bluuebunny/crossref_metadata_2025 huggingface dataset:
Paul Kendig and directional response control for planar acoustic arrays
Authors: Wilson Geoffrey L.
Published: October 2005

Paul Kendig was a pioneer in the application of techniques developed by the radar community for line arrays to the control of sidelobe response from the planar arrays used in sonar. The magnetostrictive “hair-pin” transducer element developed at the Harvard Underwater Sound Laboratory and at Penn State's Ordnance Research Laboratory lent itself easily to such control merely by adjusting the number of turns on the coils. This paper discusses briefly the development of the theory, and its application to these magnetostrictive arrays and to the piezoceramic arrays that were being developed in the early 1960s.
Paul M. Kendig—The ARL years 1966–1971
Authors: Thompson William
Published: October 2005

The leadership that Paul Kendig provided to the research efforts of the Transducer Group of the Applied Research Laboratory, Penn State University, during the indicated years is reviewed and fondly remembered, as well as his own technical contributions. The thrust of this work was on improving the design and construction of Tonpilz transducer elements and arrays, achieving directivity patterns with very low sidelobes, obtaining multiple, tilted, directivity patterns, bringing on line a new sonar transducer calibration facility, developing other experimental transducers, and guiding a variety of graduate thesis research topics.
Nearfield calibration array for hydrophones and arrays
Authors: Ferlino Philip A. , Hughes W. Jack
Published: October 2005

A plane-wave volume was synthesized with a line array of projectors in a 7- to 50-kHz frequency range enabling hydrophones and hydrophone arrays to be calibrated in the nearfield. The plane-wave volume was created using the Van Buren technique by revolving a suspended line of PZT-4 type transducers in a semicircular fashion. Results were compared with the known sensitivities and directivity patterns of the hydrophones used. Amplitude shading coefficients for the line array were determined by a computer program furnished by A. L. Van Buren [Underwater Sound Reference Detachment, Naval Research Laboratory].
Acoustical properties of a Chinese bowed string instrument
Authors: Chen Tong
Published: October 2005

The main parts of a Chinese bowed string instrument are two strings, a bridge, and a resonator. The resonator, which consists of a wood (or bamboo) cylinder and membrane, has been studied both experimentally and theoretically. The frequency of the main air resonance in the cylinder is about 2 or 3 oct lower than the lowest resonance frequency of the membrane. From the analysis of waves propagated on the string, the impulse response of the string vibration can be expressed in terms of the string parameters and the reflection coefficient at the bridge. This reflection coefficient has been measured. The sound spectrum of the instrument in bowing the string can be explained by the waves on the string and the radiation characteristics of the resonator. Sound spectra for the instrument have been obtained by playing seven notes of the musical scale. The characteristics of sound are different for bowing different strings.
Introductory Fourier synthesis with a sampling keyboard
Authors: Hansen Uwe J.
Published: October 2005

An inexpensive sampling keyboard, marketed by Tandy as the Concertmate-500 or by Casio as the SK-1, includes a prerecorded flute sound with harmonics about 40 dB below the fundamental, presenting a very effective sine wave generator. The direct output is fed into an oscilloscope. Although limited to four voices, the polyphonic output affords a simple way to introduce superposition of waves and thus introduce the topic of Fourier synthesis. The nature of beats as a difference frequency is easily illustrated by playing adjacent keys in different octaves. Wave shapes produced by adding two, three, and four harmonics as well as beats will be illustrated. This approach has been used in workshops for elementary and secondary science teachers supported with title II funds. The Tandy Corp. donated 25 keyboards for the workshops. The emphasis of the workshops is the use of music as a vehicle to generate interest in science.
A sound decomposition system based on a deterministic plus residual model
Authors: Serra Xavier , Smith Julius O.
Published: October 2005

Based on a deterministic plus residual model, a system is developed that extracts stable sinusoidal components from a musical sound and leaves a residual waveform as a result. The two components can be added to obtain an identity with the original sound. The technique is based on the short-time Fourier transform. From the set of spectra returned by the transform, the prominent peaks are detected at every frame and assigned to a number of frequency trajectories by means of a peak continuation algorithm. The relevance of this algorithm is that it detects the stable sinusoids present in the original sound (the deterministic component). Each trajectory includes an amplitude, frequency, and phase value for every analysis frame. From each trajectory, a time varying sinusoid is generated and the sum of all these sinusoids form the deterministic component. Since the synthesized waveform has preserved amplitude and phase of the original sound, a time domain subtraction succeeds in obtaining a residual waveform free of the detected sinusoidal components.
History of noise quality in the automotive industry
Authors: Geddes Earl
Published: October 2005

This paper will present a brief look at the emerging philosophy of sound quality as viewed from within the automotive engineering community. A few examples of the concepts of sound quality will be discussed focusing on their relevance to noise control in vehicles. The paper will be primarily historical in content relating how the ideas of sound quality came to be recognized as an important factor in noise control for automobiles.
Psychoacoustics in context: Studying the listener and the noise
Authors: Fleischman Rebecca N
Published: October 2005

Psychoacoustic studies of product sounds can be improved by a better understanding of what the listener brings to the evaluation of noise. Noise is interpreted in the context of a system of knowledge and beliefs about products and their operation. When correlating acoustic noise factors with listener judgments, ask the following questions about the meaning and context of noise: What are the expectations that listeners have about noise? Listeners may expect certain product-specific sounds. They may judge product quality from specific noise features based on their beliefs about the relationship between the engineering or manufacturing of machines and their acoustic properties. What is the information content of a noise? Some components of a noise may be used as a diagnostic or to cue operation. What is the listening situation? Whether the listener is an active product operator or a passive bystander could mediate evaluations of noise quality. Examples of how these and other listener factors can influence noise judgments are presented, and strategies for incorporating them in psychoacoustic studies are discussed.
Noise and meaning
Authors: Blauert Jens P.
Published: October 2005

Noise is undesired sound. The decision, however, of whether a sound is desired or undesired, is taken by the listener in the specific situation of sound exposure. A sound that is noise for one listener, may be a useful, information carrying signal for another listener and, moreover, each listener may change his mind at any time depending on the circumstances. Consequently, once a noise level is reduced so far that a physiological danger for the listeners' ear is no longer present, a further reduction of the level may not be the adequate measure to further decrease the negative impacts of the noise. Instead, a careful redesign of the complete acoustical environment at the listeners' position may be required. To this end, proper, ear-adequate methods for noise measurement and noise quality evaluation are needed. In this talk, some developments along these lines, as currently being discussed in Germany, will be reviewed and evaluated.
Acoustical testing of the Harris County Domed Stadium (the Astrodome) in Houston, Texas, preparatory to a new sound system design
Authors: Randorff Jack E. , Taylor Ashton , Longaria Omar C.
Published: October 2005

In preparation for a new sound system design, a study of the physical acoustics was performed in the Astrodome, Houston, Texas. The goat of this 4-month study was to determine reverberation time, echo-producing surface locations, noise levels, and resonant conditions in preparation for sound system design and possible future acoustical treatment. Measurements were carried out using conventional instrumentation (sound-pressure level meters, real-time audio spectrum analyzers, scientific data recorders, etc.) and with a TEF (time-energy-frequency) analyzer. Specific findings of the physical acoustics study and how these findings affected sound system design formed the basis of the design philosophy and resulted in a new sound system with improved intelligibility, pattern control, and sound pressure compared to the old sound system.
The acoustical design of the Naples/Marco (Florida) Center for the Performing Arts
Authors: Tanner Robert H.
Published: October 2005

Just over 2 years ago, in a somewhat unusual move, the Naples/Marco Philharmonic Orchestra decided to build its own concert hall, and the author was engaged to carry out its acoustical and noise control design. The resulting building, which opened officially on 3 November 1989, contains a 1200-seat hall, a 250-seat theater, and two 2-story art galleries, and was built for the unusually low sum of $19 000 000. Although the design for the main hall started out with a considerable bias towards musical performance, the usual demand for an all-purpose hall arose, leading to the inclusion of a full stage house. The needs of the concert hall were met by the provision of a very flexible orchestra shell. Although the tight schedule left no time for any acoustical adjustments, the hall was a success right from the gala opening performance by its own orchestra, and has received favorable comments from performers varying from Hal Holbrook as Mark Twain to the Canadian Brass and Sir Neville Mariner. The theater is also very flexible and will be used for everything from one-person shows and chamber music to receptions and banquets.
An application of delta modulation to active vibration control
Authors: Serbyn M. R. , Penzes W. B.
Published: October 2005

The basic functions of communication and vibration control are reviewed with emphasis on their similarities, and the constituent parts of a vibration controller are compared with their communication-system counterparts. This approach provides a convenient framework for describing and analyzing a digital bang-bang type of vibration controller utilizing two delta modulator chips for encoding and decoding. Experimental results obtained on a prototype system designed to operate in the 20- to 200-Hz frequency range are presented. Satisfactory performance has been achieved with both deterministic and random signals. The present implementation extends the capabilities of the authors' earlier designs using phase and pulse-width modulation [ISA Trans. 21, 55–59 (1982); Proc. IEEE Inst. Meas. Conf. '85, Tampa, FL, 178–181 (1985)].
Vibration distributions of adaptively controlled flexible plates
Authors: Sommerfeldt Scott D. , Bischoff Lance B.
Published: October 2005

An adaptive vibration control system has been developed, based on the filtered-x algorithm, which is capable of providing multichannel control of flexible plates. The control system has been used to investigate the modal patterns of controlled flexible plates. Two plates of different thicknesses were investigated, one with a low modal density, and the other with a considerably higher modal density. For each plate, the vibration field of the plate was measured with no control and with one, two, and four active control sources operating. In this manner, it was possible to plot the spatial vibration distribution of the plate, as well as to obtain a measure of the total energy in the plate for the various control configurations. Several different control mechanisms were apparent for different control configurations. Some of the results obtained for the two plates will be presented and discussed.
Design of discriminant functions for distortion sequences in dynamic pattern matching for speech recognition
Authors: Chang Pao-Chung , Juang Biing-Hwang
Published: October 2005

In a traditional speech recognition system, the distance score between a test token and a reference pattern is obtained by simply averaging the distortion sequence resulted from matching of the two patterns through a dynamic programming procedure. The final decision is made by choosing the one with the minimal average distance score. If the distortion sequence is viewed as a form of observed features, a decision rule based on a specific discriminant function designed for the distortion sequence obviously will perform better than that based on the simple average distortion. It is therefore suggested in this paper that a linear discriminant function of the form D = Σi = 1F w(i)*d(i) compute the distance score D instead of a direct average D = (1/T)Σi − 1Td(i). Here, the analysis of the generalized probabilistic descent (GPD) method of Katagiri et al. [ASJ Fall meeting (1990)], which offers a solution to the dynamic pattern classification problem. The GPD method is further compared with several other adaptive algorithms based on the error propagation algorithm and a heuristic method in a speaker-independent speech recognition task involving utterances of the highly confusible English E-set (b,c,d,e,g,p,t,v,z). The results show that the best performance is obtained by using the GPD method that achieved a 78.1% accuracy for the E-set, compared to 67.5% with the traditional unweighted average method. Besides the experimental comparisons, an analytical discussion for various training algorithms will also be provided.
On multiframe parameter optimization in articulatory analysis/synthesis of speech
Authors: Gupta S. K. , Schroeter J.
Published: October 2005

Articulatory analysis/synthesis results using pitch-synchronous analysis/synthesis were previously reported [Gupta and Schroeter, J. Acoust. Soc. Am. Suppl. 1 87, S39 (1990)]. In this paper, the interpolation characteristics of articulatory parameters within that framework for application to speech coding are investigated. One of the prime motivations for using an articulatory scheme for such an application is that articulatory parameters, polentially require a much slower rate of update. The parameters can be optimized once every few pitch periods and interpolated to obtain values at intermediate pitch periods. In this paper, two different interpolation schemes are presented and their results are compared. In the first scheme, the interpolation interval is fixed, say 100 ms. Since a pitch-synchronous scheme is used, the nearest pitch marker is actually used. In the second method, the interpolation interval is made adaptive. The segmentation points within the speech utterance are determined using a smoothed spectral slope measure. The experiments indicate that the first scheme tends to smear out certain phonemes if the interpolation interval is selected to be too long. On the other hand, the second scheme requires automatic determination of appropriate interpolation intervals for different speech events.
Time-varying, high-frequency bottom backscattering
Authors: Stanic S. , Kennedy E. , Ray R.
Published: October 2005

Continuous wave (cw) signals at frequencies between 20 and 180 kHz were backscattered from a shallow-water ocean bottom. Even though the source and receiver were mounted on a stable platform, the short-range (50–300 ft) bottom backscattering envelopes exhibited significant amplitude variations that increased as the grazing angles became smaller. Evidence suggests that the oceanic fine structure caused frequency-dependent shifts in the location of the insonified bottom area. These small shifts resulted in changes in the bottom scattered ping-to-ping envelope structure.
Is the ocean floor a fractal?
Authors: Herzfeld Ute C.
Published: October 2005

The high-resolution topographic structure of the ocean bottom plays an important role in acoustic reverberation. Mathematical models of the seafloor at different scales are presented, based on analyses of the spatial continuity. Survey devices are usually designed for a certain resolution, and, to date, most studies are concerned with one limited range of scale. The question arises whether the statistical behavior at one scale can be carried over to another, or what conclusions can be drawn. It has been proposed that the ocean bottom can be simulated as a fractal (an object of Hausdorff dimension strictly larger than its topological dimension). Analyses of scale-dependent measures of spatial continuity (nested variograms and covariance functions) are used to investigate whether this assumption provides a description coherent with seafloor observations. The concepts will be demonstrated in a case study, using SEABEAM bathymetric data from the East Pacific Rise.
Three-dimensional scattering from a rough fluid-elastic interface
Authors: LePage Kevin , Schmidt Henrik
Published: October 2005

Out-of-plane scattering is of interest to the Arctic noise community because of the observation of significant out-of-plane motion in ice excited by explosive sources in the water column. Because low-frequency fluid-elastic scattering apparently couples energy into subsonic flexural waves as well as horizontally polarized shear (SH) waves in the ice, radiating in all directions, some impact on Arctic transmission loss and horizontal coherence properties is anticipated. The self-consistent boundary perturbation formulation for rough surface scattering developed by Kuperman and Schmidt [J. Acoust. Soc. Am. 86, 1511–1522 (1989)] is used to estimate the mean and scattered fields for a two-dimensionally rough fluid-elastic interface excited by an incoming plane wave. The reflection and scattering coefficients determined by the full 3-D formulation are compared to earlier results, where the surface roughness was assumed to be polarized in the plane of the exciting wave only. In addition, the kernel of the wave-number integral for the scattered field is examined and it is found that significant energy is scattered into Scholte waves as well as SH waves at all azimuths relative to the incoming plane wave, consistent with the experimental observations. [Work supported by ONR.]
Computer simulations of design considerations for the direct path, bottom reverberation experiment
Authors: Fulford James K , Kalra Ashok K. , Slater Richard R.
Published: October 2005

A series of range-dependent monostatic and bistatic numerical simulations of reverberation from near-bottom-mounted source and receivers was made to investigate the experimental designs for the acoustic reverberation special research program (ARSRP). Vertical line array receivers and point sources were simulated in both monostatic and bistatic configurations to determine the time-dependent ensonified field and reverberation levels. Planar array simulations were made for bistatic configurations to determine the potential gain in both vertical and horizontal directionality. The simulations revealed some geometry related issues that must be addressed to obtain high-quality acoustic data in the high-resolution natural laboratory area. [Work supported by ONR.]
Kirchhoff-Helmholtz modeling of seafloor scattering in a Mid-Atlantic Ridge seismic reflection line: Origin of scatterers and possible masking of a magma chamber reflector
Authors: Kim Isaac I. , Orcutt John A. , Detrick Robert S. , Mutter John C. , Buhl Peter
Published: October 2005

In January 1989, multichannel seismic reflection data were collected over the MARK area (23° N) of the slow-spreading Mid-Atlantic Ridge (MAR) in hopes of imaging an axial crustal magma chamber. Unfortunately, the seismic reflection data are dominated by what appears to be scattering from a very rough unsedimented seafloor. No magma chamber reflection could be seen through the scatter. Some stronger coherent events, however, could be interpreted as dipping intracrustal reflectors. Kirchhoff-Helmholtz scattering synthetics from digital SeaBeam bathymetry maps indicate that almost all of the events seen in the reflection data originate from the seafloor and not the subsurface. A back projection algorithm was used to locate the points of origin of these seafloor scattered events. The sources of most of these scattered events are from smaller holes in the bathymetry rather than from large features, implying focusing within a Fresnel zone as the mechanism for the scattering. Combining Kirchhoff-Helmholtz transmission synthetics, using reflectivity-derived starting amplitudes, with the scattering synthetics, show that a magma chamber with an amplitude reflection coefficient as high as 0.10 would be made unobservable because of high-amplitude MAR seafloor scattering.
Electroacoustic design of the Hollywood Bowl sound reinforcement system
Authors: Schwind David R. , Cohen Elizabeth A.
Published: October 2005

This renovation began in 1988 with replacement of loudspeaker arrays used primarily for music reinforcement including orchestra, chorus, soloists, jazz ensembles, etc. The system was expanded to three discrete channels above the stage. Goals realized were improvements in the sound-pressure level uniformity, fidelity, gain before feedback, and spatial image. Several novel techniques were employed. The techniques include: (1) frequency selective filtration among multiple like drivers in a single channel to reduce audible phase interference; and (2) the introduction of delayed signal from the “far” channel into the center channel, so that extreme house right can hear left channel and vice versa. The second phase of the renovation involved replacement of the signal chain downstream of the mixing desk output, resulting in further enhancement of peak output levels. Currently, the transducers and signal chain before and at the mixing desk are being examined.
Acoustical model studies
Authors: Chiang Wei-Hwa , Cervone Richard P. , Siebein Gary W. , Doddington Harold W. , Schwab Wilhelm K. , Fausz Jerry L.
Published: October 2005

A dedicated, computer-based analysis system was developed to perform a variety of acoustical measurements in full-size rooms and in scale models. Measurements made in 1:10, 1:24, and 1:40 scale models of a band rehearsal room and a 1500-seat, multi-use theater were compared to measurements made at equivalent locations in the full-size rooms. The models were filled with nitrogen to examine the effect of air absorption on the measurements. The room was also simulated with a popular computer program with a ray-tracing program. An expanded program was written to calculate several objective parameters from the computer model. These results were compared to the measurements made in the physical models and the full-size room.
The use of physical and computer models for the audible evaluatinn of performance spaces prior to construction
Authors: Berkow Sam , Talaske Richard
Published: October 2005

The strengths, weaknesses, and underlying assumptions of commonly used physical and computer simulation methods will be discussed. A review of currently available hardware and software for the modeling of rooms will be presented along with the ultimate goals of acoustic simulation. A description of the simulation and modeling process used to evaluate the Escondido Civic Center's 1500-seat multi-use theatre will be presented along with audible recordings developed through the convolution of measured impulse responses with anechoic recordings.
Hands-free voice control of teleconferencing systems
Authors: Flanagan J. L. , Berkley D. A. , Shipley K. L.
Published: October 2005

As switched digital connectivity becomes pervasive [in forms such as the integrated services digital network (ISDN)], the opportunity increases for expanding the sophistication and utility of teleconferencing systems. A strong interest is to integrate information modalities for voice, image, data, fax, video, and broadband audio. As these teleconferencing system features expand, ease and simplicity of use become increasingly important. Hands-free voice control and natural conversational interaction become desirable for communication between the human user and the conference system. Recent advances in autodirective microphone arrays, speech recognition and synthesis, and low bit-rate coding of speech and image provide new technologies to serve sophisticated conferencing systems. This report describes an experimental system, called HuMaNet (for Human/Machine Network), which integrates multimedia capabilities into a conferencing system designed for public-switched basic-rate ISDN. This digital transport has a capacity of “2B + D,” or two circuit-switched channels of 64k bits/s each (B), and one packet-switched channel of 16k bits/s (D). The system design and conferencing features are described, including those for ISDN call setup, voice control, and access of local and remote databases for image and text, and high-quality stereo sound transmission. Operation of the system is demonstrated from a video recording.
Experimental determination of the speed of sound in solids using impact loading
Authors: Roedell Jeff , Vaidya P. G. , Bayoumi A. E.
Published: October 2005

In many applications nondestructive testing (NDT) of the physical properties is desirable. This paper describes the use of signal processing and wave theory to experimentally determine the acoustic wave speed in sample materials. Through this, an estimate of a material's modulus of elasticity and other properties can be made. The testing was done using an acoustic emission (AE) acquisition system with two surface-mounted piezoelectric transducers in conjunction with a digital oscilloscope. A longitudinal stress wave was induced in the specimen and the wave data collected. Analysis involving FFT and nonlinear equation solving was performed on a mainframe computer. For verification, steel and aluminum specimens (for which wave speeds could be empirically determined) were used. Epoxy resin specimens were also tested. The best results from these tests yielded errors of 2.2% in the wave speed for aluminum, and 1.8% for steel. However, since the results are based on the solution of simultaneous nonlinear equations that may converge to erroneous answers, a good first guess was needed in order to get reliable results. A possible development of a better equation-solving algorithm is discussed.
Assignment of shape factors for porous materials having simple pore geometries
Authors: Stinson Michael R. , Champoux Yvan
Published: October 2005

In modeling the acoustical properties of porous materials, “shape factors” are sometimes introduced, relating the behavior of real pore shapes to that which would be obtained for circular pores. The assignment of shape factors is explored by considering the propagation constant and characteristic impedance of hypothetical samples having specific, simple pore geometries (e.g., straight pores with rectangular or triangular cross section) for which the acoustical properties may be calculated exactly. The calculated results are interpreted in terms of the model of Attenborough [J. Acoust. Soc. Am. 81, 93–102 (1987)]. A value of 0.5 for the “pore shape factor ratio” is found to work well for the pore geometries considered.
Experimental and theoretical study of the structure-property relationships in composite materials
Authors: Varadan V. K. , Ma Y. , Varadan V. V.
Published: October 2005

The often used terms “tailored material” or “engineered material” refer to the increased demands made by present day engineering innovations on material properties that are incompatible in a naturally occurring material. Composite materials provide a powerful solution. But, by definition they are an inhomogeneous mixture of one or more materials. The property of the material is determined not only by the types of constituents, but the actual customization of properties requires a good understanding of the inherent (micro or macro) structure-property relationships. In this talk several theoretical models are reviewed that attempt such prediction of effective properties and response to applied fields. The strengths and flaws in such models are also examined by reviewing the comparison between such predictions and the results of experiments on controlled laboratory samples using acoustic and elastic wave propagation in such materials. Fully validated models provide the confidence needed to use them as material design packages. New trends in tailored materials such as the incorporation of handedness or chirality are also addressed.
The application of viscoelastic passive damping methodology in structural dynamics
Authors: Rao Mohan D.
Published: October 2005

Recent advances in the understanding of dynamic properties of viscoelastic materials have resulted in many innovative means to enhance the inherent damping in structural systems. Damping is now recognized as a design parameter in all stages of analysis and design of structures subjected to dynamic loading. The purpose of this paper is to describe the status of knowledge concerning the application of viscoelastic materials for passive vibration and noise control of structures subjected to dynamic loading. First, the presentation will focus on various mathematical modeling techniques and measurement methods as applied to damping in general, and viscoelastic damping in particular. The advantages and limitations associated with each model/method will be described in the context of recent experimental study of the damping of graphite epoxy composite materials and joints. Then, current research on the prediction of modal parameters (resonance frequencies, loss factors, and mode shapes) of bonded composite structural joints incorporating viscoelastic damping materials will be presented. [Work supported by NSF.]
High-temperature ultrasonic data for process monitoring and control of composites
Authors: Tittmann B. R.
Published: October 2005

An acoustic sensor system for monitoring the processing of carbon-carbon composite is presented. The acoustics sensors consist of a Lamb wave generator/receiver and an acoustic emission detector. With the aid of high-temperature waveguides these sensors are shown to detect the in situ changes in some of the key properties of plates of carbon-carbon during pyrolysis in the range of temperatures from 25 to 900 °C. In particular, changes in stiffness as a result of microcracking and decomposition are readily detected and are shown as useful to guide/revise the time-temperature profile of the carbonization heat treatment. The acoustic data show a variety of interesting features giving insight into the microstructural changes as the heat treatment proceeds. Among these are: the difference in the behavior of the symmetric and antisymmetric Lamb modes, the observation or precursors indication of stress build-up prior to delaminations, and the observation of a minimum in the temperature-dependent modulus at about 650 °C.
The composite loss factor of reinforced thermoplastic molding compounds as a function of resonant vibration frequency, fiber orientation, and temperature
Authors: Norton Richard V.
Published: October 2005

The resonant-vibration loss factor of composite molding materials is strongly influenced by the reinforcement fiber properties, the fiber orientation, the fiber:resin interphase, and the thermoplastic resin itself. Three commercially available thermoplastics were molded into plates and the plates then cut into high-aspect ratio beams at precise angles off of the 0° machine direction. The loss factor was calculated by the half-power bandwidth method from the resonant peaks to 3000 Hz, the beams being driven in resonance by a noncontacting magnetic probe. The beam data were collected at equilibrium conditions from − 50 °C to the softening point of the thermoplastic. The loss factor transitions observed as a function of temperature suggest that the resin choice, fiber choice, fiber orientation, and the manufacturing process optimization should be carried out on a composite structural design planned for acoustic applications prior to the consideration of active control of sound and vibration.
Temporal organization of rhythmic units
Authors: Krishnan Geetha , Colson Karen
Published: October 2005

This study examined the temporal organization of rhythmic units (interstress interval) produced by normal and dysfluent adults. Duration measures were obtained for selected components within rhythmic units, which varied in size from one to five syllables. For both groups, temporal compression and expansion of selected components were observed as a function of the size of rhythmic units. Stutterers, however, differed significantly from normals in rate and extent of compression. Further, results indicated that the relative timing of certain components within the rhythmic units were similar for both groups. The findings support the idea that there are language-specific timing rules that operate to regulate rate and rhythm in English. The findings also provide evidence to support the comb model of speech timing. Additional study is being conducted currently to examine these phenomena in the speech of patients with Parkinson disorder.
Compensatory effects due to vowel length in Dutch
Authors: Jongman Allard , Sereno Joan A.
Published: October 2005

The temporal characteristics of Dutch words with long and short vowels were studied. Sixteen minimal word pairs containing long and short vowels were selected. Monosyllabic noun pairs (CV:C and CVC) and their corresponding bisyllabic plural forms were recorded by five speakers. Most Dutch nouns are pluralized by adding the suffix -ə n. In the first syllable, long-vowel plural nouns (CV:C ən) contain a long vowel in syllable-final position while short-vowel plural nouns (CV:C ən) contain a short vowel followed by an ambisyllabic consonant. Segment, syllable, and word durations were measured for these stimuli. Monosyllabic nouns with long and short vowels differed only in terms of vowel duration while bysyllabic plural forms showed additional length differences. Although, contrary to earlier reports in the literature, there were no durational differences between the intervocalic consonants (syllable-initial versus ambisyllabic), interestingly, the duration of the second syllable was inversely affected by the duration of the vowel in the first syllable. Implications of these data for theories of isochrony, segmental versus syllabic loci of timing phenomena, and the phonological representation of length will be discussed.
A nondestructive bottom characterization with a model tank experiment
Authors: Arvelo Juan I. , Yuan Jian Ren , Überall Herbert , Hargenrader Louis A.
Published: October 2005

The theory of normal modes has been applied to the inverse scattering problem. The model accounts for multiple elastic and absorptive bottom sediments. The characterization is performed at a number of frequencies according to the depth of the water column. Transmission loss measurements with range are supplied to a modified Levenberg-Marquardt minimization model at each frequency. The highest frequency is resolved first to characterize the uppermost sediment of the ocean floor. After convergence to a set of acoustic properties for that sediment, the next lower frequency is used to evaluate the acoustic properties of the next deeper sediment. Some experimental measurements by Hundley and Glegg [J. Acoust. Soc. Am. Suppl. 1 87, S132 (1990)] are used to test this inverse scattering method in a model tank with an epoxy sediment over a concrete subbottom. [Work supported by ONR.]
Fresnel zone effects in the scattering of sound by intermediate length cylinders
Authors: DiPerna Daniel T. , Stanton Timothy K.
Published: October 2005

The backscattering behavior of straight cylinders is examined whose “intermediate” lengths are comparable to the diameter of the first Fresnel zone of the source/receiver pair. This “transitional region” is complex in nature as the cylinders occupy a finite number of Fresnel zones (≈ 1–5) and, in general, can only be described numerically. The scattering is described by first adapting the deformed cylinder formulation [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)] to the point-source/point-receiver combination. Numerically evaluating this expression showed the scattering characteristics to be dominated by Fresnel zone effects—oscillations in the backscatter versus length curve caused by constructive and destructive wave interferences due to phase shifts from contributions along the cylinder axis. An experiment was performed that involved measurement of backscatter versus cylinder length, and there is reasonable agreement between the results and the trend as predicted by the approximate theory. [Work supported by ONR.]
Performance limitations of hull-mounted sonar arrays in the presence of air bubbles
Authors: de Moustier C. , Sotirin B. J.
Published: October 2005

Analyses of seafloor echoes received by a hull-mounted multibeam echosounder in various sea states, wind speeds, and ship's operating conditions made it possible to quantify the performance limitations of the sonar due to bubble masking. This performance assessment included, for each weather and ship's steering conditions: the number of transmit/receive cycles lost per unit time, the relative increase in noise level during bubble masking events, and the corresponding signal-to-noise ratio (SNR). For sea states ranging from 1 to 5, the number of pings lost per unit time is directly related to the ship's speed and course. Depending on the ship, this number can reach 40% in sea state 5 for ship's speeds in excess of 9 kn while heading into the seas. Likewise, the presence of air bubbles during a receive window seems to account for an increase in the background noise level of 8 to 10 dB in sea state 3, 10 to 13 dB in sea state 4, and over 15 dB in sea state 5. In addition, variations of 20 to 30 dB in SNR for near-specular returns have been observed, from one ping to the next, during bubble masking events. In sea states 4 and above, such variations can adversely affect seafloor acoustic backscatter measurements made with hull-mounted arrays. [Research sponsored by ONR and IFREMER.]
On differential phase measurements with the SeaMARC II bathymetric sidescan sonar system
Authors: Masnadi-Shirazi M. , de Moustier C.
Published: October 2005

The SeaMARC II sonar system, operated by the University of Hawaii, determines bathymetry by measuring the phase difference produced by seafloor echoes received at two rows of transducers, roughly half a wavelength apart, and by converting these measurements to angles of arrival as a function of time. Such phase measurements are affected by noise and interferences from multiple reflections on the ocean surface and bottom. Furthermore, the noise tends to mask the distortions due to these interferences. Working in the complex domain with acoustic data recorded at sea in the Fall of 1989, a simple time-averaging filter was found to reduce the noise while preserving distortions due to interferences and hence allowing their investigation. Complex ping stacking, over an area with little change in relief, also gave a clear view of the interference phenomena. As a result, in addition to the expected multiple reflection interferences, evidence of cross-talk between the port and starboard pairs of transducer arrays was found, and mapping of differential phase angles into acoustic angles of arrival required an “effective distance” between the two transducer rows almost 50% larger than the physical distance. Implications of these findings for bathymetric measurements and applicability of the phase processing method presented here will be discussed.
The curtain effect in a multiple convergence zone environment: Implications for ambient noise and bottom and surface reverberation levels
Authors: Browning David G. , Herstein Peter D. , Christian Raymond J.
Published: October 2005

Over multiple convergence zone propagation ranges the relative spreading loss per zone, although initially high, decreases with range. The other major component of propagation loss, attenuation, remains unchanged and eventually becomes greater than the rate of spreading loss. The range at which this crossover occurs—the curtain effect [Browning et al., J. Acoust. Soc. Am. Suppl. 1 80, S54 (1986)]—is highly frequency dependent. At low frequencies the curtain effect occurs at long ranges; this allows sources or scatterers in the second convergence zone or beyond to impact the received level since they suffer only a relatively small additional loss compared to the spreading loss to the first convergence zone. For a given distribution of noise source levels or scattering strengths it is estimated what would be the resulting background level and the relative importance of events, for example, a comparison between medium strength multiple events at medium ranges and a strong event at long range. This analysis is then extended to higher frequencies where the curtain effect occurs at a range of one convergence zone or less. [Work supported by NUSC.]
Sound transmission through wood joist floor/ceiling systems: A study of the effects of sound absorbing materials and changes to the ceiling structure
Authors: Warnock A. C. C. , Morin M. J.
Published: October 2005

A wood joist floor system was constructed in the Acoustics Laboratory at NRC. Measurements of airborne and impact sound transmission were made for different types and amounts of sound absorbing material in the cavity. Differences between materials were small. Different makes of resilient metal channels were installed; all gave about the same results. Methods of improving an unsatisfactory floor were examined. Over 20 floor systems were measured. The study was funded by Canada Mortgage and Housing Corporation. Measurements were made down to 63 Hz and revealed that in many cases there are resonances occurring below 125 Hz that have a strong influence on transmission loss values at and above 125 Hz. While the causes of the resonances are not always clear, measurements to these low frequencies give a clearer picture of the effect of changes to the structure. This paper will give a summary of the results obtained.
Low-frequency resonances in glazing configurations
Authors: Tocci Gregory C.
Published: October 2005

Stiffness combinations of insulating and laminated glass often result in resonances that reduce glazing configuration sound transmission loss. Among these are mass-air-mass and mass-damping material-mass stiffness resonances. Several resonances and their effect on sound transmission class (STC) and outdoor-indoor transmission class (OITC) will be discussed. [Work partly supported by Monsanto.]
Development of Standard Guide ASTM E966, “Field measurement of facade sound isolation”
Authors: Campanella Angelo J.
Published: October 2005

Standard Guide ASTM E 966-84 (similar to ISO 140/5) describes in situ field methods of measuring the ability of windows and doors to prevent the penetration of environmental noise into a room. Recent ASTM review for reapproval resulted in more explicit method options and descriptions. Six different ways are now available where noise reduction and sound transmission loss can be measured, each distinguished by the way that the external sound field is created and measured. The user determines which of these techniques is best suited to his or her field situation. In situ sound fields are unidirectional (single loudspeaker or point source) or quasidiffuse (traffic or flying aircraft), whereas that in the two-room laboratory methods is diffuse. Three options for measuring the incident sound level are: flush, around 2-m distance (as in ISO 140/V-3.1 using traffic), and remote free-field at an equivalent distance (as in ISO 140/V-4.1 using a loudspeaker). Sound transmission loss values are adjusted for comparison with E 90 or ISO 140/III laboratory results. Point source adjustment is according to the cosine of the angle of incidence. Line source adjustment is by the “average cosine” [P. T. Lewis, J. Sound Vib. 33, Pt. 3, 127–141 (1974)], but x-, y-, and z-site dimensions are converted to elevation angle and included azimuthal angle of the traffic line as seen from the test facade. The six methods are compared with other FHWA and FAA methods in common use.
Flextensional transducer for large depth
Authors: Dufourq Ph. , Letiche M.
Published: October 2005

The air-backed flextensional transducer is particularly sensitive to static pressure stresses. The main limitations are due to shell mechanical resistance and electromechanical bar (or ring) driver amplified stresses. Generally, the design starts with a stress analysis of the shell and driver that yields the relative dimensions of both, according to frequency and power specifications. In spite of optimizated designs, presently most uncompensated flextensional transducers are limited to several hundred meters of immersion. The problem of the static pressure for a class IV and V flextensional transducer is analyzed. A new concept of a specific filtering mechanism for a deeply submerged transducer is presented. Theoretical prediction and experimental results are compared for a 1000-m submerged class IV transducer. Then prospects for future developments are discussed.
Acoustics and hydrodynamics of bubble clouds
Authors: Oḡuz H. N. , Prosperetti A.
Published: October 2005

In the last few years, it has been realized that the near-surface clouds of bubbles produced by breaking waves may play an important role in the generation of oceanic ambient noise. In addition, the clouds are potentially very strong scatterers of sound and may therefore be responsible for the anomalous backscattering data reported by several investigators. In the first part of this paper, some theoretical results are reviewed concerning the active and passive acoustic behavior of bubble clouds and are compared with experiment. In the second part of the paper, the results obtained with a simple model of the evolution of the clouds in space and time are described. The model is based on two-fluid-averaged equations and describes the motion of the bubbles under the action of buoyancy and drag.
Greenland Sea moored tomography experiment
Authors: Lynch James F. , Worcester Peter , Morawitz Werner , Pawlowicz Richard , Sutton Phillip
Published: October 2005

As part of the Greenland Sea Project, a six-element acoustic tomography array was deployed in the Greenland Sea during the period September 1988–September 1989. The purpose of the array was (1) to understand the circulation of the gyre, (2) to study the formation of the Greenland Sea Deep Water, and (3) to examine the features of acoustic propagation in an MIZ region over a yearly cycle. Supplementing the acoustic data, a number of other measurements were made. A year-long time series of wind stress over the region was produced by the British Meteorological Office. Satellite SSM/I and AVHRR measurements produced information on ice parameters. A main component of the Greenland Sea Project was a seasonal series of CTD surveys, which the tomography effectively interpolates. The data analysis has already shown a number of interesting preliminary results. Examination of the wind stress data allows us to predict, on the basis of circulation models, what vorticity our array should measure—the agreement will be a test of the models. Work has begun on assimilating the tomographic data into ocean numerical models in order to constrain them. Two rather interesting events are seen in the acoustic data during the spring, which could be candidates for overturning, particularly given evidence from other data. (CTD profiles taken by Johannessen, Swift, and Meincke have shown evidence that deep convection to 1600 m did occur during the February to March time period in the center region of our array.) Acoustically, the interaction of the sound with the surface and surface mixed layer is of great interest. [Work supported by ONR and NSF.]