fedeleluigi

How did you exactly get these readings? What instrument did you use to measure the loudspeker impedance? Anyway: with Woofer in Pi, Mid in -6 dB and Tw in -6 dB you'll have a 16 ohm loudspeaker ( an easier load but with the smallest loudspeaker sensitivity); With Woofer in 2 Pi, Mid in -3 dB and Tw in -3 dB you'll have a 8 Ohm loudspeaker; With Woofer in 4 Pi, Mid in 0 dB and Tw in 0 dB you' ll have a 4 Ohm loudspeaker (a more difficult load but with the greatest loudspeaker sensitivity). In my experience, using a tube amp you have to practically try both the amplifier different outputs and the different positions of loudspeaker switches to find out the best sonic match. Luigi

Congratulations David. By the pics you posted they would seem to have all Tonegen woofers. Although they certainly are the best "not" original AR woofer replacement, I do prefer the 200003-woofers made in USA in the same period (about 1978 to 1982) of AR 10 PI mkII and AR9. In my experience, although all original AR 12" woofer (# 200003) are considered interchangeable, every AR loudspeaker has a more balanced and natural sound with the drivers manufactured and used in the same period. At least in my listening enviorement and with my electronics. Luigi

Hi David, The answer is no, they aren't Replicas. The AR 10 PI showed in the pictures you posted are the so called "MKII" version (which had a black ID plate). Though the photos are not clear and focused, the woofers do seem not original but Tonegen replacements. Also one tweeter seems to be a Tonegen replacemet but the picturres are not clear enough, so I can't be totally sure. The 10 Pi Replicas only had Tonegen drivers an never had a sticker with a serial number. They are very rare and, as far as I know they were never exported to the USA. In the previous pages of this thread I posted a link to an old thread I originally wrote in 2003 about the story of the AR 10 Pi Replicas. There are also some photos. Luigi

Hello Tom Pete said the tweeter he tested had ferrofluid. If the ferrofluid was still in place in the magnet gap , it sealed it and consequently the space behind the dome. So, in the 200011-1 tweeters with ferrofluid the air behind the dome can't escape from under the dome into the pole-piece/magnet cavity. In other words the air is trapped under the dome and suspension. On the contrary, as regards the early 200011-1 tweeters the air can move freely because they don't have ferrofluid sealing their magnet gap. Luigi

Hi Glenn, I was referring to the 12 inch woofer. The moving mass of the 10 inch woofer is much lighter and its Xmax is smaller than the 12's. Moreover the 10 inch ferrite woofer has a bumped black plate. For all these reasons the crack of the voice coil support is rather rare in AR 10 inch woofer. As I do not usually shim woofers when I refoam them, I do not know when AR exactly changed the former for its voice coils. I usually disassemble woofers only when their voice coils or spiders are broken. Anyway in some 2ax 10" alnico woofer using foam surrounds I found NOMEX. They were dated about 1972. Nomex is a meta-aramid material developed by DuPont in sixties and is completely different from paper. It seems plastic. I do not know if AR continued using it also after the indroduction of the ferrite magnet for the 10 inch woofer. This is also why I asked you what material you had found when you shimmed your woofers. Later in some date of 1977 AR began to use aluminum for all its woofer voice coils. As regards AR 12 inch ferrite woofer manufactured from about 1970 to 1977 untill now I have never found Nomex former (but only paper former) in their voice coils . Luigi

Thank you Roy, I thought that the change had occurred later, around the middle of 1977. Anyway, one of the pictures posted by Glenn shows a woofer manufactured on the 33th week of 1977 and one of his woofers would seem to have a paper voice coil just like he remembers. Imho, the paper voice coil former used in the 12 inch woofers from around 1970 to around 1977 and the use of a not bumped back plate was the "Achille's heel" of those excellent woofers. Apart from the possibility of a hard bottoming for the flat back plate of the magnet , Imho, at the voice coil "collar" (I mean the former space between the cone and the first voice coil winding) the paper former was not "strong" enough to bear the big forces caused by the wide and violent oscillations of the heavy cone (at high volume) during many years . I do think that at AR they never imagined that there would be lovers and enthusiasts for their speakers after more than 40 years! Luigi

Hi Glenn, I hope Roy C. can chime in as he uses to shim woofers when refoaming them. Thanks again Luigi

Hi Glenn, Excellent job and thank you for sharing it! Could you please tell me what is the voice coil former material used in the woofers (200004-2 ) you shimmed? In one picture it seems aluminum, in the other one it seems paper or nomex. I'm interested in it as AR began to use aluminum for its voice coil at some point (I suppose about the middle or the end of 1977) and in one of your woofer is printed the manufacturing date (33th week of 1977) . Thanks. Luigi

I've drawn the AR-11 MKII (B) crossover schematic. I've preferred to use old style types and drawing. Hope it can be useful. Luigi Edited: better drawing

Here is the AR 10 Pi schematic coming from a copy of an original AR drawing sheet. Unfortunately the copy I have is not complete and a part of the AR drawing sheet is missing. I couldn't find this schematic in the "AR Drawings" section, so I hope it can be added to the other files somewhere in the Library in order to allow everybody to see it. I think it's a rather rare document even though, unfortunately, not complete. I have scanned it as TIFF format then I've converted it to JPEG to insert it directly into this post. To get a higher resolution, save the attached file in Tiff format. Differently from LST, in the AR 10 Pi the auto-transformer and the 3 dB step switches permitted the listener to have more flexibility with a total of 27 different combinations of driver output level (that is 27 different frequency responses) without using any attenuation resistor. The auto-transformer enabled the user to control bass output by a 3 step switch as well. Differently from midrange and tweeter, the woofer switch (Woofer Environmental Control switch) is actually not a 3 position +/-3dB step switch but a 0dB (4Pi), -5dB (2Pi) and -8dB (Pi) switch. Luigi PS: I had already posted this schematic in the Acoustic Research forum pages but I think that the most appropriate place is probably here. AR10 Pi original schematic TIFF.tif

Hello David, The AR drawing (DRG. NO. 202029, ISS. C of 14 May 1982) reports the use of N. 38 AWG insulated copper wire for the 3/4" lambda driver voice coil. It also reports 22-24 turns in all and a DC resistance from 3 to 3.7 ohms REF. Taking into account that AR 3a tweeter voice coil has about 20 turns, (that is 10-20 % less than lambda driver's), using the same wire gauge, the resulting DC resistance should be OK. Examining some AR 3a voice coil by a biomicroscope, I have counted about 8 and 12 turns for the outside and inside layer respectively. Luigi

That's why, as I had never listened to new AR3s, I started a thread asking people who could listen to them when the were new how much was the difference between AR3 and AR3a midrange frequencies as the AR3s I listened to had the midrange frequencies "too weak" in comparision with the speakers (AR and not AR) I'm used to listen to. You are one of the few who could simultaneously compare the restored midranges to the original ones using two pairs of AR3. Thank you for sharing your listening impressions. Luigi

Thank you Tom, as far as I've seen in Italy and Europe where the ADD series speakers were rather common, the polyester stuffing and the the woofer aluminum voice coil former were used very early in the "MKII" series (probably with its introduction). Anyway, although I've seen many of these speakers I haven't obviously seen all of them and now I regret I didn't note at least the serial numbers and the main characteristics of all the speakers I have analyzed. Luigi

Glenn, Thank you very much! As I said, for the first time in my life, I could listen to a pair of AR3 about a year ago. It seemed to me that they sounded with a recessed midrange. So you have confimed my listening impressions and my suspects of a very probable problem with the midranges of the AR3s I listened to. Luigi

Sorry Glenn but unfortunately English is not my native language. By a "backwards midrange band" I'd like to say that the sound pressure in the midrange frequencies is less than the sound pressure in the treble and bass frequencies. So, for example, when listening to human voices they seem smaller than usual. In other words the midrange level is lower than treble's and bass's. Maybe I could use the expression of a "recessed midrange" or "recessed midrange frequencies" but I don't know if it is correct and how to exactly express this idea in English: "less sound pressure in the midrange frequencies compared to treble and bass frequency sound pressure". Could you please tell me more about the sound differences between the AR3s with the restored and original midranges? Thank you Luigi

Hi Tom, Observing the AR 11 "Visable" I have noticed that it is a so called "MKII" version. So it seems a little strange to me that the stuffing is fiberglass instead of polyester as usually used in the "MKII" version. Also the woofer voice coil former seems not to be aluminum whereas I have usually found aluminum former during the AR 11 MKII woofer restoring. Did the early AR 11 MKII use a fiberglass stuffing and a not aluminum voice coil former for the 12" woofer? Luigi

As I said, in my experience a crossover check (carried out carefully) is always strongly recommended in a vintage speaker especially for driver safety. Luigi

Excellent advise Kent! I did forget to recommend that Jasper read the excellent work "restoring the AR-3a" . Although it only refers to 3a, he could find useful and general information about dismantling and checking a loudspeaker. Luigi

Hi Jasper, Unfortunately you should dismantle your AR 10s in any case. In my opinion, in a vintage loudspeaker it is obligatory to check carefully that everything is OK especially the crossover capacitors. After more than 40 years the original bipolar electrolytic capacitors could very probably be out of specs (abundantly) . For example I have often found the 10 uF industrial cap (used in the tweeters crossover network of AR 10 Pi and 11) more than 300% out of specs (I found some that measured more than 35 uF!) . This is very dangerous to tweeters and they can easily burn out. If you are not used to disassemble and check a loudspeaker you'd better not to do it as you could damage it. You could ask some of your friends that are skilled in this kind of works to help you. Anyway I recommend that you check your 10 Pi crossovers. There are lot of threads about recapping a crossover with bipolar electrolytic or film capacitors. I don't want to discuss about the sound of capacitors but I only recommand that you use not out of specs fresh bipolar electrolytic or film capacitors (always measure their capacitance before using. Voltage: 63V or more). Check also the crossover bobbins as I sometimes found some mistakes made during factory assembly (at least in Europe). As regards driver date of manufacturing it is usually printed on each driver back (in more recent drivers it is printed on their paper labels). With reference to tweeters, you should unscrew the 3 screws of each one. Then you can carefully remove the tweeter. It's not always necessary to disconnect the wires (although it would be very useful to clean the tweeter and wire terminals: The high notes will improve) to see the back of these tweeters. On the back of the driver you can read the tweeter part number (200011-1 but on early versions it was omissed), the number 561 and others digits that indicate the year ( in your case 75 or 76) and the week of manufacturing. For instance 7544 means the 44th week of 1975. It is very simple to remove a tweeter from the cabinet but you should pay attention to the following aspects: 1) the fabric dome is delicate and you should not damage it with the screwdriver tip and/or the screws because of the tweeter magnetsism that is very high (maximum) just in correspondence to the yellow fabric dome. 2) so you should carefully touch only the screw head by the screwdriver bit paying attention not to move close to the fabric dome. 3) after unscrewing one single screw, carefully move it away from the tweeter dome holding it firmly and when you have to screw it again be careful to hold it between you fingers firmly until it begins to screw in. If it slips out of your fingers it could be attracted towards the fabric dome damaging it. Should you decide to check your AR 10s (and as I said I recommend that you check them: your AR 10s and your ears will thank you) please let us know more about the history of these AR speakers informing us about the date of manufacturing of tweeters (and if possible of the other drivers). Luigi

Thank you Tom for answering and also for your "off topics" as they always are very accurate, instructive and informative for all of us. As you have said and as far as I know the yellow-orange 3/4-inch soft-dome tweeters never had ferrofluid. As far as I've seen the yellow-orange tweeters were manufactured until, at least, the first months of 1976. If I remember correctly, before the biginning of production of the black 3/4-inch soft-dome tweeter with ferrofluid, I think there was a brief production of black 3/4-inch soft-dome tweeters without ferrofluid very similar in construnction as the yellow-orange ones ( with the terminals crossing tweeter plasic flange still having a shape of "I" and not "L"). In other words they look like a 4 Ohm version (without ferrofluid? ) of the early 8 Ohm AR 12 tweeters. I never disassembled them ( they were functioning) and unfortunately I didn't note and do not remember their date of manufacturing. These black domes tweeters are rather rare. So I think that if Jasper's (patagorda's) 10s were assembled at the end of 1976, they could now have an "older" no-ferrofluid yellow-orange tweeter for some unknown reason (maybe the yellow-orange tweeter were used later as "replacement parts" for blown black ferrofluid tweeters that originally were used in the factory assembly). Jasper (patagorda) could check the date of manufacturing printed on the back of his 10s tweeters (and the other drivers) so we could learn more about the history of AR speakers. Unfortunately, today it is very hard to know exactly all that happened at AR during the seventies. It seems to me that (maybe I'm wrong and if so, I apologize) unfortunately none of the numerous engeneers or workmen that worked at AR in USA or Europe in the '70s writes or has written in these pages providing all of us with useful and instructive information about AR. It seems that they are not so enthusiastic about AR speakers as we are. So, unfortunately, a lot of precise historical information about those years will be lost forever. Luigi

@tysontom Thank you Tom for all the precise information you provide us. I've always thought that probably the "H" and "E" printed before the loudspeaker serial number meant Holland and England respectively but I'm not sure. Do you know anything about it? Do you know if there was any relationship between American and European serial numbers or they were completely independent? Luigi

The single loudspeaker picture you linked is definitely an original AR 10 Pi MKI (year 1975-76). Check accurately both loudspeakers are completely identical (drivers and furnitures). Also the magnetic lock "VAREC MILANO" is original. In the attached link you can see some pictures of the AR 10 Pi (Pi Greco in Italian) Replica: Luigi

Hello Jasper, Please, post some good pictures of your 10 Pi. Luigi

Thank you Glenn, Roy is very expert in repairing AR drivers so when you have a chance to compare both pairs of your AR3s, please let us know the differences. As I told, I listened to a pair of AR3 with a backward midrange band so I'm very interested in knowing how AR3 midrange frequencies really sound when the drivers are ok. Have a nice day Luigi

Happy New Year to everyone! Glenn, as usual an excellent work! As I wrote in a previous thread (http://www.classicspeakerpages.net/IP.Board/index.php?/topic/8815-difference-in-sound-between-ar3-and-ar3a/), about one year ago I listened to a pair of AR3s for the first time in my life and I noticed a backward midrange band in their sound. What about the AR3 sound in the midrange band before and after RoyC's midrange restoration? In other words, how much is the loss of output pressure and details with the old AR3 midranges? Luigi