Abstract: A hollow shell-type hearing aid is prepared from an impression of the ear. A mold is formed from the impression. An opening is cut in the mold and the mold is filled through the opening with hardenable material. The hardenable material is allowed to cure until a hard shell of the material forms on the surface of the mold. The remaining hardenable material is poured out of the mold through the opening and the shell is then removed.

Abstract: An acoustical small hearing aid designed to be worn in the concha of the auricle and made of thin-walled plastic, metal, or rubber. This invention modifies the normal conchal resonance and combines it with the ear canal resonance to shift the normal sound pressure gain of 15 to 20 dB at the tympanic membrane downward from 2600-3000 Hz to 1500-2000 Hz dB, or lower, thus providing significant sound amplification for persons with mild high-frequency hearing loss. The invention accomplishes these goals by providing a thin, hollow shell that fits snugly into the auricle and concha of the external ear so as to enclose a volume of air within the concha. An opening in the shell lets sound waves into this air volume. The ratio of the air volume and the area of the opening control the peak frequency of amplification desired, the amplitude, and bandwidth of amplification, and must be kept between 1/2 and 1/15.