There’s a bass/treble slider in Settings/System/roomname. Scroll down to Sound, then EQ. Or tap on the volume when the room is selected and then tap the slider icons to the right of the screen. 

Do you have the loudness control set under the EQ settings? Mine was set by default and it sounded terrible - far too bass heavy.

Why can’t I reduce the bass when connected via Bluetooth? I don’t have wi-fi at home and am stuck with terrible sounding bass-heavy sound? EQ should be also available universally.

Duplicate: