bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustical Design of Two Auditoria
Authors: Northwood T. D. , Rossman W. E.
Published: September 2005

Two large auditoria have just been built by the Province of Alberta in the cities of Calgary and Edmonton. Each hall is intended for a variety of uses, who conflicting requirements result in an interesting architectural and acoustical problem. The main auditorium, which seats 2700 persons, is designed for both concert use and large-scale stage presentations. Surrounding it are facilities for smaller-scale meetings, exhibitions, conventions, and social gatherings. The acoustical design was done by the Alberta Department of Public Works in consultation with the National Research Council of Canada. This paper will report on the performance of the auditoria as indicated by physical tests and by a test concert. In the design stages extensive sound absorption tests were made in the reverberation chamber on such auditorium components as wall panels, carpets, and occupied and unoccupied theater chairs. Reverberation measurements were also made in the auditoria, as the components were installed. The relation between the two sets of data will be discussed.
Effect of Practice and Feedback on Frequency Discrimination
Authors: Campbell R. A. , Small A. M.
Published: September 2005

Differential thresholds for frequency were obtained from 20 normal hearing, but otherwise unselected, subjects using the method of constant stimulus differences for 6 hours. For each subject twelve difference limens (DL's) and constant errors (CE's) were calculated. The subjects were divided into two groups of ten each: group 1 received feedback, or immediate knowledge of results, in hours 1, 2, 4, and 6; group 2 received feedback in hours 2, 4, and 6. Group 1 had considerably larger DL's and CE's throughout the six hours than did group 2. Both groups showed smaller DL's the last hour (median = 4.2 cps) than on the first (7.3 cps), with no indication that learning was complete. CE's became less variable with practice, but the median CE (−1.0 cps the first hour and −0.8 cps the sixth) showed essentially no change. The effects of feedback in the last four hours were slight and largely obscured by variability and the general improvement with practice.
Some Analogies between Pitch and Lateralization Phenomena
Authors: Nordmark Jan
Published: September 2005

Changing the time separation between two trains of pulses of identical rate produces a tone whose pitch is correlated with the magnitude of the time separation. Evidence has been advanced against the notion that the time difference tone is due to a neural time-analyzing process. Experiments were made to determine the validity of this evidence by comparing the results of pitch and lateralization phenomena produced by filtered and unfiltered pulses of different polarities. A close agreement was found to exist between the results of the pitch experiments and those made by Flanagan on lateralization of clicks. The possibility of explaining the pitch phenomena in terms of a neural time pattern is considered, and the evidence against this hypothesis found to be inconclusive.
Dimensional Analysis of Blower Noise
Authors: Maling George C.
Published: September 2005

The acoustic power/cps radiated by a centrifugal blower may be written in the form E = ρc2D3F(πDN/c, Q/πD3N,f/N), where D is the impeller diameter, N is the impeller speed, Q is the volume flow rate, f is the frequency of the radiated sound, and ρ and c are the fluid density and speed of sound, respectively. The form of the function F has been determined from measurements on three small centrifugal blowers that are dimensionally similar. The power radiated above some lower cutoff frequency (fa) may be written PWLa−∞ = 10 logD2M4+10 logk(sa,φ)+170 dB, where sa = fa/N, φ = Q/πD3N, k(sa,φ) is a function derived from the function F, and M is the tip-speed Mach number, πDN/c.

The results of the analysis are compared with the sound laws for fans.
Measurement of Ultrasonic Attenuation in Liquid Sodium and Potassium
Authors: Letcher S. V. , Beyer R. T.
Published: September 2005

The attenuation of sound between 12 and 75 Mc/sec was measured in liquid sodium and liquid potassium from their melting points to 150°C. The measured attenuation in potassium was about 10% in excess of the calculated classical value. No excess absorption was observed in sodium, and an upper limit was placed on a possible excess absorption of about 5% of the classical value.
Improved Miniature ASA Sound-Level Meter
Authors: Cunniff Joan F.
Published: September 2005

The demand for small sound-level meters which can be operated easily while held in one hand and which meet all ASA requirements, has resulted in the development of an improved model, not only meeting all existing and proposed ASA standards but also incorporating a number of new and unique features. The circuits involve a combination of transistors and subminiature vacuum tubes, providing improved signal-to-noise ratio, longer battery life, and better frequency response. Particular emphasis has been placed on convenient operation with simple controls and simple connections to companion instruments. A shell and bulkhead type of mechanical construction is employed to achieve both ruggedness and accessibility. A unique feature of the instrument is the builtin integrating networks providing acceleration, velocity and displacement measurements with a vibration pickup, as well as all optional ASA weighting networks for use with the regular microphone. The unit also incorporates a builtin electrical calibration system, adjustable equalization to match various auxiliary microphones, a special output circuit for driving analyzers and other auxiliary equipment, improved operation at low temperatures, and numerous mechanical and circuit refinements, and providing improved accuracy, convenience, stability, and reliability. A new model peak indicating meter is also available as an accessory.
Diffraction Effects in a Random Sound Field
Authors: Waterhouse Richard V.
Published: September 2005

When making measurements in random sound fields, for example in a reverberant enclosure, it is desirable to know what diffraction effects occur at a reflecting object such as a transducer, suspended in the enclosure. In the case of a sound field consisting of a traveling plane-wave train, the diffraction effects for spheres and cylinders have been well studied, and various analytical results are available. Some of these results are here extended to the case of a randomly incident sound field. The potential and kinetic energy distributions in the vicinity of a rigid reflecting sphere under random incidence are derived as functions of the diameter of the sphere in wavelengths. Corresponding results for a pressure-release boundary condition at the surface of the sphere, and for an infinite circular cylinder in a two-dimensional random field, are also given. The general effect of boundary configuration on diffraction pattern is discussed, and the random field pressure at the vertex of a wedge-shaped reflector of arbitrary angle is considered as an example. The diffraction effects are basically reciprocal, and the correspondence of the results with those for the reciprocal cases is discussed. Some practical applications of the results are considered.
Sound Radiation from an Arbitrary Body
Authors: Chen L. H. , Schweikert D. G.
Published: September 2005

A method of analysis is presented for predicting sound radiation from an arbitrary body (shell) vibrating in an infinite fluid medium. The acoustic field is described by a distribution of surface sources of unknown strength at the shell fluid boundaries, which leads to a set of integral equations. In the general case, the shell with or without an attached internal structure is described by an elastic system having a finite number of degrees of freedom. The dynamic interaction between the shell and the fluid at their boundaries is then formulated in terms of the unknown strength of the source distribution. By matrix analysis, the method has been formalized and coded in the digital computer for computation.

Numerical results of two examples are presented to demonstrate the versatility of the method, which makes possible the solution of a large class of sound radiation problems.
Propagation of a Pulse within a Sphere
Authors: Alterman Z. , Kornfeld P.
Published: September 2005

As a step in the solution of the problem of propagation of a seismic pulse in a spherical earth, an exact solution is obtained for the motion of a uniform compressible fluid sphere due to a pressure pulse from a point source situated below the surface. The time variation of pressure due to the source is represented by the difference between two step functions with rounded shoulders. The surface velocity due to sources of different duration and situated at various depths has been evaluated on WEIZAC for different angular distances. In this first communication results for a depth of source equal to half the radius of the sphere are given. The solution exhibits step-function-type and “logarithmic” arrivals, which one would anticipate from the “steepest descent” analysis of Jeffreys and Lapwood. In addition, the solution reveals diffracted pulses which have no counterpart in ray theory.
Effects of Acoustical Waves on the Electrodeposition of Chromium
Authors: Dereska Joseph , Yeager Ernest , Hovorka Frank
Published: September 2005

The effects of acoustical waves on chromium electrodeposition have been examined at frequencies of 10 and 260 kc/sec as a function of the plating solution formulation, current density, temperature, and acoustical intensity. The effects are substantially the same at both frequencies. The cathode polarization is depressed, while the current efficiency for the chromium deposition is increased slightly in most instances. Although not generally pronounced, definite modifications in the structural properties of the deposits were also found. X-ray diffraction studies of the deposits indicate that the sound waves decrease the grain size and increase the degree of preferred orientation. Likewise, the hardness of the deposits is improved. The range of current densities over which bright deposits are obtained is extended to higher values with the sound waves. Unfortunately the porosity, and hence, the corrosion protection afforded by the deposits, are decreased. Some improvements in adhesion and throwing power, however, were noted. All of these effects are negligible in the absence of cavitation. The changes in the structural properties are explained on the basis of the disruption of the concentration gradients at the electrode surface as well as the removal of surface contaminants through cavitation. (This research has been partially supported by the Ordnance Corps of the U. S. Army.)
Perturbation Techniques for Random Vibration of Nonlinear Systems
Authors: Crandall Stephen H.
Published: September 2005

The random response of vibratory systems that are only slightly nonlinear may be conveniently obtained by applying the classical perturbation method. The present paper describes and illustrates the procedure. Oscillators with nonlinearity in the stiffness elements are treated first because more-complete results can be obtained when the damping remains linear. Then, systems with more-general nonlinearities are examined. The techniques are illustrated by applications to simple one- and two-degree-of-freedom, nonlinear, vibratory systems.
Sonic Analysis of Molecular Structure
Authors: Karpovich John
Published: September 2005

The sound absorption properties of liquids are discussed. The experimental techniques for measuring sound absorption over a broad frequency spectrum are reviewed. The theory of sonic relaxations exhibited by liquids is briefly covered. This method is presented as a means of studying chemical processes with rapid reversible reactions. Experimental results are summarized which illustrate sonic molecular structure analysis.
Transient Phenomena for Acoustic Measurements
Authors: Cook E. G.
Published: September 2005

A new horizon has been opened for the application of ultrasonics to materials testing. It is now possible to generate acoustic transients such as an acoustic impulse, step, or ramp with rise times approaching 0.01 μsec. This ability permits election of the best wave form for a particular problem. Flaw detection might require a 0.1-μsec impulse, while elastic moduli studies might require an acoustic ramp. Previously workers in the field have been confined in their studies to the generation of exponentially decaying sine waves. The transient wave forms permit direct measurement of many quantities difficult to obtain by sine-wave measurements. Thickness mode piezoelectric transducers are used to generate these short-duration acoustic waves. These new techniques are the result of recent studies of the transient behavior of piezoelectric elements and the development of lithium sulfate transducers.
Some Characteristics of the Flexural Vibrations of Orthogonally Stiffened Cylindrical Shells
Authors: Hoppmann W. H.
Published: September 2005

The paper presents a résumé of a theoretical study of the problem of flexural vibrations of the walls of orthogonally stiffened cylindrical shells. Frequency equations are given for the stiffened shells. In addition an experimental method of verifying the theory is described. Experimentally determined frequencies for an isotropic as well as two different designs of orthogonally stiffened shells are given in tables. The experimental and corresponding theoretical results are discussed. A peculiar dip in the frequency spectrum which was discovered by Arnold and Warburton for uniform isotropic shells is shown to exist theoretically and verified experimentally for stiffened shells. In addition, there is shown to be a bias in the excitability of the modes of vibration as determined experimentally. The reason for this phenomenon is discussed. The principal axes of stiffness are in the longitudinal and transverse directions for the shells under study. In one case the axis of maximum stiffness is in the longitudinal direction in the other case it is in the transverse direction. As the stiffness tensor is the same for the two cases, except for orientation, an opportunity is provided for examining the effect of rotating the stiffness axes through 90°.
Flexural Wave Scattering by a Rivet on a Plate
Authors: Dyer Ira
Published: September 2005

Knowledge of the stress distribution around a discontinuity in a plate, such as a rivet, is important in determining failure susceptibility for the plate when it is acted on by disturbing forces. When the forces are time varying and of such a nature that they excite flexural waves in the plate, the stress distribution may be found by treating it theoretically as a scattering problem. The rivet imparts boundary conditions on the plate, such as plate displacement and slope equal to zero for a rigid rivet, or impedance conditions for a nonrigid rivet. The resulting stress distribution around a rivet is a superposition of the stress in the incident wave and in the scattered wave. Because the stress is high wherever the field variables change rapidly, stress concentrations are found away from the rivet at the classical shadow zone boundaries, as well as at the rivet. The stress distributions are frequently dependent because of the inherent frequency dependence of the scattering process and also because of possible frequency dependence of the rivet impedance conditions, such as resonance.
Effect of Stimulus Duration on Lateralization Threshold
Authors: Tobias Jerry , Zerlin Stanley
Published: September 2005

Measurements on experienced listeners of interaural time difference thresholds for wide-band random noise indicated that the threshold varies systematically with duration of the stimulus. In order to determine the point at which increase in duration no longer decreases interaural time difference threshold, stimulus (noise burst) duration was varied between 0.01 and 1.9 sec. Fortunately, the use of wide-band noise made it practical to employ instantaneous (but not simultaneous) rise times, and thus to specify duration precisely. A given interaural time difference was maintained throughout any particular burst, starting time included. The effects of simultaneous (and even reversed) onsets, of band-width and intensity variation are reserved for further study. Throughout the study, all stimuli were presented at a level of 65 db SPL to each phone. The duration versus interaural time difference threshold function reached asymptote at approximately 0.7 sec, indicating that the binaural system which effects the correlation necessary for a lateralization judgment may integrate information over this long a period for the kind of stimulus used.
Acoustic-Reflection Losses at the Sea Surface, Measured with Explosive Sources
Authors: Adlington R. H.
Published: September 2005

Experiments indicate that there is no loss of energy at a reflection at the sea surface over grazing angles of 10 to 55 deg in the frequency range 400 to 6400 cps.
Interaction of Vibratory Sources and Their Foundations
Authors: Plunkett R.
Published: September 2005

Conventional methods predict the effects of vibratory forces imposed by rotating electromagnetic machinery in terms of a rigid support; this ignores the dynamic interaction between the machine and the support. A better understanding of the dynamic stiffness of bearings and their supports has helped to eliminate previous discrepancies of as much as two to one between calculated and measured values of critical speeds of rotating machines. More recent work on the mechanical impedances of machines, isolation mounts, and foundations has shown that, in the audio-frequency range, isolation mounts may actually have an effective stiffness greater than those of the parts they are attempting to isolate. Some typical impedance spectra are shown for these elements and methods of calculating and improving the effectiveness of mounts under these conditions are discussed.
Electrodynamic Shaker Analysis and Equalization for Random Vibration Systems
Authors: Priest Dorman E.
Published: September 2005

The growing use of random vibration for component testing has increased the use of electrodynamic shaker systems of special design. This new equipment incorporates equalization networks to provide a flat acceleration response for constant input signals. The mobility method is used in an analysis of the loaded shaker and the results are applied to the design of compensating circuits. If the electrical resistance in the equivalent circuit is given a typical value, a third or higher order system may be attacked as a series of first-order problems, each having useful accuracy in a limited frequency region. The response of the unloaded or nonresonant loaded shaker can then be expressed as three cut-off frequencies or time constants up to the region of armature structural resonances. The response of such a system to resonant loads on the shaker table is described for each frequency region. When the system is not controlled by load resonances, the resultant equalization is generally within a decibel of the desired displacement and acceleration response between 5 cps and an upper frequency limit in the region of 2 kc. The upper frequency limit depends upon the shaker size and construction. Limitations in the use of linear compensation for the effects of typical table load resonances are discussed.
Comments on “Electromechanical Coupling and Composite Transducers”
Authors: Woollett Ralph S.
Published: September 2005

The great differences between traditional piezoelectric theory and the new coupling-coefficient definitions and equivalent circuits suggested by Toulis are reviewed. The opinion is expressed that Conventional theory is entirely capable of handling the composite transducer (which motivated Toulis' work) and that the suggested departures are, therefore, unnecessary.
Correlation of Sonic Damage with Vibration Tests
Authors: Smith P. W. , Junger M. C.
Published: September 2005

A method is outlined for evaluating cumulative fatigue damage and malfunctioning, induced in equipment and structures by intense sound fields, by correlation with results of mechanical vibration tests. Dynamic characteristics of systems are embodied in “transfer functions,” relating response characteristics to the sound field, which functions can be represented by analogs. The approach is similar to Powell's “modal acceptances” for plates. Statistical stress distribution curves for various sources can be combined and correlated with endurance curves determined by off-resonance vibration tests.
Studies with Artificial Neurons, IV: Binaural Temporal Resolution of Clicks
Authors: Harmon Leon D. , Levinson John , van Bergeijk Willem A.
Published: September 2005

A psychophysical experiment performed by Guttman, van Bergeijk, and David in 1960 showed that binaural auditory resolution of repetitively presented, closely spaced clicks improves as repetition rate is increased. We propose a model in which the action of a single neuron can account for the phenomenon; it depends on a self-inhibition function that serves to vary temporal resolution with stimulus rate. Single-spike (click) stimuli elicit output bursts of variable duration; burst lengths are controlled by an output-derived feedback whose level depends on stimulus repetition rate. An electronic model of a neuron, simulating a cochlear-nucleus unit, accurately replicates the essential features of the psychophysical data. Two time constants, estimated by extrapolation, are postulated for single units in the human auditory system.
Output Probability Distribution of a Multiplier-Averager with Partially Correlated Inputs
Authors: Jacobson Melvin J.
Published: September 2005

This paper studies the problem of determining the probability density function of the filtered output of a multiplier when the crosscorrelation function of the inputs is proportional to the autocorrelation function of the inputs. The two inputs are assumed to consist of identical signal plus uncorrelated noise. It is shown that the solution is known once the solution has been found for pure signal inputs. The general theory is applied to the problem where both inputs have the characteristics of RC-filtered white noise and where the postmultiplier filter is also an RC. Detailed results are presented when the ratio of the time constant of the premultiplier filter to that of the final filter is 34 and also when this ratio is large.
Temporal Masking of Clicks by Noise Bursts
Authors: Osman Eli , Raab David H.
Published: September 2005

Masking of clicks by noise bursts (60, 75, 85, and 95 dB SPL) was studied as a function of the temporal position of the click relative to the burst—from 50 msec before mask onset to 10 msec after mask cessation. Backward masking increases slowly at first and then rapidly as the probe approaches mask onset. Simultaneous masking is independent of the temporal position of the probe and of mask duration (10, 100, and 500 msec) and is given solely by mask intensity. No overshooting of the temporal-masking functions was found near onset or termination of the masking bursts—a finding that contrasts markedly with the results of “analogous” studies in vision.
Effect of Contactor Area on the Vibrotactile Threshold
Authors: Verrillo Ronald T.
Published: September 2005

Vibrotactile thresholds were determined as a function of frequency, contactor configuration, and contactor area. It was found that contactor area is a more important stimulus parameter than the gradient or curvature of displacement. The absolute threshold for vibration seems to be independent of frequency when very small contactors are used and independent of area at low frequencies. For higher values of these parameters, it strongly depends on both. It seems reasonable to conclude that responses to mechanical displacement of the skin are mediated by more than one receptor system, although direct evidence is still lacking.
Response of Spectrum Analyzers of the Bank-of-Filters Type to Signals Generated by Vowel Sounds
Authors: Harris Cyril M. , Waite William M.
Published: September 2005

This paper describes a study that has been made of a comparison of the response of spectrum analyzers of the bank-of-filters type to signals generated by steady-state vowel sounds. Each analyzer is comprised of a bank of one of the following types of filters: single-tuned, cascaded single-tuned, double-tuned, cascaded double-tuned, Butterworth, and Gaussian. Both constant-bandwidth and constant-mel-bandwidth analyzers were investigated. The response characteristics of these analyzers were obtained both with and without frequency equalization. A comparison was made of constant-bandwidth analyzers having bandwidths of 70, 140, and 280 cps. In this investigation, the bank of filters and the input signals to the analyzers were synthesized on a digital computer.
Use of Two Nonacoustic Measures in Computer Recognition of Spoken Digits
Authors: Hillix W. A.
Published: September 2005

Instrumentation was developed for obtaining a measure related to lip and jaw movement and a measure related to the velocity of air pulses in front of the lips during speech. These measures were used as inputs to a computer program designed to categorize decimal digits after “learning” on a sample of the digits. Waveform recordings of the measures were also presented to human observers for visual categorization. For the first measure alone, sets of digits produced by one speaker were categorized with 71% accuracy by the computer and 78% accuracy by the observers. The observers did somewhat better with another speaker. However, performance of the observers fall to about 40% when categorization of one speaker's digits was attempted using another speaker's digits as samples. These data, however, were obtained under unfavorable circumstances. When the air-velocity measure was added, the observers' accuracy increased to about 95%, and the computer's performance rose to 81% under one set of circumstances and 100% under another. It is felt that the results to date have been promising enough to indicate the potential usefulness of such measures in understanding and recognizing speech.
Effects of Secondary Flow on Screech Noise Produced by Choked Jets
Authors: Lee R. , Smith E. B.
Published: September 2005

A free jet operating at choked condition produces a discrete band of high-frequency noise caused by instability of the shocks at the exit. This is commonly called screech noise. Concentric jets of various area ratios have been operated in a reverberant box to study the effect a subsonic secondary jet has on the shock pattern and screech noise produced by the over-choked primary flow. Using a Panoramic Sonic Analyzer and a schlieren system, the change in the screech frequency and the shock structure was noted with a varying secondary jet velocity. Results indicate that, under suitable conditions, the secondary flow has a tendency to improve the stability of the shock formation and thus eliminate the screech noise.
Procedures for Estimating Noise Exposure and Resulting Community Reaction from Air Base Operations
Authors: Pietrasanta A. C. , Stevens K. N.
Published: September 2005

An air base may be considered as a complex noise source. Its noise characteristics are determined primarily by the nature of the take-off and ground runup operations of jet aircraft. The time pattern of noise produced by these operations depends on many factors including the type of aircraft involved, their flight profiles and flight paths, the time schedule of operations, runway utilization, the location and orientation of aircraft during runups, and the power settings of the aircraft. Based on a number of measurements of noise produced by jet aircraft operating on the ground and in flight, engineering procedures have been developed for computing the noise exposure that would exist in communities near air bases. Graphical aids in the form of noise contour overlays are utilized in the computation of the noise exposure. These procedures are described in some detail, and tentative relations between community response and noise exposure are discussed. An illustrative example is given in which noise contours are constructed around a hypothetical air base for a given set of operating conditions. (Supported in part by U. S. Air Force.)
Effects of Changes in the Phase Pattern upon the Sound of a 16-Harmonic Tone
Authors: Licklider J. C. R.
Published: September 2005

The observations were made with the aid of a generator that provides control over the amplitudes and phases of the individual components of a complex tone. The components were adjusted to a standard phase pattern—for example, all components at 90 degrees. Then the signal was turned off, the phase angle(s) of one or more components was (were) altered, and the signal was turned on again. With a fundamental of 250 cps, in almost every case the change in phase pattern produced a discriminable difference in pitch or timbre. In general, changing a low-frequency component produced less effect than changing a high-frequency component. The effects were greater with low fundamental frequencies than with high. In some instances, the subjective difference was sufficiently great to be of importance in music. These observations support previous indications that the auditory system is by no means “phase deaf.” The significance of the findings in relation to the critical-band theory and to the phenomenon of perstimulatory fatigue will be discussed.
Vibrations of Orthotropic, Thick, Cylindrical Shells
Authors: Mirsky I.
Published: September 2005

An approximate theory of vibrations of orthotropic, thick, cylindrical shells, in which the effect of transverse normal stress is retained, is deduced from the three-dimensional theory of elasticity. The present theory contains, in addition to the usual membrane and bending terms, the influence of rotatory inertia and transverse-shear deformation. As an application, the propagation of free harmonic waves in an infinite cylindrical shell is studied. Numerical results are given for relatively thin and thick shells of isotropic and nonisotropic materials.
Experimental Study of the Vibrations of Solid, Isotropic, Elastic Cylinders
Authors: McMahon G. W.
Published: September 2005

An experimental study has been carried out to determine the natural frequencies of vibration of solid, isotropic, elastic cylinders with free boundaries. Solid aluminum and steel cylinders having height-to-radius ratios (h/a) between 0.2 and 3.3 have been studied. Twenty of the graver modes were excited by means of a barium titanate driver loosely coupled to the metal cylinders. Six modes of circumferential order zero, seven modes of order unity, four modes of order two, and three modes of order three were studied in the range of dimensionless frequency parameter ωa/c from zero to 2.6. Sand patterns and a small vibration probe were used to determine the form of the vibrations. Where possible, the frequencies are compared with the results of existing theory.
Measurements of Backscattering of Sound from the Ocean Bottom
Authors: McKinney C. M. , Anderson C. D.
Published: September 2005

Data obtained from the measurement of backscattering of sound from the ocean bottom at 16 locations around the coast of the United States of America are presented. Data are given as a function of grazing angle and frequency for mud, sand, and gravel. The range of frequency was 12.5 to 290 kc/sec and the range of grazing angle was 1.0° to 90°. Backscattering increased with grazing angle according to the sin and sin2, depending on the value of angle and the type of sediment. Backscattering increased with frequency according to the 1.6 power for some locations. It is concluded that a knowledge of the particle structure of the bottom is useful in estimating the reverberation level.
Theory of Vortex Sound
Authors: Powell Alan
Published: September 2005

Physical arguments are followed by mathematical developments to show how aerodynamic sound is generated as a result of the movement of vortices, or of vorticity, in an unsteady fluid flow. Changes in circulation or area of a vortex ring give rise to a dipole sound field, the former being illustrated by oscillating flow about a fixed sphere, and the latter by a simple model for the aeolian tone attributable to the stretching of vortex rings. Because in a free flow there can be no change of the total vortex strength (circulation times area), there is no net dipole strength, but each moving element of vorticity still causes local dipolelike flow; each element of moving vorticity acts with some equal and opposite movement elsewhere in the flow so that together they form an oblique quadrupole, although the total effect must be reducible to an assembly of lateral quadrupoles. A cardinal result is that the vorticity in a slightly compressible fluid can be considered to induce the whole flow field, both the hydrodynamic part and the acoustic part. With vorticity taken as the common basis, a slightly compressible flow is compared to the corresponding incompressible one, which may be used in the evaluation of the sound-radiation formula. The theory is particularly well-structured to estimate sound from flows described in terms of vorticity: the sound field is determined for two rectilinear vortices spinning about an axis between them, and its basis for similarity methods is demonstrated in application to free shear flow and jet flow.
Helium Speech
Authors: Holywell K. , Harvey G.
Published: September 2005

“Helium Speech” is a term used to describe speech produced whenever an appreciable proportion of helium is present in the vocal tract. Some measurements of the formant frequencies of helium speech are given, and two simple methods for increasing the intelligibility of this speech are described. The results achieved in some preliminary tests of these processing techniques are given.
Phase Distortion of Reflected Sonar Pulses
Authors: Abramowitz W.
Published: September 2005

The phase distortion of a sonar pulse reflected at the interface of two fluid media is determined theoretically, and curves of the reflected pulse are presented for a number of phase shifts. The incident pulse is one cycle of a sine wave. There is no distortion for phase shifts of 0, π, and π/2, although in the latter case the pulse is inverted. For intermediate phase shifts, the pulse is distorted and shows both a “precursor” and “tail.”
Diffraction Constants of Acoustic Transducers
Authors: Henriquez T. A.
Published: September 2005

Diffraction constants for a sphere, a long cylinder, a ring, and a piston at the end of a long tube are derived and presented in a form useful in designing acoustic transducers.
Off-Responses to Noise Bursts at the Auditory Cortex of the Cat
Authors: Sandel T. T. , Kiang N. Y-S.
Published: September 2005

In a previous report (November, 1956, 52nd meeting of the Acoustical Society) we concluded that cortical off-responses observed in cats under barbiturate anesthesia are in fact responses to acoustic transients that appear in the signal as it is turned off. We have since found in unanesthetized cats with high spinal sections off-responses that seem to occur in the absence of such acoustic transients. This conclusion is based on the following considerations; first, these off-responses are observed when bursts of noise are turned off and are abolished by injections of barbiturates: secondly, the latencies of these off-responses are 6–8 msec longer than the latencies of the previously reported off-responses to acoustic transients: and thirdly, these off-responses occur also under stimulus conditions which produce no off-responses in the anesthetized animal (burst durations shorter than 60 msec and fall times longer than 10 msec). These findings suggest that these off-responses in unanesthetized animals may involve neurons other than those which give rise to on-responses; the possibility that inhibitory neuronal links at levels below the auditory cortex are involved will be discussed. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Thermoviscous Attenuation of Plane, Periodic, Finite-Amplitude Sound Waves
Authors: Blackstock David T.
Published: September 2005

The propagation of a plane progressive wave of finite amplitude in a thermoviscous fluid is considered. The wave is taken to be purely sinusoidal in shape at its source. The approach is through Burgers equation, which is a very good approximation of the exact equations of fluid motion when effects of nonlinearity and dissipation are relatively small but definitely not negligible. A complicated but exact solution of Burgers' equation is analyzed. The nature of the solution is found to depend strongly on a parameter Γ, which represents the importance of nonlinearity relative to dissipation. Nonlinear effects prove to be significant when Γ>1, a finding in agreement with the criterion proposed by Gol'dberg (Akust. Zh. 2, 325 (1956) [English transl.: Soviet Phys.—Acoust. 2, 346(1956)]) concerning the appearance of shock waves. When Γ>>1, simple asymptotic representations of the exact solution in terms of Fourier series may be obtained. One of these corresponds to Fay's solution [J. Acoust. Soc. Am. 3, 222 (1931)]. An equivalent “time-domain” representation shows clearly the sawtooth behavior of the wave. The sawtooth region is found to extend approximately to the point x=O.6/α, where α is the dimensional small-signal attenuation coefficient. Curves of the extra attenuation suffered by the fundamental as a result of nonlinear effects are given for values of Γ in the range 1–100 000. If Γ is large, the extra attenuation in decibels approaches the asymptotic value −12+20 log10Γ as the distance from the source becomes large. A value 1 dB below the asymptote is attained at a distance x=1/α. Application to waves in argon and air is discussed. It is found that nonlinear effects may be employed to increase the efficiency of long-range sound transmission. A possible application to low-frequency sound in the ocean is also discussed.
Role of Electrodynamic Shaker System in Simulating Vibrational Environments
Authors: Metzgar Kenneth J.
Published: September 2005

The basic philosophies of simulating vibrational environments are examined in the light of practical electrodynamic shaker systems. Two basically different approaches to simulation are discussed, both of which assume that a component attached to a structure is the subject for test. A distinction is made between the field measurements used as a basis for simulation which represent the responses of particular structures to an environment and the actual environmental forces. The first approach to simulation replaces the structure on which the component is mounted by a shaker. The motion of the shaker is then controlled in such a manner as to reproduce in a statistical sense the response of the structure to the actual environment. A second approach replaces the environmental forces which excite the structure and component by a shaker. The force output of the shaker is then controlled to reproduce the response of the structure to the actual environment. The two approaches are compared pointing out the relative advantages and disadvantages between the two with emphasis on the shaker system requirements.
Noise Levels Inside the Prototype Caravelle Twin-Jet Airliner During Flight
Authors: Miller Laymon N. , Beranek Leo L.
Published: September 2005

During recent tests of the external noise of the French commercial jet airliner “Caravelle,” noise level measurements were also made inside the aircraft during flight. Although the acoustic treatment inside the passenger cabin was incomplete at the time of the measurements, the inside noise levels were significantly lower than those of conventional propeller driven aircraft in present-day use. This is attributed largely to the location of the two jet engines at the rear of the fuselage. Noise levels are presented for a number of flight conditions. As an example, during cruise at 7100 rpm at 15 000-ft altitude, the noise levels in the forward part of the cabin were found to be in the range of 75 to 85 db re 0.0002 microbar in the low-frequency octave bands and averaged approximately 60 db in the speech interference bands of 600–4800 cps.
On the Prediction of the Attenuation of Sound Propagated Over Ground
Authors: Keast David N. , Wiener Francis M.
Published: September 2005

The attenuation of sound propagated out of doors can be separated into attenuation due to spherical divergence and attenuation due to atmospheric effects. The latter, which shall be referred to as excess attenuation, appears to be principally caused by molecular absorption, temperature and wind gradients, and turbulence. Recently, extensive field data have been obtained which have led to a series of empirical functions which enable one to predict the excess attenuation as a function of frequency and range for a given set of micrometeorological and terrain conditions. Although limited to those cases where both the sound source and the receiver are near the ground, this procedure is of great utility in estimating the noise exposure at some distance from a sound source. (This work was supported by the U. S. Army Signal Corps under Contract No. DA-36-039SC-64503.)
Elastic Waves in Lake Ice Produced by Impact of Falling Weights
Authors: Clements Donald H. , Willis David E. , Wilson J. T.
Published: September 2005

Experimental studies of the propagation of elastic waves in lake ice were made at Lake Margrethe, Michigan, and Garrison Dam, North Dakota. These studies were designed to investigate, in particular, flexural waves in the ice-water system produced by hammer drops, cylinder drops, and sledge hammer impacts on lake ice and nearby land. A method similar to the standard seismic-refraction techniques was employed for the wave studies. Flexural wave dispersion curves obtained from records of mechanical impulses on ice are, in general, consistent with theoretical curves based on the “layer” theory of Press and Ewing (1951) for the observed ice thickness and elastic parameters. Three groups of points on the observed dispersion curves obtained from Lake Margrethe data are flexural waves with frequencies from 2 to 8 cps, 13 to 25 cps, and 40 to 140 cps. The first and third groups exhibit dispersion consistent with the combined thickness of a two-layer floating ice sheet. The second group follows dispersion for a wave path in the upper thin layer only. Hammer drops on land generate flexural waves in the layer of frozen ground in the frequency range 15 to 40 cps. These waves are transmitted across the lake-shore boundary and follow a wave path in the upper thin layer of lake ice. A continuous train of flexural waves in the frequency range 4 to 140 cps was observed on records of cylinder drops taken at Garrison Dam, North Dakota. (Parts of this work were supported by Tri-service Contract No. DA-36-039-sc-52654.)
Relative Intensities of Sounds at Various Anatomical Locations of the Head and Neck during Phonation of the Vowels
Authors: Oyer Herbert J.
Published: September 2005

Speech signals from 16 different anatomical locations were recorded as subjects intoned different vowels at a constant level. Power level analyses were made to determine the relative intensity of the signals. It was found that significant difference in intensity existed among the anatomical locations. It was found that the composite intensities of the test vowels were statistically equivalent at the larynx, the sides of the neck, and at the angles of the rami. The next rank of intensity was noted at the back of the neck, back of the head, chin, and nose. The next most intense location was the top of the head, with least intensity measured at the six positions of the two temples, midback of the head, forehead, and the sides of the head above the ears. In general, previous observations of “the nearer the larynx, the more intense the sound” is borne out by this study. Some locations of lesser intensity were subjectively evaluated as providing more faithful signals. The consensus was that most faithful reproduction resulted in the vowels recorded from the forehead, with the most intense reproduction afforded by the larynx and neck areas. [Done in connection with contract AF 19(604)-1757, monitored by the Operational Applications Laboratory, Air Research and Development Command, Bolling Air Force Base, Washington 25, D.C.]
Interaction between Sound and Flow in Acoustic Cavities: Mass, Momentum, and Energy Considerations
Authors: Cantrell R. H. , Hart R. W.
Published: September 2005

This paper investigates requirements for neutral acoustic stability in cavities with a transpiring wall where there is a mean flow in the absence of acoustic disturbances. The growth rates of the acoustic fields are also considered. The method of calculation utilizes time averages of the mass, momentum, and energy-conservation equations to second order in the acoustic-field quantities. It is found that growth rate and neutral stability may be expressed in terms of only first-order quantities. The results are shown to be in agreement with those calculated from first-order admittance considerations, but differ, in general, from those of Dyer, who uses a method of calculation similar to the present paper. The resolution of this conflict is discussed. The effect of mean flow is often of considerable importance, and the extent to which flow tends to excite or damp the acoustic field is related to mode configuration and flow-field geometry. Application to the problem of determining the acoustic response of burning rocket propellants is discussed.
Speech Synthesis by Rule
Authors: Ingemann Frances
Published: September 2005

It has seemed useful for both theoretical and practical reasons to attempt to write rules for synthesizing speech on the basis of the experiments performed by colleagues at the Haskins Laboratories. Because the discrete nature of phonemes as perceptual units is not reflected on the acoustic level, it is not feasible to synthesize speech by putting together prefabricated phonemes. On the other hand, synthesis of syllabic units need not require an inventory of rules comparable with the number of syllables in the language, since the rules can be phrased in terms of the constituent phonemes and combinatorial operations. The rules can be further simplified by writing them in terms of the acoustic features that correspond to the standard phonetic dimensions of place and manner; syllables and words are then synthesized by combining the rules for the classes to which the constituent phonemes belong. An example of speech synthesized by rule will be presented. [This work was supported by the Carnegie Corporation of New York, the Veterans Administration, and the Department of Defense in connection with Contract DA 49-170-sc-2159.]
Present Status of Formoder
Authors: Chang S. H. , Bach R. , King W. F. , Sukys R.
Published: September 2005

Formoder, short for Formant-Moment Coder, is a system which utilizes slowly varying parameters and discrete linguistic features extracted from the speech spectrum for speech band-width compression. Formoder offers a different approach than Vocoder for the approximation of the speech spectrum by using FM as well as AM parameters. In addition, the use of certain linguistic features limits the dynamic ranges needed in the analyzer and synthesizer components. The system falls short of the ideal representation of a time varying dynamic model of the speech mechanism, but it holds promise for an improvement in compression ratio over that of Vocoder. This is perhaps the reason for continued study of essentially similar systems in various laboratories. This paper is intended to discuss further the above-mentioned points and will describe the present status of Formoder together with system evaluation and articulation tests. In a typical operation of the system using two formants and one moment, articulation tests show the Harvard PB word lists score over 40% and sentence score over 80%. [The research in this paper has been made possible through support and sponsorship extended by the Electronics Research Directorate of the Air Force Cambridge Research Center, under Contract AF19(604)-1039, Item I, and AF19 (604)-2198.]