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Thread: One Project Derailed == Another Given Life...

  1. #1
    Senior Member GordonW's Avatar
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    One Project Derailed == Another Given Life...

    Well, I still hadn't gotten around to building my long-anticipated S70 Alpha cabinets. And, a guy who I've worked with before (in fact, the guy who bought the mondo center channel speaker with the 2022, 2410 and 2404, for) was asking me, if I could find ANOTHER pair of L100 Centurys for him (I found him a pair for the rear of the HT which the 2022/2410 et al, center channel is in)...

    Well, I was on my trip home to see the parents for Christmas. Stopped off for the evening at an old friend's home, near Albany GA. It was before the stores closed around there, so we went out to roam about the thrift stores, pawn shops and such. Sooo... in one of the pawn shops, was this pair of BRAND NEW, UNUSED walnut-veneer cabinets, made for 12" 3-way speakers. Uncannily similar construction to JBL cabinets- I'd swear, that the same cabinet shop had built them, that built most of the JBL consumer speakers of the 1970s! These were cut, painted, veneered, and ready for speakers/terminals/crossovers to be bolted in! And despite being "brand new", I got 'em for $45 for the pair (they had been sitting for a while, they just wanted out from under what they had in 'em)!

    Now, the nice things:

    1. They're a bit BIGGER than a standard L100, mostly in height (29" tall as opposed to 24") and depth (nearly 14" as opposed to just over 12")- 2.4 cubic feet, as opposed to just under 1.6 cubic feet for a stock Century. And, the port is 4" diameter, which should help the 123A reach its full potential (the stock 3" port, according to most box building programs I run it on, is too small in diameter to avoid "chuffing" and output compression at extreme excursion at extreme low frequencies, ie, it will lose low bass if pushed hard).

    2. The mids and tweeters are ALIGNED VERTICALLY... as in the tweeter is DIRECTLY ABOVE the midrange. The mid and tweeter are offset from the cabinet centerline horizontally, which should help them not have such a pronounced "baffle ripple".

    3. The cabinets are MIRROR IMAGED, believe it or not. YES!

    Well, I decided that the woofers and mids I had saved up for the S70 Alphas, being the same drivers as the L100, would be quite OK to be "borrowed" for this project... I can always find more 123As and LE5-2s later, for the S70s, once I get somewhere on some cabinets for them. That, plus a pair of whatever LE25/LE25-2/LE25-6 tweeters I whip up, and it should be good to go.

    Got some midrange enclosures whipped up, and bonded in, the port lengths set, and the holes drilled for all the drivers. All I gotta do, is finish drilling and mounting the jack plate panel on the rears, and assemble the crossover/L-pad boards to be mounted in the front of the cabinet, then put the drivers in!

    It'll be interesting to see how this sounds- the 123A, while not optimum in 2.4 cubic feet, is FAR better behaved, at least on paper, in that cabinet than it is in the 1.6 cubic foot stock cabinet. On-paper F3 lowered from about 42 Hz, to about 36 Hz. I'm guessing this thing should THROW DOWN on the bottom end, while still having the "mondo punch" we all know from the stock L100.

    I'll try to get some pics once its finished... I'll be carrying them to work, where the digital camera is, to audition them on some SERIOUS electronics. My guess, is that it'll have the same tonal character as the L100, but with smoother bass and better imaging. Could be pretty impressive...

    Regards,
    Gordon.

  2. #2
    Dis Member mikebake's Avatar
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    THAT is really weird to run across. It would help me sleep better to know what the hell the story/history is with those cabs!!

  3. #3
    Senior Member GordonW's Avatar
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    Update

    Well, got the beasties put together.

    First impressions, in my house, running off of my old HK Award A300 integrated amp: Pretty darn decent imaging, if a little "thin" sounding in the lower midbass. Adjusted the port tuning (shortened the port from about 9.5" to about 8.5") and it helped greatly. Wound up with the midrange L-pad turned down probably at least 3 dB below "flat", but it really seemed to "come together". Very efficient... was capable of making the floor vibrate readily, on 15w/ch!

    Next, I carried them into work, and hooked them up in our Vintage/Used Equipment room. Now, they're running from a Marantz MA560 integrated amp (solid state, rated at 30w/ch, but very beefy). DAYYYUM!!! :shock: OMG! MASSIVE BASS IMPACT! I've never heard an L100 with THIS kind of sheer WALLOP on the low end. It's still punchy and "quick" like a stock L100, but BOY, does have POWER in the 35-70 Hz range! I mean, on 30w/ch, it'll make your CLOTHES SHAKE! And this is ONE PAIR of speakers, not the THREE PAIRS it took for stock L100s to do this (remember the "Creative Misuse of JBL Products" thread? ) !

    I really think the larger 4" diameter port is helping a great deal here, over the stock 3" diameter port, which according to most box-building programs, is a bit too small in area for the 123A-1 woofer. Fortunately, with a 2.4 cubic foot enclosure, getting port tuning is reasonable with the 4" port, whereas with the stock 1.6 cubic foot L100 box, a 4" port would be like, a foot-and-a-quarter long... talk about eating up cabinet volume! But, in the 2.4 cubic foot box, the 4" port has NO effective "power compression" effects at high volume- MUCH better "port coupling" to the air, seemingly, at high output levels.

    And the nice thing, is that the bass sounds "tighter" too. More definition of quick bass transients...

    I did wind up turning the midranges up to a more "normal" level with the Marantz amp... probably like -2.5 dB from "flat" referenced to the stock L100 "straight up on the pot" setting, with the tweeter at like -1. Pretty darn impressive imaging, too... images outside the boxes a bit! Not quite like the best in the imaging department I've heard (Vandersteens, Tannoy D700s, etc), but pretty impressive for 30 year old drivers!

    Overall, I'm pretty darn happy with the outcome...

    Regards,
    Gordon.

  4. #4
    RIP 2011 Zilch's Avatar
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    Call 'em "L100 Plus," we want pics, of course.

    Now you gotta build the Isobaric 4 x 123A sub to go with....

  5. #5
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    im good for a few tix.......

    how much are the raffle tix for THESE??????? lol

  6. #6
    Regis
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    Very nice write-up on these mystery cabs! I'm impressed with the description of the low end on these speakers. It's amazing what a 12" woofer can do if it's done right. They will reach down to sub 30hz (note; this is a subjective opinion!). Good score at the pawn shop, those cabs were waiting just for you !

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