11 July 2017
A short while ago a comment came up on our Facebook page about how, as hearing professionals, we want children to be able to hear within the string bean, not just the banana. This terminology was a little confusing for some (including me, as I’m not an audiologist or speech pathologist).
So, I went off on a little exploration about hearing bananas and string beans, and it turns out you can’t understand them, without first understanding a lot more information, including how to read an audiogram.
So today, we are going to go through the basics of reading audiograms.
An audiogram charts the softest sounds that a person is able to hear at various pitches. The quality of the sound is not measured by an audiogram, purely the ability to hear that sound. Audiograms are represented as a graph with frequency (low to high) on the horizontal axis and intensity (soft to loud) on the vertical axis.
Frequency is measures in Hertz (Hz). Low frequency sounds are low in pitch (like a deep voice), whereas high frequency sounds are high pitch (birds singing). For speech the most important frequencies are between 250Hz and 6,000Hz. Vowel sounds (oo, ah, etc) tend to be low frequency and consonant sounds (f, s, the, sh, etc) tend to be high frequency sounds.
Intensity is measured in decibels (dB). The lower the number of decibels the softer the sound. It’s important to note that 0 dB does not mean there is no sound, it means it is the softest sound someone with ‘normal’ hearing can hear at least 50% of the time. ‘Normal’ hearing is considered to have the softest sounds between 0 dB and 20 dB.
Decibel levels for different sound are given below, to give you some context.*
|Conversation at Home||60dB|
|Jet taking off at 25m||150dB|
Just as an aside, it is recommended that you use hearing protection for noises above 100 dB if you will be exposed longer than 15 minutes, and for any length of time for anything over 110 dB.
Creating the Audiogram
Audiograms are created during a hearing test. You can read about how we undertake hearing tests for different ages and purposes on our previous post.
The hearing test will produce different intensities of sound (loudness) at different frequencies (pitch). So you might have a low frequency sound like ‘oo’ made softly, loudly and somewhere in the middle to gain an understanding of where this sound stops being heard. It is these results that are marked on the audiogram.
Reading the Audiogram
Audiograms can be complicated things to read, and different providers may use different symbols on their audiograms, so it’s always worth checking the key to the specific one you are reading.
Some other terms you might find on an audiogram are PTA (Pure Tone Average) which is an average of the softest decibel level that can be heard at 500 Hz, 1,0000 Hz, 2,000 Hz and 4,000 Hz.
Also, before you can read an audiogram, you need to understand what constitutes each level of hearing loss.
The level of hearing or threshold is determined by the lowest level a person can hear at 50% of the time. As we mentioned earlier this is 0-20 dB in adults with no hearing loss. The levels of hearing loss are:
Mild Loss - 20-40 dB
Cannot hear soft sounds. Can hear normal conversation in a quiet room, but not in a noisy environment
Moderate Loss - 40-70 dB
Has difficulty hearing normal conversation.
Severe Loss - 70-90 dB
Can only hear very loud speech next to the ear.
Profound - 90+ dB
Can hear very little, if at all. Even the sound of a motorcycle would not be able to be heard.
The audiogram above is for someone with normal hearing.
The circles are the right ear and the crosses are the left ear.
You can see that for almost all frequencies (pitches) the lowest level they can be heard at is between 0 and 10 dB, which is in the normal range. So there is no hearing loss.
It becomes more complicated when someone has a hearing loss. The audiogram above shows a person with a hearing loss.
So, let’s look at the right ear (circles) first.
You can see that the lowest dB that can be heard is around 90dB, which falls within the profound hearing loss range. At the 110dB nothing can be heard at all (this is why there is a little arrow next to the circle, which indicates no response).
For the left ear (crosses) the softest sound this person can hear is at 40dB (at 250 Hz and 500 Hz), with other frequencies at 60dB, and some frequencies event at 80dB and 90dB.
Given the range of loss this person would have a mild to profound loss, with their greatest loss being for high frequency sounds (higher pitch).
This person would certainly require a hearing aid in their right ear, and potentially a cochlear implant in their left to give them the best access to sound.
What about the banana?
An audiogram gives an understanding of the level of hearing loss with pure tones (specific sounds at different dB and Hertz level). However, they do not give us the whole story. For example, it is important to understand how well someone understands speech.
That is where the banana comes in!
The speech banana is the area where the sound of human speech lie on an audiogram.** When these sounds are plotted by intensity and frequency on an audiogram they resemble a banana. The sounds that fall within the banana are those that are vital for an ability to lean to listen and speak.
If we overlay the audiogram from the child with a hearing loss from earlier we can see that there are many sounds the child would miss out on if they did not use a hearing technology.
In the left ear they would hear some speech, but only in the lower to mid frequencies, whereas in their right hear they wouldn’t hear any speech sounds.
As listening and spoken language specialists we aim to ensure that once a child has their technology they have access to all the sounds in the speech banana, that is why wearing hearing technology as much as possible is so vital.
And the string bean?
The string bean is used to describe the area right at the top of the speech banana. The ideal situation would be to have a child hearing everything within the string bean. This would mean that we know the child is hearing all speech sounds, which will lead to much better listening and spoken language outcomes.
If you feel your child needs a hearing test you can learn more about our services here, and call us to book a test on 08 8267 9200.
*Information taken from: http://www.industrialnoisecontrol.com/comparative-noise-examples.htm