Does size matter?
20 April 2005
Modern hearing aids are available in two basic styles: in-the-ear (ITE) and behind-the-ear (BTE). Brian Moore, Professor of Auditory Perception, University of Cambridge, discusses their pros and cons.
Behind-the-ear aids
BTE aids have a part behind the ear that picks up the sound and amplifies it. Sound is then fed via a tube into the ear canal. All the digital hearing aids currently available from the NHS are BTE aids.
In-the-ear aids
ITE aids fit entirely into the outer ear (the pinna). Some fill up the 'bowl' of the outer ear (called the concha) and are clearly visible, although not very noticeable when they are skin coloured. Others are designed to fit completely in the ear canal: these are called CIC aids.
Technology
Many people believe that in-the-ear hearing aids are more 'high-tech' because they are smaller, but this is not necessarily the case. In fact, the digital processing that is carried out within the aids is generally similar for BTE and ITE models.
Cosmetic aspects
Many ITE hearing aids, particularly the CIC type, are barely visible, which is important to some users. However, BTE aids can also be cosmetically attractive.
Some BTE aids, such as the 'Air' hearing aid made by GN ReSound, have a very small BTE part, and a very thin tube that carries the sound to the ear canal. The tube is barely visible, and is easily hidden by hair.
Another hearing aid, made by SeboTek, has a very thin wire that goes from the BTE part into the ear canal. The wire leads to a miniature loudspeaker within the ear canal that generates the sound. Again, the wire is barely visible.
Handling your hearing aids
Generally, the smaller the hearing aids, the harder it is to insert and remove them. So most people find it easier to insert and remove BTE hearing aids than ITE hearing aids. Indeed, I heard of one elderly lady who always stands in a cardboard box when inserting or removing her ITE aids. That way, if she drops one, it is easier to find!
You may also find it difficult to operate the controls on very small hearing aids, especially if this involves turning a small knob or wheel, or pressing a button. This problem can be overcome by using a remote control, but it is not always convenient to keep a remote control with you at all times.
Reliability
ITE hearing aids are very susceptible to damage caused by earwax (cerumen) entering the hearing aid. Even though many ITE aids incorporate a 'wax guard' (which needs to be periodically cleaned or changed), damage by wax remains a major cause of hearing aid failure.
Wax causes fewer problems with BTE aids, since the wax generally enters the earmould or tubing rather than the aid itself, and does not produce permanent damage. The earmould and tubing can be cleaned relatively easily, although this can require some manual dexterity and may require the assistance of a young friend or relative.
Hearing quality
When the ear canal is open, sound enters the ear canal both directly and after reflecting from one or more of the folds of the outer ear. The reflections modify the sound reaching the eardrum, and the pattern of reflections is interpreted by the brain and used to help in determining the direction of sound sources. Reflections from the outer ear are especially important in allowing the listener to determine whether a sound is coming from in front of or behind the head, and from above or below.
When an ITE aid is worn, especially a CIC aid, these reflections are picked up by the microphone in the aid, and this can help the user in determining the direction of sound sources. However, when a BTE aid is worn, the microphone is located behind the ear, so the reflections from the outer ear are not picked up. This can make it harder to identify the direction of sounds; indeed sometimes sounds are heard as coming from the aid itself rather than from the outside world.
Reflections from the outer ear mainly provide useful information for high-frequency sounds. To benefit from reflections, the hearing aid must amplify the high frequencies effectively, and the user must not have too great a hearing loss at high frequencies. In practice, this means that, for most users, the ability to tell the direction of sounds is not greatly different when using ITE or BTE aids. However, when a person has a mild high-frequency loss, an ITE aid with an extended high-frequency response may lead to improved sound localisation.
Also, with BTE aids the frequency response sometimes has peaks and dips (some frequencies are amplified more than others), which leads to poorer sound quality than with ITE aids, which tend to have a smoother frequency response. However, the frequency response of BTE aids can be made smoother by inserting small 'acoustic resistors' in the tubing or earhook (the part of the BTE aid that hooks over the top of the ear), but this requires some skill on the part of the dispenser. Many manufacturers now build acoustic resistors into the earhooks of BTE aids, to smooth the frequency response.
Directional microphones
Many modern hearing aids incorporate directional microphones that selectively pick up sounds from the front, and suppress sounds from the side and back. These microphones can improve your ability to understand speech in noisy situations, provided you look in the direction of the person you want to hear. Directional microphones can be built into BTE aids, and into the type of ITE aids that fit into the bowl of the outer ear. However, directional microphones cannot be built into CIC aids. Generally, directional microphones work most effectively in BTE aids. Therefore, if the ability to hear speech in noisy situations is important, BTE aids with directional microphones may be your best choice.
Conclusion
There is no such thing as 'the best' hearing aid. Each one has advantages and disavantages, and you should choose hearing aids that meet your personal needs and degree of hearing loss.
ITE aids may sometimes provide better sound quality, especially if you have a mild high-frequency loss, but generally the digital processing that is carried out within the aids is similar for BTE and ITE models. And be wary of trying to hide your hearing loss by wearing nearly invisible ITE hearing aids: one of the benefits of wearing hearing aids is to make people aware of a hearing loss, so that they then speak more distinctly.
