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  1. 2 Acta Physica Polonica A

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  1. 1 2015

  2. 1 2011

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  1. 2 Piechowicz J.

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Sound Wave Diffraction at the Edge of a Sound Barrier

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Piechowicz J.
Acta Physica Polonica A
|
2011
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vol. 119
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issue 6A
1040-1045
EN
The diffraction phenomenon is described by the Huygens-Fresnel principle. The review of physical laws ruling the bending of sound waves at the edge of the screen allows the effective selection of both acoustical and geometrical parameters of the screen. Sound wave diffraction theories have been developed on the basis of wave optics, when wavelength is small in comparison to the size of the obstacles, which can be also used in acoustics with the same assumptions about geometry of the system. Diffraction can be seen as a result of the interference of waves reaching the point of observation in accordance with the laws of geometrical optics and wave disturbances arising as a result of interaction with the edge of an obstacle. The paper describes a test method using maximum length sequences for determining the intrinsic characteristics of sound diffraction in situ during testing of roadside noise barriers. A scale model experiment has been performed in an anechoic room. Also, a real noise reducing device was tested in free field conditions.
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Sound Diffraction Over Noise Barriers with Added Devices Installed on the Top Edge

100%
Piechowicz J.
Acta Physica Polonica A
|
2015
|
vol. 128
|
issue 1A
A-36-A-40
EN
Airborne sound insulation index of the noise barrier panel and the sound absorption coefficient of the barrier surface are the acoustic parameters that are usually determined in specialized laboratories, however they can be also determined in situ. Acoustic characteristics of a barrier include also the diffraction index difference determined from comparison of barriers with plain top edges and barriers with added devices installed on the top edge. The index is determined from the impulse response values determined for the acoustic wave propagation path from the sound source to a set of properly distributed measurement points. By means of the same method, one can also determine the difference in a barrier's acoustic effectiveness between the plain top barrier structure and its version with added devices mounted on the top. The paper presents measurement results for three types of added devices mounted on the top edge of the barrier. The diffraction index differences have been determined for each added device type and the acoustic effectiveness for each device has been compared with the plain top edge acoustic barrier.
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