Late Production L100A and the 123A-3

[Wagner]

Hi to all.
Just acquired a pair of these in need of a little TLC.
Pulled the woofers (123A-3)
The 123A-3 is a "negative polarity" transducer, yes?
GREEN wire was attached to the BLACK terminal at the woofer in both boxes?
This runs contrary to what I thought I understood to be the JBL unconventional convention based upon what I learned while doing my recently completed L55s (LE14A, also a "negative polarity" transducer, yet wired GREEN to RED as is usually the case; Thanks Zilch!) and other reading here.
Is this correct or someone's error from the past?
Not a lot going on with the network on this one.
Thanks! :bouncy:
Thomas

[Eaulive]

Hi to all.
Just acquired a pair of these in need of a little TLC.
Pulled the woofers (123A-3)
The 123A-3 is a "negative polarity" transducer, yes?
GREEN wire was attached to the BLACK terminal at the woofer in both boxes?
This runs contrary to what I thought I understood to be the JBL unconventional convention based upon what I learned while doing my recently completed L55s (LE14A, also a "negative polarity" transducer, yet wired GREEN to RED as is usually the case; Thanks Zilch!) and other reading here.
Is this correct or someone's error from the past?
Not a lot going on with the network on this one.
Thanks! :bouncy:
Thomas

I think they are properly wired but this subject is heavily discussed here, make a search with "l100 polarity" and you should find the answer. ;)

[pmakres1]

Thomas,

I no longer own my L100's but I think I may be able to help here.. Mine were late production L100A's, and I still have one of the owner's manuals. The wiring diagram shows the Green wire connected to the Red terminal of the woofer, and the Green/Black wire connected to the black terminal of the woofer.

I've attached a copy of the wiring diagram for you.

Hope this helps....

Pete

[Eaulive]

http://www.audioheritage.org/vbulletin/showpost.php?p=1023&postcount=4

[Wagner]

Thank you very much for taking the time to post the page from your manual.
Both L100As used the same network, so there's still the damn rub of determining proper installation without knowing which woofer you had.
Except for Zilch's comments here (and others):
http://www.audioheritage.org/vbulletin/showthread.php?t=19598&highlight=123a-1+polarity

I have read many of the threads and my head is spinning. This is the closet thing I can find that would indicate, yes, the BLACK wire goes to the RED terminal on a pair of L100As with an N100 network AND a 123A-3 woofer.

I understand the tech bulletins regarding woofer service replacements when JBL says "reverse polarity" because of the different voice coil orientations, but that only helps an idiot like me on the assumption that what was in the box in the first place was hooked up correctly, COLOR WISE :banghead:

I am also not smart enough to figure out what they want, hook up wise, with only a (2) cap network in an AC circuit. :(

I need "match marks"!

Thank you,
Thomas

[Wagner]

I guess a better way to phrase my question is:
How did the designers of the late L100A with 123A-3 woofer wish for it to behave?
As an "innie or an outie"?
Knowing that would reveal all! ;)
(and I wouldn't be here asking this question for the bizillionth time! :D)
Thank you for your patience,
Thomas

[Wagner]

The L55s are "innies".
Thomas

[Eaulive]

I guess a better way to phrase my question is:
How did the designers of the late L100A with 123A-3 woofer wish for it to behave?
As an "innie or an outie"?
Knowing that would reveal all! ;)
(and I wouldn't be here asking this question for the bizillionth time! :D)
Thank you for your patience,
Thomas

Innie or outie really does not matter, the sound waves are "AC" in nature so...
What is important is to have the correct phase between the drivers within the same enclosure, and to have the correct phase between different enclosures.

Polarity is only a convention and does not affect the individual performance of a single driver.

Since the LE5-2 and the LE20-1 are to be coupled with the 123A-1 that moves outward, it's only logical to reverse the polarity of the woofer when using a 123A-3.
In that respect I think the "cheat sheet" is wrong since I own 4 L100 (not L100A) with the 123A-1, the green wire is connected to the red terminal (+ to +) and the cone moves outward, in contradiction with the sheet. :blink:

[badman]

This isn't hard. IIRC it's a positive polarity transducer, but you can easily test with a battery. hook up a AA with some scrap wire and see which direction the cone moves when you have + to + and - to -. If out, it's a positive, if in, it's a negative.

FWIW, the general consensus is that the 123A-3 is the superior transducer to 123A, with a small change in gap geometry. Rare are 2213 (NOT 2213H), which are equivalent to 123A-3. Cone kits are not interchangeable for 123A/123A-3.

Either are EXCELLENT 12"s, with powerful motors, heavy rigid cones (GREAT bass transducers), and extended flat bandwidth (heavy damping on the cone and a curvilinear profile). My best speaker by far used 123A. Shame the L100 and related speakers used such badly undersized boxes for these monster drivers, which are more at home in something like 5 cubic feet or even more.

[4313B]

Either are EXCELLENT 12"s, with powerful motors,Actually they are quite underpowered, probably the least powerful twelve JBL ever created. They were extremely popular in the L100.



While the audiophiles loathed the L100, the general public loved them and that kept JBL in business.
Unfortunately the general public now prefers Bose. :rotfl:

[Wagner]

Mine move out as per the "cheat sheet".
Thank you 4313B!
Still puzzling, the "out" "in" out" bit with the other two transducers in the box, and the network, being the same on both the "A" versions, unless there is an error or typo.

Thomas

[4313B]

Still puzzling, the "out" "in" out" bit with the other two transducers in the box, and the network, being the same on both the "A" versions, unless there is an error or typo.I'm pretty sure JBL themselves got confused about it at some point because, as some have pointed out, the documentation doesn't measure up. Couple that with reconed transducers thrown into the mix and it's all a toss up anymore. As mentioned, the battery test will reveal the polarity. I wouldn't fret over it too much. They should sound better one way or the other and that should be pretty easy to determine.

[badman]

Well, I didn't say it had the MOST powerful motor! But it's still a fairly high-powered motor. The application is different, for most home apps, I'd trade some sensitivity for more bass extension. These did a little of both- a little less magnet and a significant increase in cone weight, to give them the low Fs and high Qts. At 35Hz, it's one of the most sensitive 12"s JBL has made, at the cost of higher frequency sensitivity.

But it's a big-box, modest efficiency speaker, which is related to the heavy cone, soft suspension and accordingly high Vas. In other words, it occupies a realm somewhere between modern subs (which are generally excursion and small-box optimized), and pro woofers, made to operate with greater efficiency and at higher frequencies (not requiring deep bass).

The tradeoffs chosen work well in a home environment, but the L100 is a terrible design. The fact that it didn't sound awfully shrieky is a testament to the good balance in the 123A, as there was no low-pass filter applied. The woofer is relatively flat up into several kHz and has a well-behaved rolloff, whereas most 12"s with higher efficiency (and stronger motors) tend to have a rising response, or worse still, a nasty breakup mode.

Below is Troels Graveson's measurement of the 123A in the L100 vs. a smooth baffle. L100 is blue. Nasty diffraction artifacts. Smooth baffle is red, quite clean and very easy to work with.

http://www.troelsgravesen.dk/JBL_L100_files/wide%20baffle%20vs.%20L100.jpg

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

My own measurement of the 123A agrees with Troels (as far as trending goes- extended smooth response).

So, between the quality AlNiCo motor and overall build quality, very low loss suspension and well-damped rigid cone, and low Le (read: extended bandwidth), this transducer is, in my opinion, one of the greats.

[Wagner]

I'm pretty sure JBL themselves got confused about it at some point because, as some have pointed out, the documentation doesn't measure up. Couple that with reconed transducers thrown into the mix and it's all a toss up anymore. As mentioned, the battery test will reveal the polarity. I wouldn't fret over it too much. They should sound better one way or the other and that should be pretty easy to determine.

Thank you.
My main concern (thoughts) have been along the lines of pseudo-surround with all Vintage JBL of a common era, like the L55s with the L100As.........
.........but with this on going polarity thing, that could require a little switching of wires to sound "right"..........
AND, just to know how things were originally intended.
Thank you much for all your help and contributions.
The obvious, but, this forum is lucky to have participants like you.
Thomas

[Wagner]

http://www.audioheritage.org/vbulletin/showpost.php?p=1023&postcount=4


Thank you for the link.
Thomas

[Wagner]

Well, I didn't say it had the MOST powerful motor! But it's still a fairly high-powered motor. The application is different, for most home apps, I'd trade some sensitivity for more bass extension. These did a little of both- a little less magnet and a significant increase in cone weight, to give them the low Fs and high Qts. At 35Hz, it's one of the most sensitive 12"s JBL has made, at the cost of higher frequency sensitivity.

But it's a big-box, modest efficiency speaker, which is related to the heavy cone, soft suspension and accordingly high Vas. In other words, it occupies a realm somewhere between modern subs (which are generally excursion and small-box optimized), and pro woofers, made to operate with greater efficiency and at higher frequencies (not requiring deep bass).

The tradeoffs chosen work well in a home environment, but the L100 is a terrible design. The fact that it didn't sound awfully shrieky is a testament to the good balance in the 123A, as there was no low-pass filter applied. The woofer is relatively flat up into several kHz and has a well-behaved rolloff, whereas most 12"s with higher efficiency (and stronger motors) tend to have a rising response, or worse still, a nasty breakup mode.

Below is Troels Graveson's measurement of the 123A in the L100 vs. a smooth baffle. L100 is blue. Nasty diffraction artifacts. Smooth baffle is red, quite clean and very easy to work with.

http://www.troelsgravesen.dk/JBL_L100_files/wide%20baffle%20vs.%20L100.jpg

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

My own measurement of the 123A agrees with Troels (as far as trending goes- extended smooth response).

So, between the quality AlNiCo motor and overall build quality, very low loss suspension and well-damped rigid cone, and low Le (read: extended bandwidth), this transducer is, in my opinion, one of the greats.


Hi-jack extraordinaire! Complete with charts and graphs! :bouncy:
Did you even read the question?
Interesting stuff (seriously; although I think anyone with a computer connected to the internet and a pair of L100s knows "Troels" as well as you do. I've swapped a few emails with him myself. Nice and helpful fellow); but sadly having little if anything to do with my question.
And thanks for the battery tip. I'll make sure to put that one in the "Master's of the Obvious" file. :D ;)
Regards,
Thomas