I notice that Axiom rate the sensitivity of their speakers both in an anechoic chamber and in a room. The M80's are rated at 91db in anechoic and 95db in a room. Most other speaker manufacturers seem to rate the sensitivity in one situation only. My question is how do other speaker manufacturers rate their speakers, in an anechioc chamber or in a standard room?

I would imagine anechoic chambers aren't the most common thing in the world, so I'm curious about the answer as well. That was my way of saying I don't know.

Drew, if it's not stated otherwise, the sensitivity number is supposed to be anechoic.

John is right, unless stated otherwise sensitivity is supposed to be measured at 4 Pi (360 degrees) anechoic. It is common to see speakers designed to be mounted on or in walls labeled to be measured at 2 Pi though.

Axiom's in room, just gives a better idea of real world performance, but all speakers get the same sort of boost.

There is also a test called Quasi-anechoic. This refers to measuring the loudspeakers direct sound, before the 1st reflection. It is not conducted in an anechoic chamber but is meant to simulate such a test.
Hirsch-Houck Laboratories used to test loudspeakers in this fashion under late Julian Hirsch.
For those of you really interested in audio, I suggest reading the articles by Julian Hirsch & Ian G. Masters, very educational and engaging.

About Julian Hirsch

http://www.soundandvisionmag.com/wildcard/536/hirsch-in-print.html
About Ian G. Masters
http://www.hometheaterfocus.com/blogs/blog/archive/2006/11/22/100575.aspx

I wonder what type of room is required to achieve a sensitivity of 95db/w/m for the M80's. I have done some tests with an SPL meter and believe that I am getting about 91db/w/m in my room.

what tests are you doing to determine sensitivity in your room? not sure just holding the RS meter one meter from the m80's will give you what your seeking.

Drew, the exact details aren't known, of course, but for an increase of 4dB over the anechoic figure, also measured at 1 meter, the room contribution would indicate a somewhat livelier than average reverberation. A 3dB increase in-room is more typical. And of course measurements vary with frequency and meter used; for example, it can be noted that the NRC anechoic measurement for the M80s was 89.5dB.

What is the best way to determine sensitivity in a room? I am placing a spl meter one meter from the M80 and I can achieve peaks of 116db at one meter before clipping from my onkyo 875. The onkyo can put out about 300 watts into 4 ohms before clipping. From this
116db/300w/1m
113db/150w/1m
110db/75w/1m
107db/37w/1m
104db/18w/1m
101db/9w/1m
98db/4.5w/1m
95db/2.25w/1m
92db/1.25w/1m

approx. 91db/1w/1m

I know that I cannot be sure that my 875 is putting out the rated 300 watts at clipping and the output is significantly affected by the quality of the input signal but it must be close within 1db. Note that 116db is best case scenario with the best quality input source I could find.
If the M80's produced 95db/1w/1m in my room then:
95db/1w/1m
98db/2w/1m
101db/4w/1m
104db/8w/1m
107db/16w/1m
110db/32w/1m
113db/64w/1m
116db/128w/1m

This means that my 875 would be putting out 128w into 4 ohms before clipping. I don't think this would be correct as the 875 is rated at 140w into 8 ohms. My 875 is set to an impedance of 6-16 ohms to avoid any current limiting. When the 875 is set to 4 ohms I can hear a signficant reduction in output due to the current limiting.

So many variables, Drew. What is "clipping"; what frequency or frequencies were used for the measurements(typically an average of the midrange from about 300-3000Hz is used); what was the sound source; what was the actual impedance of the M80s for the measurements(note that the M80s aren't 4ohm speakers over most of their range, just in the bass)?