Influence of in situ, sound-level calibration on distortion-product otoacoustic emission variability
(Color online) Ideal and empirical impedance of a calibration cavity set with error values of . The top panel displays the magnitude and the bottom panel displays phase, both as a function of frequency. Each tube (with lengths ) is represented by a pair of lines. Dotted lines represent ideal values based on equations from Keefe (1984) and solid lines represent the empirical values for one sound-source channel. The lines are nearly superimposed, indicating close agreement between ideal and empirical values. Tube length can be identified by the corresponding resonant frequency (e.g., the solid and dotted lines with the first maximum at correspond with the longest tube in the set). The phase of the bottom panel does not exceed in either the positive or negative direction, signifying that the real part of the impedance value is positive, which is a physical requirement for a passive system.
Four sets of ear-canal impedance magnitudes from for three subjects. In each panel, the solid and dotted lines closer to the top are impedance values obtained with the deep probe insertion, and the solid and dotted lines lower in the panel are impedance values obtained with the probe inserted less deeply (shallow). The differences between the two solid lines and the two dotted lines were averaged to provide the estimate of intentional probe movement (the incidental change in DPOAE level introduced by the study design) for each subject. The differences between the top-solid and top-dotted lines and the lower-solid and lower-dotted lines provided estimates of unintentional probe movement for each insertion. The top two panels are representative of the types of impedance values obtained for the majority of subjects. The bottom panel is from the subject with the greatest estimated volume change for a single insertion (notice the difference between the top-dotted and top-solid lines).
Eighteen calculations of Thevenin-source (ER10-C probe) characteristics from the daily acceptable (error of ) cavity calibrations. The characteristics for only one sound-source channel are plotted. The delay value in the fourth panel refers to the measurement-system delay between stimulus generation and response recording by the sound card, a small portion of which is due to the internal travel time of the acoustic signal through the ER-10C probe. The number of cycles that occur during this time was subtracted from the phase value on a frequency basis, resulting in the values plotted in panel four.
Distributions of estimated, incidental changes in DPOAE level in response to changes in the ear-canal volume. The first two plots (deep and shallow) are estimates of unintentional volume changes due to slipping of the probe during a single insertion depth. The third plot (deep-shallow) represents estimates of the incidental change in DPOAE level that can be expected based on intentionally changing ear-canal volume by moving the probe. Outliers are not plotted in this figure. The largest unintentional change was for one subject, which could not be explained based on review of the in situ calibration spectra. While excluded from the figure, this subject’s data were included in the analyses.
DPgrams of subject means and standard deviations of noise and DPOAE levels for three calibration methods (SPL, FPL, and SIL) and three stimulus levels (20, 40, and ). Open symbols represent values obtained during deep insertion and closed symbols represent values obtained during shallow insertion.
Input/output functions of subject means and standard deviations of noise and DPOAE levels for the three calibration methods (SPL, FPL, and SIL) and four frequencies (1, 2, 4, and ). Open symbols represent values obtained during the deep insertion and closed symbols represent values obtained during the shallow insertion.
DPgrams of the mean absolute changes in DPOAE levels due to changes in insertion depth after individually correcting for the expected change in emission level introduced by the study design. The three calibration methods (SPL, FPL, and SIL) are compared for three stimulus levels (20, 40, and ). The axis differs in this figure from Figs. 5 and 6 by a factor of 5, making the differences between calibration methods more apparent.
Means for 18 repeated cavity calibrations at both room and body temperatures as a function of frequency. Phase of source pressure was not plotted as subtracting the delay complicated averaging. The delay values were within of each other.
The main effects for and interactions between calibration method, stimulus level, and frequency on the absolute change in DPOAE level between deep and shallow insertions after correcting for the incidental difference due to a change in ear-canal volume. The asterisk denotes statistical significance for .
Means and standard deviations of the absolute change in DPOAE level between insertions after correcting for the expected, incidental change. The first five rows are averaged across frequency for each calibration method and the sixth row is also averaged across level..
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