bluuebunny/crossref_metadata_2025 huggingface dataset:
Bridging the gap between single- and multibubble sonoluminescence
Authors: Matula Thomas J.
Published: July 2002

Sonoluminescence from a single bubble (SBSL) is related to sonoluminescence from a cavitation field (MBSL) by a commonality of cause (acoustic cavitation) and effect (light emission). However, questions remain as to the extent of this association. Furthermore, detailed comparisons are difficult due to the dissimilar approaches used in generating, and conditions amenable to, sonoluminescence from a single bubble versus a cavitation field. Previous comparisons of the spectral and temporal characteristics of the light emission have been limited by the sparse quantity of available data [T. J. Matula and R. A. Roy, ‘‘Comparisons of sonoluminescence from single-bubbles and cavitation fields: Bridging the gap,’’ Ultrasonics Sonochemistry 4, 61–64 (1996)]. Further comparison studies are currently underway in order to establish whether or not a more direct relationship exists between MBSL and SBSL. These studies include a near-IR spectral comparison, a comparison of the effects of doping with small quantities of impurities, and a comparison of the effects of an overpressure on the light intensity. An increased understanding of the relationship between these two phenomena should be extremely useful to sonochemistry researchers. [Work supported by DOE-EM.]
Calorimetric measurements of losses in mineral wool
Authors: Brunskog Jonas , Holmberg Dag , Wadsoe Lars
Published: July 2002

Measurements of the heat generated in mineral wool during a steady-state single-frequency dynamic process are presented. A microcalorimeter is used to register the heat. The calorimeter consists of a heat sink, i.e., a large water container held at constant temperature, a measurement volume, and a temperature gradient sensor in between. The temperature gradient is then related to the heat flux. The sensitivity of the equipment is on the order of 1 microwatt. A small rod is connected to a shaker outside the calorimeter and to a mineral wool specimen in the other end. The dissipated energy in mineral wool can then be measured during a steady-state single-frequency dynamic process. In order to obtain a value of the reversible energy, one can also measure the acceleration and the voltage to the shaker. Dry friction will cause measurement errors, but if a measurement without any sample is performed, this can partly be compensated for. The heat flux can be related to the dissipation in the mineral wool.
The bulk acoustic properties of a porous medium, derived from a single impedance test
Authors: Cummings Alan
Published: July 2002

In the majority of engineering applications, porous sound absorbing media may be treated as equivalent fluids, with vibration of the solid skeleton being neglected. Most measurement techniques for the bulk acoustic properties of such media (e.g., complex characteristic impedance and propagation constant) involve tests on large samples of material, rather complex series of tests on smaller single samples, or surface impedance tests on two small samples of differing thicknesses. Recently, however, a least-squares method [C. Braccesi and A. Bracciali, Appl. Acoust. 54, 59–70 (1998)] was employed to find values of the structure factor and flow resistivity, in a two-parameter model, from a single surface impedance curve. Though the technique proved successful, the two-parameter model is less accurate over a wide frequency range that the well-known empirical curve fitting method of Delany and Bazley. In the present paper, a least-squares method is described for determining the eight empirical parameters in the Delany and Bazley method from a single surface impedance curve. Examples of its application are given, and it is demonstrated that it gives a better fit to measured data than the two-parameter model.
Acoustic determination of water distribution in unsaturated soil
Authors: Blum Andreas , Flammer Ivo , Germann Peter
Published: July 2002

Sending acoustic pulses through soil columns, one obtains information on the soil’s elasticity characteristics and therefore on its state of humidity. In this laboratory water flow was investigated through 30×30×100-cm3 columns of undisturbed and unsaturated soil. The initial peak of the sound wave arriving at the detector is assumed to be ballistically transmitted through the soil. Its frequency is 10 kHz, thus a spatial resolution of about 6 cm is expected. The present aim is to obtain spatial and temporal information about the soil water distribution by a tomography technique. On this poster acoustic absorption and propagation time measurements during water infiltration are presented. The data are compared with conventional soil humidity measurements by time domain reflectometry.
Damping modelization of acoustic foams at low frequency
Authors: Sohbi Sahraoui , Emmanuel Mariez
Published: July 2002

The polymeric foams are commonly used as sound absorbing materials. These foams can exhibit at low frequency a resonant vibration of skeleton where the fluid damping is important. The two-phase material dynamic behavior is then described by the Biot equations. This paper examines the elasticity of air-filled PU foams through their microstructure. The foam is modeled by an elastic bars periodic network. It is shown that the orientation distribution in the space of the bars and their geometry control the macroscopic properties and the anisotropy. The study of the solid-phase deformation was based on a model developed for isotropic foams [W. E. Warren and A. M. Kraynik, J. Appl. Mech. 55, 341–346 (1988)]. An approximative evaluation of the permeability was derived from results obtained for regular arrays of parallel solid cylinders [J. E. Drummond and M. I. Tahir, Int. Multiphase Flow 10, 515–540 (1984)]. The objective of this investigation is to achieve the stress/strain and permeability tensors in the particular case of axisymmetric foams.
Long-range acoustic propagation in the nocturnal boundary layer
Authors: Di Xiao , Gilbert Kenneth E.
Published: July 2002

It is a common observation that sound travels to long distances in the nocturnal boundary layer (NBL). For such long-range propagation, the cumulative effects of turbulence can be significant even though NBL turbulence is generally much weaker than typical daytime turbulence. In this paper a 3D version is used of the Green’s function parabolic equation (GF-PE) to investigate the effects of turbulence on average levels and cross-range correlation in the NBL at distances of up to 10 km. A comparison is made between 2D and 3D predictions for 50 and 100 Hz. In addition, the cross-range coherence is computed at various ranges for the two frequencies. The implications for beamforming on horizontal arrays in the NBL are discussed. [Work supported by the Defense Advanced Research Projects Agency (DARPA).]
A privileged perceptual status for rising intensity tones
Authors: Neuhoff John G.
Published: July 2002

Recent cross-modal matching experiments have shown that listeners reliably overestimate the change of rising level tones relative to equivalent falling level tones [J. G. Neuhoff, Nature 395 (6698), 123–124 (1998)]. In a natural listening environment this overestimation could provide a selective advantage, because rising intensity can signal source movement toward an organism. In the present work, listeners heard equivalent rising and falling level tones, and in a three-alternative forced-choice task, indicated which sound demonstrated the greatest change in loudness, or whether the amount of loudness change was the same. If one sound was judged to change more than the other, listeners indicated the magnitude of disparity in loudness change between the two sounds. Results indicate a privileged perceptual status for rising intensity tones, and a greater perceptual disparity between rising and falling intensity tones as overall level increases. These results suggest an asymmetry in the neural coding of tonal rising and falling intensity sweeps, and may be indicative of localization priorities in a natural listening environment.
Is the auditory filter optimal?
Authors: Schneider Bruce A.
Published: July 2002

Gabor [J. I. E. E. London 93, 429–457 (1946)] showed that a narrow-band filter, with a Gaussian impulse-response envelope, provided the optimal compromise between good temporal resolution and good spectral resolution. The impulse-response function of this optimal Gaussian filter, however, begins before the impulse is applied, and, therefore, is not physically realizable in the auditory domain. A variety of physically realizable impulse response functions were examined to determine which one came closest to the optimal compromise achieved by the Gaussian filter. It is shown that a filter, whose impulse response function is either a gamma function or a generalized Rayleigh function, comes closest to being optimal. Moreover, these two filter types provide good fits to the data from notched-noise experiments.
Correlations between speech processing and auditory functions at 1 kHz
Authors: Noordhoek Ingrid M. , Houtgast Tammo , Festen Joost M.
Published: July 2002

Even when all relevant speech information is presented above threshold, intelligibility may still be reduced for hearing-impaired listeners. An attempt is made to relate impaired speech processing to a deterioration of specific auditory functions. Performance of hearing-impaired listeners is measured on psychoacoustic tests concerning temporal and spectral resolution, frequency and intensity discrimination, and temporal and spectral integration. All auditory functions are measured at 1 kHz. Speech reception is measured with the SRBT test (speech reception bandwidth threshold). This test determines the minimum width of a speech band with a center frequency of 1 kHz required for 50% intelligibility. A wider-than-normal SRBT can simply be the consequence of inaudibility of part of the speech signal. To account for this possibility, each SRBT is converted to an SII (speech intelligibility index, the new articulation index). This SII may be interpreted as the proportion of the total speech information required by the listener for 50% intelligibility. An elevated SII is considered an indication of impaired processing of suprathreshold speech. This may be caused by the deterioration of specific auditory functions. Relations between the performance on psychoacoustic tests and the (elevated) SII will be examined. [Work supported by the Foundation ‘‘Heinsius-Houbolt Fonds.’’]
Analysis of structure-borne sound transmission using spatial statistical distributions
Authors: Fulford Ross A.
Published: July 2002

For a source of vibration, i.e., a machine, connected to a receiving structure, i.e., a floor, the vibrational power transmitted is dependent upon the dynamic characteristics of both the source and receiver. If the source and receiver are connected at N points and with M components of motion, the exact character of each structure can only be quantified using (MN)2 frequency-dependent terms. Most often this leads to an analysis involving a vast amount of data. Upon recognition of such, together with an understanding that the terms have inherent variations, an approximate analysis method is suggested in which the precise nature of the structure’s spatial response is disregarded and instead considered as a probabilistic distribution. With the approach, not only is the amount of data required significantly reduced but, moreover, the precision with which it has to be procured is also relieved. Application is demonstrated alongside work in progress with respect to practical implementation.
The influence of sound radiation on vibration of mechanical structures
Authors: Dobrucki Andrzej B. , Zoltogorski Bronislaw
Published: July 2002

Two methods of inclusion of coupling between the vibrating structure and produced acoustic field are discussed. The first iterative method consists of calculation of successive corrections of exciting nodal forces caused by sound pressure and solving the FEM equation of the structure. It has been proved that near the resonances of the structure this method can be nonconvergent. The second method consists of calculation of the generalized complex stiffness matrix of the sound field on the surface of the structure and including it into the stiffness matrix of the structure. The resulting stiffness matrix is a full matrix, and the algorithm for solving the FEM equation system is time consuming. It has been shown that near resonances of the structure, the global mechanical power provided to the radiating structure decreases in comparison to the power provided to the nonradiating structure. Near the antiresonant frequencies, the power provided to the structure with included radiation is greater. On this basis, a simple method of calculation of mechanoacoustical efficiency near the resonances and antiresonances of the structure is derived. The considerations are useful for calculation of efficiency of electroacoustical transducers. The results of calculation for vibrating and radiating shells of revolution are given.
Cymbal-based actuator panels
Authors: Howarth Thomas R. , Tressler James F.
Published: July 2002

The cymbal flextensional element has been configured into a ‘‘1-3’’ piezocomposite-type arrangement between two stiff plates to produce a thin packaged actuator device for active noise and vibration control. This presentation will discuss the activities at the Naval Research Laboratory in developing the cymbal-based actuators from the basic element design to useful device applications. This paper will discuss the effects of spacing, element geometries, and material selections with respect to operating frequency bands and displacement profiles. Results of measured in-air immitance and laser Doppler vibrometry LDV) will be presented to discuss the output profiles. Results of a program for integrating the panels into high force applications will be described and shown. [This research was supported by the Office of Naval Research Code 321SS.]
On the link between acoustic cue distributions and categorization dependencies
Authors: Smits Roel
Published: July 2002

The HICAT model of hierarchical categorization [R. Smits, J. Acoust. Soc. Am. 103, 2980(A) (1998)] explicitly models dependencies in four-alternative forced-choice categorizations involving two binary distinctions. A philosophy has been developed which predicts which dependencies are likely to occur for a given pair of phonetic distinctions on the basis of the acoustic distributions of relevant cues in natural utterances. It is argued that, because speech perception happens under severe time pressure, listeners try to minimize categorization complexity while maximizing categorization accuracy. For certain phonetic distinctions, the cue distributions allow listeners to use simple, independent categorization strategies while still performing close to optimally. Severe coarticulation, however, necessitates a more complex strategy involving categorization dependencies which reflect dependendencies in the cue distributions. This philosophy was tested experimentally. Spectral locations of fricative and vowel resonances in syllables /si, sy, Si, Sy/ were measured on a large set of naturally spoken tokens. Based on the resulting distributions it was predicted that listeners’ fricative categorization will be dependent on the vowel categorization. Next, a categorization experiment was run using a two-dimensional fricative-vowel continuum. The dependencies inferred from the categorization data using the HICAT model will be compared to the predictions.
Reflection patterns and coloration of vowels
Authors: Watkins Anthony J.
Published: July 2002

When sounds are played in a room, the direct sound is accompanied by later-arriving reflections. If the reflections arrive within about 50 ms they are not heard separately, but seem to be perceptually incorporated with the direct sound. In addition, the reflection pattern can have a filtering effect, which can change the sound’s spectral envelope, and which might be heard as a change in timbre or ‘‘coloration.’’ Thus, colored reflected sounds tend to follow after an uncolored direct sound. It has been suggested that the reflections’ coloration is perceptually suppressed under these circumstances. The present experiment was designed to test this idea. Brief, 20-ms reflection patterns were designed that ‘‘colored’’ vowels’ spectral envelopes and which followed after a direct sound in ‘‘two-part filters.’’ Coloration was measured by changes in listeners’ identifications of vowels that are played through these filters. This was compared with the coloration in a condition with reversed two-part filters where the reflection pattern was caused to precede the direct sound. There should be more coloration in the reversed condition if there is normally suppression of coloration from later-arriving reflections. However, coloration was no greater in the reversed condition even though the reflections’ perceptual effects were substantial.
Phonetic priming of features in a naming task
Authors: Doeleman Tobey L.
Published: July 2002

The role of features in speech perception is investigated in a series of priming experiments in which subjects named CV syllables consisting of the English consonants [p, b, t, d, f, v, s, z] followed by the vowel [a]. Natural tokens were used to create sixty-four prime-target pairs which varied critically the number of features the consonants shared (0–3). The pairs were further classified into 8 stimulus sets based on the feature relationship: unrelated, identity, shared manner and voicing, manner and place, voicing and place, manner only, voicing only, and place only. Patterns of reaction times and accuracy data for the naming task are compared for the different stimulus sets. The same 64 pairs were blocked according to the voicing, place, or manner feature of the target, and presented to three subsequent groups of subjects who were thus given information about a particular feature. Results are discussed with reference to previous findings from a series of gating experiments (using the same stimulus set manipuluation) which found that subjects given place information had significantly higher scores in a consonant identification task than subjects given manner information [T. L. Doeleman, J. Acoust. Soc. Am. 101, 3111(A) (1997)].
Influence of static pressure on ultrasound propagation in plastic foams
Authors: Ayrault Christophe , Moussatov Alexei , Castagnède Bernard
Published: July 2002

The present study deals with the response of an air-saturated porous absorbing material (plastic foams) to external static pressure variation in air. Dynamics of two essential characteristics—acoustical index of refraction and transmission coefficient—are presented both analytically and experimentally. It is shown that the squared index of refraction and the logarithm of transmission coefficient depend linearly on inverse square root of pressure. The standard Johnson–Allard equivalent fluid model for porous media has been utilized. Experimental data in the pressure range from 0.2 to 5 bar at 70 and 84 kHz agree well with the model and thus provide background to a method allowing one to determine experimentally some constitutive parameters of the model. Oncoming research will define the limits of the suggested method. Some of the limits might be due to skeleton vibrations which are seldom observed in air. Promising results are obtained in tests performed with highly damping foams. Increased pressure improves the air-transducer coupling and reduces effective attenuation. It was not possible to characterize such foams earlier by ultrasonics. In addition, it does not affect scattering losses in media, thus providing an opportunity for separating scattering contribution from other losses.
Measurements of elastic properties of polymeric humidity-sensitive films at different temperatures
Authors: Caliendo Cinzia , Verona Enrico
Published: July 2002

Chemically sorbent polymeric films are commonly coated on acoustic wave devices to realize gas or vapor sensors. Temperature variations, as well as analyte adsorption, lead to softening of the film, producing a perturbation in the acoustic wave/film interaction. To achieve a high level of sensor’s performance, the chemically sensitive coating has to be characterized in terms of acoustic parameters temperature and frequency dependence. An acoustic wave device has been used as a probe of the storage and loss moduli of a thin viscoelastic film over a range of temperature (20 °C−150 °C) and of frequency (factor of more than 20). Using an equivalent circuit model of the acoustic wave/thin viscoelastic film interaction, the overmentioned moduli have been deduced as a function of temperature from the experimental data for Poly(bis-tributhylphosphine-Ni-diethynylbiphenyl), Ni-DEBP, coated acoustic device, previously tested as a sensitive layer for relative humidity detection.
Simulation of token-to-token variability in vowel production
Authors: Mooshammer Christine R. , Perrier Pascal , Payan Yohan
Published: July 2002

It has been suggested [Perkell and Nelson, Speech Motor Control (1982), pp. 187–204] that the patterns of articulatory variability observed over several repetitions of a same vowel could be explained by perceptual requirements. To further assess this hypothesis, the patterns of articulatory variability generated by the addition of noise to the motor control inputs to the tongue are studied. A 2-D biomechanical tongue model [Payan and Perrier, Speech Commun. 22, 185–205 (1997)] was used, where muscular forces are generated according to Feldman’s equilibrium point hypothesis. Target motor commands were determined for /i, y, a, e, o, u/ and noise was then added to these commands. For each vowel, ten repetitions of /əVə/ sequences were simulated. The generated patterns of variability were characterized by computing two-sigma dispersion ellipses around the target tongue position. A comparison was carried out with data collected on a native speaker of German with an electromagnetometer (EMA, Carstens AG). Simulated and collected data depict noticeable differences in orientation and size of the ellipses. This suggests that the token-to-token variability is not likely to be explained by a random inaccuracy of the motor inputs to the tongue. [Work supported by German Research Council Grant No. GWZ 4/3-1 and CNRS.]
Inventory of the used ‘‘phonetic elements’’
Authors: Sehhati Shahla
Published: July 2002

The extracted library of the phonetic elements for the speech synthesis based on phoneme cluster is extended additionally with the particularly selected elements. The auditive controlling observation and the experience by cluster segmentation have shown that the speech quality is improved by some critical phonetic combinations with the possibility of integration of the important allophone variants in the library. This paper describes the reduction of a great number of these elements into an available limited quantity and the investigation of the effectivity of extending the library with selected allophones. Generally, the criteria for the selection of combined or hybrid basic elements for speech synthesis are one of the most interesting and challenging workfields. The subjective test results confirm that, in many cases, the addition of selected allophones optimizes further the quality of the library. With earlier results [Sh. Sehhati, Erstellen von Lautelementebibliotheken under Verwendung von Phonemclustern auf der Grundlage des LPC-Sprachsyntheseverfahrens.dissertation, TU Berlin (1975)]. References: [L. Mackensen, Deutsches Wörterbuch (Südwest Verlag, München, 1967); Th. Siebs, Deutsche Aussprache, Reine und gemäβigte Hochlautung mit Aussprache Wörterbuch (de Gruyter, Berlin, 1969)].
Variation in the pronunciation of German ‘‘ein−’’
Authors: Janker Peter M. , Pompino-Marschall Bernd , Zeynalowa Seadet
Published: July 2002

Pronunciation variation of German ‘‘ein−’’ is examined (unstressed indefinite article ‘‘ein,’’ ‘‘einen,’’ as well as stressed instances of ‘‘ein−,’’ i.e., the numeral or as part of a compound) based on a larger corpus of read and spontaneous speech according to segmental variation (elisions, assimilations, etc.) and acoustic features (segmental durations, extent of formant transitions, etc.). Second, the results of a combined electropalatographical/electromagnetic-articulographical study are presented. Two male subjects uttered the items ‘‘ein’’ and ‘‘einen’’ embedded in test sentences at normal, slow, and fast speech rate. Electropalatographically tongue palate contacts for the nasal segments (duration, center of gravity of contact area) were analyzed. The EMA measurements of movement from the diphthong to nasal (or from diphthong to nasal to schwa to nasal) were done with a sensor coil mounted 1 cm behind the tip of the tongue and another one mounted on a strip of elastic foil glued to the EPG palate for sensoring velar movement. Articulatory analysis revealed quite complex gestural reductions for bisyllabic ‘‘einen:’’ Even for items without schwa elision (only at a slow rate) there is no velar closing movement for the schwa.
Imaging with a 16 000-element 2-D array
Authors: Erikson Ken , White Tim
Published: July 2002

Imaging with acoustical lenses in the low MHz frequency range using fully populated 2-D arrays offers the potential for high-resolution, real-time, 3D volume imaging, together with low power and low cost. A 2-D composite-piezoelectric receiver array bonded directly to a large custom-integrated circuit is the enabling technology for a new implementation of the original acoustical imaging paradigm. This 128×128 (16384 total) element transducer hybrid array (THA) uses massively parallel, on-chip signal processing and is intended for medical and underwater imaging applications. The system under development, which is the acoustical analog of a video camera, will be discussed in this paper.
To be nasalized, or not to be nasalized
Authors: Pan Ho-hsien
Published: July 2002

Vowel nasalization is a common process found in languages with or without phonemic contrasts between oral and nasal vowels. In English, there are no phonemic distinctions between oral and nasal vowels. Oral vowels are nasalized when followed by nasals. In Bengali and Hindi, where there are phonemic distinctions between oral and nasal vowels, oral vowels are nasalized when followed by nasals [Ferguson and Chowdhury (1960)]. In Taiwanese, which is a language with phonemic nasal and oral vowels, the presence and absence of nasality in the vowel nucleus is the major cue to lexical identification of words such as /saŋ−|bi˧/ [saŋ˧] ‘‘send rice,’’ /saŋ−mi˧/[saŋ˧m∼i˧] ‘‘send things’’ [Pan (1997)]. Thus the nasalization of Taiwanese oral vowels, which is a process based on the ‘‘ease of articulation’’ principle, would impose difficulties for lexical identification. This study used both nasal airflow and acoustical data to investigate whether Taiwanese oral vowels are nasalized when both preceded and followed by nasals in words such as /tsin-˧gɔŋ/ [tsin˧ŋɔŋ˧] ‘‘very silly.″ The results showed that Taiwanese vowels are not nasalized when positioned between nasals. It is proposed that lexical identification interacts with phonetic process and prevents the vowel nasalization from occurring. [Work supported by NSC, Taiwan.]
Influence of perturbations on chaotic behavior of the parabolic ray system
Authors: Li Xiaojun , Zhang Yu , Du Gonghuan
Published: July 2002

This paper points out that the realistic sound speed is not only a periodic function of range; there are also many other factors such as random perturbation modulating the periodic perturbation which had been investigated in previous papers. By the calculations of phase portraits, power spectra, Lyapunov exponents, etc., the influence of random perturbation on the dynamic behavior of the ray system is investigated. The study demonstrates that the random perturbation lowers the threshold from quasiperiod to chaos, and reinforces the irregularity of the trajectories which were regular originally. However, for the trajectories which were chaotic originally, the random perturbation makes their irregularity decrease slightly. Finally, the probability distribution of the Lyapunov exponent is given.
Effects of salt on bubble acoustic radiation in water
Authors: Kolaini Ali R.
Published: July 2002

Recent measurements of laboratory-generated noise by breaking waves exhibit an increase in sound-pressure levels for salt water compared to fresh water over a broader range of frequencies [A. R. Kolaini, J. Acoust. Soc. Am. 103, 300–308 (1998)]. The surprise increase in sound-pressure levels inspired the study of the effects of salt on the sound radiation by single bubbles released from various size needles. A needle assembly and a false tank (2×2×4 ft), with acoustically transparent walls placed in the middle of an anechoic tank (12×12×8 ft), were used to study the acoustical characteristics of bubbles released from needles. The false tank was filled with water that contained various percentages of sodium chloride (NaCl). In this paper, the results of experiments to examine the variations in radiated sound pressure and the change in the damping coefficient of bubbles as the salinity level increased are reported. The effects of a surfactant agent such as Triton™ 100-X and other mineral acids such as HCl on the bubble acoustic radiation are discussed. The observations show that the change in the local surface tension may not alter the acoustic radiation, whereas the local influence of the ions on water structure, possibly related to the electric repulsion, may play a dominant role in altering the sound pressure and significantly reducing the quality factor of the bubble sound.
On solution techniques for cochlear models: Reply to “Comments on ‘A method for forward and inverse solutions of a three-dimensional model of the cochlea’ ” [J. Acoust. Soc. Am. 103, 3729 (1998)]
Authors: de Boer Egbert
Published: July 2002

This note explains steps in the solution of a three-dimensional model that have been criticized. The emphasis is on “separation” of variables in the Laplace equation.
Wavefront and group velocity in relaxing and bubbly fluids
Authors: Leander Johan L.
Published: July 2002

In this paper it is demonstrated that a theoretical model for wave propagation may indeed correspond to a well-posed transient problem although the group velocity for finite frequencies becomes greater than the high frequency limit of the phase velocity, negative or even infinite. Sufficient conditions for causality are derived and the particular cases of relaxing and bubbly fluids are considered so as to show some of the properties of the group velocity concept.
Near-field responses from the round window, inferior colliculus, and auditory cortex of the unanesthetized chinchilla: Manipulations of noiseburst level and rate
Authors: Burkard R. F. , Secor C. A. , Salvi R. J.
Published: July 2002

Few studies have compared the response properties of near-field potentials from multiple levels of the auditory nervous system of unanesthetized animals. The purpose of this study was to investigate the effects of brief-duration noisebursts on neural responses recorded from electrodes chronically implanted at the round window, inferior colliculus and auditory cortex of chinchillas. Responses were obtained from seven unanesthetized chinchillas to a noiseburst-level and noiseburst-rate series. For the noiseburst-rate series, a 70 dB pSPL noiseburst was varied in rate from 10 to 100 Hz using conventional averaging procedures, and from 100 to 500 Hz using pseudorandom pulse trains called maximum length sequences (MLSs). Response thresholds were similar for the compound action potential (CAP), inferior colliculus potential (ICP) and auditory cortex potential (ACP). With decreasing noiseburst level, there were decreases in the amplitudes and increases in the latencies of the CAP, ICP and ACP. The shapes of the mean normalized amplitude input/output (I/O) functions were similar for the ICP and ACP, while the normalized I/O functions for the first positive peak (P1) and first negative peak (N1) of the CAP differed from each other and from the ICP and ACP. The slopes of the latency/intensity functions were shallowest for the CAP, intermediate for the ICP, and steepest for the ACP. With increasing rate, the latency shift was least for the CAP, intermediate for the ICP and greatest for the ACP. The amplitude of P1 of the CAP varied little with rate. All other potentials showed a pronounced decrease in amplitude at high stimulation rates. Excluding CAP P1, proportional amplitude decrease with rate was greatest for the ACP, intermediate for N1 of the CAP and least for the ICP. Responses were present in most animals at all recording sites, even for the highest rate (500 Hz) used in this study. For all potentials, the MLS procedure allowed the collection of a response at rates well above those where sequential responses would have overlapped using conventional averaging procedures.
A study of damping effects on spatial distribution and level of reverberant sound in a rectangular acoustic cavity
Authors: Franzoni Linda P. , Labrozzi Danielle S.
Published: July 2002

Based on computer simulations of sound fields in rectangular enclosures, important observations are made regarding sound pressure levels and the spatial variation of the broadband reverberant field. From these observations an empirical formula is deduced that describes the slow spatial variation of the broadband reverberant mean-square pressure in one lengthwise direction. Two room shapes were studied: an elongated rectangular enclosure and an almost cubic enclosure, both with broadband sound source(s) on an endwall. Source position, relative phasing of multiple sources, level, and placement of absorptive material were variables in the study. The numerical results for the spatially averaged mean-square pressure in the reverberant field were often not in very close agreement with values predicted from a traditional Sabine approach. The prediction was improved by accounting for the power absorbed on the first reflection and an approximate formula is given for this correction factor. The reverberant sound field is characterized by a gradual spatial variation in the direction away from the source. This spatial variation scales exponentially with the sidewall absorptivity, as demonstrated by the numerical simulations. An approximate emperical formula is shown to predict this spatial variation fairly well. The computer simulations showed elevated sound pressure levels at the enclosure boundaries, for all cases, and also in the interior, for sound fields excited by a single broadband source on an endwall. These intensification zones occur along a plane in front of the source and along a plane which corresponds to the reflection of the source, whether or not the source is on a line of symmetry.
Uncertainties in estimates of lesion detectability in diagnostic ultrasound
Authors: Wear Keith A. , Gagne Robert M. , Wagner Robert F.
Published: July 2002

Statistical properties of estimates of focal lesion detectability for medical ultrasonic imaging systems are investigated. Analytic forms for bias and variance of estimates of detectability of a lesion consisting of fully developed speckle embedded within a speckle background are derived. Bias and variance of estimates of detectability are investigated using a computer simulation and experiments on tissue-mimicking phantoms. This work offers a systematic methodology for interpreting measurements on phantoms in order to assess lesion detectability. In addition, it provides useful results which may be used to improve design of phantoms and experiments for imaging-system performance assessment.
Comments on “Capped ceramic underwater sound projectors: The ‘cymbal’ transducer” [J. Acoust. Soc. Am. 105, 591–600 (1999)]
Authors: Goodman Jerome
Published: July 2002

The paper by Tressler, Newnham, and Hughes titled “Capped ceramic underwater sound projector: The ‘cymbal’ transducer” brought back some old memories.
Acoustical analysis of infant/toddler rooms in daycare centers
Authors: Frank Tom , Golden Matthew V.
Published: July 2002

The purpose of this ongoing research is to determine ambient noise levels, signal-to-noise ratios (SNRs), and RTs in daycare centers. To date, 248 measures of ambient noise levels have been obtained in occupied infant/toddler rooms of 11 daycare centers and 109 measures in 7 of the 11 daycares unoccupied. The mean occupied levels were 57 dBA and 66 dBC and the mean unoccupied levels were 38 dBA and 56 dBC. A 1/3 OB analysis revealed that the occupied levels were relatively constant (46–50 dB) from 63 to 2000 Hz while the unoccupied levels decreased as frequency increased especially after 125 Hz. Using several different speech spectrums compared with the occupied 1/3 OB levels, estimated SNRs ranged from −3 to 12 dB. Dosimeter measurements (N=932) revealed that the occupied daycares had an average peak sound level of 103 dB, high-threshold level of 62.5 dB, time-weighted average of 55.9 dB, and noise dose of 1.3%. Additional noise measurements and RTs are currently being collected. Overall, the unoccupied dBA levels and the estimated SNRs were less than recommended in the ASHA 1995 guidelines for classroom acoustics. [Work supported by PHS/NIH (1-R01-HD31540-01A2) Otitis Media, Behavior and Attention in Daycare.]
Distributed acoustic model of the entire respiratory tract
Authors: Harper Paul , Pasterkamp Hans , Kraman Steve S. , Wodicka George R.
Published: July 2002

The anaylsis of breathing sounds measured over the extrathoracic trachea has been used to detect and monitor respiratory tract changes such as those found in asthma and obstructive sleep apnea. To begin to link the attributes of these easily measured sounds to the underlying anatomy, a lumped-element model of the acoustic properties of the entire respiratory tract (supraglottal plus subglottal airways) with varying cross-sectional area, yielding walls, and dichotomous branching in the subglottal component was developed over the frequency range from 100 to 3000 Hz. The portions of the model above and below the larynx (supra- and subglottal) predict well the distinct locations of the spectral peaks from speech sounds such as /ah/ as measured at the mouth and the trachea, respectively, in healthy subjects. When combining the supra- and subglottal portions in a complete tract model, the predicted peak locations compare favorably with those of tracheal sounds measured during normal breathing in the same subjects. In addition, the model predicts both the direction and magnitude of the relatively small spectral shifts that occur in tracheal sounds during a neck flexion/extension maneuver, indicating that measurable acoustic parameters are sensitively tied to respiratory tract dimensions.
Reduced interference distribution application and interpretation for transient acoustic events
Authors: Williams William J.
Published: July 2002

Transient acoustic events often present difficulties when using conventional time-series or spectral methods. The Reduced Interference Distribution (RID) and its derivatives have been under development [W. J Williams and J. Jeong, Time-Frequency Signal Analysis, edited by B. Boashash (Longman Cheshire, New York, 1992)] for several years. The RID was specifically motivated by the need for a better analysis tool for transient acoustic events [ONR Grants N00014-90-J-1654, N00014-97-1-0072]. The deficiencies of the spectrogram for marine mammal sound analysis were early recognized [William Watkins, Marine Bioacoustics 2, 15–43 (1966)]. Watkins’ illustrations of spectrogram deficiencies and updated results obtained using the Wigner distribution (WD) and the RID will be presented. The RID represents an attempt to retain the desirable mathematical properties of the WD while reducing the often troublesome WD interference terms. Examples drawn from several acoustic transients such as marine mammal sounds, joint clicks and vortex formations in turbulent air flow will be used to illustrate the usefulness of the RID approach. The importance of retaining such properties as proper time and frequency marginals; time and frequency support along with proper group delay and instantaneous frequency will be discussed. The value of covariance with time and frequency shifts and scale changes will also be emphasized.
Detection and identification for highlight echo using the time-frequency postaccumulation method
Authors: Zhu-Ye  , Gong-suying
Published: July 2002

The highlight distribution of underwater target in active sonar is the main characteristic for target identification. The pulse compression with chirp signal is a current method for target echo detection. But sonar highlight echo is always time-frequency fading and the background reverberation is nonstationary, so that the matched filter is not optimum to detect the highlight echo. Based on that a linear-frequency modulation signal, the peak trace of the ambiguity function (AMF) or the Wigner–Ville distribution (WVD), is linearity, the accumulations along the peak trace (APT) (analog to Radon transform in image processing) of both the WVD and cross-AMF of multi-target echo are developed in this paper. The method is applied to a simulated multi-target echo and practical highlight echoes of the target. The detection characteristics and performances are comparison for both accumulations with matched filter. The results of the analysis and simulation are shown: (1) In detection performances, the APT–WVD and APT–CAMF are superior to the matched filter if the accumulating time is selected properly and especially if the background spectra is not even. (2) In multi-target resolution, the APT–WVD is superior to the APT–CAMF. (3) The APT–WVD need not know the reference signal which can be estimated by this method.
Locating animals from their sounds and tomography of the atmosphere: Experimental demonstration
Authors: Spiesberger John L.
Published: July 2002

Calling animals are located using widely distributed receivers, and the sounds from the animals are used to map the sound speed and wind fields by means of tomography. In particular, two Red-Winged Blackbirds Agelaius phoeniceus are correctly located within a meter using recordings from five receivers spread over a 20×30-m2 region. The demonstration hinges on two new developments. First, a new algorithm for blindly estimating the impulse response of the channel is shown capable of estimating the differences in the time of first arrivals at two receivers. Since it is known that the first arrivals travel along nearly straight paths, the difference in time constrains the animal’s location to a hyperboloid, and the animal is located by intersecting hyperboloids from many pairs of receivers. Second, in order to accurately find the intersection point and map the sound speed and wind fields using tomography, a nonlinear equation is solved. The new algorithm for blindly estimating the impulse response of a channel offers a new way for locating sounds and making tomographic maps of the environment without any requirement for a model for the propagation of sound such as is needed for focalization, matched field processing, and conventional tomography.
Can the use of signal curvature improve identification of bats in flight using echolocation calls alone? A test using discriminant analysis and artificial neural networks
Authors: Parsons Stuart , Jones Gareth
Published: July 2002

Echolocation calls of bats are highly flexible and have been shown to vary within species due to habitat, foraging ecology, individual identity, family affiliation, sex, and age. Calls also vary between species due to morphology, habitat preference, and foraging ecology. Such plasticity in call design has made the development of species identification systems extremely difficult. Techniques employed previously include microphones linked to event recorders, manually tuning heterodyne bat detectors, zero-crossing analysis, discriminant function analysis (DFA) of time and frequency characteristics of calls, and synergetic analysis of spectrograms. To date, all have met with limited success. Research at the University of Bristol has combined estimates of curvature with ‘‘traditional’’ measures of echolocation calls (duration, start frequency, end frequency, frequency with most energy) to increase the precision of species identification. Call parameters were analyzed using a backpropagation neural network and DFA. Results indicate that a correct identification rate of 96% was possible for 14 species of British bats using the neural network. This compares with a success rate of 80% using the same data analyzed by DFA and represents the highest identification rate yet achieved.
The digital archiving project at the Borror Laboratory of Bioacoustics
Authors: Nelson Douglas A. , Gaunt Sandra L. L. , Bronson C. L. , Burnett Stephen C. , Hough Gerald E. , Beeman Kim
Published: July 2002

The Borror Laboratory of Bioacoustics (BLB) at The Ohio State University is a research facility with an archive of recorded animal sounds collected primarily by BLB staff and associates. The 25000 sound recordings are scientific data that require special treatment to ensure their longevity, and the BLB is, like other sound archives, dedicated to the preservation of these recorded sounds. Traditionally, sound recordings have been archived on analog 1/4-in. magnetic tape. However, magnetic tape is degraded by time, usage, and excess temperature and humidity. Additionally, access to data on analog tapes is slow. Facing loss of access to data, especially on tapes exceeding their 50-year life expectancy, we are copying the collection to digital format [compact disk recordable (CDR)] with the aid of funding from the National Science Foundation. Because digital technology has been tested and refined over nearly two decades, and CDR media for storage of digital data now sustains a viable commercial market, archives can today endorse their use. We present the limitations of analog technology, the limitations and benefits of digital technology and CD storage, and outline the production process and safeguards developed by us for this task. [Work supported by NSF DEB-9613674.]
Phase-contrast optical imaging of transient acoustic signals
Authors: Clement Gregory , Letcher Stephen
Published: July 2002

An optical imaging technique is described that utilizes a phase-contrast Fourier filtering technique to reconstruct acoustic signals in space at constant times. The system is similar to the pulsed, central-order schlieren method, but uses a Fourier filtering technique that images the actual acoustic pressure field, where the former technique reconstructs only the absolute value of the field. Signals resulting from a low-amplitude, 500-kHz, single-cycle sinusoidal pulse input to an underwater piezoceramic transducer are presented. Relative pressure fields are tomographically reconstructed in space over a series of times after the source excitation. A Hankel-transform-based algorithm exploits the cylindrical symmetry of the field for efficient reconstruction. The data are compared with synthetic signals calculated using the impulse response approach. Theory and limitations of the phase contrast system are discussed. a)Currently at Harvard Medical School, Boston, MA.