University of Edinburgh

Audiology Refresher

Presented in February, 2002

Simple ways to check a hearing aid

Checking that a behind-the-ear hearing aid is functioning to the manufacturer's specification is a technical operation requiring a sophisticated hearing aid analyser (test box). These are expensive, so are not always available to teachers of the deaf and rarely to families of deaf children. There are ways in which parents can check their children's aids purely by listening to them. Obviously results are not as comprehensive as they would be if tests were carried out with a test box, but the benefits of regular listening tests cannot be underestimated.

A simple test by parents often involves turning the volume up full, placing the hearing aid in the cupped hand, and listening for the tell-tale feedback whistle. This will only confirm that the battery still has some life left in it, and that the aid is capable of producing some sort of sound. While this is better than not testing at all, there is a much more valuable test which takes very little extra time. This test is listening to the hearing and via a stetoclip. Stetoclips are cheap to buy and are often provided free of charge to parents by the education authority or hearing aid clinic. They are comprised of a very light set of earphones forming a V shape, which a single piece of tubing attached at the point of the V. The other end of this tube then fits either onto the end of the hearing aid tone hook (elbow) or onto the metal tip of the ear mould. This allows a hearing person to listen to the aid, ensuring that it is working, and to a certain extent, to judge the quality of the sound.

Beofre switching on, the volument control should be turned to minimum (making a note of the original setting so that it can be returned to that position after the testing is complete). Turn n the aid and slowly increase the volume until it is at a comfortable levl for your own listening. Make a mental note of this level for when you repeat the test. Talk to the aid and listen to your own voice, but be careful not to rub the microphone with your fingers or clothes (it will make horrible noises!) and do not kink the tubing as this will restrict the output. Aids heard like this rarely sound really good to a normally hearing person, but if you listen in on a daily bsis, you will probably be able to detect small changes in quality or loudness. If you do not detect change, make sure that all of the tubing is free from blockages and fit a new battery. If this does not solve the problem, you need to ask a professional to check the aid in a test box.

While you are listening to the aid there are other simple checks that you can carry out. Gently squeeze the hearing aid case, espeically around the battery drawer, to check for intermittency of sound. also, put a finger on the selector switch and put gentle inwards pressure followed by horizontal and vertical pressure. Again there should be no crackling or interruption of the sounds that you hear whilst doing this. If your child uses the T telecoil position you can achieve a function check of this by switching to T (or MT) and holding the hearing aid near to a switched on television set. Doing this should produce a buzzing noise which will confirm that the telecoil is working, but it will not monitor its quality of efficiency. One final important item you may be able to check is the volume control. These sometimes carckle when adjusted or become "spotty", that is, there is a smooth increase in volume on use, then a sudden drop or increase in volume before jumping back to normal.

To check the volume control properly, you need to test it over its full range. If the hearing aids are powerful, full volume could be uncomfortable or even painful for the person testing it, or there may be feedback problems. This can be overcome by fitting an attnuator (sound level reducer) to the stetoclip. Some people simply constrict the tubing to reduce the sound level, but this can produce some undesirable side effects, and you would not be able to reproduce the same reduction each time you tested the aid. There are some reasonably priced purpose-built attenuators on the market available from Bonochord, Connevans and Oticon. After testing, please make sure that you return the volumen control to its user position, as leaving it on full could be unpleasant for the hearing aid wearer.

New Attenuators

Viennatone has just introduced some new attenuators. These are designed to be used by hearing people who want to check the performance of hearing aids over the full range of the volumen control, without finding the volume levels uncomfortable for themselves. The amount of attenuation required to check a hearing aid in this way depends upon the output power of the aid under test. If you attenuate too heavily on a lower powered aid you may find that you cannot hear any output. With this in mind, Viennatone offer three attenuators giving a choice of 20dB, 30dB and 50dB attenuation. Identification is provided by colour coding red, orange and yellow respectively. They cost £8 each, or can be purchased as a set of three for £23 excluding VAT from Bonochord.

The attenuator fits between the headset and the tubing of the stetoclip for checking behind-the-ear aids, or between thea ear receiver and the headset for checking body worn aids. Viennatone publish data showin how each of these attenuators affect saturated output response curves measured via a stetoclip. We were unable to reproduce these curves at TIC due to there being no standard approach to testing this sort of item, but we can confirm that subjectively, the attenuators functioned as expected. Any noticeable change in tone between listening with or without the attenuator should not present a problem, particularly if the listener checks the aids on a regular basis, as they would be listening for a difference in what they were regularly hearing, rather than the overall quality of sound.