Pure Tone Audiometry Explained

What is Pure Tone Audiometry?

Pure tone audiometry (PTA) is a type of hearing test used by audiologists to evaluate an individual’s hearing capabilities.

During the procedure, an audiometer—a device that produces pure tone sounds at specific frequencies—is used. These tones are delivered through earphones or bone conduction devices, and the patient signals when they can hear the sound. The softest sound level they detect is recorded.

This threshold data is then plotted on an audiogram, a graphical representation of the test results that helps determine the type and degree of hearing loss. The audiogram shows the person’s hearing sensitivity across various frequencies.

What Frequencies Are Normally Used in a PTA Test?

In a standard Pure Tone Audiometry (PTA) test, the most commonly tested frequencies are:

• 250 Hz
• 500 Hz
• 1,000 Hz (1 kHz)
• 2,000 Hz (2 kHz)
• 4,000 Hz (4 kHz)
• 8,000 Hz (8 kHz)

These cover the range most important for speech understanding (500 Hz – 4 kHz).

Sometimes 125 Hz is tested for very low-frequency hearing.

6,000 Hz is often added, especially for detecting noise-induced hearing loss.

Extended high-frequency audiometry (above 8 kHz, up to ~20 kHz) can be done in research or specialist clinics, but it’s not part of routine clinical PTA.

As a subjective test, pure tone audiometry depends on the patient’s responses and is usually conducted with adults and children who are able to follow the test instructions.

Understanding Pure Tone Audiometry

To understand pure tone audiometry, it’s helpful to appreciate the fundamentals of sound and hearing. Sound is energy that moves in waves, each wave having a specific frequency that dictates the pitch. Our ears detect sound waves within a frequency range between 20 to 20,000 Hz. The hearing threshold is the quietest sound that an individual can hear at various frequencies. Pure tone audiometry tests these thresholds to evaluate a person’s hearing sensitivity.

In audiometry, two fundamental concepts are air conduction and bone conduction.

Air conduction involves sound traveling through the outer and middle ear before reaching the cochlea. Conversely, bone conduction bypasses the outer and middle ear, directly stimulating the cochlea via vibrations transmitted through the skull.

Sensorineural hearing loss results from damage to the inner ear or auditory nerve, while conductive hearing loss is due to issues in the outer or middle ear.

Pure tone audiometry evaluates both air and bone conduction thresholds to determine the nature of the hearing loss.

Components of a Pure Tone Audiometry Test

A pure tone audiometry test includes several key elements.

The “test ear” is the ear being assessed during the examination. Masking noise prevents the non-test ear from helping the test ear, ensuring the audiogram accurately shows the hearing ability of the test ear only. For air conduction testing, insert earphones are placed in the ear canal to deliver the pure tone stimuli. The results are then plotted on a tone audiogram, which graphically represents the person’s hearing thresholds across various frequencies.

Understanding Audiograms

Audiograms play a crucial role in pure tone audiometry by visualising a person’s hearing thresholds across different frequencies. Frequencies are plotted on the horizontal axis and hearing thresholds are displayed on the vertical axis.

An audiogram offers a clear depiction of an individual’s hearing sensitivity, highlighting any deviations from the normal range. By examining the audiogram, audiologists can determine the type of hearing loss—whether conductive, sensorineural, or mixed—and assess the severity of the impairment.

Conducting the Test

To ensure accurate and reliable results, the procedure follows standardised protocols. Controlling the test environment to minimise ambient noise is crucial for creating optimal testing conditions.

Specialised equipment, including an audiometer, insert earphones and a mastoid bone oscillator, are used to deliver pure tone stimuli and record the individual’s responses.

Preparing the Test Environment

The test environment needs to be quiet and free from excessive ambient noise that might interfere with the results. This is usually accomplished by conducting the test in a sound booth, which provides a controlled acoustic setting. The sound booth is designed to minimize external noise, ensuring a quiet space for accurate testing.

Equipment Used in Pure Tone Audiometry

Pure tone audiometry relies on several specialized pieces of equipment. The central instrument is the audiometer, which generates pure tone stimuli and controls the test parameters.

For air conduction testing, insert earphones deliver pure tones directly into the ear canal.

For bone conduction testing, a mastoid bone oscillator is placed on the mastoid bone behind the ear to directly stimulate the cochlea.

This equipment ensures the accurate and precise delivery of pure tones and records the individual’s responses for analysis.

Pure Tone Audiometry Step-by-Step Procedure

The individual is seated in a quiet environment

• Test begins by establishing a baseline for the individual’s hearing thresholds
• Pure tones of varying frequencies are presented to the individual through earphones or bone conduction oscillators.
• The individual indicates when they can hear the tone
• The tester records the softest level at which the tone is detected

This process is repeated for different frequencies, and the results are recorded on an audiogram. The individual’s responses and the resulting audiogram provide valuable information about their hearing ability and any potential hearing loss.

Interpreting Results

Interpreting the results of a pure tone audiometry test involves a careful analysis of the audiogram.

This graph represents the individual’s hearing thresholds across various frequencies. By comparing these thresholds to those of individuals with normal hearing, audiologists can determine the person’s hearing level and identify any deviations from normal hearing.

The audiogram also aids in assessing the individual’s speech discrimination ability, which is essential for understanding their overall hearing function. This interpretation is a vital step in accurately diagnosing and managing hearing loss.

Reading a Pure Tone Audiogram

Understanding an audiogram involves interpreting the information shown on the graph. The horizontal axis represents the range of frequencies, indicating different sound pitches. The vertical axis shows the hearing thresholds, which are the quietest sounds the person can hear at each frequency. The graph may also feature symbols or markers that denote the type and pattern of hearing loss.

By analysing the audiogram, audiologists can assess the individual’s hearing sensitivity, identify any deviations from normal hearing, and determine the appropriate management strategies.

Identifying Types of Hearing Loss

Audiograms play an essential role in diagnosing different types of hearing loss.

Sensorineural hearing loss happens due to damage to the inner ear or auditory nerve, leading to decreased hearing sensitivity.

Conversely, conductive hearing loss arises from an obstruction or dysfunction in the outer or middle ear, hindering sound from reaching the inner ear.

Mixed hearing loss combines both sensorineural and conductive elements.

By examining the audiogram, audiologists can identify the type of hearing loss and create suitable treatment plans.

Common Patterns in Audiograms

Audiograms, which visually display data from pure tone audiometry tests, can illustrate typical patterns linked to various types of hearing impairment.

Age-related hearing loss commonly manifests as a gradual reduction in sensitivity, especially in higher frequencies.

Noise-induced hearing loss often exhibits a dip around 4000 Hz, indicating damage from exposure to loud sounds.

Distinct patterns may signify specific causes of hearing issues, such as conductive hearing loss stemming from middle ear complications. Recognising these patterns aids in diagnosing and effectively treating different forms of hearing difficulty.

Pure Tone Audiometry vs Sound Field Audiometry

Pure Tone Audiometry (PTA)

• Uses headphones, insert earphones, or bone vibrators.
• Tests each ear separately.
• Provides ear-specific hearing thresholds across different frequencies.
• Gold standard for diagnosing type and degree of hearing loss.

Sound Field Audiometry (SFA)

• Uses loudspeakers in a sound-treated room.
• Tests hearing with both ears together (not ear-specific).
• Commonly used for young children, people who cannot wear headphones, or when testing aided responses (e.g., with hearing aids or cochlear implants).
• Results are influenced by the better hearing ear.

PTA = ear-specific thresholds, while SFA = functional hearing in a real listening environment, but not ear-specific.

Closing Thoughts

Pure Tone Audiometry plays an essential role in evaluating hearing abilities and pinpointing potential problems. Regular testing, especially after 50, and clear communication with hearing professionals are important for managing any issues.

If you live in the London area and have concerns about your hearing of that of a loved one, Sound Hearing provides home visit hearing tests. We will conduct a comprehensive hearing test and advise on hearing solutions, all from the comfort of your home.