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Anatomy of a 200029-1 Tweeter


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Hello, I've decided that I want to learn how to refresh the ferrofluid in my 200029-1 tweeters.  I've read that they are not serviceable, but I went ahead and removed one of mine from an AR-91 yesterday and after I found an allen wrench to fit the small screw, one thing led to another.  I learned a lot, but have probably botched the coil.  I know what I did wrong in the process and I think these can be successfully operated on if you carefully take the right steps.  Below are some pictures of what mine look like.  The magnet construction is interesting in that there are three prism shaped reliefs machined in the outer diameter.  There's a wooden button glued on the top of the pole that looks like the same pieces used on furniture to cover screw holes.  I assume this just keeps the dome from being pushed in too far.  I haven't been able to find a post or video for repairing these, let me know if I missed something.  So, I'd like to develop and publish here a process to disassemble and repair these, but I need another donor part.  Does anyone have a dead or dull tweeter that they'd be willing to part with?  I'm not looking for freebies, I will pay for shipping and the tweeter.  Please let me know if you can help, thanks! 





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Can't help you with a spare cadaver, but you may want to look at the Drawing section of the Library for additional info. There is a full drawing with notes for the 029 tweeter, as well as better copy of the 043 tweeter, which appears to be fully identical but was re-numbered for the AR-58s speaker model. These drawings prescribe the amount of ferrofluid used - item #6 on the enlargement shows the fluid location. There is also a drawing for the magnet structure you have shown in pics. I hope you are able to get it back together and functioning again.


200029.1 magnet.jpg

200043 blow-up.jpg

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FWIW, I have experienced limitations with accessing this material, too. I use a "dated" Mac computer and typically use the Safari web browser, but with successive Safari updates I found I could no longer view this section of the Library - - it seems to be available to me only by using the Google Chrome browser.

I'll see if I can provide you with a bit more info. 

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Here are the drawing notes and parts for the 029 tweeter. Apologies for image quality, but I minimized the file size for easy display here. Better to view the high-res Library drawing, but it's over 12MB in tiff format.

The fluid is noted as "FERROFLUID, 1000 CPS, 100g." and the quantity required is .03 cc.

200029 notes.jpg

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Probably because I'm not using a PC, but I've never even heard of that browser. When you go through the drawings, it's a little bit of a slog because the labeling is not always terribly descriptive, but if you have a good lead and a little patience, the cache of AR drawings can be a trove of helpful or interesting information.

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Certainly. I plan to do a thorough how-to, but will get some photos up in the meantime.  There isn't any glue, but a double sided tape that appears to be mostly adhesive.  I'd say it's similar to a double sided masking tape, but it's quite gummy, not much paper content.


Here's the underside of the dome with the double sticky tapes still attached.  There's a gap in the tape where it was damaged during removal.  You need to be careful when lifting off the tweeter dome to not tear the tape. My preference, I believe, is to leave the tape attached to the magnet and carefully lift the edge of the dome, working around the edge evenly to avoid lifting the coil at an angle.



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I reported on the AR-11  200011-1 tweeter here, they look very similar.  Unfortunately the 

pics are dead links in my thread.  I had another thread where I repaired the other tweeter

but that seems to be gone:



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On 4/29/2018 at 10:34 AM, seventy1 said:

The magnet construction is interesting in that there are three prism shaped reliefs machined in the outer diameter.

The thread mentioned by Pete above notes that these top plates were leftovers from the assembly of AR-3a tweeters, and the V-notches were where the foam suspension blobs were poured. 

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Great assembly drawings ra.ra thanks for posting, I should go look in the library.

seventy1 is that lead in wire to the dome solid or tinsel type, looks solid in that picture?

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Just one more shout-out for the AR drawings section in the Library. As previously stated, first you have to dig a bit just to find the archive, and then they are not always immediately identifiable by their reference labels - - you really do need to poke around a bit just to get a flavor of what types of information exist there. I really like the drawings which show how all the various parts are called out and how they fit together; or to reference the dates and changes made during production; or to understand the methods or sequence of assembly. This stash of drawings, however, also has a great deal of information about performance specs (with response curves!) and measurement testing conditions for individual drivers, and is a great resource for those members who have extensive knowledge or interest in the technical aspects of loudspeaker design.  

(Edit: by the way, it was Tom Tyson who explained the origins of those v-notches.)

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2 hours ago, Pete B said:

seventy1 is that lead in wire to the dome solid or tinsel type, looks solid in that picture?

The lead wires are continuous pieces from the coil winding and appear to be solid enameled copper.  Thin as a hair and so far, impossible to solder to itself.  I broke one and have been trying to solder it back together.

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The solid wire is part of the problem, they will break if driven very hard.

I soldered to it, and attached a flex lead.  You have to remove the enamel, don't 

remember how I did it,  600 grit paper?  Nail file?  Exacto blade edge?

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  • 4 weeks later...

I'm coming back to this thread because I wanted to write up what I’ve learned, thank ra.ra for pointing out the exceptional AR print resource on CSP and to also thank india42 at AK for donating some tweeter parts that were very helpful from an educational standpoint.  What I learned was that these tweeters can be serviced without too much difficulty and that it can really make a difference. 

1)      After removing the tweeter, mark the magnet next to the positive terminal, the one with the label and red dot.


2)      Carefully de-solder the fine wire leads from each terminal.  Use as little heat as possible so you don’t burn through the hair-fine wire or melt the faceplate where the terminal is fixed.

a.       Note – the wires are so thin and fragile that I wear jeweler’s glasses to see them.  I also use a toothpick to move the wire since metal tweezers are hard to control next to the magnet.


3)      Heat the area where the faceplate is melted over the lead wire and carefully pick the wire to free it from the faceplate.  One of mine ran under the part number sticker.


4)      After both leads are free, you can remove the allen head screws holding the faceplate to the magnet.  I believe it’s a 5/64” wrench, but I may have mixed my standard and metric wrenches – whatever fits tightest.  The screws take a bit of torque to break loose.


5)      Then carefully lift off the faceplate making sure that the plastic gasket stays down on the magnet and hat the lead wires are free from the face plate.


6)      Raise the lead wires over the dome then remove the plastic gasket.


7)      Next, I used a silver Sharpie to trace around the membrane surround, marking the surround and the magnet surface.  Then use another thin line Sharpie to mark the rotational orientation.


8)      This is the tough part, the surround glued to a paper gasket that is adhered to the magnet.  I used a razor blade under the paper to gradually cut it away from the magnet.  Work slowly and  evenly around the surround.  Don’t use too much force or you may push through and damage the voice coil.


9)      I used a pinched piece of masking tape stuck to the dome to make a handle.  Lift the dome and coil out of the magnet.  Wipe the old ferrofluid off of the outside and inside of the VC with swabs dipped in rubbing alcohol.  I found a piece of old glue in the VC ID that could have been trapped between the pole and VC - not good.  I picked it out with tweezers.



10)   Clean the old ferrofluid out of the magnet gap with pieces of card stock.  I also dipped some of the paper strips in alcohol to help clean hardened FF.  Keep wiping until you’re just getting light smudges on the paper.



11)   The paper gasket, which stays adhered to the removed surround, had dry adhesive, so I applied a thin layer of rubber cement to the magnet.

12)   I bought ferrofluid from PE and put it into the smallest diabetic syringe I could find.  The AR print calls for .03 cc between the VC and magnet pole.  This is such a small amount, just 3 graduations on the syringe, that I decided to just apply it to the VC surface before placing it in the magnet.


13)   I connected the VC leads to alligator clips and played a 5 kHz tone while lowering the VC into the magnet.  Carefully align the surround to the marks you made before pressing the surround into the adhesive.  The tweeter should be playing the tone if all is well.


14)   Raise the leads, install the plastic gasket, then lower the leads and flatten on the gasket.  Align everything then place the faceplate on the magnet keeping an eye on polarity. Loosely install the screws.


15)   Turn over the tweeter and carefully solder the lead wires to the base of the terminals.  Once you’re happy with the lead wire routing, tighten the screws to medium snug.  I used a dab of rubber cement to stake the lead wires to the faceplate instead of melting the faceplate over them as manufactured.


16)   Reinstall to your cabinets and enjoy.

I have more parts and labor into my AR91s than any other speaker I’ve owned.  I replaced the surrounds on both woofers, then had to completely re-cone one due to an impacted/dragging voice coil.  I restored a sagging spider in the other woofer and have replaced all of the crossover caps.  But they still sounded like they were playing from under a blanket. The difference after ferrofluid replacement was night and day.  They were dull, tubby and really unlistenable before and now they’re clear and detailed.  I’m debating whether to dive into the midrange drivers next...  

Edited by seventy1
Hopefully fixed the photo links
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Sorry about the photo links.  I think I fixed it, but let me know if you still don't see them and I'll upload directly.  I got the recone kit from The Speaker Exchange an was very happy with the parts and support.  Although not an exact replica, the cone was similarly weighted on the backside.  The voice coil was on wrapped phenolic vs. the original vented aluminum cylinder.  Everything went together smoothly and no complaints on the performance.  I repaired my "sagging" spider with a trick found in googling for a fix other than a complete recone.  Here's what I wrote in another post:

I've had some success fixing this by spraying down the spider with a rubbing alcohol and water mix, heavier on isopropyl, then fixing the cone in a position where the spider is flat.  You can place spacers like small pieces of wood, Popsicle sticks cut to length would work, braced between the underside of the cone and basket.  Then dry the spider with a heat gun or hair dryer.  You may want to position the spider over it's neutral position.  

Before disassembly, my woofer appeared to have a "sagging spider", which I expected to be more compliant with a loss of stiffness from age.  But what I found was that it still had its stiffness or spring, but it wouldn't stay in the neutral position.  It either wanted to spring up or down, and was stretched into a concave or convex shape.  This is obviously not good for a driver.  Instead of behaving like a spring that wants to hold the cone in a neutral position with a centering force that builds with travel, a stretched spider can act like an over-center spring that has two neutral positions. After the spray/dry process described above, I was able to get it to take a different shape.  I then did the same to an assembled AR 12"and was able to flatten the spider.  No telling if this is a permanent fix, but appears to help.   

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1 hour ago, seventy1 said:

Sorry about the photo links.  I think I fixed it

Last night only some of the images appeared, but today they are all visible. Really good visual material and accompanying descriptive text. I feel like a medical student watching a delicate surgery demonstration under the Ether Dome at Mass General Hospital.

When you replaced the VC with the attached dome and paper gasket, did the dried adhesive interact with the rubber cement to provide suitable adhesion?

This is an excellent thread and tutorial, thanks for sharing. With a smidgen of courage and some deft dexterity, perhaps this will encourage others to rejuvenate some of their aging tweeters. 

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21 minutes ago, ra.ra said:

 I feel like a medical student watching a delicate surgery demonstration under the Ether Dome at Mass General Hospital.

Ha, I had to be sure to limit the coffee intake to steady my hands.  I do think the jeweler's visor is a must, at least for an old guy like me.

When you replaced the VC with the attached dome and paper gasket, did the dried adhesive interact with the rubber cement to provide suitable adhesion?

Yes, it did.  But you really just need enough tackiness to hold things in place before the faceplate clamps it all together. If I do another, I'll find a way to dilute the cement and apply it with a small brush for a smoother more uniform coating.  Or use a different lower viscosity adhesive.


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