bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation of String Instruments
Authors: Clark Melville , Schwartz Daniel , Feldman William
Published: September 2005

Stroboscopic lights and cameras are utilized to photograph the excitation and motion of piano, violin, and harp strings; high speed pictures of which will be shown. Fingers after plucking harp strings are not hit by the string, the shape of which may be easily computed. The wave character may be easily seen from the persistence of waveshape. Piano hammers hitting wound strings oscillate in the plane of the shank and hammer. The contact time (2–7 msec) is relatively independent of the speed of depression and frequency of the note (C1–C5). The piano action itself works much faster than it could be played. Very slight painting of a wound string greatly damps the sound. Terminal hammer speeds vary from 30 to 600 msec. The bow pulls the string aside without slipping. The return of the previously created pulse, reflected and inverted at the nut, snaps the string away from the bow in 15 of a period. The string deflects an equal and opposite amount before being picked up and replucked by the bow again. (This work was performed in Professor Harold Edgerton's laboratory and was supported by the National Association of Music Merchants.)
Influence of the Reed on the Vibration Frequency of Clarinet Tones
Authors: Backus John
Published: September 2005

The frequency of a clarinet tone is influenced to some extent by the lip pressure on the reed, giving the clarinettist some control over the intonation of the instrument. The resonant frequencies of the instrument measured by external excitation with the reed aperture closed are some 30–50 cents higher than the actual playing frequencies, which in turn can be varied over a range of about 50 cents. A small vibration theory of this effect has been developed based on the observation that for low intensity tones the pressure variation in the air column is practically sinusoidal [J. Acoust. Soc. Am. 32, 1493 (1960)]. A velocity potential appropriate to a vibrating air column with wall damping is assumed and is evaluated to give the required volume flow through a reed aperture whose width is varying sinusoidally with time. The result shows a lowering of frequency from that of a completely closed tube by the fractional amount ωM/2RQ, where Q is that for the clarinet, and M and R are the mass and resistance for volume flow through the average reed aperture. Values of M and R have been calculated theoretically and checked experimentally, with good agreement; these values used in the formula above give results in fair agreement with observed frequency shifts. The existence of a threshold blowing pressure is also explained. (This work was supported by the National Science Foundation.)
Electroacoustic Sensitivity of Pressure-Equalized Spherical and Cylindrical Hydrophones
Authors: Lukman Frank J.
Published: September 2005

A simple method for the prediction of the stiffness-controlled voltage response of a hydrophone configured for deep-sea operation is described. The approach utilizes previous work in this area, enlarged to include the effects of various degrees of decoupling of the acoustic field from the back face of the hydrophone. Two configurations of importance, the spherical and the cylindrical, have been analyzed, and the results presented graphically. For both cases, the equations of equilibrium and the equation of compatibility are solved and evaluated by the use of boundary conditions. These stress equations, thus generated, and the electromechanical constants are then related to yield the voltage/pressure sensitivity equations. The graphs show the effects of thickness to diameter, comparison of the air-backed to the pressure-equalized hydrophone, and the various degrees of decoupling of the acoustic field from the back face of the hydrophone. For all cases, both barium titanate and lead zirconate titanate are considered.
Directivity of Spherical Receiving Arrays
Authors: Anderson Victor C. , Munson John C.
Published: September 2005

Beam pattern and directivity index are computed for spherical volume and spherical-shell distribution of receiving elements. The limiting case of a continuous distribution of elements gives rise to simple closed-form expressions for the beam patterns. Directivity index is obtained by integration of the beam pattern. The side-lobe level of the beam pattern for the solid sphere is appreciably lower than that of the corresponding spherical shell. Comparison of directivity index shows an increasingly superior performance for the solid sphere as the acoustic radius ka becomes large. [This presentation represents results of research sponsored by the Office of Naval Research.]
Application of an Energy-Detector Model with Internal Noise to the Detection of Signals in the Presence of Pedestals at Varying Noise Levels
Authors: Pfafflin Sheila M.
Published: September 2005

An energy-detector model for monaural auditory signal detection which incorporates noise sources assumed to arise within the observer in addition to external noise is described. Its detection performance for 2-interval forced-choice experiments was calculated assuming constant internal noise and noise proportional to the square of the mean detector output. To test its applicability, data from human observers were obtained at noise levels of 60 and 80 dB SPL, for a single ratio of signal energy-to-noise spectral density in combination with various pedestals (sinusoids of equal amplitude present in both stimulus intervals). The pedestals were 90° out of phase with the signal. Results indicated that there was no significant amount of internal noise which is constant for different noise levels, and that the detectability calculated for the model under the assumption of added noise proportional to the square of the mean output of the detector conformed to the data reasonably well. Additional experiments with in-phase pedestals at noise levels 20 and 50 dB apart confirmed the absence of significant constant internal noise, but indicated the need of further modifications of the model to fit the rising portion of the curve, some of which are discussed.
Comments on Temporal Integration of the Ear
Authors: Elliott Lois L.
Published: September 2005

This paper supplements work of Garner, Eisenberg, and Fodor in studying thresholds of pure tones varying in duration among subjects with normal and impaired hearing. A rise-fall time of 1 msec was used for all stimulus durations and frequencies. The change in absolute threshold per log change in tone duration differed among frequencies for normal listeners, with lower frequencies producing larger slopes. For listeners with impaired hearing, the point at which threshold ceased to change with increasing tone duration (i.e., the “critical duration”) occurred at shorter tone durations than among normal listeners. The amount of “threshold shift” for a 3-msec tone (the difference between the threshold for the 3- and the 1000-msec tones) was inversely correlated with the subject's threshold for a 1000-msec tone of the same frequency; correlation coefficients of −0.74 (500 cps), −0.74 (1000 cps), and −0.79 (4000 cps) were obtained when all listeners (normal and impaired hearing) were included. Results are considered in relation to stimulus characteristics and critical-band theory.
In Situ Sound-Speed Measurements aboard the French Bathyscaph ARCHIMEDE at Japan
Authors: Mackenzie K. V.
Published: September 2005

In situ measurements using two Bureau of Standards velocimeters have been obtained on several deep dives. Preliminary results indicate an agreement with previous in situ measurements aboard Bathyscaph TRIESTE to 6000-m depth. Sound speeds are less than Kuwahara below 6000 m. The difference becomes more negative with depth, and reaches a value of −2 m/sec at 9000 m. This is different from the pressure effect predicted by the Wilson equations. Dives will conclude early in August, and a final precision calibration will be made. It is expected that the analysis will be complete by the time of presentation.
Acoustics of the Seattle Center Playhouse
Authors: Towne R. M. , Richards R. L. , Krahl R. B.
Published: September 2005

An 800-seat theater is one of a complex of buildings comprising the recently completed Seattle Center. This paper discusses the original design objectives, and compares the actual programing during the first 6 months of operation with that which was predicted. Data are presented on the measured reverberation times, and on the absorption added by the seating. The absorption per seat is compared with laboratory data on the same chair. Data are also shown on the sound distribution throughout the seating area as a function of frequency and source location. Several problems encountered since the opening, and their methods of solution, are discussed.
Vibration Response of Plate having Joints
Authors: McCormick James R.
Published: September 2005

The inability, at present, of mathematics to describe the vibrations of complex systems, such as loaded plates and plates having joints, requires that more experimental data be made available on the motion of such systems. When enough experimental results are obtained, it seems possible that some type of electromechanical analogy or other method may be used to describe the gross properties of such a system. Measurements have been completed of the velocity distribution along a freely suspended plate up to a frequency of 52 kc. Measurements have also been made of the driving-point velocity and velocity distribution along plates loaded along an edge and plates having welded joints. This report is concerned with results of these measurements and their significance.
Effectiveness of Partial Coverage for Constrained-Layer-Damping Treatments
Authors: Pulgrano Louis J.
Published: September 2005

A new approach to the analysis of constrained-layer-damping treatments has been developed in order to consider the behavior of partial-coverage configurations. The basic damping expressions, which are derived using strain-energy principles, are applicable to one-dimensional deformation of plates that are partially covered by constrained viscoelastic treatments. When specialized to the full coverage cases investigated by earlier authors, the present expressions are found to be in agreement. Considerable attention is given to the effect of symmetric, partial-coverage treatments on the damping of the fundamental mode of simply supported and clamped-ended configurations. Curves which present the damping, for thin treatment applications, as a function of the percent coverage and the shear parameter are included. These curves reveal the unexpected and significant characteristic that, for some values of shear parameter, damping increases rather than decreases as the coverage is reduced. This phenomenon provides verification and increases understanding of some earlier experimental results which showed that, under certain circumstances, cutting the constraining layer at regular intervals improved the performance of constrained-damping treatments.
Effectiveness of “Patches” of Treatment in the Damping of Flexural Waves in Structures
Authors: McQuillin R. J. , Kerwin E. M.
Published: September 2005

Work has been carried out to determine the characteristics of damping of extended vibrating systems by partial coverage, or “patches,” of treatment. The present study has extended earlier work [J. Acoust. Soc. Am. 33, 861(A) (1961)] and has established some criteria for the most effective use of these patches. In particular, the concept of damping efficiency has been used to measure damping effectiveness; thus, the damping of a system (relative to that for full coverage) may be evaluated as the product of the partial-coverage ratio and the efficiency. We have considered a system (beam or plate) having a one-dimensional, standing flexural wave of the form A cos kx. Both free and constrained viscoelastic layers of treatment are discussed. Curves of efficiency vs patch length are presented for constrained-layer patches for various values of shear parameter and loss factor of the viscoelastic material. Also, curves are presented which specify the optimum patch position. Experimental results are also discussed. [Supported by the U. S. Navy, Bureau of Ships Contract NObs 78799.]
Experimental Study of the Vibrations of Solid, Isotropic, Elastic Cylinders
Authors: McMahon G. W.
Published: September 2005

Existing theoretical analyses are inadequate to predict the natural frequencies of vibration of solid, elastic cylinders, particularly when the thickness-to diameter ratio (h/2a) is near unity. An experimental study has been carried out on solid aluminum and steel cylinders having h/2a between 0.1 and 1.25. Nineteen of the graver modes were excited by means of a barium titanate driver loosely coupled to the metal cylinders. Sand patterns and a small vibration probe were used to determine the form of the vibrations. Where possible, the frequencies are compared with the results of existing theoretical work.
Prediction of Pipe-Vibration-Isolator Effectiveness by Mobility-Parameter Methods
Authors: Hixson E. L. , Bohls F. O.
Published: September 2005

In fluid-pumping systems, the pump is a source of acoustic and vibrational noise. The connected piping provides a path that can transmit this noise by longitudinal, transverse, and rotational modes to other structures. To reduce this noise transmission, an isolator is required that tends to prevent motion in each of the modal directions, while providing a path for the liquid and sustaining the system pressures. The effectiveness of such an isolator in a particular installation can be predicted from the mobility parameters of the isolator and the mobilities of the attached piping. Only the longitudinal mode is considered, since no equipment was available for mobility measurements in the other directions. The measured mobility parameters for isolators designed and built at the Defense Research Laboratory are presented, along with driving-point mobility measurements with several piping-system configurations. The calculated motion transmissibility for isolators in particular piping systems is compared with the measured data.
Program to Compute Vocal-Tract Poles and Zeros
Authors: Mathews M. V. , Walker P.
Published: September 2005

A Fortran program is described for computing the poles and zeros of the vocal tract from its shape. The tract is represented as a set of cylindrical sections. Any number of sections may be used. One-dimensional wave propagation is assumed. The mouth and nose are approximated as spherical radiators. The glottis is represented as a volume-velocity source with infinite impedance. Three cases are treated: (1) a single tube excited at the glottis and radiating from the mouth; (2) a branched tube excited at the glottis with one branch for the mouth and one branch for the nose—either nose or mouth or both can radiate, (3) a single tube with excitation at the middle (corresponding to fricatives). The source can be represented either as a pressure- or volume-velocity source. The magnitude of the tract-transfer characteristic is computed as a function of frequency. The numerator and denominator of the transfer characteristic are also obtained separately to put the zeros and poles in evidence. The program is written in Fortran II and can be used on IBM 704, 709, and 7090 machines.
Fluctuations in the Reflectivity of the Ocean Surface
Authors: Brown M. Vertner
Published: September 2005

An experiment was performed in a deep-ocean basin to investigate the reflectivity of the ocean surface. Acoustic pulses were produced at depths ranging from 500 to 3000 ft and received on hydrophones at a variety of depths and horizontal ranges. The pulses were produced by gating 60-msec bursts of sine waves into sources having resonant frequencies of 170, 400, 600, and 1300 cps. Simultaneous measurements of the ocean-surface waves were made with light buoys (Splashniks) which carried accelerometers. The level of the reflected acoustic energy varies markedly from pulse to pulse. Autocorrelation of successive levels yields a power spectrum which resembles that of the ocean waves. Defining fluctuation as the ratio of the standard deviation of ∫ρ2dt to the average value of ∫ρ2dt, we find that fluctuation increases with acoustic frequency, approaching a saturation value of about 100% when the acoustic wavelength is 4 times the product of the rms height of the ocean waves and the cosine of the angle of incidence θ. Below saturation, the fluctuation is proportional to (cos θ)n, where 0.75<n<1.53 and where n decreases with increasing frequency. [Columbia University, Hudson Laboratories Informal Documentation No. 5. This work was supported by the Office of Naval Research.]
Effects of Surface Reflection on Low-Frequency Acoustic Pulses
Authors: Nichols Rudolph H.
Published: September 2005

A continuing series of measurements is being made several times each week to investigate the effects of surface reflection on low-frequency sound pulses. A high-power, bottomed sound source and 4 bottomed hydrophones at distances of 7–16 miles are used. All the instruments lie in water 2200–2300 fathoms deep in open ocean. A set of 50–100 pulses of sinusoidal signals at a given frequency and with a given pulse length is transmitted with a repetition rate of about 2 per minute. A number of such sets with various frequencies and pulse lengths constitutes a sample for a particular day. The frequencies used range from 100–2000 cps, and pulse lengths of 0.1–10 sec are employed. Measurements are made several times a week, the times being chosen to correspond to a variety of weather conditions and sea states. The effects of surface reflection on the pulse amplitude and shape, and the relations of these effects to pulse length, frequency, sea-surface conditions, and angle of reflection are discussed. [This work was supported by the Bureau of Ships.]
Causes and Implications of Instability of Individual Acoustic Paths in the Ocean
Authors: Tyrrell Warren A.
Published: September 2005

The sample data of the preceding paper (H8) indicate that long-range underwater transmission may have, at least sometimes, an inherent long-term instability of coherence. The fluctuations must be explained in terms either of changing conditions at the air-water interface or of changes in the velocity structure. From the frequency spectrum of the coherence instability, it does not appear likely that the former factor can be important. Ray calculations have been made to explore the effect of differential changes in velocity structure. Results are presented showing how the geometry of individual ray paths can be altered by small changes in certain of the oceanographic variables. The interest here is to appraise the influence of fluctuations in the physical state of the ocean, rather than to seek underlying causes as to why the ocean behaves the way it does. Regardless of our ability to understand and to interpret coherence fading, there is no doubt that it may exert a major influence on underwater acoustic systems involving long paths. Some hypothetical illustrations are given of possible degradation in system performance introduced by fluctuations in coherence. [This work was supported by the Office of Naval Research.]
Variations in Long-Range Sound Transmission in Deep Water
Authors: Young Harold J.
Published: September 2005

A program of low-frequency underwater sound-transmission tests using a fixed source at Eleuthera, Bahamas, and fixed hydrophones at Bermuda has been conducted for about a year. The signals received at Bermuda have a characteristic pattern of amplitude variation, with both short-period and long-period components. The short-period component has a spectrum of variation rates which is strongest around 0.12 cps. The long-period component varies at a rate of a few cycles per hour. The work reported here is concerned mainly with the short-period instability. One-hour samples of the signal received at Bermuda have been selected to include as wide a range of sea states and wind velocities as possible and to be distributed through the seasons. For each sample. the spectrum of short-period variation rates has been computed and the distribution of received levels tabulated. The characteristics of the samples have been examined for correlation with sea conditions at the transmitting and receiving ends of the transmission path. [This work was supported by the Office of Naval Research.]
Mechanical Shocks Produced on Hearing-Aid Transducers
Authors: Burkhard M. D.
Published: September 2005

When a hearing aid is dropped accidentally, damage may occur to the external plastic housing, any of the circuit elements contained within it. lead wires, transducers, etc. The shock amplitudes to which microphones and receivers (earphones) may be subjected in representative eyeglass and behind-the-ear hearing aids under such conditions have been measured by a simulated drop test. The peak shock amplitudes in selected orientations were unexpectedly high, ranging up to 7000 G in one hearing aid for the equivalent of a 30-in. drop on a hard floor. The lower peak acceleration for a 30-in. drop in the same orientation was the order of 100 G. The median value of peak shock amplitude for hearing aids measured was 2500 G for these conditions. Time durations of the impact pulses ranged from 96 to 335 μsec at the half-amplitude points for the simulated 30-in. drop. Representative data are given for simulated 15- and 30-in. drops from several impact directions. It is apparent from these observations that provision of satisfactory protection for shock in dropped instruments, while maintaining a degree of vibration isolation, presents a severe design problem to the hearing-aid engineer. A miniature ceramic accelerometer, which duplicated in weight and external geometry the transducer in the hearing aid, was mounted in the same way as the replaced transducer. The hearing aids were struck from 3 directions related to the position and orientation of the transducer in the hearing aid by a pendulum having mass appreciably greater than the hearing aid.
Self-Biased Condenser Microphones with High Capacitance
Authors: Sessler G. M. , West J. E.
Published: September 2005

A special condenser microphone with solid dielectric between the electrodes is described. The system employs metallized dielectric foil (14 mil thick) which is prepolarized. Therefore, no external dc bias is required. The capacitance of a unit 3.8 cm in diameter is in the order of 800 μμF. This high capacitance eliminates the need of a cathode follower, and allows the use of a long connecting cable. The frequency response of this system is flat within ±3 dB between 50 and 15 000 cps. The sensitivity of the system is −56 dBV for a sound pressure of 1 dyn/cm2 (74 dB SPL). The upper frequency limit and the sensitivity are controlled by the shape of the backplate surface. The self-noise of the microphone is considerably below that of low-noise pre-amplifiers. The upper limit of the dynamic range is set by the harmonic distortion. At 140 dB SPL, the harmonic distortion over the entire frequency range is less than 3%.
Capacitance Detector for Loss Measurements
Authors: Droney Bernard E.
Published: September 2005

A capacitance pickup is applied to loss measurements of rotating mass-loaded rods in the frequency range 0.001–10 cps. Variations of loss and modulus are studied as a function of time and frequency. The same pickup is useful for measuring any specimen where loading by the receiving unit is undesirable. An apparatus which eliminates transducer loading is described for decay or bandwidth measurements of thin film strips at frequencies up to 10 kc. [This work is supported by the Bureau of Naval Weapons and by the U. S. Atomic Energy Commission.]
Use of the Modulation Properties of Periodic Sampling in Digital Spectral Analyses
Authors: Walker Hamilton C.
Published: September 2005

When an analog signal is sampled at a periodic rate, the spectrum of the resultant digital signal will be periodic in frequency with a period equal to the sampling rate. This is commonly referred to as the modulation of folding property of periodic sampling. The experiments discussed in this paper illustrate the use of the folding property of periodic sampling as an aid to efficient digital spectral analyses of narrow-band sonar signals. In sampling an analog signal, the normal procedure is to select a sampling frequency equal to twice the highest frequency present. However, for a narrow-band signal, this procedure can result in inefficient analysis. An alternate sampling procedure, which has been discussed in the literature, is to use the signal bandwidth as the criteria for selection of the sampling frequency. Using the signal bandwidth and the folding properties of sampling as the criteria for selection of the sampling rate results in a significant reduction, for narrow-band signals, in sampling frequency, and, thus, analysis time. The experiments discussed illustrate the use of this technique for a narrow-band signal and for the more complex spectrum introduced by infinitely clipping the input narrow-band signal.
Nonstationary Response of Continuous Structures to Random Loading
Authors: Lin Y. K.
Published: September 2005

Within the framework of the normal-mode approach, a solution is presented for the transient response of an arbitrary continuous structure to stationary forcing fields. No limitation is imposed on the types of forcing correlations considered; therefore, the solution is believed to be more general than those previously reported in the literature. It is shown that, under stationary excitation, the transient response is nonstationary, and that it approaches the stationary solution of Powell in the limit as the time of excitation increases. The general solution may be further simplified, when the forcing field is also homogeneous. As an example of the application of the general theory, a detailed solution is given for a simply supported uniform beam. and the result obtained for such a simple structural model is discussed.
Experimental Characteristics of Noise from Heated Air Jets
Authors: Prindle James H.
Published: September 2005

The noise of heated air jets is found to have characteristics different from the predictions of a theory which assumes moving quadrupole sources. Jet-noise spectra (in octave bands) were measured at selected directions from the jet axis, as well as at different jet velocities. For a fixed direction of radiation, the spectra at different velocities have similar shapes and fit a single curve, if intensity levels are adjusted proportionally to an Nth power of velocity and if frequency is adjusted linearly with velocity. The value N of the velocity power law agrees, for each direction of radiation, with a moving-dipole-source theory. The linear frequency dependence. however, shows no influence of the Doppler shift which is expected for moving sources.
Ultrasonic Attenuation in Polymers as a Function of Temperature
Authors: Lange James N.
Published: September 2005

This study is concerned with determining the attenuation coefficient of various polymers in a frequency range from 1 to 15 Mc and over a wide temperature range. In particular, the attenuation in polystyrene and polyethylene is studied. The results and technique are discussed. [This work was supported by the U. S. Air Force Office of Scientific Research and by the U. S. Atomic Energy Commission.]
Ultrasonic Measurement of Lumen Diameter and Wall Thickness of Arteries
Authors: Sokollu Adnan
Published: September 2005

Ultrasound pulses of very short duration are sent through the skin into the artery to be measured. Echoes from different tissue layers and the artery are detected, amplified, and displayed by a beam of a dual-beam cathode-ray oscilloscope. The artery is identified by observing the beat of wall echoes, and an amplitude-sensitive trigger circuit is put into action. This trigger gets such an adjustment that it starts the high-velocity sweep of the second beam of the CRO with the arrival of the first echo from the near surface of the artery. By this method, the second beam displays only the arterial echoes in a very large scale, allowing a precise measurement of the lumen. A further, higher, sweep speed provides the measurement of wall thickness of the artery down to the micron sensitivity. Echoes from the far side wall of the artery will naturally move in a back-and-forth motion, corresponding to the pulsation of the artery giving an opportunity to elasticity evaluation of it. Percentage of diameter changes combined with the related pressure values in the artery provide the necessary data to compute arterial elasticity. Used frequencies: 10 to 20 Mc: pulse duration: 0.5 μsec; transducer: quartz crystal. Sensitivity in distance measurement down to 1 μ.
Acoustic Measurements in the Finite-Amplitude Beam of a Plane Piston
Authors: Gould R. K. , Smith C. W. , Williams A. O. , Ryan R. P.
Published: September 2005

A plane piston source of radius 1 cm is driven in water at a fundamental frequency of 2.58 Mc. Acoustic excess pressures near the source are 0.2–6 atm. The first, second, and, to some extent, the third, harmonics have been mapped to distances of 40 cm along and across the beam axis. Both a wire probe as described by A. B. Wood [J. Acoust. Soc. Am. 31, 1213 (1959)] and a barium-titanate cylinder 116 in. long and wide have been used, with consistent results. The probes are calibrated by integrating their response across the axis and by comparing with that of a large plane receiver previously calibrated by the reciprocity method. Another check is to compare with established theory the axial response of the receiver at the fundamental frequency and low acoustic pressures (correcting for finite size of the probes). Patterns at higher intensities are complicated and quite different from first to higher harmonics, as expected. Only partial comparisons with theory are feasible. [Work supported in part by the Office of Naval Research and performed at Brown University, where R. K. G. was a visitor for the summer of 1962.]
Sound Reflected from Seamounts in the Bermuda Seamount Chain
Authors: Northrop John , Tyson Loring E. , Ransone Morris A.
Published: September 2005

Shots detonated in the bottom of the Northeast Trough (Gulf of Maine) were monitored at SOFAR-depth hydrophone locations on the Continental Slope off the U.S.A. and off the Antillies. Stations in line with the axis of the Northeast Trough received proportionally more shots than those that were off axis. The direct water arrival was followed by a second one that was due to travel paths down the Northeast Trough and, thence, to the listening stations. Additional late arrivals were due to reflections from seamounts. Energy reflected from seamounts lying off the axis of the Northeast Trough was received proportionally less often the further off axis the mounts were, the greater their summit depth, and the greater their range. Additional seamounts, which were masked by others between them and the shot or station, did not reflect. [This presentation represents results of research sponsored by the Office of Naval Research.]
Word Intelligibility Versus Angular Relations between Talker and Listener
Authors: Thompson P. O. , Webster J. C.
Published: September 2005

Two word-intelligibility experiments were conducted under free-field conditions to determine how intelligibility depends upon the distance and angle between the talker and a group of listeners. The talker stood at the apex of a quarter pie-shaped section of listeners. In the course of experiment 1, the talker faced the center radial of listeners (0°), then rotated away from the center in 15° steps to 90°, and finally faced 135° and 180° . The listeners in both experiments either faced the talker's position (0°) or faced away from the talker's position through angles of 15°, 30°, 45°, 60°, 75°, or 90°. The results showed that speech intelligibility was quite uniform over a 90° horizontal arc centered on the speech axis, and that intelligibility was increased slightly when the listening angle was between 15° and 75° in azimuth as compared to 0°.
Cumulative Peak Distributions of Nonstationary Random-Vibration Environments
Authors: Sutherland L. C.
Published: September 2005

The distribution of peak amplitudes of a nonstationary random-vibration environment typical for flight-vehicle equipment is compared theoretically with the distribution for constant-level laboratory tests. For the latter, wide-band random-vibration single- or dual-level tests, sinusoidal sweep and resonance-dwell tests, and combined random and sinusoidal sweep tests are considered. A simple graphical procedure is illustrated for estimating the cumulative peak distribution for the flight environment. The procedure assumes the flight may be broken down into quasi-stationary periods for which a Rayleigh distribution of peak amplitudes is applicable. The result is that peak distributions of complex laboratory tests can be quickly compared to estimated peak distributions for a complete flight.
Digital-Computer Processing of Telemetered Vibration Data
Authors: Keast D. N. , Fletcher W. E. , Gibbons J. V.
Published: September 2005

The Titan II vehicle employs an on board spectrum analyzer for the study of vibration spectra measured in flight. The output of this analyzer is telemetered to the ground in digital form. This paper discusses the programming of a small digital computer for the processing and analysis of the received data. Particular emphasis is placed upon the direct use of an in-expensive computer by the engineer studying the data for on-line visual-data presentation, semiautomatic and manual editing, and computation. Program block diagrams. as well as some particular examples of the data, are presented. [This work was supported by the Titan Program, Office of Space Technology Laboratories, Inc.]
Environmental Problems with Acoustic- and Vibration-Measurement System Components
Authors: Peverley Richard W. , Nunley J. A. , Grabbe A. L.
Published: September 2005

Missile rocket-engine noise- and vibration-measurement system components are subjected to severe environments which may introduce spurious signals in the data. Thus, all components and systems must be subjected to environmental tests prior to their use to assure good data quality. Such a program is described in this paper. Several types of commercial microphones. accelerometers, preamplifiers, and cables were subjected to environmental tests, and their outputs analyzed to determine effect upon data. In addition, an entire data-acquisition system (to recorder input), including mounting brackets, was subjected to vibration tests. The results are discussed in the following manner: (a) Test data are graphically presented. (b) Test results are analyzed to predict their effect on the data. (c) The results of the prediction are compared to measured missile data. (d) Individual components and system test data are compared to show differences in results. Both good and poor data taken from missile firings are also presented to show environmental effects.
Versatile System for High-Intensity Sonic-Fatigue Testing
Authors: Van Houten John J.
Published: September 2005

The progressive wave system described is a high-intensity, sonic environmental testing unit which will simulate both random and discrete frequency noise, or a combination of both. The unit will accommodate panels up to 30×40 in. with over-all sound pressure levels to 170 dB. Electropneumatic transducers are used to generate these pressures and provide 12 000 acoustic watts. The waveforms generated are established by equalization of random noise, tape recordings of the environment to be simulated, or sinusoidal input. Structural elements may be subjected to sinusoidal sweeps in order to establish their modal response, and then a random fatigue test can be performed which simulates the operational environment. The versatility of the system eliminates the arguments of sine-random equivalents which has greatly hampered structural proof-testing of this nature.
Influence of Shear Flow on Sound Attenuation
Authors: Lambert R. F. , Tack D. H.
Published: September 2005

An experimental and theoretical study of sound propagation as an attenuating duct channeling turbulent airflow is presented. Measured attenuation constants for both upstream and downstream propagation in the low Mach-number range are compared with values predicted by a 1st-order perturbation of the linearized Navier-Stokes and mass-conservation equations. Extension of the analysis to higher Mach ranges is considered. [This work was sponsored by the National Science Foundation.]
Sound Propagation in a Triple-Layered Medium
Authors: Pierce Allan D.
Published: September 2005

A study has been made of the propagation of sound waves from a point source in a triple-layered medium consisting of a low-velocity layer sandwiched between 2 half-spaces of identical sound velocity. All 3 layers are assumed to have the same density. This model is one of the simplest exhibiting the waveguide effects studied by Pekeris, Tolstoy, Haskell, and by other authors, and is particularly amenable to analytic investigation. It is found that one may relate frequency, phase velocity, group velocity, and excitation amplitudes of the normal modes parametrically, and, on the basis of this, one may prove a number of theorems concerning the dispersion of the normal modes—one being that the group velocity of each mode has one and only one minimum. Particular attention is paid to the case where both observer and source are outside the low-velocity channel. In this event, each mode carries only a narrow band of frequencies—the width of the band decreasing with increasing mode number.
Axisymmetric Wave Propagation in Circular Cylindrical Shells
Authors: Huang T. C.
Published: September 2005

Investigation of wave propagation in shells using exact analysis within the framework of the linear theory of elasticity is tedious. A number of recent papers treats the subject with various approximate shell theories, including the effect of transverse shear and rotatory inertia. All these shell theories are based on the 1st-order approximation. The present paper is one in which an attempt of high-order approximation is made and is, therefore. a new addition to that group of shell theories. In the paper, axisymmetric wave propagation in circular cylindrical shells is investigated by the method of internal constraints with high-order coupling terms. Both flexural and extensional waves are considered. Feasibility of the method when applied to shells is explained. One example in each case is given, and results are shown in the dispersion curves. Discussion of results is based on the addition of high-order terms which become dominant in modifying the asymptotic and other behavior of dispersion curves.
Rayleigh-Wave-Attenuation Measurements
Authors: Lawrie W. E. , Baumanis A. M.
Published: September 2005

An experimental method has been developed for measuring attenuation of Rayleigh waves propagating in metal plates. Rayleigh waves are generated at one end of a plate using either a y-cut crystal or an x-cut crystal mounted on a Lucite wedge. The waves propagate along the plate, the lower part of which is immersed in water. Mode conversion occurs at the water-plate interface, and the resulting compressional wave is detected by an x-cut quartz crystal. The path length of the Rayleigh wave in the plate is varied by changing the plate position relative to the water level. Attenuation data are presented for several common metals, and the effect of heat treatment on attenuation in steel samples is discussed. The attenuation produced by several machined slots of different geometries is also shown. [This research was sponsored in part by Aeronautical Systems Division, U. S. Air Force.]
Sensitivity and Beam-Pattern Effects of Biological Marine Growths on Hydrophones
Authors: Urick R. J.
Published: September 2005

Underwater objects always acquire a growth of marine organisms when left in the water for a period of time. When a natural growth of fouling occurs on a hydrophone, a reduction of its sensitivity and a deterioration of its beam pattern may be expected. In order to estimate the severity of these effects, a small selection of hydrophones was measured after they had remained in Chesapeake Bay during the growing season of 1961. Measurements of beam pattern and receiving response were made in the fouled condition and after the fouling had been cleaned off. Reductions of axial sensitivity ranging from zero to 10 dB were found in the frequency interval 1 to 20 kc. Appreciable, though not severe, effects of the fouling on the hydrophone beam patterns were observed. Additional work is needed for making prediction estimates for surveillance systems or other uses.
Experimental Investigation of the Formation of Acoustic Echoes from Objects of Simple Geometric Shape in Water
Authors: Diercks K. J.
Published: September 2005

It is well known in sonar work that the echo returned by a target may differ considerably in shape from the incident pulse. An experimental investigation of the formation of the backscattered echo from geometrically simple targets has been carried out. Both solid targets and shells have been studied. Five pulse lengths, yielding conditions ranging from “high resolution” to “steady state,” were investigated. Selected narrow bands of frequencies (determined from observations of the backscattered echo) were covered. The experimental results are compared with existing theoretical predictions of echo formation. [This work sponsored by the Office of Naval Research.]
Sound-Absorptive Properties of Polyurethane Foams
Authors: Morimoto Y.
Published: September 2005

Polyurethane foams with identical physical properties vary considerably in their sound-absorptive properties. Determining the cause of this variation required consideration of such physical properties as porosity, cell size, percentage of closed cells, density, and elasticity. The values of these variables were measured, and the effect of each upon the sound-absorptive property of the foam was analyzed. Of the 5 variables, the percentage of closed cells appeared to have the most dominant effect; however, its value was virtually impossible to measure. The only practical measurement from which the sound-absorptive property of foam can be predicted is flow resistance. Thus, flow resistance has been used as a measure of the combined effect of all the variables. The general relationship of flow resistance to the absorption coefficient is illustrated.
Pitch of Nonuniformly Spaced Pulses in Periodic Trains
Authors: Guttman Newman , Flanagan James L.
Published: September 2005

The stimulus under study had a waveform consisting of 2 equal-amplitude pulses per fundamental peiod. Subjects signified the pitch of this challenge stimulus by matching it with a training of uniformly spaced pulses. Independent variables of the challenge were period duration T, intraperiod pulse spacing τ, and pulse polarity (++ or +−). Signal sensation level was 30 dB at 100 pps. All pulse durations were 25 μsec. The acoustic transducers were PDR-8 earphones connected binaurally in phase. Results for the ++ stimulus show: Challenge rates less than about 100 pps produce, with respect to the challenge, pitch matches which change gradually from pps/2 to pps as τ increases from 0 to 5–8 msec; for these same rates and for all other τ, the match is pps; challenge rates greater than about 165 pps exhibit sharp pps/2-to-pps transitions at the constant ratio τ/T=0.47. For the +− case, pps/2-to-pps transitions occur with increasing τ at challenge rates as high as about 265 pps; for a 420-pps challenge, as τ ranges from near 0 to T/2, the matches shift from pps/2, to approximately pps, and back to pps/2. These results provide further insight concerning the relative potencies of harmonic and pulsive components of auditory signals.
Experimental Check of Theoretical Expressions for Frequency Shift and Minimum Blowing Pressure in the Clarinet
Authors: Backus John
Published: September 2005

In an earlier paper [J. Acoust. Soc. Am. 33, 862 (1961)], a small vibration theory of the clarinet was outlined, which gives an expression for the variation of the playing frequency of the clarinet with width of the aperture between reed and mouthpiece. To check this theory, a clarinet was operated with an artificial embouchure as previously described. Measurements were made of the reed aperture, blowing pressure, and operating frequency when the clarinet was barely sounding. Frequency shifts were corrected for temperature variation and the fractional shift Δf/f plotted as a function of reed aperture. Results show a fractional shift which is approximately linear with aperture and which agrees with the theoretical value for small apertures; at larger apertures, the measured shift is some 2 to 3 times the theoretical value. The theory also predicts a minimum blowing pressure for the clarinet, which likewise depends on the reed aperture; the measured values of blowing pressure are in excellent agreement with the theoretical predictions. [This work was supported by a grant from the National Science Foundation.]
Role of Edgetone Action in an Organ Pipe
Authors: Powell Alan
Published: September 2005

The characteristics of the action for a certain edgetone geometry have been previously carefully determined [J. Acoust. Soc. Am. 33, 395 (1960)]. A family of lengthwise, symmetrical, “double” open-ended organ pipes have been designed so as to incorporate this edgetone geometry. The design is, consequently, somewhat unconventional, and it displays certain interesting and predictable features not normally present in conventional organ-pipe operation. These reveal how the organ tone depends both on the stage of the “edgetone” action and on the mode of pipe resonance, there being downwards, as well as upwards, jumps in frequency as the jet speed is increased. In addition to the prediction of the major frequency characteristics, it is also shown how the sound intensity can be estimated to an acceptable degree of accuracy. [This work received the partial support of the Office of Naval Research, under contract.]
System for the Data Reduction and Correlation of Spoken Words
Authors: Bledsoe J. D. , McConkle C. C.
Published: September 2005

A method for a combined analog-digital data reduction, correlation, and recognition of spoken words is described. The system employs bandpass filters, related electronics, digitizing equipment, and a large-scale digital computing system (IBM 7090). Methods for processing speech data into a computer for laboratory analysis are described. The application of Boolean algebra and the techniques for programming the statistical derivation of logical functions are shown, as well as examples of recognition techniques based on this system.
Hybrid Formant-Tracking Channel Vocoder
Authors: Campanella S. J. , Coulter D. C. , Early D. M.
Published: September 2005

This paper discusses design and performance of a speech-compression system that incorporates a formant-tracking vocoder for the analysis-synthesis of the vocalic utterances in speech, and a channel vocoder with 5 fixed-frequency channels and 1 tracking channel for the analysis-synthesis of the nonvocalic utterances of speech. The information is multiplexed and transmitted over eight 25-cps low-pass analog channels. For vocalic utterances, the parameters transmitted are the first 3 formants, their respective amplitudes, the frequency of pitch, and a separate vocalic nonvocalic decision signal. For nonvocalic utterances, the information transmitted is the amplitude of 5 vocoder channels. and the frequency and amplitude of 1 tracking channel covering the range from 2300 to 6000 cps, used to control a variable-frequency pole-zero filter in the synthesizer. For male talkers, this system demonstrates a mean articulation score of 87%. Confusion matrices and a demonstration tape recording are presented.