In wall speaker on wall speaker series bose virtually invisible speaker system 20 stereo colour black front colour black speaker enclosures removable speaker cover without casing wall mounting possible number of tweeters 2 treble chassis 25 mm number of subwoofers 1 bass chassis 178 mm width 239 mm height 333 mm depth 99 mm weight 23 kg area of use home cinema hifi system living room installation options wall mount