Telephone technology for the deaf and hearing impaired
Last updated: January 22, 2010.
Do you ever find it tricky communicating by
telephone—when you can't
see the person you're talking to, watch their facial expressions, and
figure out how they're reacting to the things you say? Imagine, then,
how much harder phone conversations would be if you had a hearing
impairment, especially if you relied on visual techniques like
lip-reading or sign language. It's ironic that early telephones were
designed for people with perfect hearing because Alexander
Graham Bell, generally credited with their invention, was
particularly aware of the problems deaf people faced: he had, after
all, established a school for the deaf years before he became famous
and his wife Mabel (one of his former pupils) was deaf as well. Thankfully, better technology
has since enabled the development of phones that hearing-impaired
people can use much more easily. Let's take a closer look at
how they work!
Photo: This telephone for hearing-impaired people, designed by Geemarc,
has lots of extra features. You can amplify the headset and
microphone volume. There's a loud ringer and a xenon strobe light (the white bar running along the bottom)
flashes brightly to alert you to incoming calls. The LCD display at the top tells you who's calling
(by checking the number of a call against an address book of stored names). Most of the extra features
can be turned on and off so the phone is just as easy to use if you have normal hearing. Extra-big buttons
help people who also have visual impairments.
Amplifying phones
The simplest and crudest solution to improving a phone for someone
with a hearing impairment is obviously to make it louder.
On an amplifying phone, the loudness of the handset volume is usually adjustable up to a maximum of about
100-150dB (people without hearing impairment would find this painfully loud), though the
microphone volume is usually adjustable
too (useful if one deaf person is talking by phone to another). Since
telephones are generally used by more than one person, sound
amplification may be switched on or temporarily "boosted" by
pressing a button just for the duration of a call. Often the
tone (treble-bass level) of the sound in the handset can also be
adjusted to match a person's particular hearing loss.
Photo: Right: Deaf and hearing-impaired people rely on visual information to a much greater
degree, like these two people communicating through sign language. But most can still use telephones and related technology
as well. Photo by Wendy Beauchaine courtesy of US Air Force.
Amplifiers for existing phones
If you like your existing phone and your hearing difficulty is more moderate, you could invest in a
telephone amplifier. The simplest ones are little boxes that clip or strap onto the handset earpiece
of a normal phone. They have a microphone one side (which faces the phone loudspeaker), a loudspeaker the other
(which faces your ear), and a battery-powered amplifier unit in the middle.
More sophisticated "in-line" amplifiers fit in between the handset and the base
unit so they interrupt and boost the current going from the base to the handset loudspeaker,
making the sound louder that way. Some have tone controls for added refinement of the amplified sound.
Generally, amplifiers like this boost volume by about 20-40dB.
Photo: Left: An in-line telephone amplifier is a little box that fits between the handset and the base
of a conventional phone. To use one of these, you'll need a reasonably modern phone with a detachable handset that links
to the base with a standard RJ11 connector.
Identifying calls and callers
Phones for the hearing impaired generally have much louder rings
(a maximum ring volume of 80dB is typical) and visual or vibrating
alerts (bright flashing strobe lights or vibrating buzzers similar to
those in cellphones and pagers). Hearing-impaired users often like to
have a number of extension bells and you
can buy plug-in ringers (small boxes that ring and flash) to fit to
extension sockets around your home. Some phones have LCD displays with
caller identification (also known as caller ID or caller display) so
you can see who's on the line before you decide whether you want to
answer. Others can be programmed to speak aloud the name and details
of a caller in a loud, clear voice (useful if a person has visual as
well as hearing impairments).
Inductive coupling
A hearing aid is an example of electromagnetism in action:
it uses a microphone to pick up and convert sounds to electricity,
which it then amplifies and turns back into louder sounds in a person's ear using a miniature
loudspeaker. The quality of the amplified sound can
sometimes be poor or confusing because a hearing aid will generally amplify
background noise as well as the sounds you actually want to hear.
When those sounds are produced by a loudspeaker of some kind,
such as the one in a telephone, a person with a hearing impairment
can often produce a clearer, more audible sound in their ear by
induction coupling: linking their hearing aid directly,
electromagnetically, to the sound source and switching off the microphone in their hearing aid.
Public places such as theaters and concert halls are often fitted with induction loops, which are large
circuits of wire fed with electrical signals from the same source driving the main loudspeakers.
As the signals travel around an induction loop, it produces a small, safe, fluctuating magnetic field all around it. Compatible hearing aids
will pick up these fields using a smaller loop of wire (called a "telecoil") inside them
and convert them directly into sounds. Effectively, you get a direct "feed" of the loudspeaker
to your ear, so your hearing aid receives only the sounds you want to hear and not the background noise.
Compatible hearing aids have a switch on them called the T setting that allows them to pick
up signals from induction loops. Virtually all phones designed for hearing impaired people can be used
with inductive coupling in this way.
TTY telephones
If you have a profound hearing impairment, technologies like
amplification and inductive coupling may be little or no use. One
solution is to use a telecommunications relay service (TRS)
and a TTY (teletypewriter) phone (also known as a minicom or textphone in some countries), which looks a bit like a laptop computer with
a keyboard, a small (typically one-line) display, and two round plugs
at the top where you sit your phone (sometimes called an acoustic coupler).
TTY phones can be used in various different ways. If both users have TTY equipment, you can
simply type messages at one end and have them appear on the display
at the other end. If a user with a conventional phone wants to
communicate with someone who has only a TTY phone, typically they'd
speak to an operator who'd listen to the words, type them out, and
relay them over to the display on the user's TTY phone. Although many people still rely on
TTY phones, they're less relevant now alternative technologies exist,
such as fax, email, SMS text messaging on
cellphones, and IM (instant
messaging chat) over the Internet.
Photo: A typical TTY phone, probably dating from the 1980s. Note how the phone handset sits in an acoustic coupler on top. There's a keyboard for sending messages and a one-line display for receiving them.
There's also a little printer (under the phone handset in the center) for printing out
conversations. Photo by Trevor Blake
published on Flickr
in 2006 under a Creative Commons Licence.
Cellphones
Some countries have been more responsive to the needs of
hearing-impaired people than others. In the United States, it's over
20 years since Congress passed the Hearing Aid Compatibility Act of
1988, effectively prompting phone manufactuers to make more of their
equipment usable by hearing-impaired people. Cellphones (wireless,
mobile phones) were specifically exempted from this law because, at
that time, they were still very new and the politicians didn't want
to hamper the development of the technology. Since then, things have
moved on. The Federal Communications Commission now requires specific
levels of compatibility between hearing aids and cellphones and
places requirements on wireless service providers to offer a choice
of compatible equipment to their customers. Unfortunately, similar
standards don't always exist in other countries, but raising the bar
in the United States will undoubtedly help better equipment to become
more widely available elsewhere.
Photo: Cellphones have traditionally been difficult for hearing-impaired people to hear clearly,
but they're now improving rapidly thanks to advances in technology and changes in legislation.
Further reading
Manufacturers and suppliers
- Royal National Institute for the Deaf Shop: The UK's biggest online shop for deaf and hard of hearing people offers a wide range of telephone equipment and other aids for deaf and hearing-impaired people.
- Geemarc: Manufactures phones and other communications equipment for hearing-impaired people and sells them in many countries.
- Clarity: Sells landlines, cellphones, and amplifiers for the hard of hearing under the Clarity and Ameriphone brands.
General
