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