Dr. Ross on Hearing Loss
Telecoils and Telephones
by Mark Ross, Ph.D.
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 hearing-impaired individuals 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) or completely in-the-canal (CIC) have sufficient space to include a telecoil.
Description of a Telecoil
A telecoil is an induction coil. An induction coil is simply a metal rod that is encircled by many turns of a copper wire. Placed in an alternating magnetic field, an alternating electrical current is "induced" in the copper wire. (Reciprocally, an electrical current in a wire creates a tiny 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. 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 more powerful telephone coils. Newer "T" coils include an inte grated 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 heard.
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 infra-red 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.
Underutilized and Underappreciated
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 underutilized and underappreciated resource. Even after years of hearing aid use, there are some hearing aid users who do not know what a "T" coil is, or if they have one, do not know how to use it properly. Because many mildly and moderately hearing-impaired people 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 many 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. Perhaps many consumers will elect not to use a larger or slightly more expensive hearing aid necessitated by the incorporation of a "T" coil; all, however, should be given the information to make their own choices.
The "T" and "M/T" Switches
When room loops were used in classrooms for hearing-impaired children, 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). 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, the research has shown that a telephone with a built-in amplifier may be the most useful communication option for conversing on a telephone. A key consideration is whether the speech signal can be amplified to a most comfortable listening level.
For some people, then, acoustically coupling a hearing aid to the telephone may be sufficient (i.e., not using the "T" coil and just placing the earpiece next to the hearing aid). A behind-the-ear (BTE) hearing aid is the most inefficient 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 would be the most effective. In both these latter instances, the use of a foam pad on the telephone receiver will probably improve the efficiency of the acoustical coupling. Certainly, in a quiet environment these people should be able to communicate effectively on the telephone. For the most part though, and certainly as applied to more severely hearing-impaired people using BTE hearing aids, the research supports the effectiveness of using the telecoil.
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 most hearing-impaired 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 noise. 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.
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 monitor their own speech. Any other signal arriving at the mouthpiece, however, is also slightly amplified and delivered to the earpiece along with the transmitted speech signal. The easiest and most effective way to reduce the impact of environmental noise is to cover the mouthpiece with one's hand when listening. 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. Thus, while listening to the party on the other end of the line, the sidetone feature is not operational.
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 hearing-impaired individuals. 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. We 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. No one I know assumes that listening through a "T" coil is somehow less important than through a microphone; what is happening is simply the effects of inertia and oversight. It seems as if telecoils were rarely clinically evaluated in the past and that 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 is 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 mildly and moderately hearing-impaired people 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
Hearing-impaired people 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 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 "T" coil operation. When "T" coils are used in conjunction with Induction Loop, FM, or Infra-Red systems, for some applications it is advisable to ensure that the hearing aid permits an "M/T" operation. This is necessary with children when inductively coupling the hearing aid to an FM or IR system through a neckloop, but it may also be useful for adults who, while receiving an FM or Infra-Red transmission, also occasionally wish to engage someone else in conversation.
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. Even when the degree of hearing loss telephone exchange, telephone devices for the deaf (TTY's) and relay services are available. Hearing-impaired consumers 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.