Audio Meters

 It is used to get diagnostic information about the acuity of

hearing.  Effectiveness of ear protectors & noise control measures in case of industries. HUMAN EAR. • External ear ,Middle ear ,Inner ear. • Detects acoustic signals over (20-20000)hz. • Sound enters through outer ear conducted through ear canal to ear drum which separate ear canal from middle ear cavity. • From middle ear, sound energy transmitted to receptor cells surrounded by fluids.

Disorders of hearing. EXTERNAL EAR:

Acoustic pathway is blocked (or) accumulation of foreign bodies ,hearing capacity of ear will be reduced. MIDDLE EAR: Perforated ear drum ,diseased cochlea ,etc. Due to this there is a mismatch of impedance between air & bone conduction. INNER EAR: Prolonged exposure to noise (or) due to acoustic injury, transmission of sound to the brain is not proper.

Pure tone/speech audiometer.

Audio meter is an electronic-acoustic

instrument for measuring human hearing level in terms of loudness & pitch of sounds. Hearing loss is measured in terms of decibels (-10 - 100db) for audible range of frequencies. MASKING In patients with unilateral hearing loss & bilateral hearing loss possibility of false threshold level for the poorer ear. Solved by eliminating response from better ear by masking to shift threshold to high level.

Audio meters of various types, PURE TONE:

used to obtain air conduction & bone conduction thresholds of hearing which are used to diagnose amt of hearing loss. SPEECH: Speech reception thresholds. SCREENING: To identify threshold of hearing ,with respect to noise level of workers in industries & soldiers in military services.

Basic audiometer.

It can be used as pure tone, speech, screening . Pure tone(single freq)sound wave ,it is used to

determine the hearing loss. pure tone generators generate test tones in octave steps from 125-8000hz. Signal intensity=(-10 to 100db)using the attenuator control. TONE GENERATOR consist of LC oscillator in which inductance & capacitance can be varied precisely & coupled to power amplifier. Attenuator-ladder type(10 Ώ )impedance. Signal delivered to ear by head phone.

SPEECH AUDIOMETER : Test are carried with

spoken voice to prescribe hearing aids. tape recorder delivers recorded speech, live voice with microphone amplifier for communication purpose. SCREENING AUDIOMETER : Determine threshold of hearing in presence of noise.

VARIABLE SINEWAVE OSCILLATOR : test signals

having frequencies 125,250,1000,1500,2000,3000,4000,6000,8000 hz .its operation is presented from left ear masking right ear then 30sec for each tone then right ear masking left ear. MODULATOR:2-modes, pulse mode-test signal is modulated giving a signal easily recognised by the patients. continuous mode-test signal is directly used for calibrating the audiometer.

AUTOMATIC ATTENUATOR/RECORDER:

wiper of the pen drive of the x-y recorder is attached to potentiometer in the attenuator . depending on the hearing loss the peak of curve is traced for a particular freq of the recorder. HAND SWITCH : pen drive is controlled via logic control circuit by hand switch operated by patients .pressing switch increase sound level in ear phone releasing switch decrease sound level. BUFFER AMPLIFIER : Isolates attenuator from calibration circuit. During calibration sound level of test frequency is adjusted at the correct level corresponding to a normal person.