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The word immittance refers to the speed at which a sound travels from one material to another. It is most often seen used in medical offices that specialize in hearing. Immittance is instrumental in a type of hearing test called tympanography or immittance audiology. This type of testing generally focuses on how sound travels from the middle ear to the inner ear and how pressure changes affect the ear drum. It is used to determine the nature of, and possible sources behind, hearing problems, and it is one of several tests that can help a hearing specialist determine whether a patient needs a hearing aid.
Immittance testing is usually performed by inserting a sterile probe into the middle ear that seals the ear. Once it is sealed, the probe performs pressure changes and records the ear drum changes and muscle reflex changes that occur within the ear in response to the pressure changes. Pediatricians can use this test to determine whether a child with hearing problems has fluid buildup in her ear. If the child already has fluid drainage tubes inserted into her ear, the immittance test can determine whether they are working to drain fluid.
Other types of hearing tests include sound field testing, headphone testing, bone conduction testing, and otoacoustic testing. Each type of test uses a different technique to focus on testing a specific part of the ear. Generally, the results of multiple tests are combined to give a hearing specialist a better idea of the causes of any hearing problems he finds.
Sound field testing tests how a patient hears sounds played in a room through a speaker located in the room. Headphone testing is performed by playing sounds through speakers in a headphone set worn by the patient, and can help determine signs of hearing loss in each ear individually. Bone conduction testing shows how much sound is conducted through the bones and nerves in a patient's head. Otoacoustic testing tests the inner ear and the function of the sound-conductive hairs within the ears.
In electronics, immittance is a term that describes both the impedance and admittance of an electric current. Immittance does not have a defined unit of measurement because it refers to both conditions. Impedance is a measure of the opposition to alternating current (AC) electricity. Admittance is the opposite of impedance; it is the measure of current that flows through the conductive object.