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Thread: Project M2 DIY Thread

  1. #856
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    Brother in Arms

  2. #857
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    Some exciting news.

    I spent most of the day figuring out the latest version of REW. For something thatís free itís surprisingly useful.

    My LMS PC croaked last week and l canít find the microphone cal disk anywhere despite an extensive search. The funeral is on Tuesday at my local transfer station. Fortunately l previously did a back up of all my measurements.

    Clio Pocket 2 is in my bucket list and possibly an Earthworks mic. It can measure at much higher sound levels. REW is limited to about 75 db.

    Below is a simple REW measurement of the 2451 SL and the 2430. This is not an Apples for Apples comparison as the measurements were each done on different sides of the world. Things measure a bit differently here Down Under. Just like the water spins the other way going down the plug hole. (Apparently)

    The bluish curve is the 2430. (Do not take this measurement as gospel)

    The main message of this post is that you can not only make a descent measurement at home indoors with REW but you can share measurements with other users of REW. In the help guide are instructions on how to export measurement curve data. I was also able to import REW measurement data into Leap with some fiddling around of the text file.

    How to use REW is worthy of an entire thread but you can Google REW. The help menus are excellent. All you need is the mini dsp mic if you own a Mac Pro Lap top. I figured it out in an afternoon.
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  3. #858
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    M2 horn horizontal off axis response

    Conditions
    Gated
    Smoothed 1/12 octave
    Analyser REW 75db
    Indoors
    0.5 m approximately

    Curves see legend

    On axis
    15 degrees
    30 degrees
    45 degrees

    Notes

    Initial observation: Interesting
    The 15 degree curve magnitude difference with the on axis curve is non linear. It’s almost identical @800 hertz but is 1.5dB higher at 3Khertz. Reason : Unknown. Could be a near field effect being close to the horn mouth.

    The pattern control at 45 degrees off axis is much worse at 800 hertz than 30 degrees off axis.
    My understanding is JBL recommend a listening window of 30+30 degrees. Ref owner manual.

    I continue to be impressed with the REW free download. It’s continued development has improved its capabilities for the diy loudspeaker user. Greg Timbers uses REW btw and recommended l try it out.

    For those interested here is the REW link below.

    You have a big advantage in using REW for developing and testing your loudspeaker project. Of course your ears are of vital importance. The mini dsp mic in not expensive and has been developed for REW with a mic cal file that you download from the Dayton Audio website. With a Mac laptop the set up is easy. I’ve done these measurements tonight indoors with a protractor and a tape measure. It’s much better than LinearX indoors.

    https://www.roomeqwizard.com/

    I may do some distortion tests however the REW at least with the usb mic can only be used at low levels like 75db. The usb interface may allow higher level spl tests because the monitor level and input levels of the Focusrite solo can be controlled. Yet to be confirmed.

    Any questions please pm.

    Edit: These are all unequalised measurements
    JBL 2430 voice coils in series

    For some reason all my notifications are been disabled. So l don’t receive any thread updates despite a review all my profile settings. This includes pms.

    So l have set up a direct access email visible on my profile and posts for anyone wishing to contact/connect with me on one of my posts, threads or a question related something your working on in the audio space. If your not a registered LHS member your welcome to contact me. I receive numerous email from the four corners of the world on all things audio, hifi, loudspeaker projects, crossover networks. So this is nothing new.
    I will also set up a Facebook and Instagram contact soon.

    Ask Ian on email ianmackenzieaudio@yahoo.com
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    Last edited by Ian Mackenzie; 06-13-2022 at 04:19 PM. Reason: Additional information

  4. #859
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    Another update on M2 driver measurements

    Drivers

    D2 2430 series voice coil connection (32ohms)
    2216nd

    Conditions
    Outside paved area.
    Temperature 18c.

    No driver EQ.
    No gating.
    REW measurement system with calibrated mini dsp mic / Mac Pro Laptop.
    Measurement amplifier Jaycar 20 watt digital amplifier.
    Raw curves with 1/6 octave smoothing.

    Microphone distance = D = 1 metre.
    Microphone position = JBL design point (JBL sticker on M2 horn according to JBL).

    Woofer location about 1.2 metres above ground level in 5 cu ft3 ported enclosure.
    M2 horn located x y z per JBL M2 baffle above 2216nd woofer.

    Grouped overlay measurements
    #Woofer amplitude curve level is relative to the measured signal level for 75db from the M2 horn @ 1 metre (-5db below M2 horn) Woofer sensitivity 94db 1 watt 1 metre

    # The bumps in the woofer response can be ignored due to proximity of buildings and ground surface.

    Notes on response curves
    The measured response from both drivers is quite smooth taking into account ambient noise and proximity of buildings. No gating was used to provide clarity in measurements. This is evident on the full screen measurements. Within +-2 db over the normalised range of the 2430 driver means little additional EQ other the 3Khertz bump and HF EQ. Likewise for the woofer.

    System Voicing
    A point for those looking at this closely and saying well why does JBL do xyz in the 4367 voltage drive of the woofer? Itís about voicing the overall system to be listenable in a domestic listening space. This is a pro woofer and in the context of it in domestic in- room response at the low end JBL probably felt the response from 100-800 hertz needed pulling down after subjectively assessment of the prototype. You see this in the 4367 voltage drive and the M2 voltage drive. In the M2 they augmented the bass response with additional PEQ filters for an extended f3 in the low 20 Ďs region (in- room).

    Goals
    My aim is to provide a stand up passive starter system without necessarily resorting to any LF boost. Obviously l will need to assess that moving forward. For example the passive M2 may need retuning to 32-34 hertz. Thatís not a big deal. Things like the LF inductors Dcr values impact on the optimal passive tuning because inductor dcr effects the system QESí and therefore the driver modified QTSí.

    This is well covered in Joseph DíAppilitoís text on tuning bass reflex systems.

    If your wondering l have not discovered a way of savings curves direct from REW yet.
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  5. #860
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    My next steps are :

    A. To assess parallel connection of the 2430 driver voice coils and some measurements.
    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.

  6. #861
    Senior Member srm51555's Avatar
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    Nice progress! Nice to have some measurements for on and off axis response. Shows that two listeners on the sofa will receive the same notes.

    Thanks,
    Scott

  7. #862
    Administrator Robh3606's Avatar
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    Looks good Ian

    Our measurements look very similar. I didn't gate my measurements, just used them raw, for the same reason loss of resolution. The smoothing makes it difficult get the transitions right. I had a hell of a time measuring the 2216nd. Had to do mine indoors, outdoors much better.

    Just a suggestion but why don't you start a separate thread?? This is already a long thread at over 800 posts and this may get lost in the middle at some point.

    Rob
    "I could be arguing in my spare time"

  8. #863
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    Hi Rob,

    Thanks for popping in. A new thread is a good idea.

    I am trying to encourage others to be open to trying some measurements. Once you get the hang of it itís Cool! And this REW is an easy low cost approach for anyone contemplating a project or just curious.

    My plan is to make the measurement kit mobil and do some remote measurements. My low power digital power amp can run off 12 volts.

    Guys if you have a wagon or a pickup truck what an excuse for getting out of the house for the afternoon.

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