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About Mach3

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    DIY stereo - AR speakers

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  1. Mach3

    AR-5 ?

    seen these "replacement" tweeters. I am very interested in what these are and who is selling them. As with all AR owners my tweeters are getting "old" (same with myself). Would really like to know who this guy is and what he is putting out there. I am bumping this thread so maybe it can get some attention.
  2. Many thanks to Tom Tyson and Pete B for their closely reasoned and strongly subtantiated replies. I think we all learned a LOT from these efforts - I know I did. WOW!!! I think my next move is to measure the bass response alone - as per Tom Tyson's suggestion - and get a better idea what is going on at the speaker (as opposed to the listening seat which is in a corner of the room (has a fichus tree behind it to break up the inevitable mode - but that is probably not enough)). What I would ultimately like to do is move the crossover to an external box. Going in and out through the woofer "hole" is difficult and wearing on the cabinet. Then I could install a temporary switch to evaluate the difference in response between the two circuit arrangements more easily. The bottom line is that I "hear" a subjective difference with the capacitor out of circuit. That subjective appraisal is that there is "more bass" - a LOT more bass especially in the 25 to 35 Hz region. Of course I know that such a subjective measure is open to all kinds of error and could be misleading (I have been around enough so-called "audiophiles" to know that people can hear all kinds of phantom events - and of course I may be hearing what I want to hear.) Alas!!! Such is a human condition. Again many thanks to the contributors, especially Tom Tyson and Pete B - they have provided me with a great deal of food for thought. I will return to this topic when I have better and more thorough measurements to offer.
  3. Opps!! Forgot the image. Here it is;
  4. First; thank to Tom Tyson. Your information and insight is greatly appreciated. The "mistake" is in the schematic for the AR-9 crossover that I found on this site. Apparently in the band pass crossover for the LMR (1.5" dome) there is a 6 uF cap specified - but it should be an 8 uF - the first attached image shows - as far as I know - the original factory schematic - note that there is a fold in the paper that makes an 8 appear to be a 6. I originally installed the 6 uF and the resultant was a lump in the F/R. All the measurements were taken at my listening seat - both F/R plots. I was interested in some kind of objective measurement of what I was hearing - not that such makes a whole lot of difference - I let my ears lead me, not a cloud of technical mumbo-jumbo. The only reason I have these measurements is that a friend of mine is always going on about his F/R plots and he has all the equipment needed to do such measurements. Yes the measurements were "gated" (as I recall 6 mS) otherwise the measurement is at best confused. The measurements are NOT FROM DIFFERENT SYSTEMS. Same speakers, same room, same CD player, same wiring (Cardas Golden Reference speaker wire, Kimber KCAG ICs). The amps have changed - the original was with Odyssey Audio Khartago "mono-blocks", the second was using a Pass X150.5 (best amp I have ever heard). The only thing that changed from one measurement to the other were the modifications to the crossover. Since the measurement equipment is not mine I cannot say when I will get the chance to measure the woofers per Tom Tyson's recommendations. But I will as soon as I get the chance. I do not think the second plot is very accurate below 300 Hz or so. We did move the mike around the room and in some places the speaker measured FLAT down to 25 Hz - pretty amazing for a 35 year old speaker. My measurement friend perceived that the dips and bounces in the lower range were more about "room" modes. From a subjective point of view, listening to "Dark Knight" (sound track from Hans Zimmerman) the performance with the 2500 uF cap removed is absolutely spectacular - incredibly powerful and wall rattling deep. The only reason I made the measurements was to demonstrate to the critics of this modification that the result of removing the cap was in fact demonstrably better - at least objectively. I really believe, based on Tim Holl's notes (on this site) that the 2500 uF cap was placed in circuit to preserve amplifiers of that period. Modern high quality SOLID STATE amplifiers are not fazed by low impedance dips (which I believe drops below 2 ohms with the two woofers in parallel). Given this analysis there is NO NEED for that enormous cap or the "automatic transmission" capability designed into original circuit. It only limits the lower range performance. One last note. I had occasion to hear a set of Wilson Alexia speakers ($48,000) driven by Momentum amplifiers ($30,000) in a specially treated, large, dedicated room at Audio Concepts (Dallas). The setup was done by Peter McGrath a very competent and capable employee of Wilson Audio. We are talking a $100,000 system. They played a piece from the SFO that had the organ hitting the low C (32 Hz). Some time before I had heard the Dallas Wind Symphony play a similar piece that also included the same "low C" passage. To my ears the Mighty AR-9 EASILY OUTPLAYED THE WILSON "uber" speaker. Easily. The Nine was tighter, far more articulate, and far more controlled than the "modern" speaker - and its reach into the "nether regions" was demonstrably better. So hooray for Acoustic Research - they built incredibly fine gear that even in this era stands up as an outstanding example of speakers.
  5. Some time back - maybe a year or two - I discussed the idea of removing the big cap (2500 uF) from the AR-9 crossover. My thinking was that this cap had been placed in the crossover mostly to protect the amplifiers of the late '70s. Without that cap the amp driving the speaker would have seen a load of < 2.0 ohms (two woofers in parallel). That would generally fry an '70s era receiver. So I cut the cap loose (no other mods) and promised to the forum a F/R plot of how the speaker performed without that large cap. Please find attached the "before/after" plots for my Nines. The black/green plot is the original F/R with a rebuilt crossover (all film caps AND a mistake in the crossover - the 6uF versus 8uF error due to a fold in the original factory drawing). This plot was generated using an Apple Phone app and a pink noise CD. The crossover points are approximately marked in this plot by red vertical lines. The second plot shows the F/R resolution without the cap in place. This plot was taken with an elaborate dedicated F/R measurement system including specially calibrated mike and a stand to hold it at my listening seat. Nice stuff (about $500 complete). Again a pink noise CD was used to generate the sweeps. Notice that fixing the one cap in the crossover smoothed out the high frequency response. But do notice how the low frequence area has been extended. Those peaks and valleys are more about room modes than the speaker - because as we moved the mike around the room those peaks and valleys would disappear - in fact at some places in my room the speaker was flat into the mid-20 Hz region. If you have an amplifier with sufficient drive (modern style - no tubes) you can successfully remove that big cap and actually realize an extention in your bass response - both subjective and objective.
  6. Anybody out there have an idea - even approximate - how many AR-9 speakers were made in the period 1979 - 1981? I have seen suggestions that the initial build was about 1,000 units. I have also heard, hardly more than unsubtantiated rumor, that the reason the AR-9 ceased production was that the orders were not suffiicent to keep the production line working. Any information would be appreciated.
  7. My take on the addition of a subwoofer to any planar style speaker (stat or magneto-dynamic); It seems like it should work and "complete" the speaker on the cheap. But it never does - the result is always lumpy, not coherent and the bass stands out like a light house beacon. The problem, I think, is that a planar, due to its extremely low driver mass is a very low Q device. This means that the drivers (sheets of mylar) do not ring at all - they are very well controlled. Whereas a large sub, even one muscled up with an enormous amplifier is typically a high Q device, i.e. it rings slightly (or greatly depending on the quality of the components). Any decent sub, with a 12" or > driver is pushing a huge amount of mass - and that mass resists acceleration (and deceleration as well). Consequently when integrating a sub with a Maggie type you are trying to get a very low Q set of drivers to blend with a medium to high Q device (the sub itself). It never sounds "right". Then there is the problem with getting a point source (dynamic sub) to blend with a line source (Maggie) - just doesn't work very well. The way each device launches its wave into the room is dramatically - and obviously very different. The sub stands out - and it doesn't sound like an integrated speaker - it sounds like two different speakers playing somewhat together - but not coherently. Now putting a sub with a dynamic speaker such as an AR-2ax - that should work extremely well - for an AR-2ax is a dynamic, medium Q device that launches its wave as a point source. I tried to get my MG-3.3 to work with a Velodyne (high quality sub) - it never worked well at all. For one thing the MG-3.3 was starting to roll off at about 80 Hz (manufacturers simply lie about the bass response of their speakers - all of them) - and the Velodyne could not reasonably reach that high. With the MG-20 the sub was a somewhat better blend since the 20 went down a little lower before nosediving - but still the two units were not coherent - in any shape, manner or form. I wish that a sub and a Maggie did work - but they just don't (ask Jonathan Valin at TAS about his experience - he claims it is impossible to integrate a sub and ANY PLANAR speaker). Best bet with a Maggie is to get a set of their DWM panels (like a slice of the bass section of an MG-20) - these integrate well (vertical launch and a line source with low Q) and bring up the response in the 40 Hz to 200 Hz region - but they are $750 per unit. So add $1500 to your "Cheap Maggie" - then add another $4,000 for some decent amplifier (used Pass is highly recommended) and that "cheap Maggie"? Now it is a $15000 speaker system - and the room clutter just went way up while the WAF went exponentially DOWN. Sorry - to my way of hearing a Maggie is seductive but ultimately just doesn't cut it - even if you can solve the bass problem - you are still left with a speaker that just doesn't do much in the way of dynamics - and REAL MUSIC is VERY DYNAMIC. Rock, opera, symphonic, jazz - live music simply JUMPS. Maggie types do not "jump" - they spray sound everywhere and smooth the rough edges off of recordings - and they are incredibly seductive with their sound. But not very transparent, not much imaging - incredible sound stage - and very smooth. But not my cup of tea.
  8. My take on the Maggie versus the Nine goes in almost inverse order. In the '70s I was an ardent AR fan - AR-2ax and eventually an AR-10pi. All driven by various Marantz receivers. Tasty sound. Flash forward to the early '90s - after passing through a series of unsatisifying speakers - Altec Lansing, JBL, - I was introduced to the sound of the Magneplanar - and I was taken with it. The sound was all encompassing - it seemed to be so life-like that I ended up buying a set of 3.3Rs. Driving them with tube amps (seriously underpowered) but in that era the solid-state amps were typically gritty and harsh. I was in sonic Nirvana - just very happy. I was also smitten with their appearance - tall, elegant and just really classy - at least to my eye. Eventually I moved up to a set of MG-20s - got more bass - but not exactly any slam. But the notes were there - you just had to listen for them. This covered 12 years, from about '94 through '06. All the time listening to Maggies and thinking that such was sonic bliss. I even moved up to a solid state amp (HCA-2 from PS Audio - which eventually went up in flames - but such is another story). Even with the 200+ watts of the HCA-2 I was still way underpowered for such a speaker - to get a Maggie to come to life you need at the minimum about 300 or 400 watts - of good, clean, musical solid state power (tubes need not apply for Maggie duty). All through this period I was slightly dissastisfied with the Maggie sound - I attributed my uneasiness to the lack of bass. I looked around for AR but came to realize that the "old AR" had vanished - to be replaced by speakers that bore no relation to that wonderful sound I had listened to through the '70s. Then one day I happened to listen to a friend's rig - featuring some really nice two way box speakers. And then in a flash I realized what I wasn't getting from the vaunted Maggie sound; NO DYNAMICS, and NO SOLID BASS (oh the notes were played but rather faintly). I sold my MG-20s in a week and went on a search for a speaker that had dynamics and bass. Eventually landing on a set of AR-9 that were in need of some serious TLC. Rebuilt the crossovers with all film caps, added adequate wire (the factory wire is not up to the job) and made a few other mods to the crossover (removing the 2500 uF "beer can" cap - as with modern amplifiers such is NOT needed - and removing same dramatically increases the bass response). What I am saying is that a Maggie - any model - creates a very seductive sound - immense sound stages (though incapable of imaging), rather nice tonality (as the membrane tends to smooth over everything) and a sound field that is just incredibly enjoyable - a Maggie fills a room with sound. But the price you pay for those attributes are rather high; you need enormous amplifier power, you will never get any decent bass from the thing (the 3.x series is dead around 50 Hz), there are NO DYNAMICS with a Maggie - everything gets homogenized to one volume and they really do not image at all (sound stage is great, placement is non-existent) and the tonality, while very smooth, is actually quite colored. You will be happy with your Maggie - very happy - for many years - and then one day you will hear a capable dynamic speaker (or a VERY CAPABLE DYNAMIC SPEAKER LIKE AN AR-9) and those Maggies will be gone in a flash. Recommendation? Keep the Nines in a closet or spare room. You will find your way back to them.
  9. TomTyson, The "plot" you forwarded was completely BOGUS. It was a plot that can be found on the CSP (under notes on the AR9 design) - and a copy is embedded below. Basically the "curve" you pointed out as indicating that my mod to the bass section reduced bass output ACTUALLY describes a cabinet with TWICE THE VOLUME of the AR-9 (Holl was illustrating the effect of cabinet size on Q). So - there is NO PLOT that shows that my modification in ANY way detracts from the bass output. In fact my subjective listening tells me VERY CLEARLY that the change significantly increased both the depth of the bass AND the quality of the bass. Go read Terry Holl's notes on how he came up with the crossover design - and it has everything to do with protecting amplifiers of that era and NOTHING to do with sound quality. Jeez Louse. Do you even have a set of AR-9? If so then go try the mod for yourself. You will be amazed.
  10. Here is the F/R plot taken several years back with an Apple phone app (which proved to be fairly accurate). This is in room response taken from my listening position. The red lines are "about" where the crossover points are - I don't remember what the blue line was supposed to mean - I have slept since I took this measurement. I concluded that the response increase near 7 KHz was due to the wrong capacitor being in shunt with the UMR - for it was pretty bright at the time this plot was taken. Sooner or later I will endure my friend with the full-up measurement equipment (a nice guy but he really likes to spend his time downgrading other peoples rigs - but I guess that is a big part of the hobby for some people - we seem to spend more time arguing about the kit than we do listening to it - at least some of us) - and then we can compare the two plots.
  11. To all the Flat Eathers and my other fans ;-)). By the numbers. TysonTom - the pdf file with the response plot is somewhat irrelevant. It is from Holl's papers on the design of the AR-9 and I think it is referring to cabinet size changes - not removing the coil/cap combination that Holl installed to ease the drop in impedance caused by the two woofers being in parallel. I will have to go read his papers again. As for the lowering of Q - such will attenuate the response but in truth it means that the woofers demonstrate lower sustain, i.e. they "ring" less (high Q rings more on an impulse). So the perception is that the bass is tighter, e.g. the note sounds and then ends - exactly like a real lower note. A high Q system, such as a ported box, will produce "more" bass but it will be "boomy" and tend to be one note ringing its way across your sonic landscape. As for repairing the "original" 2500 uF cap - I did so on my first rebuild - all new caps (five 500 uF NPE caps in parallel) so I am very familiar with the sound of the speaker with that particular crossover topology in place. Believe me - in my room, to my ears the removal of that band-aid for '70s style amplifiers resulted in a tremendous increase both in the quantity of bass and the quality of bass. Such of course is the absolute benchmark as I have a stereo for my enjoyment. In regards the impedance - I have measured a low of about 1.7 ohms. I am using Odyssey Audio "Khartago" mono-blocks - and they seem to handle the excursions into deep bass with aplomb. No problems (yet). My reference recording is a CD of "Dark Knight" - another fantastic soundtrack from Hans Zimmer. Highly recommended as there are some rather low frequencies in Track 1. Again this is subjective - but then again what isn't? The plots you offered are over 34 years old - and I beleve are out of context in this discussion. For RoyC and TomTyson; Look folks - maybe you do not believe that wire (specifically Interconnects and speaker wire) makes any difference. Some yahoo sits down with a length of "audiophile" wire and measures the same LRC values as that of a similar length of 18 gauge solid core wire and to you the story is over. But what the yahoo doesn't measure - such as finding the impulse response of the wire or the dielectric absorption of the wire is the real story. Gross measurements do not a refutation make. I wish you lived near - for we could settle the thing quickly by my bringing over some "real" wire and demonstrating the difference between that and your radio shack spool stuff. Which is how I learned that my flat earth viewpoint was totally wrong. Suffice it so say - if you don't believe that wire can make a difference - well then in the end it is your loss not mine. I believe the original wire in the Nine was deficient and was used merely because it was cheap and looms could be easily made - not because anybody investigated any sonic aspects of the wire. If anybody else is reading this - rewire the thing - and solder your connections. The original wire was cheap crap. If wire makes no difference then tens of thousands of people, spending tens of millions of dollars for wire, are all seriously deluded. Perhaps. But maybe the delusion lies on the other side of that divide. In re the attenuation resistors; In MY ROOM, with MY SPEAKERS, the UMR (1.5" dome) seems to get louder in a non-linear fashion compared to the rest of the drivers in the speaker as the volume increases. This means that the suitable attentuation at lower volumes is too little at higher volumes. So given the characteristics of a resistor in a situation where the temperature of the resistor in increasing, i.e. the resistance goes UP, I am attempting to introduce a resistance that varies (increases) with volume. Higher volumes will cause the underspecified attenuation resistor to begin to heat and its resistance will increase and I will be getting "more" attenuation at that point. Pretty darn clever if I do say so myself as it works extremely well. To RoyC; My perception is of course my perception. Since we are not geographically close enough to share a listening session I can only relate my subjective impressions. Of course all you can do is the same - relate YOUR SUBJECTIVE impressions. Perhaps we do not share the same perception - OK - so who cares? I don't. I am on this forum to share MY experiences with others - if you do not agree that is good - and you have shared your take on these subjects. So all readers see that there are two sides to these suggested modifications and design approaches. While I think VERY highly of AR - and particularly of the AR-9 (to my taste one of the finest speakers ever made) - I do NOT believe that what Terry Holl did in 1978 was the last word in design - particularly in his crossover (which with the cabinet is about the extent of the entire design - the drivers were already in production). Film caps change the sound tremendouly, better wire changes the sound impressively, removing that extra "bass attenuation" increases the depth and the quality of the bass. Try these modifications and report back to all of us on what you think of the changes. What will it cost you? I have a friend who has the F/R measuring equipment - but he is such a pain to listen to that I hesitate to have him bring his measuring equipment over. So I may or may not be able to get some plots up. I will include a plot (below if I can figure out how to do an insert picture) taken with an Apple phone app of my F/R immediately after I rebuilt the crossover (and rewired the drivers). This plot shows the 6 uF cap in shunt on the UMR (later fixed with the proper 8uF - note the spike at 7 KHz), and without the bass crossover improvements. Enjoy Well I couldn't determine how to get the plot in the message - I will be back later with that.
  12. Pete B, I apologize for the mix-up - for you see - I am old - when we went to school the earth was still cooling, dinosaurs were making their tracks and we walked up-hill BOTH ways ;-)). In the '70s (a period that I can dimly remember afer being released from the military in 1971 ;-)) most of the amplifiers available to the "general public" (a la Pacific Stereo out in LA) would burst into flames when presented with a 2 ohm load. Perhaps in the '80s the "better" amps came on the scene - but when Terry Holl designed the Mighty Nines (apparently you have your own pair now - congratulations) generally available amplifiers could not service 2 ohm loads. In our current era there are dozens of very good amplifiers that have no problem with 2 ohms (or less) loads. Transistor manufacturers have gotten MUCH BETTER. Designers? Well they can do no more than what the silicon makes possible - the big ticket in this era appears to be the Sanken transistors - pretty snappy sand. BTW: I offered to send you some walnut to replace some dings on your new MIGHTY NINES - give me a PM and I will be happy to send you the wood (envelope sized) and a step-by-step pictorial on how to replace a ding in a veneered surface. You will need a sharp chisel (maybe the 3/8" size would be best) and of course patience and a well controlled hand-eye ability. Some "Titebond III" wood glue is also necessary (any Homeless Depot or Lowes will have that in the paint section).
  13. Pete, Couple of things; On my AR-9 I have the 'square' magnet on the woofer. In regards the woofer crossover - I cut loose the 2500 uF cap and coil. My analysis indicated that this part of the crossover was only there to provide impedance to protect the typical amplifier (receiver) of the era. Without these two devices the two woofers in parallel would represent about a 1.7 ohm impedance at its lowest point - which would pop most amps in the late '70s. I am not sure what the plot put up by Terry Holl was attempting to say - but when I cut loose those parts I got a lot more bass - tigher (lower Q), deeper and higher volume. In re the walnut - send me a PM and I can send you pieces of real walnut that you can glue in where there are chunks missing from your veneer. Glue it down, sand it, oil it and you won't be able to see the repair. I will need your dimensions and you will have to "square up" the ding. recap, rewire and check the woofer can (air suspension chamber) for the 8" - these are always loose from the baffle (glued on OEM). Great speaker. Good luck,
  14. Shokdu, So how do you like the sound of the Emotiva gear? I have been considering that brand (the price is right) but have heard that the amplifiers are more than a little "crunchy" sounding. Is there any truth to this? As for the more expensive caps being "better" - as long as you move to a film cap (Solen, Jantzen, Dayton for example) I would agree with you. More important than brand is the tolerance - the tighter the tolerance the better the crossover behaves. The effect of bypassing, to my analysis, is no more than lowering the ESR (two resistors in parallel approach). Did you cut the 2500 uF cap out of the circuit? If you do - and the Emotiva has the "balls" to handle the resulting low impedance - your bass response will get about 100% better. Much tighter, much lower (now I hit 20 Hz without any problem) and far more tuneful. Do try it - it is amazing. I only very lightly sanded my Nines (220 grit) and then rubbed them down with Teak Oil (catalyzing resins like all the "oils"). Did a pretty good job for a box that is > 30 years old (made by Boston Coffin by the way). One of the best speakers ever made imo.
  15. Having rebuilt my Nines some comments (YMMV) The replacement of the original NPE caps with good quality film caps makes an ENORMOUS difference in the sound of the speaker. Everywhere you can afford to you should replace the electrolytics. You don't have to use Mundorf Silver/Oil (very expensive) but a Jantzen, Solen or Dayton does an excellent job. Always buy the capacitor with lowest tolerance - +/- 5% is good - even tighter is better. I replaced ALL my caps with film versions of same. If you have an amplifier that is stable into 2 ohm loads you can just ignore the 2500 uF cap - cut it loose between the cap and the coil - or where the cap/coil are tied to ground (and don't just assume your amp is stable - check with the manufacturer - and no "vintage" receiver is stable into anything much less than 4 ohms (if that)). That cap (2500 uF) and coil combination were designed to keep the impedance of the woofers high enough (~3.8 ohms) so that receivers of the time could drive the load (at resonance the 2 woofers in parallel look like about 1.8 ohms). Removal of this cap/coil combination will increase the tightness (lowers the Q) of the bass tremendously - as well as add a few Hz to the range. Once removed my Nines were playing very solidly down to 20 Hz - and the bass is TIGHT. At the fear of awakening the "all wire is the same" crowd of flat-earthers I will also suggest completely rewiring the speaker. The original wire, particularly that going to the woofers is far too small. Use 14 gauge spool wire - I used double runs of that to my woofers. I also soldered ALL the wire to the drivers. Those spade clips from the factory are always loose - and were only installed to ease assembly. Very important to check that the 8" LMR "air can" is still tight against the baffle - every Nine I have been into that "can" (which is hardly more than plywood and cardboard) has been loose and not functioning. Glue it back on - I added a brace against the rear of the cabinet to make sure that it stays in place. As for the resistors - the specification (original) is 22 watts - for my UMR (the 1.5" dome) I went to 10 watts - therefore at high volumes (high current) the resistance goes UP - and keeps the UMR in line (in terms of volume) with the rest of the drivers. I found that the UMR wants to "get out front" at high volumes - and this subtle modification serves to hold it down. Perhaps eventually the resistor will overheat and crack - and when that happens I will simply replace it. The Nine is one of the finest speakers ever made - to replace its sonic capability with a "modern" high end speaker you will be spending about $20,000 (at least and even then all you will get for your money is some ported thing and all its "phart" noises down low). Good luck
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