The RCA BK-5B is an end-addressed directional ribbon microphone originally developed in the 1950s for high-SPL situations on movie and television sets, particular for the firing of blank-round gunshots. The BK-5B was also used in recording and broadcast studios for a variety of purposes, later becoming a very popular microphone for guitar and bass amplifiers as they can be used very close to a loud speaker and offer two high-pass filter options to tame proximity effect.