bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Test Methods for Evaluating the Acoustics of Philharmonic Hall, New York
Authors: Schultz T. J.
Published: September 2005

A previous paper discussed some of the practical difficulties of measuring reverberation time in occupied halls. It showed that impulse excitation of the hall (pistol or cannon shots) may or may not give reverberation data in agreement with data obtained from steady-state excitation. “Tuning week” for Philharmonic Hall at Lincoln Center gave an opportunity for further comparison of various test methods and for the introduction of 2 new tools: a musical composition, “Catacoustical Measures,” by Boston composer, Daniel Pinkham, which was especially designed to test the acoustics of the hall; and a series of “instant people” to simulate a live audience without the usual disadvantages associated with an occupied hall. These and other tests are discussed, and a tape recording of the new musical test composition is played.
Sound-Amplification System for Philharmonic Hall, New York
Authors: Klepper David L.
Published: September 2005

The highly reverberant “music acoustics” design for Philharmonic Hall, Lincoln Center, New York, necessitated a carefully engineered speech-reinforcement system to assure satisfactory intelligibility for speech events. Two alternate and competitive “central” loudspeaker systems, having similar directional characteristics, were recommended, one employing direct-expansion radial high-frequency horns, and the other employing multicellular high-frequency horns. Also, alternate constructions were allowed for the low-frequency horns, the choice depending upon the visual requirements of the architect. The sound-reflecting panels in the hall interfere somewhat with the performance of the sound system at low frequencies. However, the system has met its design goals. Frequency-response and word-articulation tests are presented.
Measurements of the Sound Radiated by a Large Glass Plate
Authors: Greene David C.
Published: September 2005

A series of measurements was made of the sound radiated by a large glass plate which forms part of the wall of the air-wall research building of The Pennsylvania State University. For most of the measurements, the plate was excited to flexual vibrations by a point force applied at its center. Measurements included the frequency dependence of the radiated sound level, the directional characteristics of the radiated sound, and the noise-transmission properties of the compound glass walls of the building. Sound-radiation efficiencies of the glass plate are determined at several frequencies in the audio range. The experimental results are compared with those predicted by theory.
Theoretical and Experimental Results on Active Vibration Dampers
Authors: Rockwell Thomas H. , Lawther James M.
Published: September 2005

The use of active feedback elements to produce damping of multiresonant structures has been examined theoretically and experimentally. Agreement between theory and experiment for the particular case of a 48-in.-long uniform beam is quite good. Using commercially available components, a simultaneous reduction in resonant mobilities of all resonances lying below 10 kc has been demonstrated. Reductions were proportional to the mobility values prior to active damping applications, as much as 30 dB reduction having been obtained at some high Q modes. Similar behavior was observed from an actively damped aluminum shell under wideband point excitation. The limitations on the amount of damping possible are imposed by stability conditions for the feedback loop, which in turn depend primarily upon the transfer functions of the forcing and pick up components of this loop. The stability analysis for the particular components used in the beam experiment is presented.
Complex Zeros of a Triangular Approximation to the Glottal Wave
Authors: Dunn Hugh K. , Flanagan James L. , Gestrin Phyllis J.
Published: September 2005

The acoustic volume-velocity wave produced by the human vocal cords frequently approximates a triangular shape. A theoretical examination of the frequency-domain properties of the triangular wave is consequently of interest in speech analysis. The occurrence of spectral zeros in the glottal wave is of particular importance. When they fall proximate to formants, they can have appreciable influence upon the quality of voiced sounds. The present paper derives equations for the complex frequencies of the zeros. Arbitrary values of wave asymmetry (leg ratio) are treated. In a number of cases, for which the asymmetry can be expressed as a ratio of small whole numbers, exact solutions are obtained. In the less simple cases, solutions are approximated by using a digital computer. Detailed nomograms are presented for the complex-frequency loci of the zeros as a function of waveshape.
Study of Articulator Dynamics
Authors: Miller Joan E. , Pierce J. R. , Mathews M. V.
Published: September 2005

A program for pitch-synchronous formant tracking is described which operates semiautomatically on voiced portions of speech. Given the approximate pitch of a section of speech, the program locates the pitch periods, makes a spectral analysis of successive periods, locates 4 formants in each period by spectral fitting, and plots the formant trajectories and pitch for the sequence of periods. The program can also inverse filter to obtain the glottal waveform. The program is applied to study the dynamics of formant transitions as a function of speaking rate. The observed transitions are compared with the transitions which would be obtained from a simple mechanical-articulator model, in which the vocal-tract walls are represented by masses with damping driven by a suddenly applied muscular force.
Scheme for Utilizing Formant-Transition Cues in the Recognition of a Class of Prevocalic Consonants
Authors: Forgie James W. , Forgie Carma D.
Published: September 2005

A computer program has been developed which attempts to measure the formant motions associated with consonant-vowel transitions. Input to the computer is sampled, quantized spectral data. The program first locates a point ≈50 msec after the start of the vowel, and computes the frequency locations of the first 3 formants at that time which is considered to be the end of the transition. All future measurements are based on the formant locations determined at this time. The program then selects another instant of time at the beginning of the transition. The choice of this instant depends upon the type of preceding consonant, and varies in such a way as to allow fricative- and plosive-burst energy to have died away and the formants to have begun to appear. Several measurements are made on the 2 spectral patterns so selected. The measurements compare the energy in frequency bands just above and just below both F2 and F3 as picked at the end of the transition. The measurements indicate the direction and magnitude of the formant motions. Data collected to date for fricatives and plosives show consistent trends and useful separation in most cases.
Experimental Setup for Measuring the Amplitude and Phases of 60-kc Acoustic Pulses
Authors: Ewart Terry
Published: September 2005

Equipment has been developed and installed to measure the phase and amplitude of 2 independent acoustic pulses during a 1-msec overlapping sample. The equipment was designed for a frequency range of 5–100 kc, and has been used extensively at 600 kc. The dynamic range of the apparatus is greater than 40 dB, the dynamic range of the preamplifiers and amplifiers is 80 dB. The phase-angle accuracy is one electrical degree, and the amplitude error less than 1%. This equipment is part of a fixed installation in Dabob Bay. The transmission path used is 3800 ft between a fixed source and 4 hydrophones mounted on a self-leveling array. Hydrophone pairs are separated perpendicular to the transmission path, horizontally at 7, 13, and 20 ft, and vertically at 4 ft. The source and receiving array are at a depth of 200 ft, with a water depth of 400 ft. This arrangement enables phase and amplitude studies to be made either in direct transmission or in the reflection of surface and bottom signals. Results obtained with this installation are discussed elsewhere in the following paper (H5). [This work was supported by the Bureau of Naval Weapons.]
Experimental Observations of Phase and Amplitude Fluctuation in Direct Transmission in the Sea
Authors: Murphy S. R. , Ewart T. E. , Garrison G. R.
Published: September 2005

The results reported here are a set of observations taken to determine experimentally some of the effects on acoustic propagation of volume inhomogeneities in the sea. The experimental arrangement [described in the preceding paper (H4)] consists of a fixed source and a set of fixed receivers with variable horizontal spacing perpendicular to the transmission path. The transmission path is 3800 ft long and the maximum receiver separation is 20 ft. The electrical phase difference between the signals received at the 2 receivers is measured, as well as the amplitude of each signal. Observations of water temperature and currents along the transmission are also made. In the results to date, one can distinguish two cases: (1) A refractive multipath, separated from the direct return by about 100 μsec, causes phase-difference fluctuations greater than 360° and amplitude fluctuations exceeding 20 dB. (2) With the refractive path absent, the observed fluctuations are much smaller. The data in each case are explained on the basis of specific models of the sea medium. [This work was supported by the Bureau of Naval Weapons.]
Measurement of the Effect of Water Correlation
Authors: Potter David S. , McLennan Miles W.
Published: September 2005

An acoustic experiment was performed to study the effect of path separation on the difference of arrival time of short pulses between a pair of hydrophones. An array of 7 hydrophones was bottom-mounted in 1800 ft of water, and the projector was mounted on a ship held in a 3-point moor. Data were collected over a period of several days, and they exhibited the scatter common to acoustic measurements made in the ocean. Time averages of 11 000 data points, however, show clearly the effect of varying hydrophone separation from 5 to 300 ft. An estimate of the turbulent-cell size is made.
Travel-Time Fluctuations in Sound-Channel Propagation
Authors: Berman Alan , Sternberg David
Published: September 2005

A number of strings of 9 individual charges of TNT were successively detonated electrically at a depth corresponding to the sound-channel axis in the Atlantic Ocean. Signals from these charges were detected by receivers, at approximately the same depth, which were positioned at ranges of from 2–27 million ft. The experiment was designed to hold the source-receiver range constant to within ±5 ft at all ranges. The over-all timing accuracy was about 1 msec. Individual maxima and minima in the arrivals reproduced themselves from shot to shot. For each series of shots, the travel times of 12 discrete events other than the last sound-channel arrival were measured. Even at the extreme ranges, the travel-time fluctuations were less than 1 part in 105 per hour. The variation of travel-time fluctuation with range appears to follow theoretical predictions. [Columbia University, Hudson Laboratories Informal Documentation No. 8. This work was supported by the Office of Naval Research.]
Technique for Studying Continuously the Stability of Single-Path Acoustic Transmission in the Ocean
Authors: Robertson G. H.
Published: September 2005

The method of measurement depends on cross-correlating a local replica with pseudonoise signals received from a distant transmitter. Partial correlations with the energy coming over distinct paths, and, thus, occurring at different parts of the pseudonoise cycle, can be identified on a fascimile type of display chart. Furthermore, if both the replica and incoming signals are heterodyned with a stable oscillator before being cross-correlated, the carrier in the noiselike transmission can be displayed clearly on the charts, thus allowing its phase stability to be measured over long periods of time. Sample charts obtained by cross-correlating pseudonoise signals mixed with electrical noise are shown. The method has been applied to signals received simultaneously on 2 hydrophones. This allows the stability of single-path transmission to be studied. Some examples of results obtained by this technique in long-range acoustic transmission are displayed. [This work was supported by the Office of Naval Research.]
Vibration Modes Excited in Aircraft Structures by Jet Noise
Authors: Ford R. D.
Published: September 2005

If the normal mode approach is to be used for this problem, it is desirable to know the principal modes which will be excited so that some simplification may be assumed. To obtain a better idea of these modes, the response of conventional skin-stringer model structures to harmonic acoustic excitation has been measured in a laboratory. A number of those modes which occur in the first waveband have been identified by measuring the vectorial response at different parts of the structure relative to the exciting pressures. Examples of these modes are illustrated. Theoretically, the existence of the modes can be justified, and the total number and approximate form of each can be postulated. The analysis is, however, extremely complex, and, although attempts have been made to calculate the frequencies of vibration of some of the simpler modes, it seems doubtful whether all of the natural modes could be accurately predicted, even for a model structure. Similarities may, however, be drawn with much-simplified mathematical models, and a general idea of mode spacing within the waveband may be obtained. Some measured and theoretical results are given.
Vibrations of a Finite Row of Continuous Skin-Stringer Panels
Authors: Lin Y. K.
Published: September 2005

The determination of natural frequencies and normal modes is discussed for a row of skin-stringer panels which are continuous over supporting stringers, and which resembles more or less the fuselage construction for modern airplanes. The number of panels in the row is assumed finite. All the panels and the interior stringers are assumed identical. On the other hand, exterior stringers are allowed to be different from the interior ones. Formulation of the problem leads to a 4th-order symmetrical difference equation, common in problems of “repeated structures.” Relatively simple solution is obtained by assuming that each normal mode is periodic spatially. The implication of this assumption is discussed, and it is shown that the assumption is not restrictive for certain practical applications, in particular, in the study of panel response to jet noise. Two reduced cases are then discussed wherein the bending rigidity and torsional rigidity of the stringers are taken to be infinite, respectively, in each case. Analytical difficulties are greatly reduced in the special cases. It is found that, for the conventional airplane-panel construction, the natural frequencies may be computed with good accuracy by regarding the stringer-bending rigidity to be infinite. and closed-loop systems, and that the use of large amounts of normal-system operating data in condensed form combine to effect economies in time and accuracies in the transfer function (impulse functions or sinusoids are usually used). A brief recount of the theory is given with 3 suggestions for laboratory technique. Laboratory results are presented.
Boundary-Layer Pressure Fluctuation on 707 Prototype Airplane
Authors: Maestrello L.
Published: September 2005

In-flight experiments to measure turbulent boundary-layer pressure field along the fuselage of a large transport airplane at 10 000-, 20 000-, and 30 000-ft altitudes for flight speeds of from 0.4–0.67 Mach are reported. The data include power spectra and mean-square-pressure of the turbulent boundary layer, and power spectra of the boundary-layer-induced panel vibration. These data are compared with published information on the boundary-layer pressure fluctuation of a rigid wall.
Observations Relevant to the Mechanism of the Hartmann Whistle
Authors: Powell Alan , Smith T. J. B.
Published: September 2005

Phased sequences of spark-schlieren photographs have revealed several interesting aspects of the periodic-flow phenomena of the Hartmann whistle, supplementing quantitative acoustical and fluid-flow measurements. The periodic debouching of the fluid occurs in the form of a powerful vortex ring, the normal shockwave near the mouth of the resonant cavity oscillating impulsively through a large amplitude. A second normal shockwave periodically traverses the high-amplitude oscillatory “standing-wave” motion between the external normal shockwave and the end of the cavity. As a result, a periodic, impulsively starting, high-temperature air jet will be emitted from any small aperture at the end of the cavity. There is also evidence of feedback action of the sound field from the nozzle to cavity. It has been discovered that an unstable oscillatory condition also occurs over a limited range of subsonic jet speeds for certain locations of the cavity with respect to the nozzle; this range is greatly increased by the presence of a wake-producing trip or of a local reflecting surface. [This work was supported by the Office of Naval Research, under contract.]
Optimum Shading for a Conventional Acoustic Line Array of Receiving Elements Operating in a Combined-Noise Environment
Authors: Lubell A. H.
Published: September 2005

The noise environment is specified to consist of an isotropic component and a concentrated component. Allowing the concentrated component to appear at random position, with the exclusion of the main-beam region, limits the choice of shadings to the Tchebyscheff design. Selecting typical Tchebyscheff designs, computations are made of the amplitude and phase tolerances required to hold the cumulative probability of side lobes exceeding a specified acceptable value to an assigned percentage. It is found that the design side-lobe level exerts a significant influence on the required tolerances. Specifying an extremely low design side-lobe ratio results in loss of directive gain and the ability to discriminate against the isotropic component of the ambient noise. A procedure is given for selecting the most appropriate design value of the side-lobe ratio.
Ultrasonic Studies of Aqueous Solutions of Non-electrolytes
Authors: Andreae J. H. , McKellar J. F. , Edmonds P. D.
Published: September 2005

Absorption measurements were made in the ranges 1.5 to 230 Mc/sec and 0° to 45°C at various concentrations. Diethylamine solutions showed single-relaxation behavior, attributed to complex formation by hydrogen bonding. Absorption attributed to separation of phases near the lower critical solution temperature was shown in addition by triethylamine solutions. In methyl diethylamine solutions (L.C.S.T.=49°C), the transition from single- to double-relaxation behavior arising from these 2 mechanisms was observed. The absorption by n-amylamine solutions was compared with that by n-octylamine solutions, which form micelles. dμmax/dc decreased sharply at the critical micelle concentration. (μmax=maximum absorption per wavelength, c=concentration). Nine further solutes with hydrogen-bonding sites were studied. In each, the concentration for peak sound absorption (PSAC) was less than 0.5 MF, showing that more than one water molecule was associating with each solute molecular. Empirical relations between PSAC, relaxation frequency, and molecule weight were obtained. Quantitative interpretation of the measurement has been attempted in terms of models allowing for successive addition of water molecules to a complex and for breakdown of the water structure. Limiting values of bond energies, applicable to completely isothermal and adiabatic conditions, were calculated, but meaningful intermediate conditions could not be determined.
Ultrasonic Absorption in Water and Mercury between 130 and 450 Mc
Authors: Hunter J. L. , Storey W. T. , Lewis T. B.
Published: September 2005

Measurements of ultrasonic absorption have been made in water at frequencies of 270 and 450 Mc and in mercury at frequencies of 130 and 270 Mc. The measurements were made at a temperature of 22°C. Approximately 12 dB of attenuation were obtained at 450 Mc and approximately 24 dB at 270 Mc. The values obtained in water agree, within experimental error, with the accepted value of α/f2 based on measurements made at lower frequencies. The values of α/f2 for mercury are in close agreement with those obtained by G. R. Ringo, J. W. Fitzgerald, and B. G. Hurdle [Phys. Rev. 72, 87 (1947)]. However, if we follow J. Jarzynski's [J. Acoust. Soc. Am. 34, 714 (1962)] assumption of structural relaxation, ratios of volume to shear viscosity of 0.50 at 130 Mc and only 0.17 at 270 Mc are obtained. For this same ratio, Jarzynski has obtained a value of 1.3 at 68 and 92 Mc. [Supported in part by the Office of Naval Research.]
Normal-Mode Treatment of Low-Frequency Acoustic Propagation in the Deep Ocean
Authors: Carter A. H. , Williams A. O.
Published: September 2005

Frequencies of interest here are tens to hundreds of cycles/sec—too high for completely numerical wave analysis, too low for confident use of ray treatment. The standard sound-velocity structure is assumed. and, arbitrarily, a velocity contrast of 1.05 at the bottom; the exact value is unimportant in many applications of theory. Regardless of the detailed velocity structure, the normal modes are classifiable in analogy to the standard R′R′, R′SR, RR rays. The WKB method handles well all but the lowest modes; these, affecting mainly SOFAR propagation, can be computed otherwise. For cw transmission, such phenomena as shadow zones, SOFAR, and convergence zones are predicted from the general velocity profile. Convergence zones result from a stationary-phase property common to most R′SR modes, but not to RR or the higher R′R′ ones. This can be established quite generally; numerical calculations with bilinear and trilinear velocity profiles then give more-detailed information and agree with field data. Calculating intensities in convergence zones follows the theory of imperfect diffraction gratings. Disappearance of convergence at very low frequencies is analogous to the uselessness of an imperfect grating with very few rulings. [A. H. C. supported by a fellowship from Bell Telephone Laboratories, Inc., to study at Brown University, where this work was performed; A. O. W., Jr., supported in part by the Office of Naval Research.]
Spectrum Levels and Distribution Functions of Ambient Noise under Arctic Sea Ice
Authors: Milne A. R. , Ganton J. H.
Published: September 2005

Tensile cracks at the surface of shore-fast polar-pack ice appeared to be major sources for underwater, ambient noise measurements made in April 1961 in the Canadian Archipelago. Maximum cracking activity began with radiation cooling, and took place mainly within the uppermost few inches of ice of 8 to 25 ft in thickness. Noise from hummocky ice was from small-scale fractures, whereas surface cracks in frozen leads occurred less frequently and were of larger lineal extent. The resultant rms-spectrum levels accordingly differed with changes in the thermal-radiation balance, and were also a function of the propagation of sound within the water layer. Significantly non-Gaussian amplitude distributions were measured, the departure from Gaussian being dependent on both the frequency band and the areal distribution of ice activity.
Ambient Sea-Noise Directivity
Authors: Forster Carle A.
Published: September 2005

This paper reports on the Fixed Acoustic Buoy (FAB), an acoustic noise-measuring system, which was installed on the ocean floor on 10 December 1960 in 2300 fathoms of water. The system utilized a vertical array of 21 hydrophones which could be electrically steered to any one of 13 vertical angles ranging from 0° (horizontal) to 90° (vertical upwards). The array was omnidirectional in azimuth. The objective of the FAB program was to investigate ambient sea noise over the spectrum from about 800 to 5000 cps at deep depths to determine noise-spectra levels as a function of sea state and angle of arrival in the vertical plane. The system was operated for a period of 11 months, during which data were recorded on magnetic tape for processing with narrow-band filters, A-to-D converter, IBM 7090 computer, and automatic readout equipment. Spectrum levels, directivity characteristics, and statistical characteristics were determined. A mathematical model for the surface-generated sea noise was constructed from the resulting data, and is reported on in the paper “Deep Ocean-Noise Model Determined by a Deep-Line Array” by Jack G. Watson (L5).
Deep Ocean-Noise Model Determined by a Deep-Line Array
Authors: Watson Jack G.
Published: September 2005

Using the noise data collected by the Fixed Acoustic Buoy (FAB), a mathematical model for the directivity of the noise was established. This was accompanied by altering the model until satisfactory agreement was obtained between the model and the measured data. The method used was to hypothesize the directional characteristics of the noise sources and determine the intensity pattern about the deep-line array. This was done using the hypothesis and an artificial vertical-line array steerable to any position. The beam-width of this array was a small dθ and sidelobes were non-existent. The calculated intensity pattern about a deep-line array was multiplied by the beam-pattern response of the FAB and the results integrated to furnish noise power out of the array. This was done as a function of steer angle for the deep-line array. The hypothesized directional characteristics of the noise sources were modified, until the calculated noise power out of the array as a function of steer angle agreed with the noise out of the FAB as a function of steer angle.
Effect of Boundaries on the Spatial Correlation of Noise Fields
Authors: Cron Benjamin F. , Sherman Charles H.
Published: September 2005

The effect of boundaries on the spatial correlation of noise fields is investigated. Two types of noise fields are considered: namely, a volume-noise model and a surface-noise model. The volume-noise model consists of a field of plane waves, equally likely in all directions. This homogeneous isotropic noise field is modified by the addition of a perfectly reflecting soft surface. The addition of the boundary results in a nonisotropic nonhomogeneous wave field. Equations for the spatial correlation are obtained, and curves are drawn showing the dependence of spatial correlation on the orientation of the point receivers and the distance from the soft surface. This analysis is repeated for the modification of a hard bottom, and the spatial correlation results are similar to that found for the soft-surface case. The second noise model consists of directional noise sources on the surface of the ocean. A hard bottom is considered, and it is assumed that the water is deep. Equations for the spatial correlation are obtained as a function of various parameters. Curves are drawn, and the spatial correlation is shown to depend on the directionality of the noise sources, the orientation of the point receivers, and the distance of the receivers from the bottom.
Real-Time Spectral Analysis of Low-Frequency Seismic Noise
Authors: McLevey J. D.
Published: September 2005

The spectral-energy distribution of low-frequency ambient noise in the sea has been previously measured and described by Walkinshaw [J. Acoust. Soc. Am. 32, 1497 (1960)] and others. The presence of various energy bands in the low-frequency spectrum of ocean noise has not been fully accounted for. Investigations were therefore made of seismic spectra on land to see if the energy banding was also evident. Geophones sensitive to the vertical component of the ground velocity were planted at various locations in New Jersey and Massachusetts, and their output signals were subjected to real-time spectrum analysis. No sharp energy bands were found at these locations, although relatively broad ones were seen at frequencies below 30 cps. A correlation between tidal height and low-frequency spectral energy distribution was noted at Sandy Hook, N. J. Vertical ground velocities in a 1-cps band were measured at the various locations. Rms levels varied frown 0.3×10−6 in./sec to 72.0×10−6 in./sec. The lowest level observed was in reasonable agreement with measurements in England by Wilson [Proc. Roy. Soc. (London) A217, 176–188 (1953)]. [This work was supported by the Bureau of Ships.]
Measurements of High-Frequency Pulse Attenuation and Bottom Backscattering in the Sea
Authors: McLeroy E. G.
Published: September 2005

Increasing use of higher-frequency underwater acoustic devices has prompted the in situ measurement of sea-water attenuation and sea-bottom backscattering of acoustic pulses in the frequency range 150 to 2100 kc. Although the measured attenuation coefficients usually agreed closely with the viscous-relaxation theory of absorption, marked increases in attenuation were noticed on several occasions. The backscattered signal amplitude was found to depend on bottom type and frequency, as well as on grazing angle and pulse length. The normal “reflection” coefficient is closely inversely proportional to the frequency, but can be interpreted as a scattering coefficient, if the scattered level is assumed proportional to the beam cross section, which in these measurements was itself inversely proportional to the frequency. Theory indicates that the backscattering coefficient is a function of surface roughness of the bottom, rather than of particle size for the wavelengths used here. However, surface roughness is dependent on particle size.
Wave Theory for Surface and Bottom Acoustic Reverberation
Authors: Toulis W. J.
Published: September 2005

The scattering of sound by the ocean surface or bottom is generally assumed to be proportional to sinnφ, where φ is the grazing angle at incidence and n may have a value from zero to two, with the latter corresponding to Lambert's law. Wave theory indicates that the scattering form is not as simple, and requires a space-directivity factor to account for the scattering from an insonified strip on a surface. For short pulses and at small grazing angles for long pulses, plane-wave theory is satisfactory. With other situations, the space-directivity factors are similar, but require different arguments. At intermediate angles, the curvature of the wavefront for long pulses and the scattering due to random specular reflections dominate the form of the directivity space factors. Consequently, if an emperical formulation must be retained to define a scattering coefficient, and if the equivalent width of the strip is that on the wavefront, then: n=0 is satisfactory at small grazing angles; n=2 is possibly satisfactory at some intermediate angles with long pulses; while, at the other extreme, n=−4 is applicable to intermediate angles with very short pulses or to small grazing angles with long pulses.
Working Hypothesis Relating to Helicopter Noise
Authors: West H. L.
Published: September 2005

This paper presents a working hypothesis for the treatment of helicopter noise. particularly from the sonar-interference viewpoint. It applies to a helicopter hovering in free space and above a water interface. Equations for computing the values of noise transmitted into the water and to various depths beneath the water surface are derived. Slides are used to illustrate various aspects of the hypothesis and to compare predicted results with actual data.
Fatigue as an Indicator of Pitch Channels
Authors: Small Arnold M. , Yelen R. Delphine
Published: September 2005

To further test the hypothesis that periodicity pitch is mediated, at least peripherally. by neural fibers which ordinarily respond to high frequencies, the phenomenon of residual masking or short-duration auditory fatigue was employed. Pure tones of 150 and 2200 cps, and a 2200-cps signal pulsed 150 times per second all at several levels, were used in all combinations as fatigue and test stimuli. The results support the findings of Small and Campbell with respect to the masking of periodicity pitch. Perhaps the most interesting observation was that, if a pulse signal at moderate levels was used as the fatiguer, thresholds were shifted significantly for the 2000-cps and pulsed signals, but were not shifted for the 150-cps signal, even though pitch of the fatiguer corresponded to this frequency. Only when the level of the fatiguer was raised to 100 dB SPL, a level which almost certainly will give rise to nonlinear effects—i.e.—enveloped detection. did significant threshold shifts appear at the frequency of the pulse rate, 150 cps.
Binaural Interaction in the Superior-Olivary Complex of Cat
Authors: Moushegian George , Rupert Allen
Published: September 2005

Single units in the superior-olivary complex of anesthetized cats were isolated with tungsten microelectrodes, and their responses to tones and clicks observed. One of the nuclear aggregates of this complex—namely, the medial superior olivary nucleus—contains units that are sensitive to binaurally presented clicks. A click delivered to one ear produces a response which may be inhibited by a click to the opposite ear. This inhibition is effective for time differences between the binaurally presented clicks of as little as 8 μsec. Many units of this nucleus exhibit spontaneous activity and may be driven by tones. Although a tone excites a unit when it is delivered to one ear, the same tone to the opposite ear inhibits it. Units isolated and studied from other nuclei of the superior-olivary complex, e.g., trapezoid nucleus and lateral superior-olivary nucleus show only monaural responses. Finally, the configuration of the slow-wave response evoked by a click stimulus varies considerably in the various nuclei of this complex, and may be used to predict reliably the locus of the electrode tip during the experiment.
Binaural Interaction of a Click with a Click Pair
Authors: Harris Gerald G. , Flanagan James L. , Watson Bernard J.
Published: September 2005

In the binaural interaction of a single click and a click pair, it has been found necessary to have a minimum time interval of a few msec between the members of the pair in order to hear 2 sound images. This is often explained by invoking a neural refractory time. On the other hand, multiple-image lateralizations with single clicks suggest neural volleys with time separations as little as 1 msec. An experiment was performed which combined the investigation of both these phenomena. Two clicks with time separations 0.5, 1, 2, 4, 8 msec were presented to one ear, and a single click of controllable interaural time was presented to the other. Two polarity patterns (rarefaction—rarefaction vs rarefaction, and rarefaction—condensation vs rarefaction) were used at pattern rates of 2. 10, 50/sec. Condenser microphones were used as earphones. Four subjects were asked to adjust interaural time to center all discernable sound images. Two lateralizations corresponding to temporal alignment with both of the clicks in the pair were found with 8-msec and sometimes with 4-msec separation. With 1-msec separation for the pair, subjects heard only one image, but temporally aligned at both clicks. With 2-msec separation, however, no significant lateralizations were made at the second click. Analog basilar membrane displacements corresponding to the stimuli were examined. These results are discussed, together with their implications for a theory of binaural hearing.
Decision-Theoretic Speaker Recognizer
Authors: Smith J. E. Keith
Published: September 2005

A real-time computer system for identifying persons on the basis of their speech is presented. The most novel feature of the system is the facility for recognizing a speech sample as not having been produced by any of the speakers previously identified. The system can be broken into 2 distinct subsystems. In the initial phase, a large sample of speech is read into the computer through a set of 35 bandpass filters. These sets of 35 element vectors are then analyzed, using multidimensional analysis of variance. This yields a small set of linear transformations of the original filter measurements having the property that their variation between speakers is as large as possible relative to their variation within the speech of any one speaker. The coefficients defining these combinations and their variances over speakers are the input to the 2nd phase of the process. In the 2nd phase, as speech is read in it is transformed and compared with data already read, if any. The likelihood of the data having come from each of the previously identified speakers is computed. In addition, the likelihood of the data having come from the same population of speakers, but not any of them. is computed. Based on these likelihoods and on an evaluation of the possible errors, a maximum expected value decision is reached. The operator then either confirms or corrects the decision, and the new data is added to that received earlier. Thus, the available data for making a decision can be continually improved. Evaluation of the decisions depends on the error costs previously mentioned. and confusion matrices for some of the more interesting cost functions are presented.
Vibration of Indirectly Excited Structures
Authors: Lyon Richard H. , Maidanik Gideon , Coles James J.
Published: September 2005

When a large complex structure is randomly excited by its aeroacoustic environment, there are frequently smaller sub-structures which receive their excitation by energy transfer through the junctions with the parent structure. The estimation of their vibration amplitudes is discussed, using the statistical-energy method which has been previously described and applied to the sound field-structure interaction problem [R. H. Lyon and G. Maidanik, J. Acoust. Soc. Am. 34. 623 (1962)]. Detailed estimates of the vibration of a beam which is cantilevered from a randomly excited plate have been made. These estimates were then compared with experimental observations on the vibrations of a model compound structure. The agreement between the estimates and observations was encouraging. The method is believed to be applicable to the estimation of the vibration of subpanels in electronic packages and instrument-supporting trusses in aerospace vehicles. [This work was supported by the Aeronautical Systems Division.]
Spatial Correlation in Acoustic-Structural Coupling
Authors: Bozich Daniel J.
Published: September 2005

The response characteristics of beams and flat rectangular panels excited by specific acoustic fields were analyzed mathematically. The acoustic-structural coupling coefficients developed by A. Powell and others for general systems were modified and extended to beams and flat rectangular panels with free, simply supported, and clamped boundary conditions. A variable, exponentially decaying spatial-correlation distribution, which allows an analytical approximation of expected near-field characteristics, is an added feature. Numerical results of the acoustic-structural coupling-coefficient frequency spectrum indicate a marked sensitivity to changes in the spatial correlation, a measure of the force-distribution coherence over the structural area. The panel mode shapes progressively lose their wavelength selectivity as the spatial correlation decreases and, hence, respond at all frequencies. An IBM 7090 FORTRAN computer program was written to perform the numerical calculations for single beams and panels with specified boundary conditions and particular plane-wave acoustic fields. An analytical method extending the analysis to an array of beams and/or panels is developed. An approximation for irregular wavefronts is also treated along with the problem of a plane wave traveling at an angle θ with respect to a panel edge and angle φ with respect to the panel plane.
Sound Radiation in Terms of Surface Integrals Involving the “Incompressible” Pressure
Authors: Powell Alan
Published: September 2005

The inhomogeneous wave equation can be written ∇2p−(1/c2) ∂2p/∂t2 = Δ2p−(1/c2) ∂2p/∂t2, with the understanding that the right-hand side is prescribed within a specified limited region and is zero elsewhere. The retention of both terms and a double application of divergence theorem to the formal solutions yields the classic pair of surface integrals, involving knowledge of p and ∇p on the surface only. Successive long-wavelength approximations are made to yield equivalent point monopole, dipole, quadrupole, and higher-order sources (by use of a Taylor expansion). It is shown how the pressures of a corresponding incompressible flow can be used for this approximation; hence, the formulation ∇2p−(1/c2) ∂2p/∂t2≃∇2pInc−(1/c2) ∂2pInc/∂t2 can be inferred. It is especially pertinent to quadrupole radiation from a free fluid flow. [This work received the partial support of the Office of Naval Research, under contract.]
Dispersion of Axially Symmetric Waves in Composite, Elastic Rods
Authors: McNiven H. D. , Shah A. H. , Sackman J. L.
Published: September 2005

The dispersive characteristics of axially symmetric waves in infinitely long, composite, elastic rods are explored. The characteristic equation relating frequency to propagation constant is derived for 2-material rods in which a solid, circular core of one material is bounded by and bonded to a circular casing of a second material of different physical properties. The equation is explored numerically using a digital computer for 2 rods displaying different geometric and physical properties. The lowest few branches of frequency spectra are developed from the roots of the equation, and the dispersive properties of the individual modes shown are discussed. The lowest few cutoff frequencies are established for each of the 2 rods, and the radial displacement distributions for each frequency is established. Finally, conditions are established for the existence of equivoluminal modes similar to those shown to exist in plates by Lamé and Lamb, in solid rods by Onoe, McNiven, and Mindlin, and in hollow cylinders by Gazis.
Resonant Transducers in Liquid-Filled Cylinders
Authors: Sims Claude C. , Henriquez T. A.
Published: September 2005

Cavity-loaded piston transducers can be made to work at high hydrostatic pressure by operating the resonator in a liquid-filled cylinder. The measured and theoretical performance of transducers of this type with various fluids is given. This paper is an extension of the work reported in The Journal of the Acoustical Society of America, September 1962.
Echo Returns as a Function of the Mass and Elasticity of a Target
Authors: Watson J. H.
Published: September 2005

Three classical targets were ensonified by underwater explosives; (1) a buoyant 36-in-diam hollow sphere with a thin wall; (2) a 17-in.-diam solid iron sphere; and (3) an almost neutrally buoyant 17-in.-diam hollow sphere with a thick wall. The echos from the air-filled thin-walled hollow sphere and the solid sphere were as expected. The thin-walled sphere returned a short time pulse whose polarity was negative (i.e., inverted) in the frequency range of interest. The solid iron sphere returned a positive pulse. The study was undertaken to determine the return from the thick-walled hollow sphere. Since a compliant thin-walled sphere returns a negative pulse and a solid stiff sphere returns a positive pulse, the return from a target with a construction in between was expected to be complex with no definable polarity in a broad-frequency spectrum whose upper cutoff is limited. The results show that the return is made up of several frequencies corresponding to at least 2 modes of vibration. The initial polarity is obscured in the noise.
Methods for Evaluating the Loss Factor of Damping Materials and Systems
Authors: Schloss F.
Published: September 2005

A direct evaluation of the loss factor of damping materials and systems may be made continuously as a function of frequency by measuring the phase angle of one transfer impedance, i.e., the phase angle between the force at a blocked end and the motion at the driven end. The accuracy is greatest with large damping, thereby complementing other methods. Measurements are presented for several materials and structures over the frequency range 10–1000 cps.
Noise Levels of Turbojet- and Turbofan-Powered Aircraft
Authors: Marsh Alan H. , McPike A. L.
Published: September 2005

Results of ground runup, flyover, and interior noise-level surveys of DC-8's equipped with suppressed JT3C-6 turbojet and unsuppressed JT3D-1 turbofan engines are shown. At takeoff power during ground runup, the turbofan engine, producing 3500 pounds more thrust than the turbojet engine, generated a total acoustic power level which was about 2 dB lower. Flyover noise measurements showed that the over-all sound-pressure levels were about 5 dB lower with the turbofan installation; the perceived noise levels were about 5 PNdB lower. These differences were due to the change in exhaust-nozzle configuration and jet-exhaust velocity. Cabin-noise levels at cruise conditions were about the same in both types of airplanes, due to the dominance of boundary-layer noise.
Acoustic Testing over Water
Authors: Sawhill R. H.
Published: September 2005

A 15-min film showing a method for ensuring optimum atmospheric and airplane conditions during flyby noise tests on jet aircraft. Introduction by R. H. Sawhill.
Comparison of Acoustical and Telephonic Speech-Signal Instantaneous Amplitude-Density Functions
Authors: Wathen-Dunn Weiant
Published: September 2005

Recordings of speech material, read in an anechoic chamber and picked up simultaneously both by a telephone handset and by a high-quality condenser microphone, were made with a system which preserves waveform. Both signals were kept polarized. The signal from the condenser microphone is a good replica of the acoustical pressure wave, at least for the lower frequencies where the greater part of the speech energy lies; and, consequently, the statistics of the telephone signal can be compared with those of the high-quality signal to indicate the statistical transformation a given speech signal undergoes when transduced by a standard telephone transmitter. An analog-to-digital converter and a computer were used to get fine-grained histograms from which density and distribution functions of the instantaneous amplitudes of the 2 signals could be calculated, and these have been compared as to peak factor and asymmetry for a sufficiently large population, so that the statistics for English-speaking males begin to stabilize.
Logical Rules for a Multichannel Speech Analyzer
Authors: Toffler Jerome E. , Gerber Sanford E.
Published: September 2005

A detailed design plan is presented for the analyzer portion of a speech-compression system, suitable for use in conjunction with a synthesizer of the Swedish OVE type. The technique is based on the use of logical rules derived from known properties of speech. These rules are consistently applied to the outputs of a bank of 51 bandpass filters to generate frequency and amplitude parameters in the form of slowly varying control signals. The system has 2 outstanding advantages: (1) It is highly flexible, since the rules can be easily changed whenever new knowledge becomes available, (2) It provides a valuable research tool for generating new data in speech theory, as well as for verifying existing data and seeking logical conclusions. An immediate practical application is to use the analyzer as the input device to a digital data channel. Preliminary analysis indicates that high-quality speech can be transmitted with only 1200 bits/sec, approximately half the bit rate of a conventional-channel vocoder. Topics covered include logical rules and their derivations, typical working examples, a system block diagram, circuit descriptions, filter requirements, and analog-to-digital conversion.