Wireless is not a new concept–even for hearing instruments. The challenge is which technology to use and how to use it. ReSound’s John Nelson, Ph.D., & Jill Mecklenburger, Au.D., presented at the 2013 AudiologyNOW! conference an overview of hearing instrument wireless solutions, including the advantages and limitations of different systems.
Early wireless transmissions were accomplished via telecoils, infrared systems and FM systems. Today we have these new wireless technologies:
- Near Field Magnetic Induction (NFMI)
- Bluetooth (RF)
- Proprietary radio frequency (RF)
Near Field Magnetic Induction (NFMI) systems are designed to contain transmission energy within the localized magnetic field. The power density of near-field transmissions is extremely restrictive. Based on the carrier frequency and the power the near and far field crossover occur around 3-4 meters. NFMI requires a “gateway device” to communicate between the accessory (TV, mp3 player, etc) and the hearing aid. This device is typically worn around the neck and uses an inductive loop to broadcast from the gateway device to the hearing instruments.
Bluetooth is an open standard for wireless communications. Currently there are nearly 12,000 different products using Bluetooth. Communication protocols for Bluetooth must be broad and flexible enough to accommodate many uses. Right now Bluetooth uses more computational and power resources to operate than a design for an application such as hearing instruments. Near Field Magnetic Induction is typically combined with Bluetooth.
- Ease of implementation due to existing Radio Frequency chips.
- Longer battery life due to low current drain on hearing instruments.
- Transmit through almost everything.
- Short transmission distance.
- Need to wear “gateway device” around neck.
- Sound quality can be affected by orientation of the gateway device and hearing aid receiver coil.
- May encounter interference with magnetic sources.
The proprietary radio frequency system uses a radio to generate an electrical wave and an antenna to send the information. In these types of systems all of the transmission energy is designed to radiate into free space. This type of transmission is referred to as a “far-field”. The electrical wave carries the information and it can be done by using different frequencies.
Advantages of using proprietary radio frequency with 2.4 GHz Wireless Technology include:
- No “gateway device” required for media connectivity.
- Long distance signal transmission.
- Robust and reliable connections – small information packages and spread-spectrum frequency hopping which minimizes interference.
- High transmitted data capacity: bandwidth, stereo, low distortion.
- Low latency (processing delay) so no echo problems and no lip synchronization.
- Worldwide application.
- Requires a specially designed antenna.
- Requires a streaming device for Bluetooth connectivity.
Wireless technology allows patients to stream the signal from a television, radio or computer as well as Bluetooth connection to mobile and landline phones. Wireless technology can enable multiple listening environments and overcomes many of the negative aspects of hearing instrument use.