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soundminded

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  1. Allison's work was IMO brilliant and AR9 solved the problem of suckout too. Few other manufacturers to this day have managed to solve it. In fact they don't even understand it. Here's an example of a $109,000 speaker system. Compare figures 2 and 3. The suckout is about a 10 to 15 db drop between 50 and 150 hz, a loss of 90% of energy. Would you trade AR9 for this? I wouldn't. IMO AR9 beats the hell out of this. https://www.stereophile.com/content/wilson-audio-specialties-alexx-loudspeaker-measurements To make up for the lack of deep bass AR9 can produce, this manufacturer wants to sell you an additional $40,000 of subwoofers.
  2. Somewhere in the back of my cluttered mind I recall being confused about the AR3a crossover frequency being 475 hz and 425 hz from different sources. Did it change at some point during production? It always seemed to me that most loudspeaker drivers have a usable range of about 2 1/2 to 3 octaves but the full audible range is 10 octaves. Therefore in a 3 way system something's gotta give. For most speakers it's the bottom octave. But for AR3 and its derivatives it was the octave between the woofer and the midrange. This is why some people say AR5 was in some ways better than AR3a, it sacrificed some of the lowest octave to be a better match between the woofer and midrange. AR 9 was for me AR throwing in the towel on the 3 way design for achieving its goal by adding a 4th driver. Problem solved. In fact many problems solved. I wondered how other people did it. I never heard Infinity IRS but it seemed to me by using a large number of midrange ribbon drivers Arnie Nudell had solved it that way. The servo woofers crossed over at 100 hz. In IRS Beta he added a lower midrange driver because he didn't have many of his EMIM midrange ribbon drivers that IRS V had. But Paul McGowan who restored a pair admitted many shortcomings of IRS V and one was 100% harmonic distortion at some frequencies in the woofer midrange crossover region. Apparently he had a lot of arguments with Nudell about among other things including the quality of the woofers. Nudell used 6 cheap 12" woofers per channel in a sealed enclosure. In a posting about the servo system design Bascom King who designed the servo amplifier showed the open loop response of the woofers to have a resonant peak at 60 hz, suboptimal by AR standards. Small wonder the servo amplifier had to be 2000 watts. Only one driver had an accelerometer sensor for the servo circuit, the rest being assumed to have identical response. This brings up another very funny thought for me about how many audiophiles change their minds about their theology over time. In that example McGowan went from line source good to line source not necessary. Servo good to servo not necessary. Tubes bad to tubes good for input stages. Nudell's last effort before he passed away he called the IRS killer had a very similar woofer and lower midrange driver as AR9. Two side firing woofers and a front firing 6' lower midrange which was going to be replaced by an 8". However, Arnie passed away, McGowan hired a new guy and PS Audio's first speaker called FR30 is nothing at all like anything Arnie Nudell ever did. He will begin marketing it shortly. I think it will sell for around $20K a pair.
  3. The existing midrange works perfectly 99.99 percent of the time. Is it worth $200 for that extra .01 percent? Nah. Not really. My favorite turntable in the whole world is on sale in mint condition on ebay for $4000. I bought one around 1983 for around $250 still in mint condition and the factory offered me a brand new one for $450 but I didn't take it. I really wouldn't mind having another one now even though I listen mostly to CDs. But I've got about 3000+ vinyls. Do I really need another one? I've got other turntables too. Nah, not really. Even I have some commons sense.... sometimes. Crazy what people are paying these days for so called high end audio equipment. Glad I'm not an audiophile anymore. Do i use that well suspended turntable that copied the AR turntable suspension with AR9s? No, the bass of AR9 is so powerful it even knocked the laser off the track on some recordings on my old Denon CD player. Funny how you can buy a Wilson Alexandria speaker for $175,000 and then they want to sell you $40,000 subwoofers. I led a bass deprived childhood. That's what I call child abuse. AR9 has been making up for it for 37 years. Can't get enough of that bass. Incredible. IMO it does everything in the bass right.
  4. Stimpy, I used to tease Ken Kantor. He'd play his LSTs at a volume more suitable for Cerwin Vega or Klipsch than AR in his dorm at MIT. He'd constantly blow the tweeters out, take them down to AR and they'd replace them for free every time. I told him they'd keep them on a shelf under the counter so they'd be ready every time he came back for more replacements. I also told him the reason they hired him was that it was the only way they could recoup the losses they took on all of the free tweeters they gave him. Companies like AR and KLH had incredible service policies. They also had very tight quality control. From what I understand Edgar Villchur was a wonderful boss to his employees as well. And of course his products were a great value for consumers.
  5. I want to thank everyone for all of the help they've given me. I haven't posted here for a long time but I knew whenever I needed help I could always count on you guys. Thanks again. BTW, it wasn't really urgent. On some recordings when they are played very loud and there's a lot of content near the low end of its range there is a moment of harmonic distortion. It's been that way for a long time and it's not really a serious problem. It's not the amplifier or the source. I recapped the crossover network except for the cans on advice I got here with inexpensive electrolytics so that the sound would be the same as original. I had the woofers and lower midranges refoamed at the same time so the drivers were out anyway. That was 14 years ago. I just decided it might be nice to replace that one driver.
  6. Thanks David. I'm looking for an exact replacement. There are other AR midrange domes of the same size and similar type available but they aren't quite right. They are close though.
  7. I need a replacement upper midrange for AR9 part 20028. Anyone know of a source or know of one for sale. Thanks in advance.
  8. I explained how and why I re-engineered my pair. Clearly 901 offers something that is valuable to many people or it would not have lasted on the market as long as it did and it would not have sold so many units. IMO the original and series II were the best design. The criticisms of 901 are actually valid. However, being an engineer and a tinkerer I don't give up on something I like for one reason that attracted me to buy it in the first place because of something(s) I don't like and I try to see why I don't like it and what I can do about it. I'm not in this industry but I have many relevant skills I was able to bring to bear. No highs, No lows, it's Bose. There's more than an element of truth in this for 901. Why are there no lows? Because the equalizer was designed incorrectly. Further equalization fixed that but power requirements were far greater. Why were there no highs? Because what is now called a midwoofer has too much inertial mass to produce much in the way of high frequencies no matter how hard it is driven and what little it does produce would beam in one narrow direction from a 4" driver. The fix for that was to turn it into a two way biamplified speaker system. This was not nearly as easy as it sounds. The first half hearted try ended in failure. I have to admit it wasn't much of a try. The second try about 10 years later took four years to get it to where I wanted it. I've re-engineered many of my other speakers to because I don't like them for other reasons. This one though was by far the most challenging. The results were well worth the effort and the envelopment effect and other attractions of this speaker were not compromised, in fact they were enhanced.
  9. It's a tough problem. There are still a lot of AR 12" woofers out there that can be restored. The original larger Advent woofer may be comparable. Others used it including John Dahlquist in his famous DQ-10. Finding a paper cone woofer manufactured today that is a close match for the AR woofer is a tough one. There are some dome midranges around but you need to find one with a low Fs. It should be no higher than 1/2 the crossover frequency. The tweeter is the real killer. I don't know of any dome tweeters made today that come remotely close to the AR3a 3/4" tweeter for dispersion. Even the tweeter in the AR9 is no match in dispersion for the AR3a because the dome is slightly recessed. Perhaps an array of 3/8 inch mylar tweeters could work. For the crossover network you're on your own. I'd likely buy an active crossover network and triamplify it. I think the problem with a poly woofer if you can find one that's comparable to the AR 12" woofer is at the high end. It could be useful if you wanted to duplicate something like an AR9 where the crossover frequency is 200 hz. You have a wide choice of 8" paper cone lower midrange drivers usually sold as woofers.
  10. Hi, I'm back again. Sorry to disappoint you folks who hoped I was gone forever. I think the real value of Bose 901 for me was what I learned from the design. Despite its flaws, its claims some of which were valid and some absurd, it was a novel idea and a bold departure from the conventional wisdom of the day. I'll never forget the first time I saw one in a store window with its price tag. I thought who would ever be stupid enough to buy such a thing. Turned out I was and I've never been sorry about it. It was a lot of fun experimenting with it, understanding its unique qualities that made it so attractive to so many people and understanding and correcting its flaws that made it one of the most maligned products by audiophiles I've ever seen. Now for many newbee audiophiles who never heard of it let alone heard a pair it's something from ancient history that at worst gets a shrug. RIP Bose 901 and RIP Dr. Bose who built a privately owned billion dollar company from scratch starting with this product. I'll bet you laughed all the way to the bank.
  11. 12>5>6>17 among these 6 came first. Unequalized it's a better speaker than AR2ax. Equalized AR2ax beats it every which way. I own both. 17 is a 6 with a smaller woofer. This speaker has a cult following. Its shortcoming is its deep bass. Add a subwoofer and it's a very good speaker. 5 is a 6 with a beefed up woofer and two 5" high quality full range drivers used also in table radios and small package units used here as midrange units. Unequalized octave to octave balance is poor. Equalized it's probably an excellent speaker with bass that matches AR3a. 12 is 5 in a much larger cabinet for deeper bass and has an elaborate crossover that allows -,0,+ level controls for 4 frequency ranges. This was in the day before equalizers were available to consumers. There are variants of the woofers and tweeters between the various units but in some cases they are very similar. One nice thing about them is they didn't use foam woofer surrounds but they can need to be resealed. Roy has the magic goop. Use anything that hardens or cures and you've ruined the woofer surrounds. Among AR speakers AR3a was highly regarded but like most AR speakers I heard they didn't seem to have reasonable tonal balance. Equalization can probably fix that. LST is like an AR3a on steroids with 4 midranges and 4 tweeters to improve power handling and horizontal dispersion. 10pi and 11 used an improved tweeter having ferrofluid cooling. AR9 is considered the cream of the crop. It has by far the best bass and is a 4 way system. It took quite a bit of re-engineering mine to get the treble right. AR9 is in a class by itself. There is no other speaker I've ever experienced that can seem to dominate a room like AR9. Most peculiar. Unfortunately it does not have the high frequency dispersion of earlier AR TOTL models. This was pandering to those who wanted narrower dispersion. AR and KLH speakers are not known for "imaging." If that matters to you, you'd probably want to avoid them. This seems to be the be all end all for contemporary audiophiles. Frankly I don't care if the trombone player sits two feet to the left or right of the tuba player. I expect a tuba to sound like a tuba, a trombone to sound like a trombone. There are a lot of very expensive speakers out there today that can't seem to manage that.
  12. There seems to be a discrepency between the second and third thumbnails in the original posting. One shows a 40 mfd series LF blocking capacitor for the midrange array and the other shows it at 50 mfd. Otherwise all components in the midrange bandpass filter seem the same. Does anyone have an explanation for the difference? It should have at least some audible effect. LST appeared in an era before low cost consumer equalizers were available. IMO that is a much better way to adjust the electrical signal than the level controls on the speaker itself. Amplifiers were much more expensive and active crossovers also not widely available. 10 pi seems to have been designed with these limitations of that era also in mind. The Amati version demonstrates that the price for high end consumer products in general and audio equipment in particular does not reflect actual production cost but is more closely related to brand name perception. Jack up the price high enough and they will come seems to be their motto. In that era the most expensive speakers on the market were comparable to the price of a new car. Today it's comparable to the price of a new house. Things haven't improved that much but who am I to say how people should spend their own money.
  13. I still fail to see anything innovative here. 24 bit 192 khz digital audio signals, I've had that in Toshiba DVDs for four years and has been available in DVD players and recorders for as low as $30. DSP through a digital switching amplifier, old hat. (BTW on direct comparison to 1 bit 8x oversampling JVC circa 1991 it sounds identical.) Automatic room equalization, very commonly offered now even in low cost receivers from among others Sherwood and Pioneer. Heil air motion transformer tweeters, around since the 1970s, now being manufactured again and distributed by Parts Express. Looks like the subwoofers are a compact version of the AR90. By making the cones more massive, a lower system F3 can be obtained in a much smaller enclosure, a direct application of Newton's second law of motion applied to forced oscillation as simplified in the Thiel-Small cookbook. What would interest me is hearing an LvR comparison again. Others have tried it without the insight and skill to pull it off as successfully as Roy Allison did at AR. I think VMPS is one example. As for reproducing the sound of a symphony orchestra in an apartment, that is absurd on the face of it. Without recreating the effects of the acoustics of the hall it is normally heard in, even if it could be done it is not a pleasant sound. I know, I've heard many rehearsals of orchestras in practice rooms that are much larger than any room in an NYC apartment and it is not the kind of sound knowledgeable people pay good money to hear.
  14. I don't see anything particularly innovative about this equipment unless you consider the ratio of the price paid for the assembled merchandise received compared to the cost of the parts that that contribute to its function has reached a new paradigm. Everyone claims to have the best sound reproducing system in the world. Geddes, Linkwitz, Von Schweikert, Glasgal, and you could go on and on all make or imply that claim. Of course the truth is that I actually have the best one but that's an entirely separate story.
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