Dae-Up Jeong

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.

Spatial distribution of early reflections and speech intelligibility

The strong early reflections and short delay times have been known to improve the intelligibility of speech heard in rooms. D50 and C80, the most frequently used physical parameters, were developed taking this fact into consideration. However, these monaural parameters have limited applications for the practical design of rooms because of their lack of spatial information. The present work investigates how temporal changes in three‐dimensional distribution of early reflections influence speech intelligibility in rooms. A new measurement method, using a five microphone array and an omnidirectional source setup, is employed, and a series of post‐processing procedures are involved, for getting different early reflections in their spatial distributions. The changes were made for the impulse responses obtained through a five microphone array in the arrival times of early reflections from all, and the horizontal and vertical directions, respectively. Anechoic samples of the Korean language were convolved binaur...

The dependence of timbre perception on the acoustics of the listening environment

The acoustic quality of a room for music cannot easily be determined. As timbre is important in music it is possible that the perceived change in timbral quality of a sound in two spaces may give the basis for a measure of acoustic quality. The smallest perceivable change in the timbre of steady‐state stimuli was measured in different listening environments through two experiments featuring a spectral centroid and rise time, respectively. Five component harmonic stimuli at 440 Hz were employed. The centroid of the standard stimuli was fixed at 2.95, in which the median amplitude of each component of the standard was set at 0.5, while those of comparison stimuli were varied from 2.93 to 2.41 in steps of 0.02 with a negative spectral tilt. The smallest perceivable change in the rise time was also measured using complex tones containing ten harmonics of 200 Hz (F0) with linear spectral slopes of −6 dB/oct. Rise times of comparison stimuli were varied from 5 to 25 ms in 2‐ms steps, while the fall time was fix...

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.

Calculation of diffuse sound reflections in predicting room acoustics using the image method

Numerous investigations have demonstrated that diffuse reflection is one of the most important factors in predicting room acoustics by computer simulation. Recent studies have suggested several computational algorithms in order to account for diffuse reflections in the ray‐tracing or beam‐tracing method. In this study, a computational algorithm for the calculation of diffuse sound reflections in the image method is suggested and a computer simulation system is developed based on the suggested algorithm. The methodology adopted in our computer simulation system is similar to the extended radiosity method, which was developed for computer graphics. Various descriptions of room acoustics, including spatial distribution of image sound sources, impulse responses and other commonly used room acoustical measures, can be obtained from the MLS based monaural room acoustics measurement system. The measured results in a midsized rectangular classroom with/without chairs on the floor were compared with the predicted ...

A five‐channel microphone system for detecting 3‐D acoustic image sources

Measuring three‐dimensional behavior of early reflections in a sound field has been an important issue in auditorium acoustics, since they are found to be strongly correlated with the subjective experience of spatial impression in rooms. A conventional way of detecting the direction and relative amplitude of reflections is to utilize a four‐channel microphone system. This system, however, has the inherent possibility of missing some important reflections while exploring the early part of reflections. A new measurement system, which has five microphones on the apex of a tetrahedron and at the center of gravity, is proposed in the present work. The proposed system enables us to find more early reflections accurately, which previous four‐channel microphone systems might miss. A peak detecting pair matching algorithm, which gives dominant peaks of impulse response automatically by typical iteration, was adopted, since we should find exact peak positions of measured impulse response in order to calculate sourc...