MUS 493 - Dynamic Microphone - Exploded View
Video 1 - Exploded view of a dynamic microphone's transduction circuitry
How to connect a speaker for use as a microphone
Video 2 - Reversing the transduction process
A transducer is any kind of evice which converts one type of energy into another type of energy.
Transduction is the primary operating principle of power station - theremonuclear powerstations convert the energy generated by radioactive decay into heat energy, which drives turbines which generate electrical energy. Coal power stations use controlled thermal energy to move air which in turn drives similar turbines for the same process. Transducers are very important for this infrastructure, and they are also the crux of modern audio recording.
Analogue audio recording begins with transduction in the microphone. See Video 1 for a close-up animated view of the different elements in a dynamic microphone's construction which aid in the transduction process.
The theory behind transduction in the context of recording with microphones is that a magnet moving through a coil of wire creates a current. The magnet is attached to the diaphragm of the microphone, which vibrates as sound impacts it, moving the magnet back and forth inside the coil, and creating an alternating current which we know as an analogue audio signal. This variation of voltage matches the variation of air pressure in a sound pressure wave in an analogous way, hence the name.
Loudspeaker systems (as well as headphones) operate in exactly the same fashion as microphones, except in reverse. The incoming analogue audio signal creates a current through the transduction coil, which creates a fluctuating magnetic field in the pattern of the original sound, driving the magnet against the speaker cone and reproducing the sound. This system is known as a driver, but it is in essence the same circuit as that found in a microphone. However loundspeakers generally operate on much higher voltages than microphones, so it is not advisable to attempt to use a microphone as a loudspeaker. The reverse is much safer - using a moving-coil loudspeaker as a dynamic microphone is a straightforward process. Video 2 illustrates an experiment in doing just that.
Other kinds of microphones, including Condenser mics, Ribbon mics and Boundary mics operate on slightly different principles in terms of how the sound is received (E.G. The condenser generates its current based on the distance between two very thin metal plates, which requires less movement making them a relatively sensitive microphone type) but all still use the process of transduction to convert kinetic energy in a sound pressure wave into electrical energy in an analogue audio system.
Transduction Summary
- Transducers are present in many kinds of systems, E.G. Power generation as well as audio technology
- Transduction is the process of converting one kind of energy into another kind of energy
- This is achieved in a microphone by exploiting the laws of electromagnetism - where a magnet moving through a coil of metal wire will generate a current
- The transduction circuit used in a dynamic microphone is more or less identical to that used in a moving-coil loudspeaker
- The process of transduction can be safely reversed to use a loudspeaker as a microphone (however vice versa is potentially damaging to a mic)