The eardrum's ability to move freely depends on the correct air pressure conditions. Using a machine called a tympanometer the audiologist can measure the air pressure behind the eardrum. This pressure measurement tells the audiologist if the Eustachian tube is functioning normally. After the pressure is determined, short loud beeps will be presented to measure the acoustic or stapedial reflex. This contraction of the muscles around stapes protects the inner ear from loud sounds by temporarily stiffening the eardrum.

Tympanograms are grouped into 3 categories or types which relate to the amount of movement present.  Below are examples of each tympanogram type.

Type A	Type C	Type B
Pressure between +100 and - 100 No affect on hearing	Pressure between -150 and -400 Conductive hearing loss at low and high frequencies Consistent with Eustachian Tube dysfunction	No measureable pressure Conductive hearing loss at all frequencies Consistent with fluid in the middle ear

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