This laboratory has undertaken an extensive series of experimental measurements to determine the effect of barrier screens on the transmission of sound from a point source. By exercising great care in the experimental procedures, the data spread was kept within a narrow band about 1 dB wide. The results of these experiments indicate that the correct attenuation curve (in decibels vs. Fresnel number "N") for a point source is given by Fresnel's equations. This is an important determination because computer programs based on the widely used National Cooperative Research Program Report 117 use a curve suggested by the work of Maekawa that is lower than Fresnel's curve.
The results of calculations that convert this point source curve to the incoherent line source (and line source segment) case are also given.
The measurements were conducted at two frequencies, 5.19 and 10.019 kHz, and employed a variety of source-to-wall and wall-to-microphone spacings. They were carried out indoors using pulse techniques to eliminate unwanted bounces and reflections.
July 27, 2007
Rene N. Foss.
University of Washington. Applied Physics Laboratory.
- # of Pages: 75 p., 1,851 KB (PDF)
- Subject: Acoustic measuring instruments, Acoustics, Barriers (Roads), Computer programs, Diffraction, Equations, Highways, Noise barriers, Noise control, Sound, Sound attenuation, Walls.
- Keywords: Noise suprression, noise barriers, noise screens, highway acoustics, Fresnel diffraction.
- Related Publications: Attenuation of Sound as a Function of Barrier Angle, (WA-RD 24.2).
Noise Barrier Screen Measurements, Double Barriers. (WA-RD 24.3).
Vehicle Noise Radiation, Effective Height and Frequency Measurements, (WA-RD 24.4).
Field Evaluation of Single Barriers, (WA-RD 24.5).
This abstract was last modified April 29, 2008