Q: WHAT CAUSES INTERFERENCE BETWEEN DIGITAL CELL PHONES AND HEARING AIDS?
A: When using a digital cell phone, the telephone conversation is transmitted over a wireless network using radio waves. The radio waves emitted by the cell phone are referred to as radio-frequency (RF) emissions. The RF emissions create an electromagnetic (EM) field around the phone's antenna. This EM field has a pulsing pattern. It is this pulsing energy that may potentially be picked up by the hearing aid's microphone or telecoil circuitry and perceived by the hearing aid wearer as a buzzing sound.
To complicate matters, the technology for transmitting calls over a wireless network differs depending on the carrier or service provider. For example, Verizon Wireless and Sprint PCS use CDMA technology, Nextel uses iDEN technology, and AT&T Wireless, Cingular Wireless and T-Mobile use GSM technology. The interference generated by these various technologies has different characteristics, some of which may cause more annoying interference for hearing aid users than others.
Telecoil users may experience another form of interference referred to as "baseband, magnetic interference," which originates from the cell phones electronics (e.g., backlighting, display, keypad, battery and circuit board). Unfortunately, baseband magnetic interference occurs in addition to the RF-interference potentially increasing the interference perceived by the hearing aid user.
The amount of interference experienced by hearing-aid users depends on the degree of RF emissions produced by a particular digital cell phone, and how immune his/her particular hearing aids are to these emissions. This is also true for hearing-aid telecoil users, but in addition, baseband emissions from the cell phone and the hearing aids immunity to baseband emissions must be considered.
Q: ARE DIGITAL CELL PHONES COMPATIBLE WITH HEARING AIDS YET?
A: Many hearing aid wearers still experience interference when using digital cell phones, particularly if they use the telecoil for telephone communication. Although there are no hard and fast rules, people with in-the-ear (ITEs) or completely-in-the-canal (CICs) instruments generally experience less interference than people with behind-the-ear (BTEs) instruments, and newer, digital hearing aids are generally more immune to interference than older, conventional analog hearing aids.
The Federal Communications Commission (FCC) recently (7/10/2003) partially lifted the exemption to hearing aid compatibility (HAC) requirements for digital wireless phones. The cell phone industry has been given a phase-in period for compliance. For acoustic coupling to a hearing aids microphone, the new rules require each digital phone manufacturer and carrier to have 2 commercially available handsets for each transmission technology with reduced RF emissions within 2 years. For inductive coupling to a hearing aids telecoil, digital phone manufacturers and carriers have been given an additional year (i.e., 3 years) to make available 2 handsets that provide telecoil-coupling capability for each transmission technology they offer.
The new ruling also requires a standard method for measuring digital cell phone emissions (i.e., ANSI C63.19) and product labeling on the outside packaging of the phone. Volume control is not part of this new requirement. However, most cell phones do have a volume control, although there is a standardized upper limit on the sound level that cell phones can produce. For more information on the new ruling, the full report and order by the FCC can be viewed at http://ftp.fcc.gov/cgb/dro/hearing.html.
Its important to note that the FCC does not have regulatory authority over hearing aids. This authority, although somewhat limited, lies with the Food and Drug Administration (FDA). Even so, the FCC, within its report and order, encouraged the hearing aid industry to test and label their products according to the level of immunity they have to digital cell phone emissions. The FCC and FDA are working cooperatively on this issue, recognizing that compatibility requires the coordinated function of both devices.
Q: WHAT SHOULD BE CONSIDERED WHEN PURCHASING CELL PHONE SERVICE?
A: One website that is particularly helpful in sorting out wireless service providers is http://www.wirelessadvisor.com. By entering a zip code, the Wireless Advisor identifies which service providers operate in a particular area and the transmission technology each one uses.
Through anecdotal reports from hearing aid (HA) users, clinical experience, and research evidence, CDMA and iDEN transmission technologies seem to work better (although not necessarily interference free!) for HA users than GSM transmission technology. Of the largest carriers, Verizon Wireless and Sprint PCS use CDMA technology, and Nextel uses iDEN technology.
Once a service provider has been selected, the next step is to determine which cell phone handsets it supports. The service providers website is the best way to find these phone models and their features and accessories.
A very important question to ask is how long one has to cancel the service and return a phone without penalty, if they dont work for a particular hearing aid wearer.
Q: WHAT SHOULD BE CONSIDERED WHEN PURCHASING A CELL PHONE HANDSET?
A: Generally speaking, its a good idea to shop for cell phone handsets at the "full" retail telephone store of the service provider. The support personnel at the full retail telephone store are more likely to know about these issues than the personnel at electronics or office supply stores. Full retail service provider stores are also more likely than electronics stores to have phones that are "in service" which can be tried with the particular hearing aid of concern.
The design of the telephone handset may be important for hearing aid users. Look for a telephone that has a ''clam shell'' or ''flip up'' design, where the only part of the phone in the section that flips up is the speaker (where you listen to the other party). Once a carrier has been selected, see if they support handsets made with this design. This design provides some physical distance between the hearing aid and the components related to the cell phone's transmission technology that may potentially cause interference. For telecoil users, it also provides physical distance between the cell phone electronics (another potential source of interference) and the hearing aid. The greater the distance between the hearing aid and these electronics, the less potential there is for interference experienced by the hearing aid wearer.
Interference from backlighting, depending on the type of display, can be particularly bothersome for telecoil users. Backlighting is used to light the phones display window so information can be easily viewed in low light conditions. Backlighting typically turns on when the phone is turned on and then when any of the buttons on the control pad are pushed, including the volume control buttons. The ability to control whether the display is illuminated or not, and the amount of time the backlight stays lit may be important considerations for telecoil users, especially if the phone provides otherwise interference-free listening.
The Cellular Telecommunications and Internet Association (CTIA), the trade organization for the wireless telephone industry, has a website on accessibility and wireless technology. The website lists wireless phones to try if you are a hearing aid wearer. The phones are listed by manufacturer, and information is provided on which handsets may have lower levels of RF emissions and which may have inductive coupling capability.
Finally, hearing aid wearers should consider their need with regard to ring signaling. Most cell phones have a choice of distinctive ring signals and a volume control for ring signaling. Many will even have a built-in vibratory alert. A "holster" can be used to clip the phone to clothing so incoming calls can be detected through vibration. If a vibratory alert is desirable, but not built-in, there are vibrating alerting accessories available, although their performance may be less consistent than phones with this option built-in.
Q: WHAT SHOULD BE CONSIDERED WHEN PURCHASING NEW HEARING AIDS?
A: When purchasing new hearing aids, hearing aid candidates should be sure to tell their audiologist that they want to be able to use a digital cell phone. The audiologist can talk to the hearing aid manufacturers to find out which of their hearing aids have some level of ''built-in'' immunity to cell phone interference. Hearing aid components, such as microphones and t-coils, are being developed that are more resistant to interference, but this needs to be stated as a requirement.
In addition to built-in immunity, audiologists may suggest that hearing aid candidates select hearing aids with telecoils. Telecoils are required in order to take advantage of many of the accessories, such as neckloops or other add-ons, developed by both the phone industry (e.g., neckloops by Nokia and Motorola) and third party manufacturers (e.g., CHAAMP by Audex, HATIS). When audiologists discuss accessories with hearing aid patients, it's important to consider the cost of the accessory and its ease of use and maintenance.
Most accessories increase the distance between the hearing aid and the phone's antenna, thereby reducing or eliminating the effects of the interfering EM field. Neckloops, for example, inductively couple to a hearing aid's telecoil and plug into the 2.5mm plug or proprietary connector on compatible phones. These loopsets include a built-in microphone and permit hands-free use of the phone and binaural listening if the user has two hearing aids with telecoils. The phone itself can be carried in a pocket or clipped on a piece of clothing, away from the hearing aids.
The Hearing Industry Association (HIA), the trade organization for hearing aid manufacturers, has committed to including written material with hearing aids on their anticipated performance with digital cell phones. HIA has also committed to offering a 30-day trial period for new hearing aids with a full refund if a customer is dissatisfied with its performance when coupled to a digital cell phone.
Bio: Linda Kozma-Spytek is a research audiologist in Gallaudet Universitys Technology Access Program, and a doctoral candidate in audiology at The City University of New York. In the Technology Access Program, she collaborates on a number of projects for the Rehabilitation Engineering Research Center (RERC) on Telecommunications Access, funded by the National Institute on Disability and Rehabilitation Research. These research projects include investigating the compatibility of digital cellular telephones and hearing aids and the accessibility of VoIP technology in voice telephony applications for individuals with hearing loss. She can be reached at firstname.lastname@example.org .
Q: WHAT CAUSES INTERFERENCE BETWEEN DIGITAL CELL PHONES AND HEARING AIDS?