Showing papers on "Noise barrier published in 1991"

Basic study on active noise barrier

Abstract: As a trial to improve the performance of passive noise barriers by applying the active control technique, basic theoretical and experimental investigation has been made. At first, the basic conception of the “active noise barrier” is presented, in which an active control system composed of a noise detector, an error sensor, a secondary sound source and an adaptive signal processing unit is attached to a passive barrier. As a preliminary study, a simple numerical calculation was performed according to the Fresnel-Kirchhoff diffraction theory, and the adaptability of the active control has been basically confirmed. Next, 1/2 scale model experiments were performed in a hemi-anechoic room to inve stigatethe effectiveness of the active noise barrier. In this experimental study, the method combining the “filtered x LMS” algorithm and the “block processing technique” was applied as the adaptive signal processing technique. As a result, it has been found that the active noise barrier is effective for sound attenuation in low frequencies.

Parallel barrier effectiveness : Dulles noise barrier project

Abstract: In an effort to minimize the cost and maximize the effectiveness of highway noise barriers, the Federal Highway Administration (FHWA) and a National Pooled Fund Panel (made up of 14 states) funded a field study program on an experimental highway noise barrier. A test barrier was constructed in 1984 at a site at Dulles International Airport in Chantilly, Virginia. The study, conducted from May 1989 to August 1989 by the U.S. Department of Transportation, Research and Special Programs Administration, Transportation System Center (U.S. DOT/RSPA/TSC), focused on the use of absorptive treatment and tilting as a means of improving the insertion loss of two parallel highway noise barriers. Measurements were conducted with both controlled moving point sources (trucks) and an artificial fixed‐point source (speaker system). Results show (1) the addition of absorptive treatment to the roadside face of two vertical, parallel, highway noise barriers eliminated multiple reflections and was found to improve the insertion loss (2–6 dB); (2) tilting proved to be an effective alternative to absorptive treatment in eliminating the multiple reflections and subsequent degradation in performance of two vertical reflective barriers; and (3) use of an artificial fixed‐point source is not a viable test of barrier effectiveness.

Full-scale testing of single and parallel highway noise barriers

Abstract: The results of research conducted by North Central Technical College and cosponsored by Ohio's Thomas Edison Program and Empire-Detroit Steel Division are reported. Laboratory and full-scale outdoor testing of both reflective and absorptive highway noise barriers are discussed. The phenomena of single-barrier insertion loss degradation caused by the addition of a second parallel barrier was confirmed. Further, absorptive barriers evidenced performance benefits over reflective barriers in parallel tests. Single-barrier insertion loss tests supported barrier attenuation theory for the configurations tested.

3-D Sound Generated by Moving Sources

Abstract: Based on Kirchhoff’s integral equation, a time-stepping boundary element procedure is formulated by which many acoustic wave propagation phenomena can be studied. Especially, exterior radiation problems are considered where sound sources can move arbitrarily in a three-dimensional surrounding, and the scattering of the acoustic waves at obstacles is treated. Some examples of environmental noise pollution problems, like noise from airplanes flying over a residential area, are presented in order to demonstrate the wide range of possible applications.

Noise reduction by absorptive louvers

Abstract: A roadway louver was originally designed as a lighting control system for the entrance to a highway tunnel. For the purpose of noise abatement, the louver has been designed to obtain acoustical effect. The result of scale model experiment shows that the louver is more effective than barriers when the louver blade is treated with absorptive material. Further improvement, however, is required on the performance of sound absorption of the louver, in order to apply to highway noise control. This paper describes the result of acoustical tests on newly designed roadway louvers. The experiment was carried out by setting a full scale model at an opening of a reverberation room.

Metal panel with corrugated structure made of vibration damping steel plate

Abstract: PURPOSE:To prevent noise from generating by a constitution wherein either one of flat plate and corrugated plate is made of vibration damping steel plate. CONSTITUTION:The metal panel concerned consists of one corrugated plate 4, which is made of vibration damping steel plate, pinched between two flat plates 3, which are made of vibration damping steel plate. Further, the metal panel is supported as flooring material through supporting legs 9 on a concrete slab 8. Thus, lightweight and highly rigid metal panel, in which the generation of noise is small, which is excellent in noise barrier properties and has soft and high grade touch, can be obtained.

Road noise barriers as sound radiation systems

Abstract: Road traffic noise has become a significant societal problem and the noise barrier as one remedy is studied acoustically. Traditionally, as a theoretical background for installing the noise barrier, the diffraction theory of the acoustic wave by a screen has been employed. In this paper, however, the noise barrier and the road structure on which a vehicle is a noise source are treated as one acoustic radiating system. By means of the boundary element method useful for an open-region problem, a two dimensional analysis is carried out. From the results of the analysis with the cross-sectional shape of the noise barrier and the frequency as parameters, it is found that a resonance is generated for a shape with parallel faces and the noise may be spread a large distance away in conjunction with the diffraction at the edge of the noise barrier. If an unrealistic containment is not expected and a horn shape is employed, the noise can be radiated upward in the direction normal to the road surface and the diffraction does not become significant. The frequencies studied were 150 to 300 Hz which are bothersome to the human ears.