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fedeleluigi

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Everything posted by fedeleluigi

  1. fedeleluigi

    AR3a woofer recone kit

    Hi Klaus, It's very important to preserve the woofer spiders. In order to disassemble the spider from the masonite ring I use an antifog nitro diluent 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 remmants as soon as possible otherwise the glue remmants 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 coice 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
  2. fedeleluigi

    Refoam AR-9 woofer

    Mez, That's Ok if the woofer is the replacement part manufactured by Tonegen ( part# 1210003-XX). If the woofer is the original AR woofer (part # 200003), the outer edge of the foam is normally glued to a masonite ring that is glued to the metal frame. If someone erroneously removed the masonite ring you should restore it. Luigi
  3. You're welcome, Your measurements are very interesting! Please consider that 20 oz of fibergass could overdamp the late 200003 woofer generation (that is what I do hear with my ears but I never carried out measurements). To the best of my knowledge, AR 11 and 10 Pi MKII did only use 10 oz of "white" polyester in USA. The same type of white polyester was also used for the AR9 and (later) the AR9ls series. In Europe different types (with different densities and consequently different masses) of polyester were used for the AR 11 and 10 Pi MKII and only the late production in 1979 used the "white" polyester (about 9 oz). I've read the AR 11 MKI review again but, unfortunately, they do not say how the switches were set during the impedance measurement. The frequency response shows 3 curves (0, -3, -6 dB). Since only the midrange and tweeter can be attenuated, the 3 curves are exactly the same up to about 500 Hz. So the minimum (4.8 Ohm) at 80 Hz is not affected by the midrange and tweeter switch position. The minimum around 3 Ohm at 6000-7000 Hz may suggest that the switches were set for the maximum output (0 db attenuation) and furthermore the worst condition is what generally matters most. Anyway, the minimum of 4.8 Ohm at 80 Hz would seem a little high in comparision with that of the AR 3a improved that had the same 200003 woofer generation used for the AR 11 MKI and a rather similar woofer low-pass crossover network. As regards the AR-10 Pi impedance measurements (both MKI and MKII), they say that the switches were set for the maximum output (4Pi, 0dB, 0dB for woofer, midrange and tweeter respectively). Examining the AR 10 Pi crossover network, when the woofer environmental control switch is set to obtain the maximum output (4Pi), the inductance in series with woofer is 4.73 mH (1.88 mH + 2.85 mH), the capacity in parallel is 100 uF and thanks to the autoransformer, the output voltage that supplies the woofer is higher than the input one. Because of the autotransformer the impedance varies according to switch positions: the review says that when the woofer switch is set on 2Pi and Pi the minimum impedance is 7.5 and 13.6 Ohm respectively (around 100 Hz) .
  4. From the AR drawings: AR 11 MKI : 20 oz fiberglass AR 11 MKII: 10 oz (white) polyester wadding . Several types (and weights to always obtain the optimal damping) of polyester stuffing were used in the European factories for the MKII versions. As regards the white one (used only in the very late production), I've generally found a single sheet of about 250g (8.82 oz). The 10 Pi MKII of the test (Fc: 40.5 Hz) had the multi-coloured poliester (in my experience i found about 450g =15.87 oz when this type of stuffing was used). In another magazine that also tested the 10 Pi MKII, the Fc was 42.8 Hz and the woofer Fs 16.9 Hz . The suffing was multi-coloured polyester too. As said in my previous post, unfortunately, I don't have any impedance graph (and Fc) for the AR 11 MKII but I think that its Fc is similar to that of the AR 10 MKII.
  5. From what I've read in your first post your AR-11's are MKII. I coudn't found an impedance sweep for the AR-11 MKII but I've found one for both the AR-11 MKI and the 10 Pi MKI . I've also found some measurements for the AR-10 Pi MKII that essentially differs from the 11 MKII for the use of an autotransformer in the crossover network whereas the cabinet volume and drivers are the same (AR-11 MKI schematic, AR-11 MKII schematic, AR 10 Pi MKI and MKII schematic) . The FC is 40.5 Hz for the AR-10 Pi MKII (besides the impedance sweep, see also the red highlighted text) and seems to be around 36-37 Hz and 38 Hz for the 10 Pi MKI and AR-11 MKI respectively. Hope these graphs can be useful to you.
  6. Examining the AR drawings in the library, the mass without foam measured by @aquila2010 for the 200003 woofer moving mass should probably be correct ( around 70 g). The drawing #002 is dated 8 Jan 1984 and reports a mass of 41 +/-3g for the cone/surround assembly. The drawing #004 (it seems to be dated 7/1/69 ) should show the first ferrite cone/surround assembly and its mass is exactly the same as before. In other words the mass of the cone/surround assembly should have not changed during the 200003-(0/1) woofer lifespan. The drawing #299 (12-in W // 200003 // voice coil // 25-Jan-80 // 13-Feb_81) refers to the aluminum voice coil and reports a mass of 24g +/- 15% (from 20.4 g to 27.6 g) . I coudn't find the spider and dust cap masses on their respective drawings. Therefore, without spider and dust cup, the mass of cone/surround/voice-coil assembly is about 41g+24g = 65 g (anyway it could ranges from 58.4g to 71.6g taking into account the maximum variations admitted in the AR drawings) for the aluminum-voice-coil woofer. Realistically the spider and dust cup and glue could have a total mass of around 5-10 g, so the "about 70 g" without foam reported by Aquila2010 is likely correct and probably applies to the aluminum-voice-coil woofer as well. Anyhow I've several 200003 woofers disassembled but haven't a very accurate scale at the moment. If I can somehow get one I'll report all their moving masses.
  7. fedeleluigi

    AR-11 MK1. Identification and rebuild.

    This tweeter is original (MKI) . This is a replecement tweeter probably made by Tonegen / Foster. Very likely it is more sensitive/efficient in comparison to the original tweeter.
  8. fedeleluigi

    AR-11 MK1. Identification and rebuild.

    Here is an interesting thread about the masonite ring. Unfortunately I do think that you have to made it by yourself or with someone's help
  9. fedeleluigi

    AR-11 MK1. Identification and rebuild.

    JimEG, Unfortunately someone refoaming this woofer erroneously removed the "masonite" ring. You can see it on the other woofer: it is glued to the basket and the outer edge of the foam is glued to it . The masonite ring should be restored.
  10. fedeleluigi

    AR 11" woofer driver refoam (AR9)

    Pete what's exactly the problem with the woofer match?
  11. fedeleluigi

    AR 11" woofer driver refoam (AR9)

    No they haven't. As regards the 12" foam/ceramic woofers made from about 1970 to around 1977 I have always and only found paper formers, at least so far. So the AR 11/10pi MKI woofers have paper formers, the AR 11/10pi MKII and the following 12" woofers used in the 9 and 9LS series have aluminum formers. Luigi
  12. fedeleluigi

    Need help for AR-12 refurbish

    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
  13. fedeleluigi

    AR speaker measurements

    You can see AR-3a, 3a improved, Pi/One, LST, MST measurements on Library Additions and Corrections
  14. Risposta in frequenza in camera anecoica = Anechoic Response. It shows some irregularities especially at about 2500, 6000, 14000 Hz because of the destructive interferences at the microphone position caused by the use of 4 tweeters. See also the polar responses. Risposta in camera d'ascolto rilevata con "rumore rosa" attraverso filtri a terzi d'ottava = Room Response measured with pink noise through 1/3 Octave filters. Diagrammi polari = Polar Responses (note that they are not so regular. Unfortunately 4 tweeters cause a lot of constructive and destructive interferences. In other words, waves with the same frequency emitted by different drivers combine and add together or cancel depending on their phase at the point where they combine). Curva d'impedenza = Impedance Risposta ai transitori = Tone Bursts DISTORSIONE ARMONICA = ARMONIC DISTORTION at 90 and 95 dB. The II and III armonic distortions are measured at 90 and 95 dB only at 500 Hz . At the other frequencies the real SPL depends on the frequency response of each loudspeaker. In other words, for each loudspeaker, the same input voltages (Vin) that were employed to get 90 an 95 dB at 500 Hz respectively were used to measure the distortion for all the other frequencies tested. The tables show the III and II armonic distortion for all the loudspeakers tested in that issue of the magazine. Numbers out of parenthesis are III armonic distortion. Numbers in parenthesis are II armonic distortion. Vin= Voltages employed to obtain 90 and 95 dB at 500 Hz respectively.
  15. No anechoic response measurement was reported. Risposta in camera d'ascolto rilevata con "rumore rosa" attraverso filtri a terzi d'ottava = Room Response measured with pink noise through 1/3 Octave filters (switch position: 2) Diagrammi polari = Polar Responses (note that they are not so regular as 3a's. Unfortunately 4 tweeters and 4 midranges cause a lot of constructive and destructive interferences. In other words, waves with the same frequency emitted by different drivers combine and add together or cancel depending on their phase at the point where they combine). Curva d'impedenza = Impedance at different switch position (2 and 6) Risposta ai transitori = Tone Bursts
  16. Risposta in frequenza in camera anecoica = Anechoic Response Risposta in camera d'ascolto rilevata con "rumore rosa" attraverso filtri a terzi d'ottava = Room Response measured with pink noise through 1/3 Octave filters Diagrammi polari = Polar Responses Curva d'impedenza = Impedance Risposta ai transitori = Tone Bursts DISTORSIONE ARMONICA = ARMONIC DISTORTION at 90 and 95 dB. The II and III armonic distortions are measured at 90 and 95 dB only at 500 Hz . At the other frequencies the real SPL depends on the frequency response of each loudspeaker. In other words, for each loudspeaker, the same input voltages (Vin) that were employed to get 90 an 95 dB at 500 Hz respectively were used to measure the distortion for all the other frequencies tested. The tables show the III and II armonic distortion for all the loudspeakers tested in that issue of the magazine. Numbers out of parenthesis are III armonic distortion. Numbers in parenthesis are II armonic distortion. Vin= Voltages employed to obtain 90 and 95 dB at 500 Hz respectively.
  17. Risposta in frequenza in camera anecoica = Anechoic Response Risposta in camera d'ascolto rilevata con "rumore rosa" attraverso filtri a terzi d'ottava = Room Response measured with pink noise through 1/3 Octave filters Diagrammi polari = Polar Responses Curva d'impedenza = Impedance Risposta ai transitori = Tone Bursts Distorsione = Distortion DISTORSIONE ARMONICA = ARMONIC DISTORTION at 90 and 95 dB. The II and III armonic distortions are measured at 90 and 95 dB only at 500 Hz . At the other frequencies the real SPL depends on the frequency response of each loudspeaker. In other words, for each loudspeaker, the same input voltages (Vin) that were employed to get 90 an 95 dB at 500 Hz respectively were used to measure the distortion for all the other frequencies tested. The tables show the III and II armonic distortion for all the loudspeakers tested in that issue of the magazine. Numbers out of parenthesis are III armonic distortion. Numbers in parenthesis are II armonic distortion. Vin= Voltages employed to obtain 90 and 95 dB at 500 Hz respectively.
  18. Risposta in frequenza in camera anecoica = Anechoic Response Risposta in camera d'ascolto rilevata con "rumore rosa" attraverso filtri a terzi d'ottava = Room Response measured with pink noise through 1/3 Octave filters Diagrammi polari = Polar Responses Curva d'impedenza = Impedance Risposta ai transitori = Tone Bursts
  19. fedeleluigi

    AR3a Original Owner

    @AR3a MD Welcome to this forum! There is a very good and useful manual about the AR-3a restoration. On page 13 you can find how to restore the original pots or replace them with L-Pads. Personally, I do prefere to restore old pots or use voltage dividers than to use L-Pads especially for midranges. http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/restoring_the_ar-3a/restoring_the_ar-3a_full_pd.pdf
  20. fedeleluigi

    AR-11 Crossover Frequency Response Simulation

    Pete, I can't understand why you put the ESR values before and not after the capacitors (40 uF for the AR 11 and 50 uF for the 3a). Anyway, as regard the 3a, shouldn't the 0.5 Ohm resistor be situated between the 50 uF cap and the inductors? thank you for any clarification. Luigi
  21. fedeleluigi

    AR Tweeter replica/replacement

    Open the AR 10 PI "door". You should very gently detach the three black "cups" ( 5, 27 on the drawing). They are glued to wood so use a cutter blade to very delicately detach them. Be careful not to deform the black cups! Under the three cups there are three nuts (4 on the drawing) and you have to unscrew them and then the PCB can be removed. Anyway if the rivets are not oxidated, I would not remove the PCB from the cabinet. I would only detach the faston terminals one by one to clean them. Without removing the switch board you have to use a mirror or take a photo to see if the PCB rivets are oxidated or not. Obviously, also some other AR such as AR9 may have the same sort of PCB oxidation problems or some old solder joint issue. Should you decide to remove the switch PCB remember to resolder all the old solder joints present on the PCB itself.
  22. fedeleluigi

    AR Tweeter replica/replacement

    I forgot in my previous posts to suggest that you clean from oxidation the numerous electrical connectors (faston terminal) present on the switch PCB in the AR 10 PI. The faston terminal oxidation could be a cause for detail loss. Before detaching the numerous faston terminal from the switch PCB, take carefully note of their wire colour and precise position on the PCB otherwise it will be impossible to reconnect them in the right position. Probably, to be on the safe side, it's better to clean one by one. In the last picture, the oxidation present at the rivets of the faston terminals is also a certain cause of signal (and detail) loss. You should check out this possible problem as well.
  23. fedeleluigi

    AR-12 crossover

    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
  24. fedeleluigi

    AR-11 Crossover Frequency Response Simulation

    Thank you for the clarification, Pete
  25. fedeleluigi

    AR-11 Crossover Frequency Response Simulation

    Hello Pete, Thank you for sharing all these simulations. Did you measure the anecoic frequency response of the midrange? If you didn't, what midrange frequency response did you use to make these simulations? Thank you Luigi
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