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Thread: Mid-Highs with 2 x 261F Differential Drivers serially connected per side

  1. #1
    Junior Member djcl.ear's Avatar
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    Mid-Highs with 2 x 261F Differential Drivers serially connected per side

    Have long being attracted to the benefits of Differential Drivers with dramatic; less inductance, bigger thermal dissipation surface, higher Xmax and less distortion and weight.

    It simply comes as a superior driver design, at least for Mid and Low frequencies, where piston speakers shine. So I am redesigning the MIDs section of my multi-amplified active crossover-ed sound system. Aiming for rather high volume (above 120 dBs) and quality sound at DIY prices, to be used mainly at big rooms or open air.

    At first, I was attracted by a later model of a 12" differential Driver, the JBL 262F.
    Now I am, instead, seriously considering utilizing the JBL 261F 10" (2 Ohms), employing 2 units per side (L+R) serially connected to present 4 Ohms to each channel of the dedicated stereo amp.

    My main starting condition is that I already have excellent bullet tweeters for the High-Frequency section... which require from the MiD drivers to go as high at the crossover point to 3.5 kHz, no less. I have long time being searching for such MID-High freq drivers, with no or few results and always come back to the admiration of the Differential Drive (DD) design.

    Obviously using a single 12" size driver for each stereo side (L+R) would be simpler to implement than building two 10" divers per side (L+R). However, that is an insignificant consideration. I very much doubt that a 12" DD driver may reach with healthy sound as high as 3.500 Hz... particularly when specifications show xover points nearing 1,8 kHz at existing JBL DD speakers (for EON, PRX or VRX lines).
    Theoretically 10" drivers would have a better chance to reach into those higher frequencies (more so if run at higher impedance -4 Ohms- setting vs their factory 2 ohms), but I have yet to find written information that indicates these components are somehow capable of achieving such Mid-High frequencies. To further assist this possibility, I am using SUBs with a xover point of 120 Hz (and could try even higher points), so the JBL 261F will have lighter demands on the low side, as compared with their usual configurations requiring them to cover the 50-to-120 Hz lower octave.

    ///That is the idea, however I have -so far- being unable to locate specific information (Specification Sheets, Thiele and Small data) about any of both; JBL 261F 10" or 262F 12" DD models, or other similar and able DDs, in case they do exist.

    Could someone point me to specification files, links for info on these components, or related DD Ideas? Will it work? If yes/not, why?
    I'll appreciate.

  2. #2
    Senior Member Ian Mackenzie's Avatar
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    If you search the www you will find an updated list of JBL TL parameters.

    The more practical and useful approach is to use the REW free download software to measure the driver response. What you will find is these drivers are optimal up to 2000 hertz after which they enter serious break up mode. The off axis response funnels down above 2000 hertz. Typically the distortion of a HF driver rises at lower frequencies.

    If you mount the driver is a proposed enclosure you can do a series of on and off axis measurements to understand the best crossover point. REW will also measure distortion.

    Your ambitions to use them for hi quality sound up to 3500 hertz are at best optimistic.
    You might look at some of JBLs smaller wave guides with one of their newer compression driver.

    If you have a look at Joseph Crowes diy audio website he has some nice compact radial horns which might fit in with your plans.

    Good luck with your project.

  3. #3
    Junior Member djcl.ear's Avatar
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    Thank you for your answer Ian. This is my third try posting this at forums where JBL knowledgeable people gather (Harman, audiosciencereview), and so far you are the first one to reply.
    Which in part answers your first point:
    Quote Originally Posted by Ian Mackenzie View Post
    If you search the www you will find an updated list of JBL TL parameters.
    Nope, nowhere to find online (not to my access, yet) info related to TL parameters about JBL 261F (or 262F).
    Again, if someone has, please share it here.

    But then, TL parameters (to my knowledge) are not so relevant for Differential Drivers since their tech is different and one could guess the models developed with those TLs won't fit...
    iex, Xmax should be near double here and won't translate.
    Furthermore, the main use of such models is for cabinet building, and in factual terms to find minimal cabinet dimensions to attain certain low freqs, which for my needs here are mostly irrelevant.
    Nevertheless, yes, I'd welcome any data and further knowledge related to those drivers.

    Quote Originally Posted by Ian Mackenzie View Post
    The more practical and useful approach is to use the REW free download software to measure the driver response. What you will find is these drivers are optimal up to 2000 hertz after which they enter serious break up mode. The off axis response funnels down above 2000 hertz.
    That is the common guessing I've found for a normal operation for 12" or even 15" regular drivers. However the same is said for Differential Driver 12inchers that run the low freq range at 2 Ohms... My configuration of 2x 10" at 4 ohms (without the low end) could stand a chance. Also I was surprised when I saw there exist 12" EV drivers that provide usable 4 kHz at rather high output, and without novel technologies.

    I welcome your advise about the REW software, to which i'll have a look. I'd love to accurately measure JBL 261F in unusual configurations. Not something I'd be able to do just like that; It is an important investment for me (4 units) plus high shipping costs. Invest and then measure? i might will have to do that


    Quote Originally Posted by Ian Mackenzie View Post
    Your ambitions to use them for hi quality sound up to 3500 hertz are at best optimistic.
    You might look at some of JBLs smaller wave guides with one of their newer compression driver.(...)
    Good luck with your project.
    Thank you.
    Yes, it does look optimistic compared with their normal usage conditions and the info available, hence the "easying" conditions I would be implementing and my search for knowledge.

    About compression drivers... Uh oh! never liked the pressurized air concept for my waves emission transducers. Grew up with them not going upper than 18 kHz (at best).
    Then my sound system is three ways already (won't add a fourth) and I'd love to cover the important 500 to 3,5 kHz range with just a good single driver.

    I apologize if I sound stubborn, long time following this tech (and having this freq gap issue), therefore my info and arguments search here.
    Thanks again for your input.

  4. #4
    Senior Member Ian Mackenzie's Avatar
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    The TL parameters will guide you on the enclosure loading.
    Otherwise look at how Jbl used this driver.

    All loudspeaker have TL parameters regardless of design. DDD is a marketing idea. There are hundreds of dual voice coil drives with published TL data.

    Btw Dayton make some good test equipment for diy constructors.

    Your idea of a 3500 crossover will work but it will be a compromise.

    Have a look at the Heil drivers now made by several pro sound driver companies such as Beyma.
    Some Heil drivers can operate from 800 hertz up.


    Otherwise you could look at a pair of 104H Jbl drivers per cabinet and a nice high sensitivity dome tweeter mounted between them.

    Jbl actually use small diameter drivers in some in some of their pro array systems above the 10 or 12 inch differential drivers. Have a look at the brochures.

    Below is a link featuring the jbl 261F.

    It’s a compact enclosure of about 1.00 cuft3 or less with low end response to about 70 hertz. The crossover is 1800 hertz and a graph of the design. You have not disclosed your end use application ie SR or domestic use so the suitability of this driver cannot be determined other than Jbl EON which is JBl entry level SR system. Drivers for SR or music amplification are not primarily designed for high quality music playback unless otherwise stated. They are designed to be robust and played very loud with distortion being an acceptable compromise. If you compare it to the 728G also a differential driver the similarities stop there.

    My suggestion is to adopt the early Jbl approach of deliberately limiting the bandwidth of this driver so you are operating it in it’s optimal range. Your measurements and listening tests will validate this approach. This is how Jbl used its pro drivers in many of the pro 43XX studio monitors and they were a great success. This type of empirical approach is quite effective providing you put the work in. Modern simulation by computers still needs real mock ups to validate the design as such simulations rely of a number of assumptions which in practice are rarely true.

    As l mentioned get an REW test rig going and start measurements. Once you be familiar with your measurements what they mean there is no turning back. But use your ears to validate your design too. It might take several mock-up ideas before you settle on design thee as t is feasible with acceptable compromises.

    Enjoy your project and keep in touch.

    Ian

    https://reconingspeakers.com/product...r-for-lsr708i/

    https://jblpro.com/products/708i


    https://jblpro.com/zh/site_elements/eon510-spec-sheet

  5. #5
    Junior Member djcl.ear's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    The TL parameters will guide you on the enclosure loading.
    Otherwise look at how Jbl used this driver.
    (...)

    Jbl actually use small diameter drivers in some in some of their pro array systems above the 10 or 12 inch differential drivers. Have a look at the brochures.

    Below is a link featuring the jbl 261F.

    Itís a compact enclosure of about 1.00 cuft3 or less with low end response to about 70 hertz. The crossover is 1800 hertz and a graph of the design. You have not disclosed your end use application ie SR or domestic use so the suitability of this driver cannot be determined other than Jbl EON which is JBl entry level SR system. Drivers for SR or music amplification are not primarily designed for high quality music playback unless otherwise stated. They are designed to be robust and played very loud with distortion being an acceptable compromise. If you compare it to the 728G also a differential driver the similarities stop there.

    My suggestion is to adopt the early Jbl approach of deliberately limiting the bandwidth of this driver so you are operating it in itís optimal range. Your measurements and listening tests will validate this approach. This is how Jbl used its pro drivers in many of the pro 43XX studio monitors and they were a great success. This type of empirical approach is quite effective providing you put the work in. Modern simulation by computers still needs real mock ups to validate the design as such simulations rely of a number of assumptions which in practice are rarely true.

    As l mentioned get an REW test rig going and start measurements. Once you be familiar with your measurements what they mean there is no turning back. But use your ears to validate your design too. It might take several mock-up ideas before you settle on design thee as t is feasible with acceptable compromises.

    Enjoy your project and keep in touch.

    Ian

    https://reconingspeakers.com/product...r-for-lsr708i/

    https://jblpro.com/products/708i

    https://jblpro.com/zh/site_elements/eon510-spec-sheet
    Thank you Ian.
    That experimental approach (to prototype and measure) is what I'd expected people would have done here with Differential Drivers...
    I am still attentive in case someone would chime in.

    The other way you mention, "look at how Jbl used this driver" is precisely what I have been doing, apart from avidly reading when any related research is published.
    On this vein, your links about the reputed LSR 708i model are spot on about my quest.
    It uses the JBL model 728G 8" driver, inside a good enclosure and with the also famed and unique D2, all of that synergisticaly producing excellent sound.

    That said it is the same driver than the LSR 308P markII uses... and after checking careful measures/reviews, in this lower cost configuration the result has troubling levels of distortion.
    (LSR 308P is the top right figure next):
    https://www.audiosciencereview.com/forum/index.php?threads/jbl-306p-mk-ii-review-studio-monitor.18505/page-10#lg=attachment102162&slide=0

    https://www.audiosciencereview.com/f...nts-png.90119/

    These findings are coincident with other reviews online for the LSRxxx MarkII line and watching the mods to the LSR306P (next link) there are obvious reasons for the failings on the lack of enclosure bracing plus the poor electronics on the active side of these monitors (no star-connected grounds, lower quality caps, etc).
    https://mapoulin.wixsite.com/audioby...active-monitor

    Then see how the VERTEC array line twins two Mid freq drivers together... probably 2250HPL early DDs, looking like my plan for 2x 261F (picture attached)

    //All that taken in account it is plain odd that every Differential Driver we have info about is crossed at the shallow 1,6-to-1,8 kHz range. Be them 15", 12", 10", 8"...
    And after observing that -at all of those models- DDs are used as Low freq drivers... one may hypothesize, that this technology inherent larger Xmax, forces the need to utilize a comparatively wide surround to allow for the wider movement that lower freqs will request from the cone, and so such (heavier, more elastic) surrounds would add distortion to the higher freq range, if demanded from the same driver...
    Note that earlier literature referred the 18" and 12" DD drivers as "Ultra Long Excursion" ones.
    http://www.cieri.net/Documenti/JBL/T...1,%20No.34.pdf
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  6. #6
    Junior Member djcl.ear's Avatar
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    Oo oh!
    Just found this JBL information source:
    http://www.cieri.net/Documenti/JBL/T...ll/jbl-pro.htm

    Containing Thiele & Small parameters for JBL 261F and for many more JBL drivers!
    Attached Images Attached Images  

  7. #7
    Senior Member Ian Mackenzie's Avatar
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    Yeah l got 31Lt tuned to 59 Hertz (per driver) but that is only a simulation. So you might be looking at 62 Lt for two drivers with Fb 59 hertz as a starting point.
    Attached Images Attached Images  

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