Telecommunications Design & Analysis

December, 2001

Rock concerts, noise pollution and an aging population are contributing to hearing losses at earlier ages. Over 28 million people in the United States are deaf and untold others have experienced hearing loss. The 1990 Americans with Disabilities Act and The Rehabilitation Act of 1973 have various requirements for organizations to provide devices such that deaf people can communicate with callers.

Why is hearing aid compatibility important?
All hearing aids have microphones that convert sound to electrical current that is amplified and changed back into sound by the hearing aid’s loudspeaker. Many hearing aids and all hearing aid compatible phones use telecoils instead of microphones during phone calls. A telecoil is made up of a coil of wire wound around a metal core. The telecoil directly accesses electromagnetic waves produced by telephones.

When using the telephone, the user turns the hearing aid switch to the “T-switch” position, deactivating the microphone and turning on the telecoil. Without hearing aid compatibility, sound is distorted and background noise interferes with the telephone’s audio.

Which phones are hearing aid compatible?
All wireline and cordless phones manufactured or imported after January 1, 2000 are required to be hearing aid compatible. These rules include stipulations for a volume control feature for the handset. Cellular phones don’t have the requirement, however, many analog cellular phones are hearing aid compatible. No digital cellular phones are hearing aid compatible but external devices can provide the compatibility.

How can cellular phones be improved?
Headsets improve the audio on cellular and cordless phones and some such as Plantronic models are hearing aid compatible. For people without hearing aids, noise-canceling headsets improve sound quality by eliminating background noise. High-end models have volume adjustment dials.

What features are included in amplified phones?
Companies such as Walker, Ultratec and Ameriphone provide phones for hard-of hearing people. For the most part, they are available in wired as well as cordless models. Verizon supplies these phones at no charge to people with incomes under $50,000.

The volume control feature has the capability to increase volume up to 50 decibels. Tone control can enhance either lower or upper frequency sounds and some enable users to adjust outgoing as well as incoming volume for the benefit of the person on the other end of the conversation.

What about TTY services?
Employers are required by federal law to supply TTYs, (teletypewriters) for deaf people. A TTY allows deaf people to read messages spoken by callers to relay operators. Callers dial 711 to access the relay network where operators type and transmit messages to TTYs. The relay network is paid for by a fund contributed to by all carriers and operated by interexchange carriers such as AT&T and WorldCom.

Standard computers can function as TTYs if they are equipped with modems that can read Baudot, the five-bit code used by TTYs. Computers with standard modems use 8-bit ASCII code and can’t read Baudot code.

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