bluuebunny/crossref_metadata_2025 huggingface dataset:
Why an International Tuning Frequency
Authors: Young Robert W.
Published: September 2005

In October, 1953, Technical Committee 43 of the International Standards Organization, meeting in London, concurred that the frequency of the tuning A used for music should be 440 cycles per second throughout the world. This standard was recognized in the United States in 1917 by the American Federation of Musicians (and it still appears in its by-laws); it has since been reaffirmed by various organizations in this country. Sampling of radio broadcasts indicates that the standard is being observed reasonably well, but there are persistent rumors that some important musical organizations are intentionally tuning to an A of significantly higher frequency, allegedly to attain “brilliancy.” Such trends appear repeatedly in the history of the subject. Experimental evidence is lacking, however, that an enhanced musical effect is really attained. On the other hand, evidence can be produced (and is here shown for the flute) that musicians are being handicapped (and listeners are suffering!) because, for good economic reasons, musical instruments are still being produced and used today, which were originally designed for the A of 435 cycles per second and then modified by makeshift means to tune to higher frequencies. Let us look at the acoustical facts—and hold the A to 440 cycles per second.
Measurement of Sound Power
Authors: Wells R. J. , Sawyer G. N.
Published: September 2005

Automatic equipment for use in measuring sound power in an anechoic chamber is described. Data obtained with such equipment are presented, and are correlated with reverberation room sound power determinations using the same sources of noise.
Measurement of Difference in Loudness between Typing Noises
Authors: Abruzzo J.
Published: September 2005

It is difficult to ascertain the absolute loudness of typing noise by objective measurement. However, it may be practical to use such measurement to determine the loudness level difference in a comparison of the sounds from two typewriters. The requirements that must be met by an accurate measurement technique depend on the degree of accuracy required. Information pertaining to the accuracy necessary has been obtained by employment of two loudness matching procedures over a period of several months. The purpose of the tests was to determine the difference in sound pressure level of typing noise necessary to enable a person to identify reliably the louder of two typewriters operated simultaneously in a quiet background. It was found that under the conditions adopted for the investigation, differences in sound pressure level had to be nearly one decibel before they could be recognized 50 percent of the time. Characteristics of typing noise other than pressure level are discussed. The opinion is expressed that these will, in many cases, not cause significant measurement error, and that difference in loudness between typing noises can often be measured with practical accuracy by means of a sound level meter.
Performance Characteristics of Acoustically-Treated Planishing Hammer Booths
Authors: Callaway D. B. , Casiday C. C.
Published: September 2005

Noise due to planishing hammer operation is common throughout the metal fabrication industry. Because the noise is due to rapid impacts on thin metal sections, most of the noise energy is concentrated at high frequencies. Considerable noise reduction might, therefore, be expected by partially enclosing such hammers with acoustically-treated booths. An experimental installation for two side-by-side hammers will be described and performance data will be presented. Tests were performed at various stages of completion to provide information on the relative effectiveness of various parts of the structure. Greater noise reduction than anticipated was achieved between booths, especially at low frequencies. Addition of a skirt which partially closed the front opening was relatively ineffective and gave tests results which have not been explained. Addition of an absorbent barrier at a distance in front of the booths improved noise reduction both from booth-to-booth and at remote locations.
Acoustic Attenuation of Earphone-Noise Shield Combinations
Authors: Thompson P. O. , Beitscher H. R. , Webster J. C.
Published: September 2005

The sound exclusion properties (acoustic attenuation) of various combinations of earphones and noise shields were determined by the threshold-shift method. The earphones included dynamic earphones in donut cushions and hearing aid type receivers with individually molded inserts. The noise shields included conventional earplugs, muffs, and a noise exclusion helmet. Test sounds were octave bands of noise at each of the seven octaves starting with 75 to 150 cps and ending with 4800 to 9600 cps. The order of merit for exclusion of external noise, listing the best combination first, is (1) the helmet with insert-type phones, (2) the helmet with dynamic earphones, (3) the dynamic earphones over earplugs, and (4) the muffs over insert-type phones. The best combination provided 9 db attenuation in the 75–150 cps octave, 18 db in the 150–300 cps octave, 24 db in the 300–600 cps octave, 34 db in the 600–1200 cps octave, 44 db in the 1200–2400 cps octave, 54 db in the 2400–4800 cps octave, and 48 db in the 4800–9600 cps octave.
Influences of Variations in Speech Intensity and Other Factors upon the Speech Spectrum
Authors: Licklider J. C. R. , Hawley Mones E. , Walkling Robert A.
Published: September 2005

In calculating speech intelligibility by methods such as French and Steinberg's, and in other phases of the designing of communication systems, one uses the long-time-average power density spectrum of speech. Several determinations of this spectrum have been made previously, but in each case the talkers talked at a fixed level. The present observations are aimed primarily to determine how the shape of the spectrum differs from “normal” when, as is necessary in some situations, the talker raises his voice considerably above normal level. Secondary questions concern the amount of variation among talkers and among speech samples and the length of sample required for stable measurement. Results, obtained with two different spectrum analyzers, are presented. As the speech level is increased, the spectrum changes noticeably—enough to affect the outcome of intelligibility calculations. The middle- and high-frequency components are raised much more than the low-frequency components. The spectrum of normal speech has its maximum ordinate at 100 or 200 cps, whereas the spectrum of very intense speech has its maximum ordinate at 700 or 800 cps.
An Analysis of Clipped Speech
Authors: Vilbig Friedrich
Published: September 2005

The application of infinite clipping to speech has only a small influence on intelligibility. The reason for this is that clipping the original speech-spectrum only causes tolerable distortion. Since the mathematical analysis for many frequencies becomes involved to a high degree of difficulties, the theoretical investigation was restricted to 2 frequencies, a cosαt+b cosβt e.g., representing 2 harmonics of the pitch frequency. The clipping is considered to be a rectification of a rectangular curve i=f(x) where i=0 for −π<x<0 and i=A for 0<x<+π. Only the range −π⋯0⋯π is used. The resulting amplitudes are expressed as infinite sum of a product of 2 Bessel functions. The results of this calculation are confirmed by an experimental analysis. Highest distortions appear for a=b. Considering α = (α+β/2) + (α−β/2) and β = (α+β/2) − (α−β/2), the 2 unclipped frequencies represent 2 sideband frequencies of a suppressed carrier frequency, (α+β/2). By infinite clipping, the frequencies n(α+β/2)±(α−β/2) are the most important ones in amplitude, where n=1, 3, 5 ⋯. Thus, speech clipping, as applied to vowels, causes distortions mostly of frequencies above 3000 cps. e.g. n=3 or higher. But if the clipped speech is put through a 3000-cps low-pass filter, the difference between original speech and clipped speech is not very important. Since α and β and all distortion frequencies are harmonics of the pitch frequency, the good intelligibility of clipped speech is quite reasonable. An experimental analysis of several vowels and consonants has proven this theory.
Method for the Study of the Localization of Airborne Sound
Authors: Jeffress Lloyd A.
Published: September 2005

The three papers to follow present results on the localization of airborne sound, using the same subjects, the same environment—an anechoic room, and the same method for indicating the position of the stimulus to be localized. Three small loudspeakers in enclosures mounted on pedestals at ear-height and equidistant from the subject were used as stimulus sources. They were used singly in one of the experiments, and in pairs in the other two. In the second experiment the pairs of speakers used to provide the stimulus were in phase, and in the third experiment they were in phase opposition. The subject localized the stimulus sound, usually a tone, by moving a fourth loudspeaker, mounted on an arm, until the noise it emitted seemed to come from the same direction as the stimulus to be localized. The noise and the stimulus tone were presented alternately by means of an electronic switch having a rise and decay time of 100 milliseconds (to avoid switching transients), and a repetition rate of about 412 seconds. This method of localizing a sound source has the advantage over methods previously employed of keeping the subject's task in the sense modality of hearing without involving his orientation in space either visually or kinesthetically. Probe microphone measurements were made at the subjects' ears, and the pressures so determined were used in predicting the interaural time differences to be expected from the combinations of the pairs of loudspeakers. A description of the method used in making these predictions will be given.
Voicing of Electronic Organs
Authors: Tennes Charles
Published: September 2005

The control of formant and of harmonic content are considered in connection with the voicing of electronic organs. Illustrations are given with tape recordings and with an actual instrument.
Low Frequency Fluctuations of Rectified Non-Gaussian Noise
Authors: Magness T.
Published: September 2005

If a non-Gaussian noise is square law rectified, the power in the lowest frequencies can be computed if one knows the power spectrum S(ω) and the envelope correlation function E(ω1,ω2) of the input. The theory is thus related to (nonlinear) correlations between noise components at different frequencies. In certain cases it is possible to express the results in terms of more elementary parameters of the input. This occurs when the input consists of (a) a linear super-position of similar pulses which occur at random with average frequency ν0 per second, or (b) high-frequency Gaussian noise modulated in amplitude by low frequency noise of maximum frequency ν0. In each case, the magnitude of the low frequency power of the rectified noise is (approximately) inversely proportional to ν0, other parameters remaining the same. Under the direction of Dr. Philip Rudnick, some measurements on audio noises have been made. The low frequency fluctuations of rectified thermal noise, radio static and human speech are compared. It is found that while thermal noise behaves Gaussianly, the other examples conform more to models (a) or (b) with suitable ν0.
Design and Performance of a High-Frequency Electrostatic Speaker
Authors: Bobb Lloyd , Goldman R. B. , Roof R. W.
Published: September 2005

An electrostatic speaker has been developed which provides a quality of high-frequency reproduction not available with electromagnetic tweeters. The diaphragm consists of a thin plastic film bearing an evaporated metallic layer. The membrane is stretched around a semicylindrical perforated electrode on which ridges are embossed to provide clearance. The response varies less than ±2 db in the frequency range between 8 and 16 kc. The azimuthal distribution pattern is excellent, owing to the cylindrical geometry, and is essentially independent of frequency in the same range. The second harmonic distortion inherent in this type of speaker is maintained at a low level. An indication of the quality of high-frequency reproduction is provided by oscillograms of the response to tone burst signals. The speaker is in quantity production and has been incorporated in several models of home reproduction instruments.
Electrolytic Apparatus for Studying Sound Flow through Orifices in Liquid
Authors: Hillery Herbert V.
Published: September 2005

When a battery is connected between two electrodes immersed in an electrolyte, the phenomenon known as polarization occurs. This polarization limits the electric current which will flow through the electrolyte for a given potential difference. As is well known to those familiar with the method of chemical analysis known as polarography, the degree of polarization and consequent current flow through the electrolyte is a function not only of the chemical composition of the electrolyte, but also of the amount of agitation, either thermal or mechanical, which the electrolyte experiences. In this paper, an apparatus is described which allows investigation of the flow patterns resulting when low-frequency sound in liquid passes through small orifices.
Effect of the Oral and Pharyngeal Cavities on Trumpet Tone Quality
Authors: Hall Jody C.
Published: September 2005

Radiographs and photographs of trumpet players were made while the tones they produced were recorded. Detailed measurements were made of the anatomical positions assumed by each player for each tone and for spoken vowels. The vowel orientations used in producing tones in three different octaves were compared with the formant patterns evidenced in the trumpet tones. A close relationship was found to exist. The report of the results of the study will include slides depicting radiographs of the oral and pharyngeal cavities and graphic representations of the acoustical structure of the tones produced.
Speech Spectra
Authors: Burkhard Mahlon D. , Corliss Edith L. R.
Published: September 2005

This paper reports on the frequency analysis of speech. Various distortions of speech sounds, such as “differentiation,” “integration,” and “peak clipping,” have been studied in terms of both wave form and spectrum. The results can be related to articulation scores obtained for speech communication systems by previous investigators. Comparisons have also been made with published data on the spectrum levels of speech. The effects of time constants on these results will be discussed.
Variation of Acoustic Velocity with Temperature in Some Low Velocity Liquids and Solutions
Authors: Marks Graham W.
Published: September 2005

It is desirable to have more experimental data concerning the acoustical properties of liquids not only because such data will lead to a better understanding of the liquid state but also because of the immediate application of such results to the development of acoustical devices. Acoustical velocities were measured at 500 kc in a number of organic liquids and binary solutions prepared therefrom. A precision ultrasonic interferometer was employed. For the most part sound velocities were found to vary linearly with temperature. Densities were determined at 20°C. Adiabatic compressibilities at 20°C were calculated and some conclusions drawn concerning the cohesive properties of certain of the solutions. The molecular sound velocity in a binary liquid solution is the sum of the products of the respective molecular sound velocities in the pure liquids by their corresponding mole fractions all at the same temperature. Where practicable, effective molecular radii were calculated from the data. The usefulness of the molecular weight of the liquid in predicting values of the temperature coefficient of velocity is discussed. Apparently many more experimental data are needed before an adequate theoretical analysis is possible.
Ultrasonic Absorption in Aqueous Solutions of Manganous Sulfate
Authors: Smithson J. R. , Litovitz T. A.
Published: September 2005

The absorption of sound in aqueous MnSO4 solutions was studied over the frequency range 1–55 Mc as a function of concentration, temperature, dielectric constant, and with D2O as solvent. The absorption maximum in the range 1–10 Mc was verified, and also a secondary relaxation peak, not previously reported, was observed near 30 Mc. The primary relaxation frequency was decreased when the dielectric constant was lowered, while the secondary relaxation frequency was increased. The absorption cross section was increased when the dielectric constant was decreased. The activation energy was determined for both isodielectric and isocomposition solutions. Substitution of D2O as a solvent had no effect on the primary relaxation frequency but increased the absorption cross section. The secondary relaxation was not observed in D2O solutions. The results indicate that a reaction between two ions of unlike sign is not the rate-determining step in the primary relaxation process and that a reaction between ions of like sign is also improbable. All observed data can be explained on the assumption that the reaction is between two dipole molecules. This work was sponsored by the Office of Ordnance Research.
Attenuation of Sound in Para-Azoxyanisole
Authors: Curran Daniel R.
Published: September 2005

The attenuation of 10 megacycle sound pulses in the liquid crystal para-azoxyanisole is presented as a function of temperature in the region of the liquid crystal—isotropic liquid phase change. An absorption peak of optical sharpness is encountered at a temperature Tc just above the phase transition temperature. As one might suspect, Tc is dependent upon external influences. The dependence on externally applied magnetic fields is presented and the significance of these measurements is discussed. This work was supported in part by the Office of Naval Research.
Ultrasonic Absorption in Tissues; a Review
Authors: Hueter T. F.
Published: September 2005

The dissipation of vibrational energy in tissues may be ascribed to one or more of the following four loss mechanisms: (a) viscous damping; (b) structural rearrangement; (c) elastic hysteresis; (d) scattering. Each of these mechanisms exhibits a characteristic dependence of attenuation on frequency. Losses of type (a) and (b) are accompanied by velocity dispersion and losses of type (c) inherently lead to a dependence of attenuation on the amplitude of vibration. The available evidence indicates that below 20 kcps viscosity is the controlling factor. In the frequency range from 200 kcps to 10 mcps a constant loss per cycle is often observed which may be interpreted either in terms of a distribution of relaxation times or as a hysteresis due to the plasticity of tissues. In tissues of marked inhomogeneity or at interfaces between structures of different acoustic impedance, scattering produces additional attenuation. The relative roles and magnitudes of these loss mechanisms are of direct interest in medical applications of ultrasound such as physio-therapy, brain surgery, and diagnosis of abnormal growth. More general ultrasonic absorption studies are valuable for the understanding of the physics of living tissues.
Transmission of Vibrations through the Human Body
Authors: von Gierke H. E.
Published: September 2005

The behavior of the human body in receiving and transmitting vibrations is reviewed. Measurements in this area were made for two purposes: (1) to determine the pathways to the body surfaces taken by vibrational energy generated inside the body by such excitations as human speech and muscular activity of the heart, and (2) to determine the vibrations inside the body as a result of exposing the body surface to vibrations, e.g., the physical aspects of hearing (which will not be discussed in this review), cases where parts of the body surface are brought into contact with vibrating machinery or where the whole body is exposed to a sound field. The impedances measured on different areas of the body surface and their practical application to physiological, mechanical, and engineering purposes are discussed. Examples are given of how the body impedances influence the design of ballistocardiographic tables and of ear protectors and how knowledge of these impedances determines the usefulness of vibration pickups attached to the body surface. Vibration characteristics of certain parts of the body such as the skull, losvet jaw, and chest are briefly summarized. The present status of the problem of absorption of airborne sound by the body surface is reviewed and some of the unsolved questions discussed.
Experiments in Peak Clipping a Mixture of Speech and Acoustic Noise
Authors: Hawley Mones E. , Meeker Willard F.
Published: September 2005

Indicative experiments were performed to predict the effect on word articulation of various amounts of peak clipping on speech transmitted by an AN/M-33 AIC first-order pressure gradient microphone used in 120 db simulated propeller aircraft noise. 0, 12, 24, and 36 db of peak clipping and subsequent reamplification were used; +6 db/ octave pre-emphasis tilting (differentiating) and −6 db/octave de-emphasis tilting (integration) were also used in some experiments. Listeners in relative quiet (70 db) and in 100 and 120 db propeller aircraft noise heard the signals over headsets. In this situation of noise introduced before any processing, 24 and 36 db of clipping deteriorated word articulation scores under all conditions; no significant difference was observed between 0 and 12 db of clipping.
Number Telling Methods for Two-, Three-, and Four-Digit Numbers
Authors: Adler Sol
Published: September 2005

Number-telling accounts for 25% of the words used in transmission during air operations. Thus, optimum transmission methods are a necessity. Various types of repetition methods are compared for relative performance values. Two-digit numbers were tested as separate signals (i.e., “three-five”) and as a group presentation (i.e., “thirty-five”) with the former attaining significantly superior reception. Voluntary stuttering of the two digits were found to further increase their intelligibility. Three-digit numbers were tested to determine the best method of signal presentation; again the individual digits were superior. Tests indicated that straight repetition of the signal was inferior to an alternative form (i.e., “one-hundred twenty-three, I say again, one-two-three”). A counting method of three-digit transmission whereby redundancy is introduced by counting up to any digit from the two previous proved far superior to any of the best repetition methods (i.e., “six, I count: 4, 5, 6; eight, I count: 6, 7, 8”). Four methods of presentation of the four-digit numbers were compared, with the individual digit-telling style again yielding a superior intelligibility score. The above work was carried out under contract with Operational Applications Laboratory, Washington, D. C.
Your Own Voice under Earphones
Authors: Dolch John P. , Schubert Earl D.
Published: September 2005

Probe microphone measurements show that there is more over-all sound pressure underneath a talker's unactivated headset than there is directly in front of his mouth! Experiments indicate that these sound pressures are not primarily attributable to the leakage underneath the earcushions or to the voice “coming out of the ear,” but arise mainly from the coupling of a cavity to the vibrating skull. Data obtained using three commercially available earphone cushions and a variable cavity showed that the size of the cavity was a more important factor than the type of material coupling the cavity to the head. Decrements as great as 26 db were achieved in under-the-earphone sustained vowels by picking up the fundamental voice frequency and introducing it into the earphones after appropriate adjustments of its phase and amplitude. The subjective experience of talking with this “phased-sidetone” condition was surprising: the localization of the voice changed radically to the middle of the head and the subject experienced great effort in speaking—similar to a slight case of laryngitis. These results indicate that the auditory mechanism is exposed to unsuspected sound pressure when a talker is wearing commercial type headsets, and that he experiences a marked subjective change when this signal is attenuated. Parts of this research were sponsored under U. S. Army Signal Corps Contract No. DA 36-039 sc-42562.
Cavitation
Authors: Henderson M. C. , Herzfeld K. F.
Published: September 2005

Cavitation is defined as the formation of bubbles in a liquid due to under-pressure applied either once, or periodically by a sound wave. As in boiling, cavitation needs nuclei. There are two problems: What are the nuclei, and how does the bubble behave once formed? Treating the second question first, one must distinguish gas-filled bubbles, found only in gas-containing liquids, and vapor bubbles. The former grow by rectified diffusion—which takes seconds—and persist after they get out of the sound field; the latter form rapidly and disappear outside the sound field; their collapse produces a strong sound pulse. The nuclei could be either solid particles or gas bubbles protected by an organic skin. The increase of cavitation threshold with time is connected with the disappearance of nuclei. The existence of a threshold and the fact that static pressure applied and then removed increases the threshold seem to prove that the nuclei are either protected gas bubbles or nonwetting solids with inward clefts.
Scattering of Sound by Sound
Authors: Ingard Uno , Pridmore-Brown David C.
Published: September 2005

As a preliminary to an investigation of the scattering of sound by turbulence, the scattering of one sound beam by another is studied using the Lighthill formulation. The scattered sound is predicted to be composed in part of components with frequency equal to the sum or difference of those in the primary beams. These components of the scattered field have been isolated in measurements using a selective receiver and their angular distributions are compared with those predicted. This work was supported in part by the NACA.
Spherical Sound Waves of Finite Amplitude
Authors: Laird Donald T.
Published: September 2005

Nonlinear effects in the propagation of sound waves produced by a sinusoidally pulsating sphere have been studied theoretically. Various approximation methods have been found useful for different ranges of the parameters and at different distances from the source. Harmonic distortion generated in the field relatively near the source can be determined from a conventional perturbation solution. This solution has been developed in a form which permits numerical computation of the Fourier coefficients to terms of fourth order in the amplitude. At larger distances, this solution fails to converge, but a perturbation in terms of the characteristics of the partial differential equations is quite useful. Neglecting absorption, it is found that in spite of spherical divergence, which tends to retard the increase of distortion, the wave always evolves into an iterated shock wave at a finite distance, although a very great one for weak sources. The distance at which shocks are formed and the attenuation of the iterated shock wave as it propagates have been calculated for various examples. The work was supported by contract USAF 33 (616)-2772 with the Aero Medical Laboratory at Wright Air Development Center.
A Noise Helmet
Authors: Hawley Mones E. , Witchey A. L.
Published: September 2005

A helmet-like enclosure has been developed which generates high-intensity sound fields about the head of the wearer. A cylindrical chamber with a loudspeaker in the top is mounted on the subject by attaching it to football shoulder-pads. A cooling blower, a window, and fill-in material are provided. 130 db over-all noise levels have been obtained with 6 watts of audio power. Although originally conceived as a portable demonstration apparatus, the device has the advantages of being able to generate high sound levels inexpensively and to facilitate experiments involving communication from one kind of noise field to another. The original model was constructed on U. S. Army Signal Corps contract No. DA 36-039-sc-64469.
Recording-Reproducing System Using a Dielectric Storage Medium
Authors: Anderson Victor C.
Published: September 2005

A method of short-term storage of an electrical signal as a surface charge on a dielectric drum is described. An ionization recording head is used to produce a localized surface charge on a rotating plastic-coated drum, and a capacitive pickup probe is used to reproduce the signal. Basic design considerations and operating characteristics of the recording and reproducing heads are presented along with over-all response curves for an experimental recorder. A comparison with magnetic drum recording illustrates the advantages of the dielectric recorder to be found in the simplicity of probe and recording head design and the appreciably lower machining precision required. The finite life-time of the recording head appears to be long enough to be unimportant for most applications. The symmetrical recording and erasing characteristics of the recording head which are linearly proportional to potential difference between the surface charge and the applied recording voltage permit cumulative recording to be carried out for hundreds of drum revolution periods. This property of the dielectric recorder makes it uniquely suited for multiple sweep integration applications. (This work was sponsored by Bureau of Ships contract NObsr 43356 NE-120221-5.)
Review of Nonelectrical Means for Generating Sound
Authors: Bouyoucos John V.
Published: September 2005

The need for powerful sources of sound has revived interest in methods of energy transduction which are not wholly electromechanical in nature. This paper reviews some of these methods, and directs attention primarily to those mechanisms which convert the energy of fluid flow to acoustic energy. Both externally actuated and self-excited mechanisms are considered. Among the externally actuated devices are a variety of rotary and electro-dynamically driven valving systems. The mechanisms that involve self-excitation can be grouped, generally, into two classes: The first class includes phenomena, such as edge-tones, which arise from unstable flow configurations. In the second class, and of more general value, are processes involving the fluid-excited motion of solid boundaries, which result in dynamic flow-control. Systems in this group having potentially large power capacity are the devices that have been described by Aigner, Bagno, Fowle, and, more recently, by the author. The properties of these sound generators are discussed in some detail, and their capabilities as power converters are evaluated. The results of this study demonstrate that a useful basis of large-scale fluid-dynamic power conversion does exist. The field is wide open for development and exploitation. (This work was supported by the Office of Naval Research.)
Electrostatic Loudspeakers
Authors: Goldman R. B.
Published: September 2005

The increased demand for improved loudspeakers, together with the availability of new materials and techniques, has revived interest in electrostatic loudspeakers. The basic characteristics of these transducers are reviewed and comparisons made between single-ended and push-pull loudspeakers with respect to performance and ease of fabrication. Various designs, both early and recent, will be described.
Generation and Detection of Acoustic Waves by Means of the Hall Effect in Electrolytes
Authors: Campanella Angelo J.
Published: September 2005

Alternating currents at frequencies up to 1 mcps were passed through a concentrated KCl solution in the presence of a magnetic field normal to the current. Interaction with the magnetic field caused both positive and negative ions to move in the same direction normal to the field and current. The alternating force of the ions on the liquid produced an acoustic pressure in the third normal direction. This wave was propagated through a delay tube and detected. The reciprocal effect wherein the cell was used as a receiver was also investigated. Although the sensitivities are small, they are calculable for plane waves with simple theory. The receiver is a purely velocity-sensitive microphone.
Propagation of Sound in Moving Media
Authors: Franken Peter A. , Ingard Uno
Published: September 2005

The general equations of sound propagation in and through moving media have been studied previously by Blokhintzev, Rudnick and others. Transmission from a stationary medium to a moving one is particularly interesting if one allows not only subsonic but also supersonic flow velocities. Then additional critical angles and double refraction of sound may occur. In addition to this problem other examples of interaction of sound with flow in simple geometries will be considered. This work was supported in part by the NACA and the Office of Naval Research.
Reflection of Plane Sound Waves by an Irregular Surface
Authors: Parker J. G.
Published: September 2005

A plane sound wave is assumed to be incident upon a pressure release surface z = ζ(x,y), which is formed by perturbing the x-y plane in an arbitrary fashion. The solution for the reflected sound field is then expressed as a two-dimensional Fourier integral. Next the Fourier transform G(x,y) of the amplitude spectrum of the reflected field is introduced and subjected to the boundary condition at z = ζ, i.e., that the total sound pressure must vanish there. This leads to an integral equation for G(x,y) that cannot be readily solved. However, if one causes G(x,y) to depend exponentially on a phase function μ(x,y), the approximate solution of the integral equation may be represented as the solution of a partial differential equation involving μ(x,y) and ζ(x,y). A solution to this differential equation has been obtained for the case of sound reflection from a sinusoidally corrugated surface where it is assumed that the angle of incidence is sufficiently small that the reflecting boundary is completely exposed to the primary wave. The character of the reflected sound field in this case varies considerably as the frequency, angle of incidence, and corrugation amplitude and wavelength are changed.
A Method for the Determination of the Critical Angle of Reflection of Sound from the Bottom of the Ocean
Authors: Goodman Ralph R.
Published: September 2005

Single frequency sound pulses of about 0.2 second duration have been used by many experimenters to obtain information concerning the attenuation of transmitted sound in the ocean. It has been shown in the present investigation that it is also possible to obtain the critical angle of reflected sound from the ocean bottom in transmission experiments performed under certain conditions. The conditions are that the source and receiver are omnidirectional and near the surface, the water is shallow (i.e., less than about 100 fathoms) and nearly isovelocity, and the bottom surface is flat. A simple derivation has been made which predicts the pulse length of the received signal as a function of range, water depth, and the critical angle for the total reflection of sound from the ocean bottom. Critical angles have been measured for two transmission experiments made by UCDWR in 1945, using frequencies of 200 and 600 cps, and in water whose oceanographic conditions approximate those assumed in the derivation. Both of these experiments were performed over mud bottoms. The critical angles measured predict velocities in the bottom of 1.05 and 1.02 times the velocity in the water. These values are in fair agreement with measurements made elsewhere [Oliver and Drake, Bull. Geol. Soc. Am. 62, 1287 (November, 1951)[. This research was supported by the Office of Naval Research.
Sound Field Within a Region of Anisotropic Turbulence
Authors: Kraichnan Robert H.
Published: September 2005

The pressure fluctuations within a region of anisotropic turbulence are considered, taking into account the effect of mean shear. Expressions for the pressure correlation function, mean-square pressure, mean-square-pressure-gradient, and certain integral moments of the correlation function are given for the general anisotropic case in the form of single space integrals over velocity correlation functions. As an example, a model of turbulence with oriented vorticity interacting with a uniform mean shear is treated. The relation of the associated pressure correlation-function-moments to the acoustic driving force to be anticipated on a plate bounding a turbulent flow is discussed. This work was supported by the Wright Air Development Center under Contract AF 33(616)-2331.
The Excitation of Finite Strings and Bars by a Flowing Turbulent Stream
Authors: Lyon Richard H.
Published: September 2005

The excitation of finite strings and bars by random noise fields has been studied previously for the case of Brownian motion [Lear and Uhlenbeck, Phys. Rev. 38, 1583 (1931)]. It is the purpose of this paper to extend the analysis to the situation where the noise field is a turbulent stream flowing along the length. The problem is studied theoretically for the string and experimentally for both strings (metal ribbons) and bars. In most cases, there is increased excitation when the average flow velocity of the turbulence is nearly coincident with the phase velocity of waves on the string or bar. The effect of correlation lengths of the source on the excitation spectrum will also be discussed. It is found that wavelengths of the order of or smaller than the correlation length are excited strongly, particularly under coincidence conditions, while wavelengths longer than the correlation length are excited weakly.
Noise Masked Thresholds as a Function of Tonal Duration and Masking Noise Band Width
Authors: Hamilton P. M.
Published: September 2005

Noise masked thresholds for 800 cps tonal pulses 25 to 400 milliseconds long were measured in masking noise bands from 18 to 1100 cps wide. It was found that the threshold remains constant for equal values of band-width pulse length product. The threshold varies according to a formula proposed on the basis of limited data in an earlier report (T. H. Schafer and C. A. Shewmaker, U. S. Navy Electronics Laboratory Report 372, 1953): S/N = m/BT0.8, where S is the signal power, N is the noise power in the pass band of the filter, B is the band width, T is the pulse length, and m is a constant.
Some Parameters Influencing the Perception of Amplitude Modulated Signals
Authors: Small Arnold M.
Published: September 2005

The rise-fall time, duty cycle, and carrier frequency of a pulsed tone were systematically varied. Listeners matched the pitch of this signal to that of a sinusoidal comparison tone. Low SPL was used throughout. Two pitches were identified, one corresponding to the repetition rate (periodicity pitch), and the other to the carrier frequency (carrier pitch). The periodicity pitch decreased in audibility with the increase of any of the experimental variables. These variables had the opposite effect on the perception of the carrier pitch, which in general was audible only at the longest duty cycles. Individual listeners varied considerably in their ability to match the pitch of the pulsed tones. Comparison of the results obtained with pulsed sinusoids with those of pulsed thermal noise suggests that the perception of a periodicity pitch depends upon the band width and spectral location of the pulsed signal's frequency components as well as envelope wave form fluctuation. This work was done while the author was at the University of Wisconsin.
The Effect of Static Air Pressure in the External Auditory Meatus on Hearing Acuity
Authors: Hansen Ronald Gordon
Published: September 2005

The specific purposes of this study were to determine the effects of various static air pressures in the external auditory meatus on (1) threshold sensitivity and (2) hearing acuity at two loudness levels above threshold. To determine the effect of a pressure differential across the tympanic membrane on the threshold sensitivity, measurements were obtained by the Method of Adjustment for 10 ears at each of 41 frequencies (from 100 to 8000 cps) at each of four pressure conditions (−10, −20, +10, +20 cm H2O). For all pressures used threshold sensitivity was generally decreased for frequencies below 1500 cps. with a slight increase in sensitivity for frequencies between 1500 and 2300 cps and a general decrease in sensitivity for frequencies between 2300 and 8000 cps. To test the effect of pressure on loudness, five subjects made equal loudness balance judgments for six frequencies (200, 400, 1000, 1600, and 4000 cps) at 30 db and at 60 db above threshold under each of the four experimental pressure conditions. As in the threshold sensitivity study results indicated a general decrease in sensitivity for frequencies below 1000 cps and only slight effects on the higher frequencies. The effect of static pressure on speech intelligibility was also studied and in the range investigated was found negligible. This work was done at Ohio State University.
Ultrasonic Absorption in Superconducting and Normal Conducting Tin at Low Temperatures
Authors: Bömmel H. E.
Published: September 2005

Recently published measurements [H. E. Bömmel, Phys. Rev. 96, 220 (1954)] on ultrasonic absorption in lead at low temperatures showed two characteristic effects: a strong increase of absorption within a few degrees above the superconducting transition temperature and a sudden decrease below this temperature. Theoretical considerations [W. P. Mason, Phys. Rev. 97, 557 (1955); C. Kittel, Bull. Am. Phys. Soc. 30, No. 1, 42 (1955)] indicate that at very low temperatures ultrasonic absorption and electric conductivity in the normal conducting state are proportional. The same kind of measurements have been made in single crystals of tin with results similar to those in lead, although the aforementioned effects were much more pronounced in samples of very pure tin. The latter showed also a characteristic magnetic field dependence which is attributed to magneto-resistive effects. These effects are markedly different in a longitudinal and a transverse magnetic field. Possible explanation of this fact will be discussed.
Velocity Dispersion of Elastic Waves in Solids
Authors: Hughes D. S. , Kennel John M.
Published: September 2005

Various methods have been used to detect possible velocity dispersion in solids. With dilatational and shear waves poor and indefinite results were obtained. However, by cutting y-cut quartz crystals into sectors and combining certain sectors a composite crystal capable of generating a torsional wave in a cylindrical sample is obtained. With viscous coupling between the driving crystal, the sample and the receiving crystal, clear cut resonances could be identified. With low viscosity coupling the loading of the crystals appeared to be negligible. The resonances occur when the length of the sample is an integral multiple of a half wavelength. Results in Armco iron using three samples, 12 inch, 1 inch, and 2 inches long gave consistent results over the range 0.5 to 3.5 mc. The velocity was constant at 3225 m/sec from 0.5 to 1.5 mc and decreased to 3215 m/sec at 3.5 mc. Fused quartz gave a constant velocity of 3756 m/sec ± 1 m/sec over the range 0.6 mc to 2.7 mc.
Wide-Band Directivity of Receiving Arrays
Authors: Faran James J. , Hills Robert
Published: September 2005

The method of maximizing the directional gain of a receiving array (heretofore useful only at a single frequency) is extended to the case of operation at a finite band width. It appears that although the directional gain of a broadside linear array for operation at a finite band width is less than that for operation at a single frequency, it is always greater, and often considerably greater, than the gain realized by use of the single-frequency design at the finite band width. Unlike the single-frequency design, whose directional gain falls very rapidly as the operating band width is increased from zero, the wide-band designs operate with good gain over a wide range of band widths. This research has been aided by funds made available under a contract with the Office of Naval Research.
Comparison of Threshold Data Obtained by the Method of Limits and the Method of Adjustment
Authors: Corso John F.
Published: September 2005

One of the major areas of emphasis in contemporary audiology is the development of audiometric techniques for dealing with clinical problems related to permanent hearing impairments. However, few studies have been conducted which attempt to establish the relationship of threshold values obtained under the various testing conditions. The present paper describes the results obtained for 105 subjects monaurally tested in an anechoic chamber on a modified ADC audiometer and a Békésy-type audiometer. A comparison of test results for nine frequencies between 250 cps and 8000 cps for each ear shows statistically significant differences in mean threshold sound pressure levels for nearly all frequencies, with the ADC values lower in most instances. Likewise, statistically significant differences in the variability of threshold values were obtained at all but one frequency below 2000 cps, with variability less in the ADC values. There also appears to be a general tendency for the product-moment correlation between ADC and Békésy threshold values to increase with an increase in the frequency of the testing tone. These findings obtain whether the Békésy-type audiograms are read using a “midpoint curve” or a “peak curve” to provide the threshold data. Although no significant differences in the variability of “midpoint” and “peak” Békésy threshold values were obtained at any frequency for either ear, all differences in mean threshold sound pressure levels are statistically significant. The results of the study clearly reveal the effects of testing method on mean thresholds of hearing and indicate the need for the standardization of procedures in large-scale hearing tests. This work was supported by the U. S. Air Force.
Thresholds for Speech in the Presence of Interfering Speech
Authors: Siegenthaler Bruce M.
Published: September 2005

Sentence thresholds (test No. 12) were obtained for 10 adult normal hearing subjects in the presence of continuous discourse at 40 db above normal threshold. Test conditions were (1) signal and interference from same loudspeaker, (2) signal from one loudspeaker and interference from another at 180°, and (3) signal from one earphone and interference from the other phone of the set. Thresholds of the total subject group for the three test conditions were compared. Thresholds for each situation were significantly different (beyond the 0.01 confidence level) from the thresholds for each other situation. Mean threshold for the single speaker situation was 27.5 db (re: Normal Threshold), 21.3 db for two speakers and 6.6 db for the earphones. The results are in general agreement with other data regarding the masking of speech by speech and the ability of auditors to select the desired speech signal from competing speech signals. They also are in agreement with the results of the Doerfler-Stewart signal to noise ratio test for the detection of auditory malingering, in which normal auditors and peripherally deaf ears have speech thresholds 10 to 25 db below the noise level.