Using a one-dimensional finite-element approximation of Webster's horn equation to estimate individual ear canal acoustic transfer from input impedances

In many applications, knowledge of the sound pressure transfer to the eardrum is important. The transfer is highly influenced by the shape of the ear canal and its acoustic properties, such as the acoustic impedance at the eardrum. Invasive procedures to measure the sound pressure at the eardrum are usually elaborate or costly. In this work, we propose a numerical method to estimate the transfer impedance at the eardrum given only input impedance measurements at the ear canal entrance by using one-dimensional first-order finite elements and Nelder-Mead optimization algorithm. Estimations on the area function of the ear canal and the acoustic impedance at the eardrum are achieved. Results are validated through numerical simulations on ten different ear canal geometries and three different acoustic impedances at the eardrum using synthetically generated data from three-dimensional finite element simulations.Comment: 16 pages, 15 figure

Factors That Introduce Intrasubject Variability Into Ear-Canal Absorbance Measurements

Wideband immittance measures can be useful in analyzing acoustic sound flow through the ear and also have diagnostic potential for the identification of conductive hearing loss as well as causes of conductive hearing loss. To interpret individual measurements, the variability in test- retest data must be described and quantified. Contributors to variability in ear-canal absorbance-based measurements are described in this article. These include assumptions related to methodologies and issues related to the probe fit within the ear and potential acoustic leaks. Evidence suggests that variations in ear-canal cross-sectional area or measurement location are small relative to variability within a population. Data are shown to suggest that the determination of the Thévenin equivalent of the ER-10C probe introduces minimal variability and is independent of the foam ear tip itself. It is suggested that acoustic leaks in the coupling of the ear tip to the ear canal lead to substantial variations and that this issue needs further work in terms of potential criteria to identify an acoustic leak. In addition, test-retest data from the literature are reviewed

Estimation of Outer-Middle Ear Transmission using DPOAEs and Fractional-Order Modeling of Human Middle Ear

Our ability to hear depends primarily on sound waves traveling through the outer and middle ear toward the inner ear. Hence, the characteristics of the outer and middle ear affect sound transmission to/from the inner ear. The role of the middle and outer ear in sound transmission is particularly important for otoacoustic emissions (OAEs), which are sound signals generated in a healthy cochlea, and recorded by a sensitive microphone placed in the ear canal. OAEs are used to evaluate the health and function of the cochlea; however, they are also affected by outer and middle ear characteristics. To better assess cochlear health using OAEs, it is critical to quantify the impact of the outer and middle ear on sound transmission. The reported research introduces a noninvasive approach to estimate outer-middle ear transmission using distortion product otoacoustic emissions (DPOAEs). In addition, the role of the outer and middle ear on sound transmission was investigated by developing a physical/mathematical model, which employed fractional-order lumped elements to include the viscoelastic characteristics of biological tissues. Impedance estimations from wideband refectance measurements were used for parameter fitting of the model. The model was validated comparing its estimates of the outer-middle ear sound transmission with those given by DPOAEs. The outer-middle ear transmission by the model was defined as the sum of forward and reverse outer-middle ear transmissions. To estimate the reverse transmission by the model, the probe-microphone impedance was calculated through estimating the Thevenin-equivalent circuit of the probe-microphone. The Thevenin-equivalent circuit was calculated using measurements in a number of test cavities. Such modeling enhances our understanding of the roles of different parts of the outer and middle ear and how they work together to determine their function. In addition, the model would be potentially helpful in diagnosing pathologies of cochlear or middle ear origin

Measurement of middle-ear acoustic function in intact ears : application to size variations in the cat family

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 189-196).by Gregory T. Huang.Ph.D

Acoustic power flow into the ear and the auditory microstructure

An experimental technique to determine the acoustic power absorbed by the human ear at absolute threshold is described and applied to data recorded in adult subjects. A previously published method of electroacoustic probe calibration in terms of equivalent Thevenin source parameters is substantially ameliorated. Careful and detailed measurements of continuous tonal aural sound pressure (CTASP) are presented. Ear canal input impedance, reflectance and absolute power flow constituents are derived from CTASP data. Auditory microstructure, characterised by spectral periodicity, is observed and validated in CTASP, impedance, reflectance and power flow parameters at a 20 dB SPL stimulus level, but undetectable at 60 dB SPL. Periodicity in the ear canal acoustic parameters elicited at low stimulus levels is found to be commensurate with absolute threshold microstructure. An elementary analogue network model of the peripheral auditory system is formulated, enabling cochlear input impedance and reflectance to be inferred from ear canal acoustic parameters. At a 20 dB SPL stimulus level a non-zero cochlear reflectance is inferred, implying that energy propagates basally, as well as, apically. Microstructure amplitude in cochlear input impedance is shown to be 4 dB greater than that in ear canal input impedance, a consequence of decoupling of the probe from the tympanic membrane. A proportionality between transmittance and auditory sensitivity exists, implying that the ear couples more efficiently to the sound source, and consequently extracts proportionally more power, at peaks in sensitivity. However, the measured change in coupling is inadequate to wholly explain threshold microstructure. An explanation is offered by applying empirical data to a phenomenological model of power flow within the peripheral auditory system. It is argued that threshold microstructure arises predominately from a phasic interaction of the basalward and apical travelling waves effectively modifying the spatial distribution of energy within the cochlea

Simultaneous Measurement of Middle-Ear Input Impedance and Forward/Reverse Transmission in Cat

Reported here is a technique for measuring forward and reverse middle-ear transmission that exploits distortion-product otoacoustic emissions (DPOAEs) to drive the middle ear in reverse without opening the inner ear. The technique allows measurement of DPOAEs, middle-ear input impedance, and forward and reverse middle-ear transfer functions in the same animal. Intermodulation distortion in the cochlea generates a DPOAE at frequency 2f1-f 2 measurable in both ear-canal pressure and the velocity of the stapes. The forward transfer function is computed from stapes velocities and corresponding ear-canal pressures measured at the two primary frequencies; the reverse transfer function is computed from velocity and pressure measurements at the DPOAE frequency. Middle-ear input impedance is computed from ear-canal pressure measurements and the measured Thévenin equivalent of the sound-delivery system. The technique was applied to measure middle-ear characteristics in anesthetized cats with widely opened middle-ear cavities (0.2-10 kHz). Stapes velocity was measured at the incudo-stapedial joint. Results on five animals are reported and compared with a published middle-ear model. The measured forward transfer functions and input impedances generally agree with previous measurements, and all measurements agree qualitatively with model predictions. The reverse transfer function is shown to depend on the acoustic load in the ear canal, and the measurements are used to compute the round-trip middle-ear gain and delay. Finally, the measurements are used to estimate the parameters of a two-port transfer-matrix description of the cat middle ear

Using otoacoustic emissions to measure the transmission matrix of the middle-ear

Thesis (S.M.)--Harvard-MIT Division of Health Sciences and Technology, 2006.Includes bibliographical references (leaves 39-41).Here we describe an experimental method for measuring the acoustic transmission matrix of the middle-ear using otoacoustic emissions. The experiment builds on previous work that uses distortion product otoacoustic emissions (DPOAEs) as an intracochlear sound source to drive the middle-ear in reverse. This technique eliminates the complications introduced by needing to place an acoustic transducer inside the cochlea. Previous authors have shown how the complete 4x3 system response matrix, with its 12 unknowns, can be simplified to a 2x2 transmission matrix by de-coupling the middle-ear cavity and assuming the cochlear fluids are incompressible. This simplified description of middle-ear mechanics assumes that the input-output response at the tympanic membrane and stapes footplate is linear, one dimensional and time invariant. The technique allows for estimating the acoustic pressure and volume velocity at the tympanic membrane and the volume velocity of the stapes footplate, in both the forward and reverse direction, and under different boundary conditions at the stapes. The technique was applied to deeply anesthetized cats with widely opened middle-ear cavities over a frequency range of 200Hz to 10kHz. Results on three animals are reported and generally agree with previous data and a published middle-ear model.by Antonio John Miller.S.M