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Thread: 1.5" 2431H upgrade: should the 2435 BE diaphragm be the solution?

  1. #1
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    1.5" 2431H upgrade: should the 2435 BE diaphragm be the solution?

    Hello all,

    I am new on this forum. I am found of JBL audio system since 25 years!

    My system is an active 3 ways with 18" 2268H in vented box, a CMCD-81H 8" for the midrange (350 - 2kHz crossover points), and a 1.5" 2452H for the upper range.
    At first, the HF driver was a 2431H Neodynium, but its frequency response was not good above 10kHz. And despite an efficient EQ with the the DP226 FAN, it doesn't sound very good.
    So I replace it by a 2452H and it was a lot better.

    By now; I would like to improve my 2431H, and I think about the Beryllium diaphragm of the 2435H. I would like to be sure both diaphragms are compatible (2431 vs 2435), and that a 2431 with a 2435 diaphragm is really equivalent to a 2435.

    Many thanks in advance,

    Regards

    Bruno
    18" 2268H + 8" CMCD-81H + 2452 1.5" + PT horn
    Digital crossover XT DP226, AS-EBU digital input, miniDSP preamp

  2. #2
    Senior Member ivica's Avatar
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    may be 2408-1 or bms4540 or jbl 2405 or faital_pro_hf104

    Quote Originally Posted by Bruno_du_13 View Post
    Hello all, I am new on this forum. I am found of JBL audio system since 25 years! My system is an active 3 ways with 18" 2268H in vented box, a CMCD-81H 8" for the midrange (350 - 2kHz crossover points), and a 1.5" 2452H for the upper range. At first, the HF driver was a 2431H Neodynium, but its frequency response was not good above 10kHz. And despite an efficient EQ with the the DP226 FAN, it doesn't sound very good. So I replace it by a 2452H and it was a lot better. By now; I would like to improve my 2431H, and I think about the Beryllium diaphragm of the 2435H. I would like to be sure both diaphragms are compatible (2431 vs 2435), and that a 2431 with a 2435 diaphragm is really equivalent to a 2435. Many thanks in advance, Regards Bruno
    Hi Bruno,

    why not use UHF driver over 10kHz such as:

    jbl 2408-1 or
    bms4540 or
    jbl 2405 or
    faital_pro_hf104

    that are intended to be used in such frequency range.

    regards ivica

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    Hi Ivica,

    I do not want to have a 4 ways system... it would imply to change the crossover, add another amplifier (I want to stay in fully active filtering), and have more phase rotations. And the UHF could not be placed very close to the HF horn in my system.

    I can keep the 2452, which is a very good driver, but the BE diaphragm should allow extended HF and better waterfall/CSD due to its excellent damping.

    Thanks!
    18" 2268H + 8" CMCD-81H + 2452 1.5" + PT horn
    Digital crossover XT DP226, AS-EBU digital input, miniDSP preamp

  4. #4
    Senior Member ivica's Avatar
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    Quote Originally Posted by Bruno_du_13 View Post
    Hi Ivica,

    I do not want to have a 4 ways system... it would imply to change the crossover, add another amplifier (I want to stay in fully active filtering), and have more phase rotations. And the UHF could not be placed very close to the HF horn in my system.

    I can keep the 2452, which is a very good driver, but the BE diaphragm should allow extended HF and better waterfall/CSD due to its excellent damping.

    Thanks!
    Hi Bruno,

    using active (digital) network, spacial difference between VHF and UHF drivers can be 'time' compensated.

    using 4" diaphragm, may be you can reach 15~16kHz, but I think You have to use JBL Be diaphragm, or JBL Aluminum, not Truextent, but here on the Forum lot of members has much, much more experience in that field then me,

    regards
    ivica

  5. #5
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    Hi, to answer your question yes a 2435 Be will drop into a 2431.
    With your XTA 226 you should be able to eq it out to about 15khz with good results-I wouldn't push them further, as I recall the PT's work well with this driver(use the search function i think Zilch did a lot of experimentation a few years ago).
    I'm using an XTA 224. My SAM1 horns have the 2435 Be and are good up to about 14khz.
    I also use 2452 with Truextent Be on H9800 horns and enjoy good flat clean output up to about 14khz where I let them roll off naturally.
    What the Be will give you is lower distortion, less colouration, more clarity and detail, it isn't necessarily a more extended response but it will be of a higher quality.

  6. #6
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    Thank you very much Cooky1257! very interesting.

    So no more HF extension... but better quality up to 14kHz.
    I will search on the forum for Zilch experimentaions.

    Thanks!
    18" 2268H + 8" CMCD-81H + 2452 1.5" + PT horn
    Digital crossover XT DP226, AS-EBU digital input, miniDSP preamp

  7. #7
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    Not to mention the truex is a little cheaper than the 2435 phragm, last I looked. As an aside , you could put the SL phragm in your 2452.

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    Senior Member pos's Avatar
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    Hi Bruno,

    A 2435 will have the exact same problem at the 2431 above 10kHz. This problem is not caused by the diaphragm itself but by the phasing plug/horn interface.
    See Doug Button's comment here: http://www.audioheritage.org/vbullet...l=1#post147356

    In the frequency range you are targeting (the last decade IIRC) a D2430K (D2) would probably be the best solution there is, would bolt directly onto your waveguide, and would also be cheaper than a 3" Be diaphragm :
    https://reconingspeakers.com/product...l-m2-5032754x/

    FYI this is the driver used in the M2
    And this is a 32ohms driver, which will help reducing any amplifier hiss/noise/distortion problem you might have in an all active setup...
    In fact being a dual VC driver, it can be configured as a 8 ohm, 32 ohm, or dual 16 ohm driver, which leave plenty of room when it comes to amplifier choice!

  9. #9
    Senior Member jerv's Avatar
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    Hi Bruno.

    I have a combination much like yours: with the CMCD-81H as a midrange unit and PT waveguide on top of that. Very nice combo.

    I have tried various high frequency drivers, including the 2435, the D2 and the 2450SL (much like the 2452).
    I am in total agreement with pos above: the 243x units does not work really well with the PT waveguides. This is because of the horn/phaseplug interface, and it will not get better with a Be diaphragm.

    The D2 is much better.
    But best of all, both when listening and when measuring, is the 2450SL with a Truextent Be diaphragm.

    Se my advice would be to keep your 2452 drivers, sell your 2431's, and use the money to upgrade to Truextent

  10. #10
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    Hi Pos,

    Many thanks for your expertise and your detailed response!
    So it's not a good idea to use the 2435 diaphragm. 2000$ saved!

    For the moment I will go on with my 2452, which are good drivers. The D2430K seems very interesting, I will think about it for a future upgrade...

    Thanks!
    18" 2268H + 8" CMCD-81H + 2452 1.5" + PT horn
    Digital crossover XT DP226, AS-EBU digital input, miniDSP preamp

  11. #11
    Senior Member ivica's Avatar
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    Quote Originally Posted by Bruno_du_13 View Post
    Thank you very much Cooky1257! very interesting.

    So no more HF extension... but better quality up to 14kHz.
    I will search on the forum for Zilch experimentaions.

    Thanks!
    Hi Bruno,

    I have done one on-axis measurement 2450SL & PT-H95, so may be can give You some ideas.
    Reagrds
    Ivica
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  12. #12
    Senior Member pos's Avatar
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    Quote Originally Posted by jerv View Post
    The D2 is much better.
    But best of all, both when listening and when measuring, is the 2450SL with a Truextent Be diaphragm.
    That is the combination I have, and I plan to compare it to the D2 on the M2 waveguide soon.
    I thought the D2 would best the 2450Be in the >2kHz range.
    Could you describe the differences you heard once EQed?

  13. #13
    Senior Member ivica's Avatar
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    Quote Originally Posted by pos View Post
    That is the combination I have, and I plan to compare it to the D2 on the M2 waveguide soon.
    I thought the D2 would best the 2450Be in the >2kHz range.
    Could you describe the differences you heard once EQed?
    Hi POS,

    I think that there is great differences between PT-H95 and PT-F100, especially in the region under 2kHz. PT-F horns have short throat horn part, so LF loading of the driver (without internal horn such as old school 2420, 2440,41,45,46, 50).
    I have calculated acoustical impedance of the driver with OSWG horn horn flare,

    http://www.audioheritage.org/vbullet...l=1#post366503

    and it can be shown how bad loading of the drivers is present.
    I believe that the mentioned is the reason why M2 has about 4cm (almost pipe like throat), and then diffraction slot in the throat, and then fast 'flaring' horn.
    For me it would be interesting to seen D2430K driver loaded with PT-H95 horn (not PT-F95/100), as much better LF loading I would expect.

    regards
    ivica

  14. #14
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    Quote Originally Posted by pos View Post
    Hi Bruno,

    A 2435 will have the exact same problem at the 2431 above 10kHz. This problem is not caused by the diaphragm itself but by the phasing plug/horn interface.
    See Doug Button's comment here: http://www.audioheritage.org/vbullet...l=1#post147356

    In the frequency range you are targeting (the last decade IIRC) a D2430K (D2) would probably be the best solution there is, would bolt directly onto your waveguide, and would also be cheaper than a 3" Be diaphragm :
    https://reconingspeakers.com/product...l-m2-5032754x/

    FYI this is the driver used in the M2
    And this is a 32ohms driver, which will help reducing any amplifier hiss/noise/distortion problem you might have in an all active setup...
    In fact being a dual VC driver, it can be configured as a 8 ohm, 32 ohm, or dual 16 ohm driver, which leave plenty of room when it comes to amplifier choice!

    Hi Pos,
    So are you suggesting that all of the throatless/short phase plug drivers(24**) aren't a good match for the M2 horn too? I ask as looking at the pics of that horn it has a very short throat before the pinch/slot section....

    Cooky

  15. #15
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    Pos, Jery: so the D2 or my 2452 with Truextent diaphragm (should it be the same as the 2450 one)?

    For my 2431: try to sell it since more than one year but nobody wants it...
    18" 2268H + 8" CMCD-81H + 2452 1.5" + PT horn
    Digital crossover XT DP226, AS-EBU digital input, miniDSP preamp

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