If you have a delay with the PS4, chances are very good that you’ll have the exact same problem with the PS5 (as its the TV adding the delay). However a firmware update for the C9 will probably help on both systems.

Ok then sonos is dead for me. Im sick of waiting for updates that never come. A have a 2k€ tv and a 2k€ soundsystem and it wont work together

I cant be rhe only person in the world with this setup....

I don’t have a Playbase but on my Sonos Arc I get zero delay when connected via HDMI from my PS4 to my LG CX. I would expect the PS5 via eARC to be the same. Why not wait for both to be out and try and if not to your satisfaction then return the Arc? 
 

The LG C9 or CX OLED TV, PS5 and Sonos Arc is going to be a very common setup I would assume.

Have you tried setting the ‘Settings/Sound/Sound Out" on the C9 WebOS to ‘pass through’ on the optical port?

I tried every workaround imaginable.

I have the LG C9 (running firmware v04.80.03) but with the older PlayStation 3 (slim version) connected over HDMI and the Sonos Arc (connected to the eARC (port (HDMI-2) set to pass-through) and all A/V, including Dolby TrueHD, runs in perfect lip-sync here?

Oddly enough I starting noticing some sync issues yesterday too. I was using the built-in streaming apps. I’m using a CX instead of a C9 and have eARC enabled and have digital audio out set to Passthrough. The audio is ahead of the picture. I can compensate some with the tv sync setting on the Arc but struggling to get it just right. 
 

I thought eARC was supposed to eliminate sync issues?

Yes, lip-sync should be eliminated according to this comparison chart (attached) which I found online, but the Sonos Arc can only play the audio when it receives it from the LG TV.  

The LG CX model is relatively new so maybe a firmware update will resolve the matter, but note the LG TV’s have their own Lip-sync features available too, as mentioned in this link:

https://www.lg.com/us/support/help-library/lg-tv-av-sync-adjustment-CT10000018-1387832191561

I’ve seen other lip-sync matters reported with the LG CX TV - one example with another brand of sound-bar is mentioned here:

https://www.avforums.com/threads/audio-delay-with-lg-cx.2283114/

Note: the eARC pass-through option on the TV port will have no bearing on the in-built TV Apps.

Thanks for the response. Just to test it out I unplugged the Arc and tried the built in speaker  on the CX and oddly it was the same and had sync issues with the picture. I’m not sure what’s going on there. So I don’t think there is an issue with the eARC but I swear the audio and picture aren’t in perfect sync when people talk (although sound effects seem to be fine). Maybe I’m just losing my mind.

Try turning the LG lip-sync feature and eARC option ‘off’ then ‘on’ again and see if that corrects it for you.
 

Also check the Arc Room in ‘Settings/System’ and check/reset the ‘TV Dialog Sync’ and the ‘Group Audio Delay’ features for the Arc.

Hope that resolves the matter for you.

I would also try powering off fully (not standby) both the TV and Arc for 1 minute and see if that clears the problem.

Yea I’ll give that a try. Maybe I’m just sensitive to it because my wife can’t seem to tell any issues with the audio. 

Unplugging both devices for a few minutes and resetting the settings seems to have done the trick. Thanks for the tips. All looks good to me now.

Hi. I have an LG B9 + Sonos Arc + 2 One SL with a PlayStation 4 Pro and no sound problems, except that in many games I can't turn on 5.1 sound, for some reason there is only 2.0 choice. for Example, The Last of Us 2 is only in stereo, and I can't hear speech very well in the game — and I have to play with headphones. What could be the problem? Maybe it's because some games with DTS?

You need to set sound out on your PS4 to bitstream (Dolby). Last of Us 2 is in surround. Then you should be getting surround sound. Also make sure that the HDMI in on your B9 (under the sound settings on my CX) is set to bistream as well. You don’t need it for the PS4 but on your B9 also make sure to enable eARC and set digital audio out to Passthrough which will allow you to get full eARC benefits on future devices such as PS5.

Thanks. I have exactly these settings on my TV and PS4 . I think the whole problem is the localization of games in my country. But some of them work with localization in 5.1. I'll Try with other games that don't have localization.

When the PS5 with eARC comes out, how will that connection work? The LG OLEDs and the Arc only have one eARC HDMI port each. Would you connect the PS5 to the TV via standard HDMI and then TV-Sonos Arc via the eARC port? 

Exactly - eARC always goes to the Sonos Arc (confusing naming right there). TVs usually only have one eARC port, because that is all they should ever need.

I ordered the Sonos arc yesterday. I hope everything works...

What are your settings i have massive delay on the same setup. And now ps5 lg cx and sonos have same delay even if i use the optical ( hdmi adapter ).

Beginning to be tired with all Sonos lag problems that’s crazy you pay a lot of money to get problems i wish i could return all my Sonos stuff 

If it helps I've never had any audio delay with Playbar or arc and any devices: I have ps4, ps5, pc with multiple graphics card upgrades, switch, Xbox one and connected to lg c9 and Samsung ks8000 before that. All those devices and no lag