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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. IMO LST was designed to overcome some problems with AR3a. LST used the same drivers as AR3a but power handling capacity in the midrange and tweeters was quadrupled. This was before the era of AR invented ferrofluid cooling. Dispersion was increased dramatically. The AR 3a/AR2ax tweeter has the second best dispersion of any tweeter I know if, only being beaten out by Allison's own interesting design he produced for speakers under his own brand name. Allison was a great believer in wide dispersion. IMO he got it right and everyone else got it wrong. The way real musical instruments propagate sound into a room is much closer to LST than to any other speaker. The autotransformer in LST and the design of AR 10pi were at a time when graphic equalizers were not available to consumers. Now that they are, those level controls can be bypassed and the system spectral balance can be adjusted inexpensively by better means. As an owner of AR9s IMO in some ways LST was the best speaker AR ever made. In others it was AR9. Too bad there isn't one speaker that combines the virtues of both.
  5. The series III was the beginning of pandering to a lower end market that altered the balance between the cost of the speakers and the cost of the amplifier. The Series 1 and 2 were about $500 for the speakers and $1500 for an amplifier. They were acoustic suspension designes. I used the AR amplifier which actually delivered 90 wpc at 8 ohms. Starting with the series III ported design, the price inverted so that eventually you could drive the $1500 speakers with a $500 receiver. IMO the ported design sacrificed the bottom octave. Personally I thought it was an inferior product. I heard the Series 6 briefly at a Bose store in Newport Beach Ca. about 7 years ago. It has the same non existent high end I heard from my original 901s. I've redesigned mine making it a two way bi-amped system with both active and passive crossovers for the array of tweeters I added. I've posted elsewhere on this site about what I did. It took me four years to get it right. I've removed the 7 db hump at 250 hz I have and straightened out the 8 db falloff between 90 hz and 30 hz. The speaker is now even more power hungry than it was. It retains all of the desirable characteristics of the original 901 with none of its flaws. Except for its limited low frequency power handling capacity (it would take at least 3 pairs in parallel and 600 to 1000 watts of power) it will give my AR9s a run for their money and is actually superior in many ways.
  6. One minor correction about the original Bose 901 Roger, A speaker I'm very familiar with. The problem with that speaker's high end is...it doesn't have one. It cannot reproduce the top octave of sound no matter how much treble power boost is poured into it. Gordon Holt hit the nail on the head when he said the drivers had to much inertial mass. In plain language that means what we now call a 4" midwoofer makes one stinkeroo of a tweeter. At its indicated flat setting it does have a slight peak in the lower treble which is easily corrected by clicking the rotary treble control back one notch. Its other equally unacceptable problems are in the bass. Those are correctable with equalization but require massive amounts of power and multiple units. It should be noted when talking about AR3 and AR3a that many speakers of that era that were also highly regarded had a muted high end. That was the norm. Others that didn't, like Altec A7 were harsh. In the 1970s and 1980s the fashion became to produce speakers that were bright to the point of being shrill. These sold well to tyros in A/B shootouts in acoustically dead showrooms compared to better more accurate speakers. So did the booming ported designs that do not produce the deep undistorted flat bass AR speakers do. It wasn't until the customer got them home and listened to them for awhile that he became irritated by them. This created whole new opportunities of "fixes" for the industry including special wires, a rebirth of vacuum tubes, and the concept of break in. Ironically what facilitated this was the adapting dome tweeters by recessing them into small horns that narrowly beamed their highest frequency energy and making the domes out of metal that resonated, When CDs came along of course they sounded shrill. This gave rebirth to the phonograph record playing equipment industry but by then the recording companies had decisively abandoned vinyl production in favor of CDs.
  7. You have an air leak. Most likely it is between the woofer and the cabinet. Personally I like the black double sided tape Parts Express sells for this purpose. It is cheap and easy to use. I do not like putty. The putty in the AR2as I acquired had turned to glue. It took me several hours with a tool I fashioned to get enough of it out to remove the woofers. The putty in original Bose 901 hardened and cracked. Instead of removing 18 drivers I used clear GE silicone caulk to carefully seal the joints between the speaker frames and the wood and the screw heads. This is also cheap and easy to work with but takes about a day to cure, the tape works immediately. The GE silicone is also easy to remove if that's needed. Just be sure it isn't older than its use by date. If it is, volatile solvents in the mixture will have evaporated and the caulk will never cure. I found that out the hard way on another project. I had to call GE about it. Also be sure never to get any on the cones or suspensions. I think it's pretty safe and use my fingers to help form it before it cures. I just make certain to wash my hands immediately afterwards. So far none of my fingers have fallen off as a result of using it.
  8. AR knew long before 10pi and 11 it had a problem. This was why LST was created. Mid and high frequency power output capabilities where increased by a factor of 4. Horizontal dispersion, the best in the business at the time was also substantially increased. The cost of the angled cabinet had to be more than a rectangular box. The front panel adjustment of FR balance was rethought. Even so a certain individual who may have confused AR LST with Cerwin Vega blew those tweeters up on a regular basis (why didn't he fuse them?) My hunch is it got to the point when the counter men saw him coming they didn't wait to be asked, they started pulling replacement tweeters from under the counter knowing exactly what to expect. When it became obvious that this strategy was getting expensive and they didn't want to single him out by charging him for those replacements AR did the only thing it could do to recoup its losses on him...they hired him. Ken, you still out there?
  9. RoyC, In setting goals for a conventional high fidelity stereophonic sound system I chose a single objective to which everything else is subordinate. That objective is to accurately reproduce the tonality of acoustic musical instruments from recordings. For me if a sound system can't do that, whatever else it can do hardly matters, it isn't high fidelity by my definition. The more I studied the problem the more complicated it got. Timbre is only one aspect of tonality and spectral balance which affects timbre is a far more complicated subject than it first appears. The intuitive concept audiophiles have is a gross oversimplification to the point of being erroneous. Based on the understanding I developed, I have concluded looking at countless designs and no longer bothering to audition consumer audio equipment this problem has also defied engineering analysis of those working in the industry. No commercially available product or combination of products now or in the past when used as intended by their manufacturers can achieve this goal, that is they invariably fail almost every time. There may be a few experimental systems out there including my own which can come a lot closer when carefully adjusted for each recording. They take into account variables in parameters other designers haven't considered. Among these parameters is the three dimensional geometry of sound fields we hear. The inadequacy of equipment to control these variables satisfactorily is plainly obvious from their design. it doesn't mean they can't be enjoyed but they are not accurate, they can't be expected to sound like the real thing.
  10. Steve, I didn't mean to start a flame war....and I never said the sound of the AR3a was thick. The lower dynamic mass of the 10" woofer is easy to infer from the fact that the free air resonance is 26 hz against the 12" woofer's 18 hz. This is on the same page as the graphs I referenced. As one would assume the compliance of the two drivers is substantially the same having similar outer suspension and spider material, only more mass would account for a lower resonance frequency. This business about "speed" is so mixed up and confused among audiophiles it has gotten way out of hand. Let's start off with a fact. If two speakers of the same cone size and shape are playing the same signal at the same amplitude regardless of anything else they will travel at exactly the same speed at every corresponding instant. What may be different is called "group delay" which is the time elapsed between the application of voltage to the voice coil and the corresponding motion of the cone or membrane. There are many factors involved, mass being only one of them. Magnetic field strength is another. So is compliance. I have yet to see any demonstrated proof that so called time aligned or phase coherent speakers were better or even detectable from those that are less aligned. This test could only be performed with the same speaker using variable digital time delays between the drivers. Transient response and frequency response are two ways of looking at the same thing. It is the system response that is of interest to the user, not those of the individual drivers. If AR3a and AR5 woofers had the same FR at their high end the midrange would have had the same crossover point and slope and so would the two woofers. The only component differences would be to account for their different voice coil impedances. Frankly a 1 1/2 " dome driver is tough at its low end. Going by the same rule of thumb as for tweeters response should not extend below twice its resonant frequency. But looking at high quality dome midrange drivers from Morel, Hi Vi, and Dayton it's tough matching these drivers as low as 575 hz as in AR3a. AR5 pushed it up to 650. AR 9 pushed it up to 1.5 kHz and the tweeter to 7khz. Whatever difference does exist between the two speakers in this woofer to midrange crossover region can likely be reduced or eliminated with judicious equalization.
  11. The AR 12" woofer cone/voice coil assembly has greater inertial mass than the 10 inch woofer. This is of benefit at the low end of the woofer's range at the price of the high end. Recall one reason for the redesign of AR3 to AR3a was to cut the woofer's "ragged" response at the high end of the range. This required an improved midrange dome driver. Not only can the AR 10" woofer respond all the way to 650 hz to cross over smoothly to the midrange which BTW is less taxed not having to reproduce the frequencies between 575 and 650, in AR2ax it responds all the way to 1 kHz. In the same way KLH model 17 was superior transitioning from the smaller woofer to the tweeter than KLH model 6. AR5 should be a better speaker converting it to a 4 way with the addition of a subwoofer than AR3a alone. In Fact AR9 is a kind of AR5 where the size of the woofer used as an LMR is that of the even smaller AR4 series and the AR3a woofer is used (doubled) as a subwoofer. The audible superiority of AR5 over AR3a reproducing certain lower toned instruments like cellos has been noted by more than one reviewer. AR5 is therefore an overlooked "gem", an unwanted ugly duckling whose deep bass wasn't good enough for those wanting AR3as and too expensive for those who could only afford AR2ax.
  12. The tweeters are each 3/8" mylars. Unfortunately they are not adjustable, not in this configuration. Back in 1987 I went to a consumer audio show for the first time in a very long time. I liked the clarity of many speakers I heard and noticed that many high end speakers had a rear firing tweeter. I'd played with a 10 band graphic equalizer with my AR9s for years with no success. No matter how I adjusted it, it just never sounded right. I decided to take a chance. I went to Radio Shack and bought a pair of 3/8" 8 ohm mylar tweeters and placed them on top of the AR9s pointing straight up. I keep the AR9s against the wall behind them exactly as recommended by AR. I liked with I heard. Then I added another pair and another pair. Adjusting the program controls to LMR-3, UMR-6 and TW to -6 and using 10 band graphic equalizer (took 2 years) I got much better results. That's how it stayed until about 2008 when I acquired 175 4 ohm Sanyo 3/8" mylar tweeters at 28 cents apiece from Parts express. These were meant as snap ons for 6 X 9 car speakers. I arranged them to hang from each other vertically 4 per side firing sideways. I wired them in a 2 series strings which were wired in parallel combinations to keep the overall impedance a reasonable 8 ohms. (remember this is in parallel with three other 8 ohm outboard tweeters and the AR tweeter. I have never damaged or shut down an amplifier this way.) With 3.3 mfd caps for the whole bunch, the same used for each of the RS tweeters something was very peculiar. I'd created a duplicate of the strange sound I'd heard and remembered from the Snell Type AII and AIIIi. It was clear what was happening, a too strong lateral reflection at probably around 6 kHz or so created this coloration. This is done acoustically by the single Snell tweeter by gluing a piece of polyurethane to the center of the tweeter dome compromising its on axis output. I listened to it for a few hours, lost interest in it and never cared to hear it or Snell type A again. Eventually I settled on 2.2 mfd raising the crossover frequency of these 8 tweeters and the peculiar sound disappeared. Re-equalization has remained the same for the last 6 years with no plans to ever change it. With Bose 901 the opposite happened. That system is bi-amplified. At about the same time I added two of these tweeters per channel in series and placed them on top of the speaker aimed at the ceiling. This in addition to the four I'd also added horizontally 3 rear and one firing forward but the forward one having a resistor bridge network that cuts its output 75% compared to each of the rear firing tweeters. It is amazing how little sound these tweeters put out but what a powerful difference they make. I've concluded that while the human ear is not nearly as sensitive to these high frequencies as it is to midrange sounds, it makes great use of what it gets. Small differences in FR, loudness, and angle of arrival of these sounds mean a lot to what I perceive. Adjusting them for the room and matching the rest of the speaker system requires a lot of patience and perseverance. In the case of Bose 901 that took 4 years.
  13. In the library on this site there is a page which compares the FR of AR3a, AR5, and AR2ax. It is in the AR3a series frequency response and specifications. For some reason I can't cut and paste a link to it. These curves tell the story of what I hear. You can see right off the bat the low on axis output of the tweeter compared to the midranges and woofers. Despite the woofer having low sensitivity, AR3a tweeter pays the penalty of low on axis output for much better dispersion at the highest frequencies than contemporary tweeters that beam their high frequencies often making them shrill and piercing on axis. Look very carefully at the difference in the FR of the high end of the woofer for AR3a and AR5. There is more output from AR5 where it crosses over to the midrange dome, that is the dip where they have the same output is less for AR5 than for AR3a. AR2ax shows the crossover design defect where a 2 to 3 db peak at the woofer midrange crossover is to be expected from the graphs. And it is audible. The superiority of the AR3a woofer driver at the lowest frequencies over the AR2ax/AR5 driver is also obvious with AR 5's and 2ax's rolloff starting at a higher frequency and never making it to the left side of the graph which is 10 hz. It is also steeper than AR3a's. This points out a fact AR grappled with as well as all other speaker designers. A loudspeaker driver is a resonant device having a useful bandwidth of about 2 1/2 to 3 octaves. To cover 10 audible octaves with 3 drivers something always has to give and always did. AR9 killed the problem off with a fourth driver making it easy to cover the entire audible range. The added benefit of the super woofer design just added frosting to the cake. This low end capability results in a strange phenomenon unique in my experience to AR9, it can "take over" a room if you let it. It is unfortunate IMO that AR9 did not incorporate the tweeter section of LST using the same wide dispersion tweeters in multiples. I think if Roy Allison had a hand in it, it would have. To correct this I had to add 11 additional outboard tweeters per channel. They fire indirectly to create substantial high frequency reflections coming from above and to the front and sides of the listener the way AR LST does. With judicious equalization and use of the level controls AR9 is an excellent speaker by any standards. It's one flaw IMO is that it is not a direct reflecting speaker in my case between 200 hz and 6 kHz. To eliminate this flaw I'd have to design a speaker from the ground up. Altering AR9 to achieve these results with 4 additional LMRs and UMRs per channel would be an even more daunting task for me. OTOH, one day I might just try it.
  14. In the 1960s time after time AR3 and AR2ax sounded muffled, muted, lacking in treble, bland, call it what you like. Some generous people called it "polite." Phooey on politeness. My reference was and remains live unamplified performances of acoustic instruments. With musicians in my house and owning 3 pianos and assorted violins and violas, having attended countless live concerts I have the sound of live acoustic instruments well drummed into my head. One time I had a chance to directly compare the sound of AR3 with KLH model 17 for an extended period. AR3's bass was clearly far superior but from there on up there was no contest. KLH model 17 won hands down. Therefore I was surprised at what was until recently an unexplainable strong similarity between live music and recordings played through AR3 at the two demos I heard IHF trade shows in NYC in the 1960s. In the first one played against a guitar I was directly on axis and the AR3 was imperceptibly brighter than the guitar. In the second, Tom's statements to the contrary notwithstanding, The AR3s were on or near the floor while the nickelodeon was high on a table. The AR3 speakers flanked the table and AR4xs flanked the AR3s. The tonal similarity however was remarkable with full treble. In addition to most people operating these speakers with their controls in the "dot" position which is not their flattest response, as I now understand it Roy Allison who conducted the demos boosted the treble control on his Dynaco PAS3X preamplifier. This flattened the FR considerably. It was typical for audiophiles to always operate their preamps in the flat position and the obsession was so great, equipment manufacturers of better preamplifiers put a tone control bypass button on their equipment and then eliminated tone controls altogether. The last thing in the world an audiophile would consider is a graphic equalizer. That may be for the better since most in my experience don't know how to make the best use of them, expect instant results, and invariably fail. Nor are automatic equalizers called "room correction" particularly effective in correcting FR errors to the satisfaction of my ears. Having restored a pair of AR2axs when first turned on and played flat they had the same defective sound I'd remembered from the 1960s. However, with judicious adjustment of the level controls, tweeter full up, midrange slightly below the dot setting and appropriate equalization to boost the bass and treble and cut a small peak in the midrange AR2ax proved itself to be an outstanding performer with very high accuracy and not requiring outboard supplemental tweeters as all other speakers including AR9s do IMO. Placed diagonally in room corner AR2ax has the same treble sound everywhere in the room. In fact AR2ax's 3/4" tweeter has far better dispersion than AR9's recessed tweeter. Additionally AR2a and AR2ax (I have both now) demonstrated astonishingly clear and powerful bass. As of now with proper equalization I'd say AR2ax is clearly superior in every way to KLH model 6. I also have two pairs of those. However, it should also be noted that while AR2ax has outstanding bass it is not in the same league with AR9. You'd have to go some to equal that even today. The argument about HF rolloff of sound heard in concert halls to rationalize classic AR speaker performance by Villchur in the 1960s and the same argument used to design speakers for BBC in the 1980s is a flawed argument. These measurements were based on steady state response to what is clearly a transient phenomenon. The first arriving sound at the listener is the same you'd hear close up or out of doors with the strongest high frequency components that give sound their clarity and characteristic timbre. As the reflections die out the high frequency overtones die out faster than the middle and low frequencies. This can be seen in any text on concert hall acoustics in a graph of RT versus Frequency. By 8 kHz RT is usually about 50% of what it is at 1 KHz. Therefore unless you recreate the acoustics of a live venue you cannot accurately recreate the tone of instruments heard there. Most speaker designers today opt for brighter sounding speakers even though they are also wrong for recreating concert hall and opera house tonalities. At the current state of the art of home hi fi, the industry has not recognized this fact let alone addressed it. People seem happy enough with the current flaws in their equipment...for at least a week or two after they buy them when they start shopping for their replacements.
  15. AR5 should probably have been called AR2axa or AR2y. That's marketing for you. During the evolution of the AR2 series it slowly morphed into an AR3a with an AR2 woofer at which point it became AR5. The dilemma AR and everyone else faces who builds mulitway speaker systems is that loudspeaker drivers are resonant devices with a usable range of only about 2 1/2 to 3 octaves while normal human hearing is10 octaves. Something has to give and in AR's design of this era for its TOTL systems it was the match between the woofer and midrange driver. In AR3 the problem was with the woofer midrange crossover at the upper end of the woofer's range. In AR3a it was the same only the problem was with the low end of the midrange driver which had been improved over AR3. In AR2 series and AR5 it was at the lower end of the woofer's range which while remarkable for its size and cost is not nearly the equal of the AR 12" woofer. However the gain was in the woofer/midrange matchup. In some ways this makes AR5 a better speaker than AR3a at least to the way some people see it. The cost is the lower part of the lowest octave and power handling. The problem persisted until AR9 blew the whole problem out of the water with a separate lower midrange and two 12" woofers. Regrettably, at the same time AR gave in to popular market demand and compromised the dispersion of the midrange and tweeter going in the opposite direction of LST. LST was an evolutionary step up from AR3a in mid and high frequency power handling and dispersion.
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