Missouri Alternative Communication Resource Directory

Assistive Listening Devices

Assistive listening devices (commonly referred to ALD's) are mostly used by hard of hearing individuals with mild to severe hearing losses. The main function of an assistive listening device is to increase the loudness of specific sounds (in most cases the speaker) and reduce background noise, thus allowing the person with a hearing loss to better understand and hear speech. Assistive listening devices can be used with or without hearing aids.

Assistive listening devices can be used in large areas, small groups and for one-on-one conversations. The devices can be purchased and used as portable units and/or permanently installed systems depending on the type of system purchased. There are two types of assistive listening systems: hardwired and wireless.

Hardwired Systems

Hardwired systems require a direct connection (actual wire or cord) between the listener and the assistive listening device or sound source. Hardwired systems are best used in one-on-one conversation or by directly connecting the listener to a sound source (i.e. TV, radio, stereo). Examples of hardwired assistive listening devices include the PocketTalker from Williams Sound and Sonic Super Ear by Sonic Technology.

Wireless Systems

Wireless systems have an advantage over hardwired systems in that there are no cords or wires to interfere with transmission. There are two components of a wireless assistive listening device; a transmitter and a wireless receiver. The transmitter picks up signals through a direct electrical connection to the sound source (i.e., TV, stereo) or through a microphone placed close to the sound source. When the sound is picked up, the transmitter changes the sound into an electrical signal that is sent through air by way of radio wave or invisible light. The signal is then picked up by the wireless receiver worn by the individual and converted back into sound. There are three primary types of wireless assistive listening systems available: induction-loop, FM and infrared.

Induction-loop Systems

Induction-loop systems are composed of a loop of wire around the room (usually tacked around the baseboard on the floor or the crown molding around the ceiling) and connected to the output of an audio power amplifier. The loop of wire emits electromagnetic energy picked up by the telecoil (T-coil) of a hearing aid which acts as the receiver. There are also body-worn receivers and headset options available for use with the induction-loop system.

Advantages of the audio induction-loop system include low maintenance (requires more maintenance if the facility has receivers and batteries which need to be recharged or changed), low cost, simple installation and operation of a portable system, compatibility with other induction-loop systems, and the ability to be integrated into any existing PA system. Disadvantages include the inconvenience of moving a portable system from room to room and experiencing spill over (hearing conversations in adjacent rooms that are equipped with other induction-loop systems). Installing a permanent loop system may be difficult in an existing building. Some of the vendors who have audio induction-loop systems available include:

FM systems

FM systems transmit and receive sound through radio waves. The transmitter can be directly connected to the sound source (i.e., PA system, TV, radio) or can transmit sound through the use of the microphone built into the transmitter. FM systems are widely used for small and large area listening situations. Both portable and permanently installed systems are available and can be integrated into an existing PA system.

An FM system can be a very flexible and effective assistive listening system that works well in many different physical settings. FM systems can use free-standing receivers or can connect an individual's hearing aid to the FM system which allows a provider to meet the needs of a wide variety of consumers. A disadvantage of the FM system is that external feedback, such as cellular phones and radio broadcasts, may be picked up by individual receivers. Another disadvantage is that manufacturers' receivers are not compatible with one another unless special channel systems are purchased, which can be expensive. In other words, if you were to purchase a Phonic Ear FM system for a theater, the Williams Sound receiver may not be compatible unless you purchase a channel that will access the Phonic Ear System from Williams Sound. Vendors who have FM systems available include: Phonic Ear, Inc.

Infrared systems

Infrared systems are widely used in theaters, auditoriums, courtrooms, meeting rooms, etc. Permanent or portable systems can be installed into an existing PA system or one-on-one systems can be purchased. The transmitter uses invisible light waves to send sound to individuals wearing a wireless receiver.

A major advantage of the infrared system is that infrared receivers are compatible with most vendor transmitters. For example, a Sennheiser infrared system installed in an auditorium may transmit to an individual's personal Audex receiver without difficulty. Another advantage is the assurance of privacy as the sound does not travel through walls and there is no problem with "spillover" from adjacent rooms if other systems are installed. One major disadvantage is the requirement for direct "line-of-sight" between the transmitter and the receiver. Transmission can be cut off if there are any obstacles (columns, walls, etc.) present. Infrared systems may not be effective in rooms where there is a lot of sunlight. Most infrared systems have several receiver options available. One of the most widely used is the under-the-chin receiver. The major disadvantage of the under-the-chin receiver is that an individual cannot wear his/her hearing aid(s) as the receiver has rubber tips and the tips can become uncomfortable after prolonged wear. Body worn receivers can also be used with various headset options. Vendors who have infrared systems available include:

Receiver Options

There are many receiver options available for assistive listening systems which are personally worn receivers include induction neckloops for individuals who use the T-switch on their hearing aids, a silhouette inductor, walkman-style headsets, earbuds and direct audio input. Individuals who do not have a telecoil built into their hearing aid, who prefer not to use the telecoil on their hearing aids, or do not wear a hearing aid, may want use the walkman-style headsets or earbuds. A silhouette inductor works like the inductor neckloop except it is worn behind the hearing aid. With some of the infrared systems, the only option may be to have an under-the-chin style receiver, which will not work for people who prefer to wear their hearing aids with the assistive listening device. Another option that is becoming more popular when using an infrared system is a walkman-style headset which has the receiver built into the headset. Direct audio input is used by very few people since it requires a special hook-up with the hearing aid. For entities needing to respond to a wide variety of requests for assistive listening devices, it may be advantageous to have several types of receiver options available to meet consumer needs.

Soundfield Systems

Soundfield Amplications Systems amplify the speaker's voice through a wall or ceiling-mounted loudspeakers. The speaker uses a microphone/FM transmitter to transmit information through one or more loudspeakers. Personal soundfield systems are also available, whereas, you can place a speaker on the student's desk. Soundfield should only be installed under the direction of an audiologist or someone who understands room acoustics. Vendors who have souldfield systems include:

Other Considerations

The most important considerations in purchasing an assistive listening device are the clarity of amplified sound delivered to the user and the ability of the system to meet the needs of individuals with a variety of hearing losses. The quality of assistive listening devices varies from manufacturer to manufacturer. Organizations and facilities should consider gathering consumer input prior to deciding on a system to purchase.

Rental of assistive listening devices is available on a limited basis in some areas for those situations when a system is needed on a one-time basis. It is suggested that you contact national vendors to request a list of local distributors who may be able to rent assistive listening systems for special event usage.

Signage advertising the availability of assistive listening devices is also very important. Signage should be visible and easy to read. Advertising in newspapers, bulletins and brochures will let people know you have systems available.

Employees should be trained on maintenance of the systems and know how to troubleshoot the device, change the battery, charge the battery, check to see if cords and headsets are working, etc. Friendly employees who are aware of the availability of the systems will be most helpful in working with individuals who will be using assistive listening devices.