The main technical indicators of the microphone include the output impedance, sensitivity, frequency response, transient response, directional characteristics, harmonic distortion, inherent noise of the microphone, equivalent noise level ENL, maximum sound pressure level, dynamic range of the microphone, and signal-to-noise ratio.

Sensitivity

Sensitivity represents the acoustic-electrical conversion efficiency of the microphone. It refers to the open-circuit output voltage of the microphone when a sound signal with a sound pressure of 0.1Pa is applied to the microphone in the free sound field. The sensitivity shows the amount of amplification required to raise the level of the signal picked up by the microphone to line level. This value also makes it easy for the recording engineer to judge the difference in the output levels of the two microphones. Under the excitation of the same sound pressure level, the microphone with higher sensitivity produces a larger output voltage than the microphone with lower sensitivity. In general, condenser microphones are more sensitive than electrodynamic microphones, and high-impedance microphones are more sensitive than low-impedance microphones .

Using a microphone with high sensitivity to pick up sound can obtain a higher signal-to-noise ratio for the sound with a lower sound pressure level, which is beneficial to improve the sound quality, but it is easy to produce distortion when picking up the sound with a large dynamic sound pressure level.

A microphone with high sensitivity is beneficial to reflect various details of the sound source, but at the same time it is also easy to pick up more noise. The effects of the two are also different. High-sensitivity timbres are brighter and more chromatic, and low-sensitivity timbres are darker, but can sometimes soften the timbre and bring a good sense of warmth.

Frequency response

The frequency response refers to the characteristic that the sensitivity of the microphone changes with frequency, that is, the magnitude of the output voltage of the microphone for a constant input signal of different frequencies. The range of frequency response refers to the frequency bandwidth of the normal working of the microphone, also known as the bandwidth. The frequency response of a microphone can be designed to be straight, or it can be appropriately boosted or attenuated according to the needs. . The figure below shows the measured frequency response curves of certain omnidirectional, cardioid, and figure-8 microphones at various angles.

Transient response (transientresponse)

Transient response refers to the ability of the output voltage of the microphone to follow the sharp change of the input sound pressure level, and it is a measure of how fast the microphone diaphragm reflects the sound wave waveform. The vibration system of the condenser microphone has small mass, small mechanical impedance to sound waves, good transient response, and clear and bright sound. The diaphragm of the noise canceling electret condenser microphone can be made very large. In addition to the coil and the core, the quality is often large, and the response to the sound wave is slow, so the sound obtained is thicker. In contrast, the diaphragm of an aluminum ribbon microphone is much lighter. The size of the diaphragm of a homogenous microphone also has an effect on the transient response. The transient effect of the large-diaphragm microphone is inferior to that of the small-diaphragm microphone, and the sound resolution is therefore not as good as that of the small-diaphragm microphone.

Dynamic Range

The upper limit of the dynamic range of the microphone is determined by the distortion tolerance of the pickup system (microphone and preamplifier), and the lower limit is determined by the noise level of the pickup system.

For electrodynamic (including moving coil and aluminum ribbon) microphones, when the excitation sound pressure is very high, the vibration of the moving coil or aluminum ribbon has reached the nonlinear region of the magnetic circuit, resulting in nonlinear distortion. For condenser microphones, since the condenser capsule is followed by a built-in preamplifier, nonlinear distortion is often caused by overloading the preamplifier. The distortion of the microphone is usually set as the allowable upper limit of the harmonic distortion coefficient of 1%, that is to say, the input sound level when the microphone produces 1% harmonic distortion is the maximum allowable sound pressure level. In terms of distortion, the dynamic microphone is an extremely robust microphone, often achieving a total dynamic range of 140dB. Its ability to withstand high sound pressure levels and strong vibrations is much greater than that of condenser microphones, so it is often used in live performances with high sound pressure levels.

In actual recording, the low-frequency boost caused by the proximity effect will reduce the clarity of the sound, especially in speech recordings, in order to avoid excessive bass, some microphones have a low-frequency roll-off filter switch, which can attenuate effect to restore a flat, natural sound balance. On the other hand, some singers also use the proximity effect to increase the proportion of low-frequency sounds in order to obtain warmth and fullness of the singing voice, so they deliberately pick up sounds close to the microphone.

Phantom Power

When the omnidirectional electret condenser microphone is working, a DC polarizing voltage needs to be applied to the plate. Phantom power refers to a power supply method that uses a cable that transmits audio signals to transmit DC polarized power. It contains both the audio signal voltage and the DC supply voltage in the same cable. The application of phantom power eliminates the need for a recording engineer to provide a separate power supply for each condenser microphone, and the power supply does not affect other back electret microphone on the same path, such as unidirectional condenser microphone.

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