fedeleluigi

Hello Scoup, Did the LS and LSI have new crossover capacitors? If both of them had, did their crossovers use the same type and brand of capacitors? Did you test each of their driver before comparing the loudspeakers? During the comparison test, were the LS and LSI alternately placed in the same room position? Thank you for any clarification about your comparison test. Luigi

Hi Tom, Unfortunately, nowdays it’s very hard to accurately reconstruct the history of all that AR did and made. Unfortunately, many witnesses are no longer available (or the available ones do not remember the events exactly) and many important historical documents are lost. As regards the introduction of the 12” ferrite woofer, the dates of some AR drawings (magnet, cone-skiver and the spider in my previous post) would suggest that its production probably started in 1969 (please, see the attached pictures with highlighted dates). Obviously, the dates of these drawings do not prove with absolute certainty that the production of the 12” ferrite woofer definitely started in 1969. If the L.C.C., Loudspeaker Components Corporation, Lancaster Wisconsin (mentioned in some AR drawings) and today’s Loudspeaker Components, L.L.C., Lancaster Wisconsin are the same company, there might be a chance that it can still have some important documents (receipts, part orders etc.) that could be very userful for trying to establish the exact production date for some of the drivers made by AR. Luigi this drawing is the 4th in "AR Drawings" this drawing is the 316th in "AR Drawings"

Hi David, Examining the crossover photo you posted, the pots seem to have been bypassed (not in the correct way) by the previous owner. The photo is not so clear to see all the wirings precisely. When bypassing these 16 Ohm pots, the 16 Ohm resistance should be left in parallel with the respective driver (tweeter or midrange) otherwise the crossover network (in this case a 4 uF and 6 uF capacitor for the tweeter and midrange respectively) will be loaded by a different impedance and this will change the frequency cutoff and shift the crossover points in comparison with those of the original design. Obviosly, bypassing the pots (even if carried out in the correct way) does not allow to decrease and adjust the tweeter and midrange volume any longer and this could be a problem. Attached you can see the normal pot wiring, the early AR 2ax schematic and the correct and incorrect way of bypassing pots. Luigi

Differently from what is reported on some other pages of this forum (for example), the 200003 woofer spider has 7 corrugations (7 crests and 7 troughs ), not 6. Actually the 7th crest and the 7th trough seem to be a little smaller than the other ones and become almost "invisible" after the gluing between spider and cone. In other words the 7th spider groove hosts the paper cone as shown in the drawing I've made.

Hi Pete, There is a lot of information on AR Drawings about the spider of the 200003 ferrite woofer . Examining these documents carefully it comes to light that the first drawing of the AR 200003 spider dates back to 22 Jul 1969. So, most likely around this date the production of first 200003 ferrite woofer started. Revision B dates 1 Jul 1974 and apparently there was no change in spider manufacturing from 22 Jul 1969 to 1 Jul 1974 because Revision B only reports “drawing no. change" but a previous revision (O) dated 12 Sep 1972 reports "Revised Notes, DWG No. was X-3705" and something could have been changed on that occasion. Revision C (ISS. C) dates 5 Jul 1978 and apparently there is no variation about dimensions, material, treatment, supplier in comparison with Rev. B. As regards supplier, it was LCC (Loudspeaker Components Corporation, Lancaster Wisconsin). I think that the same company is still operating nowdays and they could still have the original molds/dies for the 200003 spider www.loudspeakercomponents.com . Differently from the previous drawing, on this last revision it is also reported something about the spider compliance (maybe there was some compliance variation in comparison with the previous spiders) but it's difficult to understand the standard used (where and how must the 50 grams be exactly employed? How/where do you have to measure the deflection?). You can find images of higher resolution on AR Drawings. The drawings are the 422th and the 423th but unfortunately there is no numeration. The last drawing is the 492th.

Hi Klaus, It's very important to preserve the woofer spiders. In order to disassemble the spider from the masonite ring I use an anti-fog nitro thinner as solvent. It is possible to use more powerful solvent to make faster the dismantling process but they could damage or alter the spider treatment changing its compliance. First it is necessary to gently remove the basket nets and unsolder the tinsel lead wires.Then I use a syringe to apply the solvent all around the glued spider-masonite ring. It's very important to apply it about every 2 minutes for about 30-60 minutes. This long time is necessary as the glue will soften very slowly. After 30-60 minuter you have to try to delicately separate the spider from the masonite ring beginning from the spider edge. You can use a needle (or somefthing similar). Be careful in order not to damage the spider. If the glue is still hard you just have to continue applying the solvent and wait until it softens Apply the nitro diluent where you can separate the spider from the masonite ring and keep on applying it all around the glued spider-masonite ring until you can separate them completely. After the separation you have to clean the spider and masonite ring from the glue remnants as soon as possible otherwise they will harden again and it will be annoying to remove them later. Than you have to remove the paper former of the voice coil and the glue from the spider/cone. I's very easy to remove the paper former. As regards the epoxy glue I remove it by gently using a thin sand paper until the new voice coil fits the hole. If the new voice coil doesn't have the vent holes they must be created with a good punch pliers. Voice coil should have 55-58 turns per layer and DCR should be about 2.6 Ohm. Apart from the type of former material, the voice coils of AR-12in ferrite woofers were rather similar along all their lifespan. In the AR drawings you can find the aluminum voice coil (the drawing is the 299th and is dated 25 Jan 1980). If the original paper voice coils are not too damaged (you can see it only after carefully taking the woofer apart) and if you have good manual skills you could try to restore them but it's not an easy procedure. So be very careful when removing the voice coils from the magnet gap in order not to further damage them. Luigi

Keno, you could use not original tweeters but you have to adapt the driver flange to the cabinet hole and modify the crossover network. If you want to do a good job you should use a speaker simulation software and in the end carry out some measurements. Imho, If you don't want to do all this and wish to keep the AR 12 originality as far as possible, today the best option is to use the replacement tweeters supplied by Midwest Speaker Repair. The 8 Ohm version is the correct one for the AR 12. It's a drop in replacement tweeter and If you use the 8 Ohm version you do not have to modify anything. Some members of this forum have already used these replacement tweeters (the 4 Ohm version) for some restoration of 4 Ohm AR speakers. Luigi - https://www.midwestspeakerrepair.com/shop/home-audio/mw-audio-mt-4121-75-inch-dome-tweeter/ - https://www.ebay.com/itm/AR-Acoustic-Research-Replacement-8-ohm-Tweeter-for-AR-2ax-AR5-LST-2-MT-4121-8/162689351715?hash=item25e10a8023:g:k~kAAOSwc8lZzEo4

The 20 Ohm resistor in the schematic is a misprint. Actually It is 2.0 Ohm and not 20 Ohm. You can see it from the AR 12 crossover picture. That's why the 20 Ohm resistor is not listed. In other words in the crossover network there are two 2.0 Ohm resistors and no 20 Ohm resistor is present. Luigi

@seventy1 Thank you seventy1, but the picture you post is not visible. Luigi Edit: Ok, now it's visible, Thank you

@seventy1 Could you please post some photos of all tweeter parts? Thank you Luigi

David, I'm sorry for the the snow storm and power outage. Hope they are "pessimistic" and you can have power again in a short while. Luigi

A parallel R and C circuit in series with a loudspeaker load can also be used with pro amps in order to protect them from very inductive loads. As an example, you can look at this link:https://adn.harmanpro.com/site_elements/resources/1010_1425481978/Macro-Tech-Series-600-1200-2400-Reference-Manual-130252_original.pdfthat's the Crown Macro-Tech amplifier manual. Please look at fig 3.14 at page 17. Even though the Macro-Tech amplifier were very stable amps into reactive loads, they can have problems with very inductive loads such as those caused by the presence of an autotransformer. Anyway, although the RC circuit shown in the fig. 3.14 will probably not give a flat frequency responce in the lowest frequencies (especially with a low impedance loudspeakers ) it will effectively protect the amp from most of dangerous inductive loads.

It is lowering the cap resistance. Just like when you put (2) 10 ohm resistors in parallel you get 5 ohms and when you put (2) 10 ohm resistors in series you get 20 ohms. The 2500 uF cap and the 10 Ohm resistor carry out a protective role against the inductive load caused by the presence of an autotransformer in the 10 Pi crossover network. Moreover, the 10 Ohm resistor, the 2500 uF cap and the autotransformer inductance constitute a special type of RCL network with a specific Resonance Frequency and Q factor. The resistor is important to determing both the Q factor and the Resonance Frequency of this particular type of RLC circuit. The Q factor can greatly affect the speaker bass response. You can examine the mathematics at the attached links (exersice 8 with solution). Pay attention that Q Factor, Resonance Frequency and Voltage drop through the capacitor also depend on R (R2 in the example) value. Unfortunately it is in Italian. Excercise n.8: https://it.m.wikibooks.org/wiki/Esercizi_di_fisica_con_soluzioni/Correnti_alternate solution https://it.m.wikibooks.org/wiki/Esercizi_di_fisica_con_soluzioni/Correnti_alternate#8._Circuito_risonante_con_2_R_2 Also In English you can observe how the R affects the Resonance Frequency of this type of RLC circuit at fig.5 of this link: https://en.wikipedia.org/wiki/RLC_circuit Luigi

Thanks David, I do hope some member of this forum that has an AR 10 Pi MKII or 11 MKII manufactured in the USA can share that information (type of polyester and weigh measured with a good scale). Thank you

David, In a previous post of mine I asked you to describe the type and weigh of polyester present in your 10 Pis. That was because in the two European AR factories were used different types of polyester wadding during AR 10 Pi and AR 11 MKII lifespan. If I have time to disassemble some AR 10 Pi to show it I'll take some pictures and post them. The weigh of the poliester wadding changes according to the type of polyester used. By the photo you posted I can recognize the type of poliester wadding used in your AR 10 Pi. The AR engineering file states that were used 10 oz of that type of polyester. Anyway, I've found in AR 10 Pi and 11 MKII an average of about 250g (8.82 oz, that is -12% compared to 10 oz) ) with this type of white polyester . As I'm interested in knowing the polyester weigh of the AR 10 Pi and 11 MKII manufactured in the US, could you please weigh it in both speakers? Thank you PS I post the engineering file (sheet 2) of the AR 10 MKII. It dates 18 Apr 1977, and the revision of cabinet wadding dates 9 Nov 1977. The AR 11 MKII engineering file show the same dates of revisions to new design (18 Apr 1977) and change of wadding ( item 11, 9 Nov 1977) and the signatures of the same engineer (probably Tim Holl). Thank you This is an European AR-10 Pi MKII showing a soft multi-coloured polyester stuffing but other type of stuffing were used as well. The white polyester was only used at the end of production. Obviously, the stuffing weight changed depending on the different materials.

Could you better describe the stuffing ( better if you would post some pictures of it) and exactly weigh it? Both these factors are very important for woofer damping. Luigi

I forgot to say that the switches terminals shoud also be carefully cleaned to remove oxidation. Pay close attention to how the switches are wired and double check them using the schematics. AR 10 PI switch wiring connections are rather complex! The capacitors are about 40 years old. So they shoud be checked too. You have to desolder at least one of their terminals and measure them by a good capacitance meter. Luigi

Here the original crossover schematics. Richard Lowe did an excellent work with the last update (AR10pi-CircuitNotes Version 1.1 Sep2014). By using these schematics you can check everything is wired correctly (also the switches). Luigi

Probably it could depends on your listening enviorement, amplifier, loudspeaker position or personal taste. Anyway, the 200003-1 part number you mentioned was usually used for the square magnet 12" woofer introduced with the LS series (9LS, 98LS, 78LS a and also used in the AR 58S) at the end of 1981 and manufactured until nearly all 1984. In 1985, the LSI series used Tonegen drivers. The 200003 woofer used for AR11 MKII and 10 Pi MKII, AR 9, AR 91 and 915 had the classical round magnet, aluminun voice coil former, a paper cone and a spider sligtly different from the previous 200003 and was produced from about 77/78 until just the introduction of the square magnet 12" woofer. Many years ago Kan Kantor's assistant Ruchi Goel (last post of this page) measured various AR 12" woofers and the Tonegen showed measurements rather different. Unfortunately those measurements are lost (their links do not work any longer since many years)! As said in my previous post the Tonegen woofer is definitely the best drop in replacement part for the originals AR 12" woofer. But I do think that If you want to get the best possible in terms of balance and naturalness of sound, the original woofers, manufactured in the same period as loudspakers, perform better. Untill now I haven't spent much time to try to optimize the Tonegen woofer sound by modifying crossover and/or cabinet stuffing. I think that some very good improvements could be reached. Anyhow if you are happy with the Tonegen woofer sound, don't pay too much attention to my considerations and subjective opinions. Luigi

Using a digital multimeter you can't actually measure a loudspeaker impedance. Anyway using it as you did I can read only about 10 Ohm regardless the switch positions. You actually measure only the 10 Ohm resistor in series with the autotransformer. You should check every driver has a correct DCR and is correctly wired. Woofer: red wire must be connected to positive and black wire to negative Mid: orange wire must be connected to positive and brown to negative Tweeter: yellow wire must be connected to positive and blue to negative. Driver terminals (especially tweeter's) must be cleaned well. Please, post some pictures of all the drivers. Luigi

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