Surround Placement

My suggestion is to wall mount behind the Sofa to extreme left and right as much as possible. Sonos doesn’t sell “regular on-wall surrounds” driven by an Amp...whatever they are 😂. Sonos does sell In-wall speakers by Sonance.

Wall Mount Instructions for Era 100

• https://www.sonos.com/en-us/guides/era100

Wall Mount Instructions for Era 300

• https://www.sonos.com/en-us/guides/era300

Ok, if Era300 then on the back wall, upside down, and close to the ceiling?  
 

I know Sonos doesn’t sell on-wall surrounds.  That’s why I said maybe going with 3rd party surrounds with a Sonos Amp?  Maybe I should just add those for a clean install.  Would I just put 2 speakers over the sofa?
 

My apologies as I was speaking of the “on-wal surrounds” in jest. To answer your question…

Era 300’s would an excellent choice. As to whether or not you need to invert them for mounting depends upon high they need to be mounted on the wall to void interfering with seated individuals. Typically 6 feet above floor level as long as you don’t encroach upon the 2 foot recommended ceiling clearance.

The 300s are going to give you Atmos surrounds while almost every other option won't.

100s have very limited Atmos compared to the 300s and wouldn't be on my list of preferred options. I am using them here for other reasons and while they are acceptable they are a distant second choice to the 300s.

As to mounting,  make some temporary stands and try different heights and inverted.

All good, I was just commenting on the various options out there.

1. Era 300 with maybe suboptimal placement
2. Sonance in-ceiling speakers above the listening position connected to Amp
3. 3-rd party in-ceiling or on-wall connected to Amp

From a WAF perspective, option 2 is the best, followed by 3.  Era 300’s are not small and might look a bit wonky mounted over a sofa on the back wall. The basement ceiling is 8’.

The question is what is going to sound better, Era300 or Sonance?  I think your suggestion is to put the Era’s above the sofa on the back wall pointing at the screen (upside down so the Atmos drivers are down firing), right? Shown here in green.  

Would that be true if I ran Sonance in-ceiling speakers connected to an Amp and paired with the Arc Ultra? 

The Era 300’s are the only speakers that will allow Full Immersion when used with the Arc Ultra for Dolby Atmos.

Using stands as suggested by ​@Stanley_4 is OK to compare Era 100’s and Era 300’s. You can’t accurately compare in-ceiling or in-wall speakers using stands as they need to be fully enclosed for optimal performance.

I’ve the Era 300 just in the corners of the sofa (which is placed in a wall like you) more or less at the head’s level and they perform great. I turned them 20 degrees to the listener position.

In your case perhaps the wall mounted could be the best solution, but you can also try with the stands. For the corner it will fit, but the other side perhaps it’s not nice for you to see it while you enter in the living room. 

I don’t see the ceiling solution as the best option to enjoy surround…

The Amp is only two channels, no matter what it is hooked to that is all it can provide.

The 300s are multi channel Atmos speakers, check the store page to see all the details and pictures. Yes, channel is the wrong word here but it is close enough.

That is my dilemma, I don’t have all of these speakers to test with.  

The room has a back wall but only once side wall.  The other wall is not ideal as it’s where you walk and having a big speaker 6’ off the ground right there is not workable unfortunately.  

The ceiling solution is maybe not the best, but I’m starting to think it may be my only option.  When the Amp and two speakers are paired with the Arc Ultra, what audio channels go to the surrounds?  Only the left/right surround channels or do the various other Atmos channels also get sent to the surrounds?  

I agree it may not be the best but I may not have a good location for the surrounds speakers in this case :(

I agree it may not be the best but I may not have a good location for the surrounds speakers in this case.

I guess in the audio sent to the Amp, *which* two channels go to the speakers and do the rest of the channels (rear, height) still go to the Arc Ultra? 

I don't recall seeing anything about the down-mix process when using an Atmos capable front device and single channel rear ones.

One would assume that Sonos and Dolby have something in place for that, maybe search the Dolby site?

I was suggesting test mounting for the 300s, as said for many of the rest it isn't an option. There are enough 300 options that wall repairs could get expensive if you try more than one.

​@BoboBob 

No offense however I think you’re overthinking the use of Era 300’s and the Arc Ultra. There are only two options for the Era 300’s Stand or Wall mount that are recommended/supported by Sonos. If you find a 3rd option it will likely be by a 3rd party that Sonos doesn’t support.

Also, everyone in this community are volunteers. Asking questions about which channels send what and how are questions for Sonos Engineering and design. Maybe a Moderator can gleam a bit more information to your technical questions regarding channels.

Sonos has a liberal return policy. The only way to know is to do a test on a make-shit stands for Era 100 and Era 300’s then return the pair you don’t want. 

The last option is to cut holes in your wall or ceiling and use a Sonos Amp. There’s really no more information I can provide. Good luck with your project to fully enjoy Sonos.

This is what AI had to say.  I guess it’s not full Atmos surround but I don’t think I can really achieve that with my room size/config.  I think the in-ceiling speakers are going to be my best and cleanest option.  Appreciate the help.

Fair enough, thanks for your help.  Just trying to understand my options.  

The wall mounting options are what really opens a can of worms / screw-holes!

Ear level? Higher, but two feet or more below the ceiling? Closer than two feet but inverted?

A cheap sheet of strand-board will let you try all three. Most places will even rip the board to size. Add a few screws and explore with no damage.

Honestly, for this, I don’t trust AI. It’s only able to regurgitate information it finds in the internet, and a lot of that isn’t correct, often enough. 

That being said, the copied data you’ve received seems fairly accurate. I do like the final summary ;)

The bots have read our criticisms of their crappy Sonos info, and they are apparently trying harder.

Believe me, I take everything AI spits out with a grain of salt.  In fact, I’m the one that had to write my company’s AI policy with a strict caveat that nothing AI generates gets published internally or externally without documented review by a subject matter expert on the material.  AI is a useful tool but far from perfect.