Design of background music system for smart home home theater

Home theater system design should follow the following standards and specifications:

(1) SJ/T 11217-2000 "General specification for surround sound amplifiers for home theater"

(2) SJ/T11218-2000 "General specification for a combined speaker system for home theater"

(3) The GYJ26-86 reverberation time standard adopts the "Recommended Time and Frequency Characteristics of Studios" recommended by the State Administration of Radio, Film and Television."

(4) GBJ232-82 Electrical Installation Standard adopts "Standard for Construction and Acceptance of Electrical Installation Engineering"

(5) GB50312-2000 Standard for Yangxian Line adopts “Construction and Building Complex Wiring Construction and Specification”

(6) GB/T50356-2005 Design Code for Architectural Acoustics of Theatres, Cinemas, and Multi-purpose Halls

(7) GB/T3557-94 "Cinema audio-visual environment technical requirements"

(8) GY/T183-2002 "Technical Standards for Digital Stereo Theaters"

(9) GBJ118-88 "Code for sound insulation design of civil buildings"

(10) GBJ76-84 "Reverberation time measurement specification for halls"

(11) GB50222-95 "Fire Protection Code for Interior Decoration Design of Buildings"

(12) "Code for design of integrated wiring system engineering" (GB50311-2007)

(13) "Code for acceptance of cabling system engineering" (GB50312-200'7)

Home Theater Audio System Design

1. Acoustic processing of video room

The key to designing a home theater is to acoustically process audio and video rooms according to the requirements of users. If only good audio equipment is used, and there is no good indoor acoustic environment treatment, the effect is to be greatly reduced. In addition, the design style of the audio and video room should be consistent with the overall decoration design of the user. The overall size of the room should reach the golden ratio. That is, the proportion of the length, width, and height of the audio room should not be a multiple of integer, but 1.618:1:0.618. Such as 7m in length, 4.33m in width and 2.67m in height, this can reduce the effect of standing waves in the room and make the sound quality better.

In addition, according to the external environment, sound insulation design and vibration isolation design. The sound insulation design is to isolate the noise around the room so as not to interfere with the inside and outside of the room, and to allow the sound to be diffused, but also to have proper sound absorption so that the acoustic wave reciprocating reflection will excite some natural frequency (normal frequency) sound interference, resulting in sound dyeing.

Vibration isolation is a measure to reduce vibrational radiation noise transmitted by solids. Sound travels faster in solids than liquids and gases, so solid sounds are more easily transmitted into the room. Wall-mounted air conditioners, electric motors on the ground, and vibrations of cars and train wheels can cause door and window and wall vibrations and radiate noise into the room.

In real life, the acoustic characteristics used as a video room are generally not ideal, so if the user's quality requirements for the sound are high, in addition to selecting the signal source, the equipment, but also to take some acoustic treatment on the room.

The acoustic treatment of the audio and video room focuses on the side walls and the ceiling. In principle, indoor sound waves should be treated and diffused more than absorption. The purpose is to reduce the resonance intensity and to prevent excessive use of sound-absorbing materials so that the reverberation time of the room is too short (0.3 s) to make the sound dry and not round. It is best not to have large sound-absorbing materials on the walls behind the speakers. Usually, no treatment is required. Brick walls or cement walls will make the sound full and full of vitality.

Side walls can evenly and appropriately set up some sound absorption and diffusion materials. For example, a heavy wool blanket is an excellent full-range sound-absorbing object, and thin carpets and tapestry only have absorption effects on medium and high frequencies. Wooden doorless bookcases are a good sound diffuser that can be used to adjust bass frequencies. In addition, furniture such as tables, chairs, mattresses, and sofas can adjust the sound transmission and can be used as an acoustic treatment.

Thin carpets, curtains, tapestries, etc. mainly absorb medium and high frequencies, and have a low absorption effect on low frequencies. Too much use can cause the reverberation time of the middle and high frequencies in the room to be short, making the sound Lack of color, not enough bright. Wooden boards, such as wood skirts, can effectively absorb low frequencies. However, there must be an appropriate gap between the wall and the wall when installing, and if necessary, sound-absorbing materials should be placed between them. However, remember that you cannot nail a large number of splints to the wall, and do not apply sound-absorbing blankets and drapes in the room. Otherwise, due to the large amount of high frequency absorption, it will cause the sound to dry up, reduce the details and reduce the volume.

Overhead wood flooring absorbs low frequencies. When the room is small, low frequency sounds can be prevented from overrunning. If the sound of a room sounds like a roar, thick carpets of wool can be laid near the reflections near the floor.

When the sound is harsh and the low-frequency sound is not enough, it appears to be thin--while the volume is loud and noisy, it should be set up to cover the sound-absorbing material at the reflection points of the reflections on both sides of the wall. If you find that the sound is too dry, you should remove the carpet. The sound absorbing block or cloth cushion made of glass fiber in the corner of the room can be used as the final adjustment of the reverberation time.

For the living room, due to the influence of the channel, the balance of the sound field in the room is affected, and sound absorption materials may be added on the asymmetric walls and corners to balance the reflections on both sides as much as possible.

For example, the length, width and height of a room are 4.6rn, 3.7m, and 2.5m, respectively. Although the ratio of the room structure does not reach the golden ratio, it is still ideal. The first resonance point and the second and third resonance points are not formed. The merger phenomenon does not constitute distortion, but there is also a certain low-frequency resonance within 70 Hz, and it needs to be processed when acoustic reconstruction is performed.

There are 3.7m walls on both sides of the room, with windows on one side, and the other side close to the entrance door. There are problems with either side as a curtain wall. Because the user still needs to use the windows normally, the windows cannot be sealed. The wall on the other side close to the entrance door does not have enough space. Coupled with the restriction on the length of the room, this room is not suitable for sound-transmitting structures. Through communication with the user, the final decision was made to use the side with the window as the curtain wall, use translucent velvet curtains, and select the electric curtain so that it would not affect the normal use of the windows.

Because the audio-visual room is located on the first floor of the residential building, neither the villa nor the basement, so the soundproofing of the audio-visual room is very important. In the underlying structure, a patented suspended acoustic keel layer is used to cancel acoustic waves by vibration. Acoustic materials are filled in the middle of the keel to absorb sound and achieve good sound insulation.

Four low-frequency sound-absorbing pillars were designed on both sides of the wall. Suspended sound-absorbing hanging elements were used on the walls to adjust the low-frequency resonance in the room, and the chord tuning board was used to diffuse the sound on the back wall. According to the user's preference, the sound-absorbing hanging body is decorated with the acoustic fabric of the same color as the curtain, so that the hue in the room is unified.

2. Placement of speakers

When the home theater audio system is designed, the speakers are arranged in three ways: 5.1-channel, 7.1-channel and 9.2-channel. However, in any case, the placement of the speakers should follow the following principles.

1) Direct-type full-range speakers to avoid interface reflection. The direct-type speaker is a sound box that directly radiates outwards. In theory, it is a speaker that directly couples the air with a speaker; from the appearance point of view, it is a speaker that is directly set outwards from the speaker port. This kind of sound box mainly relies on the radiation characteristics of sound waves, so that the speakers directly send sound energy into space. Under normal circumstances, the bass radiation angle of the direct-type speaker is larger than that of the high-frequency radiation. If the speaker is directly placed on the ground, the bass sound is first reflected to the ground and then reflected to the listener, and at this time, Because the direct sound emitted by the sound box is shorter than the distance traveled by the sound, the direct sound of the speaker's bass arrives at the human ear in advance, and the sound of the sound reaches the human ear, and the phenomenon of the bass “becoming first and then arriving” will appear, resulting in a heavy bass sound. The shadow makes the sound more murky.

In order to reduce the adverse effects of bass reverberation, when placing direct-type subwoofers, do not place the speakers directly on the ground or close to the corners of the wall. It is best to use a metal frame to increase the speaker height by 40cm; if the front of the speakers is strong Reflective materials (hard and smooth materials such as marble and granite floors) can also be used to absorb the sound of bass reflections by placing sound-absorbing carpets in front of the speakers.

2) Airborne subwoofers can use ground reflections. The air-flow type sound box is a sound box in which the sound of the speaker does not directly radiate outwards, that is, the sound box of the speaker diaphragm (cone) is not directly coupled with the air. The air flow subwoofer is easily recognizable in appearance, with its speakers facing outwards and front inwards. It would be better if the airborne subwoofer is placed on the ground because it can give full play to the reflection of the ground and make the bass sound thicker and fuller.

3) Listen to the sound area to obtain direct sound from the speaker. Direct sound is the sound from the speakers directly to the listener. Its main feature is pure sound, what kind of sound the speaker emits, what kind of sound the listener hears. The direct sound is not reflected by the walls, floors, and top surfaces of the room. There is no acoustic defect caused by the sound of the interior decoration materials. It is also not affected by the acoustic environment of the room, so the sound quality is guaranteed. The sound fidelity is high. A very important principle in the design of modern room acoustics is that the listening area makes full use of the direct sound emitted from the speakers and controls the reflected sound as much as possible.

4) The speaker placement should be symmetrical with the center axis of the room. Speakers should be placed symmetrically to the central axis of the room to provide an ideal, harmonious, and symmetrical sound field for the room. If the sound field is not uniform, the consistency of the volume and timbre of the listening area will be deteriorated. The asymmetrical placement of the speakers will result in fewer early reflections of the speakers facing the larger space, a lower volume, and a relatively large volume of early reflections in the room facing the smaller speakers. The uniformity of the sound field is destroyed.

5) Speaker cabinet volume and room volume should be suitable. It is best to use small cabinet speakers to play sounds in small rooms. Large rooms can use large cabinet speakers or multiple speakers to form arrays. In a small room, the potential of a large volume speaker may not be fully realized, and sometimes the sound quality is not ideal.

Front speakers (including left and right speakers) should be placed in front of the listener's field of view. The left and right channel speakers should be centered on the listener, and the angle should be within 45° to 60°. If the home theater is mainly used to enjoy movies, you can choose about 45 °; if most of the time is to listen to music instead of watching movies, then the distance between the left and right channel speakers can be increased to obtain a larger listening angle. Also note that the front speakers (including the left and right channel speakers) should be kept at the same height or near the ear height as much as possible.

The surround speakers should be placed on both sides of the listener's location and slightly behind, not just behind the location. It is installed 90cm above the human ear 60, which helps reduce the effect of positioning. Surround speakers should be directed directly at the listening area, not toward the listener, so that a diffuse, well-enveloped sound field can be created in the listening area, just like the sound field in a movie theater and dubbing room. If the surround speakers are too far forward, they will not be able to achieve enough rearward effects. For example, if the speakers are located too far back, the integration of surround and surround information with the entire sound field will be reduced.

Because the human ear is not sensitive to the directionality of the bass, the subwoofer can be placed at the corner. However, there are two things to note: First, the subwoofer must not be placed on objects that are likely to form resonances, such as a light-weight computer desk. Once this is done, when the subwoofer is working, the table is also shaken, which has a great impact on the sound quality; second, the back of the subwoofer must not cling to the wall. This is because many subwoofers are designed after being inverted. The inverted hole is backwards, if there is no certain distance, it will not play bass. Therefore, at least a distance from the wall is also required.