couldn't pass up Infinity Monitor Jr

Discussion in 'Infinity Loudspeakers' started by desmoto, Jan 26, 2015.

  1. desmoto

    desmoto New Member

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    just brought home a beautiful pair of Monitor Jrs for pocket change, found them on CL locally and scooped them up right away, thought the price was a typo...

    Very little information seems to be circulating on these specifically, more about the larger members of Infinitys 1970s lineup. These are 3-way with a 12" double-doped woofer (mmmm asbestos) , dome mid/dome tweeter. They appear totally original and the cabs (which I believe are walnut?) and grills are in beautiful condition!

    Surrounds on the woofers are shot, I've already pulled them out and will hopefully pickup new surrounds from Simply Speakers tomorrow (local for me). I'll post some pics tomorrow.

    Any info/observations/opinions would be appreciated!:thmbsp:
     

     

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  2. Bkphoto

    Bkphoto Super Member

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  3. blhagstrom

    blhagstrom Mad Scientist, fixer. Subscriber

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    You scored!

    They like a lot of power or an amp with loose damping factor.

    Mine sound great with a Concept 2.0.

    They should have original box stuffing that seems to be too much.
     
  4. chef free

    chef free AK Subscriber Subscriber

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    Those are nice speakers, the dome mids have really great dispersion. Infinity speakers from that period should have their electrolytic caps replaced, it's a simple job too. Leave the film cap on the tweeter alone, they last a long time are give part of the "Infinity Sound". While you are in there a little D5 and then some FaderLube on the crossover pots will help, they are notorious for getting dirty and sounding scratchy or cutting out all together. The cabinets from that era are a little flexible, a little bracing might really tighten up the bass. They probably need to be resealed too, just run a bead of wood glue around all the inside edges. Check for leaks around the crossover too.


    Concept 2.0 with Monitor Jr.s? You must be original owner! I got the Qb's with my 2.0, and I still have them. Interesting that you find them over stuffed, I chose the Qb over the Jr. because the Jr. didn't much better bass even with the 12" woofer. I always felt the Qb was under stuffed and I added about 50% more stuffing to the box.
     
  5. loquatious

    loquatious village elder

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    monitor jr. are ported cabinets, not sealed.






    .
     
  6. chef free

    chef free AK Subscriber Subscriber

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    Oops, I had it confused with the Quantum Jr.!
     

     

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  7. desmoto

    desmoto New Member

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    So I just finished reassembling after refoaming the woofers, inspecting everything and cleaning the cabinets. There was a ton on insulation as described. Everything appears original on the crossovers. I was eager to take them for a test drive, recommendations for replacement caps are welcome but I'm happy to report the circuits were intact and pots in good condition and the sound is excellent! :music:

    After a couple hours of listening I'm impressed. I have a later set of Infinity Crescendo series speakers (3009s, 3006s) and I've really taken to the sound, particularly the clarity and airiness of the highs (Emit-R tweeters). There aren't as detailed but have that same great soundstage and fullness, especially in the mids. Bass response is tighter than I expected and the sound overall is very full but accurate, if a bit warm. I compared these back to back with a set of Klipsch KG4s I have in the same room (the Jrs were perched on top for this listening session). They blow the KG4s out of the water while simultaneously revealing themselves as noticeably less efficient.

    There is for me and this amp at least (modest Yamaha 80wpc/8ohm .01THD damping factor 250 @ 1khz), no contest between the two, although I've yet to fall in love with the KG4 after a few weeks... my amps are all solid-state though, and people say these things need tubes.

    I don't have anything else higher wattage at the moment having sold my Pioneer 9500 mk2 recently.... although I just picked up a Sansui G7000 today that everyone says is way underrated at 85wpc. I'm going to swap a couple amps/receivers into the mix to see what sounds best. I really need to pickup a couple nice high-output amps for the 3009s and now for these. I like to buy and sell gear to keep checking out new stuff without sinking a fortune into the hobby, but I think these Jrs are going to stick around for a while... even if they sold for a couple hundred bucks I think I'd rather not part with them. Now I'm on the lookout for more old Infinitys!

    I have a set of Polk Monitor 5A in the closet that I intend to pull out and listen to alongside the Monitor Jrs to compare the dome tweeter sound. I think I'm developing a real taste for these two tweeter designs (dome and ribbon)! The horns haven't sold me yet.

    So here's some photos of the Jrs and the new Sansui... thanks checking them out and for all the input! AK is such an awesome space and resource for someone like me just coming into the hifi world.

    Happy listening!
     

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    Last edited: Jan 28, 2015
  8. Bkphoto

    Bkphoto Super Member

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    ahhh the peerless tweeter...The Polk guys love those...
     
  9. crazy-in-az

    crazy-in-az All humans are vermin... Subscriber

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    Those look nice! I would like to hear some Infinity's some day.

    Us B&O guys love 'em too!:music:
     
  10. Bkphoto

    Bkphoto Super Member

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    I'm more of an EMIT man myself....

    Ha..
     
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  11. cdfac

    cdfac AK Subscriber Subscriber

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    those are reported to be very underrated as far as vintage Infinities go, because many seem to forget that they made some very good stuff even before the EMIT debuted. enjoy them!

    i also failed to really fall in love with KG-4's, even after a rebuild of the crossovers. they are a reasonably good speaker, but just not designed for critical listening IMHO.
     

     

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  12. Coastsider

    Coastsider Curmudgeon

    The Monitor Jr is great little mid-70's Infinity speaker capable of prodigious bass from those 12" doped CTS woofers. In fact some care must be exercised relative to placing them too close to corners to avoid boomy bass. They have a slightly smaller dome mid and of course lack the Walsh tweeter of the larger Monitor IIa but still hold their own among the better Infinity's of that era. Some advantage can be gained by mounting them on short stands, a rule I have found to be true with some of the other models from the same period, and in fact the Jr's were available with optional stands that can be seen in an early iteration of the speaker arrangement in my music room.

    [​IMG]

    I have subsequently switched the Monitor IIa's with the Jr's, placing the Jr's in the corners on 18" Pangea metal stands. Getting them that far off of the floor has mitigated the boomy bass from the corner placement of which I spoke and I also added large floor to ceiling bass traps in the side/rear wall junctions. In a conventional setup I would just keep them out of the corners.
     
    Last edited: Feb 15, 2015
  13. backmd

    backmd Active Member

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    Transmission line principle for the 12 inch woofers

    Actually the Infinity Monitor jrs are transmission line and not a ported system for the woofers!
     
  14. Coastsider

    Coastsider Curmudgeon

    What is it that makes the Monitor Jr. a transmission line speaker? It has always been my impression that all of the mid-70's Infinity models to include the Monitors - the original, Monitor II, and IIa, the 2000 II and 2000 AXT, as well as the WTLC among others, were all bass port designs. In this photo from my March 2015 thread about the restoration of my second pair of Monitor Jr's, the large bass port can be clearly seen in the upper right hand corner of the cabinet which contains nothing more than lots and lots of fiberfill which was Infinity's predilection in those days

    [​IMG]

    The ports are also visible in two of the OP's photos in post #7.

    The WTLC, the Wave Transmission Line Column was unique in that it did have two woofers per cabinet, one front and one down firing as well as two small Peerless cone mid/tweeters, one front and one rear firing, and a bass port in the back but no internal structure of any kind. It also had a Walsh tweeter which was referred to as a Wave Transmission Line Driver and from which I believe the name of the speaker was derived. The Walsh WTL driver was also included in the Monitor, Monitor II and Monitor IIa as well as the 2000 II and 2000 AXT, all of which were simple bass port designs.
     
    Last edited: May 30, 2015
  15. Bkphoto

    Bkphoto Super Member

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    nice collection...
     
  16. StereMono

    StereMono New Member

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    I had been using a pair of Infinity Monitor JR's as well up until a few weeks ago. I recently purchased some wharfdale diamond 10.7 that i am in love with right now. My local store had a pair of fixed up Monitor Jr's and i didnt know much about them except from this forum. They served me well but are now sitting in my closet. I felt they were a little too Muddy for me and lacked any mid range. At least compared to my new speakers that are hitting the sweet spot. thinking of selling them or holding onto them!
     

     

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  17. curtpenn

    curtpenn Member

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    I worked for Pacific Stereo in the late '70s. Still drive my Quantum Juniors with a Concept 3.5. Also have accumulated several smaller Concept receivers over the years which I've used as Tuner/Preamps to drive a couple of pairs of Kenwood L-07 mono amps. That was the "budget" version of high-end stuff for us working stiffs in those days (and still is for some of us...)
     

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  18. chef free

    chef free AK Subscriber Subscriber

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    I still have my trusty Concept 2.0! It looks great, has a nice tuner section, and no ICs in the phono circuit. Only $237 in 1977. I used the tuner section in the '80's with a H/K integrated. The pre amp failed a while back and I have better gear but I'll get it fixed someday. I still have the original box and receipts too...
     
  19. taineasy

    taineasy Member

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    Not sure about the other models but the original Monitor 1a IS a transmission line bass design. Nudell used damping/stuffing material in varying densities to create the "reverse or in- phase" effect. Its all about wave length which can be created without internal baffles and very difficult and time consuming to design. The 1a has a LF response down to 26db +/- 4 db with a very slow roll-off. It produces clean bass into the very low 20's hz range. If you are working on a pair of these be very careful about removing and re-stuffing (6 lbs of it) the enclosure and they were individually tuned at the factory to create the proper effect. Original woofers are a must as they were hand dampened/treated to work with the enclosure. If you get tired of repairing the often temperamental Walsh tweeters a pair of Heil air motion transformers work exceptionally well as a more stable replacement.
     

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