Troy, the "LW" in the charts stands for "listening window" and the "SP" for "sound power". The listening window measures the sound over a relatively narrow(typically 30 degrees to the left and right and 10 degrees up and down)frontal area. The sound power measurement uses many more measurements(70 is a typical number mentioned by Dr. Toole)taken at angles all around the front, back, top and bottom of the speaker(these are in an anechoic chamber and include no room reflections). This is a measure of the total acoustical energy that the speaker sends into the room, not just the frontal portion of the output.
This is significant, because contrary to some misunderstanding sometimes seen, sounds at a live performance don't reach us simply from the front, but also from sides, back, ceiling and floor(unless listening outside)in the form of reflected ambience and are important for the overall enjoyment of music. The closer that the sound power curve is to the listening window curve, the better the overall dispersion ability of the speaker in reflective listening rooms.
