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

Abstract

An insert ear-canal probe including sound source and microphone can deliver a calibrated sound power level to the ear. The aural power absorbed is proportional to the product of mean-squared forward pressure, ear-canal area, and absorbance, in which the sound field is represented using forward (reverse) waves traveling toward (away from) the eardrum. Forward pressure is composed of incident pressure and its multiple internal reflections between eardrum and probe. Based on a database of measurements in normal-hearing adults from 0.22 to 8 kHz, the transfer-function level of forward relative to incident pressure is boosted below 0.7 kHz and within 4 dB above. The level of forward relative to total pressure is maximal close to 4 kHz with wide variability across ears. A spectrally flat incident-pressure level across frequency produces a nearly flat absorbed power level, in contrast to 19 dB changes in pressure level. Calibrating an ear-canal sound source based on absorbed power may be useful in audiological and research applications. Specifying the tip-to-tail level difference of the suppression tuning curve of stimulus frequency otoacoustic emissions in terms of absorbed power reveals increased cochlear gain at 8 kHz relative to the level difference measured using total pressure.

Distortion-product otoacoustic-emission suppression tuning in human infants and adults using absorbed sound power

“…The G data were linearly interpolated to calculate W a at each suppressor frequency. W a was converted to an absorbed sound power level L a defined by The present set of conductance data at the probe tip were similar to those previously reported in infants (Keefe et al, 1993) and adults (Keefe et al, 1993;Keefe and Schairer, 2011). The resulting mean power-based DPOAE STCs are shown in Fig.…”

“…The main effect of constructing the STC using the absorbed power level of each suppressor instead of its SPL was a large increase in the adult tip-to-tail level difference. This was associated with a maximum in the conductance level of adults near 4.5 kHz (Keefe and Schairer, 2011), which is related to the ear-canal standing waves in adults. The corresponding conductance levels in infants above 1 kHz were relatively flat across frequency.…”

“…Recently, stimulus frequency otoacoustic emissions (SFOAEs) in adult human ears have been compared for STCs based either on the absorbed sound power or on the sound pressure level (SPL) of suppressor tones across the range of suppressor frequencies (Keefe and Schairer, 2011). At a probe frequency of 8 kHz to elicit the SFOAE, the SFOAE STC had a greater tip-to-tail level difference and was thus narrower, when constructed on the basis of the absorbed sound power of the suppressor compared to the SPL of the suppressor.…”

Further assessment of forward pressure level for in situ calibration

“…Recently, Keefe and Schairer (2011) proposed specifying in situ sound level of the stimulus in terms of absorbed power. Similar to FPL calibration, absorbed power eliminates the influence of longitudinal standing waves and can be determined noninvasively.…”

Human middle-ear model with compound eardrum and airway branching in mastoid air cells

“…Two-tone suppression of SFOAEs indirectly estimated the cochlear gain in terms of the tip-to-tail of a SFOAE pressure suppression tuning curve (Keefe et al, 2008). Combining these SFOAE pressure data with earcanal reflectance measurements, the cochlear gain estimated from the tip-to-tail power level difference of SFOAE suppression increased with increasing frequency between 1 and 8 kHz (Keefe and Schairer, 2011). Such a cochlear mechanism based on nonlinearities in outer-hair-cell function would increase the intra-cochlear pressure levels generated at higher frequencies at sound levels close to threshold in the ear canal.…”