If a sound absorbing surface is sited near the noise source in a room, the direct energy from the source ought to incident upon that surface according to its solid angle ratio and the reflective energy incident upon the surrounding room surfaces in those area ratios. Adopting this idea, we have shown a calculating method for the average noise levels in the room, and found the noise reduction can be expected more effectively when the room has small sound absorbing power and the sound absorbing surface has the large absorbing coefficient. Also we have measured the noise levels in the room including the sound absorbing surface near the noise source. Our experimantal results almost agree with the culculated results, and we have confirmed the validity of the proposed calculating method.
In Finland, a questionnaire study about leisure-time noise exposure was conducted to 1069 young people of ages between 13 and 25. The aim was to accumulate knowledge for the risk of the hearing of young people to conserve their hearing in future. A questionnaire study of the same content as in the Finnish study, has been conducted to 1390 young people in Sendai. In this report, the results of the Sendai questionnaire study are presented. First, attributes of the respondent, their music preferences, and listening tastes are reported. Moreover, the ratings of loudness levels as well as subjective symptoms as effects of noise to hearing in everyday life, particularly in free time and leisure time activities are introduced. Information on hearing protectors, and the usage rate of heating protectors are also given.