Isn't it (for the RW-12d 24hz +/-3db?)
No, it's 24-120Hz +/-3dB. That is to say, at a given test level of output, the sub plays "flat" (i.e., with a variance of no more than +/-3dB) from 24Hz to 120Hz.
At 24Hz, the sub is down by 3dB from that test level of output - in other words, 24Hz @ -3dB. (Same thing applies to the roll-off at 120Hz.)
To list the extension figure as 24Hz +/-3dB is to imply that, at 24Hz, the sub could be down by 3dB or up by 3dB from the test level of output. AFAIK
, the latter is highly unlikely.
Whatever, it's a wash, and I like the Klipsch better with out a doubt.