• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• 제20권10호
• /
• pp.983-990
• /
• 2010

Reduction of acoustic loads of space launch vehicles can be achieved by acoustic absorbers satisfying strict cleanness requirements. This limited the use of general porous materials and requires non-porous sound absorbers. Micro-perforated panel absorbers(MPPA) is one of promising sound absorbers satisfying the cleanness requirement for launch vehicles. However, its applicability was limited to low sound pressure levels according to the acoustic impedance model of micro-perforated panels. In this paper the applicability of micro-perforated panel absorbers at high incident sound pressure was investigated in experimental ways. The absorption characteristics of a micro-perforated panel absorber was simulated according to its design variables, e.g., minute hole diameters and aperture ratios. It was shown that optimal design can be readily done by using proposed design charts. Experiments were conducted to measure acoustic properties of the designed micro-perforated panel absorbers. The results showed that acoustic resistance increases rapidly as incident sound pressure level does but change of acoustic reactance can be neglected in a practical point of view. This caused the decrease of peak value of absorption coefficient at high incident sound pressure level, but the amount of reduction can be accepted in practice. The major advantage of the micro-perforated panel absorber(wide absorption bandwidth) was still kept at high sound pressure level.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 한국농업기계학회 1998년도 하계 학술대회 논문집
• /
• pp.270-275
• /
• 1998

It was assumed that the voice of cattle is generated with the virtual white noise through the digital filter called the linear prediction filter, and filter parameters (prediction coefficients) were estimated by the maximum entropy method (MEM) , using the sound signal of the animal . The feature planes were defined by the pairs of two parameters selected appropriately from these parameters. The cattle voices were divided into three levels, that is the high, medium and low levels according to their total power equivalent to the variances of the sound signal . It was found that the straight lines could be used for recognizing tow cow and one calf for high level voices. For high and medium level voices, however, it was difficult or impossible to recognize individual cattle on the parameters planes.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• 제16권10호
• /
• pp.1036-1043
• /
• 2006

Damping materials for reducing heavy-weight floor impact noise in reinforced concrete structures were tested in apartment buildings. The effect of damping materials and an impact isolator were compared with an on-site experiment conducted in a high-rise apartment building. The loss factor of damping material analyzed more than 2 times than rubber to $1.5{\sim}2.3$, could know that Damping layer has excellent attenuation performance in side of vibration reduction. The results showed that the resonance frequency increased but vibration acceleration level decreased when the damping materials were used. The heavy-weight impact sound levels of the structure decreased substantially at 63 Hz, whereas the sound levels of the structure with the impact isolator increased.

• 정보저장시스템학회:학술대회논문집
• /
• 정보저장시스템학회 2005년도 추계학술대회 논문집
• /
• pp.71-74
• /
• 2005

The present study describes the prediction of the flow induced noise level of a high-speed rotating hexagonal disk and proposes the way how to reduce it. Since a hexagonal disk, which is used in the laser printer and named a Polygon mirror, has six sharp corners, there are low and high pressure regions on each of six edges when it rotates. Therefore, the pressure difference generates three dimension flow field and causes aerodynamic noise. The Ffowcs-Williams and Hawkings (FWH) method is employed for the analysis. We have measured the sound pressure levels and compared them with the computational results. The calculated sound pressure levels agree well with the experimental results. We modified the shape of the edges of a hexagonal disk to reduce the noise level and confirm their effects through numerical computation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.168-171
• /
• 2005

The present study describes the prediction of the flow induced noise level of a high-speed rotating hexagonal disk and proposes the way how to reduce it. Since a hexagonal disk, which is used in the laser printer and named a polygon mirror, has six sharp comers, there are low and high pressure regions on each of six edges when it rotates. Therefore, the Pressure difference generates three dimension flow field and causes aerodynamic noise. The Ffowcs-Williams and Hawkings(FWH) method is employed for the analysis. We have measured the sound pressure levels and compared them with the computational results. The calculated sound pressure levels agree well with the experimental results. We modified the shape of the edges of a hexagonal disk to reduce the noise level and confirm their effects through numerical computation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.674-677
• /
• 2005

As a passive soundscape facility, fountain is a useful way to give place such as public square, park identity and vitality. In this study, to know the optimistic distance and sound level range from fountain, sound levels due to distance were measured and subject responses were checked by questionnaire. Levels from 56dB to 68dB are recommended by subjects and moving forward to fountain decreases less comfort ratio than backward Moving forward 5m and backward 5m(total range 10m), there is little difference in comfort ratio. The results of this study could used for street furniture location design and P.A system output level.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2007년도 추계학술대회논문집
• /
• pp.687-691
• /
• 2007

It is important to increase the sound proof performance of building for reducing the influence of aircraft noise on the bais of actual survey of existed buildings. The purpose of this study is to propose the basic data for designing sound insulation of residential house. In this study, field measurement of aircraft noise Interior and outside noise level difference were carried out for 7 days in 2 residential houses. As the result, aircraft noise levels showed to be Leq $71.8{\sim}74.5$dB(A), WECPNL $82.2{\sim}83.4$ and indoor noise level were NC-55 ${\sim}63$ over acceptable NC-30 in 2 measured houses. Noise reduction effect showed to be $15.8{\sim}23.1$dB(A) in measured houses, and houses with double window were preferable to those with single window in sound proof performance. The outside sound pressure level for residential house was a little different according to the type of source. In measuring by using aircraft noise it was effected by angle and distance from measuring point, to aircraft, window area, and sound absorption of room, and so on.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2005년도 제17회 워크샵 및 추계학술대회
• /
• pp.579-582
• /
• 2005

The sound measurement techniques in IEC 61400-11 are applied to field test and evaluation of noise emission from 1.5 MW wind turbine generator (WTG) at Yongdang-Lee and 650 kW WTG at Hangwon-Lee in Jeju Island. Apparent sound power level, wind speed dependence and third-octave band levels are evaluated for both of WTGs. 1.5 MW WTG at Yongdang is found to emit lower sound power than 660 kW one at Hangwon, which seems to be due to lower rotating speed of the rotor of WTG at Yongdang. Equivalent continuous sound pressure level s (ECSPL) of 650 kW WTG at Hangwon vary more widely with speed than those of 1.5 MW WTG at Yongdang. The reason for this is believed to be the fixed blade-rotating speed of WTG at Yongdang. One-third octave band analysis of the measured data show that the band components around 400-500 Hz are dominant for 1.5 MW WTG at Yongdang and those around 1K Hz are dominant for 660 kW WTG at Hangwon.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.911-916
• /
• 2001

Structural acoustic modification method based on the structural mobility analysis is applied to reduce the structure-borne noise radiated from hard disk drive system. Sound intensity techniques and ODS(Operational Deflection Shape) techniques are also used in order to provide the structural acoustic information for the mobility modification. The sound intensity is for the acoustic visualization of the noise source locations, and the ODS is for the visualization of the vibration pattern and its dynamic characteristics of the noise sources. Using visualization information of sound and vibration, local structural input mobility is reduced in the frequency band of interest by designing asymmetrical wave-stringer structure in the wave-number domain as well as frequency domain. The overall sound pressure level is reduced by 4dB and its controlled sound power radiated from the disk drive is proved to under 2.8Bel in idle-spinning mode and 3.1 Bel in random-seeking mode, which are the lowest noise levels in the hard disk drive industry.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• 제18권7호
• /
• pp.746-755
• /
• 2008

This research presents a laboratory study on subjective response of impulsive sound caused by construction site (breaker and blasting). The sources are sampled from outdoor noise and their levels range from 40 to 75 dBA at the interval of 5 dBA. The noise unit is based on A-weighted sound exposure level(ASEL; $L_{AE}$). To make equal ASEL of listening level, finite impulse response(FIR) filter is applied to the originally sampled source to include the effect of propagation attenuation. Sixty-three subjects, forty-two males and twenty-one female, between 18 and 29 years of age, participated in the experiment. The evaluation method of jury test adopted a semantic difference method(SDM). In the test results for impulsive noise, the subjective response of blasting noise was higher than that of breaker noise. The result of %HA that has been combined responses of the three methods except for pink-noise was executed by regression analysis and was shown as the following equation.: $%HA=746.53/(1+{\exp} (L_{AE}-93.3))+0.34$.