Prediction of the Sound Pressure at the Ear Drum in Occluded Human Ears

Self Cite

In hearing aid fitting the sound pressure at the ear drum is a reference quantity, since all real ear characteristic values refer to it. Typically , the sound pressure at the ear drum is estimated by a model of an average ear canal (e. g. a coupler). Such a model cannot account for interindividual differences. Alternatively, there are methods to predict the acoustics of the individual ear canal. Some of these methods make use of the acoustic input impedance of the ear canal. In general, the accuracy of the measured impedance depends on the effort that will be made. Therefore, different methods of impedance measurements were investigated concerning accuracy and effort. The methods differ in the number of calibration measurements (and calibration parameters). They were compared on the basis of impedance measurements on different model ear canals. Measurements were done with an impedance probe consisting of a typical hearing aid receiver and a hearing aid microphone. The measurements were compared to measurements with a reference impedance probe and method. As a result, it was observed that with a single calibration measurement the maximum absolute error of the transfer impedance was smaller than 3 dB up to 8 kHz.

Section: Ear Canal Models Used For Evaluationsupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

A comparison of methods for measuring the acoustic input impedance of ear canals for hearing aid applications

Sankowsky-Rothe

Köhler

Blau

et al. 2013

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“…The most common approach includes parameterization of the external ear or the ear canal and solving the pressure at the eardrum with physics-based computational modeling. 3,15,16 Sound intensity, power flow, and the incident wave component of the sound pressure have also been used to estimate or describe the pressure at the eardrum. [17][18][19] The need for a technique that would enable direct measurement of both the pressure and the volume velocity at the ear canal entrance has been recognized at least by Hudde et al, 15 who realized that the optimum accuracy of the pressure-minima method could be obtained only through such measurements.…”

Section: A Binaural Reproduction and Hrtfsmentioning

confidence: 99%

“…In addition, the pressure at the eardrum is considered the reference quantity in audiometric testing and fitting of hearing aids. 3 Furthermore, if the HRTFs are measured at the eardrum, the fidelity of binaural reproduction with the HRTFs is not dependent on the type of headphones used. If the headphone transfer function (HpTF) used for headphone calibration in binaural reproduction is measured with an unblocked ear canal, the impedance match remains unchanged in the listening situation.…”

Section: Introductionmentioning

confidence: 99%

Estimating head-related transfer functions of human subjects from pressure–velocity measurements

Hiipakka

Kinnari

Pulkki

2012

Direct measurements of individual head-related transfer functions (HRTFs) with a probe microphone at the eardrum are unpleasant, risky, and unreliable and therefore have not been widely used. Instead, the HRTFs are commonly measured from the blocked ear canal entrance, which excludes the effects of the individual ear canals and eardrums. This paper presents a method that allows obtaining individually correct magnitude frequency responses of HRTFs at the eardrum from pressure-velocity (PU) measurements at the ear canal entrance with a miniature PU sensor. The HRTFs of 25 test subjects with nine directions of sound incidence were estimated using real anechoic measurements and an energy-based estimation method. To validate the approach, measurements were also conducted with probe microphones near the eardrums as well as at blocked ear canal entrances. Comparisons between the different methods show that the method presented is a valid and reliable technique for obtaining magnitude frequency responses of HRTFs. The HRTF filters designed using the PU measurements are also shown to yield more correct frequency responses at the eardrum than the filters designed using measurements from the blocked ear canal entrance.

“…Method M4 estimates the ear canal parameters using an optimized variant of the reflectance phase method [2,4,5]. Briefly, an ear canal model consisting of 32 lossy circular tube segments of equal length, but varying radius, is adapted to the reflectance measured at the inner face of the ear mold.…”

Section: Half T-section Ear Canal Model (M3)mentioning

confidence: 99%

A comparison of methods for estimating individual real-ear-to-coupler-differences in hearing aid fitting

Köhler

Sankowsky-Rothe

Blau

et al. 2013

Self Cite

The sound pressure at the ear drum is the reference quantity for almost all applications of sound delivery to the ear, especially in hearing aid fitting. Since hearing aids are typically calibrated using the so called 2cc-coupler, the link to the individual sound pressure at the ear drum is given by the real-ear-to-coupler-difference (RECD). Nowadays, averaged RECDs are used for hearing aid fitting, which do not account for inter-individual differences in ear canal acoustics. As a consequence, resulting coupling errors may reach 15 dB for frequencies up to 10 kHz. Alternatively, there are methods for estimating individual RECDs, based on acoustic impedance measurements at the inner face of the ear mold. These methods differ in effort (e.g. the complexity of the ear canal model and fitting algorithm) and accuracy. By using an integrated ear canal microphone, individual RECD estimation could be feasible in future hearing aid fitting. In this research, six different methods to predict individual RECDs were compared using simulations as well as real ear measurements with open and closed ear molds. As a result, it appeared that relatively simple cylindrical and conical ear canal models give the best compromise between effort and accuracy.