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Thread: Project M2 DIY Thread

  1. #466
    Member sebackman's Avatar
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    Great thread. Nice looking speakers, i’m sure you will like them.

    Just as a note, I think all D2 drivers are 20 ohms when the voice coils are connected in series. At least the ones I have had. It would also correspond to the JBL standard with 4ohms division per letter. I’m sure there are exceptions and kindly ask the more experienced JBL members to correct me if I’m wrong.

    G= 4ohms
    H= 8ohms
    I= 12ohms (I have not seen any drivers like this)
    J= 16ohms
    K= 20ohms

    And just a note on DSP, albeit doing the same job and even giving the same curves they do not all sound the same.

    Kind regards
    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  2. #467
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    You probably are onto something with the K= 20-Ohms. That said, the DCR of the 2430K is 16-Ohms (+/- .2 Ohms) as per the Tech Sheet. DCR is lower than impedance so 20-Ohms is indeed likely the nominal impedance of the D2 (D2430K). However, that will change the calculations listed elsewhere here on the passive "network" interaction. It was presumed to be a filter at 1K based on the D2 being a 32-Ohm impedance.

  3. #468
    Member sebackman's Avatar
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    I can put two D2˚s on the impedance rig on Friday and post the curves.

    Kind regards
    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  4. #469
    Senior Member pos's Avatar
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    "K" is 32 ohms nominal

    IIRC I was told "I" was skipped because it was too confusing (I, l, 1...)

    You can also add "F" to the list, for 2 ohms drivers like the 252F of the LSR12p/LSR6312p

  5. #470
    Member sebackman's Avatar
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    Here are the D2 imp sweeps. Both look reasonable the same.

    You decide.

    Kind regards
    //Rob

    Name:  D2 imp sweep 2.jpg
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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  6. #471
    Member sebackman's Avatar
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    Comps

    D2 vs 2451SL on M2. 5ms window, no smoothing. Electronic XO @ 400Hz 18db LR. LspCAD 6.0 PRO. Earthworks calibrated mic. 68cm out = FF. Dual channel measurement.

    Ripple is mostly room albeit pretty quiet room and short window. 3ms shows less ripple but no low end info.

    Used D2, new 2451SL's.

    Much more low extention on 2451. Phase good on both. Less drop off in 2451SL.

    4" driver phasing plug seem to like the M2 waveguide.

    Interesting to see what is driver and what is WG. Clearly much is WG (and/or room).

    Drop me a PM if you want the underlying data. Did 3ms, 5ms and 10ms on D2, 2451SL and 2453Ti.

    Have a nice weelend

    //Rob

    Name:  Comp D2 & 2451SL on M2.jpg
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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  7. #472
    Senior Member pos's Avatar
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    Hi Robert,

    Thanks for the very interesting data.
    It that a 16 ohms SL diaphragm?
    It would be interesting to compensate for the voltage sensitivity difference between the 32 ohms (20 ohms min) and 16 ohms (12 ohms min) diaphragm, ie about 3dB.
    (or 6 dB if this is a 8 ohms SL diaphragm)

  8. #473
    Member sebackman's Avatar
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    Hi Pos,

    The 2451SL's are 16 ohms and the dia's are brand new.

    The D2's are 20 ohm impedance, please see post with curves above. There is a peak at 1,8kHz and one at just below 900Hz, measured with DATS sweep without horn loading.

    Infact, they are almost flat impedance at 20ohms from 4k and upwards. That means that the difference between 16ohms and 20 ohms is less that 3db.

    You can have the data and run in REW if you want. They are text files.

    Kind regards
    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  9. #474
    Senior Member pos's Avatar
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    Robert, you are comparing apples to oranges here: the D2 wired in series is 32 ohms nominal with a minimum of 20 ohms (and this is what was chosen for the lpad impedance in the M2), the 2450SL J is 16 ohms nominal with a minimum of 12 ohms (like the truextent Be 4016, TAD 4001/2/3, and other JBL 4" 16 ohm drivers, including the 476).
    You either compare nominal loads, or minimum load, but not nominal with minimum.
    In both cases the ~3dB difference is still there, and should be taken into account when comparing responses, as what matters is obviously not the voltage, but the power that goes into the voice coil(s).

    This is for example what I did here when comparing the D2430K to a 16 ohms 2450Be (-3dB) and a 8 ohm 2435HPL (-6dB), and this let you see the theoritical behavior, with a difference in mass breakpoint frequency but a somewhat matched response in the midrange:
    http://www.audioheritage.org/vbullet...l=1#post362742

    There is a peak at 1,8kHz and one at just below 900Hz, measured with DATS sweep without horn loading.

    It should either be done an a plane wave tube, or on a reference horn.
    Would you measure the frequency response of a compression without a horn? Same goes with impedance measurements.

  10. #475
    Member sebackman's Avatar
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    Please see attached impedance sweep with DATS from 500Hz to 20kHz for both 2450SL and D2 mounted in the M2 waveguide. D2 is very flat 20ohm and 2451SL goes from 10 ohms to about 20 ohms at 20kHz.

    Maybe my rig is damaged but these are the actual curves on the M2 WG from the calibrated DATS system. I have no idea what DC restistance they have, have not measured.

    The first picture is the D2 only.

    The second is D2 and 2451SL in the same grapgh.

    Kind regards
    //Rob

    Name:  DATS Imp sweep M2 WG D2 driver 2.jpg
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    Name:  DATS Imp sweep M2 WG D2 driver 1 + 2451SL driver1.jpg
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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  11. #476
    Senior Member pos's Avatar
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    Thanks for these measurements!
    So the D2430K is twice the load compared to the 2450SL-J, apart in the UHF were the shorting rings of the D2 avoid the rise in impedance.
    So 3dB it is.

    Regarding the LF response, I am surprised by the huge difference in level between the two drivers, as this is not what I measured.
    Did you use a cap?

  12. #477
    Member sebackman's Avatar
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    Hi POS,

    Please bear in mind that the SL's were new but I don't know the history of the D2's.

    Measurement was done with 68cm flight distance, a bit on the short side but my room is too small. -At least in the Winter with all stuff taken in from the snow :-) .

    No cap on either measurement, just right into DATS for impedance measurement. MLS measurement above same thing, just straight from power amp. Analogue ElectronicX O 24db LR @400Hz before power amp in MLS setup.


    Following the discussion above, I’m not at all imagining or saying that we (DIY) can improve on or fully copy the M2 design and acheive the same outcome. It is a system and we typically deal with discrete parts at a time.

    By trying different drivers (or other changes compared to factory M2 spec) the result may sound good to my ears but an M2 speaker system it is not. I think member "hsosdrum" summed it up pretty good in a previous post.


    Floyd Tools circleof confusion may also very well be in play here as we mere mortals cannot achieve the double blind test with the quality worthy of drawing any far reaching conclusions.

    However, when trying various combinations of drivers on the M2 WG I find my listening results supporting the curves posted of the 4” drivers with SL and/or Be dia’s.Especially on vocals and piano.

    They do sound slightly different and I think it comes down to taste for each listener but from a scientific approach the M2 factory speaker with BSS XO and appropriate amps is probably the most accurate.


    BTW, did you see the M2 vs Revel Saloon shoot out at "avsforum",that underlines that albeit M2 is a superior
    tool from professionals in a studio it may not be the most preferred speaker in a home. I was surprised to see the results but have never auditioned the Revels against the M2’s so I have no personal view. Just relaying the results. Even Floyd Toole left some very insightful comments in the very long thread. Interesting reading.



    I saw that the prices for the D2’ drivers just got ballistic and went from original $365 in stock to $1599 to order. What on earth happened??

    Kind regards
    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  13. #478
    Senior Member ivica's Avatar
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    Quote Originally Posted by sebackman View Post
    D2 vs 2451SL on M2. 5ms window, no smoothing. Electronic XO @ 400Hz 18db LR. LspCAD 6.0 PRO. Earthworks calibrated mic. 68cm out = FF. Dual channel measurement.
    Ripple is mostly room albeit pretty quiet room and short window. 3ms shows less ripple but no low end info.
    Used D2, new 2451SL's.
    Much more low extention on 2451. Phase good on both. Less drop off in 2451SL.
    4" driver phasing plug seem to like the M2 waveguide.
    Interesting to see what is driver and what is WG. Clearly much is WG (and/or room).
    Drop me a PM if you want the underlying data. Did 3ms, 5ms and 10ms on D2, 2451SL and 2453Ti.
    Have a nice weelend
    //Rob
    Hi Rob,

    Thank You for presented us such information.

    It would be interesting to be seen such comparison between D2430K and 2451SL-1.5 drivers connected to M2 horn, measured off-axis, say about 30 o deg-off-axis. May Some of the mentioned drivers would not be so "CD type"

    regards
    ivics

  14. #479
    Senior Member pos's Avatar
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    Hi Robert,

    I have yet to try the 2450SL-Be on the M2 waveguide. That is something I intend to do, but I have some other things that need to get sorted out before that...
    And even with your wonderful adapter, changing the compression on that horn is still a pain in the ass!
    The 2451 might be a better choice with its larger bolt pattern.




    Quote Originally Posted by sebackman View Post
    BTW, did you see the M2 vs Revel Saloon shoot out at "avsforum",that underlines that albeit M2 is a superior tool from professionals in a studio it may not be the most preferred speaker in a home. I was surprised to see the results but have never auditioned the Revels against the M2’s so I have no personal view. Just relaying the results. Even Floyd Toole left some very insightful comments in the very long thread. Interesting reading.

    I looked at it briefly, but these comparisons are always difficult to make.
    I think they were running a single speaker with a mono signal?
    That sort of tests favor larger directivity speakers at lot, which the Revel probably is.



    Quote Originally Posted by ivica View Post
    It would be interesting to be seen such comparison between D2430K and 2451SL-1.5 drivers connected to M2 horn, measured off-axis, say about 30 o deg-off-axis. May Some of the mentioned drivers would not be so "CD type"
    Hi Ivica,

    I did this comparison on a PT waveguide, and in my tests the 2450SL-Be was a tiny bit (marginally) cleaner than the D2430K off axis (ie less obvious sharp defects due to the phasing plug).
    That was not what I expected as one of the main design goals of the D2430K was to get as planar a waveform as possible in the UHF.
    That says a lot about the quality of the coherent 4-slit phasing plug of the 2450/476!

  15. #480
    Senior Member pos's Avatar
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    For those interested in running the compression driver (either D2430K or 16 ohms 2450SL/2450Be/476) directly without the lpad, there is what looks like a very nice THX headphone amp currently on massdrop that is able to put 6W into a 16 or 32 ohms load, with noise/THD specs to die for (similar to the Benchmark AHB2).

    Massdrop x THX AAA 789 Linear Amplifier
    The drop is limited to 480 units, and "Estimated ship date is Oct 31, 2018 PT." !

    To put things in perspective, 6W is approximately what the D2430K receives when fed with a ~150W/8ohms amp through its lpad: not too shabby for home use, and more than what a Benchmark AHB2 would be capable of!
    I specifically asked the THX engineer there about using it on a 16 ohms compression driver (ie 12 ohm minimum load), and he said it would be fine.
    I still have a few questions that need answers (if not already answered when you read that message), but I already joined the drop anyway
    I will report back in... 8 months, when I receive the amp!

    The D2430K would of course be an even easier load for that amp (unless you go all out and decide to use two amps and drive each diaphragm with a separate channel for an acoustically balanced design )

    Another interesting application for that amp would be to drive a legacy supertweeter like the 2405, as per Greg Timbers recommendations in the 4345 thread:
    Quote Originally Posted by gtimbers View Post
    The ring radiator hates passive networks. A major improvement in the upper range would be to drive the 2405 from its own little amp. You only need 3 or 4 v rms. The 2405 does 110 dB for 2.83v. It is padded way down in the system. There is little real power at those frequencies anyway. You only need to know the voltage output of the amp, power is irrelevant. The 2405 is about 12 ohms and won't draw much current. I would use some little chip amp with a 2ond or 3rd order low level highpass in front of it. Take off the passive network to the ring and just feed it straight. Make sure the amp doesn't make a DC thump on turn on or turn off. That will fatigue the diaphragm. The amp will also have to have really low noise characteristics as any hiss will be really loud directly into the ring.
    Unfortunately the 045 would probably not be a good candidate with its 4 to 5 ohms load in the range of interest: http://www.audioheritage.org/vbullet...l=1#post339108


    Here are the specifications for those who are not registered on massdrop:
    General

    All parameters measured at 0 dB gain, 1 kHz, with balanced inputs and 300-ohm load unless otherwise noted
    Inputs: Stereo XLR-3 gold-plated Neutrik; Stereo RCA gold-plated
    Outputs: 1/4 in (6.35 mm) TRS gold-plated Neutrik; 3.5 mm TRS gold-plated; XLR-4 balanced gold-plated
    Frequency response: + 0.01 dB / - 0.01 dB 20 Hz–20 kHz; + 0.05 dB / - 0.10 dB 10 Hz–80 kHz
    Input impedance: 50 kOhms balanced or unbalanced
    Chassis: High-grade CNC-milled aluminum with bead-blasted finish
    Power supply: 24 VDC inline brick, universal input 100–240 VAC
    Dimensions: 8.3 x 9.1 x 2.2 in (210 x 230 x 57 mm)
    Weight: 3.4 lbs (1,520 g)

    Balanced Output

    Output power: 6000 mW, 16 ohms, <1% THD (watts per channel)
    Output power: 6000 mW, 32 ohms, <1% THD (watts per channel)
    Output power: 800 mW, 300 ohms, <1% THD (watts per channel)
    Output power: 400 mW, 600 ohms, <1% THD (watts per channel)
    THD: -143 dB, 300 ohms, 1 mW: 0.000007%
    THD: -140 dB, 300 ohms, 100 mW: 0.000010%
    THD: -125 dB, 32 ohms, 1 mW: 0.000056%
    THD: -123 dB, 32 ohms, 100 mW: 0.000071%
    THD: -120 dB, 16 ohms, 1 mW: 0.000100%
    THD: -118 dB, 16 ohms, 100 mW: 0.000126%
    IMD: -123 dB, SMPTE 70 Hz + 70 kHz, 300 ohms: 0.000071%
    IMD: -124 dB, DFD 18 kHz + 19 kHz, 300 ohms: 0.000063%
    Crosstalk: -127 dB, 300 ohms: 0.000045%
    Noise (A-wt): 2.4 uV, potentiometer at nil
    SNR: 136 dB, 300 ohms, <1% THD
    Gain: 2x , 8x, 16x (+6, +18, +24 dB), selectable via front switch
    Output impedance: < 0.1 ohms

    Single-Ended Output

    Output power: 3000 mW, 16 ohms, <1% THD (watts per channel)
    Output power: 1700 mW, 32 ohms, <1% THD (watts per channel)
    Output power: 200 mW, 300 ohms, <1% THD (watts per channel)
    Output power: 100 mW, 600 ohms, <1% THD (watts per channel)
    THD: -143 dB, 300 ohms, 1 mW: 0.000007%
    THD: -140 dB, 300 ohms, 100 mW: 0.000010%
    THD: -135 dB, 32 ohms, 1 mW: 0.000018%
    THD: -128dB, 32 ohms, 100 mW: 0.000040%
    THD: -125 dB, 16 ohms, 1 mW: 0.000056%
    THD: -123 dB, 16 ohms, 100 mW: 0.000071%
    IMD: -117 dB, SMPTE 70 Hz + 70 kHz, 300 ohms: 0.000141%
    IMD: -125 dB, DFD 18 kHz + 19 kHz, 300 ohms: 0.000056%
    Crosstalk: -90 dB, 300 ohms: 0.003162%
    Noise (A-wt): 1.2 uV, potentiometer at nil
    SNR: 136 dB, 300 ohms, <1% THD
    Gain: 1x , 4x, 8x (+0, +12, +18 dB), selectable via front switch
    Output impedance: < 0.05 ohms

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