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Thread: Acoustic (Air) Suspension

  1. #61
    RIP 2011 Zilch's Avatar
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    http://manuals.harman.com/JBL/HOM/Te...Sigma%20ts.pdf

    We'd have to hunt up 117H-1 T/S parameters to model it, but I'd say there's no harm in continuing with your plan to try it.

    I recall Giskard recommending port closure of JBL bookshelves when incorporating into HT with subs, but I doubt he meant that to be universally applicable.

    Clearly, the T/S parameters have to fall within a prescribed range for it to operate in true acoustic suspension, but the objective here may be different, i.e., to roll off the bass response and let the sub do its job, while also improving the dynamics and power-handling by operating the woofer closed-box.

    *****

    Please report your "findings" with closing the ports of L100s here, also, so it's all in one place for interested readers.

  2. #62
    Senior Member duaneage's Avatar
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    Like the 115, 116 and 118 woofers they are probably High Qts drivers. I would add more fiberglass as well to tame the impedance peak a bit. Another more drastic way to do this is to stretch fabric across the rear of the driver. The blanket trick will lower the Qts a bit but also lower efficiency a little.

  3. #63
    Senior Member Fred Sanford's Avatar
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    We'd have to hunt up 117H-1 T/S parameters to model it, but I'd say there's no harm in continuing with your plan to try it.
    Yeah, that's been a dead end so far for me. Replacement recommended driver is 116H-3 with slight acoustic difference from the 117H-1. All I've found so far is the 116A's T/S parameters (see below).

    I recall Giskard recommending port closure of JBL bookshelves when incorporating into HT with subs, but I doubt he meant that to be universally applicable.
    Yep, and without ever testing the L46s, I don't know if there is anything to gain sonically by plugging the port (ie: taming the L100s @ 80Hz). And, seeing as they're all stacked in my giant "pile of potential" for now, I also saw that the 3" plug fit into the L110's port, and I have used them with an M&K sub as well...they sound great already, though.

    Clearly, the T/S parameters have to fall within a prescribed range for it to operate in true acoustic suspension, but the objective here may be different, i.e., to roll off the bass response and let the sub do its job, while also improving the dynamics and power-handling by operating the woofer closed-box.
    Exactly, the surround processor can be 'told' to roll off below 80Hz, but I guess I'm looking toward attempting to preserve their longevity in a situation that they were never really designed to work in (plus, seeing if there's any accompanying sonic advantage).

    Please report your "findings" with closing the ports of L100s here, also, so it's all in one place for interested readers.
    Didn't get to fire 'em up today as planned, my wife had a job fair here in our new town, and so of course she fell last night & broke her foot. We spent the night dosing her with Sam Adams Brown Lager & tweaking her resume'. I then had to drive her to & from the job fair today, so I lost my window of window-shaking opportunity. She's a trooper, I must say, so I'm not punishing her with any audio experiments today. When my new set of L100s arrive there will have to be a welcoming party, and we'll break out the port plugs then. The new ones are also supposedly original, so I can compare to the assembled-from-seven-sources L100s I already have to see if there's an audible difference. Not 100% sure yet that they're the same exact series & x-over.

    Thanks,

    je
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  4. #64
    Junior Member DaCarlson's Avatar
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    Quote Originally Posted by Rudy Kleimann View Post
    Most people who own L100's (or other AlNiCo systems like the L26 and L36) and plug the port will notice LESS bass, and will have an urge to turn up the bass before they realize what the truth is, response-wise. And, with no flopping of the cone and all the focus on the cone control afforded by the A-S design, some may want to see how much they can get out of the woofer in this "new" box. Wouldn't want to see or hear about any "long faces" when they realize it is too late, since demagnetization is only reversible by ripping the cone out to recharge the magnet. That's all I was getting at. Moldyoldy had al;ready brought up the coil burnout issue...


    It is well known that the box size was chosen for suitability as a near-field monitor. JBL figured that any bigger cabinet would knock it out of the running. How large would be tolerated sitting atop one of the two most important -and expensive- components of a studio? (cabinet crashes onto the control surface). It was also designed to emulate the sound of the old Altec/Urei duplex monitors that were the industry standard then, while sitting out in the middle of the room with no boundary reinforcement. Hence the boomy bass.

    I find it surprising that BBPRO says the 123A in the cab is a good alignment. We all know it is not just by listening to them. Sure you didn't miss on your measurements or your math? On a box that size, a little means a lot re: percentage of volume change.

    The A-S "Q" is too high, as you can see and probably hear. That is why I said the box is too small for either, really, IMHO.

    What causes the decrease in bass when the ports are plugged? Could you great some kind of passive woofer around the port to create more bass?

  5. #65
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by DaCarlson View Post
    What causes the decrease in bass when the ports are plugged? Could you great some kind of passive woofer around the port to create more bass?
    In vented alignments, port resonance is a source of bass output in the region of the system tuning. Close the port, and the burden of reproducing those frequencies shifts to the driver alone.

    See post #14:

    http://audioheritage.org/vbulletin/s...449#post123449

    In the instance of L100 and similars, there's no less bass when the port is closed, rather merely a perception of same, as the artificial peak of the original design, intended as compensation in their use as nearfield monitors wherein there is no boundary reinforcement of low frequencies, is stripped away.

    It may certainly be argued that removing the peak comprises less bass output, but from the perspective of accurate reproduction, it's only less fake "boom," and the true bass extension actually increases, as is illustrated in the simulation curves....

  6. #66
    Senior Member Don C's Avatar
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    Has anyone tried an LE14 in a sealed box?

  7. #67
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    Quote Originally Posted by Zilch View Post
    It's been a very long time since I've worked with or listened to small closed-box speakers, a design approach pioneered by "East Coast Sound" proponents of the '60's - AR, Advent, KLH, etc.. Building DIY Minis recently led me to trying that approach with JBL drivers, with good result.
    Hello Zilch,

    I have always liked sealed boxes, and although JBL is a true love I cant really suggest anything specific other than selecting one with good excursion and using low end eq and more juice to make up for some of the bass in going for a sealed over a ported box.

    I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts. But I see this as wasteful and would prefer to choose one (probably and unfortunately non-JBL) for sealed box sub bass use.

    I can thoroughly recommend the NHT 1259 + eq. in this role. I have built subs with these (well the 4 Ohm version- not available any more) and I am very pleased with the results. That is not to say I dont love the 2245 subs I have waiting in the wings. Some info:

    http://www.madisound.com/nht1259.html
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

  8. #68
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Don C View Post
    Has anyone tried an LE14 in a sealed box?
    Yes, briefly, in S99. I wasn't paying much attention to the bass, and didn't do nearfield:

    http://audioheritage.org/vbulletin/s...4311#post74311

    http://audioheritage.org/vbulletin/s...4410#post74410

    Ported, shortly thereafter:

    http://audioheritage.org/vbulletin/s...5210#post75210

    http://audioheritage.org/vbulletin/s...5790#post75790

    Not terribly helpful. Run the sims....

  9. #69
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    Quote Originally Posted by Joe Alesi View Post
    Hello Zilch,

    I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts.
    As for modifying existing drivers- here is some info and an example which shows the way:

    http://www.birotechnology.com/articles/mass.html
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

  10. #70
    Dang. Amateur speakerdave's Avatar
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    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

  11. #71
    Administrator Robh3606's Avatar
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    The main issue I see with either one sealed Le-14 or 15 is the xmax. You may very well be able to get a good in room response but you will be SPL limited and won't really be able to add any significant boost if you are not happy with the inroom response with room gain. I will model them for you and post them. I am running a pair of 121A'a now in my second system in sealed enclosures and they sound really good. With room gain they are very nice. You have to watch the SPL though. I rarely ring the bell on the mass rings but it can happen depending on content. The LE-15 would give several db SPL advantage over the 121's.

    Rob
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  12. #72
    RIP 2011 Zilch's Avatar
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    In 6 cuft Olympus, BB6P says LE15A closed-box F3 = 80.99 Hz, and F10 = 34.21 Hz. It'll handle 2.91 W down there, for 100.9 dB output.

    Vented looks like a WAY superior alignment with Fb = 27.86 Hz, F3 = 48.2 Hz, and F10 = 25.65 Hz, 15.7W, 108.3 dB output:
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    Interesting to hear that.

    Quote Originally Posted by Zilch View Post

    What's stunning is the difference in behavior of the cone. It's loose and floppy with the port open. Once you plug the port, the effect of the enclosed air "cushion" is immediately apparent in the stiffness of the suspension.

    The 122-A in my L166 seems stiff even with the port open. Did JBL try to eliminate some of the loose boom with this woofer? Dare I plug the horizon?

    Also, the 044 tweeter, has a higher extension than that in the l100, before I go ahead and re-cap this thing, should I think about giving it a new crossover?

  14. #74
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    Smile

    what tools did you use to take these measurements?

    If possible, I'd be interested in testing my L36's, a couple of advents, the system I installed in the cars, rv and a home built no name pair.

  15. #75
    RIP 2011 Zilch's Avatar
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    Me?

    CLIO.

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