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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