In wall speaker on wall speaker series bose virtually invisible speaker system 20 stereo colour black front colour black speaker enclosures without casing removable speaker cover wall mounting possible number of tweeters 2 treble chassis 25 mm number of subwoofers 1 bass chassis 178 mm width 185 mm height 289 mm depth 89 mm weight 15 kg area of use home cinema hifi system living room installation options wall mount