How Microphones Work
Microphones simply convert a sound wave into an electrical signal. They convert audio energy into electrical energy. This is accomplished with a small, light material in them called the diaphragm. When the sound vibrations through the air reach the diaphragm, they cause the diaphragm to vibrate. This in turn will cause an electrical current in the microphone to vary. It is then sent out to a mixer, preamplifier or amplifier for use. Microphones are typically classified according to how the diaphragms produce sound.
Types of Microphones
Dynamic Microphones
Dynamic microphones typically use moving-coil technology in order to make their own voltage. This consists of a diaphragm of usually thin plastic being attached directly to a dense coil of wire. The coil has a magnet either surrounding it or at the center. As the diaphragm vibrates, the coil vibrates, and its changing position relative to the magnet causes a varying current to flow through the coil. This current is your audio signal.
Dynamic microphones are quite durable, but can be damaged when the suspension wires break, due to dropping or rough handling. Suspension wires hold the coil and diaphragm in a floating position relative to the magnets.
Dynamic microphones have to cause a whole coil of wires to move, a mountain when you're talking about little movements of air. This makes them not as sensitive as higher-grade microphones, especially to very soft sounds or high-pitched sounds, such as sibilants in speech or harmonics in music. They have a reputation of being very hardy, and some higher grade dynamic microphones can give a very clean and sensitive sound. Dynamic microphones are also known to give a “fat” sound, which is flattering to those frequencies that the human ear can hear. They are usually not expected to reproduce the sounds they pick up very faithfully.
Dynamic microphones are associated with the “live performance” sound and typically are considered durable enough for the rough stage handling of live performance. This may contribute to a loss of “clarity”, making it a second choice behind the condenser microphone for vocal performance.
Condenser Microphones
A condenser microphone is much more sensitive to sound than a dynamic mic. “Condenser” is another word for capacitor, and the microphone itself operates like a charging/discharging capacitor. Instead of moving a whole coil of wires, concenser microphones only have a thin diaphragm and solid back-plate making up the capacitor. Condenser microphones are therefore sometimes known as capacitor microphones. Sound waves strike on a pressure plate. The plate is connected to one side of a set of metal plates by means of a “plunger”. A voltage is introduced into both plates to form a capacitor. The top moving metal plate varies the charge and the microphone’s output current.
The condenser microphone will not work without a voltage applied to the plates. It does not make its own voltage. The supplied voltage is called “phantom power”. It is called this because the same wires carrying the voltage to the microphone also carry the electrical impulses of the audio signal away from the mic. These two voltages cross, but do not disturb each other, so they are called “phantom” in relation to each other.
Digital recording developments have encouraged advances in the development of condenser microphones. As standards for recording improved, the quality of recording microphones had to improve to keep up. The disadvantage to this is that the condenser microphone duplicates sound as it is, making it crucial for high quality performance.
Large-Diaphragm Condenser Microphones
This has lead to the creation of large-diaphragm condenser microphones, which use the same basic technology, but have special larger high-quality diaphragms to produce a more flattering sound. Studios usually have an array of expensive large-diaphragm condenser microphones, as each microphone would reproduce the sound in its own special way. When the correct microphone is chosen for a vocalist, the results can be extremely flattering, making the singer much better than he or she really is.
The cost of a large-diaphragm microphone is usually attributed to the R & D cost of creating a microphone that records sound the way you want it, instead of the way it really sounds. Large-diaphragm mics can also maintain most of the high-frequency sensitivity of regular condenser microphones, making them sharp enough for digital recording to do the sound justice.