|
Digital
cellphones and interference with hearing aid users
Abstract
The study, conducted on behalf of the Ministry of Health, with the
cooperation of Telecom and BellSouth, measured interference effects of two
varieties of TDMA (time division multiple access) digital phone systems, DAMPS
(digital advanced mobile phone service)and GSM (global system for mobile
communications) together with analog phones on 29 regular hearing aid wearers.
The report rated the two types of digital phones equally in terms of
interference, although the noise each type induced differed. No subjects
reported any interference from the analog phone.
Handset of different power (2W, 3W and 8W) were tested. The 8W phones caused
significantly more interference than the standard cellphones.
Hearing aid wearers had six brands of hearing aids among them, and styles of
hearing aid varied from BTEs (one with an additional microphone on a lead),
through ITEs to ITCs. Ages ranged from 24 to 83 years. The average 4-frequency
hearing loss for ears tested was 64 dB HL (range 29-108 dB).
The interference threshold varied considerably. Typically it was less than 1
meter. In a few cases there was no interference detected, and in 2 cases
interference from the 8W phone was detected at a distance of 5m.
In 20% of trials, interference occurred at a distance exceeding 1m. When the
8W phone was excluded, this fell to 11.5%.
Hearing aid type was significantly related to interference detectability -
but this effect was dominated by the impact of the one subject who had a BTE
with a microphone on a lead (which would have acted like a radio aerial).
In a few cases interference noise was audible to researchers well before it
was responded to by the hearing aid wearers.
|