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  1. #1
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    M2 diy passive crossover thread ---- from down under

    Reading on from post ................

    This is a new thread dedicated to a DIY Passive Crossover for the M2 DIY clone

    Its a lead in starter for anyone planning an M2 clone or those wishing to simplify from an active to a passive set up.
    This is not a completing alternative to the DSP crossover specified by JBL.

    I will continue to post some measurement as a means of zeroing in on the passive crossover network.

    Today I measured the 2430 driver on the M2 horn withe the voice coils wired in parallel.
    The acoustic response is compared to the 2216dn in a grouped screen shot.

    The test conditions are identical to my previous measurements:

    The DBFS reference test level for the REW Analyster was set at 75db.
    Distance = D = 1 metre


    Notes:

    The purpose of today’s measurements was to ascertain the difference in sensitivity of the parallel wiring of the 2430 driver voice coils.

    Based the the curves below the 2430 driver with its voice coils wired in parallel is between 10-12 db more sensitive than the 2216nd.

    Back in post 859 of the M2 diy thread l noted with the 2430 driver voice coils wired in series (32 ohms ac impedance) the 2216nd woofer was about 5 db less sensitive.

    So what’s the deal?

    There are advantages and disadvantages with wiring the voice coils either way. In a dsp scenario there will be 6 db less noise due to the lower driver sensitivity.

    In a passive crossover the additional sensitivity of the 2430 can be used to an advantage in the passive network for matching the sensitivity to the 2216nd woofer after normalising the 2430 response.

    For example when using dual 2216nd woofers.

    The down size is that the lower driver impedance can present a lower load impedance to the power amp at high frequencies unless care is taken.
    Attached Images Attached Images    

  2. #2
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    To repeat from the M2 diy thread these are the steps l am following.

    I hope to have the test and measure series below sorted by mid next week.

    I have received a REW file a the 2451 with SL diaphragm from Scott and compared it with my REW measurements of the 2430 driver. While the are similar the emphasis for EQ normalisation below the mass roll off point is different. I also need to compare and assess the sensitivity differences.
    I will discuss this in more detail once l have collected the data from steps B to E.

    My next steps are :

    A. To assess parallel connection of the 2430 driver voice coils and some measurements. Done
    B. Test and measure a 2447 driver on the M2 horn.
    C. Build and tests the 2216nd 6th order passive filter.
    D. Validate 2447- versus 2430 measurements and HF filter design.
    E. Build and test HP filter& EQ or any revisions for different drivers.
    F. Test and measure passive system voltage drivers and frequency response curves.
    G. Subjective assessment. Yes/No Pass. Fail revert to E.

    I hope to have cut panels for the M2 enclosures soon.

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    Update

    Some promising news. I have been able to adapt different driver impedances from 32 ohm to 5.7 ohms using the 2340 in either series or parallel voice coil connection.

    No RCL elements in the crossover need changing.

    The Tilt Adjustments work beautifully after l optimised the network impedances. See last image. The red line is the overall flat optimisation including crossover slope @ 36 db per octave.

    Range of the Presence Tilt Control is just over 1db in the 1.4khertz to 2.5 hertz region. The effect is most noticeable on brass instruments.
    Range of the Brilliance Tilt Control is 3.3db at 10,000 hertz. The rate is about 1 db per octave referenced to 2Khertz. The effect is to arrive at a comfortable HF tonal balanced when using CD horns.

    The network has yet to be fully tested. Simplified High Pass section shown only.

    I am happy with the network at this stage. My wife always said l was very clever…Bom Bom…Lol

    Hi Robert H. If you can please email me an export file of your 476 impedance and FR files from Leap for comparison. l can then check the results of a JBL conventional driver with a 12 ohm working impedance. The email address is in my signature.

    The Doctor
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    Last edited by Ian Mackenzie; 06-15-2022 at 08:47 AM. Reason: Typos

  4. #4
    Administrator Robh3606's Avatar
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    Hello Ian

    Sure working now send them latter on.

    Rob
    "I could be arguing in my spare time"

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    Senior Member srm51555's Avatar
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    Hi Ian,

    Thanks for posting the 1m measurements on the 2216nd's. I don't recall these posted anywhere here. What was the cabinet volume?

    Thanks,
    Scott

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    Hi Scott,

    The test enclosure is 5 cu ft3 was built from the plans in the JBL enclosure kit in the late 1970ís.

    Itís a semi free field test as the enclosure is on its side about 1.2m off the ground outside.

    The M2 horn was carefully positioned above the woofer.

    Another empty test enclosure was vertically positioned to supporting the test enclosure.

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