Bookshelf speaker bluetooth speaker power rating 50 watt system 2 way system speaker system 20 stereo principle active frequency response 45 22000 hz amplifier type digital power supply mains operation colour black housing material mdf enclosure functions auto onoff streaming control features volume control bluetooth pairing speaker enclosure bass reflex treble chassis 25 mm tweeter material tweeter silk bassmidtone chassis 130 mm midbass d