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Thread: JBL driver field coil conversion

  1. #16
    Senior Member ivica's Avatar
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    Quote Originally Posted by NickH View Post
    I was thinking that. If its blocked by the diaphragm I would think it would cause some issues with reflection. But if I fill the cavity with a sound absorber and seal the bottom, makes more sense.See what you did? Got me going on a damn tangent, .Well I'm waiting to buy copper anyways. Should change the thread title to filed coil conversion and phase plug modification. If a mod sees that can the change the title?I'm thinking I might try this on a 2445 first. See if I can tell the difference. I need some new diaphragms though,

    soon.does anyone know what the phase plug on a 2446 is made from?Nick
    I think that it is some zinc alloy, but no other info.
    but I think it can be made of aluminum or some 'strong' plastic....
    any how the material that will not resonate by itself


    Regards
    Ivica

  2. #17
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    I know the ones on the 2440 are Bakelite. The plugs on my 2445's look to be metal. Im going to try and do a temporary mod on one of the 2445 phase plugs tonight. I have some rope claulk that's the consistency of clay that Im going to seal some cotton into the 2 center most ports with. It doesn't harden so it will be easy to remove if I don't care for it. Ill report back. Maybe If I feel energetic Ill cart it outside and do some measurements this weekend comparing it to an unmodified 2445.

  3. #18
    Senior Member ivica's Avatar
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    Quote Originally Posted by NickH View Post
    I know the ones on the 2440 are Bakelite. The plugs on my 2445's look to be metal. Im going to try and do a temporary mod on one of the 2445 phase plugs tonight. I have some rope claulk that's the consistency of clay that Im going to seal some cotton into the 2 center most ports with. It doesn't harden so it will be easy to remove if I don't care for it. Ill report back. Maybe If I feel energetic Ill cart it outside and do some measurements this weekend comparing it to an unmodified 2445.
    Waiting for the results...

    Regards
    Ivica

  4. #19
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    Well I said I would do it tonight. But it was a long horrible day and I'm beat. I might wait tell tomorrow. Or I might get a second wind after I eat some grub.

    I also bought a coil winder off ebay. Nothing fancy, just one of those cheap Chinese ones. I figure it was only 60 bucks. I would probably spend 3 times that trying to make one.


    I'll let you know what I do, if I do a mod tonight.


    Nick

  5. #20
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    Mod done. I did it how I said I would. Cotton and moretite caulking rope. Very easy to undo if I want.

    I will post a pic tomorrow.

    Nick

  6. #21
    Senior Member ivica's Avatar
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    Quote Originally Posted by NickH View Post
    Mod done. I did it how I said I would. Cotton and moretite caulking rope. Very easy to undo if I want.

    I will post a pic tomorrow.

    Nick
    Hi NickH,

    You have been very active, but be patient while measurements and testing so the conclusions would be worth.
    I wish You great success in experiments.

    Regards
    Ivica

  7. #22
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    Its all in good fun.

  8. #23
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    Name:  2445 mod.jpg
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Size:  75.6 KB Here's a picture of the quick and dirty mod I did. Maybe Ill do some quick and dirty testing this weekend. I have to finish building my crossovers though.

  9. #24
    Administrator Mr. Widget's Avatar
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    Perhaps you could describe what we are looking at... kinda hard to tell. Is that a new throat with a concave or convex ring around it? Is that a blob of something stuck on the center of the phase plug?


    Widget

  10. #25
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    Its a standard 2445. What I did is block off the center two ports in the phase plug. Ivica was kind enough to point me in the direction of some patents of newer phase plug designs. Quite a few block the radiation from the center area of the diaphragm. what I have read state that the majority of the drivers distortion is generated here. Im guessing it has to do with the fact that these port are the shortest by a good a fair margin causing phase cancellation.


    What I did was a temporary test. I filled the ports with cotton to dissipate some of the acoustic energy. Then I used a sealant called moretite. Its a none hardening caulk with the consistency of playdoh. I just filled the exit area of the two port on the phase plug with it so the cotton wouldn't get blown out.

    Its not the most scientific approach. But it should be functional. Im going to try some rudimentary measurements as soon as I have the time.

    Nick

  11. #26
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by NickH View Post
    I just filled the exit area of the two port on the phase plug with it so the cotton wouldn't get blown out.

    Its not the most scientific approach. But it should be functional. Im going to try some rudimentary measurements as soon as I have the time.
    Hmm... seems like the guy who improves his V8 by removing a few pistons.

    With modern manufacturing techniques and powerful CAD work newer and better phase plugs have been developed, but those old dudes with their slide rules and micrometers were pretty amazing... the more we learn about driver design the more impressive the early work done at Bell Labs and elsewhere is. It never ceases to amaze.


    Widget
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  12. #27
    Senior Member ivica's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    With modern manufacturing techniques and powerful CAD work newer and better phase plugs have been developed, ....... ... the more we learn about driver design the more impressive the early work done at Bell Labs and elsewhere is. It never ceases to amaze. Widget

    Hi Widget,

    I can agree with You, especially if we look at the D2430K driver phase plug, but I believe that theoretical background of its design would be not easy to follow (even though I would like to read if anyone has a copy). But about NickH's, idea to close center slit-horn can find confirmation in the, well known white papers about Be, Al and Ti diaphragm behaviors on high frequency.

    http://www.vueaudio.com/about/beryll...n-transducers/

    http://materion.com/Products/Berylli...PAPERFINAL.pdf

    http://www.vueaudio.com/wp-content/u...APER_Small.pdf



    It seems to me that the diaphragm center has the largest amplitude of unwanted vibrations, on the other side the area of this center part of the diaphragm is relatively small percentage of the total diaphragm area (surface), so some losses of the driver efficiency is acceptable for home listening purpose, IF other results(FR response, and THD) become better.


    Regards Ivica

  13. #28
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    NO. As I said its a temporary experiment. I would not expect you to have an issue with an experiment. But maybe I missed the fact that your an Acoustic engineer and know far more about this then I do.

    Do not mistake what I've done for a lack of respect for these engineers and designer of year past at jbl.

    Its just an experiment.







    Quote Originally Posted by Mr. Widget View Post
    Hmm... seems like the guy who improves his V8 by removing a few pistons.

    With modern manufacturing techniques and powerful CAD work newer and better phase plugs have been developed, but those old dudes with their slide rules and micrometers were pretty amazing... the more we learn about driver design the more impressive the early work done at Bell Labs and elsewhere is. It never ceases to amaze.


    Widget

  14. #29
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    Yesterday I ordered 6" piece of 3" 12l14 steel bar stock. This will be turned into the center pole pieces for the woofers. The coil winder shows to be delivered tomorrow.

    I've even made a few diy cones to try in the woofers.


    making the pole pieces will take a little time. All I have to do is bore out the center and surface grind the ends so there the right side. I'll do like jbl did and glue the actual piece that make up the gap on the center pole.

    I'll post more as it comes,
    Nick

  15. #30
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    Quote Originally Posted by NickH View Post
    Im surprised in the chemical analysis of the pole piece. There 1 % carbon. But that all thats in there.

    Attachment 59066
    Element contents are usually expressed in wt. percents, not atomic..

    0.23 pct is a usual construction steel..
    For 1-1.4 Tesla gap field, nothing more fancy is needed.
    Armco iron goes up to 1.9-2.0 Teslas, and Permendur to 2.3-2.4 Teslas

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