Those Martin Logan speakers look awesome! I have a question.... does it only matter how far the speakers are away from you or does ceiling height and width of the room also determine your speakers SPL?
Speakers are linear, Low Frequencies (Subs, for example) are Omni-directional (just due to the length of the soundwave bouncing around the room). Though I haven't seen a cut off, proper, ever defined, I would expect that it is somewhere in the 200-300Hz range at a minimum, but maybe around 400-500Hz where soundwaves will tend to act more linear.
So the linear distance then is the main key. In a very large room with little to no boundary reinforcement you would lose 6dB with every doubling of distance. In a smaller room with boundary reinforcement, it would be -3dB for every doubling of distance.
(Any corrections to that would be welcome!)
To the second part of that question, Room dimensions will effect the movement of all soundwaves, but room volume really only effects the lowest frequencies in terms of pressurization effect. So, the reflections will change with ceiling height, distance from walls, etc... but that won't be an SPL effect... and neither would it apply to Subs as far as I know and understand.
(Again, corrections welcome!)
