bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical and Experimental Results on Active Vibration Dampers
Authors: Rockwell T. H. , Lawther J. M.
Published: September 2005

The use of active feedback elements to produce damping of multiresonant structures is examined analytically, and the analysis is compared with experimental results obtained for a 48 in.-long uniform beam damped at its midpoint. The analysis method involves an adaption of the conventional Nichols-chart technique and appears to be quite reliable. By using commercially available components, a simultaneous reduction in resonant mobilities of resonances below 10 kc/sec is predicted and demonstrated. Reductions were proportional to the mobility values prior to active-damping applications and also to the gain in the feedback path. The limitations on the amount of damping possible are imposed by stability conditions for the feedback loop, which in turn depend primarily upon the transfer function of the forcing and pickup components of this loop. The stability analysis for particular components used in the beam experiment is presented.
Coupling of Sound and Panel Vibration below the Critical Frequency
Authors: Smith P. W.
Published: September 2005

Prior analysis has shown that the sound power radiated from reverberant vibration of a simply supported panel is proportional to the length of the panel's perimeter when the frequency is below the critical frequency. A simple physical interpretation was made in terms of the mode shape of resonant modes. Other analyses for power radiation from a single straight boundary on an infinite panel indicated that twice as much power radiates from a clamped edge as from the simply supported edge, the spatial mean-square velocity being held constant. It is shown here that the increased radiation from clamped edges is also predictable from simple considerations of the mode shape. Moreover, among all boundaries having a purely reactive rotatory impedance and restricting transverse displacement to zero, the clamped edge is found to be the most efficient radiator. For some impedances, power radiation is found to approach zero.
On the Autocorrelation of Random Inhomogeneities
Authors: Comstock Craig
Published: September 2005

The question of singularities at the origin in the autocorrelation function of temperature fluctuations is discussed. A series of singular autocorrelation functions of an exponential character is derived from a non-singular model.
Variance of the Bearing Angle of a Discrete Linear-Difference Array in a Random Transmission Medium
Authors: Lord Gary E.
Published: September 2005

An approximate expression has been derived for the variance of the bearing angle, about the central null point, of a discrete linear-difference array. The Chernov formulation for plane-wave propagation in a random medium, restricted to small absolute values of the phase and amplitude fluctuations, is used as a basis for the derivation. It is further assumed that the phase and amplitude fluctuations are zero-mean normal random variables. A special case is considered in detail for large values of the wave parameter D = 4R/ka2, where R is the range, k is the wavenumber, and a is a characteristic correlation distance. For this case, the variance of bearing angle with range is linear and is nearly independent of the frequency.
Acoustic Radiation of a Cylindrical Bar Excited by the Field of a Ship Propeller
Authors: Tsakonas S. , Chen C. Y. , Jacobs W. R.
Published: September 2005

An infinitely long elastic beam with circular cross section is immersed in an acoustic fluid with its axis parallel to that of an operating marine propeller. The pressure field generated by the propeller and transmitted and radiated by the cylindrical beam is studied by means of Fourier-transform techniques. Analytic expressions for the pressure signals due to the scattering and radiating mechanisms are obtained at large distances from the disturbance, and a study is made of their dependence on such important parameters as propeller clearance, reduced frequencies, number of blades, propeller loading, and geometry, as well as the elastic properties of the boundary. Furthermore, closed-form expressions of extreme simplicity are developed for the propeller-induced vibratory force on the cylinder. Numerical results are obtained on the assumption of constant loading for a 2-, 3-, and 4-bladed propeller at various distances and different propeller clearances. The calculated sound pressures for realistic values of the parameters indicate that an appreciable sound level is obtained through the mechanism of the elastic-boundary reaction to the propeller motion.
Use of Stoneley Waves to Determine the Shear Velocity in Ocean Sediments
Authors: Bucker H. P. , Whitney J. A. , Keir D. L.
Published: September 2005

The velocity and attenuation of Stoneley waves that propagate along the water/sediment interface are measured. These values are then used in the determination of the shear velocity and attenuation constants of the sediment.
Backscattering of Explosive Sound from Ocean Bottoms
Authors: Burstein Aaron W. , Keane John J.
Published: September 2005

Using explosive charge sources in deep water, sound returns from the ocean bottom in a 1- to 3-kc/sec bandwidth were measured at grazing angles from 30° 90°. Data were obtained from three areas and from these data scattering strengths are calculated. Comparison is made with earlier work by Urick and Saling and the possibility of a log-tan dependency for backscattering from the ocean bottom is proposed.
Farfield Radiation Pattern of a Noise Source from Nearfield Measurements
Authors: Ferris Horace G.
Published: September 2005

An alternate theory to that of Greenspon is presented for computing farfield noise radiation from nearfield measurements. The present theory, in contrast to that of Greenspon, requires no farfield measurements, but presents somewhat greater computational difficulties. The results are given in spheroidal coordinates.
Scattering from a Sinusoidal Surface—A Direct Comparison of the Results of Marsh and Uretsky
Authors: Murphy Stanley R. , Lord Gary E.
Published: September 2005

A direct comparison is made of Marsh's and Uretsky's results for acoustic scattering from a sinusoidal surface. It is shown that Rayleigh's formulation is inadequate for the description of the scattered field.
The Ear as a Frequency Analyzer
Authors: Plomp R.
Published: September 2005

Ohm's acoustical law, as formulated by von Helmholtz, states that the human ear is able to analyze a periodic sound wave into its sinusoidal components. As far as the writer knows, there does not exist any systematic study about the limits of this law. In this paper, the results of some experiments on the number of distinguishable partials of multitone signals with harmonic as well as inharmonic components are communicated. The frequency of the lowest partial was varied between 44 and 2000 cps. The results are in agreement with the critical-band concept, indicating that the partials of a complex sound can be “heard out” only if their frequency separation exceeds the critical bandwidth. This fact supports the supposition that the critical bands correspond with the widths of the stimulating pattern of simple tones on the basilar membrane. The masking pattern of a complex tone of 500 cps, determined over the frequency range between 300 and 4000 cps, points in the same direction. An investigation of the minimum frequency separation required to distinguish the pitches of two-tone stimuli resulted in somewhat smaller values than the critical bandwidth, especially in the low-frequency range.
Estimating Noise Hazard with the Sound-Level Meter
Authors: Flanagan J. L. , Guttman Newman
Published: September 2005

A simple and rapid measurement procedure is suggested for surveying nonimpulsive, continuous-spectrum acoustic noise. The procedure includes rules for relating sound-level measurements to contemporary damage-risk criteria. The standard A-, B-, and C-scale frequency weightings of the conventional sound-level meter are exploited to make a limited estimate of the noise spectrum. On the basis of analytical approximations to the weighting functions, scale differences are calculated for a number of input-noise spectra. From the calculated differences, rules are deduced to indicate whether hearing-conservation practices are or are not necessary, or whether more-detailed acoustic measurements are desirable.
Ultrasonic Measurement of Elastic Moduli at Elevated Temperatures, using Momentary Contact
Authors: Carnevale E. H. , Lynnworth L. C. , Larson G. S.
Published: September 2005

The elastic moduli of several materials have been determined by momentarily coupling 1-Mc/sec longitudinal- and shear-wave pulses through a sample and measuring the transit time. The temperature range has been from room temperature to beyond 1000°C. Measurement of longitudinal- and shear-wave velocity is accurate to about 1%, permitting the dynamic moduli to be computed to an accuracy of about 2%. Comparison of results with published data for 4340 steel, fused silica, and 6061-T6 aluminum is good up to the highest temperatures at which data are available. The test sample is a cylinder five wavelengths in diameter by several inches long. Dimensional requirements are easily met. Accordingly, sample preparation and moduli determinations are relatively simple. Momentary coupling of longitudinal waves is achieved by employing a suitable couplant. Shear waves are coupled dry by using special probes. At room temperature, these probes have been used to measure shear-wave velocity in copper, aluminum (up to 60-ft path length), brass, lucite, steel, fused silica, glass, graphite, thoriated tungsten, and other refractory materials. The momentary-contact method is amenable to certain production-line inspection and quality-control situations where measurements of material integrity, temperature, or flaws are required at room or elevated temperatures.
Backscattering of Sound from the Sea Surface
Authors: Schulkin M. , Shaffer R.
Published: September 2005

An equation has been fitted to the available ocean-surface scattering strength data as a function of the Rayleigh roughness parameter. The Rayleigh roughness parameter is taken as the product of frequency, a roughness height, and the sine of the grazing angle of incidence. The roughness height appears to be proportional to the 5/2 power of wind speed, and may be related to the Neumann-Pierson theory of ocean-wave spectra.
Acoustic Radiation of an Infinite Plate Excited by the Field of a Ship Propeller
Authors: Tsakonas S. , Chen C. Y. , Jacobs W. R.
Published: September 2005

An infinite elastic plate is immersed in an acoustic fluid and located above an operating marine propeller. The pressure field generated by the propeller and transmitted and radiated by the plate is studied by means of Fourier-transform techniques. Analytic expressions for the pressure signals due to the scattering and radiating mechanisms are obtained at large distances from the disturbance and a study is made of their dependence on such important parameters as propeller clearance, reduced frequencies, number of blades, propeller loading, and geometry, as well as the elastic properties of the boundary. In addition, simple closed-form expressions are developed for the propeller-induced vibratory force on the plate. Numerical results are obtained on the assumption of constant loading for a 2-, 3-, and 4-bladed propeller at various distances and different propeller clearances. The calculated sound pressures for realistic values of the parameters indicate that an appreciable sound level is obtained through the mechanism of the elastic-boundary reaction to the propeller motion.
Pressure on a Vibrating Circular Piston in an Infinite Baffle
Authors: Mangulis Visvaldis
Published: September 2005

The pressure distribution on a vibrating circular piston in an infinite rigid plane baffle is expanded in terms of complete elliptic integrals of the first and second kind.
Directivity Study of the Noise Field in the Ocean, Employing a Correlative Dipole
Authors: Linnette Harry M. , Thompson Rory J.
Published: September 2005

Directivity characteristics of the ocean noise field, including the effects of surface activity of the wind, were investigated. The results of this investigation suggest that the noise field in the ocean due to over all surface activity is primarily anisotropic. A comparison of experimental with theoretical covariance curves indicates directivity function of the form S(θ) = cosnθ (in which the angle θ is measured from the vertical), characterizing the radiative processes at the surface with n largely in the neighborhood of two or three, except for low wind speed, where n approaches unity.
Quantitative Neuroanatomic Studies Implemented by Ultrasonic Lesions—Mammillary Nuclei and Associated Complex of Cat Brain
Authors: Fry William J. , Fry Francis J. , Malek Rita , Pankau Joseph W.
Published: September 2005

The results of a quantitative approach to the elucidation of the structure of the limbic system of the brain are presented. Total neuron populations and anatomically significant subpopulations of the medial and lateral mammillary nuclei of cat brain are determined. The subpopulations are measured by placing ultrasonic lesion arrays in efferent and afferent tracts and in associated nuclei, waiting for degeneration to occur, and then determining the residual populations in each case. The total neuron populations of a number of structures related directly to the mammillary nuclei are determined also. In addition, the size distribution of the nucleoli of the neurons is measured for each of the structures of interest in the population determinations. The methods and techniques that have been developed to obtain the necessary accuracy in the determination of the cellular populations are described. These include lesion placement, histologic preparation of the tissue, nuclear-boundary determination, and neuron mapping. The data presented in this paper constitute the type of information upon which a complete quantitative description of the neural circuitry of brain structures can be deduced, as will be demonstrated in subsequent papers.
Measurement of the Displacements and Nonlinearities of the Guinea-Pig Tympanum
Authors: Hoeft Lothar O. , Ackerman Eugene , Anthony Adam
Published: September 2005

Direct measurements were made of the displacement of the guinea-pig eardrum when acted upon by acoustic pressures (200–6000 cps). The mechanical nonlinearities of the ear were studied by introducing a static pressure (0 to ±3000 dyn/cm2) in the middle-ear cavity. Below 1000 cps, the ratio of the tympanum displacement to the sound pressure was frequency-independent, with a value of about 4×10−7 cm3/dyn. Above 1000 cps, this ratio exhibited a series of maxima and minima. A static-pressure difference across the tympanum changed the frequency at which the maximum occurred and generally decreased the displacement/pressure ratio. It was concluded (1) for low frequencies, the lumped-parameter description of the ear as a cavity was valid; (2) the tympanum acts as a flexible, conical plate under slight tension; (3) the measurements were best explained in terms of two nonlinearities: hysteresis and a nonlinearity of the elastic properties of the ear.
Information Rate Necessary to Transmit Pitch-Period Durations for Connected Speech
Authors: Shaffer Harry L.
Published: September 2005

The purpose of this study is to evaluate the channel capacity necessary to transmit pitch-period duration values. Using a statistical approach, the average uncertainty (entropy) of a pitch-period duration value was calculated, taking into account knowledge about the just-preceding pitch-period duration value. The data consisted of utterances from 26 speakers (13 male and 13 female); a total of 12 576 pitch-period duration values was obtained. The results show that, for pitch-period duration values quantized within 50 μsec, the theoretical channel capacity is 621 bit/sec, for the case where conditioning extends one duration value into the past.
Channel Vocoder with Digital Pitch Extractor
Authors: Tierney Joseph , Gold Bernard , Sferrino Vincent , Dumanian J. A. , Aho Everett
Published: September 2005

An experimental, digitized channel vocoder has been designed and built at the Lincoln Laboratory. This vocoder differs from previous vocoders in the design of the pitch extractor. Pitch is obtained by using a special-purpose digital computer to combine the outputs of 6 analog pitch indicators. The synthesizer uses spectral flattening to reduce spectral distortion caused by pitch variations and nonuniform filter bandwidths. For high-quality speech input, the quality of the Lincoln vocoder is considered by many listeners to be comparable to that of a voice-excited vocoder.
Velocity of Sound Measurements in High-Pressure Steam
Authors: Woodburn James
Published: September 2005

Velocity of sound measurements have been made in superheated steam at pressures from 200 to 1000 lb/in.2 and over a range of temperatures from 395° to 750°F. Experimental values are in agreement with calculated values, using existing Tables on the thermodynamic properties of steam. A variable path-type acoustic interferometer of stainless and chrome-alloy steel was used for the present work. Frequency range was from 650 to 1000 kc/sec.
New Method for the Accurate Standardization of Mechanical Oscillations of Small Amplitude
Authors: Goldberg J. L.
Published: September 2005

This paper presents the theory and first experimental observations with a new method for accurately standardizing the amplitude of small mechanical oscillations in terms of an optical wavelength. A multiple beam interferometer of the Fizeau type is used in which a simple harmonic motion of known frequency is imparted to one of the surfaces of the interferometer. The oscillating multiple-beam fringe pattern is viewed with a photoelectric detector through a slit aperture arranged parallel to the fringes. The resultant photoelectric current contains harmonics of the frequency of oscillation and a strong one is selected by tuning a detector. The amplitude of the selected harmonic is shown by analysis to depend on only three variables: (1) the aperture width R relative to a fringe spacing, (2) the geometric mean reflectance r of the two silvered surfaces of the interferometer, and (3) the peak amplitude of oscillation of the fringe pattern n0 fringe spacings. A function H (R,r,n0) is calculated as a function of n0 for certain values of R and r and it is shown to have a large number of prominent turning points. With the exception of the first, these turning points form a series with a common interval of one fringe spacing. The calculated values of the positions of the turning points are independent of R and r within ranges of variation of R and r representing realistic estimates of errors likely to occur in the values of these quantities. Experiments have shown that, provided that the center of oscillation of the interferometer is stable, the form of the relationship and, more important, the positions of the turning points can be satisfactorily reproduced. The range of amplitudes that the method is potentially capable of standardizing is at present considered to be 0.25 to 10 μ, the precise values depending on the wavelength used.
Effect of Ice Cover on Shallow-Water Ambient Sea Noise
Authors: Payne F. A.
Published: September 2005

Shallow-water ambient-sea-noise measurements in the frequency range 20 3000 cps have been made in the Gulf of St. Lawrence off the north coast of Prince Edward Island, with and without ice cover. The presence of ice is found to make a large difference both to the level and to the spectral distribution of the ambient noise. Result,are presented that illustrate both the effect of ice cover on the ambient noise and the transition from the “open-water” to the “ice-cover” condition.
Responses to Acoustic Stimuli from Single Units in the Eighth Nerve of the Green Frog
Authors: Sachs Murray B.
Published: September 2005

Single-unit activity was recorded from the eighth nerve of the green frog. All units are frequency-selective. Units most sensitive to tone bursts of frequencies below 450 cps show little or no spontaneous activity; their responses to tone bursts can be inhibited by tones of frequency above 500 cps. Many of these low-frequency units are sensitive to vibration and their responses to vibration can also be inhibited. Units with most sensitive frequencies above 650 cps are spontaneous and cannot be inhibited. These high- and low-frequency units probably originate from different sense organs within the otic capsule, and evidence supporting this supposition is presented. Ten units displaying very different response patterns are also discussed. Results of this study are compared with those of Frishkopf and Goldstein for the bullfrog.
Note on Predicting Speech-Discrimination Scores
Authors: Elliott Lois L.
Published: September 2005

A reanalysis of pure-tone thresholds and speech-discrimination (PB) scores for groups of ears with perceptive loss, mixed loss, or normal hearing showed that there is no clear superiority for the average of one set of three frequency (1000, 2000, and 3000 cps) over another set of three frequencies (500, 1000, and 2000 cps) for predicting PB score.
Vector Pitch Detection
Authors: Rader Charles M.
Published: September 2005

A scheme for detecting the fundamental periods of speech signals is described. It is based on the output signals of contiguous bandpass filters and their Hilbert transforms.
Comments on “Experimental Study of the Vibrations of Solid, Isotropic, Elastic Cylinders,” by G. W. McMahon
Authors: Pfende Egon
Published: September 2005

In a recent paper, G. W. McMahon [J. Acoust. Soc. Am. 36, 85 92 (1963)] presented an “Experimental Study of the Vibrations of Solid, Isotropic, Elastic Cylinders.” The cylindrical samples of aluminium and steel had 3 and 4 in. diameters. The aluminium samples ranged in height to-radius ratios from 0.201 to 3.29, while those of steel ranged from 0.205 to 2.48. One of the found vibration modes had been observed at circular disks of the alloy Ni-Span C with only a diameter of 0.35 in., height of 0.0727 in. (height/radius = 0.415) in the frequency range of 140 kc/sec.
Effect of Contact Area on Mechanical-Impedance Measurements
Authors: Plunkett Robert
Published: September 2005

The weighted average normal mechanical impedance of a circular area on an elastic half-space does not depend markedly on the assumed pressure distribution. Its absolute value is almost independent of frequency at least until the wavelength m equal to the circumference of the circular contact area, but the loss tangent varies almost linearly with frequency up to a value of about 1 at this cutoff. These conclusions are valid only for structures large as compared with a wavelength.
Effect of Waveheight on Surface-Reflected Pulse Amplitudes
Authors: Senko A. , Nichols R. H.
Published: September 2005

Experimental measurements have been made of both the peak and mean pressure amplitudes of acoustic pulses reflected from the ocean surface for a variety of sea states. The purpose was to investigate the influence of waveheight on the reflected signal. Pulsed sinusoidal signals were generated by a high-power sound source bottom-mounted in deep water and received on bottomed hydrophones at three ranges. The pulses were 100 msec in duration, at frequencies of 400, 750, 1000, and 1500 cps. Data were obtained at three grazing angles: 18°, 31°, and 85°. Statistics were calculated relating the variability of the reflected signal to grazing angle and waveheight. Results are given for waveheights ranging from 4 to 20 ft. In general, the mean pressure amplitude remained nearly constant with increasing waveheight at all three grazing angles. This is a continuation of work reported earlier [J. Acoust. Soc. Am. 35, 1892 (A) (1963)]. [Work supported by the Bureau of Ships, U. S. Navy.]
Timbre Cues and the Identification of Musical Instruments
Authors: Saldanha E. L. , Corso John F.
Published: September 2005

This study was designed to evaluate the relative importance of transients, harmonic structure, and vibrato as timbre cues in the absolute judgment of musical tones. Tape recordings were made of tones played on ten different instruments at C4, F4, and A4 of the equally tempered scale. Appropriate splicing and retaping procedures provided a test tape with 300 randomly ordered tonal stimuli (10 instruments × 3 frequencies × 2 playing styles × 5 types of tones). Twenty trained musicians were tested and retested on the final tape in two experimental sessions. S's were provided with a reminder list of 39 instruments (grouped into classes) and were required to identify the particular instrument for each tonal stimulus. The results of this study indicate that (1) some instruments (e.g., clarinet, oboe, and flute) are identified more easily than others (e.g., violin, cello, and bassoon); (2) more correct identifications are made at F4 than C4 or A4; (3) the best identification is made for stimuli consisting of initial transients and a short steady state; (4) a vibrato tone is better identified than a nonvibrato tone; and (5) identification is improved significantly with practice. Suggestions are offered for further research.
Long-Term Larynx-Excitation Spectra
Authors: Carr P. B. , Trill D.
Published: September 2005

One important aspect of speech research is the study of larynx excitation. which has considerable influence on the fine structure of speech waves. Data are presented in graphical form of the long-term larynx-excitation spectra derived from six frequently occurring English vowel sounds, each uttered by ten male speakers. Inverse filtering was used to isolate the larynx source. The spectral analysis was performed with a 10-cps band-width filter and averaged over a 23-sec passage. The slopes of the larynx spectra were found to vary from −8 dB to −16 dB per octave, and in one-third of the spectra regularly spaced zeros occurred. The spectra are discussed in connection with analysis-synthesis telephony.
Articulation-Test Control Circuits
Authors: Snow William B.
Published: September 2005

Articulation tests usually involve talkers, listeners, and the experimenter at three separate locations, yet require good synchronization of effort. The principal purpose of this paper is to describe a signaling system constructed to assure this coordination.
Angular Positioning of Thin Metallic Samples for Optimum Continuous-Wave Ultrasonic Imaging
Authors: Berger Harold , di Novi Roberta A.
Published: September 2005

A continuous-wave ultrasonic inspection system that yields a televised image of the ultrasound transmitted through an inspection object has been applied to the nondestructive testing of thin metalic samples. Images obtained with continuous-wave ultrasonic-imagining systems are often masked by standing-wave patterns set up between the sample and the receiving transducer. These can be eliminated by using an appropriately large angle of incidence for the ultrasound, so that the reflected ultrasonic waves are removed from the image area. Using such inspection methods with thin metallic samples, it was observed that optimum imaging results were obtained at discrete angles of incidence. The results indicate that the increased ultrasonic transmission and improved quality at these discrete angles can be correlated with the generation of Lamb waves within the samples. It is further shown that first-order Lamb-wave modes are usually preferred for optimum imaging results and that, in some cases, a choice between first-order asymmetrical and symmetrical modes can be made.
Hydroelastic Solution of the Sloshing of a Liquid in a Cylindrical Tank
Authors: Bhuta Pravin G. , Koval Leslie R.
Published: September 2005

The problem of sloshing (free surface oscillations) of a liquid in a cylindrical tank with rigid walls and a flexible bottom (a thin elastic plate) is studied for both the axisymmetric and asymmetric cases. The coupled boundary-value problem of the liquid and the elastic bottom is solved for small motions. The frequency equations are obtained and the effect of the coupling investigated. It is shown that the frequency equations reduce properly to the various limiting cases. The orthogonality of the coupled mode shapes is investigated and a theorem concerning the coupled mode shapes is proved.
Simple Method for Observing Audiofrequency Resonances and Sound Beams in Crystals
Authors: Fitzgerald Edwin R.
Published: September 2005

A very simple, inexpensive, and easily duplicated method for observing audiofrequency resonances in small samples of poly and single crystals is described. In single crystals, audiofrequency sound beams in line with one of the slip directions of the crystal are sometimes observed. The existence of the resonances and beams is attributed to the presence of internally generated particle (de Broglie) waves propagating through the crystals since the samples tested were much too small to have normal (elastic) wave modes in the frequency range of the measurements.
Finite Vibrations of a Free Rotating Anisotropic Membrane
Authors: Nowinski J. L. , Woodall S. R.
Published: September 2005

Using the von Kármán field equations extended to the dynamical and anisotropic case, large amplitude vibrations of a spinning, cylindrically orthotropic membrane are analyzed. The membrane is assumed to be free, and its deflection is represented by a simple monomial. Free nonlinear vibrations manifest the familiar decrease of period of vibrations with an increase of amplitude and show a marked dependence on the degree of anisotropy. A vibration mode associated with two nodal diameters is studied in more detail. The dependence of a representative stress on the degree of anisotropy, as well as on the amplitude of vibrations and velocity of rotation, is also discussed.
Underwater Sound Reflection from Layered Media
Authors: Barnard G. R. , Bardin J. L. , Hempkins W. B.
Published: September 2005

Underwater sound-reflection experiments were conducted in an 8-ft-diam, 7.16 ft-deep laboratory tank equipped with a transducer positioning system. A 5-in.-diam shaded, circular piston operating at 100 kc/sec was used to insonify layers of various fluid and solid media supported near the bottom of the tank by a 4 × 4-ft tray. Measurements were made to determine the reflection coefficients as a function of grazing angle for several models of layered media. These experimental results are compared with calculated values using modified versions of the equations presented earlier by Brekhovskikh. In each experiment, the sound velocity and attenuation were known for each layer and these values used in the calculations. When plane, bounded waves are incident upon well-defined layers of isovelocity, uniform density materials, the relatively simple layered mathematical models presented are sufficient to describe the experimental results.
Correlation of 630-cps Shallow-Water Ambient Noise with Wind Speed and Waveheight
Authors: Penhallow W. S. , Dietz F. T.
Published: September 2005

The sound-pressure spectrum level derived from a 13-octave filler centered at 630 cps was chosen to study the mutual associations among ambient noise, wind speed, and waveheight in Narragansett Bay, Rhode Island. Data were divided into three groups corresponding to relatively steady, increasing, or decreasing wind speeds. The results of correlation analyses indicate that waveheight is as significantly related to the sound-pressure spectrum level at 630 cps in this locate as is wind speed, provided that the wind speed is relatively constant. Wind speed is the more significant factor of the two under transient wind conditions.
Comparison of Reverberation-Room and Impedance-Tube Absorption Measurements
Authors: Olynyk D. , Northwood T. D.
Published: September 2005

Reverberation-room absorption measurements on some 50 samples of commercial acoustical materials were compared with values predicted from impedance-tube measurements on the same materials. The predictions involved calculating the random-incidence absorption for the standard 9 × 8-ft patch of material. At frequencies of 125, 250, 500, 1000, and 2000 cps, various degrees of correlation were found between impedance-tube data and reverberation-room results involving mountings 1,2, and 4 (adhesive, furring strips, and rigid backing, respectively). Of special interest were results at 250 cps in which the absorption was sensitive to type of mounting. For mountings that permitted diaphragm vibration of the material, the reverberation-room results were substantially higher than predicted values based on rigidly backed samples. Remnants of this behavior appeared at 500 cps for the thin materials, but otherwise correlation was good at this and higher frequencies. Highly absorptive materials correlated better than those with low absorption, for which reverberation-room results still tended to be somewhat higher than was predicted.
Lateral Line as a Vibration Receptor
Authors: Suckling E. E. , Suckling J. A.
Published: September 2005

The contention is made that, despite the conclusion of Dijkgraaf, the lateralis system of fish should be considered a vibration receptor. Evidence from electrophysiological experiments is presented, showing that for the species used the system is sensitive to very small amplitudes of water vibration at low frequencies.
Free-Field Correction for Condenser Microphones
Authors: Koidan Walter , Siegel David S.
Published: September 2005

Differences in the free-field corrections of 1-in. condenser microphones, caused by their different acoustic driving-point impedances, were found to be of sufficient magnitude to warrant a cautious approach to the determination of the free field response level from measurements of the pressure response level and the addition of a “standard” free-field correction.
Tuned Audio Amplifier with Controllable Resonant Frequency Provided by Modification of a Manufactured Audio Oscillator
Authors: Neustadt Herbert M.
Published: September 2005

The modification of a manufactured RC audio oscillator to provide a tuned amplifier with controllable resonant frequency is described. Formulas are given for the bandwidth and stability to be expected of such an amplifier.
Augmentation of Bactericidal Action of Germicides with Ultrasound
Authors: Shaner Edward O.
Published: September 2005

Sonification of germicidal solutions increases the bactericidal efficiency. Vegetative organisms are quickly destroyed, but spores are not. However, thermal resistance of spores is reduced.
Influence of Radiation on the Cavitation Threshold of Degassed Water
Authors: Finch R. D.
Published: September 2005

A study was made of cavitation induced in water at the center of a 12-liter spherical resonator at a frequency of 25 kc/sec. For water degassed so that the equilibrium air pressure above it was less than 4 mm Hg, the threshold was found to be 9±3 atm, provided that the sound field was not radically different from an ideal radial mode. It was also possible to obtain thresholds consistently higher and up to 80 atm in a mode in which the central maximum was enhanced. A Picker-Dresser neutron generator producing 14-MeV neutrons at a rate of 108/sec was used to irradiate the resonator, and the threshold was always lowered by 10%–50%, whichever mode was used, there being a time lapse of about 12 h for the full effect of the irradiation to take place. A 1.0 cm-thick lead screen placed over the resonator produced a rise in threshold of 10%–50% as often as it apparently produced no effect. It was concluded that neutron irradiation affects the cavitation threshold of degassed water and that cosmic radiation probably does also. The time lags encountered are evidence of a cumulative effect, whose nature is briefly discussed.
Circularity in Judgments of Relative Pitch
Authors: Shepard Roger N.
Published: September 2005

A special set of computer-generated complex tones is shown to lead to a complete breakdown of transitivity in judgments of relative pitch. Indeed, the tones can be represented as equally spaced points around a circle in such a way that the clockwise neighbor of each tone is judged higher in pitch while the counterclockwise neighbor is judged lower in pitch. Diametrically opposed tones—though clearly different in pitch—are quite ambiguous as to the direction of the difference. The results demonstrate the operation of a “proximity principle” for the continuum of frequency and suggest that perceived pitch cannot be adequately represented by a purely rectilinear scale.
Spherical Waves in Viscoelastic Media
Authors: Lee T. M.
Published: September 2005

Closed-form solutions to the propagation of spherical waves from an internal steady oscillating pressure source as well as to the transient response of a viscoelastic medium to a pressure impulse are presented. The assumption that the loss factors, quantities related to the dissipative property of a viscoelastic medium, are independent of frequency is used here for investigating the wave-propagation phenomenon due to the action of an impulse. Numerical examples for the displacement and stress functions have been used to illustrate the damping effect of a viscoelastic medium by comparing with its special case—the elastic medium. It is found that this effect shows its significance with increased traveling distance. Also, in the steady-oscillation problems it is of importance when the vibration frequency is high, while in the transient case it causes the decrease in the peak amplitude and also a time lag in the arrival of the wavefront.
Minimum Detectable Change in Interaural Time or Intensity Difference for Brief Impulsive Stimuli
Authors: Hall J. L.
Published: September 2005

Psychophysical experiments to determine the just-noticeable change in interaural time difference and interaural intensity difference as a function of over all intensity, for dichotic clicks, were performed on three subjects. Results are given here.
Transient Tones of Wind Instruments
Authors: Richardson E. G.
Published: September 2005

Oscillograph records of the initiation of sound in organ pipes and orchestral wind instruments show large variations from one instrument to another. The Paper causes of these variations and their artistic effects are discussed.
Electronic Musical Instruments—Past, Present, and Future
Authors: Tanner R. H.
Published: September 2005

The history of music is long, stretching back thousands of years into the past. The history of electronic musical instruments is short, spanning less than 50 years, but in that time notable accomplishments in artistry, ingenuity, and invention have been made. The future presents an intriguing field for surmise and speculation.
Intonation Errors Due to Discontinuities in the Valve Mechanisms of Trumpets
Authors: Webster J. C.
Published: September 2005

The doubly open-ended resonances of an air-column system were determined. This system contained the valve mechanism of a standard trumpet and various lengths of cylindrical tubing which could be removed. The valve mechanism had a permanent six-inch piece of cylindrical tubing on the side that ordinarily connected to the bell and no such permanent extension on the side that ordinarily connected to the mouthpipe. The resonances were found with the removable pieces of tubing first attached to the bell end and then attached to the mouthpipe end. If the valve mechanism acted purely as an equivalent length of cylindrical tubing the two sets of resonance frequencies would be the same. However, the two sets of frequencies differ in a systematic way as a function of frequency. This indicates that some discontinuity exists that acts differently to pressure nodes and pressure antinodes. Differences as great as 50 cents exist but the more usual difference varies between 0 and 20 cents. This type of test can be used as an inspection technique to spot faulty valve mechanisms before they get made up into a completed trumpet.
Pressure Level Ranges of Various Musical Instruments, and the Effects of Different Rooms on These Instruments
Authors: Sorensen Neil R.
Published: September 2005

The pressure level ranges for the musical notations from ppp to fff were studied for the cornet, the clarinet, the flute, and the violin. The effect upon the sound power produced by the player when in an anechoic chamber, a reverberation room, and a room designed to simulate an average living room was also studied. The results show that the different rooms have little or no effect on the total sound power produced or the extent of the sound level range from ppp to fff. The sound pressure level for an individual instrument was highest in the reverberation room and lowest in the anechoic chamber. Calculations show these differences are mainly the product of the room characteristics. The acoustical power output of the instrument appears to be constant for the different rooms within the observable experimental errors. For the average player the range of levels from ppp to fff is 19 db for the cornet, 13 db for the clarinet, 11 db for the flute, and 19 db for the violin. For a large orchestra and a large chorus these ranges are much larger, sometimes being as much as 60 db.
Vibrating Liquid Surfaces as Generators of Bubbles and Drops
Authors: Willard G. W.
Published: September 2005

Capillary vibrations of a flat liquid surface were studied in 1830 by Faraday, later became known as Faraday crispations, and still later were further analyzed by Lord Rayleigh (well described in his Theory of Sound, Chap. XX). It was known (as a nuisance) that a too vigorous vibration caused drops of liquid to be thrown into the air. It is now discovered that crispations of a flat liquid surface in air may generate a copious supply of minute bubbles of air below the liquid surface, as well as drops of liquid above the surface. The bubble and drop diameters and the half-wavelength of the sonic ripple on the liquid surface are of the same order of magnitude. Further, it is found that a vibrating drop of liquid may throw off smaller droplets into the air and that a vibrating gas bubble in a liquid may throw off smaller bubbles into the liquid. This mechanism of bubble generation is of great significance in the study of sonically induced cavitation in liquids and clarifies some past enigmas. It has been observed at audio-frequencies, at 18 kc, and probably at 2.5 mc. Known frequency formulas have been checked by observing the resonant frequency of bubbles of a range of sizes. Certain combinations of bubble diameter and frequency are especially effective in bubble formation.
Small-Scale Acoustic Streaming Effects in Liquids
Authors: Elder S. A. , Kolb J. , Nyborg W. L.
Published: September 2005

Observations (with low power microscope) have been made on isolated bubbles, forming on an inner wall of a specially devised liquid container, during irradiation with 10 kc sound. In the immediate bubble neighborhood circulatory streaming motions can often be seen. These small scale motions are especially violent if the bubble is of resonant size (about 0.6 mm diameter). It can be demonstrated that certain effects of high-amplitude sound are directly due to such motions. Studies have also been made of the circulation which takes place when a small source of oscillatory flow is situated near a fixed boundary. The vortex pattern set up in this way has been compared with that generated by an oscillating bubble. Theoretical considerations will be presented.
The Dispersion of Ultrasonic Pulse Velocity in Cylindrical Rods
Authors: Tu L. Y. , Brennan J. N. , Sauer J. A.
Published: September 2005

Velocity dispersion of compressional stress waves in cylindrical rods of 61S-T6 aluminum alloy has been investigated experimentally. Electronically generated pulses of the desired shape and carrier frequency were used to drive the barium titanate and quartz transducers. Both the pulse echo and pulse transmission methods were employed. It was found that the group velocity depends strongly on the ratio of a, the radius of the specimen, to λ, the wavelength of the stress disturbance, when the value of a/λ is less than 2.5. For instance, in the neighborhood of a/λ equal to unity, the group velocity approaches that of Rayleigh surface waves which is 0.95 times that of the shear wave velocity when Poisson's ratio equals 0.29. As a/λ is increased, the group velocity also increases and approaches the bulk velocity as a limit. When a/λ is greater than 2.5, the group velocity does not deviate appreciably from the bulk velocity. This dispersion effect disappears when pulsed shear waves are used. The experimental error is estimated to be less than 2 percent.
Transducer Design for Ultrasonic Delay Lines
Authors: McSkimin H. J.
Published: September 2005

The problem of obtaining low loss ultrasonic delay lines for switching, computer, and certain radar applications is discussed. An analysis is made of structures using half-wavelength and quarter-wavelength seals between the transducer and the acoustic medium to widen the pass band; and results are listed for both quartz crystal and barium titanate transducers. It is shown that a theoretical flat band width of approximately 46 percent can be obtained with 80 percent BaTiO3, 12 percent PbTiO3, 8 percent CaTiO3 transducers with less than 1 db loss. This band width can be increased to approximately 70 percent with a flat loss of only 4 db per transducer. Confirming experimental results are described for delay lines using quartz crystals and one-half wavelength plastic seals or one-quarter wavelength solder seals. For the latter, band widths of 85 percent of midband frequency have been obtained.
An Absolute Open Chamber Reciprocity Method for the Calibration of Hydrophones
Authors: Harrison Mark
Published: September 2005

An absolute reciprocity method for the calibration of hydrophones in an open chamber is described. The method is novel since an open chamber rather than a closed chamber is used. The method is absolute since the only quantities that must be known are mass, length, frequency, and electrical resistance which may be directly compared to the fundamental standards. In contrast to the closed chamber methods of calibration, such doubtful quantities as the stiffness of the chamber are eliminated by the set of measurements described. The measurements are performed with two hydrophones in an open column of the appropriate fluid. Only one of the transducers need be reciprocal. An auxiliary sound source is needed for obtaining the relative sensitivities of the two hydrophones. The chamber must be small compared to the wavelength. A method is provided for experimentally validating this condition to a specified accuracy in a given experimental arrangement. Consequently, for a given arrangement and a specified accuracy, an upper frequency limit exists. A lower frequency limit does not exist in principle though it may exist in practice. Typical magnitudes of the significant quantities are given and the pertinent equations are discussed.
Self-Noise of Cylindrical Microphone Windscreens
Authors: Dyer Ira
Published: September 2005

When measurements are made in a moving medium, pressure fluctuations other than sound may exist at the microphone. These pressure fluctuations are commonly referred to as self-noise phenomena. They may be associated with either the turbulent state of the medium, or the disturbance of the medium caused by the microphone, or both. This study is concerned only with the disturbance caused by inserting an obstacle such as a windscreened microphone into an otherwise steady flow. Three finite circular cylindrical windscreens were measured. They were constructed of 14-inch mesh wire covered with silk, and ranged from ten inches to twenty-five inches in length and from one inch to five inches in diameter. The results of the measurements are presented for various values of the medium velocity. These results are compared with experiments on cylindrical windscreens reported by Leonard and Cudworth. All results are empirically correlated in such a manner that it is possible to estimate self-noise of circular cylindrical windscreens as a function of the medium velocity and frequency. (This study was supported in part by a subcontract under a prime contract between Massachusetts Institute of Technology and the Department of the Air Force.)