Let’s look a little more closely at T-coils. Advocates will tell you that one of the most important things to get in a hearing aid is a good telecoil. What constitutes a good T-coil? Well, they are not as sensitive as hearing aids and require that the volume be turned up. Better T-coils have a higher sensitivity. Some may lose as much as 25dB, others only 3dB. The smaller the number the better. They should also be vertically oriented, as in the lower diagram, because they pick up the signals better in this position.
So just what is it? Delving into electronics a little, the alternating current of an audio signal creates an electromagnetic field that radiates away from the wire. When two wires are close, the electromagnetic field of one will induce a current in the other wire. The T-coil in a hearing aid is actually a small electromagnetic induction coil, i.e., a wire. NOTE: no matter what type of ALD is being used, the coupling device is receiving an audio signal that creates an electromagnetic field. The coupling device may convert the signal to sound, as in the case of headphones, or, as with neckloops and silhouettes, it may simply provide a way of getting the wire of the coupler close to the wire (the T-coil) in the hearing aid so that this induction can occur, and then the hearing aid will convert the electromagnetic field to sound.
The hearing aid microphone ONLY picks up acoustic sound waves. The T-coil ONLY picks up electromagnetic signals. The most common use of the T-coil is with the telephone, and it provides a vivid illustration of the difference between the mic and the T-coil functions on a hearing aid. Telephone speakers (as well as other speakers) contain induction coils. If an individual is using the telephone with the hearing aid on mic, he or she would put the telephone over the ear to hear. If, on the other hand, the individual is using the T-coil, he or she would place the earpiece of the phone over the hearing aid to bring the two wires to the closest proximity. If the individual is wearing a body-type aid, the earpiece of the phone may not be placed anywhere near the ear. The same applies to headphones, which also have electromagnetic fields (although some are stronger than others). Without T-coils, the headphones would be placed over the ears; with T-coils, the headphones would be placed over the hearing aids.
T-coils are susceptible to electromagnetic interference produced by microwaves, lights, computer monitors, appliances, power lines, elevator cables--anything that produces electromagnetic fields. If problems are occurring, watch for hidden sources of interference.
