Strange this. Most compliants I have seen are about the sound from apps (Sonos or Spotify) is better than TV sound with Spotify, mostly because sound from the apps will activate the surround speakers, while sound from the TV won't.

In your case what happens when you play Spotify from the Sonos app?

same things as what this guy is reporting except i have a beam (v1)

https://www.reddit.com/r/sonos/comments/dd7ut0/massive_sound_quality_difference_between_spotify/

plus a lot of others in that thread

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So I have an LG C7 connected to a Playbar (optical) which is then paired to a Sub and 2 Play One surrounds (on the other end of the room).

If I play music through Spotify on my TV, it sounds amazing, the sound is balanced pretty well between each speaker and the sub sounds great. But if I pick up my phone and start playing the same songs through the Sonos app, the quality is absolute garbage, it sounds completely drowned out, not nearly as loud despite the volume being the same and the surrounds are horrible, basically just playing the song as if they were unpaired, completely ruining the soundstage if you’re not sitting in the very center of the room.

I’ve tried changing lots of settings, tried Full and Ambient surround and it always sounds 10x better when I play anything through my TV.

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To clarify - Is it the Spotify app or Spotify via Sonos app that you are having trouble with?

point of note though don’t have surround speakers or sub just the sonos/spotify app from the phone has a much poorer quality sound and sounds  a little washed out  washed out compared to the TV via ARC and HDMI.

spotify via sonos.

Have you tried connecting via Spotify connect on Spotify app? Might work better for you