1. Lybarger S (1990) A historical overview. In: Sandlin R (ed) Handbook of hearing aid amplification: theoretical and technical considerations. Singular, San Diego, pp 1–29
2. Apaix A, Decroix G, Olivier JC (1974) La Prothése Auditive. Arnette, Paris
3. Stephens S, Goodwin J (1984) Non-electric aids to hearing: a short history. Audiology 23:215–240
4. Politzer A (1908) Lehrbuch der Ohrenheilkunde, 5th edn. Ferdinand Enke, Berlin
5. Berger K (1974) The hearing aid its operation and development, Revised edn. National Hearing Aid Society, Livonia