Ⅰ. What is a microphone?
Ⅱ. The history of microphones
Ⅲ. How do microphones work?
Ⅳ. The role of microphones
Ⅴ. The parameters of the microphone
Ⅵ. Microphone application
Ⅶ. Precautions for using the microphone
Microphone is abbreviated as MIC. It is a transducer that converts sound into electrical signals. Its classification includes dynamic microphones, capacitive microphones, electret microphones and recently emerging silicon microphones, as well as liquid microphones and laser microphones.
The role of the microphone is to convert the voice signal into an electrical signal, then send it to the mixer or amplifier, and finally play it out from the speaker. The microphone is the first link of the whole sound system. Its quality and whether it is used properly have a very important impact on the electroacoustic indicators of the entire system. In the comparison of the various components of the entire audio system, the loudspeaker (including speakers) has the greatest impact on the sound quality, and its impact on the sound quality reaches 50-60%; the second is the microphone, accounting for 20-30%; the third is the sound quality. Power amplifier, accounting for 10~20%.
In 1870, scientist David Edward Hughes invented the carbon microphone.
In 1886, scientist Thomas Edison improved the transducer of a carbon microphone into a button shape and tried to use it in broadcasting for the first time.
In 1910, the button-style carbon microphone was used for the first time in a live performance at the Metropolitan Opera House in New York.
In 1916, Edward C. Wente of the Western Electric Company developed the first condenser microphone and made a major breakthrough in the field of microphones.
In 1923, the first dynamic microphone invented by Captain H. J. Round officially came out. The dynamic microphone soon became one of the standard equipment of the BBC British Broadcasting Corporation. In the same year, Harry F. Olson of RCA ABC invented another dynamic microphone, the ribbon microphone.
In 1949, the MD4 microphone was developed by the Veneburst Laboratory. It can effectively suppress sound feedback and reduce background noise in noisy environments. This is the world's first noise-canceling microphone that suppresses feedback.
In 1961, at the Industrial Fair in Hannover, Germany, Sennheiser launched the MK102 and MK103 microphones. These two microphones interpret a new microphone manufacturing concept - RF radio frequency condenser. That is, it uses a small and thin diaphragm, which has the characteristics of small size and light weight, while ensuring excellent sound quality. In addition, such microphones are very sensitive to electromagnetic interference. They are highly immune to the effects of climate and are ideal for use in entirely new fields.
In 1966, Shure introduced two classic microphones, the SM57 and SM58. They are still highly sought after today.
In 1971, Sennheiser launched a classic microphone, the MD 441. Since then, the microphone industry has entered a stage of vigorous development.
In 1990, Neumann released the model KMS 105, a condenser designed for live performances. It sets a new standard for better quality.
The microphone acts as a transducer, converting sound waves (mechanical wave energy) into audio signals (electrical energy). The microphone diaphragm vibrates when it is affected by sound waves, and generates a consistent audio signal through electromagnetic or electrostatic principles and outputs it.
Microphones play an important role in today's world. It is widely used in various fields.
In audio equipment (microphones, speakers, and headphones), microphones convert sound to and from electrical signals and mechanical vibrations.
In the field of industrial measurement, microphones are used to detect and record mechanical vibration and other types of information to help diagnose and evaluate the operation of the machine.
In the medical field, microphones are used in medical imaging equipment, such as ultrasound scanners.
1. Signal-to-Noise Ratio (SNR or S/N)
It represents the ratio between desired signal and microphone noise expressed in decibels. The larger the signal-to-noise ratio, the less clutter is mixed in the signal, and the better the sound reproduction quality is.
2. Dynamic Range
It refers to the electrical frequency difference between the maximum undistorted signal output by the microphone and the minimum useful signal output. Too little dynamic range can cause sound distortion.
3. Sensitivity
The sensitivity of the microphone refers to the signal voltage output by the microphone under a certain sound pressure, and its unit is mv/pa. The sensitivity of the microphone can be divided into sound pressure sensitivity and sound intensity sensitivity. The sensitivity of a high-impedance microphone is often expressed in decibels (db).
The sensitivity of general dynamic microphone is about 0.7 ~ 2mV/Pa
The sensitivity of the ribbon microphone is about 0.5~2mV/Pa
The sensitivity of the condenser microphone is >5mV/Pa
The sensitivity of the electret condenser microphone is about 30mV/Pa.
4. Frequency Response
It reflects whether the output signal will change as the frequency changes when the microphone receives sounds of different frequencies. It represents the characteristics of whether the output signal can truly represent the original sound. The ideal microphone frequency characteristic is 20Hz-20kHz.
5. Output Impedance
Output impedance is also called source impedance, which is used to indicate the ability of a signal source to provide the signal presented by the lower load (input impedance). The output impedance of a microphone is usually measured with a 1kHz signal. It is the AC internal resistance of the microphone to a 1kHz signal in ohms (Ω). Microphones with a source impedance between 50 and 600Ω are low-impedance; between 1kΩ and 5kΩ are medium-impedance; and between 10kΩ and 50kΩ are high-impedance.
6. Inherent Noise
Inherent noise is the effective value of the microphone output voltage measured in an environment without external sound, wind vibration, and electromagnetic field interference. The inherent noise of general microphones is very small, on the order of μV.
7. SPL Maximum Sound Pressure Level
The maximum sound pressure level is an important indicator of the microphone parameters. It refers to the measurement of the maximum sound pressure level that a microphone can withstand up to 0.5 total harmonic distortion, indicating the highest sound level that the microphone can handle before distorting. The higher its value, the better.
8. Directivity
The directivity of the microphone indicates the sound pickup range of the microphone. We can represent this with a pointing graph. We can choose microphones with different directivity according to different sound sources.
(1) Omnidirectional: It can charge a 360-degree circle of sound, suitable for chorus recording.
(2) Cardioid: This is the most common type of pointing. The front end of a cardioid microphone is the most sensitive and the rear end is the least sensitive. This blocks unwanted ambient noise and cancels out echoes better than omnidirectional microphones. Therefore, cardioid microphones are especially suitable for live interviews and loud stages.
(3) Hypercardioid: Its pick-up area is narrower than that of a cardioid microphone, which can more effectively eliminate surrounding noise. But the back end of this microphone also picks up sound. Therefore, the loudspeaker must be placed accurately. Supercardioid microphones are best for picking up a single source in loud environments, where they provide the most effective echo cancellation.
9. Frequency Range
The microphone will pick up sounds ranging from low frequency to high frequency. Different frequency ranges are a good choice for different types of use. Every microphone has a different response curve. It has dips and peaks in certain parts of the frequency range, which ensures an ultra-smooth sound or excellent speech intelligibility.
A good example is the drum kit. Because each kick, tom, snare, and cymbal produces its own unique sound (with its own specific frequency range), you can choose the best mic to pick up your particular drum kit.
1. Sound pressure microphones are mainly used in chambers such as artificial ears.
2. The diffuse field microphone is used for diffuse field measurement, which is suitable for indoor measurement. However, some countries stipulate that the sound level meter uses a diffuse field microphone.
3. The infrasonic sensor is a microphone capable of receiving infrasonic waves. Most domestic infrasound observation stations use capacitive infrasound sensors. This capacitive infrasound sensor has been widely used in research fields such as river tide early warning, earthquake infrasound prediction and geophysics.
4. Free-field (or sound-field) microphones are mainly used for free-field tests such as anechoic chambers. It can more realistically measure the original free-field sound pressure at the point before the microphone is placed. This type of microphone is mostly used in sound level meters and noise measurements.
5. High sound pressure microphones generally refer to microphones with a dynamic upper limit greater than 160 dB. The measurement range of common sound level meters on the market is generally between 20 dB and 140 dB. However, with the development of large-scale machinery, aircraft, rockets and other military industries, people have more and more requirements for the measurement of high sound levels, even exceeding 170 dB. The upper measurement limit of the sound level meter can be significantly improved by replacing the high sound pressure microphone.
The choice of microphone should be based on the occasion of use and the requirements for sound quality, combined with the characteristics of various microphones, and comprehensively considered and selected. For example, high-quality recording and broadcasting require good sound quality, we should choose condenser microphones, aluminum ribbon microphones or dynamic microphones. For general sound amplification, we can choose the ordinary moving coil type. When the position of the speaker moves from time to time or the distance between the loudspeaker and the loudspeaker is large when speaking, such as karaoke singing, we should choose a microphone with unidirectional and low sensitivity to reduce noise interference. We should pay attention to the following points in use:
1. Connecting line
The output voltage of the microphone is very low. In order to avoid loss and interference, the connection line must be as short as possible. High-quality microphones should choose twin-core twisted metal isolated wires, and general microphones can use single-core metal isolated wires. The length of the high-impedance microphone transmission line should not exceed 5 meters, otherwise the treble will be significantly lost. The connection of the low-impedance microphone can be extended to 30~50m.
2. Impedance matching
When using a microphone, the output impedance of the microphone is the same as the input impedance of the amplifier. If the mismatch ratio is above 3:1, the transmission effect will be affected. For example, when a 50Ω microphone is connected to an amplifier with an input impedance of 150Ω, although the output can be increased by nearly 7db, the high and low frequency sounds will be significantly lost.
3. The distance between the mouth and the microphone
The distance between the mouth and the use of a directional wireless microphone will have a significant change in sensitivity and sound quality. Because the sensitivity of the microphone is inversely proportional to the square of the distance from the mouth, singers with insufficient throat strength cannot take the microphone too far from the mouth, which will reduce the volume sharply. If the volume of the amplifier is increased, it is easy to cause feedback sound. Singers with loud throats should not hold the microphone too close to the mouth, as this will make the volume too loud and cause saturation distortion of the amplifier.
Furthermore, due to the obvious proximity effect of the directional microphone (Proximity Effect). The bass gets a massive boost when the mic is brought closer to the mouth. Therefore, if your throat lacks bass, you can move the mic closer to your mouth and use the proximity effect to compensate for your bass, making your voice thicker and more magnetic. Conversely, if your voice is too deep, you can place the microphone farther from your mouth to reduce the proximity effect of the microphone and make your voice clearer and brighter.
4. Avoid using the wireless microphone facing the speaker
It is the most taboo way to use the wireless microphone close to the speaker or facing the speaker. It is most likely to produce feedback howling when used in such a situation. Most of the wireless microphones used for general singing use directional capsules. If you use the correct angle, you can reduce or avoid the feedback sound with the speaker. It is not easy to produce howling sound when the wireless microphone is used at the sides or behind the speaker. If you need to stand in front of the speaker, a vertical or horizontal angle greater than 90 degrees to the speaker can reduce feedback sound. The front of the cardioid microphone is kept at 180 degrees to the speaker, and the front of the super-directional microphone is kept at 120 to 140 degrees to the speaker to minimize the feedback sound.
5. The microphone must be vibration-proof
Most of the damage to the microphone is caused by vibration. Strong vibrations can demagnetize the magnet of the electrodynamic microphone, reducing sensitivity. It can also displace the magnetic circuit, causing the magnetic circuit to jam the voice coil or loosen the voice coil and completely damage the microphone. It can also make the distance between the poles of the condenser microphone suddenly smaller, so that the polarization voltage may break down the diaphragm. During the daily sound test, we should not blow air vigorously or tap the microphone with our hands, as this will easily damage the microphone.
