The indoor acoustic environment has a certain impact on the indoor sound field created by multi-channel speakers, and different room sounds have different spatial acoustic characteristics. Multi-channel sound system uses multiple speakers to express sound image positioning and create surround sound effects. This is not an easy task. If there is no ideal indoor acoustic environment to match, the comprehensive sound effect will not be good. .
1. The influence of indoor acoustic environment
According to the theory of acoustic psychology, the early reflected sound with a late direct sound less than 1ms in the room will significantly interfere with the direct sound, which will make the sound turbid and affect the sound image localization. Early reflections between 1 and 30 ms will have less interference on the direct sound. Combined with the direct sound, it helps to enhance the loudness, but may change the timbre of the direct sound. As for the reflected sound after 30ms, the human ear usually thinks it is a reverberation sound. In view of the above reasons, we must do a good job of acoustic treatment such as sound absorption, diffusion, and sound insulation in the audio-visual room, otherwise, excessive reverberation will reduce The clarity and continuity of the sound affect the replay sound effect.
In order to create a magnificent stereo field in theaters, the audio-visual room should not be too small, and sound-absorbing materials should be installed if conditions permit.
Second, the placement of the speakers
Under the premise of a good indoor acoustic environment, the more accurate the sound image localization and the more realistic and natural sound, the more lifelike the presence of sound and image can be displayed. First look at the placement of speakers in the theater. The distance between the left and right channel front speakers is almost as wide as the movie screen, and the front speakers are generally arranged behind the movie screen, and they can pass through the small gap of the screen to transmit sound to the audience. Therefore, this speaker can be placed at half the height of the screen. The subwoofer is not necessarily placed in a place where the front speaker group is symmetrical. A standard movie theater has many surround speakers, and these speakers, together with the front speakers, truly "surround" the audience.
After referring to the above speaker placement examples, let's go back and see how the speakers should be placed to get a better sound effect. Here, we have to pay attention to a problem, that is, the indoor playing space we encounter may be much smaller than the real theater. Below, we first discuss the placement of the three front (left, center, and right) speakers, then surround the sound box, and finally study the placement of the subwoofer.
1. The placement of the center channel speakers The front center speakers are generally placed as close to the center of the image screen as possible. The center channel speaker has a greater impact on the sound quality of movie dialogue. In order to ensure that the dialogue is accurately positioned in the center of the screen and the sound is clear, a separate speaker specially designed for the center channel should be used instead of ordinary bookshelf speakers or TV sets. Internal speakers are used instead.
Most of the center channel speakers are horizontal and horizontal cabinets, and the best placement is on the top of the TV (if the front projection display screen is used, it should be placed behind the screen), that is, it should be as close to the screen as possible. If the room space is limited, a more economical placement scheme can be used, that is, no center speaker. But at this time, the working mode of the AV power amplifier should be set to the "phantom" center channel mode, so that the center channel information is balanced out from the left and right speakers, and the sound image is exactly in the center of the screen. This is a small listening device. It is applicable to the room. Of course, it is better to have a single center speaker.
2. The placement of the left and right channel main speakers
The placement of these two speakers has a certain relationship with the position of the center channel speaker. In order to ensure the smoothness of the left and right movement of the sound image, they should be placed on both sides of the center channel speaker, and the three speakers should be kept at an equal distance from the position of the better listener in front of the screen. Generally speaking, the position of the center speaker should be set back a certain distance from the left and right speakers until the sound fields of the two can be completely combined to create a truly unified sound image positioning. The retreat distance is related to the size of the space, the listening position and the speakers used, and can be determined through experiments. In addition, the vertical height of the left and right channel speakers should not be higher or lower than 0.3m (preferably lower) than the axis of the mid/tweeter speaker, otherwise the left, center and right three If the height difference of the speakers is too large, the front sound image will feel like a jump when it shifts laterally. Generally, floor-standing speakers can meet the above requirements. If bookshelf speakers are used as left and right speakers, they should be fixed on the speaker stand to make its height meet the above requirements.
The distance of the left and right channel speakers from the screen is related to the size of the screen. If a color TV with a large or medium screen is used in a small room, the left and right channel speakers can be placed close to both sides of the screen. If the screen is small, you can make them a little further away from the screen to get a wider stereo field. But don't be too far away from the screen, so as not to give people a false feeling because the sound image position is too far away from the screen. From this point of view, there is a "congenital" deficiency-the environment is too small. To sum up, the sound directivity of the left, center, and right three-channel speakers is more important than diffusivity, that is, the radiation angle range of these three channels should be directed toward a better listening position. In this way, the influence of reflected sound from the floor, wall and roof can be reduced, and the clarity of sound image positioning can be appropriately ensured.
3. The placement of surround channel speakers Surround speakers are used to create an environmental atmosphere, and they also occupy a very important position in the entire speaker system.
A. Types of surround speakers At present, there are two types of surround speakers. One is ordinary single-pole small speakers. They are usually placed on a speaker stand or hung on the wall. Another type of surround speakers is the dipole speaker recommended by THX. Each speaker has two speakers installed back to back, and they are all connected in reverse phase. The speaker composed in this way only emits high-frequency sound to the front and rear, but cannot make low-frequency sound (even if low-frequency signal is input to it, it can not make bass because of guilt). Why is this? Let’s look at the working process of a dipole speaker. Two speakers are placed back to back in the speaker, and the two speakers are fed with signals of opposite phase. Suppose that speaker A inputs a positive signal at a certain moment. The carton moves forward to compress the front air (density increases). At the same time, the B speaker inputs a negative signal, and its low box moves backwards to make the air in front of it sparse (density decreases) so that the direction of sound waves in front of the two speakers is opposite. If the two speakers feed full-band signals, the low frequency has strong diffraction due to its longer wavelength, so that the low frequency sound emitted by the A speaker will be diffracted to the B speaker and be weakened (cancelled); and the mid-to-high frequency signal Due to its short wavelength, the poor diffraction ability of the mid- and high-frequency sound on both sides of the speaker is also small, so the cancellation effect in front of the speaker is not obvious, so the two speakers only emit mid- and high-frequency sound to the front and rear, but not low-frequency sound. Up. The purpose of using dipole speakers is to avoid overly significant directivity.
For the audio industry, dipole speakers are a very peculiar type, and this type of speakers needs to go through a certain amount of development to be mature and finalized. This kind of speaker is not full frequency band, because the frequency below 100MHz has been cut off. The reason for using such a speaker is that it only utters forward and backward at the same time and never utters to the side of the listener, and fills the listening room before the sound reaches the listener, so that it can create a suitable hearing. The accustomed surround sound loudspeaker.
B. Placement of surround speakers The placement of loop speakers should vary depending on the sound environment (room conditions) and the type of loop speakers. For speakers with left and right surround channels, the diffusivity of the sound should be more important than the directionality, which is conducive to creating a rich surround atmosphere. When placing dipole speakers, two factors must be considered: resonance and self-decay. The better anti-resonance position is 20% of the height of the indoor space from the ceiling (or the ground) (for example, the indoor height is 2.5m, the better position is 50cm above and below). In order to make the frequency response smoother, a new device called a low-frequency "trap" (absorption of low audio) can be added to eliminate the reflections that cause the sound to decay.
For direct radiating ring-wire speakers, there are many layout options that can be considered. For example: fixed on both sides of the wall, and make them point to the rear corner; fixed on the rear wall, so that they splay outwards and upwards in an inverted figure and face the junction of the side wall and the ceiling; placed on both sides against the wall On the floor, pointing upwards at the junction of the wall and ceiling, and so on. Many other programs can be designed according to the specific situation of the room. The surround sound field of a home theater is mainly formed by the sound reflection and refraction of the surround speakers on the various anti-sound surfaces in the room, and the indoor acoustic conditions of different rooms are very different. As long as patient experimentation and careful comparison, you will surely find a better placement Program.
4. Placement of subwoofer speakers Usually the subwoofer speakers are placed near the front corner, preferably more than 1m away from the corner, so as to reduce the interference of standing waves. You can also place the subwoofer speakers on both sides of the better listening position, keeping a proper distance, because the human ears are not sensitive to the directivity of the subwoofer from both sides, so the subwoofer will not interfere with the three fronts at this time. The original sound image positioning of the sound track. Of course, the better placement should be determined through experimentation.
The method described above may help to find a better placement of the subwoofer. Put the subwoofer in a better listening position (move away the nearby debris temporarily), connect its speaker cable and repeatedly play a piece of music with strong bass effects, and then listen carefully around the room. When listening, the ears are required to be close to the ground, roughly at the height of the subwoofer. When listening, find the point where the bass is the most stable, deepest, and clearest, which is the best placement of the subwoofer.