What are MIDs and HIs in terms of frequencies?

A full range speaker should have in-room deep bass response down to
20Hz. The exact break points are arbitrary, but I would define anything
below 160Hz as bass, 160-2500Hz as mids and anything above 2500Hz
as treble. Crossovers designs are not infinite in their frequency roll off
and if you set the frequency at 80Hz then some frequencies below 80Hz
will be handled by the monitor speaker and some frequencies above
80Hz still will be handled by the subwoofer.

Here's a link to webpage that shows the frequency
range of various instruments. http://www.lanissa-marx.com/
micguide.htm#Frequency%20Chart

Yes, the low E string on the bass guitar is 41.2Hz, and the low E string on a regular guitar is 82.4Hz, assuming normal tuning.

I would generally agree with Onhwy61 about the general frequency ranges. Probably most people will have slightly differenct numbers, but I'd suspect that most would agree with those general ranges.

Regarding your question as it relates to "fullrange" speakers, the speaker will actually respond below the rated frequency for at least a few Hz, and maybe even 1/2 an octave, depending on the design. It doesn't just "cut off" abruptly, but rolls off fairly quickly. So even if the bass player tunes down a step, you'll still get his open low string pretty well. The real weakness in the low bass shows up with organ music or deep electronic synthesizer notes. To be honest, with my Lowther EX3 drivers in modded Voigt Pipes, I never feel like I'm missing anything with the music that I normally listen to. I don't use a subwoofer, and I play pop, rock, jazz and classical.

Wow, as high as 160hz into the area of bass? I wasn't aware it went that high. And all the way up to 2500 goes into the mids? Geez, can the human ear even hear the highs? WOW!