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Thread: JBL Master Reference Monitor

  1. #1666
    Senior Member srm51555's Avatar
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    Quote Originally Posted by grumpy View Post
    Working entirely in one manufacturer’s ecosystem makes it a bit easier, for sure.
    So true, after finding about the line of BSS Contrio wall controls, I can’t go back!

  2. #1667
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    Diy m2

    Hi All,

    I am new to the forum. I joined as I look to construct some DIY M2's.

    Firstly, a big thankyou to all members who have contributed to such an amazing resource of information.
    I have been reading as much as I have time for, and I greatly appreciate the efforts of all who have documented and compile/tweaked settings etc.

    I sent POS a private message with some questions regarding M2 crossover design.
    I tried to post publicly, but I think my message and content exceeded maximum limits.

    Anyway, I was hoping someone might have a link to a recreated cut sheet and design plan for the M2 cabinets.
    I.e. CAD cut sheet etc. Does this exist?

    It would be amazing to get these plans, linked on the crossover google link, including the 3D file for the port design etc.

    Thanks for your assistance.
    Many thanks

  3. #1668
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    Quote Originally Posted by pos View Post
    Their purpose is padding only (the crown gain structure is probably too noisy for a compression driver), but their effect cannot be neglected and the EQ preset sure takes all this into account.
    Even with a protection cap aimed at around 200Hz (1/4 of the actual acoustical crossover frequency), with the lap the cap sees a constant 20 ohm load compared to a more complex load without. This will change its transfer frequency and the final frequency response of the system.

    One of the things I intend to do is to measure the HF combo with and without the lap (keeping only the protection cap), and see how the frequency response changes, and tweak the EQ settings to compensate for the difference...
    Hello,

    I know that is years later.

    As the discussion goes around the purpose of the resistors and capacitors.

    I see it some thing like this:

    1 the capacitors provide DC and low frequency protection well below the crossover frequency.

    2 Padding to operate up in the amplifier power range where there is less noise.

    3 with R2 in parallel with the driver and R1 in series with the driver the impedance curve is much flatter and tamer with much less resonance to disturb the frequency response.

    Thought comments, agreements disagreement?

    Thanks DT

  4. #1669
    Senior Member Ian Mackenzie's Avatar
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    If you Google M2 passive crossover there is a diagram with corrections of the capacitor mis print,

    An explanation is given of the network.

    Yes it provides attenuation of approximately 9 dB and a slow 1st order high pass passive filter at approximately 1000 hertz. This significantly improves the signal to noise ratio of a horn when used Bi amplified application.

    There is no rocket science here and l doubt Jbl spent too much time thinking about it. Greg typically uses a -6 dB fixed pad when Bi amping a horn. Those Crown amps have massive output so the M2 pad is scaled accordingly. There’s nothing to it.

    A horn without a pad will exhibit noise problems heard as residual hiss and other artifacts that erode the noise floor and resolution of the system. We don’t want that so we insert a fixed pad.

    The network is there to back the warranty and mis use of the system in the event in of an amplifier malfunction. Scroll down this link to the diagram.

    https://www.avsforum.com/threads/diy...2852530/page-4

  5. #1670

  6. #1671
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    Thanks for the replies with links.

    I have an order in at Mouser for the 3.3uf + 4.7uf capacitors and resistors.

    POS I did note in one of your links that you speak of the passive network linearizing the impedance of the D2+ waveguide.

    I believe that will be true.

    I will test that with wit the analyzer on my bench. (APx555 plus calibrated microphones.)

    Thanks DT

  7. #1672
    Senior Member pos's Avatar
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    M2 tested on a klippel test bench at Erin's audio corner:
    https://www.erinsaudiocorner.com/loudspeakers/jbl_m2/

    Name:  CEA2034 -- JBL M2 (Crown iTech 5000 Amp; M2 Base Configuration).jpg
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  8. #1673
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    Excellent waveguide, 1-2 dB too hot tweeter and cabinet could and perhaps should be a little bit better resonance-wise. It's possible that some of those resonances could come from something being loose.
    This measurement also confirms the peaking from 7-11 kHz even with the M2 version of D2 that can benefit from adjustments in the dsp.

    The compression tests shows why a big ole speaker has its merits. Excellent stuff.

  9. #1674
    Senior Member srm51555's Avatar
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    Very interesting, thanks for posting.

    He confirmed the 270hz issue that we found awhile back ago.

    Thanks,
    Scott

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