Wifi speaker series sonos play system 3 way system speaker system 21 system principle active amplifier types class d x3 digital power supply mains operation colour white front colour silver functions streaming dual speaker pairing internet radio available streaming services mog smartradio concert vault rdio stitcher siriusxm spotify juke iheartradio pandora wimp tunein allplay rhapsody deezer led displays onoff mute controllable via buttons