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Howard Ferstler

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Everything posted by Howard Ferstler

  1. I first suggest that you absolutely make sure that you located each speaker in the same place and fed it the same signals from the same channel. That way, you eliminate any boundary-related issues and any issues with your amp, preamp, or source generator. Assuming you measured correctly, this situation is most likely a problem with driver aging, but the crossover might be having problems, too. A multiple malfunction, so to speak. The pink and white noise broad-spectrum level differences would probably not be related to capacitor deterioration. I suggest you swap the tweeters and see if the differences change places above 2 kHz. If so, then one tweeter might be having problems (or perhaps even both tweeters, given their respective ages). You could also do the same thing with the woofers. That will cull out any anomalies with the crossover. Howard Ferstler
  2. The Model Four crossover was the most complex one Roy designed for a two-way speaker, excepting perhaps the still later Model Four that he configured for the Kentucky outfit that brought the speaker back to life. Most of those he used with other two-way models simply installed ballast resistors in series with the tweeter. With the Model Four, not only did he use those attenuating ballast resistors, but he also installed a tapped connection to the choke, which allowed it to better dovetail when the tweeters were adjusted in level. Because of this, the level control is more complex than usual. Howard Ferstler
  3. Some CD-6 models retained the first-order tweeter filtering of the earlier Model 6 version. Many later CD-6 models had the same crossover network as the CD-7. The earlier version of the CD-7, namely the Model 7, had that same simpler network. Howard Ferstler
  4. I need to footnote my own commentary. One other mod I did recently was to insert an 8.2 mdf capacitor in parallel with each of the tweeter ballast resistors in all four networks (4 ohms in the inner panels and 6 ohm in the outer panels), as well as tweeter 4-ohm ballast resistor in the network within the center system I built. Thpse ballast resistors basically pad down the output of the tweeters (similarly to what we get with the tweeters in the Model One), but if one inserts a proper capacitor in parallel with that tweeter, as the frequency climbs the resistor begins to become bypassed and so the current flowing to the tweeter increases. This ramps up its output as its native output tends to roll off. My mod increased the output gradually above 8 kHz, reaching a maximum of +2 dB at 10 kHz and +4 dB at 12.5 kHz. Now, this may sound like a crank move on my part, but Roy actually did something like that with the resurrected Model Four he re-designed for the Kentucky outfit. He inserted a 12 mfd capacitor in parallel with that tweeter network's 2-ohm ballast resistor in order to get those tweeters to be a bit more impressive in the top octave. I used the 8.2 ohm cap because the tweeters seemed to be rolling off above 8 kHz more than they did when they were newer. I frankly think that both his and my "updates" would have zero impact for old guys like me, but it would certainly impress product reviewers who measured those systems and marveled at how they were potently flat right out to hypersonic frequencies. I did it on a lark, and would do it again. Howard
  5. The IC feature malfunctioned right out of the box. One or the other speaker would suddenly switch a panel on or off, and nothing I did (or what Roy suggested I do) fixed things. I even taped over the sensors on the fronts of the cabinets. I checked the schematic and there was one 1500 pfd capacitor in there that had me suspicious. (Its sole function, being hooked between the two G terminals in the IC-switching network, was to keep the 12-volt feed to that network from negatively interacting with, I believe, the tweeters.) If one looks at the schematic it can be seen that its insertion was an afterthought that resulted in some post-production problems. Whether or not it was the problem (probably not, since each system had one and the chances of both being defective were slim), there was a problem and after a while, since the omni mode was my prime listening requirement at that time, I figured that I could just hard wire things and stop worrying about sudden imaging shifts in the middle of a listening session. Prior to opting for my latest dual-network solution I spent some time with the systems hard wired to the focus mode, and it did not take long for me to realize that I wanted the switching functions back. Hence, those much more extensive mods done recently. Incidentally, Bill, I still have one of the IC network wall-wart power connectors for the systems, and it is possible that somewhere in my collection of old audio gear I have the remote switching hand-set too. If you hunger for either, let me know. I can at least surely supply the wall wart. All bets are off with that controller, however. Howard
  6. Yes, in the focus mode the attenuated panels are playing so low in level that it is impossible to accurately measure their contributions. The wrap-around sound from the louder panels, cabinet shading notwithstanding, simply overwhelms them. Their output is basically inconsequential as best I can tell. With my new, dual-crossover arrangement the outer panels can be (1) turned completely off, (2) attenuated by one to two dB, or (3) attenuated by perhaps 6 dB. The second assumption is based upon what Roy got with his Model One attenuations. The third is basically a guestimate on my part, since, as I noted, it is impossible to accurately measure the level of the attenuated panel without the output of the louder panel skewing the results. Up close you can definitely tell the differences in the panel outputs, but things get dicey as you move out further and get to the prime listening locations. I have listened to the speakers in the "stereo" mode of my system (surrounds and center turned off) and the difference between the now pseudo-omni mode (outer panels down 1 or 2 dB) and either of the other modes (completely off or down about 6 dB, as per my estimate with the latter) is surprisingly slight. You get a tad better detail and focus with the focus mode (needless to say, and this will depend upon room size/shape and sidewall materials), but somewhat, although not overwhelmingly so, better spaciousness with the outer panels running nearly full tilt (with room size/shape and sidewall materials again having an impact). The 6-dB down setting splits the subtle differences. However, once the surround and center channels are engaged all bets about stereo performance, soundstaging and imaging and clarity are off. the differences, especially involving spaciousness, become slight, indeed, and even the detail and focus differences become less apparent, due to the impact of the MTTM vertical array on the center speaker. The more speakers you have in a system the more things tend to blend together into a systematic whole. I rather like it that way. Howard Howard
  7. Hey, I am back. Here is some poop on those IC-20s of mine. The IC circuit switching acted up almost from the beginning and I finally decided to hard-wire the things into the omni mode and leave it at that. I gutted the IC network, and removed the sensors and lights on the front, covering the holes with a small brass plaque that says "Allison." This was my first mod and I could pull it off, because I had the crossover and IC schematics, courtesy of Roy. The second mod, done some years later, was a complete rebuild of the crossover network, following the factory specs. This involved replacing the old, back-located crossover mount with standard 5-way binding posts and rebuilding the network (new caps, new resistors, same chokes) on a triangular-shaped board that was screwed to the interior bottom of the cabinet. While the original cap arrangement had some poly jobs for the mid and tweeter sections and one standard non-polarized job for the woofers, the replacement caps I used were all poly types, including a physically huge one for the woofers. Because the new network used up some space at the cabinet bottom, the original reversed woofer tube would no longer fit, and so I re-configured the woofers both facing forward, just like with the Model One. Because I use outboard subwoofers for the frequencies below 80 Hz the modest increase in even-order distortion caused by this change would be meaningless. More on the subwoofers, below. However, now I have even more substantially modified my IC-20s, basically installing TWO crossover networks into each. The original network had to kind of split the difference in terms of choke and capacitor values, because it had to sometimes handle both four tweeters and four mids (omni mode) and at other times handle just two of each, with only a modest amount of feedback from the greatly attenuated other-panel drivers (focus mode). This works OK, because of the wide coverage capable from the mid and tweeter drivers, but it actually was not as perfected an arrangement as Roy got with either the Model One and Model Two units, or the Model 9 and CD-9. Those have the crossover chokes and caps precisely aligned with the fixed driver loads. Yep, two separate networks in each system. The one for the inner panels is similar to the version in the Model One: two tweeters, two mids, two woofers; and with some subtle changes (slightly different series choke and capacitor values) to compensate for driver aging with the midranges, plus going to second-order filtering for the tweeters to protect them better than what was possible with the first-order filtering of the Model One. (Note that the factory IC-20 also used second-order filtering for its four tweeters, as do all of the CD and AL series systems.) The outer panels each have their own crossovers (mounted on still another board and screwed to the interior rear of the cabinet, just above the binding posts), with the parameters similar to the mid/tweeter sections of the inner panels. The mid-tweeter panel networks are wired in parallel (each is nominally 8 ohms, like a Model One, with parallel wiring delivering nominally 4 ohms), and the outer panels can be turned off with 20-amp-rated switches. No changes were made to the networks for the woofers, which run together full time. Both panels have their driver complements fully protected by a total of FIVE polyfuses, each sized for the loads involved. The original IC-20 had three. Further mods involved some additional switch work. The inner panels have permanent resistors installed in their networks and those resistors partially mimic the "concert-hall slope" Roy made possible with the Model One's own switching option. The slope chosen for the inner panels was somewhat between Roy's full slope and the less aggressive middle slope. The outer panels use slightly larger contouring resistors, given them the full-slope contour. This means that the outer panels play one or two dB less loud than the inner panels when they are turned on. An additional switch for each outer-panel section allows the option to drop the output of the turned-on outer panels about 6 dB lower than the inner panels, kind of splitting the difference between the focus and omni modes. Finally, two additional switches allow the user to decrease the output of any of the panels in operation several dB in two stages. Because of impedance differences seen by those switches when either the inner or outer panels are in operation they offer up different attenuation amounts. With just the inner panels working each switch uniformly drops the mid/tweeter output by roughly 2 dB. With both panels in operation each switch uniformly drops the id/tweeter output by roughly 4 dB. These attenuations do not change the slopes of the contouring; they just change the mid/tweeter section outputs in relation to the woofer outputs below 350 Hz. The switches used for this additional contouring and shaping are also 20-amp rated jobs, and I do not expect them to develop oxidation problems. Most members of the Allison group I belong to know that I also employ flanking "ambiance" speakers, with a pair of side-wall mounted Model Fours each 30 inches away from the front wall and sitting on 5-foot high bookcases (these Fours are also modified to pretty much mimic what Roy did with the Model Four he designed for the Kentucky people) and a pair of Model Eights (modified to mimic the network behavior of the later CD-8) at the same height and on identical bookcases flanking the listening couch further back into the room. The output levels of these four surround speakers are MUCH lower in level than what we get with the standard Dolby set-up parameters, because it is their job to add a comfortable amount of simulated hall ambiance to the classical and baroque music I listen to the most. In my case they were initially set and then modified by the program in my mid-grade Pioneer receiver. I use the Dolby "height" mode to deal with those more forward surround speakers. I can leave the receiver settings fixed, because this installation is used for music listening only. This package also has a single, floor-standing center speaker (38 inches tall, with an angled-back slightly front panel) that uses Allison mids and tweeters in an MTTM vertical array, with a single Model Four woofer. The crossover network for the mids and tweeters is identical to that for the inner-angled panels of the IC-20s, with the woofer network mimicking what we have with the CD-9. I built the cabinet myself out of thick, solid cedar and MDF. The grill is a cut-down IC-20 grill. It has no level controls, and it is set to operate about 2 dB below the standard Dolby set-up level. The installation also has two subwoofers: cylinder types, 68 inches tall, 14 inches in diameter, with Dayton Reference drivers, and with power coming from a Crown XLS1000, 350 wpc power amp. An ART equalizer contours the sub outputs below 80 Hz. This arrangement with the IC-20s allows me to both shape the radiation pattern of each system from wide (but favoring the inner angles) to the usual, dual-panel super-wide pattern, and to adjust brightness levels when faced with recordings that are a bit too brittle sounding for my taste. Most of the time I run just the inner panels, plus the center and surrounds, with the slope adjustments turned off. This is a lengthy description of what I have done, following parameters set up by Roy long ago and not wildly experimental, but with some changes that are related to driver aging. If anyone is interested I can post some photos, at least once I figure out how to do it. Howard Ferstler
  8. This is my last visit and last post. I leave the field to Zilch, speakerdave, Ken, genek, and so forth. I move on to enjoying my throwback audio systems and my recording and book collections. Incidentally, I have removed all of the attachments that I previously installed in posts (pictures, graphs, PDF article reprints, etc.), because if I leave this place my stuff leaves, too. I only wish I could eliminate all of my posted messages. Those still itching to view graphs of any kind need only scope those supplied by Zilch, but don't expect to see any photos of his listening room. PS: at least, when I was here I used my real name, which is more than I can say for some of you people. Howard Ferstler
  9. If one cares to, they can go to the "kitchen" section and check on one of my posts dealing with the "Roy Allison interview in 1992 issue of The Audio Critic, David Ranada was the interviewer." Some here may be interested, because that particular post by me (which shows up on page 3 of the series) has an attached review of the AR-303 loudspeaker done by Julian Hirsch back in 1995 (Stereo Review magazine). What may interest some people here even more is that Hirsch does A/B listening and measuring comparisons between the 303 and the AR-3a. I would post the attachement here, but I have only a limited amount of attachment space left. Howard Ferstler
  10. Attached is a copy of Julian Hirsch's review of the AR-303 in the June, 1995 issue of Stereo Review. I have to assume you were happy with his assessment, too. In it, he does a direct measuring and listening-session comparison between that newer speaker and the AR-3a. Note that he got the crossover specs wrong with the comments on the AR-3a, saying they were 550 and 6.5 kHz, when they were actually 575 and 5 kHz. Well, nobody's perfect. Interesting that the 303 woofer is run up to a somewhat higher (and more directional) frequency than that of the 3a. The important thing will be his listening/comparing work, and everybody here who owns either speaker will certainly be interested. Howard Ferstler
  11. Two points. First, it is interesting that Allison's article on imaging and directivity that I posted on the "Library Additions and Corrections" page has managed to get a total of 80 hits, while the Kitchen thread that "debated" the issue managed to get over 2500. How in blazes does anybody debate (or read debates even if they are not posting any comments of their own) about what Allison said about dispersion and NOT go and read Roy's paper? OK, OK, I know that some here went into and out of the kitchen debate numerous times and probably only accessed Roy's paper once, but did each of those 80 article readers then go into the kitchen debate over 30 times? Second, yes, the Kitchen "debate" series was finally shut down by the webmaster, no doubt because things were getting pretty heated. (I am glad to note that the final bunch of caustic messages in that lengthy thread were at least not posted by me and that most of my postings were lengthy, fairly decent, informative, and not obnoxious defenses of my postions.) However, in addition to getting heated they were also, at times, getting pretty interesting (and informative), and shutting the whole thread down in order to calm certain people down (possibly the webmaster needed more calming than anybody else) smacks of an almost theological concept of protection. Hey, if things get REALLY bad, send a warning to the participants, and if they continue to be REALLY bad, then shut the thread down. However, I do not think that particular thread was headed towards perdition at the time it was terminated, and the fact that it scored over 2500 visits shows that it was a manifestly popular session. Howard Ferstler
  12. I recently posted an additional article about Roy Allison in the Library additions and corrections section. This one is an interview Roy gave to Ranada as part of a series in the Spring/Summer, 1992 edition of The Audio Critic. In the article Roy not only discusses the Allison boundary effect (something he discovered as part of his research on the AR-3a in typical home-listening rooms), but also offered comments upon the series of live vs recorded concerts Edgar Villchur presented when both were at Acoustic Research. Virtually all AR fans should be interested in what Roy had to say about those concerts, since they relate to the real-world quality of the AR-3 speakers used in the demos. I bracketed that section in pencil marks in the draft when I first read it years ago. Howard Ferstler
  13. In the "Library additions and corrections" section I just posted a PDF copy of a draft that Roy Allison presented at the 99th AES convention in October of 1995 . It deals with loudspeaker directivity. Howard Ferstler
  14. I just posted a PDF copy of a draft that Roy Allison presented at the 99th AES convention in October of 1995 in the "Library additions and corrections" section. It deals with loudspeaker directivity. Howard Ferstler
  15. Obviously, any components other than wire will have some kind of impact on the sound of a crossover network. After all, it is the job of such components to do just that. Assuming equal resistance values, no resistor will sound different from any other. There is no esoteric characteristic that would make one sound different from another. What might matter is power-dissipation ability, however. I suggest using at least ten-watt rated versions for AR speakers of this vintage. Howard Ferstler
  16. I just got off of the phone after chatting with Harry Munz about the AR Live vs Recorded sessions a few decades back. Harry is a long-time technically adept enthusiast who also did a LOT of recording work for Gothic Records a few years back. If you have any Gothic recordings (they specialized in organ performances, with the results being some of the finest releases with those instruments that one will ever hear) you might find Harry's name printed on the back as the recording engineer. Anyway, while discussing Floyd Toole's book on speakers and rooms I brought up the AR sessions that Toole rather flippantly dismissed in the book and Harry indicated that he attended several of them. (Toole did not attend any, by the way.) With those involving the string quartets Ed Villchur first did the demos in front of a group of audio professionals, including journalists. He wanted to see how the situation would work with seriously critical listeners before putting on more public concerts. Harry was there, too, and he indicated that with his young ears (he is 82 now) he simply could not hear any difference between the live quartet ensemble and the AR-3 speakers. The listening group as a whole was stunned by the performance. Later demos in front of hobby enthusiasts were just as impressive. Harry said there were also demos done with a live guitarist and in that case he said he could detect a difference if he sat in the front row. This is because the speakers were located a bit higher up than the instrument and he could hear the vertical image shift. At a later demo he made a point of sitting further back and the differences were nil, because the distance blurred the image-shift discrepancy. Harry mentioned that some critics of the concerts (those who had not been there) have said that a quartet or guitar would be easier to reproduce than a full orchestra. Of course, if we are talking about a pair of AR-3 speakers facing off against a 90-piece ensemble in a large hall that would be the case. (Harry indicated that a multi-channel recording using lots of AR-3 systems and lots of amplifiers would have been able to do the trick, however.) Mostly, this would be because it would be impossible for even the best recording engineer to get a decent, mandatory anechoic recording of so many instruments done properly. Even with a quartet Villchur had to work to get the input balances just so. Harry has recorded a lot of ensembles (besides organs) and he indicated that a small ensemble like a quartet is actually HARDER to reproduce cleanly than a large orchestra, because the more instruments you have the more masking we have taking place, and so detail and precision become less of an issue. With a quartet, detail and precision are critical, and only a fine speaker can do the group justice. I bring this up, because in my review of Floyd Toole's book I pointed out that the Villchur demos basically undermine Toole's basic premise regarding the status of speaker design in the old days, and in this more modern age, too. Harry indicated that speakers have improved a tad (like me, he owns a pair of Allison IC-20 models), but only in areas that Roy Allison sought to improve upon: bass-range smoothness and dispersion qualities that add spaciousness and depth in typical home-listening spaces. Harry also indicated that a great pair of speakers in a so-so room will not sound as good as a merely good pair of speakers in a superb room. The room is way, way more important than a lot of enthusiasts understand. Villchur understood this with his concerts, too, of course. Both he and Harry knew that smooth response was the key with those concerts. Howard Ferstler
  17. Your Audio System is Terrific. How good are your ears? Some time back I received a remarkable piece of test software, and as best I can tell it may be the most important audio-related check disc in history. I did a review of this disc for "The Sensible Sound" years ago and I am installing an updated version of the review here for interested audio enthusiasts. It is called the “Audio-CD” (stock number 25172-02001) and is available from an outfit called Digital Recordings, in Canada. The company has a web site at: www.digital-recordings.com. It basically contains a hearing-threshold test that many of you will find much more interesting than any other audio-related test you could possibly think of, including even the most arcane ABX tests of amps and wires, or computer programs designed to analyze the blazes out of speaker systems. Most audiology exams are designed to evaluate an individual’s ability to function in a world where conversation is important. As such, the upper frequency limit of an “audiogram” printout created by such a test is usually 8 kHz – which is rather low in frequency by high-fidelity sound-reproduction standards. The lower frequency limit is usually in the neighborhood of 250 Hz. There is a reason for these general limits. If you can hear that high up and that low with reasonable effectiveness it is likely that you will be able to hear what people say without having to lace your assorted responses and comments with the words “What did you say?” or “Huh?” And out there in the real world the most important thing for most people is the ability to clearly hear what other people are saying. The Audio-CD hearing test, on the other hand, is a whole different ball game. Rather than just test for conversation-related hearing acuity, it tests for high-fidelity sound reproduction hearing acuity. The disc allows a careful participant to evaluate their threshold hearing ability over an 80-dB range, and do so at 24 frequency points from 20 Hz to 20 kHz. It does this with a degree of precision that should be able to separate the golden ears from the tin ears in a very serious hurry. OK, let’s be realistic. This is a very dangerous test disc. First, because if the person using it is not careful they will produce erroneous results. Second, because the disc has the potential to pull the psychological rug out from under just about any golden eared enthusiast who cares to fool with it. There is no baloney with this disc if it is used properly: you either have the ability to hear well or you do not. Note that I said “hear well” and not listen well. There is a difference. There are people out there with superb hearing who would be indifferent to the nuances delivered by a good audio system. On the other hand, there are also individuals out there who might not have the hearing acuity of an 18 year old, but who have worked hard over the years to recognize what is and what is not important in high-fidelity sound reproduction. And while in the best of all worlds a true audio connoisseur would combine both abilities into one ear/brain combination, I think that those with decent hearing and seriously good experience can still survive pretty well in the world of high fidelity. Still, there is no denying the value of a disc like this as a test tool, provided the individual who obtains it and uses it properly is able to live with what it reveals. This is a dynamite piece of software and only the most intrepid designer, audiophile, audio salesman, or product reviewer will be courageous enough to play around with it. The disc comes with a good introductory fact sheet and set of instructions, and basically it is easy to set up the procedure. First, however, you do need a good pair of headphones. Junk versions will not do the trick. The fact sheet mentions three models that should work satisfactorily: the AKG-K270, Sony MDR-7506, and Sony MDR-484. I used a pair of Sony MDR-V6 models, and I feel good about them, because a Sony representative told me that they are pretty much identical to the 7506 model. One on-line reviewer who evaluated the disc used Grado SR325 models with good results, and a very knowledgeable engineering friend has told me that the Sennheiser HD-280 phones are a good choice. Another, possibly best of all choice would be ear-insert headphones, such as those made by Etymotic Research. If you use a pair of headphones that do not have the ability to deliver uniform frequency response, or use a good pair improperly, the results you get with this disc may be compromised. The company offers an audio-calibration device, the DR1-R acoustical coupler, that allows you to check the linearity of a set of phones with a Radio Shack SPL meter. You can check the web site for information on that tool. It will help the really serious enthusiast insure the best overall accuracy with the disc. Initially, you have to test the performance of your CD or DVD player, to make sure that it handles the test procedure without any glitches. The disc has tracks on it to do that evaluation, and that is the first thing you should do before getting on with the test of your hearing. After certifying that the player is OK, you go on to calibrate the volume-level setting of your headphones. This involves listening to a basic pair of test tones that will determine just how far down in level you should set the gain control on your amplifier. You have to be careful doing this set-up procedure, and I advise you to find a VERY quiet part of your house to do the work. Probably, this will be your regular music-listening room, with all the doors closed and the wife and kids temporarily shunted outdoors. You might be tempted to use the CD-ROM drive of your computer, but it is likely that the cooling fan in the computer’s CPU will generate too much noise. It is ESSENTIAL that there be near-zero background noise while doing the tests. Incidentally, one way to help achieve this low background noise level is to use over-the-ear headphones, which can attenuate outside noise by as much as 30 dB. The Etymotic phones mentioned above also attenuate, because they insert directly into the ear canal. The calibration test consists of a series of test tones on track number 2 that are repeated over and over. (Track number one has an announcer giving some procedural instructions.) They are at easy-to-hear frequencies, and the idea is to set your amplifier volume control at a point where you can just barely (and I mean JUST BARELY) hear the set-up tones. If you want, you can find someone else in your family who may have better hearing than you do to do this part of the test. Use several different people if necessary, and get that amp-gain setting as low as possible. For this part of the test it is very helpful to have a preamp, processor, or receiver that has a digital dB readout indicator. That way, it will be easy to see who obtains lowest gain setting and it will also then be easy to do the test again later on by just resetting the level to the same point. Note that if you change headphones from session to session all bets are off, since different phones will have different sensitivities. (Ditto if you decided to some of the tests again with speakers, just for kicks, although headphones are your best bet, for sure.) Once the reference gain setting is discovered, leave it be. It should not be changed during the rest of the test. The remaining tracks, from 3 to 26, consists of pulsing tones that start out at very low levels in the left channel and get progressively louder at one-second intervals, with the level increasing by one dB each second. You listen until you can hear the tone in your left ear, and then make a note of the time-elapse number on your CD or DVD player’s digital readout. That number shows how many decibels up from the set-up reference level the signal has to increase to make it audible. You do this with each of the 24 different test frequencies between 20 Hz and 20 kHz, and then plot out the results on a graph that is supplied with the disc. The graph contains a pre-printed curve that basically outlines just what someone with near-perfect human hearing would be able to do. You compare your results with it and see just how golden your ears happen to be. Then, you turn the headphones around and do the test all over again with the right ear. Because there is only one graph in the kit, I suggest you go to a copy center and make quite a few duplicates to use, leaving the one that came with the disc as a master. Now, here are some observations. First, do not just do each test-tone sequence once. It is usually difficult to recognize the signal as it first rises towards audibility and so you will want to use your player’s back-scanning feature to scroll back a ways and then move forward again. Do this over and over as you begin to recognize the character of the threshold-determining signal at that specific frequency. You will discover that you can work your ways backwards quite a few seconds once you know what to listen for. This is important. You are testing for threshold hearing acuity, and to do this you have to be familiar with the tonal character of each of the test signals. Second, your honesty notwithstanding, it is good measuring practice to have someone else administer the test to you, and with you facing away from the administrator so that no non-verbal cues can be given. The person taking the test can signal the administrator with hand clues as the test progresses. You can do the test solo, by watching the elapse-time readout yourself, but you have to be honest with what you think you are hearing. Third, as I noted before, do the test in a quiet space. When I did my series, I noticed that even the slightest bit of extraneous noise made it difficult to detect some of those threshold signals. My wife discovered the same thing when I had her take the test. She became very aware of even very slight low-level interference noises, even with the Sony MDR-V6 phones. If your air conditioner is on that can have an effect. If you shift the phones on your head that can have an effect. If a car drives by your house during a particular sequence that can have an effect. Even your own breathing can mask some thresholds, as can any degree of tinnitus you might have, particularly at the higher test frequencies. Believe me, this test can frustrate even those who are maddeningly calm most of the time. The trick is to go at it carefully and methodically. Fourth, make sure that your phones are working OK. Even the ones I mentioned above can have problems. In addition, the first test on the disc is at 20 Hz, and some phones (the Sony model I used, for sure) simply cannot reproduce that signal with adequate force. As a consequence, I used my phones only from 40 Hz on up and used my F1800RII subwoofer for the 20-Hz trial. (This required re-calibrating the set-up tone for my speaker systems, of course.) I also did the full test a second time with the speakers, but found that except for the bass frequencies they made task much less workable than what I got with the headphones. Stick with the phones. Fifth, test someone in addition to yourself – particularly someone who is younger and possibly female. This can be important, because if you both do poorly at higher frequencies the problem may be with your headphones and not with your ears. Women (particularly younger women) nearly always have better hearing acuity than men at higher frequencies, so do not be afraid to drag your wife into the room and test her, too. My wife was very much not interested in doing the test, but once we got going she really got into it, and did considerably better than I did from 8 kHz on up. Sixth, be aware of the effects of the temporary threshold shift that can occur if the participant has been exposed to any loud sounds for several hours prior to doing the test. This can temporarily lower one’s hearing sensitivity. In other words, do not test anyone who has just hopped off a motorcycle, just run a leaf blower, or just finished up vacuuming the carpet. Seventh, and this is important, be aware that there is the potential to damage your hearing if you let the levels run up too far at very high frequencies in a vain attempt to hear something that you cannot hear. If you have trouble hearing any tones at a frequency just above one that you only had slight trouble with, do not attempt to go higher still and then let the levels rise to a maximum. If you cannot hear a given high frequency, going still higher up at still higher levels is not going to you any good at all. I would imagine that there are desperate people out there who would persist in running up the gain with the amplifier volume control to the point where their dog is running out of the room. Don’t be one of those people. Also, be aware that you may be in a position to fry a tweeter or headphone element just as much as you might fry your ears if you persist in trying to hear signals that you are no longer able to detect. Do not persist in doing something that might deliver high average levels to your driver elements. The disc costs $49.95. For more information go to the web site I listed near the beginning of this article. The site has buckets of information about hearing loss issues, as well as other interesting products, including a disc that can determine just how well your CD or DVD player can handle disc defects. One final note. I believe it would be a good idea if EVERY audio product tester obtained a copy of this disc, uses it, and reports his findings to his readers. I can think of no better way to objectively separate the real golden eared wire, amp, and CD player testers from those who are kidding everybody – including themselves. It would also be a good idea if every high-end audio salesman also took the test and made a copy of his chart available to his customers. Relax, sales guys, I am just kidding. Howard Ferstler
  18. I have had four Allison Model Four systems in use with my main system as surround speakers for some time. (The main channel speakers are IC-20s, with a home-built center that uses Allison drivers, and a Velodyne F1800RII to handle the low bass.) They were probably built in the late 1970s, and were in rather rough shape when they arrived at my place. (The previous owners stored them in rather sub-par locations for years, I think.) I replaced the beat-up tweeters with newer, screen-covered versions (built maybe a decade after the speakers themselves were made), and replaced the absolutely wrecked Model Four woofers with Model Five woofers that I had in storage. I also removed the corroded level controls and sealed the rear-panel lever openings. The speakers were hard wired in the "flat" mode. For a while that is all the upgrading they got. However, I recently went all out and brought the speakers fully into restored condition. I lightly sanded the boxes (not enough to remove much of the stain), restained them to make the tint more uniform, and hit them with three coats of Minwax polyurethane. This did not restore them to a fully sanded down and pristine finish, because I was afraid that sanding too much would wear through the thin veneer. However, they are better than before. I also gave a flat-black spray job to the backs of two of them, both of which were previously unfinished in the back at all. The other two were already lightly stained in back. The attached photos highlight what I did. 1. The backside of one of the units prior to the upgrade. Note the early-version binding posts. Those would only take very small wires and even with small wires they were tricky to use. Later versions used five-way binding posts, and my latest upgrade also switched to five-way binders. The black tape covers the sealed level control cutout. Note also the wall hangers and the gray pads at the rear corners that are foam spacers to keep the speakers from dinging the wall. 2. The upgrade in process, showing the two gutted boxes outdoors on my workshop's workdeck. The staining had already occurred, but the polyurethane work was not yet done. Note the new crossover network sitting on the unit behind the one in the forground. You can also see a new rear template through the woofer cutout in the foreground speaker. 3. The four crossovers, plus one of the five-way cups, plus one of the templates that would replace the existing rear template. The new template would be installed in place of the original that contained both the old binding posts and the interior crossover network. The new templates were both glued and screwed into position on the rear interior. 4. One of the new crossover networks. These would be screwed to the interior bottom. Note the screw-type barrier strip that allows one to detach the driver and infeed wires for any future mods or fixes. 5. Schematic for the new crossover network. Note the two "polyfuses." The tweeters get one and the woofer gets the other, bigger one. The diagram shows three barrier strips, but there was actually only one, with the drawing showing three for illustrative purposes. The network also has the tweeter high pass done second-order style, to better protect the tweeters than the first-order version in the original. (Note that Roy Allison himself went to a second-order network when he redid the Model Four for the Kentucky outfit some time back.) The capacitor is a polypropylene type. Parts were purchased from Parts Express, except for the .0.72 mH choke, which is from another Allison network that I cannibalized. 6. Rear panel of one of the restored units, showing the new five-way binders. As with the pre-restored version, the hooks at the top corners allow the speaker to be hung on the wall. The grey pads at the rear corners are still on hand to keep the speakers from dinging the wall. 7. One of the finished speakers hanging on the room wall. The units sound just fine (I hooked up each pair in my main system as left and right speakers to make sure they sounded and measured OK), complement the IC-20 L/R mains and home-built (with Allison drivers) center speaker in the system, and hopefully they will last for a long time. Hioward Ferstler
  19. I just posted two PDF copies of different articles on loudspeaker power needs and requirements that Roy Allison published in Sterero Review magazine, first in 1973 and later in 1980. They are in the Library Additions and Corrections section. Howard Ferstler
  20. There has been a debate going on here and there when it comes to whether or not, at least with speakers having fairly normal dispersion qualities and with them located in typical home-listening room environments, the reverberant field or the direct field dominates in the upper midrange or treble. My contention has been that with speakers having solidly wide and smooth dispersion the reverberant field will dictate the spectral balance, or the way a speaker actually "sounds," while the direct field will deal with imaging and soundstaging precision. (I continue to read the Allison and Berkovitz AR-3a/soundfield preprint I posted as agreeing with this stand.) With most classical recordings the two latter qualities are not all that critical, because you rarely get soundstaging precision and pinpoint imaging at live performances unless you are sitting in the front row or conducting. The off-axis response of a speaker will also dictate how well it integrates into a listening room, with wider/smoother dispersion allowing the system to spread out and better envelope the listener. However, some here continue to believe that the direct field dominates in terms of spectral balance at upper midrange and treble frequencies, and that since it dominates it is mandatory that the direct-field output of the speakers reaching the listener's ears be smooth and free of diffraction, crossover related, and phase-related artifacts. Some have indicated that while the total output of a speaker in all directions is vastly larger than the very narrow angled sounds reaching the listener directly, the amout of damping in a room and such things as arrival angles from reflecting boundaries will allow the direct field to both dominate in the realm of imaging and soundstaging AND dominate in the realm of spectral balance. They acknowledge the spatial impact of wide dispersion, but the spectral-balance perceptions in the midrange and treble will, for them, continue to be dominated by the direct-field output. Actually, there is no way to solidly prove this contention without going to a lot of trouble and having some very good test gear. Even if one measures the impact of the direct and reverberant fields in relation to each other, we still have the issue of how the strength of the two fields are perceived by the listener. (In some ways, this reminds me of the perennial debate about the so-called sound of amplifiers or wires.) While I see the perception issue with the direct field as it relates to imaging and soundstaging precision, some have indicated that perception also gives dominance to the direct field in the realm of spectral balance. However, I have made at least one stab at checking the relative strengths of the direct and reverberant fields at normal listening distances. I have posted a curve I drew today to maybe clarify my point of view. The info for the curve was taken from two curves that I ran recently. One measured the on-axis output of a speaker outdoors. The second curve measured the on-axis output of the same speaker system indoors. I have not posted those original curves, but I have posted the one dealing with the differences. The upper line in the diagram (the lumpy line) shows the difference in dB between an anechoic (outdoor), on-axis measurement and the on-axis measurment in the listening room. The zero line would be the relative level of the direct field, normalized. Both measurements were made at a 10-foot distance, with the microphone centered on the vertical axis between the tweeters in the vertical MTTM array on the front panel of the speaker. A photo of that speaker is included. Forgive me for it not being an AR speaker, but it does make use of Allison/RDL tweeters and good, conventional 4-inch midrange drivers with phase plugs to give them decent dispersion. The idea was to illustrate just how dominant the reverberant field is in a typially reflective and absorptive home-listeing room. The response below 400 Hz was not recorded, since what the controversy deals with involves the direct vs reverberant field dominance in the midrange and treble, especially as it relates to the dispersion qualities of the AR-3a and other AR speakers, as well as the Allison product line. (Note that I would have preferred to do the measuring with an IC-20 system, but it was impossible for me to lug it outdoors and set it up on the backyard picnic table to get it decently far from house walls and the ground.) Note that the average difference between the direct and reverberant field strengths at higher frequencies is in the neighborhood of 6 dB, which dramatizes the fact that when you bring a decently wide-dispersing speaker into a typical home-listening room environment from an anechoic environment the overall energy (with the same signal input to the speaker) that reaches the microphone (and by definition the ears) goes up by a factor of four. It is hard to believe that this increase in available, and obviously reverberant-field energy is anything but the dominant factor when it comes to spectral balance. I am quite sure that a super-wide dispersing model like the IC-20 would have had an even greater spread, and I am also sure that a speaker like the AR-3a would have done as well as the model I did use. Howard Ferstler
  21. Over the past few days (or was it weeks, or even months?), a guy who's pen name happens to be Zilch (or is it Mr. Zilch?) has been making some very negative comments about certain often highly admired, classic AR speakers (particularly the AR-3a), and by implication, Roy Allison and Edgar Villchur. That Mr. Zilch has shown up here at all, on a site devoted to "classic" products that he appears to not like at all, seems to be a bit odd. But, then again, Mr. Zilch is an odd character to begin with (bragging about his 20,000+ posts both here and on other sites is not something I would care to brag about), and so maybe he needs to vent. The series of debates has also involved information put forth by Dr. Floyd Toole in his recent book on loudspeakers and rooms, with Dr. Toole's views pretty much parallaling at least some of those put forth by Mr. Zilch. I want to more or less summarize some of my feelings about this situation. 1. Mr. Zilch dismisses the original "live vs recorded" concerts presented by Ed Villchur in the 1960s as basically a series of showboating"stunts" that do no more to prove that AR speakers (specifically the AR-3) were, and are, decent performers than the demonstations given by Thomas Edison proved that his acoustic phonographs were as realistic sounding as a live ensemble. It is obviously impossible to argue this point objectively with Mr. Zilch (even though some others here who have also discussed the issue attended some of those AR demos, including those done by Victor Campos at a later date), since the opinions involved would have to be subjective at best. Mr. Zilch did not attend the concerts (nor has he offered up info on any of the companies he admires doing demos of the same kind), and so his own opinion actually amounts to nothing. (Dr. Toole also did not attend them, which means that his dismissal of them in his book is about as vacuous as those outlined by Mr. Zilch.) Even if the AR-3 speakers only did a fair job of replicating the sound of the ensemble (although many serious audio buffs and audio journalists attending were solidly impressed), it is hard to believe that speakers with response curves as ragged as those illustrated by Mr. Zilch (and Dr. Toole) would be able to thoroughly wow so many different audio buffs. Those demos had a lot to do with the success AR enjoyed in the 1960s, and the corresponding response-curve proofs illustrated by both Mr. Zilch (here) and Dr. Toole (in his book) do more to show their wrong-headed approach to what matters with speaker sound than any weaknesses claimed by them regarding the performance of the AR-3. Both Mr. Zilch and Dr. Toole would have a vested interest in successfully dismissing those concerts, because if what Villchur did was successful then the contentions of Mr. Zilch and many of the basic conclusions put forth by Dr. Toole in his book - are wrong. 2. As one example of his approach to marketing, Mr. Zilch has tried to technically duplicate something that Karl Rove managed to do during the political campaigns of the younger George Bush. Rove managed to take the positive points and examples put forth by opposing candidates and turn them on their heads in such a way that they looked negative instead of positive. (The awarding of the Silver Star notwithstanding, recall the Rove-machine treatment given John Kerry's military service in contrast to that of Mr. Bush.) Mr. Zilch has culled some comments from an article Roy Allison had published in the Journal of the Audio Engineering Society back in the 1970s, and pretty much turned them on their heads. Basically, Allison not only validated the wide-angle performance of the AR-3a (particularly in the upper midrange and treble), but also showed that the reverberant field dominates over the direct field with good, wide-dispersion speakers properly located in a typical home listening room, at least if the listener is not sitting on top of the speakers and the room is not furnished like the inside of a mattress. Mr. Zilch continues to claim that what Allison proved was that it is the direct field that predominates, which will be judged as preposterous by anyone who has read the article. However, with the rather directional speakers Mr. Zilch seems to favor (even though he claims they are wide dispersing, in spite of documentation both he and I have posted) it might just be possible for the direct field to dominate under some conditions. Basically, Mr. Zilch has taken what amounts to a design defect with his favored models and tried to turn it into an advantage, and has attempted to use Roy Allison's own research to prove his point. Note that the preprint version of this article is now available on the Classic Speakers site (check the "recent updates" sidebar on the home page to access this large PDF file), and the article goes out of its way to prove that both Mr. Zilch and Dr. Toole are mistaken in many ways about the reverberant field and the performance of wide-dispersion speakers in real-world listening rooms. It did this long before Mr. Zilch and Dr. Toole began to formulate their counterpoint ideas. The Allison article draft eclipses any "research" done by Mr. Zilch or any of those people he claims know the score when it comes to loudspeaker sound. 3. Mr. Zilch has used another Rove tactic to reverse-engineer another advantage of the classic AR approach to speaker design, with his comments elsewhere about how nobody cares whether speakers manage to simulate live, concert-hall sound any more. Again, this is one of the strong points of the AR design approach, and Mr. Zilch is aware that if this is considered valid by enough people his commentaries about the deficiencies with the AR approach go nowhere. Consequently, he again uses the Karl Rove approach and turns an advantage on its head, thereby making it into a disadvantage. According to him, nobody cares about live, unamplified sound any more, and so what AR did in the way of response contouring and wide-dispersion envelopment are bogus and wrong headed. That even if nobody in Mr. Zilch's electronic-sound world cares about live-music sound, it is clear that many people who come to this site to discuss speakers do. Frankly, I have no problem with people liking what Mr. Zilch likes. It is a free country, and obviously there are designers out there who are happy to build to his (and their) specifications. However, there are also at least a few companies (there were more in the old days) that cater to those who like live acoustic-music performances, and it is patently unfair for Mr. Zilch to imply that they are throwbacks to an age of quaint attitudes. Mr. Zilch is a strange bird, what with that JBL logo heading up so many of his posts, not to mention him managing to write 20,000+ posts here and on other chat-group sites. (I am a fast typist, with plenty to say at times, but I am pretty sure that to do that much posting I would have to build a toilet into my computer desk.) One wonders about the LBL connection, among other things. However, there is one thing nobody here needs to wonder about when it comes to the meaning of the word zilch: The Oxford English Dictionary definition: A. n., slang (origin unknown), nothing, nil; B. adj., non-existent; C. v.t., defeat by preventing from scoring, zip. I wonder if Mr. Zilch will try to turn those definitions on their heads, too. Howard Ferstler
  22. The home page "recent updates" sidebar now has an article listed called "Allison on Soundfields" that will be of interest to fans of Acoustic Research. Just click on the title to get the draft to download. The home page, of course, is at: http://www.classicspeakerpages.net/ The info this draft contains should be of interest to any fans of the "classic" AR speaker lines. The version that appeared in the JAES is a bit later was shorter than this original that Roy sent to me some time ago. This is an almost definitive statement about the AR-3a as its performance relates to real-world soundfields and power response, and it has info in it that Roy used later on to design the LST, as well as the Allison Acoustics line. There is also info in it that relates to the AR-ax. I have received permission from the AES to post this artilce. Note that it is a large (over 25 MB) PDF (Adobe) file and will take some time to download. If the text and illustrations are hard to work with, it would be simple to print them out. Lots of paper required, unfortunately, and the photos will print slower than the text section. Howard Ferstler
  23. The home page "recent updates" sidebar now has an article listed called "Allison on Soundfields" that will be of interest to Allison Acoustics fans. Just click on the title to get the draft to download. The home page, of course, is at: http://www.classicspeakerpages.net/ While this 1970 draft was written by Roy Allison and Bob Berkovitz while Roy was still at AR, the info it contains should be of interest to Allison Acoustic fans. The version that appeared in the JAES a bit later was shorter than this original that Roy sent to me some time ago. This is an almost definitive statement about the AR-3a, soundfields, and power response, and it has info in it that Roy used later on to design the Allison line. I have received permission from the AES to post this artilce. Note that it is a large (over 25 MB) PDF (Adobe) file and will take some time to download. If the text and illustrations are hard to work with, it would be simple to print them out. Lots of paper required, unfortunately, and the photos will print slower than the text section. Howard Ferstler
  24. When I reviewed speakers for The Sensible Sound and The Audiophile Voice I also did measurements, although those measurements were secondary to the level-matched A/B comparisons I did between the speakers under review and my reference speakers. The measurements were basically just starting points that helped me understand some of what I was hearing. They did help me separate the good and great speakers from the real dogs, however. What we have below are readouts of several Allison models I checked out over the years (I did not formally review any for magazine reports, because when I did the measurements the company was already out of business), plus readouts of several other brands for reference purposes. Basically, I would use the 20-second integration feature of my AudioControl 1/3-octave, SA-3051 RTA. The curves are hand drawn, using the readouts on the RTA front panel. The test is simple. I would feed decorrelated pink-noise signals to the speaker pair, and then SLOWLY move the measurement microphone over a roughly 1 x 1 x 5 area at ear height at the listening couch. While the microphone was being moved the RTA would average out the sound being picked up and then give me a cumulative result of the 20-second input. The technique helped to reduce hot-spot reflection effects and standing-wave artifacts that one gets with measurements at a fixed location. Note that the result would be a blend of the direct and reverberant-field output, with wider dispersing speakers favoring the latter and narrower-dispersing speakers favoring the former. The idea was to get a fix on the spectral balance of the speaker at the best listening location in the room, with a mix between the direct and reverberant fields. The couch was 14 feet from the front wall, although many free-standing speakers would be pulled out some distance, with a corresponding increase in the strength of the direct-field balance. When sub/sat speakers were measured, the subwoofer was usually in the left-front corner, about 17 feet from the center of the couch. The speakers were 10-12 feet apart, depending upon how far out they were located. Note that these curves will give one an idea of spectral balance, but they will not determine things like imaging tightness, focus, soundstage envelopment and spaciousness. I would use my single-presentation and A/B comparisons to determine those attributes. All were run in my main, roughly 22 x 18 x 8.5 foot AV room, with the exception fo the Bose 901 pair curve, which was run in a still larger room belonging to a friend of mine. Curve One: IC-20 pair. These are mine. Note the room-gain at the low end. I have no explanation for the dip at 1250 Hz, but when equalized out there is no particular change to the musical sound at all. These speakers can be seen in the photo I posted some time back showing my main AV system. In my current arrangement I use a Velodyne subwoofer to handle the very low range. Curve Two: AL-130 pair. These belong to a friend of mine. Curve Three: CD-8 pair. These belong to a friend, also. Curve Four: Model 8 pair. Again, also belonging to a friend. Curve Five: Model 4 pair. This pair is also used as surround speakers in my smaller AV system. I have four more used as surrounds in my main system. Curve Six: The left and right speakers in my smaller AV system, made from scratch, which use two RDL tweeters each and one 6.5-inch Allison woofer each, with two TB Systems 4.5-inch midranges each. These speakers are illustrated in some photos I submitted of that system a short while back. The woofer is not large enough to handle low bass happily, so I use a big Hsu subwoofer for that range. Curve Seven: The center speaker in my main system. I also made it from scratch, and it uses two Allison tweeters and two Allison mids, in a vertical MTTM array, just like a single panel on an IC-20. A single IC-20 woofer handles the bass. The crossover network is a combination of what we have with the Model One and CD-9. This speaker can be seen in the same main system photo I submitted a while back, along with the IC-20s. To do this measurement I located the speaker at the left postion and fed it mono pink noise. Had to do this, because there is only one of them. Curve Eight: An NHT "Evolution" sub/sat system, with the M6 satellites and two W-1 subwoofers. I reviewed this package for The Audiophile Voice. This package listed for about $2500 when I reviewed it. Look at that tweeter response. Very clean sounding speakers, but with limited spaciousness when set up optimally. Curve Nine: Polk LSi-25 speakers. These are large systems, with powered woofer drivers. I reviewed them for The Sensible Sound. These speakers listed for about $3000 when I reviewed them. I thought they sounded a tad bass heavy. Curve Ten: Dunlavy Cantata systems that I had for some time in my smaller AV systems. I also reviewed them for The Sensible Sound. They employ a vertical MTM array using 6.5-inch midrange drivers, and with a downfiring 10-inch woofer on the bottom. Very directional speakers with a very clean sound and superb imaging, but not with particular spaciousness. These speakers listed for about $5500 when I reviewed them. Curve Eleven: Bose 901 systems in a friend's very large room (31 x 21 feet, with a cathedral ceiling running 8-10 feet) at a roughly 16 foot measuring distance. The active equalizer had been set up by him for his preferred balance. Very realistic sound with small-ensemble source materials, but anything but pinpoint imaging. The curve almost looks like what one would get with a mid-level three-way conventional speaker. Curve Twelve: Waveform MC sub/sat system. The satellite enclosures were cast-aluminum and egg shaped (exhibiting essentially zero diffraction), with a one-inch tweeter and 6-inch midrange. Two Waveform subs were used, and the crossover network was a fourth-order type. This package listed for about $5400 when I reviewed it. Very clean sounding systems Curve Thirteen: Eminent Technology LFT-8 system. This one was also reviewed for The Sensible Sound. It has dual line-source planar-magnetic tweeter and midrange drivers, with an 8-inch dynamiv woofer. The treble rolloff is not all that apparent with musical sources. These speakers listed for about $1200 when I reviewed them. Remember, curves like these are but starting points when auditioning speakers. The bottom line involves additional things like solid listening evaluations, but I feel that a speaker has to at least have decent performance with a test like this to qualify as a high-fidelity item. Howard Ferstler
  25. Zilch and a few others here have made comments about speaker dispersion and speaker sound as it relates to AR, Allison, and JBL systems and drivers. Some have indicated that wide dispersion from top to bottom is not an advantage, with directional sound being better at separating room effects from what is on the recording. I do not care to debate that issue any further, since it involves musical taste (Zilch has said elsewhere that nobody cares about live, acoustic-music, concert-hall sound any more) more than speaker technology. As tastes decline, speaker sound parallels the trend. On the other hand, in some posts Zilch has indicated that speakers like the AR-3a do not have dispersion as wide as some of the JBL brands he lionizes. Zilch has also posted pictures of some JBL system response curves to support that view, including a polar curve. I will reproduce those here, and then submit some comparison shots of various AR driver and system curves. In addition, even though this is the AR section of the Classic Speaker site, I am going to also submit some Allison Acoustics driver and system curves, as well. I do this, because so much of what we find with "classic" AR speakers was the result of work by Roy Allison. Roy's approach was an outgrowth of what Edgar Villchur came up with at the very beginning, with both men moving on to refine those basic priciples. In many ways, Allison Acoustics was a continuation of the original AR approach to hi-fi sound. Drawing 1 shows the on and off-axis response of the JBL AC16 system from 200 Hz on up. Zilch has posted this drawing elsewhere, and it shows readouts from on axis out to 80 degrees off axis. Drawing 2 shows the AR-3a (and LST) woofer output on axis and at 30 and 60 degrees off axis. The diagram shows the crossover point, and you can see that from 200 to 575 Hz the response is certainly equal to what the AC16 exhibits over that range. Drawing 3 shows the AR-3a midrange output on axis and at 30 and 60 degrees off axis. The response between 575 Hz and 5 kHz Hz is certainly wider in dispersion than the AC-16 operating over that range. Of course, the same midrange is used in the AR-LST, and since the four mounted on that system are on angled panels, the effective dispersion will be much better than the JBL model. Drawing 4 shows the AR-3a tweeter output above 5 kHZ on axis at at 15-degree intervals out to 75 degrees off axis, and nobody is going to say that its output is inferior in terms of dispersion to the JBL AC16. (This is a special curve made by Roy Allison after he left AR, and he made a point of measuring beyond the usual 60-degree point.) The dispersion contest here is really no contest at all. Again, this tweeter is on the front and angled side panels of the AR-LST, and clearly the dispersion of that system will eclipse that of the JBL model. However, even the AR-3a, with a single tweeter, exhibits wider dispersion than that JBL model. While diffraction effects and crossover artifacts will impact the direct-field output of the AR-3a and AR-LST, the very wide dispersion of those systems will insure that those direct-field artifacts will be submerged in the power-response output of the systems. The wide dispersion insures that the power response will stay uniform over the audible operating ranges of the two systems. Drawing 5 shows the power response output of an AR-3a in a reverberant chamber (the curve was run by Roy Allison), with the mid and tweeter level controls all the way up. Zilch has said that the power response output of the system sags at higher frequencies, but you certainly cannot see that here. Drawing 6 shows the power response output of the AR-LST with its level control set at the "flat" position. Obviously, you can get very flat power from this system. Drawing 7 shows the output of the Allison midrange driver that Roy came up with for his company's systems. The crossover points are at 350 and 3750 Hz, and the readouts are at 15 degree intervals from on axis out to 90 degrees off. It is hard to see all of the lines, because the super-wide dispersion characteristics have them overlapping so much. This driver is almost omnidirectional within its operating range over a 180-degree arc. When mounted on the angled panels of the Allison Model One, Model Two, and IC-20 the same angular range is increased to 270 degrees. Drawing 8 shows the output of the Allison tweeter driver that Roy also came up with for his company's systems. The crossover point is at 3750 Hz, and the readouts are at 15 degree intervals from on axis out to 90 degrees off. It is hard to see all of the lines up to 10 kHz, because the super-wide dispersion characteristics have them overlapping so much. This driver is almost omnidirectional within its operating range over a 180-degree arc. When mounted on the angled panels of the Allison Model One, Model Two, and IC-20 the same angular range is increased to 270 degrees. Even operating alone, the dispersion here eclpses Zilch's exampled JBL model. Drawing 9 shows a polar response curve that Zilch posted to highlight the dispersion superiority of a favored JBL model above about 600 Hz. Anybody can see how much the upper midrange and treble beam in comparison to the lower frequencies. From 3 kHz on up this is a very beamy speaker. This beaminess tends to make the speakers have a boxy sound, and negatively impacts soundstage realism in typical listening rooms. It tends to make them sound impressive in large, open showrooms, however. Drawing 10 shows the polar response of the Allison IC-20 system from 63 Hz on up to 16 kHz. The Allison Models One and Two have similar horizontal polar patterns. It is clear that this is a wide-dispersing speaker that has the upper midrange and treble outputs paralleling those of the lower midrange and even the bass. Note that the off-axis response is wide well beyond this 180-degree plot. Drawing 11 shows the polar response of the AR-LST, as made by a British review magazine some time ago. Since it was made in the direct field, it shows a lot of inter-driver lobing in the tweeter's range, due to the overlapping outputs of the four drivers, but it is clear that this is a very wide dispersing speaker, much more so than any JBL model Zilch has illustrated. Now, some might decry this kind of wide dispersion, but whatever one might think of it, it certainly eclipses the varying broad-bandwidth dispersion characteristic of the kind of speakers Zilch prefers, and pretty much proves that the AR-3a (let alone the AR-LST and any Allison models) is a wider-dispersing model, particularly in the upper midrange and treble, than the JBL AC16. Because of this, those speakers are much better at simulating concert-hall sound from typical classical and acoustic-instrument jazz recordings than beamier versions. Howard Ferstler
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