The chairman of this session was R. Lutz and the rapporteur was W. F. King III.
Session 5 began with an invited paper by G. Wilson, who outlined some of the procedures used to abate both air-borne and structure-borne noise in the vicinity of railway lines. He illustrated abatement techniques with case-history studies of particular problems. An interesting abatement measure described by Wilson involved the elimination of disturbing low-frequency vibrations. This problem was solved by straightening the rails, a procedure not generally specified as a requirement in North America. Wilson also touched on a problem often experienced by acousticians and engineers who deal with architects and designers. In Wilson's example, an architect, obviously oblivious to the consequences of his suggestion, wanted to cut slots in a sound barrier to make it more decorative. There were no questions after this talk.
The first contributed paper was given by Y. Zenda, who described the wide range of work begin done in Japan to control noise sources on Shinkansen lines. His talk, albeit brief, encompassed most of the problems encountered on high-speed vehicles: i.e., noise due to wheel/rail interactions, bridges, pantograph sparking, traction motors and aerodynamic fluctuations. Zenda also discussed diagnostic tools such as microphone arrays used to pinpoint sound sources. In response to a question from Barsikow, Zenda said that the speed exponent in Japan for wheel/rail noise is about 3, whereas for aerodynamic noise it ranges between 6 and roughly 7, with the higher value occurring at train speeds between 300 and 400 km/h. Zenda did not specifically say so, but these values are probably for A-weighted sound.
The next talk was given by P. J. Remington, who described an innovative technique for reducing wheel/rail noise levels by between 5 and 10 dB. All other things being equal, rolling-noise levels are inversely proportional to the size of the contact area between the wheel tread and rail head. To increase this area, Remington suggested making the shape of the wheel tread concave, with a lateral radius of curvature slightly greater than that of the rail head. Remington also discussed some of the problems that would have to be investigated before such a ''conforming wheel'' could be adopted. Hanson commented that these wheels might have difficulties staying on the rails, and this aspect should be looked into.
The next paper, given by W. F. King III, began with a brief overview of the common sources of aerodynamic noise on tracked vehicles. As an aid for estimating the importance of aerodynamic noise produced by particular vehicles, King defined two characteristic train speeds, the acoustical transition speed and the acoustical impact speed. He then showed a few results of aeroacoustical investigations of pantograph structural elements and discussed some of the low noise pantographs being tested in Japan. In answering a question asked by Hanson, King said that, on the basis of pass-by sound levels, the acoustical