Bookshelf speaker satellite speaker bluetooth speaker series dali zensor power rating 100 watt system 2 way system speaker system 20 stereo principle active frequency response 53 26500 hz noise level 104 db impedance 6 ohm crossover frequency 2900 hz amplifier type class d power supply mains operation colour brown front colour black cabinet surface walnut housing surface veneer vinyl housing material mdf enclosure led displays standby