The wireless microphone consists of a transmitter and a receiver, and is usually called a wireless microphone system. The transmitter is powered by a battery, and the microphone converts the sound into an audio electric signal. After being processed by the internal circuit, the radio wave containing the audio information is emitted into the surrounding space. The receiver is generally powered by the mains. The receiving antenna receives the radio waves from the transmitter, processes the internal circuit, extracts the audio signal, and sends it to the sound reinforcement system through the output signal line to complete the wireless transmission of the audio signal. A receiver usually contains 1, 2, or 4 receiving circuits, which receive signals from 1, 2, or 4 wireless microphones respectively, of which 2 are the most common.
So far, there are mainly the following types of wireless microphones.
1.FM wireless microphone
This type of microphone may not have been heard of by the post-90s generation. In order to get rid of the fetters of some microphone cables, people used FM radio transmission and reception principles for reference, and used FM radio or special receiver to receive and play sound after the microphone's transduction principle and audio modulation amplification transmission process. This method has simple circuit design and low cost, but the quality is poor, the frequency is unstable, and it is easily interfered by other electric waves. Of course, the sound quality effect is not guaranteed. It has basically been eliminated now.
2.VHF wireless microphone
After that, wireless microphones using the oscillation frequency of quartz crystals appeared. Because the quartz crystal oscillation frequency is relatively stable, the wireless microphone transmitter and receiver composed of it will work much more stable. This microphone has two frequency bands, low frequency and high frequency.
The low-frequency frequency is around 50MHz, the sound transmission effect is poor, and it is easily affected by other wireless signals when used, and has gradually disappeared from the market; the high-frequency frequency is between 180-280MHz, and it has both appearance design and performance. Great improvement and easy to use. Compared with FM wireless microphones, VHF microphones (referred to as V-segment microphones) have a crystal frequency-locked design, which can receive signals more stably, and the price is relatively affordable. They are mainly used in places with low requirements.
3. UHF wireless microphone
Although compared with FM microphones, VHF microphones have made great progress, but they still have a narrow expandable range, crowded frequencies when using multiple microphones, less compatible frequencies, and small signal dynamic range. They are also vulnerable to TV channels, electric welding, etc. Clutter interference such as motors.
Therefore, UHF wireless microphones (referred to as U-segment microphones for short) appeared, with frequencies in the range of 300-3000MHz (400-830MHz frequency bands are generally used, and frequency bands above 830MHz are rarely used, because the diffraction ability of frequency bands above 830 gradually deteriorates and is vulnerable to Mobile phone interference), the signal has a large dynamic range and a wide range of expansion. It can be used by multiple microphones to form a larger system. At the same time, it can better avoid the interference of clutter, and the effect of transmitting audio is better and more stable.
In addition, the UHF wavelength is shorter than VHF, so that the antenna length can be made shorter or even hidden. The internal components of the microphone can also be made smaller and more compact, making it more popular than VHF microphones in terms of size and aesthetics. It is the mainstream product on the market.
After years of development, UHF wireless microphone technology has become quite mature, and multiple types of products have been updated and iterated, such as frequency multiplier, multiplier diversity, adjustable multi-channel (PLL), adjustable multi-channel antenna diversity, adjustable multi-channel Dual-tuned diversity products, etc.
Among them, adjustable multi-channel (PLL) products are the mainstream products in the current market due to their complete functions and relatively low price. This type of product adopts phase-locked loop (PLL) technology and has multiple user adjustable channels. When users use this type of product, if they encounter external interference, they can avoid the interference by changing the working channel of the system; in addition, when multiple systems are used on the same occasion, they can use channels that do not interfere with each other to achieve simultaneous use. the goal of.
The current diversity is mainly used in some high-end products. The so-called diversity type refers to a microphone. There are two sets of receiving circuits in the receiver. The signals of the microphone are received at the same time through two antennas, and the internal control circuit detects and compares them. When the signal is strong enough, it is fixed. If one of the antennas is used, if a weak signal is detected, the switch will be automatically switched to the other antenna.
This method can reduce the dead point during close operation, expand the effective operating distance, and effectively improve the receiving effect. Because it corresponds to the same wireless microphone, two sets of the same receiving circuit are required, so the cost is relatively high, and it is mainly used for professional stage performance occasions with high requirements.
4. Infrared wireless microphone
With the development of UHF microphones, infrared wireless microphones appeared. Infrared wireless microphone is a wireless amplification system that uses infrared light as the carrier of sound signals to achieve transmission and reception.
The basic principle is similar to the UHF/VHF FM wireless system, and the process of modulation and demodulation of the sound signal is also required in the process of wireless transmission and reception. However, the carrier of the infrared wireless microphone is infrared light, and its frequency is much higher than that of the FM wireless system. Above 3G, the frequency environment is relatively clean, and there are less equipment radiating interference waves.
Compared with UHF/VHF FM wireless microphones, the main advantages of infrared wireless microphones are:
a. Safe and confidential. Since the infrared light wave carrier cannot pass through the wall, it is inherently confidential and easy to isolate, so it can effectively overcome the problem of cross-frequency between adjacent rooms.
b. Anti-interference. Infrared is not interfered by environmental sound waves and electromagnetic waves (such as mobile phones, walkie-talkies, etc.), and can achieve pure sound amplification with uniform and clear voice.
c. Good interoperability. Since the infrared light emitting and receiving of the same frequency are adopted, any receiver can be matched with any transmitter without changing the frequency point. As long as each room is equipped with an infrared receiver, you can use it directly when you bring any transmitter to any room, which is very convenient to use.
But the shortcomings of infrared wireless microphones are also obvious:
a. The coverage is small. Since the voice signal is transmitted through the infrared straight line between the microphone and the receiver, the coverage area is small. For larger rooms, the number of receivers must be increased to ensure signal reliability. The installation location requires high requirements, and blind spots are prone to occur. In order to increase the receiving effect of infrared signals, the receiver is generally installed on the ceiling, which increases the difficulty of installation.
b. It cannot be blocked. If the user accidentally blocks the infrared emission window of the microphone, signal transmission will be interrupted and sound will be interrupted.
c. Not suitable for outdoor use. When the infrared microphone is working, it needs to have a basic reflective surface, otherwise it will not be able to receive the signal. Therefore, infrared wireless microphones are not suitable for use in open environments (such as outdoors, large halls, etc.), but will have good effects in small and medium-sized relatively closed environments (such as classrooms, KTV rooms, small meeting rooms) .
5. Digital wireless microphone
With the arrival of the digital age, digital wireless microphones have also appeared. The working principle of digital wireless microphone is: sound is converted into digital signal, digital modulation, digital wireless transmission, received digital signal is converted into audio signal and output.
The advantages of this microphone are:
1. Good sound quality. The use of digital wireless microphones eliminates the need for companders for audio signal transmission, which can effectively avoid the possibility of high and low frequency phase distortion and compression noise in analog wireless microphones, and accurately restore high-quality original sounds.
2. Digital ID address recognition technology. Each receiver device adopts "one machine, one number", and each machine is factory-equipped with a unique ID identification address, and there is basically no crosstalk phenomenon, which completely solves the "crosstalk" and "crosstalk" that have not been well resolved by analog microphones. Co-channel interference" problem.
3. By allowing tighter channel spacing, digital wireless wireless systems can simultaneously use more effective compatible frequency points in a certain frequency band. This feature is very important for increasingly crowded frequency bands.
Of course, digital wireless microphones also have shortcomings, but this shortcoming has been gradually resolved. For example, the overall delay will be larger than that of analog wireless, but the delay time has now been controlled to be very short, unless the consistency requirements are very high, under normal circumstances, the delay will not be noticed. In addition, some people who are used to analog microphones feel that the sound of digital microphones is not as warm as analog. This is a matter of personal feeling, just like some people think that film movies are more textured than digital movies.
Misunderstandings of digital wireless microphones:
Many people now think that 2.4G wireless microphones are digital wireless microphones, but this is actually a misunderstanding. Digitization mainly means that both the sending and receiving signals are digital signals, and it has nothing to do with what frequency band is used. 2.4G, like UHF and VHF, is a wireless frequency modulation system, which means that UHF and VHF can also be made into digital wireless microphones. The so-called 2.4G refers to its frequency band between 2.405GHz-2.485GHz, so it is referred to as 2.4G wireless technology for short. This frequency band is an internationally prescribed free frequency band. Unlike UHF/VHF, which requires payment to relevant international organizations, this provides necessary favorable conditions for the development of 2.4G wireless technology.
Since 2.4G was applied to the microphone field relatively late, if it is made into an analog microphone to compete with UHF/VHF analog microphones, there is no obvious advantage. Therefore, digitalization is directly adopted, which takes the first-mover advantage. With the deliberate promotion of some manufacturers, many people Misunderstood that only 2.4G wireless microphones are digital wireless microphones.
In fact, in recent years, if you pay attention, you will find that there are more and more UHF/VHF digital wireless microphones on the market. Well-known microphone manufacturers, such as Shure and Sennheiser, have begun to focus on digitalization, and use UHF as their main focus instead of the 2.4G advertised by small and medium-sized manufacturers.
This is because: First of all, 2.4G is a free frequency band, so all kinds of electronic devices are in use. Although the frequency band is wide in theory, the actual usable range is very narrow and it is susceptible to interference from other devices. UHF has an independent use frequency band and is less affected by interference. After digitization, the effective frequency point has doubled compared with analog, and exceeded 2.4G; secondly, the transmission distance of 2.4G microphone is not as far as UHF microphone, because its use wavelength is longer than UHF. The microphone is short, so that the signal will be more easily blocked. On the contrary, UHF microphone has the ability to cross obstacles, and the transmission distance is longer. So from a development perspective, UHF is still the mainstream product in the digital age.
In short, whether it is UHF, VHF, 2.4G, or infrared, it is now developing towards digitization, and it will gradually replace analog to become the absolute main body of the microphone market.