Transmission Line Speakers With KEFKit Drivers. Housed in a custom Bailey transmission line enclosure, the drivers are from the KEFKIT3 that was available from 1969-78, I have seen paperwork to suggest they have updated Concerto KK3 crossovers, but I’ve not dismantled them to confirm this. These sound fantastic, and were made by my father in the 70s. I also have a box containing enough oak veneer to change the look of the speakers that can be included if required.