Nice setup :)
The thoughts you have made are really sensible, however it is not only the surfaces in the room that you need to think about but the placement of your Era300 and the 2 Sub.

I think you already have the placement of your Era300 under control which is probably the most important thing. The sound comes from the side and top of these speakers so they should preferably be placed around ear height and behind you (where you are positioned when watching a movie) preferably on stands free from the wall.

As for the sound panels, you can place them on any wall but not the ceiling as you want the height sound to be reflected back. However, I would initially settle for the back wall. A carpet is also a good idea as you do not want the sound to be reflected back from the floor.

Otherwise, go to Peter Pee's Youtube, he really knows SONOS.

Peter Pee

Hi Peter,

Thank you for your response. Yes I have the eras 300 on the stands. I have placed both subs on each side of the arc.

Regarding the panels and sidewalls, doesn’t the arc use the side walls to bounce right and left channels? if I put acoustic panels on the side walls, wont those panels absorbe the sound before bouncing to the listener? I will get some panels and experiment a little bit.

Cheers.

You are right about the ultra sending the sound out to the sides, but
since you also have the Era300 then the side sound is less important as the rest of your speakers fill this space and with much better sound reproduction. The Ultra is designed to be able to fill a room without Sub and surround. When Sub and Era300 are connected the ultra's effect of spreading the sound becomes less significant. However, its properties of course have a greater effect than earlier soundbars.

Why not let Trueplay take care of tuning the system, it should account for sound bouncing off bare walls? I'm no sound engineer...

I have already done Trueplay but I still hear reverberation. In fact I hear the sound “lower” that before Trueplay, I guess it might done it to cope with this. I have ordered some acoustic panels, I will try some different setups. My idea is to treat back and front walls as well as the floor with some thick rug. Also maybe the 4 corners and a little bit of the side walls in front and back to let the sound bounce on the middle of the side walls and be absorbed in the back wall and floor rug. I wonder what treatment Sonos does in the demo rooms.

YouTube videos should be good source for Sonos related demo/test room stuff

Except that the majority of videos uploaded to YouTube, no matter what format they claim to be in, are actually in stereo. I’d be testing with pretty much anything other than YouTube stuff. 

I meant searching for videos related specifically to room setup and sound deadening, not test audio tracks. Sorry for the imprecision

I don’t think this is very accurate.  Any sound coming from the side of the listening position, whether sent from the front soundbar or rear surround speaker, is going to be bouncing off the side wall.   I actually would say that having Era 300s + Arc/Arc Ultra means that even less of your side wall should be covered with sound absorbing material.

Before investing in expensive panels consider a home-made test rig. A few lengths of 2x2 or 2x4 lumber formed into a rectangle and a few thick blankets strapped to it is pretty effective in testing.

Use three 8 foot boards, cut two to 7.5 feet and the other in half. You can just nail them but adding inexpensive corner brackets will prove sturdier.

Don’t overlook the floor when dealing with a too live room, our adding some thick wool rugs made a huge difference, not just for audio but for general livability. Got a couple more similar rugs for non-audio rooms and they helped there too.

Thank you Stanley, I was actually watching some videos yesterday on som diy sound panels. I will do some for testing. I was also looking at doing some bass traps to put in the corners but maybe its an overkill.  

The key thing in sound treatment is to identify a problem before you start spending money. 

Given how flexible the Subis in placement there are few situations outside treatments are going to be needed.

Kick back, listnen, adjust and listen some more, get it as good as possible as a first step.