Audiometry () is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and otoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram. History The basic requirements of the field were to be able to produce a repeating sound, some way to attenuate the amplitude, a way to transmit the sound to the subject, and a means to record and interpret the subject's responses to the test. Mechanical "acuity meters" and tuning forks For many years there was desultory use of various devices capable of producing sounds of controlled intensity. The first types were clock-like, giving off air-borne sound to the tubes of a stethoscope; the sound distributor head had a valve that could be gradually closed. Another model used a tripped hammer to strike a metal rod and produce the testing sound; in another, a tuning fork was struck. The first such measurement device for testing hearing was described by Wolke (1802). Pure tone audiometry and audiograms Following development of the induction coil in 1849 and audio transducers (telephone) in 1876, a variety of audiometers were invented in United States and overseas. These early audiometers were known as induction-coil audiometers due to... Hughes 1879 Hartmann 1878 In 1885, Arthur Hartmann designed an "Auditory Chart" which included left and right ear tuning fork representation on the x -axis and percent of hearing on the y-axis. In 1899, Carl E. Seashore Prof. of Psychology at U. Iowa, United States, introduced the audiometer as an instrument to measure the "keenness of hearing" whether in the laboratory, schoolroom, or office of the psychologist or aurist. The instrument operated on a battery and presented a tone or a click; it had an attenuator set in a scale of 40 steps. His machine became the basis of the audiometers later manufactured at Western Electric. Cordia C. Bunch 1919 The concept of a frequency versus sensitivity (amplitude) audiogram plot of human hearing sensitivity was conceived by German physicist Max Wien in 1903. The first vacuum