Calibration of ear canals for audiometry at high frequencies

Area of Science:

• Acoustics
• Bioacoustics
• Auditory Physiology

Background:

• Accurate measurement of sound pressure at the ear canal's inner end is crucial for audiology and hearing aid fitting.
• Existing methods may lack precision, especially at higher frequencies (8-20 kHz).
• Coupling sound sources to the ear canal requires impedance matching for reliable acoustic transmission.

Purpose of the Study:

• To develop and validate a procedure for determining absolute sound pressure at the medial end of the ear canal.
• To investigate the frequency-dependent gain of the ear canal using a novel calibration technique.
• To provide accurate acoustic measurements for the 8-20 kHz frequency range.

Main Methods:

• A transducer coupled via a lossy tube, impedance-matched to the ear canal, was used.
• A microphone near the ear canal entrance measured the response to a transducer-applied impulse.
• The impulse response's Fourier transform was corrected using an all-pole function derived from spectral minima to estimate medial sound pressure.

Main Results:

• The procedure allows for absolute sound pressure determination in the 8-20 kHz range.
• Individual ear canal gain functions were derived, relating medial pressure to blocked-tube pressure.
• The average adult ear canal gain increased by 2-12 dB from 8-20 kHz, aligning with ear canal models.

Conclusions:

• The described procedure offers a reliable method for measuring sound pressure within the ear canal at high frequencies.
• The findings contribute to a better understanding of ear canal acoustics and provide data for hearing research.
• Potential sources of error in the calibration process were identified and discussed.