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AR3a tweeter pots. Are they still necessary?


Carlspeak

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I’m going to ‘stir up’ some old dust bunnies here related to AR3a tweeters and rheostats. However, I think it’s time we face the realization that vintage 3a tweeters have sonically become ‘tired’ and simply don’t put out the highs they used to.

It has become increasingly apparent to me the AR3a tweeter pot at this point in time is basically no longer a useful adjustment tool. The reason I suspect is because the 4 ohm vintage ¾ inch tweeter’s sensitivity has become diminished over time and thus that 1 ¾ ohms of adjustment cushion originally spec’d by AR’s engineers must now be used up just to keep the highs at a seemingly acceptable level.

This conclusion was arrived at following a number of recent crossover and pot upgrades I have done that were followed by SPL measurements. In virtually every case the tweeter pot had to be set to max increase in order to get the on-axis response curve beyond 5 kHz as flat as possible with the rest of it. Anything less in the setting created a significant fall off in tweeter response.

These circumstances caused me to go back and review the results of my AR3a pot setting survey (CSP 2/27/07). I got 5 responses involving 14 sets of speakers and every response came back “tweeter pot set at max”. I also went back and reviewed Ken Kantor’s tweeter study that led to the recommendation regarding ABT’s replacement tweeter fitted with a parallel wired 0.07 mH coil. The study clearly shows the modern ABT tweeter to be about 5 dB more efficient than what KK called the “AR3a new” tweeter. Interestingly, that ‘new’ tweeter could barely muster 90 dB output measured with a generous 2.83 V input signal at a meager distance of ½ meter. Doubling that distance to the standard 1 meter efficiency test distance would drop its measured efficiency another 6 dB; putting it below the efficiency of the woofer which generally runs about 88 dB or so in my tests. Ken’s study further shows that when he used a pot in a test circuit, it was always set a ‘max’. So, what purpose does the pot serve as far as having the option to adjust it is concerned? There’s nowhere to go but down!

On Plane (Jerry) claims he picks up about 1 dB with his oft recommended pot bypass scheme. He’s taken considerable flack for that but, he may have something there. Heck, if you going to run your tweeter pot a max anyway, what’s there to lose with a low cost bypass if you seek some more treble?

In another approach, someone took considerable time and effort to develope a rotary stepped attenuation switch loaded with resistors to replace old pots. Unfortunatly, this device may not see it's potential utility if it always set at max anyway.

Another alternative way to gain some additional high end output is a modern tweeter. ABT has been identified as having a drop in unit which sells for over $60 ea. I have identified a 1 inch 6 ohm Seas tweeter that has a 90 dB efficiency used in my Super-Mod kit. It’s not a drop in though. A simple adapter plate must be fabricated to adapt the Seas smaller OD to the large OD shelf it mounts into. However, the finished Super-Modded 3a does have plenty of rheostat adjustment room to spare. Of course, those will argue the off axis response won’t match the original 3a tweeter and that’s true. But, I don’t find that to be a serious hindrance vs the advantages gained.

I fully realize a new tweeter defeats the main objective of a true restoration project. In any case, we all must weigh the pros and cons with regard to good sound reproduction vs good looks and value.

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I’m going to ‘stir up’ some old dust bunnies here related to AR3a tweeters and rheostats. However, I think it’s time we face the realization that vintage 3a tweeters have sonically become ‘tired’ and simply don’t put out the highs they used to.

It has become increasingly apparent to me the AR3a tweeter pot at this point in time is basically no longer a useful adjustment tool. The reason I suspect is because the 4 ohm vintage ¾ inch tweeter’s sensitivity has become diminished over time and thus that 1 ¾ ohms of adjustment cushion originally spec’d by AR’s engineers must now be used up just to keep the highs at a seemingly acceptable level.

I fully realize a new tweeter defeats the main objective of a true restoration project. In any case, we all must weigh the pros and cons with regard to good sound reproduction vs good looks and value.

Having spent considerable time experimenting with the AB Tech (and other tweeters) in the 3a, I agree with Carl...

The old tweeter's day appears to be about over. That goes for the 8 ohm version in the AR-2ax and AR-5 as well.

The suspension is stiffening and the foam under the dome is mostly dust.

Roy

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I know NOTHING from a technical side re speaker design and all the impressive specs and testing that folks here mention. However, after Recapping my AR3A's a couple of weeks ago, I found that the if I put the mid or tweeter controls at max - where they were prior to recapping - there is too much Hi freq response IMHO. They are set now with both controls on both speakers at the 9 oclock position. The max position of both is close to 12 oclock so there is a good bit of high response still available.

This is based on music and test tone listening - I have no equipment that can test freq response per se. Of course, this is based on our personal taste/hearing so I can't claim this is in the least scientific. I have used music from CD and vinyl sources, from Classical to old 60's rock, to current pop. My wife thinks these 3as are magnificent with Miles Davis "Sketches of Spain. I can't deal with jazz but she's a real fan.

I'm not saying that the concern over degraded drivers is wrong. But I'm thinking that like any product, how the speakers were cared for probably has a lot to do with their condition. The worst thing for any device is to NOT be used. I would expect a speaker that just sat for years in somebody's attic/basement/wherever, to be in much poorer condition mechanically than a speaker that is regularly used.

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I know NOTHING from a technical side re speaker design and all the impressive specs and testing that folks here mention. However, after Recapping my AR3A's a couple of weeks ago, I found that the if I put the mid or tweeter controls at max - where they were prior to recapping - there is too much Hi freq response IMHO. They are set now with both controls on both speakers at the 9 oclock position. The max position of both is close to 12 oclock so there is a good bit of high response still available.

This is based on music and test tone listening - I have no equipment that can test freq response per se. Of course, this is based on our personal taste/hearing so I can't claim this is in the least scientific. I have used music from CD and vinyl sources, from Classical to old 60's rock, to current pop. My wife thinks these 3as are magnificent with Miles Davis "Sketches of Spain. I can't deal with jazz but she's a real fan.

I'm not saying that the concern over degraded drivers is wrong. But I'm thinking that like any product, how the speakers were cared for probably has a lot to do with their condition. The worst thing for any device is to NOT be used. I would expect a speaker that just sat for years in somebody's attic/basement/wherever, to be in much poorer condition mechanically than a speaker that is regularly used.

Some folks will have more luck than others with the old timers. Ken Kantor's test results, as well as the half dozen or so 4 and 8 ohm versions of this tweeter I have dissected, all point to variable performance at best, and marked degradation at worst.

The main problem is extension into lower frequencies as the suspension loses elasticity. The decomposed foam under the dome alone can alter damping, affect the voice coil gap, and generally alter the tweeter's response.

Attached are a couple of photos of one of the specimens I dissected. The foam suspension, as well as the foam under the dome, was literally dried up and crumbling. All of the tweeters I have dissected had the same foam issue under the dome, but some had better suspension foam due to the protection provided by the butyl rubber coating.

I have changed my position on the use of l-pads with these tweeters because the l-pads allow a bit more output, while still providing some adjustment options. Of course care must be taken not to overdrive these relics, and an l-pad could increase that risk somewhat at its "maximum" setting, when the system is driven at a high volume.

post-101150-1200633432.jpg post-101150-1200633465.jpg

Roy

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Roy, I agree with your comment regarding Mexicomikes experience. As they say in forum jargon, YMMV. Still, I'm pretty certain that by-and-large, most tweeters are not performing up to their original standards. :rolleyes:

I also dissected a 3a tweeter recently and found the same as you. Here's my picture.

post-100237-1200658220.jpg

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Roy, I agree with your comment regarding Mexicomikes experience. As they say in forum jargon, YMMV. Still, I'm pretty certain that by-and-large, most tweeters are not performing up to their original standards. :rolleyes:

I also dissected a 3a tweeter recently and found the same as you. Here's my picture.

Carl,

I've never seen an AR3 first hand, and given my part of the world seems to have been more enamored with JBL rather than AR, it's doubtful I ever will. Does your documented experience with deteriorating AR3 domed tweeters have any impact or bearing on the condition of tweeters in other AR speakers?

If I can find it, I'll dig out my pink/white noise generator this weekend set up my SPL/ spectrum analyzer and actually test my speakers response.

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Roy/Carl

Although we are very pleased with the sound of our 3as, it is entirely possible (likely) that they don't reach anywhere near their original top end - I can't hear beyond around 13-14khz now; when I was in my 20's I could hear dog whistles and other supposedly "ultrasonic" sounds. So although the 3as have plenty of treble to me, perhaps they don't and I don't miss it anyway.

I was under the impression (which could be wrong) that the foam was added by AR to reduce the treble response. If that's the case, wouldn't the deterioration of the foam tend to increase the treble?

Can the foam be replaced?

Can the tweeters be re-"suspended?"

Are those three dots of "glue" around the dome the "suspension?"

I saw that Vintage AR has a service - I think it was for midranges but maybe tweeters too - where they can be restored with a fairly high success rate.

Hey, maybe "normal" deterioration of the speaker AND the foam perfectly compensates for each other! (that is meant to be humorous!)

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Carl,

I've never seen an AR3 first hand, and given my part of the world seems to have been more enamored with JBL rather than AR, it's doubtful I ever will. Does your documented experience with deteriorating AR3 domed tweeters have any impact or bearing on the condition of tweeters in other AR speakers?

If I can find it, I'll dig out my pink/white noise generator this weekend set up my SPL/ spectrum analyzer and actually test my speakers response.

I'm am generally suspicious of any of these original, vintage mids and tweeters simply because these were the first of their ilk and getting them to work at the time probably was the top priority - not how long they will keep their original performance.

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I know NOTHING from a technical side re speaker design and all the impressive specs and testing that folks here mention. However, after Recapping my AR3A's a couple of weeks ago, I found that the if I put the mid or tweeter controls at max - where they were prior to recapping - there is too much Hi freq response IMHO. They are set now with both controls on both speakers at the 9 oclock position. The max position of both is close to 12 oclock so there is a good bit of high response still available.

Same here. Every couple of years I spritz a bit of contact lube into the pots of my 2ax's and exercise, then put on a record (the same record for the past 28 years, btw, a 1960's lp of Brandenburg Concerto #1) and play with the pots. Both pots have always ended up in the same place, at the "a" in "increase" (or about 10 o'clock, if you prefer). Both speakers are original (including original caps) except for replacement woofers installed in the mid 90's and new grille cloth put on a few months ago. Perhaps the fact that I'm the original owner and these speakers have spent their entire lives in the same environment I live in (I have a very narrow comfort range for temp and humidity) and have never been stored in somebody's garage or attic have something to do with it. Or perhaps over time my speakers and my ears have both lost high frequency response at the same rate. :rolleyes:

Last year my beloved AR amplifier was trashed by movers, and while I'm awaiting the restoration of a replacement unit we've been using my wife's old Sony stereo. During this time, I've found it necessary to back both pots down to 9 o'clock.

BTW, I auditioned 3a's and 5's back in 74 when I was speaker shopping, and I thought the 3a's sounded a bit short on mids and highs compared to their amazing bass when they were new, which is why I opted for 2ax's (I couldn't tell any difference at all between 2ax's and 5's except for their prices). I wonder if people are just overestimating how much of both the 3a had in the first place?

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These circumstances caused me to go back and review the results of my AR3a pot setting survey (CSP 2/27/07). I got 5 responses involving 14 sets of speakers and every response came back “tweeter pot set at max”.

Carl, I managed to dig out an old review article on my AR-2ax (from "High Fidelity" magazine). Their recommendation for tweeter and mid settings in 1972: tweeter on max, mid "just a touch" below max. I found these recommendations a bit excessive for my taste at the time, and still do today.

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BTW, I auditioned 3a's and 5's back in 74 when I was speaker shopping, and I thought the 3a's sounded a bit short on mids and highs compared to their amazing bass when they were new, which is why I opted for 2ax's (I couldn't tell any difference at all between 2ax's and 5's except for their prices). I wonder if people are just overestimating how much of both the 3a had in the first place?

Unfortunately nothing lasts forever. We start dying from the moment we are born. So do manufactured objects. Even diamonds, the hardest substance known will evaporate slowly although it may take eons under normal conditions to detect their changes. How quickly AR tweeters deteriorate depends like all things on the materials they were made from and the conditions they were in during their lifespan. Heat and moisture are usually enemies of manufactured articles, heat accelerating molecular motion and water playing many roles such as serving as a good environment for mold spores which exude corrosive enzymes to grow in. The only way to know the signifigance of the deterioration an AR tweeter has undergone and whether or not it is out of spec is to measure it and use the same performace criteria that were used to pass or reject them at the time of their manufacture. After 40 years given the limitations of the materials used, most existing today would probably fail inspection. With today's technology, it should not pose a real challenge to a world class speaker manufacturer such as Vifa or Peerless to reverse engineer this or any other driver and manufacture a very close duplicate, it's merely a matter of money. They could also improve the design and materials making tweeters achieve the initial design intent to an even greater degree with greater longevity. Again, it's just a matter of whether or not they see sufficient profit in it. Because they don't do this, it's clear they are not at all convinced. And this is not surprising since the philosophy of tweeter design goals today are different than those of AR's. So what can be done? For those units still operating, using a dedicated amplifier in conjunction with a 1/3 octave equalizer may be able to compensate for loss of sensitivity and changes in frequency response. Dispersion is probably almost exclusively a function of the geometry of the dome so if it is not damaged, it may be possible to restore the sound by these compensating measures. The real difficulty in finding a modern replacement tweeter is the dispersion. We've discussed this and it seems to me that there is no one driver today which comes even remotely close to an AR3a type in this regard currently being manufactured. There may be some tricks to improve what is available though. When the Snell Type AIIIi was introduced shortly after Peter Snell's death, I saw it at a trade show and asked the woman demonstrating it (I think it was his mother???) why there was a small piece of foam glued to the center of front of the tweeter's dome. She said it was to improve dispersion. Neat trick! Another trick might be to try an array akin to what I have suggested in the thread comparing the sound of AR3a to LST. It may boil down to whether it is restoration of the appearance you are looking for or the sound. Even Edgar Villchur probably would have agreed that there is usually more than one way to skin a cat.

BTW, I also thought the high frequency output of AR3 and AR3a sounded somewhat limited back when they were sold in stores and we have discussed this at length before. One of my theories is that it has to do with the way vinyl phonograph records were made often using Altec A-7s as studio monitors and equalizing the final mixdown signal to compensate for their inherent shrill high frequencies. CD's made using B&W 801s and 802s as monitors would probably fare much better on AR3/3a and generally sound shrill on lesser speakers which beam their hf output in a sharp focus. No tweeter or even a treble control to tame FR irregularities in those new high end sound systems either. Another is that dealers deliberately adjusted the tweeter and midrange levels to minimum because relations between many of them and AR were not good. Most dealer audio demo rooms I've been in also seem to me to be on the acoustically dead side. No problem today though, each speaker you hear seems brighter than the last, a real hook to sell to inexperienced listeners. Then they spend their lives looking for ways to mitigate it like special wires, vacuum tubes, vinyl records. That's today's market for you.

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BTW, I also thought the high frequency output of AR3 and AR3a sounded somewhat limited back when they were sold in stores and we have discussed this at length before. One of my theories is that it has to do with the way vinyl phonograph records were made often using Altec A-7s as studio monitors and equalizing the final mixdown signal to compensate for their inherent shrill high frequencies. CD's made using B&W 801s and 802s as monitors would probably fare much better on AR3/3a and generally sound shrill on lesser speakers which beam their hf output in a sharp focus. No tweeter or even a treble control to tame FR irregularities in those new high end sound systems either. Another is that dealers deliberately adjusted the tweeter and midrange levels to minimum because relations between many of them and AR were not good. Most dealer audio demo rooms I've been in also seem to me to be on the acoustically dead side. No problem today though, each speaker you hear seems brighter than the last, a real hook to sell to inexperienced listeners. Then they spend their lives looking for ways to mitigate it like special wires, vacuum tubes, vinyl records. That's today's market for you.

I'm a bit skeptical of that theory, because my impression of limited mids and highs was ONLY about the 3a. The 5 and 2ax (which I eventually selected) sound just fine to me. I've never been one of those "no tone control" high-end listeners. My tone settings are probably flat 90% of the time, but that remaining 10% just irritates me too much to not have the ability to do anything about it.

I think my dealer must have gotten along better with AR, He had just about every bookshelf speaker in the AR and KLH lines set up for demo (as I recall, he was still nagging AR for his LSTs at the time and said he didn't have space for KLH Nines), and once we had narrowed my interest down to 3a, 5 and 2ax he swtiched them back and forth between several different amps and even allowed me to fiddle with the speaker pots so I could hear what their adjustment ranges were. Of course, the fact that I walked in and told him I was shopping for a pair of speakers, an amp AND a R-R tape deck that took 10" reels may have had something to do with that. :rolleyes:

I have looked several times at the "AR3a Super Mod Kit" that Carl has on his website. Given my original opinion of the 3a's low-mid-high balance and the fact that the original drivers have transmuted into unobtainium anyway, if I ever found myself in possession of a pair of 3a's whose drivers needed replacing I would definitely be interested.

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You're all going to love this:

http://www.classicspeakerpages.net/library...vel_contro.html

Basically, what Villchur is saying is that setting mid and tweeter levels to full is "flat," turning them down below full suppresses mids and highs, and this is necessary because everyone in the world, from recording engineers to amplifier designers, have their settings too bright to compensate for the high frequency shortcomings of everyone else's speakers.

So AR speakers have no settings that "boost" mid or treble; "full" is what you use with an amp and recordings that don't have "excessive" highs, but most everything you're going to listen to does have excessive highs. The dot in the center is just AR's estimation of how excessive the rest of the world has their mids and highs set.

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Roy/Carl

I was under the impression (which could be wrong) that the foam was added by AR to reduce the treble response. If that's the case, wouldn't the deterioration of the foam tend to increase the treble?

Can the foam be replaced?

Can the tweeters be re-"suspended?"

Are those three dots of "glue" around the dome the "suspension?"

I saw that Vintage AR has a service - I think it was for midranges but maybe tweeters too - where they can be restored with a fairly high success rate.

Larry (Vintage AR) has been attempting midrange voice coil repairs with some success, but the tweeters are a completely different animal. The 3 blobs of orange material (4 for the AR-3 tweeter) are the suspension, and consist of urethane foam. Tom Tyson has described the manufacturing process of the old tweeters a number of times here, and the bottom line is that repairs are virtually impossible. A replacement tweeter is the only viable solution. Although the AR-3 orange dome tweeter has the same type of foam suspension, it has fiberglass under the dome. Additionally, later AR tweeters that do not use foam for suspensions have more conventional construction, and are more repairable.

As I mentioned above, the limited excursion will have an effect on lower frequencies as well. It will manifest itself most noticably as less midrange clarity, and a more "tubby" quality on vocals. The level control may still be required to tame some upper response irregularities (which will also be influenced by the foam's condition under the dome), but will not be of assistance to the compromised mid/upper mid frequencies.

Roy

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You're all going to love this:

http://www.classicspeakerpages.net/library...vel_contro.html

Basically, what Villchur is saying is that setting mid and tweeter levels to full is "flat," turning them down below full suppresses mids and highs, and this is necessary because everyone in the world, from recording engineers to amplifier designers, have their settings too bright to compensate for the high frequency shortcomings of everyone else's speakers.

So AR speakers have no settings that "boost" mid or treble; "full" is what you use with an amp and recordings that don't have "excessive" highs, but most everything you're going to listen to does have excessive highs. The dot in the center is just AR's estimation of how excessive the rest of the world has their mids and highs set.

Makes sense to me and explains why I turned them down then and still turn them down now! Per the letter, Mr. V is even suggesting the amp's treble control be advanced a bit to produce truly flat response. Re "flat" response...In the mid 80's I bought a DBX 20/20 equalizer. It could adjust the response automatically to "flat" anywhere in the room using a supplied mic. I did this using my Nestorovic 5as speakers (ex wife owns them now). The "Flat" response, which required considerable treble boost to achieve at the listening position, would make your ears BLEED with ANY pop recording. It was literally painful. I found that I didn't much care for "flat" response at the listening position! :rolleyes:

I realized later that all this is artificial anyway. Diminution of the high freqs is occurring the instant the sound wave leaves the instrument/device/whatever that is producing it. So by the time it gets to your ear - unless your ear is only a few inches away - it has much less high freq energy than it did. It seems to me that EVERYTHING has a high freq loss and the amount depends on how far away you are. SO who knows how the heck something "should" sound?

In the last hour or so I've been listening to various selections with the AR3a tweeter/mids on max again just to see...It's too much treble for me on just about anything.

I can confuse myself so thoroughly with all this that I should probably sell all the stereo stuff and stick with the Ipod and earbuds! :)

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On Plane (Jerry) claims he picks up about 1 dB with his oft recommended pot bypass scheme. He’s taken considerable flack for that but, he may have something there. Heck, if you going to run your tweeter pot a max anyway, what’s there to lose with a low cost bypass if you seek some more treble?

Right you are, Carl, on the tweeter pot! By-pass it completely.

There is so little music in those higher frequencies and most of us old f**ts can't hear it anyhow. If you've never done the toilet paper tweeter test (TPTT) on your 3-ways (AR-3, AR-3a, AR-2ax, AR-5, etc), you are in for a treat.

Put on your favorite music and get a roll of tp. Now, place one end of the open core over the tweeter (center the tweeter as best you can). Then put your ear up to the other end. (The soft fibers of the tp will help absorb some of the unwanted frequencies.)

What you hear is the tweeter and it's simply amazing how little sound it actually produces!

Then move the core to the mid-driver and it's just about overwhelming how much sound it produces.

Naturally, it's not as simple as that. Both drivers should be capable of putting out equal level of spl. It's just that the distribution of frequencies in music greatly favors mid-range over tweeters.

Anyhow, getting back to Carl's issue, I totally by-passed the tweeter pots. This should give us a small gain in tweeter output (.5 to 1.0 db).

Even with this small gain, my AR3a's tweeters are woefully inadequate when compared to my TSW-610's (Teledyne era AR's). Further, the TSW's cross at the same frequencies as the AR-3a's.

Mid-pots are a totally different story. Initially I by-passed them as well only to discover that in so doing we "give back" that slight tweeter gain. Here I recommend soldering the pots to max and leaving the 16 ohms in parallel with the mid drivers.

Regards,

Jerry

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