• The Journal of the Acoustical Society of Korea
• /
• v.31 no.8
• /
• pp.507-513
• /
• 2012

The room modes were showed as the peaks and dips on the low frequency response of the loudspeaker, and were one of the biggest obstacles to reproduce the sound. In order to reduce the occurrence of resonance, equalizing is performed at one position, and the frequency response to be equalized is valid only at that position. Performing the equalization would improve the flatness of the frequency response a little, but it cannot eliminate the ringing. Another method is that it is located the speaker at the specific position where the room resonances were not frequently happened. However, there may be the practical limitation that you may not be able to install the speaker at the position to be wanted. One of the practical solutions to decrease the production of resonance in room is the use of bass trap. In this paper, the practical limit for the room tuning using an equalizer and the room optimization will be discussed. The use of bass traps to solve the resonance problem that is always happened in the room is also proposed.

• The Journal of the Acoustical Society of Korea
• /
• v.27 no.4
• /
• pp.163-170
• /
• 2008

Most of receiving rooms for the measurement of floor impact sound have rectangular shapes with couple of meters of dimension, with reflective finishing, no furniture, no curtains. Modal overlaps in those condition are the major reason for the low reproducibility, and as a matter of course, the low credibility. It is the major purpose of this study that searching for a better measurement method which mitigate the effect of modal overlap on measurement. Two ways of methods are tested. One is the way described in ISO standards which enables controlling the room modes of receiving rooms, the other is the way which enables to get more precise spatial averages in receiving rooms with room modes. It is not easy maintaining the reverberation time of low frequency bands in the range between 1s and 2s, though it is proven to be effective controlling the room modes with base traps. Space-time average SPL's through combinations of rotating microphones are easy to measure, and have good consistencies with average SPL of entire receiving room.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.5
• /
• pp.75-85
• /
• 1998

This paper presents the procedures and technique of the decision on the decision on the mount in a diesel engine development newly. To assess the vibration chara- cteristics of the engine plus transmission, their inertia moments are calculated for three engine versions. i.e., NA(Naturally Aspirated), TC(Turbocharged) and TCI(Turbocharged and Intercooled). These data are used to determine the mount layout and stiffness values affecting the noise quality of an engine as well as a vehicle. The main purpose of this paper is to design the mount rubber having the optimal stiffness characteristics through the investigation of the calculation results and the mount conditions when an engine is installed in a vehicle using the existing engine mount room. Thus, this paper describes the optimal mount positions, rubber stiffnesses, natural frequency, mode shapes and so on using ADAMS program to apply the newly developed engines to three different vehicles.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.2
• /
• pp.49-55
• /
• 2006

Measurement of impact sound insulation of floor, by current Korean Standard KS F 2810-2. is to be made with peak levels over 4 point in a receiving room. But it is often the case that there is inconsistency in results at various receiving points in the receiving room. Such variations obviously have effects on the repeatability and reproducibility of measured data. The result shows that there are even 10 dB deviations in 63Hz octave band frequency range and relatively less variations are occurred in other low frequency ranges. Such variations seems to be coming from modal overlaps of the receiving room. According to current rating method of floor impact sound. KS F 2863-2, that may affect on the single number latins scheme. From the result of tests in this study, there are 2dB to 6dB differences in the sin91e number with the combination of measurement points. This means that the reduction of measurement variations from the microphone positions is needed for a better credibility of measurement results.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.77-77
• /
• 2009

ELV(; End of Life Vehicles)를 비롯한 최근 환경 동향은 자동차 전장 모듈에 대하여 다양한 무연 솔더 적용을 요구하고 있다. 특히 자동차 엔진룸과 트랜스미션은 가동 중 고온 및 진동의 지속적인 영향을 받기 때문에 이와 유사한 환경에서의 신뢰성 연구가 필요한 시점이다. 이에 본 연구에서는 Sn3.5Ag, Sn0.7Cu, Sn5.0Sb 솔더 조성에 대하여 복합환경 조건하에서 접합부 신뢰성을 평가하였다. 복합환경을 구현하기 위하여 $-40{\sim}150^{\circ}C$ 범위의 온도 사이클과 랜덤 진동을 동시에 인가하였으며, 진동 가속도 3G, 진동주파수는 10~1000Hz 로 설정하여 자동차 환경을 충족하였다. 복합시험의 1 cycle 은 20 시간이며, 총 120 시간의 시험 동안 진동의 영향 및 진동과 고온이 동시에 작용하였을 경우의 영향에 대해 비교하였다. 테스트 모듈 제작을 위해 450 um 의 솔더볼이 적용되었으며, 각 조성의 솔더볼을 이용하여 BGA test chip 제작하였고, 제작된 BGA test chip 은 다시 daisy chain PCB 위에 실장 및 리플로우 공정을 통해 접합되었다. 테스트 동안 In-situ 로 저항의 변화를 관찰하여 파단의 유무를 판단하였고 전자주사현미경을 통해 파괴 기전을 평가하였다. 복합시험 시간에 따른 전단강도를 측정하였으며, 각 조성에 대하여 상이한 전단강도 변화를 관찰하였다. 계면 IMC 형상은 전단강도 변화에 영향을 주었으며, 특히 높은 온도가 IMC 성장을 촉진시켜 전단강도 감소에 영향을 주었다. 본 복합환경 시험 조건에서는 Sn0.7Cu 가 가장 안정적이었으며, 파단면을 관찰한 결과 연성파괴 모드가 관찰되었다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.10
• /
• pp.1169-1176
• /
• 2010

The RF front-end for L1/L2 dual-band Global Positioning System(GPS) receiver is presented in this paper. The RF front-end(down-converter) using low IF architecture consists of a wideband low noise amplifier(LNA), a current mode logic(CML) frequency divider and a I/Q down-conversion mixer with a poly-phase filter for image rejection. The current bleeding technique is used in the LNA and mixer to obtain the high gain and solve the head-room problem. The common drain feedback is adopted for low noise amplifier to achieve the wideband input matching without inductors. The fabricated RF front-end using $0.18{\mu}m$ CMOS process shows a gain of 38 dB for L1 and 41 dB for L2 band. The measured IIP3 is -29 dBm in L1 band and -33 dBm in L2 band, The input return loss is less than -10 dB from 50 MHz to 3 GHz. The measured noise figure(NF) is 3.81 dB for L1 band and 3.71 dB for L2 band. The image rejection ratio is 36.5 dB. The chip size of RF front end is $1.2{\times}1.35mm^2$.