Microphone was devised to intensify and amplify small sounds, making them more distinctly audible and comprehensible, thereby facilitating long distance communication. The first microphone was invented and developed to be used as a telephone voice transmitter. The word microphone is taken from two Greek words. They are micro, which means small, and phone, which means communication.
A microphone is a form of a transducer that changes sound from one form to another. It converts sound waves, existing as patterns of air pressure, into electric signals and eventually back to sound waves through speakers. There are several techniques that can be employed in constructing a microphone but the most commonly used technique is the magneto dynamic design.
In a dynamic microphone, sound waves emitted from a source cause movements in a thin metallic diaphragm and an associated coil of wire. A magnetic field is developed around the coil with the help of a magnet and as the coil moves within this field under the effect of the sound waves, it produces an electric current. The amount of current produced depends on the velocity of that motion, so it is velocity sensitive.
The dynamic microphones are of two different types, ribbon microphones and moving coil microphones. A ribbon microphone consists of a metal ribbon which is thin. And it is balanced in a magnetic field. The ribbon is connected electrically to the output of the microphone. The vibration of the ribbon within the magnetic field generates the electrical signal.
The moving coil microphone is something different. Here a small movable coil is placed inside the magnetic field. There is a diaphragm with which the coil is attached. Sounds enter there through a windscreen. And then the diaphragm is moved by the sound waves. With the vibration of the diaphragm, the coil moves and produces a current there through electromagnetic induction.
The other popular type of microphones is the condenser type. Here the diaphragm is mounted close to a rigid back plate and a battery is connected to the plate, thereby creating an electric charge between them. The amount of charge depends upon the voltage of the battery, the respective surface area of the diaphragm and the back plate, and on the distance between them. The distance between them changes in accordance with the movement of the diaphragm in response to the sound.
The sensitivity of a microphone depends on how much electric output is produced by a given sound. Any microphone will produce distortion. If it is overdriven by loud sounds such sustained overdriving can have the effect of causing permanent distortion of the diaphragm. This affects the performance and quality of sound even at ordinary sound levels.
The distortion characteristic of the device is what determines its price, and it depends on the amount of care taken in constructing and mounting the diaphragm.
What you have read is only a very simple explanation of how a microphone works. Though this is not comprehensive information about microphones it will give you some idea about the functioning of them.
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