Originally Posted by 4DHD
That is not completely true. If mains are shoved into corners, the soundstage will suffer...it will be pinched.
Whenever possible, mains should have 4~5 ft to the side walls or even more to develop a wide soundstage. And the farther out from the back wall also better, as in a deep soundstage.
The exception to that being the speakers are horns, say the JBL Everest II, with its dual 15" woofers, the one closest to the wall is switched to low bass. The horns direct the mids/highs to the center of the room.
But the crawl test for the sub is the best thing to do for sub placement. Sometimes that ideal placement can be quite surprising. In the room I designed/built in my last US residence, the optimal sub placement was right where the mains were located. Something that does not happen often.
I think you are confusing first reflection points with room interaction. Yes most, if not all, speakers will sound better when away from boundaries, but that is not the room itself. That is just a first reflection point. A first reflection point can be anything. A table, book case, etc. Subs are different. The sound waves produced by subs are long enough that the room as a whole affects the frequency response depending on where it is placed relative to the seating position. This is the reason for the peaks and nulls a person experiences when walking around the room. These peaks and nulls can and often are in the magnitude of over 10dB - 15dB swings. This is the reason why it is recommended that a properly set up system have multiple subs. Multiple subs placed properly throughout the room will smooth out the frequency response across a broader area. If you've ever walked around your room with the sub running you will notice that there are spots in the room that the bass is boomy and reinforced while other spots the bass is considerably less present. Depending on the frequency, these spots will be different. Even a shift as small as a foot can make a big difference. This is an effect of the room and the placement of the sub.
You simply do not experience this with satellite speakers. Satellite speakers have a whole different set of issues, but those issues are more of first reflection points and sound treatments (absorption/diffusion panels, carpets, rugs, etc) can help with that. Your example of the horn tweeters reinforces my point. Horns are more directional than dome speakers so the first reflection points are minimized so are less affected by nearby boundaries. Frequencies produced by subs are very long and omnidirectional so small first reflection points like tables, book cases, etc. have very little effect on the response curve. With satellites, what you hear is primarily the source of the sound, meaning the speaker. Your position relative to the direct wave source will impact the frequency response more so than the room will. The room will smear or color the sound due to secondary reflections, but it won't cause huge swings in frequency response like it would with subs. This is why off axis measurements are given for satellite speakers and why those measurements are important.