Masaru Koyasu

On the New Reverberation Chamber with Nonparallel Walls (Studies on the Measurement of Absorption Coefficient by the Reverberation Chamber Method, II)

The details of the new reverberation chamber are given. It has a volume of 513 m 3 and is surrounded by nonparallel walls. The results of model room experiments previously reported have been used to determine the shape and volume of this chamber. At 500 cps., the reverberation time of empty chamber was 22 seconds. The position of the microphone and the sound absorbing material did not affect the reverberation time of this chamber. This fact would show that the sound field of this chamber would fulfill the requisite for the diffuse sound field which is the premise of the reverberation chamber method.

Accuracy in sound power level determination by the scanning intensity method

The method of determining sound power levels of noise sources by the sound intensity technique has been specified in ISO 9614 Part 1 (precision, engineering, and survey grades by the discrete point method) and Part 2 (engineering and survey grades by the scanning method). In addition to these, the work of drafting, Part 3 (precision grade by the scanning method) has just started in ISO/TC43/SC1/WG25. In order to obtain data for the specification of the measurement accuracy of the scanning intensity method, a basic experimental study has been done. In this study, an artificial sound source (a loudspeaker array) with complicated sound radiation characteristics and two actual sound sources (a vacuum cleaner and a compressor) were used as the sound sources under test. The sound power level of each sound source was determined in each 1/3 oct band from 50 Hz to 6.3 kHz and those in the octave band and A‐weighted values were calculated from the values in the 1/3 oct bands. From these results, the measurement rep...

Dependence of Sound Absorption Coefficient upon Area of Acoustic Materials

reverberation chamber and also obtained a more extensive range of absorption coefficients than that of Chrisler. The reverberation chamber used for this research has a volume of about ,surrounded by nonparallel walls. The empty chamber absorption extends from 2.7 to 8.2 for the frequency range from 250 to 2000 cps. Sample materials were several kinds of mineral wool blankets with different thicknesses, placed on the center of the floor of this chamber. The dimensions of sample materials are shown in Table I. In order to obtain the absorption coefficient for the sample area less than ,we followed the method that was adopted by Table I. Dimensions of sample materials.

On the Relation between the Reverberant Sound Absorption Coefficient and the Normal Incidence Absorption Coefficient of Fibrous Materials

Now, we measured the normal incidence and reverberant absorption coefficient of fibrous materials. To explain th coerrspondence beetween these two coefficients, a new statistical method for random field was derived. The reverberation chamber used for this research is the chamber of our institute, which was constructed in 1956. This chamber has a volume of 513 surrounded by nonparallel walls, and the reverberation time for the empty chamber is 22 sec at 500 cps. It was shown experimentally that the assumption of a diffuse sound field would be nearly Reprinted from The Journal of the Acoustical Society of America, Vol.30, No.12, 1163-1164, December, 1958 Copyright, 1958 by the Axoustical Society of America. Printed in U.S.A.

Acoustical Properties of Trumpets

Acoustical properties of the B♭ trumpet were investigated. By comparing two trumpets judged to have good and poor musical quality, respectively, it was found that the air leakage at the pistons reduced the Q value of the resonance. An irregular frequency distribution of the higher normal modes of the trumpet was also studied. The effect of the connecting condition of the tube and horn of the trumpet on the harmonic relation of the normal modes of the air column was studied. The measured resonance frequencies were found to agree well with the maximum driving point radiation resistance computed for various combinations of tube and horn.

Studies on sound and vibration generated by household appliances. II. The determination of vibromotive force of waste disposers by a comparison method

The household food waste disposer is attracting attention as one of the leading disposal systems in Japan, and it is thought that disposers will be installed in many condominiums from now on. Sound and vibration which are generated by a disposer will come under fire as a new noise source. To popularize the disposer in Japan, reduction of the sound and vibration which are generated by disposers is an important matter. In this paper, as a standard method for measurement and evaluation of the vibration which is generated by disposers, the determination of the vibromotive force level of disposers is studied by the comparison method. As a result, it is clear that the vibromotive force level of a disposer is influenced by the kinds of food waste, but the frequency characteristic is relatively unaffected, a behavior similar to that found for sound power level.

Studies on sound and vibration generated by household appliances. I. The determination of sound power level of a waste disposer by the comparison method

A household food waste disposer is attracting attention as one of the leading disposal systems in Japan, and the possibility that a disposer will be installed at many condominiums from now on is under consideration. Sound and vibration, which are generated by a disposer, are being considered as a new noise source problem. To popularize the disposer in Japan, the reduction of the sound and vibration generated by the disposer is an important matter. In this paper, as a standard method for measurement and evaluation of sound generated by the disposer, the determination of sound power level of a disposer by a comparison method in a hard‐walled test room is studied. As a result, the accuracy of measurement for the sound power level of the disposer is practically confirmed. Also it is clear that the sound power level of the disposer is influenced by the kinds of food waste, but frequency characteristics are scarcely affected.

Studies on sound diffusion in reverberation rooms in Japan

During the 1960s, round‐robin tests on the measurements of sound absorption coefficient in reverberation rooms had been carried out extending over four times in Japan. One of the main objectives of these investigations was to find a sensitive and useful measure of sound diffusion in reverberation room. Two kinds of indices, the ratio of horizontal to vertical mean energy during decay process and the directional distribution of spatial correlation coefficient, were adopted for the evaluation of the degree of diffuseness. Most of reverberation rooms in Japan have nonparallel walls in order to obtain diffuse sound field. Moreover, suspended diffusing plates are often used to improve the degree of diffuseness. Compared with the case of rectangular room, relatively small number of diffusers would be sufficient to obtain the same order of diffuseness. An essentially important factor would be the volume of the room, and for measurements at low frequencies, extremely large volume would become necessary. Thus, it would be desirable to use two or three reverberation rooms with different volumes in order to cover the whole frequency range. In parallel with these investigations, theoretical studies on the sound field in rectangular reverberation rooms have been carried out extensively.

Measurements of the Sound Absorption Coefficient and the Sound Transmission Loss at the Kobayasi Institute of Physical Research

During the past three years, five reverberation chambers were constructed in our institute. These chambers are now used for the measurements of the sound absorption coefficient and the transmission loss. Chamber No. 1 has a volume of 513 m3 surrounded by nonparallel walls, and the reverberation time of this chamber is greater than 20 sec at 500 cps. In this chamber, the position of the microphone and test specimens does not affect the absorption coefficient. Chambers No. 3 and No. 4, which are used for transmission loss measurements, have a volume of 164 m3, respectively. The shape of these chambers is similar to chamber No. 1. The opening between these two chambers is 3.3 m by 3.3 m. Under chamber No. 4, there is chamber No. 5, which is used for the receiving room for impact sound transmission loss measurements.