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Thread: 2440 vs. 2441

  1. #1
    Administrator Mr. Widget's Avatar
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    2440 vs. 2441

    I was talking to a friend who has made custom Be diaphragms for JBL large format drivers... he told me that his Be diaphragms will work with 2440(375) motors but not 2441 motors as the gap depth, not width, is shorter and the new diaphragms will not fit properly. I have always been under the impression that the 2441 was a 2440 with a different diaphragm.

    I know oldmics has a collection of older 375s, if anyone could verify the gap depth of the 375 or 2440 vs. the 376 or 2441 I'd really appreciate it.

    Widget

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    Super Moderator yggdrasil's Avatar
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    I have a 2441 I can measure tomorrow. I'll pass on removing the red wax seals on my 375's just now... (they work)
    Johnny Haugen Sørgård

  3. #3
    Senior Member Guido's Avatar
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    Widget does this mean you have access to Be Dias for 2440 Drivers?

    Are they available for forum members?

    Did you ever measure one with Clio?
    BLS Reference on Passlabs XA 30.5 + Everest DD66000 clone on Pass XA 100.5

  4. #4
    RIP 2010 scott fitlin's Avatar
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    2440

    Quote Originally Posted by yggdrasil
    I have a 2441 I can measure tomorrow. I'll pass on removing the red wax seals on my 375's just now... (they work)
    I have two 2440 drivers sitting on a shelf, I will measure these as best I can. Then post info!
    scottyj

  5. #5
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by Giskard
    What is the width of the top plate on the 2440 and on the 2441?
    Looks to be about 19/64 (I think that's about 8mm) on the 2441.

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    Hi Widget

    I know oldmics has a collection of older 375s, if anyone could verify the gap depth of the 375 or 2440 vs. the 376 or 2441 I'd really appreciate it.
    - I also happen to store some 2440s & 2441s here at home .
    - I'll measure the top-plates tonight ( from the outside )
    - I also believe I have a single 2441 ( with its' diaphragm removed ), making an actual in-gap measurement doable, tonight also .
    - As implied already, an outside measurement ought to suffice here.

    Anyways <>

    PS - Oh , here are some shots from an eBay seller called "Audiobin" who demags / rebuilds / & remags these big guys ( he is unfortunately caught up in a dispute with the German buyer who purchased the set shown ) . Widget you might want to speak with this guy. He's stated some interesting things in his eBay sale copy .
    Attached Images Attached Images      

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    RIP 2010 scott fitlin's Avatar
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    Gap Depth on 2440

    Using a card in the gap, and marking it, then measuring it, I come up with 10/32 in. depth for the gap of a 2440 driver. I am not sure if my measurement is accurate, but seems to be fairly so. I am using a Brown and Sharpe set of calipers to measure with.
    scottyj

  8. #8
    Administrator Mr. Widget's Avatar
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    He may be mistaken, but has been a reliable source of info in the past. Hopefully with this group on it we will come up with a definitive answer.

    Quote Originally Posted by Guido
    Widget does this mean you have access to Be Dias for 2440 Drivers?

    Are they available for forum members?

    Did you ever measure one with Clio?
    I have not measured one, but did listen to a pair and was impressed. I am investigating the possibility of having a small batch run. I'll post the pricing and availability info when I get it.

    Widget

  9. #9
    Senior Member edgewound's Avatar
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    2440 and 2441 are physically identical, along with the 2445, 2446, 2447, 2450, 2451 all being mechanically identical...that's why the diaphragms are intechangeable. 2482, 2485's don't share these interchangeabilities, but Radian Audio does manufacture aluminum diaphragms for these beasts.

    Hope that helps,

    Edgewound

  10. #10
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by edgewound
    2440 and 2441 are physically identical, along with the 2445, 2446, 2447, 2450, 2451 all being mechanically identical...
    That is what I have always been told... are you certain of the gap depth?

    The published specs are different with the 2440 rated at 20,500 gauss and the 2441 at 18,000 gauss.

    I have always assumed that this was due to different measurement techniques.

    Widget

  11. #11
    RIP 2010 scott fitlin's Avatar
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    As long as......

    Quote Originally Posted by Mr. Widget
    That is what I have always been told... are you certain of the gap depth?

    The published specs are different with the 2440 rated at 20,500 gauss and the 2441 at 18,000 gauss.

    I have always assumed that this was due to different measurement techniques.

    Widget
    If the gap depth of 40 and 41 are the same, I am down to try some Be diaphragms for my JBL,s!

    Lets do it once we got our answers!
    scottyj

  12. #12
    Senior Member edgewound's Avatar
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    Gap depths have to be the same for diaphragm interchangeability. The gaps are deeper in the 2482 & 2485 that came with phenolic diaphragms. My 1976 JBL Professional with catalog with 2440 & 2482 says 20,500 gauss for all the large format drivers, my 1980 catalog says 18,000 gauss for both 2441 & 2482....both catalogs state 118dB sensitivity for these same drivers. I can't explain the difference in gauss....you're theory sounds good.


    I haven't measured them,though...for the diaphragms to be truly, usefully interchangeable, the top plate gap depths must be the same for the voice coils to be symmetrical from either end of the gap...or they'd be terribly distorted.

    Thanks,

    Edgewound

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    2441 Gap Depth

    2441 - As best as I can measure ( cardboard in the gap / with a sharp line drawn across top ) ; the depth appears to me as 8 mm .

    - Perhaps your contact is referring to a difference in the coil-winding depths between the two diaphragm types.

    - Does he by-chance attach these new Be domes to an existing old coil/surround with its' bakelite ring ?


    - did you look at the contact info mentioned within my last post ?

  14. #14
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    External Measurements for ; 2441 & 2440 top-plates

    Hi Widget,

    - Both the 2440 & 2441 drivers that I just measured have 8 mm thick top-plates ( measured on the outside of the driver ) .

    - These measurements were done by "eye" under a Luxo magnification lamp using a "see-through" plastic ruler over-laid onto the actual metal. This ruler is marked in both "Imperial" & "Metric" measurements.

    - FWIW ; I believe that most magnetic measurements are more commonly referenced into the metric system .

  15. #15
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Earl K
    - Does he by-chance attach these new Be domes to an existing old coil/surround with its' bakelite ring ?


    - did you look at the contact info mentioned within my last post ?
    I am not sure how they are made.

    I did read that auction info... I agree completely about the frequent unseen deterioration etc. It is too bad he only has an oscilloscope and a 1/3 octave RTA to verify performance... after going to that trouble better measurement gear would yield a higher level of consistency.

    I received a PM from oldmics stating that the phase plugs for both the 2440 and 2441 are identical part numbers and therefore it is most likely that they have the same gap depth. I think my friend might have measured a defective 2441 or made another type of error in coming to the conclusion that 2440s and 2441s have different gap depths.

    Widget

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