An audio metric or hearing test, is part of an ear examination that is carried out to evaluate a person’s ability to hear certain sounds clearly. This is done by simply measuring the ability of sound to reach the brain. The sounds we hear start as the vibrations of fluid (air and liquid) and solid materials in our surrounding.
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The vibration of particles produces sound waves, which vibrate at a certain frequency (speed) and height (amplitude). The height of the sound wave determines how loud (volume) the sound is going to be. The vibration or speed of a sound wave determine how high or low the sound is likely to be (pitch). When these sound waves travel through the ear, they are turned into nerve impulses. These nerve impulses are then sent to the brain, which “hears” them.
How to prepare for the hearing test
No special form of preparation is required before the test. However, try to remain still and be quiet during the test to allow for accurate recording to be made. Basically, the health professional will inform you on what you are required to do during the test.
How is the test performed?
These tests measure your ability to hear sounds that reach the inner ear through the skull (bone-conducted sounds), and sounds transmitted through the inner-ear canal (air-conducted sounds). There are three main classes of audio metric tests.
Whispered speech test
Also referred to as speech audiometry, this test determines how well you perceive the sound of words. You will be asked to wear headphones and sit in a soundproof booth. The health professional will then recite a list of words at different decibel levels.
The audiologist will ask you to repeat the words aloud. If you haven’t heard the word clearly, the professional will whisper back a bit louder. This test takes approximately 10 minutes to administer.
Tuning fork test
This procedure involves making a two-pronged device vibrate to produce a tone. The tuning fork is tapped and held in the air on each side of the head. The purpose of this test is to assess how sound moves through your ear canal.
The test measures your ability to hear by air conduction. After being tapped the fork is placed against the mastoid bone behind each ear to test bone-conduction.
Pure tone audiometry
This test is carried out using an audiometry machine. The audiometer plays tones that vary in pitch and intensity. During the rest you will again be required to wear headphones while sitting in a soundproof booth.
Pure tones of controlled pitch and intensity are delivered to one ear at a time to test air conductivity. You will be asked to press a button or raise a hand when you hear a sound. The minimum volume required to hear each sound is then graphed. A bone oscillator is placed against the mastoid bone of each ear to test bone conduction.
What does the test show?
Pure tone audiometry, charts the hearing level of different tone intensities in both ears. On an audiogram chart, blue X’s show the left ear’s results and red O’s show the right ear’s results. Hearing loss is categorized as:
-Normal: less than 25 dB HL
-Mild: between 25-40 dB HL
-Moderate: between 41-65 dB HL
-Severe: between 66-90 dB HL
-Profound: more than 90 dB HL
So what exactly is normal results? This is the ability to:
-Hear a tuning fork through air and bone.
-Hear a whisper, normal speech or the ticking or a watch.
-Hear tones from 250 Hz to 8,000 Hz at 25 dB or lower.
As noted earlier, there are different degrees of hearing loss. In some levels, patients lose the ability to hear high or low tones, and in others patients lose only bone or air conduction. The following conditions are known to affect test results or cause hearing loss.
-Chronic ear infections
-Age-related hearing loss
-Ruptured to perforated eardrum
-Occupational hearing loss
Some medications can affect the inner ear e.g. certain antibiotics (such as gentamycin or neomycin), large doses of salicylate (e.g. aspirin) and diuretics, which cause hearing loss.
Who should the test be carried out on
-Everyone, as part of a routine examination.
-People who are often exposed to loud sounds, maybe in the course of their work.
-Children or teenagers who can’t hear well in class hence have problems speaking.
-People who feel that they are experiencing some hearing loss maybe due to age.