Measurement of non-linear distortions in the vibration of acoustic transducers and acoustically driven membranes (original) (raw)
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AIP Conference Proceedings, 2016
Laser Doppler Vibrometry is an intrinsic highly linear measurement technique which makes it a great tool to measure extremely small nonlinearities in the vibration response of a system. Although the measurement technique is highly linear, other components in the experimental setup may introduce nonlinearities. An important source of artificially introduced nonlinearities is the speaker, which generates the stimulus. In this work, two correction methods to remove the effects of stimulus nonlinearity are investigated. Both correction methods were found to give similar results but have different pros and cons. The aim of this work is to investigate the importance of the conical shape of the eardrum as a source of nonlinearity in hearing. We present measurements on flat and indented membranes. The data shows that the curved membrane exhibit slightly higher levels of nonlinearity compared to the flat membrane.
Distortion product otoacoustic emissions measured as vibration on the eardrum of human subjects
Proceedings of the National Academy of Sciences of the United States of America, 2007
It has previously not been possible to measure eardrum vibration of human subjects in the region of auditory threshold. It is proposed that such measurements should provide information about the status of the mechanical amplifier in the cochlea. It is this amplifier that is responsible for our extraordinary hearing sensitivity. Here, we present results from a laser Doppler vibrometer that we designed to noninvasively probe cochlear mechanics near auditory threshold. This device enables picometer-sized vibration measurements of the human eardrum in vivo. With this sensitivity, we found the eardrum frequency response to be linear down to at least a 20-dB sound pressure level (SPL). Nonlinear cochlear amplification was evaluated with the cubic distortion product of the otoacoustic emissions (DPOAEs) in response to sound stimulation with two tones. DPOAEs originate from mechanical nonlinearity in the cochlea. For stimulus frequencies, f1 and f2, with f2/f1 = 1.2 and f2 = 4-9.5 kHz, and ...
Acoustics
The ear is able to detect low-level acoustic signals by a highly specialized system including a parametric amplifier in the cochlea. This is verified by a numerical mechanical model of the cochlea, which reduces the three-dimensional (3D) system to a one-dimensional (1D) approach. A formerly developed mechanical model permits the consideration of the fluid and the orthotropic basilar membrane in a 1D fluid-structure coupled system. This model shows the characteristic frequency to place transformation of the traveling wave in the cochlea. The additional inclusion of time and space dependent stiffness of outer hair cells and the signal level dependent stiffness of the string enables parametric amplification of the input signal. Due to the nonlinear outer hair cell stiffness change, nonlinear distortions follow as a byproduct of the parametric amplification at low levels constituting the compressive nonlinearity. More distortions are generated by the saturating displacements of the str...
The Measurement System for Experimental Investigation of Middle Ear Mechanics
2011
This paper presents a measurement system for non-contact measurements of vibration parameters of the structural elements of the organ of hearing. It proposes an original methodology of in-vitro measurements of the human ear, round window membrane motions. It was found that the Scanning Laser Doppler Vibrometry (LDV) technique is a useful research tool in micro- and nanometer scales, not only for technical, but also for biological objects.
Evidence from Mössbauer experiments for nonlinear vibration in the cochlea
The Journal of the Acoustical Society of America, 1974
The Mfssbauer technique has been applied to the measurement of vibration of the basilar membrane in the squirrel monkey cochlea. Both steady-state and transient responses have been recorded in the 7-8-kHz locus of the cochlea. The steady-state response indicates that the basilar membrane vibrates nonlinearly for frequencies of stimulation near or greater than the characteristic frequency. The nonlinearity can be observed at the lowest levels of stimulation, 70-80 dB SPL, for which measurements could be made. The nonlinearity extends to lower frequencies and the basilar membrane transfer function tends to broaden as SPL is increased. Rapid postmortem changes occur in the cochlea: (1) the amplitude of the transfer ratio (basilar membrane/malleus) decreases 10-15 dB over a period of several hours with a downward shift of 1.5-3 kHz in the characteristic frequency of the basilar membrane at a given location; (2) the low-frequency slope of the transfer ratio settles to 6 dB/octave by 6 h after death; (3) the slope of the phase of the transfer function increases as the characteristic frequency decreases; (4) the basilar membrane vibrates linearly after death. The transient response was. studied using acoustic clicks of approximately 150-/x duration, presented in sequences of 100 000 to 400 000. The transient response has an early component which has a fast decay and a second component which has an extremely slow rate of decay and which displays nonlinear behavior. Preliminary results for the vibration of Reissner's membrane in the 13-kHz region of the cochlea are also reported. Subject Classification: 65.26. 10 kHz. In the frequency range around 10 kHz the MSssbauer technique allows measurement of amplitudes 40-60 dB lower than what is possible with light microscopic techniques as used by Be'kgsy. Measurements can thus be performed at sound-pressure levels of 70-100 dB SPL with the MSssbauer effect. Unfortunaiely, the MSssbauer technique has only a 15-20 dB dynamic range and the possibilities for measuring distortion products are limited. Most of the direct measurements indicate that the vibration amplitude of the cochlear partition is linear. B•k•sy (1960) found the vibration of Reissner's membrane in cochleas obtained from cadavers to be linear at all but noxious stimulus intensities. According to Johnstone and Taylor (1970) the motion of the basal portion of the guinea pig basilar membrane is linear when mea-588
Biophysics of the cochlea II: Stationary nonlinear phenomenology
The Journal of the Acoustical Society of America, 1996
Nonlinearities affecting cochlear mechanics produce appreciable compression in the basilar membrane ͑BM͒ input/output ͑I/O͒ functions at the characteristic frequency for sound-pressure levels ͑SPLs͒ as low as 20 dB ͑re: 20 Pa͒. This is thought to depend upon saturation of the outer hair cell ͑OHC͒ mechanoelectrical transducer ͑MET͒. This hypothesis was tested by solving a nonlinear integrodifferential equation that describes the BM vibration in an active cochlea. The equation extends a previously developed linear approach ͓Mammano and Nobili, J. Acoust. Soc. Am. 93, 3320-3332 ͑1993͔͒, here modified to include saturating MET, with a few corrections mainly concerning tectorial membrane resonance and OHC coupling to the BM. Stationary solutions were computed by iteration in the frequency domain for a wide range of input SPLs, generating BM I/O functions, frequency response envelopes, and two-tone distortion products. Traveling-wave amplitude envelopes were also computed for a fixed suppressor and several suppressed tones in order to evidence the phenomenon of two-tone suppression ͑frequency masking͒ at the mechanical level. All results accord nicely with experimental data.
Study of the Transient Response of Tympanic Membranes Under Acoustic Excitation
Conference Proceedings of the Society for Experimental Mechanics Series, 2013
Characterization of the transient response of the human Tympanic Membrane (TM) subjected to impulse acoustic excitation is important in order to further understand the mechanics of hearing. In this paper, we present results of our initial investigations of the transient response of an artificial fully-constrained circular membrane as a simplified model of the TM. Two different optical methods used in our investigations are Laser Doppler Vibrometery (LDV) and Pulsed Double-Exposure Digital Holography (PDEDH) for single-point and full-field-of-view measurements of displacements, respectively. Applying Hilbert Transformation methods to the measured displacements allows determination of the transient characteristics of the membrane, including damping ratios and time constants, which are also computed and compared with corresponding FEM models. We expect to use this method in the investigation of the transient response of TM of specific species.
Traitement du Signal, 2019
X-parameters, a powerful solution to the simulation of nonlinear microwave components, can be used for other wave systems with distributed parameters. This paper introduces Xparameters to the acoustic field to deal with highly nonlinear large signals and boundary conditions. Firstly, an elastic membrane was selected to serve as the nonlinear boundary. Then, the equivalent electronic lumped model of the elastic membrane was established based on its nonlinear differential equation (NDE). The X-parameters of the model were determined by poly-harmonic distortion modelling. Then, an electrical analogy of the nonlinear system was established by two port method. The simulation and experimental results show that the properties of the elastic membrane were characterized well by the X-parameters.
Efferent Insights into Cochlear Mechanics
AIP Conference Proceedings, 2011
Medial olivocochlear efferent (MOCE) effects on tone-evoked basilar membrane (BM) vibrations are analyzed in terms of the vector differences between BM responses with and without MOCE stimulation. The technique is sensitive to rapid (i.e., "fast", τ ≤ 100 ms) changes in both the amplitude and the phase of the BM responses, and reveals MOCE effects over much wider frequency and intensity ranges (for a given BM location) than previously envisioned. The findings confirm and extend previous suggestions that MOCE effects are brought about by at least two different, outerhair-cell based mechanisms. The effects on BM responses to characteristic frequency (CF) tones are consistent with suggestions that the MOCEs affect both the stiffness and the damping of the cochlear partition (damping effects dominating at low levels, and stiffness effects dominating at high levels). The analyses also indicate that MOCE activity can enhance, rather than inhibit, BM responses to low frequency tones (well below CF)-albeit by miniscule amounts. If one assumes that all of the mechanical effects of MOCE activation are brought about via gain changes in a single "cochlear amplifier" [4], these results seem to reveal that this amplifier exhibits a frequencydependent transition from negative feedback (below CF) to positive feedback (near CF). This scenario is reminiscent of the type of amplification proposed by Mountain et al. a long, long time ago [9].