The SDL 400 is a 2-way hi-fi speaker for use in stretch ceilings. The speaker is available with Bluetooth and WLAN receiver BTR / WR205 (SDL 401-M), with Bluetooth receiver and radio BTR 205 (SDL 402-M), with radio HLS 51 Basic (SDL 403-M) or as passive loudspeaker (SDL 400-S). or as a passive speaker (SDL 400-S). The SDL 400 is installed completely invisibly behind the stretch ceiling and sounds thanks to its crossover specially developed for this application, still very natural through the stretch ceiling. It is equipped with a 4" woofer and a tweeter. Despite its very flat design of only 48mm, it surprises with good bass reproduction thanks to its integrated bass reflex technology. Up to 3 more SDL 400-S can be connected to one SDL 400-M.