Microphone Transducer Types and Design

Dynamic Microphones	Operate by electromagnetic induction to generate an output signal voltage. Electrically conductive metal is made to cut across the flux lines of a magnetic field and a current of specific magnitude and direction is generated within the metal.
Two Basic Types	Moving Coil microphones and Ribbon microphones

The Moving Coil microphone can be one of two designs, either a pressure pickup system or a pressure-gradient pickup system. This capsule design is for a pressure system mic and therefore supports an omnidirectional response pattern. Sound waves coming to the diaphragm at (A) are equal in their action on the moving coil system regardless of direction. (B) shows the moving coil (voice coil) and (C) is the permanent magnet that establishes the flux field. Not labeled in this graphic are air chambers, an important part of the design. These act as resonators and help to create a flat frequency response due to anomolies inherent in the design.

The design properties of the moving coil do not inherently provide for linearity - that is, the equal and uniform response to frequency. Without proper acoustical or mechanical damping in the design of a dynamic mic, the instantaneous velocity of the voice coil will not be uniform and will peak either near 150Hz or 1KHz depending on the design. To achieve a more uniform response a felt resistive damping ring is used to control the motion of the voice coil - it may be said therefore that the motion of the voice coil may be said to be resistance controlled.