Best place for a Sub in my mini Theater

I have worked in a very wide/short room like yours.  Having speakers on the widest front wall lacked a lot of bass/midbass.  In my specific room (which was very close to the 10' x 20' of yours), I had the best results from putting the speakers in the corners.  It also naturally boosts the bass frequencies if it's corner loaded (of course other rooms may have different responses).

Also, agree on 2 or more subs, but it's all about budget, right?

It's actually the limitation that you have to put the viewing panel / main speakers on a long wall.  I always recommend that people use the "short wall" for placing the tv / screen / main speakers because it usually works out better acoustically in this fashion.  But this isn't always doable in certain rooms (like yours).

If you have to use the long wall for the main screen (like your room), then the subwoofer would be best in a corner for sure.  In my opinion, the main left/right speakers should be relatively close to the center channel.  I would say you could get away with putting the main speakers probably about 25% away from the corner.  The left/center/right should be close enough where they present a more "cohesive" sound.  You could always try them in the corners if you want, but you should definitely put some acoustic absorption panels within the corners to prevent standing waves in the midrange area.  In the corners of such a wide room, I would worry that you won't be able to identify direction of sound sources between the front left/right and the surround left/right, since they are so widely placed.

For surrounds, technically the left/right surrounds should be at the same height as your ears.  However, this is not always possible and can become difficult in a small room where you have one person that is closer to a surround speaker (i.e. if you're on the left, the left speaker is 2 feet away, but it's 5 feet away from the person on the right).  So you have to make some decisions and compromises on placement so that surround speakers are somewhat equalized between all audience members. 

I have a small room (at only 11 feet wide) and my surround speakers are on the side walls about 1.5 feet above listening.  It works out okay, but there is still a little imbalance even with 2 people on my loveseat. 

In your room, I would consider these positions:

1. Bookshelves mounted on stands and directed towards the listeners. (your idea).

2.  Mounted on the back ceiling about 25% into the room angled down towards the listeners.

3. Mounted on the side walls maybe about 5% into the room at listener height (as long as there are no doors blocking).  The sound would reflect off the back wall for the listeners, which is find for surrounds.

4. Mounted on the back/top of the side walls angled towards the listeners.

Options 2/3 will have the surrounds placed far away from the listeners, which should decrease the imbalance where a listener may hear the left surround more than the right surround.

I actually like your idea of putting the surrounds on stands.   This allows you to adjust the position to where you think it sounds best.

Yeah, have the surrounds be in-wall on the back wall wouldn't work too well because the left/right surrounds should really be aimed directly at the listeners.

There is an additional "rear surrounds" channel that can be process in 7.1 processors, but you don't have the room for this.  You really need space behind your couch, since the "rear surrounds" are processor ambient sound that will be reflected around on the rear side walls.  These "rear surrounds" are fine being mounted in-wall.

If you have to or want to use in-walls for your surrounds, they are definitely best on the side walls, but as you said, there is a physical block at one of the locations.

I generally don't recommend in-wall speakers because once you mount them, you cannot move them.  There are some tweaks such as changing the position or toe-in that can improve the sound.  It just depends.  If you are putting the couch right up against the back wall, then I think you will be fine if you choose to place normal tower speakers for your fronts.  Regular speakers have a benefit in that they are completely enclosed.  With in-wall, you are basically putting them into an infinite baffle loose enclosure.  Not the best, but they work.  Though, with in-wall, you generally don't have a problem with tweeter refraction on the edge of the cabinets.

Also, with in-wall speakers, you are limited to using CL rated speaker wire, which are generally the low cost version and most of them are basic stranded (even Audioquest and Kimber).  Don't know what your budget is.

Another thing is room acoustics (including bass).  Can you give me the exact room size, including the ceiling height?

http://www.audiogurus.com/learn/speakers/speaker-placement/100

I cannot see a "dipole switch" on that CP380IDC.  It would not be a dipole speaker because it only has 1 woofer and 1 tweeter. 

I have seen some "dipole in-wall" speakers, but they use small drivers that are angled into each other.  It's not going to be a true di-pole because a di-pole speaker really needs to be outside the wall in a cabinet so that the sound can reflect or "plane" directly off the wall itself.

You can look at the Silver FX di-pole surround, but it's really only dipole from 2.5khz up, since it only has one "direct firing" woofer.

The Gold FX does a better job at di-pole since it has two sets of midrange and tweeters - firing both forward and backward.  The "direct firing" woofer is find because it's very difficult for us to identify the direction/source of bass/midbass frequencies.

However, in your situation a di-pole wouldn't work because you don't have space behind your couch.  If you really wanted, the only way I see is to somehow mount a di-pole directly on the ceiling at the back of the room about 25% away from the side walls.  This way, it will reflect across the ceiling as well as the side walls.

My own preference is for direct sound on the surround speakers because it's more impactful and better resolution.  It all comes down to a personal preference.

yeah, I wouldn't build a mini wall because it can mess with acoustics. If you don't like the idea of bookshelves on stand, then I would probably mount them in the ceiling.  If you want to use the wt380idc for surrounds, I would mount them in the ceiling about 10-15% away from the side walls (or as long as it gives you some equalization between listeners).  The wt380idc is actually a pretty good one because it’s completely sealed in its own enclosure and you can tilt the tweeter a bit to direct a little more towards the listener.

Also, not laughing on your ceiling height because we all have our environment limitations.  I am actually asking for a reason:

https://amcoustics.com/tools/amroc?l=10&w=20&h=7&ft=true&r60=0.6

Based on your exact room size, it appears that you have a bass node at 56hz and a couple more at 80 and 84hz.  If you get your subs in the room and still feel you are lacking bass, then you can add some acoustic treatments to absorb the bass.  If you wanted to do this, I would call GIK Acoustics and have them make a special T55 Scopus trap (they will do this).  The traps are 24” x 24” and probably around 8-9” thick.  Cost will probably be around $240 each.  I would buy 4 and stack them in the rear floor corners.  I know it sounds like a lot ($960), but this is essentially like adding another subwoofer.  The T55 scopus will actually absorb a little at the 80-84hz area as well.

I have two huge 12” subwoofer cabinets in my room powered by a 1,000 watt amplifier.  I also have two sets of tuned membrane bass traps, one pair for 63hz and another pair for 50hz.  It wasn’t until I added the 50hz tuned membrane traps that I had a significant increase of bass in the 40 to 60 hz area!  So the size and power of the subwoofer doesn’t really matter if you have room nodes that are cancelling out the bass frequencies.

You can always do this in the future if you feel you need to.

That actually makes things more difficult, lol.

https://amcoustics.com/tools/amroc?l=10&w=25&h=7&ft=true&r60=0.6

Nodes at 45hz, 56hz, and 67hz.   Best you could probably do is get two T50 and two T70 Scopus. (or as many as you want.)