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Thread: Imaginary Equivalent Tuning

  1. #1
    Member linear's Avatar
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    Imaginary Equivalent Tuning

    According to the “Project K2” literature, “Imaginary Equivalent Tuning” (IET) was a new concept developed by Greg Timbers for the S5500 loudspeaker. By using two LF drivers, each in its own ported enclosure with different volumes and tunings, he claimed to provide a “better balance between the high speed of Bessel tuning and the flat frequency response qualities of Butterworth tuning”. Subsequently, this technique was also used in the M9500 speaker.

    So, is “IET” really a “better mousetrap? What do you S5500 and M9500 owners think? Did Greg Timbers ever publish a “white paper” on the idea? Has anyone ever built a custom speaker with “IET”? Did “Project May” consider using “IET? I would love to see some more discussion and technical information on this idea.

    It looks like the S5500 and M9500 may be the only JBL speakers that ever used “IET”. (The current JBL S5800 seems to have its two LF drivers in a common enclosure, since the exploded view in the Technical Manual shows only one set of ports at the bottom of the cabinet.) However, I seem to vaguely remember some older JBL speakers that used something called “stagger tuning”. Could “IET” have been used previously under another name? Comments?

  2. #2
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    - There's merit in discussing the different sorts of asymmetrical tunings .
    - For Instance; I use an asymmetrical tuning that combines sealed with vented , all in an MTM setup .


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    Senior Member CONVERGENCE's Avatar
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    STUDIO MONITORS WITH SEPERATE COMPARTMENT

    This concept was also made for Japanese recording studios in the ealy 80's using a 416b ALTECLANSING WITH A 6048H DUPLEX ALTEC AND A SUPER TWEETER .They were 4 way monitors. Here is a view.


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    The staggered tuning and different enclosure volumes for the S5500 and M9500 came from necessity, the IET came from Marketing "necessity". The whole point of the thing was to get the low midpoint of a MTM system up higher by having more volume in the lower box. This plus a kick base put the horn closer to ear level, at least for the Japanese for whom the systems were developed. At that time, I felt that by having different volumes and different tunings we could spread the various enclosure and tuning resonance frequencies over a range making them less of a problem. It seemed like a good idea at the time, and it certainly works fine in those two systems. I'm not sure it actually buys anything over two enclosures of the same combined volume that are split equally other than moving the center point.

    The original K2.S9500 had two equal volume enclosures. The lower one had a partition to make it the same volume as the top box. I have always felt that this was a waste of volume which is a very important factor in woofer performance so we haven't done it again. The bessel tuning was thought up by another Engineer here at the time. The thought was to get the best possible transient response from the woofer section. The bessel tuning requires a rather small volume with an extremely low tuning. I believe those boxes were 2 cu ft tuned to 26 Hz. Although fast, the lack of output around the knee, made them expremely bass shy, subjectively.

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    Quote Originally Posted by gtimbers
    the IET came from Marketing "necessity".
    By this I assume you mean marketing to the Japanese high end consumer? or perhpas it was simply the continuing drive for differentiation in a crowded marketplace?
    Out.

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    Senior Member louped garouv's Avatar
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    WOW

    welcome Mr. Timbers.....

    Thanks for the background....

  7. #7
    RIP 2011 Zilch's Avatar
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    How gratifiying it must be to know that we're still building B380's and repairing BX63A's to run 'em here, 20+ years later.

    http://www.lansingheritage.org/html/.../1983-subs.htm

    Sorry, off topic, but I couldn't help myself....

    [Well, it IS about bass, kinda.... ]

  8. #8
    RIP 2010 scott fitlin's Avatar
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    Hello

    Welcome Mr. Timbers.
    scottyj

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    Quote Originally Posted by louped garouv
    welcome Mr. Timbers.....

    Thanks for the background....

    Yeah, look at me, not so much as a weclome or howdy-do!

    Welcome to the forum. It's a nice place to be. Lots of JBL fans here, as I'm sure you know.
    Out.

  10. #10
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    Yes Greg welcome from the Great White north, We love JBL up here as well

  11. #11
    Member DRG's Avatar
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    Quote Originally Posted by gtimbers
    The staggered tuning and different enclosure volumes for the S5500 and M9500 came from necessity, the IET came from Marketing "necessity". The whole point of the thing was to get the low midpoint of a MTM system up higher by having more volume in the lower box. This plus a kick base put the horn closer to ear level, at least for the Japanese for whom the systems were developed. At that time, I felt that by having different volumes and different tunings we could spread the various enclosure and tuning resonance frequencies over a range making them less of a problem. It seemed like a good idea at the time, and it certainly works fine in those two systems. I'm not sure it actually buys anything over two enclosures of the same combined volume that are split equally other than moving the center point.

    The original K2.S9500 had two equal volume enclosures. The lower one had a partition to make it the same volume as the top box. I have always felt that this was a waste of volume which is a very important factor in woofer performance so we haven't done it again. The bessel tuning was thought up by another Engineer here at the time. The thought was to get the best possible transient response from the woofer section. The bessel tuning requires a rather small volume with an extremely low tuning. I believe those boxes were 2 cu ft tuned to 26 Hz. Although fast, the lack of output around the knee, made them expremely bass shy, subjectively.
    Thank you.
    People who make sound their business depend on JBL for their sound.

  12. #12
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    Yes,

    - Thanks for the insight on IET.


  13. #13
    Senior Member stevem's Avatar
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    Quote Originally Posted by linear
    According to the “Project K2” literature, “Imaginary Equivalent Tuning” (IET) was a new concept developed by Greg Timbers for the S5500 loudspeaker. By using two LF drivers, each in its own ported enclosure with different volumes and tunings, he claimed to provide a “better balance between the high speed of Bessel tuning and the flat frequency response qualities of Butterworth tuning”. Subsequently, this technique was also used in the M9500 speaker.

    So, is “IET” really a “better mousetrap? What do you S5500 and M9500 owners think? Did Greg Timbers ever publish a “white paper” on the idea? Has anyone ever built a custom speaker with “IET”? Did “Project May” consider using “IET? I would love to see some more discussion and technical information on this idea.

    It looks like the S5500 and M9500 may be the only JBL speakers that ever used “IET”. (The current JBL S5800 seems to have its two LF drivers in a common enclosure, since the exploded view in the Technical Manual shows only one set of ports at the bottom of the cabinet.) However, I seem to vaguely remember some older JBL speakers that used something called “stagger tuning”. Could “IET” have been used previously under another name? Comments?
    I have built enclosures with IET tuning using a pair of 1401Nd drivers with the same tuning used for the M9500 monitor, which is 4.1 cu feet and 28Hz for the bottom box, and 2.8 cu feet and 35 Hz for the top box. I decided not to use the MTM design because I have incorporated a midrange in my design as well. One woofer is about 5 inches off the floor, and the second woofer is almost touching the first. The midrange (a 2012H) sits above this in it's own box. On top I use a 2450SL with a 2332 horn. It sounds pretty good, but I have been recently toying with the idea of dropping the mid and going with an MTM design, which would make the system very similar to the DMS-1. That monitor used a single enclosure for both woofers, which I don't think is as good as having each driver in it's own compartment. Greg's post is interesting because I can see how the larger volume raises the center of the horn to where I want it, at ear level. I think I will go with the split tuning again for this reason, and because it keeps the overall system size down.



    Hey Greg, how about convincing the powers that be at JBL to make more of their newer hi-tech drivers available to us DIYers? Who knows, maybe we might come up with something you can market!

  14. #14
    Tom Loizeaux
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    Welcome Mr. Timbers

    Greg,
    It's an honor to have you post in this Forum. It's also gratifying to know that you read this Forum from time to time. I also imagine you get some satisfaction from seeing how devoted, knowledgable and appreciative so many of us are for your efforts and the great products from JBL over the years.

    Tom

  15. #15
    JBLGUY
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    M Timbers

    Welcome Sir and always room for more JBL devotee's


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