bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of a Narrow-Band Noise as a Function of the Interaural Correlation of Both Signal and Masker
Authors: Wilbanks W. A.
Published: November 2005

This study is an extension of some work that we reported at the St. Louis Meeting of the Society [J. Acoust. Soc. Am. 38, 929 (A) (1965)]. The signal, a 135-Hz noise centered at 250-Hz, was partially masked by continuous wide-band noise. The correlation of both signal and masker were varied between +1.00 and 0. With a correlated masker (N0), detection is about 14 dB better with an uncorrelated signal (SU) than with a correlated signal (S0), and about 16 dB better than with both signal and masker presented monaurally (NmSm). These masking-level differences (MLD's) diminish as the correlation of the signal is increased to unity, and as the correlation of the masker is decreased to zero. The results suggest that sizeable MLD's are obtained under those conditions where the addition of the signal results in a decrease in the correlation between the stimulus events at the two ears and, presumably, decreased synchrony between the neural inputs to the binaural-detection mechanism. [Research supported by the National Institute of Mental Health.]
Mechanism of Glottal Vibration for Vowels and Consonants
Authors: Halle Morris , Stevens Kenneth
Published: November 2005

It is suggested that the positioning of the vocal cords and the manner in which they vibrate may be quite different, depending upon whether the supraglottal tract is unconstricted, as in vowels, or whether it is constricted to some degree, as in stops, fricatives, and certain semivowels. An analysis of the mechanism of larynx vibration and measurements of air-flow events during speech shows that vocal-cord vibration of the type that occurs in vowels cannot be maintained during voiced consonants, and that adjustments in vocal-cord positioning and tension must be made if vibration is to continue. Since these adjustments require a certain time interval to be effected, they account—at least in part—for the frequently noted differences in vowel length before voiceless consonants, nasals, and voiced obstruents. [This work was supported in part by the U. S. Air Force, under contract, and in part by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, under a grant.]
Studies of Variations in Glottal Aperture Using Photoelectric Glottography
Authors: Ohala John
Published: November 2005

A photoelectric glottograph utilizing transillumination of the larynx was constructed to sense variations in glottal aperture. Treating the ac variations in glottal area as equal to the variations in sound pressure at the level of the glottis (a reasonable approximation for most modes of phonation), a spectral analysis of the “glottal wave” during running speech revealed a spectrum whose shape changed during changes in the pressure differential across the glottis, e.g., during voiced stops. Simultaneous recordings of the glottographic and acoustic signals during steady-state “creaky voice” (or “vocal fry”) revealed that the number of glottal openings were greater than or equal to the number of sound pulses. Glottal openings in creaky voice typically occur in groups of two or three, but only the last of each group invariably has sufficient energy to excite the vocal tract. This explains the disparate findings in previous studies of creaky voice which were solely physiological or solely acoustic. [Work supported by National Institutes of Health, U. S. Department of Health, Education, and Welfare, and the Office of Naval Research.]
Vocal-Cord Spectra Derived from Glottal-Area Waveforms and Subglottal Photocell Monitoring
Authors: Wendahl Ronald W. , Coleman Robert F.
Published: November 2005

This paper reports a study wherein four subjects, phonating at two separate frequencies, were examined by photocell monitoring and simultaneous ultrahigh-speed photography. The glottal area waveforms from the film and the photocell output waveforms were compared by Fourier analyses. Comparisons of the two spectral displays confirm the findings of previous investigators, in that while the two methods produce similar waveforms, particularly of the same period, differences exist in the spectral properties of the waveforms thus derived. Differences in spectra may be attributed to phase-angle variations in the photocell monitor, or other such variables. Basic requirements for a photocell system with acceptable reliability are described.
STROL Study of Vocal-Fold-Area Change as a Function of Pitch
Authors: Coleman Robert F. , Hollien Harry
Published: November 2005

Previous studies by Hollien have demonstrated the effect of changing fundamental frequency upon the cross-sectional area of the vocal folds. These earlier investigations, however, were based upon conventional laminagraphic x-ray techniques which produced a composite image of the vocal folds during their entire complex cycling. The experiment reported in this paper is a replication of the former studies, but utilizes STROL, a stroboscopic laminagraphy device which allows examination of the cross-sectional area of the folds at 36° phase-shift intervals throughout the vibratory cycle. In addition, animation of the phase-shift pictures allows observation of the apparent motion of the vocal cords in cross section. In this study, subjects phonated at a constant intensity at three separate fundamental frequencies. The results support Hollien's earlier conclusions, in that, as fundamental frequency increased, the cross-sectional area and mean thickness of the folds decreased.
Comparison of Two Methods of Measuring Subglottal Air Pressure during the Production of Speech
Authors: Lieberman Philip , Mead Jere , Knudson Ronald , Leith David , Macklem Peter , Wilson Norma
Published: November 2005

Subglottal air pressure was measured during the production of unemotional declarative sentences, yes-no questions, sentences with emphasized words, and simulated emotional discourse. Pressure was directly measured by means of a tracheal puncture and simultaneously measured indirectly by means of an esophageal balloon. The subglottal air pressure was calculated from the esophageal pressure by compensating for the elastic recoil of the lungs. The calculated subglottal air pressure was found to be within 1% of the directly measured pressure. It was necessary to compensate for the elastic recoil of the lungs when calculating the subglottal pressure from the esophageal balloon even when short sentences were produced. Otherwise, the calculated subglottal air pressure at the end of the utterance was too high. The positive error can be as great as 30% for an utterance having a duration of 2 sec.
Absence of Syllabic “Chest Pulses”
Authors: Lieberman Philip , Griffiths John D. , Mead Jere , Knudson Ronald
Published: November 2005

Subglottal air pressure was measured during the production of short test phrases, sentences, and simulated emotional discourse. It was found that peaks in the subglottal pressure function consistently delimited a syllable only when it was deliberately emphasized. Other small peaks in the subglottal-air-pressure function appeared to be consequences of changes in the impedance of the upper airway. The test phrases hippity hoppity and hippity poppity was examined. It was found that the subglottal air pressure contours were similar except for a pressure minimum of 6 cm H2O in hippity hoppity for the medial /h/. The respiratory system thus acts like a current source insofar as subglottal air pressure is a function of the upper-airway impedance. The articulatory basis of the syllable apparently does not consist of overt “chest pulses” that delimit syllables. Other possible articulatory correlates of the syllable are discussed.
Acoustic Admittance of a Subsonic Wall Boundary Layer
Authors: Morfey C. L.
Published: November 2005

At frequencies such that the steady (dc) boundary layer over a solid surface is acoustically thin, the effect of the boundary layer on incident sound waves can be incorporated into the surface acoustic admittance. The dc layer can interact with the sound field in two ways. (1) Mean-flow gradients modify the acoustic (ac) boundary layer. If the ac layer (viscous and thermal) lies within the dc sublayer—where mean-flow properties vary almost linearly with distance from the wall—it is possible to estimate the modified ac layer admittance. (2) Outside the ac layer, sound waves are refracted by mean-velocity and sound-speed gradients. This further modifies the over-all surface admittance, but the effect is small in the frequency range over which the admittance concept applies (boundary layer thickness<<wavelength).
Tone Generation by Subsonic Flow Through Sharp-Edged Circular Nozzles
Authors: Heller Hanno H.
Published: November 2005

Intense discrete-frequency tones are generated when gases flow at high subsonic flow speeds (0.3<M<0.8) through circular orifices with sharp edges on both ends and with diameter-to-length ratios of approximately 1 to 2. These tones are shown to result from a feedback mechanism; their generation does not require the presence of adjacent resonators. Schlieren-optical photographs are presented that indicate a periodic vortex shedding. Because the feedback wave is superposed on the flow, the frequency of the tone, which is identical to the vortex-shedding frequency, is not directly proportional to the flow velocity; a frequency law relating Strouhal and Mach number, is presented. [This work was done while the author was at the Institut für Technische Akustik der Technischen Universität Berlin, and was sponsored by the Deutsche Forschungsgemeinschaft.]
Turbulence Measurements of the Mixing Flow of a Nozzle with a Single V Notch
Authors: Potter R. C.
Published: November 2005

Hot-wire-anemometer measurements are reported for the cold subsonic turbulent mixing region formed by a circular nozzle with a 45° notch. Such a nozzle simulates a single corrugation, typical of those used for jet-engine silencers. The measurements showed that the notch flow induced a large secondary flow, causing a rapidly widening mixing region. The intensity of the turbulence in this initial mixing region was slightly reduced from that measured in the corresponding mixing region from the opposite circular side of the nozzle. (15 minutes) The scale of the turbulence was found to be similar in both mixing regions. These results were used to estimate the sound produced by various parts of the flow. The fact that the turbulence scale and intensity do not increase in the wider mixing region formed downstream of the notch results in less noise generated. Possible techniques for optimizing corrugated nozzle silencers are then considered.
Frequency Spaces for Cylindrical and Spherical Enclosures
Authors: Kligman Ronald , Waterhouse Richard
Published: November 2005

The normal-mode frequencies for a rectangular enclosure may be depicted as points on a rectangular lattice in a three-dimensional Cartesian-frequency space. This results from the uniform spacing of the zeros of the sine and cosine functions that comprise the solution to the wave equation in rectangular coordinates. In the case of cylindrical or spherical enclosures, the wave equation in the corresponding coordinates yields solutions that contain functions whose zeros are not uniformly spaced. Such are the Bessel and spherical Bessel functions. Thus, the points representing the normal-mode frequencies of such enclosures do not lie on a regular lattice. However, it is shown that because the spacing of the higher-order zeros of these functions approaches uniformity, the frequencies of the corresponding higher modes can be represented by a rectangular lattice with good accuracy. This is a convenience in estimating the numbers of modes lying within a given frequency interval. [Work supported by the U. S. Navy Office of Naval Research.]
Reception and Self-Noise of Simple Lines and Perforated Pipes in Motion
Authors: Eichler Ewald
Published: November 2005

Extended acoustic receivers that sample a pressure field by means of a simple propagating wave and their realization in the form of a microphone-terminated perforated pipe are studied. Motion through the medium subjects a receiver to apparent changes of frequency, to loss of surface reactance, and to flow noise. The receiver gain generally decreases with increasing velocity. In the perforated pipe, the phase speed of sound generally exceeds the speed of sound in the free medium; because of the Doppler effect, however, true and end-fire reception is still possible, at least at one frequency. The flow noise for a number of receiver lengths and axial velocities is calculated on the basis of several models of the homogeneous and inhomogeneous turbulent boundary-layer pressure field. The experimental data, whether obtained in the wind tunnel or in free fall through the atmosphere, lie generally higher. [Supported in part by the U. S. Navy Office of Naval Research.]
Response of a System of Point Transducers to Turbulent Boundary-Layer Pressure Field
Authors: Jorgensen D. W. , Maidanik G.
Published: November 2005

The responses (in a given frequency band) of systems of flush-mounted “point” transducers to the pressure field in a turbulent boundary layer are analyzed. A system of flush-mounted transducers has the properties of a spatial filter whose properties can be varied by varying the sensitivities and separations between the constituent transducers of the system. It is shown that by properly adjusting the sensitivities and the separations, a substantial reduction in the response can be achieved. This reduction is considered with respect to the corresponding response of a single point transducer having a sensitivity equal to the sum of the absolute sensitivities of the point transducers of the system. Particular examples are presented for systems consisting of two and three point transducers. Comparisons of the responses of these systems with the response of a uniform transducer of finite size are discussed.
Acoustical Problems Associated with the Use of Microphones in an Oxygen Mask
Authors: Sebesta George J. , Mellen Arthur J. , Hofer Alan , Carlisle Richard W.
Published: November 2005

Speech communication is required by military flight personnel at all times, including high-altitude operations during which an oxygen mask is worn. Carbon microphones have been used until recently, with consequent disadvantages concerned with intelligibility and sensitivity to noise. A first step toward increased fidelity and reliability was the introduction of dynamic noise-suppressing microphones and a preamplifier, the latter being adapted to fit into the space previously occupied by a connection plug. Although the frequency response is smooth, the acoustical characteristics of the mask are such as to enhance low frequencies and there is a problem with “barrel-like” tone. Furthermore, the available dynamic microphones are somewhat bulky and in the standard mask, cause discomfort in the region of the nose. A more recent development is the application of a variable-reluctance, balanced-armature microphone only 316 in. thick, mounted in the front of the pre-amplifier casing. The various arrangements and measuring setups are described.
Frequency-Dependent Propagation Loss in the Deep Sea
Authors: Urick R. J. , Blaik Maurice
Published: November 2005

The energy density of explosive sounds was measured for five low-frequency bands using hydrophones in the body of the deep sea at various ranges from 1 to 110 mi and various source depths from 800 to 12 000 ft. Analyses of observed propagation loss show considerable frequency dependence across frequency bands in the interval 25–1600 Hz. The three lowest frequency bands—namely, 25–100, 100–200, and 200–400 Hz—generally show lower propagation loss than the two highest bands (400–800 and 800–1600 Hz), but the details show a complicated dependence on depth and range. For most of the data, the spreading loss was found to be between cylindrical and spherical beyond five miles. Convergence-zone effects are identified as functions of depth, range, and frequency.
Prediction Model for Shallow-Water Sound Transmission
Authors: Urick R. J.
Published: November 2005

For predicting the transmission loss to long ranges in shallow water with downward refraction, when only a fragmentary knowledge about the bottom is available, a theoretical model is derived leading to a particularly simple expression for the loss in terms of the water depth, velocity gradient, and bottom-reflection loss at small grazing angles. This latter quantity, for which no measurements are extant, is approximated through computed curves of reflection loss at the boundary of a semi-infinite absorptive fluid. A test of the model is provided by two sets of field data. One consists of recent measurements by NEL at 1.5 kHz, along with core-sample measurement of bottom density and sound velocity, in several Pacific Ocean areas. The other comprises a hitherto-unpublished transmission survey at 12 kHz made in 1944 by WHOI around our East and Gulf coasts. For this mass of data, the only information about the bottom is contained in words like “mud” and “sand.” Reasonable agreement with both sets of data is found. The model appears to be useful for making approximate predictions of transmission loss in shallow water.
Acoustic Field in an Inhomogeneous Medium with Boundaries
Authors: Deavenport Roy L.
Published: November 2005

The acoustic potential is derived for a continuous-wave (CW) point source located in a laminar inhomogeneous liquid overlying an elastic solid. The velocity-depth profile in the liquid may be a single varying function or a series of layers, each of which can have a varying velocity-depth profile. A pressure-release surface is assumed. The bottom consists of a solid elastic layer, which may have a limited prescribed variation in the Lammé parameters and density. Normal components of velocity and stress are matched at all interfaces. The field is given in terms of a resolvent Green's function contour integral, where the integrand is a function of the characteristic matrices of the liquid and solid layers. The resulting expression is different than those given by Brekhovskikh and Tolstoy. [This work was sponsored by the U. S. Naval Ship Systems Command.]
Propagation Loss in a Heterogeneous Medium Bounded by a Rough Surface
Authors: Higgins L. L.
Published: November 2005

A general method is described for calculating the average sound-intensity field due to a directional source in a fluctuating refractive and absorbing medium contained within a random-scattering and -absorbing surface. The following is assumed—the radiation is completely incoherent as a result of random fluctuations of the medium and surface; radiation propagates along ray paths determined by the given average sound-velocity field; the statistical properties of the rough surface are given on the average surface. An integral equation determines the intensity at the average surface. The intensity in the medium is the sum of radiation directly from the source and an integral over the whole surface of scattered radiation directly for points of the surface. The method is applied to surface-duct propagation in the sea and numerical results are discussed from a simplified adjustable-parameter model of the ocean. [Work supported by U. S. Navy Ordnance Systems Command.]
Contour Charts of SOFAR Speed and Axis Depth in the Pacific Ocean
Authors: Johnson Rockne H. , Norris Roger A.
Published: November 2005

Sound speeds, calculated from the physical properties of sea water as measured at hydrographic stations, were used to construct contour charts of SOFAR-speed and SOFAR-axis depth for the Pacific Ocean. Wilson's formula was used for the calculation of speed. Data were averaged for 1° squares, plotted, and smooth contours were drawn manually. Speeds averaged along great-circle paths are compared with those measured for explosions. The charts show steep gradients along the Antarctic convergence and at the convergence of the Oyashio and Kuroshio extension. The region of highest speed, as well as greatest axis depth, was that extending eastward from Australia to about the 150°W. The charts are used in a program for calculating source coordinates of earthquake T phases.
Evaluation of Intensity-Modulated Recording for Ultrasonic Diagnosis
Authors: Reid John M.
Published: November 2005

An evaluation of current intensity-modulated recording systems has shown that they will not produce identical records from the same echo pattern. Differences in the records are due to two factors: the recording transfer function, and the ways in which the zero signal level or “baseline” is established and maintained. To find a correlation between ultrasonic echo patterns and the underlying tissue structure, it is essential to be aware of the changes in records that are due to the recording equipment. Lack of knowledge of a particular equipment can have a disastrous effect upon attempts to duplicate the results of another investigator. Differences in the transfer functions of current equipment arise from the use of different types of cathode-ray tubes and recording film as well as the use of a video differentiator. An additional effect of not maintaining a constant zero level is to increase the variability of the amplitude of received echoes. Several tests have been devised by which the processing inherent in a particular type of equipment can be assessed and by means of which the changes introduced by different combinations of characteristics can be demonstrated.
Performance Limitations on the Ultrasound Image Converter
Authors: Jacobs John E.
Published: November 2005

In recent years, the ultrasound image converters have become available in such a form as to lend themselves to routine day-to-day use. The systems are capable of resolving detail in the order of a few hundred microns at sound levels incident of 10−7 W/cm2. The greatest difficulty presently associated with the systems is the need for liquid immersion of the object being examined. It is the purpose of this discussion to delineate the various factors controlling the performance of the system and, through motion-picture film, show the application of the image system to typical problems in medicine and biology.
Use of an Adapter Ring for Calibration of Large Circumaural Earphones
Authors: Wilber Laura Ann , Swindeman John , Hogue Ann , Goodhill Victor
Published: November 2005

Routine calibration of large circumaural earphones has long been a problem due to lack of a standard coupler, variability found with placement on a brass plate coupler, and difficulties in probe tube calibration techniques. In order to provide a practical solution to the above problems so that a pair of large circumaural (Pedersen) earphones could be used routinely, four studies were carried out at UCLA. In these studies, a Plexi-glass adapter ring was developed that, when fitted with a standard artificial ear and attached to the earphones, furnished a method whereby routine acoustic calibration of the earphones could be carried out easily and repeatedly. Comparisons were made between the Pedersen earphones and TDH 39 earphones using: (1) the adapter ring and artificial ear; (2) a probe tube; and (3) psychophysical techniques. These comparisons made it possible to achieve a method for routine calibration of the large circumaural earphones. The above studies also indicated some problem areas in the use of certain psychophysical techniques such as loudness balancing.
Acoustic Wavemotion in the Human External Ear
Authors: Shaw E. A. G. , Teranishi R.
Published: November 2005

The pressure distributions generated in an external ear replica by a nearby point source have been measured with a probe microphone. Five normal modes have been clearly identified, M1 at 2.9 kHz that is essentially the λ/4 resonance of the canal proper with a large end correction, M2 at 5.5 kHz the fundamental depth resonance of the concha with large radiation damping and weak canal coupling, M3 at 9.3 kHz related to the first transverse resonance of the concha, M4 at 11.2 kHz, and M5 at 12.8 kHz a pair of modes related to the second transverse resonance. M1 and M2 are consistent with limited measurements on real ears and are easily reproduced in a simple geometrical model. Above 6 kHz, transverse wave-motion in the concha is largely responsible for large variations of response with angle of incidence. Real ears, replica, and model all exhibit relatively low on-axis response in the 8-kHz region.
Discriminations Among Simulated Sonic Booms
Authors: Little J. W.
Published: November 2005

A waveform generator was constructed that provided for the introduction of sounds represented by four different waveforms into a box 21 in. square, 25 in. high, and with an 18-in. speaker mounted in the top of the box. The four waveforms were an N wave, a differentiated N wave, one-half square wave, and a differentiated one-half square wave. With their heads sealed in the small box, 16 subjects made discriminations among the six different pairs of stimuli. That the subjects could not discriminate between an N wave and a differentiated N wave, or between a square wave and a differentiated square wave, reproduces the results of Zepler and Harel (1965), but with different equipment and psycho-physical technique. Using earphones, their experiments showed that the loudness of the N waves is determined by the two rising parts (pulses), while our experiment shows that when the pulses are identical in amplitude change and direction, discrimination is not possible. That subjects could discriminate among the four pairs of stimuli where compression was compared to rarefaction is probably caused by the nonlinear characteristics of the ear, but could also result from air leakage at the neck seal.
Loudness and Annoyance of Clicks
Authors: Silbiger Herman R.
Published: November 2005

This investigation was concerned with the subjective effects of high level impulses of short duration, to add to previously reported data [H. R. Silbiger, J. Acoust. Soc. Am. 38, 937(A) (1965)]. The principal parameters under investigation were the click shape, duration, and peak pressure level. The last ranged from 98 to 159 dBt. Subjects gave magnitude estimates of the loudness of the clicks and rated the subjective disturbing effects on an annoyance scale. The developed annoyance scale appears to be linear with positive peak pressure level. The slope of the average loudness function was 0.8. Data on the difference limen for these clicks will also be reported. Because of the level of the stimulus clicks, the subjects' thresholds were continuously monitored, and temporary threshold shift curves were obtained for both single and multiple click presentations. These data again show evidence of both positive and negative TTS, with the amount of negative TTS decreasing as the number and level of stimulus clicks increases.
Loudness and Annoyance of Impulsive Office Noise
Authors: Rothauser Ernest H. , Urbanek Gunther E. , Pachl W.
Published: November 2005

A study has been made on the evaluation of natural impulsive noises by subjective and objective procedures. One special example was used to get an indication of whether existing objective calculation methods might give sufficient agreement with subjective tests. The office noise sample studied bursts from a single typewriter operated at repetition rates between 1.5 and 15/sec. A forced-pair comparison procedure of the constant stimulus type was used for the subjective evaluation. This choice has been prompted by the good results that we obtained with a corresponding method for speech quality measurements. In the subjective tests reported here, we asked for loudness and for annoyance comparisons. Two types of broad-band noise were utilized as reference signals. In addition to this, narrow-band noise centered at 1000 Hz was used to calibrate the two broad-band noises subjectively, and was also compared directly to the test noise. The subjective measurement results of this study are compared with those obtained by several well-known objective methods for noise rating and loudness evaluations.
Noise Reduction Studies for a Multistage Axial Flow Transonic Compressor
Authors: Chestnutt David
Published: November 2005

It is the purpose of this paper to describe an aircraft-type transonic compressor built especially for noise research studies and to present some preliminary results. This compressor is unique in that it is adjustable over a very wide range of operating conditions. Initial test results indicate that the relative-tip Mach number is a dominant factor in noise generation. Results of systematic measurement studies for a range of pressure ratios, rotational speeds, and inlet flow angles suggest that variation of in-flow angle may be an effective technique for markedly reducing inlet noise radiation during high-tip speed operation.
Achieving Noise Reduction Economically
Authors: Jelinek R. E. , Nordby K. S.
Published: November 2005

The noise control activity of an acoustics group at a development laboratory dealing mainly in computer peripheral equipment is presented. The cost of product noise control increases rapidly as machines progress in hardware development, becomes expensive when tooling is completed, and usually prohibitive after release to production. The goal, therefore, is to implement noise control early, i.e., on the designer's drawing board before hardware exists. However, to development engineering, noise control is only one of many factors to be considered within limitations of budget and schedule. Therefore, the acoustics group must have an effective program to ensure proper noise control emphasis during various phases of development. The program of the group is presented: before-hardware participation in machine development; recommendations of machine acoustical objectives based on experience and market requirements; prediction of noise-control measures required to make machines meet their acoustical objectives from design layouts and power-level measurements of components and subassemblies; evaluations of complete machines in a semianechoic chamber; interactions with industrial design, human factors, heat transfer, installation planning, product test, and manufacturing quality control groups.
Analytical and Experimental Studies of Sound Pressures in Ducted Propellers
Authors: Fricke Werner , Bissell John R.
Published: November 2005

Various types of VTOL aircraft and air-cushion vehicles under development utilize ducted propellers. Consequently, knowledge of the sound-field inside ducts is required to develop design criteria for lightweight duct structures of sufficient acoustic fatigue life. The paper presents an analytical approach for predicting the rotational sound due to blade loadings in propeller ducts, based on definable propulsion quantities. The sound field in the propeller plane is represented by expanding the rotating net propeller blade pressure distribution in a suitable series, being a solution of the wave equation that satisfies the boundary conditions associated with the duct and hub. The equations obtained allowed a calculation of the spectral and spatial sound-pressure distribution along the axis and radius. The validity of the analytical approach was investigated by exploring the sound field of a full-scale model duct under measured operational conditions. These experiments were conducted in the large-scale wind tunnel at NASA Ames Research Center. An additional experimental study was conducted on the effect of increased tip clearance on the sound pressure. [Program sponsored by NASA Headquarters.]
Recent Research Relative to Perceived Noise Level
Authors: Wells R. J.
Published: November 2005

This paper is a progress report on a joint project involving the General Electric Company and Bolt Beranek and Newman Inc. Certain refinements in the computation of perceived noise level are under consideration. A new method of spectral integration of annoyance relative to the rating contours is examined together with possible revisions in the correction procedure employed for pure tones. Possible slight changes in the basic NOY rating contours will also be discussed. Correlations of jury tests with annoyance calculations are improved by these changes.
Measurement of the Power Output of Pure Tone Sources in a Reverberation Chamber
Authors: Maling George C.
Published: November 2005

A true rms voltmeter (80-sec integration time) and a moving microphone have been used to measure the space-averaged mean-squared sound pressure (p̄2) in a reverberation chamber produced by pure tone sources and air handling devices that produce discrete tones. The data are in good agreement with previous results [IBM J. 11, No. 5 (1967)]. The statistical stability of an estimate of p̄2 may be determined from n = 2l/L where n is the degrees of freedom of the estimate, l is the microphone path length, and L is the correlation distance for the sound pressure. For a pure-tone source, the change in power output W with source location in the chamber has been measured in the frequency range 500–2000 Hz, and has been found to be in good agreement with theory. For an air handling device, measurements show that the power radiated at the blade passage frequency and its harmonics are less dependent on source location than the output of an ideal (monopole) source. The statistical stability of an estimate of W has been determined as a function of frequency.
Digital Implementation of a Noise Rating Meter and Transient Analyzer
Authors: Lang William W. , Maling George C. , Taylor William A.
Published: November 2005

The “back-door” approach to noise level evaluations described by R. H. Peterson [J. Acoust. Soc. Am. 37, 1197(A) (1964)] has been implemented on a general-purpose digital computer. The method is useful for evaluating the noise radiated by a machine or other source that produces single or repeated bursts. With this method, the octave-band spectrum and noise rating of a single machine cycle or other transient are determined after one or more segments of the signal are attenuated. This enables the noise control engineer to identify those portions of the transient that contribute significantly to the noise rating. The Cooley—Tukey algorithm is used to compute the power spectrum. The transient is segmented into short (8.192 msec) records so that the methods developed by Welch [IEEE Trans. Audio Electron. 15 (1967)] may be applied. Applications to transients produced by representative IBM machines are presented.
Spectrum Produced by an Ultrasonic Resonant Cavity
Authors: Breazeale M. A. , Chang Ching-Tu
Published: November 2005

A spectrum analyzer is used to examine the ultrasonic spectra produced when large-amplitude ultrasonic waves are caused to resonate in a water-filled cavity. The cavity, consisting of a plane transducer and concave reflector, produces frequency components that in some cases are neither integral submultiples, nor integral overtones, of the driver frequency. [Research sponsored by the Office of Naval Research.]
Characteristics of the Shock Wave Generated in Air by a Blasting Cap
Authors: Sadwin Lippe D. , Christian Ermine A.
Published: November 2005

The propagation of the shock wave generated in air by a very small surface explosion, a commercial No. 6 electric blasting cap, has been studied. A large number of time-resolved pressure histories were recorded with piezoelectric transducers at distances over the range of 10–265 ft from the explosion point. The observed range of peak air shock pressures was from 0.3 lb/in.2 down to 3 × 10−3 lb/in.2 Comparisons with TNT surface burst data for much larger explosions show that the peak pressure-distance attenuation exponents are the same. Based on these pressure-distance data, the yield of the No. 6 electric blasting cap used is approximately 0.5 g of TNT. Even at the lowest peak pressures measured, the wave shapes are characteristic of typical airblast shock waves. An essentially triangular positive pressure phase is followed by a negative pressure phase of much lower amplitude and longer duration. This is unlike the signatures of sonic booms that are highly symmetric. The effect of the asymmetry on the energy density spectrum of the blasting cap is also discussed.
Transient Reflection of Acoustic Waves from Fluid Velocity Discontinuities
Authors: Friedland Allan B. , Pierce Allan D. , Moo Charles C.
Published: November 2005

A theoretical treatment is presented of the reflection of line source generated acoustic waves from an abrupt discontinuity in the ambient fluid velocity. The model employed is that of a homogeneous, compressible, isothermal fluid with negligible viscosity, thermal conductivity, and gravity effects, occupying infinite space. In the upper half region, the fluid is assumed to have a constant horizontal ambient fluid velocity, while in the lower half region, it is assumed at rest with a horizontal line source embedded in it. The time dependence of the line source is arbitrary. The method of Cagniard is employed to find a full-wave exact solution for the acoustic radiation in the lower-half space. Various anomalous features of the transient solution are discussed concerning their dependence on the fluid Mach number in the upper half space. The peculiar features of reflections at Mach numbers greater than 2, which was predicted by Miles and Ribner for incident plane waves, is discussed in some detail.
Total Reflection, Phase Changes, and Caustics
Authors: Tolstoy Ivan
Published: November 2005

The simple theory and pertinent acoustic evidence, relating to the classic frequency-independent phase changes upon total reflection, are briefly reviewed. Of particular interest are experimental results showing the effect of such phase changes in modifying the shape of propagating pulses. Thus, it is well known that, in the plane wave approximation, if a narrow pressure pulse is totally reflected off the plane boundary of a high velocity medium, the reflected pulse may develop a tail. This is interpreted physically by the fact that a frequency independent phase change φ corresponds to a delay τ=φ/ω, i.e., a delay inversely proportional to the angular frequency ω. The mechanism of tail formation is thus a delay. In the process of total reflection, it takes time for the energy to penetrate into the high-velocity medium and to be restored back into the medium of incidence. Of particular interest in both ocean and atmospheric acoustics is the case of total internal reflection in a medium of continuously increasing velocity. Standard asymptotic approximations, identical to those used in quantum theory, show that when certain conditions are fulfilled, an effective phase change of π/2 takes place. This of course implies the deformation of pulses upon total reflection, appearance of tails, etc. Some remarkably clear experimental evidence showing this effect has been obtained in recent years. It has sometimes been proposed that similar effects are predicted by the so-called phase changes at a caustic. This is not so. The subject of phase shifts at caustics and loci is well known to students of optics and diffraction theory. The theory shows that factors of eiπ/2 (caustics) or eiπ (foci) make their appearance in the solutions describing the local field in the simple harmonic case. However, the mechanism by which a caustic or focus is produced is important in defining precisely the significance and limitations of the eiπ/2 or eiπ factors in any given case, especially when applied to the spectra of broad-band disturbances traveling through the system. Thus, in the latter case, if one accepts the π/2 caustic phase shift at face value and applies it to a narrow pulse, one runs afoul of the causality principle. On the other hand, it is obvious that a caustic is simply a geometrical construct: The only thing that happens there is an interference between arrivals along neighboring rays, a phenomenon which cannot, in a linear approximation, leave any permanent imprint upon a pulse traveling through such a region. Thus, these “phase shifts” are localized effects, which cannot be applied indiscriminately to the spectra of pulses traveling along the edges of caustics or through foci. [Hudson Lab. of Columbia Univ. Informal Documentation No. 144. This work was supported by the U. S. Office of Naval Research.]
Focusing of Underwater Step-Waves near a Caustic
Authors: Silbiger Alexander
Published: November 2005

The pressure field near a caustic (convergence zone) is analyzed for transient pulses with vanishing rise time. On the caustic, linear acoustic theory predicts a singularity of the order of (t−ta)−1/6 at the shockfront, ts being the arrival time of the front at the caustic. The corresponding total impulse remains finite. Factors limiting the peak pressure are discussed. Theoretical results are compared with data obtained by the Naval Ordnance Laboratory with explosive sources in a flooded quarry. [This work was supported by the U. S. Office of Naval Research.]
Geometrical Acoustic Propagation with Frequency Dependence
Authors: Solomon L. P. , Ai D. K. Y.
Published: November 2005

One characteristic of geometrical acoustic solutions is their frequency independence. Geometrical acoustics stems from the solution of the eikonal equation that is a form of the wave equation in the limit of infinite frequency. Since the effects of the medium and the boundary conditions on the acoustic fields are definitely frequency dependent, it is desirable to obtain approximate solutions that reflect this dependence on frequency. Although data are available on propagation losses for signals of different frequencies, geometrical acoustics does not offer a means of comparison. An asymptotic expansion in terms of inverse powers of the frequency is presented. The first term in the expansion obeys the eikonal equation; all the ray-path solutions obtained from geometrical acoustics are applicable. Here, the first term of the expansion, which is the geometrical acoustic field, is obtained in closed form using a simplified profile in which the first derivative is continuous everywhere. The calculation of the higher-order terms then involve operators that have known variable coefficients which are functions of the lower-order solutions.
Ray Propagation through a Moving Nonhomogeneous Medium, with Linear and Exponential Variations
Authors: Tripathi I. D.
Published: November 2005

Two simple models of the ocean are considered. In the first model, the body of water is assumed to be moving along the horizontal or x axis with a velocity that decreases linearly with depth. The speed of sound in this medium is assumed to also vary linearly with depth when the medium is at rest. In the second model, the water velocity along the x axis is assumed to decrease exponentially with depth and the speed of sound is assumed to vary exponentially with depth when the medium is stationary. The vector eikonal equation is used to find the ray path in these two ocean models, and the expressions for the ray path and its slope are derived and plotted. Previous work in this field is reviewed, and its scope is discussed. [This work was sponsored by the Acoustics Program Office of Naval Research under contract.]
Study of the Effect of Plane Boundary Location in the Analysis of Characteristic Dispersion
Authors: DiNapoli F. R. , DeFanti D. J. , Middleton F. H.
Published: November 2005

The mathematical analysis of the characteristic dispersive effects of a continuously stratified ocean requires obtaining a solution to the reduced wave equation that simultaneously satisfies the existing boundary conditions. The relative ease with which the dispersion information can be extracted from this boundary value problem is influenced by the location of the boundaries. The desired eigen values for a finite ocean are often embedded in an intractable transcendental equation, the solutions of which are usually obtained through the application of numerical techniques. However, if the physical problem is approximated by an ocean of infinite extent, the characteristic values are given by an exact, explicit, and easily obtained relation. The purpose of this work was to study the effect of this approximate mathematical model upon the characteristic dispersion of the medium. This was accomplished by comparing results from both models for a number of both single- and double-valued sound velocity profiles. In both cases, the exact solution was sought in terms of hypergeometric functions. For the infinite ocean model, further restrictions were applied so that the solution might be expressed in terms of Jacobi polynomials. [Research supported by U. S. Naval Underwater Sound Laboratory, New London, Connecticut.]
Hydrodynamic Generation of Distortion in Mechanical Cochlear Models
Authors: Tonndorf Juergen
Published: November 2005

Displacements of the partition of mechanical cochlear models are invariably larger toward scala tympani than towards scala vestibuli [J. Acoust. Soc. Am. 31, 608 (1959)]. Recent experiments showed that the degree of demodulation of beat signals varies inversely with the viscosity of the cochlear fluids. This finding, together with other previous ones, permits an explanation for the entire phenomenon. For high viscosities, the boundary layers on both sides of the partition are broad. The longitudinal vectors of the two-dimensional trochoidal fluid motion run parallel to the plane of the partition to considerable depths on either side, i.e., the trochoidal pattern is essentially orthogonal. With lesser viscosities and narrowing boundary layers, however, the horizontal vectors tend to follow the envelopes over the traveling waves, thus causing a ldquo;discontinuity” in the trochoidal pattern immediately adjacent to the partition, around the region of maximal amplitude. The notion that this latter “field distortion” might be the direct cause of the observed nonlinearity is supported by two previous findings: (1) the demodulation originates in the region of maximal displacement; and (2) the degree of demodulation varies with the stiffness gradient, i.e., it depends upon the sharpness of the amplitude maximum. [This work was supported by grants from the National Institutes of Health.]
Interdependence of the Cochlear Microphonics and Summating Potentials upon the Endocochlear Potential
Authors: Honrubia Vicente , Ward Paul H.
Published: November 2005

The resting potential of the scala media (EP) in the first turn of the guinea pig's cochlea was altered by the application of currents. The EP as well as the cochlear microphonics (CM) and the summating potential (SP) were enhanced when the source electrode was in scala media, whether the sink electrode was in the scala tympany or scala vestibuli. Using the scala media electrode as the sink for the current, caused decreases in these potentials. A linear relationship exists between the changes in the cochlear responses, CM, and SP (in decibels), and the changes in the EP. The SP increased or decreased by 1 dB for a 10% variation in the EP value. The corresponding change in the CM was one-third of the change in the SP. [This work was supported by the National Institute of Neurological Diseases and Blindness Research Grant.]
Prediction of the Volume of the Middle Ear Cavity from Cochlear Microphonic Measurements
Authors: McArdle Florence E. , Tonndorf Juergen
Published: November 2005

Previous experiments with a mechanical model of the eardrum and bulla cavity suggested that this system functions in certain respects like a Helmholtz resonator. Subsequent measurements in cats demonstrated an antiresonant peak in the cochlear microphonic sensitivity function that depended upon the dimensions of an experimental opening in the bulla. The present study attempts to use the Helmholtz resonator analogy to predict the volume of the cat's middle-ear cavity directly from its microphonic sensitivity curve. Resonant frequencies (fres) were determined empirically for a series of cats. Using the known dimensions of length le, and cross-sectional area S of an opening in the bulla, the volume V of the cavity was predicted from fres = c/2π(S/leV)12. For each animal, the prediction was checked by filling the spaces with liquid to determine their equivalent volume. [Work supported by grants from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]