I have two Play 5s. Regardless if using Sonos or the Spotify app, only one of the speakers plays music at regular volume. The other one I can hear really faintly. I have reset router, reset Controller and still no difference. I checked in aetttings and the two speakers are present and show Operating in boost mode.
Best answer by buzz
If the units are a stereo pair, make sure that the L/R Balance control is set to the mid point.