Question
What makes a hearing aid completely wireless?
Answer
It is a common misconception that wireless hearing aids use Bluetooth. In fact, most so-called "wireless" hearing aids on the market today rely on a technology called near field magnetic induction, and use a Telecoil to receive a signal sent from an intermediary device (a neck loop transmitter), which is worn around the user's neck. A main limitation of this technology is that the transmitter must be within 3 feet of the hearing instrument. These hearing instruments do not contain Bluetooth technology. The Bluetooth connection only exists between the neck loop transmitter and the audio device (for example a television or other audio device) which translates the Bluetooth signal into a near field magnetic induction signal.
Recent technological breakthroughs in the miniaturization of radio frequency antennae have enabled hearing instruments to embed the radio antenna inside the hearing instrument. This approach provides a direct connection from the hearing aid to the wireless audio transmitter (typically connected to the television or other audio device), eliminating the need for the user to wear any intermediary device around their neck and allowing them to be up to 30 feet from the transmitter. These devices operate on 2.4 GHz.
2.4 GHz is a widely used and globally accepted frequency band and is used by most cordless phones, video game consoles, home wireless networks, garage door openers and many other common everyday wireless items. The 2.4 GHz platform can communicate directly, device to device. As mentioned, the induction/T-coil-based "wireless" hearing aids require the user to wear a neck loop to transmit the signal to the hearing aids. In addition, the Bluetooth communication between the audio device and neck loop transmitter introduces significant time delays, which can cause disturbing echo or lip-synch effects when watching television.
Another misconception is that hearing aids that operate on 2.4 GHz encounter interference because it is a commonly used wireless platform. Hearing aids using the 2.4 GHz wireless technology safeguard against interference in two ways. One is by transmitting exceptionally small data packets. With each data packet being only 0.00016 to 0.0005 seconds long, there is a high probability of uninterrupted transmission for that reason alone. A further safeguard is frequency hopping. This means that each time a new piece of data is to be sent, a new channel out of 35 possible channels is picked for the transmission. Because other devices in the 2.4 GHz band use different channel selection strategies, they virtually always steer clear of each other. This approach of "hopping" among channels has virtually eliminated the interference many used to experience with early cordless phones. This same approach to frequency hopping can now be found in hearing instruments and prevents annoying interference between wireless devices.
For more information, please visit our website, www.gnresound.com or the ReSound Web Channel on AudiologyOnline. You can also join GN ReSound on Facebook at www.facebook.com/GNReSound.
Jennifer Groth, M.A., is Director of Audiology Communication at GN ReSound, where she is responsible for product definition and audiology-driven support for products in the market. She has served in roles such as research audiologist and product manager through the course of her career. She holds a Master of Arts degree in speech pathology & audiology from the University of Iowa.
