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AR2a'x' Interesting upgrade story


Carlspeak

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I recently finished some restoration work on a pair of AR2a's the owner swears were upgraded by himself to an AR2ax. He purchased a kit from AR for the purpose of replacing the original pair of AR2a paper cone midranges that were mounted at an angle in a depressed, plastic cup.

The kit consisted of a phenolic ring tweeter and a new, thick MDF mounting board to cover the old hole. Below is a picture of one of the speakers.

Needless to say, I was a bit surprised a cone tweeter would/could be used as a midrange for this speaker. The back of the unit is marked with p/n 1200008-0 on a stick on lable as best I can tell. The magnet back plate is marked with 593TNJ. There is a second label that's red with the words: "service replacement unit ......"

A phenolic ring tweeter is available today from Parts Express. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=270-252. For some odd reason, the link isn't working. You'll have to look up the part number at the end of the link address to view the details of the tweeter PE offers.

There is a second one available that is 4 ohms at about 1/2 the price of the 8 ohm unit. PE touts it as a "faithful reproduction of the classic "phenolic ring" tweeter developed by CTS and used by Marantz, Altec, Acoustic Research and many others!".

Upon replacing the 4 & 6 uF caps and cleaning the pots, I decided to run some tests to see what the response would be like. Below are three shots of test results that told the story of just how this phenolic ring tweeter 'fits' into the acoustic realm of this AR2a.

The first test I ran was a basic one with the tweeter set at max and the phenolic ring 'mid' backed off a bit. At 1 meter on axis, the test result was quite a surprise with a very flat response from 60 hz (near field woofer) out to almost 17 kHz @ -3dB each end (also note the very good 45 deg. off-axis response - green trace).

I wondered, how could this be with two tweeters carrying the load above woofer cut off? I then ran three separate near field measurement tests of each driver. This test clearly shows how the phenolic ring tweeter (red curve) fits in. It starts to roll off at about 3 kHz, whereas the original dome tweeter starts rolling off at about 7 kHz. Also note how flat the response is of the phenolic ring tweeter - quite a performer indeed. I ran a 3rd test with just the woofer and phenolic ring tweeter (blue trace) and a 2nd one with just the woofer and dome tweeter (red trace). Here it becomes clear what the phenolic ring tweeter is doing to fill in the critical 2 to 10 kHz range the dome tweeter is no longer capable of handling. It's also quite evident by the blue trace in that last test that this speaker could easily funtion as a 2-way with just the woofer and phenolic ring tweeter.

It's also worth noting the 3 Holmimpulse tests are displayed with 1/6th octave smoothing.

I wonder how many AR2a owners out there have this "x" upgrade. Those that do now have an explanation of how a tweeter was used cleverly by AR in this application.

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AR-2 originally started out as a 2-way, and 2a seemed more like the 2 with a supertweeter added than a true design change to a 3-way. Even the 2ax kept a fairly high woofer/mid crossover frequency that seemed more like what you'd expect to see on a 2-way.

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I recently finished some restoration work on a pair of AR2a's the owner swears were upgraded by himself to an AR2ax. He purchased a kit from AR for the purpose of replacing the original pair of AR2a paper cone midranges that were mounted at an angle in a depressed, plastic cup.

The kit consisted of a phenolic ring tweeter and a new, thick MDF mounting board to cover the old hole. Below is a picture of one of the speakers.

There is a second one available that is 4 ohms at about 1/2 the price of the 8 ohm unit. PE touts it as a "faithful reproduction of the classic "phenolic ring" tweeter developed by CTS and used by Marantz, Altec, Acoustic Research and many others!".

Carl,

This is new and conflicting information. The AR-4, the original ("old") AR-2x and both the old and new 2ax used the 3 1/2" driver with the metal mesh and the fiberglass damping--never a CTS PR driver. That CTS driver was used by many manufacturers 'back in the day' as a good inexpensive tweeter, but was never shown in any AR lit or in any AR specs. Never.

It would be very interesting to find out from this gentleman when exactly he purchased this upgrade kit from AR, or was it from some AR 'field service center' or other source not truly associated with the 'real' AR?

If you look in the late-60's AR lit (when they were offering these upgrade kits) they quite clearly show the dual 5" angled mid/tweeters being replaced by the single 3 1/2" mesh/fiberglass unit--not a PR tweeter.

The PR unit may work very nicely, but I don't think it is a genuine AR part. Remember, AR continued to use the 3 1/2" mesh/fiberglass unit through 1975 (when the 2ax was phased out)--long past the mid-late-60's time frame when the 2-to-2x and 2a-to-2ax upgrades were being offered. There would be no reason at all for the CTS PR unit to ever have been used by AR, if you look at the timeline logically and accurately.

(Of course, I could be wrong......)

Steve F.

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The PR unit may work very nicely, but I don't think it is a genuine AR part. Remember, AR continued to use the 3 1/2" mesh/fiberglass unit through 1975 (when the 2ax was phased out)--long past the mid-late-60's time frame when the 2-to-2x and 2a-to-2ax upgrades were being offered. There would be no reason at all for the CTS PR unit to ever have been used by AR, if you look at the timeline logically and accurately.

(Of course, I could be wrong......)

Steve F.

I am inclined to agree with Steve. I have seen a number of these, and they have always been equipped with the typical metal grille-over-fiberglass covered 2ax midrange. They also ALL had a resistor in parallel with the mid to lower the dcr to that of the original dual/parallel mids (which was quite low, btw).

Roy

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What do the AR historians have to comment on the label and markings I described that were on the back of the replacement 'mid'?

That's a good question Carl...and I think I figured it out. The "TNJ" indicates the mid was made by Tonegen in Japan. Tonegen began supplying parts to AR sometime in the 80's. I'm willing to bet your replacements came from AB Tech, when that outfit was actually trying to properly duplicate replacement parts. AB Tech was considered the only "authorized" source of replacement parts when the AR we know and love was throwing in the towel.

That mid is definitely not an original 2ax driver, and all of the original mounting boards I have seen were painted black. The original AR factory 2a to 2ax conversion kit was offered in the 60's and into the 70's (the 2ax was introduced in the mid/late 60's). The kit is not listed in any AR parts list from at least 1977, on.

It is good to know, however, it seems to work well.

Roy

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That's a good question Carl...and I think I figured it out. The "TNJ" indicates the mid was made by Tonegen in Japan. Tonegen began supplying parts to AR sometime in the 80's. I'm willing to bet your replacements came from AB Tech, when that outfit was actually trying to properly duplicate replacement parts. AB Tech was considered the only "authorized" source of replacement parts when the AR we know and love was throwing in the towel.

That mid is definitely not an original 2ax driver, and all of the original mounting boards I have seen were painted black. The original AR factory 2a to 2ax conversion kit was offered in the 60's and into the 70's (the 2ax was introduced in the mid/late 60's). The kit is not listed in any AR parts list from at least 1977, on.

It is good to know, however, it seems to work well.

Roy

Hi Roy

I posted here a few photos of the AR-2AX 3 1/2" mid range driver mounted on the black painted adapter plate Aug 31st.

"AR 3 1/2" multipurpose driver".

They clearly show the homemade wire resistor which is mounted on two metal spacers to keep the wire clear of the cabinet.

I mentioned that I have seen, on more than one occasion, the same driver, less fiberglass, under the mesh.

It may have been on AR-4's or else I have some here in my rescue assortment of hifi goodies.

I have never peeled off any meshes yet to see what is actually under it for a driver.

There is some numbers visible in the photos.

I have never heard who made the 3 1/2" driver for AR, only the dual cone drivers.

The adapter board does not appear to be like any other I have seen anywhere.

Not a big issue but the chromed flat head machine screws were never used either, maybe subbed as a stop gap though.

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That's a good question Carl...and I think I figured it out. The "TNJ" indicates the mid was made by Tonegen in Japan. Tonegen began supplying parts to AR sometime in the 80's. I'm willing to bet your replacements came from AB Tech, when that outfit was actually trying to properly duplicate replacement parts. AB Tech was considered the only "authorized" source of replacement parts when the AR we know and love was throwing in the towel.

That mid is definitely not an original 2ax driver, and all of the original mounting boards I have seen were painted black. The original AR factory 2a to 2ax conversion kit was offered in the 60's and into the 70's (the 2ax was introduced in the mid/late 60's). The kit is not listed in any AR parts list from at least 1977, on.

It is good to know, however, it seems to work well.

Roy

My customer picked up his 2ax's today. He did find a record of a check to AR for $18 and change written in 1985 but it didn't show what the payment was for. [this could have been the kit because it consisted only of two pieces of MDF and two PR tweeters]. He also recalls what he thought was driving to Dedham or thereabouts to an AR service center to get the kit. Asked about AB tech services, he did not recall them at all.

Was ABT called something else in 1985 perhaps?

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  • 3 weeks later...

Carl:

Did you test the PE phenolic tweeters. I was wondering how they compared to the original AR 2a and 4x tweeters and the other replacements being offered. There seems to be a lot of interest in AR 4X tweeter replacements and yet confusion about the actual impendence of the originals. Why does PE push their 8 ohm version over their 4 ohm one as a replacement for the 4x if the actual impedance of the 4X tweeter was much lower than 8?

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Yes, I did buy a couple of the PE tweeters and tested one of them. Below is the result of an on axis test. As you can see, there is a formidable hump in the response just over 1 kHz. Otherwise, the response is nice and flat, just like the OP test. That hump wasn't evident with the tweeter I tested in the OP. The other solid line is 3rd harmonic distortion. It shows -40 dB in it's operating range. Not bad.

It took some doing, but I was able to empirically put together a crossover design which allowed me to couple it with an Advent Masonite ring woofer. At this point I haven't taken it any further but if motivated some day, will build a box that puts the PE tweeter 2.5 inchs behind the woofer so their acoustic centers line up for a nice time aligned design.

I don't know the answer to your last question. Perhaps they got mixed up with their claims? You can write to PE and ask them your question..... :-)

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Why does PE push their 8 ohm version over their 4 ohm one as a replacement for the 4x if the actual impedance of the 4X tweeter was much lower than 8?

pb8000,

You are confusing resistance (dcr) with impedance. The original 4x tweeter is considered to be an 8 ohm driver, with resistance of around 5 ohms. The "8 ohm" PE phenolic ring tweeter is stated to have an impedance of 8 ohms and resistance of 6.9 ohms. It is a slightly closer match to the original 4x tweeter than the 4 ohm version is. I have tried both versions in the 4x, and found they really are not a match to the original tweeter. Carl's measurements are consistent with my subjective impression...peaky midrange (and annoying, imo). The best feature of these replacement tweeters is that they fit the AR-4x cabinet and screw holes.

Roy

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pb8000,

You are confusing resistance (dcr) with impedance. The original 4x tweeter is considered to be an 8 ohm driver, with resistance of around 5 ohms. The "8 ohm" PE phenolic ring tweeter is stated to have an impedance of 8 ohms and resistance of 6.9 ohms. It is a slightly closer natch to the original 4x tweeter than the 4 ohm version is. I have tried both versions in the 4x, and found they really are not a match to the original tweeter. Carl's measurements are consistent with my subjective impression...peaky midrange (and annoying,, imo). The best feature of these replacement tweeters is that they fit the AR-4x cabinet and screw holes.

Roy

I'm sure that peaky response hump can be tamed in a 4x application as well. I just don't have a 4x in my possession to work on a xover mod that would accomplish that. Anybody care to loan me one? I'll glady do the work and publish here.

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I'm sure that peaky response hump can be tamed in a 4x application as well. I just don't have a 4x in my possession to work on a xover mod that would accomplish that. Anybody care to loan me one? I'll glady do the work and publish here.

IIRC, Zilch found this tweeter to be a very nice upgrade to the 4x

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-822

without significant crossover mods...just need to fab a mounting plate, and put a ring of felt around it....there's details in a thread over on audiokarma....

I'd love it if someone did a faithful reproduction (in response, not just appearance) of the Roy Allison designed tweet used on the 6,7,8,4xa,17,18,93,94 and others..

there's a 2" peerless fullranger over at parts-express that might be a nice replacement, too...

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I apologize for not introducing myself when I posted my question about AR 4x tweeters. I’ve been hanging around and reading here for a couple of years. This summer, the 40th anniversary of my AR5s which I purchased in 1971 while grad school, I decided it was time to restore my 5s. I followed the AR3a restoration guide using the AR5 recommendations in the many knowledgeable and helpful posts by Roy, Kent, Carl and others. I was so pleased with the results (hearing the 5s as I remember them and having them look like new with new linen grill cloth) I decided to get another set of ARs for my study. I bought AR 4xs which I should get soon. The seller says the tweeters are dead. Anticipating that I may have to replace them, I began to do research and found very little enthusiasm for the available AR 4x tweeter replacements. I was surprised because of the popularity of these particular speakers right now. Having played string bass in the orchestra in high school and having listened to mostly classical vinyl all these years, I know what I want to hear. So that is why I (and I am sure many others) wanted to know the impressions of the available tweeter replacements for the 4X.(both technical and subjective) of those of you whose know the ARs so well.

Or, if the available replacement tweeters are not satisfactory in sound, rather than change the speaker with new driver holes, I’m prepared to change the crossover to reduce the harshness of the newer tweeters. (Sorry that I confused impedance with resistance in my first post). Would you suggest changing the crossover or using something other than a cone tweeter?

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I believe the PE 8 ohm phenolic ring tweeter should work out fine and not require an adapter plate.

A 13 uF cap and parallel 0.3 mH coil should tame that 1100 hz hump.

I would give Carl's suggestion a try. The cost is low, it fits the hole, and it looks the part. Even if it only gets you into the ballpark, some minor tweaking may be all that is necessary. It would be nice to have a good recommendation. This issue is certain to come up more often in the future.

Roy

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I apologize for not introducing myself when I posted my question about AR 4x tweeters. I’ve been hanging around and reading here for a couple of years. This summer, the 40th anniversary of my AR5s which I purchased in 1971 while grad school, I decided it was time to restore my 5s. I followed the AR3a restoration guide using the AR5 recommendations in the many knowledgeable and helpful posts by Roy, Kent, Carl and others. I was so pleased with the results (hearing the 5s as I remember them and having them look like new with new linen grill cloth) I decided to get another set of ARs for my study. I bought AR 4xs which I should get soon. The seller says the tweeters are dead. Anticipating that I may have to replace them, I began to do research and found very little enthusiasm for the available AR 4x tweeter replacements. I was surprised because of the popularity of these particular speakers right now. Having played string bass in the orchestra in high school and having listened to mostly classical vinyl all these years, I know what I want to hear. So that is why I (and I am sure many others) wanted to know the impressions of the available tweeter replacements for the 4X.(both technical and subjective) of those of you whose know the ARs so well.

Or, if the available replacement tweeters are not satisfactory in sound, rather than change the speaker with new driver holes, I’m prepared to change the crossover to reduce the harshness of the newer tweeters. (Sorry that I confused impedance with resistance in my first post). Would you suggest changing the crossover or using something other than a cone tweeter?

Hi there

The AR-4X is a gem of a speaker that likely started more hifi interests than any other speaker in it's day.

I haven't heard any numbers that were manufactured during it's long and well reviewed history.

If you were happy with stock AR-4X's, then buy an original AR-4X used tweeter off ebuy or other.

Should run you less than $25.00 and is a direct fit.

I've heard nothing about deterioration of the tweeter.

Then the capacitor and pot is all you need to worry about, unless you need to refoam the woofers down the road.

It wasn't the perfect tweeter but it sure gave a lot of speakers a run for the money.

Of course if you want to experiment, good luck.

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If you were happy with stock AR-4X's, then buy an original AR-4X used tweeter off ebuy or other.

Should run you less than $25.00 and is a direct fit.

This is still a good option.

The glue around the edge of the cone is often deteriorating, but it is easy to fix with fresh glue. They have held up better than the old dome tweeters...no decomposing foam.

Roy

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This is still a good option.

The glue around the edge of the cone is often deteriorating, but it is easy to fix with fresh glue. They have held up better than the old dome tweeters...no decomposing foam.

Roy

Hi Roy

I bought two tweeters off ebuy and they arrived individually wrapped in bubblewrap.

When I let the first one unroll, the sticky surround glue stuck to the bubblewrap and pulled the cone out the frame.

OOPS!

The glue in the AR-4X and dual cone AR-2 series tweeters continue to have sticky surrounds and need to be untouched by anything.

If they are wrapped face to face with no spacers, they will destroy each other when separated, in my experience.

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  • 2 weeks later...

I believe the PE 8 ohm phenolic ring tweeter should work out fine and not require an adapter plate.

A 13 uF cap and parallel 0.3 mH coil should tame that 1100 hz hump.

I received the pair of AR4x and confirmed that the tweeters were dead as the owner had said. (The tweeters were not originals - they were phenolic ring cones - “made in USA- D3220" pulled from some other speaker with a 3uf capacitor added). I’m getting the PE 8 ohm phenolic ring tweeters tomorrow with the recommended coils and capacitors. Are you (Carl and Roy) saying that I should add to the stock crossover a 13uf capacitor in series after the pot and then the .3mh coil in parallel with the tweeter? Is that considered a second order high pass filter (12db/octave)? PB8000

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I received the pair of AR4x and confirmed that the tweeters were dead as the owner had said. (The tweeters were not originals - they were phenolic ring cones - made in USA- D3220" pulled from some other speaker with a 3uf capacitor added). Im getting the PE 8 ohm phenolic ring tweeters tomorrow with the recommended coils and capacitors. Are you (Carl and Roy) saying that I should add to the stock crossover a 13uf capacitor in series after the pot and then the .3mh coil in parallel with the tweeter? Is that considered a second order high pass filter (12db/octave)? PB8000

You can add the cap before the pot (as is done with most AR xovers) or after it. Parallel the coil to ground. Let us know how it sounds.

I'll be getting my hands on 2 pairs of 4x's to own next week and am anxious to do a number of experiments with them.

1) Confirm the 2nd order components I recommended do indeed integrate the PR tweeter well with the 4x woofer

2) Continue to experiment with stuffing materials to optimize LF performance

3) Try speakerdave's mod to independently confirm his work

Here's a link to a 'mod' thread done long after this one. The link provides detail on a series of PRT trials done on 4's. Sorry about this AR2ax thread getting hijacked into a 4x thread.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7561#entry95985

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You can add the cap before the pot (as is done with most AR xovers) or after it. Parallel the coil to ground. Let us know how it sounds.

I'll be getting my hands on 2 pairs of 4x's to own next week and am anxious to do a number of experiments with them.

1) Confirm the 2nd order components I recommended do indeed integrate the PR tweeter well with the 4x woofer

2) Continue to experiment with stuffing materials to optimize LF performance

3) Try speakerdave's mod to independently confirm his work

if you wanted, search audiokarma for some of Zilch's work with the 4x....might want to try/verify his work he did using this tweeter:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-822

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