The Journal of the Acoustical Society of America, 2013
ABSTRACT Preventing occupational hearing damage requires close monitoring of workers' hea... more ABSTRACT Preventing occupational hearing damage requires close monitoring of workers' hearing. Implementing Distortion Product Otoacoustic Emissions (DPOAEs) in-field is a sensitive and feasible approach provided that a combination of minimal measuring time and infrequent false-positives-i.e., cases where elevated background compromises DPOAEs-is found. This paper investigates how measurement time can be reduced by carefully selecting the tested frequency span and resolution, and how false-positives are minimized by comparing DPOAEs acquired in noise with DPOAEs previously obtained in optimal test conditions. To test this, DPOAEs have been registered with a 1/8-octave band resolution from 841 Hz to 8 kHz for 60 subjects, in quiet conditions and in white noise levels ranging from 54 dB(A) to 90 dB(A). Measurement accuracy is confronted to decrease the measurement time as a function of frequency resolution and range. Diagnostic importance and sensitivity to background noise is addressed for different frequency regions. Within-subject variation of DPOAEs in noisy conditions is assessed both between different noise conditions and between subsequent probe placement. Obtained test-retest statistics quantify normal variability and allow within normal working routines to select for further investigation persons with DPOAEs falling outside this range.
The Journal of the Acoustical Society of America, 2008
The use of in situ measurements of hearing protectors&amp... more The use of in situ measurements of hearing protectors' (HPD's) attenuation following the microphone in real ear (MIRE) protocol is increasing. The attenuation is hereby calculated from the difference in sound levels outside the ear and inside the ear canal behind the HPD. Custom-made earplugs have been designed with an inner bore that allows inserting a miniature microphone. A thorough understanding of the difference, henceforth called transfer function, between the sound pressure of interest at the eardrum and the one measured at the inner bore of the HPD is indispensable for optimizing the MIRE technique and extending its field of application. This issue was addressed by measurements on a head-and-torso-simulator and finite difference time domain numerical simulations of the outer ear canal occluded by an earplug. Both approaches are in good agreement and reveal a clear distinction between the sound pressure at the MIRE microphone and at eardrum, but the measured transfer functions appear to be stable and reproducible. Moreover, the most striking features of the transfer functions can be traced down to the geometrical and morphological characteristics of the earplug and ear canal.
This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a ... more This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a passive non-linear earplug or an active level-dependent earmuff was worn. Since none of the standardized attenuation measurement techniques, REAT (real ear at threshold), ATF (acoustic test fixture), or MIRE (microphone in real ear), is designed to test both types in real-wearing condition, OAEs, suitable for detecting subtle changes in the functional integrity of the cochlear outer hair cells, are used. First, DPOAEs (distortion product) and TEOAEs (transiently evoked) of 24 subjects were compared before, immediately after gunfire practice, and after one hour of non-exposure. Secondly, both types of OAEs were evaluated in 31 subjects before and after exposure during a five-day military practice. Significant differences existed between the ears in most cases; the emissions from the right ear had a tendency to be more robust. There were no significant changes in OAEs either before and after exposure, or in the second experiment over multiple days. These findings suggest that the HPDs are able to prevent cochlear damage.
Age-related anatomical and morphologic vestibular deterioration has already been elaborated. Demo... more Age-related anatomical and morphologic vestibular deterioration has already been elaborated. Demonstrating a corresponding degradation in physiologic function, however, entails a much higher challenge. The objective of this study was to investigate age-related changes using rotational tests, caloric tests, and the vestibular-evoked myogenic potentials (VEMP) test. Eighty healthy human subjects (38 men and 42 women) ranging in age from 18 to 80 yrs participated in this study and were subjected to an extensive vestibular test battery. Function tests included sinusoidal harmonic acceleration tests, a pseudorandom rotation test, velocity step tests, a caloric test, and a VEMP test. No significant age trends were noted for the sinusoidal harmonic acceleration test and velocity step tests response parameters, in contrast to subtle decreasing gain values with advancing age for the pseudorandom rotation test. Increasing slow-component velocity values were measured with the caloric test, whereas the frequency parameter showed no relevant age changes. The largest age trends were detected with the VEMP, with decreasing amplitudes, increasing thresholds, and decreasing N1 latencies. All asymmetry parameters remained stable across the different age categories. Only subtle age changes could be demonstrated with the rotational and caloric tests, in contrast to more pronounced age trends with the VEMP.
ABSTRACT The performance of hearing protectors can be assessed in situ by measuring the sound pre... more ABSTRACT The performance of hearing protectors can be assessed in situ by measuring the sound pressure inside the ear canal following the Microphone In Real Ear (MIRE) protocol. Thus a custom-made earplug has been designed with an inner bore, allowing the insertion of the MIRE measurement microphone. However, the actual exposure level can only be accurately predicted if the relationship, henceforth called transfer function, between the sound level at the microphone and at the eardrum is known. Previous research has revealed that the transfer function can be precisely approximated with an individualized FDTD model, but a simplified method is needed for practical implementation due to the time-consuming nature of this numerical technique. In this matter, a one-dimensional analytical model appears inadequate, hence an approximation to the detailed FDTD model based on digital filter design is proposed instead. Two different approaches have been applied to estimate the individualized filter coefficients: multiple linear regression and Multivariate Orthonormal Vector Fitting (MOVE). In general, both methods can predict an individual's transfer function quite accurately if the length of the earplug's inner bore and the length of the residual part of the ear canal behind the protector are known. However, MOVE seems more reliable for ears with a longer residual part.
ABSTRACT This paper investigates the relationship between wind turbine noise annoyance, exposure ... more ABSTRACT This paper investigates the relationship between wind turbine noise annoyance, exposure indicators, operational characteristics and environmental variables. A six-month field experiment at an industrial site near a residential area includes regular on-line annoyance reports, continuous 1/3-octave band noise level registrations, periodic sound recordings, data on electricity production per minute and meteorological observations. Here the risk of high annoyance does not only depend on the angular blade velocity, but also on the wind turbines' nacelle position relative to the location of the dwellings, i.e. the wind direction. This directivity effect can be captured when noise parameters such as the background noise level caused by other sources and a so-called fluctuation-indicator are introduced, the latter calculated from the 1/3-octave band spectra to quantify the periodic part of wind turbine noise. In addition, the calculated turbine's specific emission levels are closely related to the angular blade velocity, and an important parameter to predict the risk of high annoyance. Finally, these results suggest that operational restrictions based on wind direction together with the angular blade velocity might help to reduce noise annoyance while preserving cost-effectiveness.
The Journal of the Acoustical Society of America, 2013
ABSTRACT Preventing occupational hearing damage requires close monitoring of workers' hea... more ABSTRACT Preventing occupational hearing damage requires close monitoring of workers' hearing. Implementing Distortion Product Otoacoustic Emissions (DPOAEs) in-field is a sensitive and feasible approach provided that a combination of minimal measuring time and infrequent false-positives-i.e., cases where elevated background compromises DPOAEs-is found. This paper investigates how measurement time can be reduced by carefully selecting the tested frequency span and resolution, and how false-positives are minimized by comparing DPOAEs acquired in noise with DPOAEs previously obtained in optimal test conditions. To test this, DPOAEs have been registered with a 1/8-octave band resolution from 841 Hz to 8 kHz for 60 subjects, in quiet conditions and in white noise levels ranging from 54 dB(A) to 90 dB(A). Measurement accuracy is confronted to decrease the measurement time as a function of frequency resolution and range. Diagnostic importance and sensitivity to background noise is addressed for different frequency regions. Within-subject variation of DPOAEs in noisy conditions is assessed both between different noise conditions and between subsequent probe placement. Obtained test-retest statistics quantify normal variability and allow within normal working routines to select for further investigation persons with DPOAEs falling outside this range.
The Journal of the Acoustical Society of America, 2008
The use of in situ measurements of hearing protectors&amp... more The use of in situ measurements of hearing protectors' (HPD's) attenuation following the microphone in real ear (MIRE) protocol is increasing. The attenuation is hereby calculated from the difference in sound levels outside the ear and inside the ear canal behind the HPD. Custom-made earplugs have been designed with an inner bore that allows inserting a miniature microphone. A thorough understanding of the difference, henceforth called transfer function, between the sound pressure of interest at the eardrum and the one measured at the inner bore of the HPD is indispensable for optimizing the MIRE technique and extending its field of application. This issue was addressed by measurements on a head-and-torso-simulator and finite difference time domain numerical simulations of the outer ear canal occluded by an earplug. Both approaches are in good agreement and reveal a clear distinction between the sound pressure at the MIRE microphone and at eardrum, but the measured transfer functions appear to be stable and reproducible. Moreover, the most striking features of the transfer functions can be traced down to the geometrical and morphological characteristics of the earplug and ear canal.
This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a ... more This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a passive non-linear earplug or an active level-dependent earmuff was worn. Since none of the standardized attenuation measurement techniques, REAT (real ear at threshold), ATF (acoustic test fixture), or MIRE (microphone in real ear), is designed to test both types in real-wearing condition, OAEs, suitable for detecting subtle changes in the functional integrity of the cochlear outer hair cells, are used. First, DPOAEs (distortion product) and TEOAEs (transiently evoked) of 24 subjects were compared before, immediately after gunfire practice, and after one hour of non-exposure. Secondly, both types of OAEs were evaluated in 31 subjects before and after exposure during a five-day military practice. Significant differences existed between the ears in most cases; the emissions from the right ear had a tendency to be more robust. There were no significant changes in OAEs either before and after exposure, or in the second experiment over multiple days. These findings suggest that the HPDs are able to prevent cochlear damage.
Age-related anatomical and morphologic vestibular deterioration has already been elaborated. Demo... more Age-related anatomical and morphologic vestibular deterioration has already been elaborated. Demonstrating a corresponding degradation in physiologic function, however, entails a much higher challenge. The objective of this study was to investigate age-related changes using rotational tests, caloric tests, and the vestibular-evoked myogenic potentials (VEMP) test. Eighty healthy human subjects (38 men and 42 women) ranging in age from 18 to 80 yrs participated in this study and were subjected to an extensive vestibular test battery. Function tests included sinusoidal harmonic acceleration tests, a pseudorandom rotation test, velocity step tests, a caloric test, and a VEMP test. No significant age trends were noted for the sinusoidal harmonic acceleration test and velocity step tests response parameters, in contrast to subtle decreasing gain values with advancing age for the pseudorandom rotation test. Increasing slow-component velocity values were measured with the caloric test, whereas the frequency parameter showed no relevant age changes. The largest age trends were detected with the VEMP, with decreasing amplitudes, increasing thresholds, and decreasing N1 latencies. All asymmetry parameters remained stable across the different age categories. Only subtle age changes could be demonstrated with the rotational and caloric tests, in contrast to more pronounced age trends with the VEMP.
ABSTRACT The performance of hearing protectors can be assessed in situ by measuring the sound pre... more ABSTRACT The performance of hearing protectors can be assessed in situ by measuring the sound pressure inside the ear canal following the Microphone In Real Ear (MIRE) protocol. Thus a custom-made earplug has been designed with an inner bore, allowing the insertion of the MIRE measurement microphone. However, the actual exposure level can only be accurately predicted if the relationship, henceforth called transfer function, between the sound level at the microphone and at the eardrum is known. Previous research has revealed that the transfer function can be precisely approximated with an individualized FDTD model, but a simplified method is needed for practical implementation due to the time-consuming nature of this numerical technique. In this matter, a one-dimensional analytical model appears inadequate, hence an approximation to the detailed FDTD model based on digital filter design is proposed instead. Two different approaches have been applied to estimate the individualized filter coefficients: multiple linear regression and Multivariate Orthonormal Vector Fitting (MOVE). In general, both methods can predict an individual's transfer function quite accurately if the length of the earplug's inner bore and the length of the residual part of the ear canal behind the protector are known. However, MOVE seems more reliable for ears with a longer residual part.
ABSTRACT This paper investigates the relationship between wind turbine noise annoyance, exposure ... more ABSTRACT This paper investigates the relationship between wind turbine noise annoyance, exposure indicators, operational characteristics and environmental variables. A six-month field experiment at an industrial site near a residential area includes regular on-line annoyance reports, continuous 1/3-octave band noise level registrations, periodic sound recordings, data on electricity production per minute and meteorological observations. Here the risk of high annoyance does not only depend on the angular blade velocity, but also on the wind turbines' nacelle position relative to the location of the dwellings, i.e. the wind direction. This directivity effect can be captured when noise parameters such as the background noise level caused by other sources and a so-called fluctuation-indicator are introduced, the latter calculated from the 1/3-octave band spectra to quantify the periodic part of wind turbine noise. In addition, the calculated turbine's specific emission levels are closely related to the angular blade velocity, and an important parameter to predict the risk of high annoyance. Finally, these results suggest that operational restrictions based on wind direction together with the angular blade velocity might help to reduce noise annoyance while preserving cost-effectiveness.
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