The website is being upgraded......
The website is being upgraded......
always adhere to the customer-centric, through customized solutions and products to create value for customers; Build a win-win ecosystem with suppliers, partners and customers to promote audio and video technology progress and industrial development!
The main reason for whistling in the sound reinforcement system is that the sound of some frequencies in the system is too strong. When the volume of the microphone is raised, because these frequencies are too strong, they first reach the strength conditions required for whistling, forming a positive feedback, and self-excited oscillation occurs at this frequency. The frequency of self-excited oscillation is different from that of the roar. When the microphone pickup is used in the sound reinforcement system, the sound isolation measures can not be taken between the pickup area of the microphone and the playback area of the speaker, and the sound emitted by the speaker is easily transmitted through the space to the microphone, resulting in feedback whistling. Generally speaking, the problem of whistling exists only in the sound reinforcement system, and the conditions for producing whistling are not available in the recording and restoration system.
Solutions to prevent whistling:
Because the frequency curve of microphone pickup and sound production equipment is not an ideal flat straight line (especially some poor quality playback equipment), as well as the acoustic resonance of the hall sound field, the frequency response fluctuates greatly. The frequency equalizer can be used to compensate the sound amplification curve, and the frequency response of the system can be adjusted to an approximate straight line, so that the gain of each frequency band is basically consistent, and the sound transmission gain of the system can be improved. Equalizers with more than 21 segments should be used, and parametric equalizers should be configured where the requirements are relatively high, and feedback suppressors can be used when the requirements are higher. In fact, when the feedback self-excitation occurs in the sound reinforcement system, its frequency is only a pure tone fixed at a certain point, so as long as a very narrow band notch excise this frequency, you can suppress the system whistling.
In highly demanding occasions, such as some live singing places, it is common to use audio feedback automatic suppression device, which can automatically track the feedback point frequency, automatically adjust the Q value bandwidth, automatically eliminate the acoustic feedback and maximize the protection of sound quality. The principle is to suppress whistling by trapping waves. For example, Sabine's FBX series feedback suppressor, which is a 9-segment narrow-band automatic voltage limiting device controlled by a microcomputer, can better distinguish the feedback self-excited signal from the music signal, can react quickly when the system appears self-excited, and set a very narrow digital filter at the feedback frequency point, and its notch depth will be automatically set. The filter bandwidth is only 1/3 octave, and such a narrow notch band almost has no effect on loudness and timbre.
One of the most effective ways to both avoid whistling and increase the volume of the PA is to pick up the microphone as close to the source as possible, and the microphone should be non-directional. Here it is clear that the pickup attenuation of directional microphones (especially sharp directional microphones) remote sound sources is very small, and adjusting the distance has little effect on improving the volume of the amplification and preventing whistling. Whether the sound reinforcement system is easy to scream is not directly related to the sensitivity of the microphone. But highly sensitive microphones are sharp directional, easy to produce whistles. Shortening the distance between the device and the audience can actually improve the loudness of the PA. The total gain of the system can be reduced appropriately. If coupled with a wide directional near-field speaker, the microphone can be slightly farther away to avoid whistling. For the direct feedback sound field of the speaker, the farther the microphone is from the speaker, the better, and the closer the speaker is to the listener, the better. The microphone should be placed on the back of the speaker radiation direction, if the microphone is likely to be carried around, the speaker should be placed where the microphone cannot get very close.
Reverse phase cancellation to prevent self-excitation is common in high frequency amplifier circuits. Two microphones of the same specification can be used in the audio amplification circuit to pick up direct sound and reflected sound respectively, and the phase of the reflected sound signal can be cancelled out before entering the power amplifier through the reverse circuit, which can effectively prevent whistling from self-excitation.
The self-excited roar of the PA system, its feedback loop is positive feedback, if the microphone signal is phase modulation processing, it will destroy the self-excited phase conditions, so as to prevent the self-excited roar of the system. Some data show that when the phase deviation value is 140°, the stability is the best; Moreover, the higher the frequency of modulation, the better the stability of the system. In order to make the processed sound quality without too much distortion, the maximum allowable value of the phase modulation frequency is 4Hz.
Of course, these methods above are relatively professional, in fact, the most practical is to avoid the microphone and the sound of the microphone opposite, so that it will be the most direct to prevent whistling, the general whistling is also equivalent to the sound of the wireless cycle reached a critical point produced. In addition, if it is not used for professional studio recording, try to choose a single-pointed microphone, so that you can prevent the surrounding noise from being collected by the microphone and too much sound feedback.