noise control
Usually, concert halls, theaters and other halls require very low indoor background noise. Therefore, the location of these halls is very important and should be as far away from outdoor noise and vibration sources as possible. In addition, it is necessary to investigate, measure and simulate the noise and vibration of the site environment in order to provide a basis for the sound insulation design of the hall building envelope. Ensure that the hall can meet the predetermined indoor noise standards after completion. In addition, another important task of architectural acoustics design is indoor sound quality design.
(2) Sound quality design
Sound quality design usually includes the following tasks:
1. Determine the shape and volume of the hall.
2. Determine the sound quality design index and its optimal value. It is an important task of sound quality design to select the reverberation time, clarity, intensity index, lateral energy factor, binaural cross-correlation coefficient and other sound quality evaluation indexes according to the use function of the hall, and to determine the best values of each index.
3. Acoustic design interface of orchestra pit, orchestra platform, box, balcony and hall.
4. Calculate the sound quality parameters of the hall. When the plan and section of the hall and the design scheme of the box, box, orchestra pit and orchestra platform are drawn up, the sound quality parameters of the hall can be calculated.
5. Design the acoustic structure. In addition to the above architectural factors, the sound quality of the hall is also closely related to the interior decoration materials and structure. The structural design of acoustic decoration usually includes the selection of interface materials and the drawing of structural design drawings, and it is necessary to specify the technical parameters of materials such as area density, apparent density, thickness, perforation rate, aperture, hole spacing, air layer thickness behind, keel spacing and so on.
6. Computer simulation of sound field. Detailed sound field analysis and sound quality parameter calculation of hall buildings depend on three-dimensional computer simulation of sound field.
7. Scale model test. For important halls, in addition to computer simulation, it is usually necessary to establish a certain scale hall model for acoustic test of the scale model.
8. Subjective evaluation of hearing. Audibility technology is through analog calculation. Or the binaural impulse response obtained by model test is convolved with the "dry signal" of music or language recorded in the anechoic room, and the sound signal with hall influence is output for the subjects to listen to the sound quality effect of the hall in advance. This is a high-tech in the field of architectural acoustics developed in recent years.
9. Architectural acoustics measurement. Architectural acoustics measurement includes noise and vibration measurement, sound insulation measurement of enclosure structure, sound absorption measurement of important materials and structures, and sound quality parameters measurement of hall.
10. Provide suggestions for electroacoustic system design. For the hall where electro-acoustic system needs to be installed, architectural acoustics experts still need to cooperate with sound engineers to provide suggestions on equipment selection, design and installation of electro-acoustic system.
1 1. Organize subjective evaluation. For important halls, it is the last important link of architectural acoustics design to organize special performances and subjective evaluations after the completion of the project to test the sound quality effect of the completed hall. Accurate prediction of room sound quality has always been the ideal pursued by architectural acoustics researchers. The measurement of hall sound quality model is an important means of architectural acoustic design. With the development of software technology, computer simulation of sound field has become a reality. In recent years, the method based on finite element theory has been used to simulate the high-order fluctuation characteristics of sound, and some progress has been made in low-frequency simulation.
The distribution of short-delay reflected sound in the hall is an important factor to determine the sound quality. In the scale model, the distribution of short-delay reflected sound measured by using electric spark as pulse sound source has a good correspondence with the distribution of short-delay reflected sound in the actual hall, which has important reference significance for determining the size and shape of the hall in the design stage. Reverberation time is a recognized quantitative sound quality parameter, and the reverberation time of the hall to be built can be predicted through model test. Sound field inhomogeneity is also an important quality parameter.
The measuring system, method and result of the model test are the same as the actual Hall, but the measuring frequency should be changed according to the scale ratio S of the Hall model. Sound waves with different frequencies, especially high-frequency sound waves, propagate in air medium, and the attenuation caused by air absorption is very different under different temperature and humidity conditions. Therefore, the measurement results of reverberation time need to be corrected according to the influence on air absorption, and have sufficient accuracy.
For the measurement of short-delay reflected sound distribution, the scale ratio S of hall sound quality model is generally 1/5 or110, and some are 1/20. However, due to the limitation of test equipment and high frequency, the accuracy is affected to some extent. When measuring reverberation time, the scale ratio S is 1/20, which can only correspond to frequencies below 1000Hz or 2 000Hz in the actual hall. The recommended scale ratio S is not less than110, and the measurement of reverberation time and sound field unevenness can be extended to 4000Hz in the actual hall. The measurement accuracy of short delay reflected sound distribution is also very high.
The shape of the inner surface of the model, some of which fluctuate slightly, has little influence on the reflection and diffusion of sound waves, so it can be simplified appropriately when making the model. However, the fluctuation of wavelength equal to or greater than 2000Hz in the actual hall must be retained and cannot be omitted. Because these parts will have a great influence on the inhomogeneity of sound field. In fact, it is very difficult to completely match the sound absorption coefficients of all parts of the inner surface of the hall including the audience with the corresponding sound absorption coefficients of all parts of the inner surface of the hall and the audience within the measured frequency range, so an error of 10% is allowed.
In order to avoid the high background noise in the model, the dynamic range can not meet the requirements and affect the accuracy, the shell of the hall sound quality model must have enough sound insulation. The size, shape and sound absorption of stage space have great influence on the distribution, reverberation time and sound pressure level of short-delay reflected sound in the audience hall. This part should be included in the model test. The sound absorption of stage space should also be simulated accordingly.
The sound source signal used to measure the distribution of short-delay reflected sound is the pulse sound generated when the capacitor is discharged, which is suitable to be used as the pulse sound source signal in the model test. The center position of the sound source is defined as the center of the general performance area, and the height is equivalent to the height of the crowd. The position and height of sound source for measuring sound field inhomogeneity are the same as those for measuring reverberation time. The common method to measure the distribution of short-delay reflected sound is to amplify the received direct sound and reflected sound signals and display them on the oscilloscope with time as the horizontal axis, that is, the impulse response spectrogram (echo diagram).
The receiver microphone can be a condenser microphone or a spherical piezoelectric crystal microphone with high sensitivity. The diameter of the microphone should not be too large to prevent the cylindrical shape of the microphone from affecting the sound field at the receiving position. When measuring, it is necessary to record the temperature and relative humidity of the air in the model, so as to correct the deviation that is lower than the actual reverberation time of the hall due to the excessive absorption of high-frequency sound air in the model.