Audiology
The Measurement of Hearing
Hearing is measured by determining how well a person can hear a range of
frequencies of sounds. There is a specific procedure used to gather this
information, which then is generally plotted on a graph called an audiogram.
Below is a sample audiogram form:
Across the top of the audiogram are numbers representing various
frequencies of sounds that are typically tested. Low frequency sounds are
represented on the left side of the audiogram, while high frequencies are on
the right. Frequencies are measured in hertz (Hz), or kilohertz (KHz). This
audiogram form depicts frequencies in KHz. The range of frequencies on the
audiogram corresponds to the range of frequencies most needed for verbal
communication purposes. Occasionally intermediate frequencies of 0.75, 1.5,
3 and 6 KHz may also be tested and plotted.
Going from the top to the bottom of the audiogram is the intensity scale in
decibels (dB). “ISO” refers to the International Standards Organization which
is a worldwide association that sets standards for a wide range of physical
measurements. Softer sounds are represented at the top of the audiogram,
while loud sounds are at the bottom. The actual values plotted on an
audiogram at the different frequencies are called thresholds. A threshold is
defined as the intensity at which a person can hear a specific sound 50% of
the time. There is a standardized procedure to determine thresholds.
Generally an audiogram will show the hearing results for both the right and left
ears. As such there are different symbols used to differentiate the hearing
results for each ear. However, before proceeding with this topic, two other
concepts need to be introduced.
