Normal threshold of hearing
The modal value of the thresholds of hearing at a specified frequency of an adequately large number of otologically normal subjects within the age limits of 18 to 25 inclusive.
Note: 1 Measured sound pressures should be converted to the corresponding sound pressure levels in decibels before the modal value is taken.
Note: 2 An otologically normal subject is a person in a normal state of health who is free from all signs or symptoms of ear disease and from wax in the auditory canal.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM