Comparison of in-situ calibration methods for quantifying input to the middle ear

Abstract

Sound pressure level in-situ measurements are sensitive to standing-wave pressure minima and have the potential to result in over-amplification with risk to residual hearing in hearing-aid fittings. Forward pressure level ͑FPL͒ quantifies the pressure traveling toward the tympanic membrane and may be a potential solution as it is insensitive to ear-canal pressure minima. Derivation of FPL is dependent on a Thevenin-equivalent source calibration technique yielding source pressure and impedance. This technique is found to accurately decompose cavity pressure into incident and reflected components in both a hard-walled test cavity and in the human ear canal through the derivation of a second sound-level measure termed integrated pressure level ͑IPL͒. IPL is quantified by the sum of incident and reflected pressure amplitudes. FPL and IPL were both investigated as measures of sound-level entering the middle ear. FPL may be a better measure of middle-ear input because IPL is more dependent on middle-ear reflectance and ear-canal conductance. The use of FPL in hearing-aid applications is expected to provide an accurate means of quantifying high-frequency amplification.

Further assessment of forward pressure level for in situ calibration

“…The findings from studies comparing behavioral thresholds expressed as in situ FPL or SPL have been more consistently positive (Withnell et al, 2009;McCreery et al, 2009;Lewis et al, 2009). A pattern observed across these studies is that thresholds expressed in dB SPL tend to show "notches," or better thresholds than expected, at standingwave null frequencies.…”

“…Behavioral Thresholds: Withnell et al, 2009McCreery et al, 2009;Lewis et al, 2009). Regarding DPOAEs, response magnitudes can be affected by as much as 20 dB when stimuli calibrated in SPL are adjusted for standing-wave nulls (Siegel and Hirohata, 1994;Dreisbach and Siegel, 2001).…”

Specification of absorbed-sound power in the ear canal: Application to suppression of stimulus frequency otoacoustic emissions

“…Based on analyses of measurements between 0.25 and 6 kHz, Withnell et al (2009) proposed that either forward pressure or the fraction of total pressure at the tympanic membrane that is not reflected at the tympanic membrane be used to specify behavioral hearing threshold rather than total pressure. Calibrating the ear-canal stimulus according to forward pressure level has also been suggested for hearing-aid applications using probe-microphone measurements in the ear canal Lewis et al, 2009) and compared with calibrations using total pressure level in DPOAE measurements (Burke et al, 2010). Lewis et al (2009) also described a calibration method based on the sum of the forward pressure magnitude and the reverse pressure magnitude.…”

“…Calibrating the ear-canal stimulus according to forward pressure level has also been suggested for hearing-aid applications using probe-microphone measurements in the ear canal Lewis et al, 2009) and compared with calibrations using total pressure level in DPOAE measurements (Burke et al, 2010). Lewis et al (2009) also described a calibration method based on the sum of the forward pressure magnitude and the reverse pressure magnitude.…”

A transmission-line model of back-cavity dynamics for in-plane pressure-differential microphones

“…Replacement of a subsystem by its Th evenin equivalent is common in the study of transducers. [16][17][18][19] Each subsystem is labeled in Fig. 11.…”