bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory-Evoked Potentials from Cochlea to Cortex as Influenced by Activation of the Efferent Olivo-Cochlear Bundle
Authors: Desmedt J. E.
Published: September 2005

The crossed olivo-cochlear bundle (OCB) of Rasmussen was stimulated stereotaxically in acute experiments on cats immobilized by Flaxedil and prepared either under pentobarbital, or chloralose, or with a high-spinal section. Middle-ear muscles were cauterized. The efferent effects on sound-evoked potentials were titrated as equivalent dB changes in sound energy by a matching procedure taking into account the intensity function of the responses to sound alone. Maximal inhibition of the N1 auditory-nerve response to click was equivalent to a −25-dB decrease. The potentials evoked in cochlear nucleus, superior olive, inferior colliculus, medial geniculate, and auditory I area of the cerebral cortex when expressed similarly in equivalent dB changes disclosed a decrease proportional to that of N1. The anomalous Ruben-Sekula effect—i.e., reduction of cortical auditory potential without concomitant change in N1 during brainstem stimulation—was shown not to involve the OCB inhibition but to depend on a cortical refractory state subsequent to spurious stimulation of second-order auditory axons by inadequately placed electrodes. With suitable precautions, pure OCB stimulation was achieved in most of our experiments, and interference from this effect thus excluded. The OCB activation also paradoxically potentiates the cochlear microphonic potential (CM), but the change amounted at most to a +4-equivalent-dB increase in sound energy. This increase receptor potential, while important for understanding the synaptic mechanisms of the inner ear, is ignored by the central nervous system, since acoustic signals are simultaneously suppressed in the auditory nerve (Fig. 13). Various parameters of OCB effects were analyzed in detail, e.g., voltage, duration, frequency and number of shocks delivered to the bundle, and interval between the conditioning stimulation and the testing sound. More than three shocks at a frequency higher than 50/sec are needed to produce detectable changes in N1 or CM, and 40 shocks at 400/sec will generally produce maximal effects. The dissipation of the changes after OCB stimulation is rather slow and has an exponential time constant of 90 to 180 msec. These and other intrinsic features of olivo-cochlear axons may be reflected in the operational characteristics of the whole centrifugal extrareticular auditory control system (CERACS), for which the OCB is one of the peripheral effector links.
Inhibitory Mechanism of the Vestibular System in Man in Comparison with Hearing
Authors: Groen J. J.
Published: September 2005

Adaptation of the organs of hearing and equilibrium is compared. The latter is demonstrated in normal individuals under different circumstances, appearing in the form of inhibition of vertigo and nystagmus. Apparently, the adapted state persists longer in the vestibular system than in hearing. The growing influence of the vestibular inhibitory efferent system in man is demonstrated in a newborn infant.
Difficulties in Seismic Prospecting Resulting from Bubbles in Fluids
Authors: Parr J. O.
Published: September 2005

Small percentages of gaseous bubbles present in fluids or semifluids can cause serious difficulties in seismic prospecting. Shot-hole fatigue, reversals of polarity and large times for short intervals in deep-well surveys, reflections coming into the side of a geophone line from surface anomalies (particularly in water), and variations in the seismic velocity through water in the Gulf of Mexico, can be caused by bubbles. Both records and theoretical data are shown to substantiate this hypothesis.
Some Measurements of Cavitation
Authors: Meyer Erwin
Published: September 2005

In previous publications we have discussed a series of experiments on the critical pressure for the onset of cavitation and the spectrum of the cavitation noise. The behavior of an individual cavitation bubble is of even greater interest, and has been studied in two types of experiments. (1) In the study conducted by L. Bohn, the sound of a parabolic array of magnetostrictive transducers at 22 kc/sec is picked up at the focal point by a small probe microphone, a very thin nickel wire with all but the tip shielded against the incident sound by a plastic tube (frequency range up to 1 Mc/sec). The reaction of the oscillating bubble on the tip is recorded and its spectrum is analyzed. (2) In the study conducted by E. Mundry a vibrating nickel rod (2.5 kc/sec) is used, one end of which dips into water. The bubbles originating and oscillating at the lower surface are photographed by a high speed movie camera (100 000 frames per sec) and the sound waves of the collapsing bubbles are recorded by a Schlieren-method. The results of both studies are discussed with regard to different qualities of water and different sound amplitudes.
Interaction of Elastic Waves in an Isotropic Solid
Authors: Jones Gerald Lee , Kobett Donald R.
Published: September 2005

Nonlinear elasticity theory is used to investigate the scattering of two intersecting, plane, elastic waves in a homogeneous, isotropic medium. A criterion for the occurrence of a strong scattered wave is derived. The criterion is formulated as a relationship between the first-order elastic constants of the material, the angle between the intersecting wave vectors, and the ratio of wave frequencies. The exact formulation also depends on the type of intersecting waves, i.e., longitudinal or transverse. The amplitude of the scattered wave is found to be proportional to the volume of interaction and dependent on the third-order elastic constants of the material. Numerical results are given for wave scattering polystyrene.
Electromechanical Coupling and Composite Transducers
Authors: Toulis W. J.
Published: September 2005

Measurements with composite types of transducers indicate that both the classical definition of the electromechanical coupling factor and the equivalent circuit for a piezoelectric transducer require revisions for improved consistency. The effective coupling coefficient depends on the proportion of the piezoelectric material that is employed electromechanically rather than being independent of it as implied by existing definitive formulations. Furthermore, the inherently usable coupling decreases below the fundamental resonance frequency so that it approaches zero at very low frequencies. At higher frequencies the inherent coupling factor may approach the ultimate value at a frequency specified by the dimensions and characteristics of the piezoelectric specimen in a transducer. For the equivalent circuit, the measurements favor a parallel rather than a series form for the motional or transformed mechanical impedance because the frequency for parallel resonance remains invariant with the proportion of the piezoelectric specimen that is excited electromechanically.
Multichannel Threshold Audio-Noise-Reduction Circuit
Authors: Rogers Edward S.
Published: September 2005

The object of this research has been to investigate the possibility of developing a noise-reduction circuit that could extract speech intelligence from a signal in which the intelligence was masked by noise. The problem has been attacked experimentally by building a 110-channel threshold noise-reduction circuit. Each channel contains bandpass filters and a nonlinear device to improve the signal-to-noise ratio in the channel. A number of tests have been performed to evaluate the circuit. The results show that the threshold noise reducer is capable of improving the over-all signal-to-noise ratio of a noisy speech signal, and it is capable of separating some speech components from noise. However, the operational effectiveness of the device for the improvement of speech intelligence is marginal.
Prediction of Temporary Threshold Shift after Noise Increase
Authors: Selters Weldon
Published: September 2005

Temporary threshold shift (TTS) can be predicted as a function of exposure time and level when the level is constant. This experiment now indicates several other things: (1) After a noise-level increase, if exposure time is adjusted by the equivalent-exposure rule, the usual TTS function for the higher level will predict subsequent TTS growth. (2) Brief test periods introduce errors in exposure time, which may be corrected by multiplying the observed TTS by (tn+ti)/tn where tn is exposure time and ti is test time. (3) An acceleration in TTS seems to occur at about 6 min. This means new equations will be necessary to predict TTS for exposure times less than 6 min.
Post-Mortem Acoustic Impedance of Human Ears
Authors: Zwislocki J. , Feldman A. S.
Published: September 2005

By means of a portable acoustic bridge, it is now possible to measure the acoustic impedance at the eardrum of fresh human cadavers. Comparison with the acoustic impedance determined by the same method and with the same instrumentation on live subjects shows that the impedance increases considerably after death. Consequently, results obtained on cadaver ears cannot be applied directly to the middle-ear function during life.
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 it approaches the stationary solution of Powell in the limit as the time of excitation increases. An additional verification of the general theory is provided in that it is reducible to the known result given by Caughey and Stumpf for a single-degree-of-freedom system. The general solution is further simplified when the forcing field is also homogeneous. The statistical dependence in the response of different modes is illusstrated in an example of a simply supported uniform beam.
Acoustic Focusing with Spherical Structures
Authors: Toulis W. J.
Published: September 2005

A variety of structures in the form of spheres can provide sharp focusing and directivity gains comparable to those from a circular piston with the same diameter. With an isotropic refractive sphere, spherical aberration does not impair focusing except for angular resolutions of the order of a few degrees and less. Luneberg lenses with compliant tubes or refractive liquid packets eliminate spherical aberration, but the focal distance may change as a result of dispersion in the resultant index of refraction. The outer shell of a Luneberg lens alone, and without the inner core, provides an angular resolution which is comparable to that for the full lens, but with a decrease in the directivity gain which is not as great as the reduction in the amount of refractive matter. Primary feeds with considerable directivity are essential for all types of lenses except those with the focus near the outer surface of the lens.
Psycho-Acoustics: Applied and Misapplied
Authors: Burris-Meyer Harold
Published: September 2005

Until the mid 1930's, the effect of sound on man was the subject of more speculation than investigation. Occasional frightening demonstrations, such as the brain storm scene from Elmer Rice's Adding Machine reported to this society in 1939, only helped to perpetuate myths about the auditory lethal ray, the sound which would drive people mad, the inaudible sound which paralyzes. In 1940 the National Defense Research Committee addressed itself to the problem of discovering effects of sound on man which might aid the war effort. In 1941 a pilot project was established to investigate and to devise means and procedures for applying useful phenomena if any should be discovered. The activity of this project was sometimes successful, sometimes not, but always spectacular. This paper treats of early applications, some not previously disclosed, instructive though unsuccessful experiments, and subsequent related developments.
Effect of Noise Dependence on Correlation Detection and Measurement
Authors: Jacobson Melvin J.
Published: September 2005

This paper is concerned with the effect of noise cross correlation on the detection of a signal in noise by means of a correlation detector. It also considers the effect of noise cross correlation on statistical errors arising in the approximate measurement of signal cross correlation by the sample mean of the output of a multiplier-averager. In the detection problem, the probability of detection and sample size are investigated under the influence of noise cross correlation. In a specific application, the effect of noise cross correlation is determined in the case of a spherical, isotropic noise field. Detailed results are presented when the inputs have the characteristics of RC-filtered white noise and when the detector includes a finite-time perfect averager. In the measurement problem, the influence of noise cross correlation on the accuracy of correlation measurement is studied from a probability standpoint. Here, too, the required increase in sample size is investigated.
Some Acoustic Measures of the Fundamental Periodicity of Normal and Pathologic Larynges
Authors: Lieberman Philip
Published: September 2005

Pitch perturbations were computed by measuring the differences between the durations of adjacent fundamental periods from recorded acoustic waveforms. Sound-synchronized high-speed motion pictures of the vocal cords were also taken with a laryngeal mirror. It was found that pitch perturbations reflect variations in the waveshape of the glottal area wave, as well as variations in glottal periodicity. Perturbations having an absolute value ⩾0.5 msec are apparently induced by transients in the air-pressure drop across the glottis, which may in turn be caused by changes in vocal-tract configurations. Speakers with longer fundamental periods tend to have larger perturbations. The pitch perturbations of 23 speakers with pathologic larynges were measured. Certain of the speakers who had pathologic growths on their vocal cords had larger pitch perturbations than did normal speakers with the same median fundamental periods. The “perturbation factor,” which was defined as the percent that perturbations ⩾0.5 msec occurred, was computed for each speaker. The magnitude of the perturbation factor may serve to detect certain types of pathologic laryngeal conditions.
Acoustical Design of U.C.L.A. Music Building
Authors: Knudsen Vern O. , Delsasso L. P.
Published: September 2005

The authors worked in close cooperation with the architects and Music Department throughout the entire design, construction, and furnishing of the building. Measurements of the sound insulation and of reverberation characteristics were made in Schoenberg Hall (525 seats), Rehearsal Rooms, and Practice Rooms during and after construction of the building. An optical study of reflections in a two-dimensional model (devised by R. W. Leonard and described by him at the June, 1954, meeting of the Acoustical Society) was used to determine the shape of the ceiling for Schoenberg Hall that would provide a uniform distribution of sound throughout the seating area. This objective was well realized; for a sound source (a band of “white noise” centered at 500 cps) on the front of the stage, the sound level drops, on the average, only about 1.5 db from the front to the rear seats. Optimum reverberation and diffusion are obtained from strips of absorption on the side walls. The reverberation curves and the sound insulation data for typical rooms will be reported.
Air-Conditioning Equipment Noise Levels in Residences
Authors: Mikeska E. E.
Published: September 2005

Data are presented showing room noise levels from residential air-conditioning equipment measured in a number of homes in Austin. The measurements cover a range of equipments of different types, mountings, cost, and age.
Experiments Relating to the Perception of Formants
Authors: Morton John , Carpenter Alan
Published: September 2005

Experiments are described which suggest that, for human perception, the information concerning the location of a formantlike complex sound is contained in the two most prominent harmonics. This result is limited to the condition where adjacent harmonics are more widely separated than the width of a critical band.
Absorption of Finite Amplitude Sound Waves in Liquids
Authors: Narasimhan V. , Beyer R. T.
Published: September 2005

Earlier measurements of the sound absorption coefficient as a function of the excess pressure amplitude, made by Towle and Lindsay, have been repeated and extended. The results in water indicate that the rate of increase of α/ν2 with excess pressure amplitude becomes less with increasing frequency. Such results are qualitatively in accord with the theory of Fay but are in disagreement with the earlier results of Towle and Lindsay. Measurements are also reported for an electrolytic solution with a relaxation frequency in the frequency range studied (3–9 Mc). The results indicate a reduced effect of the increase of α/ν2 for higher concentrations as well as for higher frequencies. [Supported in part by the Office of Naval Research.]
Parametric Acoustic Array
Authors: Westervelt Peter J.
Published: September 2005

This paper presents the theory of highly directional receivers and transmitters that may be “constructed” with the nonlinearity of the equations of fluid motion.
Scattering of Sound by an Elastic Prolate Spheroid
Authors: Silbiger Alexander
Published: September 2005

The scattering of a plane wave by an elastic prolate spheroid at arbitrary angle of incidence is formulated by means of an expansion in spheroidal wave functions. The structural response of the spheroid is expressed in terms of a surface impedance operator. Even for a homogeneous elastic solid or shell, the impedance operator generally couples the spheroidal modes of the acoustic medium, and hence numerical solutions involve the inversion of an infinite set of linear equations. However, a number of special cases are considered here for which direct solutions can be obtained. These include resonant mode scattering and low-frequency scattering.

When one of the structural modes is excited by the incident wave at its resonant frequency, it may radiate with such intensity as to mask radiation by other modes. The conditions under which this type of scattering can take place are shown to be very restrictive.

When the acoustic wavelength is large and the frequency is small compared to the lowest natural frequency of the structure, the scattered field can be analyzed into uncoupled monopole and dipole fields. Simply asymptotic expressions, not involving spheroidal functions, are presented for a spheroid with finite compressibility and inertia as well as for the limiting cases of rigid and fixed boundary and pressure-release boundary.
Three Experiments Concerned with Pitch Perception
Authors: von Békésy Georg
Published: September 2005

Three experiments indicate that the place of the excitation along the basilar membrane determines pitch perception. (1) Without changing the periodicity of a tone, its pitch can be raised or lowered by masking. (2) The changes in the size of a sound image produced by masking can be explained in terms of the place theory of hearing. (3) Pitch sensations seem to be connected in an orderly way to place of excitation along the basilar membrane, since it is possible to observe the time differences required by the traveling waves to reach the different places along the membrane.
On Spectra and Directivity of Jet Noise
Authors: Ribner Herbert S.
Published: September 2005

On the assumption of locally isotropic turbulence superposed on the mean jet flow, the broadly peaked noise spectrum is derived in terms of a sum of two bell-shaped spectra peaked an octave apart. The proportions vary with direction θ from the jet axis. being dominated by the “bass” spectrum at small angles and the “treble” spectrum beyond, say 70°. This is accomplished by a factor ∼cos4θ for the “bass” spectrum. For small angles (e.g., 30°), points of the resultant curve are amplified (vertical shift) by convection of the eddies and “Doppler” shifted (less than the full amount) in frequency. It is suggested that an increase in amplification toward the left may move the amplified peak in that direction. This could occur if somewhat downstream of the potential core the dominant noise emitters were located sufficiently close to the axis to be convected substantially faster than those in the mixing region.
Effect of Sound Waves on Heat Transfer
Authors: Westervelt Peter J.
Published: September 2005

A criterion recently derived by the author predicts the sound-pressure level at which sound begins to increase the rate of heat transfer. The application of this criterion to recent experiments is discussed, and it is concluded that, while theory and experiment are in essential agreement, more experiments covering a wider range of variables are needed in order to test the full range of applicability of the theory.
Nonlinear Properties of Circular Orifices
Authors: Thurston George B. , Hargrove Logan E. , Cook Bill D.
Published: September 2005

The results of an experimental study of the nonlinear fluid flow properties of thin, square-edged, circular orifices are described. Liquids are used at low frequencies. The flow conditions considered are a sinusoidal oscillation of the fluid in the orifice and a sinusoidal oscillation with a steady component added. It is found that for the sinusoidal flow condition the pressure differential developed across the orifice contains higher odd harmonics. The addition of a steady flow component adds even harmonics to the pressure as well as influences the magnitude of the odd harmonics. In this case the steady pressure component is a function of the magnitude of both the sinusoidal and steady flow components. (This work was supported by the Office of Ordnance Research, Department of the Army, under Contract No. DA-23-072-ORD-583.)
Acoustical Wave Propagation in an Air-Filled Cylindrical Tube
Authors: Fisher Raymond C.
Published: September 2005

From differential equations describing the behavior of a gas in a cylindrical tube are derived the characteristic impedance and propagation constant, analogous to similar quantities in the electrical transmission line. Curves are presented from which these quantities and others can be easily derived for dry air, knowing the driving frequency, mean temperature, mean pressure, and tube radius. Zero temperature variation and gas velocity at the tube wall are assumed. The equations include temperature, particle velocity, pressure, viscosity, thermal diffusivity, density, compressibility, and frequency. Experimental data on a tube 1/16 in. in internal diameter at driving frequencies from 2 to 29 cps are compared with the theoretical curves of characteristic impedance and propagation constant derived from theory. The agreement between theory and experiment is shown to be excellent. The design curves and procedure should prove helpful in the design and performance prediction of aircraft instrumentation systems. Curves are also presented from which the impedances of acoustic cavities can be computed. Experimental tests confirm these to an accuracy sufficient to justify their use in design. An outline of the experimental procedure and equipment is presented. (The work was done in the Physical Research Laboratory of Boeing Airplane Company.)
Experimental Study of Noise Reduction in Centrifugal Blowers
Authors: Embleton T. F. W.
Published: September 2005

Several centrifugal blowers with forward, backward, and radial blades have been studied experimentally at various speeds, capacities, and pressures. Attention was concentrated on the methods of noise reduction that are applicable to blowers of any type. It is shown that sound at the blade-passage frequency and its harmonics may be reduced as much as 12 dB either by locating the cutwater at the optimum clearance from the impeller (0.17 in. in the particular blower described), or by sloping the edge of the cutwater relative to the tips of the impeller blades. These two effects on sound-pressure level are additive. Broadband aerodynamic noise originating within the impeller may be reduced 1 or 2 dB by twisting of the impeller blades. For the proper amount and direction of the twist, this latter noise-control measure also results in an improvement of mechanical efficiency (up to 10%) though at the expense of decreased capacity (typically 5%–10%). Further noise reduction is achieved only with decreased efficiency.
Observation of Elastic-Pulse Propagation in Axially Symmetric and Nonaxially Symmetric Longitudinal Modes of Hollow Cylinders
Authors: Fitch Arthur H.
Published: September 2005

Experimental measurements of group velocity in both axially symmetric and nonaxially symmetric longitudinal modes of hollow cylinders are presented and compared with theoretical values. Wavepropagation in a 5052 aluminum-alloy specimen was excited by Gaussian-shaped rf pulses applied to ceramic barium titanate thickness longitudinal-mode transducers on the specimen. The specimen had a value of Poisson's ratio σ = 0.33 and a ratio of wall thickness to mean radius of 0.3. Preferential excitation of the nonaxially symmetric modes was accomplished by transducer shaping. The experimental results were in good agreement with calculated values.
Violin Resonances
Authors: Caldwell C. L.
Published: September 2005

A fruitful method of studying the action of the violin is to consider it as a system of generators (the strings) and resonators (the body). The body has many resonances, some being caused by the air inside, others being caused by the wood. These two sets of resonances were separated. A tiny microphone was placed inside a violin, which was then buried in sand to dampen the wood resonances. The F holes were kept clear. The violin was placed in a swept-frequency sound field. This gave the air resonances alone. In addition to the main Helmholtz resonance, others were found, together with notches in response due to standing waves. Next, a magnetic driver and a pickup were attached to the violin, which was placed in a vacuum system. This yielded the wood resonances alone. The peaks became more prominent in the absence of radiation resistance. Finally, the total response of the violin was obtained in air, using the magnetic driver and both the microphone and the magnetic pickup. Since the pickup does not respond to the main air resonance, interactions between the two sets of resonances are weak.
Methods of Estimating Fatigue-Curve Parameters with a Limited Number of Specimens
Authors: Coleman John J.
Published: September 2005

Two different methods for estimating fatigue-curve parameters with a limited number of specimens are described. In the first method, the progressively increasing load procedure for fatigue testing, originally developed by Prot, is analyzed. By mathematical analysis, it is possible to derive a formula which explains Prot's empirical formula and can be used to generalize linearly increasing load methods. As a consequence, a short-time procedure is made available for estimating endurance limit and other fatigue-curve parameters, as well as for providing reduced S-N data. In the second method, the accuracy of estimate of the mean fatigue curve vs sample size is also investigated in order to determine the nature of this variation so that there can be a quantitative basis for making a decision on optimum sample size.
Some Effects of Spectral Content and Duration on Perceived Noise Level
Authors: Kryter Karl D. , Pearsons Karl S.
Published: September 2005

A number of experiments were conducted in which listeners equated a wide variety of sounds with respect to noisiness (equal acceptability) and loudness. The principal findings are as follows: (1) On the basis of data obtained from approximately 250 subjects, new equal-noisiness contours and tables for use in the calculation of perceived noise level were determined. (2) Over a range of durations from 112 to 12 sec, sounds were judged equally acceptable when the sound-pressure level was reduced by 412 dB for each doubling of duration. Variations in rise and decay times from 12 to 4 sec did not significantly influence the judgments. (3) Combining a pure tone of sufficient intensity with a band of filtered white noise caused subjects to judge the sound as noisier than the same band of noise at the same over-all sound-pressure level as the tone-plus-noise. On the other hand, the judged loudness of the band of noise, keeping over-all level constant, was not appreciably affected by the addition of the tone. (4) Calculated measures of perceived noise level (PNdB), loudness, and the readings on A, B, C, and “flat” scales on a sound-level meter were determined for a variety of “real” and artificial sounds of equal duration when these sounds were judged to be equally noisy or acceptable. Considering both absolute values and variability in the results, the order of merit, from best to worst, of the various measures for predicting the judgment data was as follows: PNdB, phons Stevens, phons Zwicker, “flat,” C, B, and A scale of a sound-level meter.
Some Factors Influencing the Effective Auditory Intensive Difference Limen
Authors: Loeb Michel , Binford John R.
Published: September 2005

Observers were required to detect changes in intensity in signals of two types: (1) a continuous Gaussian noise to which increments were added randomly and infrequently; (2) a sequence of pulses, 0.5-sec duration occurring periodically at 2.5-sec intervals to which increments were added infrequently and randomly. For each of the types of task, several levels of discrimination difficulty were employed. It was found that the changes in intensity of the steady noise were more readily detected than comparable changes in intensity of pulses. At intermediate difficulty levels, the number of detections of increases in the steady signal declined with time on task; and, at intermediate and high difficulty levels, the number of detections of louder pulses declined with time. Progressive increases in response latency were also noted in some of these conditions, and there was a general tendency for false detections to decline with time on task. Possible explanations for the differential discriminations of changes in intensity of the steady and pulsed stimuli are discussed.
On the Statistics of Spoken English
Authors: Denes P. B.
Published: September 2005

A variety of statistical information about spoken English was obtained. The data are the results of analyzing a considerable body of conversational material and narrative taken from “Phonetic Readers”; the analyses were carried out by using a digital computer. The principles for selecting the speech material are discussed. Counts were obtained for the frequency of occurrence of phonemes, for the digram frequencies of phonemes, for word length, etc. Stress was taken into consideration, and many of the statistics were obtained separately for stressed and unstressed syllables. In addition, the frequency distribution of minimal pairs was obtained. Minimal pairs are the phoneme pairs that minimally distinguish one word from another. All results were evaluated from the articulatory point of view. It was found that, in spoken English, dental and alveolar articulations predominate and that manner rather than place of articulation is the dimension that carries by far the greatest functional load.
Design of Narrow-Beamwidth Transducers
Authors: Kossoff G.
Published: September 2005

The design of focused transducers used to narrow the beamwidth over a finite distance in the nearfield region is outlined. A computer program was used to optimize the transducer's geometrical shape for beamwidth improvement, and off-axis computations for plane and focused transducers were programmed to check the improvement in beamwidth so obtained. The results of these computations show that a simple parameter can be used to describe and compare the degree of focusing of such transducers.
Analysis and Design of a 3-Gc/sec Quartz-Cavity Resonator as a Hypersonic Source for Liquids
Authors: Stewart James L. , Stewart Ellen S.
Published: September 2005

A series-equivalent circuit for a quartz plate driven at high harmonics is given, and a simple analysis developed for the re-entrant cylindrical microwave cavity with an X-cut crystal in the gap. Expressions are derived for the efficiency and sensitivity of such a system as a hypersonic transducer for use with liquids at room temperature and 3 Gc/sec. Design equations are developed for the crystal and cavity dimensions which maximize the efficiency. These show that the crystal should be less than 100 μ thick and plane-parallel to one-fiftieth of an optical wavelength to minimize the absorption and alignment losses, respectively. The cavity should have a “square” cross section with a post height e2 times the post radius. Efficiencies of 40% and 65% are theoretically possible with quartz crystals 100 μ and 35 μ thick radiating into water at room temperature. A companion paper will discuss experimental results.
Experiments Concerning the Vortex Whistle
Authors: Chanaud Robert C.
Published: September 2005

An experimental investigation was conducted on the vortex whistle in both air and water. Relevant parameters are shown to be the Reynolds number, Strouhal number, and nondimensional tube length. Theory and physical considerations lead to the supposition that sound generation is caused by a circular distribution of dipoles whose phase angle varies continuously around the periphery of the tube exit so that points diametrically opposed are always exactly out of phase. Deductions from this model are in close agreement with experiment. The sound frequency has been shown to be identical with the precession frequency of the unstable vortical motion and the evidence suggests that it is simply related to the angular velocity of the steady fluid motion. Acoustic feedback from surfaces remote from the flow does not influence the whistle.
A Portable Impedance Tube
Authors: Berendt Raymond D. , Schmidt Henry A.
Published: September 2005

A lightweight impedance tube has been developed primarily as an instrument for practical research. It can be used also for precision measurements of acoustical-impedance and sound-absorption coefficients in both laboratory and field installations, over the frequency range 400 to 900 cps. It is useful for the development and manufacturing control of acoustical materials, acceptance testing of acoustical installations in the field, and determination of aging, staining, and redecoration effects on the absorptivity of acoustical materials. Experimental results are presented.
On the Effect of Atmospheric Turbulence on Sound Propagated over Ground
Authors: Ingard Uno , Maling George C.
Published: September 2005

The sound field above a plane boundary has been calculated by assuming that both the direct and reflected waves fluctuate in amplitude and phase. The pressure field is described in terms of a time-dependent mean-square pressure (p̄2) whose statistical properties are studied. The mean and variance of (p̄2) have been calculated by assuming that the turbulent fluctuations are normally distributed. The results are compared with some experimental data obtained outdoors over a large rigid boundary. Most of the experimental data have been found to be in good agreement with the calculations.
Notes on Nonuniform Shock Propagation
Authors: Meyer R. E. , Ho D. V.
Published: September 2005

The propagation of a spherical or cylindrical shock wave in a gas, the propagation of a plane shock in a stratified atmosphere, and the travel of a shock through ducts of various kinds belong to a family of closely related physical problems involving thoroughly nonlinear acoustics. In all such situations, the changes in the shock are partly due to the nonuniformity of the environment into which the shock travels, but the development of the shock is also determined in part by nonlinear acoustic wave interactions occurring behind the shock. A discussion of the physical process taking place behind the shock leads to the derivation of a wave-strength relation offering a precise comparison of the relative influence which the environment and the acoustic waves have on the local development of the shock. One interpretation of this wave-strength relation leads to Whitham's approximation for the case of negligible wave influence. Another interpretation leads to a higher approximation for the initial stage of shock propagation. The connection with some recent asymptotic work is also indicated.
Radiation Impedance of a Source near Reflectors
Authors: Waterhouse Richard V.
Published: September 2005

In general, a reflecting environment influences the sound-power output of a radiating source. A theoretical treatment is given for the reaction of any specularly reflecting environment on a point source. The starting point is the acoustic impedance for a point source in a free field; the real part of this impedance gives the free-field power output of the source. By analogy with this acoustic impedance scalar field of simple form is derived that gives at any point in a reflecting environment the real and imaginary parts of the reflected impedance seen by a point source placed there. A similar treatment is applied to a line source. The reflected impedance is calculated for a point source between parallel reflecting walls and for a line source in a wedge reflector. Cases where the enclosure completely surrounds the source are of interest, particularly in the measurement of the power output of a source by the reverberation-chamber method. An extreme case is treated where the source reaction is maximized, that of a point source at the center of a hollow sphere. The source reaction is calculated as a function of wall impedance and source bandwidth. This case provides bounds for the variation with position of power output of most, if not all, sources in enclosures. Some experimental data that fall within the bounds given are presented for a sound source in a reverberation chamber.
Transverse Vibration of Simply Clamped Beams
Authors: Snowdon J. C.
Published: September 2005

Expressions are derived for the input impedance and transmissibility of simply clamped beams excited to transverse vibration by both central and off-center forces. The influence of beam damping is considered in detail. It is shown that regions of attenuation, which appear in the transmissibility curves of beams excited simultaneously by one central and two symmetrical off-center forces, can be of significant magnitude and extend through a significant range of frequencies. Further, by suitable choice of the position of the off-center forces or, in the one case considered, by suitable choice of their phase, it is possible to remove selectively the resonant peaks that are normally present in the transmissibility curves of the beams.
Relation of Hearing Loss to Noise Spectrum
Authors: Plomp R. , Gravendeel D. W. , Mimpen A. M.
Published: September 2005

Because of the many uncontrollable factors, field studies to investigate the relation of hearing loss to noise spectrum are not very suitable. Assuming a close relation between temporary and permanent hearing loss to exist, experiments are done to find the “relative traumatizing power” of different frequencies. Octave bands of noise are used as a stimulus to investigate the threshold shift at one frequency (one-half octave above the center of the noise band), as well as the integrated threshold shift over all frequencies. From these data isotraumatic lines are derived, representing as a function of frequency the sound-pressure levels which give equal threshold shifts. These lines have a minimum at about 3600 cps with steep slopes below and above this frequency. A review of recent literature shows that generally flatter curves are found. This difference is discussed, but no reasonable explanation can be given. Considerations based on field studies give the impression that a steep isotraumatic line is more probable than a flat one. It is proposed that the isotraumatic line found by the authors, shifted to an appropriate level corresponding with a minimum of 75 dB, may have some value as a criterion line to conclude whether a noise spectrum will induce hearing losses or not.
Existence Region of the Tonal Residue II
Authors: Ritsma R. J.
Published: September 2005

The present article is an extension of an earlier study of the frequency region in which a tonal residue can be established for an harmonic complex of three frequency components. A description will be given of measurements carried out to determine the influence of the number of components and of the spectral envelope of a filtered periodic pulse wave on the extension of the original frequency region. This extension was measured for two pulse repetition rates, i.e., 200 and 280 cps. It is found that a tonal residue can be heard if, and only if, at least three components of an harmonic complex sound, consisting of more components, are situated within the frequency region of the tonal residue for a three component complex. Implications of this rule with respect to the operation of a theoretical pitch-extractor are presented.
Sounds of the Highland Bagpipe
Authors: Harris Cyril M. , Eisenstadt Maurice , Weiss Mark R.
Published: September 2005

An analysis has been made of the sounds of the Highland bagpipe. This instrument consists of a leather bag fitted with five pipes: the blowpipe through which the player fills the bag with air, the chanter that has eight open holes on which the melody is played, and two tenor drones and one bass drone, which produce harmonious steady tones. This study was made of the sounds produced by four individual pipers, each using his own instrument. Three of the pipers had considerable professional experience—the fourth was a young beginner. Spectral analyses were obtained for each drone and the chanter sounding separately under otherwise normal playing conditions. The harmonic structure of these sounds was investigated as a function of a number of parameters including blowing pressure, length of drone, and aging of the chanter reed. Transient as well as steady-state conditions were studied.
Physical Measurements of Equally Speech-Interfering Navy Noises
Authors: Klumpp R. G. , Webster J. C.
Published: September 2005

The sound level of each of 16 diverse noises was adjusted so that loudspeaker-reproduced rhyme words at a level of 78 dB (C) at one meter were reduced to 50% word intelligibility. Spectrum analyses (octave band and 20-cps band), physical measurements (C, B, A, DIN 3 sound-level meter weightings), calculations [Speech Interference Levels (SIL)], and peak fittings [to noise criteria (NC)-type curves] were made to find which method came closest to agreeing that the noises were equally speech-interfering.

SIL calculations that included the octave 300–600 cps predicted the speech-interference aspects of the 16 noises best. The A and DIN 3 weighting networks, the conventional (600–4800 cps) SIL, and use of a restricted region (350–2800 cps) of NC-type curves gave the next best prediction. The poorest predictors were the B or C frequency-weighting networks and use of the NCA, NC, or ISO contours over their total frequency range.
Digital Computer Simulation of a Sampled-Data Voice-Excited Vocoder
Authors: Golden Roger M.
Published: September 2005

A sampled-data system representing a 10-spectrum channel voice-excited vocoder (VEV) has been simulated on an IBM 7090 digital computer. This type of simulation permits studying readily the effects of changes in major vocoder parameters, such as excitation, analyzing filter bandwidth, etc., without the lengthy waiting periods required for equipment changes. Programming for the simulation was accomplished by the use of a program compiler that allows specification of a sampled-data system in functional-block form. The system represented by the simulation was, in general, determined by finding sampled-data equivalents (z transforms) of the filters and circuits used in an analog VEV. The derived z transforms were then used to realize functional-block representations for the sampled-data filters and circuits. However, to prove economically the feasibility of simulating an entire vocoder, the great number of bandpass filters needed were synthesized initially by using a unique and computation timesaving design. Speech processed by this simulated sampled-data system is of excellent quality and often is better than that processed by some analog VEV's. The computer program requires about 172 sec to analyze and resynthesize 1 sec of recorded speech.
Theory of Bubble Pulsation and Cavitation
Authors: Houghton Gerald
Published: September 2005

First- and second-order perturbation methods for small amplitudes have been used to obtain periodic solutions to the modified Rayleigh equation that are applicable to the adiabatic pulsation of bubbles in liquids. It is demonstrated theoretically that bubble pulsation is a damped oscillation whose fundamental frequency is a function not only of hydrostatic pressure and surface tension, but also of liquid viscosity, and that integral overtones of the fundamental may exist at large amplitudes. A theory of vibration-induced cavitation is presented in which the Rayleigh equation is transformed into an equivalent Mathieu equation for small radial motions. The onset of cavitation at small pressure amplitudes is found to be a sharp function of frequency, bubble radius, and hydrostatic pressure, and it is shown that there is a frequency and bubble size above and below which, respectively, cavitation will not occur. Applications of bubble pulsation and cavitation phenomena to pumping and mass transfer operations are discussed.
Acoustical Properties of Water-Filled Sands
Authors: Nolle A. W. , Hoyer W. A. , Mifsud J. F. , Runyan W. R. , Ward M. B.
Published: September 2005

Experimental studies were made of the propagation of longitudinal waves in several mixtures of water with quartz sands fractionated as to particle size. The most probable particle size in the several samples ranges from 0.01 to 0.07 cm. The experimental frequencies were approximately 400 to 1000 kc/sec. Additional measurements in the same frequency range cover the reflection and scattering of underwater sound from essentially plane surfaces of these aggregates. The velocity and attenuation data are related satisfactorily to a well-known analysis for a porous acoustical material having a pliable skeleton. The reflected signal, as a function of angle of incidence, behaves approximately as expected from the conditions for continuity at the plane surface, when the appropriate complex index of refraction is used. The scattering data are compared with the analysis based on a random distribution of scattering amplitude per unit volume, with autocorrelation distance proportional to the particle size. The analysis predicts the limiting behavior of scattering coefficient with respect to particle size and frequency, but predicts a more rapid fall of scattering amplitude beyond the critical angle than was observed. The magnitude and autocorrelation properties of the fluctuations in scattered signal as the apparatus was translated to scan the sand surface were observed, and found to correspond approximately to a model based on a Gaussian distribution of local scattering amplitude.
Comments on Impact-Noise Measurement
Authors: Mariner T.
Published: September 2005

The ISO tapping machine does not rank-order floors according to the relative noisiness of the underlying room when the floors are subjected to hard-heeled, female foot traffic. Therefore, the criteria outlined in the recently released FHA Bulletin ♯750, based on the ISO tapping machine, should not be accepted as a de facto national standard.