Sound Fluctuations Research Articles

1508 乱流中に置かれた二次元鈍頭物体から放射される空力騒音と後流の静圧変動の関係について(J11-2 流れと音の相関計測,J11 流体関連の騒音と振動)

1508 乱流中に置かれた二次元鈍頭物体から放射される空力騒音と後流の静圧変動の関係について(J11-2 流れと音の相関計測,J11 流体関連の騒音と振動)

Temporal resolution properties of human auditory cortex: Reflections in the neuromagnetic auditory evoked M100 component

Previous work has provided evidence for a brief, finite (∼35 ms) temporal window of integration (TWI) in M100 formation, during which stimulus attributes are accumulated in processes leading to the M100 peak. Here, we investigate resolution within the TWI by recording responses to tones containing silent gaps (0–20 ms). Gaps were inserted in 1 kHz tones in 2 conditions: +10 ms post-onset (10 ms masker) wherein the masker and gap of longest duration (20 ms) were contained within the initial 35 ms of the stimulus and +40 ms (40 ms masker) wherein all gaps were inserted +40 ms post-onset. Tones were presented binaurally and responses sampled from both hemispheres in 12 adults using a twin 37-channel biomagnetometer (MAGNES-II™, BTi, San Diego, CA). Results—10 ms masker: M100 latency was prolonged and amplitude decreased as a function of gap duration, even with the shortest duration (2 ms) gap, indicating that integrative processes underlying M100 formation are sensitive to fine-grained discontinuities within a brief, finite TWI. Results—40 ms masker: M100 latency and amplitude were unaffected by gaps inserted at +40 ms, providing further evidence for an M100 TWI of <40 ms. Conclusion: within a brief integrative window in M100 formation, population-level responses are sensitive to discontinuities in sounds on a scale corresponding to psychophysical detection thresholds and minimum detectable gap thresholds in single unit recordings. Cumulatively, results provide evidence that M100 resolution for brief fluctuations in sounds reflects temporal acuity properties that are both intrinsic to the auditory system and critical to the accurate perception of speech.

Anisotropic field of background internal waves on a sea shelf and its effect on low-frequency sound propagation

The space-time spectral characteristics of the field of background internal waves (IW) are obtained for two oceanic shelf regions (the Atlantic shelf of the United States and the Kamchatka shelf) and analyzed. Within the framework of a numerical experiment, it is shown that the observed anisotropy of the IW field may considerably affect the low-frequency sound fluctuations in the aforementioned regions and, in particular, may change the interference invariant of the sound field.

Noise in the ED

Background The impact of noise pollution on both the patient and the care provider has been extensively studied in the neonatal intensive care unit and in other critical care units. Noise pollution makes errors more probable and is one of the risk factors for provider burnout and negative outcomes for patients. The Environmental Protection Agency (EPA) recommends that the acceptable noise level in a hospital should not exceed 40 dB. Objectives The purpose of this study was to record and analyze noise in a large urban level I emergency department (ED) and compare to the EPA guidelines. Methods A 3-channel dosimeter Quest Q300 (Quest Technologies, Oconomowoc, WI) was placed as a stand-alone unit on the wall of the resuscitation booth in the ED. Sound was sampled 16 times per second for 12 hours and was recorded as peaks and averages for each minute. The dosimeter was then placed in the pocket of a medical student with a small 8-mm shoulder-mount type 2 microphone. The medical student followed an emergency medicine resident throughout an 8-hour shift in the main resuscitation area while monitoring and logging sound fluctuations in the environment. Sound pressure levels were logged in real time and subsequently correlated to the recorded peaks. Sound was sampled 16 times per second and recorded peaks and averages for each minute. Results In the initial part of the study, the time-weighted average was 43 dB. The average sound levels peaked approximately 25 times over 12 hours. Individually measured peak levels of 94 to 117 dB occurred every minute. In the second part of the study, the time-weighted average was 52.9 dB. Conclusions When compared to EPA accepted noise levels for hospital (40 dB), the ED under study had excessive noise on a regular basis. There are easily identifiable sources of noise pollution in the ED. By identifying and modifying sources of noise, stress in the ED may be decreased.

Influence of internal waves on vertical coherence of sound propagation in the East China Sea

Literature of the last two decades has shown that internal waves are a major factor determining sound field fluctuations [Zhou et al., J. Acoust. Soc. Am. 90, 2042–2054 (1991); Lynch et al., ibid. 99, 803–821 (1996)]. Due to its time-dependent and anisotropic nature, internal waves can cause both temporal and spatial variations in the sound speed profile and hence, the acoustic field. In this paper, a model is built to study the range and azimuthal dependence of wave propagation in the presence of internal wave activity. The results are based on an in situ experiment ASIAEX in the East China Sea where intense tidal driven internal waves were recorded. The model explains the observed decorrelation after long range propagation (20 km) and in certain directions relative to the internal wave wavefront.

Observations on fluctuations of sound transmission and temperature field from the ASIAEX 2001 South China Sea experiment and inversion of the characterizations of internal tides (waves)

Abstract Two conclusions are obtained by analyzing the fluctuation data of the temperature field and the sound transmission in the South China Sea from ASIAEX 2001 volume interaction experiment. First of all, the peak-to-peak value of the particle vertical mean displacement due to the internal waves exceeds 40m. Secondly, the peak-to-peak value of the sound transmission fluctuations represented by the pulse leading-edge fluctuations of the travel-time average exceeds 100 ms. Based on that, the major components of the internal waves are obtained by analyzing the spectrum of the temperature field fluctuations. The spectrum structures of the temperature field fluctuations in the across-shelf and the along-shore directions are compared respectively, and the spectrum structures of the sound transmission in such two different directions are also compared. The multi-path signals and the travel-time of the pulse are respectively used to capture the information of the sound transmission fluctuations, and their spe...

Using optimized surface modifications to improve low frequency response in a room

A case study of improving sound energy distribution at low frequency in a small orthogonal room is presented in this paper. The effects of the geometric modifications of wall surface on the sound frequency response have been investigated in depth. In order to find the optimal modifications for the wall surface, an optimization procedure, based on finite element analysis, has been developed. The uniqueness of this method is that it takes both modal redistribution and sound diffusion into account during optimization process. As a result, the promising improvements of sound frequency response have been obtained at the frequencies around 100 Hz in all rooms tested, particularly in those where the serious modal concentrations are met. The maximum reduction of sound fluctuation in such a room could reach a mount of 4.6 dB. The work opens up the possibility of improving low frequency sound quality by a means that considers both modal changing and surface scattering at same time.

Frequency dependence of the sound fluctuations in the presence of internal solitary waves in SWARM’95

In this paper the propagation of sound pulses in a shallow-water region in the presence of internal soliton train (IS) traveling approximately across an acoustic track of 15 km is studied. Broadband sound pulses were produced by an airgun (shots with frequency band about 30–120 Hz) and an electromechanical (J15) sound source (LFM sweeps with frequency band 50–200 Hz). Experimental data show significant correlation of sound fluctuations with IS motion. In addition, difference in the excitation source causes different modal energy partitioning in the waveguide. Modeling is carried out within the framework of the theory of vertical modes and horizontal rays (or PE in the horizontal plane). Calculations give a good agreement for temporal fluctuations of the sound energy for the sources used. It is shown that frequency dependence of intensity fluctuations is connected with the frequency dependence of refraction index of horizontal rays due to the 3D nature of these fluctuations. [Work supported by ONR and RFBR, Grant 03-05-64568.]

Sound fluctuations due to horizontal refraction in the SWARM-95 experiment

Fluctuations of the sound field measured in the SWARM-95 experiment are interpreted as manifestations of three-dimensional effects in shallow-water sound propagation. It is shown that features of the received sound signal, along an acoustic track placed at 5° to the crests of propagating internal soliton trains, can be explained by significant horizontal refraction of the sound waves. This refraction leads to a remarkable redistribution of the energy in the horizontal plane as has been recently remarked by other investigators. These features are specifically: (1) a high level of fluctuations of the sound energy (up to 6 dB) which are synchronous in time and have same amplitude over depth of waveguide and (2) anomalies in the arrival times and amplitudes of separate waveguide modes. A theoretical analysis based on the theory of vertical modes and horizontal rays is presented, along with computer modeling of the experiment. Analytical estimations of the observed effects as well as results from numerical modeling are in a good agreement with experimental observations and are consistent with simulations. [Work supported by ONR and US CRDF Award No. VZ-010-00.]

Sound scattering by spatially localized inhomogeneities in a shallow-water waveguide in the presence of internal waves

A method is developed for solving the problem of sound scattering by concentrated inhomogeneities in a waveguide of small depth in the presence of internal waves (IW) typical of an oceanic shelf. The sound field fluctuations related to the motion of a model scatterer (a soft spheroid) and to the propagation of the IW are calculated and analyzed. It is shown that the field of internal waves considerably affects the scattered sound field even when the source-receiver and source-scatterer distances are relatively small (about several kilometers). This effect depends not only on the amplitude of the IW, but on their propagation direction as well.

Sound scattering in shallow water in presence of internal solitons

Sound scattering by localized inhomogeneity (object) in a shallow-water waveguide is studied. Influence of internal solitons (IS) traveling in the sea, on the scattered field is considered. The problem is analyzed within the framework of theory of the sound scattering in the waveguide developed by the authors, where the scattering matrix is expressed through modal decomposition including the scattering amplitude of the object in free space. The peculiarity of the given work is the taking into account of additional modes conversion due to IS. The waveguide and IS are modeled on the basis of experimental data (sound-speed profile, bottom relief, IS parameters, etc.) collected in the Japan Sea. The inhomogeneity is selected in the form of soft spheroids with dimensions characteristic of gray whales (eschrichtius). Calculations of amplitude fluctuations of the low-frequency sound field at the receiving point are carried out for moving spheroid and different orientations of acoustic track with respect to direction of propagation of IS. It is shown that sound fluctuations have essentially different characteristics for longitudinal and transversal propagation of IS. [Work supported by RFBR, Grant No. 00-05-64752.]

PSYCHO-CIRCULATORY RESPONSES CAUSED BY LISTENING TO MUSIC, AND EXPOSURE TO FLUCTUATING NOISE OR STEADY NOISE

This study investigated the effect of steady noise, fluctuating noise and music on circulatory function. Pulse-wave and blood pressure were continuously measured in 35 healthy young females who listened to three types of music or were exposed to steady noise or fluctuating noise, synchronized with each type of music with respect to intensity variations. The pulse-wave did not change during any exposure conditions. Regarding blood pressure, several modes were observed. The critical level for a blood pressure change was estimated to be 54 LAeqduring exposure to steady noise. The frequency of high-intensity peaks in the mode of sound fluctuation was associated with elevation in blood pressure. The blood pressure change was analyzed by distinguishing the intensity variation in sound fluctuation from other attributes of music. The effects of music on blood pressure were modified not only by the melody and timbre of the music but also by emotional responses during listing.

Acoustic effects caused by high-intensity internal waves in a shelf zone

The sound field fluctuations caused by high-intensity, solitonlike, quasi-plane internal waves crossing a fixed acoustic path at different angles are numerically modeled for natural conditions of the shelf zone of the Sea of Japan. The horizontal refraction of sound is considered for the case of an acoustic path parallel to the internal wave front.

Sound fluctuations caused by internal waves in a shallow sea

Estimates are presented for the fluctuations of the parameters of low-frequency sound fields in shallow-water regions of the Barents Sea, in the presence of seasonal internal gravity waves. The objective of the experiments is to reveal the main mechanisms that govern the sound fluctuations and their statistical parameters on paths of moderate lengths (50–60 to 100–120 km). Another objective is to determine the features of the sound interaction with internal waves for the sound speed profile of the summer—autumn type for which the water stratification is most pronounced. As the probing signals, continuous tonal ones produced by bottommoored sources at the frequencies about 100 and 300 Hz are used along with the 1/3-octave noise signals with the central frequency 1000 Hz, which are generated by a source deployed from a vessel. For the signal reception, both fixed bottom-moored hydrophones and a vertical chain of hydrophones are used, the chain also being deployed from the vessel. The water temperature, the salinity, and the thermocline displacements are monitored with standard hydrographic sensors. The following main results are presented: the estimate of the degree of correlation between the sound fluctuations and the parameters of the water layer, the comparison of the fluctuations in the signal amplitude envelope with the data obtained in other regions, and the estimate of the statistical parameters of the signal amplitude fluctuations, including their dependence on the path length. One more result consists in the proof of the wave nature of the interaction of sound and internal waves, which manifests itself in a strong dependence of the sound interaction with internal waves of discrete frequencies on the frequency of the probing signal and on the angle at which these wave beams intersect. An attempt is made to explain the observed phenomena by the synchronism in the interacting sound and gravity waves. The data obtained can be used to analyze and compare the fluctuations of the sound fields in the ocean, especially in shallow-water regions.

Space-time sound fluctuations due to internal solitons in shallow water

In this paper results of numerical modeling of sound propagation in shallow-water waveguide with internal waves are presented on the basis of experimental data about internal solitons (IS) registered in the Japan sea [A. N. Serebryany, Sov. Phys. Oceanol. 27, 225–226 (1987)]. These IS constitute some sequences of oscillations with amplitude up to 10 m moving toward coastal line with the velocity about 0.25 m/s. The wavelength of separate oscillations in this group is about 325 m; total length of the packet is about 4 km. Three-dimensional sound-speed distribution is constructed using the mentioned data. On the basis of this model, space-time fluctuations of intensity of the sound propagating in such medium are calculated. The modeling is carried out within the framework of the parabolic equation method in the horizontal plane and the modal approach in the vertical one. These fluctuations can be interpreted as the forming of a sound waveguide in the horizontal plane; space-time scales of fluctuations correlate with space-time scales of IS. Different numerical examples are presented; possible experimental setup is discussed. [Work supported by RFBR, Grant 00-05-64752.]

Horizontal refraction and sound fluctuations caused by internal waves packets in shallow water

The subject of the paper is to consider the propagation of a low-frequency sound field in shallow water in the presence of solitonlike internal waves (SLIW). It is assumed that SLIW spread approximately across the stationary acoustic trace. The problem of sound propagation is considered within the framework of 3-D model of the shallow water. The theory of ‘‘horizontal rays and vertical modes’’ is applied to take into account influence of horizontal refraction due to SLIW. As shown in the paper SLIW can lead (periodically in time) to ‘‘focusing’’ and ‘‘defocusing’’ of the horizontal rays or, in other words, to the periodic appearance of ‘‘horizontal waveguide.’’ Estimations of the sound fluctuations due to SLIW demonstrate that the amplitude of fluctuations can reach up to 10–20 dB (between moments of the ‘‘focusing’’ and ‘‘defocusing’’). The next effect conditioned by internal waves is horizontal filtering of vertical modes, where we have separate focusing and defocusing rays, corresponding to different vertical modes at different points of horizontal waveguide. The results presented in the paper can be used as the basis of remote sensing of the internal waves packets in shallow water. [Work supported by RFBR, Grant 97-05-64878.]

Electronic sound generating device for generating musical sound adding volume fluctuation to predetermined harmonics

Electronic sound generating device for generating musical sound adding volume fluctuation to predetermined harmonics

Onboard acoustic recording from diving northern elephant seals.

This study was the first phase in a long-term investigation of the importance of low-frequency sound in the aquatic life of northern elephant seals, Mirounga angustirostris. By attaching acoustic recording packages to the backs of six translocated juveniles, the aim was to determine the predominant frequencies and sound levels impinging on them, and whether they actively vocalize underwater on their return to their rookery at Ano Nuevo, California, from deep water in Monterey Bay. All packages contained a Sony digital audio tape recorder encased in an aluminum housing with an external hydrophone. Flow noise was minimized by potting the hydrophone in resin to the housing and orienting it posteriorly. The diving pattern of four seals was recorded with a separate time-depth recorder or a time-depth-velocity recorder. Good acoustic records were obtained from three seals. Flow noise was positively correlated with swim speed, but not so high as to mask most low-frequency sounds in the environment. Dominant frequencies of noise impinging on the seals were in the range 20-200 Hz. Transient signals recorded from the seals included snapping shrimp, cetacean vocalizations. boat noise, small explosive charges, and seal swim strokes, but no seal vocalizations were detected. During quiet intervals at the surface between dives, the acoustic record was dominated by respiration and signals that appeared to be heartbeats. This study demonstrates the feasibility of recording sounds from instruments attached to free-ranging seals, and in doing so, studying their behavioral and physiological response to fluctuations in ambient sounds.

The Characteristics of Fluctuation of Sound of Flowing Water in the River from the Viewpoint of Soundscape

The purpose of this study is to find the characteristics of sound environment from point of view of OM fluctuations in the river space, that is, the physiolbgical effect of environmental sound on man. In the area of river improvement and river conservation work have tended to put importance to landscape from visual approach. But, in the future, it is necessary that the basic idea of acoustic approached called soundscape compared with visual approach is discussed in the river design.

On optimization possibility for ocean acoustic tomography system

This work shows results of sound signal amplitude fluctuation measurements in comparably narrow envelope frequency spectrum interval from 1.5 to 6.0 mHz obtained on different stationary tomographic systems - 100 km, 100 Hz in Barentz sea and 320 km, 400 Hz in Okhotsk sea. Use of this range, from our point of view, in any ocean region allows to decrease influence of two meeting ocean wave processes - surface wind waves from high frequency side and internal as well as long surface waves from low frequency side. This interval according to several previously fulfilled oceanographic researches could be considered as some kind of transparency window for different natural ocean processes responsible for sound fluctuations spectrum. Measurements presented demonstrate such possibility and allow to choose optimal envelope frequency analysis interval for tomographic systems installed in quite different regions.