ODHHS Information and Technical Assistance Series
Hearing Aids and EMI (Electromagnetic Interference)
(Source: Galluadet University)
Most hearing aids are equipped with special circuit, called a telecoil or "T" switch. This circuit picks up electromagnetic energy from telephones, neckloops, and room loops so that the hearing aid user can understand speech or enjoy music without interference from background noise.
In the past, telecoils were so weak that even people who turned up their hearing aids to full volume had difficulty picking up the desired signals from the telephone or assistive listening devices connected to the television, radio, or stereo. Hearing aid manufacturers have begun to realize the importance of the telecoil in providing communication access in the workplace as well as in social situations, and have begun designing them so that they have more sensitivity.
But this has created new problems. When the telecoil's sensitivity is increased, so is the possibility of interference from other electromagnetic sources, such as fluorescent lights, electric motors, overhead projectors, computer monitors, printers, and other equipment.
For example, a deaf or hard of hearing person who wants to plug a neckloop or room loop into the CD-ROM sound jack of a computer must adjust the loop system volume high and keep the hearing aid volume relatively low so as not to pick up electromagnetic interference (EMI) from the computer. It also helps if the hearing aid user sits back from the monitor.
Hearing aid companies realize that this interference is a problem, but they say that simply putting a filter into the hearing aid will not help. The interference from a computer monitor occurs every 50 Hertz over the entire frequency range of the audio spectrum. Comb filters will work in such cases, but this solution is not technologically feasible at this time.
Why can't computer monitors and other equipment be manufactured that does not cause this interference? Deaf and hard of hearing people may need to force the computer industry to make design changes. There is precedent for such an effort; it is because of pressure from deaf and hard of hearing people, most telephones manufactured today are hearing aid compatible. And efforts continue in the United States and abroad to prevent GSM and TDMA cellular telephone transmission, because they causes significant (and even painful) interference to hearing aids and their users (see Consumer Groups Wary on GSM).
A final word: people with profound hearing loss who use their hearing aids for awareness only often enjoy listening to music. Electromagnetic interference would be a problem for them as well.
One way to deal with EMI now is to use a hearing aid that has what is called a Direct Audio Input (DAI) interface. This is a behind-the-ear hearing aid with a jack that can be connected to a cord which can then be plugged into any sound source. Since DAI is an electrical connection, electromagnetic interference is minimized. However, you can sometimes pick up radio frequency interference (RFI) from a computer's central processing unit, or CPU. Try moving the DAI cord around until the interference goes away.
Consumer Groups Wary on GSM
The FCC is being petitioned by many consumer groups to investigate the safety and interference dangers of a digital technology called Global System for Mobile Communications (GSM). GSM technology has been used in cellular telephones in Australia and Europe, and has caused pacemakers to change speed or skip beats, automobile airbags to deploy without warning, and hospital lifesaving equipment to suffer serious malfunctions.
Both the United Kingdom Department of Health and the German Health Ministry have issued warnings about the dangers of GSM technology. GSM technology used in cellular telephones can cause severe interference in hearing aids. Whenever a GSM telephone is used by or near an individual wearing a hearing aid, a loud (and even painful) buzzing noise will occur in the hearing aid.
Consumer groups want the FCC to investigate this technology and find out if something can be done to prevent the interference (e.g., banning or altering the technology). Another possibility is to shield each hearing aid, but this may be a technologically difficult and expensive solution.
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This document is one of a multi-part series.
Document created with input from Cynthia L. Compton, Assistive Devices Center, Department of Audiology and Speech, Gallaudet University, and was originally distributed in the 1995 Aug 08 issue of TFA Technical Topics.