Some issues worthy of attention in the construction of digital cinema

With the great development of China's cultural industry, the construction of the national digital cinema screening hall has developed rapidly, and it has sprung up everywhere and thrived. It has played an extremely important role in the cultural construction of various places. It also received fruitful economic and social benefits. The effect of the double harvest of spiritual civilization and material civilization has been achieved. However, we cannot help but ignore the fact that there are many "digital cinema" screening halls that are also under construction. In some places, millions of dollars or even tens of millions of funds have been invested. Due to the lack of scientific arguments and scientific technical management, blindly chasing projects, resulting in annual losses, the lessons are extremely profound. There are many reasons for this. We think the following should be noted:

1. The "Code for the Design of Cinema Architecture" is a guide for the construction of the "Digital Film" screening hall. Investors should be familiar with its contents and should not be sloppy.

In recent years, some “Digital Film” screening hall construction units have invited us to participate in the on-site technical management as a “Party A representative”. Therefore, I was fortunate to have contact with experts from the China Film Science and Technology Research Institute and benefited a lot. I am familiar with the contents of the "norms", the meaning of the terms, and a lot of new knowledge. For example, in the construction of the "Digital Film" screening hall, the basic requirements of the auditorium and the differences in the basic requirements of the auditorium in the original specification have been correctly recognized. In the past, according to the recommendations of the specification, the length of the auditorium was determined according to the relationship between the delay time and the distance of the sound. The length of the hall can be 36m to 40m, and the reflection surface of the back wall of the hall is used to strengthen the sound level of the rear seat. But with the advent of movie stereo, especially analog stereo, which has evolved into digital stereo, the above approach is not appropriate. Too long delay sound will cause the sound and picture to be out of sync, and the sound phase positioning of the main speaker and the surround sound speaker will cause interference, which affects the effect of digital stereo; the size of the auditorium in the new specification is reference GY/J183- The technical standards of the 2002 digital stereo cinema are not more than 30m in length and 1.5±0.2:1 in length and width, which is extremely important for new cinemas. For example, in addition to the live load on the floor of the auditorium, the static load generated by the increase of the steps should also be considered. The standard value of the floor uniform live load is taken from GB50009 "Building Structure Load Specification". This problem should be highly valued by the builders in the renovation of old cinema venues. To learn from the lessons of the "stand collapse" that have been seen before, it must not appear in new and rebuilt theaters! The designer must promptly propose to the owner to ensure the safety of the cinema construction.

The economic benefits of modern cinemas depend to a large extent on the level of their technological content and the quality of their technology. That is to say, economics is subject to its technical constraints. Of course, the level of performance of a theater's technical performance is also affected by the size of the cinema's investment and operating efficiency. This is especially true in the construction of the "Digital Film" screening hall. For example, the construction of the "Digital Film" screening hall of Fujian Jinyi Plaza and Wanda Plaza, because of their large investment, advanced equipment, and better auditorium environment, the income is relatively high, which is a typical example. For the construction or operation of the "Digital Film" auditorium (hospital), it should truly recognize the profound meaning of "science and technology are the primary productive forces." In today's environment of entering the market economy, there is no such thing as pure technology that is not subject to economic constraints and does not serve the economy. Only technical measures that bring benefits to the audience and improve efficiency are valuable. Only when the funds are in place and can reach the funding level of the project construction can the project be launched. Do not arbitrarily reduce the objectives and technical requirements of the "Cinema Building Design Code" for the short-term economic benefits, and reluctantly find a place to simply decorate, install digital cinema equipment, and put a soft chair on the digital cinema. The consequences of doing so are dangerous. It is possible to repeat the same as the construction of the "video hall" in the 1980s, and it is also a quick mistake. Investors should understand the JGJ58 2008 cinema architectural design specification, which is a guide for the construction of the “Digital Cinema” screening hall.
Second, the audio-visual environment design of the cinema is a highly technical job. It must be performed by a technician who has mastered relevant film technology and communicates with the construction industry.

The audio-visual environment design of the cinema is based on the film screening process. With the corresponding architectural design means, through the comprehensive control of the quality of the sound and picture information of the film or digital film in the cinema, the audience can feel the most Good audiovisual effects. Therefore, relevant research and design must be performed by technicians who have mastered relevant film technology and can communicate with the construction industry. In this way, the quality of the construction of the cinema will be guaranteed.

A qualified audio-visual environment design should provide a reliable and comprehensive process foundation for the civil engineering design of cinemas and cinemas, and guide the completion of the entire civil design.

Giving the audience the visual and audio effects that the audience should have is the goal. In the entire theater design, the audience should be placed in the first place, and everything is for the audience. This is both the starting point and the end point of the audio-visual environment design. This basic guiding ideology is embodied not only in the establishment of the control system framework for audiovisual quality, but also in the selection of specific control indicators. For example, the "Specifications" clearly pointed out that the multiplex cinema built in commercial buildings, although there are many good, but also subject to some restrictions. For example, the plane size of the auditorium should be adapted to the grid modulus of the original building. The height of the auditorium should match the frame structure of the original building. Due to the large scale of the multiplex cinema building and the large difference in the use requirements, it is necessary to determine the height of each auditorium and the projection room in combination with the size of the auditorium, the technical requirements and various technical parameters. The level of the building must be determined according to local conditions. scale. It is recommended that technical management or quality control departments at all levels should intervene as soon as possible. However, it is also necessary to prevent the tendency of control and detection to be too strict and too dead. Because a movie theater construction project is related to various factors such as geographical conditions and funding. It should be arranged according to local conditions. Of course, giving up management and arbitrarily lowering the standard is definitely not advisable. Home Theater Network welcomes you!
Third, the visual environment design of the auditorium should be based on the provisions of the "Regulations", but also to select the best design plan according to local conditions, to achieve the best visual effects in the theater construction.

In the cinema, the visual environment of the auditorium mainly refers to the relationship between the audience in the horizontal and vertical directions and the image on the screen. The goal of the visual environment design is to make the audience area in a better position relative to the image on the screen both horizontally and vertically.

The horizontal visual design of the cinema is based on the screen size and correctly defines the boundaries of the audience area. It is actually considered in the following aspects: First, when the viewer is too close to the image on the screen, especially the lens with strong sense of presence will cause discomfort such as dizziness in some viewers; second, the audience distance If the image is too close, the particles of the image, the perforations on the screen, the seams, etc. may affect the viewing effect of the film; third, the viewer is too close to the screen, and may exceed the coverage angle of the main speaker behind the scene, directly affecting the stereo effect. Of course, the audience can't be too far away from the screen, and one inch of land is one inch of gold, so as not to affect the number of seats in the audience. In addition, if the front row of viewers is too far away from the screen, the viewing angle and listening angle of the audience in the back row will become too small, so the stereo displacement and space will be lost, and the stereo effect will be greatly reduced. Therefore, engineers are required to have a wealth of on-the-spot experience, comprehensive consideration of various conditions on the site, and to make the best visual environment design. I can't take it for granted by the drawings.

The vertical visual environment design of the cinema is mainly aimed at achieving the viewer's unobstructed view of the image on the screen. Ensure that the audience can see all the pictures in different positions in the audience area to achieve the best appreciation. In this respect, it is mainly based on the selection of the height of the viewpoint and the selection of the super high value of the line of sight. At the same time, it is necessary to take into account the initial situation of the original building structure of the auditorium, which requires comprehensive knowledge of the designer. In general, the height of the seat step ground is minimized while ensuring that the viewer's line of sight is unobstructed. Because the rise of the stepped ground will increase the load on the auditorium, and the investment will be more. At the same time, the audience is not very convenient to walk in the passage during the show. Of course, we must emphasize local conditions and safety.

Fourth, the acoustic environment of the auditorium should be designed to minimize the “processing” of the cinema's sound reproduction, especially the harmful “processing”. The goal of the acoustic environment design of the cinema is to give the cinema a sound that matches the sound of the film being shown.

The acoustic design of the auditorium should include both construction and electro-acoustic work. In the design of the audience hall, Jiansheng design and interior decoration design complement each other. In order to ensure the best acoustic effect in the auditorium, the material selection and structural form of the indoor acoustic decoration design should obey the requirements of the sound design. At the same time, the appropriate installation position of the electroacoustic equipment should be given according to the requirements of the electroacoustic design. Both the decorative effect and the sound field sound quality effect are guaranteed.

The interaction between Jiansheng and electroacoustic design is an important condition for the auditorium with good sound quality. Jiansheng design is a body design, that is, early reflection sound field design to avoid acoustic defects. It focuses on the design of the auditorium and the elimination of acoustic defects, the control of reverberation time and its frequency characteristics, and the suppression of noise. The electroacoustic design is also called the sound field design. The electroacoustic design in the cinema is focused on controlling room constants. The selection and arrangement of electroacoustic equipment should ensure the uniform distribution of the sound field in the audience hall, the reasonable direction of the sound radiation and the sound quality of the film. In order to expand the listening range of movie stereo in the audience hall, the following aspects must be considered: First, the audience design should be appropriate; second, the speaker installation position and height should meet the objective conditions of the auditorium sound field; third, the speaker The characteristics must meet the technical conditions of the movie stereo sound; fourth, the relative distance between the main channel speaker and the surround sound speaker behind the screen should satisfy the sound phase positioning condition of the movie stereo (not to exceed the sound distance of 50ms). Home Theater Network welcomes you!

The full-band sound absorption of the back wall of the auditorium can effectively control the back wall echo of the auditorium and its interference with the surround sound field. The rear wall of the screen is treated with medium and high frequency sound absorbing materials, which can effectively control the high frequency reflection sound after the screen, which is beneficial to the sound image localization of multiple sets of main speakers behind the screen.

The auditorium of the cinema is actually the soundproofing room for film recording. It can also be called a reduction room for recording. It is different from the acoustic design of other halls. It only needs to restore the effect of the recording (that is, the film recording effect can be restored without distortion). The sound quality is determined by the effect of the original film recording.

From an acoustic design point of view, it requires the auditorium to have a flat reverberation frequency characteristic and a short reverberation time. The stereo movie hall requires a shorter reverberation time. In 1995, IS()/WD12610 proposed the formula for calculating the reverberation time of a movie.

RT60≤0.027477V0'287353 (s)

RT60 reverberation time (s)

V-room volume (cubic feet)

The calculation formula for the upper limit of the reverberation time is defined in the technical standard of the GY/J183-200 digital stereo cinema with the upper and lower limits (see related information).

With the development and popularization of digital stereo theaters, the acoustic requirements for cinema buildings are getting higher and higher. The reverberation time frequency characteristic extends one octave to each end. Therefore, the difficulty in building sound design is relatively high. We must master the performance of the various sound absorbing materials to be used. There are many types of sound absorbing materials, and each type of sound absorbing material has a sound absorption range with a certain frequency characteristic. The sound absorbing materials used in the theater decoration are not blindly stacking various sound absorbing materials on the market wall, but based on the acoustic characteristics of the sound absorbing materials and the acoustic requirements of the theater sound design. And the arrangement, so that the sound absorbing material is fully functional. It must be emphasized that engineering procurement must be subject to design requirements.

Fifth, we must pay attention to the selection of transmission cables and connectors.

In a movie digital stereo system, signal transmission between various devices must be interconnected by cables. The quality of the cable used in any format and format is critical. In actual work, it is often because the transmission characteristics of the cable are neglected at a certain point, then the audio equipment may not achieve the best technical characteristics because the matching cables and connectors are not selected, and the audio-visual effect is It will be worse. There are many lessons in this regard. For example, a unit recently showed a "mosaic" failure in the middle of the screen when the "Digital Movie" was shown. The result was checked or not due to cable failure. This kind of failure has occurred in Fujian and should be taken seriously.

As the saying goes, "Good horses are well equipped with saddles." Now the cost of equipment in the movie hall is very high, ranging from hundreds of thousands to millions. It can't be considered that several devices can be connected, thus ignoring the requirements of the program quality transmission index and the requirement to select the transmission cable that matches the device. The application of impedance matching cable is an important part of the sound (visual) frequency indicator can not be ignored. In addition, when plugs and sockets are mated, it is necessary to maintain the closest contact, which is also an important technical work in the quality and technical specifications of the audio (frequency) system.

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