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tysontom

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  1. C. Victor Campos

    Brad, thanks for that clarification on the "Shop Talk" show on WBUR-FM. I apologize for misstating that detail in my short tribute about Victor Campos; I was actually unsure of his exact participation and relied on something I read from another source. I was originally aware of his work on "Adventures in Sound," but I let the two programs run together in my description. Thanks again, —Tom Tyson
  2. KLH Model 6 restoration- no driver access

    The KLH Six If the grills are stretched tightly against the front molding edge and can't be removed by Velcro attachment, it's likely that the Sixes you own have the epoxied woofers, early versions. Until the mid-1960s, KLH (Henry Kloss) developed a method for mounting the speakers by epoxying the magnet assembly to 1-inch electric-pipe conduit and then the pipes epoxied hard to the speaker's baffle board. No removal here. Ostensibly, this obtuse Kloss design method assured consistent quality control, "+/- 1.5 dB!" In reality, this design nearly bankrupted the company (despite the huge success of the excellent sound quality of the original KLH Six) because of the problem of access for repair. It simply couldn't be properly done out in the field unless one had extra grill panels, extra woofer cones/voice coil assemblies and so forth. The speakers invariably had to be returned to the factory, and after the war-surplus, mil-spec crossover capacitor ran out, KLH began using a cheap capacitor "Synchro XP," known to fail after a few years. Tweeters would go silent because of this failure (happened to the Model Four as well), and repair required the following: 1. Cut the grill cloth down the middle and rip it out of the way. The grill was wrapped around the front baffle board and stapled to the back side to keep it straight and taught. 2. Once exposed, get the knife out again and literally cut out the woofer cone and surround, cut the lead wires and the spider assembly, rip out the cone -- good or bad. 3. Reach in through the "hole" of the woofer, past the epoxied magnet assembly, and attempt to make repairs inside the cabinet in the "dark." 4. Once all of this is completed, reverse the process with new cone, voice coil, spider, surround, new grill and black under-ticking, and you're there. So, that is what you are up against if you have the early version. Hope this helps. --Tom Tyson
  3. C. Victor Campos

    C. Victor Campos C. Victor Campos, 84, from Framingham, Massachusetts, an alumnus of Acoustic Research from 1960 until 1963 and again from 1974 until 1979, died on December 11, 2017 after an extended illness. Victor briefly worked at AR's Music Room in New York in 1959 and later worked in customer services and assisted Ed Villchur with the production of the Live-vs.-Recorded series in the early 1960s. In 1963, Victor went to competitor KLH Research and Development Corporation to work in customer service and engineering under Henry Kloss, but he returned to AR in 1974 working with the Advanced Development Division's new speakers. During these years, Victor produced a superb series of FM broadcasts out of Boston, "Adventures in Sound" and "Shop Talk." These broadcasts were done with master tapes without compression, usually challenging a FM listener's high-fidelity equipment; i.e., if you did not possess AR heavyweight loudspeakers in your system, you were likely to sense distortion during playback! These were superb reel-to-reel tapes done on Ampex AG-440 machines and similar high-end transcription recorders. In the mid 1970s, Victor produced the excellent Neil Grover (drums)/AR-10π live-vs.-recorded demonstrations that showed the extremely capable and accurate reproduction of the AR-10π, especially reproducing the bass drum at high levels. This was a very difficult demonstration—in ways more difficult than the Fine Arts or Gustavo Lopez demonstrations—requiring enormous amplifier peak levels of over 800 watts per channel to reproduce the peak acoustic levels. Steve F on this site attended at least one of those demonstrations and can elaborate on the effectiveness of that demonstration. Much of the credit for the success was due to Victor Campos' understanding of amplifiers, loudspeakers and tape recorders, and he was able to produce excellent results during these LvR demonstrations. Before Victor left AR (he was also at Adcom and NAD through the years), he was very instrumental in the development of the AR9 tower loudspeaker. Initially, Victor wanted the AR9 to be a "powered" speaker complete with built-in amplifiers for woofers, midrange and tweeters, but he was not successful in that quest! At times, Victor could go overboard: when the AR-10 was being developed, a problem occurred with hinge on the fold-out solid-walnut access door on the front. It would bind and stick. Victor wanted to quit "experimenting" and simply cut to the chase: add ball bearings to the hinge! Of course, this was much too expensive, and a proper hinge was developed which worked well without problems. His influence was felt! Victor was an intelligent but sometimes impatient person, yet he accomplished a great deal in the years he was at Acoustic Research and KLH. He will be greatly missed! —Tom Tyson 12Dec2017
  4. ar3a midrange vs ar11 midrange

    As Roy stated, there aren't any significant differences between any of the 1½-inch AR-3a/AR-11screened- midrange drivers, hard-wired or back-wired. After AR moved over to Norwood in 1973, the AR-3as were assembled with identical back-wired midrange drivers that were used in the AR-10/AR-11 series. These AR-3a versions were noticeable by the addition of the Velcro-attached grills and the small, blue Norwood label on the back panel. There is a definite spectral-balance difference between the AR-11 and the AR-3a because of the different tweeter and crossover and, therefore, the balance of the midrange output in the AR-11 would seems slightly different from the AR-3a. AR worked on the crossover to clean up the on-axis output for flatter output. Also, by changing the crossover, I don't believe that Acoustic Research reversed the polarity of the midrange/tweeter in the AR-10/AR-11 in relation to the woofer as was done by Roy Allison in the earlier 3-way "classic" AR speakers to reduce lobing around the crossover frequency. —Tom
  5. I'm afraid it has happened?

    On further thought, it occurs to me that the slots are on the outside of the dome/voice coil, and thus may not necessarily affect air movement inside the dome. I also suspect that the early domes before Ferrofluid might be less affected by the space under dome than later ones with fluid. The gap would allow a small amount of air to pass inside the voice coil past the pole piece. With Ferrofluid (on both sides of the coil), air would be trapped under the dome.
  6. I'm afraid it has happened?

    Many of the new-style (cloth) AR-10/AR-11 3/4-inch tweeters used the same magnet assembly and top plate as the original AR-3a tweeter, thus having three slots around the pole piece that were used for the foam suspension in the 3a tweeter. Since no foam was used in the AR-11 dome, air can escape from under the dome into the pole-piece/magnet cavity below the dome. This would in essence increase the volume under the dome. --Tom
  7. AR 5's: The bargain AR

    AR-5s are 8-ohm speakers and the AR-3a/58s are 4-ohm speakers, and when you switch from one to the other with the same preamp input-voltage gain, the AR-3a/58s have a 3 dB advantage due to lower impedance (drawing more current for a given voltage level), making them seem more efficient. Actually, the AR-5 and AR-3a are very close in sensitivity. --Tom Tyson
  8. I'm afraid it has happened?

    Right. It was strictly a figure of speech, not a "literal" interpretation. I thought that would be self-evident. The point was made that no tweeter can possibly be rated (on its own) for 75 watts, and that was the point I was trying to make with reference to the new AR replacement tweeter. That new one is not likely to have significantly better power rating than any of the older AR 3/4-inch tweeters. It is simply a matter of mass, dome weight and the voice coil weight. To significantly increase power-handling capability, the coil must be heavier, and this is unacceptable in a good tweeter. In terms of instantaneous bursts of energy, I think the AR-LST was originally tested to 5,000+ watt peaks at one point without any ill effects, but this is strictly short-term bursts of energy. The AR-3a 3/4-inch tweeter can probably sustain a little over 5 watts, long-term steady-state energy, before burning out. The later Ferrofluid 3/4-inch black-dome tweeter could probably take 8-10 watts long-term energy, but not much more. --Tom
  9. New AR-9 Project

    Stimpy is exactly right. Here is Tim Holl's preliminary data on the prototype AR9 from December 9, 1977:
  10. New AR-9 Project

    I may have misinterpreted your comments. "Removing the overfill yields tremendous bass gains" implies that you felt it was better or improved. But what I was trying to say is that pretty much everything on the AR9 and AR9Ls (and other AR speakers) was put there for a reason. The goal was to have flat response and neutral, low-distortion reproduction. If you remove (or add) fiberfill to the bass enclosure, you will be changing the damping of the woofers, and if you remove material, the "Q" will go up and damping will go down. The damping is very critical to the proper performance of this speaker, so a removal of the material in the cabinet will definitely cause a rise in bass output at resonance, giving a sense of bass gains.
  11. New AR-9 Project

    What theories about the AR9 woofer Crossover? The crossover is 200 Hz, but I think you are referring to the woofer resonant circuit, described above, right? One word of advice: don't try to redesign it or modify it if you want the system to perform properly. If you have a full acoustics-testing laboratory, you might be able to make worthwhile changes, but that is unlikely. The AR9 design was truly optimized for flat, linear output in the deep bass. It is not perfect, but it is not far from it. The design took over two years to complete from start to finish if I understand it correctly, literally thousands of hours of testing and design work, so it was not an insignificant effort on the part of those engineering and marketing personnel! AR threw a lot of weight behind the design and spent considerable R&D money developing it. The company went all out on the tower speakers, and the results show it. I made a mistake in my original description above. The AR9's woofer impedance-crossover design was I believe primarily the work of Alex P. deKoster, not "DeCosta," as I stated. I apologize for the gross misspelling of his name. He became Chief Engineer working under Engineering Director Tim Holl. Much of the design was a collaboration of several engineers, including James Kate, Alex deKoster, Tim Holl, and others, and long-time visionary C. Victor Campos (Campos worked at AR in the early 60s and left in the mid-60s for KLH, but he returned again in the 1970s). I don't think any one person can take full credit for the design of the tower speakers of that period. These guys are quite a bit older now and have long-since retired from the audio rat race. After spending many years working around loudspeakers, most have lost interest in the intricate details of the products they designed, and most have moved on to other things. So, it is not easy to get these veterans to "drop in" to visit the website. We have been very fortunate to have Ken Kantor visit over the years to give us insight on these products, so we have to be thankful for what we can get. --Tom Tyson
  12. AR9 Teledyn Big LF Caps where?

    You might want to consider measuring the caps before you replace them.
  13. Carl, I tend to be a purists on these things, and it's not always the best approach I must admit! The 28w Scan-Speak woofer is expensive but very impressive and has most of the other parameters close to the AR-12W woofer, and it would be literally bullet-proof with any kind of input power. It does seem very over-damped to me (too much magnet), but it could certainly be made to work! If it could be made to operate flat down to resonance in the 3/3a cabinet, that would be a good thing along with a lower mid-crossover, but the 3a midrange can't go much lower. Some interesting challenges. --Tom
  14. Carl, even if it would work, it is too small for the AR-3/3a opening. It is 279.9 mm (11-inches) in diameter, and the AR woofer is 12-inches in diameter except along the flat sides, so it would never work without some sort of special flange. It's also a massive, subwoofer-type driver and as such is designed for a very low crossover into the midrange. It has output well into in the low midrange area, but it is very peaky and rough up there—as much as 10 dB rise at 1000 Hz—thus it would probably sound terrible above 200-300 Hz. In contrast, the standard AR 12-inch woofer is +/- 1.5dB from 38-1000 Hz. It is also highly overdamped (-3dB at 45 Hz in a sealed 1.5 cu. ft. enclosure vs. -3dB at 35 Hz for the AR woofer in the AR-3/3a). It would add little and take away a lot. I think this woofer would be far better suited for its own custom enclosure with a dedicated equalized amplifier and crossover network. This same question was raised about using the NHT-1259 woofer (NHT 3.3 woofer) in the AR-3/3a. It would work, but it wasn't perfectly suited. —Tom Tyson
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