bluuebunny/crossref_metadata_2025 huggingface dataset:
Underwater-Acoustic-Transmission Measurements
Authors: Whitmarsh David C.
Published: September 2005

The results of underwater-acoustic-transmission measurements carried out in the Key West area during the summer of 1962 are summarized. An absorption coefficient of about 2 dB/kyd was found for a 2-msec-long, 18-kc/sec signal, transmitted at a repetition rate of 1/sec, in 60°–70°F water. It was found that the directly received pulse-amplitude fluctuation varied as the square root of the range. There is also some indication that fluctuation decreases with depth. Surface-reflected pulses show, on the average, a loss of about 1 dB on reflection in a very low sea state; surface-reflected pulses show much greater fluctuation than the direct pulses, and the fluctuation tends to decrease with range.
Deficiencies of the Dynamic Transmission Loss
Authors: Schultz T. J. , Watters B. G.
Published: September 2005

This note presents a brief critique of a recently proposed method for the measurement of airborne transmission loss.
Duality in the Electromechanical-Coupling Factor
Authors: Toulis W. J.
Published: September 2005

Two electromechanical-coupling factors are distinguished in order to account for the behavior of transducers at low frequencies, as well as in the vicinity of mechanical resonance. The existence of the two coupling factors requires that the equivalent circuit be reinterpreted but not revised.
Implosions as Sources of Underwater Sound
Authors: Urick R. J.
Published: September 2005

The sound produced by imploding cavities in the form of glass bottles is described quantitatively. Although the efficiency of energy conversion is found to be very low, the energy generated is sufficient to suggest the usefulness of implosions as safe, cheap, and portable sources of underwater sound.
Amplitude of P-Head Waves
Authors: Donato R. J.
Published: September 2005

An analysis is made of the P-head-wave amplitude to be expected at liquid-liquid and liquid-solid interfaces. The minimum range at which the asymptotic approximation for the range dependence of the head-wave amplitude holds is shown to be smaller for the liquid-liquid than for the liquid-solid case. The range dependence and absolute magnitudes of the head-wave amplitude are determined experimentally by using ultrasonic techniques and are compared with the results obtained from analysis.
Effect of High Sound Levels on the Intelligibility of Speech in Noise
Authors: Pollack Irwin , Pickett J. M.
Published: September 2005

Word intelligibility tests were carried out with earphones at sound levels up to 130 db for several noise and speech spectra. In the absence of masking noise, little change in the intelligibility of isolated monosyllabic words was observed for over-all speech levels up to 130 db. With background noise, however, word intelligibility deteriorates with an increase in over-all level although the speech-to-noise (S/N) ratio was held constant. For the normal speech spectrum and white noise, the deterioration in intelligibility at high levels increases as the S/N ratio is decreased. Control tests demonstrate that the deterioration in intelligibility observed at high levels is not due to distortion in the equipment before the ear. In fact, peak clipping of the mixed signal at moderate sound levels produce less loss in intelligibility (as a function of decibels of peak clipping) than simply increasing the over-all sound level of the unclipped signal above a critical level.
Scattering of Sound by Isotropic Turbulence of Large Reynolds Number
Authors: Ford G. W. , Meecham W. C.
Published: September 2005

Lighthill has given an expression for the intensity of acoustic radiation scattered from turbulent fluids. He finds that such scattered energy is proportional to the square of the Mach number of the turbulence and is also proportional to the value of the energy spectrum function at wave number equal to the magnitude of the change in the wave vector during the scattering. If it is supposed that the turbulent region has a Reynolds number sufficiently large to give rise to an inertial subrange, one can obtain information concerning the spectrum of the scattered radiation. The result is that the scattered spectrum centers about the incident frequency, as expected. The height of the spectrum at the incident frequency is proportional to the Mach number and is a complicated function of the scattering angle. The width of the peak is proportional to the Mach number of the turbulence, as could be expected since the frequency spread is the result of Doppler effects within the turbulence. Furthermore, the width is proportional to the 23 power of the incident frequency and to sin11 (12Θ), where Θ is the scattering angle. These last results follow from the assumption of the inertial subrange.
Nonlinear Response of a Circular Membrane to Sinusoidal Acoustic Excitation
Authors: Chobotov V. A. , Binder R. C.
Published: September 2005

The exact nonlinear differential equations of motion for free symmetric vibration of a circular membrane have been derived and solved, approximately, by a perturbation procedure and the Ritz-Galerkin technique. The resulting Duffing equation with a hardening-spring characteristic for the fundamental mode of the membrane was solved for the ratio of the nonlinear to linear period of free vibration. Theoretical expressions for air virtual mass, damping, and the nonlinear spring stiffness were used to obtain an approximate solution to sinusoidal excitation of the membrane. The results from an experimental program for sinusoidal acoustic excitation of a nonlinear circular membrane have been presented. Construction of the membrane fixtures and a capacitance-type transducer used for transient- and frequency-response displacement measurements on several Mylar and aluminum membranes is described. Experimental data on the air virtual mass, frequency response at various ambient air pressures, dynamic mode shape, and damping are shown. The theoretically derived “backbone” curves of the Duffing-equation frequency response appeared to be in very good agreement with the experimental data. The damping was found to be nonlinear, with some indications of being nonviscous as well.
Comparison of the Take-Off Noise Characteristics of the Caravelle Jet Airliner and of Conventional Propeller-Driven Airliners
Authors: Miller Laymon N. , Beranek Leo L.
Published: September 2005

This paper presents comparative noise data obtained during recent tests on the French Caravelle twin-jet airliner and on large propeller-driven airliners in measurements at Orly Airport in Paris and at New York International Airport at Idlewild. Data are analyzed in terms of noise levels, spectrum content, and noise duration for several take-offs over measurement positions located at points corresponding to residential areas near present-day airfields. [This work was sponsored by the Port of New York Authority.]
Nonstationary Shot Noise
Authors: Lin Y. K.
Published: September 2005

This paper introduces the concept of a nonstationary shot noise, which may be viewed as Poisson-distributed impulses with varying impulse strength. The response of a linear system to the excitation of a nonstationary shot noise is then determined by using the method of Fokker-Planck. The more general result obtained here is reducible to the known solution associated with stationary excitation.
Normal Mode Vibrations of Systems of Elastically Connected Parallel Bars
Authors: Seelig J. M. , Hoppmann W. H.
Published: September 2005

This paper presents the development and solution of the differential equations of motion of a system of n elastically connected parallel beams. Using the results developed for the general n-beam system, the particular case of a two-beam system was analyzed in detail. The frequencies and associated mode shapes for various support conditions are presented explicitly. Vibration experiments were performed to ascertain the degree of applicability of the theory. It was found that at least up to the eighth mode reasonably good agreement obtains.
Interaction Radiation Resistance for a Line Array of Two and Three Magnetostrictive-Stack Transducers at an Air-Water Surface
Authors: Stumpf F. B.
Published: September 2005

The interaction radiation resistance for a line array of two and three hairpin-type, nickel, magnetostrictive-stack transducers at an air-water surface was measured. The transducers are resonant near 20 kc/sec and have square radiating faces whose sides are 0.38 of the wavelength of sound in water. The interaction, radiation resistance was studied as a function of number, separation, driving force, and phase of the interacting transducers. The circuit used to measure the radiation resistance is discussed, and the graphs of the interaction radiation resistance with transducer separation for several conditions are presented. It is shown that it is possible to have a transducer behave as a sink if the nearby transducers are different enough in driving force and phase.
Normal Vibration Frequencies of a Stiff Piano String
Authors: Fletcher Harvey
Published: September 2005

This paper deals with the normal modes of vibration of a stiff piano string. The equations that govern the vibration of a solid string are developed along traditional lines. They are modified to apply to strings having a solid-steel core upon which are wrapped one or two copper windings. The bass strings of most pianos are made this way. Two boundary conditions are considered: namely, (1) pinned by sharp knife edges at both ends and (2) clamped at both ends. Formulas for the partial frequencies for both of these conditions are developed. The partial frequencies that are calculated by these formulas are compared to the experimental values obtained on an upright Hamilton piano. The experimental values appear to agree somewhat better with the pinned boundary condition rather than the clamped boundary condition, although the differences are not much greater than the observational error. It was found that the formula fn = nf1[(1 plus; Bn2)/(1 + B)]12 gives values of the partial frequencies that agree with the experimental ones where n is the number of the partial, f the fundamental frequency, and B a constant that can be calculated from the dimensions of the wire.
Kramers-Kronig or Dispersion Relations in Acoustics
Authors: Mangulis Visvaldis
Published: September 2005

It is shown that one can find the radiation reactance if the radiation resistance is known at all frequencies, and vice versa.
Relation between the Radiation Impedance, Pressure in the Far Field, and Baffle Impedance
Authors: Mangulis Visvaldis
Published: September 2005

It is shown that for an arbitrary-shape rigid piston in an infinite planar baffle, on which the boundary condition is (pressure) = (normal velocity) × (acoustic impedance of baffle), the radiation impedance of the piston, the baffle impedance, and the pressure amplitude in the far field, normal to the piston, are simply related.
Comments on “Preliminary Investigation of the Equivalence of Acoustically and Mechanically Induced Vibrations” by L. Marin and R. C. Kroeger
Authors: Wang Paul
Published: September 2005

In a recent paper, Marin and Kroeger presented some test data comparing the responses of simple cantilever beams under an acoustical-pressure field and under mechanically induced vibratory motions. This discussion offers some additional analyses intended to fulfill the objectives sought by the aforementioned authors. It is observed that proper correlations are indeed obtainable.
Long-Range Multiple Arrivals Received at Deep Hydrophones from Shots in the Gulf of Maine
Authors: Northrop John , Tyson Loring E. , Ransone Morris A.
Published: September 2005

Shots of 1000, 2000, and 3000 lb of TNT, detonated on the bottom of the 150-f (fathom) Northeast Trough of the Gulf of Maine, were monitored at deep hydrophone locations on the continental slope off the United States of America, Bermuda, and the Antilles. Four types of arrivals were received from these shots: (1) ground arrivals, which were received at distances up to 250 miles from the shot; (2) direct arrivals that traveled along great circle, all-water paths to receivers up to 1800 miles away; (3) indirect arrivals that traveled down the Northeast Trough and thence to the receivers; and (4) reflections from seamounts that lie off the mouth of the Northeast Trough.
Normal-Mode Sound Propagation in Shallow Water
Authors: Bucker H. P.
Published: September 2005

An extension of the normal mode dispersion equation is developed that applies to a variable velocity water layer lying over an absorbing bottom. The effect of bottom absorption on the shape of group-velocity-vs-frequency curves (mode curves) is examined for a special case, showing that there will be no frequency of minimum group velocity (Airy frequency) if the bottom absorption is sufficiently large. A high-frequency cutoff of the mode curves is predicted as the normal consequence of a velocity structure in the water layer. Calculated mode curves are shown to be in good agreement with experimental curves obtained in a shallow-water area of the Bering Sea.
Single-Number Criteria for Room Noise
Authors: Young Robert W.
Published: September 2005

Subjective noise ratings by executive office personnel, reported at the time that the NC curves were introduced [L. L. Beranek, J. Acoust. Soc. Am. 28, 833–852 (1956)], have been correlated with various physical measures derived from the 17 noise spectra originally published. The rank-order correlation coefficients (in parentheses) for the respective physical measures are: A-sound level (0.96), B-sound level (0.96), NC level (0.95), NCA level (0.95), N level per ISO proposal (0.96), speech-interference level (0.86), speech-interference level based on the three octave-band levels from 300 to 2400 cps (0.91), calculated loudness level (0.96), perceived-noise level (0.96), 40-noy-weighted sound level (0.95). With only one exception each, loudness level and perceived-noise level for the 17 airbase office noises are 13±1 dB greater than the A-sound level. Some type noise spectra of various shapes are provided, along with an auxiliary table, to facilitate estimation of the several physical measures simply by curve-matching. Since subjective ratings of office noise appear to be correlated with the A-sound level as well or better than with other commonly known noise ratings, and since the A-sound level can be measured readily with widely available meters, it is recommended as a replacement for the NC level in single-number specifications for office noise.
Dual-Frequency Ultrasonic Pulse-Echo Testing
Authors: Gericke Otto R.
Published: September 2005

The problem of defect-size determination by means of ultrasonic pulse-echo testing and the benefits accrued from the utilization of a system that permits simultaneous testing at two different frequencies are discussed. The design of a dual-frequency pulse-echo test system employing only a single ultrasonic transducer is described, and its usefulness is examined for discriminating between disklike discontinuities (flat-bottom holes) of various diameters. In addition, experiments are described that indicate that the frequency dependence of ultrasonic-energy losses and the longitudinal-wave velocities in materials can be determined faster and with a higher degree of reliability by dual-frequency testing than by conventional methods. Also reported is an experimental investigation of the frequency dependence of transducer coupling in contact testing involving interposed layers of liquid couplant.
Successive Diffraction Theory for Diffraction of Light by Ultrasonic Waves of Arbitrary Waveform
Authors: Hargrove L. E.
Published: September 2005

A theory is developed for the diffraction of light by arbitrary, periodic, ultrasonic plane waves of sufficiently high frequency, large amplitude, and/or beamwidth that significant refraction of light occurs within the ultrasonic beam and that the Raman-Nath approach is no longer applicable. Under such conditions, the emerging-light wavefront is significantly amplitude-modulated in addition to the phase-modulation considered in the Raman-Nath approach. The final diffraction spectrum is considered to result from N successive diffractions by N adjacent sections of the ultrasonic beam. The results are expressed in a form suitable for computation by iterations using a high-speed computer.
Speed of Sound in Four Primary Alcohols as a Function of Temperature and Pressure
Authors: Wilson Wayne , Bradley David
Published: September 2005

Sound velocities have been measured in methyl, ethyl, n-propyl, and n-butyl alcohol for temperatures and pressures in the ranges 0°C < T < 60°C and 14.7 lb/in2 < P < 14000 lb/in2. The data obtained for ethyl alcohol have been used to compute the ratio of specific heats for this alcohol.
Elastic Vibrations of Paraboloidal Shells of Revolution
Authors: Hoppmann W. H. , Cohen M. I. , Kunukkasseril V. X.
Published: September 2005

This paper presents a discussion of the theory of vibration of a paraboloidal shell of revolution. The theory is that usually associated with the work of A. E. H. Love. Observations are made concerning the equations of motion that include both flexural and membrane stresses, those that relate to flexural and membrane stresses for shallow shells, and finally those that apply to membrane stresses only. Results are also presented for an extensive experimental study of the vibrations of two models of thin paraboloidal shells.
Dilatationless Circumferential Modes of Vibration of a Ring
Authors: Liu C. K. , Langhaar H. L.
Published: September 2005

A circular elastic ring or a segment of such a ring may vibrate linearly in a dilatationless natural mode, such that the particles oscillate normal to the cross sections and the deformations of all cross sections are identical. Circumferential modes of a solid disk or a sector of such a disk constitute a limiting case. This type of motion was discovered by L. Pochhammer, who observed that nontorsional circumferential modes of vibration can exist in a solid circular cylindrical bar. He also studied dilatationless longitudinal modes of vibration of a circular cylindrical bar, which may be regarded as circumferential modes for a torus of infinite radius. Pockhammer did not note that the modes that he discussed can occur in rings and prismatic bars. Each shape of cross section presents a boundary-value problem, since the lateral surface must be free of stress.
Experimental Study of Dilatational- versus Distortional-Straining Action in Material-Damping Production
Authors: Mentel T. J. , Chi S. H.
Published: September 2005

It has been conjectured that damping effects due to dilatational straining, small enough to be masked by experimental scatter in the usual test setups, might be significant under conditions of pronounced dilatational straining such as can occur in plate vibrations. For this purpose, a special machine was constructed to measure material damping in thin-walled, cylindrical specimens subject to combined internal pressure and and axial cyclic loading. Tests were carried out on a number of manganese-copper alloy specimens for which the usual uniaxial, cyclic-stress, damping properties had already been established (and published). The new tests extended the ratio of dilatational- to distortional-strain energies from the fraction that occurs under uniaxial stress up to the maximum factor of about 2/3, which is possible under biaxial stress. The results display a small but definite contribution to the material damping by the dilatational-straining action. As a consequence, a modified formula is suggested for the specification of material damping in plate vibrations.
Rheological-Model Concept
Authors: Sperry William C.
Published: September 2005

The theory of rheological models considers series and parallel combinations of lumped elements that are assumed to behave mechanically like the constituent phases of a material, but that, apart from this mechanical behavior, have nothing in common with the real medium. Usually, the elements are elastic springs, viscous dashpots, and dry-friction bodies. The behavior of real materials can be described only approximately by models. However, in principle, any degree of approximation can be achieved by an indefinite number of model elements. Models subjected to impressed harmonic forces are represented by complex constants that, for linear models, are mechanical impedances, dependent upon frequency, with the element characteristics as parameters. Nonlinear models result from the inclusion of dry-friction bodies that are approximated by viscous dashpots that absorb the same energy per cycle. For these cases, the model constants are again defined as mechanical impedances but differ from those for linear models in the sense that they are dependent upon driving-force amplitude as well as frequency. The use of a generalized model constant gives generality to equations of motion and adds no complications to the mathematics. Applications can be made for lumped and continuous media, both solid and fluid. For generalized forces, models are represented by real-time-dependent operators.
Plate Damping due to Thickness Deformations in Attached Viscoelastic Layers
Authors: Ungar Eric E. , Kerwin Edward M.
Published: September 2005

Energy dissipation due to thicknesswise motion of viscoelastic layers attached to plates is analyzed in order to supplement previous analyses of damping due to shear, flexural, and in-plane extensional motions. It is shown that the thicknesswise motion may constitute an important damping mechanism for relatively soft and thick viscoelastic layers at frequencies corresponding to standing-wave resonances in the damping layer. The general behavior of thickness-compression damping layers is discussed on the basis of a relatively simple analysis, and reasonable agreement between theory and experimental results is demonstrated.
Backward Masking: Different Durations of the Masking Stimulus
Authors: Elliott Lois L.
Published: September 2005

No differences were obtained in the backward masking produced by masking stimulus durations of 25, 50, and 100 msec for either monotic or dichotic masking.
Symmetry of Energy-Transfer Ratios for Elastic Waves at a Boundary between Two Media
Authors: Kühn G. J.
Published: September 2005

A proof is presented that the energy-transfer ratios of the various elastic-wave modes reflected and transmitted at a plane boundary between two media are symmetrical and equal to the product of the forward- and backward-reflection coefficients. This relationship is shown to hold for several types of lossless boundary conditions at a solid-solid interface.
Generation and Reception of Elastic Waves via a Plane Boundary
Authors: Lutsch A. , Kühn G. J.
Published: September 2005

The generation and reception of ultrasonic waves are discussed with the aim to improve existing wedge-type angle probes used for nondestructive testing. A number of wedge materials are discussed, and it is shown that constructions using separate transducers for the generation of shear waves and reception of compressional waves in the wedge yield a higher echo-transmission factor, larger signal-to-noise ratio, and a larger monitor signal than constructions using one transducer only.
New Method for Calculating the Vibration Frequencies and Mode Shapes for Inhomogeneous Beams
Authors: Greensite A. L.
Published: September 2005

A method is developed whereby the natural frequencies of a nonuniform beam may be determined in a relatively straightforward manner. The novelty of the present approach stems from the fact that dynamic programming techniques are employed to eliminate the need for an initial guess as to modeshape (Rayleigh-Ritz) or frequency (Myklestad). The basic scheme herein developed may be applied with minor modification to a wide class of elasticity problems that can be formulated in terms of minimization of an energy integral.
Longitudinal Vibration of Internally Damped Rods
Authors: Snowdon J. C.
Published: September 2005

The response to sinusoidal vibration of single and coupled systems of internally damped rods has been determined theoretically. Analysis of the vibration of uniform and exponentially tapered rods has usually been simplified by the assumption that the lateral dimensions of the rods are small in comparison with the wavelength. In one example, however, the vibration of a uniform rod of significant lateral dimensions has been determined from an approximate theory given by Love, in which a lateral-inertia correction is introduced. In the Love theory, the vibration of the rod is governed by both the Young's modulus and the shear modulus of the rod material and by the damping factors that are associated with these moduli.
Electrical Responses of the Auditory System to Different Types of Transient Stimuli
Authors: de Boer E.
Published: September 2005

In physiological experiments on the cat's auditory system clicks have often been used because of their ability to produce synchronized neural firings. In this study the class of impulsive stimuli has been extended. The electrical signals fed to the earphone are close approximations to members of the family of singularity functions. In the present experiments doublets, impulses, step, and ramp functions have been used. Each of these functions is the time integral of the previous one, with a conversion factor involving the time dimension. The actual wave form of the acoustic stimulus at the animal's eardrum could not be observed. The above-mentioned integral relation, however, holds for what may be thought of as the linear part of the system. As a typical result, it has been found that the peripheral neural response, N1, to the step is equal to that of the pulse provided the pulse has the same height as the step, and a length of 20 μsec. This holds over a fairly large range of amplitudes (20–40 db). Similar results have been found for the other signals. Preliminary results will also be reported with respect to both microphonic and cortical responses to the above-mentioned stimuli. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Harmonic Distortion in Cochlear Models
Authors: Tonndorf Juergen
Published: September 2005

The envelope over the train of waves traveling along the cochlear partition is asymmetrical: the distal slope being steeper than the proximal one [G. von Békésy, J. Acoust. Soc. Am. 19, 452 (1947)]. In experiments on models, this asymmetry was seen to increase with intensity. Since the mean revolving velocity of Békésy's “eddies” also varies with intensity, artificial “eddies” were introduced into the model while the intensity remained constant. Thereby the asymmetry of the envelope was also increased. Propulsion of the “perilymphatic” fluids by the “eddies” converts particle motion (ordinarily in closed orbits) [Juergen Tonndorf, J. Acoust. Soc. Am. 5, 558 (1957)] into cycloids. As the eddies accelerate along the partition (see the paper by Tonndorf), the cycloids expand with distance, its velocity attaining a sawtooth-like pattern. The asymmetry of the envelope can be explained satisfactorily by the combined effect upon the partition of the distorted cycloids in both “perilymphatic scalae.” However, the same theoretical considerations lead to asymmetry of the displacement pattern of the partition and to an effect similar to peak clipping, both of which increase with distance. This distorted displacement pattern in the distal region of the partition in turn affects particle motion in the adjacent fluids, whence the distortion is propagated proximally by the eddies to be resolved in the usual way (see the paper by Tonndorf) along the cochlear partition. [This research was supported in whole or in part by the U. S. Air Force, under Contract No. AF-41 (657)148, monitored by the School of Aviation Medicine, UASF, Randolph Air Force Base, Texas.]
Endolymphatic Oxygen Tension in the Cochlea of the Guinea Pig
Authors: Misrahy George , Hildreth K. , Shinabarger E. W. , Clark L. , Rice E.
Published: September 2005

Oxygen tension of the endolymph in the scala media of the guinea pig cochlea was measured using a micropolarographic technique. Near the stria vascularis, the oxygen tension was 55–75 mm Hg. Deeper in the scala media it decreased gradually to 16–25 mm Hg. Following sound the oxygen tension fell below normal with very gradual recovery. Breathing pure nitrogen reduced the oxygen tension rapidly. On rebreathing air it usually returned to normal as rapidly overshooting for one or two minutes. If recovery from anoxia was slow no overshoot occurred. Breathing 10% carbon dioxide in air increased the oxygen tension more than pure oxygen. On return to normal air the oxygen tension fell back to normal or slightly below if the animal had previously breathed pure oxygen.
Reciprocal of the Mean Free Path
Authors: Batchelder Laurence
Published: September 2005

The geometry of a rectangular enclosure is examined from the viewpoint of the absorption of reverberant energy. For diffuse sound, the significant quantity is not what is implied by the term mean free path but rather the mean reciprocal of the pathlengths. For particular modes, the reciprocal of the pathlengths can vary widely from its mean value and introduce a corresponding uncertainty in the relation of decay rate to absorption coefficient. Although no simple expressions have been found for enclosures of general shape, the range of variation from mode to mode seems to be nearly as great as for rectangular enclosures. This paper was written independently of a related one by F. V. Hunt [J. Acoust. Soc. Am. 36, 556-564 (1964)] and their simultaneous appearance is purely a coincidence. Hunt's paper is concerned primarily with reconciling the various formulations of the mean free path, whereas this paper stresses the variation of mean free path and the inversely related collision frequency for isolated normal modes.
Dynamic Force Measuring System for Machinery Vibration Measurements
Authors: Barraclough T. W. , Collier R. D.
Published: September 2005

The system consists of four piezoelectric force gauges, which are installed under machinery feet and are terminated in a large siesmic mass. Individual force gauges are designed to measure the vibratory forces applied normal to the piezoelectric elements. The instantaneous voltage developed is directly proportional to the instantaneous applied vibratory force. The outputs from the (four) force gauges are fed through a set of four cathode followers where the outputs are combined in two ways: (1) as a phasor sum to provide a single vertical force measurement, (2) adding the outputs of two gauges, subtracting the outputs of the other two gauges and introducing electrical equivalent moment arms, to provide torque measurements about the axis through the center of gravity of the machine. These fundamental measurements are based on force and torque equations developed from the six motions of an assumed rigid body. At the fundamental frequency the vertical force measurement, Fy, is a measure of static unbalance and the torque measurement, Tz, is primarily that of dynamic unbalance. Confirming experiments have been performed. The response of the system is 10–2000 cps calibrated within ±5%. The system is used to balance assembled machinery and to select quiet machines based on discrete frequency analyses.
Note on Binaural Masking-Level Differences at High Frequencies
Authors: Durlach N. I.
Published: September 2005

A quantitative “black-box” model is developed for use in interpreting certain data on binaural masking-level differences at high frequencies. The basic idea of this model is that these differences are the result of variations in the extent to which the envelopes of the signals presented to the two ears of the listener are unequal.
Shake Table for Calibration of Velocity Pickups
Authors: Wescott J. W. , Prout J. H. , Follett W. H.
Published: September 2005

A Shake Table was developed and built by the Engineering Research Institute to calibrate low-frequency (0 to 200 cps) velocity pickups. The platform that supports the pickup to be tested is 6 in. in diameter and will support a load of approximately 30 lb. This makes the use of a table limited by force it can deliver except at very low frequencies. The table will operate with a 10 lb load to a frequency of 150 cps. The platform displacement is 0.125 in. peak-to-peak. The platform and its load are supported by air bellows. This is an improvement over a spring support due to the fact that it has greater damping and it is more easily adjusted to different loads. The adjustment consists of just putting more air in the bellows. The table is driven by a dc push-pull power amplifier. This delivers a current to a tapped coil on the Shake Table that is located in a magnetic field. The field is set up by a coil energized by 24 volts. The power amplifier can be driven by any convenient source delivering about 1 volt. (Parts of this research were supported by Tri-service Contract No. DA-36-039-sc-52654.)
Noise Control Treatment for a 15-Passenger Commercial Helicopter
Authors: Miller Laymon N. , Beranek Leo L. , Sternfeld Harry
Published: September 2005

In 1955 a noise measurement and noise reduction study was carried out on a military model H-21 helicopter. Based on this study, two commercial versions of this helicopter were constructed early in 1957 by the Vertol Aircraft Corporation for the French Government for use in the recent International Air Exposition in Paris. This paper presents the noise control treatments contained in the commercial helicopters and compares inside noise levels before and after the treatment. The noise reduction achieved by the treatment in the passenger cabin averages approximately 5 db in the low-frequency octave bands and 20–25 db in the high-frequency octave bands. The resulting noise levels inside the completed helicopters are comparable to those of commercial fixed-wing airliners.
Ultrasonic Attenuation and Velocity in Heavy Water Vapor
Authors: Law A. , Lindsay R. B.
Published: September 2005

The velocity and attenuation of 66-kcps sound have been measured in D2O vapor over the temperature range from 32° to 140°C at pressures somewhat below atmospheric. The relaxation contribution to the attenuation in D2O vapor is found to be approximately 2.2 times that in H2O over the temperature range studied.
Hydrodynamic Stability of the Jet-Edge Whistle
Authors: Lyon Richard H.
Published: September 2005

This paper deals with the ability of present day knowledge of hydro-dynamic stability to predict the onset of oscillation in a jet-edge whistle. Neutral stability curves for the free jet and the thin plate will be studied for their relation to this problem One finds that no immediate or obvious connection exists between the frequencies produced in these systems and the frequencies produced in the whistle when the jet and plate are combined. A series of experiments are described which lead to an experimentally determined neutral stability curve for the jet-edge whistle. These experiments indicate a strong destabilizing influence of the edge on the jet flow. A discussion of the physical basis of this destabilizing effect follows. (This work has been sponsored by a grant-in-aid from the Graduate School of the University of Minnesota.)
Energy Balance in Acoustic Streaming
Authors: Westervelt Peter J.
Published: September 2005

The power required to maintain the Eckart type of acoustic streaming is calculated and found to be of sufficient magnitude to contribute measureably to the attenuation of large amplitude sound waves. A second problem has also been solved. When sound interacts with objects, streaming occurs due to the vorticity sources localized near the surface of the objects. An energy theorem is proved which is valid for objects small compared with the wavelength of sound and which enables the energy dissipated by the streaming motion to be expressed entirely in terms of the first-order oscillatory motion thus obviating the need for calculating the second-order streaming motion. [Work supported jointly by the U. S. Air Force (Wright Air Development Command) and the Office of Naval Research.]
Sound Transmission through Thin Plates at Oblique Incidence
Authors: Eichler E. G. , Lambert R. F.
Published: September 2005

Transmission loss measurements of thin, rectangular aluminum plates employing the (0.1) acoustic mode of a wave guide are described. Theoretical transmission loss formulas are derived for the limiting cases of small and large ratios of plate span to plate thickness. In the case of large ratios, a “mass law” formulation is obtained which exhibits an angular dependence characteristic of the (0.1) mode. Almost complete sound transmission predicted for angles of incidence near grazing is verified experimentally for all plates studied. Some discrepancies between theory and experiment for small ratios are discussed and an attempt is made to empirically correct the calculations. These discrepancies are here attributed to imprefect boundary clamping and internal plate dissipation.
Collective Sound Mode in a Two-Component Fluid
Authors: Liboff Richard L.
Published: September 2005

Starting with two Boltzmann-like equations, a kinetic theory is made of the long-wavelength disturbances that propagate in a two-component neutral fluid. A transition is observed from separate adiabatic sound speeds for each gas in the case of weak coupling to the single adiabatic sound speed of the gas mixture plus strongly damped relative motion in the opposite extreme of strong coupling between the gases.
Plant Resonance of Seismometers
Authors: Willis David E. , Wilson J. T.
Published: September 2005

A seismometer resting on an elastic medium can be regarded as a simple damped oscillator. Methods for measuring the “plant” resonance of seismometers are discussed along with the various parameters affecting the resonance. Laboratory measurements on sand and rubber, and field measurements on different types of soils were made using an electromechanical oscillator to generate elastic waves. The results are tabulated and the correlations with resonances observed in machine foundations are discussed.
Seismic Level Recorder
Authors: Bugalski H. J. , Johnson J. C.
Published: September 2005

The seismic level recorder is a sensitive recording ac vacuum tube voltmeter. The prime intention in the design of this recorder was to provide a portable level data system which could be left operating unattended for long periods of time. The seismic level recorder incorporates a high gain seismic amplifier connected to a peak-to-peak rectifier whose output is fed through a logarithmic driver to an Esterline-Angus ink recorder. The frequency response is 1 to 100 cps at the 6 db points. Provisions have been made for plugin 12 db octave band-pass filters. The calibrated scale covers approximately a 50-db range of signals allowing a wide variety of detectors and signals to be explored. (Parts of this work were supported by Tri-service Contract No. DA-36-039-sc-52654.)
Acoustic Rays in an Ocean with Heat Source or Thermal-Mixing Zone
Authors: Lugt Hans J. , Uginčius Peter
Published: September 2005

The eikonal equation of ray acoustics is discussed for the general case, with the index of refraction a function of the three space coordinates. Two examples illustrating the influences of a two-dimensional heat source and a thermal-mixing zone on the acoustic-ray paths are presented. Numerical results show that, for long-range acoustical ray tracing, inhomogeneities of the ocean in the horizontal plane can cause refraction effects, which are not negligible in comparison with effects due to vertical inhomogeneities. Rays, which travel in the vicinity of a heat source, can be refracted as much as 6°. Thermal-mixing zones can increase the range of shadow zones near the ocean surface up to 50%. Even new shadow zones can be formed.
Clipping and Transmission Methods
Authors: Vilbig Friedrich , Haase Kurt H.
Published: September 2005

Methods and techniques of (1) audioband (AB) clipping, (2) single side band (SSB) clipping, (3) double side band (DSB) clipping, and (4) partial band (PB) clipping both with and without control, will be explained and discussed in relation to distortion, intelligibility, and power gain. Assuming constant power gain, the above methods are arranged in order of increasing understandability and decreasing distortion, provided they are not further distorted during transmission. If the signal is influenced by fading, Doppler effects, or atmospheric disturbances during transmission, the modulation envelope becomes the important factor. For a rectangular modulating signal the resulting envelope will also be rectangular in AB and DSB. It is related to the shape of the modulating signal in SSB and PB but it is no longer rectangular. To suppress transmission distortions, clipping at the receiver can only be used in AB and DSB, for it would introduce additional distortion in SSB and PB. When distortion in transmission is considered, the various methods of clipping will be rank-ordered in a different sequence.
European Experience with Sound-Insulation Requirements
Authors: Brandt Ove
Published: September 2005

Most of the world's major nations, with the exception of the United States of America, have sound-insulation requirements in their building codes. The purpose of this paper is to describe the experience of several European countries with such requirements. Typical procedures in common use are discussed: there are several variations in the basic definition of sound insulation, the method of interpreting test results, and, finally, the method of influencing or controlling building practice. An important consideration is the information to be gained from various possible types of test. Experience indicates the desirability of three stages of testing for a new type of construction: (1) laboratory tests on individual components; (2) tests on a partial assembly of wall and floor sections; and (3) tests on the completed structure. At each stage, problems are usually found that had not been anticipated earlier.
Mathematical Expressions for Speech Sound Spectra
Authors: Haase Kurt , Vilbig Friedrich , Drake Alvin
Published: September 2005

Mathematical expressions, developed for the harmonic line spectrum of vowels and for the noiselike spectrum of consonants, will be shown. In both cases the spectrum content is encircled by the envelope. This is characterized by several peaks which identify the formant or quasi-formant frequencies. The spectrum can be seen as a modulation of these formant frequencies by a properly chosen pitch or noise pulse. The distortions which appear if this approximate sound representation is transformed by a nonlinear device producing square and higher order terms will be investigated and discussed. The distortions can be measured by the harmonic distortion factor. For the same distortion factor the influence of the distortion frequencies may be quite different depending on the energy distribution in the sound spectrum and the coefficients of the nonlinear device. Taking these characteristics into account provides a method for correlating the harmonic distortion factor with understandibility.
Impact-Noise Recommendations for the FHA
Authors: Schultz T. J.
Published: September 2005

Because of increasing complaints of disturbance from impact noise in multifamily dwellings, the Federal Housing Administration plans to include in their Minimum Property Standards some recommendations for the control of this noise. A study of the existing noise codes and several surveys of public reaction to household noise has led to (1) the recommendation of a criterion of acceptability for floor/ceiling constructions in multifamily dwellings; a listing of floor/ceiling structures commonly used in the U S A, classified as to their ability to meet the criterion, and (2) a set of recommendations and suggestions regarding important structural details. This paper gives the results of that study and tells how they were arrived at.
Word Intelligibility of Time Compressed Speech
Authors: Klumpp R. G. , Webster J. C.
Published: September 2005

By sampling, compressing, abutting, storing, and speed reduction, Fairbanks and associates have shown that comprehension is good for: (1) connected speech compressed 50% (0.5) in time, and (2) a single PB list compressed up to 0.15. In 1929, Fletcher and associates using turntable speedup with its attendant frequency distortion found that CV, VC, and CVC syllables dropped rapidly in intelligibility at speedup corresponding to time reductions of 0.8 (down about 30% at 0.7). In one case a complex technique using simple language showed great advantage. In the other case a simple technique showed limited advantage using difficult speech material. In our work on message (simple language) storage schemes, the desirability of obtaining time compressed speech with simple modifications of existing equipment has become evident. Preliminary experimental data show that by using speedup of tape-recorded speech, numbers, and flight phrases can tolerate time compressions of 0.6 without serious loss in intelligibility, and PB words lose only 5% in intelligibility with a time compression of 0.7.
Effect of Monaural Fatigue upon Pitch Matching and Discrimination
Authors: Elliott D. N. , Sheposh J. , Frazier L.
Published: September 2005

Using binaural pitch-matching data, the effect of moderate poststimulatory fatigue upon the ear's “tuning” was determined at several frequencies. In addition, the effect of the fatigue upon pitch discrimination was measured. Upward shifts in pitch were observed at TTS's of 20 dB at both 2800 and 5600 cps; however, the shift at 5600 cps is questionable since it was not statistically significant. From these data, Ruedi's observation that the direction of postfatigue pitch shifts reverses (decreases rather than increases) for frequencies above 4000 cps is questioned. There was limited evidence that fatigue results in poorer pitch discrimination; however, such effects were not marked. Possibly, monaural data would have resulted in more-clearcut effects.
Continuous Analysis Speech Band-Width Compression System
Authors: Bayston T. E. , Campanella S. J.
Published: September 2005

An investigative program conducted at Melpar under U. S. Air Force sponsorship has resulted in the development of a speech band-width compression system capable of transmitting speech within a total band width of 150 cps (as compared with 3000 cps for speech transmission by conventional means). This system consists of an analyzer which extracts from the acoustical speech signal six vocal analog control signals, a suitable transmission link, and a synthesizer which employs the control signals to reproduce the essential features of the original speech. The vocal analog control signals vary slowly in time because of natural physical constraints, and thus require considerable less transmission band width than the original acoustical signal. Articulation tests conducted on the system have resulted in scores of 67% for PB (phonetically balanced) word lists and 88% on Spondee word lists. A breadboard model of this system will be described and tape recordings of processed speech will be presented. [This work was supported by Contract AF33 (600)-3.]