In-the-Ear Measurements of Interference in Hearing Aids from Digital Wireless Telephones

ABSTRACT

Digital wireless telephones produce audible and often annoying interference in hearing aids. A standard, ANSI C.63.19, has been developed for measuring electromagnetic emissions from wireless telephone handsets as well as immunity in hearing aids. Based on the test results for a handset and a hearing aid, an estimated prediction of usability for that combination of devices can be made. One question that arose during the development of the standard was the acoustic signal-to-interference ratio (SIR) requirements for various levels of telephone usability as rated by hearing aid wearers. An experiment was conducted in which 42 hearing aid wearers listened to a telephone conversation through a dummy wireless phone while interference levels were varied using a second phone programmed to deliver a controlled electromagnetic field. Real-ear recordings of the speech with interference were made at each rating point of usability. Signal analyses of the recordings indicate that for 90% of the subjects, SIRs in the 28- to 32-dB range were needed to achieve a rating of Highly Usable, SIRs in the 20- to 24-dB range were needed for a rating of Minor Limitations on Use, and SIRs in the 12- to 15-dB range were needed for a rating of Major Limitations on Use.

KEYWORDS

Electromagnetic interference - digital wireless telephones - hearing aids - usability ratings - speech-to-interference ratio

REFERENCES

2 It is likely that the revised standard will use slightly different symbols than those cited.

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