Understanding an Audiogram

An Audiogram is a charting tool used to display a person's ability to hear at different pitches (or frequencies).  A typical hearing test plays different pitches of tones for a person at different loudnesses.  The results from the hearing test can be plotted on the audiogram.

A Typical Audiogram 

Typical Audiogra
This audiogram depicts the ability of a person to hear in each ear at six different frequencies.
The audiogram that you see here is an example of what a hearing test might produce.  There are two series of data plotted on the graph: the results for the Left Ear and the Right Ear.  It is standard convention to have the right ear display as circles and the left as 'X's.

Sometimes, if the test is not done with earphones, both ears are tested together.  Testing both ears together can lead to deceptive results, and could prevent a hearing problem from being discovered.  On this audiogram, if both ears are tested together, the resulting data points are plotted as squares.

On the right side of the audiogram you see the level of hearing loss associated with the chart: normal, mild / moderate, and severe.  Many audiograms break these categories down further to normal (< 25), mild (25-40), moderate (40-70), severe (70-90), and profound (>90).

It is typical for a person who has nomal hearing loss associated with age to have a greater hearing loss at the higher frequencies than at the lower frequencies, as shown in this example.  This example also shows a right ear that hears worse than the left ear.  It is not uncommon for one ear to hear betterr than the other.  But this might also indicate a problem in the test (if it was an at-home test).

Intensity

Typical Sound Intensities
Typical Sound Intensities as Related to an Audiogram
The intensity of a noise measures the amplitude of the sound wave.  For hearing testing, this is measured in dB (decibels).  The healthy ear can hear some frequencies better than others, so the amplitues (measured in dB) are shifted so that 0 dB (at the top of the scale in this case) represents the threshold of hearing (or the softest sound a normal healthy person can hear).

This chart shows that normal speach is at around 50dB.  That means that if a person's hearing loss is at about 50 dB, they will not be able to hear the conversation (at least not enough to understand it).

A lawnmower on the other hand, it a loud noise (depending on the type and how far from it you are).  Care should be taken with loud noises to prevent damaging your hearing.

Frequency

Audiogram Frequencies
Audiogram Frequencies Compared to Musical Instruments and Notes
Frequency, in Hertz, represents the number of cycles per second of a tone.  The larger the number, the higher the pitch.

The vertical lines on the audiogram represent different frequencies.  As the figure shows, the left side of the chart is for lower-pitch sounds like a Tuba.  And the right side of the chart is for higher-pitch sounds like flute.  The typical hearing test consists of 6 different frequencies that span the normal range of human hearing, especially the range of speech recognition.

Many of the consenants consonants (k, f, s, th, etc.) in normal speech are associated with higher frequencies.  A person that has a greater hearing loss in the higher frequencies may have a more difficult time understanding the speech, but could hear it loud enough.

 
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