bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory-Threshold Recovery after Exposures to Pure Tones
Authors: Hirsh I. J. , Bilger R. C. , Burns W.
Published: September 2005

A modified Békésy-type audiometer was used to obtain a continuous recording of the auditory threshold before and after monaural exposures to different durations and intensities of pure tones. Preliminary studies confirmed the observations of S. N. Reger that the amount of temporary hearing loss following a 1-minute exposure to a 1-kc tone is greater when the stimulating tone is 20 db above threshold than when it is 80 db above threshold. This surprising result led to an investigation of the dependence of temporary hearing loss on the duration and the intensity of exposure tones. Recovery curves for the threshold at 1 kc following exposure by 1 kc indicate that exposure tones at or above 60-db sensation level yield a rapid recovery followed by either a slowing down of the recovery process or a second rise in the threshold. Following exposure to a 20-db tone, however, this rapid recovery is not so apparent and therefore, when the temporary threshold shift is measured soon after exposure, the apparent loss after 20 db is greater than for higher intensities. The hearing loss two minutes after exposure does not change with increasing exposure level until the sensation level exceeds 80 db. Also, temporary hearing loss does not change significantly with exposure durations from 15 sec to 1 min, but increases as the durations increase to 2 and 4 minutes. These findings do not hold when the threshold for 1400 cps is measured following exposure to 1 kc. Here, temporary hearing loss increases directly with duration for sensation levels at 80 db or above, and it increases directly with level for sensation levels greater than 60 db. Although these results are somewhat obscured by large differences among individuals, the recovery curves and their dependence on intensity and duration of exposure point to more than one underlying recovery process. This work was carried out in connection with Contract No. 18(600)-131, Supplemental Agreement S1 (54-1317), between Central Institute for the Deaf and the United States Air Force.
Effects on Threshold Sensitivity of Exposing the Normal Ear to Pure Tones and White Noise over Sensation Levels of 10 db to 100 db
Authors: Reger Scott N.
Published: September 2005

By means of a modified Békésy Audiometer, with which it is possible to measure a temporary threshold shift (TTS) resulting from a sound exposure within a few seconds after termination of the stimulus, it was found that: (1) measurable shifts occur after 10 db sensation level (SL), 10 second exposures; (2) greater shifts occur for the exposure tone following 20 db SL one-minute exposures than comparable shifts following 80 db SL one-minute exposures; (3) at low intensity level exposures the greatest shift occurs for the exposure frequency. At progressively higher intensity level exposures a shift develops for frequencies progressively higher than the exposure frequency until at relatively high exposure intensity levels the maximum shift develops for frequencies from one-half to one octave above the exposure frequency; (4) low intensity level white noise exposures result in significant shifts for white noise but negligible shifts for pure tones. Relatively high intensity level white noise exposures result in significant shifts for both white noise and pure tones.
Results of Noise Measurements on Wind Tunnels
Authors: Medwin H. , Pietrasanta A. C. , Dyer I.
Published: September 2005

Noise measurements have been made on three supersonic, blowdown wind tunnels at The James Forrestal Research Center, Princeton University. The tunnels have test sections 4 in. × 8 in. to 2 in. × 212 in. in size, operate at supply pressure to exhaust pressure ratios ranging from 7 to 40. In order to evaluate only noise associated with the shock system in the diffuser, acoustical measurements were made in the tunnel exhaust plena and outside the tunnel walls. These measurements have yielded information about acoustic power levels and spectra associated with such shock systems under various tunnel operating conditions. Based on these data the Mawardi-Dyer work [O. K. Mawardi and I. Dyer, J. Acoust. Soc. Am. 25, 389 (1953)] has been extended for blow-down tunnels to show that efficiency of conversion of tunnel mechanical stream power to acoustic power is a function of the supply to exhaust pressure ratio.
Acoustical Properties of Carpet
Authors: Harris Cyril M.
Published: September 2005

Data are presented on the acoustical properties of carpet. Values of absorption coefficient, acoustic impedance, and flow resistance are given for carpet having various physical properties. This work was supported by a grant from the Carpet Institute, Incorporated.
Cavitation and Polymer Degradation
Authors: Roberts Winston , Yeager Ernest , Hovorka Frank
Published: September 2005

Various dilute polymer solutions have been subjected to ultrasonic waves from a spherically concave transducer at 600 kc/sec. The decrease in molecular weight of the polymers has been examined as a function of the gas saturation of the polymer solution and the static pressure. If cavitation is suppressed either by degassing or by the use of high static pressures with only partially gas-saturated solutions, degradation does not appear to occur even at intensities approaching 103 watts/cm2 or acceleration amplitudes of 109 cm/sec2. With gas-saturated solutions, the degradation of the polymers decreases with increasing static pressure. The dependence of the rate and extent of degradation on ultrasonic intensity has also been studied with other equipment providing relatively uniform ultrasonic fields. In polymer solutions of relatively high viscosity, the development of the cavitation field is a slow process. Visual observations at 600 kc/sec indicate that only a few bubbles form initially and each of these bubbles grows until of sufficient size to support a low order surface wave. Very small bubbles are then seen to stream from each parent bubble with the most common case involving two streams in diagonally opposite directions. (This phenomenon is similar to that reported by G. Willard, paper C1, 47th meeting, Acoustical Society of America, June, 1954.) After a few seconds, the whole field is filled with such bubbles. This research was partially supported by the Office of Naval Research.
Sub-Lethal Effects of Vibratory Energy on Pseudomonas fluorescens
Authors: Shull J. J. , Reid J. J. , Kinsloe H. L. , Ackerman E.
Published: September 2005

The rate of kill (i.e., loss of ability to reproduce) of microorganisms exposed to high-intensity sound fields is dependent upon the intensity of effective cavitation in the suspending medium. Effective cavitation, and therefore rate of kill, can be suppressed by both reduced and excess pressures applied to the system. However, experimental procedure does not permit ruling out factors other than cavitation except to limit them to negligible amounts. Under conditions of reduced effective cavitation, on the other hand, sub-lethal physiological changes in Pseudomonas fluorescens have been demonstrated. Increases in dehydrogenase activity of whole cells have been induced by exposure to the sound field of a Raytheon 9-kc vibrator operated under reduced pressures. Such changes apparently are related to molecular size of the substrate involved.
Surface Tension Bubble Resonances
Authors: Ackerman E. , Proctor T.
Published: September 2005

The vibratory motion of a gas bubble immersed in a fluid is theoretically discussed for modes whose restoring force depends primarily on the surface tension. The characteristic functions for these modes and the resonant frequencies have been computed. The Q of the bubbles and the acoustic scattering cross section have been computed for air bubbles in water; damping due to radiation and viscosity are included. The effect of a slightly ellipsoidal shape on the resonant frequency has been studied using second-order perturbation calculations.
Intonation in Ensemble String Performance
Authors: Shackford Charles R.
Published: September 2005

In ensemble string performance, when no open strings are used, players are entirely dependent on their adaptation to the forces exerted by the tonal world when it is put to artistic uses. The tendency of tones to group themselves around a main tone with varying degrees of dependency upon it, the natural acoustical laws governing simultaneously sounding tones of different pitch, and the dynamics of melodic and harmonic progression all effect intonation. The degree to which each one influences the intonation of a given passage is dependent on the degree to which the passage permits each of these considerations to operate. Specially designed apparatus has made it possible to determine the pitches of all tones in all parts and hence the sizes of all harmonic and melodic intervals from a single performance of a musical selection. It is possible now to show how the forces described in the foregoing actually influenced the pitches of tones in the case of performances by three different string trios.
Ultrasonic Measurements in Liquid Helium
Authors: Chase C. E.
Published: September 2005

Recent experiments on the propagation of ordinary (“first”) sound in liquid helium are described, and the results are related to various aspects of the liquid helium problem. The first measurements of the velocity were made by Findlay, Pitt, Grayson Smith, and Wilhelm in 1938, using an interferometric technique at 1.338 Mc/sec. These results were later extended to higher pressures by the same authors. Measurements of both velocity and absorption were later made by Pellam and Squire, using a pulse technique at 15 Mc/sec. The author has measured velocity and absorption at 2.0, 6.0, and 12.1 Mc/see, using a technique similar to Pellam and Squire's and extending the measurements down to 0.85°K. The 12.1-Mc/sec results were then extended to 0.1°K by the technique of adiabatic demagnetization. These results showed that the frequency dependence of the absorption is characteristic of a relaxation process and agreed qualitatively with the theoretical predictions of Khalatnikov. The attenuation goes through a maximum somewhat below 1°K and falls smoothly toward zero at absolute zero. The velocity below 1°K is practically independent of temperature and has the value 240 m/sec. Experiments are now being undertaken by Whitney to improve the accuracy of these results and extend them to higher pressures. Measurements of the velocity at increased pressures by Atkins and Stasior, and some extremely accurate interferometric determinations of the velocity by van Itterbeek, are also described.
Theoretical Aspects of Sound Propagation in Liquid Helium
Authors: Tisza L.
Published: September 2005

It is a characteristic feature of the low-temperature modification of liquid helium that temperature differences propagate in forms of waves instead of producing a dissipative heat conduction. In these thermal waves or “second sound,” temperature variations play a role similar to pressure variations in first or ordinary sound. Although our understanding of the molecular mechanism behind these phenomena is still far from satisfactory, the experimental and theoretical study of the two sound waves has contributed significantly to the clarification of the situation.
Recent Experimental and Theoretical Work on Vibrational Relaxation in Gases
Authors: Slawsky Z. I.
Published: September 2005

The ideas underlying the effect of some types of impurities on the acoustic relaxation in gases will be discussed. Experimental methods for studying such phenomena over a wide range of temperatures and densities based on the production of normal shocks will be presented and some recent results reported.
Measurement of Molecular Relaxation in Gases at Elevated Temperatures
Authors: Lebel J. D. , Mawardi O. K. , Young J. E.
Published: September 2005

A high-temperature facility suitable for carrying out measurements of acoustic absorption in gases is described. The absorption data have been evaluated from a determination of the width of the response curve for various lengths of a resonant cavity. Temperatures up to 850°C have been obtained, with the gas pressures being a few inches of water in excess of the ambient pressure. The usable range of frequencies extends from about 2 kc to 5 kc. Representative data showing the temperature dependence of the molecular contribution to the total absorption will be shown for air. [Sponsored by Air Force Contract AF 33(616)-149.]
Ultrasonic Absorption in Water Vapor
Authors: Brickl D. , Nyborg W. L.
Published: September 2005

Water vapor is known to be unusually effective as a “catalyst” in accelerating vibrational relaxation processes in gases. It is surprising that, although extensive sound propagation studies have been made in gases where H2O gas is an impurity, relatively little work has been done on the latter gas by itself. In this paper results will be reported on absorption measurements now being made on pure water vapor at temperatures in the 20–80°C range and at various pressures less than the respective saturation pressures for the different temperatures. A pulse technique is employed using a carrier frequency of about 115 kc. The general setup is essentially that described at a previous meeting by Wight. Over parts of the range the measured absorption exceeds classical predictions. [Supported in part by the Office of Naval Research.]
A Method of Ultrasonic Absorption Measurements in Liquids
Authors: Barnes Roswell P. , Beyer Robert T.
Published: September 2005

Apparatus will be described for measuring ultrasonic absorption in liquids using the modified radiation pressure method reported by McNamara. An amplitude modulated ultrasonic beam from a movable source is directed against a condenser microphone mounted in the bottom of a vertical tank. The membrane of the microphone responds to the variations in radiation pressure resulting from the modulation of the beam. The variations of capacitance of the microphone are used to frequency-modulate a Franklin oscillator. After frequency multiplication and limiting, the FM signal is detected by a Foster-Seeley discriminator from a commercial receiver. The low-frequency signal corresponding to the modulation wave form is put through a preamplifier, a decade attenuator, and a tuned amplifier, and it is then measured with a peak-to-peak reading comparison voltmeter of high resolution. Some sample data will be given and the results compared with those from other methods. [This work was supported in part by the Office of Naval Research.]
Identification, Discrimination, and “Matching from a Sample.”
Authors: Pollack Irwin
Published: September 2005

A valid experimental comparison between the absolute identification and the relative discrimination of aspects of elementary auditory displays is difficult when each is independently examined in separate experiments. In the present study, simultaneous examination of the identification and discrimination was carried out with a set of “matching from sample” procedures. In each case, the listener attempted to identify the sound level of a tone selected from a “catalog” of sound levels. The various procedures differed solely in terms of the opportunity to “match” the signal with the catalog. Significant improvements in performance are associated with increased accessibility to the catalog, especially under finely subdivided conditions encompassing a wide range of sound levels.
Observations on the Relationship between Frequency Discrimination and Psychological Phenomena
Authors: Harrison Bertram M.
Published: September 2005

Extensive use of the frequency discrimination method of hearing testing has inspired an effort to correlate certain of the results with psychological characteristics of the subjects. Tabulation of the data has led to some conclusions which have interesting possibilities.
High-Intensity Sound and Shock Waves
Authors: Keller Joseph B.
Published: September 2005

High-intensity sound, or macrosonics, differs from ordinary sound in its manner of propagation. All parts of an ordinary sound wave travel with the same speed (the sound speed). However, in high-intensity sound the pressure maxima travel faster than the pressure minima. Consequently, high-intensity sound waves become distorted as they travel. This distortion may become so extreme that a discontinuity or shock wave develops when a maximum tries to overtake a minimum. Such a shock wave will start out very weak but will grow in size and then, perhaps, decay again. All of these effects are illustrated by the example of a piston moving periodically at one end of a semi-infinite tube. The free vibration of the gas in a closed tube is also examined and found to be modified by the foregoing effects. Similarly the sound waves produced by a piston at one end of a closed tube are found to be affected, in some cases shocks developing and in other cases the wave forms merely being distorted. Similar phenomena occur in three dimensions, as can be seen from a new theory of the propagation of high-intensity sound in three dimensions. This theory includes a new phenomenon, the possibility of refraction caused by intensity variations on a wave front. It also leads to shock formation in certain cases, and describes the way in which the shocks propagate, grow, and decay. The theory is an extension of a previous theory of weak shocks which was called geometrical acoustics. It too is a geometrical theory.
Some Second-Order Effects in Macrosonics
Authors: Westervelt Peter J.
Published: September 2005

The force owing to radiation pressure on an object of any shape and having an arbitrary normal boundary impedance can be expressed in terms of the asymptotic scattering functions for the object [J. Acoust. Soc. Am. 23, 312 (1951)]. It will be shown that this specification of the radiation force is valid for any obstacle irrespective of whether it is possible to specify a normal boundary impedance. Two typical obstacles having nonlocal boundary conditions are a metal disk and a lossy bubble. A simple relation between the radiation pressure in a plane standing acoustic wave and the acoustic impedance will be given. Equations for the generation of acoustic streaming have been derived in terms of Brillouin's radiation stress tensor [J. Acoust. Soc. Am. 25, 60 (1953)]. It is emphasized that these equations are valid for any nonreacting fluid irrespective of the loss mechanisms involved. For the special case of a barotropic fluid, W. P. Raney has shown that these equations reduce to those obtained by Medwin and Rudnick [J. Acoust. Soc. Am. 25, 538 (1953)]. [This work has been supported jointly by the Office of Naval Research and the U. S. Air Force, Wright Air Development Center.]
Modified Analysis for Plane Traveling Waves of Finite Amplitude
Authors: Fay Richard D.
Published: September 2005

The speed of propagation of the pressure in a sound wave may be expressed by S = S0 [1 + A (1 + 1/γ) (p/P0) + ⋯], where A is a pure number. In the classical analysis A = 12, whereas reliable measurements, both of the rate of attenuation of a repeated saw-tooth wave and of the rate of increase of the second harmonic in an initially sinusoidal wave, indicated that A ≃ 13. An analysis of a rectangular wave in a fictitious fluid medium without viscosity indicates that 13 is in fact the correct theoretical value for A. In such a wave, the ratio of the density in the wave to the density in the undisturbed medium may be accurately expressed in terms of the speed of propagation and the particle velocity. The speed, S, can then be found from a criterion for energy conservation. Assuming that the density is given by this same relationship in a traveling wave of any form, it is found that both pressure and velocity are propagated at a speed in which A = 13. The difficulties in justifying this assumption on theoretical grounds have not yet been overcome.
Radiation Force Acting on a Sphere in a Cylindrical Sound Field
Authors: Embleton T. F. W.
Published: September 2005

Corresponding problems of the radiation forces acting on a rigid spherical obstacle in a progressive plane or spherical sound field have been examined previously [L. V. King, Proc. Roy. Soc. (London) A147, 212–240 (1934); T. F. W. Embleton, J. Acoust. Soc. Am. 26, 40–46 (1954)]. In these cases the sound field and scattering obstacle both have symmetry about the line joining the center of the obstacle to the source of the sound field, but for a cylindrical field there exists only a lower degree of symmetry. A more general expression has now been obtained for the radiation force in terms of the complex amplitudes of spherical harmonics required to synthesize the incident sound field—for the cases of greater symmetry this reduces to the simpler expressions previously obtained. The first 20 nonzero amplitudes have been evaluated for a cylindrical sound field, and it is shown that the force is one of attraction near the source, becomes zero at a certain distance, and at a greater distance is a force of repulsion. This is qualitatively the same as for spherical waves, but for any given size of obstacle or frequency of the sound field the point of zero force is always nearer to the source in a cylindrical field. Experimental results will be reported.
A Simple Radiation Pressure Float for the Measurement of Ultrasonic Output
Authors: Henry George E.
Published: September 2005

A simple radiation pressure float can be used to measure the gross acoustic power beamed upward into a body of liquid by a transducer having lateral dimensions that are large compared to a wavelength. This float balances the upthrust of acoustic radiation force against the downward force of gravity, assuming an equilibrium position of partial immersion in the liquid. The preferred design eliminates any need for external guides or constraints: the float is self-centering. Criteria for a successful design are set forth. The interpretation of radiation pressure measurements is discussed briefly.
Transient Performance of Transducers for Ultrasonic Materials Inspection
Authors: Cook E. G.
Published: September 2005

A report of the investigation of pulsed transducers being progressed at the Sperry Products Engineering Laboratory; use of new mathematical and experimental techniques to analyze transient performance of thickness mode x-cut quartz plates; acoustic output for electrical inputs of step-function, sharp unidirectional pulse, and sine wave packet; a low-pass filter technique for short-pulse generation.
Calibration of Stiff Microphones by Means of a Grille
Authors: Gerber Henry
Published: September 2005

The grille method of microphone calibration utilizes the electrostatic force of attraction between the microphone diaphragm and another electrode. It is shown in this paper that the above method can be applied to the calibration of very stiff microphones which require a large driving force to give a measurable output. The maximum pressure which can be achieved depends on the breakdown voltage between the electrodes, the allowable distortion, and the desired accuracy of measurement. These factors are examined in detail, and it is shown that a very accurately measurable pressure greater than 50 microbars can be exerted on a microphone diaphragm. Experimental data confirming the theoretical results are given.
Description of Altec 21-BR Type Microphones and Operating Characteristics
Authors: Hilliard J. K. , Fiala W. T.
Published: September 2005

The details of construction of the 21-BR miniature condenser microphones and associated power supply are given. Factors contributing to inherent electrical noise, acceleration, and microphonic outputs are analyzed. Microphone sensitivities, frequency response, polar patterns, and operating temperatures are given. Accessory equipment for field calibration, probe tube use, and linearity tests will be described.
On Thermo-Acoustic Transduction in a Potential Flow
Authors: Mawardi Osman K.
Published: September 2005

The interaction between an acoustic field and a thermal field is worked out for the case of a sound wave propagating down a channel in which the convection of heat occurs in a potential flow. The analysis restricted to inviscid fluids shows that the magnitude of the sound wave is reinforced as it propagates through the thermal field. The extent of this reinforcement is given in the form of an amplification factor which depends on the parameter of the flow and on the frequency of the sound wave. [This work was supported in part by the U. S. Air Force under Contract No. AF 33(616)-149.]
Experimental Study of the Scattering of Sound by Flowing Turbulence
Authors: Lamb George , Lyon Richard H. , Pridmore-Brown David C. , Ingard Uno
Published: September 2005

The method used in experimental study of the scattering of sound by sound reported earlier [J. Acoust. Soc. Am. 27, 1002(F3) (1955) and National Advisory Committee for Aeronautics Contract NAw-6405 report, March 23, 1955] is applied in a corresponding investigation of scattering of sound by a turbulent flow. The turbulent region is a “sheet” jet emanating from a diffuser. A monochromatic ultrasonic beam is passed through the sheet, and scattered energy having a continuous frequency spectrum is measured on the back side of the sheet. The angular distribution for various frequencies is measured. It is found that the angular location of the maxima of scattering can be predicted from a simple Doppler shift calculation assuming that the turbulent velocity field is not changing with time. In fact, the angle of a scattering maximum with frequency f0 (1 + Δ) is obtained from sin θ = [Δ/M (1 + Δ)], where M is the Mach number of the flow. The angle of scattering θ is positive for downstream angles, negative for upstream angles. Our work is essentially directed toward the experimental verification of these simple theoretical predictions. The relation above has been checked for various values of Δ and M with fairly good agreement between predicted values and experimental results. [Supported by Contract NAw-6405 with National Advisory Committee for Aeronautics.]
Some Laboratory Experiments with a Sing-Around Velocimeter
Authors: Greenspan Martin , Tschiegg Carroll E.
Published: September 2005

The velocimeter described in the preceding paper has been used to locate the temperature at which the velocity of sound in water has a maximum. The temperature coefficient has been measured in the neighborhood of this turning temperature (73.81°C). It turns out that the velocity-temperature curve is very flat near the maximum so that water at 73.81°C provides an excellent standard liquid for calibration and intercomparison purposes, especially in the field. The velocimeter has also been used to measure the effect of dissolved air on the sound velocity in water 0°C and at 31.8°C. Measurements were made in water about 10% saturated and 100% saturated with air. The difference was less than 1 part in 105 at either temperature.
Some Factors Determining the Response of the Skin to Ultrasound
Authors: Bell Eugene , Argyris Thomas S.
Published: September 2005

Skin of intact white mice was irradiated with focused ultrasound of one megacycle frequency. Placed at the focus of a polystyrene lens, skin was exposed for 30 seconds to 30 watts of acoustic energy delivered from the second face of the lens. Skin of half the animals was in the growing phase of the hair growth cycle, while that of the other half was in the resting phase. Forty-eight hours following irradiation, skin in the growing phase was ulcerated, whereas skin at rest showed only slight keratosis. The temperature rise in the skin during irradiation indicates that skin either at rest or in growth absorbs equal amounts of energy. It is therefore not a difference in the amount of energy absorbed, but the condition of the skin at the time of irradiation which determines the nature of the response. Others in this laboratory have shown that skin at rest is equally or more susceptible than skin in the growth phase to damage by x-rays or methylcholanthrene. Since the present study indicates that skin at rest is far less susceptible than skin in the growth phase to damage by ultrasound, it is apparent that the mechanism by which ultrasound acts on the skin is not the same as that by which x-rays and methylcholanthrene act.
Nature of the Vocal Cord Wave
Authors: Miller R. L.
Published: September 2005

The shape of the vocal cord wave or glottal puff is an important parameter in any analog representation of the vocal mechanism, since the final speech wave is a function of both the generator wave shape and the transmission characteristic of the vocal tract. The shape of this wave has been determined by two independent methods: (1) by measuring the area of the vocal cord opening as a function of time through the use of motion picture studies, and (2) by the use of a network having a characteristic which is the inverse of the first vocal resonance. Harmonic analysis of some of the typical shapes indicates that a uniform distribution of harmonic amplitudes is a rarity; instead there is a tendency for the distribution to have a cyclical variation of the form (sin kn + c)/n2. The use of the inverse network method has also served to bring out several other interesting aspects of speech production such as the relation of the onset and amplitude of excitation of the higher resonances with respect to the vocal cord wave.
On the Separation and Measurement of Formant Frequencies
Authors: Schroeder Manfred
Published: September 2005

A method of separating and measuring formant frequencies is described. The procedure is based on various weightings of the short-time power spectrum of the speech wave to be analyzed [Chang et al. Proc. Inst. Radio Engrs. 39, 147 (1951)]. The performance under a variety of disturbances such as noise, spurious pulses, and low-frequency distortions is studied and compared to the respective performance of the conventional rate-of-axis-crossings method of frequency measurement. Another comparison is concerned with the influence of the fundamental frequency. In all cases the method proposed here seems to be remarkably superior. First experimental results on the measurement of the first, second, and third formants are given for a variety of vowel and semivowel sounds.
Articulation Reduction by Combined Distortions of Speech Waves
Authors: Martin D. W. , Murphy R. L. , Meyer Albert
Published: September 2005

Previous investigators have shown that speech waves can undergo any one of a number of severe forms of distortion in low ambient noise levels without serious reduction of word articulation. There are well-known notable exceptions (e.g., center clipping). However, it is not enough to avoid these exceptional forms of distortion. In the study reported here it has been demonstrated that combinations of speech wave distortions, which individually are quite innocuous with regard to word articulation, can be devastating in their combined effect, even in the absence of serious noise. Four types of speech-wave distortion were tried, individually and in combination, as follows: gross attenuation of high-frequency components, multiple echo, random amplitude modulation, and gross irregularity of response-frequency characteristic. Ambient noise was also a controlled environmental condition in some phases of the investigation. [This work was sponsored by the U. S. Air Force under Contract AF33 (616)-2320.]
On Acoustical Cues for Stop Consonants
Authors: Halle Morris , Hughes George W. , Radley Jean-Pierre A.
Published: September 2005

A study has been conducted of the two major cues for stop consonants: the burst of the stop release and the transition of the formants in the adjacent vowels. Detailed frequency vs intensity spectra of the bursts were prepared, while the transitions were studied by means of Sonagraph records. Possible criteria for identification were developed and tested. In order to assess the efficacy of the two major types of cue, perceptual tests were conducted with isolated segments containing either stop bursts or vowel transitions alone. [This work was supported in part by the Signal Corps, the Office of Scientific Research (Air Research and Development Command), and the Office of Naval Research.]
A Formant Tracker for Speech Sounds
Authors: Chang S. H. , Dolansky L. O. , Howard C. R.
Published: September 2005

The central frequencies of the principal resonance regions, or formants, have been found to contain sufficient information to resynthesize intelligible speech, as far as vowels and other nonturbulent sounds are concerned. When a single formant is isolated by filtering, one-half the average zero-crossing density, ρ0, is shown to be a convenient approximation to the formant's central frequency. Filters which are controlled electronically by a preliminary approximation to the first-formant frequency, in such a way as to isolate the first two formant regions, have been built and tested. LP and HP filters for the first and second formants, respectively, are based on a circuit by Linvill which uses a transistor negative-impedance converter. An alternate filter of the tuned-circuit type has proved more satisfactory for the first formant. The variable elements in the HP and tuned-circuit filters are Increductors, while the LP filter uses a circuit based on the Miller effect to represent an electronically controllable capacitor. [The research in this paper has been made possible through support and sponsorship extended by the Electronics Research Directorate of the Air Force Cambridge Research Center, under Contract No. AF19(604)-1039, Item I.]
Underwater Sound Reflection from a Surface with Corrugations of Sawtooth Form
Authors: Proud J. M. , Tamarkin P.
Published: September 2005

The distribution in angle, frequency dependence, and dependence on incident angle of the amplitude of radiation reflected from a pressure-release surface with corrugations of sawtooth form will be described. If circumstances permit, these experimental results will be compared with the predictions of a theory of rough surface reflection developed by Meecham. The experiment is carried out in a tank of water on which is floated the corrugated surface. Acoustic radiation is beamed at the surface from below and the reflected field is scanned with a microphone. The acoustic wavelength range lies between 0.5 and 1.5 cm. The pressure-release corrugated surface has a spatial period of 1.96 cm, a projecting vertex angle of 90°, and a steep leading edge with a length of 0.32 cm. [Work supported by the Office of Naval Research.]
A Survey of the Noise Attenuation Characteristics of Navy Air Traffic Control Towers
Authors: Beitscher H. R. , Webster J. C.
Published: September 2005

The sound-pressure levels of a standardized noise source were measured in octave bands both inside and on the catwalk just outside the cab of fifteen control towers. A twin-engine Beechcraft, positioned 100 feet from the base of the tower was used as a standardized source. The attenuation for the towers averaged 20–27 db in the octave bands between 75–9600 cps. The attenuation for four modern navy towers, currently the standard navy structure, was about 5 db better in the octave bands primarily affecting speech 600–1200, 1200–2400, 2400–4800 cps. These values of attenuation were then used to rate these towers with regard to Speech Communication Criteria. The results indicate that the current navy structures are adequate for communication in the towers for airfields with piston-driven planes, but communication difficulties should be expected in the presence of jet planes. Tapes recorded in the control towers will be used to demonstrate the accuracy of these predictions.
Motorcycle Noise Testing in Bermuda
Authors: Hadley Walter C.
Published: September 2005

In Bermuda, experience is showing that intelligent use of a noise meter, coupled with vigorous legislation, can reduce motorcycle noises to a very noticeable extent. The machines are run on rollers in a small reverberant test shed, sound level being measured by a General Radio 1551 A meter operated in the “flat” position, as preliminary tests showed that this procedure would rate the machines in close accordance to the ear and with the desired accuracy. After preliminary testing, a limit of 93 db as measured by this procedure was imposed on all new auxiliary cycles (small motorcycles) being sold, which resulted in the development of quieter models by several makers. Recently, the same limit has been extended to all the auxiliary cycles on the island, which must be tested and licensed by October 1. To date, more than 4000 noise tests have been run in connection with this program, and these are summarized in the paper. Experience has shown that testing is quick and convenient, with a high order of reproducibility and accuracy. Dealers and owners appear convinced that the tests are fair and accurate, and very noticeable progress is being made in noise abatement.
A Study of the Jet Noise Problem Aboard Aircraft Carriers
Authors: Pietrasanta A. C.
Published: September 2005

Noise from jet aircraft interferes with communications in important spaces aboard aircraft carriers. Measurements of sound pressure levels made in these spaces during normal jet operations at sea are presented. It was found that these levels could be estimated from a knowledge of the jet engine operating conditions and the physical properties of the structures involved. For a suggested speech communication criterion noise reduction requirements for shipboard spaces based on estimated noise levels of present and future jet aircraft are discussed. [This work was supported by U. S. Navy Bureau of Ships.]
Noise Produced by Jet Aircraft during Ground Runups
Authors: Pietrasanta A. C. , Galloway W. J.
Published: September 2005

Data on the characteristics of the noise fields around several jet aircraft during ground runups, and the method of measurement, were reported previously [Adone C. Pietrasanta, J. Acoust. Soc. Am. 25, 140(A) (1954)]. Using the same technique, similar measurements have been made on a number of additional single and twin-engine jet aircraft. These data have been used to develop a design procedure for estimating both the directivity pattern as a function of frequency and the over-all acoustic power level from a knowledge of the jet engine operating conditions. An empirical design curve for estimating the increase in power level for after-burner operation is presented. [This work was supported in part by the U. S. Air Force.]
Acoustical Evaluation of Jet Engine Test Facilities
Authors: Doelling N. , Galloway W. J. , Pietrasanta A. C.
Published: September 2005

Procedures are described for determining the over-all acoustical effectiveness of an engine test cell as well as the noise reduction characteristics of individual cell components, including intake and exhaust acoustical treatments, doors, walls, etc. These procedures were utilized in performing acoustical measurements on a series of engine test facilities. Results of this program are discussed, including a specification of the total acoustical effectiveness of three of these test facilities. [This work was supported by the U. S. Air Force.]
Radiation Efficiency of a Linear Array of Point Sources Applied to Suction Roll Silencing in Paper Mills
Authors: Thiessen G. J. , Embleton T. F. W.
Published: September 2005

Small linear phase changes introduced in a uniform linear array of point sources do not cause any appreciable change in the energy radiated until the phase variation along the line becomes equal to that which occurs in the wave in space. Then the efficiency begins to drop rapidly. The efficiency will, of course, be a periodic function of the phase shift. If the excitation of the point sources is due to regularly recurring pulses whose timing varies linearly along the array then the phase variation will be directly proportional to the frequency of the different components. This sort of excitation may be made to occur in paper mill suction rolls. (These are hollow cylindrical shells which are perforated with a pattern of holes through which water is drawn from the paper by means of stationary suction boxes.) Models in which the phase between adjacent holes is varied by the use of different drill patterns have been studied for arrays of sources one foot and 20 feet long. The experiments agree qualitatively with theory on all points and indicate that a noise reduction of at least 15 db can be obtained by choice of a suitable drill pattern.
Auditory Fatigue from Audio Analgesia
Authors: Kryter K. D. , Weisz A. Z. , Wiener F. M.
Published: September 2005

Intense auditory stimuli (combinations of “noise and music”) are being used to some extent in dentistry and medicine for their analgesic effects. Maximum-exposure durations and intensities of noise and music are specified to avoid any undue amount of auditory fatigue. These specifications are based upon previous damage-risk criteria and research data appearing in the literature on this subject and upon the findings of a series of experiments in which the hearing of subjects was tested before and after exposure to noise and music. The results of these new experiments are compared with the calculations made with formulas developed by Ward, Glorig, and Sklar for predicting the auditory fatigue from exposure to noise. The predicted and obtained results are in very close agreement.
Phoneme Selection for Studies in Automatic Speech Recognition
Authors: Shoup J. E.
Published: September 2005

Two alternate methods for the selection of speech material to be used in studies in automatic speech recognition are suggested. Preference is given to the selection of a restricted set of phonemes from which words and sentences may be constructed for analysis. The selection can be based on the high frequency of occurrence of the individual phonemes, on the high yield of words by the phonemes, or on some combination of these two criteria. A combination of the two criteria appears to be most satisfactory. The phoneme selection was derived from the 500 most frequently occurring words, as given by Thorndike and Lorge. Some consideration was also given to the frequencies of occurrence of the phonemes. The phonemes are presented in cumulative order according to the number of words by which the list is increased as each successive phoneme is added.
Measurement of Ultrasonic Wave Velocities for Solids in the Frequency Range 100 to 500 Mc
Authors: McSkimin H. J.
Published: September 2005

Apparatus for measuring ultrasonic wave velocities and hence elastic moduli by means of phase-comparison methods at frequencies as high as 500 Mc is described. Gated harmonic generators for providing pulse-modulated rf of accurately known carrier frequency and circuits for electrical coupling to resonant quartz-crystal transducers are discussed. Application to measurements on small specimens, with illustrative data for cadmium telluride, is made.
Determination of the Nonlinearity Parameter B/A for Water and m-Xylene
Authors: Adler Laszlo , Hiedemann E. A.
Published: September 2005

The rate at which harmonics are developed during the propagation of an initially sinusoidal ultrasonic wave of finite amplitude depends on the nonlinearity of the compressibility of the medium. Thus, determinations of the harmonics as a function of propagation distance may be used to determine the parameter B/A (describing nonlinearity). A method which circumvents the effects of absorption in the medium is developed and used to determine the parameter B/A for water and m-xylene. This method utilizes optical determinations of the second harmonic component of a distorted 3.0 Mc ultrasonic wave at various distances and initial pressure amplitudes. The second harmonic was isolated by use of a calibrated acoustic filter plate. The values obtained for the nonlinearity parameter are B/A = 6.2±0.6 for water and B/A = 9.6±1 for m-xylene.
Irradiation of Plastics with Focused Ultrasound: A Simple Method for Evaluation of Dosage Factors for Neurological Applications
Authors: Lele P. P.
Published: September 2005

Irradiation of strain-free methacrylate with a single beam of focused ultrasound in adequate dosages results in the development of trackless focal alterations within the plastic. These alterations, easily visualized with polarized light, are egg-shaped regions of stress and are probably thermal in origin. There is a consistent and reproducible relationship between ultrasonic dosage and the size of these “lesions,” comparable to that obtained when the brain of the cat is similarly irradiated. The use of methacrylate as a preliminary test medium permits rapid evaluation of the probable effects of varying dosage parameters as well as of the repetitive (and long term) stability of the ultrasonic output.
Sound-Insulation Ratings and the New ASTM Sound-Transmission Class
Authors: Northwood T. D.
Published: September 2005

A survey is made of past and present systems for rating the sound-insulation value of building walls and floors. It is observed that in most countries ratings based on “average” transmission losses have been replaced by systems that compare transmission-loss characteristics with a standard contour. An example of this approach is the new sound-transmission class contained in ASTM E90-61T. This is discussed from various theoretical and practical viewpoints, and it is concluded that the sound-transmission class is a useful rating system for common architectural problems.
Influence of Surface Coatings on Impedance and Absorption of Urethane Foams
Authors: Schwartz Manuel , Gohmann Edmund J.
Published: September 2005

The acoustic impedance and absorption characteristics were investigated for open-celled urethane foams with and without surface coatings. The variables considered were the foam thickness, cell size and density, and the coating material mass and thickness. The application of thin films of area density in the order of 0.005 g/cm2 to the foams resulted in an increase in the absorption for the foams of 12 and 1 in. thickness with variable results for foams of 2 in. thickness. The addition of coatings of density in the order of 0.05 to 0.45 g/cm2 increased the absorption at a frequency of 240 cps but otherwise decreased the absorption. The results were essentially independent of the nature of the surface coating and, within limits, depended largely on the surface mass per unit area. Also noted was an absorption increase which was attributed to the vibrating of the surface material in one of its natural modes.
Electronic Acoustic Image Converter
Authors: Goldman Richard G.
Published: September 2005

The history of the electronic acoustic image converter is briefly recapitulated and some experimental work being carried out in this laboratory is described.
Hydrophone Design for a Receiving System in which Amplifier Noise is Dominant
Authors: Woollett Ralph S.
Published: September 2005

The transducer parameters which are of most importance in determining the merit of a hydrophone for a receiving system in which amplifier noise is dominant are described. Disagreement is expressed with a recent statement by P. M. Kendig that transducer efficiency ultimately determines the signal-to-noise ratio for this type of receiving system.
Measurement of the Thermal-Noise Spectrum of Water
Authors: Ezrow D. H.
Published: September 2005

Experimental values have been obtained for the thermal noise spectrum of water in the 1.0–2.5 Mc frequency range. The procedure was based on measurement of the radiation resistance of thin-disk transducers loaded by water. A comparison is made with the theoretical thermal-noise spectrum of an ideal medium calculated by assigning equipartition energy to the acoustic modes. Agreement to better than 3.6% was found between the experimental values and the theoretical spectrum.