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  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Any frequency response that can be achieved through modifications at the crossover network level can be achieved at the preamplifier signal level with active equalization, invariably with much greater control. Further control over FR and relative levels can be achieved with active crossover networks and bi-amplification. The advantages are many including not presenting a risk to the power amplifier by creating a very low impedance load that could destabilize or damage it. IMO the current design trend for very complex crossover networks to replace better control offered at the low signal level so that amplifiers can be operated without such signal processing is an unfortunate choice. So called room correction systems are nothing more than automatic equalization with a different name. Unlike manually operated equalizers they don't offer the same degree of user control or flexibility.
  6. From the "for what it's worth" department, the best speaker in the world of the month award for January 2005 goes to.....(fanfare) TA-DA....NHT 3.3. I've always wondered what AR's bottom line would have looked like if a certain somebody hadn't blown out about a zillion LST tweeters every....xxxx and gotten free replacements What if that certain someone had bought Cerwin Vega speakers instead. I'm sure this is a very fine speaker and and excellent value but if you get them, be warned by the design engineer, it doesn't matter what part of a room you put them in so long as you adjust their position precisely with a micrometer
  7. I haven't heard the NHT 3.3 however I do have some observations about AR9 which I've owned for 29 years. AR9 as manufactured did not have accurate treble. There was no amount of FR tweaking between level controls and an equalizer that could get it accurate. Only substantial modification of the system's high frequency dispersion using a 11 outboard indrect firing tweeters per channel and careful tonal rebalancing could mitigate AR9s problems. Additional equalization is still required. AR9 recognized the problem that a 3 way system has covering the entire aludible range. Most drivers have a useful range of about 2 1/2 octaves to 3 octaves at most (IMO.) Something's gotta give and with AR speakers the region between the woofer and LMR always did one way or another. AR speakers also always had a tendency to a high end rolloff starting with AR3 and it never seemed to be satifactorily resolved to my ears. The modern trend is towards brighter more directional high frequencies. IMO this is a mistake, AR got it right with wide dispersion. AR9 does not have HF dispersion equal to older models as can be seen by the small recess between the tweeter dome and the front faceplate. I think it was a misguided concession to the more modern trend but it was earlier on in the late 1970s and therefore did not fully compete with modern speakers that can sound shrill and require you to sit where X marks the spot. Tonegen 1259 was patterned after the AR 12" driver I think with Ken's help. It's Vas is nearly twice as great requiring a larger box. With side firing woofers room placement is even more critical for bass response than it usually is for other speakes. Ken positioned Stereophile's test pair in their room using a micrometer :-) I'm not surprised without further optimization of AR9 it came out second best to NHT 3.3's treble, it would have been surprising if it didn't. However, given a choice between the two and knowing how to improve AR9 I would not trade. AR9 when restored (were the comparison speakers restored before auditioning?) it's one of the most potent bass makers I know of, far more capable even with a good 60 wpc amplifier than anything required in my 400 square foot 4000 cubic foot live listening room.
  8. Having two pairs of AR3as allows for some interesting experimentation with placement. Were I in such a fortunate circumstance the first thing I'd try is placing each pair side by side towing the outer speakers outward and the inner speakers inward in an arrangement similar to LST. This would further increase AR3a's already excellent lateral dispersion. Then I'd try them with the inner pair toed out and the outer pair toed in which should have a similar effect except you'd never be far off axis of at least one midrange and tweeter for each channel. Then I'd pull them away from the walls and try them as a direct/reflecting pair. If you have four separate channels of amplification and at least one equalizer you can experiment with the front facing and backward facing pair at different loudnesses and equalizations to copensate for the absorption/reflection properties of the reflecting wall. You could angle the backwards facing pair toed in or out to determine how different dispersions affect the overall sound field. Two pairs of AR3as will not achieve the same low frequency reach as a single pair of AR9s, they are tuned differently but they will double the power handling capacity to the point where any perceived loss of bass by pulling the speakers away from the walls and rasing them on stands could be compensated for with equalization without overdriving them (not easy to do in any event.)
  9. This scheme is not advisable although there probably isn't any risk of damage to your amplifier. The voltages are not likely to divide uniformly at all frequencies if for no other reason than differences in the resistances of the potentiometers will make each speaker's complex impedance different from the others. It will also vary due to other seemingly minor differences such as different actual capacitance values. The effective amplifier damping factor will be below one for each of them. The best method is to use multiple amplfiers, one amplifier channel per speaker. If you have two pairs this means two stereo amplifiers or four monoblocks. Adjust the settings one pair at a time to try to get them to match each other as closely as possible.
  10. 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.
  11. 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.
  12. 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.
  13. I don't know what puzzles me more, the prices asked for this class of equipment which seems outrageous when you consider the cost of DIY versions of them, especially the speakers or where there is a market for it. Considering how much of it is being offered the market there must be people somewhere buying it but I can't imagine where. People I know who can afford it aren't interested. I thought it was crazy when a home audio system cost as much as a new car, then a new luxury car. Now some of them cost as much or more than houses. Do they really perform better than mine? I'm not convinced by a long shot.
  14. Hi Vern. It's been a long time since I've seen your posts around here. I didn't try these other tweeters. They didn't do what I was looking to try anyway. And of course they are much more expensive. The mylar tweeters seem to do exactly what I want them to. They are small, cheap, and easy to find. The last batch I bought were so cheap I got 400 of them for $20. That's on top of about another 175 sitting in my basement that ran about 28 cents each. What I'm going to do with all of them I don't know. But if I burn a buch of them up, at least there won't be much to cry about. I've had 4 Tonegen ribbons in my basement for the longest time too. I don't know what I'll do with those either. They were part of a large batch of drivers I bought at a low fixed price. The rest weren't much to crow about.
  15. When I refer to absolute vector distortion, I'm referring to the overwhelming majority of sound propagated by a source. There are other types of vector distortion. (BTW, when you invent something, you have the liberty of putting whatever name you like on it.) Here's a simple example of what I mean. Next time you are at a piano bar or someone is playing a piano in a hotel lobby or a buskar (street musician) is playing a violin, or whatever, walk around the musician and the instrument. Notice that the tone of the instrument hardly changes at all. The rare exception may be a singer or a piano with its lid propped open. You'll lose some high frequencies when you're behind those. Now put your speaker in the middle of a room or better yet in your back yard and walk around it. Notice how the loudness changes. Much louder when you are in front of it, not nealy as loud when you are behind it. Because the vector propagation in different directions is so qualitatively different, in your listening room, the speaker can never sound like the musical instrument. This is because the sound propagated in different directions is reflected by the room differently in the two cases. Important reflections which give life to the musical instrument are quantatively absent and qualitatively different from the speaker. The sound coming out of it will always sound like its coming out of a box because most of it reaching you, especially at high frequencies is. Except for Bose 901. It is just about the only speaker where the sound actually seems to be alive in the room with you as though it was coming from actual musical instruments. This was IMO the reason it was so popular. Too bad its sound was so badly flawed in other ways that prevented it from reproducing the timbre of musical instruments accurately. The tendency of the 4" driver to beam or for 1" tweeters to beam for that matter compared to the midrange and woofer in ways real musical instruments don't propagate their high frequencies radically differently from other tones gives rise to another form of geometric distortion. My model explains these and many more. It takes a novel approach to the phenomenon of acoustics. It is this approach which is at the heart of my discoveries about sound and other inventions that arose from it including the one I patented. That idea may yet have the possibility of a new lease on life. That's why it remains unpublished. BTW, without these enhancements, the Alison speakers are probably a better bet for most people IMO. They will at least play the top octave of the audible spectrum. That's very important if you can hear it.
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