About those stereo and multi-channel speaker delay issues

[Home Theater Network HDAV.com.cn] Stereo Hi-Fi system (high-fidelity system) and multi-channel AV system (home theater system) are the two camps of the audio equipment market. These two audio systems have many common features. At the same time, there are a lot of different things. For many audio users, you may only know a few key points, such as installation, placement, connection, etc. In fact, there is a very important place. Perhaps forgotten, it is the speaker's own sound delay problem Delay (Audio Effect).

Due to the design of the audio room and the design of the product itself, the sound playback effect is often subject to a lot of interference. We must correct these interferences through various techniques, such as the delay of the sound. The following is a detailed explanation for everyone.

â–ŒThe appearance of sound delay

This problem is actually very large, covering a lot of content, we can use two aspects to analyze, that is, subjective and objective two factors, in the subjective factors of the sound system, the sound system itself will make the sound appear Delay, from the source to the playback end, from the digital to the analog, all aspects will make the sound delay, there is more to explain here. Another objective factor is the problem of listening to the sound environment, such as sound insulation, acoustics, and interior decoration. These will cause the sound to be subjected to various secondary reflections during the playback process, so that the sound effects in the room are generated. There are all kinds of differences and differences, so the sound effects of not having two audiovisual spaces in the world can be exactly the same.

▌ Stereo Hi-Fi system (high fidelity system) delay

Everyone knows that the transmission form of sound waves is a sinusoidal waveform with alternating positive and negative. This positive and negative is the phase we say. The phase of the sound wave is positive in the positive half cycle, and the phase of the sound wave is negative in the negative half cycle. If there are many speakers or sound sources, if the sounds arrive at the same place, if the time is inconsistent, the sound will be blurred and unclear. It will always sound squeaky; there may be different phases of sound waves. It is possible that there will be a positive and negative one, and the energy will cancel each other out. The energy offset is wasted, but unfortunately, it will cause the sound pressure to drop. If the sound pressure drops, the gain needs to be increased, which may lead to the level output. Too large to cause signal distortion, damage to the unit, causing loss and adverse effects.

In addition to providing a beautiful sense of hearing, the sound should be clean and powerful, and the professional audio equipment should be guaranteed to operate normally. Because the above problems lead to unsatisfactory results or equipment damage is also a common thing, then we must find ways to eliminate such hidden dangers, delay test and phase adjustment of the speaker. Of course, before we make adjustments, we have to figure out why the sounds of multiple speakers arrive at the same place are inconsistent. This article will specifically analyze the causes of this phenomenon.

Control of sound wave transmission

Some people may say that the low frequency runs slowly and the high sound runs fast. It sounds very reasonable. In fact, there is absolutely no reason. From the physics point of view, the speed of sound propagation in the air is related to altitude, temperature and humidity. There is no frequency or not. Our speakers are in In the same environment, it seems that it has nothing to do with the above factors. So, what other reasons can cause this phenomenon?

The most direct reason is that the position of the speakers is different, resulting in the difference in the time of the sound wave transmission to the same position and the phase difference. Nowadays, the design of audio-visual system, basically few people pay attention to the problem of speaker placement, which leads to many problems. This is one of the reasons. Through the adjustment of delay, the effect can be improved. The well-known eight methods of speaker placement are also considered based on such factors.

Solving the problem of the location is not handled properly, not necessarily, there is another reason, that is, the structure of the speaker box is different, resulting in deviation of the transmission time of the sound wave, especially the structure of the ultra-low speaker and the full-range speaker. The units of the full-range speakers are basically installed on the speaker panel, but some ultra-low speaker units are installed inside the cabinet. The transmission of sound waves must first come out through the interior of the cabinet, and it takes time. Therefore, it will also cause a difference in time. It also needs us to deal with it.

换 horn's transduction process

Some people may find that the unit of my subwoofer is also installed on the speaker panel. The sound wave transmission does not go through the inside of the cabinet. There are no problems for the above two reasons. How is there a time difference? Here is the result. A deeper reason for the energy conversion time of the horn. We know that the horn is a transducer element that converts electrical energy into heat and sound energy. We don't discuss thermal energy first. We only introduce the problem of sound energy conversion. Does the horn directly convert electrical energy into sound energy? Maybe a friend will say it. The horn is not an electro-acoustic conversion component. In fact, the phono-electrical conversion that we have seen is only one end and one end. The electric energy enters and the sound can come out.

In fact, the energy conversion has a middle part, and this middle part also contains three energy conversion processes. First, the electric energy enters the horn voice coil. After the power is turned on, the voice coil generates motion through the electromagnetic induction of the magnetic circuit of the horn, that is, the electric energy is first converted into kinetic energy; then the voice coil moving in the magnetic circuit drives the paper cone to move, leading to the air before and after the paper cone. Vibration, at this time, the kinetic energy of the paper cone that drives the air vibration is converted into sound energy.

The conversion process of these three kinds of energy has been seen as a physical conversion process. Since it is impossible to complete the physical conversion process at the same time, it takes a certain amount of time to complete. Then, what is the conversion time?

In the first process, if the moving part of the horn is moving, an external force is required. This external force is the electric energy entering the voice coil, and the electric power is generated by electromagnetic induction. Then the external force is related to the input electric power and the magnetic flux, and the same horn, input. The higher the power, the shorter the conversion time, the different speakers, the different structures, the different performances, the different magnetic fluxes, and the conversion time.

Next, with external force, it takes time to make the paper cone move, but this time is related to the weight of the vibrating part of the horn. The shorter the weight, the shorter the time, and the easier it is to move. Then let's look at the structure of the horn. The large-diameter paper cone is heavier than the small-diameter paper cone. Then, under the same external force, the small-diameter paper cone will move first, which means that the small-diameter paper cone will take less time to move. So from this point of view, the smaller the aperture, the faster the sound wave transmission speed. In front of us, the low frequency transmission is slower than the high frequency transmission. In fact, it should be said that the woofer transmission is slower than the tweeter transmission.

â–ŒMulti-channel delay problem

Compared with stereo, the biggest difference of multi-channel is that it can generate more “sound image”. Stereo uses two channels to virtualize one stereo image, while multi-channel is virtualized by multiple channels. A number of sound images are produced, so if the sound is delayed, then the "sound image" will be out of shape, or not so real, and deviate from the enveloping effect and effect of the film. Unlike stereo, the stereo sound delay is easier to detect, because once the human ear only pays attention to a sound image, the adjustment of the sound is obvious after adjustment by EQ and EQ.

However, multi-channel becomes very complicated. First, there must be a matching test signal, followed by complex positioning and EQ adjustment. Therefore, many people will use the test tool to complete the delay correction, but in any case, the multi-channel delay The time correction is a very arduous process, which also puts very high demands on the design, construction and commissioning of the entire multi-channel system. We will not explain more about the content.

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Note: This article is transferred from HIFI. The article is an independent view of the author and does not represent the position of the home theater network.