This article is mainly about the related introduction of the microphone, and focuses on the detailed explanation of the common power supply mode of the microphone.
Microphone, whose scientific name is microphone, is an energy conversion device that converts sound signals into electrical signals. It is a transliteration of the English word "Microphone". Also called microphone and microphone. In the twentieth century, microphones developed from acoustic-electric conversion through resistance to inductive and capacitive conversion. A large number of new microphone technologies were gradually developed, including microphones such as aluminum ribbon and moving coil, as well as the widely used condenser microphones and electrets. Body microphone.
The wireless microphone is divided into three frequency bands, the FM section. VHF section, and UHF section. The following is a brief introduction to the performance of each frequency band, use occasions, etc., I hope to provide you with a little help when buying [1].
1. FM segment:
Everyone knows FM radio. The frequency of FM radio is 88-108MHz. The frequency of wireless microphones in the FM band is higher than 108MHz. Generally between 110-120MHz, so the FM radio signal will not cause interference to the FM radio microphone, but it will be interfered by other clutter [1].
The advantages of FM wireless microphones are: the circuit structure is simple, the cost is low, which is conducive to the production of manufacturers, but the disadvantages are: poor sound quality, the frequency will change with time/environment temperature, often there will be poor reception, disconnection, and interference. Big. Screaming into the microphone will cause intermittent sound. Use occasion: Very low requirements for use, and not much requirement for sound quality. FM wireless microphone can be used in this case where only sound is required [1].
2.VHF section
The VHF section is usually referred to as the V section, and the frequency is between 180-280MHz. Due to the high frequency, there is generally little interference. The frequency lock of crystal is adopted, and there will be no frequency conversion, and the receiving performance is relatively stable. V-band wireless microphones generally have two circuits, the first circuit; the high-frequency part only uses a 2003 integrated IC. Including. Signal reception, radio frequency amplification, frequency mixing, frequency discrimination, etc. are completed in one step. Sensitivity is not high, the frequency part adopts 31101 circuit. The audio is compressed and expanded, and the sound quality is greatly improved compared to FM. The receiving performance has been improved by a notch [1].
Advantages: stable reception. Short-distance communication is rarely interrupted. The shortcomings are: the high-frequency part is not stable, the audio frequency response is not wide enough, and the professional use effect is not ideal. Use occasions: general households, where the performance is relatively stable and the sound quality is decent. . This type of wireless microphone can be used [1].
The second circuit: the high-frequency part adopts discrete processing, high-frequency amplification, and intermediate-frequency amplification. Frequency mixing and frequency discrimination. Step-by-step processing, better effect, higher sensitivity, and more stable performance. The audio processing part adopts 571 circuit, which has better sound quality and wider audio frequency response [1].
Advantages: stable performance, good sound quality,
Use occasions: KTV hall, home. For small and medium-sized concerts, the effect is ideal.
3.UHF segment
UHF segment is generally called U segment. The frequency is generally 700-900MHz. Such a high frequency basically has no other external frequencies that can interfere, and most of the U-segment uses SMD components. The performance is very stable, there are generally three kinds of circuits in U. The audio reasonable circuit all adopts the latest 571 circuit, and the sound quality is better [1].
The first type: single frequency. Similar to the V band frequency circuit, high frequency amplification, intermediate frequency amplification. Frequency mixing and frequency discrimination. Step-by-step processing, high-amplification in several episodes for amplification, audio processing adopts 571 circuit design, clear sound quality. Use occasions: When it is not satisfied with the V segment, the requirements for use are not very high. Or if there is interference in the environment where the V-segment machine is used, this type of model can be used [1].
The second type: adjustable frequency type; this type of machine is controlled by a microcomputer program. The high-frequency oscillation is controlled by a phase-locked loop (PLL). Generally there are multiple channels adjustable. Thousands of adjustable frequency points are available for selection. Effectively avoid interference, multiple machines can be used at the same place at the same time without interfering with each other. If there is interference, adjust the frequency point to other frequency points to avoid interference, squelch control. The audio processing adopts a brand-new design with stable performance. Use occasions: this type of machine is used in many high-end KTV rooms. Small and medium-sized concerts. Or require multiple colleagues to sing, the effect is ideal [1].
The third type: diversity; the so-called diversity is diversity reception, one is single-frequency diversity. One is tunable frequency trial diversity. This type of machine has the functions of a U-segment machine, and each channel uses a two-way receiving circuit system. For example, there is a dead point in the receiving system of one channel, and the signal can be received in another channel, which effectively avoids the signal dead zone, greatly improves the technical level of the whole machine, and ensures the stability of the received signal and continuous reception. This type of machine is more advanced wireless microphone. The farthest use distance can reach more than 200 meters. Use occasions: various large and medium-sized concerts. The use environment is very demanding and the use environment is more complicated. This type of machine is the best choice.
What are the common power supply methods for microphones
Phantom Power
Phantom power supply is the most commonly used power supply in the field of professional microphones today. Phantom power supply was invented by telegraph engineers. They use a balanced transmission line as a conductor, and the earth as another conductor to form a signal loop. In this way, a wire can be saved. Since the power supply transmits the common mode signal, it has no effect on the differential mode signal on the balanced transmission line. So even if noise enters the power supply, it will not affect the transmitted signal.
Section 7.4 of IEC 61938 gives the standard for phantom power supply. The phantom is usually 48VDC, and now there are also 12VDC ones. There was a 24V power supply version (P24) for a while, but it has now been eliminated.
Microphones that use phantom power usually use XLR connectors, which are also called Canon heads. Some microphones now use 6.35mm (1/4 inch) headphone connectors.
If our existing preamplifier has only single-ended signal amplification capability, we can also use only one of the differential signal lines to extract the signal, as shown in Figure 2. This method has a slightly poorer anti-interference ability, but it is sufficient for most applications. A lot of practice has proved that the noise of the microphone signal mainly comes from the background noise of the recording environment rather than the noise of the electronic circuit. But many people may not face this conclusion.
Common microphone types
The microphone is a very personal item for musicians, and many factors must be considered when choosing. In a wide variety of microphones, there is no theorem such as "a certain microphone is the best". Each type of microphone has its own unique properties and uses, and the sound quality produced is also different. Let’s take a look at 7 common microphones.
Dynamic microphone
The meaning of "moving coil" is that the wire coil closely connected to the diaphragm moves continuously in the magnetic field according to the change of sound pressure, thereby generating a current that changes in proportion to the amplitude of the sound wave. In this way, the acoustic signal is converted into an electrical signal.
The coil of the dynamic microphone cuts the magnetic field to directly generate current, so the dynamic microphone does not need power supply. The advantage of a dynamic microphone is its simplicity and practicality. The disadvantage is that due to being "dragged" by the wire coil, the response speed of the diaphragm to fast-changing sound waves is not as fast as other types of microphones.
It is difficult for a dynamic microphone to pick up the high-frequency part of the wiper's high energy, but when picking up a strong kick or snare drum sound, the dynamic microphone can have a satisfying performance. Dynamic microphones are also often used to record the sound from electric guitar speakers.
Dynamic microphones are often used for vocal recording, which is largely a "traditional custom." Because the previous condenser microphones were bulky and fragile. But although condenser microphones designed specifically for live vocals abound, their more expensive average prices tend to make people more inclined to choose dynamic microphones that can also do their job well.
Small diaphragm condenser microphone
The condenser microphone is designed based on the principle of electrostatics. The diaphragm and the back plate constitute a capacitor unit. The vibration of the diaphragm with the sound wave causes the potential difference between it and the back plate to change, thereby converting the acoustic signal into an electrical signal. Condenser microphones generally have built-in amplifiers because the output of the condenser unit is very weak. Condenser microphones require an external 48 V phantom power supply or battery.
The significance of choosing a small-diaphragm condenser microphone is that those small diaphragms with a diameter of about 12 mm are very sensitive to the vibration of sound waves. The larger the diaphragm is, the less sensitive it is to the sound that is not facing the microphone, and the more obvious the sound staining caused by resonance.
If you want extremely accurate sound effects, then a small-diaphragm condenser microphone is the best choice. It should be noted that a more precise sound is not necessarily a more satisfying sound. Sometimes a precise sound does not sound so dynamic and powerful. But if you want to record the sounds of nature completely and truly, a small-diaphragm condenser microphone should be your choice.
Large-diaphragm condenser microphone
In the past, microphone manufacturers could not make the diaphragm as exquisite as it is now. All condenser microphones at that time should be called "large-diaphragm condenser microphones." Of course, there is no dividing line to define what is a "large diaphragm" and what is a "small diaphragm". As mentioned earlier, a size of about 12 mm can be called a "small diaphragm", and a size of 24 mm or more can be counted as a "large diaphragm". When buying a microphone, we will find that some microphones that look very large have a surprisingly small diaphragm inside, so the size of the diaphragm is a microphone parameter that requires our special attention.
The advantage of a large-diaphragm condenser microphone is that it can give you the kind of sound that the recording studio particularly admires-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 higher the frequency of the sound, the more obvious the directionality of the large-diaphragm condenser microphone. If you are facing the microphone, this is not a problem, but if you use two microphones for stereo reception, the sound from the side may not be ideal.
Vacuum tube microphone
The design and manufacture of this type of microphone can be traced back to the early days of condenser microphones. At that time, since transistors had not yet been widely used in large-scale applications, the built-in amplifiers of condenser microphones were all vacuum tubes. Although some vacuum tube microphones used to have small diaphragms, most of the vacuum tube microphones we see now have large diaphragms.
The advantage of the vacuum tube microphone is that the vacuum tube amplifier is prone to produce a very pleasant and comfortable distortion effect, that is, "warm sound". For vocals, this kind of warm distortion is often used as a panacea.
Unlike other types of microphones, vacuum tube microphones have become very popular since the age of vacuum tubes have long passed, and their prices are often high.
Ribbon microphone
The ribbon microphone is a special dynamic microphone. The diaphragm of the traditional dynamic microphone is tightly connected with the wire coil, while the aluminum ribbon microphone combines the diaphragm and the wire coil to form an aluminum tape (or metal tape). Because the aluminum ribbon is very thin and light, the sensitivity of the aluminum ribbon microphone to sound waves can be comparable to that of a condenser microphone, but the sound of the general aluminum ribbon microphone is relatively dark.
The ribbon microphone can record clear but slightly dim sound. This 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.
Electret microphone
The electret microphone is a special condenser microphone. We already know that the principle of a condenser microphone is that the amount of polarized charge on the capacitor changes, thereby generating electrical signals at both ends of the capacitor to achieve acoustic-electrical signal conversion.
The electret material is a material that can permanently retain these charges after adding charges. Using this principle, the electret material on the diaphragm or the backplane provides the constant voltage required by the capacitor unit, which can save the power supply of the microphone. However, the work of the microphone built-in amplifier still requires battery or phantom power. It should be noted that battery-based electret microphones are less sensitive than phantom-powered ones, and have a weaker ability to handle the maximum sound pressure.
Electret microphones are widely used in handheld devices because of their low cost and miniaturization. An electret microphone with an internal integrated FET preamplifier can provide high performance. Many of the most accurate microphones in the world today are electret microphones.
Piezo microphone
Piezoelectric microphones are also called crystal microphones, and their principle is to use the piezoelectric effect of certain materials-that is, sound causes the deformation of the material to produce a voltage change.
Piezoelectric microphones are now mainly in the form of contact microphones. A typical example is a guitar pickup. The piezoelectric microphone directly picks up the physical vibration of the sound source instead of the sound wave vibration in the air. The advantage is to isolate the sound of the instrument from other sounds. However, the sound picked up in this way will not be particularly real, so the application of piezoelectric microphones is more limited.
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