Just to perhaps clarify or at least expand upon Alan's comments about early side wall reflections and the work of Dr. Toole and his colleagues, some references to his book "Sound Reproduction" might be helpful. There are numerous discussions, including graphs, which cite his research and other scientific investigations in this area over many years. Just a few relevant summaries will be quoted.
At p.161: "In the audio community,it is popular to claim that reflected sounds within small listening rooms contribute to degrade dialog intelligibility. The concept has an instinctive "rightness", and has probably been good for the acoustical materials industry. However, as with several perceptual phenomena, when they are rigorously examined, the results are not quite as expected. This is another such case".
After pointing out that the architectural acoustics field has long recognized that early reflections improve speech intelligibility, there follows at p.162: "For speech, reflections at the same level as the direct sound contribute usefully to the effective sound level, and thereby the intelligibility, up to about a 30 ms delay".
Suggestions about acoustical treatment which is actually beneficial for home listening are given at several points, but as to attempting to eliminate early side wall reflections, this was due to "...alarmist cautions about comb filtering(see Chapter 9)or degraded speech intelligibility(see Chapter 10)or masking of other reflections within recordings(Olive and Toole, 1989). When examined, none of these turned out to be problems"(p.503). Specifically, p.504: "If the loudspeakers have good off-axis performance, and especially if the customer likes to listen to stereo music, my recommendation is to leave some blank wall at the location of the first lateral reflections from the front loudspeakers. An area with a small dimension of at least 4 feet(1.2 m) centered on the reflection path is sufficient".
