The standard hearing test, known as pure-tone audiometry, uses a series of simple tones or “beeps” to measure hearing sensitivity. The purpose is to find the quietest sound a person can hear, called the hearing threshold, at various pitches. No fixed number of beeps exists for a test because the total count is entirely dependent on the individual’s hearing and how many repetitions are needed to accurately find that threshold. The procedure is a systematic search that involves testing multiple frequencies in both ears, often leading to a variable number of tones presented during the appointment.
The Procedure for Determining Hearing Thresholds
The process of finding a hearing threshold begins by testing a range of frequencies, typically starting at 1000 Hertz (Hz). The audiologist systematically checks a standard set of frequencies for each ear, moving through low pitches like 250 Hz and 500 Hz, and higher pitches from 2000 Hz up to 8000 Hz. The full test involves measuring the softest sound a person can hear at all these points, which is a maximum of seven frequencies per ear for a basic evaluation.
To establish the softest level a person can hear, the audiologist uses a standardized technique referred to as the “down 10, up 5” procedure. After presenting an initially audible tone, the sound intensity is reduced in 10-decibel (dB) steps until the patient no longer responds. The intensity is then increased in smaller 5-dB steps until the person responds again, which causes the number of beeps to fluctuate greatly.
This repetition continues until the audiologist confirms the lowest intensity level at which the patient responds to the tone at least 50% of the time. The number of trials needed for a single frequency is directly affected by the patient’s consistency in responding. If a person is inconsistent, more beeps will be presented as the audiologist repeats the ascending and descending intensity adjustments to isolate the true threshold.
Each frequency tested in each ear requires this threshold-finding search, meaning the “down 10, up 5” process is performed a minimum of 14 times for a basic air conduction test. The initial frequency of 1000 Hz is often retested at the end to check for response reliability, potentially adding more beeps to the total count.
Air Conduction Versus Bone Conduction Testing
A complete hearing evaluation requires measuring sound sensitivity through two distinct pathways to determine the location of any hearing issue. The first is air conduction testing, which uses headphones or insert earphones to deliver tones through the entire hearing system, including the outer ear, middle ear, and inner ear. This process measures how well sound travels naturally to the cochlea.
The second method is bone conduction testing, which uses a bone vibrator placed behind the ear on the mastoid bone. This vibrator bypasses the outer and middle ear by sending vibrations directly through the skull to stimulate the inner ear. By testing these two separate routes, the threshold search process is repeated, though bone conduction is typically only tested at a limited set of frequencies (500 Hz to 4000 Hz).
The comparison between the air conduction and bone conduction results is a powerful diagnostic tool. If a hearing loss is present, the difference between the two sets of thresholds, known as the air-bone gap, helps localize the problem. A loss seen only in the air conduction results suggests a conductive hearing issue in the outer or middle ear, such as an ear infection or eardrum perforation.
If both air conduction and bone conduction thresholds show a similar degree of hearing loss with no significant gap, it points to a sensorineural hearing issue. When both types of testing show a loss, and a gap is present, the diagnosis is a mixed hearing loss.
Interpreting the Audiogram
The culmination of the pure-tone audiometry test is the creation of the audiogram, which is a graphical map of the hearing thresholds. This chart displays the softest sound heard at each frequency for both ears. The horizontal axis represents the frequency or pitch of the tone, ranging from low pitches (250 Hz) to high pitches (8000 Hz).
The vertical axis represents the intensity or loudness of the sound, measured in decibels (dB), with the quietest sounds at the top of the graph. The lower a symbol appears on the graph, the louder the sound had to be for the person to hear it. The plotted points are connected to create a visual representation of a person’s hearing sensitivity.
Specific symbols are used to differentiate the results for each ear and test type.
- Air conduction thresholds are marked with an “O” for the right ear (often red).
- Air conduction thresholds are marked with an “X” for the left ear (often blue).
- Bone conduction thresholds are marked with symbols like “<" for the right ear.
- Bone conduction thresholds are marked with symbols like “>” for the left ear.
These plotted symbols allow the audiologist to classify the severity of any hearing loss. The classification is determined by where the plotted points fall on the vertical axis, with thresholds between 0 and 25 dB considered within the normal hearing range. Hearing loss severity is categorized into levels such as mild, moderate, severe, and profound, based on the average of these plotted thresholds.