tysontom

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  1. Why did AR do the LST?

    "Why did AR do the LST? That’s an intriguing question." The genesis of the AR-LST is interesting. After Ed Villchur retired from AR, his long-time friend and treasurer, Abe Hoffman, took over as president of the company. Hoffman guided AR through the late 1960s until the end of his 5-year employment contract with Teledyne Corporation in 1972, but was "let go" by the company in that year to be replaced Victor Amador, who knew little about the about the high-fidelity audio industry. Amador lasted not quite two years before he was sent packing, and Teledyne appointed Martin "Marty" Borish to be president. Previously, in 1967, Teledyne brought in Borish to conduct AR's "overseas operations.". He was made Vice President International, stationed in AR's Houghton-Regis, England, operation and had close contact with agents throughout Italy (the largest market), Germany, France and England. While VP International, Borish was approached by AR's biggest international customer, Italy, requesting a "high-end" AR system to compete with the best products from Quad, KEF, Wharfedale and the like. They requested a speaker with prodigious power-handling capability and flat acoustic-power output, beyond anything produced in Europe at the time. The Italians had great influence on AR, so Borish returned to Cambridge and sat down with Roy to discuss this new product. At the same time, commercial customers and recording studios in the US were calling for the same thing, so Roy set about designing the AR-LST, a speaker ultimately with four-times the power-handling capability of the AR-3a and with flatter, adjustable-slope acoustic-power response. The AR-3a woofer was known to be robust, so using four midrange and four tweeters was the answer, arranged in the special cabinet we know as the AR-LST, clearly one of the finest loudspeakers of all times. This complex project design apparently began in the 1968 to 1969 time-frame, as suggested by Steve, and was not an insignificant project through its completion and introduction in 1971. AR-LST File Image 1971 --Tom Tyson
  2. Yeah, you might even take it further if the "source" material is the guide to the ultimate AR-speaker sound reproduction. For the Live-versus-Recorded Fine Arts Quartet and AR-3 speakers, the playback was done through an Ampex AG-350-2, playing at 15 ips on full two track. This gave the Ampex a nearly flat 30-18,000 Hz and a S/N ratio of about 60 dB (some "hiss" could be heard by listeners very close to the front of the concerts). For the Nickelodeon-AR-3 LvR demonstrations, a Magnecord 1028 2-track recorder was used, also at 15ips and flat from 30-18kHz at about 58dB SNR. The original master tapes used in the AR Live-vs.-Recorded Fine Arts Quartet and Gustavo Lopez guitar concerts Ampex 350, type used in the Fine Arts Quarter and Gustavo Lopez recordings Magnecord 1028-2 two-track, 15ips recorder used in the AR-3/Nickelodeon LvR. --Tom Tyson
  3. Pictures of my very first AR-3a's (Thanks Roy!)

    Congratulations, bassment142! You got an early pair of AR-3as -- likely 1967-1968 judging by the tweeters -- that are very original. What are the serial numbers? What was the date-stamp on the tweeter that was removed? There are not too many of those early versions floating around, and it's good that you have Roy to help you with them! Hope you didn't have to do too much with the crossover. --Tom Tyson
  4. L1590's! Now what?

    Owlsplace, (notice that I spelled "Owlsplace" correctly this time, sorry about that before!), when the Ferrofluid oil is mixed together, the tiny metal particles -- like a metal dust -- are evenly dispersed throughout the special, high-dollar synthetic-oil solution. The particles are fine enough that they stay mixed in the solution like the pigments in a tube of oil paints, and once in the magnetic gap, the solution is then strongly attracted to the magnet pole pieces (this being the center pole piece and the top-plate structure forming the "gap"), thus conducting a great deal of the heat that can develop in the voice coil and distributing this heat onto the actual magnetic structure itself (the pole pieces). It is the strong magnetic lines-of-force across the north-south gap that hold the solution precisely in the gap without allowing it sag down by gravity or to drain off. Some drivers have the FF solution on only one side of the gap, and it never migrates to the other side. Others have the solution on both sides of the gap. The oil can eventually evaporate, of course, but it is a very special synthetic oil (and the good stuff is extremely expensive) and will supposedly last a very long time, except in cases of abusively high amplifier input levels for extended periods of time. I understand that this can cause accelerated evaporation or "boiling" of the FF because of the excessive thermal build-up. —Tom Tyson
  5. L1590's! Now what?

    Owlspace, perhaps you are visualizing the drivers as "straight-through" voice-coil gaps, open on the back, thereby enabling you "apply some solvent with a brush and blow out the residue on the other side." Bingo, job done, but the problem is that the magnet assembly's bottom plate and pole piece are staked together and attached to the powerful ferrite magnet with epoxy and mangetic force; but not only that, the metal particles will cling like crazy to the magnetic surfaces, and unlike dirt or dust particles, they will try to move around in a circle before they come out of the gap. Unfortunately, there is no way to remove the "back" of the driver, either the midrange or tweeter. So now you take compressed air and blow the metal particles down into the magnet assembly, causing them to cling to the magnet itself or on the bottom of the gap. Most likely this would be the end of this driver. This is the reason that you see repair done to voice-coil gaps with pieces of masking tape and not compressed air. Nevertheless, this is only part of the problem: when you go to replace the old Ferrofluid (if successful doing it), you must then know how much -- and at what viscosity -- new fluid to add to the gap. The proper amount determines the performance of the driver to a large extent. Who has that spec? Who has the original driver response graphs, etc. Just about anyone could get a mid-range driver or tweeter to "function" again, but to get it to sound right is another thing altogether. Most speaker-repair outfits steer clear of repairing tweeters for this reason. --Tom Tyson
  6. A/D/S/ L1590

    Attached is the owner's manual for my pair of ADS L1590/2 loudspeakers, and it may have some helpful information for those with the series 1 as well, but there are some differences, some noted on the final page. ADS_L1590-2_Owners-Manual_Tyson980.pdf --Tom Tyson ***Update: the manual supplied by ADS was actually for the Series 1; but rather than print a brand-new owner's manual for the Series 2, ADS added a supplement at the very end (shown with my manual) describing the differences. Therefore, this manual works for either the Series 1 or Series 2.
  7. Why did AR do the LST?

    rl1856: This is an interesting message, and while it contains some truths, it's mostly based on imagination and presumption. As the old saying goes, "a beautiful hypothesis slain by an ugly fact." Therefore, taking each paragraph individually, here is my admittedly long-winded assessment of your comments: 1. The AR5 was an excellent speaker; much better than the 2ax and in some ways better -in room- than the 3a. The cost of the 5 was too close to that of the 3a, while most consumers could not discern a difference between the 5 and 2ax. Their loss. There is actually some truth to this statement about the AR-5 vs. the AR-3a; the cost of the AR-5 was too close to the AR-3a, and there were some "in-room" differences in favor of the AR-5 over the AR-3a. The AR-3a had a heavier spectral balance than the AR-5, and it therefore sounded a bit different in a room because of this balance, despite the nearly identical measured acoustic-power response above 500-600 Hz. The AR-5 sounded a bit "clearer," for lack of a better description, throughout much of the midrange, than the AR-3a, mainly because of the power of the AR-3a woofer. The AR-5 didn't particularly outshine the AR-2ax except in spaciousness and acoustic-power output into a room and, in fact, did not sound as good as the AR-2ax in the near-field response. The AR-2ax was more directional, however, and the crossover from the woofer to the 3.5-inch midrange was much higher than the AR-5's crossover to the 1.5-inch dome tweeter, and thus dispersion in the lower midrange was much to the AR-5's advantage. Because of the stellar acoustic-power response of the AR-5, however, it was more spacious and 3-dimensional in sound (vs. the AR-2ax) once well back in the reverberant listening environment. 2. Why was the LST created ? Criticism of the 3a design and changes in the marketplace. The AR-LST was created because of "criticism in the marketplace" of the 3a design? Hardly! Some individuals and anti-AR critics complained about the "laid-back" or reticent quality of the AR-3a's spectral balance, but the overwhelming critical acclaim and magazine reviews of this speaker were simply stellar, probably never exceeded in perceived excellence by any other product ever reviewed in the audio press. In 2010, The Absolute Sound, a tweak, golden-ear magazine by any measure, and not one to like any establishment loudspeaker—especially Acoustic Research—voted among all its editors that the AR-3a was the 2nd most important loudspeaker in the history of audio. That's a pretty good endorsement. So, the AR-LST didn't come about because of "criticism in the marketplace" of the AR-3a's design 3. The 3a had a stepped driver response with the response of the midrange roughly 3db lower than the woofer response, and the tweeter response an additional 3db lower (and -6db relative to the woofer). The actual sensitivity of the AR-3a drivers is not identical across the board, as suggested in this statement, but this statement is based on the AR-3a published data sheet (1967) that shows the relative output—superimposed as if a total-system frequency response—on a single graph. "The 3a had a stepped driver response...." This is nonsense. If you listened 3-4 feet in front of an AR-3a, this so-called "stepped" response might be bothersome (but not as much as the interference effects and diffraction). But no one listens up that close, and what one hears in the reverberant field is overwhelmingly reflected energy with only a small percentage of "direct" energy from the AR-3a. This is simply because the 3a has outstanding dispersion, and once you are just a few feet back from the speaker, depending on the room constant, you are hearing reflected energy with directional clues only in small proportions. So, what about the reduced sensitivity of the AR-3a midrange and tweeter? In the reverberant field, this lack of on-axis energy does show up in a slightly downward-sloping extreme treble response, but the total energy in the reverberant field is astonishingly flat and uniform all the way out to nearly 20kHz! The most amazing part of this is that some speakers with flat treble energy on axis out to 20kHz, actually sound duller than the AR-3a back in the reverberant field. This is the magic of wide dispersion into the listening environment. 4. However the 3a was designed to replicate the listening perspective of a 10-15th row seat at a classical concert. Translated to a domestic room, that meant far field positioning. AR recommended a listening distance of 12-15 foot from the plane of the speakers. Excellent dispersion characteristics of the AR dome drivers meant that the sound reaching a listener 12-15 feet away would be a mix of direct and reverberant content. Thus the overall balance in situ would seem to be better than what measurements would imply. 10th-15th row seat at a classical concert? Huh? Speculation, but in truth the spectral balance did mean somewhere farther back in the concert hall. Yes the AR-3a was designed to be a speaker listened to back in the reverberant field. AR intentionally chose dispersion over efficiency of the midrange and tweeter to get the desired acoustic-power response. And it is true that the overall balance "in situ," was better than what the measurements would imply, but understanding the meaning of the AR-3a measurements is not what happened here. Again, AR superimposed—into one graph—the output of each driver measured anechoically to let the reader understand what each driver was capable of doing. It was not a "system frequency response," as is interpreted by poster rl1856, and it was never intended to be interpreted the way that rl1856 has read it. Those response measurements were there to show the linearity and smoothness of each individual driver, not its efficiency or more correctly, sensitivity. But look at competitive speakers, such as the Large Advent, the JBL Century L100, Dynaco A25 or others with greater-efficiency tweeters on axis, and look at them within their acoustic-power output framework. In the near field, these speaker are decidedly "brighter" and more "forward-sounding" than the AR-3a, yet back in the reverberant listening field, each of those speakers sounds less 3-dimensional or "spacious" than the AR-3a! Some actually sound downright dull well back in the reverberant field because the lack of total acoustical energy reaching the listener's ears is slightly truncated due to poorer dispersion. The simple reason is that what we hear back in the reverberant field in most moderately absorptive rooms is predominantly reflected energy, and if a speaker has less than stellar off-axis output, the integrated acoustic-power response will be more "drooped" and poorer. Acoustic-power response of a quite-expensive JBL speaker (higher in ranking than the Century L100). Note the rapid fall-off in treble out into the upper midrange and treble. This measurement was done in AR's "house-of-horrors" reverberant test chamber in 1967. Acoustic-power response of the AR-3a and AR-5, taken in AR's "house-of-horrors" reverberant test chamber in 1967. 5. Consumers agreed with and the AR approach and by the late 1960's AR had a 60% market share. Wrong again. AR had a 32.2% market-share in 1966, the highest of any loudspeaker manufacturer in the history of the high-fidelity industry, but it never had 60%! 6. What happened? Critics were persistent in noting the stepped measurement response of AR speakers. The composition of the market changed, with younger buyers who preferred pop music gradually replacing older buyers who preferred Classical and Jazz. Pop buyers had a preference for flat response, like what they head at a concert. Competing speaker designs delivered flatter FR, with AR like bass and could play rock music at appropriate levels. Dynaco A25, Advent, EPI, Boston Acoustics, and of course the JBL 100. Again, there's no such thing as "stepped-measurement response," as in the AR speakers; but yes, the high-fidelity market did change, and classical music gradually became less popular than pop music, no argument here. Pop buyers were simply less discerning about replicating the "concert-hall" experience; rather, they were looking for bright, overpowering midrange ("honkiness" in some cases) and "in-your-face" treble response, often experienced up close within a narrow listening window. It was therefore not "flat" response that pop-music lovers wanted so much as thumping bass (predominantly 60-80 Hz) and high clarity in the midrange and treble. This was the illusion of "hi-fi" sound for many of the later baby-boomers and perhaps millennial music-lovers. Not all were that way, of course. 7. The inherent flaw of AR dome speaker design was fragility. The drivers could not handle large amounts of power nor could they produce loud SPL at the listening position. The AR-3a was not "fragile." It was low in efficiency (sensitivity) and impedance, and therefore it drew a huge amount of amplifier current at low impedances when playing at high output levels. For example, the AR-3a could absorb 400 watts for 2 seconds continuously within its thermal rating, and it could sustain instantaneous peaks of 1000 watts; however, tweeters were easily overpowered by amplifiers not up to the task or by listeners wanting to listen to electronic or pop music at "true" levels. Both of these conditions usually accompanied one another. So, the AR-3a was by no means a "fragile" design. 8. AR wanted to produce a speaker that addressed critics and the needs of a changing market. That meant a flat in room response and loud in room SPL. The solution was multiple dome drivers arranged across a 120 degree plane. Measured response was indeed flat in room (+/- 3db 50hz-15khz), with the ability to absorb prodigious amounts of power, and play at 105db+ for extended periods of time. No, this wasn't the reason for the AR-LST. It was not designed to "address the critics and needs of a changing market." This is not the place to go into the reasons for the etiology of LST, but what rl1856 says is just speculation and imagination. It is true that the LST could produce even flatter acoustic-power response than the AR-3a, and it could produce higher sound outputs with lower distortion than the AR-3a, and it could handle significantly higher input power (one reviewer friend of mine said that he once measured brief, instantaneous peaks of nearly 5,000 watts into the LST). But the LST wasn't produced for this reason. 9. However this solution brought additional problems. Audible phase distortion between the multiple dome drivers and the need for a very complex auto former driven crossover. In reality the LST was not suitable for a wide range of listening rooms. There was absolutely zero (zilch, nada) "audible phase distortion in the reverberant field with the AR-LST." Again, speculation and imagination. If you measured an LST at 1 meter on axis, and then you measured again a little below the first measurement, and so on, you would get all sorts of phase shifts, anomalies and irregularities, but that's not what you hear with the LST, because no one listens up close to this speaker, ever (well, some have). Therefore, the interference effects are "swamped" in the reverberant field, and you could never detect any phase distortion, even if your life depended upon it. The autotransformer was a "spectral balance" control, not a phase corrector! It was designed to give different spectral balances, all relative to the midrange, in the LST from flat to sloped output. It had nothing to do with "phase distortion," which is a serious misnomer. 10. The LST led directly to the AR9, which solved many of the problems of the LST. Single forward facing dome drivers eliminated phase distortion. Ferofluid (first used in the AR 10pi and AR 11) significantly raised the power handling ability of the dome drivers. The result was flat in rooms response, loud SPL and a design that was more room friendly. Like the 3a, and LST, the 9 advanced the state of the art. The AR-LST did not lead directly to the AR9. The LST happened to be the flagship of the "classic" AR product line during the early 1970s, but the AR-10Pi was the next flagship, and then product development lead to the tower speakers and the famous "electronic automatic transmission" developments. There were distinctly different approaches for different needs. In actuality, the AR9 probably will not handle more peak power than the LST, if as much, especially into the critical mid-range and treble frequencies. It definitely will in the deep bass! It is very true that each of these speakers (and the all-conquering AR-3 preceding the AR-3a) advanced the state of the art! So there you have it. "A beautiful hypothesis slain by an ugly fact." Things aren't what they seem to be, but I think the intent was to give forth some ideas on what the writer had on his mind. —Tom Tyson
  8. "Perhaps actual measurements of the AR1-J130 combo alone indicated weakness in the midrange ? Was this weakness only apparent in a large scale application, or would it be audible in a normal listening room?" Could you explain how you came to this conclusion? I've never seen this referred to in any of the literature on this subject, and I don't think Julian Hirsch or anyone else noted any "weakness" in the midrange.
  9. When the question was asked about how well the AR-1 (usually the AR-1W) and Janszen 130 electrostatic tweeter integrated, "in the absence of a system crossover network," it should be noted that an LCR crossover network resides in the Janszen unit itself. The integration was excellent and quite seamless. AR-1s and Janszen electrostatic had been used together for many years, and Arthur Janszen chose the AR-1 over the big Bozak (including the Concert Grand) as the preferred setup to be used with his electrostatic tweeter. Janszen subsequently joined with Henry Kloss at KLH to use the 130 with the new KLH Model One, dual-woofer system and the Model Two single-woofer systems. The big KLH setup was very expensive in those days, but it was a very good combination. In the spring of 1956, the New York Audio League (Julian Hirsch and others) used Four AR-1 speakers, two Janszen (one 130 and one "utility" model) electrostatic tweeters and a single Bozak B-305 midrange were used together for the New York Audio League's live-vs.-recorded comparison with an Aeolian-Skinner pipe organ in Saint Mark's Episcopal Church, Mount Kisco, New York. This combination proved to be very accurate in reproducing the big pipe organ, and this made "believers" out of hundreds of audiophiles on the spot in attendance at this concert. Critical acclaim and rave reviews that followed—especially regarding the AR-1—made this AR/Janszen combination a favorite for many years that followed. —Tom Tyson
  10. Thanks. Yes, I've heard the AR-1W/JansZen 130 combination several times over the years, and the sound was very good. Some audiophiles to this day still use this combination. The electrostatic was clean and transparent, and it always had great appeal for that electrostatic "clarity" and detail. The horizontal dispersion was predictable considering the angled front face, with each panel being very directional in its forward plane. Vertical dispersion was nil due to the panel's highly directional nature. Overall, it was a good system, but power-handling was limited. When the AR-3 came along in 1959, the AR-1W/JansZen combination began to fade into obscurity, with only a few holdouts. The AR-3 had the same clarity as the JansZen, but it had much superior dispersion and better acoustic-power response. --Tom Tyson
  11. AR amplifier: headphones, Delrama

    Claudel, I just now read in detail your post from back in October and your interesting story about Vietnam and your AR Amplifier, AR Turntable and a pair of AR-4x loudspeakers. What you had was a excellent combination that was pretty much unsurpassed for a small but very accurate sound-reproducing system! To this very day there aren't many systems that size that would sound better! Overall, I don't see that we're in too much disagreement, but I think I can see some discrepancies in dates, etc. The AR Amplifier was definitely introduced at the New York High Fidelity Music Show in October of 1967, but it is true what you say that the first full year of production was 1968. If you got your amp in December, 1968, it was well into production with many thousands of units having been produced, and your unit was by no means an early version. I'm pretty confident that first production commenced about that time of its introduction in 1967, as the amplifier had been pretty carefully sorted out and tested for several months leading up to its introduction. There may have been some delay, but not much. AR was eager to get it into the hands of dealers worldwide. The first AR Amps definitely had the closed-in perforated screen that covered the heat sinks, and the amp had adjustable bias and several other things that were changed later on. The first AR amps did, of course, have the "Inc" printed on the front panel beside the "AR" inscription. This changed to "AR" at some point after the amp went into production because there was no more "AR, Inc." after 1967. It was simply "AR" and then "Teledyne AR." AR was sold to aerospace company Teledyne, Inc., in June of 1967. I suspect that when the stock of "AR Inc." plates ran out, all new ones were printed with simply "AR," but this may have been well into 1968. Early AR Amplifiers had a tendency to overheat (although some soldiered on indefinitely while the back of the case would get so hot you could not touch it), and many went into failure mode and would blow out the output fuses, etc. Those who foolishly over-rode the protection fuses would find huge dc-offset in the output, which would fry any woofer's voice coil and "freeze" the woofer in place. That's another story, but it was not uncommon, and this failure happened to two of my early amps driving my AR-3 loudspeakers. AR took care of everything, of course, and I suffered no damage to the 3s. To improve the heat-sink heat dissipation, the screen cage was pulled back away from the heat sinks to allow better air flow, and this helped the amp run a bit cooler (though AR Amps always dissipated a lot of heat once running along). This happened sometime in 1968, but I'm unsure of exactly when it occurred. I've attached some images that may clarify this situation. Note, too, that unless you bought your AR equipment in Europe of Asia (not the US commissary), you would not have come in contact with Delrama, Inc., the AR exporters of equipment prior to AR's UK and Holland plants. This is an original "file" photograph taken of the Amplifier before it was officially introduced in 1967. Photo was consigned to me. This shows a close-up of a rather battered early version (#131) AR Amplifier made around November, 1967. Shows the "AR Inc" on the front panel. This was used until well into 1968 or perhaps 1969, but probably after stock was depleted of old units. Thanks, —Tom Tyson
  12. Steve, remember, the vertical divisions are 1/2 dB. The reference level is about 1 dB above the "0" reference level shown. I know that the woofer is actually flat to within +/- 1.5 dB from 38-1000 Hz anyway, so no correction would be warranted. You would be hard-pressed to find any woofer made at any time that is flatter in that range; if there is one, I'd love to see the measurements on it (and I'm not talking about computer simulations). You can barely detect 1 dB, and this is at the very top of the operating frequency for that woofer; and most would cross over at a lower frequency when possible. The biggest problem with the top end of the woofer's output is the increasingly directional characteristic of this crossover frequency. It would be better to cross it over at 500-750 Hz if possible, not 1 kHz. The woofer was measured free-field, with the sealed AR-1 enclosure buried flush with the ground, radiating into 2 Pi steradians, the precise way to measure the woofer. There is no practical change that could be made to the woofer's crossover that would make it appreciably flatter in output, and really the big question might first be the measured response characteristics of the JansZen tweeter. --Tom Tyson
  13. ar_pro, There are no published JansZen Model 130 frequency-response curves (to my knowledge), just the "spec'd" radiation angle, pretty much determined by the shape of the enclosure itself. Do you have the actual curves themselves? It's hard to determine how actually smooth the response, but it can be assumed that the electrostatic tweeters performed well under most circumstances. --Tom
  14. Here is the AR-1/AR-3 woofer frequency response, one of several done on the AR woofer. As for the JansZen 130 tweeter, I don't think there were any published frequency-response graphs on that speaker, mainly because Neshaminy Electronics (JansZen) did not have an anechoic chamber in the early days. The AR woofer was nearly perfect in its low-frequency response and distortion characteristics. AR-1/AR-3 woofer measurements. These tests were made outdoors facing into half-space. --Tom Tyson
  15. A/D/S/ L1590

    ADS L1590/2 Ferrofluid Question: The question of the Ferrofluid magnetic fluid evaporating in the magnetic gap in mid-range and tweeter domes of the ADS L 1590/2 and L1290/2 is addressed in these comments below from another thread on this site, "L1590's! Now what?," and I thought it would be useful to bring it over to this topic on the 1590 that I started quite some time back, since there is much more technical information present here. I am not aware of a true problem with the voice coils in the ADS 1590 or 1290 or the other ADS models using versions of the 2-inch and 3/4-inch dome drivers; it is possible that some speakers that had been driven abnormally hard at high-acoustic levels might suffer evaporation of the oil in the gap, but under normal use this is somewhat unlikely. Comments below address this question, but the important thing is that evaporated Ferrofluid will cause distortion, lower output and uneven response, and these effects would be quite audible. —Tom Tyson Posted 14 November 2015 - 07:17 PM: Well, picked them (L1590s) up yesterday and have them hooked up now. Very, Very Nice as others have said here (TT) Impressive. I am running them with my Adcom GFA5500 and a tube preamp. My room is on the smaller side so I think that will be plenty. All drivers seem to be in good order but would like everyone's impression on weather or not I should send the tweeter/mids down to Arizona to be looked at and serviced. You can see a slight impression in one of the woofer dust caps too. --DavidDru Posted 17 November 2015 - 12:33 AM: I contacted ADS repair guru Richard So down in AZ. He think these would benefit from service to the Mids and Tweeters. Old Fero Fluid gets muddy I guess. Something you probably wouldn't realize until they are serviced and get them back and hear a difference. He has a special for all 4 for $225 that I will probably take advantage of. Posted 17 November 2015 - 05:05 AM: DavidDru, That Ferrofluid issue has become a topic of a lot of discussion. If the fluid dries up, the midrange and tweeter would likely sound distorted and "muddy," and the high-frequency mid-range and treble response would fall off precipitously. But on the other hand, if you think the sound is clean without distortion, there's a good chance the Ferrofluid hasn't dried up. I have both L1290s and L1590s, and I don't detect any distortion or change in the character of the sound, but I would have to say that neither pair of ADS speakers was electrically abused (over-driven) over time, so I don't suspect any real issue with the tweeters (or the crossovers, for that matter). In short, I don't detect too much difference from when they were new, but hearing memory is short, so it's not possible to know precisely. If you are a risk-taker, you can remove a mid-range driver and a tweeter, and you can actually remove the aluminum top plate and inspect the gap and the voice coil to see if the material has dried. The dome and coil assembly can be re-installed, but it is still a slightly risky proposition. The only real test would be to measure the tweeters' response anechoically, and that would not be easy to do without taking the drivers out of the cabinet and measuring them -- with crossover in place -- individually for on-axis frequency response to see if they match the original measurements (only a few response graphs are present in some of ADSs original lliterature). On the other hand, sending them off to be "checked" for that would mean that a new dome/coil assembly would have to be installed, and the old magnet assembly/gap would have to be completely cleaned out and replaced with fresh Ferrofluid, and that is a very, very difficult thing to do since the Ferrrofluid is a magnetic substance in an oil base, and those magnets are very powerful. In other words, unless it was done by the factory -- which no longer exists -- it's very likely that the end result could be worse than when you sent them in for repair. As they say, "if they ain't broke, don't fix them!" —Tom Tyson Posted 17 November 2015 - 12:33 AM: Ferrofluid does also reduce Q of resonance. Measuring Q or at least max impedance will take only few minutes and may give clue how things are? This is not fool proof method as coil scraping to dried fluid will also reduce Q, Best Regards Kimmo Posted 17 November 2015 - 11:04 PM: Kimmo, Yes, measuring the impedance at resonance might be good, but it would need to be compared with the original factory curve for reference to determine any changes. Does anyone have that? I suspect not, insofar as specific measurements were proprietary during the ADS production years, to my knowledge. There were generic measurements that were published, but not specific measurement curves. It's the same with the frequency-response measurement of an original vs. an old one; unlike AR, for example, there were few, if any, published response and distortion curves, per se, of the ADS drivers other than in promotional literature. ____________ ***Probably the only thing to do now would be to listen carefully to determine if there is an audible problem. If one of the speakers had been previously played at very high output levels -- especially over extended periods -- the temperature of the voice coil would be very high, and this would accelerate changes to the Ferrofluid in the gap (even cause the magnetic fluid to boil), but under normal conditions, no one seems to know how long the Ferrofluid will remain in the gap without going bad. I've heard 15 years, but that's also the "half-life" of urethane-polymer foam surrounds, so that age period for Ferrofluid is probably internet "conjecture." I honestly don't know the answer to "how long." It is clear, of course, that if new oil is put in the gap, the old stuff has to be removed, and that job is very, very difficult due to do because of the strong magnetic strength of the ADS magnets and the narrow voice-coil gap. Metal particles from the Ferrofluid would be left behind, too. I suspect that those metal particles and any oil residue left would be highly resistant to removal, so I just don't know how it could be effectively accomplished. Also, it's nearly impossible to get beneath the gap; i.e., on the underside, because of the back plate/pole piece assembly that are staked together. Therefore, all removal would have to be done from the top, and I've seen attempts at doing this, but none was definitive and the outcome was questionable. And, once all of this was done, the driver would have to be measured for smoothness, uniformity and impedance, as well as for sensitivity, and the measurements would have to be compared with the original impedance curves and response curves, for which none were published (for the public) by ADS. —Tom Tyson 11/21/2015