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Thread: Best replacement for the 121a? (L212 ultrabass)

  1. #1
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    Best replacement for the 121a? (L212 ultrabass)

    Hi

    My name is Louis and I am from Denmark. I have been looking at this forum a few times before, but know i need some help.

    I bought a pair of Jbl L212, not in great condition, but they are pretty rare arround here so i couldn’t resist. My good friend Søren picked them up for me, and now they are stand-in in his livingroom.
    There’s a few things that i need to fix, mostly woodwork, new tweeters, new cloth and some other tings (i havn’t seen them yet) But i realise I have some work to do.

    But at some point in their life someone threw away the 121a from the sub and replaced ot with a K120-8. That’s pretty far from a good replacedment. But What is? I would like to go with the original 121a or Maybe a 2203, but they seem extra rare and hard to find. I will of couse keep looking. But What is a “more easy find” replacement?

    any help is apreciated.

  2. #2
    Senior Member macaroonie's Avatar
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    Welcome to the forum

    here's a pair in Italy

    https://www.subito.it/audio-video/jb...-243171728.htm

  3. #3
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    Quote Originally Posted by macaroonie View Post
    Welcome to the forum

    here's a pair in Italy

    https://www.subito.it/audio-video/jb...-243171728.htm
    Thanks

    I have seen the ad, i have hoped to find just one- idealy a 121a, which is more correct. If i buy two i would have an expensive spare.

    But thanks for your input. Hopefully those two can save a pair of 4315 somewhere ind the world.

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    The devil is in the detail

    I guess what you need, is to know what differences there are between the K120 and an 121A, and what replacement drivers from JBL that would be closer to the 121A, but not as hard to find.

    I hope someone can make a list for you, with ideas - something like:
    The 121A is very hard to find, but IS the perfect fit.
    the 2203H is easier to find, but is a little away in terms of performance/originality to the 121A
    the K120 is very easy to find but very different in terms of performance to the 121A.

    the question is, how to draw out a line of suitable replacements to the 121A, that are easier to get your hands on :/

    I suppose the idea here, is to minimize expenses as much as possible for a replacement that'll work, until the "real deal" turns up?

    A little background info:
    ----------------------------------------------------------
    As I was the one who picked up the unit (you can't really call it a pickup, when it was on the fourth floor of a small apartment complex - more like putting yourself between it and the floor and let gravity do it's thing) I can testify to the performance issues with using the K120 driver:
    That driver seems to be much harder to drive, and not as punchy in the bass as intended with this system. Even with the amp level cranked up, it is barely noticeable.

  5. #5
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    You might want to familiarize yourselves with ( & then review ) the limitations of a single B212 ( UltraBass ).

    There are multiple threads about this very subject here at LHF.

    4313B was the only long-time LHF poster who really knew much about this transducer ( so search out his thoughts on the 121H ) .

    Here's one thread as a start to get you going.

    Personally, I'd be looking at a different amp and something like a pair of Eminence Lab12's .



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    As is evident from the posters thoughts about originality, I think the goal for this project, is to keep it as close as possible to original specifications.
    So it is a question of, how close can you get to the 121A, with another driver, until a 121A gets available.

    So "improving" or "modding" the speaker/amplifier - I think that lies outside the posters original question

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    It is a nice sub Heather!
    As I mentioned in a previous post, I do not think the poster or thread-starter needs advice in terms of getting a sub, or how to get more or better sound - but more in how he can get this set back to original spec - and until that, how he can get it going with a proper JBL driver, that fits the performance of the 121A better than what has been put into it now.

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    As Santashooter wrote. This project is about keeping these speakers original, or as original as possible. So different subs or modding is not an option, or something I am interested in.

    I thank you guys for your posts, but it's not a direction i am talking.

    I am simply looking for som advice in which JBL driver i can use in the sub if i can't find a 121a or until I find it. Is it a 122a or a 126a or something else.

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    The 121H had an MMS value of @ 150 grams due to the ( extremely heavy ) 95gram mass-ring riding on top of the voice-coil former ( therefore, net MMS was about the same as a 2231/5 and was using the same powerful motor as those fifteen inchers ) but in a smaller 12" format .

    Unless one is willing to put a JBL car subwooferin that B212, there is no replacement ( made by either JBLpro or JBLhome ) that meets that heavy cone spec.

    Study JBL's ts parameters and find this out for yourself ( all the MMS values are listed ).

    Simply put, that type of driver just doesn't seem to exist in JBL's current inventory.

    Stepping back into a 2203 ( having a 100gram MMS value ) is the next best option ( & it's also NLA ).
    - JBL made a few 12" HiFi woofers with an approx 90-100 gram MMS . These all had 3" voice-coils.
    - 122a, 126H, 128H, le120H ( all use 3" voice-coils with weaker motors moving lighter cone assemblies making them more woofers > than sub-woofers )

    The le14 has a solid heavy cone with a weighty MMS ( 140grams ) figure using the same motor and 4" voice-coil as the 124 & 136 > too bad it's a 14" and won't fit without modifications to the baffle board of the B212 .


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    Hi Louis,

    Keeping it "original" means keeping it iddle or unsatisfactory, not really any better in my view.

    Whereas putting a more suitable temporary replacement driver keeps you going in a more acoustically acceptable way in the meantime (i.e. while you're chasing a ghost).

    Your search may last a long time, so Earl's ideas do make a LOT of sense. What's the difference between wanting a non suitable JBL that may also be NLA and using another brand that may "fit like a glove"? Just the JBL name on the driver? You have to help yourself also.

    I think you should reconsider the priorities: purchasing the JBL name VS an acceptably working subwoofer... Since you're in Europe there's tons of manufacturers there where you may well find a good fit even some at reasonable prices: SB Acoustics, Tymphany, Seas, Scan-Speak, etc. for example; and more expensive ones such as B&C, RCF, Faital Pro plus many others...

    All you need for a reasonable fit are driver dimensions and to try to match as close as possible the T/S parameters (a response curve would also be nice). BTW I have not seen the T/S for 121a in JBL's table though the ones for the 122A are there. Regards,

    Richard

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    Hi Earl and Richard

    Thank you for both your reply’s. I understand that the 121a is very hard to find, if possible at all. I will keep looking though - the next best thing as Earl says is the 2203 which is hard to find as well. So i can see the point in buy a cheaper and working driver that fits like a glove, and get a working sub. I Think you guys are right about that.

    If Anybody could post a link to a driver that fits i would be happy

    I can’t find a lot of info on the 121a. How long away is the 2203H. Like Earl said - it’s The Next best thing, But is it at all a good replacement when the Price is 3-400$?

    Thanks

  12. #12
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    Hi Louis,

    To me the next best thing (easier, cheaper AND finding a nice condition one) is to look elsewhere, period. I've given you many European names to look at, and hereby add Morel to my first list and 18 Sound to the second one.

    I've done driver replacement searches 4 or 5 times up to now and its a LOT of work, including software modeling of the new prospect in the present box, which I don't feel like repeating again at this time. Even more so when very little info is available on the original woofer. Sorry.

    Richard

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    Hi Louis,

    Maybe the easiest way for you, instead of trying to "duplicate" the 12" 121a driver for which you know very little, would be to approach the problem from the other end (i.e. from the box end instead of the driver end).

    Take the box as a given, measure precisely its internal dimensions re net volume and port dimensions, to figure out Vb and Fb (If need be, I may be able to help you on this in spare time).

    Then, among the brands mentioned or others, based on driver size and budget, look for a new driver that would be a technically appropriate companion for this box. In your shoes, if the box is good, this is what I would do, saving the work of making a new box.

    Naturally, this implies you know driver/box dimensions, box Vb, Fb and have access to driver/box software modeling with new woofer T/S parameters in order to run some scenarios involving the most interesting candidates.

    It's possible that you may not be faced with a large selection of 12" woofers, after important dimensions (e.g. baffle hole cutout, driver depth, etc.) and buget are considered, leaving you with less software work and easier choice!

    If the K-120 dimensions fit the box well it should be a good guide to start with. Maybe the box permits a little "cheating" on driver dimensions or on box volume (Bullock temporarily used some books in the box when Vb was a little too high for a driver. I'd rather use some wood blocks for permanent fill in such case). There are many ways to save a good box, if need be, even when driver hole cutout is a little to large. Regards,


    Richard

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    Senior Member macaroonie's Avatar
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    I could be wrong here , look into reconing the K 120 with an aftermarket 121 cone set , mass ring and all.
    Ken Haerr is your man . Upland speaker in Ca.

    http://www.uplandloudspeaker.com/

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    Quote Originally Posted by macaroonie View Post
    I could be wrong here , look into reconing the K 120 with an aftermarket 121 cone set , mass ring and all.
    Ken Haerr is your man . Upland speaker in Ca.

    http://www.uplandloudspeaker.com/
    Hi. Thanks for your reply. And Can find only one aftermarket kit - https://qsr.net.au/shop/speaker-reco...1a-recone-kit/ - i could try reconing the k120-8 with that kit. I have no idea if thats a good idea though.

    Quote Originally Posted by RMC View Post
    Hi Louis,

    Maybe the easiest way for you, instead of trying to "duplicate" the 12" 121a driver for which you know very little, would be to approach the problem from the other end (i.e. from the box end instead of the driver end).

    Take the box as a given, measure precisely its internal dimensions re net volume and port dimensions, to figure out Vb and Fb (If need be, I may be able to help you on this in spare time).

    Then, among the brands mentioned or others, based on driver size and budget, look for a new driver that would be a technically appropriate companion for this box. In your shoes, if the box is good, this is what I would do, saving the work of making a new box.

    Naturally, this implies you know driver/box dimensions, box Vb, Fb and have access to driver/box software modeling with new woofer T/S parameters in order to run some scenarios involving the most interesting candidates.

    It's possible that you may not be faced with a large selection of 12" woofers, after important dimensions (e.g. baffle hole cutout, driver depth, etc.) and buget are considered, leaving you with less software work and easier choice!

    If the K-120 dimensions fit the box well it should be a good guide to start with. Maybe the box permits a little "cheating" on driver dimensions or on box volume (Bullock temporarily used some books in the box when Vb was a little too high for a driver. I'd rather use some wood blocks for permanent fill in such case). There are many ways to save a good box, if need be, even when driver hole cutout is a little to large. Regards,


    Richard
    I Think you are on to something. Thanks. I Think i could be a costly option buying different 12” trying to find one who matches the 121a as you say - I have very little info on.

    i will look in to this option. Thanks again.

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