According to requirement of more silent accommodation in a ship, a high sound insulation performance of panel which is installed in a residence area is required. The performance of sound insulation is usually evaluated by measurement in standardized test facilities. There are two types of test facilities to measure a sound insulation performance. One is two reverberation chamber is placed face to face. This chamber shapes in dissymmetry. This shape could ensure to make a reverberant field. The other type is two rectangular parallelepiped rooms are placed face to face. This type is named 'type II' in ISO140-1. In rectangular parallelepiped room, it is difficult to ensure reverberant field. Due to the shape of test facilities, 'standing wave' is able to exist in the room. Standing wave causes a high variation of sound pressure. Therefore, it should be controlled. And too much long or short reverberation time could affect to sound reduction index (SRI). Therefore, reverberation time should be also controlled. For this reason, some requirements by ISO140-1 should be satisfied. First of all, distribution of sound pressure and reverberation time is measured to check a sound field status of initial test facilities. Sound pressure variation in 100 Hz (in 1/3 Octave) was verified that was a very high and reverberation time exceeded the requirement of ISO140-1. This study suggests a method to satisfy reverberation time in requirements of ISO140-1 (Requirements for laboratory test facilities with suppressed flanking transmission). An evaluated frequency range is from 100 Hz to 3150 Hz in 1/3 Octave. Therefore, three kinds of sound absorber which has different sound absorption character in this frequency range are designed to adjust the reverberation time. The first sound absorption mechanism is using a vibration of plate and film. This type is for low and middle frequency range, below 1000 Hz. The second one is using a porous sound absorption material. This type is effective in high frequency range, over 1000 Hz. The third one is applying resonator principle. A resonance frequency of this resonator is designed after verifying status of sound field. Each absorber is designed to have a different frequency characteristic in a sound absorption. It can make easy to control the reverberation time even in any test facilities which has different status of the reverberation time. A sound absorbing power per each frequency is obtained by measurement of sound absorption in a reverberation room (according to ISO354). An adjustment of reverberation time have been intended by a combination of theses three types absorber, in a whole frequency range where should be evaluated. To find out a rational combination, simulation using 'Eyring formula' was performed before experiment. Through this process, the number of each type absorber was decided. And after installation of the absorbers in the test room, reverberation time is measured. The result of measurement is compared with assumed value. To compensate a difference between the measured value and the calculated value, combination of absorbers is modified again. Finally, an optimized combination of sound absorbers that satisfy requirement of ISO140-1 could be decided with minimized absorber number.


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    Title :

    Sound field adjustment using sound absorber in the ISO type sound insulation test facilities


    Contributors:


    Publication date :

    2010


    Size :

    6 Seiten, 12 Bilder, 2 Tabellen, 4 Quellen


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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