• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.12
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• pp.6993-6997
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• 2014

The aim of this study was to experimentally investigate the sound quality characteristics, such as sound deflection, sound pressure level and frequency characteristics of a magnetic type speaker in an anechoic chamber to overcome the sound quality and voice-coil temperature problems. To accomplish this, the sound quality performance of the magnetic type speaker was tested according to the magnetic fluid amount and magnetic field intensity. The sound deflection, sound pressure level, and frequency characteristics were measured using the Smarrt program. As a result, at a magnetic fluid amount of 2.4 ml, the sound deflection and the sound pressure level of the magnetic type speaker were enhanced by comparing with those of the general type speaker. The frequency characteristics and the sound pressure level of the magnetic type speaker were enhanced greatly with increasing magnetic field intensity from 8.06 mT to 9.10 mT. In addition, the sound deflection of the magnetic type speaker was 0.01% lower than that of the general type speaker.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.28-38
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• 2014

The effects of geometric parameters (stack position, stack length, resonator tube length) and varying input power over acoustic energy output were investigated. The acoustic laser kit (Garret 2000) was used for the construction of TA lasers. A series of sound pressure level measurements in different orientations did not differ significantly confirming that the sound wave generated could be assumed as a spherical wave. An increase in acoustic pressure was recorded with respective increase in input power, stack and resonator tube lengths owing to their relative influence over heat transfer rate and critical temperature gradient across the stack.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.42.2-42.2
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• 2011

Noise generated from wind turbines has been predicted by numerical methods. Sound pressure level(SPL) on the turbines is predicted after aerodynamic analysis is carried out by Wind Turbine Flow, Aeroacoustics and Structure analysis (WINFAS) code. The level of each panel of acoustic sphere is determined by the sum of tonal, turbulence ingestion and airfoil self noise. With the noise source database, the acoustic sphere, SPL on the ground is calculated using the model based on acoustic ray theory. The model has been designed to consider the effects on the condition of terrain and atmosphere. The variations of SPL on the ground occur not only because of the different source level but also because of the nonuniform distributions of the sound speed along the height. Hence, the profile of an effective sound speed which is the sum of the contribution of sound speed to a temperature gradient and a wind speed variation is used by the theory based on atmospheric stability. With the integrated numerical method, the prediction of sound propagation on the wind farm is carried out with the states of the atmospheric stability.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.1
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• pp.81-91
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• 1994

Combustion noise involved with chemical heat release and turbulent process in turbopropulsion systems, gasturbine, industrial furnaces and internal engines is indeed noisy. The experimental study reported in this paper is made to identify a dominant combustion noise in jet flames. Gaseous propane and kerosene fuel have been used with air as the oxidizer in a different jet combustion systems. Combustion and aerodynamic noise are studied through far field sound pressure measurements in an anechoic chamber. And also mean temperature and velocities and turbulent intensities of both isothermal and reacting flow fields were measured. It is shown that axial mean velocity of reacting flow fields is higher about 1 to 3m/sec than that of cold flow in a gaseous combustor. As the gaseous fuel flow rate increases, the acoustic power increases. But the sound pressure level for the spray flame decreases with increasing equivalence ratio. The influence of temperature in the combustion fields due to chemical heat release has been observed to be a dominant noise source in the spray flame. The spectra of combustion noise in gaseous propane and kerosene jet flame show a predominantly low frequency and a broadband nature as compared with the noise characteristics in an isothermal air jet.

• Journal of Korea Foundry Society
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• v.31 no.3
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• pp.145-151
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• 2011

Metallic foam has been known as a functional material which can be used for absorption properties of energy and sound. The unique characteristics of Al foam of mechanical, acoustic, thermal properties depend on density, cell size distribution and cell size, and these characteristics expected to apply industry field. Al-Zn-Mg-Cu alloy foams was fabricated by following process; firstly melting the Al alloy, thickening process of addition of Ca granule to increased of viscosity, foaming process of addition of titanium hydride powder to make the pores, holding in the furnace to form of cooling down to the room temperature. Metal foams with various porosity level were manufactured by change the foaming temperature. Compressive strength of the Al alloy foams was 2 times higher at 88% porosity and 1.2 times higher at 92% porosity than pure Al foams. It's sound and vibration absorption coefficient were higher than pure Al foams and with increasing porosity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.786-789
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• 2005

An acoustic total or partial enclosure is widely used to reduce the sound pressure level propagating from a noise source. However, the performance of the acoustic enclosure is decreased by its inherent limitations such as temperature rise or acoustic pressure build up inside the enclosed acoustic field. In general, a silencer is installed to overcome these limitations, for large amount of air can be exchanged through the silencers. In this reason, a parallel baffle type duct silencer with acoustic resonators is studied to reduce the transmitted noise from a transformer. In this silencer, the high frequency components of the transmitted noise over 360Hz are effectively absorbed by the parallel baffles and the other ones, 120 and 240 Hz, are reduced due to the presence of Helmholtz resonators. Large sound attenuation is achieved by applying the sound resonating barrier to the large transformers in a substation.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1E
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• pp.3-6
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• 2001

Sound pressure level (SPL) measurements were performed on a controlled test track vehicle coast-by runs of a passenger vehicle with six different sets of tires across a range of temperatures. A small but significant reduction of noise level with positive temperature increases was observed for some tires. The temperature gradient of the different tires at 80㎞/h ranged from -0.07 to + 0.01 dB/℃. Frequency analysis of the tire noise identified that noise content in the range of 1,300 to 1,900Hz was particularly sensitive to temperature changes. Differences in SPL due to speed and tire type were much greater than that due to temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.251-257
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• 1998

Active mufflers have been mainly applied in the large industrial engine due to considerable expense for implementation, but a necessity of development has been increased by the tightened regulation of exhaust noise and the request of high power. In this study, the active muffler prototype for installing in an automobile is designed and constructed. The active muffler is designed so that the primary noise and the control sound are propagated as a plane wave in the outlet. Therefore, the error microphone could be placed outside the high temperature centers of the tail pipe, and the noise radiating to the outside could be reduced in the whole areas around the outlet. For evaluating the control performance of the prototype, the control experiments of band-pass filtered random signal and the modulation of sinusoidal signal which are generated from the primary noise speaker as practical exhaust sound level are implemented. And to investigate the radiation pattern from the outlet of tail pipe and the noise reduction level of points placed adjacent to the outlet, the sound level of adjacent points of thirty is measured.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.6
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• pp.445-451
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• 2016

The Inconel 718 alloy is a well-known super-heat-resistant alloy and a difficult-to-cut material. Inconel 718 with excellent corrosion and heat resistance is used in harsh environments. However, the heat generated is not released owing to excellent physical properties, making processes (e.g., adhesion and thermal fatigue) difficult. Tool condition monitoring in machining is significant in reducing manufacturing costs. The cutting tool is easily broken and worn because of the material properties of Inconel 718. Therefore, tool management is required to improve tool life and machinability. This study proposes a method of predicting the tool wear with non-contacting sensors (e.g., IR thermometer for measuring the cutting temperature and a microphone for measuring the sound pressure level in machining). The cutting temperature and sound pressure fluctuation according to the tool condition and cutting force are analyzed using experimental data. This experiment verifies the effectiveness of the non-contact measurement signals in tool condition monitoring.

• Journal of the Korean Solar Energy Society
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• v.32 no.2
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• pp.105-112
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• 2012

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100 mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200 mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm,20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.