bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of wind-wave generated bubbles on sonic boom noise penetration into the ocean
Authors: Rochat Judith L. , Sparrow Victor W.
Published: July 2002

Supersonic aircraft, particularly the projected high speed civil transport (HSCT), fly over the ocean to minimize the sonic boom noise impact on land. This noise interacts with the ocean surface, causing an underwater pressure disturbance. In steady, level supersonic flight at less than Mach 4.4 over a homogeneous ocean, the underwater disturbance is a decaying evanescent wave persisting in depth to 100 m or more. Realistically, however, the ocean is not homogeneous and contains wind-wave generated bubble clouds near the surface. In the current research, a two-dimensional finite difference simulation is used to predict underwater sound levels due to a sonic boom impinging on an ocean with bubble layers near the surface. Each of the bubble layers has an approximate sound speed appropriate for its corresponding depth; bubbles in the ocean can cause the sound speed to drop as low as the speed of sound in air. In this presentation the effects of bubble layers on the sonic boom noise penetration will be described. Preliminary results show that one can get propagating waves in the upper bubble layers but only evanescent waves below the layers. [Work supported by NASA Langley Research Center, under Grant NAG 1-1638.]
Auditory motion aftereffects with varying interaural time differences
Authors: Uematsu Hisashi , Kashino Makio , Hirahara Tatsuya
Published: July 2002

After prolonged listening to a sound moving across the horizontal plane (adapter), a stationary sound (test) can be perceived as moving in the opposite direction. In experiment 1, the magnitude of the auditory motion aftereffect for 500-Hz tones was measured as a function of adapter velocity using the method of constant stimuli. Apparent sound movement was produced by varying only interaural time differences (ITDs). In each trial, an adapter whose ITD varied in the range of ±600 μs with a given rate (velocity) was presented for 10 s, followed by a 1-s test whose velocity was chosen randomly from seven values surrounding zero. Subjects judged whether the test moved to the left or right, and subjective stationary points were obtained. Negative aftereffects were observed when the adapter velocity ranged between 300 and 600 μs per second. In experiment 2, the magnitude of the aftereffect was measured as a function of the frequency difference (Δf) between pure-tone adapter and test, using the same procedure as experiment 1. The aftereffect was reduced with increasing Δf, and disappeared when Δf was 1/2 oct. The results will be discussed in terms of ITD–change detectors each tuned to a specific range of ITD change and frequency.
Head movements in localization
Authors: Yost William A. , Mapes-Riordan Dan
Published: July 2002

Head movements in all three planes were measured while listeners localized a pulse of transient sounds (train of 100 μs broadband impulses) located in the frontal azimuth plane. The eight loudspeakers were at the same height as the head of the seated listener. They were located every 25.7° from +90° to −90°, where 0° is straight ahead. Some listeners were able to see the eight sound sources, while for other listeners the sound sources were hidden from view. In addition, listeners were instructed differently in terms of the necessity for high accuracy or fast reaction. In all cases, the primary means of the listener locating the sound source was head movements. Listeners were instructed to face the source of the sound so that their nose was facing directly at the perceived sound source. The results will be discussed in terms of processing sounds in dynamic listening situations. [Research supported by the Air Force Office of Scientific Research and a Program Project Grant from the NIDCD, DC00293.]
One-channel time-reversal in a chaotic two-dimensional silicon cavity
Authors: Draeger Carsten , Fink Mathias
Published: July 2002

Acoustic time-reversal experiments usually need large arrays of transducers. An element reduction normally decreases the aperture and thus degrades reversal or focusing quality. However, one can use reflections to increase artificially the transducer aperture. It is shown that in a reflecting cavity with negligible absorption, a time-reversal of a pointlike source can be performed using a single element. The wave field is measured by the transducer over a long period of time at a point inside the cavity, and then the time-reversed signal is reinjected at the same location. The wave field thus created forms wave fronts of the same shape as the initially emitted ones, but propagating in the opposite direction. They finally collapse at the location of the initial source, leading to excellent focusing which is not aperture limited. The difference between a perfect and a one-channel time-reversal can be quantified. A chaotic shape of the system guarantees a successful time-reversal; in some regular cavities, the procedure fails. One-channel time-reversal experiments have been successfully carried out using elastic waves in a silicon wafer. Finite-difference computations simulating a time-reversal of a two-dimensional scalar wave field complete this work.
Effect of noise and solvents on hearing: Findings from three field studies
Authors: Morata Thais C. , Franks John R.
Published: July 2002

A holistic approach to studying the workplace as a combination of physical, chemical, biological, and organizational factors is receiving growing attention. This approach includes initiatives to investigate the potential interaction between noise and chemicals. NIOSH has conducted three cross-sectional studies on the effects of solvents on hearing, alone or in combination with noise. Audiometric thresholds were compared with ISO 1999 estimates, and the prevalence, risk ratios, and predicted probability of developing a hearing loss were calculated. In all of the investigations, solvent mixtures which had toluene as a main component were found to affect the hearing of workers exposed to low noise levels. Considering the multiplicity of chemicals that are used occupationally and evidence that some are ototoxic, it is conceivable that numerous populations are being underserved regarding hearing loss prevention since the permissible exposure levels for chemicals do not take into account their potentiation of hearing loss. Workers who are exposed to A-weighted noise levels below 85 dB time-weighted average are not required to be included in hearing conservation programs. Furthermore, methods currently used in hearing conservation (e.g., hearing protectors and noise control) may be insufficient, or even inappropriate, for workers exposed to both chemicals and noise.
Teaching musical acoustics as an introduction to engineering technology
Authors: Collier Robert D.
Published: July 2002

The design and performance of musical instruments is a course which is designed to: (a) motivate first-year students to select engineering through hands-on learning, and (b) provide students in music and the liberal arts with an appreciation for its role in the enhancement of both music making and music listening. This course may be viewed as an alternative to traditional science courses. The mechanisms of sound generation illustrate the interdisciplinary factors involved in instrument design: materials and structures, aero and structural dynamics, vibration, mechanical systems and controls, and signal analysis. Most importantly, musical acoustics serves to demonstrate the significance of human factors in engineering design and performance. The core of the course is in the students’ laboratory experience in which they investigate instruments of their own choosing and which is augmented by field trips and lecture demonstrations by noted musicians. This paper includes the course outline and structure, examples of student projects, and their response.
Active noise control with multiple, correlated reference signals
Authors: Tu Yifeng , Fuller Chris R.
Published: July 2002

The application of active noise control has been extended from single noise source, one-dimensional acoustical fields to complicated multiple noise source, three-dimensional acoustical fields. The application to a multiple noise source environment usually requires multiple reference sensors to generate a complete vector of reference signals. A widely adopted control configuration feeds each reference signal into a different control filter. This approach suffers from the problem of ill-conditioning when the reference signals are correlated. The problem of ill-conditioning results in slow convergence rate and high sensitivity to measurement error especially when the FXLMS algorithm is applied. A practical method is presented to pre-process the reference signals based on the Wiener filter theory and Gram-Schmidt orthogonalization which overcomes these problems. Simulations and experiments have been conducted to verify the issues associ- ated with multiple reference ANC when the signals are correlated. The results presented are consistent with the theoretical analysis. [Work supported by ONR.]
Frequency dependence of decoupling filters for multichannel feedforward active noise control
Authors: Cabell Randolph H. , Fuller Chris
Published: July 2002

The performance of multichannel feedforward LMS-type control algorithms is improved if control is implemented in noninteracting coordinates. A decoupling matrix can be applied to sensor inputs and actuator outputs to transform the harmonic feedforward control problem into an orthogonal (i.e., principal component) coordinate system. Convergence of the adaptive algorithm is faster in the principal coordinate system, and sensitivity to sensor noise can be reduced by eliminating components associated with ill-conditioning. One question that arises is how quickly the decoupling matrix changes with frequency. This is important for control systems where the excitation frequency might wander about a nominal value. Results of a numerical study of this frequency dependence show that the decoupling matrix is stationary around a resonance, and has the highest rate of change between resonances. However, in some cases the matrix remains stationary between resonances. The frequency dependence of the decoupling matrix will be discussed for three control systems: a simply supported plate, a plate radiating into a half-space, and an enclosed cavity. [Work supported by NASA Langley Research Center.]
Comparison of controller power requirements for output feedback control of broadband structural acoustic radiation
Authors: Smith G. Clark , Clark Robert L.
Published: July 2002

Performance comparisons of active structural-acoustic control system designs with respect to controller power requirements are important for practical implementation. In this work, a broadband measure of controller energy usage per unit of input disturbance energy is developed. This metric is the H2 norm of the system transfer matrix from the disturbance signals to the control actuator signals. Comparisons of acoustic performance are made for three output feedback controllers, each designed to reduce one of the following variables: (1) sound power radiation; (2) structural modal velocity; and (3) structural velocity at twelve discrete points. All three controllers were designed such that their controller power requirements were equivalent. An array of five, exogenous, point-force disturbances were used to drive a plate model, and each control system utilized the same three colocated point-velocity sensor and point-force actuator pairs. Analytical results demonstrate that the cost functional based upon sound power places a greater emphasis in controlling the low-frequency bandwidth. This controller provides 2.5-dB greater sound reduction than design ♯2 in the third octave band including the first radiation mode and 2.7-dB greater reduction than ♯3 in the same band. [Work supported by NSF Career Program CMS-9501470.]
Perception of features in the identification of English consonants
Authors: Doeleman Tobey L.
Published: July 2002

The perception of voicing, manner, and place of articulation was investigated in a series of gating experiments in which subjects identified English consonants in six different duration conditions. The stimuli were created from natural speech consonant tokens excised from C[a] syllables. The consonants were then gated to include 10% to 50% of the total consonant duration from the onset, to which vowel babble was appended in order to make listeners less sensitive to the absolute duration of the stimuli. In experiment 1, subjects were presented with eight consonants [p, t, b, d, f, s, v, z] and results were analyzed in terms of correct identification for the following features: voiced or voiceless, stop or fricative, and labial or alveolar. In experiment 2, subjects were presented with two mutually exclusive sets of stimuli (subsets of the stimuli from experiment 1) such that the information for a particular feature was given (e.g., voicing given in the sets [p, t, f, s] and [b, d, v, z]). A comparison of the results of the two experiments will show whether certain feature information facilitates the perception of any other feature. Results will be discussed in relation to a psychological model of speech perception.
The identification and discrimination of a non-native nasal series by Bengali and American English listeners
Authors: Harnsberger James D.
Published: July 2002

Predictions based on the perceptual assimilation model (PAM) (Best, 1995) concerning the perception of non-native contrasts rely primarily on three factors: the contrast in question, the inventory of native categories, and the degree of gestural similarity between them. To determine if these factors are sufficient for predicting listeners’ difficulties, nasal contrasts from three languages, Malayalam, Marathi, and Oriya, varying in place of articulation (bilabial, interdental/dental, alveolar, and retroflex), syllabic position, and vowel context, were presented in an AXB discrimination test and an identification test with category-goodness ratings to sixteen speakers each of American English (AE) and Bengali. AE and Bengali were selected for their similar nasal series ([m], [n], and [■]). However, Bengali differs from AE in its use of dental and retroflex oral stops. PAM should predict equivalent performance for both subject groups. However, a pilot of this study demonstrated poorer performance by Bengali listeners on dental-retroflex (34.6% mean correct to AE 53.6%) and interdental-alveolar (33.2% to AE 69.6%). The implications of these results for phonological and phonetic factors in the perception of non-native contrasts will be discussed.
Nonnatives’ perception of English sentences presented in noise
Authors: Meador D. , Flege James E. , MacKay Ian R. A.
Published: July 2002

This study built on earlier investigations of the effects of noise on speech identification by nonnative speakers. Oyama showed that the ability of native Italian subjects to identify speech in noise was inversely related to their age of arrival (AOA) in the United States [J. Psycholinguist. Res. 5, 261–283 (1976)]. Mayberry and Fischer showed that more phonological and fewer semantic errors are made the later sign language is acquired, indicating that late learners allocate more attention to bottom-up processes [Mem. Cognit. 17, 740–754 (1989)]. Subjects in the present study were native English (NE) and Italian/English bilinguals differing in their AOA in Canada. The stimuli were naturally produced, semantically unpredictable English sentences. Subjects repeated as much of each sentence as possible as it was presented at successively higher S/N ratios (−6, 0, 6, 12 dB). NE subjects outperformed the bilinguals, despite the latter’s lengthy residence in Canada (M=35.4 years). The bilinguals’ performance varied inversely as a function of AOA. Scores were also related to individual differences in phonological short term memory. Additional analyses will determine whether late learners allocate more attention to bottom-up processes than do NE subjects. [Work supported by NIH.]
Reduction of requirements and restrictions for near-field acoustic holography in cavities
Authors: Kay Kelly Q.
Published: July 2002

Recently, Williams and Houston developed a near-field acoustic holography (NAH) method for generic cylindrical cavities [Proc. Internoise 96, 2553–2558]. Previously, cavity NAH methods required restrictions or gross assumptions, which limited their use to specific cases. The Williams–Houston method, on the other hand, is valid inside any practical cylindrical boundary. The method, though, requires prior measurement of the near field of all boundaries, whether they contain sources or not, even when boundaries are locally reacting with a known acoustic impedance. Also, because of singularities in the Green’s function used, reconstructions could not be performed at some frequencies. This work is based on the Williams–Houston method, and presents several significant improvements and contributions. Most importantly, scattering off locally reacting cavity boundaries is accounted for in the Green’s function, reducing the required number measurements and processing, for a given resolution. As well, Green’s functions are solved for with consideration given to the uniqueness and existence of the acoustic field to allow reconstructions to be performed over a continuous range of frequencies. A set of cavity NAH Green’s functions are developed in Cartesian coordinates, extending the method to parallel walled rectangular (box) cavities. Reconstruction results comparing the methods will be presented.
Pulsed beam pre- and post-processing for localized inverse scattering
Authors: Melamed Timor , Heyman Ehud , Felsen Leopold B.
Published: July 2002

Well-collimated short pulse wave packets, also termed pulsed beams (PB), provide new options for local forward and inverse probing of targets or of a propagation environment. The spatial-temporal resolution achieved under the PB excitation conditions furnishes an unambiguous measure of where the ‘‘physical’’ signal resides, in contrast to frequency-domain procedures that must rely on more intricate phase discrimination. In this paper, PB forward and inverse modeling is applied to scattering by three-dimensional weak (Born-type) inhomogeneities with finite support in an otherwise homogeneous background fluid. By performing space–time and wave number–frequency analysis and synthesis in a phase space setting, conventional slant-stack tomography is pushed to its ultimate localization by PB pre- and post-processing. The implications of this scenario with respect to resolution and related issues are discussed. It is shown that this strategy reduces the inversion of the illuminated space-time scattering cell to a pseudo-one-dimensional problem determined by the orientation of the incident and scattered beam axes. Illustrative examples are included.
Applications of binary noiselike sequences to the simultaneous measurement of multichannel system functions
Authors: Rollow Douglas , Swanson David C.
Published: July 2002

A variety of binary sequences exhibit known correlation properties which can be exploited to simultaneously measure system functions in a multiple-input, multiple-output system. This work considers the practical application of codes such as linear maximal sequences and Gold codes for these measurements, and experimental data are presented for a fluid–structure interaction problem. Applications in multichannel active noise control systems and to the measurement of mutual coupling factors in transducer arrays are discussed. [Work supported by the Exploratory and Foundational fund, Applied Research Laboratory.]
An overview of ray chaos
Authors: Brown Michael G. , Tappert Frederick D.
Published: July 2002

Important aspects of ray chaos will be reviewed, emphasizing topics which relate to the Hamiltonian structure of the ray equations. Topics to be discussed include integrable and nonintegrable ray systems, action-angle variables, the breakdown of canonical perturbation theory, the KAM theorem, area-preserving mappings, power spectra, Lyapunov exponents, and the notion of a ‘‘predictability horizon.’’ Connections between ray chaos and chaos in the classical limit of quantum mechanics will be discussed. The notion of ‘‘wave chaos’’ will be introduced. The important, and as yet unresolved, question of whether ray-based wavefield representations break down under chaotic conditions at a range which is proportional to the logarithm of the acoustic frequency will be discussed. [Work supported by ONR.]
Quantum chaos in a stochastic model
Authors: Tappert F. D. , Wolfson M. A.
Published: July 2002

An idealized problem in the theory of long-range ocean acoustic propagation through randomly fluctuating mesoscale structure is reformulated as a time-dependent quantum mechanics problem with a time-varying Markovian potential function. The effective Planck constant is ℏ=δε−2/3, where δ=(k0l)−1≪1 measures diffraction, and ε≪1 is the strength of the mesoscale structure. Also k0 is the acoustic wave number and l is the scale length of the mesoscale structure. In the formal classical limit (ℏ→0), the parabolic ray equations are nonintegrable and the relative motion of two particles for small initial separations exhibits chaotic behavior characterized by a positive Lyapunov exponent, ν∼ε2/3/l. It is shown that this physically relates to the exponential proliferation of caustics. A generalized wave kinetic equation (GWKE) is derived for the evolution in phase space of the two-particle Wigner function. The GWKE is analytically examined for ℏ≪1 by a novel boundary layer method, called the ‘‘extended quantum notch method,’’ which yields several important results: First, the ‘‘log breakdown time (range)’’ tb∼ν−1log(ℏ−1) is obtained where semi-classical theory breaks down due to the saturation of caustics, and it is shown that this is the range where the scintillation index saturates to unity; and, second, a wave (quantum) manifestation of classical chaos is found to be the exponential decay of the scintillation index beyond its peak value. [Work supported by ONR.]
Hot topic in architectural acoustcs: Auralization
Authors: Campbell Richard H.
Published: July 2002

High-speed computers and digital signal processing have brought us to the point where it is possible to hear a convincing simulation of the acoustic environment of an auditorium. A number of researchers around the world have contributed for years to this field and they have now assembled the major pieces of the puzzle to make this powerful tool, called ‘‘auralization,’’ work well enough to judge acoustic quality. One needs a computer model of the acoustic space including placement of sources and receivers, an appropriate source signal, a binaural spatial transfer function from free-field pressure to eardrum pressure, and a headset which has a known equalization function from the electrical signal to the wearer’s eardrum. A typical auralization session first runs the room computer model gathering sound ray arrival data at one receiver from a source. This receiver signal is then convolved with the binaural HRTF to produce a binaural electrical signal for the headset, which is equalized to achieve flat subjective response for a particular headset. The results are astonishing but positional accuracy in 3-D space is yet to be completely evaluated. Auralization provides an extra and independent layer of design security. Importantly, acoustic disasters can be avoided.
Subharmonic imaging with gas-filled microbubbles
Authors: Shi William T. , Forsberg Flemming , Goldberg Barry B.
Published: July 2002

The nonlinear properties of gaseous contrast agents can be used to create new ultrasound imaging methods, such as harmonic and subharmonic imaging. Those methods are capable of separating the echoes from the contrast bubbles in blood and those from surrounding tissue. Harmonic images are produced by transmitting sound pulses at one frequency, but receiving echoes at double that frequency, while subharmonic images receive echoes at half that frequency. Experiments revealed that the subharmonic component of echoes from some contrast agents, at relatively high acoustic pressure, was greater than the second-harmonic component. Since harmonic imaging suffers from a reduction in image contrast, due to second-harmonic generation during ultrasound propagation, as well as second-harmonic leakage from the transmitted signal, this finding makes subharmonic imaging an attractive alternative to harmonic imaging. Harmonic response measurements with a pulse–echo arrangement and subharmonic images obtained with a modified scanner will be presented. The acoustic pressure threshold for subharmonic generation was found to be quite different for contrast agents with different compositions. The optimal transmitted ultrasound pulses and the reception strategy for subharmonic imaging will also be discussed.
Attention blinks in pure tone rapid auditory presentation
Authors: Goddard Kim M. , Isaak Matthew I. , Slawinski Elzbieta B.
Published: July 2002

When a target in a rapid (11 items/s) series of visual items is attended, the perception of a subsequent probe is impaired if the probe occurs within 500 ms. If this attentional blink (AB) reflects central processing limitations, then an AB should be found using auditory stimuli. Existing investigations, however, have used compressed speech stimuli, namely spoken letter or digit names. Because these stimuli are susceptible to visual recoding, the possibility that the AB reflects a vision-specific bottleneck cannot yet be dismissed. To redress this problem, pure tones were used in place of compressed speech stimuli. Participants heard rapid auditory streams comprising 20 tones ranging in frequency from 1000 to 2500 Hz. All tones were 50 dB except the target and probe, which were more intense on independent random halves of the trials. Participants detected the loud target and then detected whether the stream contained a second loud tone. Preliminary results show an auditory AB. The AB appears to reflect general, modality-independent limitations. Future work will examine the relationship between the visual, compressed speech, and pure tone ABs. If the AB reflects central limitations, the magnitudes of the three ABs should correlate positively. [Work supported by NSERC.]
Laterality differences between children who clutter and stutter
Authors: Blood Ingrid M. , Blood Gordon W. , Tellis Glen M.
Published: July 2002

Cluttering is a disorder of speech and language processing resulting in rapid, dysrhythmic, sporadic, unorganized, and frequently unintelligible speech. It is an impairment in formulating language and can be accompanied by accelerated speech [Daly (1992)]. Numerous similarities have been reported between cluttering, stuttering, and central auditory processing disorders. This study examined cerebral dominance and processing using 120 trials of a consonant–vowel dichotic listening task in 15 subjects (5 children who stuttered, 5 children who cluttered, and 5 children with no disfluency problem). Results revealed that during the free recall task, significant right ear advantages (REA) were found for all control subjects. REAs were reported for 3 of 5 children who stuttered and 2 who had left ear advantages (LEA). Children who cluttered exhibited 4 no ear advantages (NEA) and 1 REA. During the directed right ear and directed left ear listening tasks, children who cluttered and control subjects showed strong ear advantages. Children who stutter showed mixed findings on these tasks. The discussion includes the use of dichotic ear advantages in differentiating children who stutter and clutter.
Insert earphones: Calibration and reference thresholds
Authors: Frank Tom
Published: July 2002

Since their introduction in 1984, insert earphones (Etymotic ER-3A and EARtone 3A) have gained widespread popularity for numerous applications in audiology, hearing science, and for different hearing aid fitting procedures. This informational poster describes several procedures that can be used for output calibration using different coupler types specified by ANSI, IEC, and ISO. This will be done by describing step-by-step calibration procedures. Further, ANSI and ISO insert earphone reference threshold levels for pure tones and speech will be presented for different coupler types.
Cross-linguistic speech rhythm in a phrase repetition task
Authors: Tajima Keiichi
Published: July 2002

Language-specific and language-general aspects of speech rhythm were explored in a repetitive speech production task, whereby native English and Japanese speakers repeated phrases in time with an auditory metronome. Subjects were instructed to repeat each phrase (e.g., English ‘‘Give the dog a bone’’) once per metronome beep, aligning the beginning of the phrase with each beep. The rate of repetition was systematically manipulated by varying the metronome rate from slow to fast across trials. Rhythmic properties of the utterances were investigated by marking the vowel onset of each syllable, and expressing it in terms of phase with respect to the beginning of the current repetition and that of the following repetition. Preliminary results indicate that, while there was considerable variability across speakers and repetitions, there was a language-general tendency for prominent syllables to cluster around rhythmically motivated phases, such as 1/2 or 2/3. For a subset of the data, abrupt jumps from one stable phase to another were also found, suggesting quasi-categorical modes in rhythmic speech production. The data further address language-specific issues such as the nature of stress-timing in English, and the role of supra-moraic, ‘‘foot’’-level units in Japanese rhythm.
Sentence duration as an index of overall proficiency in an L2
Authors: Guion Susan G. , Flege James E. , Liu Hua , Yeni-Komshian Grace
Published: July 2002

Maximum reading rate in the native and second language has often been used to assess bilingual balance. In the present study, the duration of L2 sentences produced at a nonmaximal rate was measured. The subjects were 24 native English (NE) speakers and 240 native Korean (NK) speakers assigned to ten subgroups based on age of arrival in the US (2–22 yrs). The subjects repeated 21 aurally presented English sentences following a delay. The durations of sentences that were produced without pauses or repetitions were measured. The NK subjects who arrived in the US after the age of 9 years produced sentences that were significantly longer than did the NE subjects. Significant correlations were found to exist between the Koreans sentence durations and age of arrival in the US: (1) self-estimated use of both Korean and English; (2) the number of segmental errors produced in English sentences; and (3) knowledge of English morphosyntax (assessed by a 144-item Grammaticality Judgment Test). The correlation with amount of education in the US was nonsignificant. Taken together, these results suggest that sentence duration may serve as a useful index of overall proficiency in an L2. [Work supported by NIH.]
Sound absorption characteristics of open brick/block absorbing walls
Authors: Tachibana Hideki , Sakamoto Shin’ichi , Mukai Hikari , Cho Tong-Jun
Published: July 2002

Brick and block walls with openings and backing air space with porous materials are often used in auditoria as a sound absorbing treatment. These kinds of walls have a frequency-selective sound absorption property in low frequencies, which is usually explained as the Helmholtz resonator consisting of the air volume in the part of the opening and the backing cavity. In addition, these types of wall often have different peaks of sound absorption coefficient in higher frequencies (around 1000 Hz, in the case of 10-cm thickness of the brick/block). In this study, this sound absorption effect has been investigated by theoretical consideration, reverberation room measurement of a real construction, and a 1/10 scale model experiment, and it has been clarified that the sound absorption is caused by the effect of open-pipe resonance which happens in the openings. In addition to these studies, the effects of the Helmholtz resonance and open-pipe resonance have been visualized by numerical analysis and physical experiment using the Kundt’s dust tube method.
Sound absorption by seats in concert halls, occupied and unoccupied, and average sound absorption by the interior surfaces of halls—II
Authors: Beranek Leo L. , Hidaka Takayuki
Published: July 2002

The average sound absorption coefficients for the interior surfaces of eight halls, in which all finishes were completed before installation of seats, were determined from reverberation measurements. When the chairs were installed, their absorption coefficients, both occupied and unoccupied, were also determined from RT data. Five of these halls have lightly upholstered seats, one has medium upholstered seats, and two have heavily upholstered seats. The data are compared with the 15-hall data of Chap. 5 in Beranek [Concert and Opera Halls: How They Sound, Acoustical Society of America (1996)]. A survey of the chair design in those 15 halls has produced a correlation between chair construction and the words: ‘‘lightly,’’ ‘‘medium,’’ and ‘‘heavily’’ upholstered. The new data permit more accurate estimation of reverberation times as a function of frequency than previously found by comparing the details of a hall-in-planning with the constructions and seats of these eight halls.
Design considerations for Boettcher Hall, a vertical surround symphonic facility
Authors: Jaffe Christopher , Madaras Gary , Bradley John S.
Published: July 2002

In the early 1960s, Dr. Leo Beranek correlated reflection patterns in concert halls with qualitative listening experiences. Over the years, practitioners and other researchers have confirmed the validity of his work, proving that the direction, amplitude, frequency composition, and arrival time of the reflections define quality, regardless of room geometry. This paper discusses methods for achieving qualitatively preferred listening experiences in vertical surround halls such as Boettcher Concert Hall in Denver, Colorado, and the difficulties that can arise when breaking the mold of a traditional shoe-box hall.
A multiple target acoustic scene representation model for bat echolocation signals
Authors: Liang Min , Palakal Mathew J.
Published: July 2002

Determination of the distance to targets from echo delay is an important aspect of echolocation in bats. Neurophysiological studies suggest that the tonotopically organized delay-sensitive neurons (DSN) found in the cortex of bat encode target distance. These studies also indicate that in the tonotopic area, the DSNs in each active ensemble share the same range acuity and the acuity systematically improves over a period of time. A biologically plausible model is suggested here to understand how the bat assembles responses to echoes from multiple targets. This model consists of three stages in cascade: (1) an auditory periphery system (APS); (2) a self-organization neural network (SONN) and; (3) a cortical representation neural network (CRNN). The inputs of APS are the pulse-echo (PE) signals and the outputs are the time-frequency spike trains of PE. SONN self-organizes to the spike trains of PE in frequency index. CRNN has the same architecture of SONN but with a specific neuron response function, y(T,δ,f)=I(δ,f)Φ[a1T(δ−an2β1)/an2]Φ (f−β2), to achieve the multi-resolution. In this function, Φ(.) is the negative second derivative of a Gaussian function, I(δ,f) is the spike amplitude of frequency component f arriving at time δ, T is the time onset of echoes after vocalization, a1 and a2>1 are constants, n is a negative integer, β1 is the minimum best delay, and β2 is the best frequency. The response maps of CRNN at different T form the multi-resolution representation of the acoustic scene. Simulations are carried out for the proposed model using phantom targets and the results are compared to neurophysiological findings. [Work supported by NSF.]
Fish resonance absorption spectroscopy
Authors: Diachok Orest I.
Published: July 2002

Measurements of the absorption coefficient were made at 12 km between 0.6 and 5.0 kHz at a shallow water (83-m) site in the Gulf of Lion in September, 1995. At night absorption lines due to dispersed sardines at 1.3 kHz at 25 m and sardine schools at 1.5 kHz at 60 m were evident. One hour before sunrise the resonance frequency, f, of dispersed sardines increased with time, becoming 2.7 kHz at sunrise, as dispersed sardines descended to 65 m; and in the following 15 minutes f decreased to 1.7 kHz, as dispersed sardines formed schools, as evidenced by echo sounder records. The signal loss at 2.7 kHz at sunrise, attributed to dispersed sardines at 65 m, was 35 dB; the signal loss at 1.7 kHz during daytime, attributed to sardine schools at 65 m, was 15 dB. The shift in f and the decrease in absorptivity that occurred during the transition are in accord with theory: Close proximity between fish in school at 65 m causes both f and the scattering cross section to diminish (Feuillade, 1996). The latter is proportional to the extinction cross section which, together with n (number per unit volume), control the absorptivity. Estimation of n from absorption spectroscopy measurements, and the hypothesis that marine mammals might exploit this phenomenon, will be discussed.
Evaluation of a three-dimensional fractal model of ultrasound scattering in liver
Authors: Phillips Daniel , Cramblitt Robert , Parker Kevin J.
Published: July 2002

It is postulated that a major source of scattering in liver is the collagen rich structure of the vessels that comprise the hepatic vasculature system. This collagen rich hepatic vessel structure manifests itself as the branching pattern of the vessels in three dimensions. Past study of these branching patterns in other organs such as the lung has resulted in data and models which have ascribed a fractal description to their organization. A computer based model has been developed of the portal vasculature system of the human liver based on anatomical, physiological data and precepts as well as a fractal methodology. A thin, planar slice of the model is used to represent sites of ultrasound scattering. A simple model is utilized to calculate the ultrasound scattering from the cross sections of the thin-shelled cylinders used to represent the collagen component of the vascular walls. Simulation of the radio frequency scattered waves is carried out along with envelope detection to allow analysis of the first and second order statistics. The resultant statistics are analyzed in light of the parameters utilized to define the model and their variation.
Ultrasonic backscattering of blood in simple oscillatory flow
Authors: Lin Yu-Hong , Shung K. Kirk
Published: July 2002

Ultrasonic backscattering of porcine whole blood (hematocrit at 40%) was measured by a 10-MHz catheter mounted transducer in a mock flow loop at different flow rates controlled by a roller pump and a pulsatile pump. The amplitude of the oscillatory flow was fixed at 40 cm/s and the baseline velocity was set at three different levels, 0, 20, and 40 cm/s, to change the shear rate range. As the flow rate increases from 0 to 40 cm/s to 20 to 60 cm/s, the peak of cyclic variation of the backscattering signal leads more of the peak of the mean flow velocity. At 40 to 80 cm/s, the magnitude of cyclic variation drops from 4 dB to 1.5 dB. It was found that at the two lower flow rate ranges the backscattering signal increases with shear rate if the mean shear rate is below 150 l/s. When the shear rate further increases, the backscattering signal decreases. The wave form of the cyclic variation is also altered as the baseline shear rate changes. Results show that, in simple oscillatory flow, the amplitude and the timing of the peak of ultrasonic backscattering from whole blood are affected mainly by the shear rate which mediates red cell aggregation.
Infrasound method for bone mass measurements
Authors: Donskoy Dimitri
Published: July 2002

Studies of application of acoustic energy for noninvasive skeletal diagnostics have shown feasibility and demonstrated the advantages of utilizing acoustic techniques for bone mass measurements. Unlike conventional radiological techniques, acoustic techniques emit no radiation, are low cost, and utilize equipment which is portable and easy to operate. Although a significant number of acoustic tests have been performed, these techniques have not been used as bone diagnostic tools in clinical applications because of the difficulties in the interpretation of measurements. Thus, ultrasound velocity and attenuation depend on density as well as on certain other properties of bone. The effect of soft tissues creates additional difficulties in the interpretation and use of these techniques. The proposed infrasound method involves measurements of the ‘‘rigid body’’ resonance of a tibia or ulna with the use of specially designed arrangement, which greatly simplifies a biomechanical model of tibia (ulna). This makes the measurement and its interpretation much more accurate. Numerical analysis of the developed model showed that the mass of bone and its loss can be accurately measured and these measurements do not depend on variation in bone flexibility and soft tissue parameters. An experimental setup was arranged and in vivo measurements were conducted and proved the basic concept of the proposed method. [Work supported by NASA.]
Modification of Biot’s theory of porous materials
Authors: Tavossi H. , Tittmann B. R.
Published: July 2002

Acoustic waves in porous material are traditionally investigated by using Biot’s theory to describe the elastic wave propagation in such materials. However, experimental results obtained by models of porous media made of cohesionless particles forming loose solid matrix with fluid-filled pores, contradict the above theory at high frequencies. These results show that the acoustic wave speed as a function of frequency and particle size goes through a maximum and then decreases with frequency until a cutoff frequency is reached, whereas Biot’s theory predicts an asymptotic increase of propagation speed with frequency, without a wave cutoff frequency. The theoretical analysis and the experimental investigation are presented that modify and adapt Biot’s theory to the cohesionless porous materials. The equations describing these modifications to the theory take into account the following effects: the contact surfaces between the solid particles, their number concentration, the size of the solid particles, the depth at which they are situated, the external pressure, their random arrangement, and the propagation direction of the acoustic waves.
The behavior of transient elastodynamic waves at a linear slip interface
Authors: Verweij Martin D. , Chapman Christopher H.
Published: July 2002

A method is presented for the analysis of the transmitted and reflected transient elastodynamic wavefield at a fracture that may be modeled as a linear slip interface. This interface model implies that the traction is continuous at the fracture, while the displacement may show a jump discontinuity that is proportional to this local traction. To start with, for both the SH and the P/SV wave systems, transform domain expressions are determined for the transmitted and reflected wavefields at the interface. Subsequently, an almost completely analytical transformation back to the space-time domain is carried out. The method provides the exact time domain transmitted and reflected waves (including the body wave, interface wave, and head wave contributions) that are caused by a spatially curved, incident wavefield due to a point source. Various numerical results are given. For the SH case, the directionally dependent filter behavior of the fracture is shown. For the P/SV case, first the reflection, transmission, and conversion of body waves is presented. The next set of results involves the interface wave contribution and includes pictures of the particle movement on both sides of the fracture. Finally, the presence of headwaves in case of SV→P and SV→SV reflection is shown.
Growth of masking by harmonic complexes with high crest factors
Authors: Leek Marjorie R. , Summers Van
Published: July 2002

There is a strong link between the discrimination of small phase changes in highly peaked harmonic complexes and the sensation level of the stimuli. This relationship may stem from a differential ability across listeners to code dynamic amplitude changes within waveform periods. To test this hypothesis, growth of masking was measured for flat-amplitude harmonic complexes varying in phase structure and level. Maskers were constructed with odd harmonics in cosine phase and all even harmonics shifted in phase from 0 to 90 degrees. Masked thresholds were measured for a 5-ms Hanning-windowed probe centered either at the primary peak of the masker waveform or at a secondary peak near the midpoint of the period. Growth-of-masking functions when the probe is placed at the primary waveform peaks are generally linear. However, in normal-hearing listeners, masking of probes placed at the secondary peaks grows more nonlinearly. Reduced masking observed at low stimulus levels may be related to compression of the high-amplitude primary peaks which act as forward maskers. Differential forward-masking by the large primary peaks across listeners with normal hearing and those with hearing impairment will be related to the ability to discriminate complexes with differing phase structures. [Work supported by NIH.]
Optimal interstimulus interval for auditory discrimination of intensity, duration, and frequency for normal adults
Authors: Biswas Amitava , Watson Charles , Barlow Steven , Gygi Brian , Drennan Ward
Published: July 2002

Ten normal-hearing college students performed two-interval, two-alternative, forced choice discrimination tasks designed to determine the optimal range of interstimulus (ISI) intervals for auditory discrimination of intensity, duration, and frequency. Stimuli were randomized (roved) along frequency, intensity, and duration dimensions to reduce monotony and minimize the listener’s reliance on a remembered standard. The center frequency was 500 Hz, the center duration was 30 ms, and the center intensity was 75 dB SPL. Differences to be discriminated were from 0.75 to 3.0 dB for intensity, 1.5 to 6 ms for duration, and 7 to 20 Hz for frequency. Interstimulus intervals were studied from 70 ms to 15 s. Maximum discrimination scores were observed in the range of ISIs from 1.0 to 3.0 s, for all three stimulus dimensions. These preliminary findings suggest the operation of a common, dimension-independent, sensory processing mechanism within the central nervous system. [Work supported by NIH and Neuro Logic, Inc.]
An architecture for wave interaction with complex environments
Authors: Felsen Leopold B.
Published: July 2002

Active classification of structures is an example of wave interrogation of complex environments. An algorithmic architecture is suggested that decomposes global complexity into problem-dependent clusters which interact across interfaces. A cluster is treated either analytically (preferably based on good physics) or numerically, deterministically and/or stochastically, etc., and the interconnects between clusters map representations on one side into those on the other side, subject to the continuity requirements of the relevant field equations. Projecting the field problem onto the cluster boundaries gives rise to a network formulation that impacts the analytic as well as numerical strategies. This field-based approach is coupled to, and modified by, considerations of signal processing. The challenge in the implementation is to effect an ‘‘optimal’’ decomposition into tractable clusters, and to treat each cluster problem in a fashion that anticipates its role as part of a larger conglomerate, taking into account the limitations imposed by the intended pre- and post-processing. Example scenarios are presented to illustrate these concepts.