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Cheryl D. Davis, Ph.D., Coordinator
WROCC Outreach Site at WOU
Regional Resource Center on Deafness
Western Oregon University
Monmouth OR 97361
Phone: 503-838-8642 (v/tty)
Users have described assistive listening devices as a technology that has changed their lives and something that they would never be without again; even so, many individuals who have a hearing loss have never used them.
Why use ALDs?
Hearing aids help individuals by increasing the volume in the range of frequencies they cannot hear. Unfortunately, hearing aids cannot discriminate between the sounds one wants to hear, and those one does not want to hear. Although newer hearing aids with directional microphones have improved listening in noisy environments, hearing aids still amplify all sounds within the prescribed frequency range within about 20 feet of the student, making hearing in classroom settings extremely difficult.
Additionally, research has shown that students with normal hearing can understand clearly if the sound they want to hear is 6 dB louder than the background noise (signal-to-noise ratio). Students with a hearing loss need a 15-25 dB SNR to achieve the same results (Blair, 1990). Hearing aids do nothing to improve the signal to noise ratio, in fact, they can make it worse by amplifying everything.
How do ALDs help? ALDs consist of a microphone, a transmitter and receiver system, and a coupling device to get the signal to the ear, such as headphones. The instructor speaks into the microphone. The microphone is attached to a transmitter, the transmitter sends the signal to the receiver that the student has with him at his seat. The student's receiver picks up the signal and sends it to the coupling device, such as headphones. There is a volume control on the receiver, so that the student can turn it up or down as needed. The student can turn up the volume on the instructor's voice without turning up the background noise (i.e., improve the SNR). It's that simple.
Who would benefit ALDs? The benefit received depends on the severity of the loss. ALDs aid in speech reading in more severe losses, and help reduce dependence on speechreading for milder losses. For more severe losses, ALDs may only help the individual pick up voice inflections; however, this helps the individual interpret meaning. Individuals with and without hearing aids, and individuals with cochlear implants may also benefit from ALDs. Because ALDs help bring the target speech directly to the ear and thus help reduce auditory distractions, they may also help certain individuals with learning disabilities and attention deficit disorders. The bottom line is that educational settings are communication intensive environments. ALDs will be extremely beneficial to individuals with a wide range of hearing loss.
Assistive Listening Device Systems
There are three major ALD transmission systems. There are large area and small, personal versions available for each transmission system. Range varies with the system from under 100 feet to more than 500 feet. The receivers generally run off batteries, as do personal FM transmitters. With the appropriate coupling device, each system can be used with or without hearing aids.
FM. The personal FM transmitter is about the size of a pager, and has an on/off switch and a jack for a microphone. The instructor plugs in the microphone and clips it close to her mouth, turns the transmitter on, and begins speaking. The FM receiver looks very similar and, like other receivers, has an on/off/volume control, and a jack for headphones or other coupling device. The student wears the receiver, which intercepts the signals and plugs in headphones or another coupling device to transmit the sound from the receiver to the ear. FM uses radio waves to transmit the signal across the distance. Similar to a radio station, the receiver and transmitter must be tuned to same frequency to work. It provides the greatest amount of decibel output, and so it may be preferable to those with more severe losses.
Infrared. Infrared uses infrared light to transmit the signals, similar to remote controls and VCRs. While you must have a direct line of sight with remote controls, infrared systems have a wider area of coverage than this. Some older systems will require a more direct line of sight than the newer systems. Light does reflect off surfaces, so the signal can often be picked up from a variety of directions.
There are several different versions of IR receivers. All will have a light-intercepting diode on them. This diode must not be covered (e.g., stored in a pocket) or the signal will be blocked. Some are worn like headphones and have the diode on top, others are worn like a stethoscope and the diode hangs under the chin. Still others look similar to the receivers described above for personal FM systems and can hang around the neck or placed on the desk. This last type is the most versatile. Individuals who wear hearing aids often have problems wearing headphones or the stethoscope-type headsets. When you purchase receivers, make sure that a variety of coupling devices (e.g., neckloops or headphones) can be plugged into them.
Electromagnetic Induction Loop. This is the only system that is properly referred to as 'a loop'. The system consists of a loop of wire that is powered by an amplifier, and a microphone. The amplifier must be plugged into a power source. The wire loop transmits electromagnetic waves that carry the signal, not unlike stereo or telephone speakers. An area as small as a table or as large as a room can be looped. Professionals should set up large areas, as dead spots (areas where no sound is picked up) can result.
If the user's hearing aid is fitted with an option called a telecoil, he will not need an external receiver. He would enter the looped area and flip his hearing aid to "T" to pick up the signals. Unfortunately, only about 30% of hearing aids sold in America today contain telecoils. In order for those without hearing aids (or those whose hearing aids do not have telecoils) to use the system, you should also have a supply of induction receivers on hand. These receivers look like the FM receivers described above, and headphones can be plugged into them. (These receivers are also useful to service providers to test to see if the neckloops are functioning properly.)
Unfortunately, everything that is powered by electricity gives off some electromagnetic energy that causes interference in the form of static or a hum. Some sources of interference are noticeable, while others are not. This is not the system to use in a computer lab. With some sources of interference, such as lighting ballasts, simply changing seats helps.
The systems are relatively simple in concept. Application to real-life situations may require some troubleshooting. One person speaking is easy to set up, because you have only one person to mic. What if there are questions from students in the class? The hard of hearing student would not be able to hear the question because it was not spoken into the microphone. The teacher should repeat questions into mic, or pass mic to student for long comments. What if there are multiple speakers, for example, a panel? The transmitter can be plugged into PA systems so that everything that is said into any of the mics attached to the PA system will be sent to the receiver. This is true for video and CD viewing, as well. The transmitter can be plugged into the electronic device auxiliary out so that the sound will be sent to the receiver without cutting off the sound for other students.
What if the hard of hearing student is called on to respond? This is a problem because the student may not be able to hear his own voice when using the telecoil option on his hearing aid. He is only picking up what comes into the teacher's mic. There are receivers (the piece that stays with the student) that have a jack for an additional microphone. This mic will pick up the student's voice and will allow the student to hear comments from neighbors. It also works well if the class is split into small groups.
What if the student is reluctant to use ALDs, even though you feel certain they would receive some benefit from them? Many times students who are unfamiliar with ALDs will be reluctant to use them. Encourage students to try out the equipment in safe environments outside of the class, for example, in a meeting with you in your office. Also, explore students' fears with them. Provide them with the coping skills they need to gain confidence so that they can handle any problematic situations that may arise. Self Help for Hard of Hearing Persons and the Association for Late Deafened Adults are two excellent support groups. E-mail lists can also be provide a great deal of help. The WROCC Outreach Site at Western Oregon University website includes several e-mail lists, and how to join them, including two excellent ones: Beyond Hearing and Say What Club, as well as vendor information, and more detailed information about assistive listening devices and communication access.
References and Resources
Blair, J.C. (1990). Front-row seating is not enough for classroom listening. In Flexer, C., Wray, D., & Leavitt, R (Eds.) How the student with hearing loss can succeed in college: A handbook for students, families, and professionals. Washington, D.C., Alexander Graham Bell Association for the Deaf.
Cederbaum, E.J. (1996). What's the buzz? NCOD Network News, 1, 1-3. Northridge, CA: National Center on Deafness, CSUN.
Davis, C. (2000) Internet Resources Related to Hearing Loss. http://www.wou.edu/nwoc/ald.htm
Davis, C. (1999) Demystifying Assistive Listening Devices: The Devil is in the Detail. http://www.wou.edu
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