- The paper presents the research on the influence of perforations on the surface of a sound absorbing material on the sound absorption coefficient. The porous sound absorbing material used in this ...research was made from fir sawdust and polyurethane binder, and to improve its design and/or its sound absorbing properties, it was used a layer of cork with and without perforations. The sound absorption coefficient was determined using an impedance tube and in accordance with the experimental determinations it was observed an improvement at frequencies higher than 1100 Hz in the case when the cork layer was perforated.
In this paper, electroless Ni-P plating on polyethylene terephthalatefabrics (PET) with different weight percentage gains was fabricated in the laboratory. The effects of weight percentage gain on ...the properties of air permeability, electromagnetic shielding performance, sound absorption, thermal stability and tensile were investigated. The results showed that the exponential relationship between air permeability and weight percentage gain could be obtained. Similarly, the linear relationship between fabric thickness and weight percentage gain could be obtained. As the weight percentage gain increased, the shielding effectiveness increased, whereas the surface resistance decreased at first, and then reached to a certain level. When the distance of air gap behind fabric and the frequency of sound wave were given, the sound absorption coefficient increased with increasing weight percentage gain at first, reached a maximum value at the weight percentage gain of 90% and then decreased beyond 90%. The tensile properties of the electroless Ni-P plated polyethylene terephthalate fabric were greatly influenced by the thickness of the coated metal. The linear relationship between tensile strain and Young's modulus existed.
Because nonwoven fabrics can significantly attenuate acoustic energy through their high porosity and small fiber diameter, they have been widely used as sound-absorbing materials in various ...industries. Along with microfiber nonwoven fabrics, novel nanofiber nonwoven fabrics possess excellent sound absorption properties owing to their fineness. In this study, the sound absorption characteristics of composite materials composed of microwebs and nanowebs were carefully investigated using a stacking structure and the number of layers.
Statistical energy analysis model for cabins was built based on the VA One platform. In addition, separate calculation was conducted on the structural vibration-caused and airborne noise of a power ...generator, and their contributions to the noise in different cabins were analyzed. Results show that structural vibration-caused sound was transmitted farther and contributed more to the noise in distant cabins. With the help of the principles of reverberation room, a statistical energy analysis model for calculating sound absorption coefficient and reverberation time was built. A sound absorbing material suitable for the major frequency range over which noise occurs can be chosen based on its sound absorption coefficient curve and the frequency features of cabin noise. By comparing schemes, we identified a sound absorption and isolation case that helps cabin noise and reverberation time meet requirements, providing reference for vibration and noise reduction in cabins.
백합나무 횡단면 흡음성능의 방사방향 변이 강춘원; Chun Won Kang; 이용훈 ...
목재공학,
07/2011, Volume:
39, Issue:
4
Journal Article
Peer reviewed
Open access
국산 산공재 중 구조적 특징이 목재흡음에 적합하다고 생각되는 백합나무 목재 횡단면의 흡음성능과 기체투과성의 방사방향 변동과 폭쇄처리 영향을 관찰하고자 무처리와 폭쇄처리 목재원반에서 방사방향위치가 다른 원형시험편을 재취하여 전달함수법과 CEP (capillary flow porometry)법으로 흡음률과 기체투과성을 각각 측정, 비교하였다. ...측정주파수범위에서 폭쇄처리 횡단면의 흡음률이 무처리재보다 높은 흡음성능을 나타내었으며 횡단면에서는 대경 도관이 다수 존재하여 다공질형흡음에 유용한 연속된 모세관이 다량 존재하는 사실을 확인할 수 있었다. 방사방향으로는 심재부위에서 채취한 시험편보다 변재부위에서 채취한 시험편의 흡음계수가 높은 흡음률을 나타내었으며, 기체투과성도 변재부위가 심재부위보다 높은 수치를 나타내었다.
Radial variation of sound absorption capability and air permeability of yellow poplar (Liriodendron tulipifera) wood in cross sectional surface and effect of steam explosion treatment were estimated by the two microphone transfer function method and the capillary flow porometry, respectively. The sound absorption coefficients of steam explosion treated wood was higher than those of control wood and these values increased with frequency. Abundant and big vessel may behave as sound absorbing pore observed on the cross sectional surface of yellow poplar wood. The sound absorption coefficients and air permeability of sapwood were higher than those of heartwood for Liriodendron tulipifera.
To improve the acoustic treatment of facings and provide appropriate solutions for noise control at workplace, it is necessary to develop methods of acoustic characterization of the walls in ...industrial halls. Sound absorption coefficient measurement in industrial rooms is however quite a difficult task because of the partially reverberant conditions. This work describes the measurement of the sound absorption coefficient of flat panels subject to small angle sound incidence, in an industrial hall using an experimental device equipped with an acoustic array. The directivity of this array has been optimized so that the major part of the received acoustic energy would come from one portion only of the investigated facing, this, in turn attenuating the reflected beams due to the reverberation. This new device includes an impulse sound source targeting the panels. The present article focuses mainly on the sound source design and implementation. It also describes some sound absorption measurements carried in a semi-anechoic chamber and in an industrial hall in order to examine the performance of the device. Sound absorption coefficients of several standard liners obtained through this device have been compared to those resulted from the two microphone technique.
Introduction & Objective: Noise is one of the most important harmful agents in work environment. In spit of industrial improvements, exposure with over permissible limit of noise is counted as one of ...the health complication of workers. In Iran, do not exact information of the absorption coefficient of acoustic materials. Iranian manufacturer have not laboratory for measured of sound absorbance of their products, therefore using of sound absorber is limited for noise control in industrial and non industrial constructions. The goal of this study was to design an impedance tube based on pressure method for measurement of the sound absorption coefficient of acoustic materials. Materials & Methods: In this study designing of measuring system and method of calculation of sound absorption based on a available equipment and relatively easy for measurement of the sound absorption coefficient related to ISO10534-1 was performed. Measuring system consist of heavy asbestos tube, a pure tone sound generator, calibrated sound level meter for measuring of some commonly of sound absorber materials was used. Results: In this study sound absorption coefficient of 23 types of available acoustic material in Iran was tested. Reliability of results by three repeat of measurement was tested. Results showed that the standard deviation of sound absorption coefficient of study materials was smaller than 3×10-2. Conclusion: The present study performed a necessary technology of designing and producing of impedance tube for determining of acoustical materials absorption coefficient in Iran.
Kundt's tube and reverberant chamber are common methods for determining the sound absorption coefficient or acoustic impedance of materials. These measurement methodologies are well-known and ...standardized, albeit not being practicable in-situ and requiring the isolation of samples of the material under test. Furthermore, Kundt's tube results are affected by the size and the diameter of sample, and by the tube length, while reverberant chamber ones by the room dimensions and diffusiveness. In literature, noncontact techniques for sound absorption coefficient and acoustic impedance measurement are widely debated. In this paper, three different noncontact systems for measuring the sound absorption coefficient have been investigated: a pressure-velocity probe, a Laser Doppler Vibrometer, and a spherical microphone array featuring 64 capsules. The three methods have been evaluated through in-situ measurements of materials with known acoustic characteristics: Basotect G+ and Expanded Polystyrene. Furthermore, the results obtained with the standard test signal, i.e., white noise, are compared with the exponential sine sweep technique, which provides an increased signal to noise ratio, and allows for removing nonlinear high order distortions and acoustic reflections. As a main contribution of this work, it will be shown that microphone arrays are an optimal solution for measuring the sound absorption coefficient.
This paper test sound absorption coefficient of different air voids specimen in reverberation chamber and low noise pavement field testing, which gets main frequency band range of pavement noise is ...315~5000Hz, noise arrives at the peak of about 500Hz; the relationship of microphone height and sound pressure level is not obvious; the porous asphalt mixture which air voids is more than 20% has the upper sound absorption coefficient at the frequency of 400~1000Hz, and its noise reduction effect is obvious; There is a linear relationship between the air voids and the maximum absorption coefficient of asphalt mixture, increasing air voids can cause larger absorption coefficient; sound-absorbing property of the low noise asphalt pavement is one of the dominant mechanism of mitigation traffic noise.
