Summary
Measured how a hearing aid's default telecoil setting compares with its microphone setting after the microphone has been fitted to a prescription.
Key findings
- Measured 52 behind-the-ear hearing aids from one manufacturer, returned from repair to a university clinic, whose microphone programs had been fitted to the NAL-NL1 prescription with the telecoil left at the manufacturer's default.
- In a 2-cc coupler, averaged over 11 frequencies, the default telecoil and the programmed microphone gave about the same output.
- Frequency by frequency, the default telecoil was significantly quieter than the programmed microphone at 200 Hz (by 15.2 dB on average) and 400 Hz (by 6.0 dB), and louder at 4,000 to 6,300 Hz (by about 6 to 7 dB). The discussion sums up the 200-400 Hz shortfall as 6 dB. The authors suggest the low-frequency shortfall may explain why users complain the telecoil is not loud enough.
- Shows that the standard single-number check (RSETS, a high-frequency average) can look close to zero while the low frequencies are cut, so it can miss this mismatch.
- Also reports pilot real-ear measurements with a speech-weighted signal on 39 of the aids, in which the default telecoil was 20.9 dB below the programmed microphone at 200 Hz and 12.6 dB at 400 Hz, offered to encourage equipment makers and standards writers to support speech-like telecoil test signals; a few aids from a second manufacturer appeared to match more closely, but there were too few to analyse.
- The pilot real-ear section used a silicone demonstrator ear on a tripod, not measurements in participants' ears. The microphone input was 70 dB SPL; the authors later established that 65 dB SPL would have matched the 56.2 mA/m telecoil input.
- The acknowledgments identify NIH NCRR grant TL1 RR024995 and equipment provided by Frye Electronics (FP40 telewand, footswitch and demonstrator ear); they do not specify that it was lent. The Figure 5 explanation defines positive differences as microphone output greater than telecoil output.
- The readable abstract independently confirms 52 hearing aids from one maker in the coupler condition, 39 in the real-ear pilot, and significantly lower mean telecoil output at 200 and 400 Hz. It gives neither the size of those differences nor the repair history. The archived bibliographic metadata identifies NIH grant TL1 RR024995.
Limits
One manufacturer's aids, measured in a coupler with no listener outcomes. The study concerns telephone listening; the authors note that telecoils also receive loops and neckloops, but loop listening was not tested. The authors note a level mismatch in the real-ear pilot. One Results sentence reverses the direction of the frequency-specific differences; the abstract, discussion and Figure 5 sign convention support lower telecoil output at 200 and 400 Hz. This record cites the authors' manuscript in PubMed Central.
Read the original
pmc.ncbi.nlm.nih.gov/articles/PMC4354810
Cited in
- Which hearing devices can receive which systems?Open
- Auracast, hearing loop, infrared, RF or Wi-Fi: which suits which room?Disputed
- Are telecoils switched on and set up well enough for loops to work?Not reliable yet
Cite this source
Putterman DB, Valente M. Difference Between the Default Telecoil (T-Coil) and Programmed Microphone Frequency Response in Behind-the-Ear (BTE) Hearing Aids. Journal of the American Academy of Audiology 23(5):366-378. May 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC4354810/ (accessed 13 October 2026).
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