Government laboratory tests hearing aids and mobile phones

AMTA contracted the National Acoustic Laboratories (NAL) to characterize the interactions between GSM 1800 MHz digital mobile telephones and hearing aids. NAL had previously conducted similar studies on the interaction of GSM 900 MHz.

The 900 MHz radiofrequency (RF) test set up was modified to operate at 1750 MHz. Subjective levels of interference produced in hearing aids were tested under various conditions. The research studied the immunity levels of hearing aids, possible bystander interference and the subjective effects of nineteen people using hearing aids in both microphone and telecoil mode.

The study confirmed that a hearing aid with a medium level of immunity to RF interference provided protection against bystander interference at a distance of one metre from a 1750 MHz GSM operating at maximum transmit power which confirmed the C1 Classification used in the Australian Standard AS 1088.9 for the frequency range 1700 to 2000 MHz. With respect to the subjective tests, all of the hearing aids with a medium or better RF immunity had a limit of interference between 0 and 35 mm from the ear. In telecoil setting the limit of interference ranged between 75 and 5000 mm from the ear.

The researchers made the general comment that currently available hearing aids used in this study had a greater immunity to RF interference than those models generally available a decade or more ago. However, base band interference excluded use of telecoil mode for hearing aid users of GSM 1800 MHz digital mobile telephones.

The full report can be viewed here.