Watkins woofer white paper

Discussion in 'Infinity Loudspeakers' started by geoff727, Jan 18, 2010.

  1. cdfac

    cdfac AK Subscriber Subscriber

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    true, the white paper does make things look cleaner than they really are, at least for the 4.5 implementation, but a variation of less than a factor of 3 with a max just above 6 Ohms is quite good for sealed box measurements i've seen. OTOH, the RSIIb has a woofer peak at 14 Ohms with a minimum value around 3 Ohms (I could be a bit wrong, the scale on that German magazine's plot isn't shown).

    there is also mechanical impedance that is SPL-dependent and thus more difficult to take into account - i'm not really sure how well those impedance-measuring devices do at getting an accurate total impedance value though - could make things look better OR worse.
     
  2. kmanusa

    kmanusa AK Subscriber Subscriber

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    Yep and I only measured impedance magnitude, not phase, so it is an incomplete picture. The 4.5 certainly earns it's 4 ohm nominal impedance rating from Infinity.
     
  3. jimreeves

    jimreeves Poopy & Me Subscriber

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    I'd have to assume his plots are only pertinent to the watkins speaker system he designed, don't you think? Seems like every interview I've seen that Bill gave regarding the Infinity implementation of his watkins dual-drive was a refutation of Arnie's designs.

    I'd really like to see the nuts and bolts (LCR) of his speaker, along with the internal volume and stuffing desity. Then to know whether he made any design compromise to keep the box size down, cost cutting, etc.
     
  4. pentode

    pentode New Member

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    I too would like to see the nut and bolts of his speaker. Does someone have a Watkins Woofer that is beyond repair that can be used to obtain material data? Some of the things I would like to know are: coil material (aluminum, copper), coil wire diameter and length for VC1 and VC2, the type of motor (over/under hung), magnet weight.
     
  5. bnt59

    bnt59 New Member

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    hi i'm new to the sight needed some info on the qls-1 towers so i joined since this seemed to be the best sight for reliable info questions have to do with the qls mids first i just found a match set and need to know if they are worth rebuilding or do i part them out bases are the watkins seem to be good probably need new surounds and have not tested the ribbons yet any help would be helpfull
     
  6. Nikkoholic

    Nikkoholic Active Member

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    You should likely rebuild the mids; they are not available and don't come up too often in auctions. The Ribbons do come up periodically in auction. Be aware the ribbon tweeters are wired in series so if one goes out you will likely experience what seems to be 2 failures (they are wired in 4 pairs vertically).

    As for the Woofers, these can be refoamed locally, or replaced with new units available through Watkins Engineering. Bill Watkins is still around and he is the original designer of this speaker and currently still manufacturers them as replacement parts.

    Pictures would be nice if you could post them. However this may not be the appropriate thread.
     
  7. bnt59

    bnt59 New Member

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    thanks for the info nikkoholic i am new so what do you mean by not the right thread
     
  8. cdfac

    cdfac AK Subscriber Subscriber

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    he means that this particular discussion/thread is pertaining to the Watkins woofer, specifically the white paper. if you have a question about the QLS1, you should ask on an existing QLS thread or start your own new thread in the Infinity forum.
     
  9. jimreeves

    jimreeves Poopy & Me Subscriber

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    Welcome to AK bnt59! Your best bet is to start a new thread (discussion) in the Infinity forum with your specific questions. Everyone here would agree it's a great idea to save a vintage pair of Infinities!
     
  10. jt45

    jt45 Super Member

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  11. Pete B

    Pete B AK Member Subscriber

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    First off, let me mention that both coils will see the same "motional impedance" scaled by their DC resistance because after all the VC motion is the same for the two coils. The low tuned LC is used to deliver more power to the low Z driver winding at the closed box resonance Fc. The L in series with the other winding is the crossover element for the upper crossover point and is probably larger than text book in order to provide baffle step compensation. The cap in series with the high Z winding is to reject LF noise such as record warp. The system when properly tuned should not have a dangerously low Z impedance but I doubt that perfectly flat was a goal over having good crossover behavior/slopes.

    Nice speakers by the way!
     
  12. Pete B

    Pete B AK Member Subscriber

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  13. Pete B

    Pete B AK Member Subscriber

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    Seems that some of the Infinity Watkins systems had a reputation for
    being very difficult to drive due to a very low impedance dip. Watkins
    talks about the issue of the impedance dip (1.75 ohms) on rec.audio.opinion.
    Turns out Nudell added mass to the woofer to lower Fc, but did not retune
    the drive circuit. Interesting that a properly tuned Watkins system presents
    an almost resistive load to the amp and therefore should be easy to drive.
    It should be straightforward to retune the Watkins circuit and make these
    old systems even better than when they were new:

    "Now, the fun begins...
    Mr. Nudell wanted a spec down to 20 HZ, he got to
    18, as I recall, by adding ~35 grams of mass under
    the dust cap, _BUT_ he did not re-tune LC to the
    lower resonant frequency, leaving vc-2 operating
    somewhat above the new fundamental resonance, and
    creating a low impedance in that area. "


    The full post from rec.audio.opinion by Bill Watkins:

    Trevor, I believe it's time I explained what happened
    here. My dual-drive woofer works so:
    A second voice coil (vc-2) is wound over the main voice
    coil (vc-1) in the woofer, this second coil having a
    single layer and very low impedance. Now vc-2 would
    normally have an impedance too low for safe operation.
    However around fundamental resonance the impedance of
    _any_ coil will ~triple. Now we activate vc-2 _ONLY_
    in the region of fundamental resonance (around 45 Hz)
    and it rises to ~8 ohms or so (being ~2.5 in the
    first place) which is safe. This is accomplished with
    an LC circuit tuned to 45 HZ and with the Q of the LC
    circuit adjusted to provide the response shape and
    impedance desired. Please note that the exact value
    of vc-2 and the characteristics of the LC circuit give
    _COMPLETE_ control of the impedance. The benefit of
    the dual-drive may then be taken in extended bass or
    higher efficiency in a given size box, or a smaller
    box for a given efficiency or bass extension.

    Now I set the parameters of the original QLS-1 in a
    prototype and shipped it to Infinity. It had a minimum
    impedance of 3.2 ohms, acceptable for a 4 ohm speaker.
    At that time we were operating a retail store selling
    Infinity. Our first shipment of the QLS-1's arrived,
    we tested a pair and found the impedance to be
    ~1 3/4 ohms from ~50 - 80 HZ. Now, the fun begins...
    Mr. Nudell wanted a spec down to 20 HZ, he got to
    18, as I recall, by adding ~35 grams of mass under
    the dust cap, _BUT_ he did not re-tune LC to the
    lower resonant frequency, leaving vc-2 operating
    somewhat above the new fundamental resonance, and
    creating a low impedance in that area. My name
    was already on the royalty agreement, which had no
    stipulation to cover such... I did voice my
    disapproval to no avail.

    If you check, you will find our WE-1, built and
    marketed by _my_ company had no impedance problems,
    and neither did thousands of other speakers we
    built have any impedance problems. Perhaps this
    makes things clear for the technical people here.

    Bill Watkins
     
  14. jt45

    jt45 Super Member

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    Pete B just curious about that 35 grams of mass added behind the dust cap, would that be the white material in the quick pic below of a Watkins woofer on a QLS1 I did some work on ?
    Looks like caulk !

    [​IMG]
     
  15. jimreeves

    jimreeves Poopy & Me Subscriber

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    Great info Pete, thanks for finding this! Back in post 15 I mentioned that my QLS's came to me with 1400mfd and 1600mfd caps, not 1100mfd and 1400mfd as per the schematic. I have no means to measure the inductors to see if they match the schematic. Perhaps there was a later change (my pair are early) that dealt somewhat with the impedance dip?
     
  16. Pete B

    Pete B AK Member Subscriber

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    Yes that is probably it since you'd normally see glue there and there might be something of higher mass underneath it. I doubt that he modified everyone so they probably revised the woofer at some point.
     
  17. Pete B

    Pete B AK Member Subscriber

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    I don't have much experience with these so I don't know one way or the other. I did hear several different models years ago and always liked them.
     
  18. hntjr

    hntjr Member

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    87
    The Creative Technology Of Infinity Speakers

    I worked at Tech Hifi from 1976-84. Inifinity had some of the nicest literature and marketing pieces, one of which was The Creative Technology Of Infinity Speaakers 17 pages. I scanned it into my computer this morning after seeing a request for a white paper on the Watkins Woofer. The brochure, although not a white paper, has 7 pages on the WW, several on emit and emim and has several blow up expanded pictures of them, all done in that Infinity quality. Problem is I can not figure out how to get the brochure into Audio Karma. I tried to attach it, but the paste does not work. It's in jpeg. Can anyone help me? I think all you Infinity fans would really enjoy this brochure if I could get it on AK.
     
  19. jimreeves

    jimreeves Poopy & Me Subscriber

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    That would be great hntjr, and welcome to AK!
    You can attach jpegs or pdfs if you click 'post reply' rather than use 'quick reply' and use the 'manage attachments' button and browse to the files on your computer.
     
  20. FidPup

    FidPup New Member

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    I have a copy of an article New Loudspeaker with Extended Bass written by William H. Watkins published in Audio magazine in December, 1974.

    This is a technical five-page paper discussing enclosure and crossover design for the Watkins woofer, and includes pertinent graphs and formulas.

    I don't know if this article is the "white paper" referred to in this thread, but I have made a PDF scan of the article.

    I could post the PDF file here, but I don't know if doing so would violate any copyright laws. Does anyone know?

    I can email a copy of the article on request.

    Ken
     

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