The microphone (also mic or mike) is an electro-acoustic device / gear that converts sound vibration into corresponding electric impulse. Microphones are most commonly used to convert audio signals (speech or music) into electronic form for later amplification or recording purposes.
How was the microphone invented? The history of the microphone
The microphone is in fact the first “instrument” invented in the long list of the recording and playback equipment, excluding the wires themselves, of course.
The first “microphone” experiments were made in the early 19th century. The first actual microphone was made by a physics student named Emil Berliner in 1877. He sold the patent to the Bell Telephone Company. This microphone was used in early telephones but was improved to meet the needs of the newly invented radio.
The carbon microphone was invented by David Edward Hughes in 1878, but its mass production did not begin until the 1920s. Microphones were thus used in radios and telephones for which they were of sufficient quality, but the sound quality produced by the microphones for sound recording was too poor and their frequency response was uneven.
The first dynamic and capacitor microphones were developed in the 1930s. The principle of the dynamic microphone was discovered and patented by Ernst Siemens 1874. The mobile coil microphone is based on the same idea as a dynamic loudspeaker, a copper coil in a magnetic field that generates electric current from a movement. The dynamic microphone provided a clear improvement over the audio quality of the previously used carbon microphone.
The manufacture of a capacitor microphone became possible after the invention of the electron tube in the 1910s: a high-impedance amplifier was required to measure the voltage changes of the capacitor capsule, which does not load the capsule and thus discharge its electrical charge. Dynamic and capacitor microphones were incorporated into applications by major radio companies as their sound quality was significantly higher than previous microphones. In the 1970s, the FET transistor largely displaced the tube in the amplifier section of the capacitor microphone.
The piezoelectric microphone, or crystal microphone, was also commonly used in the 1930s and 1950s. Based on the piezoelectric phenomenon, this microphone was able to produce much higher voltages than the dynamic microphone, making it well suited for home use, for example. Originally, the material used for piezo microphones was salt crystals, and today various plastics and ceramic materials are used. Nowadays, the most important applications of the piezo microphone are in acoustic treadmills and ultrasonic transducers .
How Microphones Work? What are the four types of microphones?
What is a Dynamic microphone?
The dynamic microphone works in the opposite way to the dynamic speaker. At its simplest, the dynamic microphone consists of four parts: a diaphragm, an electrically conductive coil, a magnet with hubs and conductors. The coil is attached to a diaphragm that engages with the frame with flexible suspensions, similar to a speaker element. Without movement, the film will vibrate.
Then the coil attached to the membrane also moves in the magnetic field and AC voltage is induced on it. The wires carry this weak electrical signal to the amplifier, which amplifies the signal to be displayed or recorded. The dynamic microphone is by far the most common microphone and reproduces both instrumental and vocal performance under demanding conditions. Dynamic microphones are particularly popular in concert use because of their durability, quality and still good playback.
The special case of a dynamic microphone, a magnetic microphone, is based on a permanent magnet and a fixed coil. The direction of the magnetic flux in the coil is controlled by a thin steel tongue which is moved by the microphone diaphragm. The best known example of a magnetic microphone is probably the Shure “Green Bullet”, originally designed as an announcement microphone, but has become more common as a harmonica microphone.
The electric guitar microphone works on the principle of a magnetic microphone. In it, the guitar tongue regulates the magnetic flux inside the reel.
Dynamic microphones are always sensitive to external magnetic interference. To eliminate these, the highest quality microphones use a so-called humbucking coil. This coil contains the same number of turns as the microphone voice coil itself, but is connected in series with the voice coil in reverse phase, whereby the magnetic field picked up by the two coils is canceled. In the humbucker microphone of the guitars, the halves of the voice coil are connected similarly.
What is a Condenser Microphone?
The principle of a condenser microphone is more complicated than that of a dynamic microphone.
Instead of a dynamic microphone diaphragm and a coil, the capacitor microphone has a so-called capacitor consisting of a thin, thin metal film that receives sound waves and a perforated electrode.
The sound pressure causes the metal film to move farther and farther away from the electrode and through that the electric charge changes. This change produces a weak signal that is too small to be used in this way. Therefore, the microphone itself – or very close to the signal path – must have a preamplifier that amplifies the signal. The condenser microphone is the most sensitive of the microphones and picks up the highest and lowest frequencies quite easily.
For sound measurements, the condenser microphone is popular because it has a very smooth frequency response. Large-diaphragm condenser microphones are the most sensitive, but on the other hand they cannot withstand the same sound pressure as the smaller ones without permanent changes in sensitivity.
Measuring microphones typically have a sensitivity of 50 mV / Pa for large one-inch microphones, while sensitivity is typically 5 mV / Pa for small quarter-inch microphones. Small-diaphragms withstand more pressure and some impact.
The frequency response of small microphones can be extended far ultrasonic range, over 100kHz, but larger microphones usually only have a frequency response of up to 20kHz.
The most important of the special versions of the condenser microphone is probably the RF microphone. In it, changes in the capacitance of the capsule are measured at the radio frequency. The fixed frequency oscillator supplies a signal to the tuning circuit, which is capacitated by a microphone capsule which momentarily tunes the circuit to an upstream or downstream current.
The output voltage of the tuning circuit is amplified and supplied to the microphone output. The advantages of an RF microphone are low noise and moisture resistance in difficult recording conditions. Indeed, the Sennheiser MKH Series microphones implemented with this technology are popular, for example, in the film and television recorder toolbox, despite their relatively high price.
What about electret microphone?
In the electret microphone, the electrical charge required by the capacitor capsule is permanently transferred to the plastic material of the back electrode of the capsule by heat treatment. Thus, the microphone does not need external polarization voltage, so it only needs 1-9V for the amplifier. Electret microphones have become common place due to their low production costs, especially on mobile devices.
What is a Tape microphone?
Tape microphones are, in a way, dynamic microphones, with the difference that their diaphragm and coil are one electrically conductive tape placed between magnets. Otherwise, the tape microphone works essentially like a dynamic microphone.
What about Carbon microphone?
The carbon microphone used in the early days of the telephone and the radio contained carbon granules pressed between two metal plates. The pressure fluctuations caused by the sound were transmitted to the carbon granules, the resistance of which varied with the pressure.
If an external DC voltage was applied to the metal plates, an electric current passed through the microphone, the intensity of which followed changes in resistance in accordance with Ohm’s law . This stream could, at its simplest, be fed directly into the loudspeaker , which repeated the vibrations as sound.
What is a Electromagnetic microphone?
Unlike typical sound recording microphones, the electromagnetic microphone does not react to the sound but to the vibration of the metal tongue. A good example of using an electromagnetic microphone is the electric guitar , where the microphone reacts to the vibration of the tongue.
Electromagnetic microphones can be used in principle in any type of instrument with metal strings; such as electric edges or electric basses.