”Mom, stop shouting into the phone—I can hear you just fine.” That’s what happens when I talk to my 77-year-old mother. And my experience is not atypical, for today the aging of the population means that more people are suffering from hearing loss. In fact, 4 million to 6 million people in the United States currently use hearing aids. Even more need them but don’t wear them, although a greater proportion of this population is likely to start using hearing aids as they get both more effective and more attractive.
At the same time, there are over 280 million cellphone subscriptions in the United States, for cellphones are rapidly becoming a ubiquitous and essential form of communication in today’s global society.
It’s a given that a growing number of hearing-aid users are cellphone users as well. But like The Odd Couple ’s Felix Unger and Oscar Madison, these two fundamentally good technologies cannot always live together in close proximity without conflict. At issue is electromagnetic compatibility.
As a result, hearing-loss advocacy groups have increased their pressure on industry and the U.S. government to make sure hearing aids and cellphones work together, allowing hearing aid users access to the entire range of wireless voice and data services. Compatibility standards do exist, but they’re struggling to evolve as quickly as technology advances.
The rapid move to integrate additional transmitters such as Wi-Fi and Bluetooth into cellphone handsets further complicates the situation. Hearing-aid consumer groups have insisted that such multiband cellphones be hearing-aid compatible for every transmitter. But the wireless industry is worried about expanding the reach of standards, fearing that the threat of products being labeled incompatible could discourage cellphone manufacturers from adding new technologies to phones, which would slow down the introduction of new features. To help address both concerns, the American National Standards Institute Accredited Standards Committee (ANSI ASC C63) has begun coordinating research planning and intends to begin presenting preliminary data to the Federal Communications Commission, while the FCC works through the official process of revising compatibility standards.
Cellphones emit electromagnetic energy in their assigned RF range, most commonly in discrete bands from about 700 megahertz to 5 gigahertz. When transmitted close to a hearing aid, this RF energy can couple with small wires and circuitry that act as surrogate antennas and generate very small electrical currents. These currents are not continuous but intermittent; they follow the modulation structure of the RF signal. If the frequency of the on-off-on pattern is in the audio range (2 hertz to 20 kilohertz), the hearing aid’s transducer may convert it into an audible sound.
Meanwhile, cellphones can produce a smaller level of unintentional emissions, some of which can also fall within the audio, or acoustic, range. These emissions come from the battery, oscillator, switches, and other electronic components. While the level of these unintentional emissions is tiny compared with intentionally emitted RF energy, a hearing aid receives signals in this acoustic range much more efficiently. Both of these sources can create annoying background noise during a phone conversation.
At the same time, room in the electromagnetic spectrum for communication is becoming harder and harder to find, as cellphone users push to receive more information and cellphone network operators try to make more money by fitting more people into a frequency space. As a result, cellphone service providers are designing new signals with increasingly complex modulation schemes to make them more efficient. Wireless signals are also becoming very dynamic, meaning that the modulation and carrier frequency can change to provide more capacity when sending and receiving data or to provide more room for others during quiet periods. In addition, transmitters will soon be able to sense other transmitters in their environment and adjust to maximize efficiency and coexistence.
These increasingly complex wireless signals can create different types of noise—a low hum, a sharp buzz, or even a Bronx cheer—which can be more than a little distracting in the middle of a conversation.
When the FCC classified cellphones as essential forms of telecommunication in 2003, it made them subject to the 1988 Hearing Aid Compatibility Act. Oscar and Felix had to start getting along. Landline phones and hearing aids worked together fairly well from the beginning; they don’t emit RF energy, and they don’t contain as many sources of low-frequency emissions as cellphones do. In addition, thanks to the large size of these devices, manufacturers can install an additional telecoil transmitter for direct communication with the telecoil, a spool of wire that responds to a changing magnetic field, in hearing aids.
The ANSI ASC C63 standards committee, established in the 1930s to deal with the general issue of measuring and controlling electromagnetic emissions from all sorts of electronic equipment, published the first hearing-aid compatibility standard (ANSI C63.19) in 2001. The committee has since revised it twice, most recently in 2007. The standard describes limits and test procedures that address the need to control electromagnetic immunity (resistance to interference) in hearing aids and electromagnetic emissions in cellphones, and establish acceptable levels of background noise for hearing-aid users.
The current version of ANSI C63.19 describes methods to assign each cellphone an M (acoustic) and T (telecoil) rating for its emissions. A user can expect a normal level of compatible operation from a cellphone with a rating of M3/T3. For most hearing-aid users, that would mean hearing some background noise, but not enough to be annoying during a call of moderate length. An M4/T4 rating would correspond to excellent performance and no background noise for the majority of users.
The FCC currently requires cellphone manufacturers and network operators to certify that a significant portion of their handsets that operate using CDMA, GSM, iDEN, or 3G signals earn the ANSI C63.19 standard rating of M3/T3 or higher.
Over on the hearing-aid side, however, the situation is less clear. While the ANSI standard includes a test method and rating system for electromagnetic immunity, the U.S. Food and Drug Administration (FDA) does not currently require hearing-aid manufacturers to comply with these limits, although some hearing-aid manufacturers have begun voluntary labeling. Generally, the immunity of hearing aids on the market today is at a level of M2 or M3; that is, they can work with an M3-rated cellphone handset in a way that is not annoying. Hearing-aid users who purchase cellphones in retail stores can look for the hearing-aid-compatible rating and test them on the spot.
That’s not the end of the story, however. Wireless technology is a rapidly moving target, often outpacing the standards and regulatory processes. For example, Wi-Fi came quickly to the cellphone world, being implemented on handsets before standards bodies could revise the standard governing hearing-aid compatibility to take Wi-Fi into account. On the horizon, a number of other emerging wireless signals may soon be common on cellphone handsets to support broadband (WiMax, Long-Term Evolution), short range (Ultra-Wideband, ZigBee), and other forms of communication. Standards makers must be ever vigilant to keep pace with this rapid evolution of technology to save hearing-aid users from being shut out of a wireless world.
About the Author
Joseph J Morrissey received his Ph.D. from Stanford University in 1992 and has worked with Motorola for the past 12 years. He participates in standards efforts and designs and manages industry funded research to evaluate the potential health effects of RF energy emitted by cellphones and other wireless devices. He is also on the faculty at Broward College, in South Florida.