Abstract: A hollow telephone receiver comprises a body, a vibrating diaphragm, a coil, a front piece, a magnet, a yoke, a sound adjusting cloth and a terminal plate. The vibrating diaphragm, coil, front piece, magnet, yoke, sound adjusting cloth and the terminal plate are placed into the body sequentially. Thus, the coil winds the cylinder at the lower end of the yoke and is located within the front piece and the magnet. While the upper circular hole at the upper end of the yoke is adhered with the sound adjusting cloth and the terminal plate so that after a hollow telephone receiver is assembled, a hollow portion is formed at the center thereof. Therefore, as a sound is expanded and compressed by the vibration of the vibrating diaphragm. The amplitude of the sound wave will complete concentrate at the hollow portion and is collected at the lower portion of the cylinder of the yoke.

Abstract: A thin-type speaker having a secondary diaphragm. The speaker including an enclosure, a diaphragm, a yoke, a sound coil, a magnet, and a washer. The surface of a first diaphragm is covered by a secondary diaphragm. The secondary diaphragm is made of sponge, cloth, paper, cardboard or isolating fabric. A thin-type speaker constructed according to the invention can produce larger tensioning as the power increases so that the speaker has a substantially larger flat effective bandwidth and less vibration noise.