bluuebunny/crossref_metadata_2025 huggingface dataset:
Unusual Low-Frequency Signals Observed in New Zealand Waters
Authors: Kibblewhite A. C. , Denham R. N. , Barnes D. J.
Published: October 2005

From time to time, strong underwater transient sounds have been detected in New Zealand waters. Much of this activity appears to be biological in origin, and some of it is obviously similar to underwater signals observed in other parts of the world. Other components are by no means so well known and provide further interesting examples of pulses in which the energy is confined to a narrow band of frequencies around 20 cps. These pulses are described.
Observed Onset of Acoustic Streaming
Authors: Pigott M. T. , Strum R. C.
Published: October 2005

Most aspects of acoustic streaming were considered understood in 1954. The time dependence of its onset, however, was controversial when Liebermann's measurements, valid for slowly developing streaming, were criticized. The criticism cited a report that streaming was present only 20 msec after turning on the acoustic source. Using a thermistor bead as flow meter, we have observed the time dependence of the onset of streaming in two fluids of widely different viscosity, each in two vessels of different geometry. The time dependence of the streaming velocity is described as follows: There is zero time derivative at the start. This is followed in succession by a positive second derivative, inflection point, and negative second derivative which persists during an approach to a steady state flow. From the start to the inflection point, the flow velocity v depends on time t according to v = btp where b and p are empirical constants. The exponent p appears to be a nearly fundamental property of streaming onset while b is sensitive to the experimental circumstances. Important to the controversy is that the development is safely slow enough to validate Liebermann's measurement technique, typically taking two seconds to reach the inflection point and five seconds to reach 90%. of steady flow.
Dimensional Analysis of Vowel Spectra
Authors: Plomp R. , Pols L. C. W. , van de Geer J. P.
Published: October 2005

Traditionally, the formant frequencies are regarded as the most important characteristics of the frequency spectra of vowels. It is possible, however, to approach the differences between vowel spectra in a more general way by means of a dimensional analysis. For a particular vowel, the sound-pressure levels in each of a number of frequency passbands can be considered as coordinates of a point in a multidimensional Euclidean space. Different vowel spectra will result in different points. Frequency spectra of 15 Dutch vowels were determined with 18 bandpass filters (10 speakers). The analysis indicated that the “cloud” of 150 points can be described by four independent dimensions that are linear combinations of the original 18. The percentage of total variance “explained” by these dimensions were 37.2%, 31.2%, 9.0%, and 6.7%, respectively. This approach presents interesting perspectives for the development of vowel-discrimination equipment.
Viscosity Determination by Means of Ultrasonics
Authors: Fittipaldi F. , Ragozzino E.
Published: October 2005

It has been shown that the phenomenon of persistence of diffracted lines in water suspensions of starch at different temperatures and also in water solutions of sucrose at different concentrations and constant temperature is related to the viscosity coefficient of the medium in terms of diffusion theory. Therefore, we propose a method for the determination of viscosity coefficients by means of ultrasonics.
Evaluation of the Performance of Active Sonar Receivers
Authors: Bartram James F.
Published: October 2005

A method is devised for evaluating and comparing the performance of receivers used in an active sonar application. The basis of comparison is the level of background noise that will just bring the maximum signal excess, after system adjustment, to zero, given a propagation loss. The better system is the one that can withstand the higher level of background noise before the maximum signal excess goes to zero. This method is applied to the polarity-coincidence correlator and, for comparison, aural detection. It is found that the polarity-coincidence correlator compares favorably with aural detection.
PEST: Efficient Estimates on Probability Functions
Authors: Taylor M. M. , Creelman C. Douglas
Published: October 2005

An adaptive procedure for rapid and efficient psychophysical testing is described. PEST (Parameter Estimation by Sequential Testing) was designed with maximally efficient trial-by-trial sequential decisions at each stimulus level, in a sequence which tends to converge on a selected target level. An appendix introduces an approach to measuring test efficiency as applied to psychophysical testing problems.
Response of a Linear System to Nonstationary Shot Noise
Authors: Chen T. C.
Published: October 2005

The response of a linear system to nonstationary Gaussian shot noise is examined from a more general point of view. The system parameters, including those of a filter, are considered to be of such a general nature that the matrix associated with the rate of the first-order transition moment in the corresponding Fokker-Planck equation may have multiple eigenvalues. The more general approach taken here yields a result that may be reduced to the existing one for systems with simple eigenvalues only. An example is given at the end to illustrate the application of the general expressions for the mathematical expectation and the covariance function of the response.
Average Control for Sinusoidal- and Random-Vibration Testing
Authors: Usher Theron
Published: October 2005

Time-division multiplexers (TDM) have found application in providing control from the average of several acceleration magnitudes for swept-sinusoidal vibration tests and, also, control to the average of several acceleration spectral densities for wide-band random tests. The vibration testing systems using the TDM are described. Pertinent system parameters are determined mathematically in order to limit signal harmonic distortion for the sinusoidal case, and to limit test-level modulation and spectral spreading for the random case. A special case for sinusoidal testing in which a narrow-band tracking filter is used on the output of the TDM is also discussed.
Practical Model of Shallow-Water Acoustic Propagation
Authors: Macpherson J. D. , Daintith M. J.
Published: October 2005

An approximate model of shallow-water propagation based on ray theory and a simple representation of the medium is presented. Simple equations are derived, which take into consideration the water depth, bottom slope, reflection losses and velocity gradients in the water. Two practical illustrations of propagation on Sable Bank in isovelocity and negative velocity-gradient conditions are given. The conclusion is reached that, under isovelocity conditions, the reflection loss at the surface is controlling propagation loss, whereas under negative velocity-gradient conditions the surface is unimportant and the bottom reflection loss dominates. Comparison of surface reflection loss is made with other measurements.
Diffraction of Acoustic Pulses by Obstacles of Arbitrary Shape with a Robin Boundary Condition
Authors: Shaw Richard Paul
Published: October 2005

The diffraction of arbitrary plane acoustic pulses by arbitrary scattering obstacles whose boundary offers inertial but no elastic resistance is considered. The specific problem of a long cylinder of square cross section struck laterally by a unit step pressure pulse is solved numerically in two forms: Part A—the surface pressure distribution is obtained for “heavy” scatterers; and Part B—the surface normal velocity is found for “light” scatterers. There is a region of overlap where either form is applicable. The results indicate that a change in surface mass density has a significant effect on the pressure solution for heavy scatterers but that the velocity solution for light scattering obstacles remains very close to the solution for a completely free scattering surface for a wide range of surface mass densities.
Further Comments on Fitzgerald Resonances
Authors: Hopkins I. L.
Published: October 2005

E. R. Fitzgerald has concluded that experiments performed by the author and explainable in simple mechanistic terms really confirm Fitzgerald's theory of particle waves. In this letter, it is shown that if the matter is clearly understood, the particle-wave theory is superfluous.
Pulsed Wide-Band Ultrasonic Measuring Bridge for Liquids and Solids
Authors: Danielmeyer H. G.
Published: October 2005

This apparatus was built to measure small changes of sound absorption and sound velocity with frequency and temperature in molecular crystals, using a one-way pulse transmission through a sample of constant length. It is shown that these changes are sufficient to determine relaxation parameters. A single sideband technique is employed, covering the frequency range 40–440 MHz. The ultrasonic part consists of two parallel transmission paths. One contains the sample to be measured. This path is chemically resistant and vacuumtight. Solid specimens can be grown between two surface-excited X-cut quartz rods. The other is a reference path containing a cutoff waveguide attenuator and an ultrasonic line, which is adjusted to have the same properties as the first path with no sample present.
Thermodynamic Theory of Bubble Nucleation Induced in Liquids by High-Energy Particles
Authors: Sette D. , Wanderlingh F.
Published: October 2005

A theory is proposed on the creation of microbubbles in liquids by ionizing particles. A thermodynamic point of view allows one to specify the conditions required for the growth of the gaseous embryos statistically present in liquid. In the case of aerated water, the process shows the existence of an energy threshold for the production of 1-μ-radius bubbles as required for ultrasonic cavitation; the theoretical values of particle energy agree with experimental results. Also proposed is a mechanism for one qualitative determination of the stable existence of microbubbles in water.
Interpretation of Ultrasonic Experiments on Finite-Amplitude Waves
Authors: Thurston R. N. , Shapiro M. J.
Published: October 2005

An analysis was made for the purpose of relating higher-order elastic constants to the growth of harmonics in an initially sinusoidal wave. It is supposed that the face of a semiinfinite nondissipative elastic medium—for which the equation of one-dimensional motion is ü = (∂2u/∂x2)g(∂u/∂x)—is subjected to the sinusoidal displacement u = u0 cos(ωt−φ). The function g(∂u/∂x) is given as g(ξ) = (1/ρ0)[M2+M3ξ+M4ξ2+⋯+Miξi−2], where Mi depends on elastic constants up to and including order i. A solution, including the effects due to terms as high as M5 in the function g(ξ), is expressed as u = u0 Σn{Dn sin[n(ωt− Kx)]+En cos[n(ωt− Kx)]}+F(x), where the summation over n goes from 1 to ∞. Dn and En are expanded in powers of a Mach number M and a dimensionless distance X (M = ωu0/c0, X = ωx/c0, c02 = M2/ρ0). It is found that as u0 → 0, the limiting value of the ratio of the second-harmonic amplitude, H2 = u0(D22+E22)12, to u0M is given by −M3X/8M2, independently of M4, M5, etc. Thus, with M2 already known, M3 can be calculated from an experimental determination of this ratio. Similarly, it is found that the limiting value of the ratio of the third harmonic amplitude to u0M2 depends on elastic constants only up through order four.

[Tutorial material is included to make the paper reasonably self-contained and to relate the present analysis to corresponding work for fluids. Careful derivations show that purely longitudinal waves in elastic solids and nondissipative fluids are governed by an equation of motion of precisely the same form. Hence, with appropriate choice of the parameters, an analysis of the one case applies equally well to the other.]
Finite-Amplitude Distortion in Air at High Acoustic Pressures
Authors: Burns Stephen H.
Published: October 2005

This paper treats a problem of acoustic-wave propagation in which the effects of finite amplitude are comparable with the effects of boundary dissipation. The analysis starts with a differential equation for the scalar potential, which embodies thermal boundary dissipation and the quadratic nonlinearities of the propagation, and a differential equation for the amplitude of the vector potential, which embodies viscous boundary dissipation. The acoustic pressure is constrained (for both analysis and experiment) to be a pure sine wave at the start of the tube, and the particle velocity and variational temperature are constrained to vanish all along the wall of the tube. A fourth-order perturbation solution of these equations gives an accurate harmonic analysis (through the fourth harmonic) of the acoustic pressure as a function of axial distance along the tube. Measurements are reported of the harmonic distortion of waves having initial peak pressures as high as 0.1 bar at a fundamental frequency of 445 Hz in air. These waves propagated in tubes of diameters 1.587, 2.66, and 5.26 cm. The tubes were terminated after seven wavelengths or before the experimental shock-formation distance, whichever came first. The theory is confirmed in all essential details.
Electromechanical Filter Composed of Transversely Vibrating Resonators for Low Frequencies
Authors: Konno Masashi , Kusakabe Chiharu , Tomikawa Yoshirô
Published: October 2005

An electromechanical bandpass filter that is suitable for low frequencies is described. The mechanical filter consists of two transducer-resonators and two couplers, of which the transducer-resonators vibrate transversely and are coupled at their nodal points with the torsionally vibrating couplers. Each transducer-resonator consists of two pieces of electrostrictive material with a basis reed sandwiched between them. Also, in this paper, the effects of impedance of electrostrictive material on the basis reed are analyzed. In order to analyze the mechanical vibrating system, mechanical network theory is adopted.
Thickness/Twist Vibrations of a Truncated, Linearly Tapered, Crystal Strip
Authors: Loutzenheiser C. B. , Denkmann W. J.
Published: October 2005

The thickness/twist vibrations of a truncated, linearly tapered, quartz-crystal strip are investigated. The frequency equation is expressed in terms of Bessel functions, with the order, in general, a large irrational number. Frequencies and mode shapes depend on two geometric parameters expressing the taper and a length/thickness ratio. Numerical values for several modes and a range of the geometric parameters are given for AT-cut quartz to illustrate typical results. Frequencies are only slightly higher than for a corresponding uniform strip, and depend mainly on the maximum thickness of the tapered strip. Motion of the strip is concentrated at the thick end, even for very slight taper, but spreads gradually across the strip as the taper is reduced, approaching in the limit the response of a uniform strip.
Bechmann's Number for Harmonic Overtones of Thickness/Twist Vibrations of Rotated-Y-Cut Quartz Plates
Authors: Mindlin R. D.
Published: October 2005

Two methods are described for calculating Bechmann's number for harmonic overtones of thickness/twist modes in rotated Y-cut quartz plates: one based on an exact solution of the equations of elasticity and the other based on an asymptotic form of the exact solution. The latter leads to an explicit formula for Bechmann's number and it is shown to give results very close to the former—which requires extensive computations.
Mechanical Immittance- and Transmission-Matrix Concepts
Authors: Rubin Sheldon
Published: October 2005

The concept of immittance (impedance or admittance) and transmission matrices for application to the vibration of mechanical systems is reviewed. The properties and interrelationships of the formulations are presented. The experimental measurement of the elements of the matrices is explored from a conceptual standpoint. Included is a discussion of the correction of the data taken under other than ideal conditions of constraint. Some general applications of the matrices are illustrated.
Mechanical Impedance and Mobility Concepts
Authors: O'Hara G. J.
Published: October 2005

It is the purpose of this paper to discuss fundamental concepts involved in mechanical impedance and mobility. The equations used in the formulation of the concepts are examined for meaning and content. It is demonstrated for any prescribed structure that every possible observed mobility element is independent of the number and location of the other measurement points, and every possible observed mechanical impedance element is not. The effects upon the mobility and impedance arrays are discussed for simple expansions and contractions of the tensor. Numerical examples are used to illustrate some of these points.
Measurements of the Effect of Geometric Scale on Structural Impedance and Radiated Sound
Authors: Schloss Fred , Reader Wayne T.
Published: October 2005

Two wooden structures resembling ribbed flower boxes geometrically scaled in the ratio of 4 to 1 were driven in air and water with sinusoidal forces; transfer impedance and radiated sound measurements were made. It was found that the resonant frequencies of the lower modes of the two structures were in the ratio of 1 to 4 within a few percent; reciprocal transfer impedance measurements were essentially idential; transfer impedance measurements at symmetrical points of the same structure were almost idential; and at up to 600 cps—referred to the larger of the two vessels—the impedance magnitude and radiated sound averaged over small frequency ranges scaled in the ratio of 16 to 1.
Failure Detection by Mechanical Impedance Techniques
Authors: Tatge R. B.
Published: October 2005

In present practice, the decision as to whether a device has suffered damage as a result of exposure to a severe environment is generally based on operability during and after exposure, and visual inspection. Since these measures do not necessarily disclose the presence of mechanical faults, particularly in sealed units that are to see service, a need exists for a purely structural test to tell if a failure has occurred. Mechanical impedance techniques offer an opportunity for structural characterization to determine whether or not a device conforms to a predetermined standard or has suffered a change as a result of its history. From reference to network theory, it can be shown that changes in the resonant and antiresonant frequencies are sensitive indicators of change in a structure; these have the advantage of being relatively easy to measure with accuracy. The length of time that the structure must be excited in order to make the necessary measurements for such a test can be minimized by using random-noise rather than swept-sine excitation. With proper instrumentation, the results obtained with the two are equivalent.
Frequency and Time Analysis of Polyphonic Music
Authors: Tove P. A. , Ejdesjö L. , Svärdström A.
Published: October 2005

Apparatus has been constructed to give a two-dimensional diagram with a three dimensional representation of frequency, time position, and amplitudes of tones in polyphonic music. The apparatus consists of a frequency analyzer with constant relative bandwidth and sliding frequency setting, combined with a repeating (loop) tape recorder and an XY recorder with an auxiliary pen-deflecting mechanism for small, fast deflections. Examples of analyzed music are shown demonstrating the advantages of this method, which gives at a glance a survey showing frequency, time position, and amplitude, and thus offers objective notation and analysis of music.
Determination of the Vocal-Tract Shape from Measured Formant Frequencies
Authors: Mermelstein P.
Published: October 2005

We model the vocal tract as a lossless acoustic tube and consider the relationship between the resonant frequencies and the cross-sectional area function. Empirical results show that if the logarithm of the area function is band limited preserving only 2n Fourier components, the lowest n pole and n zero frequencies of the admittance function measured at the lips uniquely determine the area coefficients. The formant frequencies determined from the speech signal, the normal resonant frequencies of the vocal tract, correspond to the admittance poles. They alone do not suffice for unique area determination unless the even area coefficients are constrained to specified values or some other physical contraints are imposed. The output-admittance zeros are not obtainable from the speech signal, as they correspond to resonant modes for closed-lip boundary conditions. The above results allow the synthesis of band-limited vocal-tract shapes from admittance functions that have only their low-frequency singularities specified. They can be generalized to any system exhibiting wave propagation primarily in one dimension only, for example, nonuniform transmission lines, and allow a low spatial-frequency synthesis of the system from two sets of low-order eigenvalues.
Stimulated Brillouin Scattering: Measurement of Hypersonic Velocities in Gases
Authors: Madigosky W. M. , Monkewicz A. , Litovitz T. A.
Published: October 2005

Measurements made by several investigators of hypersonic velocity using stimulated Brillouin scattering in gases are considered. It is shown that the several investigators disagree, both in the experimental and “expected” values. A careful analysis of the expected values shows that the data of Rank et al. are in good agreement with adiabatic values predicted from lower-frequency ultrasonic data.
Transient Solution for Sound Radiated into a Viscous Fluid
Authors: Blackstock David T.
Published: October 2005

Sinusoidal vibration of a plane at the edge x = 0 of a viscous fluid causes sound to be radiated into the fluid. The motion begins at time t = 0. Of primary interest is the transient signal. The wave equation, which in this case is of third order because of the presence of viscosity, is solved by changing the form of the viscosity term slightly. The approximation made is justified as long as αλ≪1, where αλ is the dimensionless attenuation coefficient. The altered equation is reducible to the diffusion equation, whose solutions are well known. One of these solutions is adapted for the present problem. It turns out that the transient part of this solution can be represented in terms of the error function of complex argument, a tabulated function. The transient proves to be significant in the vicinity of the main wave front x=c0l. When the wave is first generated, the transient is very weak, but it grows in importance as the wave travels away. Near the point x = 1/α the transient has its maximum amplitude. The diffusive character of the transient is shown by the fact that if the transient signal is integrated from t = 0 to t = ∞, the integral never vanishes, not even at x = ∝. Improved solutions are also discussed.
Extrinsically Induced Acceleration Waves in Elastic Bodies
Authors: Gurtin Morton E. , Walsh Edward K.
Published: October 2005

In this analysis, we consider the propagation of acceleration waves in a general nonlinear three-dimensional elastic medium. We assume that a propagating discontinuity in the extrinsic body force and heat supply has induced a discontinuity in the acceleration field and seek to determine the amplitude of this and other discontinuities in the mechanical and thermodynamic fields associated with it. At first we derive an explicit relation for the amplitude of the induced acceleration wave for the case in which thermodynamic influences are neglected. Then, considering the material to behave first as a nonconductor and then as a definite conductor, corresponding expressions are derived for the amplitude of the induced waves.
Sound Attenuation in Liquid-Solid Mixtures
Authors: Duykers L. R. B.
Published: October 2005

The sound attenuation in liquid-solid mixtures in the audio-frequency region seems to be caused by the viscous drag loss, due to the difference in velocity between solid and liquid. Attenuation caused by dilute concentrations of particulate matter in the oceans agrees with published experimental results at audio frequencies. General agreement is conceived with published experiments on marine sediments.
Surface Pressures Generated by Pistons on Large Spherical and Cylindrical Baffles
Authors: Junger M. C.
Published: October 2005

The classical solutions for pressures generated by pistons on spheres or infinite strips on cylinders are wave-harmonic series, which converge poorly for large ka. For pistons on cylinders, the pressures are given by inverse transforms that must be evaluated numerically. The present formulation overcomes these difficulties. Adapting a technique used in antenna studies, the wave-harmonic series for pistons on spheres and strips on cylinders are transformed into Watson-Sommerfeld series that converge rapidly except on and near the piston. Here, a Kirchhoff approximation ignoring surface curvature is used. For rectangular pistons on cylinders, analytical integration of the Watson-Sommerfeld series yields an explicit solution: Wave-fronts spread circumferentially with the creeping-wave velocity and axially with the sound velocity, forming elliptical traces on the cylinder. Pressures decay more gradually with axial than with angular separation. For the latter,pressures decay as θ−12e−Aθ, as compared to e−Aθ for strips on cylinders and (sinθ)−12e−Aθ for pistons on spheres.
Fluctuations and Directionality in Ambient Sea Noise
Authors: Rudnick P. , Squier E. D.
Published: October 2005

Measurements of relative intensity of ambient sea noise in an octave band at 1 kc/sec for 32 directions of arrival in three dimensions are reported. The results, although obtained with improvement equipment, do not differ from those reported earlier by Becken. Some basis exists for questioning array performance. Rectified beam outputs, averaged for 1 sec, are found to have much more variability, particularly on a time scale of one or more minutes, than would be implied by Gaussian statistics.
Effect of Transducer Size, Shape, and Surface Sensitivity on the Measurement of Boundary-Layer Pressures
Authors: White Pritchard H.
Published: October 2005

The measurement of a random pressure field by a transducer of finite size is subject to error because the transducer senses the spatial average pressure over its face rather than a point value. Methods of correction for this effect under certain conditions have been developed previously; however, many important parameters of the system have been neglected. The present study shows the effect of various boundary-layer parameters, as well as the shape of the transducer, upon the measurement error. The effect of nonuniform surface sensitivity of the transducer is also considered. This factor brings about an effective smaller transducer size, but also can lead to serious errors in cross-correlation analysis.
Name for Unit Radian Frequency
Authors: Strasberg M.
Published: October 2005

The term “avis” is proposed as the unit of angular frequency.
On the Use of the Stimulated Brillouin Scattering Technique
Authors: Bucaro J. A. , Carome E. F.
Published: October 2005

Consideration is given to several processes that may lead to errors in velocity-of-sound studies employing the stimulated Brillouin scattering technique. These include multimode operation of the laser light source and amplification of the scattered light in the laser cavity. When these effects are eliminated, the measured vhl velocities are in good agreement with the results of ultrasonic studies made at lower frequencies.
Vibrational Relaxation in Benzene
Authors: Carome E. F. , Singal S. P.
Published: October 2005

The results of a recent Brillouin scattering study of benzene are reconsidered in terms of double relaxation of the vibrational specific heat. It is shown that under this condition there is no discrepancy between the relaxation times determined from light scattering and ultrasonic absorption measurements.
Matrix Formulation in Acoustical Analysis of Mechanically Driven Fluid Systems
Authors: Wang W. M.
Published: October 2005

Mechanically driven fluid systems are inherent acoustic-wave generators because of their motion and should thus be classified as time-variant. As a direct consequence, the acoustic wave in the system will consist of a series of discrete components at the fundamental time-varying frequency and harmonics thereof, and will lend itself to Fourier-series representation. Previous works assumed the moving part to be a constant-current source in a time-invariant acoustic equivalent circuit as a convenient approximation. This work, however, describes the matrix formulation of a solvable linearized time-variant equivalent circuit for these systems. By use of matrix theory, a general solution with better accuracy for acoustic wave throughout a fluid system is derived. The solution is within the capability of a large digital computer. Later, the simplification of the time-variable element into a constant-current source approximation is described.
Mode Conversion in the Long-Wavelength Limit
Authors: Lange James N.
Published: October 2005

Conversion of energy from the first-order longitudinal to the first-order transverse mode is observed in the long-wavelength limit for guided-wave propagation in solid cylinders. This conversion process increases the attenuation of a multiply reflected longitudinal pulse and occurs in a localized region near any deviation from cylindrical symmetry in the waveguide.
Cross Section of a Circular Cylinder with an Impedance-Loaded Strip along a Generatrix
Authors: Deschenes M. J.
Published: October 2005

An expression is obtained for the monostatic cross section of a circular cylinder when the cylinder sustains a surface impedance load which is constant over its surface, except possibly on a narrow strip along a generatrix. To get this expression, an integral formulation of the problem is obtained, and a discrete matrix approximation is taken. The matrices are diagonalized, and the problem is reduced to a scalar one. Then, because the finite series in the resulting expressions are discrete forms of well-known integrals, these integrals are replaced by their exact values. The resulting expression is well suited to study the effect of strip width and strip impedance load on the cross section of a circular cylinder. The expression is then used to study the effect which certain nonhard strips have on the cross section of the hard cylinder.
Pitch of Complex Tones
Authors: Plomp R.
Published: October 2005

The question of whether the pitch of complex tones is based either on the frequency of the fundamental or on the periodicity of the sound as a whole was studied. Fifteen naïve subjects compared the stimuli A =  ∑ n=112 an cos(2πnft) and B =  ∑ n=1m an cos[2πn(0.9f)t]+ ∑ n=m+112 an cos[2πn(1.1f)t] and had to decide which of the two stimuli, presented successively during 200-msec intervals, was higher in pitch. The results showed that for m = 1 (fundamental of B was 10% lower in frequency than that of A, and all other harmonics were 10% higher in frequency than A) the pitch changed according to the harmonics for f < 1400 Hz and according to the fundamental for f> 1400 Hz. For m = 2, 3, and 4, the corresponding transition frequency was about 700, 350, and <125 Hz, respectively. This holds for both an = 1 and an = 1/n. The experiments support the view that the pitch of complex tones is based on periodicity rather than on frequency. The description of the experiments is preceded by a historical review.
Acoustic Waveguide Having a Variable Section
Authors: Ford R. D. , Lord P. , West M.
Published: October 2005

A waveguide for the measurement of oblique plane-wave reflection from absorbents has been constructed. The device operates in the 1-kHz region. The unique feature of the guide is its moving wall, which permits a range of angles of incidence at a single frequency. Impedance of flexible polyurethane foam has been measured as a function of angle of incidence.
Conical Reflection of Ultrasound from a Liquid-Solid Interface
Authors: Diachok Orest I. , Mayer Walter G.
Published: October 2005

Optical techniques are employed to investigate reradiation patterns of ultrasonic waves incident on flat liquid-solid interfaces. It is shown that, for Rayleigh-angle incidence, reflection takes place into a cone rather than only into the forward direction. The apex angle of the cone is found to be twice the Rayleigh angle.
Ultrasonic-Velocity Measurements and B/A for 1-Propanol at Pressures to 10 000 kg/cm2
Authors: Hagelberg M. Paul
Published: October 2005

Sound-velocity data are reported for 1-propanol at 30°C and at pressures to 10 000 kg/cm2. It is found that the sound velocity varies with pressure at the rate of 0.59 m/sec kg−1 cm−2 initially. The rate of variation decreases as the pressure is raised, with the value at 8000 kg/cm2 being 0.106 m/sec kgminus;1 cm−2. The velocity at 10 000 kg/cm2, 2976 m/sec, is approximately two and one-half times that at 1 atm. From these velocity data, B/A′, the pressure-variation term in the nonlinearity parameter, is calculated over the same pressure range. It is found that B/A′ decreases with pressure at a decreasing rate so that the value at 10 000 kg/cm2 is only slightly more than one-half the atmospheric-pressure value of 11.3. These results are compared with the corresponding results for water, for which both velocity and B/A values have previously been published. An Appendix gives values of (B/A) for mercury at high pressures.
Frequency-Offset Method for Measuring Phase Shifts at Ultrasonic Frequencies
Authors: McSkimin H. J.
Published: October 2005

The frequency of a stable oscillator is periodically offset a small amount, then restored to its original value. The resulting change in phase of the oscillator output with respect to its original value can conveniently be related to the average voltage of a dc pulse generator that produces the frequency offset. For application to the ultrasonic pulse-echo method, phase shifts for a selected echo can readily be measured by using the oscillator output as a calibrated phase reference. Two circuits for doing this are described. Several desirable features of the method are: (1) phase shift is measured at a fixed frequency; (2) phase can be varied continuously over a wide range, with essentially linear calibration; (3) application to measurements at high frequencies can be made; (4) automation of phase shift measurements with strip recorder readout can be obtained; and (5) fractional resolutions of approximately 2 in 107 can be attained for low-loss ultrasonic units. By way of illustration, experimental results are listed for measured phase shifts at 300 and 500 MHz— as required in a study of the dynamic shear properties of di-n-butyl phthalate.
Scattering by Spherically Symmetric Inhomogeneities
Authors: Frisk George V. , DeSanto John A.
Published: October 2005

The Jost-function formulation of quantum scattering theory is applied to classical problems involving the scattering of a scalar plane wave by a medium in which the velocity is a function only of the spherical radial coordinate. This technique is used to solve the radial differential equation for scattering from a constant spherical inhomogeneity. The radial equation can be converted into an integral equation incorporating the Jost boundary conditions. The l−0 partial-wave integral equation for a constant inhomogeneity is solved using an iteration procedure (the first two iterations are considered). The Jost function and l−0 cross section σ0 are plotted as a function of kR1, where k is the wavenumber in the surrounding medium and R1 is the sphere radius. The iterative technique is good for long wavelengths (kR1≪1) and any ratio of wavenumbers in the scattering and surrounding media. For shorter wavelengths and small ratio of wavenumbers (e.g., k1/k = 1.1, where k1 is the wavenumber in the scattering medium), it gives a good approximation to σ0 for the entire range of kR1 considered (0⩽kR1⩽2π). For shorter wavelengths and larger ratios of wavenumbers (e.g., k1/k = 1.5, 2.0), it gives a good approximation to σ0 out to approximately kR1 = 3π/4. More general problems using this method are also discussed.
Deconvolution for Removing the Effects of the Bubble Pulses of Explosive Charges
Authors: Hovem Jens M.
Published: October 2005

A disadvantage of using explosive charges in underwater acoustic experiments is the undesired influence from the bubble pulses. Considering the phenomenon under investigation as a linear system, the effect of the bubble pulses can be removed by applying the technique of deconvolution or inverse filtering. This operation can best be performed on a digital computer. By using the Fast Fourier Transform, the deconvolution operation can be conveniently done in the frequency domain considerably faster than it could be done previously. An example of deconvolution for the removal of the bubble pulses in connection with bottom-reflection studies is demonstrated.
Importance of the Fresnel Correction in Scattering from a Rough Surface. I. Phase and Amplitude Fluctuations
Authors: Melton D. R. , Horton C. W.
Published: October 2005

Three rough surfaces 32 in. by 32 in. in size were made of a pressure-release material. The amplitude and phase of a pulsed wave scattered in the specular direction were measured at a frequency of 95.8 kHz for grazing angles from 6° to 80°. The theoretical approach of Gulin was used successfully in the Fresnel approximation to predict the observed amplitude and phase fluctuations for a Rayleigh parameter less than 0.6. Experimental measurements were extended to a Rayleigh parameter of 7.4. The observed fluctuations in the amplitude reached saturation at a Rayleigh parameter of 2.0 and fluctuated about this maximum as the parameter increased to 7.4. The fluctuations in the phase increased with the Rayleigh parameter, but there is some evidence that the phase fluctuation, like the amplitude fluctuations, saturates.
Pressure Threshold for Acoustic Cavitation
Authors: Skinner L. A.
Published: October 2005

The threshold sound pressure for gaseous acoustic cavitation follows from analysis of the equilibrium state, bypassing the initial-value problem and complicating transient effects. Resonance is considered in detail. A simple approximate threshold formula is established.
Effects of a Horizontal Sound-Speed Gradient on Ray Propagation in a Channel
Authors: Warfield J. T. , Jacobson M. J.
Published: October 2005

The sound-speed gradient is assumed to be a vector of constant magnitude and constant horizontal direction. Ray geometry, travel time, and spreading loss are derived for rays having an arbitrary initial direction at a point source and experiencing multiple boundary reflections in a horizontal channel. Rays intercepting an arbitrarily placed receiving point after experiencing a given number of boundary reflections are isolated and studied. It is shown that the changes in travel time and spreading loss caused by the presence of the gradient are approximately proportional to the component of the gradient in the horizontal direction of the receiving point. A calculation is made of the total field at a fixed receiving point due to a CW source as a function of the magnitude and direction of the gradient. Large changes from isospeed values are found in both the intensity and phase, including the occurrence of an interference null associated with a sharp offset in phase. An approximate formula shows that the change in phase, except for the offset at a null, is also proportional to the range component of the gradient.
Effects of Roughness on Measured Wall-Pressure Fluctuations beneath a Turbulent Boundary Layer
Authors: Aupperle F. A. , Lambert R. F.
Published: October 2005

This paper reports measurements of the cross-spectral density of the wall-pressure fluctuations beneath a turbulent boundary layer for three different surface-roughness conditions. The roughness consisted of sparsely populated, uniformly distributed sand particles—each roughness being distinguished by the sand-particle size. Separate studies of the spectral density and of the lateral and longitudinal narrow-band normalized space-time correlations were made in order to determine the cross-spectral density of the wall-pressure fluctuations. The results indicate that only the spectral density is strongly dependent on roughness size, for the roughnesses examined. To relate quantitatively the spectral densities measured on each surface, the roughness was characterized in terms of Nikuradse's equivalent sand-roughness parameter. The spectral density was then normalized, using this roughness parameter, the shear velocity, and the local coefficient of skin friction. Also, for the roughest surface, the pressure fluctuations in the vicinity of a particle and the correlation of these fluctuations with pressure fluctuations at some distance from the particle were examined in order to determine any observable effects of the local flow about the particles. The results indicate that the local flow can be ignored, provided that the roughness size is not too large. The measurements do not reveal any direct relation between the cross-spectral densities measured on rough surfaces with those measured on smooth.
Theoretical Analysis of Compressor Noise
Authors: Lowson M. V.
Published: October 2005

A theory is presented for the discrete-frequency sound radiated by axial-flow fans and compressors. The theory is based on the noise radiation from the fluctuating forces on either a rotor or a stator stage due to interactions with upstream components. The model used is a cascade of point forces, one on each blade, radiating into free air. It appears that, provided that the correct phase relations are retained, this model may be expected to give accurate predictions of farfield noise even for long, hard-wall duct cases. Both over-all power and directionality curves for the sound radiation are presented, and methods are given for calculating the fluctuating forces acting from the wake geometry. Once wake geometry is defined, the theory enables one to perform calculations of the noise observed at any point. Preliminary agreement with experiment is demonstrated. Virtually all significant compressor design parameters can be included in the theory, and therefore it appears that the theory could be used in tradeoff studies to minimize noise at the preliminary design stage of an engine.
Comment on “Normal Modes of Combined Structures” [W. L. Fourney and G. J. O'Hara, J. Acoust. Soc. Amer. 44, 1220–1224 (1968)]
Authors: Leibowitz Ralph C.
Published: October 2005

Contrary to the statement by Fourney and O'Hara [J. Acoust. Soc. Amer. 44. 1220–1224 (1968)], it is shown that Kennard (as well as his colleague Leibowitz) did present a means of finding the normal mode shapes of a mass-spring oscillator attached to a beam.
Comments on “Vertical Directionality of Ambient Noise in the Deep Ocean at a Site Near Bermuda” [E. H. Axelrod, B. A. Schoomer, and W. A. Von Winkle, J. Acoust. Soc. Amer. 37, 77–83 (1965)] and “Ambient-Noise Directivity Measurements” [G. R. Fox, J. Acoust. Soc. Amer. 36, 1537–1540 (1964)]
Authors: Crouch Wayne W.
Published: October 2005

Two studies of the directionality of ambient sea noise in deep water, one by Von Winkle et al. and the other by Fox, are compared. The divergences of the directionality functions of the two studies, when normalized near the horizontal, range from 0 to 5 dB for moderate and high sea states. They range from 8 to 20 dB for low sea states. The divergences can be attributed to differences in the experimental and analytical procedures.
Relaxation in Kaolin-Water Mixtures
Authors: Duykers L. R. B.
Published: October 2005

From data published by Urick [J. Acoust. Soc. Amer 20, 283–289(1948)] and Hampton [J. Acoust. Soc. Amer. 42, 882–890 (1967)], a relaxational model is proposed to account for sound absorption and dispersion in kaolin-water mixtures. Empirically derived formulas show agreement with both sets of data.
Model Testing of Auditoriums
Authors: Knudsen Vern O.
Published: October 2005

This report first reviews the history of model testing as an aid to the designing of auditoriums, beginning in 1913 with Sabine's spark photography [W. C. Sabine, “Theater Acoustics,” Amer. Architect. 104, 257 (1913)] and eventuating with the more sophisticated Spandock three-dimensional models [F. Spandock, “Akustiche Modellversuche,” Am. Physik 20, 345–60 (1934)] scaled down to 1:10 and 1:5, including models with improvements by Japan's NHK Laboratories. It also reviews the two-dimensional optical model tests we use at UCLA [as developed by R. W. Leonard “Simplified Optical Modeling for Auditoriums,” J. Acoust. Soc. Amer. 26, 937 (A) (1954)], which are expedient for determining approximately optimal shapes in plan and sections, followed, when deemed necessary, by tests of three-dimensional models (optical and acoustical) that range in scale from 1:1 to 1:4, for critical (often repeated) segments of walls and ceiling, and down to 1:24, for the walls, floor, and ceiling, which can be examined separately and as progressively assembled into the complete model of the auditorium. Examples are presented of procedures and findings in connection with the acoustical designing of several multipurpose auditoriums and a theater in the round (220°) with thrust stage. Acoustical model testing reveals diffraction effects and echoes (or their absence) and helps in the designing of auditoriums that optimize early reflections, diffusion, reverberation, and sound-level distribution.
Instrumentation for Acoustic Modeling
Authors: Watters B. G.
Published: October 2005

Acoustic models are usually built so that one can make the same kind of measurements he would make if the full-sized space or structure were available. Thus, much of the instrumentation needed for model work is the same as that used to evaluate completed projects. Other instruments must be high-frequency analogs of conventional equipment in order to accommodate the model's frequency and time-scale factor. This paper deals with instrumentation and techniques that have proven useful in acoustic models with scale factors ranging from about 1:3 to 1:24. Suitable high-frequency microphones, spark-discharge sound source, cathode-ray-tube “graphic level recorders,” and similar equipment are discussed.
Digital Simulation of Sound Transmission in Reverberant Spaces
Authors: Schroeder M. R.
Published: October 2005

Digital computers, through their capability for accurate simulation of complex phenomena, have permitted new insights into a number of important problems arising in sound transmission in reverberant spaces: (1) Reverberation theories, based on the geometrical acoustics, are being refined by ray-tracing studies on digital computers. These studies have revealed significant discrepancies in existing reverberation-time formulas and unexpected large dependencies of the decay rate on the shape of the enclosure and the distribution of sound-absorbing materials. (2) Starting with reverberation-free speech or music signals as inputs, computers can add echoes and reverberation with specified delays, spectral content, and decay characteristics. The computer produces several output signals that—when radiated from loudspeakers in an anechoic chamber—produce, at a listener's ears, sound-pressure waves resembling those in real halls. To ensure “externalization” and proper directions of echo arrivals, the computer program is based on the measured sound diffraction around the listener's head. This digital simulation method is useful to “preaudit” architectural designs before construction and to investigate subjective correlates of a wide variety of reverberation processes. (3) Digital computers have made possible the simulation of frequency and space response of stationary sound fields and the calculation of their statistical properties. These properties are important for the design of electroacoustic systems and the evaluation of measurements in reverberant enclosures.