The D 550 is a unidirectional dynamic microphone. It has been designed primarily for tough onstage use on bass instruments including kick drum, tuba, trombone, bass amps, etc. and uses a patented AKG Varimotion diaphragm. The wide frequency response of this microphone slightly emphasizes the mid and high frequencies to ensure a powerful sound. The D 550 has a cardioid polar response. This means the microphone is most sensitive to sound arriving from in front of it, less sensitive to sound arriving from the sides, and hardly responds to sound from the rear. This pickup pattern is virtually the same for all frequencies ("frequency independent"). The strong plastic housing and the wire-mesh outer grille of the D 550 protect the transducer system from damage.