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PubMed2000

In situ estimation of sediment sound speed and critical angle

Understanding the basic physics of sound penetration into ocean sediments is essential for the design of sonar systems that can detect, localize, classify, and identify buried objects. In this regard the sound speed of the sediment is a crucial parameter as the ratio of sound speed at the water-sediment interface determines the critical angle. Sediment sound speed is typically measured from core samples using high frequency (100's of kHz) pulsed travel time measurements. Earlier experimental work on subcritical penetration into sandy sediments has suggested that the effective sound speed in the 2-20 kHz range is significantly lower than the core measurement results. Simulations using Biot theory for propagation in porous media confirmed that sandy sediments may be highly dispersive in the range 1-100 kHz for the type of sand in which the experiments were performed. Here it is shown that a direct and robust estimate of the critical angle, and therefore the sediment sound speed, at the lower frequencies can be achieved by analyzing the grazing angle dependence of the phase delays observed on a buried array. A parametric source with secondary frequencies in the 2-16 kHz range was directed toward a sandy bottom similar to the one investigated in the earlier study. An array of 14 hydrophones was used to measure penetrated field. The critical angle was estimated by analyzing the variations of signal arrival times versus frequency, burial depth, and grazing angle. Matching the results with classical transmission theory yielded a sound speed estimate in the sand of 1626 m/s in the frequency range 2-5 kHz, again significantly lower the 1720 m/s estimated from the cores at 200 kHz. However, as described here, this dispersion is consistent with the predictions of the Biot theory for this type of sand.

Journal Article↗

PubMed2002

A linearized Eulerian sound propagation model for studies of complex meteorological effects.

Outdoor sound propagation is significantly affected by the topography (including ground characteristics) and the state of the atmosphere. The atmosphere on its part is also influenced by the topography. A sound propagation model and a flow model based on a numerical integration of the linearized Euler equations have been developed to take these interactions into account. The output of the flow model enables the calculation of the sound propagation in a three-dimensionally inhomogeneous atmosphere. Rigid, partly reflective, or fully absorptive ground can be considered. The linearized Eulerian (LE) sound propagation model has been validated by means of four different scenarios. Calculations of sound fields above rigid and grass-covered ground including a homogeneous atmosphere deviate from analytic solutions by < or = 1 dB in most parts of the computed domain. Calculations of sound propagation including wind and temperature gradients above rigid ground agree well with measured scale model data. Calculations of sound propagation over a screen including ground of finite impedance show little deviations to measured scale model data which are probably caused by an insufficient representation of the complex ground impedance. Further calculations included the effect of wind on shading by a screen. The results agree well with the measured scale model data.

Journal Article↗

PubMed2002

Computational aeroacoustics of phonation, part I: Computational methods and sound generation mechanisms.

The aerodynamic generation of sound during phonation was studied using direct numerical simulations of the airflow and the sound field in a rigid pipe with a modulated orifice. Forced oscillations with an imposed wall motion were considered, neglecting fluid-structure interactions. The compressible, two-dimensional, axisymmetric form of the Navier-Stokes equations were numerically integrated using highly accurate finite difference methods. A moving grid was used to model the effects of the moving walls. The geometry and flow conditions were selected to approximate the flow within an idealized human glottis and vocal tract during phonation. Direct simulations of the flow and farfield sound were performed for several wall motion programs, and flow conditions. An acoustic analogy based on the Ffowcs Williams-Hawkings equation was then used to decompose the acoustic source into its monopole, dipole, and quadrupole contributions for analysis. The predictions of the farfield acoustic pressure using the acoustic analogy were in excellent agreement with results from the direct numerical simulations. It was found that the dominant sound production mechanism was a dipole induced by the net force exerted by the surfaces of the glottis walls on the fluid along the direction of sound wave propagation. A monopole mechanism, specifically sound from the volume of fluid displaced by the wall motion, was found to be comparatively weak at the frequency considered (125 Hz). The orifice geometry was found to have only a weak influence on the amplitude of the radiated sound.

Acoustics↗

PubMed2004

Coherence function and mean field of plane and spherical sound waves propagating through inhomogeneous anisotropic turbulence.

Inhomogeneity and anisotropy are intrinsic characteristics of daytime and nighttime atmospheric turbulence. For example, turbulent eddies are often stretched in the direction of the mean wind, and the turbulence statistics depends on the height above the ground. Recent studies have shown that the log-amplitude and phase fluctuations of plane and spherical sound waves are significantly affected by turbulence inhomogeneity and anisotropy. The present paper is devoted to studies of the mean sound field and the coherence functions of plane and spherical sound waves propagating through inhomogeneous anisotropic turbulence with temperature and velocity fluctuations. These statistical moments of a sound field are important in many practical applications, e.g., for source detection, ranging, and recognition. Formulas are derived for the mean sound field and coherence function of initially arbitrary waveform. Using the latter formula, we also obtained formulas for the coherence functions of plane and spherical sound waves. All these formulas coincide with those known in the literature for two limiting cases: homogeneous isotropic turbulence with temperature and wind velocity fluctuations, and inhomogeneous anisotropic turbulence with temperature fluctuations only. Using the formulas obtained, we have numerically shown that turbulence inhomogeneity significantly affects the coherence functions of plane and spherical sound waves.

Journal Article↗

PubMed2005

Aeroacoustic production of low-frequency unvoiced speech sounds.

A theoretical approach to describing unvoiced speech sound production is outlined using the essentials of aerodynamics and aeroacoustics. The focus is on the character and role of nonacoustic air motion in the vocal tract. An idealized picture of speech sound production is presented showing that speech sound production involves the dynamics of a jet flow, characterized by vorticity. A formal expression is developed for the sound production by unsteady airflow in terms of jet vorticity and vocal-tract shape, and a scaling law for the aeroacoustic source power is derived. The generic features of internal jet flows such as those exhibited in speech sound production are discussed, particularly in terms of the vorticity field, and the relevant scales of motion are identified. An approximate description of a jet as a train of vortex rings, useful for sound-field prediction, is described using the scales both of motion and of vocal-tract geometry. It is shown that the aeroacoustic source may be expressed as the convolution of (1) the acoustic source time series due to a single vortex ring with (2) a function describing the arrival of vortex rings in the source region. It is shown that, in general, the characteristics of the aeroacoustic source are determined not only by the strength, spatial distribution, and convection speed of the jet vorticity field, but also the shape of the vocal tract through which the jet flow passes. For turbulent jets, such as those which occur in unvoiced sound production, however, vocal-tract shape is the dominant factor in determining the spectral content of the source.

Acoustics↗

PubMed2006

Sounds from an oil production island in the Beaufort Sea in summer: characteristics and contribution of vessels.

The objective of this study was to determine the levels, characteristics, and range dependence of underwater and in-air sounds produced during the open-water seasons of 2000-2003 by the Northstar oil development, located in nearshore waters of the Alaskan Beaufort Sea. Specifically, sounds originating at the island itself (from construction, drilling, and oil production activities) were compared with sounds produced by vessels performing island support. Sounds were obtained with boat-based recordings (at distances up to 37 km from Northstar), a cabled hydrophone (distance approximately 450 m), and with autonomous seafloor recorders (distance approximately 22 km). Vessels (crew boat, tugs, self-propelled barges) were the main contributors to the underwater sound field and were often detectable underwater as much as approximately 30 km offshore. Without vessels, broadband island sounds reached background values at 2-4 km. Island sound levels showed more variation (lower min, higher max) during construction than during drilling and production. In-air broadband measurements were not affected by the presence of vessels and reached background values 1-4 km from Northstar. However, one airborne tone (81 Hz) believed to originate at Northstar was still detectable in the spectrum 37 km away.

Journal Article↗

PubMed1987

Central to peripheral sound propagation in excised lung.

The time it takes audible sound to travel from the trachea to the pleura in five intact, excised horse lungs and one dog lung inflated with several gases was measured. Regression estimates of sound speed at total lung capacity (TLC) using straight line distance from the carina to the pleura are: helium, 775 +/- 60.5 m/s (means +/- 95% confidence limits); air, 282 +/- 23.5; carbon dioxide, 219 +/- 25.5; sulfur hexafluoride, 142 +/- 43.5. With the exception of sulfur hexafluoride, these speeds are 15%-20% less than the free-field speed of sound in each gas. Total airway length did not predict time delay any better or worse than straight line distance, but the high correlation between these two predictors (r = 0.94) prevents showing either to be the more predictive. In one lung, airway length was partitioned according to airway diameter. A regression using partitioned airway lengths significantly improved time delay prediction (p less than 0.001) over an unpartitioned model. Sound speed in the trachea equals free-field sound speed. Sound speed in air-filled airways 1 to 25 mm in diameter equals 268 +/- 44 m/s. We conclude that the first sound to reach the surface travels in the airways for at least 90% of the distance, spending at least 87% of the total travel time there.

Acoustics↗

PubMed1980

Sound recognition in relation to aural language comprehension in aphasic patients.

This study was undertaken to determine whether some aphasic defects in aural language comprehension might be a reflection of cognitive impairment which also affects the recognition of meaningful, non-verbal sounds. Defects in sound recognition were consistently associated with aural comprehension defects of at least comparable severity and the majority of aphasics with impaired aural comprehension failed sound recognition. Although some aphasics with impaired aural comprehension performed normally in sound recognition, their language comprehension impairments were not of lesser severity than those shown by aphasics failing sound recognition. The relationship between sound recognition and reading comprehension was different in nature from that between sound recognition and aural comprehension.

Adult↗

PubMed1999

Sound lateralisation in patients with left or right cerebral hemispheric lesions: relation with unilateral visuospatial neglect.

OBJECTIVES: To localise the brain lesion that causes disturbances of sound lateralisation and to examine the correlation between such deficit and unilateral visuospatial neglect. METHOD: There were 29 patients with right brain damage, 15 patients with left brain damage, and 22 healthy controls, who had normal auditory and binaural thresholds. A device was used that delivered sound to the left and right ears with an interaural time difference using headphones. The amplitude (an index of ability to detect sound image shifts from the centre) and midpoint (an index of deviation of the interaural time difference range perceived as the centre) parameters of interaural time difference were analysed in each subject using 10 consecutive stable saw toothed waves. RESULTS: The amplitude of interaural time difference was significantly higher in patients with right brain damage than in controls. The midpoint of the interaural time difference was significantly more deviated in patients with right brain damage than in those with left brain damage and controls (p<0. 05). Patients with right brain damage with lesions affecting both the parietal lobe and auditory pathway showed a significantly higher amplitude and deviated midpoint than the controls, whereas right brain damage with involvement of only the parietal lobe showed a midpoint significantly deviated from the controls (p<0.05). Abnormal sound lateralisation correlated with unilateral visuospatial neglect (p<0.05). CONCLUSIONS: The right parietal lobe plays an important part in sound lateralisation. Sound lateralisation is also influenced by lesions of the right auditory pathway, although the effect of such lesions is less than that of the right parietal lobe. Disturbances of sound lateralisation correlate with unilateral visuospatial neglect.

Analysis of Variance↗

PubMed1979

Response of nonhuman animals to speech and to species-specific sounds.

Three questions relate to how nonhuman species respond to speech and species-specific sounds: (1) Do nonhuman species perceive human speech in a human-like fashion? (2) How do nonhuman species perceive their own vocalizatios? and (3) How does human perception of animal sounds differ from the animals' perception of those sounds? Four methodologies are available for studying an animal's perception of sounds: (1) discriminative conditioning; (2) habituation-dishabituation; (3) playbacks in captivity; and (4) playbacks in situ. Each of these techniques has a different degree of ecological validity and has different intrinsic biases toward the conclusions one might draw. Experiments using these methodologies for each of the three questions are reviewed and the methodological problems of each are discussed. A two-stage model of perceiving species-specific sounds is presented which accounts for both categorical perception of sounds and within category discrimination of sounds.

Animal Communication↗

PubMed1980

Sound stimulation and its effects on the pituitary-adrenocortical function and brain catecholamines in rats.

The purpose of the present study was to investigate in rats, the effects of sound stimulation upon both the pituitary-adrenal activity (evaluated by the levels of serum corticosterone (B)) and brain dopamine (DA) and noradrenaline (NA). Serum B in rats placed inside the experimental chamber without any sound stimulation was increased and brain DA decreased. For this reason, prior to any sound application, animals were kept in the experimental chamber for 115--120 min, when values had returned to basal levels. The results obtained on the effects of sound frequencies between 500 and 4,000 cps indicated a greater response in the rat pituitary-adrenal system to the lowest frequency (500 cps) we studied. Adrenal cortex hyperactivity occurred in the initial stage of daily repeated 500 cps sound stimulation. During extended periods of daily exposure, the activity of the pituitary-adrenal axis gradually diminished. Changes in the pituitary-adrenal activity, induced by sound stimulation, are closely related to changes in brain NA. The results obtained suggest that at least some of the effects of sound stimulation might be mediated by brain noradrenergic pathways and agree with the hypothesis concerning the existence of a central noradrenergic nervous component which could participate in the control of ACTH secretion.

Acoustic Stimulation↗

PubMed1994

Temporary change of compound action potential amplitude after intense sound exposure.

Intense sound induces a temporary or permanent threshold shift. The aim of this study is to make an experimental model for temporary threshold shift (TTS) using guinea pigs. In this study, two kinds of sound exposure were used for inducing a threshold shift in the guinea pig; one of 110 dB SPL at 10 kHz for 10 min and the other of 120 dB SPL at 10 kHz for 5 min. The former condition produced different levels of reduction in compound action potential (CAP) immediately after sound exposure and different steady levels of CAP amplitude after recovery (within 120 min) in 10 guinea pigs. The latter condition produced a total loss of CAP amplitude immediately after sound exposure in 8 of 9 guinea pigs, and this condition continued for 120 min in 7 of the 9 guinea pigs. Additionally, in 2 of 3 guinea pigs which were exposed the sound of 120 dB SPL at 10 kHz for 5 min, the CAP amplitudes were almost the same as those of control animals 1 day after the exposure. One the basis of these results, we consider the sound of 120 dB SPL at 10 kHz for 5 min to be the optimal intensity and frequency of sound and duration of exposure for producing a TTS in the guinea pig.

Acoustic Stimulation↗

PubMedDate not supplied

The emphatic and pharyngeal sounds in Hebrew and in Arabic.

This study addresses physiological, acoustic, and linguistic issues in the production of the emphatic sounds [in text] and the pharyngeal sounds [in text]. Approximately 300 minutes of video recordings were obtained from nine Hebrew and Arabic speakers, using a fiberscope positioned in the upper pharynx and simultaneous audio recording through an external microphone. We also studied a cineradiographic film of three Arabic speakers. Results clearly show that all the emphatic sounds, when pronounced as such, share pharyngealization as a secondary articulation. A constriction is formed between the pharyngeal walls and the tip of the epiglottis, which tilts backwards. To a lesser degree, the lower part of the root of the tongue is also retracted. The data show that all the emphatic and pharyngeal sounds we studied are made with qualitatively the same pharyngeal constriction. However, the pharyngeal constriction is more extreme and less variable for the pharyngeal sounds, where it is the primary articulation, than for the emphatic sounds, where it is a secondary articulation. Because the same sort of pharyngealization is seen for all the emphatics, we use a common notational symbol, [in text], for all of them, including [in text] in place of /q/. We note that where pharyngeals and pharyngealized sounds were realized, the Hebrew and Arabic speakers produced them in essentially the same way.

Humans↗

PubMed1996

Acoustic analysis of snoring sound in patients with simple snoring and obstructive sleep apnoea.

Snoring, a symptom which may indicate the presence of the obstructive sleep apnoea syndrome (OSA), is also common in the general population. Recent studies have suggested that the acoustic characteristics of snoring sound may differ between simple snorers and OSA patients. We have studied a small number of patients with simple snoring and OSA, analysing the acoustic characteristics of the snoring sound. Seventeen male patients, 10 with OSA (apnoea/hypopnoea index (AHI) 26.2 events x h(-1)) and seven simple snorers (AHI 3.8 events x h(-1)), were studied. Full night polysomnography was performed and the snoring sound power spectrum was analysed. Spectral analysis of snoring sound showed the existence of two different patterns. The first pattern was characterized by the presence of a fundamental frequency and several harmonics. The second pattern was characterized by a low frequency peak with the sound energy scattered on a narrower band of frequencies, but without clearly identified harmonics. The seven simple snorers and two of the 10 patients with OSA (AIH 13 and 14 events x h(-1), respectively) showed the first pattern. The rest of the OSA patients showed the second pattern. The peak frequency of snoring was significantly lower in OSA patients, with all but one OSA patient and only one simple snorer showing a peak frequency below 150 Hz. A significant negative correlation was found between AHI and peak and mean frequencies of the snoring power spectrum (p<0.0016 and p<0.0089, respectively). In conclusion, this study demonstrates significant differences in the sound power spectrum of snoring sound between subjects with simple snoring and obstructive sleep apnoea patients.

Acoustics↗

PubMed2006

The description of cough sounds by healthcare professionals.

BACKGROUND: Little is known of the language healthcare professionals use to describe cough sounds. We aimed to examine how they describe cough sounds and to assess whether these descriptions suggested they appreciate the basic sound qualities (as assessed by acoustic analysis) and the underlying diagnosis of the patient coughing. METHODS: 53 health professionals from two large respiratory tertiary referral centres were recruited; 22 doctors and 31 staff from professions allied to medicine. Participants listened to 9 sequences of spontaneous cough sounds from common respiratory diseases. For each cough they selected patient gender, the most appropriate descriptors and a diagnosis. Cluster analysis was performed to assess which cough sounds attracted similar descriptions. RESULTS: Gender was correctly identified in 93% of cases. The presence or absence of mucus was correct in 76.1% and wheeze in 39.3% of cases. However, identifying clinical diagnosis from cough was poor at 34.0%. Cluster analysis showed coughs with the same acoustics properties rather than the same diagnoses attracted the same descriptions. CONCLUSION: These results suggest that healthcare professionals can recognise some of the qualities of cough sounds but are poor at making diagnoses from them. It remains to be seen whether in the future cough sound acoustics will provide useful clinical information and whether their study will lead to the development of useful new outcome measures in cough monitoring.

Journal Article↗

PubMed1994

DETECTION OF AIRBORNE SOUND BY A COCKROACH 'VIBRATION DETECTOR': A POSSIBLE MISSING LINK IN INSECT AUDITORY EVOLUTION

Extracellular recordings from nerve 5 in metathoracic legs of Periplaneta americana disclose a sense organ that is extremely responsive to vibration but also detects sound (best response near 1.8 kHz) with a sensitivity similar to some insect auditory organs. The energy required from an auditory signal for a criterion response is similar or even smaller than for an optimal vibratory input. Responses originate in the subgenual organs (SGO) in the proximal tibiae, and cross-modal adaptation indicates that the same cells respond to both vibration and sound. Sound is picked up directly on some internal structure, not via sound-induced substratum vibration. Adaptation at different frequencies discloses no frequency-selectivity in the SGO. The nerve response is a burst of synchronized impulses at a frequency, fR, of approximately 300 Hz, that is practically invariant both with sound intensity and within the burst, suggesting that fR might represent some underlying resonance phenomenon, either of the SGO or of air in the tracheal system. The latter possibility is ruled out by observations made while the tracheae are perfused with HeO2. Similar responses can be recorded from the pro- and mesothoracic legs. Although Periplaneta is thought to be deaf and appears to ignore loud tones presented to the home colony, a more sensitive assay detects small leg movements in response to sound, confirming the presence of a functional auditory sense. The SGO is suspended from an expansion of the leg trachea, which may function to enhance sensitivity to vibration. This linkage preadapts the SGO to detect airborne sound transmitted in the tracheal system, and contact vibration may also stimulate the system in part by deforming the tracheae. It is proposed that auditory organs of crickets evolved from an ancestral SGO that already possessed dual responsiveness by subsequently developing effective vibration-isolating filters.

Journal Article↗

PubMed1995

The role of the tymbal in cicada sound production

1. The tymbal of Cyclochila australasiae consists of a biconvex membrane bearing alternating long and short ribs anteriorly and an irregularly shaped tymbal plate posteriorly. These sclerotised regions are coupled together by the surrounding highly flexible cuticle, which contains resilin. Dorsally, there is a thick pad of resilin, which functions as a spring, returning the tymbal to the out position and maintaining the stress on the long ribs. 2. Contraction of the tymbal muscle causes the tymbal plate to swing inwards, acting as a lever so that the surface of the tymbal moves through more than twice the distance of muscle shortening. This produces an inward movement and twisting of the dorsal ends of the long ribs, which then buckle in sequence, with each rib undergoing a sudden deformation from a convex to a V-shaped profile. Buckling takes place at the rib's weakest point, which is the narrow, highly sclerotised mid-region. 3. Inward buckling of the tymbal generates a loud click with a dominant frequency around 4 kHz. Resonances close to 4 kHz can be demonstrated in a buckled-in tymbal when driven by internal sound or by vibration at the tymbal plate. These resonances occur in sealed cicadas and those in which the abdominal air sac has been opened at both its anterior and posterior ends, which shows that the resonances are not due to the air sac; the tymbal itself is a resonant system. The maximum amplitude of tymbal vibration occurs at the V-shaped dimples in the centre of the long ribs. 4. When the tymbal plus abdominal air sac system is driven by vibration at the tymbal plate, the Q3dB of the sound radiated through the tympana is about 12.5, which is approximately the sum of those of the tymbal (Q=9.3) and of the air sac (Q=3.4) resonators. When the tymbal is not loaded by the air sac, i.e. in the sealed cicada and open cicada preparations, the Q3dB of its resonance is higher, between 13 and 20. 5. The click produced as the tymbal pops out is over 20 dB quieter than the in-click and has a dominant frequency around 6 kHz. When driven in the resting position, resonances are found close to 6 kHz but there is only a weak general vibration of the ribs and tymbal plate. When the tymbal is pushed in gradually, the resonant frequency changes from about 5.5 kHz to about 4.3 kHz as the tymbal buckles inwards. The left and right tymbals of the same insect may differ slightly in their acoustic properties. 6. As the tymbal buckles inwards, it displaces a volume of approximately 6 µl into the abdominal air sac volume of about 2 ml. The resulting sound pressure inside the air sac attains peak values of 155159 dB SPL; the root mean square values are 141144 dB SPL. The mean peak value just outside the tympana is 148.5 dB SPL. 7. Overall, the present work supports and extends our earlier model of cicada sound production: the tymbal click provides a coherent resonant source that drives the abdominal resonator, from which sound is radiated via the tympana. At the same time, the system provides the pressure transformation between muscle power and sound power that is desirable for efficient sound radiation.

Journal Article↗

PubMed1977

Sound spectroanalytic diagnosis of malfunctioning prosthetic heart valve.

Sound spectroanalysis was carried out for diagnosis of malfunctioning prosthetic heart valves in 50 cases, which consisted of 31 mitral, 14 aortic, 4 mitral+aortic and 1 tricuspid valve replacements with the age ranging from 17 to 57 years. Types of prosthetic valves used in this series were Starr-Edwards silicon ball valves, metal ball valves, disc valves, Kay-Shiley valves, Smeloff-Cutter valves and a Björk-Shiley valve. The system used in this study consisted of a moving coil microphone, a preamplifier, a filter (160/24 db octave) and a sound spectrograph (Rion Co. S.G. (7). Contour sound spectrograms (SSG) were drawn and peak frequency, wave pattern and frequency-intensity curves were investigated as characteristics of implanted valvular function. Peak frequencies of valvular opening and closing sounds were recorded between 1800 to 5000 Hz and differed according to the types of prosthesis. In mitral+aortic valve replacements, valvular sounds of two prostheses were clearly separated and this finding was very useful for determining the prosthesis which fell into malfunction. Decrease in peak frequency of valvular sounds or abnormal wave patterns in contour SSG were observed in 9 cases (18%). Of 9 cases, 4 cases underwent re-replacement and 2 cases died of congestive heart failure. Operative or autopsy findings gave proof to the findings in sound spectroanalysis.

Adolescent↗