bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave Propagation in Fluid-Filled Tubes
Authors: Junger Miguel C.
Published: September 2005

The mechanism of wave propagation in fluid-filled tubes is well known for tube walls having large radial impedances; in this case, energy propagates in discrete modes whose order numbers are defined as the number of nodal circles in their pressure distributions. The propagation phenomena are reviewed here for wall reactance values extending from −∞ through the pressure release condition characterizing tube resonance to +∞. It is shown that the modes lose their identity in this process, viz., that a transition occurs from the nth to the (n−1)th mode as the tube wall changes from a slightly massive to a slightly stiffness-controlled condition. A paradoxical situation arises in that the propagation mechanism of a given mode in a pressure release tube depends upon whether this condition is approached through positive or negative reactance values; this difficulty is purely semantic and connected with the mode number definition. All modes, including the zero mode in massive tubes, have cut-off frequencies, determined by the wall reactance. For the zero mode in slightly stiffness-controlled tubes, wave propagation is a skin effect in the fluid layer nearest the wall, buut distingished from R thayighele waves by absence of a nodal circle.
Thermal Relaxation in Gaseous N2O as Affected by Small Additions of H2O and D2O Vapors
Authors: Wight Howard M.
Published: September 2005

Measurements were made to compare the relative effectiveness of H2O and D2O molecules in influencing thermal relaxation in N2O gas. Thermal relaxation times were obtained from absorption measurements taken in N2O-H2O and N2-D2O mixtures. The “direct” absorption technique was employed in conjunction with pulsed sound waves having a carrier frequency of 110 kc. Data were taken in the region of 100–700 kc/atmos and at a temperature of 21°C. Commercial anhydrous N2O was used in this research. In dried N2O a value of 0.153 was obtained for the maximum amplitude absorption coefficient per wavelength. Measurements were taken at vapor concentrations of 0.39%, 0.77%, and 1.14%; an average value of 1.70 was obtained for the relative collision transition efficiencies of N2O-H2O and N2O-D2O. This value is comparable to the figure of 1.86 obtained by D. Sette and J. C. Hubbard [J. Acoust. Soc. Am. 25, 994 (1953)] for CO2-H2O and CO2-D2O. This work was supported by the Office of Naval Research.
Auditory Testing of a Simplified Description of Vowel Articulation
Authors: House A. S. , Stevens K. N.
Published: September 2005

An auditory test to establish the adequacy of an idealized specification of vowel articulation is described. Articulatory configurations of the vocal tract are specified by means of three numbers: the position of the point of greatest constriction, the degree of constriction at that point, and the size of the mouth opening. The stimuli in the recorded test are the outputs of 279 such configurations of an electrical vocal tract analog. All sound samples are highly similar in duration, intensity, start-stop characteristics, and fundamental frequency and inflection. The instructions to subjects are standardized, and are of two types: one restricts responses to one of nine vowel categories while the other permits a nonvowel response as well. Subjects were experienced in phonetic transcription. The ranges of articulatory configurations identified as given vowels by the subjects are plotted as contours, and these data are compared to results of other investigators. Certain disagreements are pointed out and discussed. The results, in general, show good agreement with previous data, and demonstrate, therefore, the adequacy of the three-number articulatory description. This work was supported by funds from the Air Force Cambridge Research Center.
Finite Amplitude Acoustics
Authors: Lindsay R. B.
Published: September 2005

Interest in the phenomena associated with the transmission of finite amplitude sound waves of all frequencies in media of all kinds has become so great that the adoption of a name for this new field of acoustics now appears to be in order. An obvious choice is macrosonics. The present paper is a review of certain recent aspects of the subject. The classical nonlinear wave equation leads to solutions which often have no physical significance except when rather special approximations are introduced. The introduction by R. D. Fay of viscous terms has led to interesting results and certain generalizations of these will be compared with recent experimental measurements of the attenuation of large amplitude waves both in air and in liquids. More attention should probably be paid to the specialized exact solutions of the dissipational nonlinear wave equation found by K. Bechert. The need for the generalization of relaxation time absorption mechanisms to the large amplitude case will also be stressed. Certain high-energy phenomena such as cavitation, radiation pressure, and acoustic streaming will be mentioned briefly.
Technique for Evaluating Impact Type Noises
Authors: Hardy H. C. , Tyzzer F. G. , Hall H. H.
Published: September 2005

Although impact noises are the most common type of intense noise in industry, no convenient technique of measuring them has been developed. A technique for such measurement will be described which has advantages over other methods in that no assumptions are made on the response of the ear to peak pressure, duration of impulse, total energy, or reverberation effects. The new technique is based on the concept of a broad band masking noise being equivalent to the impact noise with respect to the spectrum shape. The spectral distribution of nearly all industrial impact noise is, of course, of a broad band nature. The equivalent masking noise is obtained by using several broad band noises with a wide range of spectrum slopes to mask the impact noise. The spectrum-weighted noise which masks the impact noise most efficiently, that is, at a level having the least loudness, is considered to be the equivalent masking noise. Application of this technique to drop forge noise in a factory gave an equivalent masking noise with a flat spectrum in octave bands and levels of about 115 db per octave band for operators located about three feet from the forge hammer frame. Noise slopes of +12, +6, 0, −3, and −6 db per octave gave a three-to-one range of masking loudnesses with a minimum at 0 db per octave. Masking tests were made in the laboratory by means of magnetic tape recordings of the impact noises. The following paper describes a portable equipment for making such tests in the field.
Small Reverberation Chamber for Measuring the Sound Absorption of Materials at High Frequencies
Authors: Bishop D. E.
Published: September 2005

Construction of a model reverberation chamber, patterned after the Riverbank reverberation chamber on a scale of ten to one, allows measurement of the sound absorption coefficient of materials over the frequency range from 4 kc to over 30 kc. Knowledge of the absorption coefficients of materials at high frequencies is important in acoustic model studies of large silencing structures and of auditoriums. The model is also intended for study of the effect of changes in room configuration which might be considered for the full size reverberation chamber. Sound sources used in the model include a WE 633 dynamic microphone and an electrostatic tweeter. Instrumentation, measurement techniques, and limitations of reverberation time measurements at high frequencies are discussed. The absorption coefficients of a few materials useful in model work are presented.
The Analogy between Cochlear Fluid Motion and Formation of Surf on Sloping Beaches
Authors: Tonndorf Juergen
Published: September 2005

Perilymphatic fluid motion in the cochlea on vibratory stimulation of the stapes creates an interface phenomenon along the cochlear duct, known as the Travelling Bulge (Békésy). Between this event and surf on sloping beaches, although the latter is a surface phenomenon, exist several similarities, which allow for an analogy in principle: wavelength is gradually lessened (“crowding”) and amplitude is built up toward a maximum (position is frequency dependent) beyond which it declines rather steeply; also eddies are formed. Analysis of surf as the more tangible of the two phenomena (especially that of the first crests of a steep wave front arriving at a slope) indicates that surf is caused by interaction of two events: (1) “shallow-water” opposition and (2) reflection. The first one causes a slowdown in wave velocity with subsequent crowding and amplitude buildup; these in turn are responsible for the onset of eddying. Thereafter, energy dissipation is critically increased, causing amplitude to decrease again.—The second (reflection) creates a shearing effect between the terminal phase of one wave (wave of translation) and its successor; thus, by accentuating the eddying and the dissipation of energy, surf is established as a confinement in space of eddying waves.
Sonochemistry and the Organ of Hearing
Authors: Angeluscheff Zhivko D.
Published: September 2005

Modern life with its wailing sirens, screeching cars, blaring radios, TV, and roaring jet planes—all carrying high-frequency ultrasonic spectra—is potentially dangerous. Progressive deafness is a sequel of sonic-ultrasonic (us) impact upon the organ of hearing. Sonic energy as a mechanical force has been widely explored. The chemical aspect of the problem has been fully neglected. Chemical reactions on the biological structures of the labyrinth can be initiated by infinitesimal amounts of vibratory energy. The electrokinetic potentials initiate migration of ions. If the impact is of a limited capacity and duration, the response of the organ of hearing is within its physiological range, the damage is a temporary one, and reversible. If the impact is sustained, the enhanced damage becomes irreversible and progressive failure of the hearing is in the making. The ultrasonic components of sound produce an intense agitation in the labyrinthine fluid. The temperature is raised, the thermokinetic effect accelerates the rate of chemical reaction. As ultraviolet light is chemically more potent than the visible part of the spectrum, because of very short waves and greater number of vibrations/second, so are the us of shorter and greater number of waves—of greater penetrating power—due to greater absorptions. us permeates the bunched particles of the colloids, disperses them, accelerates the rate of chemical reaction, and advances: in bone, proliferation of new bony tissue; in blood, increase of Gamma globulin, fibrinogen, hemolysis, etc.; in nerve, exit of potassium ion which inhibits and paralyzes nerve function.
Electrical Admittance of Radially and Circumferentially Polarized Barium Titanate Cylinders
Authors: Haskins J. F. , Walsh J. L.
Published: September 2005

In extending the usefulness of barium titanate in the field of ultrasonics, an accurate description of the electrical and mechanical properties of radially and circumferentially polarized cylindrical tubes is needed. Formulas are derived for the electrical admittance of thin-walled tubes polarized in either manner. These formulas describe the electrical behavior of ceramic tubes and, furthermore, show the manner in which particular modes vanish for certain critical dimension ratios. In the case of radially polarized cylinders it is shown how one of the principal modes vanishes when the length is equal to one-half the circumference. In the circumferential case another principal mode vanishes when the ratio of the mean radius to the length is ∼0.6. The data presented shows the excellent agreement between the admittance formulas and the experimental measurements for a number of cylinders with different dimension ratios. It is also shown how the concept of the unidimensional clamped dielectric constant for piezoelectric bar resonators can be extended to the two-dimensional cylindrical cases. The general form of the admittance formulas is compared to that of a simple bar resonator, and it is shown how the electromechanical coupling coefficient enters the formulas.
Comparisons between Pure Tones and Noise Bands as Stimuli for Ear Protector Attenuation Measurements
Authors: Webster J. C. , Thompson P. O. , Gales R. S.
Published: September 2005

To reduce the effects of standing waves in a quiet but nonanechoic room, it is often desirable to use bands of noise instead of pure tones for certain non-earphone listening tasks. When noise bands are used for determining thresholds it is not the whole band that determines the threshold but only a critical band within the broader band. For open-ear thresholds the center frequency of this critical band is near the upper end of bands below 1200 cps because the ear becomes more sensitive as the frequency increases. For ears occluded with ear protectors the center frequency of the critical band below 1200 may be near either end or in the center of the broad band depending on the attenuation-frequency characteristic of the ear protector. If the attenuation increases with frequency faster than the ear's sensitivity then the critical band may be near the lower frequency limit of the broader band. Where this uncertainty in frequency is considered important, bands narrower than octave bands should be used. The magnitude of errors due to using noise bands will be discussed, as will certain of the distinct advantages of using noise bands.
Nonabsorptive Silencing System for Stationary Test Facilities and Portable Ground Mufflers
Authors: Hirschorn Martin , Zecca Robert , Potter Stannard M.
Published: September 2005

The development of this nonabsorptive silencing system is the result of the maintenance problem encountered by the Air Force and aviation industry through the use of absorptive silencing systems in connection with noise reduction installations for turbo-jet, ram-jet, and rocket engines. The problem of keeping absorptive blankets, copper-wool, or stainless steel wool intact while exposed to a high velocity and high temperature exhaust gas stream is well-known and has been responsible for the high replacement costs of exhaust silencing systems. Nearly one year of engineering development time was devoted to model studies before a working model of a silencing system was obtained which is entirely dependent on configuration. Using only acoustic filters and resonators this silencing method demonstrates that high acoustic attenuation can be obtained without the use of absorptive materials. Special consideration was given to maintaining a low pressure drop at high velocities. Full scale and model data will be presented giving acoustic performance and pressure drop characteristics as well as comparative cost charts. The name of the new silencing system is Dura-Stack.
Noise Levels in State College, Pennsylvania
Authors: Bateman William F. , Ackerman Eugene
Published: September 2005

A survey has been made of the acoustic noise levels existing on the university campus and in the surrounding town. Most residents of State College feel that it is a quiet community when compared to larger cities. The survey described here was undertaken to compare the noise levels of a large city with those of State College. Although representing only a limited number of observations the data strongly suggest the following conclusions: (1) For similar locations there are no significant differences in the character of the spectra or the levels observed in State College as compared to a large city, and (2) The high noise levels (greater than 85 db over-all) observed in cities as a result of very heavy traffic and industrial noise are very seldom observed in State College. Where these do occur, such as downtown during the daytime, the frequency of occurrence is sufficiently low so as to constitute considerably less than one percent of the hearing experience of an average resident. The work was supported in part by contract No. AF33(616)-2626. This material was included in W.F.B.'s M.S. thesis and in WADC Technical Report number 54-227.
Red Blood Cell Destruction by Cavitating Sound Fields
Authors: Lombard David B. , Ackerman Eugene
Published: September 2005

Work is in progress on an investigation of the breakdown of erythrocytes subjected to cavitating radio-frequency sound fields. These fields are produced by three bowl-shaped barium titanate ceramic transducers, each having a different resonant frequency. The bowls are driven as much as an octave off resonance by a special electronic generator; a range of 60 kc to 1 mc is covered. Acoustic pressures of greater than 1 atmos rms in water are obtained, and are measured with a barium titanate ceramic probe-type hydrophone. A 300 to 1 dilution of whole blood in saline is placed in a test tube and suspended in the sound field. A built-in optical densitometer measures the density of unbroken cells, and the result is plotted versus time on a graphic recorder. Breakdown rate is calculated from the curves thus obtained. Preliminary studies have been made with erythrocytes of man, cow, sheep, and rat. Results show a definite dependence of red cell breakdown rate upon frequency. This relationship varies from one species to another, and definite resonances are observed for all. This investigation is being supported by a research grant, H-1769 from the National Heart Institute, of the National Institutes of Health, Public Health Service.
Resonant Absorbers and Porous Absorbers with Resonant Cavities
Authors: Skudrzyk Eugen
Published: September 2005

In connection with the construction of a series of halls in Vienna, the largest having a volume of a million cubic feet, cheap and effective absorbers had to be found. The absorption values were to lie between 70 and 80% from 250 to 1000 cps and to fall off at higher frequencies to compensate for the increasing absorption of the audience and that of the air. More than 600 frequency curves had been measured, and all absorbers finally fulfilled the set conditions. They were tuned to 500 cps to give the required low-frequency absorption and, after tuning, damped until the absorption maximum dropped to about 75%, when the frequency range then was of the required width. Three of the studied absorbers of particular interest are: (1) Aluminum sheets 0.5 mm thick, perforated with narrow slits, and corrugated to increase stiffness, manufactured in rolls 20 m long and 1 m wide. The sheets are backed by basalt wool (5 kg/m2). (2) Bricks 10 cm thick, 13 of the cross section being taken up by channels traversing them, the air mass in the channels being tuned by a highly damped air space. These absorbers are to be used in the training and the ball halls where mechanical rigidity is imperative. (3) Frigolith—this is a porous polystyrene material, extremely light, cheap, not hygroscopic, fireproof, and can be colored. Since its pores are closed, it is a poor sound absorber, but its intrinsic absorption suffices to damp resonant cavities cut in the material. The final absorber unit is made up of a box containing a grill like a honeycomb, each grill space communicating narrow channels with the exterior.
Absorption of 10-Mc Sound in Polycrystalline Superconducting Indium
Authors: Bohm H. , Morse R. W. , Tamarkin P.
Published: September 2005

The results of measurements on the absorption of 10-Mc sound in rods of polycrystalline, superconducting indium will be described. Although the absolute absorption coefficient has not been measured, the dependence of a related quantity, the transmitted pulse height, on temperature has been determined for two samples of indium of different purity. The temperature range covered extends from approximately 4.2°A to 1.5°A. Generally, the temperature dependence of transmitted pulse height in superconducting indium resembles that in superconducting tin [L. Mackinnon, Phys. Rev. 98, 1181 (A) 1955], but with the less pure sample, at least, the relative variation over the temperature range covered is not as large as with tin. [Work supported in part by the Office of Naval Research.]
Calculation of Thermal Relaxation Times in Gases
Authors: Lukasik Stephen J.
Published: September 2005

Collisional excitation of molecular vibration and rotation in diatomic molecules is discussed. The features of molecular structure that are pertinent and their significance for the exchange of energy between internal and external degrees of freedom are pointed out. The most important physical information necessary for the calculation of inelastic scattering cross sections, the interaction potential, is treated in detail. In particular, the Lennard-Jones potential, commonly used in such calculations, is shown to be too “hard” for small molecular separations. Finally, calculations of the vibrational excitation probability in nitrogen are presented and compared with existing experimental work and the calculations of Schwartz and Herzfeld. [Supported by Contract N5ori-07861 with the Office of Naval Research and AF33(616)-149.]
Limitations of Human Operators in Handling Competing Voice Messages and Advantages Gained by Storage
Authors: Webster John C. , Solomon Lawrence N. , Sharpe L.
Published: September 2005

Experiments were performed showing performance abilities when guarding one, two, three, or four of four potentially competing voice message channels. Two, three, or four six-second messages overlapped in various degrees and these multiple message complexes occurred every fourteen seconds. Separating two messages into each of the two ears and/or placing filters (high-pass, low-pass, and band-pass) in three of the four channels aided in guarding one or two stations. Increasing the response complexity from writing to speaking or transposing (and writing) the message content increased the frequency of errors by about 10%. When guarding two stations, the percentage of errors was approximately 50%, indicating that only one message (or half of each) was being received. Increasing the number of competing messages present or the degree of overlap among messages increased the errors in receiving. When messages on three of the potentially competing channels were stored and heard on the call of the operator, one, two, or three stations could be guarded with only a slight increase in errors or total time. When all four channels were stored and heard “on call,” any or all stations could be guarded at near perfect accuracy and with no increase in time.
Dependence of Localization on Azimuth
Authors: Galginaitis S. V.
Published: September 2005

In a study to determine binaural thresholds for azimuth difference [Schmidt, Van Gemert, De Vries, and Duyff, Acta Physiol. Pharmacol. Neerl. 3, 2–18 (1953)] it was found that, at high enough frequencies, one or more regions of low localization sensitivity exist at the higher azimuth values. This suggests the use of a “null” method as a useful technique to gather information on the localization process. Two loudspeakers, whose separation could be changed, were sounded alternately. The subject, seated in a rotating chair, could change his azimuth at will. The regions in which the subject seems to hear the sound coming from only one source are then determined. For frequencies below about 1200 cps, only two such regions exist, at the expected 90° and 270°. For frequencies above about 1400 cps, more than two such regions exist. At intermediate frequencies, two or more regions may exist, depending on speaker separation. Possible explanations for these results will be discussed.
Acoustic Streaming Resulting from a Resonant Bubble
Authors: Elder S. , Nyborg W. L.
Published: September 2005

Detailed study has been made of the second-order velocity (vortex) field near a resonant bubble, as well as of the first-order (sound) pressure field. The bubble is situated on the surface of a 10-kc vibrating diaphragm at the bottom of a transparent-walled vessel. The pressure field was explored with a small BaTiO3 probe. The streaming field was examined by observing the motion of small particles through a binocular microscope. The fields have been studied as a function of amplitude and of the viscosity of the liquid surrounding the bubble. At least three separate regimes of streaming may be observed at different sound amplitudes. For one of these regimes, the streaming pattern is found to vary with acoustic boundary layer thickness in a manner analogous to that which has been reported by others for streaming near small solid obstacles. “Source” mechanisms for the generation of the streaming will be discussed. Several aspects of the problem appear to be important: (1) interaction of the bubble-scattered spherical wave with the plane boundary; (2) special physical properties of the bubble surface as affected by contaminants; and (3) the influence of surface (“capillary”) vibrating modes. [This work was supported jointly by the U. S. Air Force and the Office of Naval Research.]
Acoustic Streaming in the Vicinity of a Sphere
Authors: Thrasher Robert W. , Westervelt P. J.
Published: September 2005

Considerable work has been done recently on the problem of acoustic streaming in the vicinity of a cylinder [Holtzmark, Johnsen, Sikkeland, and Skavlem, J. Acoust. Soc. Am. 26, 26 (1954); Raney, Corelli, and Westervelt, ibid. 26, 1006 (1954); S. Skavlem and S. Tjötta, ibid. 27, 27 (1955)]. Carlton Lane has completed an extension of this work to the case of a sphere [J. Acoust. Soc. Am. 27, 1003(A) (1955)]. Although Lane uses the approximation method of Raney et al., this present project applies the numerical integration method of Holtzmark et al. to the sphere. A precise stream function obtained by Lane has been integrated exactly to obtain an expression containing algebraic and trigonometric components and the exponential integral. From this expression it is possible to obtain streamlines which are accurate at greater distances from the sphere and for lower frequencies than those of Lane. [This work has been supported by the National Science Foundation and the U. S. Air Force, Wright Air Development Center.]
A Note on Pitch-Synchronous Processing of Speech
Authors: David E. E. , McDonald H. S.
Published: September 2005

Voiced portions of speech wave forms are quasi-periodic in nature. This property arises from repeated excitation of the slowly changing vocal cavities by glottal puffs. Knowledge of this periodicity affords a means for reducing the channel capacity necessary to transmit a speech signal. One proposal [H. W. Dudley, U. S. Patent No. 2,115,803, May 3, 1938] to this end involves eliminating N − 1 of every N pitch period before transmission, where N is chosen small enough so that variations important to the ear-cortex in the intraperiod wave form are preserved. Thus, provided consonants are similarly chopped, the channel capacity in bits/second can be reduced by 1/N. At the receiver, missing parts are restored by interpolating them in a predetermined way, for example, by simply repeating each of the received periods N − 1 times. Circuits for operating on monotone speech demonstrating this principle have been constructed. Experiments with N = 2 to 5 indicate that minor distortion, which appears as submultiples of the pitch harmonics, is thereby introduced. Consonants are little affected by the chopping. A similar scheme which involves eliminating portions of the wave form in each period was also investigated. Less satisfactory results were obtained here, since the intraperiod wave form carries the phonemic information. A magnetic tape demonstration illustrating these points will be given.
Speech Compression
Authors: Vilbig Friedrich
Published: September 2005

One can distinguish between physical compression when only the physical characteristics of the speech oscillations are used, and linguistic compression if, beyond that, rules are used which are found by linguistic investigation. We shall consider here only the physical methods. They can be divided into two groups. In the first group, which may include several variations, every frequency of the original band is divided by a factor n by means of frequency division, or time element skipping. On the receiver side, the original frequencies are then restored by means of frequency multiplication, or time element repetition. By the second group, on the transmitter side, the so-called analyzer builds from specific characteristics of the speech oscillations certain code-signals. These are transmitted in a narrow frequency band channel and control a speech synthesizer on the receiver side. The code signals contain statements about the excitation and the system functions. The excitation function indicates whether the air stream propelled by the lungs either excites the vocal cords producing a pitch frequency modulation when vowels are being uttered, or if unmodulated, produces a kind of noise, for example, if consonants are spoken. The system function indicates the varying positions of the mouth organs in the form of “envelope curve” of the speech spectrum. Four variations of the code-signal system differ by the method of transmission of the system function “envelope curve.” (1) In the earliest system, the Bell Vocoder, the mean values of 10 or 16 frequency band sections of the envelope curve are measured and transmitted through 10 or 16 frequency channels. (2) In the Scan Vocoder, we scan the envelope of the short time-frequency spectrum, for example, 30 times per second. The scan voltage is then transmitted through only one narrow band frequency channel as an envelope curve. (3) In the Pulse Vocoder, the envelope curve is transmitted after a transference to a succession of pulse groups. (4) By the Formant Vocoder, instead of the whole envelope curve, only three signals corresponding to the three envelope resonance frequencies (Formant frequencies) are transmitted. The system developed by the Air Force Cambridge Research Center is a Scan Vocoder which can be converted into a Pulse or Formant Vocoder by the exchange of a controlling unit. Also we obtain a unit system which makes it possible to combine the systems with others; for example, with the synthesizer of Lawrence, the Formant extractor of Flanagan, or the Formant extractor of Northeastern University. By means of block diagrams, the equipment on hand will be discussed. How it works will be demonstrated by the playing of a record.
Noise Duration as a Cue for Distinguishing among Fricative, Affricate, and Stop Consonants
Authors: Gerstman Louis J.
Published: September 2005

An earlier experiment [Gerstman, Liberman, Delattre, and Cooper, J. Acoust. Soc. Am. 26, 952 (1954)] demonstrated that variations in the duration of a change in formant frequency can serve as an effective cue for distinguishing one class of speech sounds from another. The duration cue was found to operate independently of place cues; i.e., it served to distinguish the stop b from the semivowel w, both of which are articulated at a speaker's lips. Exploratory work now suggests that another temporal cue, noise duration, operates in much the same fashion, distinguishing among classes of sounds produced at the same place in the mouth. A tape recording of the spoken syllable ∫a (as in shop) was progressively shortened by cutting off increasing amounts of the noise portion with which the syllable begins. When the noise portion was approximately half its original length the syllable was heard as ∫a (as in chop), and when most of the noise had been removed the syllable was heard by some listeners as ka and by others as ta. (Inasmuch as ∫a and t∫a are both produced at a point in the mouth that lies be|tween the places where k and t are formed, the listeners' uncertainty as to whether the stop is k or t is understandable.) Thus the consonant, originally a fricative, became an affricate and then a stop. The experiment has been repeated with more highly controlled synthetic speech patterns. Here it was found that a second cue of some importance was the time required by the friction to rise to full intensity. [This work was supported in part by the Carnegie Corporation of New York, and in part by the Department of Defense in connection with Contract DA49-170-sc-1642.]
Some Acoustic Cues for the Fricative Consonants
Authors: Harris Katherine Safford
Published: September 2005

An earlier experiment [Katherine S. Harris, J. Acoust. Soc. Am. 26, 952 (1954)] has shown that discrimination among the unvoiced fricatives of American English, f, θ, (thin), s, and ∫ (shin), in consonant-vowel syllables depends partly on the characteristics of the noise portion of the speech sound, and partly on the characteristics of the vocalic portion of the syllable (in particular on the second-formant transition). A second experiment has been performed with synthesized fricative-vowel syllables in order to specify further the characteristics of the cues in the two parts of the syllable. For that purpose we varied (1) the lower cut-off frequency of the noise, (2) the intensity of the noise relative to the intensity of the vocalic part of the syllable, and (3) the second-formant transition of the vowel. The results show that as the intensity of the noise is decreased relative to the intensity of the vocalic portion of the syllable, f and θ identifications increase relation to s and ∫ identifications. The s identifications are greatest when the lower cut-off frequency of the friction is at 3600 cps, ∫ identifications when the cutoff is at 2000 cps, and f identifications when the cutoff is at 1200 cps. Identifications of θ are equally likely for all cut-off frequencies. Suitable second-formant transitions for each of the four fricatives can be predicted approximately from knowledge of their articulatory places of production. [This work was supported in part by the Carnegie Corporation of New York, and in part by the Department of Defense in connection with Contract DA49-170-sc-1642.]
On the Transmission and Confirmation of Messages in Noise
Authors: Egan James P.
Published: September 2005

In several experiments, the restrictions imposed upon the communication process by an articulation test were relaxed by increasing the number of events in the communication sequence. A communication event (CE) is the transmission of a message from the source to the receiver followed by the return of a message (correct or incorrect) from receiver to source for confirmation. Although both source and receiver serve as talker and listener, the relation between them is asymmetric. Since the source knows the original message, he must accept or reject the message sent back to him according to some criterion. Various types of CE's arise depending upon (1) whether or not the receiver correctly hears the message, and (2) whether or not the source confirms the message returned by the receiver. The various probabilities associated with these events are investigated as a function of speech-to-noise ratio. The behavior of the source is examined in terms of the relation between the two conditional probabilities associated with a correct and with an incorrect confirmation. If each message is sent repeatedly until all are confirmed, a sequence of CE's is generated. A simple mathematical model accurately describes this process. [This research was supported by the U. S. Air Force.]
Sound Scattering Problems in the Ocean
Authors: Hersey J. B.
Published: September 2005

Observations of sound scattering in the open ocean have shown not only the wide spread occurrence of stratified scatterers there but also have indicated ways in which acoustical methods can be employed to describe the distribution of life in the open ocean. One method employs the broad-band spectrum of an explosion fired at shallow depth as a sound source. The scattered sound is also received at shallow depth. The resulting data can be interpreted as variation in scattering cross section as a function of depth on the assumption of uniform horizontal layering of the scatterers. Detailed spectrum analysis shows that scatterers having different scattering spectra are found at different depths, and that they behave differently in their vertical migration. The identification of characteristic spectra with animal types has been advanced by observing that the spectrum of some layers is modified during their vertical migration in a way that suggests that the scatterers are fishes with swim bladders. Moreover, it is indicated that these spectrum changes will be useful in studying the function of swim bladders in fishes. Another approach to the problem of identifying deep sea sound scatterers is to combine sound scattering observations and photography. This technique has been used only a short time, but it has produced a number of pictures from which the scatterer could be positively identified.
Sound Propagation in Wedge-Shaped Regions
Authors: Kearsley Elliot A.
Published: September 2005

This paper considers the problem of characterizing the sound field of a line source in a semi-infinite region including a plane of media discontinuity forming an angle with a free surface. The general problem is shown to involve two difficulties: (1) The discontinuity in density results in non-orthogonal normal modes of the velocity potential. (2) The discontinuity in sound velocity makes the boundary value problem nonseparable. When density alone is discontinuous, the normal modes of a function, which is the product of the square root of density and the velocity potential, are orthogonal. A normal mode expansion for the solution of this problem is found. This solution serves as a Green's function for a perturbation solution of the problem which includes a small velocity discontinuity as well. [Work supported by the Office of Naval Research.]
Transmission of a Spherical Wave through a Thin Elastic Plate
Authors: Lamb George
Published: September 2005

The sound field obtained from the transmission of a spherical wave through a thin elastic plate has been calculated. The field is expressed in the form of an outgoing spherical wave with an amplitude factor containing angular dependence. For the case in which the ratio of the velocity of flexural waves in the plate to the velocity of sound in the outside medium is greater than unity, the amplitude factor exhibits a strong maximum for the angle at which trace matching takes place. [Supported by Office of Naval Research Contract N5ori-07861.]
Elastic Wave Dispersion in a Cylindrical Rod
Authors: Oliver Jack , Bowie Glenn
Published: September 2005

Previous experimental investigations of elastic wave dispersion in cylindrical rods used either standing wave or narrow band pulse techniques. By applying a wide band, short duration, pulse technique both phase and group velocities over a much greater range of values of a/λ, where a is the radius and λ the wavelength, may be studied. Experimental points for the first longitudinal mode and the flexural mode are in excellent agreement with the theoretical curves of R. M. Davies [Trans. Roy. Soc. (London) A240, 375 (1948)] and G. E. Hudson [Phys. Rev. 63, 46 (1943)]. The minimum of group velocity for the first longitudinal mode and the maximum for the flexural mode are clearly recorded. Additional points corresponding to propagation in the higher longitudinal modes may be identified.
On the Diffraction of a Spherical Sound Wave by a Plane of Finite Height
Authors: Lehman Alfred
Published: September 2005

A study has been made of the diffraction of a spherical wave by a partition in order to investigate the shielding properties of a wall. Measurements carried out in an anechoic chamber will be compared with a theoretical analysis based on the Kirchoff-Kottler and Sommerfeld-Carslaw black-screen treatments. [Supported in part by Contract NAw-6405 with National Advisory Committee for Aeronautics.]
Speech Privacy in Buildings
Authors: Cavanaugh W. J. , Farrell W. R. , Hirtle P. W. , Watters B. G.
Published: September 2005

Obtaining adequate speech privacy in modern buildings is one of the important goals of the architect and consultant. This paper deals with the development of a rating method which takes into account the several factors influencing speech privacy. Our work in this area began with a brief laboratory study. The results indicated that speech privacy is related to speech intelligibility rather than to level. The initial experiments were supplemented with an analysis of about 40 case histories representing about 400 pairs of spaces in different kinds of buildings. There appears to be good correlation between the articulation index of intruding speech sound and the reactions of building occupants.
Photographic Film Detection Methods for Ultrasonic Field Visualization
Authors: Berger Harold , Kraska I. R.
Published: September 2005

Some confirming evidence is presented to support the idea that the direct action of ultrasonic waves on a photographic emulsion is influenced to a great extent by the softness of the emulsion Significant increases in the photographic speed of an emulsion to ultrasonic exposure have been obtained by soaking the emulsion in water before the exposure in order to soften it and thereby make it more sensitive. Another method for obtaining photographic images of ultrasonic fields is also discussed. By exposing film, without dark-room techniques, to ultrasonic radiation in an iodine-water solution, it has been found that the emulsion tends to change color in the irradiated areas so that the ultrasonic image can be observed as it forms. In addition to this advantage, this method is capable of relatively good speed and yields fine grain images which do not appear subject to fading.
Ultrasonic Bonds for Use at Liquid-Helium Temperatures
Authors: Levy Moises , Rudnick Isadore
Published: September 2005

A process is described for sealing quartz crystals to metals with epoxy resin which has proven to be very dependable for low-temperature work.
Generalized Form of the Sonar Equations
Authors: Urick R. J.
Published: September 2005

A form of the sonar equations is obtained which is applicable to short transients as well as to pulsed cw waveforms. The equations, in terms of the energy density of the source, are independent of the wave shape of the generated transient and of the echo. They reduce to the ordinary sonar equations for relatively long pulses of constant intensity, and are particularly useful for prediction purposes in applications like explosive echo ranging.
Human Discrimination of Auditory Duration
Authors: Creelman C. Douglas
Published: September 2005

A series of experiments measured human ability to discriminate between durations of auditory signals presented in a noise background. Independent variables were the signal voltage, the “base” duration T, and the increment duration ΔT. Separate experiments assessed the effect of each of these on discrimination. A decision-theoretical model is presented, based on a “counting mechanism,” which operates on impulses generated over the relevant durations. The source of these impulses is assumed to be random. Limitations on performance come from uncertainty regarding the end points of the time interval and from limited memory. The decision processes underlying the model are presented as a general theory of duration discrimination.
Power Flow between Linearly Coupled Oscillators
Authors: Lyon Richard H. , Maidanik Gideon
Published: September 2005

The power flow between two independently and randomly excited harmonic oscillators is calculated assuming small linear coupling. It is found that for conservative coupling the power flow is proportional to the temperature (average modal energy) difference of the two oscillators. The constant of proportionality is symmetric in the parameters of the two modes and is positive definite although its magnitude depends on the relative sign of the inertial and stiffness coupling. An equivalent circuit for the energy flow between the modes is developed. Finally, we apply the formalism to obtain the motion transmitted through a two-stage vibration isolator. The method is then extended to the problem where two multimodal systems interact. A particular application is the power flow between several structural modes and a reverberant acoustic field. The reverberant sound field is considered as a temperature bath in which the structural modes are immersed. Using this model the steady-state partition of energy between the two systems and the parameters which govern this partition are computed. Analog circuits for this problem are also constructed. The radiation resistance for some of the normal modes of a beam are calculated and results of the formalism are illustrated experimentally.
Isopreference Method for Evaluating Speech-Transmission Circuits
Authors: Munson W. A. , Karlin J. E.
Published: September 2005

This exploratory paper describes a modification of the paired comparison technique for deriving a one-dimensional scale for rating speech transmission systems on the basis of listener preferences. The numbers on the scale, which run from 0 to 100, are called “Transmission Preference Units” (TPU), and are intended to be used to evaluate any speech transmission system, regardless of the noise or distortions encountered, provided the system is less preferred than the reference condition, namely, real speech at 1 m. If the TPU ratings for two transmission systems are known, it is believed that the difference can be used to predict the percentage of users who would prefer the system with the higher rating.

Subjective listening experiments have been conducted with a small group averaging seven observers for rating a large number of speech transmission conditions on the TPU scale. Equal preference contours were determined on speech level-noise level planes for several different frequency bands. The listening tests require only simple A-B preference comparisons of two brief samples of speech heard consecutively.

The data suggest that the basic requirement of transitivity, essential for a simple useful one-dimensional rating scale, may be satisfied for many types of transmission conditions. Thus if transmission condition A is judged to equal condition B in preference, and condition B equals C, then A and C were also found to be judged equal. This apparently holds even though A, B, and C are circuits differing widely in their physical parameters.

This study is reported at this stage in the hope that other laboratories may become interested in checking and extending the limited scope of the work reported here. Such confirmation is necessary before a simple one-dimensional TPU scale can be postulated and used with confidence for precise evaluations. For the purposes of this work, two circuits are considered to be equal in preference when half of the judgments of the group favor one and half favor the other circuit; it does not follow that individual observers are indifferent in their preferences for the two circuits.
Efficiency of Circular Sources and Circular Arrays of Point Sources with Linear Phase Variation
Authors: Embleton T. F. W. , Thiessen G. J.
Published: September 2005

The intensity and power radiated from circular ring sources and circular arrays of point sources are derived from first principles. The shape of the radiation patterns and efficiency of power output are studied as a function of phase changes between different parts of the source and of the ratio of the over-all source dimensions to the wavelength of the sound field. These expressions are applicable to the reduction of noise from such sources as centrifugal and axial blowers and aircraft propellers. The relationship between the mathematical phase parameter and such mechanical quantities as the number of blades is described. As in the case of the linear source the radiated power drops if the phase parameter exceeds a certain critical value. However, the drop in the power for the circular source is greater than that for the line source. For the circular source alone the anomaly exists wherein the power—at most ratios of the source diameter to sound wave-length greater than about 0.6—is greater for a source “de-phased” by small amount than for one having all elements radiating in phase.