Acoustic consequences of evaluating hearing aids via stethoscopes and listening tubes

A stethoscope or listening tube with a custom earmold is routinely used to evaluate the acoustic output of a hearing aid. The diameter and length of t he tubes of these listening devices cause changes in the acoustic output re lative to the in situ condition. To compare these effects across commonly u sed listening devices, three stethoscopes and three listening tubes were ev aluated with two different hearing aids when six different complex stimuli were used as input signals. In general, the listening devices resulted in a decrease (up to 20 dB) below I kHz, an increase (up to 20 dB) between 1 kH z and 2 kHz, and a decrease (up to 30 dB) above 2 kHz relative to the in si tu output. These changes should be considered when making decisions regardi ng hearing aid status on the basis of listening checks via stethoscopes or listening tubes.