Originally Posted by mtnboydl
If I'm crossing the Titans at 60hz, most of the nulls will be subwoofer sensitive (right?) because of the shorter wavelengths with higher frequencies. Having two subs will also smooth that out somewhat.
Your 17'9" is room width is going to result in width modes at 32Hz, 64Hz, 95Hz, 127Hz, 159Hz, 191Hz, etc. See graph below for locations of the peaks & nulls for the first 4 of those problem frequencies.
When looking at the graph, imagine the width of your couch superimposed on the middle 7 or 8 feet (or however wide your couch is). Some listeners will be sitting in loud peaks while other listeners will be sitting in deep nulls. To address length modes, the couch could be moved away from the midpoint of room length (where frequency response is worst) to a location where the peaks & dips were less intense. Can't use that approach to address width modes because the midpoint of room width (where frequency response is worst) happens to be the money seat. So have to use a different approach, one that actively cancels the width modes.
The locations of the modal peaks & nulls are fixed (which is why room modes are sometimes called standing waves), but their intensity can be changed by placing the sources of bass (subs & speakers) at null locations, which will prevent modes from resonating. IF you decide to place your 2 subs and 3 front speakers for mode cancelling, here are the nulls to place them in:
Centre the subs at 1/4 room width in from the side walls.
Centre the woofers of L/R speakers at 1/6 room width in from the side walls. Centre speaker at the midpoint of room width.
Should minimize the peaks & nulls of first 5 width modes (32Hz, 64Hz, 95Hz, 127Hz, 159Hz), resulting in smoother bass response AND greater consistency across the seating area. Again, it's free (placement doesn't cost anything). I would cross over the L/C/R speakers to the subs at 80Hz, so that the 64Hz width mode is cancelled mostly with the subs rather than the speakers.
Looks like a 150" screen at 13' is under your suggested 50deg angle, so I'll stay with 150.
IF you decide to place your L/R speakers in the above locations, they will be spread 142" apart (centre of woofer to centre of woofer). A 150" screen is 131" wide. So the speakers will end up just outside the screen. You might need to shrink the screen size by a few inches to accommodate the speaker cabinets.