US Patent 7174148 Receiver housing with frequency response improvement

A receiver includes a rear yoke inside a housing, a first acoustic paper bonded to an annular base of the rear yoke to block a rear open side of a tubular body of the rear yoke, an annular magnet supported on the annular base around the tubular body, a front yoke disposed at a front side of the magnet, a vibration diaphragm stretched in front of the yokes, a voice coil suspended in an annular space between the yokes, a tubular cushion fitted into the tubular body of the rear yoke, and an annular cushion (or annular step) set between the magnet and the tubular body, and a second acoustic paper covering an air hole at a rear side of the housing.