1. 1) ISO 7029, “Threshold of hearing by air condition as a function of aged and sex for otologically normal persons” (1984).
2. 2) M. Koyasu, T. Ouchi, H. Ohkawa, S. Kuwano, M. Yasuoka and Y. Kariya, “Effect of background sound in public spaces on speech articulation by aging,” Proc. WESTPRAC, pp. 827–832 (2000).
3. 3) S. Kuwano and S. Namba, “Longitudinal survey on sound environment in the case of students,” Tech. Rep. Noise Vib. Acoust. Soc. Jpn., N-2003-19, pp. 1–8 (2003).
4. Report of the Committee of the Social Survey on Noise Problems