Question
What interaural attenuation values do you recommend using with insert earphones?
Answer
I would like to start with interaural attenuation (IA) values for the TDH-39 and TDH-49 circumaural earphones to help define IA values for inserts. Based on data from Chaiklin (1967) on TDH-39s, Killion, Wilber & Gundmundson (1985) on TDH-39s and Sklare & Denenberg (1987) on TDH-49s, average IA values across all frequencies for air conduction was around 60 dB. Typically, a more conservative number of 40 dB is used as this was found to be the minimum IA level found in these studies.
Moving onto inserts! Killion et al. (1985), Konig (1962) and Sklare & Denenberg (1987) found average IA values of around 80 dB with minimum IA levels of 70 dB. You could therefore use 70 dB as the IA for inserts. Clinically, I have often seen audiologists use an even more conservative value of 60 dB.
It is for these large IA values and other reasons (patient comfort, infection control, ambient noise reduction, ear canal collapse) that use of insert earphones has been recommended in many clinics.
References
Chaiklin, J.B. (1967). Interaural attenuation and cross-hearing in air conduction audiometry. Journal of Auditory Research, 7, 413-424.
Killion, M.C., Wilber, L.A. & Gundmundson G.I. (1985). Insert earphones for more interaural attenuation. Hearing Instruments, 36(2), 34.
Konig, E. (1962). On the use of hearing aid type earphones in clinical audiometery. Acta Otolaryngologica, 55, 331-341.
Sklare, D.A. & Denenberg, L.J. (1987). Interaural attenuation for Tupephone insert earphones. Ear and Hearing, 8, 298-300.
Dr. Dybala is the President and Editor-in-Chief of Audiology Online, the world leader in online hearing health education and information. He earned his Masters and Ph.D. in audiology from the University of Texas at Dallas / Callier Center. He has experience as a clinical audiologist specializing in adult and pediatric hearing aid fittings, and as research audiologist and lecturer in the area of adult amplification. Dr. Dybala was one of the internet pioneers for the profession launching the first internet based audiology company and built and maintained several ground breaking and innovative web sites for the profession. He currently holds an appointment as an Adjunct Assistant Professor of Audiology at the University of Texas at Dallas where he teaches an Au.D. level amplification course. He volunteers as President of the Scott Haug foundation board and also serves as a peer reviewer for the International Journal of Audiology.
