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Hearing Aid Devices

adult-Hearing-aid-styles.jpg Credits: Oticon

A hearing aid is an electronic device that can be worn inside or behind the ear. It amplifies sounds in the environment, including speech, so that they become louder and clearer to the hearing-impaired individual.

How does a hearing aid work?

A hearing aid has three basic parts: a microphone, amplifier and speaker. Sounds are picked up by the microphone, converted into electrical signals and sent to the amplifier. The amplifier increases the loudness of the signals and sends them to the ear through the speaker.

Styles of hearing aids

There are three basic styles of hearing aids. They differ in size, placement on/in the ear, and the amount of amplification they provide. The audiologist will recommend the most suitable style of hearing aid based on the patient's audiological configuration and needs. 

  1. Behind-the-ear (BTE) hearing aids are worn behind the ear and require the use of a custom-made ear mould. They are suitable for mild to profound hearing losses.
    A miniature version of the BTE called the slim-tube BTE is available. It fits behind the ear with a narrow plastic tube inserted in the ear canal and is suitable for mild to severe hearing losses.
  2. Another miniature BTE hearing aid style called the receiver-in-canal (RIC) hearing aid is also available. Unlike the slim tube BTE, the RIC has a thin wire connected to a speaker unit that is inserted into the ear canal. It is suitable for mild to severe hearing losses.
  3. Custom hearing aids include in-the-ear (ITE), in-the-canal (ITC) and completely-in-canal (CIC) hearing aids. ITE hearing aids are made to fit the outer ear completely and are suitable for adults with mild to moderately severe hearing losses. ITC and CIC hearing aids are made to the size and shape of the ear canal. Both types are suitable for adults with mild to moderate hearing losses.

paediatric-hearing-aids.pngFor children diagnosed with hearing loss, early intervention through fitting of hearing devices is crucial to provide the child with good access to sounds during the critical period of speech and language development, which typically occurs during the first two years of life.

For children, BTEs are recommended because the earmoulds can be replaced as they grow older. Today, hearing aids often come in a wide assortment of colourful designs to cater to the paediatric population.

Frequently Asked Questions

General Questions

​1. How do I care for my hearing aid?


Your hearing aid comes with an instruction manual. Please read it carefully for tips on hearing aid care and maintenance. The audiologist will also instruct you in detail once you obtain your hearing aid.

Hearing aids are generally not waterproof and their electronic components can get corroded from excessive sweating, rain or even moisture in the air. Therefore, it is important to keep your hearing aid in a dry place, for instance, in a dry jar with a silica gel, or in an electronic dry box every night.

You should also refrain from dropping the hearing aid as its internal components might get damaged. Another common problem is having earwax trapped in the sound bore. Therefore, make sure you clean your hearing aid regularly, as instructed in the manual, to prevent wax blockage.

2. How long does it take to get used to wearing a hearing aid?

The period one takes to get used to his/her hearing aid varies from person to person, especially when the hearing loss has been taking place gradually over many years.

Hearing aids not only make speech louder but also background noises. Hence, following a conversation in a noisy environment can be difficult.

Even though new hearing aid technology in digital hearing aids can suppress noise and make speech in noisy situations clearer, it is not equivalent to normal hearing. Nonetheless, with patience, perseverance and practice, listening can become an enjoyable experience again.

3. Will there be any side effects from hearing aid use?

Although a battery is being used in the hearing aid, the voltage (1.4V) is too low to emit any harmful radiation. Sudden loud sounds such as thunder would not cause any trauma as most hearing aids have a filter to block out sounds which are too loud.

4. Will my hearing change after wearing the hearing aid?

There is no evidence to show that one’s hearing will change with hearing aid usage. A properly fitted hearing aid will help you to hear better and not damage your hearing. Changes in hearing tend to be caused by other factors such as age, diseases, or medication, regardless of hearing aid usage.

5. Will small hearing aids fall off or drop into the ear?

The shape of one’s ear will be cast into a mould and custom-made into an ear shell so that the hearing aid will fit snugly in the ear. If the ear shell is properly made and placed in the ear, it should not fall off or drop into the ear when one engages in non-vigorous activities such as walking and eating. In addition, the ear shell also prevents the sound from ‘leaking’ out of the ear and hence improves the quality of sound. Therefore, one does not usually get a hearing aid instantly but has to wait for the ear shell to be made.

6. Is it better to wear one or two hearing aids?

Wearing hearing aids in both ears may offer some advantages, such as being able to hear better in noise, an improved ability for sound localization and overall clarity.

7. How much do hearing aids cost?

The cost of one hearing aid ranges from about $650 to $7000, depending on the technology level of the device. 

8. Is there any guarantee that I will benefit from the hearing aid?

There are some people who will not benefit from hearing aids. The hearing aid amplifies sounds, making it easier for the patient to hear more clearly. However, it does not guarantee better speech understanding. Every individual is different and their outcome varies. Therefore, during the consultation session with the audiologist, the patient will have a chance to try on the hearing aid before making a decision to purchase.

9. What if I can’t afford a hearing aid but I need one?

Those experiencing financial difficulties will be referred to the Medical Social Services department for assistance.

10. What can hearing aids do? What can't hearing aids do?

What hearing aids can do:

  • make speech and environmental sounds louder
  • allow you to hear more sounds that you previously don’t hear. They help you become more aware of your surroundings.
  • make speech, your own voice and environmental sounds sound differently from the way they sound before
  • help you to hear better in one-to-one or face-to-face conversation
  • work best in picking up speech and sounds within 1 meter

What hearing aids cannot do:

  • restore normal hearing
  • change your hearing or stop the progression of hearing loss
  • eliminate background noise completely
  • remove the need for visual cues and contextual information


FAQ for Parents

1. Why do audiograms obtained at different centres vary?

Calibration of audiological equipment and soundfield rooms ensures that testing levels meet required international standards. As such, results of hearing tests obtained should be similar in all centres, and if the child responds reliably, a 5-10dB variability is acceptable.   

All our equipment have been calibrated and will be recalibrated every six months to ensure that our test conditions meet with international standards. Recalibration showed the initial calibrations were correct. We are confident that our testing levels have been/are correct and will continue with weekly biological calibrations to ensure test reliability.

In some previous audiograms obtained at other centres, no masking of the better ear has been used when testing the worse ear. When there is more than 40 dB difference between ears at any frequency, a narrow band noise needs to be used to mask out the good ear when testing the worse ear. Masking ensures responses are only coming from the worse ear. If masking is not used we might think the worse ear has more hearing than it really does due to cross hearing.

Audiologists need to be mindful of false responses, which is when a child responds in time with a stimulus but has not heard the sound. Children can fall into a pattern of responding, and so it is very important to vary the stimulus interval time and use non-stimulus trials often during the testing session.

2. What is the recommended volume for my child’s hearing aids?

In SGH we have chosen to use the Desired Sensation Level (DSL) hearing aid fitting prescription method primarily because it is the only current method specifically designed for use with children. Other popular fitting methods were designed for adults with an acquired hearing loss and adapted for use with a paediatric population.   

The DSL rule prescribes more gain than other fitting rules particularly at 2000 Hz. Research has shown that 2000 Hz is the key frequency for intelligibility of speech. In order to give a child access to the softer high frequency components of speech, the volume may need to be tuned higher to match the DSL targets. The volume control and internal settings will be verified with an aided audiogram and/or aided speech discrimination test for each ear.    

We do not recommend that aids be worn on full volume due to distortion that may occur. If aided testing indicates that the child does not have adequate access to the speech range with current aids appropriately adjusted, more powerful aids need to be considered. If no significant benefit is observed during a trial of the most optimal aid fitting, a cochlear implant would be the next consideration.

3. Why do the aids sound so loud and will this damage my child's hearing?

As most parents have normal hearing sensitivity, the aids will sound loud, particularly if your child has a severe or profound loss. However, speech should still sound clear on the user volume. It is recommended that parents do listening checks daily to ensure the aids are working properly and that the clarity of the sound is acceptable. 

Another advantage of the DSL paediatric fitting method is that uncomfortable loudness level and maximum power output targets are generated from the measured hearing levels. This means that we are able to predict with accuracy the level at which a sound becomes uncomfortably loud for a particular child based on his or her audiogram. The aid can then be set so that loud sounds do not exceed these levels. Care is then taken to observe for any adverse reactions such as startling eye blinking, crying, or attempts to remove the aid in the presence of loud sounds. Such evaluations will be done in the clinic. However, parents are always asked to watch out for and report any such behaviors in daily use. The maximum output levels can then be reduced accordingly, to ensure the child's comfort when wearing aids in noisy situations and most importantly, that the child's residual hearing remains intact.

4. What causes feedback?

We are all familiar with the shrieking feedback which occurs when a microphone is held too close to a speaker. Feedback is caused by amplified sound being 'fed back' into the microphone of the hearing aid. Causes of feedback include damage to the ear mould, the tubing, the earhook or the hearing aid itself. However, the most common cause is a poorly fitted ear mould. If the mould does not seal well in the ear, the amplified sound will leak out of the ear canal back into the microphone and cause whistling or feedback. The more powerful the hearing aid and the higher the recommended volume, the greater the risk of feedback will be. And there is a greater need for a properly fitted mould.   

You can perform a simple test to isolate the cause of feedback:

  1. Turn the aid on. Most aids will whistle.

  2. Block the sound bore. The aid should stop whistling. If it stops, the cause of the feedback indicates a poorly-fitted ear mould. Then, have new moulds made.

  3. If the aid does not stop whistling with the sound bore blocked, check for damage to the ear mould, tubing, earhook or aid itself. Then, send the aid for repair.

5. How do I know when my child needs new ear moulds?

As young children grow, the shape of their ear changes. This means that new moulds will be needed approximately once every three months. However, many children need a change of new moulds more often. In very hot and humid climates, such as Singapore, mould materials may shrink quickly and harden easily, which means new moulds need to be made often.

Your child will need new ear moulds if:

  1. feedback is occurring on the recommended volume setting
  2. the mould appears loose in the ear
  3. the mould material is becoming hardened or discolored
  4. the mould or its tubing has been damaged

It is recommended that parents monitor the fit of the mold closely and try to order new moulds as soon as the old ear moulds begin to appear hard or loose. DO NOT WAIT FOR FEEDBACK TO OCCUR as sometimes it may take new moulds up to 2 weeks to be ready! It is usually a good idea to have both new moulds made at the same time to avoid several trips to the hearing centre.

It is not uncommon for new moulds to give feedback due to problems with the ear impression taken or during the mould-making process. If the child cannot wear the new moulds on the recommended volume without feedback at the fitting appointment, ask for new impressions to be taken immediately. Decreasing the volume to reduce feedback is not a solution as the child will not hear optimally on a lower volume setting.

Children's moulds should be made of a soft flexible material such as soft silicone to ensure a good seal in the ear and less risk of injury during play. Check that the new moulds seal tightly in the ear but do not cause soreness.

6. Does my child need a libby horn in the ear mould?

Despite modern technology, hearing aids typically give inadequate gain above 3000Hz for those with a sloping audiogram of a moderate to profound hearing loss. However, it is possible to boost the high frequency response of a hearing aid by modifying the ear mould tubing so that the mould has a larger diameter at the sound bore (opening in the ear) instead of the earhook. This creates a horn shaped sound channel, which emphasises the frequencies between 2000Hz and 4000Hz. A 4mm Libby horn can boost the aid response by 15 dB at 4000 Hz. However, in order to place a 3mm Libby horn in the mould, the ear canal diameter must be at least 5mm.   

Unfortunately, boosting the high frequency response also results in an increased risk of feedback in high power hearing aids. In certain cases, the risk of feedback may be too great to recommend an acoustic horn. If it is likely that the boost in the high frequencies will not offer access to speech sounds at 4000Hz, a horn is usually not recommended.


7. If my child has only mild hearing loss does he need to wear a hearing aid?

YES! Any hearing-impaired child with a hearing loss greater than 40dBHL in the better ear should be fitted with a hearing aid as soon as a reliable measure of the hearing sensitivity is obtained. Studies show that even minimal hearing loss can have significant impacts on speech and language development, attention behavior, learning capacity and social development.


8. What is the earliest age a child can be fitted with a hearing aid?

A child’s hearing sensitivity can be assessed as early as the first day of life using objective diagnostic tools such as otoacoustic emissions (this test measures an echo from the cochlear, which tells us how well the inner ear is working), ABR (auditory brainstem response test) and SSEP (steady state evoked potential test), which indicates frequency specific hearing levels in each ear. Therefore, a child as young as a few weeks old can be fitted with hearing aids.


9. What is the purpose of the damper or filter in the earhook or mould tubing?

A typical Behind The Ear (BTE) hearing aid frequency response has peaks at different frequencies. These peaks may prevent increasing the gain of the hearing aid to match optimal targets at other frequencies. A damper or filter simply flattens out any unwanted peaks in order to match the aid response more closely to the target response. The dampening effect is usually centered on 1000Hz. Dampers also help to reduce feedback and limit the maximum power output of the hearing aid. That is, the loudest level to which the hearing aid will amplify a loud sound. This is important for protecting your child's residual hearing and improving his tolerance of the hearing aids in noisy situations.


10. Does my child need a FM system and what advantages do FM systems offer over hearing aids or cochlear implants alone?

Hearing aids and cochlear implants function best in ideal listening conditions, such as in a quiet situation with the speaker in close proximity to the hearing impaired child. We have all experienced difficulty in hearing when there is noise in the background, so likewise, it is difficult for a child to listen and learn in a noisy classroom.

A child with hearing sensitivity within the normal range requires speech to be 2 times louder than the background noise to understand a speech signal. However, a hearing impaired child needs a speech signal 10 times louder than the background noise to comprehend the speaker. The most effective means to improve the signal to noise ratio is by the use of the FM system. The speaker wears a remote microphone and transmitter while the child wears a receiver. The receiver connects to the hearing aids and receives direct audio input from the speaker's microphone. As the speaker's microphone is positioned close to the mouth (10 cm is ideal), the child hears the speaker as if he is very close by, regardless of the distance between them. This gives mobility to a teacher in a classroom and assists the teacher greatly in gaining the child's attention from a distance.

When using the FM system, both the speaker's microphone and the child's hearing aid microphone should always be active. The FM microphone is given priority over the hearing aid microphone when the speaker is talking. However, the child is still able to monitor his own voice and those of his classmates around him using his hearing aid microphone.         

The Ministry of Education provides the FM system free for all hearing impaired children attending primary schools. Please ask your audiologist for the FM system request letter and you should submit the letter when registering your child in a primary school. Your therapist can give you further advice.

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