The M30BX is a battery powered version of the M30. The M30BX delivers the same calibrated performance as our M30 reference mic without the need for phantom power. The M30BX is an affordable reliable 30kHz reference microphone. It utilizes a very small, very accurate omnidirectional element, a carefully crafted stainless steel body and innovative circuitry to deliver flat time coherent response from 9Hz to 30kHz. The M30 has become the defacto standard reference for Smaart, MLSSA, SIMM and TEF. The M30 is the most cost effective measurement mic which you can trust. It exceeds the specified requirements for all audio band measurement systems.