• Title/Summary/Keyword: impedance measurement tube

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A Study on the Sound Transmission Loss Measurement of Sound Isolation Sheets (차음시트의 음향투과손실 측정에 관한 연구)

  • Lee, Dong-Hoon;Kang, Moon;Lee, Ju-Weon;Jung, Gab-Cheol;Kwon, Young-Pil
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.11a
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    • pp.409-414
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    • 2000
  • A new impedance tube method is presented for the measurement of transmission loss of sound isolation sheets. The two-microphone method based on the sound decomposition theory proposed by Seybert and Ross is reviewed in this impedance tube method, which has been used for the determination of absorption coefficient of absorptive materials as well as transmission loss of automotive mufflers. Sound transmission losses for rubber, polyvinyl and asphalt sheets are measured in an impedance tube and reverberation room facility, respectively. By comparing two measurement methods, the reliability of impedance tube method used in this study is validated. From the experimental results, it is shown that the accuracy of sound isolation capability obtained by the impedance tube method depends upon the microphone spacing and the distance of the first microphone from the test sample surface.

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Development of a Practical Two-Microphone Impedance Tube Method for Sound Transmission Loss Measurement of Sound Isolation Materials

  • Ro, Sing-Nam;Hwang, Yoon;Lee, Dong-Hoon
    • International Journal of Air-Conditioning and Refrigeration
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    • v.11 no.3
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    • pp.105-113
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    • 2003
  • This study developed a practical two-microphone impedance tube method to measure the sound transmission loss of sound isolation materials without the use of an expensive reverberation room or an acoustic intensity probe. In order to evaluate the validation and applicability of the two-microphone impedance tube method, sound transmission losses for several sound isolation materials with different surface density and bending stiffness were measured, and the measured values were compared with the results from the reverberation room method and the theory. From the experimental results, it was found that the accuracy of sound transmission loss obtained by the impedance tube method depends upon the diameter size of the impedance tube (i.e., tested sample size). For sound isolation materials having relatively large bending stiffness such as acryl, wood, and aluminum plates, it was found that the impedance tube method proposed by this study was not valid to measure the sound transmission loss. On the other hand, for sound isolation materials having relatively small bending stiffness such as rubber, polyvinyl, and asphalt sheets, the comparisons of transmission loss between the results from the impedance tube method and the theory showed a good agreement within the range of the frequencies satisfying the normal incidence mass law. Therefore, the two-microphone impedance tube method proposed by this study can be an effective measurement method to evaluate the sound transmission loss for soft sound isolation sheets having relatively small bending stiffness.

The Limit and Application of Two-microphone Impedance Tube Method to the Sound Transmission Loss Measurement of Sound Isolation Materials (차음재의 음향투과손실 측정에 Two-Microphone Impedance Tube Method의 적용과 한계)

  • Lee, Seung;Ahn, Min-Hong;Lee, Dong-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.05a
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    • pp.883-888
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    • 2002
  • This study describes the limit and application of the two-microphone impedance tube method to the sound transmission loss measurement of several sound isolation materials with different physical properties. For the sound isolation materials having small flexural rigidity, it is shown that the two-microphone impedance tube method is validated to practically measure the sound transmission loss. For the sound isolation materials having large flexural rigidity, on the other hand, it is found that the two-microphone impedance tube method is no longer valid to measure the sound transmission loss because the regions of resonance and mass law are moved into the higher frequencies. In addition, in order to accurately measure the sound transmission loss of sound isolation materials, their size should be decided based on the consideration of the effect of acoustic excitation on their vibration response.

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Multi-Termination Technique for the Measurement of Characteristic Impedance and Propagation Constant of Sound Absorbing Materials Using an Impedance Tube

  • Lee, Jong-Hwa;Ih, Jeong-Guon
    • The Journal of the Acoustical Society of Korea
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    • v.25 no.2E
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    • pp.79-84
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    • 2006
  • Acoustic characteristics of a sound absorbing material can be identified, if the characteristic impedance and propagation constants are known, which have generally been determined experimentally. One easy method determining these two essential parameters is to measure the one dimensional wave characteristics in the impedance tube. In th udy, the effects of backing conditions on the impedance tube measurement have been examined using several pairs of generally used end conditions. The results showed that the measured values are similar for most pairs of end conditions: however, it was observed that the measured characteristic impedance for different thickness did not agree well for some pairs. In this work, the multi termination method, using three or more known backing con ns, was suggested to reduce such random errors, which are mostly caused by the test procedure. Employing three terminations as a set, comprised of a rigid end, an end with porous material, and an end with a backing cavity, it was demonstrated that improved measured results could be obtained for an open cell PU foam varying widely with three different thicknesses.

Note on the Two-Microphone Methods for the Measurement of Acoustic Impedance (음향 임피던스 측정을 위한 이중 마이크로폰 기법에 대한 고찰)

  • SEO, SEONGHYEON
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.2
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    • pp.163-169
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    • 2018
  • The present article discusses about the measurement techniques of acoustic impedance that becomes one of the important acoustic characteristics of various boundaries found inside of propulsion systems. Acoustic characteristics including acoustic impedance and reflection coefficient can be often assessed and estimated by use of the two-microphone method. Theoretical expressions of acoustic impedance and reflection coefficient measured in an impedance tube are presented for both cases with mean flow and without flow, and the practical application of the method through calibration is also provided. The acoustic impedance and the reflection coefficient are related with axial locations of microphones, thermodynamic characteristics of gas inside, and the transfer function between the pressure wave measurements at multiple locations.

Impedance Tube Measurements of Sound Absorbing Materials: Sensitivity Analysis on Backing Conditions (임피던스 관을 이용한 흡음재의 특성 임피던스 측정: 배후조건에 따른 민감도 분석)

  • 이종화;이정권;박봉현;김병훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.888-891
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    • 2001
  • Effects of backing conditions on the impedance tube measurement are investigated experimentally, by using several pairs of generally employed end conditions. The results show that the measured values are similar for most of pairs, except the case of using an open pipe condition. In addition, the random error is investigated in the viewpoint of the variation of test conditions. The multi-termination method is suggested for minimizing such a random error.

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Measurement of acoustic impedance of porous woven hoses in engine intake systems in the presence of mean flow (유체의 흐름이 있는 엔진 흡기계용 직조관의 음향 임피던스 측정 및 전달손실 예측)

  • 이정권;박철민
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.05a
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    • pp.996-1000
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    • 2002
  • A porous tube, comprised of a resin-coated woven fabric has recently been used as an effective component for use in intake systems of internal combustion engines to reduce the intake roaring. For the prediction of the acoustic performance of an engine intake system with a porous woven hose, the acoustic wall impedance of the hose must be known. Because of its peculiar acoustical and structural characteristics, the accurate measurement of the wall impedance ofa porous woven hose is not easy. A new measurement technique is proposed herein, that is valid over the low to mid frequency ranges. The acoustics impedance is inversely estimated from an overdetermined set of measured pressure transmission coefficients for specimens of different lengths and the reflection coefficient of end termination. The method involves only one measurement, and, as a result, it is very simple. The measured TL for samples with arbitrary conditions, arbitrary porous frequency, arbitrary length, and arbitrary mean flow condition, are in reasonably good agreement with values predicted from curve-fitted impedance data.

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A study on the performance of the perforated tube exhaust muffler (다공형 배기 소음기의 성능에 관한 연구)

  • 권영필;이동훈;방정환
    • Journal of the korean Society of Automotive Engineers
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    • v.14 no.6
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    • pp.48-59
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    • 1992
  • This study is on the performance of the perforated tube muffler when it operates as an exhaust silencer with through-flow, steady or pulsating. Theoretical estimation of the insertion loss was made by means of transfer matrix and by using the impedance equation for the perforated tube obtained for the case of low-speed steady through-flow. Experiment was performed for the measurement of the insertion loss at two flow conditions. The one is a steady flow from the exhaust pipe of an idling diesel engine. The effect of the through-flow velocity and steadiness on the muffler performance was obtained. By comparing the theoretical prediction with the experimental result, the validity of the impedance equation in the theoretical model was discussed. It has been found that steadiness as well as magnitude of the through-flow has a significant effect on the performance of the perforated tube muffler. Especially, the self-noise due to the pulsating flow in the engine exhaust system must be taken into account for the prediction of the muffler performance.

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Method of deriving the acoustic impedance and sound absorption coefficient of materials by manipulating electrical impedance of a loudspeaker (스피커의 전기적 임피던스를 이용한 시료의 음향임피던스와 흡음계수 도출 기법)

  • Doo, Sejin
    • The Journal of the Acoustical Society of Korea
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    • v.40 no.3
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    • pp.254-260
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    • 2021
  • When measuring the sound absorption coefficient of a specimen, a reverberation room which is costly or an impedance tube which has limitations in measuring low frequencies have been engaged. In this paper, a new measurement method of acoustic impedance or sound absorption coefficient has been suggested, which does not need microphones and only uses electrical impedance measurement data and derived Thiele/Small parameters of a speaker. The theory of this method has been described using equivalent circuit of the loudspeaker and acoustic properties of a test specimen are measured to demonstrate the validity of this method. It was confirmed that this method can easily measure the sound absorption coefficient in the low frequency band, which was previously difficult to trust. The advantages, limitations, and applicability of this method are discussed.