What is a Differoid?
Differoid is short for Differential Cardioid. "Differential" means that the mic works on the difference in sound pressure betwen the front and rear of the mic diaphragm. Such a mic is noise cancelling, so it rejects sound at a distance (such as guitar amps or drums on stage and PA speakers). "Cardioid" means that the mic rejects sound arriving from behind the microphone, such as floor monitors.
By rejecting distant sounds and rear-arriving sounds, the Differoid provides outstanding gain-before-feedback and isolation. For more information,
click here (37.9 K pdf file).