室内の音圧分布を与えるBeranekあるいは石井の式の適用範囲

抄録

To calculate the distribution of sound pressure level in a room given by a simple source of sound lacated in it, Beranek's formula or Ishii's formula has been practically used. However, in a large room, it has been often found that the calculated values of sound pressure level are not in good agreement with the observed ones, except when the mean absorption coefficient of the room is exceedingly small. Then, to obtain the applicable limit of these formulae, a formula has been derived geometrically which gives the distribution of sound pressure level in a room, and the values calculated from these three formulae have been compared with the observed values in an auditorium and a broadcasting studio. It was found that the values calculated from Beranek's formula and Ishii's formula show an error of 2-4. 5 dB at a distance greater than 10 m from the sound source in an ordinary large room whose mean absorption coefficient is 0. 2-0. 3, whereas the values calculated from the formula derived here show a good agreement with the observed values. When the absorption coefficient of a room is smaller than 0. 05, all values calculated from these three formulae agree well.