”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.