original drivers.

Roy

[tysontom]

>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

[Steve F]

Now that Tom has accurately recounted the developmental history of the AR 12" woofer in beautifully complete, correct detail, I'd like to add my opinion to this discussion with regard to the calling of this driver an "11-inch" driver.

Long-time members of this forum know that this is a pet peeve of mine, and for those of you for whom this is a repeat, I apologize in advance.

Herewith, then, is a re-run of two of my postings from almost two years ago:

">>#1751, "RE: Real McCoy ! New AR eyeball mid"

In response to Reply #0

>>11" Woofer part #1210003-2

Aren't we tired of outsiders calling the AR 12-inch woofer an "11-inch" woofer?

People should know better, for two reasons:

1. Industry-standard practice is to measure the frame diameter of a woofer, NOT the piston diameter or the surround diameter. Measured this way, the 3a's woofer is 12 inches. Any woofer--AR's, KLH's, Advent's, anyone's-- would be less than the formal measurement if you went strictly by piston diameter.

No one is trying to "get away" with anything or fool anyone. It's just the standard way that drivers are identified.

This leads to reason no. 2

2. AR had 10-inch woofers and 12-inch woofers. If some parts supplier insists on foolishly and inaccurately referring to an AR 12-inch woofer as an "11-inch" woofer, then there is the all-too-real possibility of a less experienced hobbyist ordering the wrong driver for their speaker.

AR called it a 12-inch woofer. For the sake of industry-standard practice, ordering accuracy, and historical consistency, the woofer should be called what it is: a 12-inch woofer. Period. People need to stop this nonsense.

Steve F.

#1756, "RE: Real McCoy ! New AR eyeball mid"

In response to Reply #5

The AR 12" woofer measures 12" across the wide part of the frame, 11.5" across the truncated section of the frame, 9.5" from mid-surround to mid-surround, and 8.5" from the inside of the surround (the actual "cone" diameter). Smaller drivers are correspondingly smaller. As I said, driver diameters are wider than the actual cone measurement, but this is just the way the industry measures drivers.

The issues with Layne and others calling the 3a/LST woofer an 11" woofer are these:

1) First and foremost, it serves no useful purpose. Calling the driver an 11" driver does not impart any new, helpful information to the end user. How do you benefit by Layne--or anyone else-- intentionally mis-identifying the woofer as an 11" woofer? The answer is, of course, you don't benefit at all. It's just bad information on their part, potentially misleading, and historically inaccurate.

2) It seems as if Layne and others want to demonstrate how clever and discerning they are by their "discovery" of the actual size of this well-known, historically-significant woofer. It's almost as if their thought process is, "Well, all you hobbyists out there THINK it's a 12" woofer, but we're the real experts, and we've discovered that it's only an 11" woofer."

It's so childish. Calling it an 11" woofer benefits no one, confuses the issue, incorrectly re-writes history, ignores industry standard measurement practices--all for the sake of what? Convincing themselves that they've "discovered" something? Padding their own ego?

I have zero tolerance for non-productive, wasted communication that imparts inaccurate data."

OK, I've said my piece. It's a 12" woofer. On this site, we know better. Case closed.

Steve F.

[RoyC]

Thanks Tom! You sure explained the "tweaking"! Most of us are definitely groping in the dark without the historical insight you provide.

I still much prefer the original woofers and consider the Tonegen a solution of last resort in the AR-3a. Regardless of the similar specs, in my opinion, it really doesn't have the tangible deep bass of old. I think that accounts for the lack of warmth you mentioned. It also muddies the upper mid/lower bass when matched with the old mid and tweeter.

It seems to be better, however, with the newer (AR-11 on) drivers of higher sensitivity.

If you send an unfiltered recorded signal through a 1970 version and a Tonegen on the bench, they sound like different drivers!

Roy

[RoyC]

I'm guilty, I know better and I apologize!

I have referred to it as such only when in discussions about "replacement drivers". There is no other "12 inch" woofer on the market that I'm aware of that will fit into that small 10 1/2" hole and a 10 incher will fall through :-)! With that said, your point is well taken!

I'm all for the original woofer anyway.

As a long time lurker on this board my comment about Tom's valuable insight extends to you as well, Steve.

Thanks,

Roy

[Pete B]

Thanks Tom for the detailed information.

I've got the old AES article on the AR-1 which confirms the 43 Hz for Fc and shows a frequency response plot for 180 deg radiation, amplifier damping factor of 1. This is a very low damping factor and I'm not sure if the woofer was directly driven. Qtc will be lower with a high damping factor amplifier.

Was there a woofer inductor in the AR-1? Does anyone have the DC resistance for the inductors used in the various designs?

It is interesting that Villchur offers that "A system with a Q of about one has the flattest response curve and does not ring appreciably." He also refers to "The well-known family of universal Q curves" provided in Beranek's Acoustics. I just had to take a look in my copy and at least the curves are accurate but the interpretation is a bit off. A Qtc of one is loosly speaking "flat" "give or take" in that the response crosses zero dB at resonance, but there is some peaking above resonance and it is not monotonic. Strictly speaking it is not perfectly flat.

We say in modern control theory and filter design that a Qtc of .707 has a maximally flat amplitude response (AR). It is also know as a Butterworth alignment. This alignment has a monotonic rolloff in that the response always has a downward slope which is not true for responses with peaking. It is the highest or maximum Q value that has no peaking in the frequency response or that is monotonic and this is why it is referred to as maximally flat.

It is also universally accepted in modern control theory and filter design that a Qtc of .5 is critically damped. This is also known as a Gaussian alignment. It is the highest Qtc value that has no ringing in the transient response (TR). Qtc values below critically damped are referred to as overdamped and also do not ring, and above as underdamped and always have some ringing.

Qtc Output at Fc Features Name

-------------------------------------------------------------

<.5 Overdamped TR

.5 - 6 dB Critically Damped TR Gaussian

>.5 Underdamped TR

.707 - 3 dB Maximally Flat AR Butterworth

1 0 dB 0 dB at Fc peaking above Fc Chebyshev

>.707 Peaking in AR Chebyshev

Beranek also suggests that Qt should be unity for "flat" response down to the lowest frequencies. Many would say that strictly speaking this is an error since it is not monotonically flat and there is some peaking.

[Guest Ken Perkins]

This has been an EXCELLENT thread! I find it interesting, refering to the Advents, that they (at least mine) have an Fb of 41 hz with a Qtc of .9, which would pretty much hold to the original design of the AR-1/AR-3 woofer/box response. Close enough, anyway. It's further interesting the fact that they would hold up after all these a years, including a refoam job!

[RoyC]

>2. AR had 10-inch woofers and 12-inch woofers. If some parts

>supplier insists on foolishly and inaccurately referring to an

>AR 12-inch woofer as an "11-inch" woofer, then there is the

>all-too-real possibility of a less experienced hobbyist

>ordering the wrong driver for their speaker.

Although I initially felt compelled to apologize for referring to our beloved woofer in a less than 12" way, I feel a point made by Mluong303 on another thread needs to be reiterated. A conventional 12" foam surround will not work with this woofer. I just conducted a survey of major foam surround replacement websites and found that it is almost universally referred to as an AR 11 inch woofer and they sell their kits accordingly. With AR speakers changing hands faster than Christmas fruitcakes on Ebay, and this website increasingly mentioned as a place to find out how to repair or restore your purchase, maybe its a good thing that this issue is brought up from time to time. If this website is really worried about misleading the "less experienced hobbyist" then maybe historical nomenclature is not as important as finding the right repair kit. There are many more folks replacing foam surrounds than replacing the strangest shaped 12" woofer on the planet! At what point does "insider arrogance" become more misleading than "outsider ignorance"?

[RoyC]

Hey Pete,

The AR#9 inductor (2.85mh) was used with this woofer in the '3a and by my measurement with an inexpensive LCR meter its .9+ ohms. Some of us have found that an AR#7 inductor (1.9mh) was used with the cloth surround woofer in some early '3a's and that measures .7+ ohms.

Roy

[Steve F]

There are really two separate discussions taking place. Let’s identify them and address them independently:

Discussion No.1—How to describe a 3a/LST/9 woofer for replacement of the surround:

The point was made that if someone were to ask for a generic 12" surround kit, they might be supplied with a JBL 12" surround that wouldn’t fit the AR 12" woofer because the JBL is too big. This seems at first glance to be a valid consideration, but if it’s thought through, the logic is specious. What the parts suppliers should do is identify what woofers their various surround kits are meant to used with. If supplier ABC has a surround kit for the 3a/LST/9, they should identify it as "Surround kit for AR 12-inch woofer." Calling it an "11-inch" woofer still confuses things in the customer’s mind, since no such woofer has ever existed.

Take the plight of Mr. Casual Customer. Mr. Customer has owned ARs for a long time. Now they sound a little "funny." He takes off the grilles, notices that the surrounds have rotted out and calls his friend, Mr. Stereo Expert. Mr. Expert says, "Hey Casual, it’s no big deal. What you should do is call Supplier ABC and ask for a re-surround kit. Just tell them what speakers you have, and they’ll send them out. You’re a handy guy; you won’t have any trouble doing the work yourself."

So Mr. Casual calls ABC and says, "I’ve got these AR-3a speakers. The owner’s manual says the woofer is 12 inches, so I guess I need a 12-inch AR surround kit."

ABC says, "Well, for your speaker, we have an 11-inch kit, not a 12-inch kit."

"Huh? My manual says 12 inches. I’m confused. Why do you want to sell me an 11-inch kit if my manual says 12 inches?"

See the problem? Misidentifying it as "11-inches" helps nothing and potentially causes confusion. As to the "JBL’s 12 inches is larger than AR’s 12 inches" argument, this is particularly vacuous. Every manufacturer’s parts are specific to that manufacturer. When you go into an auto parts store to buy an air filter for a Chevy 3.8-liter 6-cylinder engine, you don’t ask for a generic "6-cylinder air filter." You ask specifically for a Chevy 3.8-liter 6-cylinder air filter. The air filter for Ford’s 3.0-liter engine is still a Ford "6"-cylinder air filter, even though it’s smaller than the Chevy filter. We don’t all of a sudden refer to the Ford as a 5-cylinder engine.

The various suppliers should identify their surround kits by the woofers and brands with which they’re meant to be used. If they identified their surround kits as "AR 12-inch surround kit, for use with AR models 3a, LST, 11, 10Pi, 9, 91, 910, etc," there would never be any problem or confusion. They shouldn’t re-write history or try to be too clever. This isn't arrogance on our part. There is simply no upside benefit to Layne and others referring to the 3a woofer as 11 inches. No upside at all. But, a very definite potential downside. So why do it?

Discussion No. 2—What we call these woofers on this Forum

We should call them 12-inch woofers amongst ourselves, because we know better--right?

Now if you’ll excuse me, we’re having a houseful of people later on today for our annual Christmas Eve dinner, and if I don’t get down there to help my wife pretty soon, she’ll strangle me with those 11" surrounds.

Happy Holidays, everyone.

Steve F.

[Pete B]

I just noticed that the driver motor flux densities are given in the AR literature for several models and there are at least two different values:

11/12" woofer:

AR-10pi 9,800 gauss

AR-9 9,800

AR-11 8,200

[Pete B]

Roy posted this information in another thread:

Here's a link:

http://www.classicspeakerpages.net/dc/dcbo...id=&page=6#5409

Here's his post:

Since my negative experience with the replacement (Tonegen) woofer in AR-3a's, I've been obsessed with the differences between the various versions of AR 12 inchers. I have collected 3 versions to date not counting the original cloth surround version and the Tonegen. The earliest from a '71 AR-3a has a very soft spider and can be identified by an easily observable masonite ring upon which the foam surround is mounted. I also have identical woofers from 1972 and 1974 AR-3a's.

The other two versions are from the late 70's (AR-9) and possibly early 80's (from an unknown model). The observable differences in these from the '74's are noticably stiffer spiders, a smaller hidden masonite flange ring, a (now deteriorated) foam facing on the flange and the absence of the basket screen (on the early 80's version).

The Tonegen (#1210003-2A from 1994) seems to have the stiffest suspension of all and of course no basket screen. The two 70's woofers are labeled #200003 and the later one (80's?) without the basket screen is a #200003-1. With the exception of the screen, the late 70's 200003 and the later 200003-1 seem identical and have the same stiffer spiders. They need re-foamimg so I cannot comment on sound yet.

Although I've done most re-foaming myself in the past, I plan to have some work done by Millersound due to his reputation and to use as a source of comparison.

Roy C.

[Pete B]

Hi Roy,

I've got a pair of AR 11/12" woofers out of AR-11s from the late 70s, both part #200003 (MADE IN U.S.A.) without any dash number. These do not have the screen material over the back and they do have the small hidden masonite ring. The original owner of these 11s informs me that no work has ever been done to the woofers, and they've never been replaced.

The first woofer (#1) out of what I'll call system #1 seems in good shape and only needs replacement of the foam edge. This one is marked: 561 7830 and has an RDC of 2.49 ohms.

The second woofer (#2) was damaged when driven with excessive power (300W), and the voice coil rubs in such a way that the cone sticks wherever you leave it. I believe it may have bottomed also since it sounds as if some windings are loose. It is marked: 561 7838 and has an RDC of 2.37 ohms.

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?

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?

Pete B.

>Roy posted this information in another thread:

>

>The other two versions are from the late 70's (AR-9) and

>possibly early 80's (from an unknown model). The observable

>differences in these from the '74's are noticably stiffer

>spiders, a smaller hidden masonite flange ring, a (now

>deteriorated) foam facing on the flange and the absence of the

>basket screen (on the early 80's version).

>

>The Tonegen (#1210003-2A from 1994) seems to have the stiffest

>suspension of all and of course no basket screen. The two 70's

>woofers are labeled #200003 and the later one (80's?) without

>the basket screen is a #200003-1. With the exception of the

>screen, the late 70's 200003 and the later 200003-1 seem

>identical and have the same stiffer spiders. They need

>re-foamimg so I cannot comment on sound yet.

>

>

>Roy C.

[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?

[soundminded]

"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."

Correct me if I'm wrong Tom but I think this was the truest version to the ideal of the acoustic suspension principle. Virtually no mechanical restoring force at all. The later versions are a compromise to practicality and reliability.

[Pete B]

Hi Tom,

Thanks for the info, I prefer not to shim as you also mention and this is how I've always done it. I think the longer coil causes it to bind more easily than most, and I do notice that if I apply equal pressure I can get smooth motion. I use the method you mention of testing the motion while the glue is wet.

I noticed that both cones have 3013 F stamped on the back in white. Do you know the source for the cones?

The top and bottom plates measure .50" thick but are very slightly tapered at the edges. The magnet is .74" thick.

I'll test the Bl once I get these refoamed, they should be the lower strength given that they're out of AR-11s.

Do you have a preferred source for parts such as edges and voice coils?

How about ink to restore the black cone? One is faded more than the other. Anyone know what type of ink was used originally?

The only difference between these and the ones Bret shows here:

http://www.classicspeakerpages.net/dc/user_files/305.jpg

are that these have the date code stamped on the back, have decorative black foam around the outer rim, do not have the screen, and the masonite does not go as close to the screw holes. The cone, dust cap, frame, magnet, top and bottom plates look the same.

Pete B.

>>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?

[RoyC]

Hi Tom and Pete,

The only magnet differences I've observed have been between a '71 version and all the rest. I've attached photos. The '78, '74, and '72 versions have the same dimension's as Pete's '78.

The Tonegen's magnet actually has a smaller diameter by about half an inch than the others, with all other dimensions being the same.

I believe it was Bret that noticed differences in the published BL specs in the 10pi.

Pete, Millersound said that the '78 spiders were shot and replaced them. I didn't think to turn them upside down as you did. Maybe mine were the same as yours and I just thought they were "stiffer" because they were bottomed out..They did sag.

Roy

[RoyC]

The Tonegen is the one marked "'94" in the photos above. "3013" was stamped on the '74 cone but no "F". None of the other cones were stamped at all.

Roy

[Pete B]

Thanks for the info Roy. I believe that ceramic magnet materials have been getting better and better over the years. I noted that the Bl values were grouped around 10, 11.75, and 13 in this thread:

http://www.classicspeakerpages.net/dc/dcbo...5393&page=#5399

I then also found different gauss values for the 11 and 10pi which supports this theory in the AR literature as reported in post 5795 of this thread:

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#5797

Having worked in engineering I can tell you that things do not always go as planned, the marketing literature could be what was planned and prototyped. It's possible that they decided it was too much trouble to stock the two different drivers and went into production with a common part. However, we do see that samples seem to show different values which I believe is simply early 1974 time frame production, and late 1978 time frame where magnet materials just got a bit stronger. It's possible that around the time the 10pi and 11 were being designed and planned that they had stock of both woofers and the logical thing was to put the stronger magner version in the 10pi and weaker in the 11, until they ran out. Then they would all get the stronger version. This is pure speculation on my part but it is how things go in the real world.

Pete B.

[Pete B]

Hi Roy,

I notice that your 71 woofer has an indentation in the round magnet but I don't know how much of a difference that might make. What is the part number for those probably not 200003?

Does anyone know if the -1 on the 200003 part number indicates the square magnet?

I didn't know that there was a square magnet version of the 200003-1, this is the first I've seen of it:

http://www.kujucev.com/ar/ar12inch_a.jpg

The square magnet and plates might make the difference in Bl from 10 to 11.75 and this supports my theory that there were differences in early and late production. Now we know there were differences, the question is if they explain the differing Bl. The square magnet made to standard dimensions might just provide a bit more material/strength.

Bret were DUT 2,3,4,7 square magnet versions by any chance?

Pete B.

>Hi Tom and Pete,

>

>The only magnet differences I've observed have been between a

>'71 version and all the rest. I've attached photos. The '78,

>'74, and '72 versions have the same dimension's as Pete's

>'78.

>

>The Tonegen's magnet actually has a smaller diameter by about

>half an inch than the others, with all other dimensions being

>the same.

>

>I believe it was Bret that noticed differences in the

>published BL specs in the 10pi.

>

>Pete, Millersound said that the '78 spiders were shot and

>replaced them. I didn't think to turn them upside down as you

>did. Maybe mine were the same as yours and I just thought they

>were "stiffer" because they were bottomed out..They did sag.

>

>Roy

>