bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Sounds in Rooms
Authors: Mintzer David
Published: September 2005

Previous work on acoustical transients, where the result is obtained by a Fourier analysis of the steady-state response of the system, has been considered by Morse and Bolt. Their results are in the form of a summation over resonant modes, and do not give a simple picture of the effect of each reflection. The case of transients in one dimension (plane-waves) is solved here by applying the Laplace transform to the wave equation for the velocity potential, and to the boundary conditions. The boundary conditions assumed are a given particle-displacement at x=0 and a series resistance-inertiance-compliance termination at x=l. The transformed velocity potential is then expanded as a series, and the inverse transform is obtained in the form of a (finite) series of terms, the nth term representing the effect of the nth reflection from the termination. The same method is also applied to the case of a rectangular room with a point source arbitrarily located in it and each wall having an arbitrary impedance. By using plane-wave expansions around image points we may solve the transformed wave equation in the form of a series of integrals, which are then approximated. The inverse transform is then taken, and the velocity potential is obtained as a summation over the reflections between the walls of the room. The oral presentation of this paper will be confined to a brief description of the method and to graphical presentation of the results.
The Ripple Tank as a Device for Studying Wave Propagation
Authors: Rix H. D.
Published: September 2005

The ripple tank has proven to be a useful instrument for studying wave propagation, particularly wave patterns arising from inhomogeneities in the medium. We have built a tank 3 ft. by 2 ft. in which we produce ripples in tap water with a mechanically driven vibrator consisting of a strip of plate glass. The wave field is observed directly or photographed by means of stroboscopic illumination, the wave crests acting as lenses to focus the transmitted light in a plane at a convenient height above the water surface. Refraction, interference, and diffraction effects are produced with the help of obstacles made of glass or plastic. Both phase and amplitude measurements are possible to a fair degree of accuracy. Good agreement has been found with the calculated acoustic field resulting from transmission of plane waves through a vertical cylinder of warm air. We have been able to simulate rather closely in the ripple tank the radiation field experimentally observed in air above a high frequency piston source a few wave-lengths in diameter. The ease with which certain types of acoustic field, for which no specific theory exists or which would be difficult to measure directly, can be simulated and observed makes the tank an important research tool in the acoustics laboratory.
Scattering of Ultrasonic Waves in Water by Cylindrical Liquid Filled Obstacles
Authors: Tamarkin Paul
Published: September 2005

The scattering of an underwater ultrasonic beam from effectively infinitely long cylindrical liquid filled obstacles is studied. The wave-length of the radiation used is 1.3 mm and the obstacle diameter is 13 mm, thus placing this type of scattering between the extremes of scattering from obstacles large compared with the wave-length, and scattering from very small obstacles. In a previous paper the obstacles studied were air and steel, affording the two extremes of ρc mismatch, and the scattering was found to be a diffraction phenomenon. The present communication describes the scattering patterns produced by a cylinder of methyl alcohol, the first of a series of liquids used to determine the type of scattering (i.e., diffraction, refraction, or combinations) produced, as the ρc of the obstacle is varied slowly from values smaller, to values greater than that of water.
Transmission of Reverberant Sound through Double Walls
Authors: London Albert
Published: September 2005

In a previous communication the transmission of reverberant sound through homogeneous single walls was investigated theoretically and experimentally. The attenuation of an obliquely incident plane sound wave upon transmission through a single wall was computed and using the customary reverberant sound field statistics the attenuation was integrated over all angles of incidence to give the average transmission loss. A similar technique is employed in this paper in studying the transmission of sound through a double wall consisting of two identical single walls. The materials comprising the double walls are the same as was used in the single walls, i.e., aluminum, plywood, and plasterboard. From the single wall experimental results, an expression for the wall impedance, Zw, for each material, was determined, this expression containing terms which include the effects of the mass, dissipation or resistance, and flexural motion of the wall. This value of Zw is used in the double wall theory to compute the transmission loss for a double wall. Good agreement was obtained between theory and experiment.
The Sound Absorption of Perforated Rigid Facings Backed by Porous Materials
Authors: Sepmeyer L. W. , Leonard R. W.
Published: September 2005

A chart for designing specialized absorption characteristics utilizing perforated rigid facings backed by porous materials has been presented by R. H. Bolt in [J. Acous. Soc. Am. 19, 917 (1947)]. In order to check the validity of these charts, reverberation chamber measurements have been made on six different combinations comprised of three different perforated facings and two different porous backing materials. The perforated facings were selected to yield maximal absorption in the range 300 to 2000 cycles per sec. and the flow resistance of the backing materials differed by approximately 10 to 1. The results of these measurements in comparison to the values predicted by the charts and the measured surface impedance of the backing material will be presented.
The Acoustic Impedance of a Bubbly Mixture and the Determination of its Bubble Size Distribution Function
Authors: Davids Norman , Thurston E. G.
Published: September 2005

A statistical method is developed which enables an analytical bubble size distribution to be formulated from the rough size grouping usually obtained with practical methods of experimental observation. This method is applied to data taken from photographs of bubbly, turbulent water. The resulting function is used with certain known formulae for evaluating the acoustic impedance of such a mixture. A brief physical interpretation of the effects predicted by the theory is given.
Kinetic Theory Equations for Sound in Gases
Authors: Harrison Henry
Published: September 2005

By applying Enskog's first-order solution of Boltzmann's equation one can find kinetic theory analogs of Rayleigh's equations of continuity, momentum, and energy. By specializing these equations to one dimension, one obtains equations describing the propagation of plane waves of arbitrary amplitude. By further restricting these equations to small amplitude perturbations on a uniform medium one obtains a first-order wave equation, containing all loss effects. This kinetic theory equation is almost identical with the equation which Rayleigh uses to discuss viscous losses alone. The heat flow losses which Rayleigh finds appear to be the result of the rather artificial concept of heat conductivity used in the theory of continuous media. A change to the kinetic theory equations would, apparently, increase the gap between theoretical and measured values of sound attenuation in gases.
An Experimental Study of the Velocities of Rayleigh and Lamb Waves
Authors: Frederick J. R. , Martin A. E.
Published: September 2005

Over the surface of a solid medium of infinite thickness Rayleigh waves may be propagated. As the thickness of the medium approaches the order of magnitude of the wave-length of the vibrations Lamb waves are produced. These may be either of a symmetric or antisymmetric type across the thickness of the material, and they travel with their own characteristic velocities depending on the ratio of wave-length to material thickness. Measurements of velocities were made with an ultrasonic reflectoscope by either using a single Y cut quartz crystal to generate and receive pulses of the waves, or by using a separate receiving crystal. The frequencies used ranged from one to 15 megacycles. Measurements are reported on a variety of solid materials and the results are compared with the theory.
Ultrasonic Radiation from an Ideal Piston Source
Authors: Heller G. S.
Published: September 2005

The Rayleigh formula for acoustic radiation from an ideal piston source reduces, under suitable approximation given below, to the ordinary Fresnel integral for diffraction through a circular opening. The Fresnel integral is usually expressed in a series of Bessel functions (Lommel function of two arguments) and reduces in the region of validity, to the correct solution along the axis, to the Fraunhofer solution at large distances, and agrees with R. B. Lindsay's solution on a cylinder based on the piston and coaxial with it. In this expansion, the first term represents the Fraunhofer solution but all the terms of the series must be included to give the solution along the axis. An alternative expansion can be given in which the first term represents both the Fraunhofer solution at large distances and the solution along the axis. This expansion is much easier to handle for regions near the axis than the first. For a piston of radius a, these expansions are valid for points at a distance d from the center of the piston within a cone of half-angle θ coaxial with the piston such that (a/d) sin2θ≪λ/a, where λ is the wave-length, and where (a/z)2≪1, z being the distance along the axis from the center of the piston.
The Threshold of Hearing for Continuous and Interrupted Tones
Authors: Rosenblith Walter A. , Miller George A.
Published: September 2005

The quiet threshold of hearing for tones, as measured with earphones, shows large variations depending upon the method of presentation of the tones. When the tone is continuous the threshold may be much higher than when the tone is interrupted. This difference is especially marked at high frequencies. For both continuous and interrupted tones the thresholds were determined (1) by starting above threshold, and progressively decreasing the intensity, and (2) by starting below threshold and progressively increasing the intensity. With tones interrupted at slow rates the threshold for the descending series lies below the threshold for the ascending series. This is the usual result obtained with this method. However, when the tones are continuous the descending threshold may lie far above the ascending threshold depending upon the frequency, and the starting point for the descending series.
A Precedence Effect in Sound Localization
Authors: Wallach Hans , Newman E. B. , Rosenzweig M. R.
Published: September 2005

The fact that sounds are localized in reverberant surroundings points up a critical problem which has not been explored sufficiently. A brief description will be given of experiments we have done which demonstrate that there is a precedence effect, whereby the first in line of a series of closely spaced sounds is the one which determines the place where the sound is heard. This demonstration of the importance of first arrival makes clear how we are able to discount the ambiguous clues from the reflected sounds of an ordinary hard-walled room. More extended measurements of the precedence effect have been made by synthesizing a sound out of four clicks arranged to give first one pair to the two ears representing one location, then a second pair to the ears representing a different location. Two parameters have been studied systematically, the interval between first pair and second pair, and the temporal disparity of the second pair. All measurements were made by varying the disparity of the first pair until the fused sound appeared to be in the middle of the head. Results of these experiments will be discussed.
Intensity Distribution in Ultrasonic Beams
Authors: Keck W. , Heller G. S. , Nixon J. D.
Published: September 2005

A pulse method has been used to investigate the intensity distribution in the ultrasonic beam produced in water by vibrating quartz crystals having disk- and ring-shaped electrodes. The plot of intensity vs. angular position was observed directly on an oscilloscope screen. Measurements were made at a frequency of about 1 mc sec.−1. The intensity distribution found for the disk agrees closely with theory and with results which have been obtained by other methods in this laboratory. Most of the energy is confined to a narrow cone with a small fraction of the energy appearing in side lobes which become practically negligible about 8 diameters from the source. For ring sources the intensity distribution is similar to that for a disk. However, the cone of the main beam becomes narrower as the ring is made thinner, as predicted by Williams, Heller and Hellens (J. Acous. Soc. Am. 20, 583 (A) (1948)). In addition a larger fraction of the energy appears in the side lobes, which are discernible at greater distances from the source than in the case of the disk.
Asymptotic theory of propagation in curved and nonuniform waveguides
Authors: Ahluwalia D. S. , Keller J. B. , Matkowsky B. J.
Published: October 2005

To treat guided wave propagation in curved nonuniform waveguides, such as atmospheric, oceanic, and solid earth ducts, two methods of analysis are presented. The first is the ray method of Keller and Rubinow, which has been applied to waveguides by Maurer and Felsen. This method is illustrated by applying it to a straight uniform guide, for which it yields the exact result. It is also applied to a guide with concentric circular walls, and yields the asymptotic form of the exact result. Then it is applied to a gradually changing guide and yields a result which includes that of Rayleigh for narrow guides. The second method, which involves stretching of the transverse coordinate, has been applied to water waves by Keller to narrow guides by Matkowsky and to various guided wave problems by Rulf. It is applied to gradually changing guides and yields results which are more accurate than the ray method results for such guides.
Open discussion on the forecasting of flyover noise from static test data
Authors: Hanson D. B.
Published: October 2005

Aircraft noise specialists are becoming aware that aircraft static and flyover noise signatures can be quite different. Most aircraft engine and propeller noise research is carried out on static test stands; however, the forward flight condition is most critical for annoyance and certification. This is discussed in light of the invited papers.
Propagation of ultrasound in tissue
Authors: Carstensen Edwin L.
Published: October 2005

In spite of extensive applications of ultrasound in diagnosis, therapy, and even surgery, there are still many problems to be solved in the basic physics of sound propagation in tissues. Sound absorption occurs primarily at the macromolecular level. There is evidence to indicate that this absorption can be profoundly modified by macromolecular interaction. The specific physical or chemical relaxation mechanisms responsible for the absorption are unknown. The macroscopic inhomogeneities in tissue affect sound propagation and can lead to artifacts in certain methods of measurement of tissue absorption. The problem of localized heating at interfaces and the question of linearity require investigation.
Intracellular events in plant tissues produced by gas microbubbles at ultrasonic frequencies
Authors: Gersboy A. , Miller D. L. , Nyborg W. L.
Published: October 2005

Experiments have been carried out with two arrangements to determine the influence of gas bubbles on interactions between ultrasound and biological cells and tissues. Biological test objects included monocotyledons, dicotyledons, and lower-order plants. One arrangement makes use of a tapered Mason horn at 85 kHz. In some experiments, a gas bubble of near-resonant size is formed by electrolysis or trapped in a small recess drilled in the tip of the horn. When the bubble is set into oscillation in the vicinity of plant cells in which contents are free to move, patterns of microeddying and particle rotation are observed in some of the cells. These are similar to motions reported previously for cells whose boundaries are set into vibration by other means. In other experiments, the bubbles under investigation exist inside the plant tissue, formed of intracellular gas. When sound passes through the tissue, movements occur preferentially in cells adjacent to these intracellular bubbles. In the second arrangement, cells or tissues are sonated at a frequency of 1 MHz while under view with optical microscopy. With Elodea, it is found that if the sound level is raised somewhat above the threshold for generalized cavitation, some of the cells appear to trap bubbles of gas. After this has occurred, microstreaming motions and rotations occur in cells adjacent to the captured bubbles. Motion pictures will be shown to illustrate findings.
Meaning and measurement of “degree of lateralization”
Authors: Harshman Richard A.
Published: October 2005

An attempt will be made to clarify what is meant by “degree of lateralization” and to discover the conditions under which one can conclude that “X is more lateralized than Y.” These notions are made explicit by reference to idealized “criterion experiments” for each of two different concepts of lateralization: hemispheric ability lateralization and hemispheric use lateralization. A person's “true” degree of lateralization on a task is then defined in terms of the scores he would get on a criterion experiment with that task. Indirect procedures such as dichotic listening or dichoptic viewing are normally necessary to provide a practical means of testing degree of laterization in the laboratory. The problem of finding the “best” scoring procedure for such tasks can be redefined in terms of finding functions which will transform the obtained scores on these tasks into good estimates of what the degree of lateralization scores on the appropriate criterion experiment would have been, had it been performed instead. Usually, the “best” lateralization estimating function is not known. It is therefore suggested that any conclusions of relative degrees of lateralization based on indirect (e.g., dichotic) experimental data be tested for “robustness,” i.e., tested to see that the conclusions remain the same regardless of which of the various plausible scoring procedures is used. A good rule is: if the conclusion remains valid for both POE and POC measures of laterality, it will remain valid across a broad family of plausible measures and is “robust.”
Sabine's formula
Authors: Joyce W. B.
Published: October 2005

Sabine's reverberation-time formula, the mean-path-length expression 4 × (volume) ÷ (surface area), and related concepts are reviewed and generalized with an emphasis on technical and historical misconceptions that survive in the contemporary literature. Electroluminescent-diode design and other applications for his formula are noted.
Applications of the variational formulation of geometrical room acoustics
Authors: Ghaffari Ali , Pierce Allan D.
Published: October 2005

This paper extends and improves the variational formulation previously described by A.D. Pierce at the Los Angeles meeting [J. Acoust. Soc. Am. 55, 431(A) (1974)] for estimating the directional spectral density as a function of propagation direction and/or position in reverberant rooms. The revised formulations specifically exclude the contribution of waves coming directly from the source and include the case when the walls are either diffuse or specular reflectors. The insertion of a directionally independent spectral density in the variational indicator for the specular reflecting wall case leads to that derived for the diffusely reflecting wall case. Numerical techniques are described and specific cases are reported which give the reverberant field at each of the six walls as a function of source position and wall absorption. For small absorption, the deviation from that corresponding to uniform energy density is independent of absorption, suggesting that the state of ideal diffuseness (as regards spatial uniformity) cannot be achieved, even in the limit of perfectly reflecting walls.
Transmission loss measurement by small reverberation chambers
Authors: Tsui Chung Y. , Voorhees Carl , Yang Jackson C. S.
Published: October 2005

Even though the measurement of transmission loss by the two-room method is well established and documented, the application has traditionally been applied to architectural structures such as wall panels and doors. This requires the construction of rooms of large volume with thick walls, which was severally reported in acoustic journals. Nevertheless, there exist panels whose sizes are small with respect to the wall thickness due to their inherent applications or other considerations such as costs or difficulties in fabrication. These panels are not apt to be tested in large rooms with thick walls because of the resulting deterioration in diffusivity due to the existence of a tunnel between the chambers. In such cases, smaller rooms with correspondingly thinner walls may be used to advantage in the determination of the transmission loss. This paper describes the construction of a pair of twin reverberation chambers in the shape of a pentagonal parallelepiped with an inclined roof. Acoustic characteristics such as diffusivity, cutoff frequency, and reverberation time of the rooms are presented. Results of transmission loss measurements in aluminum and carbon-epoxy composite specimens are also reported. [Supported by NASA Grant NGR 21-002-350.]
Ultrasonically produced functional alterations in biological systems
Authors: Brady J. K. , Dunn F.
Published: October 2005

Irreversible functional changes produced in living systems by intense ultrasound are being studied quantitatively using the young mouse, approximately 24 hours after birth, as the experimental animal. The anesthetized animals, which are essentially poikilothermic, are exposed to ultrasound at the lumbar enlargement of the spinal cord and paralysis of the hind limbs serves as the end-point. Threshold dosage data are now available in the frequency range 0.26–1 MHz and in the temperature range approximately 0°–50°C. Attempts to detects cavitation originating within the specimen, as a possible mechanism responsible for the functional alterations, have been negative. [Supported in part by the National Science Foundation.]
Intense sounds as payoffs in a simulated signal detection task
Authors: Zerdy G. A. , Molino J. A.
Published: October 2005

In most psychoacoustic signal detection tasks, sounds are presented as signals. In this experiment they were presented as payoffs or punishers. Twelve students performed a simulated signal-detection task in the form of a numeric guessing game. Payoff contingencies consisted of a one-cent reward for every correct decision and a 3-sec burst of a 2000-Hz pure tone for certain incorrect decisions (85, 95, or 105 dB SPL). Differential acoustic costs significantly biased the subjects' responses under conditions where the subjects could not choose an optimal decision criterion in order to maximize monetary gains (d′ = 0). Criterion shifts in the predicted directions were also observed where such optimization was possible (d′ = 1.2). The latter result was confounded, however, by unequal average baseline criteria resulting from the random assignment of subjects to subgroups. Implications of these results for scaling the aversiveness of sounds with a signal detection paradigm are discussed. The results suggest that, when traded against monetary reward, the costs of these sounds were relatively small.
Foreign versus American speaker identification using majority formant minimum value decision criterion
Authors: Hayre H. S. , Patel B. M.
Published: October 2005

Five words were selected to be spoken by ten speakers. Each word was spoken four times by each speaker, and the first three of these utterances were processed and averaged to generate the comparison with the reference formant data obtained from the fourth utterance. The audio data were recorded on a magnetic tape recorder, sampled, and Fourier spectrum analyzed on an IBM 360/44-HSI-SS 100 Hybrid Computer. The resulting power spectra were quantized using five quanta levels, and one-half of the quantum level was used as a threshold. The total power under each formant was divided by its peak level in order to determine its equivalent frequency extent. The reference formant level (a) was used to calculate the second moment of the data formant (b) about the reference level. This technique was employed only in the case when two or more formants (a majority criterion) overlapped, and then 6a minimum value decision criterion was used to determine identification, where all reference formants are used to determine these moments. Preliminary analysis of the results using three foreign-born and six American-born males indicates that a South American male is easier to identify as compared to a South-Indian-born person. Furthermore, American females seem to be more easily identifiable than Texan males. Further work in this area is under way.
Saturation effects in a parametric receiving array
Authors: Bartram James F.
Published: October 2005

In a joint paper [J. Acoust. Soc. Am. 52, 121(A) (1972)], Westervelt and the author showed a way to account for the effects of saturation due to shock formation in a parametric transmitting array. The same basic method is used here to add the effects of saturation to the Berktay-Shooter treatment of parametric receiving arrays [J. Acoust. Soc. Am. 54, 1056 (1973)]. The result is a simple closed-form solution for the loss due to saturation as a function of the ratio of the shock formation distance to array length.
Acoustical response of elastic structures obtained by integral transform methods
Authors: Überall H.
Published: October 2005

The response of submerged elastic structures to transient acoustic signals may be described in terms of the classical Rayleigh (normal mode) series while analyzing the time dependence by the Fourier or Laplace transformation method. In this way, elastic circumferential waves on cylindrical and spherical shells generated by incident pulses have been studied indirectly, via the scattering echoes, by Hickling and the Texas group. Other workers (e.g., Huang and Geers) have obtained the shell response itself by this method. The slow convergence of the normal mode series for high frequencies (short times), and its inability to describe shock-front behavior, suggest its conversion by means of the Watson transformation into a residue series (e.g., Horton, Überall et al., Junger, and Tang) which leads to results of immediate physical significance. Identical results are also obtained by a Fourier transform in the angular variable (Friedlander; Payton, Mishra, and Huang) and consist in (a) structure-borne, fast elastic-type circumferential waves, (b) water-borne, slow Franz-type circumferential waves, and (c) external, geometrically reflected waves. Most studies deal with short-time features of pulse responses, a few also with long-time properties. Geophysical applications concern elastic-wave scattering by occlusions and cavities.
Particular vented box loudspeaker system based on a sixth-order Butterworth response function
Authors: Newman Raymond J.
Published: October 2005

In most instances, the size and appearance of a loudspeaker system is dictated by its low-frequency reproduction element. Recently republished information [A. N. Thiele, “Loudspeakers in Vented Boxes: Part I,” J. Audio Eng. Soc. 19, No. 5, 382–392 (1971); “Loudspeakers in Vented Boxes: Part II,” J. Audio Eng. Soc. 19, No. 6, 471–483 (1971)] offers information that is of great value to designers attempting to optimize design within a given size format. Considerations of the efficiency and cone excursion characteristics of direct-radiator loudspeaker systems indicate several desirable features possessed by vented systems that may aid in optimization. A particular system of only 0.025-m3 internal volume capable of radiating appreciable acoustic power to 32.7 Hz has been fabricated. Each complete system consists of a loudspeaker in its enclosure together with a complementary filter of the type described by Thiele as his alignment 15. The resultant small-size format of the system is particularly well suited to domestic use.
Comparative outdoor tests of measurement microphones
Authors: Djuric S. V.
Published: October 2005

A group of 12 microphones was used in the tests: two conventional air condenser microphones, five ceramic microphones, and five electret condenser microphones. Microphones were located on the roof of a building in Concord, Massachusetts. They were continuously exposed to outdoor environment from November 1972 to October 1973. Performance of microphones was checked daily with a special setup. At the beginning and at the end of the testing period all microphones were checked in a laboratory and changes of important parameters were recorded. Both air condenser microphones had several catastrophic failures during the testing period, and one of them had to be replaced because of a large permanent sensitivity shift. Ceramic and electret condenser microphones did not have any catastrophic failure, and their performances were essentially alike. Statistical evaluation of measurement data is presented and measuring setup described.
Predictions of equal-loudness functions from absolute identification performance
Authors: Singer E. , Braida L. D.
Published: October 2005

Listeners were asked to identify 1000-Hz tone pulses chosen at random from a set of 13 stimuli which differed only in intensity. In one experiment, the pulses were presented in quiet; in a second, they were presented in a background of wide-band noise. In both experiments the set of signal intensities ranged from a few decibels above the detection threshold to 90 dB SPL. As predicted by the preliminary theory of intensity resolution [N.I. Durlach and L.D. Braida, J. Acoust. Soc. Am. 46, 372–383 (1968)], the same total sensitivity was measured in both experiments. However, the shapes of the cumulative sensitivity functions differed strongly according to the presence of the background noise. Preliminary results indicate that masked and unmasked intensities of equal loudness (as measured in a monaural loudness balance experiment) correspond to equal values of cumulative sensitivity with respect to threshold. Thus resolution measures in absolute identification experiments can be used to predict matching stimuli in loudness balance experiments.
Theoretical prediction of propagation loss
Authors: Bartberger Charles L.
Published: October 2005

This paper takes a broad look at the problems and techniques involved in the theoretical prediction of propagation loss in the ocean. Most propagation loss models in current use are based on ray theory, because of the relative simplicity with which ray solutions can be obtained and computations performed, even for range-dependent environments. However, ray theory is only an approximate solution of the wave equation and can lead, particularly at low frequencies, to erroneous predictions in sound channels and in the vicinity of caustics and shadow zones. The classical approach to exact solutions has been in terms of normal modes, based on separation of variables in a horizontally stratified environment. Developments in recent years have significantly advanced the state-of-the-art. With the application of wave corrections, ray models can now be extended to compute the field in the vicinity of caustics and shadow zones. In the wave approach, improved models have been developed using normal modes and other techniques, approximate solutions have been applied to range-dependent environments, and an efficient technique has been developed for the direct numerical integration of a modified form of the wave equation.
Modifications to ray theory near caustics
Authors: Holford R. L.
Published: October 2005

An important feature of underwater propagation is the occurrence of convergence zones, or regions of unusually low transmission loss. In the ray interpretation, such regions are characterized by the focusing of rays along a caustic surface at which the field, according to geometrical acoustics, becomes infinite. As is well known, diffraction effects provide for a smooth transition from an interference field pattern on one side of the surface to a exponentially decaying field on the other. Although a classical treatment of this problem exists, based on the WKB approximation, it is not generally appreciated that the theory is of quite limited applicability and that, in some situations, it fails completely. On the other hand, a recent treatment of the problem by Kravtsov and Ludwig, based on the theory of uniform asymptotic approximations, not only succeeds where the older theory fails, but it provides the connection (heretofore lacking) between the boundary-layer fields adjacent to the caustic and the geometrical-acoustics field which holds far away. The modifications to ray theory implied by the newer theory are discussed (both for smooth and cusped caustics), and it is thereby shown how the caustic boundary-layer field can be related to the local ray geometry.
Evaluation of methods for comparing propagation models
Authors: Blatstein I. M.
Published: October 2005

Comparisons of the various methods for computing underwater acoustic fields can serve several useful purposes. The accuracy of results obtained using a new method can be verified by comparisons with results from a previously validated method or by comparisons with an exact solution to a sample problem. Also, results from standard methods (ray, normal mode, FFP, Green's function, etc.) can be compared in order to evaluate the relative merits of each method for particular cases of interest. For purposes of discussion, we arbitrarily divide sound velocity profiles into one group consisting of single layer or single function profiles and another group consisting of arbitrary profiles. As examples of the first group, we discuss work by Pedersen and Gordon, who compared ray theory and normal mode theory; Wood, who compared ray and uniform asymptotic solutions with exact solutions; and others. As examples of the second group, we discuss work by DiNapoli (FFP and normal mode), Spofford and Tatro (ray theory with caustic correction, and normal mode theory), and Blatstein and Überall (ray theory, normal mode theory, and modified ray theory), The advantages and disadvantages of the various types of comparisons will be discussed.
Visualization of vibration and sound using scanning and holographic methods
Authors: Watson E. E. , Hannon R. J.
Published: October 2005

Two scanning techniques are now being used to determine the vibrational patterns and farfield sound radiation of complex vibratory systems. One technique is a nearfield scanning apparatus which scans the vibrator and gives a three-dimensional display on graph paper of the nodal patterns. The other scanning technique uses the principles of holography to locate farfield sound sources on the vibrator. These two methods, coupled together, have demonstrated a unique capability to locate acoustic sources and hot spots on vibratory systems.
Loudness adaptation: further studies with the tracking method
Authors: Ahaus W. H. , Stokinger T. E. , Wylde M. A.
Published: October 2005

An experiment was conducted to determine if the duty cycle and period of a train of tone pulses presented simultaneously to the comparison ear influence in any way the adaptation measured at the opposite (test) ear. Eight normal-hearing listeners were adapted for 5 min to a steady 1-kHz pure tone at 60 dB SPL. Using a tracking procedure, adaptation over the 5-min period was measured under each of five comparison-signal conditions, each comprised of pulse trains having different on/off ratios. The five on/off ratios (in milliseconds) were: 200/800 (20% duty cycle); 500/500, 200/200, and 800/800 (50% duty cycle); and 800/200 (80% duty cycle). Listeners received each condition ten times. The comparison signals had a frequency of 1000 Hz. There was a clear tendency for adaptation to increase as the duty cycle of the comparison tone increased from 20% to 80%. This was evident even when attempts were made to take into account the extent to which the pulse trains might have been perceived as less loud than continuous signals at the same level (the so-called LOT effect). For comparison tones with a constant (50%) duty cycle, the same amount of test-ear adaptation was measured whether the on-time of the signals was 200, 500, or 800 msec. [Work supported by the Research and Education Committee, Oklahoma City Veteran's Administration Hospital, under Project No. 20-69.]
On the noise level of ears and microphones
Authors: Killion Mead C.
Published: October 2005

Although it is well known that the self-noise of the human ear is less than that of many microphones, little has been published directly comparing the noise level of ears and microphones. When a microphone is to be used in a hearing aid, however, it is sometimes of interest to known how soft a sound the wearer can hear if he turns the gain up far enough. If the noise spectrum of the microphone is known, the “aided pure-tone threshold” which can be achieved with that microphone can be calculated by utilizing the extensive literature on the masking of pure tones by noise. Following French and Steinberg [J. Acoust. Sac. Am. 19, 90–119 (1947)], one can turn the tables and calculate the apparent noise spectrum of the ear considered as a microphdne. Such a calculation indicates that an acute young ear has an apparent A-weighted noise level of 20 dB SPL. Experimental verification has been obtained on a new hearing aid microphone designed to be quieter than the human ear. A review of the experimental technique again calls attention to one pitfall in the routine use of the difference between aided and unaided thresholds as a measure of hearing aid gain.
Invariance of talkers' choral spectra
Authors: Bordone C. , Pisani R. , Sacerdote G. , Dubes R. , Tosi O.
Published: October 2005

The purpose of this study was to determine whether or not amplitude spectra of the “choral” speech [T. Tarnocsy, “Determination du spectra de la parole avec une methode nouvelle,” Acustica 8, 352–358 (1958)] of a talker maintain some relative invariance, irrespective of the language spoken and the occasion the speaker recorded. The algorithm used to make this determination was the HICLUS, which implements Johnson's hierarchical clustering algorithm on the CDC 6500 computer at the Michigan State University [S. C. Johnson, “Hierarchical Clustering Schemes,” Psychometrika 32, 241–254 (1967)]. All pairs of amplitude spectra from a total of 180 were compared, using as a similarity measure the sum of the absolute differences between amplitudes of the same frequencies. In approximately 75% of the cases, the processed data clustered according to subject before clustering according to language or occasion of recording. This suggests that the choral spectra of each speaker have unique characteristics independent of the language of text read, and that these unique characteristics tend to be stationary during the lapse tested. Choral amplitude spectra (63–6300 Hz) from 20 speakers, 14 male and six female, who recorded in three languages (Piamontes, Italian, and French) were utilized in this study. A total of 180 10-second loops of choral recording, each of them dubbed from 14 single-track recordings of different materials from the same speaker, constituted the source for each spectrum.
Normal-mode program with N2 linear layers
Authors: Stickler D. C.
Published: October 2005

Normal-mode expansions provide a low-frequency complement to the high-frequency ray theoretic methods. These methods are useful in environments where the sound speed and density profiles are essentially stratified, i.e., these parameters have a weak dependence on range. They also provide a means of confirming the validity of other approximate methods for which a direct error analysis is not possible. The theory of such expansions is well established, but their implementation is sometimes difficult. In the present program, the sound speed and density profiles in the ocean and the bottom are approximated and the resulting approximation is solved exactly. The nature of the profile approximation is as follows: The depth coordinate is partitioned into N layers such that in each layer the square of the index of refraction may be approximated by a straight line and the density by a constant. The Z-dependent portion of the pressure field can then be expressed in terms of Airy functions. The results are compared with a modified NRL program [A. V. Newman and F. Ingenito, “A Normal Mode Computer Program for Calculating Propagation in Water with an Arbitrary Velocity Profile,” NRL Rep. 2381 (Jan. 1972)] and with the FFP program [F. DiNapoli, “Fast Field Program for Multilayered Media,” NUSC Rep. No. 4103 (1971)] for a set of examples presented at the recent ONR Non-Ray Tracing Workshop, May 1973. In addition, the effects of the continuous spectrum are considered. [Supported by Naval Ordnance Systems Command.]
Coding of directional information by neurons in the superior olivary complex of bats
Authors: Jen P. H. , Suga N.
Published: October 2005

The superior olivary complex is the lowest place where binaural interaction essential for sound localization first takes place. Unlike other mammals, the S-segment of Myotis lucifugus is very large, but its accessory nucleus is absent. Single units in the S-segment generally discharge more than one impulse for a 40-msec tone burst at 80 dB SPL. When a loudspeaker was moved only a few azimuth degrees around the head at a constant distance, the average number of impulses discharged by a single neuron systematically changed, but it fluctuated even when the identical stimulus was delivered at a given azimuth. Therefore the responses were statistically treated to determine how small an azimuth difference single neurons in the S-segment could code. Out of 48 neurons studied, 45% of the neurons could code a 0.5°–2.5° azimuth difference around the median plane at a 75% correct level by changing the number of impulses. Seventy percent of the neurons could code an azimuth difference of less than 5°. If activities of these neurons on the left and right sides are compared with higher-order neurons, as originally proposed by Békésy, a 1.2°–2.5° azimuth difference would be detected by the bat at 75% correct level. [Supported by NSF Grant GB-40018.]
Category boundaries for linguistic and nonlinguistic dimensions of the same stimuli
Authors: Sawusch J. R. , Pisoni D. B. , Cutting J. E.
Published: October 2005

At the previous meeting of the Society we reported finding a shift in the category boundaries for tonal stimuli as a function of the relative number of occurrences of each stimulus in the series. No such shift was found in the category boundaries for synthetic stop consonant-vowel syllables. However, it could be argued that tonal stimuli are not appropriate control stimuli for speech sounds. To examine this possibility, identification functions were obtained for a series of synthetic CV syllables that varied simultaneously in both place (/ba/ to /da/) and pitch (/lo/ to /hi/). The distribution of occurrences of stimuli for the place and pitch dimensions were varied independently. When subjects judged pitch, the category boundary shifted toward the more frequently occurring stimulus. In contrast, when they judged place, no shift in the phonetic boundary was observed. These results agree with our previous findings and suggest that unlike the arbitrary categories for nonspeech stimuli, phonetic categories may have a naturally determined basis. These results are also discussed with regard to some recent findings on possible feature detectors in speech perception.
Synthetic English speech by rule
Authors: McIlroy M. D.
Published: October 2005

A relatively small computer program produces synthetic speech from English text for a phoneme-driven synthesizer. The speech is not inflected, but within that constraint is deemed intelligible on at least 97% of the words in typical runing text. The program works almost entirely by rules, most of which have a stereotyped form. Since no large dictionary is needed, secondary storage is not used. All the rules are given, together with examples of their behavior.
Propagation of radiation from a finite beam or source through an anisotropic random medium
Authors: Beran M. J. , McCoy J. J.
Published: October 2005

In a previous paper we solved the problem of propagation of a plane wave in an anisotropic random medium. The characteristic correlation distances in the horizontal propagation direction were assumed to be large compared to the radiation wavelength, while in the vertical direction these distances were assumed to be of the same order or smaller than the wavelength. For this medium, we derive here the equation governing the propagation of the coherence function for a finite beam or source. This equation is then averaged over the vertical direction and solved. The solution is given in terms of a definite integral over the horizontal spectrum of the index of refraction field. The point source solution and the plane wave case are given as special cases. Explicit solutions are given for the propagation of an acoustic field in the ocean under conditions where the spectrum is dominated by the effects of internal waves.
Analysis of the effect of a Rossby wave on sound speed and transmission in the ocean
Authors: Baer R. N. , Jacobson M. J.
Published: October 2005

A Rossby wave is assumed to he present in the ocean, and its effects on density, pressure, current, and sound speed are examined and analyzed. The zeroth-mode solution can have only a negligible effect on sound speed while the first-mode solution is significant. For parameter values consistent with the Sargasso Sea area, the dispersion relation has as one solution an east-west wavelength of 210 nautical miles and a period of 114 days. This first-mode solution predicts the gross behavior of observed sound speed versus depth variations, and provides striking agreement with measured curves of constant sound speed. The effects of a Rossby wave on underwater sound transmission may be discussed, also. [This work was supported in part by Acoustics Programs, Office of Naval Research.]
Perceptual features of hard-of-hearing subjects' judgments of 16 English consonants in filtered and non-filtered conditions
Authors: Danhauer J. L. , Singh S.
Published: October 2005

The subjects were four young adult, male, college students with bilateral sensorineural hearing losses of 40–60 dB at and above 4000 Hz and normal hearing for the remaining frequencies. They were paid to listen and respond to sixteen English consonants in the context /ə_ɪ|/. The 1680 stimuli were presented in ABX sets for the experimental conditions of 4000-Hz low-pass filtering and no filtering. The subjects' responses were analyzed by INDSCAL to find perceptual features utilized by the subjects in their processing of the 16 “true” consonants in English. The data were analyzed in six- through two-dimensional spaces. Similar solutions were found in all dimensional spaces and experimental conditions. The features in the two-dimensional space and their weights were sibilant (40%) and continent (16%) for the 4000-Hz low-pass condition. For the non-filtering condition they were: sibilant (30%) and continuant (17%). Sibilancy was weighted substantially higher than continuancy. These features were also found for normal-hearing subjects under similar conditions. The features were compared to subject's pure-tone thresholds.