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Thread: Project M2 DIY Thread

  1. #781
    Senior Member DogBox's Avatar
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    Driver with the Waveguide

    Hey Scott,

    Sorry, didn't mean to confuse the issue.. Yes, I saw those great schematics by EarlK, they were great! I always try to study these

    schematics to try and learn and figure out how it's all put together. From what you did putting in the 2451; I happened to get lucky with

    a guy here in Australia selling near new pairs of 2450SL's! So I grabbed the opportunity before I tried to order the D2430K.

    About a week or so ago, I ordered one, as getting two would mean over $1000 [AUD] spend and attracting duties and taxes and too much extra $$$...

    The lovely lady I deal with told me that I got their last one.. more might be coming end of this month OR in 8 weeks time! Don't feel so bad having to

    build up the credit card again while I wait.. So I will have the choice of either 2450SL or D2430K as they become available. Could always stock up on

    some Solen Fast Caps from Parts Express if the tweeters take their time. I was hoping to just simplify the 4367 schematic and go from there, really..

    How 'is' the top end with the 2451SL? Does it roll off much around the 18k - 20kHz area? Being a 4" diaph - it wouldn't have too much top, would it?

    So, i'm countersinking holes in the Flanges and tapping all the holes in the Waveguides and figuring out my drawings for the Cabinet Maker I know nearby

    to cut all my timber to size. I want to use the good old "chipboard" or pyneboard as I know it. I feel it makes a better cabinet. Even if it is a bit heavier..

    Will keep an eye out for developments on the forum or this thread! Would make a good book this thread would!!!

    Kind Regards,
    Steve

    ...

  2. #782
    Administrator Robh3606's Avatar
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    I was hoping to just simplify the 4367 schematic and go from there, really..

    Hello Steve

    How 'is' the top end with the 2451SL? Does it roll off much around the 18k - 20kHz area? Being a 4" diaph - it wouldn't have too much top, would it?
    It should be fine. I am using 476Mg's on the M2 waveguide and 2453SL's on PTH1010's. Both had enough top end on either waveguide so you should be OK.

    As far as a passive M2 I have an almost running with 2216Nd and the 476Mg's on M2 waveguides and it's a fun speaker.

    If you are running an all analog system and don't want to deal with DSP it's a great alternative.

    Rob
    "I could be arguing in my spare time"

  3. #783
    Senior Member DogBox's Avatar
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    476Mg with Truextent Be (?) Diaphragm?

    Quote Originally Posted by Robh3606 View Post
    It should be fine. I am using 476Mg's on the M2 waveguide.. had enough top end [with the M2]... waveguide so you should be OK.

    As far as a passive M2 I have an almost running with 2216Nd and the 476Mg's on M2 waveguides and it's a fun speaker.

    If you are running an all analog system and don't want to deal with DSP it's a great alternative. "I did invest in a UltraDrive Pro DCX2496 for DSP - as well!"

    Rob
    Hi Rob,

    Thanks! for the confident note! I looked on as you built your M2 version with great interest. I also recognised the sealer/sound deadener you

    used on the inside of the cabinet. How good do you find it?

    Without looking at the thread you wrote [I do have it Bookmarked, with others..] I was of the impression you used the Truextent Be diaphragms, didn't you?

    I have a few too many pressing items to get before I can think of affording a pair of those! and wouldn't know who to get to fit them? Don't trust myself

    that much! However, I did get some aquaplased D16R2451SL beauties for the occasion[2450SL]. Taking quite a while to get all the goodies as I'm trying to

    use the best I can get to maximise my chances of a good end product. How much of the 4367 crossover did you begin with? I saw the wonderful graphs

    you did along the way... I regret not spending the $3700+ bucks [US] and getting a good crossover program many years back.. hate to see what it costs

    these days. But you could see the changes you made on the frequency plot on the fly to see results before using a soldering iron! A simulated response

    program. Blew me away when I first saw it.. Many books later I am still using pencil and paper and formulas for a reference!

    Will go and find that thread again and take a better look! Appreciate the interest and Help!!

    Kind Regards,
    Steve

    ...

  4. #784
    Administrator Robh3606's Avatar
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    Hello Steve

    I was of the impression you used the Truextent Be diaphragms, didn't you?
    No I didn't see any reason to go that way. I have the aquaplas coated Mg which both sound and measure great. I would love to get a pair of diaphragm's but they are not available. You should be fine with SL diaphragm's to start but if you go the Be route expect to have to update the crossover network.

    How much of the 4367 crossover did you begin with?
    None I started this before the 4367 was available. I did look at it as a reference though when it came out.

    I also recognised the sealer/sound deadener you

    used on the inside of the cabinet. How good do you find it?
    I found it years ago and used it originally to coat aluminum horns. I tried it on scrap MDF to see if it was compatible and it worked out well. I purchased a pail and have enough left for one more set of cabinets. I used it with my Array 1400's Be clones as well. It both seals and helps dampen the cabinets.

    Rob
    "I could be arguing in my spare time"

  5. #785
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    JBL M2 cabinet dimensions/CAD file

    Hi guys,

    I was wondering with so many JBL m2 clones being made, has anyone correlated cabinet dimensions, cabinet volumes, port information etc into a single working design doc?
    This seems to be the missing information for anyone wanting to take this build on.

    I am personally chasing the best copy of the M2 cabinet I can. A document or render which show all panel sizes and dimensions.

    Would this exist?
    Thanks so much

  6. #786
    Senior Member DogBox's Avatar
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    General Port Information

    Hi Scott and Robh and others,
    In my hunt for extra info on speaker design and anything new that comes to light; I found this article from the aes.org about port tube end flaring. Remembering that
    there was quite a bit of discussion about the "new style of port" that is used in the M2, I thought others might like to take a look too.
    https://www.aes.org/tmpFiles/elib/20210719/20683.pdf hopefully should give you the paper that is free from the Society. Haven't read it all yet but wanted to share.
    As the previous poster has stated, not a lot of 'definite' info has been put down but one "can" read this thread AND the JBL Master Reference Monitor thread and
    gain a LOT of insight into what makes this wonderful speaker/monitor tick.
    Hopefully this paper will add to the collection of information and be of help.

    Kind Regards,
    DogBox
    [Steve]

  7. #787
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    Quote Originally Posted by pos View Post
    I did not have time to measure the 2540SL-Be of the M2 waveguide yet, but today I did some measurements comparing the original passive network (albeit with different resistors and caps brands) and a simple 30uF Solen cap, in an effort to get back those 9dB of passive attenuation and be able to use an amplifier with roughly 1/10 of the power...
    I can share the preliminary correction adjustments if anyone is interested.

    By the way, does any of you leave near Reykjavik?
    ---------------------------
    POS, This is very old I know ...... but I am also interested in using a small amp and would love to "recover" the -9dB attenuation from the 2-resistor voltage divider. If I simply use a 30uF protection cap, what are the corresponding changes for the DSP filters (my prototyping will be on a Behringer DCX 2496).

    Thanks, I have searched the threads, but found nothing (sorry if you are having to repeat your answer),

    -Tom

  8. #788
    Senior Member pos's Avatar
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    Hi Tom,

    I did a first test in 2016, but never published (nor implemented!) the results.
    I did revisit this last February, and ended up with a set of 8 additional EQ points that have to be added to the original EQ.
    The cap is a 30uF Solen MKP (SCR MKP). The amp is a THX789 (same amp for both measurements, with lpad and cap, so can be factored out).
    The response tracks the original lpad version within +/- 0.1dB from 300Hz to 20kHz.

    I did not try to refactor the original correction, as I am using convolution with rephase, and any arbitrary number of EQ points can be used without issue.
    You will have problems with a DCX though, as the original correction is already using all the available resources of the device.
    Also please note there is a shelving filter, and these tend to have variable definitions from one manufacturer to the other (different "cutoff" frequency definition, dB/oct vs Q, etc.). Here the cutoff is the center of the shelf.
    EQ are of constant Q type, as used in the DCX and many (most) other devices (not the proportional Q type used in minidsp devices, but they can be converted using a simple formula).
    One EQ point is also above 20kHz, which is also impossible to do in many devices.

    Anyway, here are the additional EQ points, to be added to the HF section (not the main signal!) :

    - gain -9dB (in DSP or in amp)
    - shelving low 750Hz -10dB Q=0.6
    - PEQ 720Hz +2.5dB Q=3.2
    - PEQ 895Hz -0.22dB Q=2.0
    - PEQ 1550Hz +1.4dB Q=2.4
    - PEQ 2400Hz -0.25dB Q=3.0
    - PEQ 3050Hz +0.6dB Q=2.8
    - PEQ 4300Hz +0.13dB Q=1.8
    - PEQ 25000Hz +0.6dB Q=0.7

  9. #789
    Senior Member pos's Avatar
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    Additionally, here is a simplified version using only 4 EQ points and a filter, tracking within around +0.4dB/-0.2dB from 400Hz to 1kHz, and +/-0.2dB above that:

    - gain -9dB (in DSP or in amp)
    - 1st order high pass 1kHz
    - PEQ 720Hz +1.6dB Q=3.2
    - PEQ 1550Hz +1.5dB Q=2.4
    - PEQ 3200Hz +0.6dB Q=1.9
    - PEQ 20000Hz +0.5dB Q=0.8

  10. #790
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    POS, Thank you. This is very helpful. You have saved me hours and hours of time. -Thanks again

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