Phones and hearing aids
Jerry L. Yanz · The Hearing Journal · 2005
The ability to connect with the world via telephone is critical. The phone is likely our most used technology in a high-tech world, and the nature of our dependence on it evolves over our lives.1 Wearers of hearing instruments, however, face challenges with telephone use that often compromise the benefit they receive from today's advanced hearing technology. This article offers a brief history of key issues with telephone use by hearing instrument wearers and solutions designed to improve their success. Finally, it will discuss a new Bluetooth® device that holds promise for eliminating many of the unresolved issues and problems that arose rather recently with the advent of mobile phones. ACOUSTIC FEEDBACK In 1947, Sam Lybarger developed a solution to the problem of acoustic feedback that is generated when a telephone receiver is held close to a hearing instrument.2 Taking advantage of the inductive leakage from the phone's dynamic receiver, Lybarger placed a receiving coil in the instrument, thus providing an alternative transduction path for the phone output. For the first time, a person wearing hearing instruments could use the phone effectively without acoustic feedback. The ensuing 50-plus years have seen varying degrees of success with the telecoil. Early on, inadequate control of telephone design led to wide variability in the strength of the inductive field emitted by phones. Telephone design for use with amplification has since been standardized, and hearing instrument compatibility is now mandatory in the U.S. for all landline phones and a growing percentage of mobile phones. While the telecoil proved a boon to those who wore hearing instruments, recurrent issues have compromised its success.3 Some of these issues and their resolution are outlined below. Signal level The output of early hearing instruments in telecoil mode was often weaker than in microphone mode. As a result, wearers often had to turn up the volume control to be able to use amplification in inductive mode. This situation was caused by a lack of amplified telecoils or inconsistency in the electromagnetic output of the telephone handset. In today's hearing instruments, amplified telecoils are more the rule than the exception, and the best telecoils are also fully programmable. Furthermore, landline telephones now meet minimum requirements for magnetic flux strength, pursuant to the 1988 Hearing Aid Compatibility Act and using criteria set forth in EIA Standard RS-504, which was first issued in 1982.4 Electromagnetic noise Sources of electromagnetic interference (EMI), including fluorescent light fixtures, dimmer switches, computer power supplies, monitors, copiers, and fax machines, can create a buzz in a hearing instrument equipped with a telecoil. While shielding efforts have provided some relief, finding refuge from these noise sources can be challenging in today's electronic environment. Telecoil and telephone position The transfer of an inductive signal depends on proximity and position of the sending and receiving coils. Thus, positioning a telecoil in a hearing instrument is an important and sometimes challenging task, especially in custom products. Even with a well-positioned telecoil, the hearing aid wearer faces an additional challenge in finding the optimal position of the phone relative to the hearing instrument. Compton discusses the relations between telecoil sensitivity and orientation,5 and Revit describes, from the perspective of a hearing instrument wearer, the maneuvers needed to find the “sweet spot” when using a telecoil.6 Switching Some patients have difficulty manipulating, or even finding, the small switches on hearing instruments that turn the telecoil on and off. Most dispensing practices have encountered the occasional wearer who comes into the office complaining that his hearing instruments are not working, only to find that the switch has been inadvertently left in the telecoil position. The development of the Touchless Telecoil®, an automatic telecoil introduced by Micro-Tech in 1999, has helped many hearing instrument wearers use the telephone more effectively. When the telephone handset is brought close to the ear, the proximity of the telephone receiver engages a reed switch in the hearing instrument, which automatically switches from microphone to telecoil mode. When the telephone handset is moved away, the reed switch disengages, and the hearing instrument automatically goes back to microphone mode. DIGITAL MOBILE PHONES POSE NEW PROBLEMS The biggest revolution in telephone communication in recent years has been the phenomenal growth in digital mobile phone use. Today we are connected with one another from more locations than ever, and we no longer rely on cables to communicate. However, the rise of digital mobile phones has presented hearing instrument wearers with even more challenges than their hard-wired predecessors did. Some mobile phones use a piezoelectric receiver, which, since it produces no inductive field, renders telecoils useless. Until recently, mobile phones were exempt from the Hearing Aid Compatibility Act, which requires an inductive field from landline phones. To complicate matters further, the radio frequency signal sent by digital mobile phones is turned on and off rapidly, or modulated. The resulting rapidly switched signal creates an audible buzz in many hearing instruments.7,8 The effect on wearers can range from annoyance to a complete inability to use the phone. Alternative devices have been designed for use with mobile phones and hearing instruments. HATIS® Corporation, for example, offers a device that sends the mobile phone output via a cable to a silhouette inductor positioned over a BTE. This arrangement allows the user to place the phone far enough from the BTE that mobile phone interference does not compromise the signal. An in-line microphone picks up the wearer's voice to send it back to the phone. Bear in mind, however, that any inductive signal is subject to EMI. In July 2003, the Federal Communications Commission (FCC) ordered the mobile phone industry to assume responsibility for designing phones that would cause reduced interference in hearing instruments. At the same time, the FCC rescinded the previous exemption of mobile phones from mandated compatibility with hearing instruments. As a result, the mobile phone industry was required to develop phones that could be used with telecoils. The FCC set a timetable stipulating deadlines by which a certain percentage of a company's phones must have reduced interference so they could be used with hearing instruments. The mandate culminates in February 2008, when half of all mobile phones must produce lower interference and also be compatible with hearing aid telecoils. ELI: A NEW SOLUTION Recently, a new device has been released to the market that appears to have the potential to solve many of the remaining problems encountered by hearing instrument wearers when they use a digital mobile telephone.9 Developed by the Starkey family of companies, the ELI (ear-level instrument) uses Bluetooth technology to send an audio signal between a digital mobile phone and a wearable module attached to the direct audio input (DAI) boot of a BTE hearing instrument (Figure 1).Figure 1: ELI module attached to the DAI boot of a BTE hearing instrumentBluetooth is a short-range, wireless, digital communication standard. Devices designed to the Bluetooth standard can convey either audio signals or data from one device to another in a secure, point-to-point, digital link that is highly resistant to most sources of interference. It is found in a growing number of electronic devices, including digital mobile phones, computers, PDAs, printers, fax machines, and audio equipment. ELI is thought to be the smallest Bluetooth device currently on the market, with dimensions of 27 × 16 × 11 mm and a weight of just 5.2 grams (Figure 2). It attaches to the DAI boot of a BTE hearing instrument via a standard three-pin connector. Alternatively, it can be used with non-DAI-equipped instruments, either BTE or custom, by attaching it to a special neck loop (Figure 3), the output of which is picked up by the telecoil in the hearing instrument. (The adapted neck loop will be available in the near future.) A microphone on the end of the ELI module picks up the wearer's voice and sends it back to the mobile phone.Figure 2: ELI module showing the Master Control, LEDs, microphone, and three-pin connector.Figure 3: ELI mounted on a neck loop specially adapted to accept the three-pin Europlug connector. The Adapted Neck Loop will be available on the market in the near future.When ELI is attached to a DAI boot, an incoming call rings through it and is heard through the hearing instrument. The wearer answers the call by pressing the device's master control button. The same button is used to hang up and reject calls and to turn the device on and off. When a signal comes from ELI through the DAI boot, it suppresses the hearing aid's microphone signal. When the call is finished, ELI disengages, and the instrument returns automatically to microphone mode. A compelling feature of ELI's design is that it uses the wearer's own hearing instrument to process the audio signal. Thus, all frequency shaping, gain, and compression characteristics, which are already established for acoustic inputs, are applied to the signal from the mobile phone. This new device has the potential to solve, or at least lessen, most of the issues of telephone use faced by hearing aid wearers, including the most challenging issues presented by digital mobile phones. Here are some of the benefits that using ELI offers: v Acoustic feedback is not an issue because the phone is not close to the hearing instrument. v Adequate signal strength is ensured by the programming and volume control setting of the hearing instrument and is further controlled by the volume control of the mobile phone. v Electromagnetic noise is handled by the inherent nature of Bluetooth signal processing. A technique called frequency hopping, in which the carrier frequency randomly changes 1600 times per second across a defined spectral band, eliminates most sources of audible interference. v Although the Bluetooth signal passes through walls without significant degradation, it has more difficulty with the human body. The position of the mobile phone relative to the ELI module is a factor with some mobile phones and seems to depend on the antenna design of the phones in question. Some phones provide a better signal for ELI if they are held on the same side of the body. In any case, this positioning task is less burdensome than being required to position a phone relative to a BTE telecoil. v Switching takes place automatically if ELI is attached directly to a DAI boot on the hearing instrument. A call comes in, and the signal from ELI suppresses the microphone signal; the call ends, and the microphone switches back on. When the device is used with the neck loop, the wearer must hear the ring from the mobile phone, switch the instrument to telecoil position during the call, and return it manually to microphone mode after the call is completed. v Digital mobile phones obviously are not a problem with ELI, since it was designed specifically to provide hard-of-hearing people with effective access to digital mobile phones. The modulation-induced buzz, which has been such a limiting factor, is gone. The most convenient way to use ELI is with a Bluetooth-enabled mobile phone, and the selection of such phones is growing rapidly. Alternatively, one can attach a Bluetooth adapter or transmitter to a non-Bluetooth phone to provide a wireless connection to ELI. Adapters available on the market, including those from Jabra and Belkin, function almost like a Bluetooth-enabled phone, except that the user must press a button to disconnect the Bluetooth signal and restore microphone function at the end of a call. Other uses In addition to its current primary role with mobile phones, ELI can also be used to receive a signal from some other Bluetooth-compatible devices, such as televisions, radios, and MP3 players. A Bluetooth adapter can be attached to any conventional audio device that will send its output to ELI, thus enabling it to serve as a more general assistive listening device. Europe has embraced Bluetooth technology more rapidly than the United States. Not only are there more Bluetooth devices in general, but, in particular, Bluetooth-enabled landline telephones are available there. LIMITATIONS Although the development of ELI seems to mark a noteworthy advance in telephone access for the hearing-impaired, it does have some limitations: v Bluetooth is a point-to-point technology. As such, it is not now a candidate to replace group amplification systems, such as infrared transmitters, room loops, or FM transmitters dedicated to serving hard-of-hearing people. New Bluetooth profiles are under constant development, and they may soon offer an alternative to these group systems. v The Bluetooth signal from the hearing instrument is only as good as the mobile phone signal itself. Digital phone strength varies from one service provider to another and from one location to another. While ELI eliminates the modulation-induced buzz of a digital phone, it cannot restore a signal that is inherently weak or noisy due to the idiosyncrasies of mobile phone reception. v Environmental noise became an issue as soon as telephones left our living rooms and traveled outdoors. If you use your phone outdoors on a windy day, the wind will create turbulence in the microphone, whether it is the microphone of ELI or the mobile phone itself. Likewise, cars are inherently noisy and will remain so when ELI is picking up the signal. These noise sources will be more troublesome to the person on the other end of the conversation than to the ELI user. v Currently, ELI's battery life provides 2.5 hours of continuous use per charge, which is adequate for the vast majority of telephone talkers. However, it may become a limiting factor for people who rely on their mobile telephone for their work or simply for extensive contact with the world outside. For those who need more usage each day, one solution is to have two ELI modules for daily use that can be recharged overnight. Recharging takes only 90 minutes. Also, while ELI's battery life may be generous for telephone conversations, it might seem limiting when the device is used for television viewing or other entertainment purposes. v The DAI input of some manufacturers' hearing instruments is incompatible with ELI. Even though most manufacturers use the IEC standard Europlug connectors, for which ELI is designed, what happens beyond the boot is not standardized. Testing thus far has produced mixed results: Boots and BTEs from some manufacturers work without modification; others require modification; still others are not compatible at all. Further experience will add to our knowledge of which instruments can be used with ELI via their DAI connections. We can state with confidence, however, that ELI will work effectively via the neck loop with any telecoil-equipped instrument. All DAI-equipped instruments from the Starkey family of companies are wired to accept ELI without modification, and a trimmer on every DAI boot allows adjustment of ELI's output level to optimize sound quality. SUMMARY Following the development of the telecoil, there was a long period in which little was done to improve access to telephones for hearing aid wearers. However, in the past 6 years, there have been several important advances in this area. As the latest in the progression of telephone solutions for the hearing-impaired population, ELI promises to have a considerable impact on the communication habits of hearing instrument wearers. Bluetooth can be considered an enabling technology, in that it allows streamlined communications between devices without wires or cables. When viewed from the perspective of the needs of hard-of-hearing people, ELI is a Bluetooth device that enables a large population to access modern telephone technology and make the best use of this old tool that has kept us in touch with the world for so many years. More information on ELI is available at www.elihearing.com. DIFFERENT ISSUES ARISE WITH CICS When completely-in-the-canal (CIC) instruments first reached the market in the early 1990s, it was hoped that they would eliminate, or at least reduce, the incidence of acoustic feedback by virtue of their relatively low gain and output and their deep seal in the ear canal. While some CICs may have increased resistance to feedback, they have not been the panacea that many people expected. In 2003, Micro-Tech released a Touchless Telephone Response option that can be used in CICs. Since they are too small to accommodate a telecoil, CIC instruments are fitted with the same automatic switching mechanism as the Touchless Telecoil. In this design, the presence of a phone close to the ear leaves the hearing instrument in microphone mode, but switches it into a memory where programmable parameters have been adjusted to reduce feedback, with minimal impact on the signal from the telephone.