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Thread: Acoustic (Air) Suspension

  1. #76
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    Nasties in the 123A

    Hi Zilch:

    Halfway down the page below we see some measures of the 123A. Looks like you may have been picking up baffle diffraction artifacts, compare the smooth response on the curved baffle to the nasty jaggeds from the terrible diffraction of the stock box.

    http://www.troelsgravesen.dk/JBL_L100.htm

    Also, this is a beast of a woofer and deserves a beast of a box, the L100 are painfully undersized. The driver is made with subwoofer optimized thiele smalles, but happens to avoid the most serious misbehavior up until the kHz range. It's much more efficient than most subs, with a .5 Qts (or so) and a 25Hz Fs with a 90-91dB ref. efficiency. One could easily get a lot of output with 50W in a 6 ft. sealed box.

  2. #77
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    I have noodled around with this a bit in BB6P. Clearly there is more to be investigated as to their utility beyond the original application. I believe they may run out of excursion in large closed boxes, but let's nobody take my word for that without doing the requisite modeling.

    Several DIYers have built EconoWaves with them, but nobody's done the heavy lifting with respect to optimizing the lowpass filter for that combination.

    At one point, Gordon provided insight into using them in bandpass alignments for subs. All fun stuff, and I believe 2213H, a particular favorite, may still be available new from the factory....

  3. #78
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    While the locals are pretty obsessive round these parts, the 123A also makes a superb open-baffle driver. The (relatively) high Qts and low Fs mean there's a solid amount of bass to work with, and the reasonably high xmax means you can do some EQ.

  4. #79
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    Quote Originally Posted by badman View Post
    While the locals are pretty obsessive round these parts, the 123A also makes a superb open-baffle driver. The (relatively) high Qts and low Fs mean there's a solid amount of bass to work with, and the reasonably high xmax means you can do some EQ.
    Yeah, it's too bad we haven't seen anyone run with a project like that. I've never been much of a fan of the pancake twelve but I am glad that some of you guys have found other uses for it.

    It is a part of our history.

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    I'll post some project details at a later date I suppose. It's not really a JBL project, more a project with a JBL, but certainly it's a woofer that doesn't get the love it deserves

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    I always thought that the 123a-1 did some things better than the other 12" woofers like the 122a, 126a and 128H. It just seems to transition better to an LE5 series midrange driver. The 2213H with the ceramic magnet does not sound as good as the 123a-1 to me at least. I don't think it has anything to do with the magnet material but rather a design change.

    Mike

  7. #82
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    2213 vs. 123A

    I have the AlNiCo versions of both, and the 2213 has a little higher Qes and lower Le in the examples I have. This appears to be due to a revision of the voicecoil winding, from what I can tell. The 2213H was one of the early ceramics, as far as I know, and lacks some of the features that brought the later ceramics 'up to snuff' like the SFG polepiece shaping and shorting ring. I could be wrong here, though, as I've looked for a datasheet and not found one.

    The AlNiCo 2213 is the same as the 123A-3 fwiw. I do prefer the less obstructive frame on the 123A though vs. the 2213/123A-3.

  8. #83
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    LE15A, 5.5 cubic ft., port vs closed box

    Quote Originally Posted by speakerdave View Post
    The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.

    I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.

    David
    Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):
    Attached Files Attached Files

  9. #84
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    Quote Originally Posted by Mannermusic View Post
    Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):
    Could you elaborate as to how you conducted the test?

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    "old fashioned" test gear

    Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM

  11. #86
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    Quote Originally Posted by Mannermusic View Post
    Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM
    That would explain some of the things I was seeing in the plots. Very good.

  12. #87
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    Quote Originally Posted by Mannermusic View Post
    Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM
    You know, there are some computer programs that act as a sweep generator and then record the output using a condenser mic. Some can compensate for room reverberations and they provide a nice graphical plot.

    You need a good electric condenser mic like Behringer ECM8000 from Parts Express.

    You need a preamp that supports 48 VDC phantom power and a sound card in your computer. Software should be available free on line.

    The whole process can be done in under 10 seconds using the PC. I have a similar setup. The Behringer mic is very good and cheap.

  13. #88
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    Quote Originally Posted by Zilch View Post
    Take NO prisoners!

    Two-way @ 1.2 kHz.

    [Windowed HF, cyan, bottom.]
    That looks more like a 2213 than a 123A, according to the position of the connections VS the mounting holes.

    Did the L-100 ever came with 2213s ?

  14. #89
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    Nope. What is is?

    The answer is here:

    http://www.audioheritage.org/vbullet...9&&#post132559

  15. #90
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    Quote Originally Posted by Loren42 View Post
    You know, there are some computer programs that act as a sweep generator and then record the output using a condenser mic. Some can compensate for room reverberations and they provide a nice graphical plot.

    You need a good electric condenser mic like Behringer ECM8000 from Parts Express.

    You need a preamp that supports 48 VDC phantom power and a sound card in your computer. Software should be available free on line.

    The whole process can be done in under 10 seconds using the PC. I have a similar setup. The Behringer mic is very good and cheap.
    Interesting... any programs in mind?
    I already have an Earthworks M30 microphone that I use with my RTA

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