For the next couple of weeks Hearing International will review Induction Loop Systems and consider the status of their use in the international community. In the past couple of years, at least in the US, we have heard a lot about the use and proliferation of induction loop systems and how beneficial they could be to the hearing impaired if they were available in more places. A project spearheaded by the Hearing Loss Association of America and the American Academy of Audiology called “Get in the Hearing Loop” with a goal of increasing the use of induction loops across the US. Kirkwood (2011) indicates that the”Get in the Loop” project is beginning to have some steam in the United States indicating a major chain of theaters has signed on to the project and National Public Radio has just lately informed the public on the benefits of these systems. Although this is a major effort to “Loop America”, these induction loops have been used for years in Europe for churches, public buildings, in private businesses and elsewhere. Audiologists everywhere have known for quite some time that induction loops are an inexpensive, assistive listening device that can be used effectively by a major share of the hearing impaired in a variety of situations. In the USA, induction loops made their first appearance as an imported product after World War II and initially generated significant interest that peaked in the late 1960’s and early 1970’s, especially in schools for deaf and hard of hearing children. Although there are many reasons why US interest waned and later lagged behind in the use of induction loop technology and was replaced by the availability of improved AM, FM and infrared technologies that offered great benefit. Further, during the past 3-4 decades, Americans generally used smaller in-the-ear hearing instruments that were not generally equipped with telecoils to utilize induction loops technology. Meanwhile, 0ver 85% of Europeans used behind-the-ear instruments with telecoils spurring the use induction loops (Blaha, 2004).
Currently, in the US and around the world, induction loops are seen as an inexpensive method of augmenting hearing aid performance in places of worship, cinema,playhouses, public buildings and other places.`
Where did These Loops Come From?
Hendricks and Lederman (2011) report that 1998 marked the 60th anniversary of induction loop systems and hearing aid telecoils. The first patented magnetic induction loop communication system was invented by Joseph Poliakoff in Great Britain in 1937. The first wearable hearing aid to incorporate a telecoil and capable of using an induction coil is reported to be the Multitone VPM in 1938 (pictured left, Bauman, 2011a). The Multitone VPM (Vest Pocket Model) was manufactured by the Multitone Electric Co. Ltd. of London, England and was very small for its time measuring 3¼” by 2½” by 1”. Bauman (2011a) The first portable hearing aid to incorporate a telecoil was the first instrument to be able to use the induction loop system invented by Poliakoff.
How Do These Systems Work
There are actually quite a number of references on the net to how induction loops work to amplify sound. While most are from manufacturers or distributors of these products, Rudisill (2010) writes that loop systems and telecoils work together with hearing aids to help hard-of-hearing people hear better. On another detailed site presenting the specifics of how these systems work, Bauman(2011b) presents that a loop system consists of three basic components: a microphone or other input device, a loop amplifier, and a loop of wire. Hearing instruments equipped with telecoils make up the receiving side. She further indicates the simplicity of these systems. All that is necessary to set up an induction loop system is to plug the loop amplifier into a wall socket, plug, an input device (such as a microphone) into the loop amplifier, string a loop of wire around the perimeter of the listening area, connect the ends of the wire to the loop amplifier, and turn it on. As presented in the illustration by Compton (1991) (Left) Audio signals are picked up by the microphone or directly from some sound source like a TV or stereo, amplified by the loop amplifier and travel through a loop of wire surrounding the listening area. The wire loop is used instead of (or in addition to) regular loudspeakers. As the sound signal travels through the loop of wire, it produces a magnetic field in the looped area that mirrors the frequency and intensity characteristics of the original sound signal. Now, it is the hearing aid telecoil’s job to convert the loop’s magnetic signal into sound that can be heard. When the switch on the hearing aid moves from microphone (M) to telecoil (T), what;s happening is theat the hearing instrument is connecting a small coil of wire to the input of the hearing aid’s amplifier instead of its microphone. This tiny coil of wire is sensitive to nearby magnetic fields such as the one produced by the loop system. The changing magnetic field in the room loop induces a corresponding electrical signal into the telecoil. The hearing aid amplifier then amplifies this signal and a faithful reproduction of the original speech signal is heard (Bauman, 2011b).
Rudisill (2010) offers a concise discussion of the benefits and limitations of these induction l0op systems.
1. Loop/telecoils have several big advantages over regular hearing aids
A. No feedback !
C. They are much cheaper than (say) buying a second hearing aid.
2. Loop/telecoils also have some problems over regular hearing aids
A. Telecoils can pick up electrical interference. Loops produce electrical interference.
B. Except for their use in telephones, loops require some preparation (i.e wiring).
C. Telecoils take up space, and are not available in very tiny hearing aids.
The main advantage of loop systems is that they are inexpensive ways to hear things like the telephone or TV. The main problem with them is that they may pick up hum or static from electrical equipment and wiring and also that they take up space in the hearing aid.
Although some feel that Loops are not a good idea for people with mild hearing problems, Sterkens (2011) feels that those with even a mild hearing impairment using instruments equpped with a telecoil can benefit from the induction loop. Loops are a good idea with people who are struggling to hear, even with powerful hearing aids. FM systems are even better, but they cost more money and take up more space on your ear.
Be here next week when Hearing International will review where the world is in the process of induction looping……
Bauman, N. (2011a). Vacuum tube hearing aids. The Hearing Aid Museum. Retrieved november 27, 2011: http://www.hearingaidmuseum.com/gallery/Vacuum%20Tube/OtherMakes/info/multitonevpm.htm
Bauman, N. (2011b). How do loop systems work. Center for Hearing Loss Help. Retrieved November 27, 2011: http://www.hearinglosshelp.com/articles/loopsystems.htm
Blaha, R., Hearing aid telecoils: numbers in the US market. Masters Thesis: Ohio State University, Deartment of Speech and Hearing Sciences, 2004. Retrieved November 27, 2011: http://etd.ohiolink.edu/view.cgi/Blaha%20Rebecca.pdf?osu1129571996
Compton, C.L. (1991) Assistive Devices: Doorways to Independence. Annapolis, MD: Single-handed Productions.
Hendricks, P. & Lederman, N. (2011). PartII: Induction loop systems, history and advancements. Oval Window Audio. Retrieved November 27, 2011: http://www.ovalwindowaudio.com/articles/loopworld.htm
Kirkwood, D. (2011). Hearing loop campaign spreads and grows, as does coverage in the media. Hearing Health and Technology Matters. Retrieved November 30, 2011: http://hearinghealthmatters.org/hearingnewswatch/2011/hearing-loop-campaign-spreads-and-grows-as-does-coverage-in-the-media-2/
Rudisill, H., (2010). Loop systems and telecoils for hearing aids. In T. Hain (Ed) Dizziness-and-balance.com Retrieved November 27, 2011: http://www.dizziness-and-balance.com/disorders/hearing/hearing-aids/images/tcoil.html
Sterkens, J., (2011). Personal communication. Email comment to author 12-2-2011.