Condenser Microphone
From WikiRecording
A condenser microphone is also known as a capacitor microphone. It converts sound energy to electrical energy by modulating the charge across an air capacitor formed by a flexible diaphragm and a fixed backplate. When sound waves move the diaphragm, the capacitance changes. In DC-polarized condenser microphones (the most common general type) the resulting fluctuation in voltage creates an electrical approximation of the sound wave; in RF condenser microphones the varying capacitance modulates a radio-frequency carrier which is then detected to recover the audio signal.
Active circuitry is required to transform the very high impedance of a DC-polarized capsule's output to a usable low impedance. Phantom power is commonly used to supply current to this circuitry. Other methods include dedicated power supplies (most often seen with tube condensers) and batteries (often seen with electret condensers).
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Characteristics
In a condenser microphone the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. Since the plates are biased with a fixed charge (Q), the voltage maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation:
where Q = charge in Coulombs, C = capacitance in Farads and V = potential difference in Volts. The capacitance of the plates is inversely proportional to the distance between them for a parallel-plate capacitor. (See capacitance for details.):
Condenser microphones can be expensive and require a power supply, commonly provided from mic inputs as phantom power, but give a high-quality sound signal and are now the preferred choice in laboratory and studio recording applications.
Types of Condenser Microphones
Large Diaphram - Solid State Microphone
Small Diaphram - Solid State Microphone
Large Diaphram - Tube Microphone
Small Diaphram - Tube Microphone
Back Electret Microphone
PZM Microphone
Types in Detail
Large Diaphragm Condensors:
Large diaphragm condensors usually have capsules over one inch in diameter. Many people assume that a larger diaphragm gives more bass, but this is incorrect. The larger diahragm requires more energy to be set in motion, therefore it can be described as "slow sounding," relatively speaking. This characteristic tends to smooth out transients and gives the source a "smoother" and "rounder" sound. This combined with the detail and clarity that a condensor capsule is capable of often makes the large diaphragm condensor an ideal choice for vocals and other critical applications. Large diaphragm condensors are extremely versatile as a class; each model adds its own unique color to a source. However, on a source with lots of fast transients, a finger picking acoustic guitarist, for example, the slower response may smooth out the complex details of the music too much for some situations.
Small Diaphragm Condensors:
Small diaphragm condensors are often used when a fast, detailed, and clean sound is desired. They are very popular on acoustic guitars, drum overheads and pop piano. They are rarely used on vocalists because their small diaphragms are easy to overload with small gusts of wind.
Tubes vs. Solid State:
Until sometime in the 1960's or 1970's, all condensor microphones had tube power supplies and tube amp stages. Many engineers tout these older models as more musical, richer, sweeter sounding, etc.. The solid state models are however equally usable and exhibit a different character. Some theorize that this comes from the distortion characteristics of the two types of devices and the way this adds certain harmonic frequencies to the signal. Solid state devices are sometimes described as sounding cold or harsh, most likely an effect caused by the solid state amp's rapid rise of odd order harmonics - which are less musically related to the fundamental - that can occur when the device is overloaded. Tubes are often described as warm or rich. This may be caused by the slow rise in both even and odd order harmonics that actually corresponds fairly well to the way the human ear "overloads" under loud volume pressures. It should be noted that FET's are often used in microphones as well. They are a solid state device that has different distortion characteristics from non-FET type transistors. They sound closer to tubes, but retain some solid state charcater. Tube microphones usually have a dedicated power amplifier that the microphone is plugged into before the signal is sent to the console sometimes they also use a special cable with 5 pins. Some power amplifiers for tube microphones also have settings that control the polar pattern of the mic.
Sources
Wikipedia's Microphone Article
