| 摘要 |
PURPOSE:To align a speaker to the direction of the plane waves of noises over a wide range and to eliminate the need for limiting the diameter of a duct by arranging the speaker at nearly the center in the duct in such a manner that the spherical waves radiated therefrom and the plane waves of the noises align. CONSTITUTION:The speaker 5 is so provided at the center of the section of the duct 1 that its aperture faces the same direction as the direction of the plane waves of the noises. The plane formed by the speaker 5 is the spherical waves in its aperture and becomes the plane waves the furtherer from the aperture. The direction of the spherical waves faces the same direction as the direction of the plane waves of the noises in the aperture of the speaker 5 in such a case. These spherical waves are used for canceling the noise and form a wide range of the cancelation region and, therefore, the effect of the cancelation is greatly improved. The speaker 5 is hung from the duct 1 and the aperture of the speaker 5 is formed as small as possible; further, the shape of an enclosure in the rear part is formed to a stream like a cannon ball, by which the air current loss and the generation of whizzing sounds are prevented. |
