Guest Bret Posted May 21, 2005 Report Share Posted May 21, 2005 I wish you'd repost that photo here, Roy, so that people who were avoiding the other thread can see it.Did you give us all the information you had on that tweeter? What I'm asking is, "do you know how it was stored?" Or "where did it come from?" or anything along those lines.And another thing. . . you have this one apart. Were you the one who brought this up a long time ago? When you took it apart did you have any hope of putting it back together? Did you? Did it work?If this is happening to all our drivers, do you see anything to do but abandon our loved relics?As you said, this is something to worry about.Bret Link to comment Share on other sites More sharing options...
RoyC Posted May 22, 2005 Report Share Posted May 22, 2005 Hey Bret,That was a distorted sounding tweeter that I acquired about a year ago and dissected a couple of weeks ago. I previously had a 1970 speciman in which the foam under the dome was almost dust, but I didn't remember to take a picture before ditching it. I imagine the stuff could get into the voice coil gap. It might explain why there seems to be a noticable difference in performance between some of the many tweeters of this type that I've used. I'm not aware of any way to fix these babies.The good news is that if it is a problem, it is probably confined to the AR-3a/2ax/5 using this type of tweeter. I have no idea what is under the domes of the earlier red dome tweeters used in the AR-3 era however. Maybe Tom T. can offer some insight.The second photo is of a 1976 AR-12 (8 ohm version of the AR11/AR10pi tweeter). The material under the dome is not foam but a felt pad with no signs of deterioration, and is glued in place.Roy Link to comment Share on other sites More sharing options...
Rlowe Posted May 22, 2005 Report Share Posted May 22, 2005 Roy,The attached shows a "boken" tweeter from an AR90 manufactured in 1991 from AB Tech I assume.1200084AB - 9195HIt doesn't appear to have any "padding/foam". I thought I'd post this pic for interest sake.It went to sleep. Link to comment Share on other sites More sharing options...
tysontom Posted May 23, 2005 Report Share Posted May 23, 2005 >Roy,>>The attached shows a "boken" tweeter from an AR90 manufactured>in 1991 from AB Tech I assume.>>1200084AB - 9195H>It doesn't appear to have any "padding/foam". >>I thought I'd post this pic for interest sake.>>It went to sleep.>>Great image. This tweeter doesn't have any padding because the pole piece has a raised section to prevent the "poking-finger" syndrome -- the foam under the dome was the original means of this, along with damping. Since that tweeter is the AR-90 version, it would have ferrofluid damping, another reason for not needing anything under the dome. Note the "vestigial" top-plate slots, used originally in the AR-3a-type tweeter for the urethane-foam suspension. The top plates were probably common to all the 3/4-inch tweeters, regardless of diaphram material.--Tom Tyson Link to comment Share on other sites More sharing options...
tysontom Posted May 23, 2005 Report Share Posted May 23, 2005 >Hey Bret,>That was a distorted sounding tweeter that I acquired about a>year ago and dissected a couple of weeks ago. I previously had>a 1970 speciman in which the foam under the dome was almost>dust, but I didn't remember to take a picture before ditching>it. I imagine the stuff could get into the voice coil gap. It>might explain why there seems to be a noticable difference in>performance between some of the many tweeters of this type>that I've used. I'm not aware of any way to fix these babies.>>The good news is that if it is a problem, it is probably>confined to the AR-3a/2ax/5 using this type of tweeter. I have>no idea what is under the domes of the earlier red dome>tweeters used in the AR-3 era however. >Maybe Tom T. can offer some insight.>>The second photo is of a 1976 AR-12 (8 ohm version of the>AR11/AR10pi tweeter). The material under the dome is not foam>but a felt pad with no signs of deterioration, and is glued in>place.>>Roy>Roy, that first image is obviously the AR-3a-style hard-dome tweeter, judging by the foam suspension. Under that dome was a small pillow of urethane foam, same material basically used in the surrounds and so forth. Once deteriorated, the foam probably causes serious problems in frequency response and as you indicated, could get down into the gap causing further problems. That deterioration is probably endemic to most of those tweeters, sadly, but you never know until one is dissected. Incidentally, the best way to dissect is to cut down around the suspension and lift the entire voice coil and diaphram together. This way you can see what is going on with the coil itself. I think that the foam pad was not used after the hard-dome AR-3a tweeter; after that, AR used a felt pad -- similar to the business-end of a pool stick -- under some of the tweeters.The 1-3/8-inch AR-3 tweeter used a small hemipherical section of glass fiber under the dome, same as the material that is on the outside of the AR-3 and AR-3a midrange domes. Incidentally, the reason for the fiberglass on the outside of the dome under the protective grill was to apply an equal pressure against the dome to counteract the pressure under the dome. This material under the dome helped to further damp the already magnetically overdamped phenolic diaphram. If you look at the tone-burst photographs of the 1-3/8-inch tweeter, you can tell why it is so good. You cannot detect ringing at any frequency, under any circumstance. The overall response is also nearly ruler-flat in its operating band, another good indication of proper transient performance. This fiberglas under the dome should never change, and thus the tweeters would not be affected by this material. On the other hand, the suspension was urethane foam, and this did begin to deteriorate as time went on, and the suspensions became looser. The dreaded "popped dome" syndrome is a case in which the dome physically pops out of the gap due to the suspension material breaking. This was more common than burned-out voice coils. --Tom Tyson Link to comment Share on other sites More sharing options...
tysontom Posted May 23, 2005 Report Share Posted May 23, 2005 >Hey Bret,>That was a distorted sounding tweeter that I acquired about a>year ago and dissected a couple of weeks ago. I previously had>a 1970 speciman in which the foam under the dome was almost>dust, but I didn't remember to take a picture before ditching>it. I imagine the stuff could get into the voice coil gap. It>might explain why there seems to be a noticable difference in>performance between some of the many tweeters of this type>that I've used. I'm not aware of any way to fix these babies.>>The good news is that if it is a problem, it is probably>confined to the AR-3a/2ax/5 using this type of tweeter. I have>no idea what is under the domes of the earlier red dome>tweeters used in the AR-3 era however. >Maybe Tom T. can offer some insight.>>The second photo is of a 1976 AR-12 (8 ohm version of the>AR11/AR10pi tweeter). The material under the dome is not foam>but a felt pad with no signs of deterioration, and is glued in>place.>>Roy>One further comment about the first tweeter (AR-3a) image: this was one of the 2nd generation, back-wired versions, and the quality control on (some of) these tweeters got so bad that many of domes were glued in lop-sided. I think that the tweeters were out-sourced to someone else, and the quality was poor in some instances. Many were used in the replacement-parts side of the house only. Maybe the deterioration is confined to this later version.--Tom Tyson Link to comment Share on other sites More sharing options...
RoyC Posted May 23, 2005 Report Share Posted May 23, 2005 Now that you mention it Tom, it was holes in the clear flexible material around the perimeter of the dome (between the orange foam suspension blobs) that made me investigate this tweeter further. I have a another tweeter from 1975 with similar holes where it looks like the material wasn't properly applied. It sure could indicate the quality control issue you mentioned.I have not seen the "holes" in any of the earlier front wired tweeters. Those areas look to be a conduit for stuff to get into the voice coil gap from the outside, regardless of what the foam is doing under the dome.The only other tweeter I've dissected was a front-wired 1970 era 8 ohm version from an AR-5 about a month ago. Unfortuately the damping material was more deteriorated than the one in my photo.Thanks for the info!Roy Link to comment Share on other sites More sharing options...
tysontom Posted May 23, 2005 Report Share Posted May 23, 2005 >Now that you mention it Tom, it was holes in the clear>flexible material around the perimeter of the dome (between>the orange foam suspension blobs) that made me investigate>this tweeter further. I have a another tweeter from 1975 with>similar holes where it looks like the material wasn't properly>applied. It sure could indicate the quality control issue you>mentioned.>>I have not seen the "holes" in any of the earlier front wired>tweeters. Those areas look to be a conduit for stuff to get>into the voice coil gap from the outside, regardless of what>the foam is doing under the dome.>>The only other tweeter I've dissected was a front-wired 1970>era 8 ohm version from an AR-5 about a month ago. Unfortuately>the damping material was more deteriorated than the one in my>photo.>>Thanks for the info!>Roy, the clear material that was formed around the edge of the dome on the hard-dome tweeters was clear butyl-rubber, applied to protect the voice coil from dirt and so forth, and to give the tweeter some restoring force. Once holes appear in that coating, the voice coil is no longer protected. The three urethane-foam pads are poured-in urethane foam that would set in place, and this foam was the actual suspension system for the tweeter's dome. It seems that by the mid-1970s the jigs for these tweeters must have been worn out, out of spec or altogether lost such that a few of these later tweeters (these are all characterized by the solder lugs or eyelets on the outside of the tweeter) were very haphazzard affairs in some cases. Some domes were crooked and set at an angle in the gap! I had several of these tweeters that I got directly from AR back in the mid-70s that were defective and had to be replaced; no telling how many were far from AR's original spec. Note that all of the pre-1974 hard-wired versions were *very* carefully made, and each was individually tested and inspected before being installed in a speaker.The bottom line is that during the mid-to-late 1970s AR was trying to supply service parts for all the old ARs that were out there, but somewhere along the line the manufacturing gigs were probably missing or broken. Soon thereafter AR discontinued these parts. Ironically, when Villchur was at AR -- from 1954 until he sold the company to Teledyne in 1967 -- his policy was to maintain parts for all AR speakers sold. He mandated that, but this policy was soon remanded, and the company reverted to the "support-period" philosophy that most companies now use: five to seven years after the last date of manufacture.--Tom Tyson Link to comment Share on other sites More sharing options...
Pete B Posted May 24, 2005 Report Share Posted May 24, 2005 >Hey Bret,>That was a distorted sounding tweeter that I acquired about a>year ago and dissected a couple of weeks ago. I previously had>a 1970 speciman in which the foam under the dome was almost>dust, but I didn't remember to take a picture before ditching>it. I imagine the stuff could get into the voice coil gap. It>might explain why there seems to be a noticable difference in>performance between some of the many tweeters of this type>that I've used. I'm not aware of any way to fix these babies.>>The good news is that if it is a problem, it is probably>confined to the AR-3a/2ax/5 using this type of tweeter. I have>no idea what is under the domes of the earlier red dome>tweeters used in the AR-3 era however. >Maybe Tom T. can offer some insight.>>The second photo is of a 1976 AR-12 (8 ohm version of the>AR11/AR10pi tweeter). The material under the dome is not foam>but a felt pad with no signs of deterioration, and is glued in>place.>>RoyHi Roy,The foam helps to reduce reflections off the top plate which cause cavity resonances under the dome. Many tweeters are built with felt or cotton, some have experimented with wool damping material and I'm sure these would be a safe, probably better, substitute when repairing one of these tweeters.I have several ideas for rebuilding these tweeters but have not yet had one to disect. I'm not sure how to rebuild the suspension exactly as original, I wonder if the shipping foam in a can is the same type as original for the suspension? I'd probably prefer one cut from flat foam or rubber which would then also act to protect the gap.I'd also suggest adding light weight ferro fluid and tinsel lead in wires.Question: Do most of these tweeters fail with breaks in the voice coil wire, or by overheating?Pete B. Link to comment Share on other sites More sharing options...
RoyC Posted May 25, 2005 Report Share Posted May 25, 2005 I really don't know what the most frequent cause of death to these tweeters is/was, but after removing the voice coil of the one in the above photo, there is no doubt the foam is a problem. The foam suspension just crumbled (the darker orange in the photos below) upon cutting the butyl rubber coating.It looks like this tweeter may even have had issues with the foam in the gap since manufacture. You can see in the photos that the coil former has an imperfection on the inside as well. After looking at the construction of this thing I'm amazed they got any two to sound the same!Roy Link to comment Share on other sites More sharing options...
Pete B Posted May 25, 2005 Report Share Posted May 25, 2005 Is the voice coil former in those pictures paper and not aluminum?Most modern tweeters have aluminum formers, or at least paper with a very thin aluminum layer.Most of the better modern tweeters make dome/voice coil replacement easy with drop in replacement parts: http://madisound.com/images/product/small/600058.jpgLots more replacement parts here: http://www.madisound.com/cgi-bin/index.cgi...id=141931.21326The Dynaudio D21-2, expensive and no longer available:http://www.madisound.com/images/product/small/D-21_2.jpgI notice that people seem very concerned about using a replacement tweeter. But this is a very simple tweeter without any pole vent or chambers which add complex resonances that might be hard to duplicate. The AR tweeter is a simple closed box radiator, Fc, and Qtc define it's small signal piston range behavior. I believe it is low on sensitivity and it would be better to find a 6 or 8 ohm unit with similar voltage sensitivity, Fc, and Qtc which will run cooler for a given output level. It's not that complicated.Pete B. A mish-mash of tweeter tests: http://www.zaphaudio.com/tweetermishmash/ Link to comment Share on other sites More sharing options...
tysontom Posted May 25, 2005 Report Share Posted May 25, 2005 >I really don't know what the most frequent cause of death to>these tweeters is/was, but after removing the voice coil of>the one in the above photo, there is no doubt the foam is a>problem. The foam suspension just crumbled (the darker orange>in the photos below) upon cutting the butyl rubber coating.>>It looks like this tweeter may even have had issues with the>foam in the gap since manufacture. You can see in the photos>that the coil former has an imperfection on the inside as>well. After looking at the construction of this thing I'm>amazed they got any two to sound the same!>>RoyIn the 1-3/8-inch AR-3 dome, the biggest cause of failure was metal fatigue of the aluminum voice-coil wire lead-outs. These wires would eventually break at the point where the wire exited the dome, even though there was a half-circle loop before the wire was taped to the top plate. In that phenolic dome, the voice coil is aluminum wire, wound over a special former, but placed "in space" when mounted in the driver -- no bobbin used on any of the AR-3 mid- or high-range drivers. "Popped dome" was the second-biggest failure, caused by excessive current sufficient (in the presence of a very strong magnetic field) to cause the dome to separate from the foam suspension pieces. A few suffered from thermal damage; but with a 7500 Hz crossover, it had to be a clipping amp in most instances to cause that problem.http://www.classicspeakerpages.net/dc/user_files/452.jpgAR-3 1-3/8-inch Tweeter. Excellent quality control. Failures usually occurred at the lead-out point or separation of suspension.In the 3/4-inch AR-3a tweeter dome the voice coil was made of a fine copper wire, and the wire was wound over a bobbin, or former, usually made from aluminum or nomex-like paper. Failures in the AR-3a tweeter usually resulted in thermal burn-out of the wire itself. Not many had "popped domes," from what I gather. This tweeter also did not have ferro-fluid in the gap; that came later in the AR-10/Pi-AR-11 tweeters going forward. AR did achieve excellent QC with this tweeter, as with the AR-3 tweeter, by individually testing each and every tweeter in the anechoic chamber, and comparing it to a "standard" to within 1 dB across the band. There was apparently always a healthy percentage of failure, and the bad ones would be re-cycled.http://www.classicspeakerpages.net/dc/user_files/454.jpg1969 AR-3a hard-wired 3/4-inch tweeter. Excellent quality control. Failures usually thermal damage caused by excessive power.However, by the time of the back-wired versions, as I mentioned before, the QC was not as good, and no two of these might have sounded the same. I don't think AR was too concerned about the QC of this tweeter by the mid-1970s since it was to be used primarily as a service part for older AR-3as (and all the other AR speakers using the 3/4-inch hard-dome tweeter).http://www.classicspeakerpages.net/dc/user_files/455.jpg1975 AR-3a back-wired 3/4-inch tweeter. Questionable quality control and performance uniformity in some instances. --Tom Tyson Link to comment Share on other sites More sharing options...
RoyC Posted May 25, 2005 Report Share Posted May 25, 2005 Tom,Thanks for the pics and insight.Those early tweeters do look good, yet I'm not surprised they had alot of rejects. They could not have been easy to build by hand.Pete,Although I'm mostly a traditionalist with AR's, I agree that it probably isn't too soon to be thinking of alternatives to the '3a tweeter and its 8 ohm counterparts in the '2ax and '5.. The problem is that there seems to be no true modern "drop-ins". The mounting flange would have to be very large to fit the cabinet hole which is a bit over 3 1/2", and the crossover would have to add a parallel inductor at the very least (like the AR-11). The '3a tweeter naturally rolled off at a very high frequency by today's standards. It was a very unique animal. I wonder what AB Tech is offering for a gazillion bucks these days.By the way, how did you guys get your photos to be small enough to fit on the page? Thats why I've been attaching but not including it with the text..too big.Roy Link to comment Share on other sites More sharing options...
ninohernes Posted May 25, 2005 Report Share Posted May 25, 2005 >>I wonder what AB Tech is offering for a gazillion bucks these>days.I just replaced tweeters in a pair of AR-3a's for a friend of mine, with replacements from AB Tech. Each tweeter was only like $60 or something. They are very nice sounding, quite close to the original. The only difference is they are a bit more efficient than the originals, and they are all back wired. Also, I do believe that they are fluid cooled. Very similar if not the same as the tweeters used in the AR-303. Link to comment Share on other sites More sharing options...
Guest Ken Perkins Posted May 25, 2005 Report Share Posted May 25, 2005 If one can afford them, the excellent Hiquphon OW1 would be an perfect replacement tweeter for three ways with the "East Coast" sound. They actually hold up very well to about 2.5k (second order electrical) and Bud Fried used them for years with simple first order series crossovers. It's my favorite 3/4" dome and comes in a variety of coatings and vc damping.http://www.ellisaudio.com/hiquphon.htm Link to comment Share on other sites More sharing options...
RoyC Posted May 25, 2005 Report Share Posted May 25, 2005 Hi Joe,I purchased a pair of tweeters about 8 years ago from AB Tech for about that price. They both had issues from day one, and had a tendency to cut out periodically. I eventually traced the problem to bad voice coil lead connections and fixed them.They sounded very different (in a harsh way) than the old tweeters but I got them to sound Ok by using the AR-3a "Limited" crossover from the early 90's. That required a change to a 4uF cap, and the addition of a parallel .16mh inductor. This arrangement also uses common 8 ohm l-pads and the mids required lots of attenuation. On the other hand, the old tweeters did not sound so good when I tried them with that crossover....Did yours come with foam on the front of the mounting flange? Maybe they sell different replacements now. Mine were made by Tonegen.Roy Link to comment Share on other sites More sharing options...
Pete B Posted May 27, 2005 Report Share Posted May 27, 2005 Roy,Yes, The 3a tweeter had a very high Fs and included this electro-acoustical rolloff or high pass as part of the crossover response - it is critical. It is a second order high pass that combined with the first order electrical XO should form a 3rd order response, however the complex input impedance makes it not so simple. It appears to start as a second order rolloff around 5 kHz and eventually breaks to 3rd order. I agree that the additional inductor is important, and perhaps a third order electrical filter would work even better with some tweeters. This could be verified through simulation and measurement.I only mentioned rebuilding these tweeters for those who want as close as possible to the original. It is labor intensive and probably not economical for most, some collectors and those who enjoy doing the work might be interested.It would be very useful if an inexpensive dome/coil assembly for a modern tweeter could be adapted to the old AR, this would offer an easy, low cost repair.Pete B.>Pete,>Although I'm mostly a traditionalist with AR's, I agree that>it probably isn't too soon to be thinking of alternatives to>the '3a tweeter and its 8 ohm counterparts in the '2ax and>'5.. The problem is that there seems to be no true modern>"drop-ins". The mounting flange would have to be very large>to fit the cabinet hole which is a bit over 3 1/2", and the>crossover would have to add a parallel inductor at the very>least (like the AR-11). The '3a tweeter naturally rolled off>at a very high frequency by today's standards. It was a very>unique animal. >>I wonder what AB Tech is offering for a gazillion bucks these>days.>>By the way, how did you guys get your photos to be small>enough to fit on the page? Thats why I've been attaching but>not including it with the text..too big.>>Roy>> Link to comment Share on other sites More sharing options...
RoyC Posted May 28, 2005 Report Share Posted May 28, 2005 >It would be very useful if an inexpensive dome/coil assembly>for a modern tweeter could be adapted to the old AR, this>would offer an easy, low cost repair.Hey Pete,That would be convenient! The only similarities between the old '3a tweeter and the "replacement" that I experienced was that it fit into the cabinet. At the time it was considered to be the universal AR replacement tweeter. I just checked the Simply Speakers website. It currently sells what looks to be that tweeter and advertises it as a replacement for the AR-3a, 2ax, 11, 5, 9, 91 "and others"....Huh? I think not. Roy Link to comment Share on other sites More sharing options...
Pete B Posted June 19, 2005 Report Share Posted June 19, 2005 Hi Roy,Yes, it seems that the main concerns of some parts suppliers are does it drop in and produce sound then, from their perspective, it "works".I'm willing to help as I've said before, but I've not had any AR-3as or LSTs here to measure. I offered to disect a failed AR-3a tweeter but no one offered to send one. I'd actually like to sample several to see the failure modes. I would also want to measure several working units to determine, Fc, Qtc, etc. but I don't expect anyone to send any working units.Pete>>It would be very useful if an inexpensive dome/coil>assembly>>for a modern tweeter could be adapted to the old AR, this>>would offer an easy, low cost repair.>>Hey Pete,>That would be convenient! >>The only similarities between the old '3a tweeter and the>"replacement" that I experienced was that it fit into the>cabinet. At the time it was considered to be the universal AR>replacement tweeter. I just checked the Simply Speakers>website. It currently sells what looks to be that tweeter and>advertises it as a replacement for the AR-3a, 2ax, 11, 5, 9,>91 "and others"....Huh? I think not. >>Roy Link to comment Share on other sites More sharing options...
Guest Bret Posted June 22, 2005 Report Share Posted June 22, 2005 >I would also want to measure several working units to determine, Fc, Qtc, etc. but I don't expect anyone to send any working units.<Why not? Tweeters are relatively cheap to ship.Once upon a time I offered to send you some working speakers and arrive with them! On the other hand, I feel like I've "done my bit" with the woofers and it's someone else's turn. You'd think one enthusiast or another would have a spare or two hanging around.Bret Link to comment Share on other sites More sharing options...
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