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

  1. #16
    Join Date
    Mar 2011
    San Diego, CA

    121a replacement for ultrabass

    This thread has hinted at car subs, for which JBL has an unbeatable reputation, but we seem to shy away from that, and not merely for the 4 ohm (usually) impedance. Please allow me to suggest the 122a, with 3" voicecoil -though obsolete/ NLA, is not rare, and is vlf champ of its era, and not so inarticulate as the 121(and fits in the same box) On that path to listenable lower bass next is 129H and 128H, and le120h, each better for music than theater... these could allow use (with possible vent length modification) and easy return if 121 shows up

  2. #17
    Senior Member
    Join Date
    Aug 2003
    La Habra, California USA
    Just checked, Speaker Repair Pros in garden grove (successor to OCS) has an aftermarket 121A kit for $145. It has the full 4" voice coil and I assume it has the proper mass ring and foam surround. IIRC, It should normally use the same 12" basket and 4" voice coil gap as the 2203A and alnico magnet assembly, or use the later ferrite version 2203H frame and magnet since the ferrite and alnico assemblies should be equivalent except for SFG enhancements.

    Seems to me that since we know we can build 2203-type clones with 2203 recone kits (if you trust the aftermarket kits) with JBL 2204 baskets, we should be able to use the 121A kit in a much more available 2204 frame assembly unless the 121A magnet assembly and circuit is vastly different. To me, it's at least a start, and by building such a unit, gives you at least a starting point for measuring how this new driver might be reasonably close to the original 121A.

    If one is going to the trouble of rebuilding the UltraBass, it should be noted that the amp module used was underpowered even for its time. IMO, leave the ulatra bass amp cosmetics there and hang or hook up a subwoofer amp of solid construction (no plate Amps please) of at least 150-200W to drive the Single UltraBass or build a matching version, source another driver and use two bass units.
    When faced with another JBL find, Good mech986 says , JBL Fan mech986 says

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