抄録
The SEA introduced by Crocker & Price is an effective method which explains the complicated mechanism of sound transmission through finite walls. However, there is large discrepancy between the SEA values and the measured values at low frequency domain, since the random incidence mass law deduced for infinite wall was applied to the coupling loss factor η_<13> for nonresonant transmission. To calculate η_<13> more strictly, this paper introduced the radiation factor Q which is related to the wall area. The modified SEA shows that resonant transmission cannot be ignored below the critical frequency f_c when the internal loss coefficient η_<int> and the wall area is small, and it is necessary to determine quantitatively both the η_<int> and the edge condition. A quantitative tendency of η_<int> and edge condition was obtained by experimental studies. Below f_c, edge condition is estimated by the coupling loss factor η_<rad> for resonant transmission, and η_<int> value is independent of wall area but increases in proportion to wall thickness. Above f_c, the following results were obtained. The energy loss at edge significantly influences TL. TL decreases in proportion to the degree of edge fixation because the energy loss at edge decreases. η_<int> value including the energy loss at edge is independent of wall thickness under the same edge mounting but increases as the wall area becomes smaller, since the rate of energy loss at edge increases. Calculated TL using suitable values of η_<int> and edge condition agreed favorably with experimental measurements in the mass control and coincidence effect region.
