Hearing Aid Compatibility for Digital Wireless Phones

Hearing aid compatibility (HAC) for digital wireless phones was not, until recently, a Federal Communications Commission (FCC) requirement. One of the primary reasons the FCC reconsidered the HAC exemption for wireless cell phones is their movement within daily life from a secondary source of telecommunications access to a primary source (FCC, 2003). The term most often heard when talking about cell phone use is "ubiquitous." This is obvious from the moment one ventures outside his own home to work, shop, and play, as well as while in transit to these different activities. To help us better understand the penetration of cell phones in our everyday lives, we can look at annual survey statistics collected by the Cellular Telecommunications and Internet Association (CTIA). Currently, the United States (US) population is approximately 280 million (US Census Bureau, 2000), and there are a little more than 215 million subscribers to wireless phone service (CTIA, 2006). This number of subscribers is roughly equivalent to the total number of men, women and children in the US between the ages of 14 and 80. When we consider that only about 10 % of the US population has hearing loss, and of that subgroup just one out of five, or around 6 million individuals wear hearing aids (NIDCD, 2006), it is easy to understand how regulation, rather than market pressures, would be required to ensure the compatibility of digital wireless phones with hearing aids.

Sources of Interference: Microphone and Telecoil

The compatibility problem between hearing aids and digital wireless phones is primarily one of electromagnetic interference. The source of interference between digital cell phones and hearing aids in microphone mode is related to the radio frequency (RF) transmission that takes place between the cell phone and its network during a call. Although the RF transmissions are well above the audio frequency range (800 - 1900 MHz), the rate at which these transmissions modulate (pulse on and off) falls within the audio frequency range (e.g., 217 Hz for GSM*). The high frequency radio waves are extremely short (e.g., 1 cm) which means any small length of wire, such as the leads between the input transducer and preamplifier of a hearing aid, can act as an antenna, pick up the transmission and allow for extraction of the low frequency RF modulation by subsequent components, such as the preamplifier. The extracted modulation or pulsing does not have a smooth, symmetric onset and offset, but rather a rapid onset, gradual decay, and a slower offset. This modulation characteristic not only produces audible interference with a fundamental frequency at the repetition rate of the pulsing, but interference which includes harmonics of the fundamental frequency, as well as possible non-linear frequency components that occur across the audio spectrum. All digital cellular transmission technologies create a broadband interference; however the spectral and temporal characteristics of cellular transmissions vary, and therefore the perceptual characteristics of the interferers vary as well. Because the strength of these RF transmissions can vary due to, among other things, the distance between the cell phone and nearest cell tower, the degree of interference experienced can also vary during a call and from one call to another with the same phone.

Hearing aids in telecoil mode can be affected by the RF transmission and additionally by magnetic sources of interference. Because all the components of cell phones are housed in the handset, a battery is required to supply the current needed to drive the cell phone electronics, such as the display, keyboard, and circuit board. The magnetic fields generated as a by-product of this current flow can be an additional source of interference for hearing aids in telecoil mode because these fields are affected by the RF transmissions much the same way hearing aids are affected. The resulting magnetic interference is also referred to as baseband interference. This interference source is particularly problematic because telecoils, by design, are sensitive to magnetic fields regardless of whether the source is interfering noise from the handset electronics or the speech of the calling partner on the phone call.

Considerations for HAC in Cell Phones

HAC requirements for cell phones must address the handset's interference potential; this should not be the only consideration when trying to ensure accessible wireless telecommunications for hearing aid users. Speech is the intended signal for any telephone, therefore adequate signal strength for the speech to be comfortably loud to the hearing aid user is needed whether the input to a hearing aid is acoustic or magnetic. Likewise, the acoustic and magnetic frequency responses of the telephone need to be appropriate to ensure that the speech spectrum is faithfully represented within the available bandwidth. The level of the incoming speech signal to the receiver can vary considerably across telephone calls, as the average speech intensity from one speaker to another is not constant. In addition, the environment within which the call is made may contribute unwanted noise, making the ability to adjust the signal volume desirable for individuals with and without hearing loss. Since magnetic coupling is orientation sensitive, the direction as well as the strength of the magnetic field components generated by the telephone need to be adequate for use by the receiving hearing aid telecoil. The magnetic source size needs to be large enough to easily and reliably achieve and maintain natural positioning by the hearing aid user between the phone and their hearing aid's telecoil. Unintended signal (i.e., noise such as the RF interference generated in hearing aids by cell phones) levels need to be low enough to permit use of the phone. Defining the level of noise can be accomplished by limiting the absolute noise level, by establishing a minimum signal to noise ratio, or both. Whether the above hearing aid compatibility needs are met depends in large part on which ones are addressed through the standards process or by government regulation.

Standards

Electromagnetic compatibility (EMC) needs are generally specified through industry standards. A standard is a document established by a consensus of experts in the field and approved by a recognized body. Standards typically specify both the measurement methodology and the appropriate performance criteria to meet compatibility requirements. The standard is then used to assess whether or not a product conforms to the performance criteria. Compliance with a standard is voluntary, unless the standard is adopted by the government as part of the regulatory framework, wherein the standard becomes a mandatory requirement. When products do not meet voluntary standards, the consumer has little recourse. However, when products do not meet mandatory standards, the consumer can bring an informal complaint under the enforcement guidelines of the regulatory agency overseeing compliance, which helps ensure resolution of the complaint in a timely manner. Standards are considered living documents and may undergo changes if deemed necessary by the standards body responsible for establishing the standard; however, the regulatory agency would need to consent to the changes in order to make the updated standard part of the regulatory framework.

American National Standards Institute (ANSI) C63.19

The standard which specifies the measurement methodology and the appropriate performance criteria for hearing aid compatibility in digital wireless phones is ANSI C63.19. Members of both the hearing aid and cell phone industries have participated in the standard's development. Determination of the performance criteria has been based largely on research performed by the University of Oklahoma Wireless Electromagnetic Compatibility Center, the Rehabilitation Engineering Research Centers on Telecommunications Access and Hearing Enhancement, and Etymotic Research, Inc. Motorola and Cingular have also recently made substantial contributions to the data used as a means to make informed decisions about performance criteria in the standard. The developers of the standard recognized the necessity of the cell phone and hearing aid industries to modify their own products for compatibility to be realized. In the case of cell phones, RF emissions would need to be reduced, while at the same time the internal immunity of hearing aids to those RF emissions would need to be increased. Therefore, ANSI C63.19 specifies the measurement of the RF emissions associated with telephone handsets and the measurement of the immunity of hearing aids to these RF emissions. This is done separately for both microphone and telecoil coupling in hearing aids. If the RF emissions associated with the telephone handset are low enough, then parameters associated with the inductive coupling capability of the telephone handset, such as magnetic field strength, magnetic signal-to-noise ratio, and magnetic frequency response, may also be measured. The concept of the standard is that independent measurement of the characteristics of the handset and hearing aid will predict the performance level of the system when used in tandem. Compliance with the standard is mandatory only for telephone handsets. The FCC, which lifted the provisional exemption for wireless phones under the HAC Act of 1988 and points to the standard as part of their rulemaking, has regulatory authority only over telephones, not over hearing aids.

FCC Hearing Aid Compatibility Requirements

In 2003, when the FCC extended the HAC Act of 1988 to wireless phones and required the capability of effective use with hearing aids, it instituted a phase-in period for compliance of a limited number of handsets. Now, in addition to referring to a phone's inductive coupling capability, HAC also refers to a reduction of RF interference from the handset. This does not mean, however, that all compliant wireless phones must be capable of working effectively with all hearing aids, but rather only with those hearing aids that meet a minimal immunity requirement for use with compliant digital wireless phones. Hearing aids that are designed for use with compliant digital wireless phones include those with an ANSI C63.19 immunity rating of at least 2 (on a scale from 1-4 with higher numbers representing more immunity) for either microphone and/or telecoil coupling. The intent of the standard was to determine the performance of a particular cell phone with a particular hearing aid by adding the "M" or "T" immunity rating of a hearing aid to the corresponding "M" or "T" rating of a cell phone. The "M" refers to microphone coupling while the "T" refers to telecoil coupling. When adding the immunity ratings of the cell phone and the hearing aid, a sum of 4 predicts that the combination of cell phone and hearing aid is usable. In this case "usable" means that someone could successfully complete a brief phone call, but this combination of cell phone and hearing aid would not be acceptable for normal, regular phone use. The goal of the FCC requirements is a sum of 5, or a HA rating of at least M2 and T2 plus a cell phone rating of at least M3 and T3. This combination predicts that the cell phone and hearing aid would be acceptable for normal, regular phone use. A sum of 6 or greater predicts that the cell phone and hearing aid combination would be highly usable, providing excellent performance of the system. Audiologists should be aware that these categories for hearing aid compatibility are not a guarantee of performance for each individual hearing aid user, but rather a prediction based on the individual measurement of two devices. The expectation is that the predictions will hold true for most hearing aid users and provide a starting place in their search for a cell phone. With systems having category sums of M5 or greater, a hearing aid microphone user has reduced likelihood of experiencing annoyance due to interference from a digital wireless phone. With systems having category sums of M5/T5 or greater, a hearing aid telecoil user has reduced likelihood of experiencing annoyance due to interference and improved likelihood of being able to effectively couple inductively to a digital wireless phone.

The first compliance date during the phase-in period was September 16, 2005, at which time wireless service providers who had national coverage were required to offer at least two hearing aid compatible handset models for each air interface. An air interface represents the way in which a cell phone "talks" to its service provider's towers. Cell phones operate using one of several different RF air interfaces, depending on the service used by the wireless provider (e.g., CDMA* is used by Sprint PCS and Verizon Wireless, GSM* is used by Cingular Wireless and T-Mobile, iDEN* is used by Nextel). For the larger service providers, 4 handset models or 25% of the total number of handset models offered were required to be hearing aid compatible. These models were required to comply with a minimum rating of M3 for RF emissions under the ANSI C63.19 standard. Compliant handsets should be compatible with hearing aids that have a reasonable amount of immunity (i.e., an immunity rating of 2 or greater). The "M" rating is most important for hearing aid wearers who use acoustic coupling to a cell phone. The higher the "M" rating, the less likely the hearing aid user is to experience interference when the hearing aid is set in microphone mode while using a cell phone. M4 is the highest "M" rating a cell phone can receive. Acoustic output is not evaluated as part of this rating, and there is no FCC volume control requirement for wireless handsets.

On September 18, 2006, the microphone coupling requirement was expanded for the larger carriers, increasing the number of handset models from one to five which must be compliant by FCC regulations. At the same time, the telecoil coupling requirement went into effect. Large wireless service providers were required to offer at least two handset models on each air interface that complied with a minimum rating of T3 for telecoil coupling under the ANSI C63.19 standard. In order for a phone to receive a "T" rating it must first be rated at least an M3 for RF emissions. This rating is most important for hearing aid wearers who use inductive coupling to a cell phone. The higher the "T" rating, the less likely the hearing aid user is to experience interference while the hearing aid is set in telecoil mode using a cell phone. T4 is the highest "T" rating a cell phone can receive. This requirement primarily benefits hearing aid wearers who use the telecoil feature for the majority of their cell phone usage. Compliant handsets should be compatible with hearing aids that have a reasonable amount of immunity, but not necessarily with every hearing aid.

As of February 18, 2008, the number of handsets offered for each air interface that must be compliant with an M3 rating for RF emissions will increase to 50% of the handset models available from a national wireless service provider. This final date was meant to coincide with the end of the five-year sunset period during which the analog service requirement will be eliminated. Analog service was very important for hearing aid wearers during the early deployment of digital service since analog transmissions do not cause interference in hearing aids. The FCC requirements are designed to ensure that some hearing aid compatible cell phones will be available from almost every wireless service provider and phone manufacturer. Following the September, 2006 deadline, the FCC will reevaluate the state of hearing aid compatibility for digital cell phones with an eye toward universal, 100% compliance.

FCC Labeling Requirements for HAC in Cell Phones

Manufacturers are required to identify handsets that meet or exceed the FCC requirements. Only cell phones that test to a rating of at least M3 or M3 and T3 will be labeled as HAC. Labels indicating the "M" and "T" rating of a cell phone will appear on the outside packaging of cell phones, while an explanation of the package labeling will appear in the product insert. The phones themselves are not required to be labeled. Phones that only have an "M" rating either did not meet the required level for telecoil coupling compatibility or were not tested for compliance. Phones that lack an "M" or "T" rating either did not meet the required level for microphone or telecoil coupling compatibility as defined in the FCC rule or were not tested for compliance. Possible compliant ratings include: M3; M4; M3/T3; M3/T4; and M4/T4. Service providers are required to ensure that labels are visible in order for hearing aid users to determine which handsets might best meet their needs. Consumers can expect to find labels on in-store price cards. Price cards and package labeling may include (1) only the ratings, (2) the ratings plus the following verbage: "Rated for hearing aid compatibility:" or (3) the ratings plus the symbol in figure 1.



Figure 1. Symbol used in cell phone packaging and inserts to indicate a handset's HAC rating.

Consumer Testing of Digital Wireless Handsets

Audiologists should encourage their clients to try cell phones before they buy one. Full retail stores of service providers must have all of their hearing aid-compatible phones available with service to try. The goal of this requirement is to provide consumers an opportunity to test available HAC wireless phones in order to evaluate the volume and interference levels of a given wireless phone. Once a hearing aid user has identified a cell phone they can use in the store, the hearing aid wearer should ask about the terms of agreement. The FCC has encouraged service providers to offer flexible return policies so the consumer has adequate time to assess a wireless phone during real-world use, but this is not a requirement. Hearing aid users should inquire about how long they have to cancel the service and return a phone without penalty if the cell phone does not work with their particular hearing aid outside the store. It is the customer's responsibility to make sure any cell phone that does not work adequately with their hearing aid is returned before any early termination fees go into effect.

For hearing aid wearers who find they are interested in unrated handsets, there are several phone characteristics that may influence the amount of interference they could experience, including the air interface used by the service provider, the cell phone style, and the availability of backlighting controls. Research (Kozma-Spytek and Harkins, 2005) indicates that CDMA and iDEN are perceived to cause less annoying interference for some hearing aid wearers. Likewise, the "clam shell" or "flip-up" design was also found to cause less interference. These designs tend to provide greater separation between the hearing aid and RF transmitter than the "candy bar" style. The ability to control the backlighting, another potential source of interference for telecoil users, may be an important consideration. Backlighting is a variable that can be controlled on some wireless devices but not all. Since interference from backlighting may not be tested when determining a wireless device's rating, telecoil users will want to pay attention to this feature, even if the handset is rated for telecoil coupling.

Hearing aid users may find that other features and services of cell phones may improve their overall experience using cell phones. Many cell phones provide volume control, vibrating alerts, and selectable ringer tones for incoming calls. Using text messages to communicate, in addition to voice, is a service that many cell phones support.

Hearing Aid Immunity

Under the ANSI C63.19 standard, hearing aids are expected to have a rating as well. This rating, called an immunity rating, would indicate how susceptible a hearing aid was to interference-causing RF emissions from a cell phone. Since the FCC does not have regulatory authority over hearing aids, there are no requirements for the hearing aid industry to achieve a certain immunity rating for their hearing aids. Even so, the FCC rule does encourage the hearing aid industry to test and label their products according to their level of immunity to RF emissions. Also, recall that compliant wireless phones must be capable of working effectively with only those hearing aids that are designed for use with compliant digital wireless phones (i.e., those hearing aids having an immunity rating of at least 2 for either microphone and/or telecoil coupling).

Hearing aid manufacturers have committed to producing hearing aids that meet the level 2, 3, or 4 category for immunity according to ANSI C63.19. Over the last several years, many hearing aid manufacturers have increased their use of components that are less susceptible to cell phone RF emissions. Tests on a large number of hearing aids from the major hearing aid manufacturers have shown that over the 6-year period from 1997 to 2003, the immunity of hearing aids to RF emissions has increased by more than 30 dB for microphone coupling (DELTA, 2003b). However, hearing aids in telecoil coupling mode are more susceptible to interference from cell phones than hearing aids in microphone coupling mode. While component manufacturers now offer RF immune telecoils, similar data on hearing aid immunity improvements for telecoil coupling is not available.

RF Immunity Labeling for Hearing Aids

The Hearing Industries Association (HIA) indicates that its members are ready to label appropriate devices with adequate guidance from the Food and Drug Administration (FDA) (C. Rogin, personal communication, June 23, 2006). To that end, HIA has submitted draft label language and is currently waiting for a response from the FDA. The draft language includes a statement indicating that the digital hearing aid has an RF immunity rating of at least M2 and should provide good performance with digital cell phones that are rated M3 or better. A strong "try them together before you buy" message that applies to both a new phone and new hearing aids is also included in the draft language. HIA has not yet addressed telecoil labeling. Until hearing aids are labeled, audiologists should consult directly with the individual hearing aid manufacturer for the most up-to-date immunity information on a particular hearing aid. While the FCC can only encourage, rather than require, hearing aid manufacturers to label their products, they have indicated that they will re-examine their jurisdiction over hearing aid manufacturers if progress toward labeling is judged inadequate and impedes the goal of achieving hearing aid compatibility for consumers.

In addition to the HIA's commitment to identify hearing aids with higher immunity levels, they have also committed to a 30-day trial period and remanufacture or replacement of new hearing aids (RF immunity rating of M2 or better) if a customer is dissatisfied with their performance when they are coupled to a digital cell phone. If a customer remains dissatisfied with the hearing aid's performance, even after the aid has been remanufactured or replaced, a full refund will be provided.

New Hearing Aid Selection and Trial

When selecting new hearing aids for a client, audiologists should routinely include questions about cellular telephone use as part of the needs assessment. In particular, they should inquire about the frequency and nature of their client's cell phone use, their current cell phone make and model as well as their service provider, their preferred and current method of telephone coupling, and the degree to which they currently experience interference. Audiologists should inquire with hearing aid manufacturers about the RF immunity of hearing aids in their product line being considered for their client. Recall that microphone and telecoil coupling modes are rated separately; thus it is important to inquire specifically about the coupling mode the client will use for cell phone listening.

Audiologist should suggest that their client consider the placement of a telecoil in their hearing aid. Since available accessories (e.g., neckloops) which distance the cell phone from the hearing aid to reduce interference and provide hands-free cell phone use rely on inductive coupling, a telecoil is an important option to discuss with clients. A vertical telecoil placement would permit both adequate coupling to the cell phone and to any accessory that relies on inductive coupling. Unlike landline phones, cell phone requirements for magnetic field strength are equivalent for both the axial and radial components. Therefore, a vertical or horizontal placement of the telecoil within the hearing aid should result in an equivalent experience, all other things being equal. For landline phones, a horizontal telecoil placement perpendicular to the faceplate of an in-the-ear hearing aid or side of a behind-the-ear (BTE) hearing aid case is generally considered ideal for telephone use because the axial field strength requirement is higher than the radial requirement (Kozma-Spytek, 2003).

If the client is being fit with a BTE hearing aid, audiologists may want to suggest they consider a direct audio input (DAI) feature. DAI is the means by which products such as Ear Level Instrument (ELI) DirX by Starkey or SmartLink SX by Phonak connect directly or through a receiver to a hearing aid and provide Bluetooth connectivity to Bluetooth enabled cell phones. It is also the case that ELI or the receiver can connect to a neckloop. In this case, the Bluetooth connection to the cell phone is still accomplished using ELI or SmartLink, but the connection to the hearing aid is accomplished through an intermediary inductive device.

Finally, audiologists should inform their clients of the HIA's commitments regarding the performance of their new hearing aid (only if RF immunity rating is M2/T2 or better) when coupled to a FCC HAC compliant digital cell phone. If your client has a cell phone, but he/she is uncertain about whether it is HAC compliant, there are a number of ways to easily find this information. Remember the handset itself will not be labeled. The website Phone Scoop (www.phonescoop.com), allows you to look up a particular phone and find its corresponding HAC rating, if one is available. A call to the phone manufacturer's accessibility representative should also provide this information, as will looking up the phone's user manual on the Internet.

Conclusion

Audiologists have the ability to positively affect their clients' experiences using cell phones by providing them with accurate, up-to-date information regarding the compatibility between their phone and hearing instrument. There are many websites that provide useful information regarding hearing aid compatibility for digital cell phones, including websites by the Cellular Telecommunications Industry Association (CITA) and the Alliance for Telecommunications Industry Solutions (ATIS)-Hearing Aid Compatibility Incubator. CTIA (www.accesswireless.org) has a variety of information on accessibility and wireless technologies. The ATIS website (www.atis.org/hac/haclinks.asp) contains resources for people with hearing loss and hearing health professionals, as well as the FCC Rules. Both websites have a downloadable brochure for consumers who use hearing aids. This brochure is updated periodically and may be printed for distribution to clients. There is a similar brochure on the websites for hearing health professionals.

Accessible wireless phones have become a reality for many hearing aid users. However, understanding what to expect from the shopping experience and cell phone/hearing aid performance with the new FCC requirements can be challenging. The role of the hearing health professional will be particularly important as clients ask questions and seek advice regarding the use of hearing aids and cell phones. In addition to a source of information on hearing aid considerations for cell phone use, audiologists can provide valuable information and guidance to their hearing aid clients on considerations for their cell phone purchases as well.

* CDMA - Code Division Multiple Access; GSM - Global System for Mobile Communications; iDEN - Integrated Digital Enhanced Network

References

CTIA, The Wireless Association™ Estimated US current wireless subscribers. Retrieved August 21, 2006 from www.ctia.org.

Danish Electronics, Light & Acoustics: Improvement in Hearing Aid Immunity. Project No. A930005-1, performed by the Technical-Audiological Laboratory for EHIMA. Odense, Denmark: Delta, 2003b.

Federal Communications Commission. Report and Order in the Matter of Section 68.4(a) of the Commission's Rules Governing Hearing Aid-Compatible Telephones WT Docket No. 01-309, RM-8658. August 2003.

Kozma-Spytek, L., and Harkins, J. (2005). An evaluation of digital cellular handsets by hearing aid users. Journal of Rehabilitation Research & Development, 42(4), Supplement 2, 145-156.

Kozma-Spytek, L. (2003). Hearing aid compatible telephones: History and current status. Seminars in Hearing, 24(1), 17-28.

NIDCD, Statistics about Hearing Disorders Ear Infections and Deafness. Retrieved August 21, 2006 from www.nidcd.nih.gov/health/statistics/hearing.asp.

US Census Bureau, State and Country QuickFacts. Retrieved August 21, 2006 from quickfacts.census.gov/qfd/states/00000.html.

Acknowledgment

The thoughtful review and helpful comments of Judith Harkins, Professor of Communication Studies/Director, Technology Access Program, Gallaudet University; Scott Isabelle, Principal Staff Engineer, Motorola Mobile Devices and Julie Verhoff, Research Audiologist, Rehabilitation Engineering Research Center on Hearing Enhancement, Gallaudet University are greatly appreciated.