This was originally published as a post in June, 2008. We’re still getting so many views, and the info is so vital to anyone who has hearing loss, I decided to create separate page. Hope you find it helpful!
Last month I completed a project on audiograms for a class. Realizing many people with hearing loss don’t understand what all the symbols mean, I thought I’d condense it into a blog. I am not an audiologist, nor an “expert” on audiograms. I’m just a person with hearing loss, so if something doesn’t make sense, I suggest you ask your audiologist. This is just a very short, simplified overview. I’ve also included links at the bottom for further reading.
In order to understand an audiogram, first you need to understand sound. There have been entire books written about sound alone, but I’m going for simplicity here.
Why does a frog sound different from a bird? Sounds vibrate at different speeds. Low sounds vibrate more slowly than high sounds. Here’s an illustration of low frequency sound (on the bottom) vs high frequency (on top).
The piano above is a great way to illustrate low-pitched vs high-pitched sounds. Of course many sounds are lower than the lowest piano key. Likewise many other sounds are higher-pitched than the highest piano key. Additionally, there are pitches between each key, and so on. Audiologists do not measure every single pitch known to man; they only measure a few pitches at certain intervals to give them an idea of how you might be affected by hearing loss.
You already know some sounds are loud and some soft. A loud bus can sound soft in the distance. It becomes louder as it gets closer. It is the same sound near or far; only the intensity has changed. The loudness of a sound (intensity) is measured in decibels (dbs). Below, the horizontal lines of the audiogram represent the loudness of sounds (decibel intensity).
This makes perfect sense if you think about it. When you turn the volume up on your CD player, the pitch of the music you’re listening to stays the same. You recognize a piece of music whether the volume is high or low, unless it’s too low to hear. Intensity levels measured on audiograms range from about 5 dbs (very soft) up to 110 or 120dbs (very loud).
Putting it all together, your audiogram may look like this if you have good hearing:
Now let’s look at the “speech banana.” Most speech sounds fall in a banana shaped area of the audiogram called the speech banana.
Misunderstanding speech is what sends many of us to the doctor when we first begin losing our hearing. As you can see, some sounds like ‘th’ and ‘s’ fall in the high pitch ranges, while other sounds like ‘m’ and u’ fall in the low pitch areas. Many people have significant hearing loss in some pitches while their hearing remains good in other pitches. Depending on your hearing loss, you may have difficulties hearing high pitched sounds or low pitched sounds. The speech sounds you hear well may drown out the speech sounds you don’t hear. This is why, when we lose our hearing, we may feel like we hear a lot of sound, but there may no clarity. We are only hearing some sounds. This is also why it seems to others that we can “hear when we want to hear.” We can literally hear better sometimes. Depending on what is said, there will be more or less blanks to fill in.
Some people place the number of English phonemes at around 40, however others say it’s impossible to know how many phonemes there are because of all the different English dialects. Additionally, some people speak a blend of English dialects. Your hearing threshold and exposure to various dialects can impact understanding when you have hearing loss. Also, when you lost your hearing– if you lost hearing pre-lingually as opposed to post-lingually– makes a difference.
Further, individuals all differ in speech comprehension. Two people with the exact same hearing thresholds may not hear exactly the same way. This can be hard for some to understand, but think about runners. All feet are different. Some people have flat feet, some don’t, some people are bow-legged, some may have scar tissue from old injuries, some legs are short and others long. Many factors determine how fast you run. It’s the same with hearing. Many factors determine how well you understand the sounds you hear besides measurements plotted on your audiogram. There are differences in how all your parts work together, as well as voices you’re used to and dialects, and many other variables.
As I mentioned above, when people lose their hearing they don’t necessarily lose all their pitches equally. A common type of hearing loss is the “ski-slope” where low tones remain intact, while high tones drop. There is also a reverse ski-slope, a “cookie bite” and reverse cookie bite.
Why does this happen? If you look at the picture of the cochlea below, you will notice different areas of the cochlea are responsible for detecting different frequencies.
Often the nerves in only one area of the cochlea are damaged, while other nerves remain healthy. A similar analogy would be experiencing numbness in just one part of your leg after having a bad accident.
During sickness, parts of the cochlea may become damaged. Those parts may not react to sound unless amplified. When a hearing loss becomes severe to profound, amplification may no longer do the job adequately. A person can begin to experience pain with loud amplification while simultaneously unable to hear– especially when other parts of the cochlea still work just fine. The cochlea has become dysfunctional.
Below is an example of the common ski-slope hearing loss. The slope can be steeper or less steep. Notice the severe hearing loss at 4000 hertz, but “normal” hearing at 1000 hertz. Without hearing aids, this person will hear ‘m’ and ‘u’, but not ‘f’ or ‘s’. Listening to speech becomes a constant game of fill-in-the-blanks.
The circles indicate measurements for the right ear.
The x’s indicate measurements for the left ear.
What are the brackets on an audiogram? While the “air conduction” test determines hearing threshold (the blue line below), audiologists also perform a bone conduction test, with a vibrator placed near the cochlea. This can help the audiologist determine whether there’s a problem with the cochlea or some other part of the ear. The brackets indicate the results of the bone conduction. They usually look like this > but sometimes they look like this ].
Below there’s a disparity between the bone conduction and air conduction results. The cochlea seems to be working fine, as shown by the brackets. In this case, doctors determined it was due to infection of the middle ear.
For Further Reading: