Evaluation of noise in hearing instruments caused by GSM and DECT mobile telephones.

The annoyance of noise in hearing instruments caused by electromagnetic interference from Global Systems for Mobile Communication (GSM) and Digital European Cordless Telecommunication (DECT) mobile telephones has been subjectively evaluated by test subjects. The influence on speech recognition from the GSM and DECT noises was also determined. The measurements involved 17 hearing-impaired subjects. The annoyance was tested with GSM and DECT noise, each one mixed with continuous speech, a mall environment noise, or an office environment noise. Speech recognition was tested with the DANTALE word material mixed with GSM and DECT noise. The listening test showed that if noise level is acceptable so also is speech recognition. The results agree well with an investigation carried out on normal-hearing subjects. If a hearing instrument user is to be able to use a telephone without annoyance, the input-related noise level must not exceed 47 dB SPL for GSM and 46 dB SPL for DECT.