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soundminded

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  1. It seems like an awful lot of trouble to go to to improve what was Acoustic Research's least expensive loudspeaker of the time, clearly their maximum compromise of performance for the sake of economy. When AR set about building a better model, they took an entirely different route, they built three way systems recognizing the inherent difficulties of matching only two drivers to cover ten octaves.
  2. As an aside, the addition of the inductor shunted across the voice coil will convert the crossover network from a first order high pass filter to a second order filter. The correct values for this inductor depend on the series capacitor and the Voice coil impedence. Handy on line calculators for Butterworth alignments and Linquist-Riley alignments are available all over the internet. When properly aligned to a Butterworth configuration, both filter elements will have the same 3db down frequency. As the frequency goes up, the impedence of inductor goes up because X(L) = 2pi*f*L. As the frequency goes down the impedence of the capacitor will go up because X© = 1/2pi*f*C. This creates a 12 db per octave falloff below the cutoff frequency instead of 6 db. This further restricts power to the tweeter at frequencies of interest only which is the frequeny range above the crossover frequency. This reduces the risk of burnout by avoiding inadvertently overdriving the tweeter below its crossover frequency. Adding the resistor will alter the Q of the filter circuit I think increasing it. If L is too small, its effect will be minimal, even inaudible. The problem with re-engineering these speakers with modern replacements is that the philosophy of modern speaker design has as its intent to restrict dispersion while in this era, AR's intent was to acheive the widest dispersion possible. This is why satisfactory replacements to restore the origional performance now seems next to impossible. Personally I have experimented with 3/8" polypropylene tweeters from Audax but not in this context. It has fairly wide dispersion for a modern tweeter. There may be ways to modify these tweeters to improve dispersion otherwise they may have to be installed in multidirectional arrays. I'm considering building one now myself.
  3. I think Mark Levinson was an early experiment which proved that audiophiles would pay big money for the prestige brand cache even if there was nothing substantive in either engineering or materials which justified those prices. The entire high end audio mystique is built around this now long proven fact that many people think that if something costs more to buy and is carefully marketed, it must be better. There is no reason to believe that the European made drivers are superior or even equal to the AR manufactured drivers but because Amati/Levinson said they were, there were more than enough people willing to pay for them. Funny how this is always justified as "research" when in fact it is invariably nothing than laughable tinkering and marketing when compared to what real scientific research and engineering are about. In recent years, it seemed to me that excluding the box, you could reverse engineer many high end loudspeaker systems for around 5% or less and certainly under 10% of their manufactured cost by simply buying the drivers at retail. What's more, the crossover networks could be made equal or superior using off the shelf active crossovers and multi-amplification than the passive designs ordinarily employed. Most of the drivers are either off the shelf or minor variants of off the shelf units so that when replacements are needed, the speaker system manufacturer becomes the sole source and can charge what he pleases. I'm talking about TOTL speakers from companies like Von Schweikert and Wilson which cost over $100,000. Frankly, whether objectively or subjectively judged I would expect the AR equipped driver version of the Cello Amati/LST to outperform the foreign made driver version but that's just a guess. Certainly we have discussed the inferiority of the semi-horn loaded dome tweeters in terms of dispersion before and this seems exactly correct but the very purpose of the design of LST was to devise a speaker system which further improved the lateral dispersion of AR3a's already excellent dispersion, otherwise why not just build it as another rectangular prism? This is why the HiVi tweeter cited in the other posting is no match for the AR3a/LST tweeter. The graphs linked in that posting tell the story. The HiVi tweeter is down 8db at 15 khz 30 degrees off axis compared to its on axis response (84 vs 92) while the AR tweeter is down only 5 db 60 degrees off axis. By comparison, the HiVi essentialy fires most of its top octave as a narrow beam. One would expect a considerable change in tonal balance as one moves in a circle from one extreme at 180 degrees left of the speaker to the center to 180 degrees to the right from an LST using the HiVi replacement tweeters compared to one with the original AR manufactured tweeters. I'd also expect the possibility of reflected hot spots from high frequency reflectons off the side walls as a consequence of the inner and outer tweeters' beaming characteristics. I would like to have been a fly on the wall the first time Sidney Harman got the amplifier design teams from Mark Levinson and Crown in the same room after he owned both companies and asked them to debate why a Mark Levinson amplifier should cost five to ten times as much as a comparably performing Crown amplifier. What a heated argument that must have been. Of course, Sidney Harman would have no problem raking in all those extra windfall profits on the Levinson units if people were still willing to pay the price. (Would you trade your Crown Reference amp for a Levinson? I wouldn't.) If there's one thing Sidney is fond of, it's big profits.
  4. On a more serious note "Ideas for Updated AR Library Section" One thing every library needs is a "shusher" and if it's a large library, a shusher-in-chief and assistant shushers. It's an onerous thankless job but someone has to do it. Being that this is a cyber-library, it will need a cyber-shusher. I made a few inquiries to see if Max Headroom had retired and might be available but his timesharing load of projects precludes him from helping out. Sorry I can't volunteer myself, I'm also maxed out. Good luck finding someone though. Minor detail but I thought it might be important :-)
  5. >While working on the repair and component upgrading of the >subject crossover, I became curious about exactly how the two >function switchs affect the frequency response. The switch >markings on the back of the speaker are rather vague (i.e. the >2500-7000 switch I call switch "A" has a 'lo, mid >and hi' setting). The greater than 7000 Hz switch I call >switch switch "B" has the same markings. But, what >do they accomplish exactly acoustically? > >The model 5 brochure claims "far more precise and >repeatable adjustments than do the simple variable resistors >offered for high-frequency adjustment of most multi-speaker >systems." > >I thought that a bit ambitions; claiming a 3 position switch >could be more precise than a rheostat of the type used in the >early Acoustic Research speakers. > >Anyway, using a function generator, Tenma digital dB meter, >spare cone midrange and dome tweeter (neither are KLH >products), I generated 108 data points via separate dB >measurements of each driver at 6 different frequencies (2-12 >kHz @ 2kHz intervals) while changing the two switch positions >in 9 different combinations of settings. > >Obviously, because I used NON KLH drivers in the tests, I >can't say with any certainty, what would occur with original >KLH drivers. However, I expect the general up/down trends to >be about the same. > >Here is what I found. (Write me directly at the email address >below and I will send the original M'Soft Excel file >containing the raw data matrix, charts and additional details >of the study). Please ignore the absolute dB readings. Only >the trends are of value in this study. There is no explanation >why the drop in dB level in the midrange at the 4 and 12 kHz >levels. The function generator power setting was set constant >for each driver over the frequences tested but was lowered to >a starting level of 80 dB for the more efficient midrange >driver. > >1)At 2 kHz level there was virtually no change in output of >either driver at the "A" lo switch position. 1-2 >increase in dB level was measured at the mid and hi positions >when switch "A" was moved to the mid and hi >positions. >2)At the 4 kHz level, the tweeter increased about 7 dB going >from lo to hi settings. The midrange stayed about the same or >dropped a few dB at the "A" switch mid and hi >positions. >3)At the 6 kHz level, the tweeter responded about the same >with about a 3 dB increase going from lo to hi. The midrange >driver dropped a bit again as in 2). >4)At the 8 kHz level, about the same results as the 6 kHz >level. >5)At the 10 kHz level, there was about a 2 dB increase for the >tweeter going from lo to hi. The mid dropped again. >6)At the 12 kHz level, the tweeter increased 3-5 dB while the >midrange behaved the same as in 2)-5). > >carlspeak@aol.com > >It's all about the music > >Carl >Carl's Custom Loudspeakers This project illustrates several points about speaker restoration. Because the midrange and tweeter are not KLH 5 model drivers, this speaker is not a KLH model 5, not anymore than a Dhalquist DQ10 is a larger Advent. That is not to say it may not be a better speaker, it's just a different speaker. The level switches on KLH Model 5 operate a low pass filter for the high range and a bandpass filter for the midrange both being in the tweeter circuit. The design and performance of such a circuit depends on the electrical characteristics of the driver which includes both its resistance and its inductance, in fact its complex impedence as a function of frequency. The use of generic crossovers or of a crossover designed for one driver but connected to another can have unpredictable results, often those not exactly intended by the original crossover design. Often designers will start with a standard design such as a Butterworth or Linquist Riley configuration and then tweak it so that it conforms to no standard design but optimizes it according to their own criteria. Measuring speakers in a meaningful way is also a very difficult problem because how the measurement is made can strongly affect the results. Often measurements are made one meter from the drivers on axis in an anechoic chamber using a calibrated microphone whose response is subtracted out, the drivers are measured individually and the results spliced or presented separately on the same graph. I think this is how AR did it. One problem in measuring drivers simultaneously or assuming their integrated response is that in the crossover region, there will be phase cancellations and reinforcements which not only depend on frequency but on the relative locations of the drivers and the microphone. Close miking can also be affected by diffraction of the baffleboard. KLH model 5 is less prone to this than model 6 because model 6 has side panels which project beyond the front baffleboard creating far more early reflections where model 5 doesn't. Speakers like AR9 use sound absorbing material to further reduce baffleboard reflections. Finally, the sensitivity of the replacement drivers is critical to maintaining timbral balance of the overall system, even a db or two difference between the original and replacement drivers can have a noticable effect. In the 1960s when Model 5 was designed and built, the tools available for speaker designers to tweak their designs were far fewer and more primitive than we have today. A project to reverse engineer a speaker like KLH model 5 using contemporary parts is far easier if you have a properly functioning model 5 as a reference and availability of digital active crossovers networks and a 1/3 octave equalier available. This makes selection of the replacement drivers and the ultimate design of a suitable passive crossover to match the optimal performance of the drivers much faster and easier. Once the optimal filter FR is determined, a passive equivalent to obtain the same or similar results is simply a matter of plugging the driver parameters and the desired FR into a software program and it will design a close match for you which you can further tweak.
  6. The AR2a added the orange "fried egg" tweeter to AR2. I've got a pair of both AR2a and AR2ax, both right now in need of repair. Sadly, I accidentally damaged one of the AR2a woofer voice coils by overloading it. It's the old cast frame type and I was suprised at how excellent it really is. Deep bass was astounding, definitely better than KLH 6. Unfortunately, the rest of the range was not so good IMO. There seems nothing special about these midrange drivers and the tweeter puts out very little sound even when the pot is bypassed. Are mine both defective? I don't think so there is no sign of any distortion out of them, just very weak output even with the caps replaced. However, by adding three 3/8" polys, one direct and padded down and two indirect, and a little judicious adjustment of the tone controls on my Pioneer SX950 receiver, they played beautifully, very satisfactory sound, very well balanced and very clear. Unfortunately I've run out of spare equalizers, I think I could do even better. Haven't done anything with the AR2axs yet. The woofers are the stamped frame type and need refoaming and I have to clean the pots and replace the caps. Maybe later this year if I find some time.
  7. I seem to remember the KLH Model 4 from an old Lafayette Radio catalog as a 2 way 12" acoustic suspension speaker system somewhat larger than Model 6 but looking very much like it externally having the same open weave off white grill cloth, same KLH logo badge in the corner. I never actually heard a pair. The library spread sheet says it had 2 12" woofers, I thought it had only one. (You'd think with 2, it would need a much larger enclosure like AR9.) It was priced about the same as AR3 and was intended to compete directly with it. The data on the spread sheet says KLH Model 5 was produced from 1968 to 1972 as was the Model 12. That's how I remember it also. I guess it's a little strange for the models 4 and 6 to both predate model 5 but I'd never heard of Model 5 until the late 60s. I do recall model 9 early on and I heard it at an IHF show at the Trade Show Building in NYC just around 64. At the time, some people considered it the state of the art.
  8. It's easy to reduce the sensitivity of a tweeter or midrange driver. If it's an 8 ohm tweeter, put an 8 ohm resistor in parallel with it and a 4 ohm resistor in series with the pair. This will reduce its efficiency by 6db without affecting the crossover network. You can do the same with a 4 ohm tweeter by putting a 4 ohm resistor in parallel with it and a 2 ohm resistor in series with the pair. For other sensitivity attenuation values, use the handy calcluator on this link; http://www.bcae1.com/lpad.htm Just be certain that the resistor wattage is rated high enough. Usually 5 watt resistors are fine but if they get too hot, try 10 watts. It shouldn't cost much over about $1 a speaker if that.
  9. Look at the top drawing in the link I gave carefully. You will see that despite a little confusion, there are only three terminals to the outside world. These are the white, red, and blue lines. Amplifier (or in the case of a midrange or tweeter level control the crossover section output) is wired across the combined shunt and series resistance, the white and red wires. The speaker is wired between the fixed common white and varible blue wires. So the white wire is common to both input and output. The L-pad is wired internally so that as one resistance value increases, the other decreases keeping the combined circuit the same total resistance from the amplifier's or crossover's point of view. BTW, in order to correctly substitute the proper fixed resistors for the potentiometer to replace it and make it non adjustable, you could use the table or calculator built into the web site but in order to get the one setting which will give the factory recommended "flat" response, you'd have to know at least one of those values, either the shunt or series resistance.
  10. This is easy to understand, you don't have to be an engineer. A potentiometer is nothing more than a variable resistor. It has three terminals. Two are the connections to each end of a fixed resistor, often a piece of coiled resistance wire. The third is connected to a moving contact which makes contact with the wire at one point along its length depending on where you position it. This can be used to control the volume of a speaker in either of two ways. You can use just two of the terminals so that the potentiometer is a variable resistor in series with the speaker, the crossover elements, and the amplifier. As the resistance increases, the current in the circuit is reduced, as it decreases the current increases. This is how the volume is changed. This was the case in the midrange circuit of AR2a (and it didn't work very well at all.) The other way is to apply the output voltage of the crossover network across the fixed resistor and apply one fixed leg and the variable terminal to the speaker. In this way the potentiometer works as a voltage divider. As the potentiometer is adjusted, the voltage to the speaker at its maximum is the full volatage of the crossover output applied to the speaker which is in parallel with the fixed resistor. At the other extreme, the volatage applied to the speaker is zero because it is the voltage between one fixed terminal and the adjustable one which is at the same position as that terminal. The problem with this scheme is that as you adjust it, it changes the resistance the crossover network sees and this not only adjusts the speaker volume, it changes the crossover frequency because its exact value is an element in the way this filter circuit works. An L-pad is designed to change the volume of the speaker without changing the resistance the crossover network is connected to. It consists of two potentiometers ganged together mechanically and wired together electrically internally. One is in series and one is in shunt. As you decrease the resistance of one, you are increasing the resistance of the other so that the total remains the same from the crossover network's point of view. This allows you to change the volume of the midrange and tweeter without changing the crossover frequency or slope so the adjustment only "shelves" the output of the driver, it doesn't change its frequency response. This is the scheme most manufacturers who incorporated midrange and tweeter level control used. L-pads are practically universally designed and manufactured to be used with 4 ohm and 8 ohm speakers. You'd be hard pressed to find one for a different load although they may exist. Here's a link for a pictorial view and another explanation. "http://www.bcae1.com/lpad.htm" BTW, you will never see one used to control the volume of a woofer. This is because putting any resistance in series with the woofer compromises its performance by lowering the amplifier's damping factor, that is its ability to control the woofer's inherent tendency to spurious resonances. It's not a problem with midrange or tweeter drivers however because of their low moving mass. Volume controls for subwoofers are invariably in the amplifier's earlier gain stage where they have no such effect on the amplifier output/woofer circuit.
  11. soundminded

    "Classic" Snells

    Peter Qvortrup is not an engineer by training. He was in sales. Needless to say, I find his "unconventional" philosophy inconsistant with my own views and experience. Not having heard any of his products, I can only make tentative conclusions and conjecture about them based on what he has put on his web site, his own postings, and that of people who own or have listened to his products. I have surmised that his tweeters are made by Scanspeak but I may have guessed wrong. His drivers are clearly not off the shelf units. That and the lack of hard technical facts and specifications invariably raises a red flag and makes alarm bells go off for me. However, I must admit that my own views are also unconventional but not even remotely like his. Aside from his kits, he has three basic loudspeaker models E, J, and K which loosely follow their Snell counterparts. All are 8" 2 way bookshelf systems optimally intended for corner placement. Each model has the same drivers in all of its variants which he calls levels but one model does not necessarily have the same drivers as the others. K is a sealed unit, E and J are vented and in larger cabinets. Each level seems to have been "tweaked" to a greater degree than the level below it using more exotic wires, crossover components, and possibly different box materials. As I said, with his most expensive unit, A/N E level 5(?) he supplies among other things enormous capacitors in separate enclosures which include 100 pounds of silver. He regards speaker enclosures as a musical instrument maker would regard the resonant box of a string instrument like a guitar In his ad copy, he cites the work of Leo Beranek but I only know Mr. Beranek as an acoustical architect and founder of the firm Bolt, Beranek, and Neuman, among the world's greatest acoustical architectural firms. I haven't seen anything related to any work he ever did with loudspeakers. I also find it odd that in the densely populated, highly affluent and sophisticated market of Central New Jersey, he doesn't have a single distributor or dealer. Audio Note has a full range of products which includes cd players, turntables, arms, cartridges, amplifiers, wires, and of course speakers. And like some other exotics who cater to current audiophile fads, he is a strong proponent of class A low power SET amplifiers. I think he offers a pair of 8 watt monoblocks for over $100,000 each. So you could conceivably send him half a million dollars to buy his stereo equipment. Or you could buy a lifetime of tickets to concerts and have enough left over for an occasional dinner out. :-)
  12. soundminded

    "Classic" Snells

    My friend drove his A IIs with a Spectrascan amplifier which I think was rated at 100 wpc. One speaker bass unit needed a replacement woofer which I think was manufactured by Becker. Obviously, the drivers were not the equal of AR's, certainly not the LF unit but it worked surprisingly well for a lesser model driver in its era. I think the A II used a 10" AS design and the A IIIi went to a 12" unit but I'm not sure. Peter Qvortrup has said If I recall him correctly that he considers the AIIIi to be the best speaker ever made but he cannot duplicate it to his design standards because of the difficulty of the crossover problem, one crossover point being as much as he can handle so far. As I said, I am skeptical of what he says but I remain as openminded as I can be to someone who is selling a pair of 8" 2-way bookshelf speakers for $125,000 and finds it necessary to incorporate over 100 pounds of silver in the crossover network capacitors. BTW, he has had Scanspeak or someone manufacture tweeters for him without ferromagnetic fluid which he claims dampens their performance compromising them. He also builds his best cabinets out of Russian birch which he claims has the optimal resonant characterisitcs. I frankly don't understand his philosophy claiming to tune the cabinet resonances rather than surpress them which is the goal of most other speaker designers. From what he has said, efficiency is an important characteristic of a successful loudspeaker design (what does that say about AR speakers or electrostatic designs?) His rhetoric on his web site is rather pompous and condescending relegating users of all of his competitor's products as "living in audio hell." I'll stick around for at least a while longer, I'm still waiting to meet Dante and Don Juan. :-)
  13. soundminded

    "Classic" Snells

    I first became aware of Snell when a friend of mine acquired a pair of A IIs which I heard in the early 1980s. I was astonished by its clarity and naturalness of sound and although it wasn't perfect, it was clearly a superior product in many ways. I later heard the J and K and was not at all impressed. By the mid to late 1980s after Peter Snell had tragically died, I heard the A IIIi at a trade show and was even more impressed than by the A II. I think one of Peter Snell's greatest contributions was his realization that what counts is not just flatness of on axis frequency response but the frequency response which reaches the listener. This completely changes the performace criteria and therefore the design requirements of loudspeakers and changes issues of dispersion and room acoustics from "by the way" to one of the central problems which must be addressed in truely successful designs. It also helps explain why speakers which measure similarly by the methods often used sound so different. It got me started thinking about how to solve this problem and experimenting with indriect firing drivers to compensate for the inadequacies of those which fire forward as well as room interactions. Peter Qvortrup originally of Holland owns a company Audio Note based in the UK which among other products has refined the designs of Snell E, J, and K each offered in various formulations by applying different drivers, special cabinet materials, exotic wires, and crossover components and tuning them in ways I personally don't quite understand. This has resulted in very expensive products (from about $1000 to $2000 a pair for a low end version of A/N K up to $125,000 a pair for one version of A/N E) which seem to have gained a highly enthusiastic following mostly in Europe and Canada although less so here in the US. He has made them very efficient so as to be useful with low powered vacuum tube amplifiers which he also sells. Although I am skeptical of his claims, I'm curious and keep an open mind hoping for an opportunity to hear them and judge for myself. There aren't many places in the US where they are sold and demonstrated and none convenient to my home.
  14. "The loose-spider phenomenon is completely normal for the AR woofer; the older the woofer, the less mechanical restoring-force the spider would provide. For example, the earliest ceramic-ferrite AR-3a woofers (with the wide masonite flange) were considerably looser than the woofers you describe from 1978." Correct me if I'm wrong Tom but I think this was the truest version to the ideal of the acoustic suspension principle. Virtually no mechanical restoring force at all. The later versions are a compromise to practicality and reliability.
  15. "AR4x was absolutely amazing reproducing that 1905 nickelodeon at >the trade show almost keeping up with AR3 at a fraction of AR3s >price. But in the showrooms with almost any recordings, the KLHs >just sounded more like live music. Again, I don't follow you here. Without an instant reference to a live performance, how can you make this judgement? Could this be personal preference? " Ah but there was a reference to a live recording. AR didn't just compare the Nickelodeon to AR3 but to AR4 as well. Both speaker systems one at a time as I recall it at the New York City consumer audio show (it has been 40 years but that's the way I remember it.) I think in the era of the early to mid 1960s the choice of equalization of commercial recordings during mixdown and/or perhaps the choice of microphones and their placement compensated for the characteristic voicing of the monitor speakers. While speakers like KLH6 and KLH 17 had much smoother response curves than say A7, they were more similar to it than was AR3 or AR4. Therefore when played through KLH6 say, those speakers sounded more accurate than AR3. Just a theory. The creation of a commercial recording is likely much different than a carefully controlled laboratory experiment and demonstration. The decisions of the commercial recording company may take the limitations of the equipment the recording is likely to be played back through into consideration so that it sounds best to the greatest number of people.
  16. Once again this shows the strange dichotomy between the accuracy of AR speakers reproducing recordings made under the most carefully controlled conditions and the seemingly more natural sounding and accurate reproduction of KLH speakers playing recordings made commercially. AR4x was absolutely amazing reproducing that 1905 nickelodeon at the trade show almost keeping up with AR3 at a fraction of AR3s price. But in the showrooms with almost any recordings, the KLHs just sounded more like live music. Personally, I attribute it to the coloration of the recordings of the day. Many studios in the US used Altec A7s which had a rather harsh upper midrange so characteristic of the horn drivers of the day and recordings made in Britain often used a comparable Tannoy. I recall how excited one sales rep from Altec was telling me he had just sold 59 A-7s to Columbia Records and another telling me that Tannoy was modifying their Concentric Monitor to sound slightly brighter to compete head to head with the Altecs. If the recording is equalized to sound flat in the studio in the final mixdown then the more accurate AR speaker will reflect that sounding muted and remote while the more forward KLH speaker will compensate for it. What a strange irony that the more accurate speaker loses out at all to the design which overcomes the consistant limitations of the recording industry. Today many studios use B&W 801s and 802s which have an entirely different tonal balance. Personally, I find the tonal balance of CDs much more consistant than vinyl phonograph records ever were and once a system sound is equalized to sound reasonably well balanced, it seem more satisfactory on a higher percentage of recordings than was the case in the past.
  17. KLH had a reputation for consistancy of the performance of their speakers. The promised specification was that every production unit would be within +/- 1db of the prototype. I assume that they stuck to that. This was a remarkable achievement for a company producing so many units especially in that era.
  18. Wonderful science, awful engineering. Performance especially in light of cost was a dream, but a necessary repair is little short of a nightmare. Only repairable at the factory which is now a continent away and probably isn't even willing to look at one. No user replaceable parts inside. No way to even get inside short of a crowbar or a sawzall. If I never need another serious repair, it may very well be the end. What a shame.
  19. I purchased a pair in the summer of 1965 serial Nos 39709 and 004940 used. They were apparantly very early models having the woofer cast into the baffle board and the grill cloth non removable. They were the first serious loudspeaker I owned. Immediately on delivery, one tweeter didn't work. I called KLH and they sent me a carton I used to ship it back to them in and the total cost was about $5 for shipping one way. They repaired it and shipped it back for free and offered me an apology. Try to get that today from something you bought even new. Unfortunately, mine are not so beautiful. They were apparantly the unfinished utility versions and the previous owner had painted them brown. You can still see the signs of where a tool was inserted to pry the baffleboard loose in this original repair. Both have been back to the factory while it was still in Cambridge mostly for crossover network repairs. At least once, they removed the cone of one of the woofers to work through the basket and then reconed it. This was not one of their better ideas and the design was of course later changed to have a removeable woofer with an integral full basket. One day I will reseal the surrounds but I'm sorry to say it will be at the sacrifice of the grill cloth material. That's life. I've always loved the sound of these speakers and although they don't test as well as AR3 or AR3a in may important respects, they always sounded more musical to me in their timbral accuracy and clarity of instuments using commercially made recordings. IMO, they are lightyears ahead of AR2a. Interestingly, on another message board, their smaller counterpart KLH 17 seems to have become a sort of cult speaker. Go figure. Kloss claimed in his advertising that a great deal of thought went into what he called the octave to octave balance of these speakers and if that means what other people call "voicing" it shows. He said in an interview that he would always use equalization in his subsequent designs to contour the frequency response of his drivers and that he had heard a competitor's model (he didn't say which one) which out KLH6ed the KLH6. Times change and progress eclipses prior achievements and frankly, the way my AR9s are configured now, they have the same basic musical balance as KLH6 (accuracy is accuracy no matter how you arrive at it) but beat them by far in every conceivable way. However, even after 40 years, I still enjoy listening to these speakers very much, a sure indication of their inherent attributes and remarkable value. They were far ahead of their time.
  20. The double wall sand filled enclosures may have been designated WD90 or possibly W90/2. Memory fades.
  21. "In spite of its reputation as power hungry speakers, the vast majority of the AR1/AR3/AR3a era speakers were used with low power amps by today's standards, and not typically played at very loud volumes." It's hard to remember that in the 1950s and 1960s a true 60 watt rms per channel amplifier was by the standards of the day a very powerful amplifier and only a handful of the most expensive models engineered for use as high fidelity even existed. 25 wpc was still a fairly expensive amplifier. For audiophiles on a budget, the logical solution to unaffordable McIntosh and Marantz amplifiers was Dyanco whose circuits were simple, straightforward, reliable, and easliy reproducible. Further savings were possible by constructing them as kits, something you don't see much of today anymore. There were others which were satisfactory although many considered them a notch or two down such as HH Scott, Fisher, Harman Kardon, Sherwood, Pilot, Bogen, Eico, Heathkit, and even Lafayette Radio (don't laugh, in 1960 they had a large 60 wpc power amplifier and a stereo preamp with about one million knobs and switches on it.) There is a major difference between the kinds of music and applications for most home audio sound systems of today and those of that era. Audio equipment then had a very specific goal and that was to accurately reproduce the sound of what is now refered to as acoustic instruments, principly and most demanding were instruments used to play "classical" music and serious jazz. Subtle differences in timbre between a Stradivarius and a Guarnari violin or between a one particular Steinway piano and another were very important. Audio playback equipment was part of a chain which could be considered analagous to a camera requiring a high degree of "photographic" accuracy. Also by today's standards, much of that music was not loud most of the time, the only truely loud music reserved for climactic crecendos. By those standards, much of today's music is vulgar and synthetic and as unpopular as it is, I personally can't give those standars up entirely. Today we live in a different world where most home sound systems have to do double duty as HT reproducing the experience of bombs exploding all around you, jet planes flying 20 feet over your head, 100 car railroad trains roaring between your legs as you watch the best excuse industry can devise at an affordable price as a home substitute for a theater movie screen. Music, or most of what is called music today is often in part or wholey synthesized from purely electronic circuits or if any of it ever had any origins in the real "acoustical" world has been so electronically manipulated as to have little recognizable resemblance to its origins. (Ever hear a "celebrity vocalist" on TV sing on say a Christmas show live without his reverb unit, his sound engineer at a mixing board, his 100 piece orchestra? You hear just how pathetic they really are when they are acoustically naked.) My best system's speakers are AR9 and I believe that the suspensions are stiffer than the older drivers. They are certainly stiffer than the original cloth surrounds and probably stiffer than AR3a, 10pi, and LST surrounds. I can't say if this makes them less true to the original acoustic suspension principle but they perform very very well IMO judged by their intended use and they can reproduce jet planes with the best of them when they are called upon. They can certainly shake my room and rattle my windows with my 60 wpc MosFet amp I built as a kit from Sound Values of Ohio (also known as Sound Valves) for $200 10 years ago (why didn't I buy several?) And who was Sound Valves? They were the last known source for spare parts for Dynaco whose inventory they had bought out. Alas, like the rest, they are gone forever.
  22. "Not an easy driver to replace...and probably not wise given the collector status these old speakers have achieved" Are there comparable alternatives for the experimenter and tinkerer who wants to build something comparable with currently available parts? It seems to me that achieving an F3 of 42 hz and a Q of 0.5 in a 1 1/2 cu ft sealed box is something other manufacturers can't or don't want to do. Even the Tonegen 1259 requires twice the volume. That's rather disappointing from an industry which has had fifty years to plagerize and build on this design. Is it that they just don't like it? Do you consider the relatively low sensitivity of this woofer to be an advantage? My first thought is that given how relatively inexpensive high powered amplifiers are today, it is because it gives you so much leeway to match it to other drivers of varying sensitivities and still maintain overall balance without bi amping tri amping to achieve the right level match. What are your thoughts?
  23. I'd go to a large electronics parts supply house first. Don't forget to check the dimensions of the original, diameter and height as well as voltage. I had a lot of trouble finding a suitable replacement for the caps that failed in a Dynaco SCA80Q until I ordered them from Soundvalves (no longer in existance). The originals were made in Scotland. The replacements were......Mallory. Surprise surprise. I think CRC is a large manufacturer also. Maybe Panasonic. You might check to see if the thermal conductive grease for the output transistors has dried out too. Let me know if you replace your capacitors and it works. That wouldn't have been my first guess for overheating. In fact come to think of it, I'not sure what would cause that. Bias current drift in the output transistors??? Bias control pots can get noisy just like any other pots.
  24. I'm using a Mosfet 120 I built as a kit about 11 years ago to drive AR9s. I think it's a fine amp. It was sold by Soundvalves also known as Soundvalues in Ohio who had bought up all the old Dynaco stock. This amp was kind of a successor to the Dynaco Stereo 120 designed by Klauss and Peterson who where quite famous. It's birdgable to 240 watts mono and always seems to run cool. It has a nice big power supply and sounds excellent to my ears. I took it to a friends house shortly after I completed it and several of us compared it to many fine amplifiers he had on hand including some Haflers and it held its own without any problems. My only regret is that I didn't buy several more. At $200 a pop for a box of parts and 7 hours of very easy assembly, it was a steal. It can easily make the AR9s thunder in a room of about 4000 cubic feet.
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