bluuebunny/crossref_metadata_2025 huggingface dataset:
Reporting on the work of the French commission for vibroacoustic software validation
Authors: Gagliardini L. , Valor C.
Published: July 2002

Between 1993 and 1996, a French group gathering most of the national laboratories and companies involved in vibroacoustics modeling, as well as major European vibroacoustic software producers, worked at producing reference results for elementary vibroacoustics problems. Four calculation cases and one experimental case were examined. These cases mainly consist of plates, coupled with finite or infinite fluid media, and submitted to point force loading. Calculations or measurements were carried out in the overall frequency range of 20 Hz to 20 kHz using analytic, when possible, numerical, and energetical methods. Results consist of narrow-band and third octave plots of averaged quantities such as mean squared velocity or radiated power. The spread in between results provided by various members of the group is shown. Individual results are justified by scientific references that were not discussed.
Experimental characterization and finite-element modeling of a Lexan ribbed panel
Authors: Capone Dean E. , Hambric Steve A.
Published: July 2002

In 1994 an in-depth investigation was proposed to characterize the structure-borne noise characteristics of a set of standard test systems [C. B. Burroughs, J. M. Cuscheiri, and J. M. Carroll, Proc. Noise-Con 94, 541–544 (1994)]. The studies would serve to validate the experimental, analytical, and numerical techniques used in the analysis of the systems. As a part of this effort, the response of a Lexan ribbed panel was investigated both experimentally and numerically. The drive point admittance and operating deflection shapes of the panel were used to characterize the vibration response. The operating deflection shapes were measured using a scanning laser Doppler system. The presence of the ribs on the panel results in both global and local modes within the panel. The experimental results compare favorably to the results from a finite element model of the panel. Comparisons to an aluminum ribbed panel with the same dimensions of the Lexan panel are also presented. The shift in panel resonanance frequencies due to material properties is illustrated in the experimental results, and correctly predicted in the finite-element results.
Laser vibrometer dynamics testing of a lexan ribbed panel test structure
Authors: West Robert L. , Saunders William R. , Burdisso Ricardo A.
Published: July 2002

The lexan ribbed panel test structure is one of three ‘‘standard’’ test structures used within a round-robin test/analysis study. The objective for the overall study is characterization of both vibration and structure-borne acoustics of these test structures. Furthermore, the study seeks to establish a baseline for the evaluation of various experimental and analytical techniques and their applicability for characterizing these structures. This paper describes the experimental setup, the acquired data as well as the resulting dynamics characterization of the ribbed panel machined from lexan. The panel is 1.52×0.91×0.006 m overall with four equally spaced ribs 0.4 m apart. The panel is suspended by shock cord to simulate a free-free boundary condition and is excited by an electromagnetic shaker resulting in primarily out-of-plane motion. In this study, the vibration characterization is derived from mobility FRFs from accelerometer data. The mobility FRFs are also used to establish ten frequencies for multisine testing using a scanning laser Doppler vibrometer. A new technique is used to extract a spatially continuous, three-dimensional dynamic response field at all ten frequencies. Acoustic characterization of the panel is accomplished through sound pressure level measurements at a few spatial locations at the same ten frequencies.
SEA analysis of the T-beam and acoustic cavity using alternative SEA approaches
Authors: Cuschieri Joe
Published: July 2002

SEA results have been generated for the T-beam structure using two different approaches—a home grown SEA solution and a solution generated using a commercial SEA package. The results generated from these two approaches, while both generally matching the experimental mean results, are different. In this paper, possible reasons for the differences in the results are explored by analyzing the determined coupling loss factors, other components in the solution and the solution in general. The same type of analysis is performed for the acoustic cavity structure. In this case as well, SEA results are generated using the alternative SEA approaches. From a comparison of the full and intermediate SEA results obtained from the different approaches, the possible reasons for the differences are investigated. The two main conclusions of this study are that, (a) when using SEA as a predictive tool, very much depends on the input model and the basis of the solution; (b) the predictive results have to be treated with some caution. [Work sponsored by NASA Langley.]
Numerical implementation and marine applications of an energy finite element formulation
Authors: Vlahopoulos Nickolas , Garza-Rios Luis Octavio , Mollo Christopher
Published: July 2002

The statistical energy analysis (SEA) is an established numerical technique appropriate to high-frequency vibro-acoustic analysis [R. Lyon, Statistical Energy Analysis of Dynamical Systems: Theory and Applications (MIT, Cambridge, MA, 1975)]. The energy finite element analysis (EFEA) constitutes a recent theoretical development [O. M. Bouthier and R. J. Bernhard, ‘‘Models of space averaged energetics of plates,’’ AIAA J. 30(3) (March 1992)]. In this work a numerical implementation of the EFEA is utilized for analyzing two marine structures, and numerical results are compared to SEA solutions from VAPEPS. First, a plate assembly representing the engine foundation of a frigate ship is analyzed. Previous SEA results and test date are available in the literature and they are included in the comparison [R. Lyon, ‘‘In-plane contribution to structural noise transmission,’’ Noise Control Eng. J. 26, 22–27 (1986)]. In the second application the structure of a fishing boat is modeled by both methods. The results are compared, and the EFEA is further utilized for identifying design modifications. [Work supported by the Michigan Sea Grant.]
Children’s perceptual weighting strategies for speech are not as flexible as adults
Authors: Nittrouer Susan , Miller Marnie E. , Crowther Court S. , Manhart Mary Jane
Published: July 2002

Mann and Soli (1991) showed that adults modify their perceptual weighting strategies for the same phonetic decision based on the order of segments within syllables. The authors exmained whether children similarly modify their perceptual weighting strategies. Fricative-vowel (FV) and vowel-fricative (VF) syllables were constructed with synthetic fricative nosies varying from /∫/ to /s/, and natural /ɑ/ and /u/ portions with transitions appropriate for a preceding or a following /∫/ or /s/. Spectrograms revealed that the acoustic information about fricative identity provided by the vocalic portion was impoverished for VF compared to FV syllables. These stimuli were played in their original order to adults and children (ages 7 and 5) in experiment 1, and in reverse order in experiment 2. Results for adults and, to a lesser extent, for 7-year-olds replicated earlier results showing that the perceptual weights assigned to acoustic properties within the vocalic portion differ depending on segmental order. In contrast, results for 5-year-olds suggested that these listeners applied the same strategies during fricative labeling, regardless of segmental order. Thus the flexibility to modify perceptual weighting strategies for speech according to segmental order apparently emerges with experience.
Prosodic boundaries and syntactic branching in Japanese and English
Authors: Ingram John C.
Published: July 2002

This paper explores communalities and differences in prosodic boundary marking in English and Japanese. Kubozono (1989) observed an interesting asymmetry in Japanese: that the onset of a right branching syntactic constituent is characterized by sudden pitch rise, not observed at the onset of a left-branching constituent, which he attributed to the phonetic realization rule of a metrical boost. Left-branching constitutes the unmarked direction of embedding in Japanese phrase structure. English is overwhelmingly right branching in its syntactic structures. The metrical boost proposed by Kubozono is similar to the mechanism of f0 baseline resetting often proposed to explain juncture marking at major phrase boundaries. English has a prosodic asymmetry, parallel to the Japanese case, whereby prosodic boundary marking is required, at the boundary of certain left-branching constituents. The paper seeks to replicate Kubozono’s observations and to compare the phonetic realization of juncture in Japanese and English from pairs of syntactically ambiguous left- and right-branching phrasal constructions. A perceptual experiment was conducted to ascertain that Japanese listeners reliably employed prosody to disambiguate the utterances. Acoustic measurements of fundamental frequency and segment duration were made to assess Kubozono’s theory of a metrical boost.
The Göteborg Organ Art Center: An international research center for organ history, organ building, teaching, and performance practice
Authors: Kleiner Mendel
Published: July 2002

The multidisciplinary Göteborg Organ Art Center (GoArt) project focuses on historical instruments as primary-source documents for performance practice research. Models of instruments are studied to fully document the design and quality of building materials and historical building procedures to explore and reconstruct the aesthetic and practical process of assembly, thereby recovering craft knowledge lost during 20th century industrialization. The project strives to achieve a level of quality in tone-production and craftsmanship not attained since the historical period, providing future organ-builders with functional knowledge of historical craft techniques and the extremely high-quality standards of historical instrument models. Research studies are made in collaboration with the Chalmers University of Technology on antique and contemporary pipe materials, development of new materials with the same properties as the old ones, studies of airflow systems and their effects on tone production in organ pipes, collection and analysis of information about the scaling, dimensions, and design of organ pipes, studies of tone production in organ pipes, and the relationship between organ and room acoustics. This presentation will focus on interaction between organ and church acoustics, studies on subjective perception of organ tone, and flue pipe modeling.
Monitoring airgun sound levels with an array of hydrophones in an ocean bottom cable
Authors: Greene Charles R. , Norman Robert G.
Published: July 2002

In shallow water, three-dimensional seismic surveys for oil and gas sometimes use a large array of hydrophones on the bottom as receivers for sound pulses originating from an array of airguns. There is concern that intense airgun pulses may disturb or (at close range) injure protected marine mammals like seals and whales. Permits to conduct the surveys often require that the pulse levels at various distances be measured to determine or verify safety zone radii. Protected animals observed within the safety zone may be cause to interrupt the survey. However, the sound field around the airgun array depends on aspect and local propagation conditions as well as distance. These details have been difficult to study with conventional methods. An array of 600 hydrophones in the ocean bottom cables was deployed by the seismic contractor during a survey in the Alaskan Beaufort Sea. Each pulse was received and recorded simultaneously at all hydrophones while the airgun source moved across the receiving array. This method can provide detailed empirical data on the sound field at relatively low cost. [Work supported by BP Exploration (Alaska), Inc., Anchorage, AK, hydrophone data provided by Northern Geophysical of America.]
Simulation of ultrasonic propagation, scattering, and attenuation in the human chest wall
Authors: Mast T. Douglas , Hinkelman Laura M. , Waag Robert C.
Published: July 2002

A finite-difference time-domain model for ultrasonic pulse propagation through soft tissue [Mast et al., J. Acoust. Soc. Am. 102, 1177–1190 (1997)] has been extended to incorporate absorption effects as well as longitudinal-wave propagation in cartilage and bone. This extended method has been used to simulate ultrasonic propagation through anatomically detailed chest wall models. The inhomogeneous chest wall structure is represented by two-dimensional tissue maps determined by staining chest wall cross sections to identify connective tissue, muscle, fat, cartilage, and bone, scanning the stained cross sections at 300 dpi, and processing the scanned images to assign a tissue type to each pixel. Each pixel of the tissue map is then assigned a sound speed, density, and absorption value determined from published measurements to be representative of the local tissue type. Computational results for wavefront distortion including amplitude fluctuations, arrival time fluctuations, and waveform distortion show qualitative agreement with measurements performed on the same specimens [Hinkelman et al., J. Acoust. Soc. Am. 101, 2365–2373 (1997)]. Visualization of simulated tissue-ultrasound interactions in the chest wall shows possible mechanisms for image aberration in echocardiography, including effects due to reflection and diffraction from rib structures.
Coupled thermal-acoustic simulation results with temperature-dependent tissue parameters for therapeutic ultrasound
Authors: Hallaj Ibrahim M. , Cleveland Robin O. , Roy Ronald A. , Holt R. Glynn
Published: July 2002

Recently the authors used direct simulations of the transient acoustic pressure field to calculate heat energy deposition and, thus, temperature fields in two-dimensional tissue like media [J. Acoust. Soc. Am. 102, 3172(A) (1997)]. It is known that acoustic-induced temperature rises will alter the properties of the medium in hyperthermia situations. In this presentation the simulations are extended to simultaneously solve the wave propagation and tissue heating problems so that the effect of temperature-dependent tissue parameters can be accounted for directly. In other words, there is a continuous feedback of temperature on the sound propagation parameters, which in turn affects the thermal energy deposition. The simulations are second order accurate in time, fourth order in space full wave calculations using the finite-difference time-domain technique, and allow for finite-amplitude wave propagation in an inhomogeneous, thermoviscous fluid. The model allows for spatially and temporally varying sound speed, density, attenuation coefficient, and nonlinearity parameter, as well as variable thermal properties and perfusion. Acoustic pressure, thermal dose, and tissue temperature are calculated, and conclusions are made regarding qualitative and quantitative aspects of focusing behavior contrasted to the case where the propagation and thermal parameters are kept constant. [Work sponsored by ONR and DARPA.]
On the optimizing of the effective electromechanical coupling coefficients of piezoceramic bodies
Authors: Aronov Boris , Brown David A.
Published: July 2002

The effective electromechanical coupling coefficients are defined based on the expression for internal energy of a piezoceramic body. By means of this definition, conditions are obtained under which an effective coupling coefficient for any given deformation distribution can be maximized and shown to be equal to a corresponding coupling coefficient of the piezoceramic material. A simple practical way to optimize the effective coupling coefficients of transducers by changing its electrode shape is discussed. Examples of transducers vibrating in longitudinal and flexural modes are considered.
Thirteen sonic booms of space shuttles approaching Edwards Air Force Base, 1988–1993
Authors: Young Robert W.
Published: July 2002

Thirteen sonic booms of space shuttles approaching Edwards Air Force Base, 1988–1993, were measured at a site 10 miles west of EAFB with Brüel & Kjaer 2230 Precision Integrating sound level meter ♯1082228; CEL-493/2 Precision Integrating Impulse sound level meter ♯198107; CEL-238A Secondary Processor ♯151020; GenRad 1982 Precision sound level meter ♯0169; Rion NL-11 Precision Integrating sound level meter ♯1140255; RACAL 4D7680-3 tape recorder ♯11224. On 30 Jan 1992 sound-pressure levels were peak flaT 133 dB; peak Awt 127 dB; max fast Cwt 113dB; max fast Awt 98 dB. Sound exposure levels flaT 126 dB; Cwt 108 dB; Awt 90 dB. On 16 May 1992 sound-pressure levels PKT 131 dB; MXFC 112 dB; MXFA 95 dB. Sound exposure levels CSEL 107 dB and ASEL 91 dB. Some 8 min before a space shuttle landing the latitude, longitude, altitude, and Mach number at 1-s intervals were supplied by AEROPAC. By Carlson theory, W. J. Galloway calculated for 30 Jan 1992 slant distance of 89 kft to sound-measurement site from origin of the sonic boom where Discovery was flying Mach 1.6, altitude 68 kft above mean sea level. On 16 May 1992 the slant distance was 88 kft from origin where Endeavor was flying Mach 1.6, altitude 72 kft.
Prediction of SR-71 sonic booms by THOR and Thomas codes
Authors: McAninch Gerry L.
Published: July 2002

A major concern of recent sonic boom work has been accounting for the effects of molecular relaxation on sonic boom waveforms. Several new codes accounting for these effects have been developed since sonic boom research was reinitiated. In order to validate these codes, sonic boom signatures generated by an SR-71 aircraft have been measured near the aircraft and at several altitudes below the aircraft and on the ground. In the current study, two computer codes, the Thomas code and a highly modified version of THOR, have been used to propagate some of the sonic boom waveforms measured near the SR-71 aircraft to the ground, and to altitudes at which the waveforms have been measured. The results of this study will be presented. The results from the Thomas code provide two things. First, they provide an indication of the prediction capability available when the current sonic boom research began. Second, they provide an indication of the validity of the results provided by THOR, by providing reasonable estimates of overall signal length and amplitude. The results from THOR provide an indication of the capability provided by the research supported in the last few years.
Active control of a mechanical interface by use of power-flow control laws
Authors: Houston Brian H. , Kraus Larry A. , Herdic Peter C. , Photiadis Douglas M. , Corsaro Robert D.
Published: July 2002

The active control of dynamic mechanical impedance is of general interest due to a variety of potential defense and civilian applications. These include control systems to minimize aircraft and aerospace vehicle interior acoustic levels. Control of impedance or mechanical power flow at a boundary is one of the most challenging in active control due to the requirement for the collocation of sensors and actuators. In addition to the challenge of developing the devices, some of the technical issues include the selection of the appropriate physical control law, the degree of interconnectivity (local versus global control), device linearity, component and processor delays, system identification, and performance versus robustness tradeoffs. Recently, single node experiments were carried out at NRL’s Laboratory for Structural Acoustics with an integrated passive/active device that minimizes mechanical power flow. The results of these experiments will be discussed with a focus on the application of different control approaches and the physics involved. a)Also with SFA, Inc., Lanover, MD20785.
Reduction of total powerflow in a fluid filled pipe using an active/passive approach
Authors: Kartha Satish C. , Johnson Marty E. , Fuller Chris R.
Published: July 2002

This presentation describes the implementation of active/passive approaches for the reduction of total acoustic power flow in fluid filled pipes. Active/passive systems are essentially passive devices whose properties can be altered using a control system. For example, a Helmholtz resonator has been fitted with a variable neck aperture allowing the resonant frequency of the device to be altered. Other passive devices such as a delay line and a quarter wavelength tube have been used as active/passive devices. These active/passive devices have been designed to gain maximum performance (trade-off between flexibility of application and control authority). Various sensing approaches using PVDF (polyvinylidene fluoride) cables/films and an array of microphones have been tested and are compared. The various active/passive approaches developed have been compared to totally active approaches in terms of flexibility and control authority. [Work supported by University of Karlskrona/Ronneby.]
Adaptation to altered feedback in speech
Authors: Jones Jeffery A. , Munhall K. G. , Vatikiotis-Bateson E.
Published: July 2002

This study focuses on how the control of fundamental frequency (F0) of the voice is influenced by modulations of auditory feedback. A methodology analogous to one used in visual perturbation studies of limb movements was used. In these studies, optical feedback is distorted and subjects adapt to the transformed conditions by relearning the spatial coordinates used in visuomotor control. It was investigated whether F0 control would exhibit an analogous adaptation response to altered auditory feedback conditions. Subjects were exposed to pitch-shifted auditory feedback through headphones while producing (a) sustained vowels and (b) sentence material. The F0 feedback was increased in 2 cent steps that were not noticed by the talkers. Both aural- and bone-conducted masking noise were used to minimize feedback from the true F0. During the transformed feedback condition, subjects decreased their pitch in response to the increasing pitch feedback. However, preliminary analyses did not reveal evidence of adaptation to the auditory transformations. This was examined by unexpectedly introducing normal feedback trials to test for ‘‘aftereffects.’’ Results will be discussed in terms of sensorimotor learning and the role of internal models of sensory feedback in speech motor control. [Work supported by NIH NIDCD Grant No. DC-00594 and NSERC.]
Improved precision in field measurements of sound from large ID fans
Authors: Bradley Wayne E.
Published: July 2002

An electric utility was receiving complaints about noise from their power plant from residences nearly 2 miles away. An onsite and off-site noise survey confirmed the neighbors complaints, and indicated that the sound was coming from the plant ID fans via the stack. Most of the complaints occurred when the plant went to low load at night. A study was therefore undertaken to determine how the fan sound level varied with plant load. A simple, reliable, and inexpensive means was sought to make repeatable fan sound pressure level measurements without penetrating the stack. Both narrow-band and 1/3-oct band measurements were taken from fixed and scanned microphone locations at the fans, in the stack annulus, and on the boiler roof during boiler ramp ups and ramp downs. A sampling methodology was developed with a high degree of precision allowing reliable measurements of ID fan blade pass frequency tone level versus plant load. Subsequent noise measurements evaluated modifications to the fan inlet, cutoff, blade tips, and fan speed with a relatively high degree of precision.
Reverberation room qualification using the m-sequence as multitone signals
Authors: Chu Wing T.
Published: July 2002

There is a revised interest in replacing the time-consuming and burdensome methods in the current ANSI and ISO standards for qualifying reverberation rooms for sound power measurements of discrete frequency sources. With the advent of digital signal processing, a combination of a deterministic multitone test signal and an FFT routine could be used to perform a fairly quick qualification test. A more elegant method using the m-sequence as the deterministic multitone signal has been tested in the IRC/NRC laboratory. This method has the advantage that it is relatively immune to external background noise so that the near field response of the test loudspeaker could be determined outdoors without using an anechoic room. In addition, all the required frequency components in the different one-third octave bands can be obtained in one single measurement. A detailed description of the procedure and results obtained will be presented.
Ultrasonically enhanced sedimentation—Results of an empirical scale-up approach
Authors: Spengler Johannes , Jekel Martin
Published: July 2002

Ultrasonic standing waves are suitable for both coagulation of dilute suspensions and thickening of already settled sludge. For each purpose the right choice of process parameters and reactor design is important. The used ultrasonic effects are acoustic radiation and acoustic as well as hydrodynamic particle interaction forces. Acoustic and convective streaming cause shear stress on particle clusters and can therefore disperse aggregates. To achieve good efficiency at high flow rates, these undesirable streaming effects must be controlled, especially for the realization of larger reactors. One suitable measure is to divide the sonicated volume into several smaller parts separated by thin polyethylene films. Basic investigations in various batch and continuous flow lab systems led to an empirically derived scale-up concept. A prototype 3-MHz transducer array consisting of 16 single piezos used for coagulation has been developed and manufactured in cooperation with ELAC Nautik (Kiel). Preliminary results of two new pilot plants (sonicated volume 10 L for coagulation, respectively, 70 L for thickening) show good performance of the reactors. Comparison with previous lab scale data prove the applicability of the scale-up method as it will be presented at the meeting.
Experimental investigation of dynamics of sonoluminescing bubbles
Authors: Kato Yuichiro , Hayashi Shigeo , Tanaka Kenji , Kobayashi Hiroshi
Published: July 2002

Light scattering was carried out for a cavitation bubble trapped in a spherical flask. A He–Ne laser of 7 mW was used as the light source and the scattering angle was 90 deg. A function generator was used as the trigger source and a digital phospher oscilloscope for averaging the data. Changing the drive voltage resulted in differences in the signal waveform above and below the sonoluminescence threshold; a sonoluminescing bubble had the maximum radius greater than a dark bubble did, but showed smaller rebounds. This suggests that energy concentration is made possible by tight and symmetric collapse of the bubble. Sonoluminescence signals were also retrieved for a few hours with no laser light, and a discontinous drift was noted in the appearance time on the oscilloscope, suggesting that a bubble may have drifted in space discontinuously. [Work supported by Grant-in-Aid for Scientific Research, Ministry of Education, Science, and Culture, Japan.]
Contralateral suppression of transiently evoked otoacoustic emissions by harmonic complex tones in humans
Authors: Micheyl Christophe , Maison Stéphane , Carlyon Robert P. , Andéol Guillaume , Collet Lionel
Published: July 2002

Variations in the amplitude of transiently evoked otoacoustic emissions (TEOAEs) produced by a contralateral complex tone were measured in 26 normal-hearing human subjects. TEOAEs were evoked using a 1-kHz tone pip at 60 dB SPL. The contralateral complex consisted of harmonic components with frequencies between 400 and 2000 Hz; it was presented at levels ranging from 40 to 50 dB SL and its fundamental frequency (F0) was varied. In experiment 1, the dependence of TEOAE amplitude variations on the F0 of the contralateral complex was measured by varying the F0 from 50 to 400 Hz in octave steps. The results revealed a nonmonotonic dependence of TEOAE amplitude variations on contralateral F0, with significantly larger TEOAE suppression for F0’s of 100 and 200 Hz than for F0’s of 50 and 400 Hz. Experiment 2, in which the harmonics were summed in alternating sine–cosine phase instead of constant sine phase, showed a shift of the function relating TEOAE attenuation to F0 towards lower F0’s, indicating that the waveform repetition rate, rather than harmonic spacing, was the actual factor of the dependence of contralateral TEOAE attenuation on F0. Furthermore, significantly smaller suppression was observed with the alternating-phase complexes than with the sine-phase complexes, suggesting an influence of the waveform crest factor. Experiment 3 showed no difference between the contralateral TEOAE attenuation effects produced by positive and negative Schroeder-phase complexes. Overall, these results bring further arguments for the notion that contralaterally induced medial olivocochlear bundle (MOCB) activity, as measured through the contralateral suppression of TEOAEs in humans, is sensitive to the rate of temporal envelope fluctuations of the contralateral stimulus, with preferential rates around 100–200 Hz.
Simplified calculus to estimate the acoustical absorption of nonplanar materials
Authors: Pfretzschner Jaime , Simon Francisco , Rodriguez Rosa M. , de la Colina Carlos
Published: July 2002

The absorption curve, in function of the frequency, in hard-backed layers of granular materials, shows undesirable series of maxima and minima related to the layer deep. In order to increase the efficiency of these absorbing materials, it is necessary to smooth their frequency response curve. It is obvious that one of the easiest solutions consists of modifying the layer surface with selected profiles (e.g., wedges). For these situations, a simplified method of analytical calculus for the valuation of the absorption, in function of the frequency, has been developed. The validity of the theoretical approximations has been checked against experimental measurements in different test samples by means of a standing wave tube. Additionally, the application of this study to the design of absorbent acoustic noise screens, against traffic noise, made with recycled rubber crumbs of tires, is also presented. [Work supported by a LIFE project.]
Absorption and scattering characteristics of a modified Schroeder diffuser
Authors: Jarvinen Antti , Savioja Lauri , Melkas Kaarina
Published: July 2002

The modified Schroeder diffuser was presented in an earlier study [A. Jarvinen et al., J. Acoust. Soc. Am. 103, 3065(A) (1998)]. Results from the simulations with various numerical techniques were also reported. The developed structure is simpler than the traditional Schroeder diffusers and the total volume of the diffuser is utilized. The acoustical properties of the structure are studied further and optimized for different applications. Three-dimensional numerical simulations using boundary and finite-element methods and finite-difference time domain method are used and results are verified with scattering and absorption measurements. In addition to the previous study, simulations include structural coupling. This opens up new possibilities for adjusting the structure for different purposes such as broadband absorber. The low-frequency absorption effect [H. Kuttruff, Appl. Acoust. 42, 215–231 (1994)] can be taken into account by including the acoustical properties of the materials into calculations. Furthermore, this type of construction is applicable as a modular acoustic panel. The advantages of the modified diffuser construction are shown in comparison to traditional designs with similar acoustic characteristics.
Mode counts for rooms and waveguides
Authors: Morfey Christopher L. , Wright Matthew C. M. , Yoon Seong-Ho
Published: July 2002

The density of modes in a room (3D) or waveguide cross section (2D) is known to be approximated at high frequencies by expressions involving room volume and surface area, or (in 2D) the area and perimeter of the waveguide cross section. Deviations of the actual mode count from the smoothed approximation are studied numerically and analytically, for simple shapes: rectangular (2D and 3D), and annular (2D). Periodic clustering of eigenvalues, associated with cyclic rays [R. Balian and C. Bloch, Ann. Phys. 69, 76–160 (1972)], is demonstrated at high frequencies. Expressions are given for estimating the standard deviation of 2D and 3D mode counts from their smoothed values, in a finite frequency band, when one dimension is much smaller than the others.
An extension of the transfer function method described in ASTM E 1050-90 for its use in semianechoic conditions
Authors: Picard Lopez Miguel Angel , Solana Quiros Pedro , Urchueguia Schoelzel Javier Fermin
Published: July 2002

The wave tube described in the above standard requires a rigid end characterized by a very high impedance, ensuring the correctness of the measurement of the sample-specific acoustic impedance. This method can also be employed for the measurement of other characteristic parameters associated with fibrous materials, more specifically, its dynamic flow impedance. If the rigid end is removed and the tube is enlarged with a piece containing absorbing material, the tube termination impedance is obtained when measuring without the probe. This impedance is affected by the tube modal response, which is a function of the tube’s length. If a fine slice of the sample (as compared to the wave length inside the tube) is then used, and again an impedance measurement is performed, the values obtained are in phase with the first measurement (without sample) and differ by the amount of the dynamic flow impedance of the sample. Measurements have been performed with Rockwool samples of different densities giving good results, as shown in a recent J. Sound Vib. paper. The advantage of this method is that measurements can be done with a nonideal end, as its effects are taken into account in the evaluation procedure.
Perception of harmonic complexes in budgerigars (Melopsittacus undulatus)
Authors: Dent Micheal L. , Dooling Robert J. , Leek Marjorie R.
Published: July 2002

Many studies have shown that birds have auditory spectral resolving powers similar to mammals, but it has long been thought that they are superior in analyzing temporal information. To investigate the ability of budgerigars to process rapid temporal cues within complex waveforms, birds were required to discriminate among harmonic complexes with identical long-term spectra, but with temporal waveforms that differed in envelope shape or fine structure. Using operant conditioning procedures, birds were trained to discriminate a highly peaked waveform, created with all components starting in cosine phase, from waveforms with a random selection of phase for each component, creating a flatter envelope shape. In a second experiment, birds discriminated between harmonic complexes that were identical in both spectrum and waveform envelope, but that differed in the fine structure within fundamental periods. In both experiments, birds could easily discriminate among waveforms with fundamental frequencies up to 800 Hz, with some decrement in performance at higher frequencies. Humans are unable to perform similar tasks for frequencies higher than about 300 Hz, suggesting that time processing of complex sounds in the avian auditory system may preserve information presented at rates at least three times the limits shown for humans. [Work supported by NIH DC00198.]
Frequency discrimination and advertisement call in the aquatic clawed frog, xenopus l. laevis: Qualifications for interindividual recognition
Authors: Elepfandt Andreas
Published: July 2002

The acuity of frequency discrimination was tested in the clawed frog, xenopus l. laevis by means of conditioning. xenopus is completely aquatic and communicates acoustically on the bottom of ponds. For conditioning, a tank was built in which pure tones could be presented to the animal. The paradigm was discrimination of water surface waves contingent upon the underwater tone presented simultaneously, i.e., distinguishing a wave presented with tone A from a wave with tone B. Frequency discrimination was best in the range 1600–2000 Hz, where relative discrimination up to 2% was found. This range matches the range of the dominant frequency in the frog’s advertisement call. Whereas there is considerable variation between individuals, the dominant frequency of a given individual is very constant, varying by less than 10–20 Hz even when the hormonal status of the animal or the temperature of the water is changed. Thus the animals can distinguish between calling males on the basis of the dominant frequency. In the field, males establish territories whose location may remain constant for weeks up to years, so that stable neighbor relationships are formed. In such a situation, recognition of the neighbor’s call may be advantageous.
Sound propagation in natural environments
Authors: Glaser Evelyn B.
Published: July 2002

The basic model of acoustic communication in animals is one of transmitters, receivers, and a transmitting pathway in between. The acoustic features of each component involved determine the acoustic behavior of animals in natural environments. The aim of this work is to describe the alteration of sounds propagating through a natural habitat by measurements and modeling. Birdsongs and various artificial sounds are broadcast and recorded at five distances at different habitats (temperate meadow and desert). The sounds are designed to match several acoustical characteristics of birdsongs. The signals of two microphones are recorded simultaneously with a DAT-recorder and analyzed off-line. The transfer functions between the referenced loudspeaker output and the respective recording inputs are then computed. The resulting distinct patterns for the power-spectra depend on the spatial arrangements of the transmitter and the receivers and the acoustic impedance of the transmitting pathway. Important spatial features are the horizontal and vertical distance between transmitter and receiver and their distance to the surface. The amplification and damping of the sounds can be explained by the interference of the directly transmitted and the reflected wave. The measured and the computed spectral patterns show a high degree of similarity.
Mode diffusion and pulse broadening in shallow-water acoustic propagation
Authors: Odom Robert I.
Published: July 2002

An acoustic signal propagating in a range-dependent shallow-water waveguide is scattered and attenuated as a result of interaction with medium heterogeneities. An initial signal pulse consisting of a few modes will spread in time linearly with propagation distance as energy is redistributed among available modes due to mode coupling. Over longer propagation distances in a random waveguide, modal energy reaches equilibrium, and the average modal energy becomes constant. (The modes are, of course, subject to geometric spreading, intrinsic attenuation, and radiation losses, but it is assumed that all modes are equally affected so that, locally, the energy per mode is a constant.) Energy propagates at a velocity that is an average of the group velocities for individual modes. The pulse width grows mores slowly now as the square root of the propagation distance, rather than linearly. This transition to square-root broadening in randomly perturbed multimode fiber optic waveguides is well known and observed. Employing a diffusion equation for the modal acoustic energy in a random shallow-water waveguide with an elastic bottom, heterogeneity-induced pulse broadening is investigated for realistic environmental properties. [Work supported by ONR.]
Normal mode propagating through rapid range-dependent shallow water
Authors: Li Fenghua , Zhang Renhe
Published: July 2002

When the normal modes propagate through the range-independent shallow water, the different normal modes are separated into different wave packets in the time domain because of the different group velocities. If the normal modes propagate through some kinds of shallow water which are rapidly range-dependent due to the bottom or the fluctuation in the water column, etc., coupling between different-order modes will happen. And even the same normal mode at the receiver will be divided into two or more wave packets in the time domain, each packet representing the energy coupled from the different normal mode at the source to that mode at the receiver. Those divisions provide a lot of useful information about the rapid range-dependent environment. The divisions of one normal mode are calculated by a coupled mode code which is developed based on BDRM theory, and are also used to estimate the simulated rapid range-dependent environment in this paper. [Work supported by NSF of China.]
Analysis of active hydroacoustic system’s parameters versus conditions of sound propagation in inland water
Authors: Gawrysiak Jacek
Published: July 2002

The paper contains the numerical calculations of a dependence between the shape of the sound velocity profiles in inland water and sonar parameters such as: directional pattern, range, signal-to-noise ratio, and so on.
The genetic algorithms for the optimization of distributed loudspeaker systems
Authors: Fillol Corinne , Legros Claude P.
Published: July 2002

In reverberant and highly noisy environments, public address systems are often used in order to improve the speech intelligibility. Nevertheless, a number of common problems are generally encountered with such installations. Too many distributed loudspeaker systems suffer an inappropriate utilization of loudspeakers which leads to an excessive excitation of reverberant field and a poor audience coverage decreasing the intelligibility. Two rules of thumb have been well formulated to optimize uniformity of audience coverage, but both of them did not take in account the emission of the loudspeaker in its acoustic environment. Too many sound systems, in factories and public spaces, are therefore ineffective and do not respect the safety standards. Nowadays, it is possible to predict the acoustic performance and to simulate the radiation of a sound system in space by the means of geometric approach. The utilization of such a program with natural algorithms allows the optimization of the positioning and the number of loudspeakers by considering the acoustic characteristics of the room and sources. The performance of this method is applied in the case of choosing a best configuration from 16 possible loudspeaker locations in a classroom in order to obtain an optimum speech intelligibility and allow a smaller cost of renovation.
Natural frequencies of a fluid-filled anisotropic spherical shell
Authors: Chen W. Q. , Ding H. J.
Published: July 2002

In this paper, the general nonaxisymmetric free vibration of a spherically isotropic elastic spherical shell filled with a compressible fluid medium is investigated. To this end, the three-dimensional elasticity solution method recently developed by the authors [H. J. Ding and W. Q. Chen, Int. J. Solids Struct. 33, 2575–2590 (1996)] is employed. The effect of fluid is considered by introducing a relation between the normal displacement and the normal stress of the shell at the inner spherical surface. It is shown that the coupled vibration can be divided into two independent classes as in the case of empty spherical shell. The exact three-dimensional frequency equations are then derived. As the exact elasticity solution can serve as a benchmark to check various approximate theories, frequency equations of three typical shell theories are also presented. Numerical examples are given and comparisons between four theories are made.
Development and analysis of a two-stage beamformer for multiple correlated interferers using rectangular array
Authors: Lin T.-T. , Lee T.-S.
Published: July 2002

A two-stage two-dimensional (2-D) beamformer is proposed for signal enhancement in an environment of multiple correlated interferers using a rectangular array. In the first stage, subarray beamformers are constructed which exhibit reliable interference cancellation using difference- preprocessed and spatially smoothed data. A secondary combining of all possible subarray beamformers is then performed to fully exploit the array aperture. It is shown that, compared to the conventional one-stage optimum beamformer, the two-stage beamformer performs equally well and requires a much lower complexity of implementation when a suitable subarray size is chosen.
Thermoacoustic instabilities of highly premixed flames in combustors and boilers
Authors: Sattelmayer Thomas , Pankiewitz Christian
Published: July 2002

The attempt to reduce the formation of pollutants from combustion processes has led in recent years to the development of novel low-temperature combustion processes. Confined flames of this type exhibit a number of instability mechanisms, which can lead to unacceptable combustion noise or even to severe damage. The instability mechanisms, which appear in cases of technical interest, are reviewed and explained. It is shown that a realistic model for the description of the instability requires a proper representation of the contribution of the flame as the driving element. To date, nonlinear transfer functions have to be deduced from combustion experiments, but attempts to derive transfer functions numerically have already been published. In the past, modeling efforts were strongly focused on longitudinal modes. Although circumferential modes are of technical importance, they have not yet been fully understood. In this case, a complex interaction of the nonlinear flame with the linear acoustic system has to be taken into account and the transition between modes becomes more important. Since a satisfactory description of the interaction is not yet available, active instability control techniques have been proposed. Their limit in cases of technical interest will be discussed.
On validity of mean-field approximation in thermoacoustics
Authors: Gusev V. , Bailliet H. , Lotton P. , Brauneau M.
Published: July 2002

Thermoacoustic heat flux is convective in its physical nature. In the present communication it is demonstrated that the problem of analytical description of thermoacoustic heat flux is identical to the problem of closing moment hierarchy in the theory of fluid turbulence. In the case of harmonic acoustic oscillations, spatially inhomogeneous time-averaged temperature distribution is related to temperature oscillations at fundamental frequency. However, the first (fundamental) harmonic depends on the second harmonic of temperature field, which in turn is related to the third harmonic, and so on. In analytical models of thermoacoustic devices the harmonics of temperature oscillations are usually neglected. This so-called ‘‘mean-field’’ approximation results in the description of thermoacoustic heat transport as a diffusion process (with an effective thermal diffusivity depending on acoustic wave power). In the present communication it is demonstrated that mean-field approximation is not just inappropriate for the description of thermoacoustic heat exchange between gas-separated solid plates, but it is also not valid in all the cases where the characteristic spatial scale of mean temperature variation does not significantly exceed the amplitude of gas displacement in standing acoustic wave (for example, near the terminations of the stacks and heat exchangers). [Work is supported by DGA.]