Some of you may call it mic or mike, a short from microphone, but it's the same thing. You may have wondered about how it work, at least the basic principles and/or about the types of mikes on the market. Well... you found the right article for that.
From the technological point of view, any microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Most microphones today use capacitance change (condenser microphone), electromagnetic induction (dynamic microphone), piezoelectric generation or light modulation to produce an electrical voltage signal from sounds (as mechanical vibration). In all of the cases the ouput voltage or current is proportional to the sound signal. Besides the variety of basic mechanisms, microphones can be designed with different directional patterns and different impedances. Sometimes other characteristics such as diaphragm size, intended use or orientation of the principal sound input to the principal axis (end- or side-address) of the microphone are used to describe the microphone.
As you already know, they are used on daily basis in many applications such as telephones (classical and fixed, mobile phones and smartphones), motion picture production, radio and television broadcasting, digital cameras, speech recognition, VoIP, etc. But their origin dates from nintheen century: Thomas Alva Edison and Emile Berliner filed patent applications for the first versions of carbon microphone in March and June 1877. After a long legal battle Thomas Edison was considered as the creator of the microphone.
The sensitive transducer element of a microphone is called its element or capsule. A complete microphone also includes some means of bringing the signal from the element to other equipment, as integrated in the devices found into an earlier pharagraph, and often an electronic circuit to adapt the output of the capsule to the equipment. For example, a wireless microphone contains a radio transmitter.
Dynamic microphones
They work via electromagnetic induction, are also called moving-coil microphones. They are robust, relatively inexpensive and resistant to moisture... and they are preffered for on-stage use.
Dynamic microphones use the same principle as in a loudspeaker, only reversed: a small movable induction coil, positioned in the magnetic field of a permanent magnet, is attached to the diaphragm. When the sounds enter through the windscreen of the microphone the waves moves the diaphragm, it vibrates and the coil moves in the magnetic field, producing a varying current in the coil through electromagnetic induction.
A single dynamic membrane does not respond linearly to all audio frequencies, that's why some microphones utilize multiple membranes for the different parts of the audio spectrum and then combine the resulting signals - that can be expensive.
Advantages: relatively cheap and rugged, can be easily miniaturized.
Disadvantages: the uniformity of response to different frequencies does not match the results of the ribbon or condenser microphones.
The condenser microphone
The condenser microphone was invented at Bell Labs in 1916, it is also called a capacitor microphone or electrostatic microphone. The diaphragm of the mike acts as one plate of a capacitor (or condenser, as you may know it), the vibrations produce changes in the distance between the plates. There are two types of mics, depending on the method of extracting the audio signal from the transducer: DC-biased microphones and radio frequency (RF) or high frequency (HF) condenser microphones.
Advantages: best overall frequency response makes this the microphone of choice for many recording applications.
Disadvantages: expensive, may pop and crack when close miked, requires a battery or external power supply to bias the plates.
Electret condenser microphone
An electret microphone is a type of capacitor microphone invented by Gerhard Sessler and Jim West at Bell laboratories. The name comes from electrostatic and magnet: a static charge is embedded in an electret by alignment of the static charges in the material, much the way a magnet is made by aligning the magnetic domains in a piece of iron. An electret is a ferroelectric material that has been permanently electrically charged or polarized. The externally applied charge described above under condenser microphones is replaced by a permanent charge in an electret material.
The vast majority of microphones made today are electret microphones: nearly all microphones used for cell phones (mobile phones), computers and headset are electret condenser types.
Advantage: good performance and ease of manufacture, hence low cost.
Ribbon microphone
They use a thin, usually corrugated, metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone's output, its vibration within the magnetic field generates the electrical signal.
Ribbon microphones are similar to dynamic (moving coil) microphones: they both produce sound by means of magnetic induction. Basic microphones detect sound in a bi-directional pattern because the ribbon, which is open to sound both front and back, responds to the pressure gradient rather than the sound pressure. Other directional patterns are produced by enclosing one side of the ribbon in an acoustic trap or baffle, allowing sound to reach only one side.
Advantages: adds "warmth" to the tone by accenting lows when close-miked, can be used to discriminate against distant low frequency noise in its most common gradient form.
Disadvantages: Accenting lows sometimes produces "boomy" bass, very susceptible to wind noise, not suitable for outside use unless very well shielded.
Carbon microphone
It's also known as a carbon button microphone (or sometimes just a button microphone). It use a capsule or button containing carbon granules pressed between two metal plates like the Berliner and Edison microphones.
A voltage is applied across the metal plates, causing a small current to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound waves, applying a varying pressure to the carbon. The changing pressure deforms the granules, causing the contact area between each pair of adjacent granules to change, and this causes the electrical resistance of the mass of granules to change. The changes in resistance cause a corresponding change in the current flowing through the microphone, producing the electrical signal.
Carbon microphones were once commonly used in telephones.They have extremely low-quality sound reproduction and a very limited frequency response range, but are very robust devices.
Piezo-electric microphone
The phenomenon of piezoelectricity is the ability of some materials to produce a voltage when subjected to pressure. A piezo-electric microphone (crystal microphone) uses this phenomenon to convert vibrations into an electrical signal. An example of this is the potassium sodium tartrate, a piezoelectric crystal that works as a transducer that is used also in the microphone and as a slimline loudspeaker component.
The high impedance of the crystal microphone made it very susceptible to handling noise, both from the microphone itself and from the connecting cable.
Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples and to record sound in challenging environments (for example underwater under high pressure).
Fiber optic microphone
It converts acoustic waves into electrical signals by sensing changes in light intensity, instead of sensing changes in capacitance or magnetic fields as with conventional microphones: the light from a laser source travels through an optical fiber to illuminate the surface of a reflective diaphragm. Sound vibrations of the diaphragm modulate the intensity of light reflecting off the diaphragm in a specific direction. The modulated light is then transmitted over a second optical fiber to a photo detector, which transforms the intensity-modulated light into analog or digital audio for transmission or recording.
Fiber optic microphones possess high dynamic and frequency range, similar to the best high fidelity conventional microphones. They are ideal for use in areas where conventional microphones are ineffective or dangerous because fiber optic microphones do not react to or influence any electrical, magnetic, electrostatic or radioactive fields.
Advantage: fiber optic microphones are robust, resistant to environmental changes in heat and moisture, they can be produced for any directionality or impedance matching. The distance between the microphone's light source and its photo detector may be up to several kilometers without need for any preamplifier or other electrical device, making fiber optic microphones suitable for industrial and surveillance acoustic monitoring.
Laser microphone
They can be used to pick up sound at a distance from the microphone equipment: a laser beam is aimed at the surface of a window or other plane surface that is affected by sound. The vibrations of this surface change the angle at which the beam is reflected, and the motion of the laser spot from the returning beam is detected and converted to an audio signal.
