Measurement of spatial information in sound fields by closely located four point microphone method.

When we estimate a sound field in a room, it is important to grasp the spatial informa-tion, especially of the early reflection periods. In this paper we'll discuss a way to grasp the spatial information of sound fields from impulse responses measured at closely located four points, the origin and three points of the same distance (3∼5cm) from the origin on the rectangular coordinate axes. From these four impulse responses the coordinates and powers of virtual image sources are calculated by correlation technique or intensity technique. Concert halls, opera theaters and many other sound fields are measured by this technique. The distributions of virtual image sources and directivity patterns of some concert halls are shown.