An audiometer tests hearing sensitivity. A pure-tone audiometer electronically generates pure tones as signals for hearing testing. Use an audiometer with the required frequencies and a method for precisely controlling the intensity of the tones. 

Basic accessories include earphones and earphone cords attached to the unit. Some audiometers have specialized accessories that are not necessary for screening. 

All pure-tone audiometers have certain basic controls and switches in common: 

1. Power Switch turns the instrument on and off. 

2. Frequency Selector changes the frequency of the test tone. Frequency ranges must be from 250 Hz to 6000 Hz. Frequency selector dials may also show, with a smaller numeral, the maximum intensity output in dB that the audiometer can produce for that particular frequency. 

3. Hearing Level Dial (or Attenuator) controls the intensity of the test tone. Hearing threshold level readings on this dial usually begin at 0 dB and are calibrated in 5 dB steps, or smaller. 

4. Output Selector Switch determines which earphone will transmit the output signal (tone). Some audiometers may also have a “Group” or “Bone Conduction” position on this switch. 

5. Tone Interrupter or Tone Presentation Switch is a button, bar, or lever used to present or interrupt the test tone, depending upon the position of the Tone Reverse switch. 

6. Tone Reverse Switch provides a choice for the tone to normally be ON or OFF. Some audiometers have a two-position Tone Reverse switch. 

7. Type of Tone Switch provides a choice for the type of tone: pulse, warble, or constant. 

Hearing Level (HL) for Pure Tone: the minimum hearing level at which an individual is able to respond 100 percent of the time to a series of tone presentations. 

Attenuator: a control capable of decreasing the amplitude of an audiometer’s output signal without distorting its frequency.