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Further assessment of forward pressure level for in situ calibration
Journal article   Open access   Peer reviewed

Further assessment of forward pressure level for in situ calibration

Rachel Scheperle, Shawn Goodman and Stephen Neely
The Journal of the Acoustical Society of America, Vol.130(6), pp.3882-3892
12/2011
DOI: 10.1121/1.3655878
PMCID: PMC3257756
PMID: 22225044
url
https://doi.org/10.1121/1.3655878View
Published (Version of record) Open Access

Abstract

Quantifying ear-canal sound level in forward pressure has been suggested as a more accurate and practical alternative to sound pressure level (SPL) calibrations used in clinical settings. The mathematical isolation of forward (and reverse) pressure requires defining the Thévenin-equivalent impedance and pressure of the sound source and characteristic impedance of the load; however, the extent to which inaccuracies in characterizing the source and/or load impact forward pressure level (FPL) calibrations has not been specifically evaluated. This study examined how commercially available probe tips and estimates of characteristic impedance impact the calculation of forward and reverse pressure in a number of test cavities with dimensions chosen to reflect human ear-canal dimensions. Results demonstrate that FPL calibration, which has already been shown to be more accurate than in situ SPL calibration, can be improved particularly around standing-wave null frequencies by refining estimates of characteristic impedance. Better estimates allow FPL to be accurately calculated at least through 10kHz using a variety of probe tips in test cavities of different sizes, suggesting that FPL calibration can be performed in ear canals of all sizes. Additionally, FPL calibration appears a reasonable option when quantifying the levels of extended high-frequency (10-18kHz) stimuli.

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