The Core Sound Omnidirectional MI microphones are based on a pair of Matsushita (Panasonic) miniature omnidirectional electret condensor cartridges. They are electrically and mechanically modified so as to record extremely loud sounds with very low distortion, and to eliminate mechanical resonances in their bass response.

Before Core Sound's modifications, the Matsushita cartridge's frequency response is specified flat within 1 dB from less than 40 Hertz to more than 15 kiloHertz. Typically they are within 1 dB up to 20 kiloHertz and down less than 5 dB at 30 Hertz. After modification, the modified cartridges (especially the battery box version -- see below) sound better than that, typically within 1 dB from 20 to 20,000 Hertz. We match the pair to within one dB of each other. Sensitivity of the modified cartridges is approximately -66 dB (0 dB = 1 Volt per microbar). The microphones are nominally omnidirectional but their pickup pattern is modified by the absorption and reflection characteristics of surfaces close by. Their noise level is typical of 1/4-inch electret condensor microphones, approximately 30 dBA. This is comfortably below the ambient noise level just about everywhere except the quietest recording studios. The microphones have a dynamic range of over 90 dB. They are designed to operate into a nominal impedance of at least 4.7 KiloOhms.

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