• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.666-670
• /
• 2006

It has been considered that scattered sounds have a positive effect on a hearing impression of a sound filed. This study investigates the degree and the quality of a scattered sound field by using the acoustical parameters and autocorrelation function(ACF) of impulse responses. The acoustical parameters and fine structure of the ACF of an impulse response were used for the evaluation of the scattered sound field. The relationship between the scattering coefficient of surfaces with various hemisphere diffuser configurations and the acoustical parameters and ACF parameters of impulse responses was investigated.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.1E
• /
• pp.16-20
• /
• 2005

A novel scheme to measure the speaker information in speech signal is proposed. We develope the theory of quantitative measurement of the speaker characteristics in the information theoretic point of view, and connect it to the classification error rate. Homomorphic analysis based features, such as mel frequency cepstral coefficient (MFCC), linear prediction cepstral coefficient (LPCC), and linear frequency cepstral coefficient (LFCC) are studied to measure speaker specific information contained in those feature sets by computing mutual information. Theories and experimental results provide us quantitative measure of speaker information in speech signal.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.525-528
• /
• 2002

The speed of sound, transmission coefficient, and attenuation are measured around the center frequency 1 and 2 MHz in solid materials such as bone, sediment, rubber, and Lucite materials. Common and different characteristics of such materials in the sound speed, transmission coefficient, and attenuation are discussed. Ambiguities in estimating such acoustic characteristics we also addressed. Ultrasonic properties of the first and second kind waves are clarified for different materials. Discussions are concentrated on classes of sound speed, broadband ultrasonic attenuation (BUA), and correlations of sound speed and BUA with apparent density. New correlations of inverse sound speed square and BUA with apparent density are suggested.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.183-186
• /
• 2004

Biot's theory and a modified Biot-Attenborough (MBA) model are applied to predict the dependences of acoustic characteristics on frequency and porosity in cancellous bone. The phase velocity and the attenuation coefficient predicted by both theories are compared with previous in vitro experimental measurements in terms of the mixed, the fast, and the slow waves. Biot's theory successfully predicts the dependences of phase velocity on frequency and porosity in cancellous bone, whereas a significant discrepancy is observed between predicted and measured attenuation coefficients. The MBA model is consistent with reported measurements for both dependences of phase velocity and attenuation coefficient on frequency and porosity. Based on the theoretical predictions from the MBA model, it is suggested that the attenuation coefficient of the mixed wave is dominated by the fast wave in the low-porosity region while it is dominated by the slow wave in the high-porosity region. This provides a qualitative explanation for the nonlinear relationship of attenuation of the mixed wave with porosity in cancellous bone.

• The Journal of the Acoustical Society of Korea
• /
• v.10 no.3
• /
• pp.13-18
• /
• 1991

In this study, the analysis technique of fracture stress using the reflection coefficient of SAW reflected from a brittle solid with surface crack has been studied. Fracture stress of brittle solid with surface crack has been obtained by the function of the critical stress intensity factor and the maximum normalized stress intensity factor of the crack in the body. And the maximum normalized stress intensity factor of a surface crack can be inferred from a measurement of reflection coefficient of SAW. In experiment, the surface cracks ranging from 0.5mm to 0.9mm in crack depth has been made at the center of each Pyrex disc, and the SAW wedge transducer has been set up for the pitch-catch mode. It has been compared the theoretical values of the fracture stress calculated from the reflection coefficient of SAW with the values of the fracture stress measured from UTM.

• The Journal of the Acoustical Society of Korea
• /
• v.34 no.6
• /
• pp.493-498
• /
• 2015

Complex acoustic signals can be formed in a water-filled acoustic pulse tube under some exciting conditions. It makes difficult to measure plane-wave reflection coefficient with the pulse tube for low frequency bands. In this study, using COMSOL Multiphysics we show that the tube wall excitation generates complex acoustic field of nonplanar mode as well as planar one. From such field incident or reflected planar mode can be decomposed respectively with a modal decomposition method, two-dimensional Fourier filtering. It makes possible to more accurately determine the plane-wave reflection coefficient of acoustic specimen with time gating.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.3
• /
• pp.254-260
• /
• 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
• /
• v.22 no.3E
• /
• pp.133-140
• /
• 2003

A time series simulation is presented by a ray approach for the simulating the received waveform of a broadband acoustical signals interacting with the ocean boundaries. The environment is assumed to be horizontally stratified, and the seafloor is described in terms of homogeneous fluid half-space. The ray approach includes the effects of reflection from the air-water, water-sediment interface and phase shifts due to boundaries interaction. To generate time series, we assume that the acoustic energy propagates from source to receiver along eigenrays and represent the action of the bottom on the incident wave by a linear filter and characterized in the frequency domain by the transfer function. As example application, the time series for an explosive source in a shallow water environment is calculated and analyzed in terms of acoustical process. good agreement with measured time series is demonstrated.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.3
• /
• pp.115-128
• /
• 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
• /
• v.36 no.6
• /
• pp.401-406
• /
• 2017

This paper presents the performance assessment of several key algorithms conducted for amphibian species sound classification. Firstly, 9 target species including endangered species are defined and a database of their sounds is built. For performance assessment, three feature vectors such as MFCC (Mel Frequency Cepstral Coefficient), RCGCC (Robust Compressive Gammachirp filterbank Cepstral Coefficient), and SPCC (Subspace Projection Cepstral Coefficient), and three classifiers such as GMM(Gaussian Mixture Model), SVM(Support Vector Machine), DBN-DNN(Deep Belief Network - Deep Neural Network) are considered. In addition, i-vector based classification system which is widely used for speaker recognition, is used to assess for this task. Experimental results indicate that, SPCC-SVM achieved the best performance with 98.81 % while other methods also attained good performance with above 90 %.