bluuebunny/crossref_metadata_2025 huggingface dataset:
Loudness Summation and Spectrum Shape
Authors: Scharf Bertram
Published: September 2005

The loudness of 3-tone complexes was studied as a function of the intensity relations among the three components. Generally, for a given SPL and a given frequency separation (ΔF) between the two side bands, a 3-tone complex was loudest when its spectrum was flat, i.e., when the components were equally intense. Two types of spectra were investigated: (1) peaked spectra, for which the loudness of the complex was measured as a function of the intensity difference between the middle component and the less intense side bands, and (2) sloped spectra, for which the loudness was measured as a function of the slope of the line spectrum. Although for both peaked and sloped spectra, the loudness of complexes whose ΔF was greater than a critical band decreased as the shape of the spectrum became less and less flat, the decrease in loudness was more rapid for the peaked spectra. The loudness of complexes whose ΔF was less than a critical band changed little as a function of either peakedness or slope. Moreover, the data suggest that reducing the relative intensities of one or both side bands has a similar effect upon loudness as does changing their frequencies to produce a smaller ΔF; both types of change usually produce a reduction in loudness. (This research was supported by a grant from the National Institute of Health, U. S. Public Health Services.)
Some Experimental Results Using a Scanned-Line Array to Determine the Direction of a Sound Wave
Authors: Whitmarsh D. C. , Pigott M. T.
Published: September 2005

An attempt is being made to employ independent hydrophone elements uniformly spaced along a straight line to deduce the bearing of an incoming plane sound wave. Upon sampling the outputs of the hydrophone elements in succession, one simulates a single hydrophone moving relative to the sound wave. The signal measured in such a case would have a frequency of f=f0 (1 − α cosθ) where f0 is the frequency of the sound, α is the ratio of the scanning speed to the sound speed, and θ is the bearing angle to be deduced from a measurement of f. A method to accomplish this was outlined in a paper presented at the June, 1960 meeting of the Society. Since then a hydrophone about four feet long containing 134 independent elements has been obtained and the necessary switching and sampling circuits built to test the method experimentally. Measurements made in a laboratory tank confirm the theoretical results very nicely for a steady signal. These together with the results obtained using a pulsed signal and the effects of noise on the system will also be presented.
Compressional Velocity Determination for the Bottom Layer between Cape May and Montauk Point
Authors: Barakos Peter A.
Published: September 2005

Pressure waves generated at different ranges on the continental shelf and slope by explosions of one pound of TNT were received by hydrophones connected by sea cables to a fixed station in the ocean. An extensive analysis of the dispersion in the water wave covering five different courses within a 150-mile radius from the receiving station was made with over 400 charges in all the seasons of the year. In general, for shallow water the received pressure wave displays certain features which 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 used to interpret the experimental results.
Ultrasonic Techniques in Ophthalmology
Authors: Baum Gilbert , Greenwood Ivan
Published: September 2005

Ultrasonic visualization is clinically important in ophthalmology because it makes possible accurate diagnosis of conditions existing in the soft tissues of the orbit and the light-opaque eye. No other diagnositic method short of surgery can yield comparable information. Short-pulse, focused-beam, 15-Mc apparatus is used. Serial distance-azimuth scans are displayed on a radar PPI and are photographed. Inherent resolution is better than 0.2 min. Technique topics to be discussed include: high resolution, compound scanning, quantitative reflection coefficient measurement by a photo-densitometric method, artifact identification, and three-dimensional ultrasonograms. Illustrative clinical ultrasonograms and their interpretations will be presented.
Sonic Block Silencing for Axial and Screw Type Compressors
Authors: Sobel J. A. , Welliver A. D.
Published: September 2005

The sonic block concept has proven to be an extremely effective method of reducing compressor radiated noise. This type of silencer is based upon the classical fact that when a fluid is traveling in a direction opposite to and at a speed equal or greater than the velocity of propagation of a disturbance in that fluid, then the disturbance cannot be transmitted upstream through the fluid. Since the principle of operation involves only direction and relative speeds, its acoustical performance is independent of frequency. The amount of noise reduction is limited only by (1) suppressor wall noise radiation; (2) noise escape through boundary layer at the sonic block; and (3) fluid acceleration noise. This paper describes sonic block designs for turbojet engine axial compressors and small industrial screw type units. Actual noise reductions are presented for a 225 lb/sec axial flow compressor and a 2 lb/sec Lysholm type unit. In the case of the high speed axial flow unit, high frequency blade noise was submerged below the levels of background noise. Noise reductions, ranging from 28 48 db, were measured from 20–10 000 cps for the screw compressor.
Noise Rating Method for Fluorescent Lamp Ballast Transformers
Authors: Sperry William C.
Published: September 2005

The noise radiated from a composite fluorescent lamp system (ballasts, lamps, fixtures, and supporting structure) is dependent to some degree upon the physical and geometrical characteristics of all components. Analytical representation of the composite continuum is inhibited by many difficulties, not the least of which is the wide variation in the various composite systems that can occur. However, the mechanical impedance concept presents a powerful tool for systems of this type where selected measurements can be performed to greatly reduce the analytical effort. Theory is presented to analytically represent the composite system in terms of mechanical impedance. Measurements utilizing a force sensor were made for a number of ballasts which yield information useful in the general theory. A rating method was devised for the ballasts, independent of the rest of the system, which compares their noise-generating capabilities. The method is based upon the measured results of over-all force levels increasing monotonically with input electrical power. (This research was sponsored by Sola Electric Company.)
Noise Characteristics of Several Types of Cooling Tower Installations
Authors: Hoover Robert M.
Published: September 2005

Results of noise measurements of five cooling tower installations are presented. Included are data on: (1) both induced and cross draft flow towers using indirect drive, slow speed propeller fans; (2) a forced draft tower using centrifugal fans; and (3) an induced draft tower with a direct drive, medium speed propeller fan. These data include both measurements of fan and water flow noise at close-in and distant positions. Also, as two of the tower installations were enclosed in office building penthouses, some of the data can be used as a basis for measures aimed at controlling the transmission of airborne noise from the cooling tower penthouse to occupied spaces in the building. Noise control measures employed at these cooling tower installations are briefly discussed, and where possible the data are related to previously published procedures for estimating cooling tower noise spectra and levels.
On the Problem of Sound Reduction in Vehicles
Authors: Betzold C.
Published: September 2005

The development of modern rail and road vehicles has been accompanied by greater attention to acoustical considerations, particularly as they contribute to travel comfort as well as safety. In general, there is strict separation of the four applications: (a) airborne sound absorption; (b) structure-borne sound absorption; (c) structural sound isolation; and (d) airborne sound isolation. It is recommendable that greater use be made of the combination of these techniques in order to attain worthwhile reduction of the sound levels in vehicles. Synthetic materials suitable for airborne isolation and structure-borne absorption have been on the market for several years. In addition to the mentioned acoustical-physical requirements, there are also special technical requirements related to vehicle designing. Such may be light weight, resistance to gasoline, diesel oil, and weather; durability, mechanical strength, etc. Within the range of problems of vehicular acoustics, the special problems of airborne noise isolation by means of special synthetic materials will be treated.
Quartz Crystal Accelerometers and “Charge” Amplifiers
Authors: Studier W. A.
Published: September 2005

Measuring systems using these components have excellent sensitivity over wide ranges of temperature, permit precise measurements of accleration to 50 000 g through frquency range of 0.1 cps to 50 kc, and feature the capability of simple, direct calibration by quasi-static methods. Quartz crystal accelerometers are unsurpassed for linearity, complete freedom from hysteresis, negligible deflection under load, and ability to withstand severe overloads without damage. The recent development of the “charge” amplifier provides industry with a new and very useful tool. (Theory of operation, applications, and advantages are reviewed in detail.) Three calibration techniques are described. The extremely high insulation resistance of quartz transducers is exploited in the design of the “charge” amplifier to enable calibration at high working levels by direct application of weights to the seismic mass. After calibration in the “near-dc” mode, the system is returned to drift-free, dynamic operation with no loss of accuracy. Intermediate level calibration involves comparison with a laboratory standard servo-accelerometer; accelerations between plus and minus one g are calibrated by precise orientation of the instrument in the earth's gravity field.
Techniques for the Rapid Estimation of Accelerometer Natural Frequencies
Authors: Clements E. W. , Stone M.
Published: September 2005

In order to determine the usable frequency range of an accelerometer, it is necessary that its natural frequency be known. Three simple methods for approximately determining natural frequency are described: measurement of the ringing frequency excited by electrical and mechanical pulse inputs to the accelerometer and measurement of the accelerometer's impedance as a function of frequency. While subsidiary to more refined calibration techniques, these methods are useful because of their speed and simplicity and because they may be utilized with the accelerometer in place. Results obtained for several piezoelectric acceleromeetrs are given.
Low-Amplitude Nonlinear Theory of Plane Progressive Waves
Authors: Blackstock David T.
Published: September 2005

As the title suggests, this is a theory of plane waves of finite amplitude which is intermediate between traditional small-signal theory and exact nonlinear theory. It is based upon a certain assumption concerning the relation between wave amplitude and distance from the wave source. When this assumption holds, as it does in a large class of cases, one can simplify substantially Earnshaw's exact but highly unmanageable solution for plane waves. Application of the same assumption to the differential equations governing plane-wave propagation allows one to derive a useful approximate nonlinear wave equation. The exact solution of this approximate equation is the same as the simplified version of Earnshaw's solution. One interesting feature of this theory is that the form of the approximate nonlinear wave equation and its solution are the same in Eulerian and Lagrangian coordinates. A specific example will be discussed, namely the wave motion produced by sinusoidal motion of a piston in a lossless tube. It is found that the work of many past investigators can be unified by this theory. The limits of validity of the theory will also be discussed. (Part of this work was carried out at Harvard University with support from the Office of Naval Research.)
Reflection of Sound from a Nonuniform Periodic Boundary
Authors: Heaps H. S.
Published: September 2005

The concept of surface impedance is used to investigate theoretically the reflection of sound from a nonuniform boundary whose irregularities possess a periodic variation. The method used is similar to that of Lysanov [J. Acoustics USSR 4, 47 (1958)]. By supposing the impedance to be a certain function of the angle of incidence, the results may be applied to determine the sound reflected from a sinusoidal interface between two propagating media. Numerical results are presented to indicate the dependence of the reflected radiation upon the form of the impedance variation, the angle of incidence, and the wavelength of the sound.
Acoustic Response of a Rectangular Cavity Excited by a Moving Airstream
Authors: Lassiter L. W. , Plumblee H. E. , Gibson J. S.
Published: September 2005

A recess or cavity in an aerodynamic body in motion is usually subjected to intense acoustic and aerodynamic response. This response involves the combined effect of a random aerodynamic “buffet” and discrete acoustic resonances. A theory has been developed to define the acoustic resonant response, using the radiation resistance of a rectangular cavity as an intermediate step. The acoustic model of the cavity is that of a rectangular room with five walls rigid and one “soft.” Comparisons of theoretical and experimental response are made at Mach numbers from 0.2 to 5.0. Movies are shown illustrating the boundary layer phenomenon associated with the resonant response of the cavity. (This work supported by a Wright Air Development Division contract.)
Concurrent Repetition of a Continuous Flow of Words
Authors: Sergeant Russell L.
Published: September 2005

This study was designed to evaluate the effect of rate (68, 127, 180 words/min) and intensity (20, 40, 60 SRT) of stimulus presentation, and of practice, upon concurrent repetition of a continuous flow of heard words. Subjects were 33 enlisted men. A three-part tape was made to obtain an SRT, to present a pretest trial, and to present three PB-50 lists read as continuous speech. Intelligibility scores were assigned to each subject's taped repetitions. Twelve subjects had an 8-day practice with other PB lists. Analysis of variance yielded an F associated with practice significant beyond the 0.5% level. The F's for rate and intensity were significant beyond the 0.1% level. Pearson r's were calculated between performance level and six psychological and auditory tests. Only the r of +0.54 with the Seashore Rhythm test was significant. It was concluded that: (a) Performance improves with increased intensity of heard speech, and with practice; (b) Performance increases when the rate of stimulus presentation is decreased; (c) A positive relationship exists between performance and scores on the Seashore Rhythm test; (d) Under proper conditions of rate and intensity, some persons can be trained to perform with more than 90% intelligibility.
Study of Intelligibility Improvement with Out-of-Phase Connections of Headphones
Authors: Greenberg D. , Benecke H. O.
Published: September 2005

Previous work on the effect of interaural phase relations on the masking of speech by white noise, suggested the possibility of improving communication in ambient noise by simply reversing the connections of one earphone of the headset to produce out-of-phase reception. A series of intelligibility tests was conducted at the U. S. Naval Air Development Center, Johnsville, Pennsylvania, in 1949 to determine whether improvement could be obtained under conditions simulating those encountered in naval aircraft. Headphones in use then were almost entirely connected in-phase. The results of intelligibility tests, performed with listeners subjected to 119 db of simulated reciprocating-engine aircraft noise, showed that for low and intermediate signal levels, the out-of-phase scores averaged only about five percentage points higher than in-phase scores; for high signal levels, the out-of-phase scores were about five percentage points less. The overall results did not indicate any significant advantage for the out-of-phase connection for communications in naval aircraft.
Decision Functions for Voiced-Unvoiced-Silence Detection
Authors: Lochbaum C. C. , David E. E. , Mathews M. V.
Published: September 2005

At the June, 1960, Acoustical Society of America meeting, we described a voiced-unvoiced-silence detection procedure. It incorporated two independent threshold decision rules, one operating on the zero moment of the speech spectrum for the spoken-silent choice, the other operating on the first moment for the voiced-unvoiced choice. A generalization of this procedure involves a decision which depends jointly on the two moments. This paper compares the performance of this process with the simpler one. Value functions placing specified weights on the nine possible outcomes of this 3×3 detection situation were defined, and decision rules maximizing the values were computed. Maximum likelihood, maximum likelihood weighted by prior probabilities, and rules tailored to vocoder applications were studied. Probabilities of the six possible confusions and the three correct answers were computed for all rules. Data for the evaluation consisted of twenty 3-sec utterances by two men and two women. Voiced, unvoiced, and silent intervals in these speech samples were established visually from spectrograms. Performance depends, of course, on the value functions, but at most a reduction of 13 in the over-all error rate over the simple rule was achieved.
A Miniature Universal Lightweight Military Microphone
Authors: Simshauser E. D. , Carrell R. M.
Published: September 2005

A group of moving-coil noise-cancelling microphones has been developed which exhibits a sensitivity approximately 6 db greater than previous microphones of equivalent size, weight, and bandwidth. This gain is the result of an asymmetrical internal construction which results in cardioid directional characteristics. A result of this construction is a microphone which is small enough for an oxygen helmet and light enough for boom use, having a sensitivity of 40 μv/d cm2 with a 150-omb load, which is compatible with Army and Navy microphone circuits. The equivalent circuits and design philosophy are described. (The work was supported by a U. S. Air Force contract.)
Learning to Identify Nonverbal Sounds
Authors: Swets John A. , Green David M. , Winter Earl F.
Published: September 2005

Research is under way to determine whether or not the techniques of automated teaching (active participation of the learner, immediate feedback, presentation of items conditional upon the learner's recent past performance, etc.) will significantly facilitate learning to identify nonverbal sounds. We suspect that parametric study of the lesson variables will define a teaching procedure that produces results surpassing the limitations on identification ability disclosed by previous research. This paper describes the research design and apparatus, and the results of the experiments conducted to date. In this study, a PDP-1 digital computer is used to realize a large number of teaching machines—the program permits the experimenter to set up a lesson in any format desired. The computer exercises simultaneous control over independent lessons for several subjects, and produces a complete record of the lesson as well as analyses of the data at the completion of the lesson. The computer also generates the sounds to be learned; it constructs any of a very large number of sounds with an average access time of 0.2 sec. Variables under study include the procedure for selecting the sound to be presented on a given trial, the reinforcement probability, the kind of feedback, the nature of the sounds, and the mode of response. (The research reported here is supported by the U. S. Navy Training Devices Center, Port Washington, New York, under contract for a Human Engineering project.)
Experimental Studies of the “Least Stable Waveworm.”
Authors: Breazeale M. A.
Published: September 2005

The “least stable waveform” of a finite amplitude wave is that in which the maximum pressure gradient is in the trailing edge of the wave. It can be formed by reflecting a distorted finite amplitude wave from a resilient boundary. By using a pulse technique, the increase of distortion of a finite amplitude wave, and then on reflection from a resilient boundary, the decrease of distortion, are shown. The effects of resilient and rigid boundaries on the diffraction of light by standing ultrasonic waves are demonstrated. For comparison, diffraction patterns for finite amplitude progressive waves are shown. (This work was supported by the Office of Naval Research.)
Tapped Delayed-Line Detector for a Modified Chirp Signal
Authors: Rowlands Richard O.
Published: September 2005

The technique of pulse compression by the use of a linear frequency-modulated signal in conjunction with a delay network as detector is well known. If the duration of the signal is T and the instantaneous frequency varies from f0 to f1, the slope of the delay network must be −T/(f1−f0). Since the Doppler effect keeps the product T(f1−f0) constant, the quotient varies as the square of the Doppler shift, and so this signal is only usable if the Doppler shift is small. This paper describes a modified chirp signal and its matched filter detector that are not subject to this limitation. It is shown that the signal x(t) defined by the equation x(t)=A cos [(2πf0/K) log 1/(1−Kt)]0⩽t⩽T=0t<0 and t>T possesses the property that the ratio between any 2 adjacent intervals enclosing m cycles of the signal is a constant. It is further shown that a delay line with taps spaced in a geometrical progression is a matched filter for detecting this signal. The matched filters for Doppler-shifted signals may then be formed by extending the progression at each end and connecting together the same number of adjacent taps.
Noise Generation by Open Turbulent Flames
Authors: Smith T. J. B. , Kilham J. K.
Published: September 2005

In order to provide fundamental data on the acoustic energy released by combustion processes, measurements were made of the noise arising from open turbulent flames. These studies of the acoustic radiation from premixed open flames, which relate the characteristics of the noise to the various geometric and fluid-flow parameters defining the flames, are described. Examination of the combustion-noise spectra showed that their peaks could be expressed by a constant value of the Strouhal number (fmax⋅D/Ub), where D is the burner-port diameter and Ub the normal burning velocity. The acoustic power (P) generated by a turbulent flame was found to be related to the fluid-flow parameters by the expression P∝q2⋅Ufn(Ub), where q is the mixture flow rate and U the flow velocity. In this expression, the exponent of the mixture velocity varies in such a way that the rate of increase in acoustic-power output with mixture velocity is greatest for low values of the combustion velocity, and is reduced as the combustion velocity increases. [This work was supported by the Joint Research Committee of the Gas Council and by The University of Leeds.]
Analysis of the Sound in the First Surface Shadow Zone of a Deep Point Source by Use of the WKB Approximation
Authors: Leach Richard F.
Published: September 2005

A normal-mode solution of the wave equation can be written as φ=e1ωl ∫0∞ J0(Kτ) F (Z,K)dK, where F(Z,K) is a solution of (d2F/dz2) + [ω2/c2−K2] F=0. The specific F(Z,K) can be determined for a deep-source shallow receiver by using the WKB approximation with the usual point source and surface-boundary conditions. This solution can then be written as an infinite series of integrals, each of which is identifiable either as a real or a complex ray. This solution is not applicable in the immediate vicinity of the ray-turning (horizontal) points. The first integral (the upcoming ray) is evaluated by the saddle-point method. Where real rays exist, the usual ray equations are obtained, except for a slight correction to the intensity equation. It can be shown that this solution can be continued around the ray-turning point to give an evaluation of the sound in the shadow zone. This solution will yield results similar to Pekeris' for his simple shadow case, and is similar in some respects to the work of Keller and Seckler. It justifies the use of ray optics after a caustic. It also justifies caustic-intensity calculations based on ray optics. More important, it shows that the signal form is unchanged, if it is propagated by real rays, and is modified if it is propagated as a complex ray.
Digital Simulation of Basilar-Membrane Motion
Authors: Flanagan James L. , Bird Carol M. , Hause A. Dickeson
Published: September 2005

In previous work, a computational model was derived for describing basilar-membrane displacement in the human ear. The model specifies membrane displacement at arbitrary points for known sound pressure at the eardrum. Its mathematical tractability makes it an attractive tool for digital analysis of speech and other auditory signals. It has, therefore, been approximated in terms of sampled-data functions and programmed for a digital computer. The present simulation represents the motion at 40 points along the membrane. The equivalent spacing of the points is 0.5 mm, and they span the frequency range 75 to 4600 cps. Two different processings of the membrane-displacement information so obtained are described. One is a rectification, smoothing, and power-law amplification of the displacement function at each membrane point. At a given instant of time, therefore. the successive outputs represent values of a short-time amplitude spectrum as produced by the frequency weighting of the membrane. A second processing produces a measure approximating the mean rate of neural firings at successive membrane points. Both processes reflect speech features, such as formant structure, voicing, and friction. and suggest several possibilities for speech analysis.
Individual Differences in the Cues for Localizing Pure Tones
Authors: Harris J. Donald
Published: September 2005

Studies of the minimum audible angle (maa) at 0° elevation and at 0°, 30°, and 60° azimuth, for frequencies from 200–6400 cps corroborated Mills' data in detail, except that it was found possible to measure man at 1600 even at 60° azimuth, if constant errors were controlled. Four techniques were used in an effort to understand individual differences among four well-trained listeners: (a) tape-recorded tests of interaural intensive discrimination at several frequencies and simulated azimuths; (b) recordings of intensive differences at the entrances to the ear canals fitted with dual-probe microphones, in response to pure tones at various frequencies and azimuths; (c) continuous fixed-frequency Békésy audiometry as the loudspeaker moved a total of 10° slowly through the 0° azimuth; and (d) tests of sensitivity to interaural delay in microseconds (apparatus kindly arranged by Dr. J. F. Curtis). These tests enable one to assign rational explanations for individual differences in maa, and point toward a more nearly correct assessment of the relative contribution of the several auditory cues to localization. In particular, the role of interaural intensity seems less than has commonly been thought; and sensitivity to time-of-arrival does not disappear at frequencies where the ear becomes insensitive to phase as such.
Diffraction of Acoustic Waves by Objects of Finite Dimensions
Authors: Steinberg Bruce , Harbold Mary L.
Published: September 2005

An extended study of diffraction of acoustic waves in the audible range is currently under progress in the anechoic chamber at Temple University. A probe microphone has been constructed by coupling to a 12-in. Bruel and Kjaer (B&K) capacitor microphone a rigid steel tube with a precision-drilled 1-mm-diam hole. The output is fed into a B&K audio-frequency spectrum analyzer and recorder. Since the measuring apparatus is so important in experimental studies in diffraction, extensive tests have been run to check the free-field characteristics of the chamber and the frequency and directional response of the probe microphone. As a test of the precision of the apparatus, the diffraction patterns for rigid cylinders and spheres have been analyzed for various values of ka (ratio of circumference to wavelength) from 0.2 to 10. To obtain continuous readings, the microphone has been mounted to rotate at 2 rpm. The results have followed theory predictions in every respect, and the details of the “bright spot” and the numerous lobes at higher frequencies are clearly revealed by the continuous recordings. Studies on cylinders and spheres in 2- and 3-dimensional arrays have been investigated. It is hoped that generalizations drawn from these results will lead to suggestions for mathematical approaches to solutions. [This work was supported by a Research Grant from Temple University.]
Transducer Calibration from Near-Field Data
Authors: Trott W. James
Published: September 2005

The theory for obtaining free-field sensitivities, far-field transmitting responses, and directivity of any shape of underwater-sound transducer is derived from Huygens' principle and compared with other near-field theories. Standard far-field calibration facilities, including the pattern recorder. can be used to calibrate any transducer in terms of far-field characteristics at a near-field test distance of a few centimeters. A specially designed transducer array is required. No computation is involved in obtaining the far-field pattern from measurements in the near field. Only the near-field sound pressure is measured to compute the far-field transmitting response. The free-field sensitivity is obtained from the equivalence of the Huygens' wavelets in the near field of the measuring transducer to a free-field plane wave. The required size of a calibrating tank is substantially reduced by this near-field method. Continuous wave, pulsed sound, or noise can be used for the measurements. The design and construction of the calibrating transducer are discussed and data from measurements are presented.
Logarithmic-Periodic Underwater-Sound Projector
Authors: Walther Klaus
Published: September 2005

In this paper, the performance of a logarithmic-periodic projector for underwater sound is described. The projector consists of a barium titanate cylinder driving a logarithmic-periodic mechanical-waveguide structure of approximately 12-in. length (material: brass). The mechanical waveguide has the form of a disk-loaded cylindrical rod of variable cross section in which the disk diameters expand with a linear taper along the axis. The acoustic-power output from the projector stays constant within ±1.5 dB over a frequency range from 38.2–130 kc. Electroacoustic efficiencies η larger than 60% are obtained over nearly this entire frequency range; η⩾70% is realized in the frequency range between 41 and 72 kc. Details of the acoustical logarithmic-periodic operation are discussed. Analogies and differences in comparison with the well-known logarithmic-periodic antennas for electromagnetic waves are pointed out.
Measured Shock-Wave Ground-Pressure Patterns from Aircraft in Maneuvers
Authors: Maglieri Domenic J. , Lansing Donald L.
Published: September 2005

Ground-pressure measurements are presented for fighter aircraft in various maneuvers involving accelerations along the track and perpendicular to it. Complex wave patterns, and so-called “super-booms” in which pressure buildups occur, are presented for some representative cases. Results obtained from an array of ground-measuring stations are correlated with tracking and weather information and with theory. Computed ground-pressure patterns show good agreement with measurements for some specific maneuvers.
Analysis of Gear Whine in Automobiles
Authors: Raelson Verner J.
Published: September 2005

A whine in the noise background of a coasting automobile presented a quality-control problem to the manufacturer. The objectionable signal had the character of a sinusoidal sound whose frequency was velocity-dependent and which faded in and out of the background noise as speed decreased from 70 to 20 mph. This whine was attributed to the differential gears. The analysis undertaken to determine the nature of the whine, its association with the differential gears, and the explanation for the details characterizing its occurrence are described. In addition, the design of an instrument to be used in the inspection line for detection of incipient noisy cars is presented. [Supported by American Motors Corporation, Kenosha, Wisconsin.]
Vibration of Stiff Piano Strings
Authors: Fletcher Harvey
Published: September 2005

This paper reviews the work on the theoretical aspects o[ the vibration of piano strings. For solid strings, it deals with 2 boundary conditions: namely, (1) when the string is pinned with knife edges but not clamped, and (2) when the ends are clamped. In an actual piano, the condition is somewhere between these two. The theory is developed so as to apply to wrapped strings. In this case, the stiffness restoring force is principally due to the solid core rather than to the wire wrapped around it. Experimental values of the partial frequencies of piano tones from an upright piano are compared to the theoretical values. The partial frequencies from any of the strings can be represented by the formula fn=nf0(1+Bn2)12, where n is an integer and f0 and B are constants which can be determined from any 2 experimental values of the partial frequencies f>n. These constants can also be calculated from the physical constants of the wire and its tension, provided the exact boundary condition is known. A comparison between the experimental and theoretical values of these constants is given.
Binaural Pitch Phenomena
Authors: Fourcin Adrian J.
Published: September 2005

The possibility of having a sensation of pitch associated only with a bilateral presentation of acoustic stimuli to the listener was first discovered by Huggins [Cramer and Huggins, J. Acoust. Soc. Am. 30, 413–417 (1958)]. Huggins employed a single, smooth-frequency-spectrum noise generator, and fed its output directly to one ear, but via an all-pass phase-changing network to the other. In the present work, the possibility that this effect is a by-product of a process of auditory localization has been considered. This has led to the experimental use of a family of new binaural pitch-producing stimuli obtained from a multiplicity of independent, smooth-spectrum noise generators which operate in conjunction with continuously variable all-pass delay lines. Each stimulus configuration may be associated with a simple localization pattern. The pitch associated with a particular pattern depends both on its form and on the magnitudes of the delays involved. Pitch-matching measurements with these stimuli and a comparison with the more complex pattern of localization which might be associated with the Huggins stimuli support the view that these binaural pitch phenomena are mediated by a process akin to localization rather than by a central frequency-analysis mechanism.
Articulation-Effectiveness Measure Applied to Processed Speech
Authors: Barker Boone A. , Latorre Victor R.
Published: September 2005

An area of increasing importance to the military is that of secure and jam-resistant transmission of voice information. As digital techniques are the more promising means of achieving jamming protection and secure encoding, it is necessary to consider the effects of the analog-to-digital-to-analog processing on the speech itself. The articulation-effectiveness measure will be used to compare the reconstituted speech resulting from various processing methods, such as infinite clipping, delta modulation, and selective amplitude sampling. The results are presented as articulation effectiveness as a function of quantization level for the various schemes, and as a function of various types of modulation used. The articulation-effectiveness measure is a numerical measure of sound articulation, the importance of each sound being weighted by its frequency of occurrence.
All-Transistor Hydrophone Preamplifier
Authors: Durgin Charles B.
Published: September 2005

A low-frequency piezoceramic hydrophone preamplifier has been developed which utilizes a field-effect transistor in the input stage in lieu of the usual vacuum tube. Input impedance and noise performance are comparable to those obtained from a vacuum-tube input stage. The preamplifier is designed for operation from a constant-current power supply; a single pair of wires carries both power-supply and signal-output voltages. The preamplifier has a complement of 4 transistors. including the input stage. Frequency response is from below 10 to above 10 000 cps. Close-loop gain is 40 dB, open-loop gain is in excess of 60 dB. With the design hydrophone of −88 dB re 1-V/μbar sensitivity and 500 pF capacitance, the equivalent noise input is below sea state “0” over the operating frequency range. Per-cycle-bandwidth dynamic range is in excess of 80 dB, and harmonic distortion is less than −60 dB relative to the signal. Operating temperature is limited to a range of about 30°C because of the temperature sensitivity of the field-effect transistor, and component selection is necessary because of the parameter spreads of the field-effect transistors.
Sound-Measuring Set
Authors: Campbell J. R. , Allman R.
Published: September 2005

The sound-measuring set is a stable, reliable, battery-powered, portable field instrument designed for underwater acoustic measurements at frequencies from 50 to 70 000 cps. A high-impedance, low-noise hydrophone preamplifier of special design is used with the hydrophone to limit self-noise to a level equivalent to a sea-state one. The hydrophone is designed to operate to depths of 1000 ft with armored signal cable. The system includes a means for quick calibration at frequencies of 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 40, and 70 kc, at levels of −30 to −90 dBV in 10 dB steps. The set is flexible in that it contains 2 gain paths with attenuators and filters for each. The 2 paths may be connected to a single hydrophone or used individually with 2 hydrophones. Outputs are provided to operate other instrumentation. Transistors are used throughout in the circuitry.
Ultrasonic Absorption and Relaxation Times in Nitrogen, Oxygen, and Water Vapor
Authors: Fujii Y. , Lindsay R. B. , Urushihara K.
Published: September 2005

The absorption coefficient α is measured in nitrogen, oxygen, and water vapor by a direct travelling-wave method which employs a pulse-modulated signal of about 65 kc. The apparatus used is a modification of that previously reported by C. Ener, O. Herbjørnsen, Y. Fujii, and L. Nyborg [J. Acoust. Soc. Am. 32, 929 (1960)]. Argon is used as a calibrating gas, and the experimental values of α agree with the theoretical classical values within 1%. The rotational relaxation times in nitrogen and oxygen for 22°C and 1 atm are obtained from the experimental excess absorption and other thermodynamic quantities as (7.6±0.6) × 10−10 sec for nitrogen and (5.1±0.4) × 10−10 sec for oxygen. The coefficient α in water vapor is measured for temperatures between 42° and 183°C and over the range of angular frequency/pressure from 1 to 50 Mc/atm. In this range, no absorption peak is observed. The observed excess absorption over classical is considered to be due primarily to vibrational relaxation, since the excess absorption increases with the temperature nearly proportionally to the specific heat of the vibrational state with the lowest eigenfrequency, whereas the specific heat of the rotational states remains practically constant with temperature. If the excess absorption is completely due to vibrational relaxation, this permits the calculation of a relaxation time, which at 1 atm is found to lie in the interval from 0.8×10−8 to 2.0×10−8 sec. This is of the same order of magnitude as that reported by other observers for higher temperature. (This work was supported by the Office of Naval Research.)
Effect of the Size and Shape of a Hydrophone on the Received Flow-Noise Level
Authors: Skudrzyk E. J. , Haddle G.
Published: September 2005

The flow noise recorded by a hydrophone inside the boundary layer of a moving body depends on the size and the shape of the hydrophone. A fish-shaped hydrophone is 15 db more sensitive to flow noise when its axis is perpendicular to the lines of flow than when its axis points in the direction of flow. At very low frequencies, the opposite effect takes place: the hydrophone with its axis transverse to the flow is less sensitive to flow noise. The flow-noise level also depends in a very complex manner on the area of the hydrophone and on the intermittency of the turbulence. The experimental results give information on the intermittence and the unsteadiness of the turbulence, and make it possible to estimate the transverse correlation distance of the space-Fourier components of the turbulence.
Vibration Response of Beam-Column Structures
Authors: Miller D. F.
Published: September 2005

The higher audio frequencies are becoming of great interest in vibration studies, due to structure-borne noise considerations. In the uniform beam-column structures described, meaningful results are obtained when shear, rotary-inertia, and impedance terminations and corner joints are included. A distributed analysis is obtained using a multipole matrix representation of each beam-column section, containing transcendental functions as matrix elements. This is a generalization of the four-pole matrix used for distributed electrical or acoustical transmission lines. Beam bending in two principal planes is given by the Timoshenko beam equations, allowing shear and rotary-inertia effects. Axial elongation and torsion of each section are included. Several examples are discussed. The sidesway excitation of a plane frame composed of three I-beams with 90° corners shows important effects due to beam shear and corner flexibility. A simple three-dimensional frame composed of three equal beam elements and 90° corners correlates almost exactly with experimental results for at least ten modes of vibration, limited only by experimental techniques. Here, effects of torsion and elongation of the beam elements were significant. Impedance and response curves, resonant frequencies, and mode shapes are shown for these examples.
Transient Calibration of Accelerometers by a Photographic Technique
Authors: Mintz Fred , Holloway R. A. , Sutherland W. W.
Published: September 2005

Apparently anomalous results obtained in telemetered signals from accelerometers led to an attempt to obtain a transient calibration of the accelerometers by optical-photographic techniques. The purpose of this was to provide a check on accelerometer performance under shock motions, independent of the steady-state calibration or of the transient performance of comparison standard units. The technique developed made use of continuous-motion film camera and macrophotography to provide a magnified streak image of the motion of the accelerometer. Simultaneously, the electrical signal from the accelerometer, displayed on an oscilloscope screen, was photographed on the same film. Semiautomated data-reduction equipment was employed to integrate the accelerometer trace and differentiate the displacement trace, providing a means of comparing the steady-state calibration and transient output of the accelerometer.
Differential Sensitivity to Masking of the Evoked-Response Complex in Unanesthetized Cats
Authors: Teas D. C. , Kiang NELSON Y.-S.
Published: September 2005

The evoked-response complex (ERC) recorded with implanted electrodes from lightly restrained unanesthetized cats includes a late negative voltage (60–80 msec latency) as well as the familiar early positive voltage (8–12 msec latency). ER1 may be recorded also from the anesthetized animal, but the late negative component is not present after anesthesia is administered. ER1 remains stable as the “state” of the animal changes from awake through sleep, but the late negative voltage disappears. When a continuous masking noise is introduced, ER1 is made progressively smaller as the level of the noise is increased, whereas the late negativity is unaffected until the highest levels of noise are reached and the entire ERC is masked. If the noise level is below that at which complete masking occurs, and the animal is given prolonged exposure to both noise-plus-signal, a positive voltage at a latency of about 40 msec is the only component of the ERC which remains.
Effect of Chronic Section of the Eighth Nerve in the Cat
Authors: Ruben R. J. , Hudson W. , Choing A.
Published: September 2005

The N1 and N2 recorded at the round window have been found to be present for 24 hours after complete section of the eighth nerve. Cats with eighth-nerve section were used in a series of experiments to determine if the N1 and N2 persisted for longer periods of time than previously reported. The opposite ear was destroyed at the time of the terminal experiment. In all the animals tested, cochlear potentials were found to be normal. The findings revealed that the N1 and N2 persisted in the completely sectioned eighth nerve up to 72 hours after operation. At this time, the N2 began to disappear. At 4 to 5 days postoperatively, both the N1 and N2 completely disappeared leaving a new phenomena in its place. This phenomena is called the W phenomena. It occurs at approximately the same time that the N2 did. It is a biphasic positive potential. This potential does not change polarity if the click-stimulus polarity is changed; it is more sensitive to anoxia than the cochlear potential, and behaves in many ways like a nerve potential. It is felt that this potential was not the dc potential that has been observed by others, because it occurs so late after the cochlear response. Histological examination of the ears of the animals revealed complete section of the eighth nerve with no preservation of the cochlear nucleus. There was marked degeneration of the spiral ganglion cells in the modiolus; however, consistent with previous findings, Scarpa's ganglion remained intact. It is felt that the W response may either come from the few remaining ganglion cells in the modiolus or that it may originate from the neural epithelium which is innervated by the fibers from Scarpa's ganglion.
Measurements on the Propagation of Sound Waves in Capillaries
Authors: Remenvik C. J. , Kovasznay L. S. G.
Published: September 2005

The hot-wire anemometer was adapted to the measurement of attenuation and phase velocity of sound waves in long capillary tubes in the presence of laminar mean flow. Two hot wires were placed across the inside of the capillary tube at two different locations. One end of the tube was connected to the sound source (a loudspeaker driver), the other end to an air tank and a pump. The air was driven through the tube at variable speeds. The dimensions of the tubes measured 11 to 15 ft long with an inside diameter of 0.030 in. By comparing the two hot-wire signals, the velocity of propagation and attenuation were measured. The frequency of the generating signal ranged from 100 to 12000 cps. By changing the distance between the two hot-wire stations, attenuation and phase shift were obtained in function of distance of propagation. For a comparison with theoretical predictions, a theory was developed by using decomposition into modes [L. S. G. Kovasznay, “Turbulence in supersonic flow,” J. Aeronaut. Sci. 20 (October 1953)]. [This work was sponsored by Project Squid (Office of Naval Research), Princeton, New Jersey.]