Summary
Common microphones can be divided into dynamic microphones, condenser microphones and ribbon microphones according to their working principles. The structure of a dynamic microphone is very simple. Its working principle is that the diaphragm inside the microphone drives the coil to vibrate and cut the magnetic lines of force to generate electrical signals, which are mostly used to pick up relatively loud sound sources. Condenser microphones, which are slightly more complex than dynamic microphones, require additional phantom power to supply power, but have higher sensitivity than dynamic microphones. The principle of the ribbon microphone is to use a small aluminum ribbon as the diaphragm to generate signals.
Main microphone types
Dynamic microphones do not require an additional power source because they use simple active components that convert acoustic energy into electrical energy. Compared with condenser microphones, dynamic microphones are not sensitive enough, but they can usually handle higher sound pressure levels. The Shure SM57 is the most common dynamic microphone. It is constructed like a small speaker cone with a diaphragm attached to a coil surrounded by a magnet. When a sound wave hits the diaphragm, it moves the coil in the magnetic field, thereby generating an electrical signal.
Aluminum ribbon microphones, such as the Cascade Fat Head, use a small aluminum ribbon as the diaphragm to generate signals. When the aluminum strip moves with changes in air pressure, it interferes with the magnetic field and generates a signal. Ribbon microphones were very popular from the mid-1930s to the 1950s.
Condenser microphones usually require an external power source. The core is a capacitive sensor with two charged elements (a fixed piece and a thin movable diaphragm). The movement of the diaphragm under the action of sound waves will cause the capacitance between the components to change, thereby generating electrical signals.
Large-diaphragm condenser microphones, such as Audio-Technica AT4040, have a diaphragm diameter of about 1 inch or more, and are usually of side-address design. Their relatively large surface area can capture a large amount of sound energy and provide an excellent signal-to-noise ratio.
Small-diaphragm condenser microphones, such as Neumann KM-184, are characterized by a diaphragm of about half an inch or less, and are usually pencil-shaped, generally end-address designs. Their lighter components are easily propelled by air, allowing them to accurately capture transient sounds.
Other types of microphones
The electret microphone has the characteristics of small size, wide frequency range, high fidelity and low cost, and has been widely used in electronic products such as communication equipment and household appliances. Some elements of the electret microphone are made of permanently charged materials.
Charcoal microphones are common in old telephones and public address systems. When the charcoal is compressed by the air pressure, an electrical signal is generated. Due to their imperfect design, the frequency characteristics of carbon microphones are poor and the noise is relatively large.
The contact microphone is not actually a microphone at all, but a mechanical sensor. When the piezoelectric material they use shrinks and expands on the vibrating surface, an electronic signal is generated.
Directivity
The directivity of a microphone is a description of the sensitivity of the microphone to sounds from all directions in space. Most microphones are unidirectional, but some microphones can switch their directivity. Common microphone directivity is as follows:
The omnidirectional microphone will evenly record sounds from all directions.
The cardioid pointing microphone has the best reception effect for the sound from the front of the microphone, while the sound from other directions will be attenuated.
Supercardioid and strong cardioid pointing are similar to cardioid pointing, but will cancel out more sound from the side of the microphone. The gun-shaped pointing microphone is a type of microphone that requires a single direction of the limit. The best receiving angle is a small cone-shaped area directly in front.
The figure-of-eight direction means that the microphone can pick up sounds from the front and back directions better, but it picks up sound from both sides very weakly. All ribbon microphones are pointed in a figure of eight.
Practical application
One of the key parts of the recording process is the selection of the most suitable microphone and the positioning of a given sound source. Although there are no hard and fast rules on the choice of microphone, people usually follow several common practices. For example, dynamic microphones are usually used for larger sound sources, such as guitars and drums, because they can handle high sound pressure levels, while condenser microphones are mostly used for acoustic instruments and vocals because they can capture more detail and clarity. Degree and low noise.
Although it seems common practice to use a bright microphone on a high-pitched guitar amp or a soft ribbon microphone on a baritone singer, a good rule of thumb is to do the opposite and use a microphone to balance the sound. The timbre of the source. For example, an aluminum tape microphone can be used to reduce the extreme overtones of a brass instrument.
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