bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise Control of a Flare Stack
Authors: Hersh A. S. , Seebold J. G.
Published: October 2005

As part of its noise abatement program, the Standard Oil Company of California has undertaken to reduce the noise radiated from the flare stacks serving the new process plants at the El Segundo Refinery. These flares, used to burn excess refinery hydrocarbon gases, have to operate smokelessly. To accomplish this, high-pressure steam jets are used to discharge a turbulent steam-air mixture into the combustion zone. This system, although muffled, proved to be an intolerable source of noise in the adjacent community. An examination of the noise spectrum indicated that the mixing between the steam ejected from the 34-in.-diam primary nozzle and the ambient air was a major source of noise. A series of exploratory model scale tests were conducted in an effort to reduce the noise. By replacing a single 34-in.-diam nozzle with a multiple nozzle, the radiated noise was reduced by 16 dB. The multiple nozzle configuration and the experimental program leading to its design are described.
Three Component Silencing System for Plastic Granulators
Authors: Arrington J. R. , Winnerling H. A. , Pizzirusso J. F.
Published: October 2005

High-speed granulators and cutters used in the processing of plastic materials are known for their high noise level, characterized by a peaked sound spectrum that is a function of operating speed. This paper describes a three-component silencing system with almost universal application in this type of machinery. Studies revealed that most of the cutting noise was airborne, with only a small fraction radiating from the panels and frame of the machine. The silencing system consisted of three absorption type mufflers, one each for the material feed slot, rotor housing, and the discharge chute. Absorption was provided by various thicknesses of Scott Acoustical foam and Scottfelt. A 10-dB reduction in Lw was obtained. Three types of foam absorption material were tested in this prototype design.
Undergraduate Engineering Research in Acoustics
Authors: Hemond C. J.
Published: October 2005

Senior theses in acoustics by undergraduate mechanical engineering students have been successfully undertaken at the University of Hartford for many years. Prerequisites are required courses in Vibrations and Applied Acoustics. Source material is available from extensive library facilities in this field maintained at the University. The purpose of this paper is to report for the first time results of selected student projects. Topics of student activity include: development and enactment of a model zoning code and noise ordinance for the student's home town; a series of related projects for the development of acoustic transducers and systems to measure fluid noise within piping systems; ongoing projects for the development of instrument techniques to determine the interrelation of self-generated aerodynamic noise and sound attenuation in corregated ducts; an investigation of the noise level of variety of power mowers and the effect of their random operation in a suburban development on the background levels of that development; and the use of lead sheeting to improve the transmission loss of walls within and between apartments in existing multifamily dwellings.
Effect of Trapping on the Ultrasonic Velocity in a CdS Acoustic Amplifier
Authors: Krischer Charles , Ingard Uno
Published: October 2005

Measurements of the ultrasonic velocity for piezoelectrically stiffened transverse waves in CdS were made as a function of applied electric drift field, electrical conductivity, and acoustic-wave frequency. By modifying White's theory [J. Appl. Phys. 33, 2457 (1962)] to include the effects of electron trapping with nonnegligible relaxation time [I. Uchida et al., J. Phys. Soc. Japan 19, 674 (1964)], we obtain a theoretical expression that gives good agreement with the experimental results, covering a frequency range of 30–350 MHz, and a range of electrical conductivities from 10−5 to 10−2 (ohm-cm)−1 Additionally, when strong electron-trapping relaxation phenomena occur, the theory predicts, for the case of an applied electric field with electron drift opposite to the acoustic-wave propagation direction, an enhancement of the ultrasonic velocity in semiconducting CdS, above the piezoelectrically stiffened value for the insulating material. Experimental data verifying this effect are given. [This research was supported by the U. S. Navy (ONR) under contract.]
Water Immersion Technique for Measuring Attenuation and Phase Velocity of Longitudinal Ultrasonic Waves in Plastics
Authors: McSkimin H. J. , Andreatch P.
Published: October 2005

The complex transmission coefficient for a plastic specimen immersed in water (or other suitable liquid) is determined through use of a phase meter and a calibrated attenuator. Heterodyning the received rf pulses directly to viedo signals with a 10-Hz beat frequency makes possible (1) the use of a commercial low-frequency phase meter and (2) an increase in S/N ratio of approximately 20 dB [H. J. McSkimin and T. B. Bateman, J. Acoust. Soc. Amer. 45, 852–858 (1969)]. By way of illustration, measurements for loss tangent and phase velocity of polyethylene are listed for frequencies of 0.4–2.0 MHz and temperatures of 20°–60°C.
Sound Absorption in Pure D2S and CO2/D2S Mixtures
Authors: Shields F. Douglas , Carney George P.
Published: October 2005

Sound absorption measurements in pure D2S at 300° and 400° K indicate a vibrational relaxation with a relaxation time of 4.8 × 10−8 sec atm, which is independent of temperature. The mixture measurements, when compared with theoretical curves calculated for a series relaxation process, indicate that energy is exchanged between the exicted vibrational levels of the two molecules. The results confirm the theory that the bending vibration in CO2 exchanges energy primarily with the rotational motion of the D2O molecule in a collision. [This work was supported by the U. S. Office of Naval Research.]
On the Propagation of Sound Waves in Two-Phase Fluids
Authors: Rentzepis G. M.
Published: October 2005

The governing equations for the propagation of sound waves through a dispersed two-phase fluid are derived. The fluid considered is composed of two phases of a fluid in a state of thermodynamic nonequilibrium such as evaporating or condensing droplets entrained in the vapor phase, which is slightly superheated or at the saturation state. The field equations show that the propagation of the waves can depend on a change-of-phase function, which when put equal to zero reduces the equations to the standard ones. It is shown that the change-of-phase function depends on the pressure, and it becomes oscillatory with respect to time with the passage of sound waves. The influence of the change-of-phase function on sound propagation, attenuation, and intensity are found to be significant when the function's value is not small.
Measurement of Absorption and Velocity of Ultrasound in Liquid Alkali Metal Alloys
Authors: Kim M. G. , Letcher S. V.
Published: October 2005

Ultrasonic absorption and velocity measurements have been made in potassium-rubidium and sodium-cesium alloys at temperatures from their melting points to 250°C. Sound velocities decrease linearly with increasing temperature. Rao's constant and Wada's constant computed from the sound velocity data vary almost linearly with concentration. Absorption measurements in sodium-cesium alloys suggest a substantial molecular association, but potassium-rubidium alloys do not exhibit any detectable molecular association. The distilled liquid metals were transferred to the measurement apparatus and were studied under a high-purity argon cover gas. The transducer was in direct contact with the sample without the aid of adhesives or bonding agents. [This work was supported, in part, by the Office of Naval Research.]
Relaxation in Liquid Mixtures
Authors: Davenport J. M. , Hunter J. L.
Published: October 2005

The absorption of sound has been measured in binary mixtures of several Kneser liquids whose relaxation spectra are well known (e.g., CS2 and CH2Cl2). The measurements were made as a function of concentration at frequencies both below and above the relaxation frequencies of the component liquids. In addition, for certain critical concentrations the absorption was measured as a function of frequency over a range from 10 to 810 MHz. Because the relaxation curves of Kneser liquids cross at many points, it is possible to choose measurement frequencies at which the two component liquids have equal absorption. The absroption at such frequencies may show either maxima or minima as a function of concentration and the extremal absorption may differ considerably from that in the pure liquids. The measurements are interpreted in terms of relaxation of the vibrational specific heat with four relaxation times involved. [Sponsored by the Office of Naval Research.]
Experimental Sound Scattering from Inhomogeneous Media
Authors: Mole L. A. , Hunter J. L. , Davenport J. M.
Published: October 2005

These measurements had their origin in an attempt to detect scattering of sound from binary mixtures of critical liquids near the critical temperature. Our method of measuring the scattered signal indicates almost negligible scattering in contrast to the measurements of Brown and Richardson, which show considerable scattering. For this reason we have also conducted measurements with suspensions and bubbles, for comparison. The measurements are presented, and the method and apparatus are described and contrasted with those of Brown and Richardson. [Sponsored by the Office of Naval Research.]
Scattering of Longitudinal Waves From Cavities in a Solid
Authors: Franzblau Michael C. , Kraft David W.
Published: October 2005

The ultrasonic pulse-echo technique has been used to study the absorbtion due to scattering of longitudinal waves from cavities in a solid, in the range of ka from 0.03 to 4.5 (k is the longitudinal wave vector, a the cavity radius). Experimental results obtained from specimens of sintered tungsten bars and pore-bearing tungsten filaments are consistent with the theory of Ying and Truell [J. Appl. Phys. 27, 1086 (1956)] for the scattering of a longitudinal wave from a single spherical cavity embedded in an elastic medium. Metallographic analysis revealed that both types of specimens contain narrow distributions of scatterer radii, centered at 20 μ in the filaments and 2 μ in the sintered bars. These results, along with the frequency dependence of the attenuation measured from 5 to 350 MHz, were used in conjunction with the theory to obtain estimates of the number density of scattering centers. Analytical techniques for extracting the scattering contribution from the total attenuation are discussed.
Development and Application of the Nearfield Measuring Array Technique in the Field of Underwater Sound
Authors: Trott W. James
Published: October 2005

In underwater sound, the trend to increased directivity and longer wavelengths for improved detection capabilities has caused problems in transducer calibration by conventional farfield test procedures. Within the past 10 years, calibration in the nearfield of a source has been developed and proven by several measurements. The theory of the plane-array technique is described. Examples of the application of plane arrays and line arrays to measurement problems are discussed. The array shading function developed for nearfield measuring arrays is shown to have other applications.
Determination of Radiated Power from Array Velocity Data
Authors: Tseo Gudin , Gruber George
Published: October 2005

To determine the effects of acoustical interactions on the performance of low-frequency bare sonar arrays, the parameters affecting the power levels and directivity patterns of hexagonal and linear scale model arrays of acoustically small (ka∼1) sound projectors were studied. In this paper, we consider the effects of interelement coupling on the radiated power. Power calculations are based on surface- (head-) velocity measurements of the interacting transducers. Using equivalent-mechanical-network representation for the piston-type radiators, the radiation resistances are computed from Q-data and/or from head-velocity data. Elements with various self-radiation resistance to mechanical resistance ratios (0.45<r<6) were constructed to test the applicability of the maximum-power-transfer theorem to arrays. In the case of seven-element hexagonal arrays, the linear superposition of the interaction effects of the six outer neighbors on the center element was tested. The effects of phasing the center elements in hexagonal and linear arrays on the radiated power were determined. [Work supported by NSF, Engineering Division, and ONR, Acoustics Programs.]
Prediction of Directivity Patterns from Array Velocity Data and Comparison with Measured Patterns
Authors: Gruber George , Tseo Gudin
Published: October 2005

In this paper, we examine the effects of interelement coupling on the steered directivity patterns of the hexagonal and linear bare scale model arrays discussed in the previous paper. Farfield pattern, axial pressure, and directivity factor computations are based on measured surface velocity distributions. Farfield pressure measurements verified the predictions drawn from (nearfield) velocity data. Experiments confirmed that interelement coupling has a much greater effect on the power radiated by a close-packed low-frequency array than on its radiation pattern. The results of phasing the center element in seven-element hexagonal arrays and those of steering the elements in a five-element linear array are presented together with computed values.
Nearfield Measurements of a 7.7-kHz Free Flooded Cylindrical Ring
Authors: Sinsky J. A.
Published: October 2005

Precision acoustic nearfield pressure and phase measurements have been made of a radially oscillating free flooded cylindrical ring. The measurements were made in the NRL Acoustic Research Tank Facility using a pulsed signal technique and an automatic scanning system. Pressure profiles are shown and discussed including: (1) a profile taken directly in front of and parallel to the face of the ring and (2) a profile containing the axis and a diameter of the ring and perpendicular to its face. Intrinsic nonuniformities or asymmetries in the construction of the ring, which went undetected in the conventional farfield radiation patterns, are seen clearly in the nearfield scans. Plots are made of pressure and phase versus distance from the plane of the ring.
Effect of Temporal Auditory Summation on the Human Stapedius Reflex
Authors: Djupesland G. , Zwislocki J. J.
Published: October 2005

The effects of temporal auditory summation on the threshold of audibility and on loudness are well known. We have investigated whether similar effects can be found in the contractions of the stapedius muscle. The contractions were elicited by means of 2000-Hz tone bursts and were monitored by means of acoustic impedance changes at three criterion levels: a visual threshold level, 20% and 50% of maximum response. Our results indicate an unexpectedly prounounced duration effect. The sound intensity required for a criterion response had to be lowered by about 25 dB when the signal duration was increased from 10 to 100 msec. The same was approximately true for all criterion levels. The time constant of integration appears to be about the same as in auditory threshold measurements.
Electrical Traveling Waves in the Chinchilla Cochlea
Authors: Benitez L. D. , Templer J. W. , Eldredge D. H.
Published: October 2005

Appreciation of the spatial as well as temporal gradients for cochlear microphonic voltages (CM) is difficult when these voltages are presented as functions of time at each of only three places. To assist visualization of these relations, spatial displays of voltages along the basilar membrane at successive intervals were inferred from the measured CM traces. The only necessary assumptions were no sharp discontinuities in the spatial gradients and uniformity in the changes of velocity and magnitude of each CM peak as it travels apically from the base. From the spatial displays, we have made animations of the electrical traveling waves in response to low-frequency and high-frequency acoustic clicks and to tone pips at 150, 500, and 2000 Hz. The broad spatial patterns of CM stand in sharp contrast to reported tuning curves for single auditory neurons. Also we derived new spatial patterns for rates of change of CM voltage in time from the spatial patterns of instantaneous CM. A motion picture of these traveling waves and of the derivatives with respect to time will be shown.
Cochlear Microphonic and Action Potential Thresholds during Acute Salicylism
Authors: Wilpizeski C. , Tanaka Y.
Published: October 2005

Guinea pigs were prepared with indwelling rigid depth electrodes located in the auditory nerve or flexible electrodes placed on the round window membrane. Absolute thresholds (VDL) were traced by the experimenter over 3-min periods by controlling stimulus intensity with a motor driven recording attenuator so that electrophysiological responses displayed on an oscilloscope were kept just detectable from the baseline. Threshold traces were obtained from restrained, waking animals under control conditions and at 2, 4, and 24 h following single injections of 300 mg/kg of sodium salicylate solution. Stimuli were continuous or pulsed trains of 1, 100, 250, or 1000 clicks/sec. Cochlear microphonic threshold traces showed little or no shift, while action potential thresholds were elevated 5–9 dB 2–4 h after injection. No differences between pulsed- and steady-stimulus conditions were demonstrable during salicylism for either CM or AP responses. Envelopes of traces (width in decibels showed no systematic differences between types of response or experimental conditions.
Combination Tones on a Nonlinear Cochlear Model
Authors: Stewart J. L.
Published: October 2005

A linear electric circuit model for motions of the basilar membrane was modified by introducing nonlinear diode elements so as to represent mechanical displacements that occur more readily in one direction than in the other. The specific nonlinear site or structure in the cochlea is not necessarily represented by the model; it may be some part of the organ of Corti, it may result from rigidity of scalae walls, and/or it may arise from fluid streaming near the oval window. Patterns on linear and nonlinear ears are compared for two specific tone combinations, the simple difference tone f1 − f2, and the more complex 2f1 − f2 case. At least three explanations for perception of these difference tones, with and without presence of a third exploring tone, can be offered. Waveforms for clicks and voiced and unvoiced speech sounds are also presented, and similar phenomena are observed. In general, strongly augmented activity occurs in the apical part of the cochlea when nonlinearities exist, and for the 2f1 − f2 component, an unusual pattern also occurs in the region most responsive to f2.
Tensile Strength of Superheated Liquids
Authors: Apfel Robert E.
Published: October 2005

A novel technique has been developed for studying the properties of liquids under conditions that are not ordinarily accessible. This technique involves the use of an acoustic standing wave field established in a column of one liquid in order to trap an immiscible droplet of another liquid. In this experiment, an ether droplet suspended in glycerine was superheated and acoustically stressed until the combination produced an explosive liquid-to-vapor phase transition. The measured trade off between tensile stress and superheat, as causes of this vapor cavity formation are in gratifying agreement with the theory of nucleation in pure liquids. [This work supported by the Office of Naval Research.]
Dynamics of Vapor-Filled Cavities
Authors: Neppiras E. A. , Finch R. D.
Published: October 2005

A theoretical study has been made of the dynamics of vapor-filled cavities using linear approximations and taking into account evaporation and condensation and the thermal transport properties of the liquid. Results for stiffness, damping, and resonance frequency have been obtained for the liquids helium, nitrogen, and water. Results of experiments carried out at frequencies around 10 kHz are discussed in the light of the theory. [This work was supported by NSF grant.]
Single Guided Mode Theory of Long Range Infrasonic Propagation from Nuclear Explosions
Authors: Pierce Allan D.
Published: October 2005

The trend of research on the problem of giving an adequate theoretical interpretation to the pressure waveforms recorded following nuclear explosions has been towards progressively more realistic models of the atmosphere, resulting in lengthy numerical computations to determine and superimpose the atmosphere's natural modes of guided propagation. Such computations and existing data indicate that the earliest portion of such waveforms may be attributed to a pseudomode analogous to that predicted by Lamb for the isothermal atmosphere. Recently, Bretherton and Garrett have succeeded in isolating and deriving the dispersion relation for this mode using perturbation techniques. In the present paper, this analysis is extended with the derivation of an approximate set of partial differential equations not involving height, which include the effects of winds, horizontal gradients, and nonlinearities, and which may be considered as governing the two-dimensional propagation over the earth's surface of the Lamb mode. The solution for nuclear explosion excitation is given for the case of a stratified atmosphere with farfield nonlinear effects neglected and is compared with numerical computations based on the multimode theory.
Calculations of the Properties of Finite-Amplitude Waves Propagating from High-Altitude Grenade Explosions
Authors: Ramsdale Dan J.
Published: October 2005

Meteorological sounding of the upper atmosphere using the Acoustic Grenade Technique is accomplished by exploding rocket-borne grenades in the altitude region 30–90 km and recording the acoustic pulses from these explosions on a ground-based microphone array. The recorded acoustic pulses from the grenades exploded below 60 km are quite distinct, facilitating the measurement of the amplitude and length of the positive phase of the wave. Otterman [J. Acoust. Soc. Amer. 31, 470–474 (1959)] Reed [J. Acoust. Soc. Amer. 31, 1265 (1959)], and more recently Groves [Project Firefly 1962-1963 (Ed. N. W. Rosenberg), AFCRL-64-364, p. 351] have published theoretical methods for calculating the amplitude and length of the positive phase of the wave. The relevant analytical expressions for all three methods are identical in form. Numerical results show that although the three methods yield different absolute amplitudes and lengths, their relative amplitudes and lengths are nearly the same. The lengths predicted by Reed and Otterman agree reasonably well with the measured values, while those predicted by Groves are approximately one-half the measured values. Measured absolute amplitudes are not yet available for comparison with the theoretical values. [This research was supported by the National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland.]
Comparison of Spectral Analyses by Two Different Forms of the Complex Exponential Technique
Authors: Carvell Robert
Published: October 2005

Two forms of the complex exponential algorithm, one having an exponential amplitude damping factor, the other exclusive of such a factor, are considered. Analyses of simulated time series, consisting of several discrete undamped sinusoidal functions combined with pseudorandom numbers representing noise, are utilized as a basis for comparing the representation effectiveness of the two forms of the algorithm. The study is limited to simulated time series having positive S/N ratios. The accuracies of the frequency and amplitude representations, as well as the processing gain of the two algorithmic forms, are compared. The differences between representations by the complex exponential algorithms and Fourier techniques are denoted. [Research supported by the Naval Ship Systems Command under Office of Naval Research Contract.]
Computer Synthesis of Acoustic Processor Performance
Authors: Rodgers G. F.
Published: October 2005

The technique of acoustic spectral analysis by use of a recirculating delay line has been reported in the literature by J. Capon and others. This technique involves summation of M samples in a delay-line loop, in which successive samples are frequency shifted by an amount equal to the reciprocal of the delay time. Performance degradation occurs when there is a mismatch between the incremental frequency shift and the loop delay. This paper examines the quantitative effect of this mismatch upon processor performance. A computer model is developed and its performance perturbed by introducing a parametric series of design tolerances. The computer model is analyzed from two separate approaches, a deterministic and a probabilistic method. Effects on system Q and the number of recirculated samples M are presented.
Response of an Acoustic Homing System to Multiple Signals
Authors: Horwath T. G. , Noiseux D. U.
Published: October 2005

The response of an acoustic homing system, which receives simultaneously acoustic signals of various frequency spectra emanating from a set of sources spatially distributed, is investigated. The analysis is conducted in spectral (wave-vector and frequency) space. The spectrum of the multiple signals is applied to the filtering function of the sensor array and the frequency filtering of the signal processor. The signal processor includes a frequency tracking loop. The guidance of the homing system and the sensor array represent a spatial tracking loop. The decision criteria of the homing system of selecting one signal in preference to others and of tracking the selected signal source are emphasized. The results, which are presented in form of rejection coefficients of interfering signals as a function of their spectral distribution, are in good agreement with experimental data obtained under typical conditions. Design criteria essential for improving the performance of the homing system in the presence of multiple signals are derived and discussed. [This work was initiated and conducted at the Systems Application Division of U. S. Army MERDC, Fort Belvoir, Virginia 22060.]
Simultaneous Measurement of Subglottal and Supraglottal Pressure Variations
Authors: Hiki S. , Koike Y. , Takahashi H.
Published: October 2005

The short-term variations of the subglottal and supraglottal pressures during phonation were measured simultaneously, utilizing two identical miniaturized solid-state pressure transducers [Y. Koike, J. Acoust. Soc. Amer. 46, 96–97 (1969)] inserted into the trachea and the pharynx through the nostrils, to obtain a direct estimation of the waveform of the pressure difference across the glottis at a close distance. The magnitudes of these short-term variations and the phase relations between them were analyzed, and their effect on the vibration of the vocal folds is investigated on the basis of a mechanical model of the laryn. Simultaneously with the above measurements, the vibration of the outer skin surface of the trachea was picked up with a 14-in.-diam condenser microphone coupled with a rubber pipe. The resulting waveform displays considerable agreement with that of the subglottal pressure, and it is shown that the contact microphone output may be applicable to the study of the detailed properties of the amplitude and phase spectrum of the subglottal pressure variation or of the glottal sound by taking into account the transmission characteristic of the tracheal wall and the acoustic impedance of the trachea. These characteristics can be calculated from the results of the above measurements. [This study was partially supported by a USPHS grant and by NASA contract.]
Cinegraphic Observations of the Larynx during Voiced and Voiceless Stops
Authors: Lisker Leigh , Sawashima Masayuki , Abramson Arthur S. , Cooper Franklin S.
Published: October 2005

Observations of laryngeal operation in running speech were made with a flexible fiberoptics bundle passed through the nose and coupled to a cinecamera. A previous report based on observations of a single subject concluded that English sounds with predominant noise source, i.e., the aspirated stops and voiceless fricatives, are produced with separation of the arytenoids, and that sounds with predominant quasiperiodic source are produced without such opening. The present paper extends our study to three speakers of American English, but limits attention to sounds not always distinguishable on the basis of earlier observations: unaspirated /p,k/ and /b,g/. Our present data indicate that these two classes are almost always different in respect to positioning of the arytenoids. The few anomolous cases include both /b,g/ with slight separation of the arytenoids and pulsing interruption, and /p,k/ with neither of these phenomena. Aside from articulatory “noise,” these cases may be explained by reference to factors such as coarticulation or context effects and the relative timing of laryngeal and supraglottal activities. [This research was supported mainly by the National Institute of Dental Research.]
Effects of Auditory Masking on Intraoral Air-Pressure for Consonants
Authors: Brown W. S. , Brandt John F.
Published: October 2005

Previous research has demonstrated that a speaker has a high degree of control over his articulatory behavior when asked to repeat sentences several times in exactly the same way. The present research was designed to investigate the use of auditory cues during phonation. Normal-hearing speakers were instructed to read each of five sentences 25 times in exactly the same manner. While the speakers were talking, a masking noise was presented binaurally through earphones at several sound-pressure levels (up to 110 dB SPL), which the speakers were instructed to ignore. Measures of peak and integrated intraoral air pressure, SPL, and total phonation time were made to determine the stability of the utterances. As expected, SPL and intraoral air pressures increased with increases in the masker SPL. However, the increases were slight in comparison to published data suggesting that speakers utilize sensory-motor information other than auditory to control and maintain constant articulatory behavior.
Cricothyroid and Vocalis Muscle Function in Some Simple Sentences
Authors: Harris K. S. , Gay Thomas J. , Lieberman P. , Sawashima M.
Published: October 2005

Using needle-electrode techniques, recordings were obtained of the vocalis and cricothyroid muscles during running speech. Their role could thus be assessed in controlling the variations of fundamental frequency that occur in some simple forms of statements and questions. Results for a few speakers show that (1) the vocalis and cricothyroid tend to behave similarly; (2) the typical terminal pitch rise for questions is accompanied by activity in both muscles; (3) a heavily stressed syllable will be accompaied by laryngeal muscle activity, but this activity is conditioned by the presence or absence in the terminal question rise. [This research was supported by the National Institute of Dental Research.]
Fourier Analysis of Cochlear Nerve Fiber Responses
Authors: Molnar C. E. , Pfeiffer R. R.
Published: October 2005

Period histograms of discharges of single cochlear nerve fibers in response to continuous sinusoidal stimuli have been Fourier analyzed, and the amplitudes and phase angles of the fundamental and low-order harmonics determined as a function of stimulus level and frequency. Measurements of the phase angle of the fundamental by this technique are closely repeatable and typically vary less than 20° over a stimulus level range of 40–50 dB. Fundamental phase angles are extremely sensitive to stimulus frequency. For example, phase shifts of as much as 8π rad over a stimulus frequency range of 300 Hz–1.7 kHz have been observed. Plots of the fundamental phase angle versus stimulus frequency can be closely fitted with two straight lines, with the change in slope taking place at a frequency near the characteristic frequency of the particular nerve fiber. Similar plots of phase shifts of harmonics are consistent with the existence of identical time delays for the fundamental and harmonics. Our findings are based upon observations of more than 45 different nerve fibers in the cat. [This investigation was supported by PHS research grants from the National Institutes of Health.]
Some Observations on Effect of Electrical Stimulation of Crossed Olivocochlear Bundle on Cochlear Potentials (Guinea Pigs)
Authors: Konisihi T. , Slepian J. Z.
Published: October 2005

Changes in cochlear potentials were recorded in the basal turn of the cochlea in anesthetized and paralyzed guinea pigs, when the crossed olivocochlear bundle (COCB) was electrically stimulated on the floor of the fourth ventricle. The optimal parameters of stimuli to COCB used to produce the slow negative potential in the scala media were approximately the same in guinea pigs as in cats. Besides augmentation of cochlear microphonic (CM) and inhibition of action potential (AP), the stimulation of COCB resulted in increase of the positive summating potential (SP). These changes in sound-evoked responses were dependent on the parameters of both electrical stimulation of COCB and acoustic stimuli. CM in response to tone bursts of high frequencies showed little augmentation, while changes of SP were predominant. AP was more suppressed in low intensities of tone bursts than in high. The electrical stimulation of COCB failed to alter these changes in cochlear potentials after introduction of acetyl-choline-blocking agents (atropine and d-tubocurarine chloride) into the scala typmpani. [This study was supported by the PHS.]
Sound Level versus Time for Noise Exposure
Authors: Young Robert W.
Published: October 2005

In assessing the noisiness of a succession of varying noises, or the risk of damage to hearing, some kind of “tradeoff” between sound-pressure level and duration of sound is usually assumed. Judgment tests of noisiness of sounds simulating aircraft flyover and runup reported by Kryter and Pearsons [J. Acoust. Soc. Amer. 35, 866–883 (1963)] and Pearsons (FAA ADS-78, April 1966) were interpreted by the latter to mean that a reduction in maximum SPL ranging from 6 dB, for sounds of a few seconds duration, to 2 dB, for sounds lasting 60 sec, was equivalent to a halving of duration, the duration being taken as the time within which the varying level was within 10 dB of the maximum level. It is here shown that if an “effective duration” is derived from a time integral of the squared sound pressure (or to some other power as appropriate) and the maximum sound pressure, it is possible to relate on a single scale the several sets of measurements in which standard sounds of different time patterns were used, without arbitrary fitting at points of overlap. With the effective duration (which is simply the elapsed time for a constant sound), the relation between level and duration for equal noisiness is nearly the same over the entire range from 2 to 60 sec, and can be represented almost equally well by 3, 4, or 5 dB for halving of duration.
Subjective Evaluation of General Aviation and STOL Aircraft
Authors: Ollerhead J. B. , Adcock B. D.
Published: October 2005

Experiments were conducted in a progressive wavefield, in which a group of subjects evaluated the noisiness of more than 70 general aviation, short take-off and landing (STOL), and conventional commercial aircraft sound recordings. A paired-comparison technique was employed and the experimental procedure was automated as far as possible to minimize errors. All signals were subjected to “real time” 13-oct analysis in order to calculate a number of time-integrated rating scales. Comparisons calculated and judged noisiness values are presented and the effects of tonal content, during, and other factors are discussed. [Work supported by the Federal Aviation Administration under contract.]
Effects of Temporal and Spectral Combinations on the Judged Noisiness of Aircraft Sounds
Authors: Pearsons Karl S. , Bennett Ricarda L.
Published: October 2005

Tests were performed in an anechoic chamber using 20 college students to determine the judged noisiness of stimuli varying both temporally and spectrally. The investigations were divided into three test series. The first test series used 30 stimuli with six different time patterns and five different spectra. The second test used stimuli selected from the first test but modified to include signal durations ranging from 1 to 100 sec. Duration in this case is the amount of time the stimuli were within 10 dB of the maximum level. The stimuli for the third test consisted of recordings of turboprop, turbofan, turbojet, and helicopter flyovers. The results indicated that the most accurate predictor of the judged noisiness was preceived noise level using a tone correction suggested by the FAA and an integrated measure of duration. To illustrate the improvement in noisiness predictability of EPNL over PNL, the results of Test II (duration test) are used. For this test, 75% of the data was within 4 dB of the standard for EPNL with the FAA tone and integrated duration measure as compared to 11 dB for PNL.
In-Flight Exterior Pressure Fluctuation Measurements on the Boeing Model 737 Airplane
Authors: Bhat W. V.
Published: October 2005

The in-flight fluctuating pressures were measured with a microphone array, which consisted of seven flush mounted 14-in. B & K microphones. The flight-test measurements were carried out at the two locations (28 and 67 ft from nose) in a level flight at Mach numbers of 0.78 and 0.45 and also when stationary, on ground, at MTO power (on the aft array only). Various aerodynamic parameters were calculated. The PSD measurements for the forward position compared favorably with the laboratory measurements. Root-mean-square pressure fluctuation was found to be 3.53 times shear stress at the wall or 0.0056 times free-stream dynamic pressure. Wide-band space-time correlation measurements indicated slightly higher decay rate, which was attributed to angle between fuselage axis and flow direction in a level flight and also to the effects of fuselage curvature. Over-all convection velocities ranged between 0.5 and 0.8 times true air speed. The measurements at the aft location showed higher noise levels compared to the forward location. This was due to the contribution of the radiated noise from the jet engine. A similar conclusion is drawn from the wide-band space-time correlation measurements at the aft location.
Model Study of High Bypass Jet Noise
Authors: Ancell J. E. , Shapiro N.
Published: October 2005

A study of jet noise from high bypass fan-jet engines is being conducted with a 4.2-in. diam coannular model nozzle, approximately 1/20th scale. Initial tests, with heated central primary and cold annular secondary, have covered a range of secondary to primary velocity ratios from 0 to 2 and absolute velocities up to 1500 ft/sec. Farfield measurements have exhibited quite normal behavior with regard to acoustic power as a function of velocity and with regard to spectrum shapes and directivity patterns. Attenuation of the noise from the primary jet, due to shielding by the annular secondary jet, has been observed for certain limited range of ratios of secondary to primary velocity, and is greatest at the higher frequencies, with some reduction of the over-all SPL and of the sound power level.
Application of Theory to Compressor Noise
Authors: Ollerhead J. B. , Munch C. L. , Lowson M. V.
Published: October 2005

Theoretical results for the discrete frequency noise radiation by axial compressor stages [M. V. Lowson, NASA CR-1287 (March 1969)] are applied in some detail to some experimental cases. Reasonable agreement is found and provides some justification for the simplifying assumptions made in the original theory. The results of a design parameter study are also presented showing the principal acoustic effects of the major engine design variables. For the configurations studied, it is concluded that inlet swirl is a most significant parameter in engine noise optimization and also that reductions of rotor tip Mach numbers below about 0.8 are of comparatively little value. [Work supported by NASA Langley Research Center under contract.]
Broad-Band Noise Attenuation in Acoustic Ducts with Airflow
Authors: McNeill H.
Published: October 2005

The wave equation with flow subject to impedance boundary conditions and harmonic plane wave entrance conditions is solved for an acoustically treated duct tested in a reverberation facilitiy. The solution is obtained in terms of an expansion of non-orthogonal eigenfunctions. The eigenvalues are obtained by numerical analysis using a modified Newton/Raphson technique on an appropriate Riemann surface. The equation for energy flow in the duct is obtained from a second-order estimate of the time averaged sound intensity in the duct integrated over the duct traverse area. The spectra in the inlet and exhaust chambers of the reverberation facility is obtained and attenuation is calculated for selected duct configurations. Good agreement is obtained between the attenuation predicted by the theoretical model and that measured in the reverberation facility. The presence of nonlinear boundary impedance effects is postulated as a possible source of error in relating spectrums obtained from the experimental model.
Some Acoustic Characteristics of Two Subsonic Interacting Jets at Low and High Temperatures
Authors: Bielak G. W.
Published: October 2005

A study has been conducted whereby the acoustic characteristics of two subsonic parallel jets exhausting from 1-in. diam nozzles have been determined as a function of the temperature of the jets and their lateral spacing. The nozzle exit conditions investigated were a Mach number of 0.78 at stagnation temperatures of 540° R and 1520° R, respectively. Acoustic evidence of flow-flow interactions whereby the interference of the two jets alters the sound generation properties of the flow, and sound-flow interactions whereby the sound generated by one of the jets interacts with the flow of the other jet has been obtained. It was found that, for the high frequencies, observation points in the plane of the two jets at angles near to the axes of the jets are “quieter” than corresponding points in the plane normal to the plane of the two jets where the sound levels were equal to those levels which would be expected if the two jets generated sound independently. In general, the “suppression” in the plane of the two jets increased with increasing frequency and decreased with increasing angle from the axes of the jets. Increasing the temperature of the jets further increased the “suppression” in the plane of the jets.
Edge Noise Caused by Two Turbulent Wall Jets
Authors: Chanaud R. C. , Hayden R. E.
Published: October 2005

A study was made of the sound generated by two turbulent wall jets on opposite sides of a finite length plate. The mean Mach number was sufficiently low such that the predominant sound field was a dipole one associated with the interaction of the jets and the down-stream edge of the plate. This sound might be called trailing edge noise. Narrow-band frequency spectrums and directivity of the sound field were obtained along with wall pressure spectra and cross correlations. Discussion of the relationship between these quantities is given along with their relationships to the quantities that describe the mean flow field. The sound field was separable into that caused by the plate wake and that caused by the jets directly. When the wall boundary layer is smaller than the plate thickness, the wake noise is predominant. Leading edge noise caused by a variable length plate on the centerline of a quasi-two-dimensional jet was also examined.
Underwater Vibrations of Piezoelectric Ring Transducers
Authors: Wilkinson J. P. D. , DaCosta M.
Published: October 2005

A general numerical method is described for the study of the underwater vibrations of piezoelectric ring transducers. The transducer is modeled as a shell of revolution that is driven by a potential applied to electrodes on its surface or in its interior. The shell is made of a piezoelectric ceramic that may be polarized in the radial, axial, or circumferential direction. Prestress may be induced in the shell by a layer of fiberglass wrapping or by an axial precompression bolt. The analysis allows the calculation of the magnitude and phase of the radiation pressures in the fluid, the stresses induced in the shell, and such quantities as the piezoelectric coupling coefficients and the electrical admittance. Numerical examples are given to illustrate some typical results from a computer code based on the numerical method.
EATRAN—A Computer Program for Transducer Design
Authors: Wesner J. W.
Published: October 2005

EATRAN is a digital computer program for use in the design of electroacoustic transducers. Prepared with the transducer designer in mind, rather than the computer expert, the program accepts as input data the physical parameters with which the designer is familiar, and it produces a combination of verbal, pictorial, and graphical output which give him both a quick “feel” for performance and also detailed design information. Selection from among built-in electrical analog circuits representing different transducer configurations is controlled by the presence or absence of data items describing configuration features. Provision for multiple plots on a single frequency-response graph, plus simplified input for specifying minor data changes, facilitate observation of the effects of parameter variations on transducer performance. Initial application of the program has been to a moving coil receiver, and, except for local anomalies, the computer frequency-response curves have correlated well with experimental results for corresponding configurations.
Microphone Thermal Agitation Noise
Authors: Olson Harry F.
Published: October 2005

In electrodynamic microphones, there are two major sources of thermal agitation noise, namely, the electromotive force due to the thermal agitation of the electrons in the conductor and the electromotive force produced by the motion of the diaphragm due to the thermal agitation of the molecules impinging upon the diaphragm. In commercial microphones, the thermal-acoustic noise is far below the thermal-electric noise. Therefore, in order to detect the thermal-acoustic noise, a special high-sensitivity ribbon velocity microphone was designed and built. The presence of the thermal-acoustic noise was detected and measured in this microphone. The theoretical and experimental data correspond for both the thermal-electric noise and the thermal-acoustic noise.
Design of a Porous Pipe Microphone for the Rejection of Axial Flow Noise
Authors: Noiseux D. U. , Horwath T. G.
Published: October 2005

A porous pipe allows weak coupling between acoustic pressures outside and inside the pipe. A single microphone element is located at one end of the porous pipe. Only the waves traveling towards the microphone are preserved; the porous pipe includes a solid internal cone, which produces an anechoic termination for waves traveling in the opposite direction. The design yields the specific flow resistance of the porous pipe and the cone shape for the anechoic end. The axial sensitivity of the porous pipe microphone is found to be unity when the microphone element has a high acoustic impedance. The directivity follows that of a uniform line with uniform delays. The filtering action of the porous pipe microphone for the turbulent-boundary-layer noise is calculated for a simple model of flow noise. Experimental values of microphone sensitivity, directivity, and flow-noise rejection are presented. [This work was initiated and supported by the Systems Application Division of U. S. Army MERDC, Fort Belvoir, Virginia 22060.]