Validity of a temporary threshold shift (TTS) detector for use with portable listening devices

Recent studies on the use of portable audio listening devices indicate that while sustained listening at the maximum output volume of the unit is potentially hazardous with most devices, personal habits and listening preferences during actual use are such that only a 5-10% fraction of users may be at high risk of developing permanent hearing damage. Given the explosive increase in sales for these devices in recent years, this nevertheless represents a very large number of individuals worldwide. In this project, self-administered auditory temporary threshold shift (TTS) measurements are investigated as a possible tool to raise user awareness on the potential risks of portable listening devices when used at excessive levels. Users are presented with a sequence of 10 tones varying in levels near threshold using their device, and are asked to count the number of tones heard before and after the listening session. Counting less tones after the exposure indicates the presence of a TTS. Test-retest reliability measurements indicated that a TTS of 5 dB or more could be detected with this method. A validation study is currently being carried out in a laboratory setting with a group of users with normal hearing. Subjects must listen to music with their own devices for a one-hour session in a simulated bus noise environment. Thresholds are measured prior to and after exposure using the proposed method of counting and a fixed-frequency adaptive tracking method as control. Listening levels are also monitored using a KEMAR manikin. Preliminary results indicate that a fraction of subjects develop a TTS of 5 dB or more, which is typically shown with both threshold methods. Interestingly, these subjects all listened to music at levels exceeding 90 dBA during the session. It is hoped that such a tool could help users self-detect potentially hazardous situations and foster safer listening practices.