Development of a double-membrane sound generator for application in a voice-producing element for laryngectomized patients.

For voice rehabilitation after total laryngectomy a shunt valve is usually placed in the tracheo-esophageal (TE) wall, thereby enabling the production of a TE voice. Some patients, however, are unable to produce a voice of sufficient quality. Furthermore, the TE voice is low pitched, which presents a problem especially for female laryngectomized patients. The voice quality after laryngectomy might be improved by introducing a voice-producing element (VPE) into the TE shunt valve. In this study a sound generator was developed that is suitable for application in such a VPE. This sound generator consists of two elastic membranes placed parallel inside a circular housing. A substitute voice source is created when the membranes start to vibrate via a constant flow of air passing between them. To determine the optimal membrane configuration for proper functioning under physiological conditions, up-scaled physical VPE models with different membrane geometries were evaluated using in vitro experimental tests. For certain membrane geometries the tests showed that a basic sound, containing multiple harmonics, could be successfully produced under physiological air pressure and airflow conditions. The fundamental frequency (60-95 Hz) and sound pressure level (57-78 dB, at 15 cm microphone distance) were regulated via changes in the driving pressure, thereby enabling the possibility of intonation in laryngectomized patients' speech. The obtained frequency range is considered appropriate for producing a substitute voice source for female patients. The geometry considerations in this study can be used for the development of a true scale VPE that can be evaluated clinically, to eventually replace the voice after laryngectomy.