Good drivers, these ones. Peerless MB 55mm pleated orthodynamic dipoles, used in the TDS-5M, B&O U70, Magnat RT-10, and several others. Sound great in an open implementation. This is the 57-hole version, there are different ones with larger, less plentiful holes in the magnets, but the diaphragm is the same for all of them. High max input, nice midrange, extension is slightly lacking but overall very nice sounding in the right implementation.