In the problems of architectural noise controll, it is sometimes necessory for us to deal with collective source consisted of many independent noise sources.

For example, when we wish to design a quiet building in central districts of a city, a street on which many vehicles are running is one of the most important noise source, and in this case the street would be regarded as a belt type collective source.

And opening of a room also would be assumed as a two-dimentional collective noise source when it is looked from outdoor free field, as the sound field in the room is usually diffused one.

The distinctive characteristic of such a collective noise source is that the rate of noise decay by distance varies according to the type and dimentions of the collective noise source.

In this paper, first, the theoretical properties of collective noise source are discussed in Part 1, and the various rates of noise decay by distance from model collective sources which are measured in B.R.I. laboratory are described and compared with theoretical values in Part 2.

And then the practical application of properties of collective sources are discussed in Part 3.

* Manuscript received on January 23, 1968.
** Research Member of Building Research Institute, Ministry of Construction