A common misconception about deaf people is that they cannot hear at all— ‘stone deaf’ to the man or woman in the street. In fact, nearly all deaf people can hear some sounds but these will be much quieter, fragmented and distorted.

There are different types of hearing loss and they are usually described in terms of the decibel level at different frequencies.

What are ‘decibels’?

Decibels (dB) are used to measure the loudness of sound. A quiet whisper is about 30dB compared to normal conversation which is about 60dB. The level of a shout close by would be about 80 or 90dB as would that of a lorry passing you in the street. A jet engine at 50 metres emits a noise of about 120dB.

A individual’s hearing loss is described in decibels. A loss of 80dB means that sounds have to he 80dB or more before that person can just hear them. A person with normal hearing can hear them at 10-15 dB. The point at which a sound can just be heard is called ‘the threshold’.

What is profoundly deaf?

There are four levels of hearing loss: mild, moderate severe and profound

A mild loss

sounds at 40dB or less are not heard, so hearing conversation may not be too much of a problem.

A moderate loss

hearing starts between +1dB and 70dB which would make hearing normal conversation difficult without hearing aids.

A severe loss

sounds are begun to be heard between 71 and 95dB and a normal conversational voice could not be heard at all without hearing aids.

A profound loss

A loss greater than 95dB and even a loud shout close by would not be heard without hearing aids.

What is frequency’?

The frequency of a sound is what gives it it’s different pitch, the difference we hear between a low note played on a piano and a high note. The ‘higher’ the sound, the higher the frequency. Frequency is measured in Hertz (Hz) and kilo Hertz (1kHz = 1000 Hz).

Your child is likely to hear at some frequencies better than others which is why the hearing tests include different frequency sounds. People talk of a ‘high frequency loss’ when the higher frequency sounds (the high notes) are the most difficult for a child to hear.

Which type of loss is particularly significant because it affects the understanding of speech. Most vowel sounds (a,e,i,o,u) in English are low frequency but many consonants, like s, t, k, are high frequency so someone with a high frequency loss would not hear the s in ‘us’.

What is an Audiogram?

An audiogram is a graph which shows how loud (ie the dB level) sounds have to be at each frequency for the child just to hear them - the thresholds. Audiograms represent the loss for the right and the left ear by two separate lines on the graph since the loss can be different in each ear. When levels of deafness are described as ‘profound’ etc, this means that the average of the levels of loss at different frequencies in the better ear falls into the limits described above.

Each child’s audiogram is different. Ask your child’s teacher of the deal to explain your child’s audiogram more fully.

What does a hearing aid do?

A hearing aid makes sounds louder i.e. it amplifies them. A child with a severe loss, for example, who has a 75dB threshold (i.e. without her aids she can only hear sounds louder than 75 dB) might, with the right hearing aids, be able to hear some sounds at 50 dB or less. The new level at which she can just hear sounds is called the “aided threshold”.

Hearing aids will not restore full hearing; a deaf child will always be deaf but the effects of hearing loss can be lessened by providing the right hearing aids.

'Deaf Children Talking - the Parents' Guide to the Natural Aural Approach' provides more information about how to help your deaf child learn to listen and talk.