OT: speaker frequency response - technical stuff

[JIMFOWLER@prodigy.net]

this is a basic issue but one to which i never found 
an answer so here goes: could somebody please discuss 
frequency response regarding speakers? for example, 
low E on a bass is about 41Hz right? so the 
fundamental will be that same measurement, right? why 
or how is it that i see plenty of bass cabs rated 50Hz-
XkHz? doesn't speaker X need to be rated at least as 
low as the fundamental of the lowest note produced on 
instrument Y?

just some clarification, if you would...

thanks.

-jim