johnieo Posted February 13, 2005 Report Share Posted February 13, 2005 Several Forum threads have discussed seemingly different AR-3a issues, such as sound preferences of Alnico versus ceramic drivers and the correct value of the woofer crossover inductor. One post asked when, and at what serial number, did the Allison-designed ceramic driver AR-3a replace the Alnico driver. These appear to be one issue.Roy C and I have compared information from several sources and observed that the switch to the ceramic driver in the AR-3a occurred in late 1969 with serial numbers larger than the 28,000s but less than 43,000. This somewhat narrows Tom Tyson’s post, which showed that the change occurred in 1969 after tens-of-thousands of AR-3as were produced. Most importantly, we never found a #9 woofer inductor used in the crossover of any AR-3a originally manufactured with an Alnico driver. All these early speakers were found to have an AR #7 (1.9 mH) inductor. Speakers manufactured with ceramic-magnet woofers all contain an AR #9 (2.85 mH) woofer crossover coil. There are too many AR-3as “out there” with #7 woofer coils for this to be accidental. Modeling of the #7 coil with the new woofer predicts increased output in the 300-500 Hz region and a higher crossover frequency as compared with the #9 coil. This agrees with what each of us heard—but could not explain—in our own speakers. It is likely that during initial testing of the new driver, AR made changes, such as the inductor size, to maintain its smooth response. We have all been told that the two woofers are completely interchangeable. They may be very nearly equivalent—-a tribute to Allison’s design—-but they require different crossovers.The opinion that the Alnico has a "warmer" sound than the ceramic driver probably resulted from comparing the sound after installing a ceramic driver in an early cabinet without changing the #7 coil. Other listeners may have compared as-manufactured early and late AR-3as and found little difference.Bottom line—the driver and crossover must be matched. This information can be beneficial to those contemplating the replacement of an original Alnico woofer with an AR ceramic magnet woofer.John O’Hanlon and Roy C. Link to comment Share on other sites More sharing options...
ninohernes Posted February 14, 2005 Report Share Posted February 14, 2005 Good info! Thanks guys! Link to comment Share on other sites More sharing options...
Guest loudsubz Posted February 23, 2005 Report Share Posted February 23, 2005 Yes great info. Its good to finally put a rest to this issue with some solid facts. Link to comment Share on other sites More sharing options...
RoyC Posted February 25, 2005 Report Share Posted February 25, 2005 Thanks guys!Our findings support information posted by Steve F. (reply to post #2884 in Nov of '03) regarding AR's acknowledgement of a 575 to 525Hz woofer/mid crossover change "some time" before publishing the revised specs in 1974.The increased inductance of the #9 coil over the #7 fits with the lower crossover point and any necessary compensation for the difference between the two types of woofers.Roy C. Link to comment Share on other sites More sharing options...
tysontom Posted March 4, 2005 Report Share Posted March 4, 2005 >Several Forum threads have discussed seemingly different>AR-3a issues, such as sound preferences of Alnico versus>ceramic drivers and the correct value of the woofer crossover>inductor. One post asked when, and at what serial number, did>the Allison-designed ceramic driver AR-3a replace the Alnico>driver. These appear to be one issue.>>Roy C and I have compared information from several sources and>observed that the switch to the ceramic driver in the AR-3a>occurred in late 1969 with serial numbers larger than the>28,000s but less than 43,000. This somewhat narrows Tom>Tyson’s post, which showed that the change occurred in 1969>after tens-of-thousands of AR-3as were produced. >>Most importantly, we never found a #9 woofer inductor used in>the crossover of any AR-3a originally manufactured with an>Alnico driver. All these early speakers were found to have an>AR #7 (1.9 mH) inductor. Speakers manufactured with>ceramic-magnet woofers all contain an AR #9 (2.85 mH) woofer>crossover coil. There are too many AR-3as “out there” with #7>woofer coils for this to be accidental. Modeling of the #7>coil with the new woofer predicts increased output in the>300-500 Hz region and a higher crossover frequency as compared>with the #9 coil. This agrees with what each of us heard—but>could not explain—in our own speakers. It is likely that>during initial testing of the new driver, AR made changes,>such as the inductor size, to maintain its smooth response. We>have all been told that the two woofers are completely>interchangeable. They may be very nearly equivalent—-a tribute>to Allison’s design—-but they require different crossovers.>>The opinion that the Alnico has a "warmer" sound than the>ceramic driver probably resulted from comparing the sound>after installing a ceramic driver in an early cabinet without>changing the #7 coil. Other listeners may have compared>as-manufactured early and late AR-3as and found little>difference.>>Bottom line—the driver and crossover must be matched. This>information can be beneficial to those contemplating the>replacement of an original Alnico woofer with an AR ceramic>magnet woofer.>>John O’Hanlon and Roy C.John and Roy,This is an excellent and insightful post. However, I believe it to be somewhat hypothetical due to the lack of definitive data. The woofer choke might have been changed, but I don’t think in the timeframe you mention. Besides, the original drawing for the AR-3a crossover shows Coil #9, PN 4726, which would be the Alnico-woofer version. I have some subsequent original blueprints on the AR-3a, but due to a recent move I am unable to get to a lot of my AR historical information at this time.Nonetheless, I recently spoke with Roy Allison (designer of the AR-3a), and he indicated that he was quite certain that no changes were made to the original choke values on the AR-3a during the transition from the original AR-3 cast-frame, Alnico version to the newer, ceramic-ferrite stamped-frame woofer, occurring during 1969. In fact, Roy was emphatic that there were no crossover changes made to the AR-3a until his departure in 1972. This first, highly compliant, ferrite woofer was very close to the AR-3-style Alnico woofer in nearly all parameters, and its measured response was nearly identical to the Alnico woofer in the deep bass, but significantly flatter in the upper operating range due to improvements in cone and skiver materials. Thus, modifications to the choke would have been unwarranted.More importantly, however, were the big changes made to the AR-3a (and the other AR speakers) in the 1973-1975 timeframe by the “new” Vic Bubber’s Teledyne/ADD engineering team, which included: (1) changes to the crossover from Chicago Industrial to Sprague/Callins electrolytic capacitors; (2) lowering of the woofer-midrange crossover from 575 to 525 Hz; (3) adoption of the back-wired MR and HF drivers; (4) utilization of the less-compliant new-generation 12-inch woofer and (5) the Velcro-attached, white-linen grill cloth. Significantly, the crossover change and the adoption of the less-compliant woofer (AR increased stiffness in this woofer to improve reliability and reduce warranty-service costs in the face of the new crop of high-powered, solid-state amplifiers coming into use in the 1970s) would be consistent with a change in the coil in order to revamp (increase) the woofer’s response just above resonance to compensate for the compliance changes.Finally, I own three pairs of original-condition AR-3as, one is a 1967 version, another is a 1970 version I believe, and the third is a 1972-73 model. I am reluctant to rip into them just to look at the woofer coil, but I will if we cannot satisfactorily determine what and when changes were made to the AR-3a.--Tom Tyon Link to comment Share on other sites More sharing options...
Guest loudsubz Posted March 4, 2005 Report Share Posted March 4, 2005 Tom:I helped aid in John and Roy's findings with the choke differences.I took some pictures of the ar-3a's I had in my basement and there was in deed a choke change, so thats what sparked Roy's further investigation into this.If need be I can post my findings. Link to comment Share on other sites More sharing options...
RoyC Posted March 4, 2005 Report Share Posted March 4, 2005 Hi Tom,Thanks for helping us sort this out. Far be it from me to question our founding fathers...but..As I posted in the woofer thread, I have identified a significant number of pre-70's alnico woofered '3a's with the 1.9mh inductor. I have been into and have collected info on a larger number of ceramic woofered AR-3a cabinets from 1971, 1972 and on...not one has the 1.9mh; all having the 2.85mh #9 inductor. I have yet to see any other arrangement than alnico/1.9mh and ceramic/2.85mh in a survey of nearly 20 cabinets ranging from serial #07xxx(1968) to 96xxx(1974).It should be noted that no other changes/differences have been observed, other than the capacitor-type evolution, in any of these crossovers, including the alleged out-of-phase-with-the-woofer mid/tweeter wiring. (ALL drivers in all the surveyed cabinets were wired (+)to(+) and (-)to(-)). The only other possible inconsistency has been the exact amount of fiberglass in some of the cabinets.I'd hate to be the motivation for you to break open your AR-3a's, but I'm willing to bet on the results if you do. I'll travel to your neck of the woods and buy you dinner and new mortite if you don't have a #7 coil in your alnico cabinet and #9's in the other two:-).Thanks again for your interest and assistance, Tom.Roy Link to comment Share on other sites More sharing options...
johnieo Posted March 4, 2005 Author Report Share Posted March 4, 2005 It is true that we are making a hypothesis, but one does so based on a reasonable quantity of data and then searches for cases that do not fit. So far, no such instances. In the course of my 47 years of electronic-related work, I have seen many cases where the drawings are never ultimately corrected to reflect, precisely, the finished product, so I tend to believe what I see, rather than what I read. (See for example, the 122-uF woofer capacitor in the Forum archived drawing of the early AR-11. It shows the 72- and 50-uF caps in SERIES!)Another example, the attached jpg file depicts yet one more parted early AR-3a crossover board listed on e-Bay a month ago. Its early AR-3a drivers were listed in adjacent auctions. I added arrows that point to the inked "7" used by AR to mark its coils. The numeral is clear at high magnification. One can see that these coils are hot-glued and aluminum-riveted in place as they would have been assembled at the factory. Modeling shows that the inductor change affects the high-end woofer response (300-500 Hz). The low-end response (f sub 3) could be affected by the respective differences of .56 and .78 Ohm in the 7 and 9 coil resistances. The two coils are wound on identical spools; unless one looks carefully, one will not see the difference in winding OD. Link to comment Share on other sites More sharing options...
tysontom Posted March 5, 2005 Report Share Posted March 5, 2005 >Hi Tom,>Thanks for helping us sort this out. Far be it from me to>question our founding fathers...but..>>As I posted in the woofer thread, I have identified a>significant number of pre-70's alnico woofered '3a's with the>1.9mh inductor. I have been into and have collected info on a>larger number of ceramic woofered AR-3a cabinets from 1971,>1972 and on...not one has the 1.9mh; all having the 2.85mh #9>inductor. I have yet to see any other arrangement than>alnico/1.9mh and ceramic/2.85mh in a survey of nearly 20>cabinets ranging from serial #07xxx(1968) to 96xxx(1974).>>It should be noted that no other changes/differences have been>observed, other than the capacitor-type evolution, in any of>these crossovers, including the alleged>out-of-phase-with-the-woofer mid/tweeter wiring. (ALL drivers>in all the surveyed cabinets were wired (+)to(+) and>(-)to(-)). The only other possible inconsistency has been the>exact amount of fiberglass in some of the cabinets.>>I'd hate to be the motivation for you to break open your>AR-3a's, but I'm willing to bet on the results if you do. I'll>travel to your neck of the woods and buy you dinner and new>mortite if you don't have a #7 coil in your alnico cabinet and>#9's in the other two:-).>>Thanks again for your interest and assistance, Tom.>Roy and John,Wow! These are compelling arguments, and I cannot really refute the evidence you have found. I am confounded by the comments made by the designer (although Roy Allison is remarkably bright and capable, he could have forgotten some details along the way) that no changes were made to the AR-3a while he was there. But that has been many years ago, and there were several speaker engineers working around those designs on a day-to-day basis. Chuck McShane was certainly instrumental in the AR-3a design and development, and perhaps we should ask him. Alex Barsotti of AB Services might also remember these details from his Customer Services days at AR.Finally, I will go back (once I can locate them) and look through some blue-line drawings and prints of the AR-3a crossover to see if I can find anything. I do know that at least two of my drawings show the 3700 woofer (Alnico) being used in conjuction with the 2.85 #9 coil. I am a bit reluctant to break into my AR-3as, but for the sake of "science," I would be willing to make the plunge.--Tom Tyson Link to comment Share on other sites More sharing options...
johnieo Posted March 5, 2005 Author Report Share Posted March 5, 2005 >I added arrows that point to the inked "7" Ignore the right-hand arrow! It is pointing to a "4" on the large mid coil. The woofer coil number in the right crossover is not legible. Sorry, another senior moment. Link to comment Share on other sites More sharing options...
RoyC Posted March 5, 2005 Report Share Posted March 5, 2005 That sounds like a plan, Tom! We certainly can't hold anything against Mr Allison if it turns out that he didn't remember that small detail after 35+ subsequent years of incredible projects and accomplishments. I'm just glad that you and others "who were there" are willing and able to engage in these discussions.One of the few things that I actually remember from those days is not being able to afford AR-3a's! The rest is very fuzzy! I'll stock up on mortite just in case....Roy Link to comment Share on other sites More sharing options...
Guest loudsubz Posted March 5, 2005 Report Share Posted March 5, 2005 To add I have a few pictures of my dad's Ar-3a Link to comment Share on other sites More sharing options...
Guest Bret Posted March 5, 2005 Report Share Posted March 5, 2005 >One of the few things that I actually remember from those days is not being able to afford AR-3a's!<I'll second that. The hours I spent gazing longingly into the AR brochure probably account for my never having read "War and Peace."Bret Link to comment Share on other sites More sharing options...
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