【 Weak current College 】 audio engineering often encountered some phase---Power By 【 China power house network 】

Audio system phase is very abstract, involves many related issues, where we discuss projects often encounter some of the more vulnerable to the issue of "phase".
In physics, the phase concept is reflected in the AC signal at any moment of the status of physical quantities. AC signal is of size and direction of change over time.
Sound system, often encounter problems on phase, typically, the sound of phase is on sound field in the sense of relative change, so they have the same and the influence of relative sound system.
Columns: two frequency same audio signal from the amplifier output, if a speaker cable RP, then the phase difference is called the phase difference, or is called from. In physics, the phase difference of the two is equal to 180 °. This situation is called reverse phase, or reversed.
In a real project, we would often encounter these problems about phase:
1. first, the sound system of power phase, if a set of system equipment used by the power of different phase (e.g. power amplifier using phase supply, mixer or peripheral used another phase supply), when the device consumes power level is not uniform, phase high and low of differences arising out of, will make some devices voltage high or low result does not work correctly, the entire system brings some interference effects, such as: Hum, current sound and so on; there may be differences caused by excessive phase and equipment damage.
Phase 2, speaker unit, with the frequency of the audio signal from the amplifier output, if a pair of speakers with a reversed-phase (commonly referred to as the "+" and "-" pole connected backwards), then the speaker unit produces AC phase difference, audio signal offset each other, the low-frequency signal sound reinforcement is very obvious weakness, the sound becomes dry, will return in the high-frequency, affecting the entire PA system debugging and the overall effect.
3. audio sources pickup parts, microphone also exists phase, if you have multiple microphone at the same time, there is a microphone RP would cause an overall imbalance tone generation, pickup the handset closer to the user, be offset by the signal. While the same phase of the second branch of the microphone closer together pickup, causing signal overlap, and increase the positive feedback, resulting from stress, this phenomenon is more common in karaoke. At the same time can be a test, the second branch of the same phase lap microphone, turn it into a 180 ° relative to pick-up, will obviously felt sound pressure is low, or even no signal output.
4, power amplifier, also phase, at the output terminals use a four-core plug is easier to understand the output polarity, banana plug has a distinct Red Black second port for identification, but when the amplifier using the bridge, the attention signal input control (usually A common extension) of the red as cathode, another input control (usually a B channel) in the red for the negative electrode.
5 grades better sound mixer, generally includes phase switch, in the use of different models of several branch parallel to pickup the handset, if abnormal voice, or weak, you can set one microphone channel phase switch pressed determine whether phase problem. 2 singers together singing "soulful", if the handheld microphone close relative horizontal position, you will find pick-up signal, press the speed at which a microphone phase switch to resolve the problem. As a professional sound reinforcement engineering technical personnel, if your system appears reversed phase, it is not acceptable, because this is only one interpretation, your speaker cable is connected backwards (or signal wire welding backwards), in addition to poor quality products, the speaker itself and power amplifier and other peripheral appear phase reverse connection possibilities are very low.
In our work, the contact of the "phase" of the main problems are often reversed phase, phase shift is rarely encounter, unless our own design divider or audio signal processing circuit. For example, the treble strings of a capacitor, the phase difference of 90 degrees.
And RP in practical application is very easy to find, there are two simple ways to solve this problem:
I. phase for circuit, now domestic phase detector is very cheap, less than 300 yuan, Canon, direct plug in the RCA, 6.3 other interfaces that can be directly detected lines for inverse problems. But not all of them are even better after a time, because the middle two threaded Cable RP, was negative. Instead, a section of a geological survey. This should be the engineering installation must pass by the program.
Second, for the amplifier to the speaker is reversed, you can listen directly through the sense of the judgment. If you feel there is a lack of grip
So, you can put all the Mono signal at the same time sent to two-channel mixing console, and then through the PAN (sound like positioning knob) are positioned on the left, right, left and right through the mixer main output sent to left and right speakers. And then keep the two input channels of one channel phase, another channel utilization phase switch button to switch to low-frequency invert obviously full-grown strong, medium fullness of the description phase without problems.
Technology forum comments: sound reinforcement systems, because the microphone signal output line or speaker power signal input cable polarity reversed and system phase distortion and other reasons, causing all kinds of sounds-phase or phase-shifting problems. The relationship between sound phase correctness (especially RP), will have a direct impact on the quality of sound reduction. However, at present, many small and medium-sized sound engineering technician appears to be on the system of RP didn't pay close attention. Most audio workers join the system, not finished taking into account the phase of the microphone and speaker; in equipment and systems for the adjustment, nor taken into account as adjustment and may bring a series of phase distortion, this is a modern sound system, will no doubt be a shortcoming. Hope this article can give more engaged in small and medium-sized engineering application of friends.