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jviss

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Posts posted by jviss

  1. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    3 minutes ago, JKent said:

    I’ve seen it done. But it totally changes the speaker system so it’s no longer a classic AR. Some people throw out original woofers if they have foam rot and replace them with something off the shelf. Crossover design is a complex art/science, not “one size fits all”.  You’re doing it the right way. 

    Oh, that's a shame to throw away the original woofers.  One can get foam kits, as I'm sure you know.  

    Yes, when I get mine apart I'm going to test the old cap, and characterize the crossover - I think my audio generator has a sweep function, I don't recall!  If so I can put it all on the scope and see how it behaves, adjust the pot and see how it moves the cutoff.  Then replace the cap, clean/replace the pots, and test it again.  

  2. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    It would be interesting to see a crossover plot at various pot settings for this network.  

    Also, I wonder if folks don't just punt on restoring these networks and just install a crossover board form, for example, Parts Express, which can be had for around $12.  No adjustment, but then, so what?

    (I paid $8 for just the caps!)

  7. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    1 hour ago, JKent said:

    \Many of us have used Ohmiites. The thing is you have to make an enclosure or use a little box to keep fiberglass out of their open backs. The originals were made by Aetna-Pollak (sp?) and had closed backs. 

    Interesting.  I'll have to see what's inside when I open them up.  My recollection is not 100%, but I recall when I purchased these two new Ohmites that I was convinced that was what was in there originally.  I wonder if they have boxes to keep the insulation out?

    I also wonder why they go bad!  Ha, ha.  Corrosion, I guess.  I also recall that these Ohmite units can be refurbished, so I'll save the old ones.

    Then I'll have to do some research on adjusting them.  

  8. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    30 minutes ago, JKent said:

    PS. Parts Express sells nice foam gasket tape. In a pinch you could use adhesive foam window weather stripping or get a brick of duct seal in the electrical department. It’s like modeling clay and you can roll 1/4” diam worms to seal the driver to the baffle

    Ah, gotcha!  You know, I have some really good butyl tape, I think I'll use that.  

  12. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    6 hours ago, JKent said:

    Two thoughts:

    1. As Roy said your pots are almost certainly the cause of the tweeter problem. They can be cleaned (sometimes) but you’re better off replacing. I don’t know what you have on hand but L-pads work well. 
    2. In my experience the Aida cloth has too tight and regular a weave to look right and maybe even to sound right. Michaels sells CharlesCraft Irish Linen cross stitch material in “Tea” color, 28 count, that works well. One roll is enough. 
    https://www.michaels.com/product/charles-craft-28-count-irish-linen-needlework-fabric-10357706?michaelsStore=1098&inv=1

    Thanks.  I installed the cloth and it looks great and sounds great, too.  I might try the one you recommend, though, as I have more speakers to do.

    The pots I have are new Ohmite RHSR15R 15Ω 25W rheostats, which is what I believe are what is originally in my speakers.  

    I just ordered new caps for the crossover, Dayton 20µF 250V polypropylene caps.  I feel stupid, here I am a retired electrical engineer and I don't know why I selected this value and type except that's what I gleaned reading these posts.  

    I'm open to recommendations on refurbishing speakers, and on sealant for the speaker to cabinet interface.  

    Thanks.

  13. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    Wow, thanks @JKent and @RoyC!  So glad you experts are on here, and helping.  

     

    I really have to dig into these.  I love them!  I replace the grill cloth today, with this stuff from Michael's:

    https://www.michaels.com/product/loops-threads-aida-cloth-cross-stitch-fabric-oatmeal-10357727

     

    They still sound great, but as I said, the right tweeter is about silent.  I'm going to open both of them and rebuild the crossovers and test the whoofers and tweeters.  As I mentioned, I have a couple of new rheostats, so perhaps I'll swap those in, too.  

    Cheers,

    jv

     

  14. AR4x Crossover Rebuild Check

    in Acoustic Research

    Posted

    Gee, I hope you folks are still here monitoring this thread!  I have two pair of AR4x speakers, plus a pair I gave to my son.  I'm just starting my refurb/restoration.  The first pair I will work on was purchased new by my Dad, approximately 1969.  Serials FXI76350 and '356.  Only real prob now is low/no output from one tweeter; could be the crossover network.  I am replacing the nicotine-stained grill cloth with cross-stitch linen I got at Michael's.  I have a couple of new rheostats on hand if needed.  I'm assuming I'll be replacing the caps.  

    Wish me luck!  

     

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