The diaphragm is attached to a coil which fits into a specially shaped magnet. When the diaphragm moves, a current is induced in the coil. The graph shows how well the microphone responds to sounds from different directions. This microphone is called cardioid because its response is heart-shaped. The ribbon microphone only has one piece of wire in the magnetic field.
Some microphones use a coil rather than a single wire.
The coil fits into a magnet which is similar to the one in the diaphragm loudspeaker. The perfect microphone would always pick up all frequencies equally well. Unfortunately none do. Different microphones are suited to different tasks. Recording engineers need to choose the right microphone - and there are hundreds to choose from.