How the Main Types of Microphones Work - The Basics

Introduction

Microphones come in a variety of different shapes and sizes but they also have different ways in which they convert acoustic sound into an audio signal. All microphones are transducers, they convert acoustic energy into an alternating current (AC).  

Dynamic Microphones 

Dynamic Microphones work in the opposite way to speaker cones. They are made up of a stiff diaphragm with a finely wrapped wire core. The wire is suspended precisely within a high level magnetic field. (Huber and Runstein, 2014) When the air pressure hits the diaphragm, the coil moves linear to the amount and frequency of the air pressure. This in turn causes the coil to cut across magnetic flux, caused by the permanent magnet. (Huber and Runstein, 2014) This creates an electrical signal, AC that mirrors that of the original acoustic sound wave and this is sent down the output wires.

Ribbon Microphones 

Ribbon microphones also work with electro magnetic induction. However they consist of an extremely thin strip of corrugated aluminium is suspended between two permanent magnets. When the sound pressure enters the microphone it causes the aluminium to move and this in turn induces the magnets, again replicating the acoustic wave through an AC current.

Condenser Microphones 

Condenser Microphones operate on the electrostatic principle. The capsule consists of two diaphragms a thin movable one and one fixed to the backplate. These form a condenser, an electrical device capable of holding an electric charge. (Huber and Runstein, 2014) When sound pressure is applied to a condenser the thin diaphragm moves causing the distance between the two diaphragms to fluctuate. This recreates the motion of the acoustic wave and is sent as an AC current through the output. 

Magnetic Flux - the amount of a magnetic field passing through a surface

AC - Alternating Current goes between plus and minus poles recreating the compression and rarefaction of an acoustical sound wave

References - Huber, DM Runstein, RE (2014). Modern Recording Techniques. 8th ed. Burlington: Focal Press. p110-113