Teach you to improve the quality of sound playback

As we all know, the acoustic environment of the listening room has a much greater impact on the playback effect of the sound system than any other audio equipment. Although there are many ways to improve the acoustic environment, too much treatment of the listening room will cause a mistake. For example, it is of course very good to let the sound diffuse. The diffusion diffuses the sound in all directions and avoids the occurrence of echoes. However, if there are diffuse surfaces everywhere in the room, the sound image localization of the stereo will be deteriorated It spreads to the four directions and cannot be accurately focused into a sound image.

The room acoustics in a small room are more complicated. Although many audio books and periodicals specifically introduce this, they can't express exact and pertinent opinions. The problem is that there are many contradictions, and different experts have also expressed different opinions. But regarding the indoor acoustic environment and the significant impact of the speaker placement and listening position on the sound reproduction effect, there is consensus. This article will not talk about those esoteric principles and those weird ways to deal with the indoor acoustic environment. We only introduce some simple and practical methods that everyone can do to deal with the indoor listening environment.

1. Lay a thick carpet on the ground.

The most likely to seriously reflect the sound wave is the ground. Although the carpet is not effective for low frequencies, the first thing to do is to try to absorb some high frequency reflections. The early reflections formed in the first 5mS (milliseconds) or a few milliseconds after the direct sound will become part of the direct sound, and because they come from the same direction, they will be heard. It should be avoided that the pure sound speakers are mixed with some high-frequency sounds reflected from the ground. And because it is not possible to add some soft padding to the ceiling, if you do not lay the carpet on the ground, there will be two parallel and strong reflection surfaces, and the sound waves will be reflected back and forth between the ground and the ceiling, thus Make the sound unpleasant.

2. Hang curtains on the windows.

In some concert halls, always avoid reflective glass. In the listening room, because the walls are close to each other, the reflected sound generated by the glass is easily annoying. You can try to hang curtains that can be opened on the windows, and then draw the curtains while listening to music. In addition, do not place bookcases and furniture with glass front panels in the listening room.

3. Try to destroy the reflection of the parallel wall.

Parallel walls, like the ground and ceiling, may have endless reflections, resulting in "multiple echoes", making the sound unpleasant. You can slap your hands vigorously. If you hear an echo, it means there is something wrong in the listening room. Bookshelves, especially bookshelves with randomly placed books, can act as a diffuser of sound waves, which can cut off the reflection of those parallel surfaces. Although there are many specially made sound diffusion screens for sale, several bookshelves are placed in the listening room It can play a very good effect.

4. Paste some foam on the "mirror reflection point" of the tweeter.

Unless the sky canopy is as tall as a church, some foam blocks should be pasted on the "mirror reflection point" of each tweeter of the speaker. The so-called "mirror reflection point" refers to the point that when a mirror is placed at a certain point on the ceiling (or ground), the tweeter in the mirror can be seen from the listening position. Although the treatment of the ceiling does not have to be as strict as the treatment of the ground, it is still very beneficial to be able to do appropriate treatment. Comparing Figure 1 and Figure 2, it can be seen that when the mirror reflection point of the ceiling is pasted with foam with a thickness of only a few millimeters and an area not exceeding 0.1m2, the indoor listening environment has been improved.

5. The reverberation should not be too long.

Pasting some small foam blocks on the mirror reflection point does not make the listening room change too much. However, if you stick a large piece of foam or hang a relatively thick curtain, it will make the replayed music sound dull because of too much sound absorption. Thin and light sound-absorbing materials will absorb high frequencies well, but will not work at low frequencies. Generally, the thickness of the sound absorbing material is roughly equal to the half wavelength of the sound wave, so as to play the role of sound absorption. For a 10kHz sound wave, the wavelength is only 3.4cm, so a foam with a thickness of a few centimeters can absorb high frequencies; however, for a low frequency of 200Hz, because the wavelength is as large as 1.7m, the thickness is only a few centimeters Naturally, the bubble will not help. Therefore, there will obviously be a tone imbalance in the listening room. Most people will hear a sound field with reverberation, and high frequencies will be absorbed more often than low frequencies.
6. Slightly close to some speakers to listen.

Sometimes, for occasional attempts, you may wish to sit a little closer to the speakers to listen to music. In fact, many people often listen to music because they are sitting away from the box, so they are actually listening to the room rather than the speakers. Listening closer will be a pleasure. Although it may not be as real as listening to the sound coming directly from the speaker, it is not without merit as a comparison of audition standards. By the way, in fact, almost all recordings are monitored in the "near field" regardless of whether the recording is good or bad.

7. Ground reflection is a major source of sound pollution.

As mentioned earlier, sound-absorbing materials can absorb the high-frequency parts of the early reflections on the ground and ceiling. The early reflections referred to here are those that arrive within the first 5mS of the direct sound. The sound waves reflected back so quickly will merge with the direct sound. The two top octave bands of these early reflections will only produce some harsh sounds, but the frequency bands will produce sound stains. It can be seen from FIGS. 3 and 4 that there is ground reflection and some basic processing on the listening room to eliminate the situation after ground reflection.

After eliminating the reflection, the mid-band is ideal, and the response is smooth. This is why those line-source speakers will confuse some buyers. Since there is no longer a delayed ground reflection (or more precisely, the combination of ground and ceiling and speakers no longer produce reflections), the sound stain of the speakers will be reduced by itself. However, for a point-source sound box, you will still be able to buy less sound, as shown in Figure 5. The problem is that in order to obtain such good characteristics, it is necessary to spread large pieces of foam on the ground. Of course, it can be put on temporarily while listening to music, and removed when not listening. Just placing some thick foam on the mirror shot can solve the problem.

However, the reflection of the side wall is another matter. In order to be able to increase the "space sense", some people would like the reflection of some side walls as well. Due to the extremely tall and spacious concert hall, the reflections on the side walls will not be reflected until after a certain period of time. Therefore, it sounds pleasant to people. But in the listening room at home, because the reflection from the side wall returns too quickly, it is not so nice. I have tried affixing sound-absorbing materials on the mirror reflection points, and also placed some bookshelves near the side walls to diffuse the sound waves. However, how to deal with it has to pass the actual test. Note that if you want to use stronger side wall reflections to increase the sense of space, you have to specifically buy those speakers with good off-axis response.

8. In order to obtain the most appropriate low frequency, it is necessary to repeatedly test the speaker.

Regarding the placement of speakers, this problem is more complicated, and only a brief introduction can be made here. There are two factors that affect the placement of the speaker, one is the room resonance mode; the other is the effect of the boundary of the listening room on the radiation impedance of the speaker. According to the Allison effect, when the boundary is one-ninth wavelength away from the pronunciation unit, the pronunciation unit will not be loaded by the reflection of the boundary. Therefore, the sound radiation power of the speaker at this frequency is less.

Although it is possible to use computers and specialized programming software to determine the best position of speakers and listeners, it is still worth advocating to spend several hours on repeated trial and error. Remember that the bass pronunciation unit in the speaker is away from the ground, and the distance between the side wall and the rear wall should be selected as different as possible. According to the general placement principle, the square of the median of these spacings should be roughly equivalent to the product of the maximum spacing and the minimum spacing. If you place the speaker closer to the corner of the wall, the bass will be enhanced.

You can use the "tremble" (Warble tone) and sound pressure level meter to test, if the speaker placed in a certain position can hear more sound below 300Hz, it proves that the speaker has been placed. If there is a conditional use of an RTA spectrum analyzer, it is easier to determine the placement of the speakers. You should be patient with the placement of the speakers, and you have to try it repeatedly instead of being discouraged, because through hard work you will surely be surprised. As shown in Figure 5, as long as the original pair of speakers is good, you will find that after you repeatedly tried the pendulum, your own set of audio equipment is really not bad.

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