Microphone is one of the most widely used electro-acoustic devices in audio system. Its function is to convert the voice signal into an electrical signal, then send it to the mixer or amplifier, and play it out from the speaker. In other words, the microphone is used to pick up sound in the audio system. It is an important part of the whole sound system. The quality of its performance has a great impact on the entire audio system.
Ⅰ. Types of microphones
There are many types of microphones. We can classify them according to the principle of energy conversion, according to the way of sound wave action, according to the number of output signals and according to the transmission mode of electrical signals.
1. According to the principle of energy conversion
Dynamic microphones are also called dynamic microphones. It consists of permanent magnet, voice coil, diaphragm (sound film), output transformer and other components. The voice coil and diaphragm are fixed together and suspended in the gap of the magnetic circuit system. Its working process is opposite to that of the dynamic speaker.
The voice coil of a dynamic microphone is in the magnetic field of a magnet. When the sound wave acts on the sound membrane to make it vibrate, the sound membrane will drive the voice coil to vibrate accordingly, so that the voice coil cuts the magnetic force line and generates an induced voltage, thereby completing the sound-electric conversion. Since the resistance of the voice coil is very small, its impedance is very low, and the function of the impedance matching transformer is to change the impedance of the microphone so as to match the input impedance of the amplifier. The output impedance of a dynamic microphone is divided into two types: high impedance and low impedance. The output impedance of high impedance is generally 1000 - 2000Ω, and the output impedance of low impedance is 200 - 600Ω. The frequency response of dynamic microphones is generally 200-5000Hz, and the high-quality ones can reach 30-18000Hz.
① Moving coil microphones are relatively cheap and easy to mass produce.
② The simple structure makes it relatively strong, not easy to be damaged, and has a long service lifespan.
③ When faced with high sound pressure, it has a high saturation ability and can cope with relatively noisy environments.
④ Compared with other types of microphones, dynamic microphones have relatively high sensitivity and low distortion. Therefore, it is usually more suitable for use in lectures, recordings, broadcasts, and music screenings.
① It is difficult for dynamic microphones to overcome the good personalization advantages of other types of microphones.
② Compared with other types (such as condenser) microphones, dynamic microphones usually have poor high-frequency response. Therefore it may exhibit relatively low resolution and transparency, and cannot fully restore the original sound information.
③ The lateral reception of the dynamic microphone is not very good. That is, when the angle of the sound source changes, the response may drop; when it is slightly off-axis, the perception of some details may be lost. This may have a certain impact on some applications that require finer sound filtering.
Ribbon microphones are also called ribbon microphones, and ribbon microphones are mainly on the market today. Its working principle is similar to that of a dynamic microphone, except that its vibration system is not a voice coil and a diaphragm, but a corrugated thin aluminum strip suspended in a magnetic field. The aluminum ribbon has the dual identities of the sound-receiving surface (diaphragm) and the voice coil. The aluminum strip is vibrated by the action of the sound wave, cutting the magnetic force line to generate an induced electromotive force to achieve the purpose of sound-electric conversion. The vibration system of the aluminum ribbon microphone has a small mass, so its transient effect is good. The resonance frequency of the vibration system is very low, so that the effective frequency range of the microphone is in the quality control area. The sensitivity of the microphone hardly changes with frequency, so the frequency response curve is relatively flat. Since the length of the aluminum strip is much smaller than the length of the voice coil of the dynamic microphone, its sensitivity is also much smaller than that of the dynamic microphone. And the impedance presented by the aluminum strip is very small, so we need to add an audio step-up transformer to improve the sensitivity and output impedance. The sound quality of the aluminum ribbon microphone is soft, and it is easily damaged by external vibrations. It is generally suitable for fixed suspension in the recording studio.
① The aluminum ribbon microphone has a relatively simple structure, usually has a light volume and good mobility, and is easy to carry and use.
② Ribbon microphone with high sensitivity and low distortion. It is often used in fields such as recording and performance to capture the subtle details of audio signals, providing a more thorough and detailed audio experience.
③ Ribbon microphones generally have better linearity and relatively higher signal-to-noise ratio, so they are very useful in high-level speech and instrument audio applications.
④ The ribbon microphone has a relatively wide frequency response range and can respond to a wide range of sound signals. It is also highly transparent for greater sonic accuracy, ensuring precise sound reproduction.
① Due to the high complexity of design and manufacturing, and the high manufacturing cost, the aluminum ribbon microphone is not suitable for the market demand that requires mass production.
② The aluminum ribbon microphone is very fragile and is easily disturbed by the environment and vibration. We need to strictly protect and handle it during use, so as not to be damaged and affect the sound quality.
③ The recovery speed of aluminum ribbon microphone is relatively slow. It may be less responsive than other types of microphones to high frequency signals, so a more accurate input signal is required to avoid audio clutter.
A condenser microphone is a microphone that uses a change in capacitance to cause an acoustic-electric conversion. It is a variable capacitor with a small spacing consisting of a vibrating diaphragm and fixed electrodes. When the diaphragm vibrates under the action of sound waves, the distance between the vibrating diaphragm and the fixed electrode changes, causing a change in capacitance. If there is a load resistance R and DC polarization voltage E at both ends of the capacitor, when the capacitance changes with the sound wave, an alternating audio voltage will be generated at both ends of R.
In order to ensure low-frequency sensitivity, an impedance converter whose input impedance is greater than or equal to the output impedance of the microphone should be connected to it. After impedance transformation, it is connected to the amplifier with a transmission line. This impedance converter generally uses a field effect tube. Condenser microphones have high sensitivity, high output power, simple structure, and good sound quality, but it is not very convenient to use a power supply. Therefore, it is mostly used in theaters and demanding language and music broadcasting occasions.
① The condenser microphone has a faster response speed and can better capture the high frequency and details of the audio signal.
② Condenser microphones usually have high sensitivity and low noise level, and can provide relatively bright and detailed sound. It is suitable for application scenarios with higher requirements.
③ The condenser microphone has a wide frequency response range and high peak height. These characteristics make them suitable for various environments of real-time control and signal processing.
④ The structure of the condenser microphone is relatively simple, and it is easy to achieve multi-band response. It is easy to manufacture, sustainably maintained and precisely calibrated, and has higher precision and precision independence with efficient noise and distortion suppression, making it ideal for high-quality audio recording, industrial control and scientific research.
① Condenser microphones are relatively complicated to operate and use. It usually requires higher power consumption and supply.
② Condenser microphones are usually sensitive and susceptible to environmental interference and vibration. So it needs to be isolated accordingly to reduce background noise and cross-talk.
③ The output signal level of the condenser microphone is low, and additional preamplifiers and other equipment are required to process the output signal.
④ Condenser microphones have a greater impact on airflow, and may be distorted or damaged under extreme conditions (such as high temperature, high humidity, and strong electric field environments, etc.).
Piezoelectric microphones are made using the piezoelectric effect of crystals or piezoelectric ceramics. It has two structures of membrane type and acoustic battery type. The diaphragm piezoelectric microphone adopts a light and strong conical diaphragm, and the center of the diaphragm is connected with the center of the bimorph through a link mechanism. When the bimorph is vibrated by sound waves, an audio output voltage is generated between its two electrodes. Piezoelectric microphones are also electrostatic microphones, which are characterized by high sensitivity and output impedance, low cost, but poor temperature and humidity stability. It is not suitable for high-quality audio delivery.
① Ceramic microphone
It is a microphone made of piezoelectric properties of piezoelectric ceramic materials such as barium titanate, lead zirconate titanate, and lead magnesium niobate. After the sound wave acts on the piezoelectric material, the piezoelectric material outputs an electrical signal to achieve the purpose of acoustic-electric conversion.
② Crystal microphone
It is a piezoelectric microphone made of piezoelectric properties of potassium sodium tartrate, ammonium dihydrogen phosphate and other crystals. The sound wave acts on the piezoelectric crystal to output electrical signals to achieve the purpose of acoustic-electric conversion.
(5) Electromagnetic microphone
The electromagnetic microphone is a microphone that relies on the change of reluctance in the magnetic circuit to act as a transducer.
The carbon particle microphone is a microphone that uses the principle that carbon particles stacked in a small container change the conductivity under pressure. When the pressure applied by the diaphragm to the carbon particle group is large, the resistance presented by the carbon particle group decreases. Conversely, when the pressure applied by the diaphragm to the carbon particle group is small, the principle of increasing the resistance presented by the carbon particle group achieves the purpose of acoustic-electric conversion.
(7) High polymer microphone
It is a piezoelectric microphone made of the characteristics of polyvinylidene fluoride and other piezoelectric polymer films. After the sound wave acts on the piezoelectric film, the piezoelectric film outputs an electrical signal to achieve the purpose of acoustic-electric conversion.
2. According to the mode of sound wave action
(1) Strong pressure difference composite microphone
This is a microphone that responds to both the sound pressure and the pressure difference of the acoustic signal, and is actually a combination of a pressure microphone and a pressure difference microphone.
(2) Pressure microphone
This is a microphone that responds to sound pressure. The principle is that sound waves act on one of the diaphragms, generating a driving force proportional to the sound pressure, causing the diaphragm to vibrate back and forth, and driving the transducing part to generate an electrical output proportional to the sound pressure.
(3) Differential pressure microphone
This is a microphone that responds to the pressure difference between two adjacent points in space. Both sides of the diaphragm of the pressure difference microphone are affected by sound waves, and the force pushing the diaphragm is proportional to the pressure difference between the two sides of the diaphragm, so the electrical output of the transducing part is proportional to the pressure difference.
3. According to the number of output signals
A stereo microphone is a microphone designed for stereo sound. Generally, a stereo microphone outputs two channels of audio signals, and the two channels of audio signals are mixed to obtain stereo left and right channel signals.
(2) Mono microphone
This is an ordinary microphone, such as BM1, B1, spirit or various dynamic microphones, etc.
4. According to the transmission mode of electrical signal
(1) Wired microphone
The wired microphone is from the pickup head to the recorder or amplifier, mixer, VCD, etc., and the electroacoustic signal is connected by a visible and tangible cable. It has a wide range of uses in both professional and non-professional applications. We can see it no matter in large theaters, luxury entertainment venues or in ordinary home audio. It has the following characteristics:
① The wired microphone is easy to use.
② The phenomenon of signal loss is less.
③ Affected by the length of the cable, its moving distance will be limited.
④ In signal transmission, limited microphones often use balanced transmission to reduce interference from other electroacoustic equipment.
⑤ Compared with wireless microphones, the price of limited microphones is low, often a quarter of the price of wireless microphones of the same grade. It is the preferred type of home audio.
(2) Wireless microphone
Wireless microphones were introduced into domestic stage performances around the beginning of 1980. The wireless microphone consists of three parts: a microphone, a small radio transmitter and a receiver. The microphone converts the sound into a corresponding electrical signal, and the small radio transmitter modulates the audio signal into a radio wave and sends it out from the antenna, and then the receiver receives it and restores the original sound signal.
① It is especially suitable for mobile sound sources, such as lectures, singers, operas, dramas.
② When the screen is broadcast, it can remove redundant objects such as microphone stands and cables.
③ It does not use transmission cables, the installation is simple and trouble-free, and the actors are freed from the shackles of microphone lines.
④ The microphone head is very close to the shape of the mouth, and what is picked up is absolute direct sound with high clarity. The initial vibration state of the singing voice, soft voice singing, articulation, tooth sound, breath and other expressions are very delicate and have a clear sense of reality.
① The receiving field strength is very weak and the interference is large.
② It is interfered by mobile phones. Because it is transmitted by radio frequency, the confidentiality is poor, and it is also easy to introduce external interference signals.
③ There is noise in the transmitter due to insufficient battery power supply.
5. Other types
(1) Electret Condenser Microphone
Electret condenser microphones use an electret substance that holds a permanent charge, eliminating the need for power to the capacitor. However, the general electret microphone assembly has built-in electronic circuits to amplify the signal, so it still needs to be powered at a low voltage (normal voltage is 1.0V-10V). Such microphones are currently widely used in consumer electronics products.
① Its structure and technology are relatively mature, and its stability and durability are relatively good. It has a low damage rate in long-term use and relatively low cost.
② Its relative sensitivity and fast response time can cope with subtle changes in audio signals, and can better cope with high-quality audio recording and sound amplification.
③ Compared with other types of microphones, it has higher impedance matching and can generate larger output signals. At the same time, it adapts better to various sound sources and achieves a better signal-to-noise ratio with lower noise levels.
④ It usually has a relatively linear and wide frequency response, which can capture sound signals with considerable detail and dynamic range. So it's very useful in high level voice and instrument audio applications.
① It usually requires a dedicated cable or connector to communicate with other devices, which is not suitable for applications with high versatility.
② Its response range and noise guidance are generally relatively low, which may result in a less transparent sound output, especially in the high frequency band.
③ Its electret vibration mode will be disturbed by the environment and force, for example, the microphone may be damaged or the accuracy and stability of the microphone may be affected when the long-distance and large-amplitude rotation occurs.
(2) Dummy head microphone
Artificial head microphone is also called artificial head microphone. Unlike other microphones, it is made of wood or plastic that mimics the shape of a human head. It imitates human body organs with external ear, ear canal, and two miniature microphones are respectively installed at the end of the ear canal at the position of the tympanic membrane. When using high-quality stereo headphones to listen to the signal picked up by the dummy head microphone, the audience will get an excellent sense of presence, making them feel like they are in the scene.
(3) MEMS microphone
MEMS Microphone refers to a microphone made of MEMS (MicroElectrical-Mechanical System) technology, also known as a microphone chip or a silicon microphone. The pressure-sensitive membrane of the MEMS microphone is etched directly on the silicon chip using MEMS technology. This integrated circuit chip is usually also integrated into some related circuits, such as preamplifiers. Most MEMS microphone designs are fundamentally a variant of the condenser microphone. MEMS microphones also often have built-in analog-to-digital converters to directly output digital signals and become digital microphones to facilitate connection with today's digital circuits.
MEMS microphones are mainly used in some small mobile products such as mobile phones and PDAs. Almost all such small microphones used in the past were electret condenser microphones.
Ⅱ. How to choose the microphone correctly?
When choosing a microphone, we should consider the following factors: purpose of use, occasion, sound source, sound effect to be achieved, and special requirements for the microphone. Selecting the right microphone is not easy, and choosing an inappropriate microphone can lead to measurement errors. If you are not sure which microphone you need, the following suggestions may help you.
1. We need to choose the directivity and type of the microphone according to different sound sources and different occasions.
For example, when the voice is amplified, we can use a mobile microphone, so that the sound will be softer. When the ambient noise is relatively large, we need to choose a microphone with strong directionality. In this way, the sound from the audience or other directions can be avoided to the greatest extent, and the howling caused by the acoustic feedback can be reduced.
2. Solo or solo can be selected according to the singing style of the actors and the frequency response of the instruments
When singing solo, we usually choose a dynamic microphone. As a popular singing method, most folk songs and bel canto use condenser microphones, which usually have a wide frequency response range, soft voice, and high sensitivity to obtain high artistic effects.
In string music, because the violin has a wide frequency range and rich overtones, we should choose a condenser microphone with a flat frequency response and high sensitivity. The same is true for trumpet and saxophone. In other words, for musical instruments with wide bandwidth and delicate emotions, we should choose condenser microphones. For instruments with high energy and boldness, we use dynamic microphones.
3. The microphones used in karaoke halls and karaoke halls are generally dynamic microphones
In song and dance halls and karaoke halls, mid-range dynamic microphones can meet the requirements, and the sensitivity should not be too high. This is because most of the singers have not undergone strict training, and they often focus on pop music. The volume is often at the maximum, and they are mostly close to the microphone. The use of a dynamic microphone can prevent the sound reinforcement system gain from being too high and howling.
4. It is very important to choose the appropriate microphone according to the characteristics of different sound sources.
For example, on the surface, the two microphones are the same, but when recording a solo program in a recording studio, if a microphone with good technical characteristics and a flat frequency response curve is used, the sound picked up can be maintained. The true balance of the sound source, and the timbre is beautiful. If another microphone with a non-flat frequency response curve is used, the picked-up sound will also rise or fall with the change of the frequency response curve, thus changing the characteristics of the sound source itself, so the recorded sound will be It will appear unreal, the sound is thin, not thick enough, and the clarity is not very good.
If wearable wireless microphones are used, there are also two microphones with different frequency response characteristics, and the recorded sound effects are just the opposite. This is because the actor wears the wireless microphone on the body, and the main axis of the microphone is exactly 90° to the sound from the oral cavity, and is in the same line as the nasal sound, which will cause too much low frequency. And soft clothing will absorb high frequencies.
If you use a microphone that is not a straight line to pick up the sound, you can make up for the lack of high frequencies, reduce too much low frequency, and the recorded sound is even more crisp. Conversely, if you pick up a mic with a flat frequency response curve, because you're wearing the mic, the mic moves closer to the sound source, which raises your voice, makes your voice lower, and your voice will get worse.
Ⅲ. What factors are related to the frequency response of the microphone?
The frequency response characteristics of a microphone are related to the following factors:
1. Diaphragm: The thinner the diaphragm, the larger the area, the better the low-frequency response flatness. High-frequency sound waves vibrate fast. If the vibration synchronization of the diaphragm is not good, the high-frequency output will be small and weaker than other frequency bands, which will cause poor high-frequency distortion. If it is at low frequency, it may be because the speed of sound wave vibration is slow, the diaphragm is not easy to be vibrated and it is difficult to synchronize, and it cannot produce effective output, resulting in poor low frequency response and even distortion.
2. Overall acoustic structure: In terms of traditional microphone design, whether it is a dynamic or condenser microphone, the larger the rear cavity, the better the low-frequency characteristics.