I am just beginning the planning of my first home theater multipurpose room. This is an already finished basement so I’d rather not demo drywall or build walls, etc.
Definitely close off the big space near the stairs, so that the theater is symmetrical. That's the best thing you could do if you want good sound in there. A non load bearing wall is not a huge project for DIY. It will be very difficult to tame the echo timing in that space without a wall. HT is very locational, so if sound echos are travelling an extra 30-50 feet they will be very delayed in time, and that's very distracting and noticeable.
Of course you will need some sort of acoustic damping on the walls, ceiling and floor to reduce midrange echo so you can hear the dialog and melodies clearly.
An idea for large rooms with difficult bass modes is to place a single sealed sub right behind your listening position, and adjust it to the correct volume level, which will be MUCH softer than the main speakers which are much farther away. Your ears still get the correct bass SPL, but the room is not flooded with loud uncontrollable low bass pollution. While it is commonly believed that sound frequencies below 80Hz are non-localized you might need to lower the nearby sub's low pass filter frequency below 80Hz if you notice its location. Smaller sealed subs up front can bring the bass of the main speakers down below 60Hz if necessary, then the single big sub can take it down from there. If your stereo LR are big enough to make loud 50Hz by themselves then no need for front subs.
The larger the bass cone, the clearer and lower and louder it will play. You can play music very softly and still hear the bass clearly when you have large bass cones. Use sealed subs if you will listen to music. A larger sealed sub is equal to or better in every way to a smaller ported sub with same bass extension/SPL.
You will have to address the acoustic control of bass frequencies after everything else is in place and you can start measuring the acoustic response of the room, should you choose to go that far.
I would really appreciate any feedback on the best way to utilize this full basement space. I’ve laid it out here with what my plan is but I could install the projector screen on any of the other walls as well. Thanks!
Thoughts on speaker positioning and distances for both two channel listening and Atmos 7.1 theater?
The sub located close to front wall is good because it minimizes the delay of the front wall reflection. Your main speakers LR are too far out from front wall at 4+ feet. You will have lots of distracting midbass smear and other problems. LCR speakers should be as close to the front wall as possible, then room correction or EQ to make them flat FR. LCR+ front subs should be positioned or electronically delayed to affect the same distance to listener.
Since you have center channel speaker, the LR can be positioned wider. If the sidewalls are treated to prevent reflection the LR speakers can be moved closer to the walls to minimize the reflection delay as with front wall. Some people prefer some sidewall reflections for stereo listening, ymmv.
If you block the reflex ports of your LRC, then you can put them closer to walls without needing EQ, and you will get cleaner bass, better integration with subs, and less front wall reflection. Sometimes blocking the ports on hifi main speakers ruins their overall sound though, so ymmv. If you're choosing new speakers for this room, I would recommend sealed speakers for cleaner bass, better integration with subs, or even sealed in-wall speakers to minimize close wall reflections.
As you get things rolling, we'll be glad to help with acoustics, setup, etc. Good luck!!
