How Hearing Impaired Telephones Work

By: Diane Dannenfeldt

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How Telephone Amplifiers Work

People with hearing loss can get a special phone or a headset to help them hear on the phone.
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If you've set the volume on your phone as high as it'll go and voices still sound faint, you may want to consider a device for hearing-impaired telephones called a phone amplifier. Several options are available, including units that attach to a phone line, portable amplifier units and dedicated amplifier telephones, as well as cell phone amplifier systems.

Here's how each of these phone amplifiers works.


Phone line units -- An amplifier like this connects between a phone's handset and base to increase volume. For example, the Ameriphone in-line phone amplifier, which costs about $35, can amplify sound by up to 40 decibels. Like other similar units, it also blocks out feedback and background noise and amplifies specific frequencies to make speech clear and similar-sounding words easy to distinguish. These units usually are small enough to be portable [source:].

Portable amplifier units -- These small devices are handy because you can take them with you to use on almost any landline phone. They are inexpensive ($20 to $30) and easy to attach to the headset without disconnecting and reconnecting phone lines. By turning a dial on the Reizen Portable Phone Amplifier, for example, you can increase volume by up to 30 decibels [source: Harris Communications].

Dedicated amplifier telephones -- Amplifier telephones with added features are available for corded or cordless landline phones. These phones allow you to increase volume by adjusting an amplification dial or button on the phone and, in some cases, also adding volume with a handset boost button.

The ClearSounds CSC50 amplified corded phone, for example, allows an increase of 50 decibels with 40 coming from the phone's amplification system and another 10 decibels from the handset. The $160 phone also offers caller ID and a speakerphone [source: Beltone].

Amplified cordless phones cost more, usually $180 to $280. At the low end, a Clarity amplified 2.4 GHz (gigahertz) cordless phone that costs $180 can amplify sound up to 30 decibels and comes with caller ID and a visual ringer. Additional handsets cost $100 each. A 5.8 GHz Clarity model that costs $280 amplifies sounds up to 50 decibels and adds multiband compression, noise reduction and acoustic echo cancellation [source:].

Another option to consider with a corded phone is an amplified handset that simply replaces the one that came with the phone. Ranging in price from about $50 to $150, amplified headsets like the Walker W60-K-M-00 may be less expensive than replacing the phone [source:].

But perhaps you're looking for a cell phone solution. One of the problems in developing cell phones for the hard of hearing has been that the radio frequency signal from cell phones can interfere with hearing aids, causing buzzing or other noise. However, hearing aids often come with a telephone coil, or T-switch, that acts like an antenna. When the switch is on, the magnetic signals pass from the phone to the hearing aid, allowing the user to receive the phone communication directly through the hearing aid.

Since 2005, the Federal Communications Commission (FCC) has required cell-phone companies to provide several models that are hearing aid compatible when used with the hearing aid on the microphone setting. The FCC also requires that cell phones be rated on a scale of 1 to 4 for the amount of interference they're likely to cause with hearing aids on M (microphone) and T (telephone coil) settings. Phones that are rated M3 or T3 (good) or M4 or T4 (excellent) can be sold as hearing aid compatible. Check for an icon on the phone or its packaging that show its M and T ratings [source:].

If amplification isn't enough, you may want to consider a TDD, TTY, text phone or minicom. Go to the next page to find out how TDDs work.

TTY and TDD Technology

Technology lets people with hearing problems make phone calls over their computer like in this early IBM version.
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TTY technology gives the deaf and hard of hearing a text-based system for communicating over phone lines among themselves or with hearing individuals. Starting in the 1960s, hearing -impaired telephones that used this technology made the deaf and hearing impaired less isolated. Whether you call them TTYs, TDDs, textphones or minicoms, these devices now have four million U.S. users.

Here's how TTY works. The TTY unit itself resembles a laptop computer with a keyboard, a display screen and a modem. The user types his message, and the letters are converted into electrical signals that travel over the phone line. When the message reaches its destination, the signals are converted back into letters that appear on the receiving TTY unit's display screen or are printed out. A flashing light on the unit or a vibrating wristband alerts the recipient that a message has arrived. Some units also have answering machines [source:].


TTY owes its existence to a deaf scientist named Robert Weitbrecht. He developed an acoustic coupler in 1964 that allowed a TTY unit to be connected to a telephone. Early TTY units were large and cumbersome. By 1967, only 25 TTY stations were available, but by 1969 that number had increased to 600.

As electronic technology advanced, so did TTY. The units became smaller, less expensive and more readily available. TTY developers have used digital technology to bring computers and TTY units together. While TTY units are analog, software and a voice-capable modem with digital signal processing allow computers to talk directly to TTYs [source: Gallaudet University].

But changing technology has begun to threaten the existence of TTYs. E-mail, text messaging, instant messaging, e-paging and electronic faxing can be done from a computer with Internet access -- and without TTY. Add a Web camera and voice over Internet (VoIP) technology, and two deaf people can even sign to each other in real time.

With the arrival of BlackBerry mobile devices, iPhones and other smartphones, texting and IMing can be done almost anywhere. Picture phones with video allow signed messages to be recorded and sent, and vibrating phones make it easy for a deaf person to know when a message has arrived.

Is there still a place for TTY? Definitely among people who have used it for years and are more comfortable with it than with newer computer and mobile technology. And an argument can be made for keeping a simple TTY unit at home for emergencies. Like corded landline phones, TTYs rely on the telecommunications grid, rather than electricity, for power. So if electrical power is out in your area, you can still send and receive messages with your TTY unit.

Finding a TTY unit is easy. If you use a search engine like Google for the acronym "TTY," you'll see companies that sell these units for $250 to $600. Gallaudet University, which provides higher education for the deaf and hard of hearing, also provides a list of vendors of TTY unit, modem and software manufacturers.

With just TTY units and the phone system, people who are hard of hearing can communicate with each other. But using TTY to communicate with hearing individuals requires the use of the free Telecommunications Relay Service or related telephone relay services. Find out more on the next page.

How Relay Services Work

Relay services let callers use an assistant who transfers messages back and forth.
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If you don’t have a TTY unit or TDD, you can use a telephone relay service to communicate by phone with someone who is deaf or hard of hearing. Telephone relay services are required by the Americans with Disabilities Act, with services in English and Spanish, and regulated by the FCC. And while this variation on hearing-impaired telephones started as something like a translation service, variations like IP relay make more use of electronic technology.

The national Telecommunications Relay Service (TRS) is free and available 24 hours a day, seven days a week, to handle voice-to-TTY and TTY-to-voice calls. Various relay providers offer services in each state.


Here’s how the TRS works. The person placing the call accesses TRS from any TTY or standard phone by calling 7-1-1. The caller is connected to a communications assistant who relays communication between the caller and the recipient. A hearing caller, for example, speaks the message to the assistant, who types and relays it to the deaf recipient, who reads it on his TTY display screen. The recipient responds with a typed message, which the assistant reads to the hearing caller [sources: Occupational Safety and Health Administration and Gallaudet University].

The TRS can handle calls from computers via IP relay, as well as from TTYs. IP relay allows users to communicate using a computer and modem rather than a TTY unit. The IP relay starts with the caller’s computer or mobile device and goes to the IP relay center, which usually is accessed from a Web page.

There the call goes to a communication assistant, who sends the message on through the switched telephone system, converting it to either text or spoken word, depending on whether the recipient can hear. There is no extra charge for IP relay calls.

IP relay offers the advantage of being available through any device with Internet access. Also, transmission may be faster, and users can make multiple calls, have conference calls or browse the Web while on a call [source: FCC].

The newest addition is video relay service. It goes a step further by adding visuals to the conversation. This requires a high-speed Internet connection. Once that's established, a sign language interpreter reads the signed communication from the hard-of-hearing caller and speaks the message to the hearing recipient on the phone.

Gallaudet University provides information about both IP and video relay services.

For lots more information about hearing impaired telephones and related topics, check out the links on the next page.