In order to continuously adapt to the progress and development of social civilization and to meet people's growing cultural needs to the maximum extent, many small theaters have emerged. In the actual sound quality design of small theaters, it is actually very difficult. Many of the efforts are only due to poor sound quality, so it is very necessary to study and discuss the acoustic design of small theaters.
1. Acoustic design indicators and requirements for small theater design
Before the acoustic design of the small theater, the acoustic design indicators and requirements that meet the theater environment and quality should be developed through the study of the functions and design requirements of the small theater. Because the design level and requirements of each theater are different, but the standards for the acoustic design of the theater are similar, they all pursue high-quality sound quality and high-grade environment.
The acoustic design of a theater mainly includes the processing of noise, achieving sound uniformity, solving focus, resonance feedback and other issues as well as correct calculation of indoor reverberation. The main principles of acoustic design are: reasonable reverberation, good sound diffusivity, no sound focus, no audible vibration noise, no dead spots. Based on the basic requirements of indoor acoustic characteristics, the acoustic design of the theater is also required: with appropriate loudness; uniform distribution of sound energy; meeting the signal-to-noise ratio requirements; ensuring balanced frequency response throughout the room; selecting the appropriate natural reverberation time. In addition, the design of the scheme should be designed with reference to relevant standards. A brief description of reverberation time and noise control in acoustic design is provided below.
Reverberation time
There are many objective evaluation criteria for the sound quality of the theater, but the reverberation time is often used as the main standard for acoustic design of small theaters. The reason why reverberation time is chosen as the main indicator for evaluating the quality of sound quality is due to its important value to the quality of sound quality, and on the other hand, because of the influence of reverberation on the design of sound and the quality of sound quality among many evaluation standards. Too long will be decisive will have a great impact on the sound quality.
The indicator that describes the reverb effect of a room is the reverberation time. Because the indoor sound absorption is related to the sound frequency, the reverberation time of different frequencies is different. There is a mathematical relationship between indoor sound absorption and reverberation time (Sebin formula): T60=K*V/A, which is the sum of the sound absorption coefficient and the area product of various sound absorbing materials in the room, divided by the total surface area. The larger the volume of the room, the longer the reverberation time; the larger the average sound absorption coefficient, the shorter the reverberation time. Therefore, the effective way to control the reverberation time is to correctly select the sound-absorbing material with good effect. The selection criteria for the reverberation time of the theater are: selection of the full value of the music fullness and language clarity; according to the main functions and uses of the theater; the natural sound-based hall adopts an adjustable reverberation structure.
Noise control
Noise control is another important component in the acoustic design of small theaters. Noise can interfere and mask people's normal hearing. Usually at the position of the minimum sound pressure level in the theater, the signal to noise ratio should be greater than 30 dB. When the noise in the theater is too large, it will not only affect the audience's auditory effect, but also affect the performer's performance. Generally, the sound absorption material is used for noise control during the construction of the theater. The closer the sound absorption material is to the sound source, the higher the sound absorption efficiency, and the increased chance of the reflection sound being absorbed, which is very advantageous for noise reduction. In addition, in order to enable the audience to obtain rich early reflection sound and reduce the noise interference shielding effect, in the chamber music performance, a spherical transparent material floating cloud type music reflecting plate is often arranged above the stage, and its suspension height, inclination angle and density degree They are all adjustable to suit different audience hall layouts.
Acoustic design of the small theater
The main content of acoustic design is noise control and sound quality design, and the sound quality design includes the design of the auditorium and the control of sound quality. Since the small theater is mostly built in a relatively quiet environment, the influence of external noise on the theater can be ruled out, and the indoor noise is often controlled by installing a sound insulation door and purchasing sound insulation equipment. Therefore, the key to the acoustic design of the small theater is the sound quality design. The sound quality optimization design is often one of the decisive factors of architectural design. The sound quality design of the small theater should be carried out simultaneously with the initial stage of the architectural design, and it should run through the entire construction drawing design, interior decoration design and construction. After the completion of the work, the necessary test and identification of the sound quality, and then the sound quality design can be properly adjusted or modified to achieve better expected results.
Sound quality design must first prevent external noise and vibration from entering the room, so that the noise in the room is kept to a minimum; secondly, it is necessary to have sufficient loudness throughout the room and to ensure that the sound field distribution is as uniform as possible. For the halls that are dominated by natural sound, it is necessary to pay attention to the scale of the hall so that the room has a reverberation time that is suitable for the purpose of use. At the same time, it is necessary to prevent acoustic defects such as echo, multiple echo, sound focus, sound occlusion, and acoustic staining. The following will explore the picture and improve the sound quality of the theater through the design of the small theater and the control of the quality of the auditorium.
The design of the small theater
The body design of the theater must first determine the size of the hall. The main method for determining the shape of the hall is the geometric acoustic method (sound line method). Secondly, it is necessary to follow certain principles. The body design has five principles: to ensure that the direct sound reaches each audience; to ensure the distribution of the near-reflected sound; to prevent the generation of echoes and other acoustic defects; to use appropriate diffusion treatment; and the use of stage reflectors.
Ensuring that the direct sound reaches each listener is primarily to prevent the front viewer from obscuring the audience behind. In the small lecture hall, a podium can be set up to raise the sound source. In the larger auditorium, the ground should be raised step by step from front to back.
Ensure that the distribution of the near-resonant sound is within 50ms for the first-time reflected sound received by most seats in a small-sized hall (for example, a height of about 10m and a width of about 20m).
Prevent echoes and other acoustic defects
The most prone to echo in the auditorium is the rear wall (including the rear wall on the stage), the ceiling attached to the back wall, and the front edge of the railing. Avoid designing the back wall as a concave surface in the back wall design, which will enhance the echo. In areas where echoes are likely to occur, the angle of inclination should be appropriately changed so that the reflected sound falls into the audience near the scene or is treated as sound absorption.
Use appropriate diffusion treatment
The diffusion process is to scatter the reflected sound waves by using a undulating surface or a staggered arrangement of sound absorbing and reflecting materials. It not only eliminates echo and sound focus, but also improves the sound field spread throughout the hall, increases the uniformity of sound energy distribution in the hall, and smoothes the sound growth and decay process. At the same time, it helps to avoid strong reflections. Possible "staining phenomenon".
Stage reflectors can also be set up for small theaters that are necessary.
Control of sound quality in the audience hall
The main contents of the reverberation design of the hall include the determination of the optimal reverberation time and frequency characteristics, the calculation of the reverberation time and the selection and arrangement of the interior decoration materials. Tests have shown that the room has different uses, the best reverberation time is different, the room volume is different, and the optimal reverberation time is different. The reverberation time of the small theater is about 1.0~1.3, and the reverberation time corresponding to the intermediate frequency of 500Hz is called the best reverberation time.
The first step in the calculation of the reverberation time is based on the room usage requirements and the design values ​​for determining the reverberation time and its frequency characteristics. Then, according to the designed body shape, the volume V and the internal surface area S of the room are calculated, and finally according to the reverberation time. Calculate the formula to find the average sound absorption coefficient of the room. The improved Yilin formula is generally used: for calculation. Reverberation time design and decoration effects require a solution to be determined, and then the reverberation time calculation formula is used for checking. By repeatedly modifying and adjusting the design until the reverberation time meets the design range.
The selection and arrangement of interior decoration materials is to fully grasp the sound absorption properties of various sound absorbing materials and structures, and to determine the location of various sound absorbing materials and structures.
2, electroacoustic system design
The electroacoustic system is not only used for conferences and lectures, but also for music and drama performances. For popular music, electro-acoustic equipment is indispensable. Therefore, the scale and performance of electroacoustic systems have become one of the important factors determining the sound quality of these halls. How to arrange the speakers indoors is an important issue in the design of electroacoustic systems, and it has the closest relationship with building treatment. The design of the electroacoustic system is to make the sound pressure distribution on all the audience seats uniform, so that the sound source direction of most auditoriums is good, and the sound feedback is controlled and echo interference is avoided.
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