bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustical modal analysis is the tailpipe of a turbofan engine
Authors: Krejsa Eugene A. , Karchmer Allen M.
Published: October 2005

The results of a modal analysis of the pressure field in the tailpipe of a turbofan engine are presented. Modal amplitudes, as a function of frequency, are presented for several engine operating conditions. The modal amplitudes were obtained using an optimization routine to obtain a best fit to measured pressure auto and cross spectra. Pressure fluctuations, used to compute these auto and cross spectra were measured at five circumferentially separated locations in the tailpipe of the turbofan engine. Emphasis in the analysis was on frequencies below 2000 Hz. This frequency range corresponds to the frequency range where combustion noise, which must propagate through the tailpipe, can significantly contribute to the farfield total noise of a turbofan engine.
Cabin noise mathematical modeling for single engine aircraft
Authors: Campanella Angelo J.
Published: October 2005

Previous in-flight data [A. J. Campanella, J. Acoust. Soc. Am. Suppl. 1 69, S28 (1981)] indicated that the main source of cabin noise in single-engine aircraft, often 88 to 93 dBA at the pilot's ear position during cruise flight, arises from the engine exhaust, with the propeller noise apparent only during takeoff and full power climb. Mathematical modeling of the exhaust and propeller noise propagation from their source to the pilot's ear position was devised to optimize exhaust silencing means within the constraints presented by aerospace structures. Through comparison with in-flight data, it was found that the matching assumption should include that fact that the exhaust SPL harmonics have a velocity maximum at the exhaust outlet and a pressure maximum at the piston/cylinder source. It was further assumed that all harmonics had the same amplitude, representing an impulse source. Exhaust gas temperature, transport velocity, density, outside air temperature, cabin temperature, flight altitude, floor and window barrier (mass law), and intervening distances were included as model variables. Propeller noise was modeled after P. A. Franken and L. L. Beranek [Noise Reduction, edited by L. L. Beranek (Krieger, Huntington, NY, 1980), pp. 685–688]. This computerized mathematical model can be used to predict the effect of exhaust outlet location and a variety of exhaust silencer components on the A-weighted sound level at the pilot's ear position.
A cusp catastrophe in flow acoustics
Authors: Rehberg Ingo
Published: October 2005

The transonic flow in a duct following an abrupt enlargement of cross section leads to self-induced flow oscillations acting as a sound generator. It is shown that the frequency of the oscillation is influenced by the length of that duct: Increasing duct length will lead to a frequency decrease, but only up to a critical length lc of the duct. If this length is further increased, the frequency will jump to higher values. This jump is accompanied by hysteresis: decreasing the duct length again leads to a jump to the lower frequency at a length lc1 < lc. The above behavior is then simulated by two simple mathematical models. The transonic oscillator is represented by a nonlinear equation leading to oscillations, and the acoustic resonator, i.e., the duct, is represented by a term including a time lag. It is shown for both the experiment and the model that the hysteresis vanishes if the sound reflection at the end of the duct is decreased below a certain critical value. This behavior can be interpreted as being one of the rare examples for a cusp catastrophe of an oscillating system.
Cylindrical wave expansions of the fundamental singular potentials of an elastodynamic half-plane
Authors: Brind R. J.
Published: October 2005

The singular solutions of Lamb's problem are of great importance to the theory of scattering of elastic waves from defects lying in or close to a free surface, and specifically the scattering of Rayleigh waves from a perpendicular edge crack. Such problems occur in the fields of NDT and seismology. The singular solutions correspond to line sources of P and SV waves within a homogeneous, isotropic, linearly elastic half-plane. They have until now been expressed as Fourier integrals, but, by considering the continuation of these functions into the whole plane, we derive convergent expansions for them in series of cylindrical waves. The coefficients are functions of the depth of the source, but the expansions are uniformly convergent as this tends to zero. The expansions provide an efficient means of evaluating the expressions arising in the integral equations or infinite system of equations of a numerical approach to the scattering problem. They also yield explicit power series about the singular points, which are required for any low-frequency treatment. [Work supported by S.E.R.C. (UK) and DOE (USA).]
Rough surface effects on the spectra of ultrasonic waves scattered from symmetrical inclusions in bulk
Authors: Lewis D. Kent , Adler Laszlo
Published: October 2005

Ultrasonic wave scattering from symmetrical scattering centers embedded in a host material have been extensively studied in recent years. Most theoretical approaches assume an infinite or smooth semi-infinite host medium and smooth surfaced scatterers. Inversion routines, developed to characterize these scattering centers, assume the received ultrasonic field to be noise free and unchanged by anything but the scatterer. Surface roughness induces changes in the scattering results which can alter the characterization results in a finite sized sample. Experiments were undertaken to investigate these changes in order to determine the characteristics of a given surface, and to determine the transmission and reflection characteristics of a known randomly rough surface.
Convergence and the T matrix
Authors: Werby Michael F.
Published: October 2005

The transition matrix (T-matrix) approach has been used successfully to describe acoustic, electromagnetic, and elastic scattering by objects with a variety of shapes. This approach is based on an expansion procedure, the accuracy of which is determined by the suitability of the basis states used in the expansion as well as the number of terms employed. Initially, one represents the incident wave as well as all relevant unknown physical quantities in a partial wave expansion. The number of terms in the expansion relates to the question of convergence and defines the dimension of the matrices. The size of the matrices limits the utility of the T-matrix approach. It is possible to reduce the size of the matrices by a new approach presented here. The approach consists of treating a relatively small dimensioned T matrix for the essential incident partial waves and adding correction terms by allowing the incident waves to couple to higher order partial wave components associated with the scattering mechanism. The significance of these corrections regarding symmetry and convergence will be discussed along with computational examples.
The acoustic nearfield of cylindrical vibrators via the use of FFT methods
Authors: Stepanishen P. , Chen H. W.
Published: October 2005

This paper presents an extension of earlier works in investigating the acoustic nearfield of planar harmonic vibrators via the use of FFT methods [P. Stepanishen and K. Benjamin, J. Acoust. Soc. Am. 71, 803–812 (1982)]. In the present paper, a numerical approach is presented to evaluate the acoustic nearfield of baffled cylindrical vibrators with specified harmonic radial velocity distributions. The approach is based on the use of a combined Green's function and FFT method. The acoustic field is first represented in terms of a Fourier transform of the specified radial velocity and the resulting spectral representation is then rapidly evaluated via the use of FFT methods to obtain the spatial characteristics of the acoustic field. Extensive numerical results are presented to illustrate the spatial characteristics of the acoustic fields of finite length vibrators with axisymmetric and nonaxisymmetric distributions.
Elastic wave scattering by a fluid inclusion in an elastic half-space
Authors: Pillai T. A. K. , Varadan V. K. , Varadan V. V. , Peterson B.
Published: October 2005

A fluid inclusion in an elastic half-space is academically a challenging problem, and practically a very important one, especially in geophysics. The earth surface can be modeled as an elastic half-space with vacuum above, and various fluid inclusions (oils, minerals, etc.) under it. We present here a T-matrix solution to the problem of scattering of elastic waves from such a configuration. Numerical results are computed for the case of an oblate spheroidal fluid inclusion below an earthlike elastic half-space. The multiple scattering effects between the half-space and the fluid inclusion are studied by the different approximate expressions for the scattered field coefficients.
Spatiotemporal transduction and neural coding in touch
Authors: Johnson Kenneth O.
Published: October 2005

The sense of touch at the finger pads depends on three classes of mechanoreceptive afferents—the SA [slowly adapting), RA [rapidly adapting], and PC (Pacinian) afferents—that are arrayed across the skin of the pad in a two-dimensional array and have different spectral sensitivities. Only the SA afferents provide an afferent neural image with sufficient spatial resolution to account for human fine form discrimination, e.g., Braille character discrimination and letter discrimination [J. Physiol. 310, 117–144 (1981); J. Neurophysiol. 46, 1192–1203 (1981)]. The spatial frequency limits of this fine form discrimination are set by the spacing of peripheral SA afferents (approximately 1 per square mm). The SA afferents are particularly effective in signaling spatial information, responding much more vigorously to edges than to uniform skin deformation and displaying surround suppression [all accounted for by skin mechanics: J. Neurophysiol. 46, 1204–1225 (1981)]. Textural discrimination, which is based on dimensions much finer than 1.0 mm, appears to depend on a neural rate code consisting of the relative activities of the SA, RA, and PC afferents.
The mutability of time and space on the skin
Authors: Geldard Frank A.
Published: October 2005

Radical shifts in perceived spatial relations can occur through the operation of the principle of sensory saltation. In the realm of cutaneous sensation, where it was first encountered, and also in some auditory and visual situations, any brief stimulus preceding a second one by no more than about 300 ms will show apparent spatial displacement from its veridical position. The degree of deviation is determined primarily by temporal relations between the two stimuli but, secondarily, by intensive ones as well. Limits of the operation of the saltatory effect on the skin have been ascertained by employing a campimetric technique on representative bodily areas. From the results of such measurement, taken together with consideration of some aspects of the known neural substrate, it is possible to decide among several competing hypotheses concerning the essential seat of the phenomenon. The relation of the saltatory effect to the earlier τ and κ effects is discussed as are also the possibilities offered by all three to the solution of tactual communication problems and the allied problem of tactile displays. [Work supported by NIH Grant NS 04755.]
Vibrotactile forward masking: Evidence for channel independence
Authors: Gescheider George A. , O'Malley Martin J. , Verrillo Ronald T.
Published: October 2005

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. A 50-ms sinusoidal test stimulus was applied to the thenar eminence of the hand 25 ms after the termination of a 700-ms sinusoidal masker applied to the same site. The intensity of the masker was varied over a range of 0 to 44 dB SL. The frequency of the masker was either 15 or 250 Hz and the frequency of the test stimulus was either 15, 25, 100, or 250 Hz. The results support the hypothesis that the detection of vibrotactile stimuli is mediated by at least two receptor systems which do not mask each other.
Vibrotactile performance of normal and hearing impaired subjects
Authors: Donahue Amy M. , Letowski Tomasz
Published: October 2005

One-channel vibrotactile stimulation has been used in conjunction with auditory stimulation for acquisition of speech and language. Such dual-modality training will be the most advantageous when vibratory stimulation is optimized. The aim of this study was to measure sensitivity of untrained subjects exposed to vibrotactile stimulation. Vibrotactile thresholds and stress-pattern recognition curves were measured with two vibrators at three body placements. Five normal and seven hearing impaired subjects took part in the experiment. Two of seven hearing impaired subjects were unable to respond to applied vibrations. The results indicate that: (1) both wrist placements were less sensitive than fingertip placement; (2) vibrator plunger size had greatest effect in the most sensitive frequency range; (3) the hearing impaired subjects were equally or less sensitive than normal subjects; (4) stress-pattern recognition curves were a function of body placement but not a function of plunger size; and (5) stress-pattern recognition curves for hearing impaired subjects had lower plateaus than for normal hearing ones. Implications for vibrotactile training will be discussed. [Work supported by NIHR.]
Acoustic-phonetic aspects of consonant discrimination in children
Authors: Nelson Nancy , Wiley Terry
Published: October 2005

Consonant discrimination in preschool children was studied as a function of age, vowel environment, and presentation level. Responses to 15 consonants paired with /a/ and /i/ presented at six presentation levels were obtained for preschool children and for a control group of adults. The responses were analyzed according to four acoustic-phonetic features (voicing, nasality, place, and manner) to determine the effects of age, vowel, and level. The analyses revealed significant main effects for each variable. For all subjects, performance improved as a function of presentation level up to 30 dB SL. Children's overall performance was poorer than adults, especially in the /i/ vowel context. The vowel results were interpreted as support for a current theory of developmental speech perception incorporating primary and secondary acoustic cues (Stevens and Blumstein, 1978). When consonant-vowel (CV) stimuli with potentially ambiguous burst and transition cues were presented, adults were able to correctly identify consonants; children's performance was substantially poorer. These findings suggest that the development of test material for evaluating speech discrimination in children should be patterned after children's consonantal-perception data as opposed to adult models.
Effects of stimulus range on the identification of distorted “R” sounds in synthesized adult and child /r-w/ confirms
Authors: Sharf Donald J. , Ohde Ralph N.
Published: October 2005

Although the perceptual reality of a distorted “R” sound has been assumed by speech pathologists, recent research using full range /r-w/ continua contradicts this assumption [D. J. Sharf and R. N. Ohde, J. Acoust. Soc. Am. Suppl. 1 72, S65 (1982)]. It is known that varying the range of stimuli in speech continua affects the perceptual categories of normally produced sounds, but it is unclear if this perceptual factor affects judgments of sounds that vary from normal to distorted production. In order to extend our knowledge of the parameters which influence the perception of distorted R, we examined the effect of varying the range of sounds in /r-w/ continua modeled after adult and child vocal tracts. In several tests, which included three repetitions of each truncated continuum and two repetitions of the full range continua, subjects identified the stimuli as R, W or distorted R. The results indicate poor identification of the ambiguous stimuli as distorted R in the full range conditions, and a decrease in their identification as distorted R in the truncated range conditions. Along with previous findings, these results cast considerable doubt on the assumption that distorted R can be distinguished from the R sound that it is intended to represent. [Work supported in part by NINCDS.]
Vowel length contrast in Arabic and English: A spectrographic test
Authors: Mitleb Fares
Published: October 2005

A familiar linguistic theory tends to provide articulatory explanation or add extra segmental features to capture durational contrast between segments. This model, for example, explains height effect and tensity effect on vowel duration on articulatory basis. Thus it is widely accepted that tense vowels are relatively longer than low vowels since the approximative configuration for tense vowels is said to require a longer period than that for lax vowels. Also, the fact that low vowels tend to be longer than high ones is attributed to the degree of jaw lowering needed in the configuration for low vowels. A question, however, arises in connection with the linguistic analysis of length is how do long and short features get converted into actual time intervals? Spectrographic tests of English and Arabic minimal pairs revealed that height effect on vowel duration was the same in both languages. However, English and Arabic differed considerably with respect to durational contrast between short (lax) and long (tense) vowels. These results indicate that since temporal effects, like vowel height, seem to be universal and constant across languages, it becomes more difficult to account for some other claimed physiological effects (such as the effect of voicing on preceding vowels and the long-short contrast) in physiological terms. Hence the latter effects show considerable variation among languages. We propose, instead, that temporal structures are language—specific variables which must be taken into consideration in the analysis of a language [Research supported by Yarmouk University.]
Lateralization of simple sounds
Authors: Yost William A.
Published: October 2005

When acoustic stimuli are presented over headphones listeners usually report that a sound image appears within their head. Interaural differences in time and intensity can move the position of this image within the head. This effect is usually referred to as lateralization. We will review some of the basic results on the lateralization of simple stimuli. The relationship between lateral position and the interaural differences of time and intensity will be summarized. These results are used to predict those values of interaural time and intensity that yield an equivalent lateral position. The results from experiments which measure the just discriminable differences in interaural time and intensity will also be reviewed. The relationship between these lateral discrimination results and those from the lateral position studies will be described. The various models of lateralization all assume some type of cross-correlation operation. The cross-correlation approach to modeling these data has some strengths and some weaknesses. Results concerning the interaural differences of onset time and ongoing time will be compared. An attempt will be made to provide a general framework for the basic data concerning the lateral position and lateral discrimination of simple stimuli. The extent to which results from these lateralization experiments can account for our ability to localize sound sources in the free field will be discussed.
Anatomical substrate for sound localization
Authors: Masterton R. Bruce , Glendenning Karen K.
Published: October 2005

Behavioral, anatomical, and electrophysiological evidence indicate that the superior olives are probably the lowest-level nuclei that can provide for the quick convergence of the binaural activity necessary for sound localization and also for its integration and subsequent redistribution to the higher centers of the auditory system. Because of the nature of the convergence and sorting of the fibers ascending through the hindbrain and because the representation of the auditory field at higher centers is contralateral, the hindbrain auditory system can be profitably viewed as an acoustic “chiasm.” Since the lateral lemniscus is the lowest level of the auditory system where unilateral section results in contralateral deficits in sound localization, recent advances in knowledge about the trajectory and interconnections of fibers up to that level will be reviewed.
Physiological studies of directional hearing
Authors: Kuwada Shigeyuki , Yin Tom C. T.
Published: October 2005

This review concerns physiological studies of the neural mechanisms of sound localization. We will describe the responses of neurons in the central auditory system to sounds presented dichotically or in the free field. The free-field studies have sought to define the spatial receptive fields of these neurons and their topographical organization in the brain. Although the functional aspects of these cells are most effectively addressed by free-field methods, the mechanism by which these cells accomplish this task is best studied using dichotic stimulation. Influenced by the duplex theory and human psychoacoustics, the major focus of neurophysiological studies using dichotic stimulation has been the investigation of the effects of varying interaural phase and intensity. The neuronal responses to these stimuli and their relationship to the frequency domain will be discussed with a particular emphasis on the concept of characteristic delay. In an attempt to define the underlying circuitry, we will compare the neural responses to a model of a binaural cell. [This work supported by N.I.H. grants NS18027 (S. Kuwada), EY02606 (T. C. T. Yin), and NS12732 (J. E. Hind).]
Role of V/V + C duration ratio in the perception of [t]-[d] in German
Authors: Dittman Sibylla , Strange Winifred
Published: October 2005

Kohler [Phonetica 36, 332–343 (1979)] reported that the fortis-lenis distinction in German plosives following stressed, tense vowels was cued perceptually by the ratio of vowel to vowel + consonant closure duration (V/V + C): 0.58 = fortis, 0.75 = lenis. In the present study, analysis of a German speaker's productions indicated that V/V + C ratios for [t] and [d] following a lax vowel were 0.41 and 0.55, respectively. To examine perception by German and American-English speakers, four stimulus series were constructed by varying closure duration of digitized waveforms of the nonsense words: [e:də], [e:tə], [εdə], [εtə]. Predicted boundaries in identification functions, V/V + C = 0.67 for tense-vowel stimuli and V/V + C = 0.47 for lax-vowel stimuli, were obtained for Germans only on the [e:tə] and [εdə] series. Displacement in obtained identification boundaries for the [e:də] series and the [εtə] series suggested that closure murmur was a salient cue to the distinction. Poor identification performance by all but one English speaker demonstrates the importance of native-language experience in shaping the perception of phonetically relevant relational parameters. [Supported by NIMH.]
Competing bilingual messages as a test for second language proficiency
Authors: Webster J. C.
Published: October 2005

A competing message (selective attention} test of numeral identification was designed as a method of evaluating bilingualism. Sixteen pairs of two mathematical statements such as “Sixty less five equals fifty-five.” and “Funfzehn und drei ist achtzehn.” were recorded so that they overlapped each other in time. Multiple choice answer foils were provided for each key element in the statement. Foils and statements were chosen to be maximally confusable in each language, for example, fifteen/fifty/sixteen/sixty; two/three/five/nine; and vierzehn/vierzig/funfzehn/funfzig; eins/zwei/drei/elf. Control tests of native/native and non native/non native language items were also recorded. An English/Czech version of this test was given to English speaking members of the Institute of Psychology in Bratislava. Results showed that for those who knew English well either language was equally interfering with the other language. For those less proficient in English their native language (Czech) interfered with their non-native language (English) to a much greater extent. [Work done on NAS-USSR/CSSR Academic Science Exchange.]
Detection of French accent by native English speakers
Authors: Flege James Emil
Published: October 2005

This series of five experiments examines the ability of listeners to detect divergences from the phonetic norms of their native language. Native English-speaking listeners judged short English speech samples produced by native speakers of (American} English and native speakers of French. Computer editing techniques were used to isolate progressively shorter excerpts of speech. The listeners were able to identify the non-native speakers at above-chance levels no matter how short were the speech samples that were presented: phrases (e.g., “Two little dogs”), syllables (/tu/, /ti/), phonetic segments (/t/, /i/, /u/); and even the first 30 ms of the word “two.” Listeners identified the non-native (French) speakers equally well when presented with speech material edited from phrases read from a list and produced in a spontaneous narrative. Neither special phonetic training nor familiarity with French-accented English seemed to be necessary for listeners to detect accent. The results are interpreted as evidence that phonetic category prototypes play an important role in speech perception.
Discrimination of word-final voicing in German
Authors: O'Dell Michael , Port Robert
Published: October 2005

Traditionally, German is described as having complete neutralization of voiced versus voiceless consonants word finally. In this study native German speakers were recorded reading real words differing in the voicing of the final consonant. The recorded tokens were then randomized and played to native Germans who identified the word they heard. The listeners performed very poorly, but significantly better than chance. In addition, temporal acoustic measurements of the recorded tokens were made using duplex oscillogram and intensity curves on visicorder tracings. Statistical analysis of the acoustic measurements—nucleus duration, consonant duration, duration of voicing during closure, and final aspiration—showed significant, though small differences between intended voiced and voiceless pairs. Discriminant analysis applied to the four variables produced an acoustic criterion by which the intended voicing of tokens could be predicted with 63% accuracy, about the same as the best listener was able to do. In addition, data will be presented showing asymmetry between production and perception, in relative importance of acoustic cues and in individual subjects' discrimination performance. [Work supported by NIH.]
Process and outlook of the acoustic intensity technique
Authors: Tichy Jiri
Published: October 2005

The development of electronic instrumentation and microphone technology as well as statistical methods of signal processing allows us to measure the acoustic intensity vector with good precision in a broad freqeuncy range. The ability to measure acoustic intensity allows us to improve or simplify some basic measurements as, for instance, the sound power radiated by complex sources, absorption coefficient, transmission loss, etc. The determination of sound power flow makes it possible to improve the efficiency of noise control treatments. Another area of intensity measurement application is the exploration of basic properties of complex acoustic radiators and fields with complex boundary conditions. This paper presents a summary of achievements and projections in future applications.
Acoustic intensity measurement error for complex sources
Authors: Thompson James K.
Published: October 2005

There has been much discussion in recent literature of the accuracy of the two-microphone method of acoustic intensity measurement. The errors introduced by the finite difference formulation for intensity have been a frequent topic of investigation. However, these treatments have been limited to ideal plane wave and point sources. This paper describes a study of finite difference approximation errors for more realistic, finite sized sources. Error expressions are developed for a pulsating sphere, an oscillating sphere, and a piston in an infinite baffle. For the spherical sources, the error expressions derived are identical to those of their ideal equivalents, the point monopole and dipole. In the case of the piston source, large errors are predicted for particular conditions. For nearfield measurements along the piston axis, intensity level measurement errors can approach infinity.
A computer study of the intensity field on point-driven rectangular plates
Authors: Williams Earl G.
Published: October 2005

A computer model has been developed to help in understanding the intensity fields which exist on point-driven plates excited in air below their coincidence frequency. This study quantifies the relative importance of the edge and driver regions of the plate. Two types of boundary conditions are considered, clamped and free. The important effect of damping on the plate is born out in the results. For the clamped plate “corner” and “edge” modes (that is, corner and edge regions are dominant in intenstiy) are shown to exist in a limited frequency range below coincidence only when the damping in the plate is small. It is shown that for the plate with free edges (no moment or shear force) corner and edge modes do not occur at any frequency or damping. As the damping increases the driver begins to be locatable from the intensity patterns, an important effect in noise localization problems. It is shown how the intensity field changes on the surface of the plate as the driving frequency is raised from DC to the coincidence frequency. Both baffled and unbaffled panels are studied and the differences with respect to intensity are presented. Experimental results on unbaffled, point-driven, free panels are in excellent with the computer model.
Some comments on acoustic intensity measurement using the two-microphone method
Authors: Hickling Robert
Published: October 2005

Analyses are presented in three areas relating to the measurement of acoustic intensity using the two-microphone method. First, experimental evidence is presented to indicate the existence of a bias error of roughly 2 dB in the data obtained with the lead-wrapping method, which does not occur when the two-microphone method is used. Next an analysis is presented indicating the need to reduce the time of measurement of the two-microphone method and how this might be accomplished. The third analysis is on the effect of nearby boundaries on sound power measurement. Published information is reviewed and guidelines developed for determining the magnitude of this effect.
Determination of acoustic intensity magnitude and direction from cross-spectral information
Authors: Hurst Charles J. , Elliott Kenny B.
Published: October 2005

The measurement of acoustic intensity using the imaginary part of the cross-spectral information from two microphones has been widely discussed and used. In these studies directional information on the intensity has been obtained by turning the two-microphone probe and looking for a null condition or a change in sign of the intensity. However, the direction of the intensity vector can also be calculated from measurements if both real and imaginary parts of the cross spectrum are used. In this manner information on intensity fields can be gathered much more rapidly and with less intervention by the investigator. The equations for this procedure are given and some simple examples of measurements are shown.
Calibration of instrumentation for “acoustic intensity measurements.”
Authors: Rasmussen Gunnar
Published: October 2005

The increasing application of acoustic intensity measuring instrumentation has also increased the demand for practical calibration methods. The most general used intensity probe utilizes the two-microphone method. The accuracy probe utilizes the two-microphone method. The accuracy of the intensity measured in W/m2, and the capability to measure the intensity vector in a very reactive field depend on the equal performance of the two microphones, on the absolute pressure sensitivity and the relative phase between them. The calibration accuracy at low frequency depends mainly on the air equalization, and the high-frequency accuracy mainly on geometry. The absolute calibration of pressure sensitivity can be referred to a standardized reciprocity calibration. The long term stability is determined by rather few possible variables on the transducer side, and a test method is proposed for the electronic instrumentation. The capability to measure intensity within a reactive field of a certain strength is determined by the phase relationship between the two microphones, by their spacing Δr and by the frequency. The capability to calibrate and measure these parameters will discussed.
Coupling loss measurements using an intensity approach
Authors: Carroll G. P. , Clark J. A.
Published: October 2005

Cross-spectral methods for measuring structureborne noise intensity can also be employed to determine coupling-loss coefficients between elements of a complex structure such as a building or a ship. Experimental determinations of coupling-loss coefficients are needed in order to perform a statistical energy analysis of structural vibrations in cases where it cannot be assumed that strong coupling exists between all elements in the structure. In this talk the statistical energy analysis formulation of structural vibration problems will be reviewed. A method for determining the coupling-loss coefficient between two weakly coupled beam elements will be described. The method is based on a two-accelerometer, cross-spectral intensity measurement approach. In the case of weak coupling, high reverberation levels often exist (relative to the level of power flow between the structural elements). An experimental investigation of the errors introduced into structural intensity and coupling loss measurements will be reported. The relevance of this measurement concept to practical structural and acoustical noise localization problems will be discussed.
Control of noise by means of damping materials
Authors: Nashif Ahid D.
Published: October 2005

Although damping materials were initially investigated to increase the fatigue life of structures, their use as a means for controlling the noise level of structures has been increasing in recent years. This is partly due to the increasing availability of good damping materials along with well established design procedures for damping treatments. This coupled with the fact that whenever the damping approach is considered as an alternative one to those of enclosures or barriers, it is usually found to be a more cost effective one at a lower weight penalty. The various types of damping treatment, including constrained and unconstrained layered ones, will be described, along with their advantages and limitations. Overall design procedures for each type of damping treatment will also be given. The emphasis will be placed on knowing not only the properties of the damping material in terms of its environment but also on the dynamic properties of the structure to which the damping treatment is to be applied. From this information, the damping response of the structure can be predicted so that the expected vibration and/or noise reduction can then be established. Specific examples on the application of the damping technology in various industries, including aerospace, printing machines, machine tools, and engine components, will conclude the paper.
Acoustic resonance in heat exchanger tube bundles
Authors: Blevins R. D.
Published: October 2005

Many gas-cooled tube-and-shell heat exchangers emit an intense acoustic tone when shell side flow is brought to a certain level. The tone then persists as flow is varied. Sound levels as high as 165 dB have been measured inside heat exchangers ranging from small process units to nuclear reactors and utility power boilers. The sound is thought to be the result of periodic vortex shedding from the tubes at a frequency which coincides with the natural frequency of an acoustic mode within the heat exchanger shell. The sound within the heat exchanger shell is described by Lighthill's equation for aerodynamic sound. Sound propagation through a tube array is analogous to propagation through an array of small scatters. The speed of sound is slowed by the presence of the tubes, damping is increased, and the effective density is increased. The natural acoustic modes within the heat exchanger tube array are coupled with the modes of the entrance and exists, which are free of tubes. Thus, either numerical or matching solutions are required for the acoustic mode shapes. Tests on a variety of tube bundles in a rectangular shell are planned to measure the acoustic modes and the onset of resonance. A criterion will be established to differentiate between array geometry and damping that lead to resonance and those that are free of resonance. Models are being developed for the interaction between the coherent fluid dynamic structures and the acoustic field.
Cepstrum analysis of surface wave in acoustic signature inspection of railroad wheels
Authors: Fahmy M. N. , Finch R. D.
Published: October 2005

Surface waves are produced by hammer impact on the rim of a wheel. They travel around the wheel tread making one complete traverse of the circumference every millisecond. If a receiver is located close to the impact point, the signal shows a series of arrivals at millisecond intervals. If a crack is present in the surface, there will be an extra impulse received in less than a millisecond. Both contacting accelerometer and noncontacting microphones can be used to detect the signals. The signals were digitized and processed in time, frequency, and frequency domains and the presence of the crack can be seen most clearly by filtering the cepstrum to remove all but the initial reflection from the crack. [Work supported by ARE.]
Dependence of pressure transducer sensitivity on temperature and pressure
Authors: Kendig R. P.
Published: October 2005

The principle of reciprocity is used to provide a primary calibration of a pressure transducer. A chamber is constructed which can be pressurized and heated so that a simultaneous and accurate measurement of the secondary effects of temperature and pressure on the sensitivity of pressure transducers can be made. The conditions of elevated temperature and pressure simulates the environment of a power plant coolant loop. A calibration in this type of environment is needed for accurate qualification measurements of pressure pulsations generated by pumps operating in a closed loop. The reciprocity calibrator uses a stack of piezoceramic crystals (PZT-5) to produce a dynamic acoustic pressure variation inside the chamber. The chamber itself is filled with Dow-Corning® 710 fluid which is chemically, mechanically, and electrically stable at elevated temperatures and offers a good useful frequency range. Typical results indicate that the effect of a large static pressure change on a typical piezoelectric transducer sensitivity is less than 0.4 dB. On the other hand, the sensitivity varied inversely with temperature at a rate of 0.135%/°C (0.08%/°F). [Work supported by the Westinghouse Electro Mechanical Division, Cheswick, PA.]
Numerical solution of acoustic radiation and scattering problems using boundary elements
Authors: Seybert A. F. , Soenarko B.
Published: October 2005

This paper discusses the application of the boundary integral equation method for the numerical solution of radiation and scattering problems governed by Helmholtz's equation. Our approach differs from other surface integral methods in that we use a set of sophisticated higher-order elements developed by us for this class of problems. In particular we introduce an isoparametric element formulation in which both the surface geometry and the acoustic variables on the surface of the body are represented by quadratic shape functions within the local coordinate system. A general result for the surface velocity potential is derived. This result includes the case where the surface may have a nonunique normal (e.g., at the edge of a body). The boundary integration equation method is used to obtain numerical solutions to several radiation and scattering problems for which analytical solutions are well known.
Schlieren study of reflection of ultrasonic waves at liquid-solid interfaces
Authors: Breazeale M. A.
Published: October 2005

The study of bounded beams incident onto a liquid-solid interface has been enhanced by the development of an apodized tranducer whose output has a Gaussian distribution. With such transducers one can excite a single beam, without sidelobes, which can be studied by use of schlieren photography (or other techniques). With a schlieren system it is possible to produce colored photographs which can be used to enhance certain details. The lecture begins with a description of the schlieren system and the means by which spatial filtering produces colored images. Details of several reflection phenomena are examined by color schlieren photography, and a unified approach to an interpretation of the interactions produced by excitation of waves trapped at the interface is attempted. The lecture ends with a black and white movie showing the effect of changing the incident angle when an ultrasonic beam is incident onto a liquid-solid interface. Both forward displacement which results as one excites a Rayleigh surface wave at the interface, and the backward displacement which can result when a grating is superposed on the interface are shown. [Work supported by the Office of Naval Research.]
Nonspecular reflection and transmission effects: The general case of incident beams having an arbitrary profile
Authors: Ngoc Tran D. K.
Published: October 2005

The spectral representation approach to investigation of bounded ultrasonic beams nonspecularly reflected from or transmitted through a layered medium has been extensively developed and the key characteristics of these effects have been well understood [e.g., H. L. Bertoni and T. Tamir, Appl. Phys. 2, 157 (1973); T. D. K. Ngoc and W. G. Mayer, IEEE Trans. Sonics Ultrason. SU-27, 229 (1980)]. However, these past studies were still limited to incident beams that had to be modeled by such analytical forms as Gaussian or polynomial functions. This paper is intended to apply the spectral representation approach to the most general case where incident beams having an arbitrary profile can be investigated. The presentation will review the principal results obtained in the past and conclude with new results calculated for the general case. [This work was supported by ONR.]
Finite beam reflection from periodic surfaces
Authors: Roberts Ron , Achenbach Jan , Adler Laszlo , Jungman Alain
Published: October 2005

Analytical expressions are obtained for the reflection coefficient of a bonded ultrasonic beam from a periodic stress-free solid surface. The frequency dependence of the reflection coefficient shows a sharp minimum at a frequency which corresponds to an apparent “displaced” beam coupled along the interface and “leaks” back to the solid. These leaky waves are produced by the periodically rough surface at the solid-air boundary. These leaky waves are observed by an experimental setup using broadband ultrasonic pulses. The effects of finite beam on the reflected amplitude in the time and frequency domain will be discussed. Experimental results are in good agreement with theoretical prediction. [This work is supported by the National Science Foundation.]
Linearized travel time, intensity, and waveform inversions—A comparison
Authors: Brown Michael G.
Published: October 2005

Linearized inversion schemes involving waveform (total record), intensity (dephased total record), and travel times (intensity peaks) are used on synthetically generated arrival patterns to solve for the sound-speed structure in the upper km of a range-independent ocean model. In all three cases inversions are carried out for a variety of source center frequencies and bandwidths. The results are compared; conditions under which each inversion method performs poorly and well are outlined. The nature of the linearization approximation is discussed for each of the three types of inversion scheme as well as the methods used to solve the general linearized system. [Work supported by ONR.]
Velocity inversion for the ocean bottom
Authors: Hagin Frank G.
Published: October 2005

Since the work of Bleistein and Cohen in the late 1970s, considerable interest has been demonstrated in the problem of reconstructing velocity profiles using reflection data observed at some “surface.” The original work in this areas was a “perturbation” theory in the sense that a constant reference propagation speed was assumed and one typically solved for the relatively small change from the reference speed. Like all perturbation schemes, this approach suffers when the velocity varies substantially over the domain of interest. More recently efforts have been made to correct for the above deficiency. In particular, some progress has been made that may prove fruitful in the study of the ocean bottom. Rather dramatic refinements to the above mentioned perturbation algorithm are available when the geometry of the medium of interest is relatively simple. These approaches also hold promise of being generalizable to more complex structures. [Work supported by ONR.]
Sound-speed profile inversion using modes
Authors: DeSanto John A.
Published: October 2005

We describe a modal method to find the intervening sound-speed profile from propagated acoustic field data. The method uses the Fourier-Bessel representation for the propagated acoustic field. For a purely depth-dependent profile, the depth solution can be represented exactly as the solution of an integral equation whose kernel contains the correction to an assumed initial guess of the profile. This solution is treated in Born approximation and written using a travel length coordinate. The result expresses the data as a linear transform over the profile correction. Using asymptotics, the transform kernel can be evaluated and, for some simple cases, the transform can be inverted. An example is presented with a bilinear profile as the first guess with accompanying inversion in either frequency or depth. The former corresponds to fixed source, fixed receiver broadband experimental situations and the latter to single frequency multireceiver experiments. We also include some remarks on range-dependent profiles. [Work supported by ONR.]
An acoustic perceptual study of vocal fry, using synthetic stimuli
Authors: Keidar Anat
Published: October 2005

This study addressed the issue of whether the perception of vocal fry depends on waveform shape, or whether fry is perceived categorically only as a function of frequency. Voicelike stimuli were generated with a transmission-line synthesis program [Titze, Transcripts Care Prof. Voice (1983)] that can vary fundamental frequency (F0), open quotient (γ), and speed quotient (δ), while maintaining a realistic glottal shape. In Exp. I, all combinations of F0 (40, 60, 80, and 100 Hz), γ (0.1, 0.35, and 0.6), and δ (1.0, 2.5, 5.0, and 8.0) were judged by ten trained listeners, using a binary fry-no fry forced response method. The results reinforced previous conclusions that F0 is the primary determinant in the perception of vocal fry [H. Hollien, J. Phonet. 2, 125–143 (1974)] regardless of waveshape. Mean % judged as fry was 99.4%, 75.6%, 21.1%, and 2.77% at 40, 60, 80, and 100 Hz, respectively, with chance level performance (50%) predicted at about 70 Hz. Differences among γ and δ values were statistically nonsignificant. Experiment II included only stimuli of 40 and 60 Hz, each F0 containing all combinations of γ and δ values. A round-robin tournament was utilized, whereby each stimulus competed against every other stimulus for a total of 12(N2 − N) A − B comparisons. Although intrajudge reliability was high (r≈0.8), interjudge agreement was not consistently as high, yielding nonsignificant differences among γ and δ means, and suggesting that several waveshapes are perceptually plausible within acceptable F0's.