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Replacement diaphragm for AR-3a tweeter?


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#1 tysontom

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Posted 23 July 2006 - 06:01 PM

>>Bob,
>
>What I thought was strange was the large empty space below the
>voice coil. It seems like that the voice coil should be 3 or 4
>times longer for that space. So I guess you are saying that
>space was filled with something ? The only foam I saw was the
>orange/brown dome shaped piece directly under the dome. It is
>very brittle now and already broke in half.
>

The voice-coil length is fairly critical to maintain the little tweeter's efficiency (what little it has to begin with). If the coil were longer, the sensitivity would be dramatically reduced (much in the same manner as the acoustic-suspension woofer is low in efficiency). The reality, though, is that the tweeter dome has very little travel, particularly considering the 5000 Hz crossover, so a long voice-coil overhang is unnecessary. The space *under* the dome -- where you found the crumbling foam piece -- is filled with the foam pad to dampen the dome. It has no role in the suspension. The three notches around the periphery of the dome are there to provide space for the poured-in urethane foam (in liquid form when poured in). Once cured, the foam is resilient to give the dome a "suspension" for its little travel. The thin, clear butyl-latex coating around the edge of the gap (and covering the foam pads) is there simply to protect the gap from dust and other foreign objects. Originally, AR tried the butyl-latex as a form of suspension, but it was too stiff. AR also tried a "soft" impregnated cloth dome during the development of the AR-3, but it had poor dispersion. Several years later Bill Hecht actually patented the soft-dome tweeter, a 2-inch model that was used by McIntosh and Fisher. Its performance was good, but significantly poorer than the 2-inch AR-3 dome.

>I have not destroyed the other tweeter but that one has a
>broken wire as well. You can press your finger on top of the
>dome and the whole assembly flexes in and out but the dome is
>solid. Is this what it is supposed to do ?

The flexing is normal: there should be a very slight amount of travel. The dome should be quite rigid to the touch, which is normal for that type of dome.

--Tom Tyson

#2 Guest_The Enlightened One_*

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Posted 22 July 2006 - 11:51 PM

Thanks! That kind of diaphragm in your pictures is what I am shooting for. I know its not the same but its in the ballpark. Looks like it would fit right over the current pole and could be glued in like the AR-11.

Here are pictures of what I have now:

The dome:

http://www.classicsp..._files/1426.jpg

The foam that was under the dome:

http://www.classicsp..._files/1427.jpg

The empty tweeter:

http://www.classicsp..._files/1428.jpg

The other tweeter:

http://www.classicsp..._files/1429.jpg


>I repaired one of the newer tweeters:
>
>http://www.classicsp...ing_type=search
>
>also note post #20 in that thread.
>
>Did you confirm that a former was not used in the early AR
>tweeter?
>
>It would help to determine the pole diameter, and top plate
>opening diameter. Are these the same in the newer AR-11
>tweeter and the older AR-3a?
>
>Pete B.
>

Attached Images

  • 1426.jpg
  • 1427.jpg
  • 1428.jpg
  • 1429.jpg


#3 dynaco_dan

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Posted 22 July 2006 - 09:42 PM

That diapragm is for another brand of driver.

The tweeter in it's normal operation would probably not travel 1/64" in it's suspension.

A previous visitor from Asia last year wrote that he was working on repairing/reworking/rebuilding AR tweeters.

Nothing more has come forward since then.

The tweeters are for all intent and purpose, un-repairable to the best members on this site.

Ebay is another option more readily available.

Good luck.
VERN

dynaco_dan2@yahoo.ca

#4 Pete B

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Posted 22 July 2006 - 09:18 PM

I repaired one of the newer tweeters:
http://www.classicsp...ing_type=search

also note post #20 in that thread.

Did you confirm that a former was not used in the early AR tweeter?

It would help to determine the pole diameter, and top plate opening diameter. Are these the same in the newer AR-11 tweeter and the older AR-3a?

Pete B.

>I am restoring a lucky find at a yard sale which is a pair of
>AR-3a speakers for $5 :-)
>
>The woofers needed refoamed which I have completed. Not a
>pleasant job but its done.
>
>Both tweeters appear to be dead which I didn't understand
>because they look fine. I tried puting live speaker wires
>directly on the leads where they were uncoated and nothing,
>but the signal bled back into the woofer lightly so I knew the
>connection back was fine. On further testing one of the leads
>broke off right at the glue point so I got mad and decided to
>just dismantle the tweeter to see how it works. I used 91 %
>alcohol to disolve the three glue spots and the dome started
>to free up. I ended up soaking the whole area around the dome
>and it finally came out but half the voice coil was stuck in
>the bottom of the magnet structure. I am thinking this might
>have been the reason for failure but not sure.
>
>After looking at the whole assembly it really is very simple
>and I starting to ask myself why can't I just buy a
>replacement dome diaphragm to repair it. The aftermarket
>tweeters and used ones on ebay are insanely priced so I want
>to try to fix this tweeter.
>
>Does anyone know of a replacement diaphragm that is close to
>the original that could be glued back in place?
>
>Thanks,
>Bob
>

#5 dynaco_dan

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Posted 22 July 2006 - 09:12 PM

Hi Tom;

Excellent information from you, as always, Tom, thank you.
VERN

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#6 Guest_The Enlightened One_*

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Posted 22 July 2006 - 08:22 PM

>Bob,
>
>The reason half of the voice coil was stuck in the bottom was
>that the dome was slanted during disassembly and the coil got
>hung up on the bottom of the gap as it was being removed.
>Incidentally, that is not glue in the gap, but poured-in
>urethane foam with liquid butyl rubber around the edge of the
>dome gap. The foam was probably beginning to crumble, and
>this allowed it to be removed fairly easily.
>
>The prospect of repairing an AR-3a or AR-5 ĺ-inch dome tweeter
>has been discussed before; it seems only logical that, since a
>woofer can be re-foamed, why canít a tiny AR tweeter be
>repaired as well? It is obviously possible to repair a dome
>tweeter, but it is completely improbable to repair an old AR
>dome tweeter to make it sound anything remotely like the
>original tweeter. Knowing the exact formula for the urethane
>foam, the butyl rubber and the proper voice-coil windings,
>foam-under-the-dome and other important details are only part
>of the picture: being able to test the tweeter properly for
>distortion, efficiency and frequency response is another part
>of the picture. If you think it would be easy to do if these
>variables could be addressed, then consider that for many
>years during quality-control inspections, AR rejected *more*
>tweeters than they shipped! There is really much more there
>than meets the eye. See Fig. 1.
>
....
>
>
>--Tom Tyson
>

Thanks for the info!

What I thought was strange was the large empty space below the voice coil. It seems like that the voice coil should be 3 or 4 times longer for that space. So I guess you are saying that space was filled with something ? The only foam I saw was the orange/brown dome shaped piece directly under the dome. It is very brittle now and already broke in half.

I have not destroyed the other tweeter but that one has a broken wire as well. You can press your finger on top of the dome and the whole assembly flexes in and out but the dome is solid. Is this what it is supposed to do ?

The unfortunate part in this is that I have never heard an AR-3a tweeter so if I were to repair it I would have no idea if I was close or not. I was thinking about trying this diaphragm from Partsexpress as an option

http://www.partsexpr...tnumber=270-056

Not even sure if it would fit or not.

#7 ninohernes

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Posted 22 July 2006 - 05:50 PM

(Quote Tom Tyson)
"It is obviously possible to repair a dome tweeter, but it is completely improbable to repair an old AR dome tweeter to make it sound anything remotely like the original tweeter. Knowing the exact formula for the urethane foam, the butyl rubber and the proper voice-coil windings, foam-under-the-dome and other important details are only part of the picture: being able to test the tweeter properly for distortion, efficiency and frequency response is another part of the picture."
(End Quote)


We need Mr. Villchur to give us the "secret tweeter recipe"!
Joe Nino-Hernes
Recording, Mastering and Live sound engineer
www.srctape.com

#8 tysontom

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Posted 22 July 2006 - 05:03 PM

>
>After looking at the whole assembly it really is very simple
>and I starting to ask myself why can't I just buy a
>replacement dome diaphragm to repair it. The aftermarket
>tweeters and used ones on ebay are insanely priced so I want
>to try to fix this tweeter.

Bob,

The reason half of the voice coil was stuck in the bottom was that the dome was slanted during disassembly and the coil got hung up on the bottom of the gap as it was being removed. Incidentally, that is not glue in the gap, but poured-in urethane foam with liquid butyl rubber around the edge of the dome gap. The foam was probably beginning to crumble, and this allowed it to be removed fairly easily.

The prospect of repairing an AR-3a or AR-5 ĺ-inch dome tweeter has been discussed before; it seems only logical that, since a woofer can be re-foamed, why canít a tiny AR tweeter be repaired as well? It is obviously possible to repair a dome tweeter, but it is completely improbable to repair an old AR dome tweeter to make it sound anything remotely like the original tweeter. Knowing the exact formula for the urethane foam, the butyl rubber and the proper voice-coil windings, foam-under-the-dome and other important details are only part of the picture: being able to test the tweeter properly for distortion, efficiency and frequency response is another part of the picture. If you think it would be easy to do if these variables could be addressed, then consider that for many years during quality-control inspections, AR rejected *more* tweeters than they shipped! There is really much more there than meets the eye. See Fig. 1.

http://www.classicsp..._files/1424.jpg
Containers of rejected tweeters at AR's Norwood speaker factory 1975



So what is the best solution? I believe that finding a used working tweeter on eBay or using one of the newer AR tweeters (similar to the old tweeter) would work well. ARís generic ĺ-inch soft-dome replacement tweeter is probably the best answer, but it isnít cheap; finding an AR-303 ĺ-inch tweeter probably is less expensive, and may work nearly as well. After discussing this with forum contributor mluong303, I tried a pair of AR-303 tweeters on a pair of AR-3as I was repairing, and the results were very good. See Fig. 2.

http://www.classicsp..._files/1425.jpg
Refurbished AR-3as with AR-303 (6-ohm) tweeter replacement. Not perfect, but a good-working combination.


--Tom Tyson

#9 dynaco_dan

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Posted 22 July 2006 - 02:24 AM

>I am restoring a lucky find at a yard sale which is a pair of
>AR-3a speakers for $5 :-)
>
>The woofers needed refoamed which I have completed. Not a
>pleasant job but its done.
>
>Both tweeters appear to be dead which I didn't understand
>because they look fine. I tried puting live speaker wires
>directly on the leads where they were uncoated and nothing,
>but the signal bled back into the woofer lightly so I knew the
>connection back was fine. On further testing one of the leads
>broke off right at the glue point so I got mad and decided to
>just dismantle the tweeter to see how it works. I used 91 %
>alcohol to disolve the three glue spots and the dome started
>to free up. I ended up soaking the whole area around the dome
>and it finally came out but half the voice coil was stuck in
>the bottom of the magnet structure. I am thinking this might
>have been the reason for failure but not sure.
>
>After looking at the whole assembly it really is very simple
>and I starting to ask myself why can't I just buy a
>replacement dome diaphragm to repair it. The aftermarket
>tweeters and used ones on ebay are insanely priced so I want
>to try to fix this tweeter.
>
>Does anyone know of a replacement diaphragm that is close to
>the original that could be glued back in place?
>
>Thanks,
>Bob


Hi Bob;

Please say that you paid $250.00 and not $5.00 for the pair, please.

It upsets our value system when someone lucks out soooo well. lol

The answer to your more technical quesion will bring forth some of the best advice available on the web.

Until then, I will answer a little bit.

The domes were proprietory to AR, custom wound with no bobbins.

There is no replacement domes/coils available at this time.

Unless the chap in Asia comes forth with his progress in re-furbishing them, there is no other source.

Ebay does usually have them on their system, but they are getting scarcer as time goes along.

Good luck.
VERN

dynaco_dan2@yahoo.ca

#10 Guest_The Enlightened One_*

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Posted 22 July 2006 - 01:44 AM

I am restoring a lucky find at a yard sale which is a pair of AR-3a speakers for $5 :-)

The woofers needed refoamed which I have completed. Not a pleasant job but its done.

Both tweeters appear to be dead which I didn't understand because they look fine. I tried puting live speaker wires directly on the leads where they were uncoated and nothing, but the signal bled back into the woofer lightly so I knew the connection back was fine. On further testing one of the leads broke off right at the glue point so I got mad and decided to just dismantle the tweeter to see how it works. I used 91 % alcohol to disolve the three glue spots and the dome started to free up. I ended up soaking the whole area around the dome and it finally came out but half the voice coil was stuck in the bottom of the magnet structure. I am thinking this might have been the reason for failure but not sure.

After looking at the whole assembly it really is very simple and I starting to ask myself why can't I just buy a replacement dome diaphragm to repair it. The aftermarket tweeters and used ones on ebay are insanely priced so I want to try to fix this tweeter.

Does anyone know of a replacement diaphragm that is close to the original that could be glued back in place?

Thanks,
Bob

#11 Pete B

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Posted 11 August 2006 - 11:11 PM

Several have noted that the foam under the dome crumbles with age, and it would be wise to replace it with wool felt. This is commonly used and works very well. We should note that AR used both wood and steel behind the dome in later versions. Felt absorbs the rear wave to some extent, hard surfaces reflect causing standing waves, but a short distance pushes these well above 20 kHz.

Do you have a picture of the voice coil, like to estimate the coil
height and see if it is formerless, because the AR-11 tweeter does have a former.

Pete B.




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