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PubMed1993

Sound preprocessing by ac and dc movements of cochlear outer hair cells.

In inner and outer hair cells, a sound event results mechano-electrically in a receptor potential from the hair cells by the functioning of apical and lateral K(+)-channels. However, after this point, the signal transfer is divided. Inner hair cells (IHC) release an unknown afferent transmitter. By contrast, outer hair cells (OHC) are proposed to produce mechanical ac and dc responses. In our model, the ac components of the sound signal, the carrier frequencies, determine the response of the OHC. Usually, they respond by ac and dc movements. The rapid ac movements of OHC, for which the underlying mechanism is unknown, may respond cycle-by-cycle to and interfere with the carrier frequency of the traveling wave. Near hearing threshold, they could drastically amplify the traveling wave thus contributing to the postulated cochlear amplifier. Active dc movements of the cytoskeleton of the cell body, as well as of the cuticular plate with the sensory hairs, are proposed to respond to millisecond changes of the sound stimulus over time. Such changes could be a modulation of the amplitude (AM), i.e., an increase or decrease of the sound pressure level (SPL), which is reflected in the envelope of the traveling wave. The active mechanical dc response of OHC to the amplitude (AM) and frequency modulation (FM) pattern is then expected to result in dc position changes of the reticular lamina (RL). These should control the operation point of the stereocilia, thus influencing their transfer function and sensitivity. In addition, experimental data suggest that there are modulations of the compliance of the organ of Corti (OC) and changes of its geometry. This dc modulation of micromechanical properties and geometry of the OC by active force generation of OHCs might contribute to automatic gain control, adaptation, TTS, as well as to the homeostasis of the basilar membrane location. In particular, the motile mechanism may protect the vulnerable cochlear partition against high sound pressure levels. Moreover, according to this model, changes of the sound signal with time are expected to be encoded in the actively produced dc movements of the RL. As the signal changes may carry important information (e.g., complex sound signal modulations such as formant transitions in speech), this is extracted and mechanically encoded by the proposed active dc mechanism. It cannot be excluded that the information-carrying dc signal is transferred to inner hair cells contributing to their adequate stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Cochlea↗

PubMed2002

Activation of tyrosine hydroxylase in the lateral efferent terminals by sound conditioning.

Preconditioning to sound is a well-documented strategy to provide protections against a subsequent acoustic trauma. In the present study, preconditioning (1.0 kHz tone at 81 dB sound pressure level (SPL) for 24 h) protected ABR thresholds by 17-28 dB from an acoustic trauma (2.7 kHz, 103 dB SPL, 30 min) that resulted in a temporary threshold shift. The protection afforded by sound conditioning was shown to be blocked by the administration of 6-hydroxydopamine which disrupts tyrosine hydroxylase in the nerve terminals of the lateral efferent fibers. Furthermore, tyrosine hydroxylase immunoreactivity was up-regulated both by sound conditioning alone, and by the combined treatment of sound conditioning and acoustic trauma. In contrast, acoustic trauma alone resulted in a reduction in tyrosine hydroxylase immunoreactivity compared to unexposed controls. These findings are the first demonstration that tyrosine hydroxylase in the lateral efferents are up-regulated during sound conditioning and suggests a role for the lateral efferent system in protecting against acoustic trauma by sound conditioning.

Adrenergic Agents↗

PubMed1991

Orthodontic treatment and temporomandibular joint sounds--a longitudinal study.

Temporomandibular joint sounds are often recognized as a clinical sign of temporomandibular disorders. The purpose of this study was to examine changes in the occurrence and resolution of these sounds in patients before and after orthodontic treatment with full fixed appliances. From a pool of 324 patients who came to a university postgraduate orthodontic clinic specifically for treatment of a malocclusion, 160 were examined before and after orthodontic treatment. When joint sounds were either reported or detected clinically, the patients underwent an audiovisual examination to more precisely and objectively record the occurrence and timing of the sound during mandibular opening and closing. No statistically significant difference could be found in the change in occurrence of joint sounds among patients treated with extraction and nonextraction treatment strategies. Overall, fewer patients had joint sounds at the end of the active stage of orthodontic treatment than before treatment. Also, fewer patients demonstrated reciprocal clicking after treatment than before treatment. Therefore it appeared that orthodontic treatment did not pose an increased risk for developing temporomandibular joint sounds irrespective of whether extraction or nonextraction treatment strategies were used. A progression of signs or symptoms to more serious problems was not apparent over the time period studied.

Adolescent↗

PubMed2003

Relation of jaw sounds and kinematics visualized and quantified using 3-D computer animation.

The management of jaw pain or temporomandibular disorders (TMD) has been controversial regarding temporomandibular joint (TMJ) sounds and their implication regarding TMD prognosis. 3-D computer animation was used to visualize and quantify the internal mechanics of natural mandibular motion synchronized with TMJ sounds. Mandibular movements of four TMD patients and two healthy subjects were recorded using CCD cameras and reflective markers. Sounds were recorded with electret microphones. Magnetic resonance imaging was used to create 3-D geometric models. Visualization of the internal anatomy, mandibular condyle and glenoid fossa, revealed that the condyle initially rotated within the fossa and then moved out of the fossa along, and well beyond, the articular eminence. Power in the opening sound recordings after the condyle moved out of the fossa was significantly greater than when the condyle was within the fossa (p<0.001). The louder opening sounds were often classified as TMJ clicks, implying that clicks occur after the condyle moves out of the fossa. The 3-D computer animation should help resolve the implication of TMJ sounds regarding TMD prognosis by providing visualization and quantization of the TMJ internal mechanics during sound production.

Adult↗

PubMed2003

Bowel sounds analysis: a novel noninvasive method for diagnosis of small-volume ascites.

Ascites is more difficult to detect when only a small quantity is present. The aim of this pilot study was to determine the optimal bowel sound characteristics in order to distinguish no ascites from small-volume ascites by advanced processing of bowel sound wave patterns. This analysis results in the definition of the normal range of bowel sound patterns, thus providing a novel, simple, and noninvasive way of determining on abnormal pattern, which may reflect presence of small volume ascites. Cirrhotic patients with radiologically proven small-volume ascites and a control group were subjected to bowel sound recordings. The latter were analyzed using a denoising wavelet transform-based filter and a higher-order crossings-based technique in a blinded fashion for linearly distinguishing the two classes. Scatter plots of third-order zero crossings reflect distinct changes seen in the denoised bowel sound pattern between patients and controls due to altered transmission path, providing a distinct separation of all cirrhotic patients with small ascites from controls (P < 0.0001). We conclude that the proposed bowel sounds analysis appears to provide new information regarding the changes of the bowel sound patterns due to the presence of small-volume ascites, potentially contributing towards a safe, effective, noninvasive, and easily implemented alternative method for the diagnosis of small volume ascites at the bedside.

Adult↗

PubMed1999

Responses of auditory-cortex neurons to structural features of natural sounds.

Sound-processing strategies that use the highly non-random structure of natural sounds may confer evolutionary advantage to many species. Auditory processing of natural sounds has been studied almost exclusively in the context of species-specific vocalizations, although these form only a small part of the acoustic biotope. To study the relationships between properties of natural soundscapes and neuronal processing mechanisms in the auditory system, we analysed sound from a range of different environments. Here we show that for many non-animal sounds and background mixtures of animal sounds, energy in different frequency bands is coherently modulated. Co-modulation of different frequency bands in background noise facilitates the detection of tones in noise by humans, a phenomenon known as co-modulation masking release (CMR). We show that co-modulation also improves the ability of auditory-cortex neurons to detect tones in noise, and we propose that this property of auditory neurons may underlie behavioural CMR. This correspondence may represent an adaptation of the auditory system for the use of an attribute of natural sounds to facilitate real-world processing tasks.

Animals↗

PubMed2005

Neural population coding of sound level adapts to stimulus statistics.

Mammals can hear sounds extending over a vast range of sound levels with remarkable accuracy. How auditory neurons code sound level over such a range is unclear; firing rates of individual neurons increase with sound level over only a very limited portion of the full range of hearing. We show that neurons in the auditory midbrain of the guinea pig adjust their responses to the mean, variance and more complex statistics of sound level distributions. We demonstrate that these adjustments improve the accuracy of the neural population code close to the region of most commonly occurring sound levels. This extends the range of sound levels that can be accurately encoded, fine-tuning hearing to the local acoustic environment.

Acoustic Stimulation↗

PubMed2000

Sound and the developing infant in the NICU: conclusions and recommendations for care.

OBJECTIVE: To present the conclusions and associated recommendations for care developed by the Physical and Developmental Environment of the High-Risk Infant Center, Study Group on Neonatal Intensive Care Unit (NICU) Sound, and the Expert Review Panel. STUDY DESIGN: A multidisciplinary group of clinicians and researchers reviewed the literature regarding the effect of sound on the fetus, newborn, and preterm infant and developed recommendations based on the best evidence. An Expert Review Panel reviewed the data and conclusions. RESULTS: The following recommendations are developed from the review of the literature and are clarified in the body of the article. (1) Women should avoid prolonged exposure to low-frequency sound levels (< 250 Hz) above 65 dB(A) during pregnancy. (2) Earphones or other devices for sound production should not be used directly attached to the pregnant woman's abdomen. (3) The voice of the mother during normal daily activities, along with the sounds produced by her body and those present in her usual surroundings, is sufficient for normal fetal auditory development. The fetus does not require supplemental stimulation. Programs to supplement the fetal auditory experience cannot be recommended. (4) Infant intensive care units should incorporate a system of regular noise assessment. (5) Sound limit recommendations are to maintain a nursery with an hourly Leq of 50 dB(A), an hourly L10 of 55 dB(A) and a 1-second Lmax of 70 dB(A), all A-weighted, slow response scale. (6) Infant intensive care units should develop and maintain a program of noise control and abatement in order to operate within the recommended permissible noise criteria. (7) Care practices must provide ample opportunity for the infant to hear parent voices live in interaction between parent and infant at the bedside. (8) Earphones and other devices attached to the infant's ears for sound transmission should not be used at any time. (9) There is little evidence to support the use of recorded music or speech in the environment of the high-risk infant. Audio recordings should not be used routinely or left unattended in the environment of the high-risk infant. CONCLUSION: The recommendations, if followed, should provide an environment that will protect sleep, support stable vital signs, improve speech intelligibility for the infant, and reduce potential adverse effects on auditory development.

Animals↗

PubMed2001

Implications of sound levels generated by otologic devices.

OBJECTIVE: Exposure to loud noise can result in sensorineural hearing loss. In otology, a wide variety of devices are used that have significant noise output, both to the operator and the patient. This study quantifies and compares the sound pressure levels (SPL) of a variety of otologic instruments. METHODS: Using a calibrated sound pressure level meter, the peak and impulse sound pressure levels of several otologic instruments were determined at 1 cm from their application to human temporal bones. Devices measured were an air-powered drill with a cutting burr, an electric micro-drill, and KTP, CO(2), and erbium lasers. RESULTS: Impulse sound pressure levels for the KTP laser, CO(2) laser, microdrill, air-powered drill and erbium laser were 67, 71, 90, 105, and 105 dBA, respectively. Peak sound pressure levels were 81, 89, 102, 118, and 132 dBA, respectively. CONCLUSIONS: Use of the KTP laser, CO(2) laser, and microdrill result in impulse levels of less than 100 dBA. Although the impulse levels of the erbium laser and the air-powered drill were equivalent, the peak sound pressure levels of the erbium laser were significantly higher. These high sound pressure levels may increase the chance for hearing loss. Like any tool, lasers and drills have benefits and risks. The results of this study demonstrate significant differences in SPLs of common otologic lasers and drills. Although noise-induced hearing loss is a function of both SPL and duration of exposure, surgeons should consider these differences when selecting and applying these tools, especially when used on or adjacent to the ossicular chain and stapes footplate.

Otolaryngology↗

PubMed2006

The influence of meaning on the perception of speech sounds.

As part of knowledge of language, an adult speaker possesses information on which sounds are used in the language and on the distribution of these sounds in a multidimensional acoustic space. However, a speaker must know not only the sound categories of his language but also the functional significance of these categories, in particular, which sound contrasts are relevant for storing words in memory and which sound contrasts are not. Using magnetoencephalographic brain recordings with speakers of Russian and Korean, we demonstrate that a speaker's perceptual space, as reflected in early auditory brain responses, is shaped not only by bottom-up analysis of the distribution of sounds in his language but also by more abstract analysis of the functional significance of those sounds.

Adolescent↗

PubMed2005

General discrete modelling of lung sound production in normal subjects.

Lung sound analysis is of a major importance in diagnostic malfunctions of the respiratory system. In normal subjects, it is known that these sounds are caused by the interaction of the respiratory flows with the bronchial tree structure. However, the detailed knowledge of the reasons for the spectral characteristics of such sounds remains to be elucidated. In this paper we propose a model for normal lung sound production based on a discretization of air flow in particle-like elements. Their transport with the involved interactions is implemented using a pseudo-molecular dynamics Monte Carlo procedure. General physical principles were considered for the interaction of these elements with the bronchial tree as well as a two-body interaction potential. The particle-tree interactions and the particle-particle interactions represent the flow-tree and the internal flow interactions, respectively. According to the model, sound is produced in each bronchus with the pitch frequency inversely proportional to its dimensions and with amplitude proportional to the intensity of the interaction, also a function of the bronchus dimensions. The lung sound is then the composition of the sounds produced in each bronchus. The model was successful in approximating the spectral characteristics reported by Gavriely et al (1981, 1995) as a direct consequence of the fractal properties of the bronchial tree and the considered internal fluid interactions. Thus, the reported high-frequency spectrum with its affine property as well as the low-frequency irregularity could be reproduced.

Air Movements↗

PubMed2005

Reception of environmental sounds through cochlear implants.

OBJECTIVE: The objective of this study was to measure the performance of persons with cochlear implants on a test of environmental-sound reception. DESIGN: The reception of environmental sounds was studied using a test employing closed sets of 10 sounds in each of four different settings (General Home, Kitchen, Office, and Outside). The participants in the study were 11 subjects with cochlear implants. Identification testing was conducted under each of the four closed sets of stimuli using a one-interval, 10-alternative, forced-choice procedure. The data were summarized in terms of overall percent correct identification scores and information transfer (IT) in bits. Confusion patterns were described using a hierarchical-clustering analysis. In addition, individual performance on the environmental-sound task was related to the ability to recognize isolated words through the cochlear implant alone. RESULTS: Levels of performance were similar across the four stimulus sets. Mean scores across subjects ranged from 45.3% correct (and IT of 1.5 bits) to 93.8% correct (and IT of 3.1 bits). Performance on the environmental-sound identification test was roughly related to NU-6 word recognition ability. Specifically, those subjects with word scores greater than 34% correct performed at levels of 80 to 94% on environmental-sound recognition, whereas subjects with word scores less than 34% had greater difficulty on the task. Results of the hierarchical clustering analysis, conducted on two groups of subjects (a high-performing [HP] group and a low-performing [LP] group), indicated that confusions were confined to three or four specific stimuli for the HP subjects and that larger clusters of confused stimuli were observed in the data of the LP group. Signals with distinct temporal-envelope characteristics were easily perceived by all subjects, and confused items tended to share similar overall durations and temporal envelopes. CONCLUSIONS: Temporal-envelope cues appear to play a large role in the identification of environmental sounds through cochlear implants. The finer distinctions made by the HP group compared with the LP group may be related to a better ability both to resolve temporal differences and to use gross spectral cues. These findings are qualitatively consistent with patterns of confusions observed in the reception of speech segments through cochlear implants.

Acoustic Stimulation↗

PubMed2004

Sound localization in bilateral users of MED-EL COMBI 40/40+ cochlear implants.

OBJECTIVE: The purpose of the study was to investigate sound localization with bilateral and unilateral cochlear implants. DESIGN: Sound localization tests were performed on 20 bilaterally implanted MED-EL COMBI 40/40+ users. All subjects were bilaterally implanted during adolescence or later. Sound localization was tested in the frontal horizontal plane by using 9 equally spaced loudspeakers and speech-shaped noise bursts at randomized levels. RESULTS: The group of subjects who were bilaterally deafened after 5 to 6 yr of age (18 subjects) showed a statistically significant improvement in sound localization when using both implants, compared with when using only one. The mean deviation between the presentation azimuth and the response azimuth was 16.6 degrees when using both implants, which was on average 37.1 degrees smaller than when using one implant only. When adjusted for the localization error that was constant across loudspeakers, the mean deviation was 15.9 degrees for bilateral implant use, representing an improvement of 30.1 degrees over unilateral implant use. Statistical analysis showed that in this group, performance measures were not correlated with subject details such as age at onset of deafness or duration of unilateral implant use. In contrast, subjects who were bilaterally deafened before 6 yr of age (2 subjects) did not show a benefit in sound localization from bilateral implants. CONCLUSIONS: Bilateral cochlear implants offer a substantial benefit in sound localization to late-deafened, late-implanted subjects. The very limited data from early-deafened subjects implanted at a later age could suggest that these subjects may not benefit in sound localization from bilateral cochlear implants. It is possible that early implantation for early deafened subjects might allow better acquisition of spatial hearing, thus leading to improved localization performance.

Adolescent↗

PubMed2001

When sound affects vision: effects of auditory grouping on visual motion perception.

Two identical visual targets moving across each other can be perceived either to bounce off or to stream through each other. A brief sound at the moment the targets coincide biases perception toward bouncing. We found that this bounce-inducing effect was attenuated when other identical sounds (auditory flankers) were presented 300 ms before and after the simultaneous sound. The attenuation occurred only when the simultaneous sound and auditory flankers had similar acoustic characteristics and the simultaneous sound was not salient. These results suggest that there is an aspect of auditory-grouping (saliency-assigning) processes that is context-sensitive and can be utilized by the visual system for solving ambiguity. Furthermore, control experiments revealed that such auditory context did not affect the perceptual qualities of the simultaneous sound. Because the attenuation effect is not manifest in the perception of acoustic characteristics of individual sound elements, we conclude that it is a genuine cross-modal effect.

Acoustic Stimulation↗

PubMed1995

Spatial and morphologic aspects of temporomandibular joints with sounds.

Various spatial and morphological aspects of the temporomandibular joint may be involved in the development of TMJ sounds. The present study examines their contribution to the prediction of sounds. A non-patient sample was studied using sensitive sound measurement and panoramic radiography. It was found that temporomandibular joint sounds are common in asymptomatic subjects showing substantial variation in several spatial and morphological parameters. An autonomous contribution of spatial relationships, asymmetries or morphology of bony structures to the prediction of joint sounds could not be detected. When unilateral sounds were present, they were more likely to be found on the side with the less steep condylar movement path. Joint imaging is not indicated in the detection of relationships between bony structures and their eventual asymmetries and joint sounds.

Auscultation↗

PubMed2005

Hierarchical processing of sound location and motion in the human brainstem and planum temporale.

Horizontal sound localization relies on the extraction of binaural acoustic cues by integration of the signals from the two ears at the level of the brainstem. The present experiment was aimed at detecting the sites of binaural integration in the human brainstem using functional magnetic resonance imaging and a binaural difference paradigm, in which the responses to binaural sounds were compared with the sum of the responses to the corresponding monaural sounds. The experiment also included a moving sound condition, which was contrasted against a spectrally and energetically matched stationary sound condition to assess which of the structures that are involved in general binaural processing are specifically specialized in motion processing. The binaural difference contrast revealed a substantial binaural response suppression in the inferior colliculus in the midbrain, the medial geniculate body in the thalamus and the primary auditory cortex. The effect appears to reflect an actual reduction of the underlying activity, probably brought about by binaural inhibition or refractoriness at the level of the superior olivary complex. Whereas all structures up to and including the primary auditory cortex were activated as strongly by the stationary as by the moving sounds, non-primary auditory fields in the planum temporale responded selectively to the moving sounds. These results suggest a hierarchical organization of auditory spatial processing in which the general analysis of binaural information begins as early as the brainstem, while the representation of dynamic binaural cues relies on non-primary auditory fields in the planum temporale.

Acoustic Stimulation↗

PubMed1968

Analysis of frequency-modulated and complex sounds by single auditory neurones of bats.

1. Single unit activity in the inferior colliculus of bats was studied in relation to the analysis of frequency-modulated (FM) and complex sounds. Complex sounds were composed of tone pulse I (pure or FM tone) delivered simultaneously with tone pulse II (pure or sometimes FM tone). It was assumed that in relevant complex sounds produced by animals, an important component (e.g. a formant in human speech) occurred at the best frequency (BF) of a given neurone. Tone pulse I represented such a component (called BF component). Tone pulse II was assumed to correspond to higher or lower components according to its relation to BF. Depending on characteristics of responses to tonal stimuli, collicular neurones were classified into five types: symmetrical, asymmetrical, FM-insensitive, FM-sensitive (or FM-specialized) and upper-threshold units.2. The symmetrical unit had a wide excitatory area and no inhibitory areas and it responded with equal thresholds to FM tone pulses sweeping in either directions. This type of neurone responded to all frequency modulations (e.g. transition in human speech) of the BF component, and the response was scarcely inhibited by other components.3. In the asymmetrical unit, the extent of frequency modulation of the BF component which could excite the neurone was limited by inhibitory areas on one or both sides of an excitatory area. Inhibitory areas on the lower frequency side tended to be larger than those on the high frequency side. The limitation was more severe for frequency sweeps toward the best frequency than for sweeps starting from it. The response to the BF component was inhibited by lower and/or higher components unless these were outside the inhibitory areas. In most of the asymmetrical units, lower components were more important than higher ones in determining whether the response to the BF component could occur.4. In the FM-insensitive unit with a narrow excitatory area, inhibitory areas on both sides of the excitatory area restricted the extent of frequency modulation of the BF components which could activate the neurone. Responses to frequency sweeps toward the best frequency were strongly limited by the inhibitory areas. When the lower and/or higher components were within the inhibitory areas, the response to the BF component was inhibited. This type of neurone responded to more restricted combinations of components than did the asymmetrical units.5. The FM-sensitive unit which had no excitatory area but a large inhibitory area responded only to FM components in a certain range. Evidence was obtained that not only the range and direction but rate and functional form of frequency sweep were important in determining the excitation of the neurone. Noise bursts with various band widths did not activate the neurones. Responses of the neurones were commonly inhibited by tones within an inhibitory area so wide as to involve even frequencies in the FM component which excited the neurone. Thus, the response of the FM-sensitive unit depended not only upon the characteristics of the FM component, but also on the frequencies of other components.6. The asymmetrical, FM-insensitive and FM-sensitive units required for their activation a certain structure in the complex sound. Some of the upper-threshold units did not respond to a sufficiently strong BF component and/or its frequency modulation. Furthermore, the response of the neurone to a weak BF component was inhibited by strong lower and/or higher components in a certain range. Some upper-threshold units also had asymmetrical or FM-sensitive characteristics. Those neurones appeared to be specialized for the analysis of sound structure not only in frequency, but in intensity.7. Although various types of behaviour of single neurones were found in the inferior colliculus, a strong tendency in the neural analysis of complex sound was the restriction of conditions under which single neurones were activated. Neurones at higher levels responded to more restricted sequences or sets of sound stimuli than did those at lower levels.

Action Potentials↗

PubMed2000

Acoustic impedances at the oval window, and sound pressure transformation of the middle ear in Norwegian cattle.

In 15 cadaver ears from Norwegian cattle, sound pressure transfer functions have been measured (1) for sound input to the tympanic membrane, (2) for sound input to the oval window with the footplate in place, but with the ossicular chain removed, and (3) for sound input to the oval window with also the footplate removed. The output pressure was measured in an enclosure cemented to the round window. The data allow calculation of equivalent sound pressures at the input positions, as well as the acoustic input impedances at the oval window with intact footplate, Z(sc), and with the footplate removed, Z(c). The difference Z(s)=Z(sc)-Z(c) is the acoustic impedance contribution of the footplate and annular ligament. Z(sc) is mainly determined by the stiffness of the annular ligament at low frequencies, and by the cochlear input impedance Z(c) at higher frequencies. Z(c) is predominately resistive, a minor reactive part at low frequencies is attributed to the stiffness of the round window membrane. Z(s) and Z(c) are equal in magnitude at about 0.4 kHz. Rather close RLC fits have been obtained for all the three impedances, Z(sc), Z(s), and Z(c). The fitted values for the resistive parts of Z(sc) and Z(c) are 62.9 and 58.2 acoustic Gomega, respectively. The relatively small difference, 4.7 Gomega, is attributed to the resistance of the annular ligament. The fitted resistance of Z(s) is somewhat larger, 8.6 Gomega, but is anyway of minor importance relative to the dynamic stiffness of the annular ligament. This stiffness depends on the static pressure difference across the footplate. Each of the averaged Z(sc) corresponds to minimum stiffness. The fitted acoustic compliance is 6.89 x 10(-15) m3/Pa. The acoustic inertance plays a minor role. It is attributed to the mass of the footplate and the co-vibrating liquid in the inner ear, and has a fitted value of 4.7 x 10(5) Pa s2/m3. A sound pressure at the eardrum is equivalent to a larger pressure at the footplate, about 16 dB larger at frequencies below 100 Hz, increasing to about 30 dB at 10 kHz. In the vestibulum at the inner side of the footplate, the sound pressure at 20 Hz is about 20 dB below the equivalent pressure at the outer side. The two pressures approach toward higher frequencies, and above 1 kHz they are nearly equal.

Acoustic Impedance Tests↗