Principles of the Way Microphones Are Made

Microphones are designed to convert the sound wave pressure changes surrounding the microphone capsule to produce a corresponding electrical signal. Technologically speaking this is referred to as a transducer. Mics as they are often named, come in a wide variety of size, shape and design. Mics can usually be classified into two types namely; dynamic and condenser microphones.

The two types of microphones have very different ways of capturing sound. For instance, the dynamic mic uses Faradays law which dictates that an electrical current is induced in a conductor when it moves within a magnetic field. In dynamic mics there are two ways in which mic conductors are arranged in a magnetic field. In the first arrangement, the conductor is wound in to a coil and placed inside a cylindrical permanent magnet ring. A cylindrical core is placed inside the coil to concentrate the magnetic fields around the coil. The upper side of the conductor coil is attached to a diaphragm made of ultra-thin aluminum or plastic. When subjected to pressure changes, the diaphragm vibrates forcing the coil to move within the magnetic field and an electrical current that corresponds to the pressure changes is induced in the conductor coil.

In the second arrangement, a ribbon is suspended freely in between two permanent magnets. The ribbon is made of lightweight material like a metallic foil. When pressure around the mic varies, the ribbon moves within the magnetic field and current is induced in the metallic ribbon and lead away by the conductors.

While the two arrangements are very different, they both use Faradays law. They are both acoustical transducers that use variation of sound intensity to produce a corresponding electrical signal. Both the ribbon and coil type of dynamic mics are readily available in the market today.

Unlike dynamic mics, the condenser type of microphone uses variation of capacitance to produce a corresponding electrical signal. The design of electrical capacitors is comprised of two metal plates placed very close to each other but without any electrical conductivity. Current can only flow across the plates if one plate is at a much higher potential than the other. The two plates in a capacitor are separated by an insulator, air or vacuum.

The capacitor used in the condenser mic design has one flexible plate and one stationery plate. The flexible plate is very sensitive and moves inwards or outwards when subjected to pressure changes. The two plates are a higher potential when the flexible plate moves away from the stationery plate and vise versa. This variation of potential corresponds to the pressure changes around the device.

The electrical charge in the capsule, the enclosure that contains both the unmoving and elastic plates, is maintained by connecting it to a DC power line. T-power and Phantom power are employed to maintain the capsule at a constant potential.

if you think about it, the Mic works like a speaker in reverse and to some extent you'd be correct. Whichever kind of microphone is used, sound waves generate electrical impulses which can end up in either a digital format if you're recording or amplified to alter the volume when put through a speaker.


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