The “Touchless” T-Coil

A common complaint among many hearing aid users is the difficulty they have in switching to the T-coil (telecoil) position when the phone rings. These switches are tiny and hard to feel and require only a tiny movement from one setting to another. In the process of switching to the T-coil some people may accidentally turn the aid off. Others may have to hold the aid with one hand, while searching for the T-coil with the other – which makes answering the phone rather a challenging juggling event! People with arthritic or insensitive fingers have a particularly difficult time in using the T-coil. In brief, even if the T-coil works well, there are often just too many obstacles to overcome before this important hearing tool can be accessed efficiently. Finally, it seems that the hearing aid industry has responded to these concerns by developing a “touchless T-coil.”

In the Micro-Tech version, all the person has to do is bring the phone to his or her ear to activate the T-coil. The “switch” in this case is the telephone’s magnetic field. When the phone is removed from the ear, the T-coil is automatically disconnected. With this system, a person would never be confused about whether or not he or she has a T-coil (not an uncommon occurrence); the aid itself will announce this fact when the telephone is brought close to the ear. This is great as far as it goes, and Micro-Tech is too be commended for developing it, but it doesn’t go quite far enough.

I have a very fine pair of hearing aids that include options for directional microphones, a “noise” program (low-frequency cut) and several T-coil choices. I rarely get the full benefit of this system. Why? I forget to bring the remote with me. My choices are to put it in a pocket, hang it around my neck, or hook it to my belt. Of the three, I prefer my belt, but I’ve already broken two clips wearing it this way. Personally, I really don’t like the idea of a remote control. I would prefer all functions to be located on the hearing aid. But there are good reasons, such as easy access to necessary adjustments, why some people require and prefer remote controls. Recently, the introduction of the Watchpilot, demonstrates that a remote control does not need to be clunky and inconvenient.

Some people have more trouble hearing when they’re chewing or talking. The most likely reason for these complaints is the occlusion effect.

When people talk, sound vibrations are also produced in the ear canal through vibrations of the cartilaginous portion of the ear canal wall (the exterior two-thirds of the canal). Ordinarily, these vibrations are dissipated through the open ear canal and are not noticeable. When, however, the open ear is blocked with an earmold, the sounds are reflected back into the ear canal. This can produce a low frequency (500 Hz and below) increase of sound pressure on the order of 20 to 30 dB. This is not insignificant! New hearing aid users are often told that they “can get used to it” and to a certain extent, if it’s not too great, this may be true. But it still can be annoying and, since the occlusion effect serves no positive purpose for a hearing aid wearer, and is often a reason why people stop wearing their hearing aids, it is best that it be eliminated or reduced as much as possible. So, what can be done?

The most common “cure” is to drill a vent through the earmold, one that connects the outside air to the air pocket between the tip of the earmold and the eardrum. This will permit the sound vibrations produced by one’s own voice to escape out into the open air, as they should. However, there are some possible downsides to this. Ordinarily, hearing aids or earmolds are vented to reduce the amount of low frequency amplification that a person perceives (these are shunted through the vent out of the ear canal) or for comfort, to equalize the air pressure on both sides of the eardrum. However, vents also make it more likely for the hearing aid to produce an acoustic squeal (feedback). Thus, there is a fine line to draw between too much and too little venting. A large vent, while it may eliminate the occlusion effect, may also facilitate feedback. However, a smaller vent, while it would not result in acoustic feedback, may not help reduce the occlusion effect. So, what else can be done in the event that venting does not solve the problem?

The hearing aid dispenser does have several other options to reduce the occlusion effect besides venting. Sometimes an earmold that fits further down the ear canal will reduce or eliminate the occlusion effect. This is because most of the sound vibrations that are generated in the ear canal by a person talking occur in the exterior two-thirds of the canal; the interior one-third is the bony portion. Therefore, the occlusion effect can be disrupted if a hearing instrument or an earmold is inserted this far or greater into the ear canal. There is also a possible acoustic advantage to such a “deep canal” fitting. A given amount of sound energy generated in a smaller cavity will be higher than if the same amount of energy is delivered to a larger cavity. This means that the actual amount of sound pressure in the air pocket between the tip of the earmold and the eardrum would be greater with earmolds that extend further down into the canal.

Some complaints that apparently relate to an occlusion effect may actually be the caused by too much low-frequency amplification. This would be most apparent in people with relatively good low-frequency hearing whose aids provide too much amplification at these frequencies. The solution is obvious: reduce the amount of low-frequency amplification. But sometimes it is difficult to distinguish complaints due to the occlusion effect and those due to over-amplification at the low frequencies. Up to now, it has been difficult to actually measure the extent of the occlusion effect reported by a user. In addition to the objective increase in sound pressure, there are also someone’s subjective responses, that is the occlusion effect bothers some people more than others.

Just recently, Etymotic Research has introduced the Occlusion Effect Meter designed specifically for objectively quantifying the amount of the occlusion effect. The device contains two sound level meters and two microphones. A “probe” tube connecting to a microphone is placed alongside the hearing aid or earmold (as in a “real-ear” test), while the other microphone is hung over the external ear. With the hearing aid turned off, the person then says “ee.” The differences in sound pressures picked up by the two microphones, one inside the ear and one outside, gives the extent of the occlusion effect.

If, for example, the sound pressure detected by the probe microphone is 90 dB, and the sound picked up by the external microphone is 70 dB, then the occlusion effect is 20 dB. This is the increase in sound pressure occurring in the ear canal when someone talks while wearing a specific earmold or hearing aid.

When the occlusion effect reaches this level, often the best solution would be to take a new ear impression and extend the canal portion of the earmold or hearing instrument. In such cases, the dispenser should consider using completely soft material or a soft tip in the finished product. If the occlusion effect is about 10-15 dB, then an increase in the diameter of vent should be considered. If complaints persist, and the objective measures show only minimal amounts of occlusion, then the real-ear response of the hearing aid should be evaluated to determine if there is too much low-frequency amplification. Finally, if the measurements show major fluctuations in the occlusion effect with jaw movements, such as would occur in chewing or talking, then it may be necessary to remake the mold for a better fit using softer material.

The best advice for consumers is not to be too tolerant of the occlusion effect. If it is a persistently annoying problem, then I would recommend a repeat visit to the person from whom the hearing aid was purchased.