Getting your hearing tested: the science
There is a lot of science that goes into modern hearing testing standards. A hearing test is set up to be a carefully controlled examination of your hearing ability. Your hearing care practitioner uses a machine called an audiometer to measure your hearing. The practitioner uses the audiometer to test each your ears independently by playing sounds at different volumes and frequencies and determining which sounds you can hear and which ones you can’t hear. Complete hearing tests will include hearing and repeating spoken words, as well. The practitioner records the results, either by hand or with a computer, using symbols onto a special chart called an audiogram.
What is an audiogram?
An audiogram is a graph that displays the softest sounds you can hear at different pitches. The vertical axis of an audiogram represents the intensity or level of the beeping sounds that are tested. The levels typically range from 0-120 dB, with the lowest level at the top. The horizontal axis represents the frequency or pitch of the sound. Tones are typically tested in the range from 250Hz to 8000Hz. If you’re familiar with a piano, the sounds tested range from middle C to an octave higher than the highest note.
Your responses are plotted as units of hearing threshold level (notated as dB HTL or dB HL). This way of measuring sound levels is unique to hearing testing. Sounds in the physical world are typically measured in units that are based on actual sound pressure levels (notated dB SPL). However, a normally hearing person detects different pitches at different sound pressure levels, which would make for a very messy graph. The audiogram was standardized so that average or “normal” hearing ability is equalized across all pitches. The best hearing ability is represented by a line across the top of the graph and profound hearing loss is represented by a line across the bottom of the graph. The rest of the graph is segmented into ranges of mild, moderate and severe hearing loss.
Why is the testing done in a booth?
Testing hearing must be done in a quiet place to ensure accurate results. Often, hearing care practitioners test people in a specialized room called a sound booth. When you sit in a sound booth, most distracting noises around you are eliminated, helping the practitioner to get accurate test results. If a sound booth isn’t used, hearing care practitioners often use special earplugs or headphones to block out extra noise. A sound booth used for hearing testing is sound-treated, not sound-proof. The sound booth is often equipped with loudspeakers for testing infants, small children and patients wearing hearing aids or cochlear implants. This sound field testing is always done with the patient sitting in the acoustic center of the space.
How do I know the test is reliable?
Hearing instrument specialists and audiologists are all trained to test hearing using a similar method of presentation, for both tones and speech. This method results in responses that are repeatable across different practitioners and clinics. Another important element of reliability is the calibration of testing equipment. Audiometers are calibrated at regular intervals to ensure that they are accurate and working properly. Practitioners are also required to regularly measure ambient noise levels in their sound booths. The American National Standards Institute (ANSI) sets forth guidelines both for calibrating audiometric equipment and for measuring the amount of outside noise that is present in a sound booth.
Because of the scientific method that is carefully followed to test hearing, a professional is able to interpret your responses to determine the type and severity of your hearing loss. If your hearing isn’t in the normal range you need help right away.