• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.10
• /
• pp.1843-1850
• /
• 2000

Sound absorption coefficient for the absorptive panels comprized of a perforated plate. an absorbent material and an air gap was measured and compared with theoretical value. The absorptive panels are composed of three basic combinations (a perforated plate + an air gap + an absorbent material. a perforated plate + an absorbent material, a perforated plate + an absorbent material + an air gap). As a result. it is found that the sound absorption for low frequency range is strongly affected by the resonance produced by perforated plate and air gap. And the sound absorption for high frequency depends on the porosity of perforated plate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.762-765
• /
• 2005

The absorption materials have been used to enhance the performance of a noise barrier and improve the room acoustics. In this study, 6 products of absorptive materials generally used in Korea were chosen, and their absorption performance were tested in various conditions, that is, it was measured while changing thickness, density and air gap in their back, and measured with or without facing on their face. Finally, the absorption coefficients were compared by reverberation and impedance tube method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.201-204
• /
• 2007

다양한 공연장 및 대공간에서의 실내음향 제어를 위해서는 실내마감재료의 흡음 및 확산성능을 제어할 수 있는 재료가 필요하다. 본 연구에서는 이를 위해 알루미늄 새시를 이용한 흡음구조를 개발하였으며, 흡음특성을 조사하기 위하여 수직입사 흡음계수와 잔향실법 흡음계수를 측정하였다. 수직입사 흡음계수 측정결과 알루미늄 다목적 흡음재의 타공구조와 인서트에 의해 형성되는 공간이 공명형 흡음기의 역할을 하여 중.저주파수 대역의 흡음계수가 증가되는 것으로 나타났다. 잔향실법 흡음계수 측정결과 알루미늄 새시를 이용한 흡음구조의 형성에 따라 공명주파수 대역보다 낮은 중저주파수 대역의 흡음계수가 증가되는 것으로 나타났다. 공기층 증가에 따라 공명주파수 이상 대역에서의 흡음률은 증가되고 주파수 대역별 흡음계수 편차도 감소되는 것으로 나타났으며, 고주파수 대역의 흡음률 향상을 위한 방안이 필요한 것으로 나타났다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.902-907
• /
• 2002

An equivalent electroacoustic circuit approach of estimating the sound absorption coefficient for parallel perforated plate system is proposed. The proposed approach is validated by comparing the calculated absorption coefficients of a parallel single layer perforated plate system with the values measured by the two-microphone impedance tube method for various porosity and the number of perforated plate. The sound absorbing performances of parallel and series perforated plate systems are compared and discussed from a standpoint of frequency bandwidth with sound absorption. The proposed approach is further extended to the parallel double layer perforated plate system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.896-901
• /
• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several compartments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated plates, airspaces or porous materials. Based on these results, a guidance for the design of multiple layer perforated plate systems combined with airspaces and porous absorbing materials is discussed in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1998.04a
• /
• pp.659-663
• /
• 1998

To measure the absorption ratio and the transmission loss of a material, a usage of the reverberation room has been popular. However, the reverberation room is expensive to build it and, sometimes, test procedure is not easy. Therefore, to get the data of absorption ratio, several possible technologies has been proposed using the tube. Among these technologies, with the analysis of the spectral density, a convenient method has been introduced to measure both the absorption ratio and transmission loss. The measured data has been compared with the results of the measurement at the reverberation room.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.388.1-388
• /
• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several companments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method fur various combinations of perforated Plates, airspaces or porous materials. (omitted)

• Bulletin of the Korean Chemical Society
• /
• v.32 no.2
• /
• pp.439-443
• /
• 2011

Using the projection operator technique, a reduced density matrix theory for linear absorption spectrum of energy transfer systems is developed for the theoretical absorption line shape of the systems with non-Condon transitions. As an application, we considered a model system of OH vibrations of water. In the present model calculation, the OH vibration modes are coupled to each other via intra-molecular coupling mechanism while their intermolecular couplings are turned off. The time-correlation functions appearing in the formulation are calculated from a mixed quantum/classical mechanics method. The present theory is successful in reproducing the exact absorption line shape. Also the present theory was improved from an existing approximate theory, time-averaged approximation approach.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.857-860
• /
• 2003

We introduced the basic direction of revision for KS F 2805 (method for measurement of sound absorption coefficient in a reverberation room). It is fundamentally equal to ISO 354 (measurement of sound absorption in a reverberation room) which was state of ISO/FDIS 354. Two main points were strongly reviewed. First, the sound absorption coefficient values for Type J test specimen mounting was investigated. Next, the reverberation time difference between the conventional method and new additional one, impulse response method were compared.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.443-446
• /
• 1997

This paper raises issues in testing the absorption coefficients of sound-absorptive samples in the standing wave tube according to the Korean standard of KS F 2814. The code does not consider any effect of air-damping during test. This limitation has been shown to yield much variation of sound absorption coefficients for recent sample tests whose coefficients are less than 10 %. An improved method of calculating the sound absorption coefficients is proposed in this work and its effectiveness in real test is also illustrated. Finally, the guide line for the modification of our national standard code KS F 2814 is suggested for the future.