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Problems to be noted in the design of acoustic noise reduction in cinemas
Three soundproofing points in the acoustic design module of the cinema and five noise reduction problems need to be paid attention to. During the construction of some cinemas, we found that the construction acoustics are not understood by the owners, the technicians and construction personnel responsible for the design preparation and construction. And note that the built cinema has left a case of a sound defect. "Modern Film Technology", No. 3, 2007 (Cinema Building) column, Comrade Chen Jiang, the film-level evaluation test group of the State Administration of Radio and Television, wrote a lot about the acoustics of the theater building, such as the adjacent audience. The hall has low sound insulation, high background noise, and the reverberation time is not up to standard. The author also believes that these defects exist in the current theater construction, and now talk about some specific issues and talk about their own views.
一.About sound insulation
Most of the construction of the new multiplex cinemas is mainly based on small multi-rooms, so as to make full use of the limited area and space to maximize the number of cinemas.
As the number of film programs has increased every year in recent years, and digital films are becoming more and more popular, the size of multi-hall cinemas is also increasing year by year. In large and medium-sized cities in China, the number of audience halls in the general multi-hall cinema is more than 6, 7 more common. The more common scale is a 300 or so medium-sized cinema, and then according to the effective area of the configuration of more than 100-200 seats between the small studio, the condition can also be designed a small VIP audience hall, the formation of different sizes, diverse levels, a full range of multi-room cinema.
Since most multi-hall cinemas are located in densely populated commercial centers, or within large commercial buildings, the rental costs of the venue are relatively high, which requires owners to make full use of the rental area as much as possible, increase the number of studios, and strive for higher returns and a full range of business conditions.
Based on the above situation, the screening process designers in planning and design, can make full use of the effective space and space,as soon as possible to make full use of the rental area and take into account the complete pattern, but also should meet the relevant specifications. In order to achieve these objectives, it is inevitable that the audience hall and the audience hall to share a separation wall or a walkway adjacent situation. In such a tightly arranged studio situation, the soundproof between each other is particularly important.
l、Sound insulation between the hall and the hall
According to the Digital Stereo Cinema Technical Standard, the common separation wall separation wall between the audience hall and the audience room should have a sound insulation effect of not less than 60dB (C). And to achieve the above standard provisions, in general, there is still a certain degree of difficulty, especially to deal with low-frequency piercing.
First of all, the load of the original structure of the building is generally not allowed to be built according to the mass law of the air noise of the decibel value of the component. At the same time, the state also restricts the use of clay components with higher quality. At this time, consideration should be given to the use of other lightweight new materials to build the wall and to match the width of the cavity (some also consider the use of the light weight structure to assist the sound insulation). When using this method to separate the auditorium, it is necessary to carefully analyze and calculate, so as not to make the wall of the partition wall too thick (some thicknesses of nearly 1m after the partition wall is completed), and the effective site area is lost. It can also achieve the corresponding sound insulation effect; at the same time, it should also consider the economic factors such as the selection of materials.
Another way is to arrange an audience entrance and a walkway between the hall and the hall. In doing so, each hall can be constructed with a new material, lightly masonry wall or a lightweight structure. In this way, the sound insulation effect is very good, but the site occupancy is relatively large. To adopt this method, it is necessary to control the width of the aisle as much as possible according to the size of the hall and the relevant specifications. Under the premise of meeting the requirements of the specification, the control of the walkway of the audience will not be too wide and waste the area. At the same time, it should also be noted that the size and length-to-width ratio of the auditorium on both sides of the walkway meet the requirements of the standard, as well as the standard requirements for construction, and cannot be ignored. If a wall is not in the position of the structural beam, it is necessary to negotiate with the relevant parties to consider how to solve the load problem of the floor. Therefore, the projection process designer should pay attention to the relevant specifications and requirements of architectural acoustics when designing the process.
2. the sound separation between the audience hall and the screening room and other layout according to the "theatre, cinema and multi-purpose hall building acoustic design specifications" requirements, the audience hall and the projector room partition wall of the medium-frequency sound separation should be 45dB. However, in the actual design operation, we should also fully consider the sound insulation of the screening window and the observation window. Because of the thickness of the optical glass and the sealing of the form and other factors, it is easy to cause the sound insulation to fall short of standards. I tend to have the smaller the area of the projection window, as long as the projection light and the viewing angle are unobstructed.
At the same time, we should also consider the sound absorption and noise reduction treatment of the projector room, and design the separation wall according to the specific situation.
If the outside of the audience hall wall is a busy commercial center (such as pedestrian streets, etc.) or a busy road, at this time it is necessary to fully grasp the commercial center or busy road noise is what? What is the relative distance of the studio position from the noise source, etc. Based on the above information, the air acoustic sound insulation scheme is determined by calculation. In general, the commercial center and the general road noise will not exceed 75dB (A), the audience hall partition wall as long as a thickness of more than 200mm surface density greater than 160KG/m2 of the aemoeid concrete block wall or hollow brick wall basic ally. In case of special circumstances (e.g. neighborhoods where cars sound frequently, etc.), in order to increase the sound insulation, the wall should be thickened appropriately, or the use of materials that are heavier, or other lightweight structures to assist the sound insulation.
The partition wall between the partition wall of the audience hall and the entrance lobby or the entrance and exit walkway is relatively simple. Generally, the noise in the entrance hall is not very large, and it is basically in accordance with the above-mentioned external wall design. If the auditorium is close to other entertainment establishments (such as OK Song City, entertainment facilities, etc.), or only one wall, then it is necessary to take relative sound insulation measures.
The sound insulation design of the floor and roof should also be fully considered, because the thickness of the general floor pouring concrete is only 12 to 15 cm, so should be treated according to the different operating patterns opposite the partition. In the case of a lightweight mesh roof, measures to increase the hall insulation should be calculated based on the material of the lightweight roof and the thickness of the insulation.
Attention should also be paid to deal with the impact sound and solid wear sound and other problems.