System for estimating sound pressure levels at the tympanic membrane using pressure-minima based distance

An apparatus for measuring sound pressure level of sound in an ear canal at a tympanic membrane, comprising:

• an audio output device to play the sound;
• a microphone configured to receive the sound in the ear canal at a first distance from the tympanic membrane and to provide a signal based on the received sound;
• and
• a processor executing instructions configured to:
• perform frequency analysis on the signal and determine output as a function of frequency;
• determine a null frequency of a minima of the output according to a single measurement at the first distance;
• calculate a second distance equal to a quarter wavelength of a wave at the null frequency;
• retrieve a previously generated correction factor associated with the second distance, and
• apply the correction factor to the output to generate a corrected output related to an estimated sound pressure level at the tympanic membrane.