As a listening room, you must have a good acoustic characteristics, such as reverberation time, resonant mode, sound-stained state, sound field uniformity, and so on. These indicators are closely related to the three-dimensional size of the room and the material texture of the interface between the walls, floors, ceilings, and the placement of the speakers.
First, the acoustic requirements of the auditorium? This can also be called the hardware requirements. A room has three dimensions of length, width and height and has a minimum resonant frequency in each direction. The actual minimum resonant frequency in the room is determined by the length of the room and its wavelength is equal to twice the length of the room. For a room of 6m in length, when the speed of sound is 344m / s (room temperature 20 ° C), the lowest resonant frequency in the room is about 29Hz, which is the lowest frequency that can produce effective sound in the room. Even if the audio equipment can emit sound below the lowest resonance frequency, since it cannot form half a wavelength in the room and does not satisfy the resonance condition, it cannot generate resonance, and there is not enough effective sound pressure, so it is not optimal. effect. China Home Theater Network
The three-dimensional size of the room determines the presence of three fundamental natural resonant frequencies and harmonics at integer multiples of the three fundamental natural resonant frequencies that interfere with each other as they propagate through the room, creating a complex combined resonant frequency. Acoustically, the room can be regarded as a resonator. When the frequency of the sound source is consistent with the natural resonant frequency (normal frequency) determined by the three-dimensional size of the room, a standing wave will be formed and resonance will occur, which is the phenomenon of acoustic resonance. Sound field uniformity, acoustic staining, and frequency irregularities in the audio-visual room are all related to acoustic resonance. This resonance will add the color of the room's acoustic resonance to the original signal, causing sound pollution. Generally speaking, the loudness of a certain frequency or a certain frequency in the middle and low frequency is excessively strengthened, and the squeaking sound causes the signal reproduction loudness imbalance in this frequency band, which will greatly affect the listening effect. As for the high frequency band, the resonance distribution is relatively uniform, and the sound and dyeing is small, which is not enough to affect the overall listening effect. Therefore, the focus should be considered on the influence of the middle and low frequency bands.
In order to avoid or reduce this harmful acoustic dyeing, the resonance frequency is evenly distributed, and a prominent isolated segment or a certain frequency resonant mode is avoided. One method is to reasonably change the three-dimensional size of the room. It is conceivable to change the three-dimensional dimensions by appropriate interior decoration, making partition walls, ceilings or even removing some of the non-bearing walls (this rational transformation also takes into account the structural safety factors of the building, such as the intention to demolish a certain wall, It is best to ask for advice from construction professionals). Simply put, this is consistent with the principle of selecting the internal three-dimensional size when designing the speaker, that is, the length, width, and height cannot be integer multiples or too close. The specific sound field resonance modes, calculation formulas and related data are not listed one by one. Please refer to the related acoustic books if necessary. Here is a reference to the IEC29-B home listening room standard proposed by the International Electrotechnical Commission (IEC) with reference to European home listening rooms, as shown in Table 1 and Figure 1.
The other method is more reluctant, that is, it can be reasonably arranged while keeping the original three-dimensional size of the room, and the appropriate sound absorbing material is used to increase the interface damping of the wall surface, the floor, etc., so as to highlight a certain frequency band. The intensity of the resonance is reduced, and the resonance peak is flattened and widened, thereby reducing the influence of harmful resonance on the overall sound effect. However, this method has limited effectiveness and is only suitable for cases where the harmful resonance intensity is not large. Because if you want to strengthen the sound absorbing material to reduce the strong harmful resonance, it will also shorten the reverberation time, which will also make the sense of hearing worse, making the playback sound become dead, lack of color and anger.
Second, the reverberation time of the audition room? This is another important parameter of the audio-visual room. Reverberation is produced by the multiple reflection characteristics of the sound in the room, which keeps the sound pressure in the room for a while after the sound source stops sounding. The reverberation time refers to the time required for the sound source to stop sounding and the indoor sound pressure is attenuated by 60 dB, that is, one millionth of the time to the original sound pressure stability value. If the reverberation time of the audio-visual room is too long, the sound emitted from the front of the sound source has not disappeared, and the sound behind it appears, which makes it easy for the bass to roar, resulting in a decrease in the clarity of the signal concentrated in the middle and high frequency bands, such as language dialogue, and even the sense of orientation disappears ( Because the sound image localization is obtained by the middle and high frequency direct sound of the left and right main speakers, the reverberation sound generated by the reflection is from a plurality of orientations, directly interfering with the direct sound and affecting the correct positioning of the sound image). If the reverberation time is too short, it will make the sound thin, dry, dull, lacking color and anger. Only when the reverberation time is moderate, the overall sound effect will be full, vivid, contagious and expressive.
• The optimal reverberation time is not strictly a fixed value, even if it is specific to a listening room. It is based on the subjective experience and experience of the individual, and the reverberation time required to appreciate different program types is different. If you want to enjoy the film and television program, the reverberation time requirement is a little shorter, the sound effect will be more vivid, the character dialogue is clear, and the sound image is positioned. Appreciating pure music programs requires a slightly longer reverberation time, which sounds more comfortable, and classical music programs require reverberation time that is slightly longer than pop music. This is because different types of programs have different requirements for various aspects of post-mixing production, and a moderate reverberation time is required for playback to maximize the sound recovery. China Home Theater Network
As a home audition room, a compromise is usually taken to deal with the reverberation time, and then partially adjusted by pulling or closing the movable curtain or tapestry hanging on the wall. A large number of experiments and data show that the reverberation time of the home audio-visual room is generally about 0.4-0.6s (500Hz). The calculation of the reverberation time usually uses the following formula: t=0.16V/, where t is the reverberation time in seconds; V is the volume of the audio-visual room, the unit is cubic meters; it is the total indoor sound absorption coefficient. Table 2 shows the sound absorption coefficients of commonly used sound absorbing materials. For example, an audio-visual room is 6.2m long, 4.4m wide and 2.8m high. The ceiling and the floor are flat plastered surfaces. There is a 4m3m chemical fiber carpet in the middle of the ground. A 6m3m velvet curtain is hung on the two walls. (1cm from the wall), 4.4m2.8m chemical fiber carpet is placed on the opposite wall of the screen. Try to estimate the reverberation time of the audition room (at 500 Hz). It is found from Table 2 that the sound absorption coefficient 1 of the bare wall and the ground is 0.02, the curtain is 20.4 when the curtain is suspended from the wall 1cm, the sound absorption coefficient of the carpet is 0.28, and the total sound absorption coefficient is: ? Total = 14.42 .81+(26.24.4-43)1+26.22.82+43 3+4.42.83=23.184 The net volume of the audio-visual room is: V=6.24.42.8=76.384m3, then the reverberation time is: t=0.16V/total=0.1676.384/ 23.184=0.53s? It can be said that the reverberation time of this room is more suitable. If you consider the sound absorption factors of the audience and furniture, the reverberation time will be slightly shorter.
Third, the speaker position? When you spend a lot of thoughts and a lot of money to put the audio-visual room in place according to the above mentioned requirements, if the speaker is not properly placed, then the result is only 4 words: . One of the purposes of setting up an audio-visual room is to better appreciate the real sound effects, which has much in common with Hi-Fi appreciation. Regarding the placement of the speakers, only some of the more precautions are mentioned here.
First, the spatial acoustic characteristics of the left and right sides of the audition room should be as symmetrical as possible (not necessarily visually symmetrical), that is, the amount of acoustic reflection or absorption in the left and right spaces should be as equal as possible. The distance between the two main speakers usually requires that the angle between the main speakers and the viewer is at least 30° above 2.5m; (the best angle for pure music appreciation is 60°; and the home theater is considered The coordination of sound image, generally required at 45 °; left and right), in order to obtain a better three-dimensional sound field, but the distance or angle should not be too large, otherwise the image and sound image positioning may be inconsistent. If the sound image of the left or right part of the screen is positioned far beyond the screen, it is beyond the approximate reasonable range, which may cause the auditory effect and the visual inconsistency.
The acoustic characteristics of the audition room are directly related to the position of the speaker in the room. The position of the main speaker in the room is mainly determined by the listening experience. Place the main speaker in a corner, leave the wall for a distance or away from the side wall, and select a position where you can get a more uniform sound field resonance. In addition, properly tilt the main speaker back a few angles and raise the main speakers to see if the effect will be better (sometimes this change will be obvious, it may get quite good results). ? The characteristics of the surrounding sound box with low directivity requirements are not strictly placed. They are usually placed on the left and right sides of the viewer, but they should not be too close to the viewer. The height of the speaker should be higher than the human ear. The spacing between the two surround speakers is generally slightly less than the spacing of the main speakers. When the surround sound box is placed in place, it is generally necessary to adjust the AV power amplifier surround delay, so that the sound effects of the front and rear speakers are seamlessly integrated and perfectly integrated to obtain a satisfactory overall effect.
The center speaker is relatively fixed and should be on the same vertical line as the center of the screen. It is best to keep the main speakers, the center speaker's tweeter and the viewer's ears at the same level. If the conditions are not met, the height difference between the center treble and the main speaker tweeter should preferably not exceed 30cm. If the difference is too large, the sound level of the main speaker and the center speaker will be significantly inconsistent, resulting in the sound image of the moving object on the screen. It becomes messy, unnatural, and the audiovisual effect is greatly reduced. It is also worth noting that when selecting a center speaker, the tweeter should use the same unit as the main speaker. In this way, the center speaker and the main speaker can be well matched in frequency response curve, directivity and phase, which is also in line with the basic technical requirements of Dolby AC-3 and THX.
The subwoofer is commonly known as the subwoofer. Since the frequency of replay is generally concentrated below 120-150 Hz, it should be specially selected in the position of the audio-visual room. It must be placed in multiple positions in the room for audition. Choose a suitable location to minimize indoor smear and distortion to place it. In general, the subwoofer should not be placed in the corner of the wall, close to the wall or the center of the room, because these positions are likely to cause strong resonance.
In fact, the above aspects pointed out in this article are more popular principles. Each person has their own tastes and tastes. Each family has various actual furniture and room structure layouts. Even speakers with different structures have different placement requirements. Therefore, the establishment and arrangement of home theaters is really a matter of people. Different, local conditions.
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