Neumann KK 131 NI Omnidirectional Capsule for KM A or KM D (Nickel)KK capsule heads are part of the variable miniature microphone system. Together with the KM D (nx) or KM A (nx) output stages, the KK capsule heads form a complete microphone. KK 184 (nx) + KM D (nx) = KM 184 D (nx) or KK 184 (nx) + KM A (nx) = KM 184 A (nx). KK 131 is a free field equalized pressure transducer. The sensitivity in the free sound field is flat up to 20 kHz. In the diffuse sound field there is a roll off above 5 kHz.