• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.2
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• pp.241-248
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• 1998

The accurate measurement of the room sound level is required in environment noise control. However, it has been found that the measurement system noise always corrupts the actual noise from the sound source. In this study, a new sound level measurement technique in which the system noise is eliminated from the measured signal by the cross spectrum method, is proposed. The received signals of two measuring microphones are recorded to DAT through the pre-amplifier and digitized by A/D converter. The cross spectrum calculated from the digitized signals gives the accurate sound level since the system noise is uncorrelated with the sound source noise which we want to measure. The performance of the proposed technique is verified experimentally to be effective and the technique is found to be economic since the low cost general purpose microphone could be used in this technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.380-384
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• 2001

The household reftigerator's noise which is closely related with resident environment can hardly be evaluated its sound quality using the Korean Standards. Radiation characteristics of compressor noise consist of tonal noise in low frequency range and, or narrow band noise in high frequency range. In this study, measuring method for detecting the abnormal and low-level noise in high frequency band is presented, and control method for its reduction is proposed. After installing wall which is similar to living condition, we determined a major concerning frequency band of noise. It can be found the directivity of high frequency noise radiated from compressor by using experiment and analysis. According to isolation of noise transfer path, remarkable noise reduction is achieved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.464-473
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• 2006

This paper summarises theoretical and experimental work on the feedback control of sound radiation from honeycomb panels using piezoceramic actuators. It is motivated by the problem of sound transmission in aircraft, specifically the active control of trim panels. Trim panels are generally honeycomb structures designed to meet the design requirement of low weight and high stiffness. They are resiliently-mounted to the fuselage for the passive reduction of noise transmission. Local coupling of the closely-spaced sensor and actuator was observed experimentally and modelled using a single degree of freedom system. The effect of the local coupling was to roll-off the response between the actuator and sensor at high frequencies, so that a feedback control system can have high gain margins. Unfortunately, only relatively poor global performance is then achieved because of localisation of reduction around the actuator. This localisation prompts the investigation of a multichannel active control system. Globalised reduction was predicted using a model of 12 channel direct velocity feedback control. The multichannel system, however, does not appear to yield a significant improvement in the performance because of decreased gain margin.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.497-502
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• 2008

In this paper, we studied on an attenuation effect of automobile exhaust noise according to the direction of secondary sound source in duct ANC system. Automobile exhaust noise was recorded at 800rpm. 3500rpm and 5000rpm of a diesel engine. Directions of loudspeaker(second sound source) can be exchanged to $30^{\circ}$, $90^{\circ}$ and $150^{\circ}$ against the primary noise flow by acrylic ducts to be made for experimentation. DSP board with TMS320C6416 chip of Texas Instrument Co used to control adaptive ANC system. This ANC system is based on the single-channel FxLMS algorithm. In experiment result, when the loud speaker direction was $150^{\circ}$, the attenuation effect showed largely. In case of $90^{\circ}$ duct, the noise was a little increased. In case of $30^{\circ}$ duct, the noise was a little increased or decreased according to the frequency range and the sound pressure(dB) of exhaust noise to comply with engine rpm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.525-530
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• 2013

With the increasing the importance of emotional quality of vehicle, the sound quality of systems with electric motor components has become increasingly important. Electric motors are used for windows, seats, sun roof, mirrors, steering columns, windshield wiper, climate control blowers, etc. In this paper, a study was conducted to identify sound quality factors that contribute to customer's satisfaction and preference of the window lift system. Jury test for subjective evaluation was carried out and sound quality index was developed. Averaged sound pressure level and sharpness were significant factors when glass moves down. Also, maximum loudness at stop section and averaged loudness were significant factor when glass moves up. Noise source identification was carried out for the reduced the loudness and sharpness during glass transferred section and impulsive noise at stop section, Using the source identification result, several improvement points were applied. And finally, the degree of sound quality improvement was judged using sound quality index.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.751-755
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• 2005

We propose a sound source localization method using the Head-Related-Transfer-Function (HRTF) to be implemented in a robot platform. In conventional localization methods, the location of a sound source is estimated from the time delays of wave fronts arriving in each microphone standing in an array formation in free-field. In case of a human head this corresponds to Interaural-Time-Delay (ITD) which is simply the time delay of incoming sound waves between the two ears. Although ITD is an excellent sound cue in stimulating a lateral perception on the horizontal plane, confusion is often raised when tracking the sound location from ITD alone because each sound source and its mirror image about the interaural axis share the same ITD. On the other hand, HRTFs associated with a dummy head microphone system or a robot platform with several microphones contain not only the information regarding proper time delays but also phase and magnitude distortions due to diffraction and scattering by the shading object such as the head and body of the platform. As a result, a set of HRTFs for any given platform provides a substantial amount of information as to the whereabouts of the source once proper analysis can be performed. In this study, we introduce new phase and magnitude criteria to be satisfied by a set of output signals from the microphones in order to find the sound source location in accordance with the HRTF database empirically obtained in an anechoic chamber with the given platform. The suggested method is verified through an experiment in a household environment and compared against the conventional method in performance.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.97-103
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• 1999

As the noise of ship engine room is too loud, the engineer who works in a ship engine-room has the trouble of hearing. In this paper deals the investigation of the noise of ship engine room and cabins with the internationally allowable noise exposure level and noise exposure time. Recently, the problem of engine-room noise is more serious because of shipowner wants to make small number and larger size of cylinder. Therefore, engineers work in a ship engine-room for a long time have the trouble of hearing when they are exposed the high noise level. In this study, two kinds of vessels were used to investigate the noise of engine room, engine-control room, bridge, offices and cabins. As criteria of sound levels, A-weighted sound pressure level and octave band pressure level were used.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.165-168
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• 2000

Engine noise is one of the major causes of the interior noise, and so has been studied in various ways in recent days. Recently air induction noise has been extensively studied to reduce the engine noise. Conventional method to reduce the noise is adding several resonators to the induction system. However this causes a reduction of engine output power and an increase of fuel consumption. Thus in this study, the feasibility of applying the active noise control to the induction system is studied to the overcome the above disadvantage.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.12 s.105
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• pp.1378-1388
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• 2005

Spatial control of sound is essential to deliver better sound to the listener's position in space. As it can be experienced in many listening environments. the quality of sound can not be manifested over every Position in a hall. This motivates us to control sound in a region we select. The primary focus of the developed method has to do with the brightness and contrast of acoustic image in space. In particular, the acoustic brightness control seeks a way to increase loudness of sound over a chosen area, and the contrast control aims to enhance loudness difference between two neighboring regions. This enables us to make two different kinds of zone - the zone of quiet and the zone of loud sound - at the same time. The other perspective of this study is on the direction of sound. It is shown that we can control the direction of perceived sound source by focusing acoustic energy in wavenumber domain. To begin with, the proposed approaches are formulated for pure-tone case. Then the control methods are extended to a more general case, where the excitation signal has broadband spectrum. In order to control the broadband signal in time domain, an inverse filter design problem is defined and solved in frequency domain. Numerical and experimental results obtained in various conditions certainly validate that the acoustic brightness, acoustic contrast, direction of wave front can be manipulated for some finite region in space and time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.461-466
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• 2012

Customers want to have more convenient and comfortable vehicle. Motor-on-caliper EPB(Electrical Parking Brake) System is one of the new systems for customer's convenience. It is applied for Midsize vehicle for reducing weight/price compared to cable puller type EPB. In this paper we studied sound quality improvement of motor-on-caliper EPB system. We developed the sound quality index and suggested the interior sound quality target value. To meet the target value cascading target was also suggested. EPB motor vibration level & sound radiation level, vibro-acoustic transfer function level from EPB to interior was defined. To find out effective way of sound quality improvement and find cascading target, TPA(Transfer Path Analysis) was carried out.