Jump to content

AR-3a Fiberglass Weight


johnieo

Recommended Posts

The most commonly measured weight of AR-3a fiberglass stuffing that has been reported on the Forum is 1 lb., 12 oz (28 oz), give or take an ounce or two. These data appear to come from ~1971 or earlier models. Recently Roy C. found that speakers manufactured in 1974 contained about 20 oz.

For some time I had attempted to glean the design value from the “Assembly Drawings” contained in the Forum Archives; however, I couldn't read it when magnified. Then it was discovered that these were not scanned in the normal grayscale TIF mode, but rather in bitmap mode. After conversion to grayscale and a bit of contrast enhancement, the legiblity improved. The AR-3a Assembly Drawing dated Sept. 5, 1975 lists the Fiberglass weight as 1 lb. 4 oz (20 oz).

It is suspected that the 28-oz value we have been discussing was correct for early AR-3a cabinets. This suggests that one should not necessarily retain the existing amount of fiberglass when restoring a cabinet. Instead one should match stuffing weight to woofer. An early woofer in a late cabinet would be slightly under-damped, whereas a late woofer in an early cabinet would be slightly over-damped.

Link to comment
Share on other sites

Thanks for the info John!

It certainly is consistent with measurements I've taken of a number of AR-3a cabinets dating back to 1972.

We know that along with suspension changes that the woofer magnet strength increased in later years. I wonder if the move from alnico to ceramic magnet had a corresponding effect on magnet strength which also contributed to a change in the optimal amount of fiberglass. This could also coincide with the switch from the #7 (1.9mh) to #9 (2.85mh) inductor...food for thought.

Roy

Link to comment
Share on other sites

>Thanks for the info John!

>It certainly is consistent with measurements I've taken of a

>number of AR-3a cabinets dating back to 1972.

>

>We know that along with suspension changes that the woofer

>magnet strength increased in later years. I wonder if the move

>from alnico to ceramic magnet had a corresponding effect on

>magnet strength which also contributed to a change in the

>optimal amount of fiberglass. This could also coincide with

>the switch from the #7 (1.9mh) to #9 (2.85mh) inductor...food

>for thought.

>

>Roy

>

Roy,

As far as I know there were no actual changes to the motor (magnetic strength flux density, etc) of the ceramic magnet used on the 2000003-type 12W woofer in its many iterations. There were variances in the voice-coil cleanances in the gap and so forth, which might affect flux density and the BL (motor strength) from model to model, but the magnet was always a 54 oz. ceramic type, I believe, with approximately 7.3 lbs of high-permeable iron in the circuit. Have you seen different magnets used on the 12W (aside from the ocassional square magnet or convoluted versions)? The early Alnico woofer motor was slightly less potent, I believe, with respect to BL, but not by much.

I think it is certainly probable that AR changed the amount of fiberglas filling in the AR-3a cabinet in the 1975 back-wired version of this speaker. This would have been consistant with the introduction of the AR-11-type woofer used in the AR-3a, and this woofer was less compliant than the earlier AR-3a version of the ferrite woofer, and it had a different cone composition with a different spider and surround (and no butyl-rubber treatment). This woofer was perhaps overdamped in the AR-3a enclosure with the originally specified cabinet filling, so it is reasonable that reducing the amount and weight of the filling would raise the "peak" at resonance to bring it back up to the desirable point.

--Tom Tyson

Link to comment
Share on other sites

Tom, a couple of things:

You mentioned a change of cone material in the 1975 version of the 200003. That would be the same 200003 that's in the 10pi of the same year? The cone was definitely different between the 10pi and the 9. If so, we've got 20oz of fiberglass behind it per the assembly drawings and experience.

Second, you mentioned that you didn't know of a major change in the 200003. I believe you. The literature for the AR-11 does mention 8200 gauss, whereas the measure of the 10pi and 9 is 9800 gauss.

Since the 10pi and 11 were contemporaries, at least for a while, it wouldn't make a lot of sense for AR to have built two versions of the 200003 to go into the same cabinet.

Also, I noticed that the assembly drawing for the AR-11 shows 10 ounces of fill.

The only way I can see that this can be is if the 11 in the drawing was using fiberfill. 10 ounces of fiberfill is going to be a lot bigger than 10 ounces of fiberglass so maybe the same density?

Bret

Link to comment
Share on other sites

Bret:

The 1975 AR-3a assembly drawing calls for 20 oz. of fiberglass.

The AR-11 assembly drawing calls for 10 oz. of *polyester wadding.*

If their cabinets with equal internal volumes and by then, equal woofers, were designed to have the same cabinet Q, then the volume of air displaced by the filler would be the same for both. In other words, the weight of the two fillers should scale with their mass densities. Glass has a density of ~2.25 g/cc; polyester should be about half that--don't know exactly what polyester AR used.

Link to comment
Share on other sites

>Tom, a couple of things:

>

>You mentioned a change of cone material in the 1975 version of

>the 200003. That would be the same 200003 that's in the 10pi

>of the same year? The cone was definitely different between

>the 10pi and the 9. If so, we've got 20oz of fiberglass

>behind it per the assembly drawings and experience.

>

>Second, you mentioned that you didn't know of a major change

>in the 200003. I believe you. The literature for the AR-11

>does mention 8200 gauss, whereas the measure of the 10pi and 9

>is 9800 gauss.

>

>Since the 10pi and 11 were contemporaries, at least for a

>while, it wouldn't make a lot of sense for AR to have built

>two versions of the 200003 to go into the same cabinet.

>

>Also, I noticed that the assembly drawing for the AR-11 shows

>10 ounces of fill.

>

>The only way I can see that this can be is if the 11 in the

>drawing was using fiberfill. 10 ounces of fiberfill is going

>to be a lot bigger than 10 ounces of fiberglass so maybe the

>same density?

>

>Bret

Bret,

The cone material did change in the 1975-version of the 12W, and the thickness of the cone material was altered from the original, 1969 version. I say 1975. It might have been closer to 1976, for the very first AR-10Pi/AR-11 versions had the 1969-type (AR-3a) woofer. These woofers were shown in the initial press photographs of both speakers, and this woofer was originally shown in the AR-Pi-One pictures as well. The AR-10Pi and AR-11 *always* used identical drivers, and the back-wired AR-3as used the same woofer and midrange drivers as the AR-10/AR-11. I think the earlier 3a cone appears denser and perhaps heavier, but I’m not sure of this. The suspension (mostly spider) definitely tightened up, especially beyond the first few millimeters of axial movement, which indicates to me that mechanical damping was altered from the original woofer. The surround went from a fairly large-pore foam surround coated in butyl rubber to a smaller-pore, non-coated foam. Most likely the foam materials were improved and it became unnecessary to continue to use butyl rubber on the surround for edge damping. Through all of this AR had actually improved the woofer’s power-handling capability with only microscopic changes in distortion and bass response. There was never a “bumped” back plate for this woofer -- one would think that the cost of tooling such an improvement would not have been that expensive, but perhaps it would have been too costly to consider, and alternative methods for power-handling improvements were done.

By 1978 and the AR-9, another iteration of the same 200003-0 woofer (or 1210003-0) with an even newer cone (new dust cap as well) was introduced. If I remember correctly, this third-version woofer was even stiffer than the ’75 version. The “B” versions of the AR-10Pi/AR-11 also used this woofer, characterized by the decorative foam ring around the mounting flange and the new-style dust cap. The frames of these woofers were usually painted black I believe.

So these are three basic iterations of the 200003-0 or 1210003-0 woofer, each with slight changes or enhancements to the cone and suspensions, but containing the same magnet structure and voice-coil assembly to the best of my knowledge. Some magnets along the way were the square versions of the pancake ceramic magnet, and some of the very early woofers had indentations in the magnet sides, but in each case the total magnet size was the same to my knowledge. Free-air cone resonance remained about the same until the Tonegen version came along in the early nineties, and I think this woofer has a slightly higher resonance, but I have not had time to measure it.

If there were a change in magnet, there would have most likely been a change in part number suffix, but I have not seen this. If someone can supply more details on a possibly different version of this woofer, that would be great. If there is a picture comparing the two, that too would be helpful.

--Tom Tyson

Link to comment
Share on other sites

Tom,

I'm in a hurry don't mistake my speaking "absolutely" for my being "curt."

The timeline on the website is wrong.

I have no idea what a pi-1 is, never saw one, never heard one, haven't seen photos.

The AR 10pi was introduced no later than early 1975 as a "10pi" not a Pi-1. It was changed to the Mk 1 in May of 1975, but nobody who bought one would have known that. The monicur "10pi" pre-existed that design change (dropping of the fuse and changing the grill attaching velcro placement and amount). It was the 10pi and not a pi-1 even pre-May 1975. This is not debatable, I lifted a pre-May,1975 10-pi not three days ago. Believe me, trust me, I speak the truth.

The pre-May 1975 10pi had a 9800 gauss woofer per AR's own literature. It has a black basket per me and says 200003 right on the basket. If you pull down and read the AR-11 brochure, you will find that it, too, has a 9800 gauss woofer AND looking at the photos you can see that it is black as well, with the white tweeters.

If you will then look at the operating instructions for the Truth In Listening speakers, both the 10pi and the 11 have silver basketed woofers with black foam insert trim pieces. In the back there is a driver compliment section and the 10pi is not mentioned, but the 8200 gauss woofer is mentioned for the 11. So you're probably right. The 10pi and 11 did share drivers, it's just that the drivers changed; so any given 10pi does not necessarily share drivers with any other given 10pi or any specific pair of 11s.

If you look at the system assembly drawing for the 11, you'll find that in 1979 the stuffing was listed at 10 oz. If you'll look at the May 1975 system assmebly drawing for the 10pi, you'll see it was listed as 20 oz. Was the early 11 also 20 oz? Seems a safe bet.

I'd love to know what year the 11 was REALLY introduced and what year the black fabric ferrofluid-filled tweeters started being used; I'm pretty sure that was about 1977-1978.

Perhaps we can link this to the change from the brass to aluminum badges? Can we link some outward change (brass/aluminum; black basket/silver basket)with the change from Sprague caps (which seem to be "okay" at least) to the Callins (which are all degraded to the point of having to be replaced in my experience)?

We can go 'round with this some more later, but I gotta fly.

Bret

Link to comment
Share on other sites

I just wanted to add that it looks like the 11's first revision was also in May 1975, which would mean that the 10pi and 11 predate the introduction date of 1977 listed in the timeline. I'm having a devil of a time trying to read the 11 system assembly dates. I'll bet, if it were legible, we'd have more information about woofers than we do now.

Bret

Link to comment
Share on other sites

Tom and everyone,

I’ve been doing my best Sherlock Holmesing, but I only knew where to start because Pete had noticed the 8200 gauss spec in the Truth In Listening brochure.

In the 11 system assembly drawing the woofer is "item 2" the tweeter "item 4" and the midrange "item 20," but I can't read the "updates" well enough to be able to read when they were changed. Somewhere, looks like 1977, the thing says "Update to present. . ." then what? It appears the polyester stuffing replaced the fiberglass in 1977.

Sept 14, 1978 something added the "-1" but I can't tell for sure that this is "item 2." Looks like it, maybe. If it is, this is when the 200003 would have gone to the 200003-1 in September of 1978.

Interesting side note, my AR-9 woofers from 1978 have the 200003 sticker with no "-1" after it so the "-1" designation did *not* correspond exactly to the manufacturing of the AR-9, but came mid-stream.

So my guess as to the time line is this:

200003 labeled with a white rectangular sticker that says “200003" (with no square white sticker with red “+”) is first manufactured in 1975 or possibly late 1974. This woofer has a black basket, screen, and is 9800 gauss.

200003 labeled with the rectangular "200003" sticker and a silver basket and no screen arrives on the scene in late 1977 or early 1978. It has a 9800 gauss magnet and is used in the early version AR-9. Is it ever used in a run of 10pi or 11s? I don’t know. Rich might be able to tell us, depending on what all his 11s are.

Both of those surmises things are in-keeping with the literature we have showing 9800 on the 10pi, the early 11, and the 9 AND what we can see in the literature and from the speakers I own.

In September of 1978 the 200003 became the 200003-1, the magnet changed to 8200 gauss and this was used in the 11 during the time the “Truth In Listening” owner’s instructions were valid. We can assume that was also true of the 10pi, but we don’t have direct evidence of it.

On the May 1979 AR-9 system assembly TIF, the woofer is listed as being *either* the 200003-1 or 200003-2. . . is it safe to say the 200003-2 was introduced in 1979? Now if we only knew what the motor specs were for the 200003-2, we might really know something!

Anybody know anything else?

Thanks Tom, we’re going to get this exactly right.

Bret

Link to comment
Share on other sites

Tom,

I've now weighed the fiberglass in 8 AR-3a cabinets back to 1968, none newer than 1974, and they all have 1lb 4oz(+/-) except the 68's with alnico woofers (and #7 coils) which have 1lb 11oz and 1lb 14oz respectively.

I had one exception (a 1971) that had to do with the former owner putting too much stuffing back in one speaker and too little in its mate after (unsuccessfully :-)) trying to figure out how to make the pots work again. When I split the total between his 2 speakers I ended up with 1lb 4+oz in each.

I believe the change in the amount of fiberglass had to be much earlier than 1975.

Of the 13 woofers I have ranging from 1971 to 1993 (Tonegens) all the magnets look pretty much the same. The '71's have the indentations you described. I'm willing to bet, at the very least, that beginning with the switch away from the cloth surrounds/alnico magnets, stuffing amount and type were altered with changes to the woofers all along the way.

This all makes for interesting detective work, but, as John said above, it could be an issue for folks trying to restore old AR's to "original" condition.

Roy

Link to comment
Share on other sites

>This all makes for interesting detective work, but, as John said above, it could be an issue for folks trying to restore old AR's to "original" condition.<

And that was exactly my reason for being so doggedly interested in this subject; John's observation that we should match the damping material to the speakers.

You have just told me everything I need to know, which is that all the ceramic magnet versions of the 200003 have 20oz of fill behind them whether they are the 1969 versions or the 1975 version.

The only mystery left, as a practical matter, is what was the density of the polyester wadding that AR used behind the 8200 gauss version of the 11? If, as John intuits, it was half that of the fiberglass, then we know that 20oz of fiberglass or 10oz of polyester wadding would be the correct amount to stuff that size box, regardless of the "version" of the ceramic 200003.

The practical met the academic and finds all the version numbers ultimately don't mean a thing when it comes to stuffing a wild AR cabinet.

It does make you wonder why AR would change the 200003 to an 8200 gauss woofer magnet, doesn't it? It does me.

Bret

Link to comment
Share on other sites

>The “B” versions of the AR-10Pi/AR-11 also used this woofer, characterized by the decorative foam ring around the mounting flange and the new-style dust cap.<

Okay, Tom, after all my goings-on about much of nothing, I finally understand what you are saying.

What keeps me confused in all this is the Truth In Listening brochure's listing the 11's woofer as having 8200 gauss. I wonder if that's just a misprint? It sure has caused me a lot of grief if it is a misprint.

>The frames of these woofers were usually painted black I believe.<

Okay, my observation on this is generally pointless and totally academic, but on the 1975 version of the 200003, the entire frame was black. In the earlier version (pre-what? 1971??) the face of the frame was painted black, but the back of the basket was silver. By the 1978 version, the frame was now silver, no part was painted, and it came with the foam trim.

Bret

Link to comment
Share on other sites

Hi Bret,

I just read Tim Holl's account of the development of the AR-9 again looking for clues. He states that "the AR-11 woofer and cabinet combination represent an optimum design".

Later in the discussion of the AR-9 enclosure he states that "high density" polyester placed in the upper part of the cabinet was used to prevent standing waves.

If 10 oz of poly replaced 20 oz of fiberglass in the AR-11, its probably a good bet that it is the same "dense" stuff he refers to. AR could have gone with the same "high density" poly in the AR-11 during the development of the AR-9.

Referring to my post above, the 1974 pair of AR-3a's had the back wired tweeters and mids.

For what its worth, I also weighed the fiberglass in a 1971 pair of AR-5's. They have 10" foam surround alnico magnet woofers and 8 ohm versions of the '3a mid and tweeter. They have a tiny bit more cabinet volume than the AR-3a's (its approx 1.65-1.7 cu ft) due to a smaller woofer magnet and lack of internal bracing. Both '5's had 1lb 5+oz of the familiar yellow shredded fiberglass.

Roy

Link to comment
Share on other sites

Tim Holl also mentions the issues associated with increasing cabinet volume in his AR-9 discussion including comments about cone weight and magnet strength...so we know what AR was evaluating relative to our woofer and the evolution away from the older "optimal" design of the AR-11. Continual changes and tweaking probably occurred in most models they produced. I guess its up to the hobbyists and historians to figure it out.

I already think of the AR-3a as a "3a" and "3b"...

Roy

Link to comment
Share on other sites

>"the AR-11 woofer and cabinet combination represent an optimum design".<

And he wrote that in January of 1978 meaning that the combination he was talking about were the 9800 gauss magnet motors with 20oz of fiberglass behind them because we don't get a revision on the AR-11 woofer and stuffing until at least September 1978.

We have no way of knowing if he would still feel that way after Sept 14, 1978. Is it safe to assume either way? I don't know that it is. Let's take the converse of Mr. Holl's own explanation:

Decreasing the size of the magnet in a loudspeaker. . .is one way of decreasing efficiency. Such a change also decreases damping, raising system Q and therefore enhancing bass response at the lowest frequencies.

(My apologies to Mr. Holl and anyone reading this if some mystical engineer-exclusive hallucinogens bend space and make that untrue, although the opposite is true.)

AR might then have reduced the size of the magnet (and the strength of the motor) very much on purpose to get higher system Q and deeper "apparent" extension beginning in the fall of 1978. On the other hand, it could have been done to offset the change from heavy fiberglass to light polyester in order to put the system Q back at its original value (assuming AR decided "no more fiberglass" and so had to tweak all the drivers for polyester). Or maybe it was necessary to offset the effect of the new cone Tom mentions (if it were lighter).

In any of those cases it would be important to be able to positively identify 8200 gauss woofers so they could be reconed and damped-behind accordingly. If that's when the woofer changed to 200003-1, it would sure be handy to know that for certain (for others, it doesn't affect me). If there really was no change in woofers and the literature was printed with an error, it would be ultra-handy to know that, too.

Do you suppose we'll ever find-out?

Bret

Link to comment
Share on other sites

Just remember everyone, it's not just the weight of the stuffing you put in the cabinet that matters. It's also the installed density of the stuffing material (fiberglass or polyester or acousti-stuff) that provides the original performance the designer's intended to have relative to the adiabatic response vs its isothermal response. The density is determined by how you fluff the stuffing as you put it in. See(http://www.arcavia.com/kyle/Equations/Stuffing.html)for theory relative to box stuffing and it's apparent effect on box volume.

So, you've got to put the stuffing in properly to optimize the woofer's performance if you are a perfectionist in restoring original performance. I'm not sure the AR literature was specific relative to stuffing density. If so, you can model the fluffing requirement by simply filling a known volume with stuffing material and weighing it accurately until you get the density AR originally specified. Then you need to repeat that "fluffiness" when you actually stuff your cabinet.

Carl

Carl's Custom Loudspeakers

Link to comment
Share on other sites

I just rebuilt one of my 9ls speakers and tested it with out any stuffing man you could heir the standing wave harmonics from about 6 inches away the cabinet was screaching at you this had me worried untill i carfully restuffed it the same way it came out tight rolls it was fun to get it in I had added 6 cross braces seperated the cross overs and addded spikes the base is vary clean and it does not make any more screaching sound the base was vary muddy before i put it back in.

This is all good to know so that we get the correct stuffing and driver with the correct speaker.

Jim

this is the first of six rebuilds two 9ls two 98ls and two 78ls so i don't have to worry about mixing these drivers but I have more to do and have a lot of the older woofers I will have to go though them and carbon date them all :)

Link to comment
Share on other sites

>Just remember everyone, it's not just the weight of the

>stuffing you put in the cabinet that matters. It's also the

>installed density of the stuffing material (fiberglass or

>polyester or acousti-stuff)

The AR-3a (and AR-11) are the subjects of this thread. Both have the same cabinet volume, so it is indeed the respective weights of fiberglass (or polyester) stuffing with which we are concerned.

AR-3a: (Alnico woofer) 28 oz. fiberglass

AR-3a: (Ceramic woofer) 20 oz. fiberglass

AR-11: 10 oz. polyester wadding.

Other speakers have different specifications; AR-3as and 11s did not use AcoustaStuf.

Link to comment
Share on other sites

>Tom,

>

>I'm in a hurry don't mistake my speaking "absolutely" for my

>being "curt."

>

>The timeline on the website is wrong.

>

>I have no idea what a pi-1 is, never saw one, never heard one,

>haven't seen photos.

>

>The AR 10pi was introduced no later than early 1975 as a

>"10pi" not a Pi-1. It was changed to the Mk 1 in May of 1975,

>but nobody who bought one would have known that. The monicur

>"10pi" pre-existed that design change (dropping of the fuse

>and changing the grill attaching velcro placement and amount).

> It was the 10pi and not a pi-1 even pre-May 1975. This is

>not debatable, I lifted a pre-May,1975 10-pi not three days

>ago. Believe me, trust me, I speak the truth.

>

>The pre-May 1975 10pi had a 9800 gauss woofer per AR's own

>literature. It has a black basket per me and says 200003

>right on the basket. If you pull down and read the AR-11

>brochure, you will find that it, too, has a 9800 gauss woofer

>AND looking at the photos you can see that it is black as

>well, with the white tweeters.

>

>If you will then look at the operating instructions for the

>Truth In Listening speakers, both the 10pi and the 11 have

>silver basketed woofers with black foam insert trim pieces.

>In the back there is a driver compliment section and the 10pi

>is not mentioned, but the 8200 gauss woofer is mentioned for

>the 11. So you're probably right. The 10pi and 11 did share

>drivers, it's just that the drivers changed; so any given 10pi

>does not necessarily share drivers with any other given 10pi

>or any specific pair of 11s.

>

>If you look at the system assembly drawing for the 11, you'll

>find that in 1979 the stuffing was listed at 10 oz. If you'll

>look at the May 1975 system assmebly drawing for the 10pi,

>you'll see it was listed as 20 oz. Was the early 11 also 20

>oz? Seems a safe bet.

>

>I'd love to know what year the 11 was REALLY introduced and

>what year the black fabric ferrofluid-filled tweeters started

>being used; I'm pretty sure that was about 1977-1978.

>

>Perhaps we can link this to the change from the brass to

>aluminum badges? Can we link some outward change

>(brass/aluminum; black basket/silver basket)with the change

>from Sprague caps (which seem to be "okay" at least) to the

>Callins (which are all degraded to the point of having to be

>replaced in my experience)?

>

>We can go 'round with this some more later, but I gotta fly.

>

>Bret

Bret,

Sorry about the Pi-One reference. This was the first false-start iteration of the AR-10Pi, and although it was briefly advertised, the speaker was changed to the AR-10Pi before public announcement. The reference to it was made because it was shown with AR-3a woofers and with slide switches, rather than toggle switches, for level adjustment. The very first 10Pi's also had slide switches.

The AR-10Pi was "publicly" introduced in a Press Release by the AR sales department on 17 March 1975, and duplicate releases were made on the AR-11 and the AR-MST/1. All three speakers were introduced simultaneously, and were the first speakers of the AR Advanced Development Division. These models were the first in a series of speaker configurations that would begin to replace the classic AR models. The black-fabric dome tweeter replaced the orange/yellow dome somewhere in the 1977-78 time period, I believe, as you surmised. SteveF knows a great deal about the history of the Advanced Development Division introductions, and so forth, so I would rely on his knowledge of many of these details.

No, we can't link the brass-to-aluminum logo change with the black dome because the brass logo was still in use when the black dome was beginning to be used. Callins caps were used all the way back to at least 1975, too. I think the aluminum logo "B" version started in either 1979 or 1980, probably 1980. With that came the later-version, stiffer-type AR-9 1210003 woofer, and perhaps the end of fiberglass packing and the introduction of polyester filling for the cabinets.

--Tom Tyson

Link to comment
Share on other sites

>I think the aluminum

>logo "B" version started in either 1979 or 1980, probably

>1980. With that came the later-version, stiffer-type AR-9

>1210003 woofer, and perhaps the end of fiberglass packing and

>the introduction of polyester filling for the cabinets.

>

>--Tom Tyson

Tom: "For what it's worth;" my AR-11B with undocumented pedegree, have:

--Callins caps

--200003 Woofer

--200010-1 mid

--200011-1 hi

--aluminum logo

--polyester wadding

--all the marked manufacturing dates (R, C, drivers, cabinet) are in the range 27th--38th week of 1978, with the cabinets being the most recent. The close grouping of mfg dates suggests, but does not prove, that these were problably not subject to scavanging and are likely original.

Link to comment
Share on other sites

>>I think the aluminum

>>logo "B" version started in either 1979 or 1980, probably

>>1980. With that came the later-version, stiffer-type AR-9

>>1210003 woofer, and perhaps the end of fiberglass packing

>and

>>the introduction of polyester filling for the cabinets.

>>

>>--Tom Tyson

>

>Tom: "For what it's worth;" my AR-11B with undocumented

>pedegree, have:

>--Callins caps

>--200003 Woofer

>--200010-1 mid

>--200011-1 hi

>--aluminum logo

>--polyester wadding

>--all the marked manufacturing dates (R, C, drivers, cabinet)

>are in the range 27th--38th week of 1978, with the cabinets

>being the most recent. The close grouping of mfg dates

>suggests, but does not prove, that these were problably not

>subject to scavanging and are likely original.

>

John,

Thanks for your important input on the AR-11B. 1978 would be consistent with the introduction of the AR-9 and the "3rd" generation of 12W woofer and so forth. I do therefore believe that 1978 was probably the first year for the "B" version. The AR-11 and AR-10Pi were gone by 1981, perhaps at the end of 1980. By 1982 AR had the AR-91 in place of the AR-10/AR-11.

Interestingly, the woofer in your "B" version still had the same part number as the original AR-3a ceramic version, so it would indicate that the basic structure was the same (viz., magnet and voice coil, etc.) with other changes, such as spiders, surrounds and cone texture deemed improvements in materials and technique.

Questions:

(1) Your "B" version does have the aluminum logo plate, right?

(2) How much, if any, bracing is inside the "B" cabinet, and where is it located?

(3) Does the woofer have the foam strip around the outside mouting flange?

(4) Does your midrange driver have "pink" fiberglass under the protective screen, and is the screen painted silver?

(5) Does the tweeter have the black dome with a foam "diffraction" adhesive disk covering the top plate? A silver ring around the flange?

(6) Does the woofer, as well as other drivers, use Allen Head screws, but a smaller size 3/16-inch vs. 1/4-inch on the earlier woofer machine screws?

(7) Are there round Velcro grill-attaching pads placed on the front panel?

--Tom Tyson

Link to comment
Share on other sites

>Questions:

>

>(1) Your "B" version does have the aluminum logo plate,

>right?

Yes.

>(2) How much, if any, bracing is inside the "B" cabinet, and

>where is it located?

The cabinets are closed now, but I remember only one horizontal strip across the back side just above the x-o board, one baffle-board brace between woofer and M-T, and either one or two on each side.

>(3) Does the woofer have the foam strip around the outside

>mouting flange?

Not as received. The outside mounting flanges were bare aluminum, not a drop of black paint anywhere. The woofer identifying stickers had a small red dot on one end and two rows of type; the top row read 2000003 and the bottom row read 561-yyww.

>(4) Does your midrange driver have "pink" fiberglass under the

>protective screen, and is the screen painted silver?

Yes, yes.

>(5) Does the tweeter have the black dome with a foam

>"diffraction" adhesive disk covering the top plate? A silver

>ring around the flange?

Yes and badly decomposed. I replaced it with black felt. I would not say that there was a silver ring around the flange; there was an 1/8"-wide white ring painted on the foam about about a fourth-inch from the outer diameter of the foam.

>(6) Does the woofer, as well as other drivers, use Allen Head

>screws, but a smaller size 3/16-inch vs. 1/4-inch on the

>earlier woofer machine screws?

Woofer: 8 low-profile, round-head 3/16" Allen head.

Tweet: 3 low-profile, round-head 1/4" Allen head.

Mid: 4 1/4" flat-head #3 Philips.

I figured that this was likely to reduce obstructions.

>(7) Are there round Velcro grill-attaching pads placed on the

>front panel?

yes, eleven.

Link to comment
Share on other sites

>In any of those cases it would be important to be able to

>positively identify 8200 gauss woofers so they could be

>reconed and damped-behind accordingly. If that's when the

>woofer changed to 200003-1, it would sure be handy to know

>that for certain (for others, it doesn't affect me). If there

>really was no change in woofers and the literature was printed

>with an error, it would be ultra-handy to know that, too.

>

>Do you suppose we'll ever find-out?

>

>Bret

The test data from yor woofers offers strong evidence that there are two if not three motor strenghts if the Tonegens are included. A larger sample size would help verify this. The Bl values of 10 and 11.75 agree reasonably well with 8200 and 9800 gauss. As the saying goes, if it walks like a duck and talks like a duck ....

Bret where any of these woofers -1, or -2 versions? I've probably already asked this but it's hard to keep track.

Link to comment
Share on other sites

>Bret where any of these woofers -1, or -2 versions?<

They are not labelled as such. I don't believe that they are. I suspect the difference in Bl had a lot to do with overhang.

We will never, ever know because now that the "odd" drivers have been repaired there is no way to get new T/S parameters on them.

Bret

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...