Abstract: The concepts on the effective aperture and the effective beamwidth are proposed based on energy conservation law in this paper. Through these concepts the sound field distribution may be associated with the array configuration, and the pressure in mainbeam direction, the directivity factor and the mainbeam width may be united.
The effective aperture and the effective beamwidth of the arrays with larger dimension are computed and the following regularities are obtained: The effective beamwidth of a plane array equals the reciprocal of its area （measured by λ）; The effective beamwidth of a curve array is approximately equal to the central angle of the curve array, and are approximately a constant beamwidth; The effective beamwidth of a compensated curve array is approximately equal to the aera of projection of it onto the compensated direction.