Moving-coil microphone (moving-coil microphone [Engineering Acoustics] Moving-coil microphone, moving-coil microphone) is a device that converts sound into electrical signals. The dynamic microphone is made using electromagnetic induction. When the sound wave vibrates the diaphragm, the coil (called the voice coil) connected to the diaphragm vibrates together, and the voice coil vibrates in the magnetic field, which generates an induced current. (Electrical signal), the magnitude and direction of the induced current change. The amplitude and frequency of the change are determined by the sound wave. This signal current is amplified by the loudspeaker and transmitted to the speaker, and the amplified sound is emitted from the speaker.
When the microphone receives a sound wave, the force generated by the sound wave acts on the diaphragm, causing the diaphragm to vibrate, driving the voice coil to vibrate correspondingly, and the voice coil moves in the magnetic steel to generate electromotive force, and the sound signal is transformed into an electrical signal.
Dynamic microphones are relatively simple in construction, so they are economical and durable. They can withstand extremely high sound pressure and are almost unaffected by extreme temperatures or humidity.
Moving coil microphones are mainly composed of coils, magnets, and shells.
Dynamic microphones are simple to use, do not require polarization voltage, are firm and reliable, have stable performance, and are relatively inexpensive. But its transient response and high frequency characteristics are not as good as condenser microphones. Usually dynamic microphones have low noise, no need to feed power, easy to use, stable and reliable performance. The main features include:
1. Firm structure, stable performance, durable, low price; good frequency characteristics, flat amplitude-frequency characteristic curve in the frequency range of 50-15000Hz;
2. Good directivity;
3. No DC working voltage is needed, easy to use, and low noise.
Acoustic performance comparison
Generally speaking (with exceptions of course), condenser microphones are superior to dynamic microphones in terms of sensitivity and expanded high-frequency (and sometimes low-frequency) response. This is related to the working principle of condenser microphones that need to convert sound signals into electric current. Generally, the diaphragm of a condenser microphone is very thin, and it is easily affected by sound pressure and vibrates, which causes a corresponding change in the voltage between the diaphragm and the back plate of the diaphragm chamber. This voltage change will then be amplified by the preamplifier and then converted into a sound signal for output.
Of course, the preamplifier mentioned here refers to the amplifier built into the microphone, not what we usually call the "preamplifier", that is, the kind of preamplifier on the mixer or interface. Because the area of the condenser microphone diaphragm is very small, its response to low-frequency or high-frequency sound signals is very sensitive. The fact is indeed the case. Most condenser microphones can accurately capture many sound signals that human ears simply cannot hear.
In fact, what we usually call a dynamic microphone, in a strict sense, should be called a "moving-coil" dynamic microphone, because the sound signal of this kind of microphone is generated mainly by being closely connected to the diaphragm. The coil of wire moves continuously in the magnetic field according to the change of sound pressure. Due to the relatively large volume of the moving part, the dynamic microphone is slightly inferior to the condenser microphone in terms of response frequency range (mainly high frequency part), sensitivity and transient response capability.
Ribbon microphones (Ribbon mICrophones) are also a kind of dynamic microphones. It is mainly through the vibration of the metal sheet itself according to the change of sound pressure to drive the change of the current in the magnetic field, thereby finally generating the sound signal. Because the area of the metal sheet is smaller than that of the diaphragm and coil, this ribbon microphone has a higher response to high frequencies than a dynamic microphone, but it still cannot be compared to a condenser microphone.
The sensitivity of dynamic microphones is lower than that of condenser microphones, mainly because it
There are no corresponding electronic components to amplify and buffer the sound signal. Therefore, they usually require more gain than dynamic microphones. It is for this reason that the sound quality of dynamic microphones usually varies with the preamplifier used. However, under strong sound source conditions, this generally does not cause any adverse consequences. However, if the sound source is relatively weak, the problem may be more serious and requires special attention. Market demand is a catalyst for product innovation.
In order to solve this problem, there are indeed many dynamic microphones directly built-in preamplifiers on the market, such as the Ball moving-coil (moving coil microphone) launched by BLUE and the R122 ribbon (aluminum ribbon) launched by Royer. Microphone) and so on.
Facts have proved that they can indeed be well adapted to various preamplifiers. Since each microphone has its own unique advantages and disadvantages, if you look closely, you will find that each microphone has its own specific application context. For example, dynamic microphones are usually used in strong sound source recording environments such as guitar amplifiers, brass tubes, near-field drums, and live vocals; while condenser microphones are usually used in natural conditions or conditions that require high high-frequency response ranges. For example, the recording of drums, piano, acoustic stringed instruments, vocal recording in the studio, and orchestra and chorus recording, etc.; ribbon microphones are used in digital recording, especially percussion instruments and brass pipes. Having attention.
Of course, ribbon microphones can also be used in various recording situations such as guitar amplifiers, various acoustic instruments, and vocals. Finally, what I want to say is that any rules are only for reference and do not necessarily have to be followed. Although almost no one recommends us to use dynamic microphones for recording acoustic guitars or hanging drums, these can be tried if necessary, because the rules are dead and people are alive. In fact, in reality, we can see many phenomena similar to the use of condenser microphones in live vocal recording, while the use of dynamic microphones in studio vocal recordings, and even the use of condenser microphones for near-field recording of drum sounds, and it seems Both have achieved good results. This tells us that the key to choosing a microphone is to see if it can achieve the desired effect, rather than just following the established rules and regulations.
The dynamic microphone has a voice coil, the voice coil is fixed on the diaphragm, and a strong permanent magnet is arranged near the voice coil. This structure is equivalent to the structure of a speaker, and the diaphragm is equivalent to a paper cone.
When the microphone is working, sound waves act on the diaphragm to cause the diaphragm to produce mechanical vibration. This vibration drives the voice coil to vibrate in a magnetic field. The excitation electricity and the voice coil output audio electrical signals, which convert sound into electrical signals.
How much do you know about the choice of microphone?
Recently, I was helping the company build an audio laboratory, and I needed to buy a microphone for corpus collection. The corpus is mainly used for acoustic testing and recognition model training, so it is necessary to buy a microphone with higher fidelity and capable of restoring the original tone.
After consulting some information, the microphones mainly include the following:
1. The dynamic microphone does not need power supply. Its advantage lies in its simplicity and solidity. The disadvantage is that the response speed of the diaphragm to fast-changing sound waves is not as fast as other types of microphones. Dynamic microphones are often used for vocal recording. (Not recommended)
Question: Is the human voice a sound wave that changes rapidly?
Answer: No, even the sharper life is not a fast-numbered sound in the field of acoustics. It is really a sound wave that changes quickly only if it is metal noise.
2. Condenser microphone
The core component of the condenser microphone is the pole head, which is composed of two metal films; when sound waves cause it to vibrate, the difference in the distance between the metal films causes a difference in capacitance and generates current. Because the pole requires a certain voltage to be polarized before it can be used, condenser microphones generally need to be powered by a phantom power supply to work. Condenser microphone has the characteristics of high sensitivity and high directivity. Therefore, it is generally used in various professional music, film and television recordings, and is very common in recording studios.
Generally built-in amplifier, because the output of the capacitor unit is very weak. Condenser microphones require an external 48 V phantom power supply or battery.
Condenser microphones are divided into large-diaphragm microphones and small-diaphragm microphones. The usual saying is that the characteristic of large-diaphragm condenser microphones is that the pickup sensitivity is higher than that of electret condenser microphones, but it is not absolute.
The diaphragm is the size of the microphone's pickup diaphragm. Sound is transmitted through the air. In principle, the larger the diaphragm, the more sensitive it is. The understanding of physical phenomena is the reason. But it is not absolute. For example, the large-diaphragm condenser microphones of some well-advertised brands have insufficient sound pickup and cannot give full play to the advantages of large-diaphragm microphones.
We usually call a microphone with a diaphragm diameter greater than or equal to 3/4 inch as a large diaphragm microphone. The material of large-diaphragm microphones is generally aluminum film, aluminum-plated, gold-plated, pure gold and other materials.
The advantage of a large-diaphragm condenser microphone is that it can give you the kind of sound that the studio is particularly admired-not the most natural sound, but the sound is thick and warm, and it feels very comfortable no matter what sound is recorded; the disadvantage is that the frequency of the sound The higher the higher, the more and more obvious the directivity of the large-diaphragm condenser microphone. It is not a problem to receive the microphone directly. If two microphones are used for stereo radio, the sound from the side may not be ideal. (Although this is said, the friends who do the algorithm finally recommended a large-diaphragm condenser microphone, because the current needs of the large-diaphragm microphone can already meet the requirements)
If you want extremely precise sound reception, then a small-diaphragm condenser microphone is the best choice. However, a more precise sound is not necessarily a more satisfying sound, and sometimes a precise sound does not sound so dynamic and powerful. However, if you want to record the sound of nature completely, a small-diaphragm condenser microphone should be a good choice.
4. The ribbon microphone is a special dynamic microphone that can record clear but slightly dim sound, which makes them often used artistically in recording studios. Ribbon microphones are generally very fragile, so fragile that some brands' manuals will remind users: When holding the ribbon microphone to receive the sound, walk slowly to prevent the air from passing through the microphone too fast and causing the ribbon to displace. Like dynamic microphones, most ribbon microphones do not require external power supply (except for some built-in amplifiers). However, the output of ribbon microphones is generally relatively small, so it is better to use with a pre-amplifier.