• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.5
• /
• pp.578-583
• /
• 2016

In order to provide a basis data for design of small arms and their silencer, an experimental study on firing noise of small arms was performed around the muzzle of a gun. For this experimental comparison analysis, the target small arms were included most operating small arms in our country. The sound pressure levels were measured at a certain distance which was predetermined according to US army firing test procedure, TOP 3-2-045. By this experimental study, the sound pressure levels of 5.56 mm caliber small arms are 143 dB ~ 145.4 dB and 7.62 mm caliber small arms are 144 dB ~ 145.2 dB. Between the heavy machine gun K12 and M60, the sound pressure level of K12 is slightly lower than M60.Also silencer for K14 snifer rifle was tested. Using this result, it has been found that the reduction effect of the silencer is 15.4 dB but the improvements of silencer performance in the high frequency range have to be studied later on.

• Korean Journal of Otorhinolaryngology-Head and Neck Surgery
• /
• v.61 no.12
• /
• pp.663-668
• /
• 2018

Background and Objectives The main objectives of this study were to determine the clinical usefulness of the program-assisted and real ear measurement (REM)-assisted fitting of hearing aids. Subjects and Method Fifteen participants with moderate to moderately severe hearing loss were enrolled in this study. Objective and subjective fitting results were assessed to compare the benefits between the program-assisted fitting (using a software fitting program) and the REM-assisted fitting. Real ear insertion gain (REIG), sound-field audiometry using warble tone, and Korean Hearing in Noise Test (K-HINT) were performed as objective tests. Sound quality rating was performed as a subjective test. Results In the program fitting, 48.89% of fitting points failed to come within ${\pm}10dB$ of the REIG target. In the REM fitting, however, the percentage of failure significantly decreased to 23.33% (p=0.013). In K-HINT test, the reception threshold for speech in quiet situation significantly decreased from 50.1 dB HL with the program fitting to 44.7 dB HL after the REM fitting (p<0.001). In front noise condition, signal-to-noise ratio improved from 4.53 dB to 3.50 dB with the REM fitting without statistical significance (p=0.099). In the sound quality rating, the REM fitting ($4.27{\pm}0.56$) showed a significantly better sound quality ratings than the program fitting ($3.69{\pm}0.74$) (p=0.017). Conclusion The REM fitting showed better results in both subjective and objective measurements than the program fitting.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.3
• /
• pp.129-141
• /
• 2012

The present study aims to investigates the effects of the physical sound clarity (D50, STI) on the subjective speech intelligibility of the both Korean and Chinese languages which can be caused by increase of the sound absorption in classroom. In order to this, sound measurements were undertaken at a classroom with and without absorption materials. Also, speech intelligibility tests were conducted by Korean and Chinese students using their native languages. As the results, it was found that both sound clarity and speech intelligibility were improved with increasing sound absorption. Also, it was revealed that Chinese speech intelligibility was more improved than Korean with same impose of sound absorption. It was considered by the difference of phonetic characteristics of two languages. Analysing correlation of physical sound clarity and subjective speech intelligibility, it was shown that D50 is highly correlated with Korean (0.696) and Chinese (0.707) respectively. Also, STI was highly correlated with Korean (0.651) and Chinese (0.665). Thus, it can be concluded that D50 and STI have significant correlations with the speech intelligibility.

• Proceedings of the IEEK Conference
• /
• 1998.10a
• /
• pp.1243-1246
• /
• 1998

Three-dimensional(3-D) sound is a technique for generating or recreating sounds so they are perceived as emanating from locations in a three-dimensional space. Three dimensional sound has the potential of increasing the feeling of realism in music or movie soundtracks. Three-dimensional sound effects depend on psychoacoustic spectral and phase cues being presented in a reproduced signal. In this paper we propose an effective algorithm for the sound image expansion in television system using stereo image enhancement techniques. Compared to the other techniques of three-dimensional sound, the proposed algorithm use only two speakers to enhance the sound image expansion, while maintaining the original sound characteristics.

• The Korean Journal of Pharmacology
• /
• v.10 no.1 s.15
• /
• pp.11-19
• /
• 1974

To see if the treatments of d-amphetamine and chlorpromazine have any influence upon the orienting response and general behavioral activity, 3 groups of male Holtzman rats were prepared, namely d-amphetamine animals (1.0 mg/kg.i.p.), chlorpromazine rats (1.0 mg/kg.i.p.) and the physiological saline control animals. The general behavioral activity was examined by visual scanning using the time-sample method in the adaptation period of orienting response. The occurence of orienting response and its rate of habituation were evaluated by observing cessation of ongoing activity in response to a sound stimulus (1,000 Hz, 70 db & 0.1 sec), or turning of head toward the source of stimulus in 20 trials. Attention shift from sound to light stimulus was also tested in 10 trials. The results obtained were as follows; 1. The general behavioral activity of d-amphetamine group was significantly greater than that of control, however, the chlorpromazine animals showed the tendency to decrease in activity. 2. The d-amphetamine group showed the occurence of orienting response to sound significantly more often than that of placebo controls. However, the chlorpromazine group exhibited significantly fewer orienting response than the placebo group did. 3. The d-amphetamine group displayed no clear out habituation to the orienting response following the repetition of trials, though the placebo and the chlorpromazine groups demonstrated apparent habituation to the response. 4. The three animal groups did not differ significantly from each other with regard to shift of attention from sound to light stimulus. It is inferred that the d-amphetamine tends to increase general activity has a definite facilitative action of orienting response and a inhibitory influence upon the habituation of the latter response. On the contrary, the chlorpromazine tends to decrease general activity, has a inhibitory action of orienting response and facilitatory action of habituation of the response.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.04a
• /
• pp.760-765
• /
• 2013

Eco-friendly material applied to building would be one of the materials which is must developed for global environmental conservation and reduction of carbon dioxide. For development of eco-friendly material, a cellulose sound-absorbing material has been developed with waste paper through adjustment of various mix proportions. The developed cellulose sound-absorbing material has been tested for its acoustic properties such as acoustic absorptivity and dynamic elastic modulus. The absorptivity was evaluated by developing six samples and using impedance tube and reverberation chamber. As a result of the evaluation, 0.64(NRC) was secured in absorptivity and $4.7MN/m^3$ was indicated in dynamic elastic modulus. Also, for practical use of developed sound-absorbing material as inner heartwood in drywall, comparison test of sound reduction index was performed with existing glass wool sound-absorbing material and constructed drywall of gybsum board. The results have shown 55dB(Rw) of sound reduction index in glass-wool wall and 46dB(Rw) in cellulose.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.857-861
• /
• 2004

An active method that improves low frequency characteristics of a reverberation chamber has been proposed. Spatial uniformity of sound pressure at low frequency has been increased by applying active noise control system. The system acts as frequency selective damping materials, which decreases resonance at low frequency and leave high frequency sound field as it is. Linearity of the chamber, which is essential for sound power measurement in the chamber, is guaranteed since fixed control logic has been adopted. Simple application and tests have been done in a small sized rectangular reverberation chamber which has 400Hz cutoff, Loud speakers were used to simulate a noise source and to construct an active noise control system. The spatial distribution of a sound field at 250Hz, 315Hz and 400Hz bands has been measured before and after control. The standard deviation of sound field has been decreased from 3.4dB to 2.5dB. The results show the possibility of active control system as a sound diffuser.

• Journal of the Korean Society of Safety
• /
• v.28 no.1
• /
• pp.24-28
• /
• 2013

This article evaluates the accuracy of noise measurements for 37 noise measurement applications for iPhone 4 and iPhone 3Gs. Noise levels were measured using simultaneously a precision sound level meter and iPhones installed noise measurement applications at the levels of 70 dB, 80 dB and 90 dB at 1,000 Hz. Measurement errors were estimated by subtracting two measurements between iPhone and sound level meter. It was found that measurement errors of 34 applications(89.2%) were greater than ${\pm}2$ dB which is the maximum allowable error range for the Type II sound level meter. It was only 4 applications that measurement errors lie within ${\pm}2$ dB error range. There was no significant differences among measurements with four iPhone 4s. However, there were significant differences between the measurements with iPhone 4 and iPhone 3Gs using the same application. It was due to the different hardware specifications such as microphone. Therefore, noise measurement applications, for example, which has to utilize hardware of the smartphone, should be programmed to identify hardware specifications and to adopt appropriate correction factors upon hardware specifications. In conclusion, it is necessary to check accuracy and validity before using the noise measurement applications for iPhones. Also, it was suggested that it should develop an evaluation guideline or protocol on accuracy testing for the measurement applications using a smartphone.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.18 no.3 s.39
• /
• pp.1-9
• /
• 1990

Landscape plants as attenuator of vehicular noise were basically experimented with 8 kinds of trees and shrubs at the university nursery, and checked the attenuating effects by the planted distances, species and sound frequencies. The experimental results are shown and sumarized as follows ; 1. Most plants showed the considerable noise attenuating function in the sound frequencies of 63Hz and 1,000Hz. Tall trees such as Juniperus chinensis var. kaizuka and Magnolia grandiflora showed better effects than shrubs or small trees such as Gardenia jasminoides, Osmanthus fragnance, Osmanthrs heterophyllus, Rhododendron indicum, Chamaecyparis obtusa 'Tetragona Aurea' and Pinus paruiflora in 63Hz frequency, but shrubs showed better effects in 1,000Hz. 2. Trees showed 6~8dB attenuation and shrubs 4~5dB regardless an increase of distance between sound source and receiver in 63Hz. 10 meter width of tree belt could reduce 10 more dB, but 5 meter of shrub belt showed the same effect in 1,000Hz. 3. Trees having more leaves and wider crown showed constantly increase of attenuation of sound by the distance in 1,000Hz, and distinct increase of attenuation were observed in 2,000 more Hz.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.833-835
• /
• 2013