The use of wireless microphones points and operation principle of it
In stage performances, the artists on the stage not only singing but also have dance performances or interaction with the audience, if you use a wired microphone, will greatly limit the actors movements, microphone pickup will be affected to some extent, in order to meet the performance results quality, and ensure sound, you can use a wireless microphone. The wireless microphone transducer is the electrical frequency modulated on a carrier, to the receiver via antenna radiation point. Because it does not need an audio cable to connect the amplifier, actor activities naturally gained freedom.
The working principle of a wireless microphone
Wireless microphone is composed by the microphone, a small radio transmitter and receiver of three parts. A microphone converting sound into a corresponding electrical signal, a small radio transmitter modulated audio signal into a radio wave transmitted from the antenna, and then restore the original audio signal received by the receiver.
Modulated wireless microphone uses two main frequency modulation: one is the direct condenser microphone FM , that is the very first condenser microphone FM with direct access to the oscillation circuit, the circuit acts as a capacitor , when subjected to acoustic vibrations of the diaphragm , electrical capacitance microphone diaphragm between the plates and the consequent changes, resulting in the total capacity of the LC oscillation circuit is changed , thereby changing the oscillation frequency to achieve frequency modulation ; another is to change the in parallel with the internal capacitance of the oscillator loop active device , the oscillation frequency is changed , thereby obtaining a frequency modulation , the change in capacitance between the electrode to control the microphone sound signal by the microphone in this way is usually output to the signal after amplification modulation oscillator circuit.
First, the wireless microphone receive an audio sound signal, and then FM modulated in a UHF signal, and the signal emitted by the antenna to the space ; receiving , using an FM receiver , the received signal of high level , demodulation, the release ratio discriminator , a pre-stage amplifier stage , the final output of an audio signal .
Wireless microphone transmitter circuit block diagram shown in Figure 1. Microphone pickup acoustic space. Optional Dynamic microphone pole microphone, you can also choose electronic microphone condenser microphone pole and pole. Audio amplifier circuit to be picked up by the microphone pole level of the audio signal amplified and modulated into FM signal into the mixer circuit. The local oscillator uses quartz crystal oscillator generates VHF or UHF carrier signal into the mixer circuit. The mixer circuit and the carrier signal superimposed on the FM signal is mixed into the high-frequency amplification circuit. High-frequency amplifier circuit with a carrier level of the audio signal to be amplified. Isolation of the power transmission circuit amplifies the carrier signal, to be able to radiate into space by the transmitting antenna.
Wireless microphone receiver circuit block diagram shown in Figure 2. Reception antenna space UHF or VHF carrier signal, the signal is very weak. Therefore, you need to be amplified high-frequency amplifier circuit. The local oscillator quartz crystal oscillator which generates a 465 kHz higher than the transmitter carrier signal is fed to the mixer circuit. The mixer circuit of the carrier signals with the audio signal by the frequency mixer and local oscillator for carrier phases difference, i.e. the difference between the carrier signal off, leaving the intermediate frequency signal. IF amplifier circuit for optimum signals amplification efficiency through primary, secondary and tertiary IF amplifier audio signal modulated IF signal high-magnification. FM discriminator circuit embodiment of an audio signal to be converted into amplitude modulation of the audio signal. Preamplifier stage coupled to amplify the audio signal in order to meet the requirements of the next stage of work. Power amplifier power amplifier is small; the energy of the audio signal to be expanded, the audio signal reaches the voltage level of 0-4 dB, the input to the mixer.
2 wireless microphone use points
(1) Before using the microphone, the microphone should first understand the type and characteristics; technical indicators are often static and transient characteristics of a good microphone slightly lower, rather than higher static indicators of poor transient characteristics of the microphone better.
(2) The use of wireless microphones on stage all at the carrier frequency VHF or UHF segment. Because FM is spread in the sight of the way, so to the transmitter antenna receiver as possible.
(3) between the microphone and the receiver preferably no obstructions, especially to avoid the metal structure of metal frame, ventilation ducts, otherwise the signal will be absorbed or reflected FM cause of the induction field of the antenna on the receiver strong decrease, noise increases; nearby microphones should not have large reflective surface, in order to avoid strong reflections caused by phase interference and destruction of the natural sound. The positional relationship between the microphone and the speaker is also very important, the general requirements when using the microphone away from the speaker’s radiation pattern.
(4) Transmitter antenna must follow the body perpendicular to the ground.
(5) All transmitter antennas do not collide with the shell, or will cause Kaka sound.
(6) Avoid the antenna radiation than the blind area. Wireless microphone would make some noise on stage and pickup disappears in the blink spots. So before the show in the debugger is essential to identify blind spots, and recorded; Finally, it has to explain away the blind actor on the stage. You can also adjust the angle of the antenna to eliminate blind spots.
(7) Inversely proportional to the square of the distance and the size of the sound pickup microphone and the sound source between the microphones, the actor in the concert to be maintained between the mouth and the microphone at a distance to ensure that the language, voice sounds without blur. If the distance is too close, the bass is easy to control, resulting proximity effect; distance is too far, resulting in muffled speech. In large signal spout easily overload the microphone, leaving a serious distortion tone, generally from 10 to 20 cm taken within the scope.
(8) When using multiple microphones should be consistent with the phase of each microphone. If two microphones opposite phase, then mix into the mixer circuit signals cancel each other out, so that the sound is reduced. Therefore, when using multiple microphones branched, especially various types of microphones simultaneously mixed to adjust the phase of the microphone, the phase line.
Phase identification of the following methods are available: first used two microphones together, while receiving a sound source, when the sound improves, sending sound also increases, then the description of two microphones phase with phase; When the speech sounds when increased, sending sound but reduced and distorted, indicating that the microphone RP, which then will be adjusted over a microphone wiring to achieve the same phase. Then try the same way the other microphones.
For one sound source with two mono microphones pickup time , they need to be as close to the two microphones , each microphone or remain equidistant from the sound source , in order to avoid interference phase when added ; for two when two or more sound sources with two or more additional microphone pickup , the distance between each of the microphone is greater than three times the distance between the sound source and the microphone , to reduce the interference generated when the phase of the sum signal .
( 9 ) When a wireless microphone no sound when the receiver ‘s power to check whether there is a radio frequency signal indicating a fault or check the receiver is normal.
(10) When the working distance is too close to the microphone away from the receiver will produce a burst of noise or signal drop.
(11) If in the course of , hum or beep is too large, grounding switch the audio cable connection or need to check the receiver , if you use XLR connector on the receiver should be off the ground .
( 12 ) If the distance from the receiver antenna超过wireless microphone 60 m, by increasing the power level of the transmitter RF directional antenna or an active antenna distribution system to solve.