So I have an Arc Ultra that just arrived yesterday. It’s replaced a Beam Gen 2 and has two One SLs paired to it along with a Sub Gen 3. 
 

I found this thread after ordering the Ultra and before its arrival and was worried, so I’ve been testing it a lot over the last day. 
 

On my side, I don’t hear an issue. I’m impressed by the Arc Ultra and Atmos sounds great, as well as some 5.1 tracks I specifically tested. The surrounds on the 5.1 seemed just as full and loud as when it was paired to the Beam. 
 

Am I missing something? It is only a specific type of 5.1 mix (like DTS versus Dolby)?

Most of us have Era 100 rear speakers, but a few people said that the issue exist with some other speakers also. But I‘m not 100% sure if it‘s true or an other issue.

I had before a Beam Gen 2 and I heard the difference immediately with 5.1 content. It‘s a gigantic difference. If Sonos will not fix this issue, I will immediately install my old Beam Gen 2 (or buy other rears).

This issue exist with every 5.1 content (DTS, Dolby…) Could you test it with this official Dolby Digital Plus test files (channel ID 5.1)? Dolby 5.1 Testfiles

I would be happy for feedback. If everything works fine, the next option for me would be to downgrade my rear speakers :D

The issue is, that the arc ultra is also playing the sound of the rears. This is only when you are playing 5.1 content. Atmos works fine.

Everyone I explained this issue is able to reproduce it (if they Are also using ARC Ultra with Rears)

hi does this problem only occur after advanced Trueplay tuning?

i only tried the quick tuning with an android phone, seems okay? but i was testing with the 7.1 test clips

Trueplay doesn’t change anything in this behaviour. You need to test 5.1 clips. 7.1 and Atmos are prefect and don’t have this issue.

I can confirm that for sure DTS 5.1 does not have this problem, at least for my system. I put in my 4K of The Dark Knight and watched for some scenes that had distinct rear channel activity. Multiple times I confirmed (by rewinding frequently, with my ear against the rears and then by the soundbar) that there are distinct rear channel sounds happening only on my One SLs and not at all from the Arc Ultra itself. 

I am not sure how to run the Dolby Digital Plus test files, but I see you linked to something so I’m sure I can figure it out! If I can get it to work, I’ll test it later tonight and post my results here. 
 

​@Downsideup As I mentioned in my post, I specifically tested with 5.1 movies that don’t have Atmos. 

The issue is with Era100 & Era 300

​@Zorro88  A bit of an interesting update…

(As a reminder to anyone catching up, I have the Arc Ultra with One SLs as surrounds and a Sub Gen 3.)

I played some Dolby and DTS 5.1 test tracks on my TV.

I can unfortunately confirm that both the Dolby and DTS 5.1 official test tracks have the Ultra itself activate while the rear channels are playing, same as has been described earlier in this thread. It seems as though this issue happens across surround speakers, regardless of it being Era 300, Era 100, or Sonos One.

I’m truly not sure why I was able to identify distinct sounds on the surrounds that weren’t happening on the Ultra in The Dark Knight, but I’m willing to trust the official test tracks more than my subjective analysis. I’ll dive back in later tonight to test again with just my ears and some movie 5.1 tracks to see. I’ll update more later once I specifically test more.

​@Corry P If possible to update us on sharing this issue with the team, that would be great! I think this is clearly not by design and must be a flaw -- if the logic is that the Ultra should “help” with 5.1 rear activation, why wouldn’t that happen with the same rear channels in 7.1 or Atmos? 

For me, this Ultra was a significant investment. Could you provide acknowledgment from your team (the engineering team or whoever else is responsible for rolling out the update to fix this, specifically) that this, in fact, is an error and will be fixed at some point? An estimated timeline for a fix would be even better, of course, but at the very least, acknowledgement that this is abnormal behavior and a fix will be/is being worked on would go a long way to assuaging me (and I imagine others who are dealing with this).

Thanks in advance and thanks for your responsiveness and support thus far!

Last quick update -- I tested my system with some 5.1 content again just now. I replayed the same scene at the start of The Dark Knight (specifically the one where it zooms in slowly on the Joker standing with his mask off while the truck pulls up). I can still only hear the truck pulling up on the left rear, not from the Arc Ultra, at least until it actually pulls up on screen and then it weirdly is mainly center/right.

I watched another 5.1 mix, this time on Max, and while I only spent a few mins, the rears sounded full and distinct. There was one sound that sounded clearly in the right rear, and I did hear it softly on the right side of Arc Ultra, but it didn’t sound bad per se.

Even if the 5.1 mixes have the Arc Ultra activate, so far, it hasn’t been negatively impacting my listening experience -- I still hear distinct sounds from the rears and they are fully present.

Thanks a lot for your feedback with your Sonos One rears. Unfortnately I can‘t confirm the same with Era 100 rears. Yes, the rears are still playing some sound, but at the same time with the front. It even sounds louder there. The soundstage is moved a lot to the front with 5.1 content. It no longer feels like sitting in the middle of the sound stage, but at the very back.

Unfortunately, I sold my Sonos One a year ago and can no longer compare it with the Era 100. It seems that the 5.1 problem is less pronounced there.