bluuebunny/crossref_metadata_2025 huggingface dataset:
Bandwidth Error of Symmetrical Bandpass Filters Used for Analysis of Noise and Vibration
Authors: Sepmeyer L. W.
Published: September 2005

The most common device for analyzing sounds is the bandpass litter, usually with a bandwidth of one octave or a fraction there of, e.g., (one-half or one-third. Recently 1/3-octave filters are also being used for vibration analyses. The effective bandwidth of these filters is affected not only by the obvious design parameters of filter cutoff/frequency and the number of resonant elements employed which determines the attenuation rate outside the passband but also on the slope of the noise spectrum which is being analyzed. This paper investigates the effect of all these variables on the effective bandwidth of a symmetrical bandpass filter by means of a normalized mathematical model and expresses the result in terms of bandwidth error. It is found (1) that the bandwidth error increases very rapidly for large values of spectrum slope; (2) that the bandwidth error is symmetrical about an equal energy per octave spectrum slope and that an optimum design point for attenuation at the filter band edges exists for minimizing bandwidth error as a function of spectrum slope.
Properties of Sandwich-Type Structures as Acoustic Windows
Authors: Hickman John S. , Risty Donald E. , Stewart Ellen S.
Published: September 2005

The acoustic transmission of a sandwich consisting of a pair of plane parallel solid plates immersed in a liquid has been investigated theoretically and experimentally. Not only the dilatational waves, but also the shear waves, are considered. Results show greatly improved transmission characteristics over those of single thick metal plates with respect to dependence on both frequency and angle of incidence. Theoretical transmission curves for a sandwich of two steel plates have been prepared to exhibit the dependence of transmission on frequency, on ratio of plate thickness to wavelength and separation to wavelength, and on angle of incidence, respectively. Calculated transmission curves for single steel plates, including half-wave plates, are shown for comparison. An experimental test was made on a steel sandwich with lateral dimensions of the order of two wavelengths and plate thickness-to-wavelength (in the steel) ratio equal to 0.05. The measured transmission losses are within ±4 db of the calculated values.
Formulas for the Coefficient of Interaural Correlation for Noise
Authors: Jeffress Lloyd A. , Robinson Donald E.
Published: September 2005

Formulas for the coefficients of interaural correlation for noise are derived for the case where there are three similar sources, one ear, one for the other, and one for both; and for the case where there are two sources, one for one ear and one for both. Some confusion in the literature heaven these two formulas is pointed to.
Mutual Radiation Impedance Coefficients for Pistons on a Nonrigid Baffle
Authors: Mangulis V.
Published: September 2005

It is shown that one can define the impedance coefficients for pistons in all array on a nonrigid baffle, but the coefficients depend on the positions of all the other pistons in the array.
Interesting Anomaly in the Propagation of 5 Mc Pulses through Tantalum Rod
Authors: Kearney Joseph P. , Thaxton H. Mack
Published: September 2005

The propagation of 5 Mc longitudinal waves through tantalum reveals the excitation of a mode having a longitudinal velocity of propagation of 0.052 cm/μsec.
Measurement of Bottom Acoustical Characteristics
Authors: Bennett G. S.
Published: September 2005

An underwater spark source was used to observe acoustical characteristics of the bottom and top surfaces of a small body of water. Both are observed to be of a pressure-release nature, and there is a suggestion that the bottom is a better reflector than the surface.
Orthophonic Surfaces in Auditorium Design
Authors: Codegone Cesare
Published: September 2005

A study is made, in a particular case, of the shape to be given to the ceiling of a large auditorium such that the sum of the direct intensity and the intensity reflected by the ceiling is constant. It is assumed that the source is an arc of a circle in a horizontal plane with a uniform intensity distribution. The shape of the reflecting ceiling, which in this case is a surface of revolution, is given by a graphical construction founded upon mathematical conditions. The results may also be applied to both optical and thermal fields.
Attenuation of Ear Protectors by Loudness Balance and Threshold Methods
Authors: Hershkowitz Joseph , Levine Leo M.
Published: September 2005

The attenuations of two earmuffs and two earphone sockets were measured by three methods. Two of these methods used a loudness-balance procedure in which the subject, upon removal of the ear protectors, adjusted the ambient sound level to match the loudness to that which existed previously. This procedure was used with half-octave bands of thermal noise in a diffuse sound field and also with pure tones in free-field. The third method was the absolute-threshold-shift method using pure tones in free field and a clinical audiometric procedure.

At the low and high frequencies, results of the threshold method indicated an average of six decibels greater attenuation than was measured by the loudness-balance thermal noise diffuse field method. Since the latter method simulates actual usage more closely than the former, it is recommended that a safety factor be applied to threshold results in estimating the protection afforded in high noise ambients by earmuffs and receiver sockets.
Acoustic Impedance of an Outgoing Cylindrical Wave
Authors: Horton C. W.
Published: September 2005

The radiation impedance of an outgoing cylindrical wave is computed at a radius a for ka = 5, 15, 25, 35, and ∞. The values are used to explain the phenomenon of acoustic pumping and to show when the radial particle velocity can be approximated by i(2π/λρc) times the pressure.
Compressibilities of Mineral Acids
Authors: Bhimasenachar J. , Subrahmanyam S. V.
Published: September 2005

Adiabatic and apparent molar compressibilities of aqueous solutions of three mineral acids (HCl, HNO3, and H2SO4) have been studied over a wide range of concentrations, using the Debye-Sears diffraction effect. A new type of crystal holder suitable for work with acids has been described. The results have been discussed in terms of the Debye-Hückel theory.
U-Effect, II, an Electrokinetic Phenomenon
Authors: Fain W. W. , Brown S. L. , Lockenvitz A. E.
Published: September 2005

When a glass capillary tube filled with a column of alternate layers of mercury and an electrolytic solution is forced to vibrate mechanically, an ac voltage is generated across the ends of the column. Certain aspects of this electrokinetic phenomenon have been investigated both experimentally and theoretically. Data are presented for (1) the tube output voltage versus amplitude of vibration at fixed frequencies of vibration, (2) the tube output voltage versus frequency of vibration at fixed amplitudes of vibration, and (3) output impedance during vibration for constant unloaded tube output voltage versus frequency of vibration.
Electrokinetic Hydrophone Used at 9 kc
Authors: Holak William , Ackerman Eugene , Kinsloe Helen L. , Reid James J.
Published: September 2005

The construction and testing are described of a hydrophone functional at 9 kc and depending for its response on an electrokinetic effect. The use of the hydrophone in exploring the field of a Raytheon vibrator is discussed.
Apparatus for Measuring the Dynamic Mechanical Properties of Polymeric Materials between 4° and 300°K
Authors: Crissman J. M. , McCammon R. D.
Published: September 2005

An apparatus to measure the dynamic mechanical behavior of polymeric materials from 4°K to room temperature and at frequencies in the mid-audio range is described. The specimen is driven in its fundamental longitudinal mode of vibration by a transducer which is coupled to the sample by a glass fiber. The lower end of the sample, which hangs vertically, is coated with a thin layer of iron filings. A small permanent magnet is rigidly supported close to and directly below the lower end of the specimen, and a pickup coil detects the motion of the latter. This apparatus uses either the free decay or bandwidth method of determining the internal friction Q−1 and values as low as 6×10−6 have been obtained. Measurements from 8° to 300°K for lead and from 20° to 130°K for polystyrene are reported.
Sound Velocity and Attenuation in Bubbly Mixtures Measured in Standing Wave Tubes
Authors: Silberman Edward
Published: September 2005

Experimental measurements of sound velocity and attenuation constant in a mixture of air bubbles in fresh water, using a standing wave tube, are described. Bubble sizes in the mixtures were controlled between about 0.08- and 0.26-in. diameter, concentrations ranged from 0.03 to 1%, and applied frequencies from 60 to 20 000 cps. Bubbles in each mixture were of a single uniform size except for one series of experiments in which mixtures of bubbles of two discrete sizes were used. Attenuation constants were obtained for each mixture through a range of frequencies, including natural frequencies of the bubbles in the mixture. Velocity measurements were not obtained near the natural frequencies of the bubbles because high attenuation prevented the establishment of standing waves.

Data obtained in the tubes were reduced to mean, infinite conditions and compared with available theory. The measurements show that theory gives at least a good estimate of both velocity and attenuation constant in the region investigated.
Scattering of Sound by Sound
Authors: Westervelt Peter J.
Published: September 2005

Earlier studies [J. Acoust. Soc. Am. 29, 199 (1957)] of the mutual nonlinear interaction of two plane waves of sound with each other are extended to encompass arbitrary directions of travel of one wave with respect to the other; an exact solution to the first-order scattering process is obtained.
Mutual Interaction between Two Spheres in a Plane Sound Field
Authors: Embleton T. F. W.
Published: September 2005

The mutual forces between two spheres having their line of centers parallel to the direction of propagation of traveling plane waves may be many times greater than the usual radiation forces of repulsion exerted on a single sphere. Expressions are derived for the forces on each sphere in terms of diverging wavefunctions and coordinate-transformation functions. Numerical calculations show that the mean force on the sphere nearest the sound source has a value which oscillates with increasing amplitude as the separation between spheres is decreased, reaching a maximum value of repulsion from the source when the spheres are a quarter-wavelength apart. At smaller separations mutual repulsion between the spheres dominates. For the other sphere, the forces are always of repulsion, but increase in magnitude as the spheres are brought together.
Acoustical Radiation Pressure Due to Incident Plane Progressive Waves on Spherical Objects
Authors: Maidanik G. , Westervelt P. J.
Published: September 2005

The expression for the force exerted on a “rigid” sphere by a plane progressive wave is computed by making use of the momentum formulation. The expression is general in the sense that it allows for variation of the density of the sphere relative to that of the surrounding medium, as well as for a wide range of ka (k = wave number, a =radius of sphere). The numerical calculations are confined to the range ka ⩽ 10.
Wedge-Shaped Acoustic Horns for Underwater Sound Applications
Authors: McKinney C. M. , Owens W. R.
Published: September 2005

This paper gives the results of an experimental investigation of wedge-shaped acoustic horns used in conjunction with line hydrophones. An earlier study covered the frequency range from 50 kc to 150 kc. The measurements have now been extended to a lower value of 10 kc. Characteristic features of the horns are moderate directivity with minor lobes at least 40 db below axial response. The horns, which are constructed from aluminum planes covered with cellular rubber or Corprene, are simple devices and very easy to construct. Some related experiments concerning the basic operation of the horns are described.
Spatial-Correlation Functions for Various Noise Models
Authors: Cron Benjamin F. , Sherman Charles H.
Published: September 2005

Observations indicate that noise in the ocean is a superposition of an isotropic noise field and an anisotropic noise field originating at the surface. Models which produce such noise fields are described, and the spatial-correlation functions are obtained. The volume-noise model, which produces an isotropic noise field, consists of noise sources uniformly distributed within a sphere. A single-frequency component of each noise source is considered; the mean-square output of each is the same, the relative phases are random, and inverse spreading occurs. It is shown that for a very large sphere the spatial correlation is the same as that given by Marsh for a homogeneous isotropic noise field and by the Faran and Hills noise model, which consists of noise sources on the surface of a large sphere. The surface-noise model consists of noise sources uniformly distributed on a large circular area of a plane. The noise sources are assumed to be directional, in addition to having the properties listed above. The spatial correlation is obtained as a function of the directionality of the noise sources, the spacing of the receivers and their orientation with respect to the surface, and the electrical delay.
Optical Method for Analysis of Fluid Motion
Authors: Hargrove Logan E. , Thurston George B.
Published: September 2005

This method of showing fluid motion utilized the optical interference patterns observed in a flow birefringent liquid when viewed between crossed polarizing plates. The fluid used is an aqueous solution of milling yellow, a commercial dye product. The optical interference patterns are related to the stress distribution and streamline directions in the moving fluid. Fluid preparation and photographic techniques are described. Photographs of the patterns obtained are presented for an orifice in a thin plate and for an unbaffled tube.
Experimental Study of Mechanical Dissipation in Butt-Joined ADP Crystal Plates
Authors: Faraday B. J. , Gregan D. J. G.
Published: September 2005

In the design of resonant piezoelectric transducers of conventional type which utilize zxt 45 ammonium dihydrogen phosphate (ADP) plates vibrating longitudinally, the low-frequency limit is determined by the transverse dimensions of the mother block from which individual plates are cut. The growth habit of ADP, however, precludes significant accretion in the lateral direction. By cementing single crystal plates end to end, i.e., butt-joining, greater crystal lengths are produced and proportionately lower frequencies are attained. Severe limitations brought about by the properties of ADP as well as the necessity of having a solvent-resistant bond eliminate practically all adhesive types except the epoxide resins. Two principal factors considered for butt-joined bonds were the thickness of the bond and its relative position along the over-all length of crystal. The dissipation factor, the reciprocal of the mechanical Q, was measured for variable thickness of bond, keeping the position constant, and for variable position, keeping the thickness constant. These tests indicated that the thickness should be kept at a minimum and that the bond should be located away from the position of the antinode of stress and strain.
Condenser Earphones with Multiple Layers of Solid Dielectric
Authors: Sessler G. M. , West J. E.
Published: September 2005

A condenser earphone with multiple layers of thin solid dielectric material between a metal backplate and a metallized foil is described. The multilayer system has the advantage of providing a more uniform air-cushion between the electrodes, thus increasing efficiency and decreasing distortion.

The frequency response of this earphone has been measured on a standard 6-cm3 coupler. The response is flat within ±1.5 dB between 25 and 14 000 cps and within ±3 dB between 20 and 16 500 cps. In this frequency range the harmonic distortion is less than 1% and the intermodulation distortion is less than 3% at 100 dB SPL. Because of the phase linearity, the pulse response of the earphone is an almost true image of the applied voltage for pulses not containing frequencies above 15 000 cps.

The frequency response of the earphone has also been measured at seven human ears by the outer-ear canal method. The individual frequency response is flat within ±7 dB from 70 to 14 000 cps. For any one frequency, the sound-pressure deviation between individual ears is within ±6 dB.

The high quality of this earphone makes it useful for many purposes where preservation of signal wave-form is important, particularly in psycho-acoustic experiments.
Question of Ultrasonic Absorption Peaks in Ethyl Acetate
Authors: Beyer R. T. , Jacob K. C.
Published: September 2005

All available ultrasonic absorption data for ethyl acetate are considered. It is concluded that only one relaxation frequency exists in the range 3–100 mc.
Calibration and Free-Field Evaluation of a Pressure-Gradient Microphone
Authors: Thurston G. B. , Heiserman R. L.
Published: September 2005

The design, calibration procedure, and evaluation in a free field for a condenser-type pressure-gradient microphone are described. Procedures are carried out for determination of both magnitude and phase of the pressure gradient. The microphone responds to the differential action of the pressure at two closely spaced field points as communicated by two small probe tubes to either side of a sensing metal diaphragm. By means of a coupling-chamber calibration procedure it is possible to obtain a sensitivity factor and an error factor which may be used both to describe the precision of the internal structure of the microphone as well as to correct for its imperfections. The free-field studies analyze the directional characteristics and resolution capabilities of the microphone. The radiation characteristics of a circular orifice in a plane baffle as measured with the gradient microphone are compared with those predicted by simple field theory with regard to the relationship between the pressure-gradient magnitude and phase and the pressure magnitude and phase.
Self-Biased Condenser Microphone with High Capacitance
Authors: Sessler G. M. , West J. E.
Published: September 2005

A new kind of condenser microphone with solid dielectric between the electrodes is described. The system employs metallized dielectric foil electret and requires no external dc bias. The lower impedance 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 −59 dBV for a sound pressure of 1 dyn/cm2 (74 db SPL).
Simple Modification of Attenuation Equipment to Measure Velocity
Authors: Levy M. , Rudnick I. , Stern R.
Published: September 2005

A simple modification for making velocity measurements using existing ultrasonic attenuation equipment is described.
Evidence that the Lateral-Line Organ Responds to Near-Field Displacements of Sound Sources in Water
Authors: Harris Gerard G. , van Bergeijk Willem A.
Published: September 2005

The lateral-line organ of killifish is shown to be sensitive to a linear function of water displacements associated with the near-field of sound sources, with the displacement probably being the most important factor rather than velocity or acceleration. The near-field effect is discussed and is shown to be important not only for the lateral-line organs but also for the acoustical and vestibular organs. It is emphasized that the near-field effect introduces considerable complications into the study of the acoustico-lateralis system, and is of conceptual importance for the theory of hearing and the study of schooling fish.
Energy-Detection Model for Monaural Auditory Detection
Authors: Pfafflin Sheila M. , Mathews M. V.
Published: September 2005

In the auditory detection of a sinusoidal signal in the presence of random noise, it has previously been demonstrated that the presence of a “pedestal” or background sinusoid of the same frequency and phase as the signal increases detectability. This increase was confirmed in a two-interval forced choice experiment in which a 1000-cps sinusoid was present in one of two 0.1-sec intervals, and the noise plus pedestal were present in both intervals. Pedestals of moderate intensity in phase with the signal increased detectability. Pedestals in quadrature (90° out of phase) with the signal did not improve detectability. Very large pedestals decreased detectability irrespective of phase. A simple energy-detection model was developed and its performance compared with the experimental results. The model consists of a bandpass filter, a square-law element, and an integrator. The probability of correct detection varies with signal level in a manner similar to the auditory results. Detectability is improved by an in-phase pedestal and approaches that of a correlation detector in the limit of infinite pedestal. Detectability is not improved by quadrate pedestals. The model can be modified to predict the decreasing detectability with large pedestals.
Perception of Steady and Intermittent Sounds with Alternating Noise-Burst Stimuli
Authors: Thurlow Willard R. , Marten Anita E.
Published: September 2005

Bursts of high-pass filtered thermal noise coming from two different sources in space were alternated in time (with no time gap between bursts). Separation angles between sources from 5 to 50 deg were used, and alternation rates from 2 to 14 per sec. Duration of bursts was also varied. Subjects indicated for each sound perceived whether it was steady or intermittent, and where it was located.

When the angle between sources is small, some subjects may hear only one continuous sound, provided that the repetition rate is relatively high. More commonly, however, our subjects tend to hear one steady sound and one intermittent sound when the separation angle between sources is small; they tend to hear this pattern at wider separation angles when the duration of one of the stimuli is short. When one of the bursts has short duration, and sources are separated by 30 to 50 deg, it appears to many subjects that the short burst is markedly displaced in location. For wider angles of separation between sources, and various conditions of duration, many subjects can also hear a third steady sound between the other two. Occurrence of this latter sound has especially interesting implications for a theory of sound-localization mechanisms.
Crest and Extremal Statistics of a Square-Law-Derived Random Process
Authors: Smits T. I. , Smith D. A. , Lambert R. F.
Published: September 2005

Theoretical analysis of the crest and extremal statistics of a square-law-derived random process is presented. The differences between the crest and the extremal statistics, particularly the bandwidth dependence of the latter, are illustrated for the Gaussian-derived case. The theory is applied to the statistical response of a uniform bar in tension. Particular attention is paid to the crest distributions which deviate from the integrated Rayleigh distributions in a predictable way at large amplitudes of vibration. Experimental distributions obtained from the strain response of a uniform bar forced in its fundamental mode by band-limited Gaussian white-noise signals are in excellent agreement with calculated values.
Analysis of Nasal Consonants
Authors: Fujimura Osamu
Published: September 2005

The sound spectra of nasal murmurs in various vowel contexts have been studied by use of an analysis-by-synthesis scheme. The acoustic characteristics are described in terms of format-antiformant distributions (pole-zero locations of the transfer function for the articulatory system) in the frequency domain. It is shown that the location of the antiformant characterizes the murmur of each consonant within the class. The spectral structures are discussed with reference to the articulatory features, and acoustical interpretations of the observed characteristics of the formants and antiformant are given. Also suggested is the existence of certain gross spectral features that are characteristic of nasals as a class.
Perception of Two-Component Noise Bursts
Authors: Stevens K. N. , Sandel T. T. , House A. S.
Published: September 2005

In a series of experiments, listeners were asked to make judgments of the relative duration, loudness, and stress associated with the components of stimuli consisting of sequences of two noise bursts. The over-all duration of each stimulus was the same, and the two components were given various relative intensities and durations. All response sets demonstrate marked asymmetry, particularly those requiring a judgment of the stress pattern of the sequence.
Bonding Methods and a Bonding Clamp for Ultrasonic Measurements
Authors: Sullivan Paul F.
Published: September 2005

The results of an experimental investigation into the techniques of coupling the transducer to the specimen in making ultrasonic measurements are presented. Two major couplants, glycerine and phenyl salicylate, were subjected to tests. As a result of these tests, a bonding clamp was developed that greatly increased the reproducibility and accuracy of the measurements.
Vibrations of an Infinite, Monoclinic Crystal Plate at High Frequencies and Long Wavelengths
Authors: Kaul R. K. , Mindlin R. D.
Published: September 2005

An asymptotic solution of the frequency equation of an infinite, monoclinic crystal plate is derived. Formulas are given which describe the variation of frequency with wavelength at high frequencies and long wavelengths.
Frequency Spectrum of a Monoclinic Crystal Plate
Authors: Kaul R. K. , Mindlin R. D.
Published: September 2005

A sketch is constructed of the branches of Ekstein's frequency equation for an infinite, monoclinic crystal plate. The sketch is for the AT cut of quartz and covers a wide range of frequencies and propagation constants. The real, imaginary, and complex segments of the branches are included.
Extensional Vibrations of Thin Quartz Disks
Authors: Lubowe A. G. , Mindlin R. D.
Published: September 2005

A general solution is given for the contour modes of vibration of circular crystal disks of certain elastic symmetries. The solution is applicable to three cuts of quartz, for which the frequencies of fourteen modes are computed.
Experimental Determination of Compressional Velocity for the Bottom Layer by the Dispersion Method
Authors: Barakos P. A.
Published: September 2005

Pressure waves, generated different points along radial runs on the continental shelf and slope south of Long Island by 1-1b explosions of TNT, were received by hydrophones connected by sea cables to a fixed station in the ocean. An extensive analysis of the dispersion phenomenon in the water wave covering five radial courses within a 150-mile radius of the receiving station was made. Nearly 500 charges were examined in this analysis, and the “seasonal” effect upon dispersion was investigated. In general, for shallow water the received pressure wave displays certain features that are characteristic of the depth of the water, the velocity-depth contour in the water, the range, and the structure of the bottom. Dispersion in the water wave was also observed in a surface channel formed in moderately deep water. The observed dispersion phenomena were studied quantitatively, and the data were interpreted in terms of the bottom structure. Two- and three-layer liquid models were employed to interpret the experimental results. An expression is presented that relates all the parameters pertinent to the dispersion phenomenon.
Variation of Array Performance with Respect to Statistical Phase Fluctuations
Authors: Brown J. L.
Published: September 2005

The effect of phase fluctuations on the mean-square time-averaged output of a discrete linear array is considered under the assumption that the fluctuations are governed by a Gaussian joint-probability density function. In particular, a closed-form expression is derived for the variance of the array output over the ensemble of phase variations.
Prestressed Electrodes for Spherical Transducers
Authors: Pence E. A. , Corwin R. E.
Published: September 2005

The power-handling capabilities of ceramic piezoelectric transducers in pulsed operation at low duty rate are limited by tensile rupture. Compressive bias has been used to increase the power-handling capabilities of integral spheres; this mechanical bias has been applied by controlled nickel electroplating over the outer surface, such that the plated coating is under high tensile stress. Units formerly limited to 50 W/cm2 can now be operated at 200 W/cm3.
Distribution of Response Crests in a Bimodal System
Authors: Park G. L. , Lambert R. F.
Published: September 2005

The distribution of crests associated with a lightly coupled bimodal vibrating system under band-limited white-noise excitation has been calculated and measured. Measured crests of the strain response of a mass-loaded cantilever beam, used as the bimodal system, follow the expected Rayleigh distribution to within experimental accuracy. Noteworthy is the result that crests of four times the rms strain are obtained using a bimodal configuration, and crests of five times the rms strain are obtained when the beam is vibrating in a unimodal configuration.
Vortex Action in Edgetones
Authors: Powell Alan
Published: September 2005

The elements essential to a new vortex theory of edgetones are described with the aid of a simple flow model valid for small edges. It is shown how both the feedback to the orifice and the sound radiation may be directly attributed to the velocity field of the vortex cast off from the edge together with the sympathetic circulation about it. An upper limit to the intensity of the edgetone is discussed when the edge is very small; it depends on the size of the edge. It is shown how the small edge used by Lenihan and Richardson is quite adequate in size to support the flow pattern implied by the feedback explanations of the mechanism of edgetones. The theory is shown to be equivalent to the so-called acoustical one in which the action at the edge is represented by a dipole whose strength is associated with the fluctuating force sustained by the edge. While the rift between these two approaches to the theory of edgetones may be considered closed, it is to be noted that each may continue to have its special attractions in respect of specific requirements.
Ultrasonic Intensity Gain by Composite Transducers
Authors: Fry William J. , Dunn Floyd
Published: September 2005

The radiation of plane acoustic waves into a medium by composite layered transducers composed of a piezoelectric element and two lossless coupling media is described analytically. The increase in acoustic intensity in the medium receiving the radiation produced by the composite structure over that produced by direct coupling (piezoelectric element in contact with the medium), for the same value of the electric field strength, is considered quantitatively and the results are presented graphically. Composite transducers of the type described can be expected to achieve considerably higher ultrasonic intensities (1000-fold increase) in both unfocused and focused beams than have heretofore been realized.
Evaluation of the Variability in Audiometric Procedures
Authors: Jackson J. Edward , Fassett David W. , Riley Edward C. , Sutton William L.
Published: September 2005

This paper describes two experiments which were carried out to evaluate the variability in audiometric procedures. One was designed to evaluate the precision of the audiometric process; the other to determine the repeatability of results in individual subjects taking these examinations. Some differences were found between various instruments used and a learning effect was detected on the part of the subjects. While these differences were not considered large, it was important to determine their magnitude in relation to the study of the effect of noise on hearing.
Auditory Threshold as a Function of Forced-Choice Technique, Feedback, and Motivation
Authors: Lukaszewski J. S. , Elliott D. N.
Published: September 2005

Shifts in the threshold of hearing were determined as a function of prolonged testing (12 sessions) with four experimental groups: forced-choice-feedback, no-forced-choice-feedback, forced-choice-no-feedback, and no-forced-choice-no-feedback. The forced-choice technique was found to improve performance if used with immediate knowledge of results (feedback). Otherwise, thresholds obtained under a forced-choice procedure were poorer than those obtained under no-forced-choice instructions. Even after 12 sessions, increasing the subjects' motivation by offers of monetary rewards resulted in a further decrease in threshold.
Studies on the Aural Reflex. II. Reduction of Temporary Threshold Shift from Intermittent Noise by Reflex Activity; Implications for Damage-Risk Criteria
Authors: Ward W. Dixon
Published: September 2005

The temporary threshold shift (TTS) produced by intermittent noise was compared with that produced by steady noise. It was found that an on-fraction of 0.50 (30-sec bursts of noise alternating with 30 sec of quiet) resulted in a reduction of 50% in the TTS produced by 1200–2400- and 2400–4800-cps octave bands of noise. However, in the case of 300–600- and 600–1200-cps noise, the same on-fraction reduced the TTS to about one-third the value observed after continuous stimulation. The difference is attributed to the action of the middle ear muscles, which attenuates low-frequency sounds more than high-frequency sounds. Burst duration of 600–1200-cps noise was varied, holding the on-fraction constant at 0.50; results indicate that the same fractional reduction in TTS is produced by burst durations from 7.5 sec to 1 min. The significance of these results in regard to damage-risk criteria is discussed. In particular, the inadequacy of the equal-energy rule in assessing the potential danger of intermittent noise exposures is emphasized.
Normal-Mode Theory Applied to Short-Range Propagation in an Underwater Acoustic Surface Duct
Authors: Pedersen Melvin A. , Gordon David F.
Published: September 2005

This paper presents detailed numerical comparisons between propagation losses as calculated by ray theory and by mode theory. Both theories are based on the bilinear surface-duct model. In the image-interference region, the theories give almost identical results, the accuracy of the mode solution being limited at very close ranges by the number of modes treated. As many as 40 modes are considered. Comparison with experimental data at 530 and 1030 cps indicates that the mode theory is definitely superior to ray theory in regions where ray theory predicts shadow zones and caustics. The nature of the mode solution is examined in detail. The manner in which the mode theory produces the image-interference pattern is controlled by the detailed amplitude and phase characteristics of a large number of modes and is not readily interpreted as the interference between a direct and a surface-reflected acoustic path.
Resonance—Antiresonance of Conducting Piezoelectric Resonators
Authors: Arlt G.
Published: September 2005

The input impedance of conducting piezoelectric plates, excited to thickness vibrations, is calculated and the equivalent circuit is shown. Antiresonance and resonance appear as maximum and minimum the resistance curve. They are just as strongly excited if ω0τ = 1. (ω0 = 2π×resonance frequency, τ = RC, the relaxation time of the circuit far from resonance.) Contrary to the case with nonconducting piezoelectric resonators, higher harmonics are advantageous for determining the electromechanical coupling coefficient.
Optical Method for Ultrasonic Waveform Analysis, Using a Recursion Relation
Authors: Cook Bill D.
Published: September 2005

The intensity distribution of light diffracted by progressive ultrasonic waves is used to find the harmonic structure of these waves. A recursion relation has been found that permits the calculation of the harmonic structure from a set of simultaneous linear equations. The coefficients of these equations are obtained from measurement of the diffraction orders.
Extension of the Method of Normal Modes to Sound Propagation in an Almost-Stratified Medium
Authors: Pierce Allan D.
Published: September 2005

A theory is presented that permits the extension of the method of normal modes to guided-wave propagation in a medium with properties varying slowly with horizontal coordinates in addition to varying with the vertical coordinate. The principal assumption is the neglect of coupling between normal modes. It is predicted that different frequencies in different modes follow different horizontal paths. A ray-tracing method is described for computing these paths. The theory is then applied to the study of the dispersion of waves from an explosive source in shallow water with slowly varying depth.
Thermal Relaxation in Oxygen with CH4 and CD4 Admixtures
Authors: Schnaus Urban E.
Published: September 2005

The Napier (relaxation) frequency of oxygen has been determined as a function of methane and deuterated methane impurity at room temperature and at 100°C, using the pressurized Kundt's tube developed in this laboratory. Methane is three times as effective as hydrogen itself, and is comparable with water vapor in causing shift to higher frequencies. Deuterated methane is about 14 as effective. The shifts are in all cases linear with the (small) concentration, up to 2%.
Green's-Function Technique in the Dynamics of a Finite Cylindrical Shell
Authors: Cottis M. G.
Published: September 2005

The Reissner linearized equations of motion, including hysteretic- and viscous-damping terms, are adopted in the study of the dynamics of a finite, thin, elastic cylindrical shell of circular cross section. The integral representation of the radial displacement solution is obtained for an arbitrary, time-dependent pressure field over the shell surface and the associated Green's-function solution is calculated. In particular, the shell response to a moving shock wave (step-function discontinuity), impinging upon the shell at an arbitrary angle of incidence, is calculated. In the special case of axial symmetry, two additional waveforms are considered, that of a moving exponentially decaying shock wave and of a ramp/step-function wave. Typical numerical results are given in the form of displacement-time curves and the effects of the pressure-wave parameters (decay and rise time) are examined. The dynamic behavior of a prepressurized shell is also considered. It is shown that the Green's-function solution remains form-invariant under the introduction of an internal static pressure P0; this, in turn, leads to a simple rule for deducing the response to a given external pressure field when P0≠0 from known solutions corresponding to the case of P0 = 0.
Exact Inverse-Separation Series for Multiple Scattering in Two Dimensions
Authors: Burke James E. , Censor Dan , Twersky Victor
Published: September 2005

We consider configurations of arbitrary scatterers (s = 1, … ,N) in two dimensions, such that the circles circumscribing the scatterers do not intersect. As shown previously [V. Twersky, in Electromagnetic Waves, R. E. Langer, Ed. (University of Wisconsin Press, Madison, 1962), pp. 361–389], the solution can be written in terms of the multiple-scattered scattering amplitudes Gs, and the Gs are specified by the presumably known farfield isolated scattering amplitudes gs by a set of integral equations G(g) (which can be converted to algebraic equations involving Hankel functions of the separations bst, etc.). Among other applications, the previous paper gave the complete asymptotic series for G(g) in inverse powers of the b's; this was based essentially on Hankel's asymptotic expansion for the Hankel functions Hn. The present paper derives the analogous convergent representation of G(g) based on the exact representation of Hn in terms of Lommel polynomials. For N scatterers, we give the multiple-scattering solution as a series in H0, H1, b−n, and the derivatives of g with respect to angles. For two scatterers, we give a closed form in terms of a differential operator.
Technique for Determining the Frequency Response of Linear Mechanical Systems
Authors: Pechter L. S. , Kamel H. , Tanner L. N. , Knudsen L. J.
Published: September 2005

A technique for determining the frequency response of linear mechanical systems is presented that lends itself to solution by graphical means or by digital computer. It provides a means for analyzing multimass systems and the various types of damping associated with these systems and, in addition, provides a means for tracing the contributions of the various elements. The technique involves determining the displacement and force transmissibilities of each element of a multimass system as an individual single-degree-of-freedom system. The equations of motion are then written in terms of these individual transmissibilities and the desired response calculated by either graphical or computer methods. Because the response equations are written in terms of transmissibilities and not spring and damping constants, various types of damping can be utilized and even interchanged within a given problem without affecting complexity. In this paper, three types of damping are discussed: viscous, structural, and elastically supported viscous damping. Additional forms can be added by the user as necessary.
Scattering Theory for One-Dimensional Problems
Authors: Harrison Mark , Plutchok Robert
Published: September 2005

An analytical method is given that allows one to compute for an acoustic wave the reflection and transmission coefficients for a scattering layer such as might be encountered in the ocean where the sound velocity varies in a complicated manner. The technique described is called the method of partial waves since there is some analogy with the corresponding technique for three-dimensional scattering. The problem of a scattering layer is treated by an integral-equation method. The first iteration of this integral equation is obtained for a simple case where the exact answer is also known and is shown to give good agreement. This result is compared to the first Born approximation and is shown to be considerably more accurate. The method can also be used in idealized cases where boundary conditions are known. One such simple case is considered and the method developed in this paper is shown to yield the exact answer. The method is a quite general mathematical technique and can be adapted to the analogous problem in optics, quantum mechanics, electromagnetic, and seismic waves.
Mathematical Models for the Prediction of SOFAR Propagation Effects
Authors: Hirsch Peter , Carter Ashley H.
Published: September 2005

Various analytical models for the acoustic speed-versus-depth profile of the ocean near the sound-channel axis are examined with a view toward predicting the characteristic features of SOFAR transmission, especially the time dispersion of the multiple SOFAR arrivals. It is found that these features are accounted for only by very specific models. In particular, the one analytically tractable model that leads to the observed results appears to be given by c2 = c02(1 −| αz|β)−1, with 1 <β <2.
Tuning Resonant Sound Radiators to Achieve a Minimum Acoustic Q
Authors: Junger M. C. , Thompson William
Published: September 2005

Various techniques for tuning sound radiators so as to reduce their dimensions for a specified resonant frequency have been proposed. The effect of these techniques on the acoustic quality factor Qa is analyzed. It is is shown that the curve of Qa versus dimensionless frequency displays minimum if the tuning is achieved by adjusting the compliance while the modal mass is kept constant. For a given mode, this minimum falls within a narrow range of dimensionless frequency, whatever the modal mass. Above this range, Qa can be reduced by increasing the compliance. Below this range, Qa can be decreased by reducing either the mass or the compliance. A vibrator that is more than critically damped can be rendered oscillatory by increasing its stiffness or its compliance.
Experimental Liquid-Filled Transducer Array for Deep-Ocean Operation
Authors: Kendig Paul M. , Clarke Hugh J.
Published: September 2005

A small experimental transducer array was designed, constructed, and tested to demonstrate the feasibility of enclosing the elements in a liquid-filled housing that requires no pressure-release materials. The transducer consists of four dumbbell-type lead zirconate titanate transducer elements that are set in close-fitting cavities in a high ρc metal block. The entire housing is filled with a silicone fluid and provision is made to maintain the inside pressure equal to the pressure on the outside at all times. Presentation of frequency-response curves, electrical-input impedances, and efficiencies demonstrate that the transducer characteristics are relatively insensitive to ambient pressures up to 1000 psi, the maximum pressure available for test. The transducer is further characterized by high power capability, good efficiency, a low Q, and a high effective electromechanical coupling coefficient.
Low-Frequency Expansions for Scattering by Separable and Nonseparable Bodies
Authors: Darling D. A. , Senior T. B. A.
Published: September 2005

This paper is concerned with the long-wavelength expansion of the scattered field in the ratio body dimension to the wavelength. For scalar scattering by spheroids, prolate and oblate, hard as well as soft, the radius of convergence of the series is determined. A method is given whereby the coefficients in the expansion for a general body can be obtained from the solutions of a set of specific and classical potential problems. It is shown how the required solutions can be found for a body that is the intersection of two or more bodies, for each of which the exterior electrostatic Green's functions are known, and as an illustration the procedure is applied to a hard finite cone with a spherical cap.
Behavior of Linear Systems with Random Parametric Excitation
Authors: Gray A. H.
Published: September 2005

The behavior of linear systems with parameters that vary as “physical” white noise (very-wide-band Gaussian) is developed. The Fokker-Planck equation is used to develop moment equations, and “equivalent” systems are derived.
Optical-Correlation Detector for the Audio Frequency Range
Authors: Parks J. K.
Published: September 2005

A noncoherent optical-correlation detector of the stored reference type is described. The correlator performs real-time correlation of multiple delayed signals with the stored reference without a priori knowledge of the signal delays. The correlator makes use of real-time integration, thereby making it unnecessary to record received signals prior to correlation. An experimental version of the correlator is described, its performance is analyzed, and the predicted performance is compared with the observed performance and found to agree to within 3 dB. A signal-processing gain of 20 dB is obtained with the experimental version of the correlator.
Effect of Repetition Rate on the Loudness of Triangular Transients
Authors: Carter N. L.
Published: September 2005

The loudness of triangular transients with 0.5-msec rise time and 1-msec duration is studied as a function of repetition rate in the range of repetition rates from 1 pps (pulse/sec) to 128 pps. It is found that for each doubling of the repetition rate a reduction of 3 dB in peak level of the transients is required to maintain equal loudness.
Pitch Shifts due to Low-Pass and High-Pass Noise Bands
Authors: Webster J. C. , Muerdter D. R.
Published: September 2005

Pitch shifts in the presence of high- and low-passed noises are shown to be generally upwards. The upward shifts are when the test tones are either in or just above the bandpass of the noise and almost never toward a distant high-passed noise band. Downward shifts are rare and small in magnitude. If present and real, they shift away from high-passed noises and not toward distant low-passed noises.