US Patent 9241211 Tubular body, bass reflex port, and acoustic apparatus

A tubular body having an air flow passage, wherein an area of a cross section, in a direction perpendicular to a tube axis, of a space enclosed with an inner wall of the tubular body increases toward an open end thereof, wherein a curvature of the inner wall at an end portion of the tubular body near the open end is repeatedly increased and decreased along a circumferential direction of the inner wall, and wherein, when the inner wall in a cross section of the end portion in the direction perpendicular to the tube axis is viewed from the tube axis, a convex portion at which the inner wall protrudes in a direction away from the tube axis and a concave portion at which the inner wall is recessed in a direction toward the tube axis are repeatedly formed along the circumferential direction.