Advantages of Audiometer | Disadvantages of Audiometer
This page covers advantages and disadvantages of pure tone audiometer and speech audiometer. It mentions benefits or advantages of Audiometer and drawbacks or disadvantages of Audiometer. The definitions of audiogram, audiometry and audiometer are also described.
Introduction: Our human ear has three main sections viz. outer ear, middle ear and inner ear. It has capacity to hear sound waves with frequency range from 20 Hz to 20 KHz. These sound waves are characterized by intensity, pitch and tone. The sound waves entered through our outer ear and pass through middle ear and inner ear. These sound waves through vibrations reach our brain via nerve fibers. The received information is processed by our brain to distinguish between different types of sounds.
Each section of our ear has diseases specific to it. The common causes of these disorders in our external auditory system is due to collection of wax or fungal debris or any other foreign body. Likewise there are diseases specific to middle ear and inner ear. The loss of hearing frequency is observed first at high frequency (i.e. 8 KHz) than at middle frequency (from 1 to 2 KHz) and later at lower frequency.
What is Audiogram ?
The audiogram is a graph which plots threshold intensity of sound waves which patients can hear versus frequency. These audiograms are used to diagnose and monitor the hearing loss. Audiologists conduct hearing tests and evaluate hearing loss by checking the hearing sensitivity on the audiogram. The audiogram contains plots for normal ear and impaired ear for audiologists to compare while diagnosis.
What is Audiometry ?
Audiometry is the technique used to identify nature of hearing loss. It is used to determine threshold of hearing by recording responses of the patients. Auditory stimuli with varying intensity levels are used for recording. The various audiometric techniques and methods are employed to achieve results.
What is Audiometer ?
The audiometer is a device which evaluates hearing loss. The basic audiometer consists of three parts viz. signal generator (i.e. oscillator), attenuator and earphone (i.e. loudspeaker). Attenuator controls and specifies intensity of tones generated. The range of intensity is from 0 to 100 dB in steps of 5 dB. Oscillator produces frequencies within +/-3% of their nominal value. The generated frequencies are 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000 and 8000Hz.
Image courtesy : MAICO Diagnostics GmbH
The audiometers are of various types based on their applications and internal designs. Typically there are two types viz. pure tone audiometer (P.T.A.) and speech audiometer. The pure tone audiometer 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 to determine hearing loss associated with middle ear.
The speech audiometer plays pre-recorded speech as test signals. Patient is presented with certain words via headphone and he/she has been asked to repeat the words. The percentage of correctly spoken words are being determined. Speech audiometer is used in differential diagnosis of hearing disorder. The figure depicts one such portable audiometer from MAICO Diagnostics Germany.
Benefits or advantages of Pure Tone Audiometer and Speech Audiometer
Following are the benefits or advantages of pure tone audiometer:
➨This test helps in measuring the softest or least audible sound which a person can hear.
➨It provides ear specific thresholds and uses specific tones to provide place specific responses. It helps to identify the configuration of hearing loss.
➨The Pure tone based audiometer uses both air and bone conduction audiometry. Hence type of loss can also be identified via the air-bone gap.
The advantages of speech audiometer type are as follows.
➨It requires less time than Pure Tone Audiometer (P.T.A.) test.
➨It offers more validity (Sp. stimulus > non sp. stimulus) and it is more reliable technique.
➨P.T.A. does not determine communication ability of an individual. This is done using speech audiometer.
➨It helps to cross check pure tone threshold estimated using P.T.A.
➨Speech audiometry helps to find out different aspects as mentioned below.
• To find out hearing loss type and its degree, helps in selection of hearing aid, helps to identify functional hearing loss, helps to identify site of lesion etc.
Drawbacks or disadvantages of Pure Tone Audiometer and Speech Audiometer
Following are the drawbacks or limitations or disadvantages of pure tone audiometer.
➨Audiograms obtained are very often inaccurate.
➨It is a subjective and time consuming test.
➨It does not assess or evaluate all the features of hearing.
➨It does not identify the nature of the pathology.
➨Bone conduction test does not assess the true sensorineural reserve.
➨There are many sources of variances in the test results which are not related to hearing.
➨The pure tone audiometry technique is not perfect to identify all the losses such as "dead regions" of the cochlea (portion of inner ear) and neuropathies.
The disadvantages of speech audiometer type are as follows.
➨The results are native language specific. Hence speech audiometry tests require specific languages as per patients under test. Results vary due to language differences as well as degree of familiarity with words and sounds presented to patients under test.
➨The results are different for same patients due to lack of precise control over signal intensity and test performed by different audiologists.