Audiometer Advantages and Disadvantages: Pure Tone vs. Speech

This page covers the advantages and disadvantages of both pure tone audiometers and speech audiometers. It also includes definitions of audiograms, audiometry, and audiometers.

Introduction

Our ears are comprised of three main sections: the outer ear, the middle ear, and the inner ear. They’re capable of hearing sound waves within a frequency range of 20 Hz to 20 KHz. These sound waves are characterized by their intensity, pitch, and tone.

The sound waves enter through the outer ear and then pass through the middle and inner ear. Through vibrations, these sound waves reach our brain via nerve fibers. Our brain processes this information to distinguish between different types of sounds.

Each section of the ear is susceptible to specific diseases. Common causes of disorders in the external auditory system include the collection of wax, fungal debris, or other foreign bodies. Similarly, there are diseases specific to the middle and inner ear.

Hearing loss is often first observed at high frequencies (i.e., 8 KHz), followed by middle frequencies (1 to 2 KHz), and then lower frequencies.

What is an Audiogram?

An audiogram is a graph that plots the threshold intensity of sound waves that a patient can hear against the frequency. These audiograms are used to diagnose and monitor hearing loss. Audiologists conduct hearing tests and evaluate hearing loss by checking hearing sensitivity on the audiogram. The audiogram typically contains plots for both normal and impaired ears, allowing audiologists to compare and make diagnoses.

What is Audiometry?

Audiometry is a technique used to identify the nature of hearing loss. It determines the threshold of hearing by recording patient responses to auditory stimuli of varying intensity levels. Various audiometric techniques and methods are employed to achieve these results.

What is an Audiometer?

An audiometer is a device that evaluates hearing loss. The basic audiometer consists of three main parts:

• A signal generator (oscillator)
• An attenuator
• An earphone (loudspeaker)

The attenuator controls and specifies the intensity of the tones generated, with a typical range from 0 to 100 dB in steps of 5 dB. The oscillator produces frequencies within +/-3% of their nominal value. The generated frequencies are typically 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, and 8000 Hz.

Image courtesy: MAICO Diagnostics GmbH

Audiometers come in various types based on their applications and internal designs. Typically, there are two main types:

• Pure Tone Audiometer (PTA): Generates test tones in octave steps from 125 Hz to 8 KHz with intensity ranging from 0 to 100 dB. Pure tone audiometers are useful for determining hearing loss associated with the middle ear.

• Speech Audiometer: Plays pre-recorded speech as test signals. Patients are presented with certain words via headphones and asked to repeat them. The percentage of correctly spoken words is then determined. Speech audiometers are used in the differential diagnosis of hearing disorders.

The figure above depicts one such portable audiometer from MAICO Diagnostics Germany.

Advantages of Pure Tone and Speech Audiometers

Here’s a look at the benefits of each type:

Pure Tone Audiometer Advantages:

• Helps in measuring the softest or least audible sound a person can hear.
• Provides ear-specific thresholds and uses specific tones to provide place-specific responses, helping to identify the configuration of hearing loss.
• Utilizes both air and bone conduction audiometry, allowing for identification of the type of hearing loss via the air-bone gap.

Speech Audiometer Advantages:

• Requires less time than Pure Tone Audiometer (PTA) tests.
• Offers more validity (Speech stimulus > non-speech stimulus) and is generally a more reliable technique.
• PTA does not determine the communication ability of an individual, which speech audiometry assesses.
• Helps to cross-check pure tone thresholds estimated using PTA.
• Can help determine various aspects, including:
  • Hearing loss type and degree
  • Hearing aid selection
  • Identification of functional hearing loss
  • Identification of lesion site

Disadvantages of Pure Tone and Speech Audiometers

Let’s consider the limitations of each type:

Pure Tone Audiometer Disadvantages:

• Audiograms obtained can often be inaccurate.
• It is a subjective and time-consuming test.
• Does not assess or evaluate all features of hearing.
• Does not identify the nature of the underlying pathology.
• Bone conduction tests do not assess the true sensorineural reserve.
• There are many sources of variance in the test results that are not directly related to hearing.
• Not perfect for identifying all losses, such as “dead regions” of the cochlea (inner ear) and neuropathies.

Speech Audiometer Disadvantages:

• Results are native language specific. Therefore, speech audiometry tests require specific languages as per patients being tested. Results vary due to language differences and familiarity with the words and sounds presented.
• Results can differ for the same patients due to a lack of precise control over signal intensity and variations in test performance by different audiologists.