Real-Life Math
"The science of hearing requires a certain amount of math background,"
says Patrick Feeney. Feeney is a professor of audiology in Seattle, Washington.
"We use a scale called the decibel scale to measure sound,"
he says. "It's a logarithmic scale and we use it everyday when we test people's
hearing and compare it to normal results."
Audiologists use an audiogram
to chart results of their tests on a patient's hearing. The audiogram has
frequency (or pitch) across the top or horizontal axis and decibels (or loudness)
across the side or vertical axis.
Frequency ranges from very low on
the left side of the graph to the very high frequencies at the right. Frequencies
of 125 or 250 Hz are low tones on a piano; that is, the bass notes. High frequencies
of 8,000 Hz are very high tones; that is, the soprano notes.
Decibels
describe the loudness of the sound. Zero decibels is very soft while 110 dB
is very loud. Normal speech is around 45 dB.
The softest sound that
a person can hear 50 percent of the time is considered their hearing threshold.
These thresholds are measured and marked by an audiologist on the audiogram.
By
reading the results of an audiogram, audiologists can also determine the type
of hearing loss. There are two main types -- conductive and sensorineural.
Conductive
hearing loss occurs when the outer or middle ear doesn't work properly. Sounds
are "blocked" and don't make it all the way into the inner ear. Common causes
are too much fluid in the middle ear or too much earwax. Conductive hearing
problems are usually treatable.
Sensorineural hearing loss occurs when
the inner ear or hearing nerve becomes damaged. This happens with aging or
damage from loud noises.
This audiogram shows the charts of typical
conductive and sensorineural hearing losses. The areas above the lines represent
sounds that the person would not hear.
Ranges have been established
to help people identify their hearing loss.
| -10dB to 25 dB | normal range |
| 26 dB to 40 dB | mild hearing loss |
| 40 dB to 55 dB | moderate hearing loss |
| 56 dB to 70 dB | moderately severe hearing loss |
| 71 dB to 90 dB | severe hearing loss |
| over 90 dB | profound hearing loss |
You've just finished evaluating an elderly gentleman's hearing.
He's apprehensive that he's lost his hearing for good. These are his results:
125
Hz - 55 dB
250 Hz - 60 dB
500 Hz - 60 dB
750 Hz - 50 dB
100
Hz - 50 dB
1500 Hz - 65 dB
2000 Hz - 65 dB
3000 Hz - 57 dB
4000
Hz - 55 dB
6000 Hz - 60 dB
8000 Hz - 65 dB
Map
his audiogram and decide whether he has conductive or sensorineural hearing
loss. Is his hearing loss treatable?
At what level would you describe
his hearing loss? (See list above.)