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To monitor and understand the temporal variations of sound speed due to the changes of soil physical properties such as soil water potential, moisture content, and soil temperature under natural conditions, a long-term field soil survey has been conducted. In this study, transmitter and receiver acoustic probes, consisting of ten (five pairs) and five transducers respectively, were inserted into a prepared trench containing a soil-sand mixture in an outdoor test site. Five time domain reflectometers, five tensiometers, and five thermocouples were buried during the trench-filling at the same depths as the acoustic transducers. Measurements of sound speed, soil temperature, soil moisture content, and water potential were performed continuously, along with the measurements of surface temperature and precipitation over a period of 2 yr. Analysis of the data shows that there is a power law relationship between the sound speed and water potential. It is also found that the water potential is the dominant influence on the sound speed whereas the moisture content and temperature have relatively minor impacts. Brutsaert and Luthin's theory was employed to calculate the sound speed as a function of the effective stress. The theoretical predictions were compared with the experimental data and they are in good agreement. The study suggests that sound speed measurement could be used as a new and effective tool for water potential measurement. Abbreviations: LVD, laser doppler vibrometer; MASW, multi-channel analysis of surface waves.

The speed of sound in a bubbly liquid is strongly dependent upon the volume fraction of the gas phase, the bubble size distribution, and the frequency of the acoustic excitation. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. This effect can be audibly demonstrated using a one-dimensional acoustic waveguide, in which the flow rate of air bubbles injected into a water-filled tube is varied by the user. The normal modes of the waveguide are excited by the sound of the bubbles being injected into the tube. As the flow rate is varied, the speed of sound varies as well, and hence, the resonance frequencies shift. This can be clearly heard through the use of an amplified hydrophone and the user can create aesthetically pleasing and even musical sounds. In addition, the apparatus can be used to verify a simple mathematical model known as Wood's equation that relates the speed of sound of a bubbly liquid to its void fraction. [DOI: 10.1119/1.2907773]

An approach for accurate Doppler angle estimation for vector flow measurements is introduced, in which two ultrasound beams with known relative orientation are directed towards the same vessel, with one beam committed to perform a Doppler measurement and the other reference beam having the specific task of detecting the beam-flow angle. Validation of the method reveals that the beam-flow angle can be estimated with high accuracy and repeatable velocity magnitude measurements are possible.

We keep learning more about the history of noise calculations. It seems that the topic of the noise of a spectrum in the constant-detector-noise case was addressed more than 50 […]

A new traffic sensing technique is described that utilizes a microphone array to detect the sound waves generated by the road vehicles. The detected signals are then digitized and processed by an on-site computer using a correlation based algorithm, which extracts key data reflecting the road traffic conditions, e.g., the speed and density of vehicles on the road, automatically on site. In comparison with existing traffic sensors, the proposed system offers lower installation and maintenance costs and is less intrusive to the surrounding built environment. The results of theoretical analysis, computer simulation, and preliminary experimental results are presented. Index Terms--Digital signal processing, traffic sensing, sound.

A simple and inexpensive demonstration of acoustic monopole, dipole, and quadrupole sources utilizes four 4-in. boxed loudspeakers and a homemade switch box. The switch box allows the speakers to be driven in any combination of phase relationships. Placing the speakers on a rotating stool allows students to measure directivity patterns for monopole, dipole, and quadrupole speaker combinations. Stacking the speakers in a square, all facing the same direction, allows students to aurally compare the frequency and amplitude dependence of sound radiation from monopoles, dipoles, and quadrupoles.

To identify whether equal-appearing interval or magnitude estimation scaling resulted in a data set with a closer correlation to the physical stimuli involved 20 young adults completing two tasks. In Task 1 subjects used a 7-point equal-appearing interval loudness of 18 10-sec. samples of babble speech, presented randomly at intensities of 5 to 90 dB SPL. In Task 2 subjects used magnitude estimation scaling to rate these stimuli, presented in a randomized order. Analysis showed significantly high correlations for both scaling methods and the stimuli (Spearman rho = 1.00 and .99, respectively). Subjects can use either form of scaling to rate changes in loudness.

The influence of various numerical parameters on the computation of the basic radiation of sound from force laminar axisymmetric jets has been studied. Sound radiation is determined by a hybrid method where the hydrodynamic field is derived from an incompressible stream function-vorticity direct numerical simulation. The sound field is obtained from the compact Lighthill and Mohring-Kambe formulations. Ways of improving the acoustic analogies solution are also explored. The structure of the axisymmetric source of radiation has also been investigated for various Reynolds numbers.

This paper is concerned with the generation and application of semi-infinite Helmholtz elements in accordance with the decay function periodic infinite elements proposed by Bettess (1992). In combination with finite Helmholtz elements, they determine the soundwaves radiated by a vibrating gearbox excited by an impact hammer. The normal velocities on the surface of the gearbox have been measured for a number of different frequencies in order to obtain the dominating frequencies of vibration. Then the velocities of several dominating frequencies are applied as a boundary condition for the simulation of the sound emitted by the structure. The numerical results of the finite element calculations are compared with values obtained by measurement of the sound intensity. It is concluded that semi-infinite Helmholtz elements are as good and as easy to use as measurement techniques in order to identify the zones of main radiation. The deviation of measured and calculated emitted sound power is acceptable.

Improvements were made to the Kirchhoff method by analyzing the permeable-surface form of the Ffowcs Williams-Hawkings equation. This method was then applied to aeroacoustic calculations to account for noise generation both inside and outside of the Kirchhoff surface. Disturbance density was used as an acoustic variable to demonstrate the method's applicability. Although results were positive for model problems on jet noise prediction, additional work is needed on volume integral approximations.

To determine whether Doppler signal processing can be used to characterize streaming produced by pulsed Doppler beams, measurements of the magnitude and dynamics of radiation force and streaming were taken in vitro in blood and water. Acoustic steaming was found to be measurable in vitro at low duty factors and power levels used in pulsed Doppler velocimetry.

Combining TV holography recording with acoustic phase stepping and image processing, we measure the integrated density distribution in sound fields that propagate in air. We record a given number of two-dimensional cross sections that are tomographically backprojected to give the amplitude and phase distributions of the emitted sound field. The validity of the procedure is demonstrated.

Calculation of flow over a cavity shows that cavity flow undergoes oscillations thereby causing sound. These oscillations are regular at a low-Reynolds number and occur at Stouhal number 0.58. First the time-dependent incompressible flow is done, followed by the difference between the incompressible flow and compressible flow.

An acoustic near field study of an axisymmetric conical convergent nozzle working at a pressure ratio related to Mach number of 1.3 shows patterns in the B mode. It is a flapping mode for the thin-lipped nozzle, which precesses about the jet axis in an irregular manner. This flapping behavior is time dependent between the relative phasing between the two helices. The B mode is time dependent flapping/spinning with a thick-lipped nozzle. Bispectral analysis indicates other nonlinear interaction related to the thick-lipped nozzle.

High-order and high-bandwidth algorithms, which can function efficiently even in the absence of fine grids, provide accurate solutions for computational aeroacoustics problems. Design of high-bandwidth operators needs to be performed in an appropriate manner to mitigate possible errors in computations involving longer wavelength.

Detailed assessments of various monotonic upwind-centered scheme for conservation laws (MUSCL) models revealed the finite volume method of S. Osher and S.R. Chakravarthy to be most versatile for aeroacoustic computations. This method is versatile in comparison to other MUSCL schemes in estimating oblique shock reflection, linear wave convection, monopole radiation, vortex preservation and blade-vortex interaction.

A collection of structural acoustic research methods used by the Italian Aerospace Research Center and the University of Naples helps determine and mitigate the interior noise levels in the fuselage of commercial jet and propeller aircraft. A combination of existing methods with high frequency range methods allows the appropriate selection of acoustic and structural solutions.

The extent of interference of dynamic noise depicted at one spatial scale, with the identification of coherent motion produced by image features at a different scale, is measured using a masking process. The identification of coherent motion is mediated by a single filter, which is broadly tuned from spatial frequency. These discoveries confirm that the neurons are involved in the intermediate stage of processing the motion of objects.

The effects of the wind tunnel wall reflection on discrete frequency sound measurements of helicopter rotor rotational noise were studied to evaluate the reliability of the linear acoustic theory in wind tunnel tests. The acoustic field characteristics of the frequency source were evaluated in an anechoic chamber and compared with those obtained from experiments conducted in a duct with inherent acoustic properties. The efficiency of the linear acoustic theory was found to be significantly affected by the frequency of the duct acoustic fields.

A study was made to assess the effects of high-temperature gradients on sound transmission in an acoustic probe tube. The tube has its probe sensing end located in the hot environment and the transducer located at the cool end. The results show that a theoretically derived transfer-function can be used to correct acoustic data measured by a high-temperature probe tube. Moreover, the transfer-function model must have visco-thermal effects in the probe tube in order to be accurate. Agreement between the computed and measured attenuation is good over the frequency range from 0.4 to 6 kilohertz, with some discrepancies occurring at attenuation minima.

A computational aeroacoustics study of sound generation by a stenosis in a cylindrical pipe is conducted by using a three-part procedure. The incompressible flow is solved and used to determine a hydrodynamic correction to the constant incompressible density which is used to compute the resulting acoustic field. This procedure is found to be valid at the low Mach and Reynolds numbers, in that it yields acoustic fields that agree very well both with experimental amplitude and frequency. Moreover, the flow downstream of the stenosis is like that of a shrouded jet.

An acoustic shape design sensitivity analysis method is developed based on a boundary element application of the Helmholtz integral equation. The CHIEF method is also used as an alternative sensitivity formulation to address the nonuniqueness problem of the Helmholtz equation for certain frequencies to prevent inaccurate results. The formulations are validated using analytical pulsating sphere models with existing theoretical solutions.

In two experiments, 15 and 13 subjects estimated the loudness of 12 sound-pressure levels (38--104 dB; 6-dB intervals) of a 1000-Hz tone by the method of magnitude estimation with a modulus assigned to the first stimulus presented. The tone duration was 1 sec. and the interstimulus interval was 6 sec. The presentation order was systematically ascending-descending in one experimental and balanced-irregular in the other. The results indicate that (1) loudness is a power function of sound pressure with an exponent of 0.60 for the systematic order and 0.29 for the irregular order. (2) For both the irregular ans systematic order, a large step-size (12 or 18 dB) between the stimulus on Trial n and on Trial n-1 (or n-3) results in a slight assimilation effect. This also occurs for the small step-size (6 dB) in the irregular order. (3) The size of momentary exponents (based on two points, Trials n and n-1 or n-3) depends on the sound pressures of successive stimuli, whether the steps are positive or negative, and whether the stimuli have been presented in systematic or irregular order. For positive steps, the momentary exponent is lower for a soft tone (Trial n) than for a loud tone, whereas for negative steps the momentary exponent is lower for a loud tone than for a soft tone. These effects are more pronounced when these stimuli are presented in an irregular order. A relative judgment model is offered for magnitude estimation. It assumes that subjects judge the loudness of a stimulus in terms of three reference markers: the minimum and maximum sound pressures as well as the sound pressure of the previous stimulus.

This study was designed to investigate the effects of vocal [f.sub.o] on vowel spectral noise level (SNL) and perceived vowel roughness for subjects in high- and low-pitch voice categories. The subjects were 40 adult singers (10 each sopranos, altos, tenors, and basses). Each produced the vowel [a] in isolation at a comfortable speaking pitch, and at each of seven assigned pitches spaced at whole-tone intervals over a musical octave within his or her singing pitch range. The eight [alpha] productions were repeated by each subject on a second test day. The SNL differences between repeated test samples (different days) were not statistically significant for any subject group. For the vowel samples produced at a comfortable pitch, a relatively large SNL was associated with samples phonated by the subjects of each sex who manifested the relatively low singing pitch range. Regarding the vowel samples produced at the assigned-pitch levels it was found that both vowel SNL and perceived vowel roughness decreased as test-pitch level was raised over a range of one octave. The relationship between vocal pitch and either vowel roughness or SNL approached linearity for each of the four subject groups. KEY WORDS: spectral noise level, SNL, vocal roughness, pitch

This article discusses the Casimir effect and the design and construction of a device to measure Casimir force. Topics include spectral intensity, and the use of broadband acoustic noise as an analog.

The speed of sound in a gas can be measured with sufficiently high precision to observe real gas properties at one atmosphere and 300 K through the use of an easy-to-make cylindrical resonator. Heat capacity is shown to be able to be obtainable from speed of sound measurements.

A microspark is generated by a laser pulse focused on a graphite rod to measure the speed of sound in different gases in a science experiment. The speed of sound can be determined by measuring the time for the photoacoustical pulse to travel through a gas to a microphone detector over a fixed distance.

A time-of-flight method for measuring the speed of sound using a stereo sound board from a computer is described. Reasonable measurements of the speed of sound in different materials have been obtained using this method.

A method of estimating absolute zero on the Celsius scale through extrapolation of the measurements of the speed of sound is described. The setup measured absolute zero at -264.4 degrees Celsius, within nine degrees of the actual -273 degrees Celsius.

An experiment to determine the speed of sound in metal pipes is described. The apparatus uses a microphone and the oscilloscope program MacScope II.

The derivation of a formula to measure the velocity of a standing wave on harmonic oscillators like strings, based on the wavelength of two traveling waves, is presented.

Statistical modeling and analysis have been applied to different music-related fields, including sound synthesis and analysis. Sound can be represented as a real-valued function of time. This function can be [...]

Acoustic measurements of a Mach 2, rectangular nozzle with modified trailing edges were carried out using three microphones, placed 90 deg apart azimuthally in a plane normal to the jet axis. The measurements were obtained at three streamwise locations, with microphone angles of 90, 60, and 30 deg with respect to the jet centerline. The trailing-edge modified nozzles substantially reduced the turbulent mixing and broadband shock associated noise radiation by up to 12 dB for the underexpanded flow regime and up to 7 dB for the overexpanded condition. However, in some symmetric modifications, the very-high-frequency noise was increased for the overexpanded condition. Screech tones in the overexpanded flow condition were either reduced or eliminated for asymmetric modifications, but amplified for symmetric modifications. The trailing-edge modifications were found to not significantly alter the noise field for the ideally expanded flow condition.

With the emerging use of tracheal sound analysis to detect and monitor respiratory tract changes such as those found in asthma and obstructive sleep apnea, there is a need to link the attributes of these easily measured sounds first to the underlying anatomy, and then to specific pathophysiology. To begin this process, we have developed a model of the acoustic properties of the entire respiratory tract (supraglottal plus subglottal airways) over the frequency range of tracheal sound measurements, 100 to 3000 Hz. The respiratory tract is represented by a transmission line acoustical analogy with varying cross sectional area, yielding walls, and dichotomous branching in the subglottal component. The model predicts the location in frequency of the natural acoustic resonances of components or the entire tract. Individually, the supra and subglottal portions of the model predict well the distinct locations of the spectral peaks (formants) from speech sounds such as /a/ as measured at the mouth and the trachea, respectively, in healthy subjects. When combining the supraglottic and subglottic portions to form a complete tract model, the predicted peak locations compare favorably with those of tracheal sounds measured during normal breathing. This modeling effort provides the first insights into the complex relationships between the spectral peaks of tracheal sounds and the underlying anatomy of the respiratory tract. Index Terms--Acoustic modeling, breathing sounds, respiratory sounds, respiratory tract.

This paper studies sound and vibration transmission across a sandwich beam made of anisotropic materials. In our previous study, we have found that there is a significant increase in the transmission loss for the sandwich beam with anisotropic materials as compared with isotropic ones. This paper presents an extensive numerical study of the effects of damping, thickness of the laminae and density of the material on the sound transmission loss. This work may eventually lead to a new way of designing sandwich structures with high vibration and noise isolation performance. [DOI: 10.1115/1.1343083]