Young-Ji Choi

Some Issues in Measurement of the Random-Incidence Scattering Coefficients in a Reverberation Room

In recent years, the ISO working group has standardized the measurement methods for a scattering coefficient for surfaces in rooms, ISO 17497-1. The importance of the application of the scattering coefficient in room acoustics, particularly in a computer model to obtain reliable prediction results, has already been reported in international round robin tests. There is a need for guidelines and a reliable database of surface materials for the application of the standard method. In this study, the effect of some measurement parameters on the measurement of random-incidence scattering coefficient in a reverberation room based on ISO 17497-1 was investigated. A 1:5 scale model of the reverberation room, which has a volume of 2.4 m 3 , was employed to measure the random-incidence scattering coefficient of periodic battens. In the present work, three parameters, the turntable diameter (0.64 m and 0.84m), the air gap below the turntable (50 mm and 222 mm) and the absorption coefficient of the test sample (0.09 and 0.31) were considered. The influence of each parameter over the scattering coefficient of the periodic battens was measured and analysed. A lower scattering coefficient of the periodic battens was obtained when a turntable diameter of 0.64 m was applied. A lower scattering coefficient of the periodic battens at the corresponding real-scale frequency bands from 630 Hz to 2.5 kHz was obtained when an air gap of 50 mm was applied. The absorption coefficient of the test sample influenced the measured scattering coefficient at mid and high frequency bands.

Experimental investigation of chair type, row spacing, occupants, and carpet on theatre chair absorption

This paper examines how the individual variations of chair type, row spacing, as well as the presence of occupants and carpet, combine to influence the absorption characteristics of theater chairs as a function of sample perimeter-to-area (P/A) ratios. Scale models were used to measure the interactive effects of the four test variables on the chair absorption characteristics, avoiding the practical difficulties of full scale measurements. All of the test variables led to effects that could lead to important changes to auditorium acoustics conditions. At mid and higher frequencies, the various effects can usually be explained as due to, more or less, porous absorbing material. In the 125 and 250 Hz octave bands, the major changes were attributed to resonant absorbing mechanisms. The results indicate that for accurate predictions of the effective absorption of the chairs in an auditorium, one should use the P/A method and reverberation chamber tests of the chair absorption coefficients to predict the absorption coefficients of each block of chairs and use these results as input in a room acoustics computer model of the auditorium. The application of these results to auditorium acoustics design is described, more approximate approaches are considered, and relations to existing methods are discussed.

Effect of Sample Size on Measurement of the Absorption by Seats

This study deals with measurements of the sound absorption by seats which are one of the important parameters in the early design stage in auditorium. In this study, the effects of sample size on measurement of the sound absorption by seats are investigated to define an optimum range of sample size for obtaining reliable measurement results. In the measurements, the absorption coefficients of unoccupied seats at a scale of 1/16 are measured in a 1/5 scale-model of the reverberation chamber based on ISO 354. Various seating blocks having 9 different P/A (perimeter/area of the sample) values ranged from 0.4 to 1.37 m−1 were measured to extrapolate to the absorption coefficients of the larger seating blocks found in a real hall. The predicted results from reverberation chamber measurements were then compared to the measured values in a 1/16 scale-model of the real hall for the validation of this method. The present results show good agreement between values obtained from the hall measurements and those predicted from reverberation chamber measurements.

The Effect of an Edge on the Measured Scattering Coefficients in a Reverberation Chamber based on ISO 17497-1

The scattering coefficient has been regarded as one of the important factors to be considered in the acoustic design of a room. ISO 17497-1 provides a method for measuring the random-incidence scattering coefficients in a reverberation chamber. However, the uncertainties of this method due to the lack of details with respect to the measurement conditions have been reported. It is necessary to provide more specific guidelines for this method. The present study suggests an improved measurement method by investigating the edge effects. The scattering coefficients of a simple 1-dimensional diffuser were measured in a 1/5 scale model of the reverberation chamber based on ISO 17497-1. The effects of an edge strip on the scattering coefficients were measured and analysed. Further, several issues with respect to the sample diameter, the air gap below the turntable and the absorption of the test sample were discussed.

The effect of sound reinforcement systems on the acoustics of a large-span spaces

The present work investigate the effect of sound reinforcement systems on the acoustics of a large dome stadium using a computer simulation. The acoustics of a dome stadium was predicted analyzed by varying room absorption, as well as the configuration of speakers including their directivity, installed height, and numbers. It was found that both D50 and RASTI were improved by increasing room absorption. Larger EDTs were observed according to the increase of room absorption at mid and high frequencies. On the other hand, RT did not show any significant correlation with the changes in room absorption, which might be the effect of a forced linear fitting for non -linear energy decay process. With respect to the speaker configuration, the speech intelligibility of a sound reforcement system installed at higher placed more relied upon their directivity rather than room absorption, Also, lower placing of speakers was found to be effective in decreasing RTs regardless of room absorption.