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Thread: Truextent diaphragms measurements

  1. #1
    Senior Member pos's Avatar
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    Truextent diaphragms measurements

    Here is a set of measurements I made of the Truextent Be4016 beryllium dipahragn (16ohm version) in a 2450SL core (1.5") on the rectangular 90x50 PT waveguide (PT-F95HF).
    For comparison purpose the measurements also include other JBL OEM diaphragms.

    All measurements were taken under the exact same conditions:

    - dayton mic calibrated by cross spectrum
    - mic at ~40cm from the horn mouth (not far enough to get a meaningful response curve, but ok for comparison purpose), exact same position for all measurement
    - Studio Projects VTB1 V preamp ("tube blend" turned off)
    - creative labs sound card (line level), not calibrated
    - holmimpulse software in sweep mode
    - Ev dx46 active crossover in digital input mode, no eq or filter except a FIR HP at 600Hz (no influence on phase)
    - Ram-audio S4044 power amp set to a very moderate SPL
    - 75uf protection capacitor (shall not have much influence on phase above 1.5khz, even for the 8ohms diaphragms)
    - PTF-95HF horn (no really usable under 1khz, so only the HF response can really be compared)
    - 2450SL core (1.5" coherent wave phasing plug, 4" diaphragm, neodymium motor)

    The diaphragms under test are:

    - JBL D8R2450SL (2450SL): 8 ohms 4" Titanium diaphragm without ribs but with aquaplas, used in the 2450SL, 2452H-SL, and 475nd
    - JBL D8R2450 (2450Ti) : 8 ohms 4" Titanium diaphragm with ribs, used in the 2446H/2450H/2451H
    - Truextent Be4016 (2450Be) : 16 ohms 4" Beryllium diaphragm

    The 16ohms truextent diaphragm was of course given 3dB more level in the active crossover, so every diaphragm received approximately the same wattage, as is confirmed by the fact that the levels are matched in the low end.

    As you will see the measurements do track the ones found in the Truextent white paper quite well:
    http://www.audioheritage.org/vbullet...351#post305351


    In a second set of measurements, post #4, the 2450Be is compared to a 2435HPL

  2. #2
    Senior Member pos's Avatar
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    amplitude
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  3. #3
    Senior Member pos's Avatar
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    3rd harmonic distortion

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    impulse comparisons

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  4. #4
    Senior Member pos's Avatar
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    Truextent vs 2435HPL

    Hereafter is a second set of measurement, taken under very similar condition as the first one, this time comparing the 2450SL with Truextent diaphragm (2450Be) to a not aquaplassed 2435HPL (2435).

    Note: it is well known that the 2435 short phasing plug has a "problem" with the PT-F95HF that results in a dip at ~13khz (as well as very poor off axis behavior). This problem does not exists (or to a much lesser extend) on the H9800 and some other horns (the off axis behavior remains bad in the UHF tho, because of the 3 slits phase plug)

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  5. #5
    Administrator Mr. Widget's Avatar
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    Cool... any other horns on the horizon?

    Widget

  6. #6
    Senior Member pos's Avatar
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    I have pairs of 2332 and H9800 that I will also try to measure (but probably only with the Be, and not the other diaphragms anymore).
    I chose the PT waveguide as it was the most well behaved in the HF, and the most representative of the natural behavior of the driver.
    The H9800 will probably be the horn I will use in my final system.

  7. #7
    Senior Member Jan Daugaard's Avatar
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    Concerning SPL, you only state that the amp was "set to a very moderate SPL". Could you be more specific? 2nd and 3rd harmonic distortion vary greatly with SPL.

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    Senior Member pos's Avatar
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    Sorry I do not have any absolute SPL figure. All I can say is that it was equal for all drivers, so it can be used for comparison purpose.

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    Now, what conclusion can you draw from these measurements? Maybe i'm not right, but to me they seem much alike, at least until 12000 Hz. What happens above is very chaotic for each diaphragm. It would be interesting also to see how they behave from 500 to 1000. I say that because i have 2445 between 600 & 8000 and i'm flirting with the idea of putting Be diaphragms - collecting information about them .
    Best regards, jean

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    Administrator Robh3606's Avatar
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    Hello pos

    How much smoothing are you using?? Is that 1/6 octave?? I always liked the 2435 on the PTH1010, always seemed to work better than the other PT's

    Rob
    "I could be arguing in my spare time"

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    Senior Member richluvsound's Avatar
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    I look forward to seeing the Be H9800 plot ... Btw , are those ones you showed when you were here .... ?

    Have a wonderful Christmas Mr and Mrs Pos

  12. #12
    Senior Member pos's Avatar
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    Quote Originally Posted by jf65 View Post
    Now, what conclusion can you draw from these measurements? Maybe i'm not right, but to me they seem much alike, at least until 12000 Hz. What happens above is very chaotic for each diaphragm. It would be interesting also to see how they behave from 500 to 1000. I say that because i have 2445 between 600 & 8000 and i'm flirting with the idea of putting Be diaphragms - collecting information about them .
    Best regards, jean
    The Be has a ~3dB advantage in the midband compared to the Ti and Ti SL. That means it needs half the power to get as loud as the others, wich translates into less power compression and better dynamic.
    The Ti diaphragm has nasty breakup peaks around 12khz and 17khz.
    You can also look at the impulse responses (and imagine the resulting CSD). The SL is the smoothest, and certainly the most cost effective solution, but the Be sounds much better.

    With a 2445 you have an older phasing plug, so maybe you would not benefit that much of the SL or Be diaphragms?...

  13. #13
    Senior Member pos's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Hello pos

    How much smoothing are you using?? Is that 1/6 octave?? I always liked the 2435 on the PTH1010, always seemed to work better than the other PT's

    Rob
    No smoothing per se. It is a gated response, around 600Hz, so the response gets more precise as precision rises.
    One PT waveguide I would really like to try (with the 2450Be) is the square 95 one,to get a better vertical directivity control than the rectangular one!

  14. #14
    Senior Member pos's Avatar
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    Quote Originally Posted by richluvsound View Post
    I look forward to seeing the Be H9800 plot ... Btw , are those ones you showed when you were here .... ?

    Have a wonderful Christmas Mr and Mrs Pos
    Yes I will do these measurements also!
    I don't remember which measurement I showed you in London
    Merry christmas to you Rich!

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    I swore that 1audiohack did some plots with the Be 'phragm in a 2450 mounted to the Woody Horn (sort of a Yuichi A290 which is sort of a TAD TH4001 IIRC), but I haven't found it.

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