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Thread: Will this work?

  1. #1
    "new and improved" JBL Dog's Avatar
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    Will this work?

    I got a PM from a forum user wanting to know if a D8R475ND diaphragm is compatible with a 2445/6 driver?

    As previously stated, I'm a technical zero when it comes to this stuff


    Thanks!

    This message comes from JBL Dog

  2. #2
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    Hi JBL Dog
    Here's some info that hopefully furthers your understanding of that diaphragm . You'll still need to ask JBL PRO for their opinion on this.
    My guess is that the D8R475ND is the consumer equivalent to the D8R2450SL - of which I own a couple, fitted into 2440 motors . The 2450SL diaphragm is an Aquaplased Titanium type like the 475ND.
    In one of the earlier forums it was stated that the dome curvature of the newer 2450SL diaphragm didn't match the curvature of the phase plug for the older 2440/1/5/6 series - I don't find that to be the case . My 2450sl diaphragms are successfully installed . One was an easy "slam-dunk" fitting, the other wasn't . The problematic installation was solved by creating 8 small paper stand-offs or shims to reside directly undeneath the 8 fitting bolts - between the diaphragms' plastic surround and the top-plate of the compression driver. These shims now simulate the builtin shims that were a permanent feature of the old 2440 diaphragms. Without the shims on this one driver, the 2450sl diaphragm sat too low and too close to the bakelite phase-plug. This was all very apparent when sweeping the combination with a tone generator. The tonal manifestation was a significant loss of output along with increased distortion in all band-pass areas.
    A word of caution on using these diaphragms. They are quite "highly-damped" by the aquaplas coating. As such; all other electrical dampening elements in the playback chain should be rethought or tweeked . Some of the more significant elements include; conjugate resistors in passive crossover, L-pads, and capacitor types/configurations . This is a diaphragm that benefits from a "minimalist" approach if one can get away with it, IME .
    Hope this helps a bit .

    <> Earl K

  3. #3
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    Earl,

    small paper stand-offs or shims
    Made from a cereal box or thinner?

    dB

  4. #4
    Webmaster Don McRitchie's Avatar
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    The 475 and 2450 diapragms are not the same. There is at least the following difference. The 2450 has ribs built into the titanium dome for added strength. The 475 uses a smooth hemispherical dome.
    Regards

    Don McRitchie

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    2450SL vs 2450

    Hi

    Don; You're right, the 2450 diaphragm has ribs but the 2450SL diaphragm is different. It uses ; an Aquaplassed, rib-less dome .
    Here's a picture of one of my 2450SL diaphragms in a 2440 motor .

    db; Well you made me look. I cut up someones business card to make the shims . Additionally; one side needed to be raised more than the other ( 3 shims vs 1, oriented directly across the clock face ). Also, the shims are between the mounting bolts - not directly underneath .

    - I need to caution; That people should stay away from such unsanctioned product combinations unless they are confident they can accept/handle any unforseen consequences of mucking about with such expensive components. Having a Tone Generator or Function Generator with experience in their use, is an absolute must . For instance; My combo is operating in a recently recharged 2440 magnet which means this diaphragm is likely working within a flux level that is above the recommended norm . The 475ND motor is 16500 gauss while the 2450SL is 18000 gauss - I believe. My motors might have as high as 20000 gauss. That extra 10% of gauss should increase HF distortion - though - I don't hear it .

    <> Earl K
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    Administrator Robh3606's Avatar
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    Here's a ribbed one to see the difference. Looks just like my 093ti midranges.

    Rob
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    Last edited by Robh3606; 07-21-2003 at 04:33 PM.

  7. #7
    Alex Lancaster
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    Question remagnetizing

    Earl; Where do You get magnets re-magnetized, or better yet, how do You build a remagnetizer?

    Is it a big "C" clamp affair with a coil?

    Probably DC, I guess, but how much how long?

    Pulse type?

    Thanks.

  8. #8
    "new and improved" JBL Dog's Avatar
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    Hmmmm.........

    Thanks all the responses and special thanks to Earl K!

    Ironically, the diaphragm kits in the D8R475ND boxes are D8R2450SL's! I bought a bunch of stuff in a packaged deal. The whole time I thought I had the 475 kit. It would have been a mighty embarassing situation if I would have sold these to someone in the Far East.

    Thanks for the education!

    This message comes from JBL Dog

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    Hi All

    JBL Dog; You're welcome! As far as I know, that diaphragm component is the only K2 inspired type that we "peasants" in North America are allowed to purchase . ( Too bad the 275nd diaphragm is only rumoured to be somewhere out-there - lost at sea I suppose - - OKay, I'll quit my Harman policy bashing now )

    Alex; I have no idea how to build a magnetizer ( that will deliver that high a charge). I think all those who do know where scouped up by President R. Reagans "Star-Wars" R & D team ( these things are the infant brothers of "Rail-Guns" - so I'm told ). I've heard these things are worth at least $20,000. My magnets are sent out to a local reconer who then farms out the work . Really, because of shipping costs and cross-border "landing" taxes & duties, this type of work needs to be kept in the country. In your case, you're probably best to deal with someone in the LA area like JBL Pro or Orange County Speakers if there's no one in Mexico .

    RobH; Nice Picture ! Where's the rest of that 2450 assembly ?

    - Are your 093Ti, the same 100mm diameter ( or are they 93 mm ) with the same ribbing topology as a 2450 ? I remember studio guys saying/and demonstrating how a 2440 - flipped 180° around - with the back-cap removed -made a very nice hi-mid direct radiator.
    This old practice seems to have been the inspiration for those sought after ATC 3" soft-dome mids and the now embargoed Dynaudio D-54 and D-76 - large coil mids .

    regards <> Earl K

  10. #10
    Administrator Robh3606's Avatar
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    Hello Earl

    "Nice Picture ! Where's the rest of that 2450 assembly ?"

    Thanks not mine though! I grab good E-Bay pictures from time to time.

    "Are your 093Ti, the same 100mm diameter ( or are they 93 mm ) with the same ribbing topology as a 2450 ?"

    No the whole diaphram is about 4" but the VC is 3 " The ribs look the same I attached a picture but it's hard to see.


    I remember studio guys saying/and demonstrating how a 2440 - flipped 180° around - with the back-cap removed -made a very nice hi-mid direct radiator.

    Thats about what it is and it does sound nice. I remember those big soft dome midranges. Sounded very nice from what I recall.
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  11. #11
    RIP 2010 scott fitlin's Avatar
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    Earl

    How do those 2450sl phragms sound in the 40,s? can you describe the differences in sound from the 40 or 41 phragm? Id really like to know!

    I must admit, that little tweak looks REALLY cool!

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    Exclamation

    Hi Scott

    I'll need some time to do another set of comparisons. Maybe first, I'll post what "I think I remember" from the last shoot-out .

    regards <. Earl K

  13. #13
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    General Opinion on JBLs' 4" diaphragms

    Hi Scott
    As promised, here's my subjective opinion / bias about JBLs' larger format / 4" metal diaphragms .
    I find them all ( excluding the 2450SL & 2482 ) to sound somewhat underdamped ( & that includes the 2441 ). I've never listened to a "bubble-backed" 375 ( or the other K2 diaphragms ) so I have no opinion there . I'm talking about listening to them in smaller rooms and not in large areas where the air volume helps mitigate some of these impressions . It's somewhat like " Don't point that thing at me !!! " or " I'm out of here " .
    That's usually my thought process when confronted with these large beasts ( on small or big horn or softened up by diffusers) . My Altec 288-8K drivers aren't like this ( of course, that dome has only 1/2 the surface area which immediately rebalances the all important paper to metal ratio ) . The 2450SL/2440 has the ability "to get up close & personal" without it being hurtful . Maybe my combos are actually in a misfit situation with the whole drivers ( especially 1st gear ) torque curve thrown out of whack . Don't know / won't know until that time comes that they ever do a high level SR job - but not planning on that . I do know I like this combo alot .

    regards <. Earl K

  14. #14
    RIP 2010 scott fitlin's Avatar
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    thank you

    I think I understand what you are getting at! I have used `41,s for years. And although they are great, they can get a bit blarey if pushed hard.

    I did think about doing this, before I made my purchasing decision, but once I heard the " other " three letter brand compression driver I was doomed!

    Same basic thing for me! Upclose and personal sound that doesnt hurt you, yet has outstanding transient response and extraordinary clarity!

    Also, the diaphragms of my new drivers have some sort of what appears to be like a black netting on the back of the diaphragm.
    Last edited by scott fitlin; 07-23-2003 at 10:00 PM.

  15. #15
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    Speaking of Torque Curves

    Hi Scott
    Glad you like your 4002s. In my case, I've been ruined, in as much as I have a tough time listening to 1.75" diaphragms ( no matter who makes them ) - the loss in resolution or clarity is just too great to accept - when I know I can easily restore it by just grabbing some larger format drivers (off the proverbial shelf).

    In addition to the berylium diaphragm , I think the addition of the 5th slit in the 4001/2 phasing plug makes a big difference to the response of the large TAD drivers. Even the Radian replacement diaphragm ( the 1292 ) has roughly an extra 10 db of top end when compared to the JBL replacement type. Both Radian types use a .08 mm aluminum dome with mylar surround - strongly implying, it's not all about the metal type.

    I've heard those mesh screens on the back of the diaphragms are a protection feature in case the dome ever particalizes ( I believe the theory was to prevent the berylium parts from being inhaled - since berylium oxides are cancerous ). For a hoot, here's a picture of an early "blast-screen" - this is from a 50s vintage RCA driver meant for naval duty . I might eventually turn these 180° and create a phenolic based, 093 standin .

    regards <> Earl K
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