The influence of the surface of bogie shrouds and small barriers on their sound radiation efficiency


Common measures in noise abatement strategies of traffic noise are noise barriers. These represent a reliable and well calculable Method. On the other hand due to the required height of conventional barriers they are quite expensive and also they hinder the view of the landscape. As railway noise radiation mainly originates from the rail-wheel contact zone the application of shrouds in combination with low barriers seems to be promising. Assuming a radiation of the rails only in the vicinity of the wheels shrouds can be limited to the bogies. To date investigations dealt mainly with the dimensions of shroud-barrier systems, whereas this work focuses on the attributes of the inner surfaces. In addition to absorbing surfaces especially acoustically soft surfaces of very low acoustic impedance are accounted for. The examination of the influence of the surface impedances begins at a simulation of two different geometries using a wave approach. The calculated surface-based insertion losses are verified through the implementation of the finite-element-method and through measurements on a shroud-barrier model.

Publications

The Influence of Surface Impedances on Sound Radiation Properties of a Shroud-Barrier-Combination
Phd-Thesis, Berlin 2005 K. Johannsen
The Influence of the Surface Impedance on the Sound Reduction Efficiency of Shroud-Barrier Combinations ICA 17, Rome, 2001 K. Johannsen, M. Möser
The Influence of the Surface of Small Barriers on the Sound Reduction Efficiency of Shroud-Barrier Combinations ICSV7, Garmisch-Patenkirchen, 2000 K. Johannsen, M. Möser


Investigation of Auditory Dimensions

In general former investigations of the sensation of sound followed two different strategies. One rather technical physical and one rather psychological approach. Hearing experiments are as a matter of cause part of both approaches nevertheless these are conducted and evaluated in different ways.

The experiments in the technical physical approach consists in the presentation of artificial sounds. Certain parameters of these sounds are modified in such a way that the judgements of the jury can be used to scale certain so called "psychophysical magnitudes" i.e. loudness, pitch etc. With this strategy it is possible to develop methods of calculating the psychophysical magnitudes from the sound features. For the psychological approach any sound may be used and the jury usually has to judge the sounds using either scales of adjectives or pairs of adjectives i.e. semantic differentials. Auditory dimensions are deduced using statistical methods i.e. a factorial analysis whereupon the final outcome is a set of linear, independent, properties ('dimensions') which, hopefully, embrace all of the sounds multi-dimensional features ('Hörraum'). This method is therefore more holistic. A calculation of these dimensions from sound features is not possible.

Connections between these two strategies have been investigated whereby a hearing experiment using the psychological approach with the semantic differential and natural sounds has been conducted. To obtain a high number of dimensions a survey preceded the hearing experiment, the results of which led to a selection of adjectives and environmental sounds to use. A factorial analysis led to hearing dimensions. The psychoacoustical magnitudes of the sounds were then calculated. Finally connections between the evaluated dimensions and these parameters are determined through statistical methods as an analysis of correlation or regression.


Publications

Environmental Sounds for Psychoacoustic Testing ACUSTICA 87, 2001, S. 290-293. K. Johannsen, H. Prante
Determination of Hearing Dimensions and their Relations to Psychoacoustic Descriptors Forum99, Berlin, 1999 K. Johannsen, H. Prante
Erforschung von Hördimensionen mit Umweltgeräuschen DAGA98, Zürich, 1998 K. Johannsen, H. Prante
Zusammenhangsanalyse zwischen physikalischen Merkmalen und Hauptkomponenten der Beurteilungsattribute von Umweltgeräuschen Diploma Thesis, Berlin, 1997 K. Johannsen