In a Sonos home theater setup, the Era 300s can only be used as rear surround speakers with the Arc and Beam (Gen 2).

can i just use one era300

A single ERA 300 cannot be part of a surround system. A single ERA 300 can be a standalone “Room” or “Bonded” with another ERA 300 to form a stereo pair.

What’s with these Sonos era 300 speakers ?
I swapped my one sl speakers for these paired with my arc and sub mini ,

they sound utter garbage for music through Apple Music in spatial audio..

my old sonos one speakers sound better and louder …

 the era front driver doesn’t work with music ?

and it only sounds decent watching movies … 
 

all the audio is blasting out the arc taking over and making the rears sound low in volume low in punch and generally kind of rubbish…

sort it out  what a waste of cash and un-inspiring upgrade.