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Thread: JBL 4346 DYI with 2123H

  1. #16
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    Okay,

    I am amazed you have time for this with your new arrival!

    Firstly, l can simulate for you the voltage drives of your hybrid in Leap 5 to evaluate the overall network phase and voltage drives and compare with the vanilla 3155 network. I might be able to look at this over the weekend.

    I have the 4344mk11 network so l am familiar with its operation.

    Secondly, Looking at the drivers sensitivity of the Beyma slot looks identical but the impedance curve may not be the same as the 2405? In your post you mention a 2 db drop off @ 10 Khertz? Are you referring to the horn only or the slot only or the overall response with the Lpads full?

    If you can please provide clarity?

    If this comment relates to the level of the Beyma only we can then focus on the adjustment range of the L pad.

    If the drop off relates to a notch in the response please advise?

    Some commentary of why you think this is a phase issue would assist in evaluating the situation.

    The thing to understand with a 4 way is setting up the levels for each driver can be a challenge as can the phase of each driver. It's easy to wire up one of the driver. As l recall the mid, hf and uhf should all be in phase. I assume you have previously checked this? The polarity convention of the Beyma slot maybe different to the 2405.

  2. #17
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    thank you

    I really appreciate you taking the time for little ol' me. I am trying to finalize this project and enjoy the music.

    So, in order not to be any misunderstanding I am attaching the schematics og mr Giskard network frim which I have used the Hf and Uhf sections. The mids and lf are from the mkII.
    Let me get back to you with the drop off issue. I want to replicate the test with all drivers full on.


    In the meantime if you can Identify a voltage issue in the network i will be most grateful.


    getting back to you also on the phasing issue. I know the Beyma is different than the 2405 And I wired it properly.
    Attached Images Attached Images  

  3. #18
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    If you wish take a pic of the analyser for each test and up load for the overall response L pad full.

    Then the phase reversal of the HF (only), then phase reversal of the Beyma only.

    Then if you can the individual response of the mid, hf and uhf.

  4. #19
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    Wink

    Okay


    Can you check that the L pads are correctly connected?

    On the L pad 3 is the input from the crossover, 2 goes to the driver , 1 is ground.

    I have previewed the schematics and it needs be looked at in context that the Giskard schematic was prepared for the 2122 mid driver and the 2235 or 2245 woofer.

    The mid driver is less sensitive than the 2123 mid driver.

    I think the woofer used in the 4344mk11 is slightly more sensitive than the 2235 and is close to the 2245 woofer.

    I will need to check the voltage drives but L pad on your mid driver may not have the same range of adjustment as the HF and UHF. This relates to your comment that up full is best.

  5. #20
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    pink noise rta

    Please see the graphs

    pink noise full on lpads

    1 all drivers together
    2 mid only
    3 hf only
    4 uhf only
    5 lf only

    the dropoff is At arround 1200 hz.

    Checked on l-pads connections they are OK.
    Attached Images Attached Images      

  6. #21
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    Okay

    High level over view.

    The 1200 Hz dip is typical of these designs.

    The magnitude of the dip will vary with the actual location of the Mic in the vertical plane.

    The aim of the 4344mk11 mid filter is to equalise a rising response in the driver much like a bump and ensure a smooth transition to the horn.

    The voltage drivers are tailored to compensate for driver intereaction in the crossover region.

    The mid only response you have provided does not look right overall .

    I recommend you carefully check at this stage that the Mid filter is correctly constructed. This is a complex filter with a number of elements. Check the resister values and locations , earth connections, Inductor values and locations.

    That said the response above 1200 Hz is elevated and perhaps as a result of the mid filter not working correctly,

  7. #22
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    Please find attached the voltage drives into the standard 8 ohm test load.

    The legend shows the colour :

    Red is the Mid in the 4344mk11 filter
    Blue is the HF with the 3155 Giskard HF filter
    Purple is the HF with the 4344mk11 HF filter
    Yellow is the UHF with the Giskard filter
    Magenta is the UHF with the 4344mk11 filter.


    The important point is these are voltage drives NOT the acoustic response or a representation of how the individual acoustic responses sum at the mic position.

    The HF and UHF voltage driver are different for both the HF and UHF filters.

    However the overall levels are similar.

    The UHF filer for the 4344mk11 is lower and this is part of the design as the HF filter allows the horn to extent further into the UHF band (than the 3155 Giskard filter).

    Some of these variations are made from empirical desicisions based on actual listening and voicing of the specific drivers in use. Note the HF driver in the 4344mk11 is titanium diaphragm dusted with aquaplas .

    Before reading too much into these curves please review and check the mid filter.
    Attached Images Attached Images  

  8. #23
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    If you have an opportunity to do more measurements disconnect the woofer and connect an 8 ohm resister or a similar to the woofer network

    I have a feeling the woofer is effecting your measurements

  9. #24
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    I checked schematics and i have one question.

    The first two 2.4 ohm resistors are in parallel or in series? because i thought they are in parallel and i replaced them with one 1.2 ohm resistor. is that ok?


    secondly is it ok to replace the three parallel resistors 36 36 and 60 ohm with only one equivalent or the parallelism of resistors has a reasoning in the whole schematics? also i will not biamp.

    Never got the time to repalce the wooder with a resistor and repeat the test but i will do it as soon as i can.

  10. #25
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    Quote Originally Posted by lordoflight View Post
    I checked schematics and i have one question.

    The first two 2.4 ohm resistors are in parallel or in series? because i thought they are in parallel and i replaced them with one 1.2 ohm resistor. is that ok? Yes


    secondly is it ok to replace the three parallel resistors 36 36 and 60 ohm with only one equivalent or the parallelism of resistors has a reasoning in the whole schematics? Yes also i will not biamp.

    Never got the time to repalce the wooder with a resistor and repeat the test but i will do it as soon as i can.
    Okay

  11. #26
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    Quote Originally Posted by Ian Mackenzie View Post
    Okay
    I am curious what the mic position?

  12. #27
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    Evidence

    http://www.audioheritage.org/vbullet...CP21-F-tweeter

    If we can confirm the sensitivity is down 5 db that is an easy fix

    While this is a factor I would like to see the overall response somewhat flatter overall.

    If you can provide detail of the iPhone app and how you did the measurement l can try and emulate your results.

    Unfortunately l don't think l can source the Beyma driver easily to evaluate it.

  13. #28
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    Quote Originally Posted by Ian Mackenzie View Post
    ...I would like to see the overall response somewhat flatter overall.

    If you can provide detail of the iPhone app and how you did the measurement l can try and emulate your results.
    It'd be nice to know/see the response curve of that iPhone mic. I've never seen one, but know for certain it cannot match an Earthworks M30...
    bo

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  14. #29
    Senior Seņor boputnam's Avatar
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    Ian: I just found this work by Faber Acoustical. Unfamiliar to me so I cannot vouch for them or their work. But this response curve of built-in mics is interesting...

    Name:  iPhone mics response.png
Views: 1134
Size:  31.5 KB

    Not knowing his model number, some of that observed hi-end boost, >3kHz, could be attributable to the mic itself...
    bo

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  15. #30
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    Hi Bo

    Good point. I had not considered that!

    I was thinking if a try and to the same type of measurement here at home with my iPad mini or my iPhone 6s using the same app.

    I could then compare to my Lms precision measurement (a gated sine wave ) and work out if it's a measurement "thing" or something else.

    I must say some of those iphone analysers are quite nifty for what they are!

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