bluuebunny/crossref_metadata_2025 huggingface dataset:
Uses and abuses of the critical distance concept
Authors: Davis Don
Published: October 2005

The concept of critical distance Dc was derived from the European concept of critical radius. The introduction of the directivity factor Q, the effect of multiple sources on the reverberant field, and the identification of the architectural and electroacoustic Dc modifiers, has led to widespread use of the concept in the interface of electroacoustic systems in the acoustic environment. Misuse has frequently stemmed from a misunderstanding of when a reverberant sound field is developed, as defined by Hopkins-Stryker equations, and application to cases where no Dc is developed. Derivation of the Dc equations from the Hopkins-Stryker equation as well as from the classic Sabine equation is provided. Also discussed will be the Peutz equations which are used to determine if the sound field is sufficiently reverberant to allow the measurement of critical distance.
Acoustics is physics: Its part in over a half-century of teaching physics
Authors: Weber Louis R.
Published: October 2005

In 1926, President Mendenhall of Friends University asked me if a public address system were necessary in Alumni auditorium. As an experiment in General Physics, the reverberation period was found to be seven seconds. How Knudsen's book and rainstorm solved the problem will be described. A CSU professor, seeing students measuring auditoria asks us to sound condition his lecture hall; students hear his lecture twice! He wishes secrecy; similar requests would deplete the budget. Articulation tests, using vowel and consonant lists and db concepts are part of lecture with 310 students. An amphitheater's novel construction in Colombia with no acoustical material has excellent acoustics; I break a leg due to poor light. Measuring noise levels without a sound meter (Fletcher's Speech and Hearing); how sound velocity measurements improved piezoelectric crystal research. Professor Jones of Smith sees my experiment at 1939 New York meeting; he invites me to membership in ASA; I accept. As associated editor of Taylor manual the dearth of significant acoustic experiments submitted; how the busiest men in this field, Knudsen, Stewart, Olson contributed.
Scattering of sound by sound in the presence of turbulence
Authors: Korman M. S. , Beyer R. T.
Published: October 2005

The mutual scattering of two continuous ultrasonic beams directed at right angles to each other in the presence of turbulence in water has been investigated. The beams were each of pressure amplitude of 2.7 tm and had frequencies of 0.9 and 1.1 MHz, respectively. These ultrasonic sources (PZT-4 units of effective diameter 34 in.) were located 2.0 and 1.5 m, respectively, from their interaction region. A 1-in.-diameter water jet was located with nozzle 65 cm from the interaction region, with its direction bisecting the angle made between the two ultrasonic beams. The characteristics of the jet were determined by hot-film aneomoetry. The velocity spectrum of the turbulence was in the range 0.1–1.0 kHz. A 2-MHz transducer was used outside the interaction region, and the received signals were examined with and without turbulence. In the presence of turbulence, a sum-frequency component was detected in the received spectrum, broadened by sidebands up to ±2.5 kHz from the center frequency. The received spectrum was asymmetric relative to the 2.0-MHz component. Theoretical models of this interaction are discussed. [Work supported in part by the Office of Naval Research.]
The tuning of a Sundanese (West-Javanese) gamelan: 1893 and 1977
Authors: De Vale S. C.
Published: October 2005

Field Museum's gamelan pelog (7-tone scale), a 24-piece orchestral ensemble with 109 bronze and 18 wood sounding parts covering a 6-octave range, was brought to Chicago for the World's Columbian Exposition of 1893. Recently discovered were 33 wax cylinder recordings of the 1893 performances. Six of these cylinders recorded the tuning of individual instruments representing nearly the total range of the gamelan, including 91 of the bronze and all 18 wood sounding parts. In early 1977, the tones were again recorded along with repeated soundings of a 440-Hz tuning fork as a control. The 1893 and 1977 tunings were analyzed; frequencies and intervals compared. The results provided new insights into the stability of bronze and wood musical instruments as well as significant evidence of the gamelan's age when it arrived in Chicago in 1893. In late 1977, the tunings of some sounding parts were adjusted, and the gamelan has since been used for the teaching and performance of Javanese gamelan music. [Work supported by NEA and the Walter E. Heller Foundation.]
Physical properties of treble recorder tones suitable for baroque music
Authors: Ando Yoshinori , Shima Tatsuro
Published: October 2005

Using real and synthesized tones, we have investigated how the quality of treble recorder tones depends on their physical properties, such as harmonic structure, nonperiodic amplitude and frequency fluctuations of overtones, and noise content. By the use of a paired comparison method, the quality of the tones was judged by professional recorder players and by amateurs with some musical training. As the result, psychological interval scales of quality were constructed against (1) two parameters of harmonic structure, (2) magnitude and frequency structure of harmonic's amplitude fluctuation and (3) those of harmonic's frequency fluctuations. The best quantities are as follows: (1) Decay rate of harmonic amplitude is 4 dB/harmonic. (2) The second, fourth and sixth harmonics are some 10 dB weaker than the values calculated from this decay rate. (3) Frequency fluctuation magnitude of the second and third harmonics is about 1.7% expressed in effective value. Frequency fluctuation of the higher harmonics is rather harmful for quality.
Analysis and estimation of the high-speed railway (Shinkansen) noise and its control by barrier
Authors: Nimura T. , Ebata M.
Published: October 2005

Environmental quality standards for the Shinkansen railway in Japan have been set up to be 70 dBA in residential areas and 75 dBA in commercial and industrial areas for three years. But the counter-measure is still insufficient and there are many difficult problems to be solved to satisfy these figures. This paper estimates the noise power radiated from each part of the railway system; the lower part of the car body, current collecting system, car body, viaduct and barrier. It also investigates noise reduction by barrier. The simplest means to reduce the noise by barrier is to heighten the insulation wall. In this paper the effect of raising the wall height by 1 m over the existing one is discussed. Constructing an inverse-L-type insulation wall instead of a common type barrier, is another way to increase the noise reduction. To make it more effective, sound absorbing plates are attached to the opening of this type of insulation wall as a trial, and it is shown that the increase in noise reduction reached several dB above 500 Hz.
Characterization of acoustic emission sources, sensors, and propagation structures
Authors: Hsu N. N. , Sachse W. H.
Published: October 2005

Acoustic emission signals carry potentially useful information about the criticality of deformation source mechanisms in materials, but signal processing techniques such as threshold counting, RMS voltage recording, peak detection, and spectral analysis often failed to extract such information unambiguously. The difficulty lies in the determination of the transfer characteristics of the structure and the sensor. We report experimental results of a computer-based test system consisting of a large plate and a capacitive transducer [N. N. Hsu, J. A. Simmons, and S. C. Hardy, Materials Evaluations 35(10), 100–106 (1977)]. The transient wave propagation behavior of the plate and the transfer function of the capacitive transducer are known. Consequently, unknown sources can be characterized by solving the Töplitz matrix directly. Explicit force-time functions of simulated signals such as breaking glass capillaries, breaking pencil leads, dropping steel balls, electrical arcs, and pulsed piezoelectric transducers have been determined. These force-time functions are then used to determine experimentally the transfer characteristics (impulse-response) of various propagation structures and various ultrasonic transducers.
Studies in the digital analysis of acoustic emission signals
Authors: Beattie A. G.
Published: October 2005

The complexity of the waveforms of acoustic emission signals is strong evidence that much information is contained in these signals. The problems are, however, first, can this information be retrieved in a useable form and, second, does the information relate to the source of the emission or only to the structure in which it is generated. This paper reports the results of an investigation into methods of retrieving this information by means of signal digitization and subsequent computer analyses. Topics covered are signal digitization, spectral computations with a Fast Fourier transform (FFT), the effect of windowing on the calculations, spectral averaging, energy calculations, and attempts to calculate and use transducer transfer functions. The emphasis throughout is on methods and results and not on mathematical rigor. The paper closes with some examples of analysis of experimental data and some speculations on where digital analysis can be useful in acoustic emission tests and experiments.
Acoustic emission and inhomogeneous deformation in plastic deformation
Authors: Kishi T.
Published: October 2005

Amplitude and frequency characteristics of acoustic emission signals are estimated by the initial and boundary conditions of the dynamic equilibrium equation for a linear elastic medium. Except in some special cases, frequency responses of signals is controlled only by the frequency response function of specimens, in addition to the characteristic of the transducer. In these cases, the source mechanism of acoustic emission can be attributed to the above initial condition. This initial condition is decided by inhomogeneous deformation with respect to time and space, which gives a local inelastic strain Δε during the time interval ΔT (relaxation time) in the material. From a metallurgical viewpoint, it can be recognized that this local inelastic strain is introduced by stress concentration τb around various inhomogeneities, such as grain boundary, cell boundary, inclusion, and precipitate, and relaxation time ΔT is controlled by frictional stress τf in the matrix. According to this model, acoustic emission signals can be well understood from a viewpoint of inhomogeneous deformation, which is described by stress terms τb and τf. In addition to a historical survey of source mechanisms of acoustic emission, in this report emission signals during various type of yielding are analyzed and discussed from a viewpoint of inhomogeneous deformation.
Assessment of acoustical technology for minimizing seismic damage to urban utility system network
Authors: Jhaveri Arun G.
Published: October 2005

The Puget Sound region of Washington State is one of the most seismically active areas in the country, as demonstrated by two major earthquakes, one in 1949 and the other in 1965. The United States Geological Survey (USGS) report, A Study of Earthquake Losses In the Puget Sound, Washington Area (Open File Report 75-375), concludes that the maximum credible earthquake that can be expected in the Puget Sound area is 7.5 on the Richter Scale of magnitude, and that extensive damage would result, including the deaths of some 2000 people. Earthquakes are a potential threat to the continuous functioning of a city's lifelines (e.g. water and power utilities, communication and transportation networks); however, until recently seismic considerations have not been an integral part of the planning, design, construction, and operational phases of urban lifeline systems. Acoustical technology can play an important role in both the new and retrofitting system design as well as construction of structures, equipment, and facilities associated with such utility components as metropolitan water supply and distribution network. Vibration dampening, shock absorption/isolation techniques, and acoustical instruments for preventive maintainence and potential damage/risk analyses are specific areas of investigation discussed in this paper.
Analytical solutions for open nonshallow spherical shell vibrations
Authors: Lin G. F.
Published: October 2005

This paper is concerned with axisymmetric as well as nonsymmetric vibrations of open nonshallow thin elastic spherical shells. Without employing the usual auxiliary variables for reduction of shell motion equations introduced by Van der Neut and Berry, independent analytical solutions for middle-surface displacements are obtained and explicitly expressed in terms of associated Legendre functions. In order to gain physical insights into the free-vibration characteristics of an open nonshallow shell, theoretical calculations together with asymptotic descriptions are made of natural frequencies and mode shapes of a hemispherical shell with a free edge. The numerical predictions obtained herein compare excellently against the experimental results obtained previously by Hwang and recently in the David W. Taylor Naval Ship R & D Center, Bethesda, Maryland. Essential features of shell dynamics are ultimately displayed by normalized frequency (Ω) and nondimensional shell thickness parameter (β). Five families of natural frequencies, i.e., low Rayleigh bending, mixed bending-membrane, torsional, bending, and membrane frequencies, are found. The corresponding mode shapes exhibit distinctive displacement patterns. [Work supported by Naval Sea Systems Command.]
Nonlinear random vibration of a beam impacting stops
Authors: Davies Huw G.
Published: October 2005

The random vibration of a beam whose motion is constrained at one point by nonlinear springlike stops separated by a gap is considered. The beam is driven by white noise excitation. The beam's motion is described in terms of the unconstrained vibration modes. An equivalent linearisation method is used to obtain from the Fokker-Planck equation an approximate expression for the joint probability density function of the modal amplitudes. The equivalent linearisation includes the interactions between the unconstrained modes that are caused by the stops. An approximate expression is obtained for the mean square response of the beam to band limited white noise. An estimate based on the equivalent linear, resonant modes is obtained also for the number of impacts.
Digital simulation of impacting vibration of a cantilever
Authors: Kishi K.
Published: October 2005

The digital computer simulation method is described for analyzing the vibration of a cantilever impacting against a fixed wall. In this study, the local deformation of the impact parts are taken into account. The mechanical vibration system with which a cantilever is subjected to external forces on its arbitrary points and impacts against a fixed wall at one of these points is represented by an equivalent electrical circuit. The equations of motion of this system can be derived from the equivalent circuit. These equations are simultaneous nonlinear differential equations and can be integrated by Runge-Kutta-Gill method. In this numerical integration, the time step is chosen to 100 times the period of the highest mode of the cantilever so as to make the accumulated error minimum. Applying this method to several cases, it was found that there are evident differences between the solutions, taking into account the local deformation and those neglected. This method can easily be extended to the more general problem of impacting vibrations and is useful for the study of chattering phenomenon in a relay apparatus.
Effect of stiffener resonances on the vibration response and sound transmission loss of periodically stiffened structures
Authors: SenGupta G.
Published: October 2005

In analyzing the problem of vibration response and sound transmission through periodically stiffened plates and cylinders, the stiffeners are very often represented by line supports or by springs with equivalent translational and torsional stiffnesses. Sometimes, the effects of the stiffeners are also smeared out. As a result, the vibrational response and the transmission loss at low frequencies are often predicted to be stiffness controlled. Recent studies at Boeing has shown that in the “stiffness controlled” region, the structural response and noise transmission may be governed by the resonances of the stiffeners, depending upon the relationship between the natural frequency of the plate between the stiffeners and that of the stiffener. Therefore, noise transmission in the “stiffness controlled” region may be effectively controlled by applying damping treatment on the stiffeners. This recent understanding has grown out of the “intrinsic structural tuning” concept presented earlier (G. SenGupta and E. F. Small, J. Acoust. Soc. Am. 58, S (A)(1975). The problems under consideration are discussed in terms of (1) stringer-stiffened plates and (2) frame-stiffened cylinders. Analytical as well as experimental results are presented. [Work supported by NASA-Langley Research Center.]
Mechanical impedances of clamped rectangular plates without and with a rib
Authors: Fujiwara K.
Published: October 2005

Mechanical impedances of clamped rectangular plates without and with a rib were investigated. First, the mechanical impedances of a clamped plate without a rib were treated. The driving conditions were the one-point drive and the four-point drive with the same amplitudes and phases and the uniformly distributed force over the rectangular area. The analysis was carried out by the method to solve the simultaneous linear equations obtained by applying the series of normalized orthogonal functions to the differential equation governing the bending vibration of a plate. The results were presented by the normalized mechanical impedance as a function of the interval of the driving points. Secondarily, the mechanical impedances of a clamped plate stiffened by a rib with rectangular cross-section were treated. The driving conditions were the one point drive and the four points drive with the same amplitudes and phases. The analysis was carried out by FEM. The results were also presented by the normalized mechanical impedance and compared with that of a plate without a rib for the one-point drive and the four-point drive, and then the effect of the rib on the vibration of a rectangular plate with clamped boundaries was discussed.
Effects of fluid loading on the transmission of free waves across two ribs
Authors: Eisler T. , Crighton D. G. , Maidanik G.
Published: October 2005

The effects of fluid loading on the transmission of free waves across a single rib has been considered in the preceding paper. In this paper the transmission of free waves across two parallel ribs is considered. If the interaction between the two ribs is or can be ignored, the evaluation of the transmission can be readily deduced from that of the single rib. Of particular interest in the paper are, however, the conditions on the characteristics of the ribs, the panel, and the fluid loading under which the interaction between the ribs is significant. A number of computations illustrating this significance are presented.
Structure/air noise power ratio spectra of machine casings
Authors: Thorpe Howard A.
Published: October 2005

A formula for approximating these ratio spectra has been developed as part of Rohr's surface effects ship noise prediction methodology. These spectra are used as multipliers of measured or predicted aerenoise power spectra (Watts) of bare machine casings to predict the corresponding available machine structure-noise true power spectrum. The latter rarely is available. The formula developed for this ratio, R, is R = (1.5/c) (ρs/ρ)t(v + 300) where c and ρ are, respectively, speed of sound in and density of the fluid medium surrounding the casing, ρs is casing material density, t is casing thickness, and v is frequency in hertz. Units consistent with the dimensionless nature of R must be used. Underlying idealized theory and results will be sketched. Also, rationale for moderately adjusting constants of theoretical results on empirical grounds will be sketched. Adjustment of the initial constant is based on results of a relevant Rohr test/analysis program. The second constant is based on a Rohr study of compartment noise prediction validity involving a tested ship. [Work supported by U.S. Navy, NAVSEA, PMS304.]
Linear predictive coding and the Burg algorithm for speech analysis and synthesis
Authors: Gray A. H. , Markel J. D.
Published: October 2005

The Burg algorithm for computing reflection coefficients of speech (sometimes called the covariance lattice) is compared with the autocorrelation method of linear prediction. Certain problems for small window sizes for both methods are discussed. Three dimensional displays of spectral representations and audio tapes of synthesis are used to illustrate the practical result that there appears to be no advantage to either approach for speech processing, other than the computational efficiency of the autocorrelation method. [Work supported by the Department of Defense.]
LPC speech at 1200 bits per second using optimized frame repeat
Authors: Helms Gene
Published: October 2005

Low-cost speech synthesis is here and along with it the need for high compression of stored speech. A method for achieving speech compression to 1200 bits per second based on LPC parameters is presented. The low data requirement results from an efficient data coding procedure which incorporates a variable frame rate scheme. Which reflection coefficients are to be used and the parameter update intervals are determined using a dynamic programming procedure which maximizes frame length while minimizing a prediction residual energy ratio measure. Good quality speech can be obtained from this analysis procedure using the TMC0280 speech synthesizer. A demonstration of the speech quality will be presented.
Comparative cochlear anatomy and biophysics
Authors: Khanna S. M. , Tonndorf J.
Published: October 2005

This paper will discuss performance data of various mammalian ears, i.e., their overall sensitivities, frequency ranges, points of maximal sensitivity, directional patterns, localization by the binaural system, etc., in the light of a number of physical factors, such as head size, length of the ear canal, area of the tympanic membrane, and others. In general, these physical factors were found to be quite critical in determining the performance of the ear. Some must clearly be the result of a compromise between conflicting requirements: (a) to collect an optimal amount of acoustic energy over a wide frequency range, (b) to bring sensitivity close to its optimal value, (c) to avoid creation of dead zones in the directional pattern of hearing, and (d) to facilitate auditory localization both in the horizontal planes and in the vertical one. Its performance makes the ear an excellent early warning device, superior in this respect to all other sense organs. [Supported by NIH grants.]
Comparative biology of hearing in the mammals
Authors: Stebbins William C.
Published: October 2005

The sense of hearing has become highly developed and specialized in the mammals relative to the other tetrapods. Increases in absolute sensitivity to acoustic stimuli and in the audible frequency range, and enhanced differential acuity to the different dimensions of auditory stimuli such as frequency and intensity have contributed to the success of the mammals as a group. Evolutionary changes in the structure of the middle ear conducting system, in the cochlea, and, to a lesser extent, in the central nervous system are presumed responsible. The considerable variation in auditory capabilities in the various orders and families reflects the different selective pressures which have played a major role. In some mammals, orientation and navigation have emphasized extended high-frequency sensitivity, while in others the obvious adaptive value of a tightly knit social organization has placed a premium on the fine discrimination of the small but significant changes in the acoustic patterning of intraspecific communication sounds. Some of the factors thought to be responsible for the evolution of hearing in the early mammals will be discussed, and a comparative analysis of mammalian hearing in living species will be presented. [Research supported by NSF.]
Conversion of the vocal tract shape for spectral warping by a PARCOR analysis—synthesis system
Authors: Suzuki Hisayoshi , Ooyama Gen , Wakayama Satoshi
Published: October 2005

This paper presents a method of spectral warping for helium speech unscrambling by means of converting the vocal tract shape estimated from the PARCOR analysis. Speech produced in a high-pressure, helium-oxygen atmosphere has particular distortions. One peculiarity is a disparity in the rates of formant frequency shift and fundamental frequency shift. The formant frequency shift consists of two factors. One is due to the sound velocity change, rendering a linear shift, and the other is due to the high pressure, rendering a nonlinear shift. In order to convert the helium speech to normal speech, therefore, the authors have developed an analysis—synthesis system involving various types of conversion processes for spectral warping. The conversion process presented in this paper includes two operations. The first is to increase the number of sections in an acoustic tube model of the vocal tract for the linear shift, and the second is to modify the vocal tract area function for the nonlinear shift. Experimental examinations to determine the feasibility of this approach, and to compare it with other approaches, such as impulse response stretching and power spectrum conversion, are discussed. [Work supported by Grant-in-Aid for Sci. Res. 146089.]
Measuring the effects of echoes on speech intelligibility
Authors: Lacroix Paul G. , Atkinson James E.
Published: October 2005

Speech intelligibility was measured as a function of the time interval between the onset of an original signal and the onset of its equal amplitude echo. Scores were obtained on three different speech tests for delay intervals ranging from 50 to 700 ms. Tests included the monosyllabic Modified Rhyme Test (MRT), the multi-word CID sentences and the NSMRL Tri-word Test of Intelligibility (TTI). Delay conditions were produced by a specially constructed digital delay line. Intelligibility was most degraded when echoes occurred 200 to 250 msec after the onset of the original signal. The multi-word tests (CID and TTI) proved more sensitive than the single-word (MRT) test under all conditions. TTI test words were analyzed according to their position within an utterance. Results suggest that the TTI provides information about echo delay conditions as they affect both single and multiple-word tests. The correlation between the means for final word TTI items and the means obtained for the MRT across delay conditions was r = 0.80, while the correlation between means for middle word TTI items and the means obtained for the CID sentences was r = 0.95. These results are discussed in terms of temporal masking effects.
Two methods for synthesizing speech from sound elements in the time and frequency domains
Authors: Endres W. K.
Published: October 2005

Synthetic speech can be generated by combining individual sound elements which are either stored as time functions or represented by their spectral parameters. Accordingly, two procedures have been developed which are based on different principles and yield different speech qualities. By manipulating the time functions of vowels and consonants and reversing certain sound sequences, 200 elements are sufficient in the first procedure to obtain monotonous speech and 300, if simple prosodic effects are taken into account. Tape recordings demonstrate the results of computer simulations carried out by E. Groβmann (Berlin) in which the texts were read in in orthographic writing. The second procedure makes use of about 1200 German diphones represented by their formant data. In the synthesis, these parameters are concatenated by means of linear interpolation procedures and used to control a filter system consisting of seven digital filters (H. E. Wolf, Darmstadt). Prosodics can be added by appropriately controlling both the excitation and the time structuring of the sound sequence. For this procedure, simple rules have been developed and a hardware model has been designed for 32 audio-response channels operating in time multiplex. The speech quality achieved is demonstrated by tape recordings. Intelligibility rates are given in H. J. Braun's paper.
Ambient noise measurements in Dabob Bay and the open ocean
Authors: McConnell S. O. , Lilly J. G.
Published: October 2005

Ambient noise measurements have been made at high frequencies (7–40 kHz) to determine the vertical surface radiation pattern and spectral level as a function of environmental conditions. A multibeam acoustic lens mounted on a stable platform was used to perform the measurements. The data exhibited significant differences between the open ocean and Dabob Bay. The surface radiation pattern could be described by sin2θ (θ = grazing angle) dependence in Dabob Bay as compared to a sin θ behavior in the open ocean. The spectral slopes were found to be significantly larger in Dabob Bay as compared to the open ocean results and the Knudsen curves. The spectral level, however, was in general agreement between the two locations. The spectral level was also in agreement between the sults of other investigators, particularly the dependence on wind speed and rain rate. [Work supported by the Naval Sea Systems Command under contract N00024-78-C-6018.]
Scale model results for acoustic radiation and hull vibration characteristics of merchant ships due to point force excitation
Authors: Heine J. C.
Published: October 2005

Radiation from merchant shipping is the most important cause of low-frequency underwater ambient noise. Predictions of noise properties thus requires an understanding of the radiation characteristics—source level and directionality—of merchant ships. Since the adequate measurement and diagnosis of such properties of a full scale ship is very expensive, a 1:100 scale model of a typical 600 ft tanker was fabricated. The level of structural detail retained in the model was consistant with the frequency regime of interest, 5–50 Hz. In this paper, we describe the model and a series of measurements of the total radiated power and the structural response due to a point force applied at the location of the ship's main propulsion engine. We show that to first order the radiation from a point force is due to engine room hull vibration only, and that the total radiation impedance is relatively independent of frequency.
Ambient noise system (ANS)
Authors: Rottler D. A.
Published: October 2005

ANS has been designed and developed by NUWES as a permanently installed system for the collection, recording, and processing of underwater ambient noise data for support of underwater weapon proofing operations. This system, now operational, is located at the three dimensional (3-D) tracking range located at Nanoose, British Columbia, Canada. ANS is comprised of underwater acoustic noise sensors and a shore-based console used for signal conditioning, recording, and previewing of the data. Two strategically located acoustic sensors measure underwater ambient noise at fixed locations within the 3-D range and transmit this data back to the shore-based console via underwater coaxial cables. Electronics contained within the hydrophone and junction-box assemblies provide sequencing of operational modes, electrical calibration, signal preconditioning, and line-driver functions. Data are analyzed both on-line and by a computer controlled spectrum analyzer and may be presented as time averages of level-versus-time plots. ANS results may be corrected for range to provide source level information if a tracked vehicle is measured, and then referenced to range coordinates other than the ANS location.
Acoustic field radiated by an impulsively excited line source of finite length
Authors: Rudgers Anthony J. , Spooner Ronald L.
Published: October 2005

A new closed-form theoretical expression is derived that describes the transient acoustic pressure field that is radiated when a line source of finite length impulsively excites the fluid surrounding it. The new expression, which is obtained by solving the two-dimensional scalar wave equation by integral-transform techniques,describes the acoustic field of the finite line, in the time-domain, in terms of generalized functions. The results obtained, which support the ideas advanced in the Rubinowicz-Maggi diffraction theory, show that the field of a line source is comprised of three distinct components: a spatially discontinuous cylindrical wave (“geometrical wave”) and two directional boundary-diffraction waves radiated by the ends of the line. There is a direct analogy between the results reported in this paper and those given by Schoch in his classic paper on the radiated acoustic fields of planar sources.
Some interesting features of spherical cap transducers
Authors: Monteith Dwight , Moore Virgil , Northrup Branch , English Earle
Published: October 2005

Interesting features of spherical caps have been identified and investigated as a result of the availability of large computers which has overcome the problem of poor convergence of the wave-harmonic series for spherical cap directivity at large ka. Caps which have radial velocity excitation exhibit Fresnel diffraction effects for ka ⩾ 2π. The presence of these effects has been verified experimentally with a spherical transducer which shows an axial loss of sensitivity for conditions corresponding to the 2nd Fresnel half-period zone. Fresnel theory predicts the occurrence of directivity extrema for caps which are hemispherical or smaller. Data for prediction of diffraction effects for larger caps is presented for 2π ⩽ ka ⩽ 20π. Axially excited caps do not exhibit diffraction effects. The velocity coefficients for the wave-harmonic series for axial velocity excitation are developed. Axially excited hemispherical caps were observed to exhibit constant directivity index for ka ⩾ 0.8π. [Work partially supported by NAVSEA and NCSC.]
Diffraction effects of baffles on acoustic directivity patterns
Authors: Hughes W. Jack
Published: October 2005

The acoustic diffraction phenomena which occur at the edges of a baffle are investigated both experimentally and theoretically. Data were obtained for a sharp-edged and cylindrical-edged baffle as a function of incident pressure, angle of incidence, and frequency. Two transducers were used, one in the farfield and one on the baffle surface. Also investigated is the effect of placing small scattering barriers at the edge of the baffle surfaces. The Geometrical Theory of Diffraction is used to develop a theoretical model for the calculation of patterns. Both Sommerfeld and Malyuzhinets diffraction coefficients are discussed along with the utilization of a transition region function to remove singularities. Directivity patterns with a rigid surface exhibited ripples in the insonified region while a soft surface gave rise to a smooth directivity pattern with highly attenuated diffraction fields. Higher shadow zone levels resulted when a transducer was positioned closer to the edge of the baffle. The good agreement obtained between theory and experiment confirms the validity of the Geometrical Theory of Diffraction. [This work was supported by the Naval Sea Systems Command.]
T network models of underwater acoustic baffles
Authors: Brigham G. A. , Libuha J. J.
Published: October 2005

The two basic acoustic baffles available for use to relatively large depths (i.e., nominally about 2500 feet) in the ocean without pressure compensation are the compliant tube and spring plate types. Both have unique acoustic and stress/failure characteristics with some expected similarities. Within the frequency range in which these baffles are generally used the acoustic transmission is largest when the incident radiation is normal to the baffle plane. For this case we can easily generate a T network circuit model for each type of baffle. Different layers that have periodically related spatial construction to one another can be interfaced by joining appropriate terminals to accommodate a circuit format for the composite multilayered baffle. This paper is a brief on the background physics and analysis of the two baffles, their circuits, and a comparison of their various physical/spectral features.
Comparative organization of mammalian auditory cortex
Authors: Goldstein Moise H. , Knight Paul L.
Published: October 2005

The organization of mammalian auditory cortex shows species-specific specializations as well as organizational rules common to all studied mammals. Electrophysiological mapping of the tonotopic representation in several species indicates that features common to AI include (1) orderly representation of the entire cochlea within AI, (2) representation of a one-dimensional cochlear segment by a two-dimensional cortical belt crossing AI, and (3) radial organization of sharply tuned neurons of similar best frequency through the depth of the middle cortical layers. For some species, the AI representations resemble scaled models of one another. In most species, there are one or more orderly cochlear representations adjacent to AI. Surrounding these highly ordered fields are other fields (the “belt region”) in which neurons may not be as sharply tuned for frequency, or in which the cochlear representation may not be as orderly. “Association” fields may represent further abstractions of acoustic information, and sometimes may integrate polysensory information. Comparisons of the cortical cytoarchitecture of many species suggest expansion of “association” cortex through mammalian evolution. A most interesting species-specific specialization is human speech and its associated hemispheric lateralization.
Man as a mammal: Psychoacoustics
Authors: Yost William A.
Published: October 2005

In trying to describe the auditory capabilities of vertebrates, investigators often use measures of critical bands, temporal integration or localization. The results obtained from nonhuman animals are quite often compared to classical data obtained from man. In recent years both psychoacousticians and auditory physiologists have begun to modify the classical theories of frequency selectivity, temporal acuity, and localization. The concept of an internal filter to describe frequency selectivity has given way to more complex functions that indicate frequency regions of excitation and inhibition. Measures of the time constant of temporal integration have varied from a few to hundreds of milliseconds indicating complex temporal processing. The ability of man to accurately lateralize high-frequency sounds that contain low repetition frequencies has challenged the original duplex theory of localization. The research in these three areas will be reviewed in the context of comparative animal psychophysics.
Psychoacoustic experimentation as a prelude to musical composition
Authors: Wessel David L. , Smith Bennett , Ehresman David
Published: October 2005

Our aim is to provide musicians with a facility that aids in the characterization of the perceptual behavior of sonic material selected for potential compositional use. An interactive computer system has been developed to assist in the following precompositional activities. (1) Initial selection and classification of material: Here the musician has rapid auditory access to a large collection of sounds. A graphics based sorting and playback system is used for initial classification and organisation of events and patterns. (2) Systematic listening and judgment of perceptual relations: Here a number of well-known experimental procedures are applied to the material. These procedures include those involving detection, recognition, identification, rating, tuning and adjustment, perceptual dissimilarity judgments, and analogy and pattern transformation judgments. (3) Analysis and display of the psychoacoustic structure contained in the perceptual judgments: Here an interactive graphics based playback system is used in conjunction with descriptive statistical tools such as multidimensional scaling, clustering, and related programs that aid the development of an intuitively graspable expression of the structure in the perceptual data. Numerical and graphical tools are provided to help relate various physical measures such as those based on spectral analysis to the perceptual structure. (4) Elaboration of the material: Here programs are provided to aid in the synthesis of new events that are derived from the original material. Examples include extrapolation and interpolation procedures based on the spatial representations provided by the multidimensional scaling analyses. Examples and results of compositionally oriented uses of the system for sets of orchestral instrument timbres, woodwind multiphonics, and synthesized inharmonic tones will be provided. The structural descriptions appear to provide some insights regarding the construction of musical patterns from the elements.
Computer simulation of the piano
Authors: Nakamura Isao
Published: October 2005

The piano consists of the following mechanisms: (a) transmission of energy from the hammer to the strings, (b) propagation of energy on the strings, (c) transmission of energy from the strings to the soundboard at the bridge, and (d) acoustic radiation by the vibration of the soundboard. These mechanisms are expressed in terms of equivalent electric circuit models, and these models are simulated by computer programs. A half-sinusoidal pulse which is produced by the hammer's stroke, propagates on the special transmission line, and is reflected by the impedances of the bridge end and the fixed end. The transmission and reflection lead to the transformation and decay of the waveform. The driving force at the bridge produces the sound pressure whose waveform is determined according to transmission characteristics of the soundboard. Several waveforms and tones by means of the simulation are presented with the actual waveforms measured. The relations between some constants of the piano and produced tones are discussed.
A comparative study of sound propagation over land and water
Authors: Schomer Paul D. , Sanders E.
Published: October 2005

General experience by this author and others has shown that community noise problems are generally worse when the sound propagates over water. In order to study the differences, simultaneous measurements were made at like distances ranging from 15 to 500 m over land and water. Concurrent measurements were made of temperature gradients over the land and water. Wind effects were negligible. The sound propagation experiment was conducted using a broad band source. When the data was analyzed, the over land propagation exhibited a decay rate, substantially greater than 6 dB/octave (as expected) but propagation over water showed a 5.5 dB/octave decay rate. This is less than would be expected from spherical divergence alone and suggests the presence of a surface wave propagating at some lower order inverse R power. A surface wave with this energy is not predicted by any existing theory. Temperature gradient effects are also present but minor compared to ground cover absorption over land and the surface wave phenomena over water.
Backscatter from barriers
Authors: Medwin Herman
Published: October 2005

The sound backscattered from a noise barrier is usually approximated by substituting the radiation from an equal strength image source behind the barrier. The dependences of backscatter on barrier height and surface roughness, sound frequency, source height, and distance from the barrier have been calculated for highway noise barriers using theory for underwater scattering and diffraction at rough surfaces. These wave theory descriptions show that the image solution should be modified by two frequency dependent effects: diffraction from the barrier top and bottom can increase the low frequencies backscattered; and scatter from a rough barrier surface can significantly decrease the high frequencies backscattered. [Work partially supported by ONR.]
An equipment to detect sound radiating sources based on the acoustical holography method
Authors: Oowa T. , Hayashi T.
Published: October 2005

The equipment has a fixed or standard microphone and twelve traverse ones which are set up in line vertically and driven horizontally by a step motor. Signals from all microphones are digitized and their Fourier transforms are made in a computer. Each Fourier transform of the traverse microphone signal is multiplied by conjugate complex of the Fourier transform of the standard signal and stored in the computer. Traversing the microphones to the next position in the measuring plane, the same operations are accomplished. After one scanning with several stops, a set of digitized data is obtained in the frequency domain corresponding to all the measuring points. This may be called “a colored hologram,” since it has frequency information. As bandpass filters and analog multipliers are usually used to make a hologram, it is only “a monochrome hologram.” When a colored hologram is obtained, it should be possible to make a sound source image by Fresnel's diffraction formulas concerning any particular frequency in the computer.
Space Shuttle Payload Bay noise
Authors: Cho Alfred C.
Published: October 2005

The development of Space Shuttle Orbiter Payload Bay acoustics is presented. In the next decade, various space-bound payloads whose missions are either commercial or military will be aboard the Space Shuttle Orbiter. It is imperative that the payloads survive Orbiter's dynamic environment. This presentation includes the assumptions and analytical procedure to predict the internal noise of the Orbiter Payload Bay. The derivations of some formulas are discussed, such as; noise reduction for the Payload Bay; limited frequency to distinguish the sound transmission through thin or thick plates, using a plate equation containing the effect of rotary inertia and transverse shear deformation. The calculation of acoustic compliances of the flexible walls from a finite-element mathematical model is described. Early prediction of internal noise in 1974 from a preliminary design review configuration of Payload Bay exceeded the NASA requirement, hence, various noise suppression methods were investigated. Experimental verification of analytical result by the Orbiter 101 acoustic test is also presented.
Application of acoustic emission in the geotechnical area
Authors: Koerner R. M. , Lord A. E.
Published: October 2005

A review of the application of acoustic emission (microseismic) techniques to the geotechnical area will be given. The approach will be somewhat historical starting with the pioneering work (in the 1930's) by Obert and Duvall in the coal and metal mines and continuing up to the present where currently a host of materials and engineering problems are being investigated with acoustic emission techniques. Acoustic emission measurements in the laboratory will be described which have given insight into the mechanical behavior of rocks, soils, coal and ice. Field applications which will be dealt with include determination of the stability of mine tunnels, open pit mine slopes, underground gas storage reservoirs, and earthem dikes and dams. The use of acoustic emission techniques in earthquake prediction studies will be reviewed. [The authors' work has been supported by EPA.]