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

[RoyC]

Pete,

My '71 woofers didn't have a model label/stamp on them, but they are usually referred to as 200003. Everything else about them appears identical to the other early 70's woofers, including type of spider, masonite ring and (subjective) performance.

I have never seen a 70's version with a square magnet. I suspect that began in the early 80's from what we are observing.

Roy

[Guest Bret]

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

Late 70s production - round.

Bret

[Pete B]

The plot thickens, different magnet diameters.

Tom Tyson wrote "Can you provide pictures?" I've been thinking that I should measure every dimension on each of these woofers but did not get around to do it. I did put them down side by side and what do you know, one magnet has a larger diameter, enough that it's easily seen by eye. Here are the pictures:

http://members.aol.com/basconsultants/AR11WMAG.jpg

http://members.aol.com/basconsultants/AR11WSID.jpg

Woofer #1 on the right in the top picture, left in the bottom picture is obviously larger, that is not a shadow in the picture. Woofer #2 has a red tag stating: "Service Replacement Unit For Further exchange the original purchase Bill of Sale required" As I understood it the woofers had never been replaced, does this tag indicate that it is not the original woofer? I'll have to check with the original owner since he has a good memory of what went on with these speakers.

Woofer #2 has a magnet diameter of 6.04 inches, while woofer #1 does not fit inside the caliper which stops at 6.185", I'd say it's about 6.2".

I measured the thickness again Woofer #1 is right on the money at .75" if not .751", while Woofer #2 is over .74" but closer to .74 than .75". This is starting to split hairs but clearly woofer #2 has a smaller magnet. The back plates are both 5.5".

Woofer #1 is the one that did not fail and it would tend to have less bass excursion due to the stronger damping and reduced output in the low bass.

It's also interesting to note that the woofer that seems to be original is the stronger version, when the literature states that the AR-11 should have the weaker driver. Knowing what goes on in engineering and production this doesn't surprise me - the stories I could tell.

They probably used more than one supplier for magnets. Any other theories?

I'd appreciate it if others could measure the diameter of the magnets and report back. Dimensions of the square magnet version, and the top and bottom plates would also be helpful.

Pete B.

Here's a view of the front:

http://members.aol.com/basconsultants/AR11DYNT.jpg

>--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?

[tysontom]

>The plot thickens, different magnet diameters.

>

I've been thinking

>that I should measure every dimension on each of these woofers

>but did not get around to do it. I did put them down side by

>side and what do you know, one magnet has a larger diameter,

>enough that it's easily seen by eye. Here are the pictures:

>

>Woofer #1 on the right in the top picture, left in the bottom

>picture is obviously larger, that is not a shadow in the

>picture. Woofer #2 has a red tag stating: "Service

>Replacement Unit For Further exchange the original purchase

>Bill of Sale required" As I understood it the woofers had

>never been replaced, does this tag indicate that it is not the

>original woofer? I'll have to check with the original owner

>since he has a good memory of what went on with these

>speakers.

>Woofer #2 has a magnet diameter of 6.04 inches, while woofer

>#1 does not fit inside the caliper which stops at 6.185", I'd

>say it's about 6.2".

>I measured the thickness again Woofer #1 is right on the money

>at .75" if not .751", while Woofer #2 is over .74" but closer

>to .74 than .75". This is starting to split hairs but clearly

>woofer #2 has a smaller magnet. The back plates are both

>5.5".

>

>Woofer #1 is the one that did not fail and it would tend to

>have less bass excursion due to the stronger damping and

>reduced output in the low bass.

>

>It's also interesting to note that the woofer that seems to be

>original is the stronger version, when the literature states

>that the AR-11 should have the weaker driver. Knowing what

>goes on in engineering and production this doesn't surprise me

>- the stories I could tell.

>

>They probably used more than one supplier for magnets. Any

>other theories?

>

>I'd appreciate it if others could measure the diameter of the

>magnets and report back. Dimensions of the square magnet

>version, and the top and bottom plates would also be helpful.

Pete,

The outside diameter of the magnet being slightly different probably is a reflection of different vendors, particularly in view the relatively small differences you noted. I don't know how many suppliers AR had for magnets, but probably quite a few, as most manufacturers usually have two or three prime vendors for critical parts. Because of different manufacturers, it is also possible that the inside diameter of the magnet was sufficient to offset the different outside diameter. The square magnet is a good example. By the way, did you *weigh* the representative drivers, taking into account that the frames for all the 200003-series woofers are nearly identical, but with only superficial differences in the cones themselves? Determining the weight of the magnetic structure -- which should weigh around 10 lbs or so -- might be a closer indicator of different magnet structures. I honestly don't believe that there was a difference in that series, but I can't be sure.

I can assure you that the top and bottom plates on every AR 2000003-style woofer are .5 inches, as the two-inch diameter voice coils in all these speakers are one-inch in length, +/- a millimeter or two, allowing for the designed .5-inch voice-coil overhang. Maximum linear excursion was one-half inch, and maximum excursion before bottoming was a little over one inch.

--Tom Tyson

[Pete B]

Hi Tom,

I'll weigh them at some point if I get a chance. The former must extend past the windings somewhat as with most voice coils, do you know what that dimension is?

Thanks,

Pete B.

[Pete B]

Original owner tells me that one woofer was replaced, he did notice the magnet difference and the AR tech told him it was not a problem.

Pete B.

>Woofer #1 on the right in the top picture, left in the bottom

>picture is obviously larger, that is not a shadow in the

>picture. Woofer #2 has a red tag stating: "Service

>Replacement Unit For Further exchange the original purchase

>Bill of Sale required" As I understood it the woofers had

>never been replaced, does this tag indicate that it is not the

>original woofer? I'll have to check with the original owner

>since he has a good memory of what went on with these

>speakers.

[tysontom]

>Hi Tom,

>

>I'll weigh them at some point if I get a chance. The former

>must extend past the windings somewhat as with most voice

>coils, do you know what that dimension is?

>

Pete B,

To answer your question, there is about a millimeter or two above the coil winding, and quite a lot below the windings. The voice coil is 2-inches in diameter and about 1.02 inches in length. Following are images of two damaged AR#200003 voice coils:

http://www.classicspeakerpages.net/dc/user_files/616.jpg

(1) This AR-3a voice coil was bottomed during strife-testing, and the nomex former and coil suffered slight damage at the edge where the coil touched the back plate in 1+ inch excursions during sine-wave testing.

http://www.classicspeakerpages.net/dc/user_files/617.jpg

(2) This AR-3a voice coil was heavily damaged by extremely high power at low frequencies, causing the coil to compress the former when the coil hit the back plate violently. This coil bottomed repeatedly before deforming the bobbin.

--Tom Tyson

[dynaco_dan]

>>Hi Tom,

>>

>>I'll weigh them at some point if I get a chance. The former

>>must extend past the windings somewhat as with most voice

>>coils, do you know what that dimension is?

>>

>

>Pete B,

>

>To answer your question, there is about a millimeter or two

>above the coil winding, and quite a lot below the windings.

>The voice coil is 2-inches in diameter and about 1.02 inches

>in length. Following are images of two damaged AR#200003

>voice coils:

>

>(1) This AR-3a voice coil was bottomed during strife-testing,

>and the nomex former and coil suffered slight damage at the

>edge where the coil touched the back plate in 1+ inch

>excursions during sine-wave testing.

>

>(2) This AR-3a voice coil was heavily damaged by extremely

>high power at low frequencies, causing the coil to compress

>the former when the coil hit the back plate violently. This

>coil bottomed repeatedly before deforming the bobbin.

>

>--Tom Tyson

>

Hi Tom

With the quality of your photos, I wish I could go back in time, to when I was working at the AR local warantee depot.

When a picture is worth a thousand words, this is a great example.

It might be difficult for the average reader, who may never have seen a voice coil in their life, to imagine this type of damage.

The photos I would like to have shown, would be, Dynaco A-25 woofer

voice coils burnt like toast, without exaggerating, charred.

Common with SCA-80 and Q models which were exremely popular here, at the time.

These two were mentioned only to show that the power was adequate for hifi, not disco or rock levels.

AR-3A voice coils, after being plugged into an AC outlet in error. OOPs.

Certainly gives, a 1 amp fast blow 25 cent fuse, a certain feeling of some security from that type of damage.

Your quality photos, sure make this web site, much more interesting, to be sure.

Thank you, Tom.

[Pete B]

Thanks for the pictures Tom, very interesting.

This has me thinking again about this second woofer, I now believe after taking another look at it that the VC former bent in toward the pole piece when it bottomed and is what's scraping and causing it to stick. I've only seen this happen once before with an aluminum former and the VC would have been fine if it had bent out away from the pole piece. Formers should be flared out or even completely formed so that they're more tolerant of bottoming, IMO.

I don't have a lot of experience with Nomex formers but at this point I prefer the metal types that I've seen.

It would be good if we had replacement part numbers for the internal parts of these drivers, spider, VC, cap, cone, etc. so that we can specify them to driver rebuilders and get more consistent results. We could write a specification for the rebuild process calling out specific parts to be used, adhesive types to use, certification testing, and so on. This is the way to get consistent results.

NuWay has extensive offerings and online catalogs.

http://www.nuway-speaker.com/html/products.htm

I'm waiting for foam edges from RSSOUND and have not been getting much response to my emails. This happened with the Advent surrounds that I ordered and I understand that he is busy running a business, he did deliver and did answer my important questions in the end. What I like about RSSOUND is that the foam was a perfect fit and more compliant than other standard 10" foam surrounds that I've seen. I have a few other 10" drivers that I wish I'd used RSSOUND's Advent edge on. Is Rick from RSSOUND a member here?

Pete B.

[kkantor]

Quite some time ago, Tom Tyson entrusted me with an original 12" to test. I have been embarrassingly remiss in finishing that work. Fortunately, an engineer of mine has just delivered a big customer project and, prompted by this recent thread, I today assigned her with completing the task.

Within a few days, I should have comprehensive data to review. I'm travelling until I return from the upcoming AES show, but will not drop the ball again. (Or the woofer!)

I hope I can provide a few other technical goodies, too, to thank everyone, particularly Tom, for your patience.

-k

[Pete B]

The foam from RSSOUND arrived today with hand written answers to my questions on the receipt. Seems they mainly do business with large customers, but also provide this semi-automated service for small customers. The foam looks like a good fit and is 5/8" wide which I believe is correct for this woofer.

I unsoldered the lead in wires on woofer #2, unglued the spider which allows the entire cone, spider, and voice coil to come out as a unit. The voice coil has a tarnished bronze look on the outside top near the cone, the appearance on the inside is black anodized, and the edge has a silver aluminum color. I believe the former is aluminum but I can't explain the bronze look on the outside. The voice coil did bend in and the windings are in perfect condition. I was able to flare the former back out and it should be fine.

I notice now that the spider is stretched at high excursions and I believe this is what causes the floppy spider that some people mention. The spider was also starting to come unglued where it meets the cone/voice coil joint. I believe this was also caused by over excursion.

Pete B.

[tysontom]

>The foam from RSSOUND arrived today with hand written answers

>to my questions on the receipt. Seems they mainly do business

>with large customers, but also provide this semi-automated

>service for small customers. The foam looks like a good fit

>and is 5/8" wide which I believe is correct for this woofer.

>

>I unsoldered the lead in wires on woofer #2, unglued the

>spider which allows the entire cone, spider, and voice coil to

>come out as a unit. The voice coil has a tarnished bronze

>look on the outside top near the cone, the appearance on the

>inside is black anodized, and the edge has a silver aluminum

>color. I believe the former is aluminum but I can't explain

>the bronze look on the outside. The voice coil did bend in

>and the windings are in perfect condition. I was able to

>flare the former back out and it should be fine.

>I notice now that the spider is stretched at high excursions

>and I believe this is what causes the floppy spider that some

>people mention. The spider was also starting to come unglued

>where it meets the cone/voice coil joint. I believe this was

>also caused by over excursion.

>

>Pete B.

If possible, please send images of this speaker assembly, including both front and back views of the cone and voice-coil assembly. Which vintage 200003/1210003-series was this, date code, etc.? I could go back and look at your earlier message I suppose! I am curious to learn when the aluminum former was put into use; it may have been earlier than I originally thought. Most earlier versions had the paper-nomex former, well-known for its resistance to high temperatures. There were definite differences in spider compliance between earlier and later versions of the 12W, but a stretched spider will simulate a loose suspension as well. Incidentally, the earlier Alnico AR woofers (PN 3700) used phosphor-bronze formers exclusively, but this substance is expensive and somewhat heavy. The 3700 also had a slightly longer coil in practice than the 200003 woofer, but only a millimeter or two. When the 3700 woofer reached its excursion limits, it would not hit the back plate, but rather it would tend to loosen the bond between the voice coil and cone.

--Tom Tyson

[Pete B]

This was the second woofer that I've been referring to as #2 and it has the red service replacement tag, here's what I said about it:

"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. ... It is marked: 561 7838 and has an RDC of 2.37 ohms."

I'll try to post those pictures soon. I'm working on cleaning off the old rotted foam and glue from the frame and masonite, anyone have suggestions for a good way to do this? Any suggestions for a solvent?

Pete B.

[Pete B]

While the date code for this woofer indicates that it was manufactured in the 38th week of 1978 it does have a red tag and I wonder if the replacement woofers, or some of them, were rebuilt units.

Pete B.

[tysontom]

>This was the second woofer that I've been referring to as #2

>and it has the red service replacement tag, here's what I said

>about it:

>

>"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. ... It is marked: 561 7838

>and has an RDC of 2.37 ohms."

>

>I'll try to post those pictures soon. I'm working on cleaning

>off the old rotted foam and glue from the frame and masonite,

>anyone have suggestions for a good way to do this? Any

>suggestions for a solvent?

>

Pete,

It appears that the late-70s designation of the 200003/1210003 woofer (AR-9/AR-11B) you show is consistent the advent of the aluminum voice-coil former. The anodized-aluminum former was more robust (up to a point) and would likely dissipate heat better than the first versions. Ironically, the voice coil I showed with the flattened former was hit with peaks in excess of 1 kilowatts. That will usually do it, although the AR-10Pi/Neil Grover live-vs.-recorded drum demonstration by AR/C. Victor Campors in the mid-1970s used the ill-fated Dunlap-Clarke Dreadnaught 1000 amplifier driven to full power much of the time before failing completely. I don't believe that the woofers suffered any damage (I own one of the original pairs of 10Pis used in the demonstration, and it has all the original drivers according to the date codes), but there were some tweeters destroyed. So the woofers will definitely take a lot of peak power before damage.

One way to help in removing the glue on the woofer flange is to use denatured alcohol to soften the glue, and then carefully scrape away. It's slow, laborious work, but a clean surface is mandatory for good results.

--Tom Tyson

[r_laski]

>>It appears that the late-70s designation of the 200003/1210003 woofer (AR-9/AR-11B) you show is consistent the advent of the aluminum voice-coil former.<<

Tom, I believe you are right about when AR changed from Nomex to Aluminum voice coil formers. When AR changed the ADD line from what we on the forum have referred to as "A" model ADD speakers -- Brass logos, White/yellow fabric on tweeter, black screen on midrange... The 200003 woofer was the same as that used in the AR-3a and AR-LST -- Black flange, wide masonite ring, hex screws...

I have my Dad's AR-11 "A's" here with me. I just pryed up a small portion of one woofer dust cap (a replacement porous dustcap installed by a shop he had refoam the woofer for him, it isn't glued down very well) --

Nomex VC former, just like the AR-LST woofers I refoamed a few years back.

All the AR-11 "B", and AR-9 200003 woofers I've refoamed are the silver flange version -- all have Aluminum VC formers. Pretty good indication this is when the change from Nomex to Aluminum was made.

>>One way to help in removing the glue on the woofer flange is to use denatured alcohol to soften the glue, and then carefully scrape away.<<

Just to add my techniques --

I've used "Goof Off" and Isopropyl alcohol to loosen the glue. The alcohol works better than the Goof Off. I use Q-Tips saturated with alcohol to "scrape" the foam remnants away before going after the glue.

The best tools for scraping the glue from the masonite ring and the outer edge of the cone are razor type knifes -- X-acto, Stanley retractable blade knife, Box cutter/Wallpaper razor knife with break-off blades. Whatever type knife you use, use the BACK OF THE BLADE (not the sharp edge) to scrape. You will not cut the cone or damage the masonite when you use the back of the blade.

>> It's slow, laborious work, but a clean surface is mandatory for good results.<<

Absolutely.

Rich

[dynaco_dan]

>>>It appears that the late-70s designation of the

>200003/1210003 woofer (AR-9/AR-11B) you show is consistent the

>advent of the aluminum voice-coil former.<<

>

>Tom, I believe you are right about when AR changed from Nomex

>to Aluminum voice coil formers. When AR changed the ADD line

>from what we on the forum have referred to as "A" model ADD

>speakers -- Brass logos, White/yellow fabric on tweeter, black

>screen on midrange... The 200003 woofer was the same as that

>used in the AR-3a and AR-LST -- Black flange, wide masonite

>ring, hex screws...

>

>I have my Dad's AR-11 "A's" here with me. I just pryed up a

>small portion of one woofer dust cap (a replacement porous

>dustcap installed by a shop he had refoam the woofer for him,

>it isn't glued down very well) --

> Nomex VC former, just like the AR-LST woofers I refoamed a

>few years back.

>

>All the AR-11 "B", and AR-9 200003 woofers I've refoamed are

>the silver flange version -- all have Aluminum VC formers.

>Pretty good indication this is when the change from Nomex to

>Aluminum was made.

>

>>>One way to help in removing the glue on the woofer flange is

>to use denatured alcohol to soften the glue, and then

>carefully scrape away.<<

>

>Just to add my techniques --

> I've used "Goof Off" and Isopropyl alcohol to loosen the

>glue. The alcohol works better than the Goof Off. I use Q-Tips

>saturated with alcohol to "scrape" the foam remnants away

>before going after the glue.

>

>The best tools for scraping the glue from the masonite ring

>and the outer edge of the cone are razor type knifes --

>X-acto, Stanley retractable blade knife, Box cutter/Wallpaper

>razor knife with break-off blades. Whatever type knife you

>use, use the BACK OF THE BLADE (not the sharp edge) to scrape.

>You will not cut the cone or damage the masonite when you use

>the back of the blade.

>

>>> It's slow, laborious work, but a clean surface is mandatory

>for good results.<<

>

>Absolutely.

>

>Rich

Hi there

Another 2 1/2 cents worth from me now.

Have you tried, Acetone, which is similar to lacquer thinners, for softening the spider glue?

That is all I've ever seen used up here.

All safety procedures must be followed, read the safety haszard sheet, this stuff is not for inhaling.

I have seen a spider come off in about 30 seconds once the glue is dampened.

Just use a 1/2" wide paint brush to apply it.

Good luck.

[tysontom]

>>>It appears that the late-70s designation of the

>200003/1210003 woofer (AR-9/AR-11B) you show is consistent the

>advent of the aluminum voice-coil former.<<

>

>Tom, I believe you are right about when AR changed from Nomex

>to Aluminum voice coil formers. When AR changed the ADD line

>from what we on the forum have referred to as "A" model ADD

>speakers -- Brass logos, White/yellow fabric on tweeter, black

>screen on midrange... The 200003 woofer was the same as that

>used in the AR-3a and AR-LST -- Black flange, wide masonite

>ring, hex screws...

>

>I have my Dad's AR-11 "A's" here with me. I just pryed up a

>small portion of one woofer dust cap (a replacement porous

>dustcap installed by a shop he had refoam the woofer for him,

>it isn't glued down very well) --

> Nomex VC former, just like the AR-LST woofers I refoamed a

>few years back.

>

>All the AR-11 "B", and AR-9 200003 woofers I've refoamed are

>the silver flange version -- all have Aluminum VC formers.

>Pretty good indication this is when the change from Nomex to

>Aluminum was made.

>

>>>One way to help in removing the glue on the woofer flange is

>to use denatured alcohol to soften the glue, and then

>carefully scrape away.<<

>

>Just to add my techniques --

> I've used "Goof Off" and Isopropyl alcohol to loosen the

>glue. The alcohol works better than the Goof Off. I use Q-Tips

>saturated with alcohol to "scrape" the foam remnants away

>before going after the glue.

>

>The best tools for scraping the glue from the masonite ring

>and the outer edge of the cone are razor type knifes --

>X-acto, Stanley retractable blade knife, Box cutter/Wallpaper

>razor knife with break-off blades. Whatever type knife you

>use, use the BACK OF THE BLADE (not the sharp edge) to scrape.

>You will not cut the cone or damage the masonite when you use

>the back of the blade.

>

>>> It's slow, laborious work, but a clean surface is mandatory

>for good results.<<

>

>Absolutely.

>

>Rich

Rich,

Excellent message and great advice on the techniques for scraping the glue, etc. I think that "Goof Off" (what a ludicrous name) is xylene, but I'm not sure. It is good for removing label residue without damaging the surface. It all goes to demonstrate that the glue that AR used was not water-based, and some chemicals need to be used to improve the operation.

Thanks,

--Tom Tyson

[tysontom]

>Hi there

>

>Another 2 1/2 cents worth from me now.

>

>Have you tried, Acetone, which is similar to lacquer thinners,

>for softening the spider glue?

>

>That is all I've ever seen used up here.

>

>All safety procedures must be followed, read the safety

>haszard sheet, this stuff is not for inhaling.

>

>I have seen a spider come off in about 30 seconds once the

>glue is dampened.

>

>Just use a 1/2" wide paint brush to apply it.

>

>Good luck.

Vern,

I haven't tried acetone on the AR parts, but it's probably a great chemical to use. Ironically, I use acetone and lacquer thinner on a pretty regular basis on other projects, but I've never tried them on the AR speaker glues! I think I was surmising that acetone would damage urethane-foam materials; but after all, there is no surround to dissolve at this point! Both acetone and lacquer thinner are very volatile and flammable, so you have to be very careful with them.

Thanks for the suggestion!

--Tom Tyson

[dynaco_dan]

>>Hi there

>>

>>Another 2 1/2 cents worth from me now.

>>

>>Have you tried, Acetone, which is similar to lacquer

>thinners,

>>for softening the spider glue?

>>

>>That is all I've ever seen used up here.

>>

>>All safety procedures must be followed, read the safety

>>haszard sheet, this stuff is not for inhaling.

>>

>>I have seen a spider come off in about 30 seconds once the

>>glue is dampened.

>>

>>Just use a 1/2" wide paint brush to apply it.

>>

>>Good luck.

>

>Vern,

>

>I haven't tried acetone on the AR parts, but it's probably a

>great chemical to use. Ironically, I use acetone and lacquer

>thinner on a pretty regular basis on other projects, but I've

>never tried them on the AR speaker glues! I think I was

>surmising that acetone would damage urethane-foam materials;

>but after all, there is no surround to dissolve at this point!

> Both acetone and lacquer thinner are very volatile and

>flammable, so you have to be very careful with them.

>

>Thanks for the suggestion!

>

>--Tom Tyson

Hi again.

Lacquer thinner wasn't used, but Acetone is still being used here locally.

If I remember correctly, Acetone, is considerably more dangerous than Lacquer thinners.

Sorry, I didn't expand upon this more thoroughly, previously.

I must repeat that, "you should," "rather, "must read," the health haszard sheet on the internet.

Also read the containers caution label very carefully and abide by their recommendations.

Acetone is, as Tom points out, very flammable, but more importantly, it's not to be inhaled under any circumstances.

It has an effect on the lungs, and probably the brain as well. DUH.

It should be used either outdoors or in a well ventilated and exhausted cabinet or room.

As Tom mentions, use caution when contacting materials, if it should be something like a new surround, it will disolve it real quick, there is no time even for oops.

I have watched a local speaker repairman, from a distance mind you, use it for over 10 years.

Thanks again Tom for your feedback.

Good luck and do be careful.

[Pete B]

Thank you gentlemen for all the information. The common things that normally come to mind to remove glue are lighter fluid which is Naptha and WD-40 which has solvents and oil. Obviously work in a well ventilated area and follow the warnings if anyone tries these. I'd worry about these solvents getting into and damaging the masonite ring. Acetone probably works very well as it seems silicone sealers and glues have it. I cleaned the second woofer with Isopropyl alcohol and an old tooth brush which helped but still did not make it an easy job. I don't know what sealers are used on masonite and thought that alcohol would be safe then remembered that shellac based sealers have denatured alcohol as the solvent. The masonite looks fine in any case and probably uses a modern sealer.

It seems that both masonite rings are attached to the metal frame with clear silicone sealer/glue as it is a hard rubbery substance. The foam edge to masonite bond seems to be much more like rubber cement but of a thinner consistency, I don't know what type of glue this is. The foam edge to cone seems to be a PVA type glue.

I have a fresh bottle of the common black glue that's used for dust caps and so on and it appears to be silicone based and has an acetone smell. This seems to be what was used for the dust cap and lead in wires on the AR woofer. Theres a small amount of this black glue where the spider attaches to the voice coil, but where the spider broke away I see what looks like two part epoxy closer to the joint, which makes sense to me since a strong high temperature glue is needed here. The spider to masonite ring seems like a PVA glue. These are my observations and I welcome more input on the glue types.

Rich, did you notice if any of the woofers with aluminum voice coils were black anodized on the inside?

Pete B.

[Pete B]

Here are pictures of AR 200003 woofer, date code 561 7838 (RDC of 2.37 ohms) which was damaged by bottoming, and I believe the voice coil extended past the pole piece and over the top and stuck there. This caused part of the voice coil to bend in toward the pole piece. I've been referring to this as woofer #2 from an AR-11.

Assembly rear view:

http://members.aol.com/basconsultants/AR11WCRV.jpg

Voice coil rear view, note black anodizing, vent holes, black glue on spider, rear of dust cap can be seen, it is cloth with what seems like black silicone sealer coated on the back. the back of the former is mostly bent out toward the windings from bottoming, part bent in toward the pole piece and broke off when bent back out. The voice coil now fits perfectly into the magnet assembly, there is no binding at all:

http://members.aol.com/basconsultants/AR11WVCR.jpg

Voice coil side view, note that windings are in perfect condition, there are no shorts to the former. Note the bronze color on the top of the former, is this a treatment for better adhesion to the cone and spider?

http://members.aol.com/basconsultants/AR11WVCS.jpg

Spider separation from cone, glue near cone looks like epoxy, spider is porous:

http://members.aol.com/basconsultants/AR11WSPB.jpg

Cone front view:

http://members.aol.com/basconsultants/AR11WCFV.jpg

If this was a pro driver in heavy use I'd replace the voice coil, but I want to keep this driver as close to original as possible to maintain original performance and so that I can measure it. I'll probably run a thin bead of epoxy at the end where the former is folded up. I'd expect that the woofer will tolerate slight bottoming even in this condition, and if it bottoms hard and the coils come loose that would be a good time to replace the voice coil. Are people measuring the DC resistance of these drivers? It seems from the measurements on this site that 2.5 ohms was the typical average but this driver is lower was the lower value also common? Does anyone know the wire guage and number of turns? I suppose I could count them.

I notice that the pole piece is not extended past the top plate, this is often done to reduce inductance modulation, provide a fringe field that is more similar to the lower fringe field and to prevent the voice coil from going past the top.

Woofer #1 where the cone can be moved freely has some odd characteristics from my perspective. The spider is very loose, yet the cone moves slowly as if there's some resistance, it feels like air flow and I wonder if it's air leaking slowly through the spider which is porous. This would probably act as a combined compliance/resistance element but would be non-linear since the air volume is small. Vents in the woofer frame below the spider might eliminate this effect and improve the driver.

Pete B.

[r_laski]

>>Rich, did you notice if any of the woofers with aluminum voice coils were black anodized on the inside?<<

I've refoamed five (5) AR-11 "B" and twelve (12) AR-9 200003 woofers over the past few years. All with the silver flange.

I'm a "shimmer" when I refoam so I saw the inside of the voice coil on all of them when I removed the dust cap. The Aluminum VC formers on all the woofers were all silver, none were black anodized like the one in your pictures.

The same can be said for all the 10" woofers (pair of AR-90's) and 8" lower midranges (AR-90's and AR-9's)I've refoamed -- all silver Aluminum VC formers.

Rich

[dynaco_dan]

>>>Hi there

>>>

>>>Another 2 1/2 cents worth from me now.

>>>

>>>Have you tried, Acetone, which is similar to lacquer

>>thinners,

>>>for softening the spider glue?

>>>

>>>That is all I've ever seen used up here.

>>>

>>>All safety procedures must be followed, read the safety

>>>haszard sheet, this stuff is not for inhaling.

>>>

>>>I have seen a spider come off in about 30 seconds once the

>>>glue is dampened.

>>>

>>>Just use a 1/2" wide paint brush to apply it.

>>>

>>>Good luck.

>>

>>Vern,

>>

>>I haven't tried acetone on the AR parts, but it's probably a

>>great chemical to use. Ironically, I use acetone and

>lacquer

>>thinner on a pretty regular basis on other projects, but

>I've

>>never tried them on the AR speaker glues! I think I was

>>surmising that acetone would damage urethane-foam materials;

>>but after all, there is no surround to dissolve at this

>point!

>> Both acetone and lacquer thinner are very volatile and

>>flammable, so you have to be very careful with them.

>>

>>Thanks for the suggestion!

>>

>>--Tom Tyson

>

>

>Hi again.

>

>Lacquer thinner wasn't used, but Acetone is still being used

>here locally.

>

>If I remember correctly, Acetone, is considerably more

>dangerous than Lacquer thinners.

>

>Sorry, I didn't expand upon this more thoroughly, previously.

>

>I must repeat that, "you should," "rather, "must read," the

>health haszard sheet on the internet.

>

>Also read the containers caution label very carefully and

>abide by their recommendations.

>

>Acetone is, as Tom points out, very flammable, but more

>importantly, it's not to be inhaled under any circumstances.

>

>It has an effect on the lungs, and probably the brain as well.

>DUH.

>

>It should be used either outdoors or in a well ventilated and

>exhausted cabinet or room.

>

>As Tom mentions, use caution when contacting materials, if it

>should be something like a new surround, it will disolve it

>real quick, there is no time even for oops.

>

>I have watched a local speaker repairman, from a distance mind

>you, use it for over 10 years.

>

>Thanks again Tom for your feedback.

>

>Good luck and do be careful.

>

Hi again;

I always remember something else to rattle about after I've walked away from my computer. Duh.

I am sure most of you wouldn't use acid swabs or synthetic bristled brushes for the Acetone.

I believe that the acid swabs are synthetic material.

I, forgot to suggest a natural hair type paint brush, otherwise I think you would dip the brush into the can of Acetone, and find you wouldn't have any synthetic bristles left.

Reminds me of a time I was hunting and wanted to put gas from a non-funneled gas can into my gas tank.

I used a sterifoam cup.

Ok, only this one time.

Well, the cup did fill up once, just before the bottom and the rest of it disolved. Duh. Canadian genius at work here. NOT.

Live and learn.

[Pete B]

I quickly counted 55 (per layer) turns in the picture of the Nomex voice coil above, and 51 for the VC I'm dealing with here, I didn't double check these and I might be slightly off but here's the math using the total number of turns:

2.37 ohms * 110/102 = 2.56 ohms

The shorter coil gives the driver less ideally linear throw and slightly more before bottoming.

It seems that the windings are better packed in this driver than in the Nomex picture where fairly wide gaps can be seen in the windings, near the AR lettering in the picture for example. Tighter packing provide more wire length in the B field and therefore a higher Bl.

There's clearly an economic driver to not have to repeatedly replace drivers and I think the replacement units might have used a better voice coil.

Pete B.