• Journal of the Society of Naval Architects of Korea
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• v.55 no.5
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• pp.394-400
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• 2018

Various numerical methods have been adopted for indoor noise assessments of ship plant. Acoustical radiosity method is one of the high frequency approaches for acoustic field analysis, which assumes diffuse reflections by boundaries so that it could be efficiently applied to the acoustically diffused indoor space noise analysis. In this study, an acoustic field analysis program has been developed based on radiosity method, which could apply for acoustically large enclosures such as ship's indoor space. For this purpose, the procedure of the acoustical radiosity method has been summarized and implemented to an acoustic field analysis program using MATLAB. Numerical example for a rectangular indoor space has investigated validity of the implemented program. Steady state sound pressure levels calculated for a continuous acoustic source signal have shown good agreement with those by other solutions such as an analytic solution and a ray tracing method. Instantaneous sound pressure levels calculated for an impulsive acoustic signal have provided the clues of direct/reflected acoustic field and reverberation time.

• The Journal of the Acoustical Society of Korea
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• v.40 no.5
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• pp.452-459
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• 2021

Estimating the mutual time delay between two acoustic sensors is used in various fields such as tracking and estimating the location of a target in room acoustics and sonar. In the time delay estimation methods, there are a non-parametric method, such as Generalized Cross Correlation (GCC), and a parametric method based on system identification. In this paper, we propose a time delay estimation method based on the parametric method. In particular, we propose a method that considers the noise in each receiving acoustic sensor. Simulation confirms that the proposed algorithm is superior to the existing generalized cross-correlation and adaptive eigenvalue analysis methods in white noise and reverberation environments.

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.254-260
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• 2021

When measuring the sound absorption coefficient of a specimen, a reverberation room which is costly or an impedance tube which has limitations in measuring low frequencies have been engaged. In this paper, a new measurement method of acoustic impedance or sound absorption coefficient has been suggested, which does not need microphones and only uses electrical impedance measurement data and derived Thiele/Small parameters of a speaker. The theory of this method has been described using equivalent circuit of the loudspeaker and acoustic properties of a test specimen are measured to demonstrate the validity of this method. It was confirmed that this method can easily measure the sound absorption coefficient in the low frequency band, which was previously difficult to trust. The advantages, limitations, and applicability of this method are discussed.

• The Journal of the Acoustical Society of Korea
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• v.31 no.3
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• pp.115-128
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• 2012

This paper investigates the effects of diffuser on the acoustical parameters in music hall with consideration of the result of scattering coefficient measurement. A scale model hall of 600 seats with orchestra shell was used for experiments. The materials of 1:50 scale model was chosen through absorption coefficient measurement based on ISO 354. The model was matched to the computer simulation model in terms of reverberation time. In order to evaluate the effect of diffuser location, the measurements were accomplished with and without diffusers according to 7 configurations by diffuser-installed region; sidewall, balcony front, ceiling and so on. The following acoustical parameters were extracted from each measurement case; Reverberation time (RT), Early decay time (EDT), Clarity (C80), Center time (Ts), Sound strength (G) and Temporal diffusion (TD) from the auto-correlation function (ACF) of impulse responses. As a result, the absorption power and diffusion power were increased with number of diffusers. Accordingly RT, EDT and G were decreased by diffuser and the redirection of reflections was occurred briskly. Averaged TD was 6.05 to 6.30 by measurement cases. RT was found to be the most related factor to diffusion power (R = 0.94). The correlation between TD and EDT was high (R = 0.73). In addition, the effects of diffuser-installed location were discussed in terms of acoustical parameter variation.

• The Journal of the Acoustical Society of Korea
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• v.36 no.4
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• pp.254-260
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• 2017

The purpose of this study is to evaluate the sound absorption characteristics of a human body according to the amount of clothing worn by using reverberation method measurement method for developing standard test dummy, which can be used for testing absorption of occupied audience chair. Test method was based on the previous study (Conti et al., 2004), each experiment is conducted in the reverberation room and a subject wearing clothes is standing in that chamber. In this experiment, the sound absorption area of each frequency band according to the wearing of various material clothing was measured. As a result of measurements, the average sound absorption area of the whole frequency band was $0.25m^2-0.48m^2$ in case of a subject not wearing outer clothes, and $0.38m^2-0.98m^2$ in case of wearing of outerwear. Polyester tops by showing the maximum value, the highest characteristics in the 800 Hz to 1 kHz band among the rest of fiber materials. The outer jacket made of the wool and cotton materials show a higher absorption area as the frequency increases to the higher frequency band. The change of the sound absorption area according to the clothing amount was divided by the thermal resistance (clo) of the worn clothes and the weight per body surface area.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.92-101
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• 2016

There are many results in which acoustical conditions of a classroom play an important role for studying effects and academic achievement of students. However, there are very few guidelines or design proposals which could make appropriate acoustic environment when classrooms are built or renovated. The present study suggests various design proposals satisfying acoustic standards of classrooms based on theoretical calculation and acoustic field experiments. At first, minimum area of sound absorption was calculated which is required to satisfy the acoustic standard for domestic middle and high schools. Also, room acoustic measurements were carried out in order to investigate the acoustic performance of an existing classroom by changing interior finishing materials on ceiling and rear walls. As a result, it was revealed that reverberation time standard below 0.8 s can be acquired even if there is no sound absorption on ceiling which is a general practice executed in Korea. Specially, it was found that if partial area of ceiling would be treated as reflective with the ratio of sound absorption and reflection as 2:1, almost similar acoustic parameters of $C_{50}$, $D_{50}$, RASTI (Rapid Speech Transmission Index) and higher sound levels could be acquired in comparison with the case of entire sound absorption on ceiling.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.236-241
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• 2007

Recently, in accordance with the cultural progress and the improvement of citizen's consciousness level, it is the real situation that the construction of small-scaled Multi-Purpose Hall where various cultural events could be performed, is on increasing. However, because the most of Multi-Purpose Hall had been designed and built up without any consideration on Acoustic Factor, many problems are on occurring thereat. Because those small-scaled Multi-Purpose Hall have been mostly used with the finishing material which contains a high degree of Acoustic Absorption indiscreetly, both diffusion and reflection of sound are not establishing properly, and since the reverberation of sound is very low, in case of musical performance by musical instrument, its sound hears too arid and stiff, there occurs some acoustic defect such as it becomes difficult for music appreciation with sufficient timbre, so that the capability improvement on the matter is urgently requiring situation. On this viewpoint, this Research has caught the Authenticity of the forecasted value and actually measured value using Acoustic Simulation on the subject of the small-scaled Multi-Purpose Hall, and then intended to propose the optimum acoustic condition on the basis of the Authenticity. As the result, it could be designed a Multi-Purpose Hall equipped with the satisfactory acoustic performance compare with the time before improvement, so that it is considered that such research result could be practically used as the fundamental material when design for other similar small-scaled Multi-Purpose Hall in the future.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.22-28
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• 2001

This paper describes the implementation of a robust speaker position location system using the voice signal received by microphone array. To be robust to the reverberation which is the major factor of the performance degradation, low-frequency phase restoration algorithm which eliminates the influence of reverberations using the low-frequency information of the CPSP function is proposed. The implemented real-time system consists of a general purpose DSP (TMS320C31 of Texas instruments), analog part which contains amplifiers and filters, and digital part which is composed of the external memory and 12-bit A/D converter. In the real conference room environment, the implemented system that was constructed by the proposed algorithms showed better performance than the conventional system. The error of the TDOA estimation reduced more than 15 samples.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.43-49
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• 1997

Generally, echo cancelers of a TV conference system or a audio conference system are to carry out a real time processing in the case of the closed room having long reverberation time because the system requires much time to modify filter coefficients to environmental changes. Therefore this paper proposes a new subband adaptive filtering method using polyphase filter banks of MPEG(Moving Picture Experts Group) audio system to solve the problems. This method divides signal spectra of input and output into several frequency bands, and each band is adaptively filtered by using ES-NLMS (Exponential Step-Normalized Least Mean Square) algorithm. The optimal number of subband is determined by computational simulations. According to the results of simulation, ERLE of the subband model is 2dB smaller than general full band, calculation rate's of the subband model is decreased about 88%.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.5-13
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• 2001

It is well known that there are two experimental errors on acoustic decay measurements. ,One is due to the influence of the band pass filter the other one is that of an averaging device. In this paper the influence of the filter is investigated in detail. To minimize the influence of the filter, the product of the filter bandwidth B (3dB bandwidth) and the reverberation time T/sub 60/ of the room under test should be at least 16. Moreover, if the initial part of an acoustic decay curve is important, the strong requirement, i. e. BT/sub 60/〉64, must be satisfied. In this paper, the wavelet filter bank instead of the band pass filter bank is applied to obtain an acoustic decay curve. As a result, the influence of filter is reduced and then the value of BT/sub 60/ required for obtaining an acceptable decay curve becomes at least 4. The strong requirement for the initial part of a decay curve is also replaced by the BT/sub 60/〉16 instead of BT/sub 60/〉64.