This article appeared in the January/February 2002 issue of Hearing Loss; The Journal of Self Help for Hard of Hearing People
Telecoil and Telephones
The Most Commonly Misunderstood “Assistive Listening Device”
By Mark Ross
The hearing aid’s telecoil (or “T” coil)…perhaps the most common and most underestimated assistive listening device. The author say, “ Even though there will be some consumers who will not use a larger or slightly more expensive hearing aid if a “T” coil were incorporated, still all should be given the information so that they can make their own informed choices.”
When the topic of assistive listening devices arises, the lowly telecoil hardly enters into the discussion. Yet, the ordinary telecoil (the "T"coil) is perhaps the most common and most underestimated assistive listening device available for individuals who wear hearing aids today.
They are inexpensive, simple to operate (if one knows how), and can be incorporated in body worn, behind-the-ear (BTE), and in most in-the-ear (ITE) hearing aids. Currently, only a minority of ITE hearing aids include a telecoil, but they can be requested and included in all but the tiniest ones. Few in-the-canal (ITC) and none of the completely in-the-canal (CIC hearing aids) have sufficient space to include a telecoil.
Description of a Telecoil
A telecoil is an induction coil. It is a metal rod encircled by many turns of a copper wire. Placed in a varying magnetic field, an alternating electrical current is "induced" in the copper wire. That is, the magnetic field actually creates a tiny electrical current in the wire when it cuts across the wire (reciprocally, an alternating electrical current in a copper wire creates a tiny, varying magnetic field around it). What happens is that the coil converts (changes) magnetic energy to electrical energy, in much the same way that a microphone converts sounds waves to electrical energy. And, in the same way that the electrical current created by a microphone retains the original speech information, albeit coded in different form, so does the electrical current created by the alternating magnetic field around a telephone.
Generally, the strength of the inductive pick-up is determined by the number of turns of the copper wire around the metal axis rod. Larger rods permit more turns and thus more powerful telephone coils. Newer "T" coils include an integrated amplifier, which makes it feasible to reduce the physical size of the "T" coil and still operate effectively. Still, the smaller the hearing aid, the less room there is for a telecoil; and, thus, in tiny aids telecoils are either weaker or excluded entirely.
When a hearing aid is switched to the "T" position, the telecoil is set to detect only an electromagnetic field. The strength of the electrical current "induced" in the telecoil by the electromagnetic field is directly proportional to both the energy in the magnetic field and to the relative positions of the induction coil in the hearing aid to the magnetic field (in a telephone or wire loop). This latter consideration is particularly important; in some positions, little or no electrical current will be created in the induction coil. The magnetic field will simply "pass through" the coil without producing much, if any, electrical current. This is the reason why experienced hearing aid users always experiment with the positioning with unfamiliar telephones: to find the "hot spot" where the strongest signal is induced in the telecoil.
The potential usefulness of telecoils extends beyond their original purpose -- that is, detecting the serendipitous electromagnetic field surrounding the earpiece of early telephones (and current "hearing- aid-compatible" telephones). Telecoils can be used in any setting that provides an IL (induction loop) assistive listening system. In such a system, a loop of wire around a room (or under a rug) produces an electromagnetic field instead of, or in conjunction with, amplified sound from a loudspeaker. Telecoils can also pick up the electromagnetic signals emanating from neckloops that are placed around the neck. These are plugged into the earphone jack of FM and infrared receivers and used with small and large-area assistive listening systems. The telecoil permits hearing aid users to "inductively" couple these devices to their personal hearing aids.
Under-Utilized and Under-Appreciated
In spite of the potential contribution of telecoils for improving communication access, and in spite of a number of investigations over the years, they still appear to be an under-utilized and under-appreciated resource. Even after years of hearing aid use, many hearing aid users do not know what a "T" coil is, or if they have one, do not know how to use it properly.
Because many people with mild to moderate hearing losses can acoustically couple their hearing aids to a telephone with satisfactory results, the need for a "T" coil may not have been a factor in the hearing aid selection process. This is particularly true when its inclusion may have compromised a miniature hearing aid fitting, preferable for cosmetic reasons by some consumers and audiologists.
However, as alluded to above, "T" coils can be used for other than the traditional one of inductively coupling a hearing aid to a telephone. Even though there will be some consumers who will not use a larger or slightly more expensive hearing aid if a “T” coil were incorporated, still all should be given the information so that they can make their own informed choices.
The "T" and "M/T" Switches
When room loops were used in classrooms for children with hearing loss, one problem with "T" coils soon became apparent: a hearing aid set on "T" did not permit the children to hear themselves (self-monitoring) or the other children (child to child communication). This was because the only open microphone was the one used by the teacher. The solution was to include an "M/T" switch, in which the hearing aid can simultaneously detect both an acoustic signal and a magnetic field. This arrangement, however, added additional complications.
One complication was that, unless specifically compensated for in the hearing aid design, the "M/T" setting reduced the volume of the hearing aid by 3 to 6 dB. A second problem was that there was no separate control for the microphone and telecoil; both sources were controlled by the one volume control. Finally, an "M/T" setting made telephone usage problematical for many people, because of the problems wrought by an open microphone when talking on the telephone (e.g., audible feedback and significant changes in the acoustic response of the hearing aid). The solution was to design hearing aids with four switch positions: microphone, telecoil, microphone/telecoil, and off.
Acoustical or Inductive Coupling to a Telephone
A speech signal emanating from the earpiece of an ordinarily telephone is already slightly amplified to about 70 dB sound pressure level (or to about 50 dB point on an audiogram). For many people with mild hearing losses, this is a sufficient signal level for effective telephone communication. A hearing aid is not necessary. For those with slightly greater hearing losses, but who are not hearing aid users, a telephone with a built-in amplifier may be the most useful communication option for conversing on a telephone. In other words, a person can use acoustical coupling, the natural way of talking on a telephone. A key consideration is whether the speech signal can be amplified to a most comfortable listening level.
For some people with a hearing loss, then, acoustically coupling a hearing aid to the telephone may be sufficient. A behind-the-ear (BTE) hearing aid is the mostinefficient type to acoustically couple to a telephone. The bulk of the hearing aid prevents a close connection between the telephone handset and the hearing aid microphone. Acoustically coupling a telephone to in-the-canal or in-the-ear hearing aids, however, can be effective. In some instances, acoustic feedback can occur when the earpiece is placed tight against the ear. If this happens, a foam pad placed around the rim of the earpiece may help.
Certainly, in a quiet environment, acoustical coupling will usually permit effective telephone communication. For the most part though, and certainly as applied to more people with severe hearing losses using BTE hearing aids, the research supports the effectiveness, and indeed the necessity, of using a telecoil.
Inductive coupling refers to the use of a telecoil that detects the magnetic field around the telephone (or a neckloop or silhouette inductor). One major advantage of inductive coupling is the fact that the gain of the aid can be increased as much as desired without the occurrence of acoustic feedback (a problem reported by many people who acoustically couple a telephone to a hearing aid).
One of the biggest problems a hearing aid user faces when talking on the telephone is the presence of background noises. In addition to be being able to increase the gain to any desired level, the use of inductive coupling deactivates the hearing aid microphone (which picks up and amplifies room noise). In my judgment, this is probably the most important advantage of inductive coupling. Outside of one's own home, finding a quiet place to make a telephone call is like trying to find a quiet restaurant in our society or winning the lottery. It's possible, but not likely.
Sidetone
Contrary to a popular impression, the most advantageous way of talking on a telephone in noise is not to insert one's finger in the ear canal of the contralateral ear. Telephone handsets include a side-tone feature, in which the speaker's speech is amplified slightly and delivered to the earpiece. This permits speakers to hear and monitor their own speech. Any other signal arriving at the mouthpiece, however, is also slightly amplified and delivered to the earpiece; this competes with and may mask the person’s speech that is being listened to.
The easiest and most effective way to reduce the impact of environmental noise is to cover the mouthpiece with one's hand when listening, thereby reducing the amount of ambient noise that enters the mouthpiece. This is particularly necessary when using an amplified handset, since it will also amplify the ambient noise. Another possible option while communicating in a noisy place is a telephone that incorporates a "push-to-talk" button. This controls the operation of the side-tone; push the button and the side-tone is eliminated.
Interfering Signals
Inductive coupling can, on occasion, create as well as solve problems. Telephone installers do not pay much attention to stray magnetic fields in the vicinity of the telephone. Thus, telephones are often installed under powerful fluorescent lights or in the vicinity of power lines and electrical transformers. Each of these electrical devices may produce strong electromagnetic static. While not a serious problem at home, many public phones or those in some offices and factories are frequently installed in the vicinity of strong electromagnetic fields. Computers and other electronic equipment may also generate strong electromagnetic fields.
When a hearing aid is switched to the "T" position, this static noise is detected and amplified, severely interfering with telephone reception. Since the strength of the electromagnetic field often varies considerably with small changes of position, it is sometimes possible to minimize the noise just by moving the telephone or hearing aid position slightly. However, the length of the telephone cord limits the extent of possible positional changes. When talking on the telephone in the vicinity of electromagnetic static, it is often necessary to constantly change positions to determine where the interfering electromagnetic field is weakest. Sometime and in some places, effective telephone communication with a telecoils is simply not possible given the strength of interfering electromagnetic radiation.
Telecoil Response Changes
The audiology profession has invested a great deal of thought and effort in ensuring that the hearing aid appropriately amplifies a speech signal. There are probably thousands of articles, books, chapters, etc., concerning the electroacoustic modification which should be made for different individuals with hearing loss. While there is hardly a professional consensus in this area, each audiologist seems to have a favorite "prescription." Where a consensus does exist is that the electroacoustic response of hearing aids should be modified to fit the needs of a particular individual. All well and good and very laudable.
As soon as a hearing aid user switches the hearing aid to the "T" position, however, all bets are off. The audiologist or hearing aid specialist may have verified the microphone response of the hearing aid using a hearing aid analyzer or a probe-tube microphone in the ear; rarely, however, is the telecoil response of the hearing aid given this same careful verification. Nobody is consciously assuming that listening through a telephone is somehow less important than through a microphone; what is happening is simply the effects of inertia and oversight.
Telecoils were rarely clinically evaluated in the past and they are rarely evaluated at the current time. This disregard for the total response of a hearing aid when switched to the "T" position is particularly problematical when children are using FM systems inductively coupled to their hearing aids. Audiologists should attempt to ensure that the electroacoustic responses of a hearing aid in the "T" position are similar to that obtained in the microphone position. Many programmable hearing aids do permit this and it can make a difference.
ITE Hearing Aids
Many audiologists do not routinely recommend that telecoils be incorporated in ITE hearing aids. The reasoning appears to be that telecoils are unnecessary, bulky, an added expense, and not too effective anyway. As reviewed earlier, it is true that many people with mild and moderate hearing losses can function adequately by acoustically coupling their hearing aids to the telephone. Others, however, particularly in noisy places, will find that eliminating the open microphone will improve their speech comprehension on the telephone. In addition, including a telecoil does increase a person's options, both on the telephone and in using other kinds of assistive listening devices.
By not including a telecoil, a consumer's options are reduced, which can hardly be considered a recommended clinical practice. An amplified telecoil can be included in all but the tiniest hearing aids. Audiologists should know that a satisfactory telecoil solution can be found with most ITE hearing aids. Before a decision is made to go with the most "cosmetically" appealing aid, people should be apprised of the potential benefits of a slightly larger hearing aid that includes a telecoil.
Using the Telephone
People with hearing loss do not find the advantages and operation of a telecoil self-explanatory. They must be taught how to use it. Effective teaching is more than a didactic exercise; it includes explanation, of course, but it also includes a demonstration and a trial, and then repeated demonstrations and repeated trials. The tiny "T" switch is not always easy to position at the proper location. For most aids, a little too much movement and the aid can be turned to the "off" location. Often, in trying to move the control back to "T," the proper location may again be by-passed and the microphone position is again switched on. Some older adults, with arthritic fingers, may find it almost impossible to move the switch from the "M" to the "T" position; most people, however, with sufficient practice, will be able to move and employ the "T" coil properly.
What I have found useful is to suggest that before hearing aid users answer the phone, that they first switch the aid to the "T" position and then turn up the gain to the point where they have previously experienced sufficient loudness. Only then will they be ready to engage in a conversation. When using a strange telephone, it is necessary to adjust its positioning in reference to the hearing aid and listen for the clearest and loudest signal. For some reason, most phones seem to require a slightly different orientation.
A recent and welcome development is the advent of hearing aids with “touchless” “T” coils. All a person has to do when using one of these phones is place it close to the ear. The telephone contains a sensor that will automatically engage the telecoil. When the phone is removed from the ear, the hearing aid reverts to the previous microphone position. One problem with these aids is that strength of the magnetic field provided by both a floor induction loop and a neckloop is insufficient to trigger this feature. The industry is aware of this shortcoming and I understand that they are now taking steps to engineer a “touchless” “T”coil that can be manually overridden.
A telephone amplifier can be used in conjunction with the telecoil for those people with the most severe hearing losses. Amplifying the acoustic signal also increases the electromagnetic field, thus improving telecoil operation. When "T" coils are used in conjunction with Induction Loops, FM or infrared systems, for some applications it is advisable to ensure that the hearing aid permits an "M/T" operation. As mentioned earlier, this is necessary with children, but it may also be useful for adults who, while receiving an FM or infrared transmission, also occasionally wish to engage someone else in conversation.
Conclusion
The range of telephone possibilities that now exist, with and without telecoils, is so great that no person need be deprived of effective telephone communication.
Consumers with hearing loss who are dissatisfied with their current ability to communication on the telephone should, very politely but assertively, request that their audiologist take another look at the possibilities. Chances are the situation can be improved.
Mark Ross, Ph.D., is the former director of research and training at the League for the Hard of Hearing, and is an associate at the Rehabilitation Engineering Research Cneter (RERC) at the Lexington Center, New York. Dr. Ross writes the popular column in Hearing Loss titled “Developments in Research and Technology.”
This article is supported, in part, by Grant #H133E980010 from the U.S. Department f Education, NIDRR, to the Lexington Center.
“In spite of the potential contribution of telecoils for improving communication access, and in spite of a number of investigations over the years, they still appear to be an under-utilized and under-appreciated resource. Even after years of hearing aid use, many hearing aid users do not know what a "T" coil is, or if they have one, do not know how to use it properly.”
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