Microphone

The microphone is a transducer that converts sound into electrical signals. The invention of the practical microphone was crucial to the early development of the telephone system. On 4 March 1877 Emile Berliner invented the microphone, but the first usable microphone invented by Alexander Graham Bell. Much of early development in the design of microphones was reached at Bell Laboratories.

Emile Berliner

Microphone Types

1-Dynamic Microphones

Moving Coil
When moving a conductor within the magnetic field of a magnet, is the induction of voltage and current appears at its ends. The dynamic microphone is what most resembles a speaker. It consists of a membrane or diaphragm, coupled to a coil of very thin wire, immersed in a magnetic field of a magnet fixed. The diaphragm is supported by an elastic suspension. When this set moves due to vibration of air pressure (usually caused by a sound wave) appears in a wire coil current variation similar to the mechanical movement, because whenever a conductor moves within the magnetic field generated by a magnet, there is induction of voltage and current appears at the ends of that wire.

The mass of the assembly (diaphragm + coil) and the limited elasticity of the suspension prevents very slight variations of pressure able to put it in motion. For this reason, the microphone has good sensitivity and can not faithfully reproduce the sounds of low intensity.
The ability of the microphones respond to signals of high frequencies depends on the reaction rate of the mobile system. The heavier the set, the harder it is for him to overcome the inertia and put into motion.

Ribbon Microphone

The drawback of the "hardness" of dynamic microphones led the designers to create a variation of this type of microphone. It was then discovered the ribbon microphone.
The diaphragm was replaced by a thin strip of corrugated metal - originally aluminum - which is suspended by the points within a magnetic field of a magnet. The electrical signal generated is small compared with the microphones Dynamic Moving Coil, but as the mass of the mobile unit is smaller, the ribbon microphones have low inertial condition. However, they are less robust, since the tape is stretched vertically and therefore subject to great variations in pressure, which can easily break the tape. In addition, an output transformer is needed to correct the gain and impedance of the system.
The frequency response is more "flat" compared to Dynamic Moving Coil, but ribbon microphones may have resonance peaks usually at lower frequencies.

One of the first ribbon microphones RCA PB-31

Condenser Microphone

Neumann TML 103

The condenser microphone uses a different principle for converting sound pressure variations in electrical current. In it there are two metal plates that are electrically charged, one of which acts as a diaphragm - and thus can move with the pressure variation - the other is fixed. When we place two parallel metal plates with the dielectric (insulator) between them, we have actually a capacitor. The variation of sound pressure causes the movable plate is moving, changing the space between the plates. This causes capacitance variation, generating an electric potential difference, which can be amplified to a usable value.

To increase this small voltage, a valve or a transistor can be used as preamplifiers. It is precisely why we have microphones valve or transistors. Both are nothing more than condenser microphones, with the stage preamp built into the microphone itself. It is precisely here enters the Phantom Power to power the electronic circuitry of the preamplifier and to charge the capacitor plates, polarizing them.

Condenser microphones are extremely efficient and have high sensitivity,because the metal plate, which acts as the diaphragm, is actually a plastic filmbathed in a thin layer of conductive metal - normally gold - making it very light.This also makes the reaction rate of this type of microphone is very fast, offeringbetter transient response and high frequencies. Today perhaps the most widely used microphones in various applications, since the new technology used in themanufacture of pre-amps allow exposure to sound pressure levels exceeding140 decibels.

 

Neumann. Global benchmark.

Electret

The main difference between an electret condenser microphone and it is the latter uses a permanent polarization in the plates that form the capacitor. This would avoid the need for phantom power, but for the existence of the pre-amplifier.

The advantage is that they can be built in very small sizes and therefore are more microphones used in portable recorders. One of the problems of electrets is that they lose their charge over the long term. They can also be called "Permanently-Biased Condenser".

Tascam portable recorder

Features Overload

A microphone can produce distortions to receive high levels of sound pressure. In dynamic microphones that can happen when the coil is moved out of the magnetic field of the magnet, a capacitor in the amplifier can "saturate". Distortion constants can permanently damage the diaphragm, hindering its performance. In the case of a ribbon microphone, the tape can be stretched and even torn, disabling it permanently.