X Axis - The principal or horizontal axis of a system of coordinates, points along which have a value of zero for all other coordinates.
Xmax - The maximum peak linear excursion of a driver, called Xmech as well. Also refer to Maximum Linear Excursion.
Xmech - Refer to Xmax or Maximum Linear Excursion
Xmitter - Refer to Transmitter (Tx)
Xlim - Is expressed by Eminence as the lowest of four potential failure condition measurements: spider crashing on top plate; Voice coil bottoming on back plate; Voice coil coming out of gap above core; or the physical limitation of cone.