It is meaningless to ask "how low it can go" without specifying some number of db that the spl has declined by, relative to the response at some reference frequency (say 1kHz).
A common way of specifying bass rolloff might be something like it is down 3db at 30Hz, relative to 1kHz, and rolls off at 12db/octave below 30Hz.
If you are asking if there is a meter that will tell you at what frequency the response is down by some number of db, the answer is undoubtedly no.
Regards,
-- Al