ABSTRACT
Everyone knows what a microphone is-'a device which converts sound waves into electricity' would be a typical definition. The small movements of the coil in the magnetic field generate an Electromotive force (e.m.f.). This obviously depends upon the amount and velocity of coil movement, which in turn depends upon the pressure of the sound waves striking the diaphragm. The strip of aluminium ribbon is simultaneously the diaphragm and the conductor which moves in the magnetic field thus generating an e.m.f. The reader might care to sketch two equal sized cardioids, placed so that their axes intersect at the same point, and prove to his or her satisfaction that what we've said is at least plausible. However microphones in mobiles and outside broadcasts are much more prone to the problem, and even more so are those used by, for example, film crews doing documentaries and the like.
