Bad room for sound?

I'm starting to address the room acoustic issue with my listening room. I just measured my listening room and the dimensions of 237" by 157" are an almost exact 3:2 ratio. Is this ratio bad for sound? I would expect bass re-enforcement at some frequency.

How can I calculate that frequency? Am i correct that the lowest resonant frequency would be one full wave length across the room (which would also be one and a half full wave lengths down the length of the room)? I think that the speed of sound is about 1140 ft/sec. The room width is about 13 ft. So 1140 ft/sec divided by 13 ft/cycle equals about 88 Hz?

Also, I have hardwood floors that are old and are fairly "springy". I can feel bass vibrations in some parts of the floor but not in others. Should I add support under the floor?

Lastly, I have a Radio Shack SPL meter and I've ordered the first three Stereophile test CD's. Will I be able to measure any bass 'hump' with these tools?

I know that some of these topics have been covered in the past. Sorry if I'm repeating dead issues. Thanks all...