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Thread: slant plate lenses

  1. #1
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    slant plate lenses

    I am again rebuilding my assembly of drivers with the aim of reducing the size as much as possible. I am using two of the 'Audio article' subwoofers per side to 200Hz, crossing over to a 10" and then 375 with slant plates at 800Hz and finally to the bullet. My question is, how much baffle is needed for the small lens plate (ie the one on the JBL commercial monitors). Can the baffle end exactly at the edge and above/below the slant plate?? Or does the baffling have to extend to some degree to allow for the proper performance of the lens? On a similar note, is there a 'best' place for putting the tweeter and 10" midrange vis a vis the 375 horn? I note that JBL uses the tweeter and horn driver side by side (3434) and the midrange below, but in the 3450 has the tweeter above and the 10" (12"?) midrange on the side of horn above woofers. What, in view of horizontal dispersion is most desirable? which is acceptable? which is not acceptable?
    Wheww

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    Administrator Robh3606's Avatar
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    "My question is, how much baffle is needed for the small lens plate (ie the one on the JBL commercial monitors)."

    Take a look here for the recomendation. Looks to be 12X12

    http://www.lansingheritage.org/image...lens/page3.jpg


    On a similar note, is there a 'best' place for putting the tweeter and 10" midrange vis a vis the 375 horn?

    I like Vertical arrays but obvoiusly Horizontal works fine too. I would do the 075 on top of the slat and the 10 below to keep the 075 close to ear height. They going on stands?? Are the subs your stands?? What 10" are you using?? 2121,2122,2123,2012??

    Have Fun

    Rob
    Last edited by Robh3606; 06-13-2003 at 08:24 PM.

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    [QUOTE]Originally posted by Robh3606
    075 close to ear height. They going on stands?? Are the subs your stands?? What 10" are you using?? 2121,2122,2123,2012??

    Yes, the 075 will be within 36" to 40" which will keep the slats within ear level too. The vertical allignment _does_ make the most sense, I agree, so why did JBL, apparently, not care about the poor horizontal dispersion when mounting the 10" mid and slats side by side?
    I was hoping to use the subs/bass modules as stands but now that you mention it, possibly I'm better off to mount the vertical tweeter/slat/10" mid on it's own baffle board on an adjustable stand. Prime rational for the piecemeal construction is to make the final product movable without a crew of moving guys.
    I thought for the midrgange there was really no choice other than the 2123H..... or am I mistaken? this is, presumably, THE most important driver of any of those in the speaker. Any opinions of which ~200Hz to ~ 1 kHz driver might be the best to use?

    -regards, guenter

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    "I thought for the midrange there was really no choice other than the 2123H"

    Well Guido has a pair of 2012H's that he says are very nice.

    http://www.jblpro.com/pages/pub/components/2012h.pdf

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    Smile lots of mid choices

    Hi Guenter

    What 10" midrange do you now own ? Your woofer section is something I'm not familair with. Can you educate me about it ? Are you using passive crossovers or crossing over actively? I'd certainly keep your low-mid and hi-midrange transducers aligned - it really is important for proper imaging / though the 2311/2308 horn-lense combo is somewhat muddled in that department ( IMHO ) . These days I'm not much for tweeters - so I won't comment beyond that.

    I can't argue with the choice of the 2123 for midrange if you already have them. The models listed by RobH ( and reinforced by RobG ) are all good midrange selections. Your choice may need to be driven by availability and your actual need for driver efficiency . If you do a search for the 2122h ( within this forum ) you'll see that it's the unit of choice for mid-efficiency systems ( mid 90's ) such as the 4343 . That's what I'd try to procure if I was building a 4 way system with a 2235H ( or ME150HS) as the LF driver. The reason ? - the sensitivities are similar which helps in any passive crossover design. Also, because the 2122 has a more compliant surround ( with a lower Fs than the 2123) you can count on it going a bit lower than the 2123 which helps support your choice of a 200 hz crossover point. The 2122h is no longer sold but Giskard has access to some from JBL ( maybe they're all gone ). A 2123 with the 2245H ( 18") works - JBL did this with the 4345. I'm not sure if one can still buy the 2123h through regular channels since the 2012 has actually replaced it in the Pro world. The 2012 has a great motor/magnet system ( like a baby Altec 515 ) and perhaps it's light cone is fine for HiFi. I have some at the shop so I guess I should listen here at home to form a HiFi opinion. Maybe Guido can weigh in on this. It's published response above 1K is somewhat off-putting , but looks like it can be dealt with - with some special inductor attention. I'd love to hear the 2012 motor with a high compliance surround plus damped/laminated cone ( like a le10h cone kit ) .
    For low effiency systems ( LE - 90 db ) one can turn the le10 into a really nice midrange driver by putting it into a small sealed box. That's what I listen to right now. My system is a 2 way/3 element system with a 2440/2450sl on top ( biamped & crossed at 900 hz ) with the bass & mids handled by the le14a/le10a wired in parallel and arranged in a quasi MTM ( vertical) fashion ( horn in the middle ). Works very well . The le10 has a very nice midrange and blends( voices) well with the aquaplased 2450sl diaphragm. This gives a pretty "forward" mid system with somewhat a lagging woof / that all adds to a lot of impact, a very high resolution sound for a smaller living room ( mine is 11' by 17' ).
    The point to all this is that JBL does make quite a few, very good 10" midrange drivers ( we've left out more obscure 10 inchers - such as the 2251j which I think is unavailable to most of us).

    regards<. Earl K

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    Administrator Mr. Widget's Avatar
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    I'll chime in here with agreement on the vertical alignment scheme. In my experiments I find vertical alignment much more important to good imaging than the voice coil alignment/phasing/time alignment thing. I have no idea why JBL went from a vertical alignment in its early 4333s to the "mirror imaged" approach in later models.

    Not to bore everyone again with my current driver set up, but I am using a somewhat similar driver setup as Guenter, but with the 2202A 12" mid bass driver. I am very happy with it, but with all of this recent talk of 4343s I want to get a pair of 2121s and possibly 2123Hs and try them as well. I assume JBL went with the 2202 in the 4350/4355 for maximum SPL. Since high resolution is more important to me that maximum SPL, it may be possible that I would prefer one of these 10" drivers...

    Anyone else with experience with these various mid bass drivers?

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    "The vertical allignment _does_ make the most sense"

    A vertical alignment would fall under the "best practices" heading.

    "The 2122h is no longer sold but Giskard has access to some from JBL"

    Yes, but their price recently went up. You can buy brand new 2235H's for less...

    "I want to get a pair of 2121s"

    2122, 2123, 2012 would be better. 2121's are much more prone to break-up.

    "For low effiency systems ( LE - 90 db ) one can turn the le10 into a really nice midrange driver by putting it into a small sealed box."

    Very true. I also run the same. Nice rigid cone and a bandwidth to die for, but one has to understand that they aren't designed to make your ears bleed, which I have no interest in whatsoever anyway. The 2122H is superior in the midbass due to it's lighter cone but gives up the excellent bottom end and top end of the LE10 to gain that midrange superiority.

    "Anyone else with experience with these various mid bass drivers?"

    I prefer the 2122H for midbass. I have yet to hear a 2012H or 2020H.

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