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johnieo

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  1. Hello Dave: Thanks for your comments. No, I was not worried about crossover frequency change but whether a slope change in the network would change the character of the original (the ratio of power from each driver). But maybe that is what you wish to accomplish? Certainly Q does not affect sound in the crossover range. In addition, some have worried about the ESR of a capacitor without regard for two issues--the frequency at which their meter measures ESR, and the role of the capacitor in the crossover. For example, the impedance of a 20 uF woofer capacitor is important in the octave near crossover, so if we measure ESR of an aging cap at 8 kHz, and find it has changed, it matters not. However, if it is measured at 1 kHz, and has changed, that is a different matter. Ditto for aging caps used at low crossover frequencies, that issue is changing dielectric absorption, not changing high frequency resistance. Will be interesting to see your final results. Cheers, John
  2. Well ... my memory did not serve me at all. Let's try that again: "... found it to increase from 0.75 to about 1." sorry, neurons rot like foam. John
  3. Hello David: More than one issue in your above comments. First, AR apparently revoiced all their speakers in the late 1960s. In about June of 68, the AR-3a woofer was replaced with the new ceramic magnet based woofer, and this of course used a new cone and surround. As well, the stuffing was reduced from 28-30 oz to 18 oz of FG and its inductor changed from #7 to #9 (About serial number 38,500). Be aware that the AR published data were taken on the new ceramic magnet style woofer. Ditto for the AR-4x. Its coil was changed from #4 to #5 and FG stuffing reduced from 18 to 12 oz somewhere between June and Dec 68 (between serial numbers 175,000 and 215,000). At some point about 1971, near the end of its production run, old woofers with cloth surounds were eventually replaced with woofers with foam surrounds. I measured the system Q of several old AR-3a and old 4x and found it to be reduced from about 1 to about 0.75, if my memory serves me. These numerous changes are why I doubt anyone can "hear the sound of an Alnico magnet" My gut feeling is that AR was responding to competition by reducing Q so as to gain another hertz or two of low frequency amplitude. Some years ago, I had a pile of 4x tweeters and sent them to Roy. He had an equal-sized pile and paired them by output level as hi, medium, and low and returned same number to me as pairs. Since the units all have level controls, it did not make much difference which pair we used--loud or soft--as we could adjust the level control. My personal solution to this was to rebuild all AR-4x according to one style--#5 coil, 12 oz Fiberglass, cloth surrounds, potentiometer level control. In this way replicate the "new" 4x style. Even if the level of the weak units was not extreme with control full up, they made fine surround speakers for a small-room home theater. Also, I have used either dilute Permatex or RTS (Roy's tacky stuff) to coat the cloth surrounds, if the originals were dried and leaky. And again, my capacitor choice has been polymer dielectric, so my kids will not have to carry them to the curb after I am gone--they don't know a capacitor from a magic marker! Personally, I would doubt that you could ever make a new crossover without level controls as a subsititute for any old AR speaker that used level controls in its original design. They were intended to deal with room and placement differences; today we have the added distraction of decades of variable level decay in any vintage AR speaker. I doubt that any one tweeter pair you might obtain would be at all representative. Also, the output near crossover (1,200 Hz) will come from both drivers, so wouldn't the change in crossover order affect the overall speaker's character in the octave near crossover? Cheers, John
  4. Only two typefaces (not fonts) were used in composing this document: Times New Roman (body text, including the author's names in italics as discussed above) and Verdana (headings). Symbol typeface was used to set individual Greek letters. These are standard faces on PC machines using MSWord. MAC users will find similar typefaces Times Roman and Helvetica on their machines. The document was composed in MSWord. The program "PDF CREATOR" (space between words) was used by the Administrator to convert and secure the PDF file. I have used this same program; to my knowledge, there is no "toggle" by which one can control an imbed function. If only one or two users have had difficulty in reading the PDF file, it is likely a local software issue. Cheers, John O'Hanlon
  5. Does anyone have the crossover schematic for an AR-12? Thanks,
  6. Steve: I date from 1937; cut/paste is necessary to remember things correctly Cheers,
  7. Hello Philippe: All of the comments I have seen from crossover designers say that +/- 10% is fine. In fact most of the electrolyic are +/- 20% so 4,7 would be fine for a 5,0 uF. Hope this helps, John
  8. Hi Philippe: Before you purchase new tweeters, I would try to pull the dome out to about its original position - either with a small flexible plastic hose and a bit of vacuum, or with a sharp pin and lift carefully. If the voice coil is good and you can get the big dents out, then I am told it is not necessary to replace the tweeters. The #1 in front of the part number was added by AR at some point to allow for more part numbers. My AR-18 tweeters are part number 200014-3. I think these are what you see listed on eBay. My AR-18b tweeters are part number 200034-0, but the AR parts list gives their number as 200038-0. I think both numbers are correct. Why not try to work the tweeter domes back into approximate shape gently. If they sound good, why replace them? Either refoam the woofers or obtain a pair from Klaus. If you purchase his pair, someone will purchase your pair and refoam them - so don't throw them away! These drivers cannot be replaced. Cheers,
  9. Hello Philippe: Please do not change the crossover circuit or change either the woofer part number or the tweeter part number. I would be best to use the woofers offered by Klaus. A very long time ago someone, I believe it was Steve F., posted comments about the relative merits of the AR-18 series. The poster indicated that the AR-18bx is the next to the lowest in quality of the series, with the AR-18bxi considered ti be the lowest quality. The AR-18bx used a generic tweeter, and a lower quality woofer than was used in the AR-18b. Further, the crossover frequency was increased to 3,000 Hz, widening the range over which the woofer was asked to speak. Also, the AR-18bx use an AR-1200068-0C woofer, which was stated to be not as good sounding as the woofer used in the AR-18 or -18b. In a nutshell, the AR-18b has both good sounding woofer and tweeter, which are matched to its crossover, so it would be prudent to replace parts with original AR-part numbers, and retain the same value crossover capacitor. It's a nice sounding speaker; I have several and enjoy their sound. It is worth the effort to maintain their authenticity. Hope this helps,
  10. Hello Philippe: Voila, the crossover for the AR-18b -18s Cheers,
  11. Hi Minh: Roy Allison just reversed the "2" and "14." Got a couple of years to go to catch him, but still make more mistakes that! :-) Cheers
  12. Martin: Permatex and Armor All do different things. Armor All is a surface coating that appears to maintain the long-term flexiblity of rubber and plastic surfaces. It would appear to prevent those surfaces from drying - that is why one uses it on interior plastic auto surfaces and such. It would be applied infrequently for such purposes. Just because there is no visible effect in a day does not mean that it is not doing its job! Armor-All is, if you wish, rejuvinating these surfaces, or slowing their aging. Permatex is a thin rubber or rubber-like coating that seals. Roy C noted that it tends to mix with the existing butyl rubber; that's a good sign, it means it is bonding well with the exisiting coating. Permatex is re-sealing the cloth surround. Roy's comment about the use of solvent to remove the loosly bonded old seal before adding new material makes a lot of sense, as this keeps the final seal as thin as possible. In order to measure / hear the difference in performance, one must repair one of a pair, then remeasure / listen. Neither Roy nor I has found any thick latex or paint-based product that will not adversely affect the free resonance of a woofer. As far as we know we are the only ones who are speaking from experience with Permatex - we welcome others to try it and report their results to TCSP. Especially, if you own Woofer Tester or the like and can made a before / after measurements! Cheers
  13. Sorry if this kinda puts a damper on this topic, but we must be very careful in it's application. Why would the knowledge that a material is made from an organic compound "put a damper on this topic?" This material is no different than a hundred others found in any auto supply store. Here we are brushing on perhaps a half cc of liquid and letting the volatiles evaporate in a place where no one will breath their fumes. We simply use this material carefully like we do with any chemical. Lots less exposure than redoing a head gasket! :-) Cheers,
  14. <Other than, Tom Tyson's, please correct me if I am wrong, suggestion to use ArmorAll to rejuvinate AR cloth surrounds, 2 coats 24 hours apart, there seems to be no other information.> Armoral will not seal leaks in butyl-coated surrounds. Never has, never will. It will plug leaks for a minute to see if the cabinet is tight, then evaporate. It may well *maintain* cloth surrounds in a flexible condition; it may *soften* hard surrounds (rejuvinate), but that is not the same as patching holes big enough for a flea and all of his cousins to walk through! Armoral is used on vinyl car upholstery to maintain its suppleness - in the desert we use it on vinyl pool furniture to slow UV and chlorine attack. The material we formerly used was "Loctite Butyl Rubber Sealant" diluted with hexane or lacquer thinner to the consistency of water before applying with a brush. Unfortunately, Loctite no longer make this material. Roy C has found an alternative, which he will describe in a day or so - when he finishes gathering data. More than one of us has tried the latex glue formulations that are used for gluing surrounds and find that they increase the Fs of drivers and therefore are not suitable. It is hard to justify the price of the Orange County stuff which is likely similar to that I have used from Parts Express. The beauty of Roy's material is that it is not costly and remains flexible. But let's allow him to toot his own discovery. Cheers, John O'Hanlon
  15. Chimpetus: What is important is the phase relation between the two drivers and their matching speaker. The positive terminal of the woofer (red dot or cross) should connect to the #2 speaker input terminal. #1 terminal of the potentiometer should connect to the #1 speaker input terminal (common or negative side). "B" terminal (the wiper) of the potentiometer should connect to the tweeter terminal marked with a dab of yellow or white paint on its backside. (That terminal should be the left-most tweeter terminal as viewed from the tweeter backside.) #2 terminal of the potentiometer should connect to the capacitor and one side of the tweeter. Before you reverse those wires on the potentiometer, please remove the tweeter and see if someone changed the factory color code at the driver as well. If both reversed, all is fine; if not, fix. Electons don't really care what color insulation keeps them in line :-) Cheers,
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