bluuebunny/crossref_metadata_2025 huggingface dataset:
Engineering Design for Noise Control
Authors: Maling G. C. , Sawley R. J.
Published: October 2005

The common theme of the papers presented in this session was that noise control must be implemented early in the design stage of a product and that careful planning is required to achieve satisfactory results. Some of the papers were general in nature, considering the usefulness of acoustic analogies in solving difficult problems, or of a technique such as statistical energy analysis to assist in understanding energy flow in coupled systems. The remaining papers were more specific in their approach, describing the successful application of these and other techniques to the engineering design of equipment such as castings, hydraulic machinery, construction equipment, shuttle looms, and air-moving devices. In addition, the design of both dissipative and reactive mufflers was discussed. One paper described how simple measures of the sound level can be used to describe seemingly complex problems. This paper illustrated clearly what was implicit in all of the papers—that good engineering design for noise control requires a clear understanding of applied acoustics and an ability to determine the relative importance of the various parameters that must be considered in a noise-control problem.
A Comparison of Boehm's Design of the Flute with That of Rockstro
Authors: Worman W. E.
Published: October 2005

The flute commonly played today is basically the model developed by Theobald Boehm during the years 1846–1847. A 19th century rival was the Rockstro model designed in 1864 by Richard S. Rockstro. Boehm and Rockstro dealt with the problem of flute making in quite different ways, and both developed very playable flutes. The present paper contrasts their methods and also shows how their methods compare with the method an acoustician might use to design a flute today. Due to the double standard of pitch, low at A4 = 435 Hz and high at 452 Hz, a method of building a flute to altered pitch without redesigning it was needed. Both Boehm and Rockstro developed schemas which were practical graphical methods of altering the design to the new pitch. These schemas are compared with each other and with the basic design methods.
The Effects of On-Set Time Differences in Dichotic Stimulation
Authors: Malott J. P. , Koutstaal C. W.
Published: October 2005

Monosyllabic words that differed only in initial consonants were used for the study. The differentiating feature was the feature of place. Manner or voicing were never contrasting features. The word pairs were arranged so that they appeared truly dichotically and leading and lagging by 5, 10, 15, and 20 msec. The accuracy of timing was ±1 msec. In the dichotic condition no significant ear difference was obtained. In the LEAD+LAG conditions the ear in which the stimulus had the lead received better scores. A post hoc analysis indicated that there was a correlation of 0.73 between the word of the pair, which was perceived more frequently, and the intensity and duration of the initial consonant. That is to say, when the time and intensity of the initial consonant of a word pair are greater, it is likely to be perceived more frequently than the consonant with smaller time and intensity values.
Measurement of Directionality and Distribution in an Acoustic Field
Authors: Bartram James F.
Published: October 2005

The fact has been demonstrated previously, and is briefly reviewed here, that characteristic sounds occurring in an acoustic field can be identified by means of their first-order probability distributions. In the present paper, it is shown that still more identifying information becomes available when the directionality of the acoustic field is also measured, thus adding space processing to the previous time processing. The concept of directionality is defined quantitatively in this paper, signal processing principles, which have been derived for estimating the directionality statistic, are described, making use of the multimode hydrophone [S. L. Ehrlich and P. D. Frelich, U. S. Pat. 3,290,646, 1966 filed 6 (Apr. 1960)], and the results of playing real acoustic field data into a computer simulation of this directionality detector, together with the previously derived distribution detector, are presented. Detected in the acoustic data are a monochromatic plane wave, a rather directional transient, and nonisotropic Gaussian ambient noise.
Numerical Evaluation of Rice's Integral Representation of the Probability Density Function for Poisson Impulsive Noise
Authors: Richter W. J. , Smits T. I.
Published: October 2005

Numerical evaluation of Rice's triple integral representation of the probability density function for Poisson impulsive noise has been accomplished for the intermediate pulse repetition rate case with several meaningful waveforms. The technique used was also applied to the high and low repetition rate cases, and the results were compared with previous results. Agreement was excellent. The technique consists of obtaining the probability density function or cumulative distribution function from the numerically computed characteristic function. This was done by first subtracting a constant from the characteristic function and integrating the constant analytically and the remainder numerically. The integration is carried out separately in different regions, depending on the shape of the curve in a particular region, after which the individual integrals are added. This process overcomes some of the difficulties encountered in the past in evaluating Rice's integral.
Sources of Noise in Axial Flow Fans
Authors: Mugridge B. D. , Morfey C. L.
Published: October 2005

Experiments and theory relating to fan noise sources are reviewed with emphasis on axial flow machines. At supersonic rotor speeds, the steady shock pattern attached to a rotor is an efficient radiator of sound. In most practical cases of subsonic rotor operation, however, direct radiation from the rotor-locked pressure field is negligible compared with the indirect radiation, or scattering, caused by circumferential distortions in the steady flow field surrounding the rotor. Random timewise modulation of the distortion changes the scattered spectrum from discrete to continuous, with a gradual progression from narrow-band tones to broad-band noise as the modulation bandwidth is increased. Similar scattering occurs when a non-uniform unsteady flow impinges on stator vanes, but here the radiated frequency is that of the impinging flow. Finally, for blades operating in flows free from circumferential distortions, self-generated turbulence becomes an important source of noise. The paper describes the physical mechanisms involved in each of these processes, including the generating of unsteady lift by turbulence. Order-of-magnitude sound power estimates are compared, where possible, with experiment.
An Improved Broad-Band Low-Frequency Underwater Modular Sound Source
Authors: Donovan J. E.
Published: October 2005

An improved modular moving-coil underwater sound transducer has been added to the USRD-NRL stock of standard transducers. The single element is essentially omnidirectional throughout the frequency range 10 Hz to 4 kHz; its mean transmitting current response is 160 dB re 1 μPa in the frequency range 30 Hz to 3 kHz. Both single units and triple arrays have been used successfully at sea. The closed compensation system available with some housings can be used to depths as great as 305 m (1000 ft) without additional pressure compensation.
Low-Noise Broad-Band Hydrophone
Authors: Henriquez T. A.
Published: October 2005

A pressure-sensitive noise-measuring hydrophone for the frequency range 10 Hz to 60 kHz that is stable at hydrostatic pressures to 6.9 MPa and temperature from 5° to 35°C has been developed at the Underwater Sound Reference Division, Naval Research Laboratory. The pressure-sensing element is of a novel design that offers high sensitivity, relatively small size, and smooth response. The electrical output impedance of the sensitive element is sufficiently low that low-noise voltage preamplifiers may be used to give an end-of-cable self-noise that is lower than that equivalent to sea state zero.
Bifrequency Loudness Summation for Pure Tones
Authors: De l'Aune William , Elfner Lloyd , Franzen Ove
Published: October 2005

A signal detection rating paradigm was employed to assess the detectability of individual and simultaneous presentations of two threshold auditory stimuli. Tone A (710 Hz) and tone B (500 Hz) were presented in three possible configurations—tone A, tone B, or tone A plus tone B—and the subject was required to rate his certainty as to whether the auditory stimulus occurred in a visually delineated “first interval” or “second interval.” From these ratings receiver operating characteristic curves and detectability estimates were determined for each of the different stimulus configurations when the subject knew in advance which tone or combination was to be presented and when the stimulus configurations were randomly alternated. In the random presentations, summation appeared to occur in both the monaural and the binaural conditions. When the subject knew in advance which stimulus configuration was to occur, the detectabilities of the individual tones were facilitated and summation was not apparent. These results agree with the findings of Franzen, Markowitz, and Swets (1970) utilizing vibrotactile stimulation.
Coupler Calibration of Microphones at Abnormal Ambient Pressure
Authors: DiMattia A. L. , Fisk R. W.
Published: October 2005

Microphones, to be used at altitude or in the increased pressures of underwater diving, pose the need for calibration at abnormal ambient pressures. Free-field measurements are usually not feasible, since variable ambient pressure anechoic chambers are not normally available. Pressure calibration in a coupler can be performed conveniently in a small inexpensive variable-pressure tank. This paper describes such a system, utilizing a commercially available coupler with minor modifications. Various corrections, occasioned by the abnormal static pressures, are discussed.
Response of Deep-Ocean Sound Channels to Wide-Band Pulses
Authors: Porter Robert P.
Published: October 2005

Wide-band signals received at long range in a SOFAR channel are distorted and dispersed during transmission. In addition to temporal dispersion explained by ray theory, there is frequency structure that is best explained by mode theory. Explicit prediction of the time-frequency structure of the received waveform given the projected pressure pulse can be made for arbitrary sound-velocity profiles by using the WKB approximation. The response of deep-ocean sound channels to various pressure pulses including an impulse, an impulse pair, and a linear FM pulse has been investigated. It is shown that observed phenomena such as combined ray and mode propagation, and bubble pulse modulation of the spectrum, can be predicted by WKB mode theory.
Beam Displacements for Media with Monotonic Sound-Speed Profiles with Discontinuous and with Continuous First Derivatives
Authors: Murphy E. , Thompson M. , Olesen O. V.
Published: October 2005

A ray representation for some of the diffraction phenomena encountered in underwater sound propagation in media with nonmonotonic sound-speed profiles [E. Murphy, J. Davis, and J. Doutt, J. Acoust. Soc. Amer. 50, 101 (A) (1971)] leads to beam displacements that remove the sensitivity or pathology of ordinary ray analysis when first derivatives of the sound-speed profile are discontinuous. In this modified ray theory, diffraction phenomena take the form of frequency-dependent beam displacements for rays with vertexes near the sound-speed profile extremum. Unlike ordinary ray theory results, modified range-versus-source-angle curves are well-behaved (continuous derivatives). The analysis has been extended to monotonic profiles with discontinuous and continuous derivatives; the analysis is somewhat more complicated than for the nonmonotonic extremum examples. Here also, beam displacements remove some of the pathology in the range-versus-source-angle curves. For the smooth monotonic profiles there are displacements if the curvature of the profile is too great. For the profile with discontinuous gradients there can be oscillations in the range-versus-source-angle curves.
Regression Analysis for Averaged Decay Laws for Energy versus Range in Some Winter and Summer Mediterranean Shallow Water Sound Transmission Data
Authors: Murphy E. , Olesen O. V. , Hastrup O.
Published: October 2005

Shallow water broad-band sound transmission data from a SACLANT Centre Mediterranean program have been analyzed, in 20 frequency bands, for evidence for various decay laws for the variation of sound energy with range. The data, averaged over depth, show surprisingly smooth, reproducible variations with range. For example, exponents in power-law regression analysis of winter data (with volume attenuation removed) are close to the often-predicted 32 power with standard deviations often less than 1 dB. There is evidence, at lower frequencies, depending on sea bottom, for a range interval with better propagation (perhaps cylindrical spreading) prior to the 32 power region [see D. E. Weston, J. Sound Vibration 18, 271–287 (1971)] with a more complicated frequency dependence than idealized arguments would suggest. The pertinent aspect of the appearance of various forms of range dependence is the range interval over which they occur; prediction schemes require these limits to arrive at absolute levels. Convincing evidence for various decay laws can be found; however, the range limits may show such complicated dependence on frequency, location, and season that no useful prediction scheme will follow from such a study.
Survey of Fully Digital FFT Hardware
Authors: Kiss Agoston Z.
Published: October 2005

Although numerous methods of calculating digital Fourier spectra are known today, they are all variations of the Danielson-Lanczos (symmetry of cosine functions) or of the Cooley-Tukey algorithm (successive decomposition of one-dimensional data strings into two-dimensional arrays). Hardware implementation of an FFT algorithm can result in higher spectrum generation speed, higher real-time bandwidth of data analysis, faster refresh rate of control functions in servo-applications, or in instruments of limited flexibility geared for special applications. The cost and performance characteristics of any FFT hardware depend on how the major tasks are implemented: complex multiplication, phasor generation, data and phasor indexing, and memory management. For completeness, the less glamorous, but equally important, parts of signal analysis systems should also be considered: overall system control, data acquisition, user interface, retrieval of results, etc. Only in the context o{ the complete system can the FFT hardware be fully evaluated.
Measurements of the Source Characteristics of Continuously Radiating Sound Sources Located near a Reflecting Boundary
Authors: Jaeger E. W.
Published: October 2005

Two important characteristics of continuously radiating sources are their broad-band source levels and the spectra of their sound. But reliable determination of these characteristics, for comparable results, requires anechoic surroundings. In practice, the sound source is often located in the vicinity of some reflecting boundary, e.g., large rotating machinery, transformers or vehicles on the ground, or large transducer arrays near the bottom of the sea. Such a geometry generally causes an incorrect source level measurement and introduces perturbations in the output frequency spectrum. Theoretical studies of these effects were done in conjunction with experimental work using loudspeakers radiating sinusoidal, narrow-band, and broad-band signals. Examples of the contaminating effects of boundary reflections on narrow-band-frequency analysis and broad-band sound levels are shown, and procedures for correcting the results are introduced. Certain advantageous source-microphone configurations are shown to introduce only a negligible distortion in the shape of the output spectrum.
Measurements of the Vertical Coherence of the Sound from a Near-Surface Source in the Sea and the Effect on the Gain of an Additive Vertical Array
Authors: Urick R. J.
Published: October 2005

Using a ship as a source of broad-band sound, measurements have been made of signal coherence between two deep hydrophones separated vertically by 500 ft. The results show that the phase coherence, in terms of the clipped correlation coefficient, falls off rapidly with horizontal range of the source. This decorrelation can be accounted for by multipath interference of bottom-surface reflections. The measured rate of falloff with range indicates a bottom loss between zero and 4 dB, increasing with frequency over the range 44–350 Hz. The effect of multipath interference is to degrade the signal-to-noise gain of an array. It is easily shown that when a conventional, linear, additive array is steered in one of the multipath directions, the gain is reduced by the ratio of the intensity of the sound coming from that direction to the intensity of the total sound field.
On Impact-Induced Industrial Noise
Authors: Shinaishin O. A.
Published: October 2005

Cases of impact-induced noise in factories are discussed and the measurement of sound levels as required by government standards is described. Presented also are the methods of diagnosis of the source of the impact forces and the identification of the transmission path to larger structures and of the sound energy levels from these radiating structures. Use of cross-correlation technique in identifying major noise contributors is discussed. Methods of reducing the noise by force alteration, interrupting the transmission, and reducing the radiation are presented with their analytical and practical limitations.
Ranke Revisited—a Simple Short-Wave Cochlear Model
Authors: Siebert W. M.
Published: October 2005

Between 1931 and 1950, Otto F. Ranke published an extended series of papers on cochlear dynamics. Much of this work concerned the only published mathematical attempt (prior to the recent paper by Lesser and Berkley) to avoid the long-wave assumption accepted for mathematical convenience by every other analyst (e.g., Zwislocki). Ranke's short-wave analysis is often referenced but has been otherwise largely ignored—perhaps partly because his more comprehensive papers are in German, use rather clumsy mathematical techniques, and are full of errors. This situation is regrettable since evidence of many kinds suggests that the short-wave assumption is more reasonable than the alternate in all but the more basal parts of the cochlea at all but very low frequencies. Moreover, in the modern form described in this paper, Ranke's analysis is extremely simple and transparent, yielding virtually closed-form expressions for the important cochlear quantities. It thus helps to explain many aspects of normal and abnormal cochlear behavior, as well as to account for such features as the extraordinary insensitivity of this behavior to the way in which the system is driven (e.g., Békésy's “paradoxical motion” and bone conduction).
A Model for Discharge Activity of Single Cochlear Nerve Fibers
Authors: Kim Duck On , Littlefield Warren M. , Molnar Charles E. , Pfeiffer Russell R.
Published: October 2005

A previously reported model for basilar-membrane motion [Kim et al., J. Acoust. Soc. Amer. 53 (1973)] generates many nonlinear phenomena observed in responses of single cochlear nerve fibers including combination tones (n+1)f1−nf2, where f1<f2, but does not account for other cochlear nerve nonlinear phenomena such as distortion components f2−f1, 2f1, f1+f2, and 2f2 which we have observed. Augmenting the basilar-membrane model by adding a noise waveform, rectification, and refractory effects produces a model with spike-discharge activity of single cochlear nerve fibers as the output and stapes displacement as the input. This model simulates (a) the linear response characteristics of spontaneously active cochlear nerve fibers at sufficiently low input levels (Littlefield et al., paper K5); (b) most of the nonlinear response characteristics of single cochlear nerve fibers at moderate-to-high input levels; (c) the smooth transition from the linear to the nonlinear response patterns; and (d) the observed lack of suppression of spontaneous activity by an externally applied tone. [This study was supported in part by grants from the U. S. Public Health Service.]
Easy Access to the Auditory Nerve in the Mongolian Gerbil
Authors: Sokolich W. G. , Smith R. L.
Published: October 2005

The anatomy of the Mongolian gerbil, Meriones unguiculatus, makes the internal auditory meatus easily accessible from a ventrolateral approach through the hypertrophied bulla. The pinna can be removed and the bulla opened with only superficial blood loss. The spiral modiolar artery and vein within the internal auditory meatus then become visible through the translucent medial wall of a tiny air cavity adjacent to be basal turn of the cochlea. The cavity is formed as the cross-sectional area of scala tympani is reduced by the dorsal course of the round-window membrane. A glass microelectrode can be advanced through an opening made in the translucent wall of the cavity for recording from single units. In preliminary experiments, units have been held for periods in excess of half an hour. Their responses to standard stimuli were similar to those reported for other mammals. Their responses to special very low frequency waveforms showed excitation during both motion and static displacement of the basilar membrane toward scala tympani and inhibition during motion and displacement toward scala vestibuli.
Representation of the Cochlea within the Inferior Colliculus of the Cat: Isofrequency Contours
Authors: Merzenich M. M. , Reid M.
Published: October 2005

The three-dimensional pattern of representation of the cochlea within the inferior colliculus has been investigated by determining the “best frequency” of 1846 neurons and 546 neuron clusters studied in 111 penetrations in 20 anesthetized cats. All penetrations were histologically reconstructed. These studies have revealed the following: (1) Auditory responses were encountered in the pericentral nucleus, and a crude tonotopic organization could be demonstrated within it. A reversal or discontinuity in the orderly progression of best frequencies was frequently seen across the boundary of the pericentral and central nucleus, with lowest frequencies encountered along their mutual border. (2) The central nucleus is exquisitely tonotopically organized. Functions relating represented cochlear position to penetration depth derived for penetrations all across the central nucleus were parallel. Reconstruction of rows of penetrations allowed for definition of isofrequency contours and reconstruction of cochlear place representation within the three dimensions of the central nucleus. (3) In penetrations perpendicular to defined isofrequency contours, represented cochlear place was seen to be a near-linear function of penetration depth. These experiments provide the framework for investigation of the functional significance of the highly ordered representation of the cochlear across the three dimensions of the central nucleus of the inferior colliculus. [Supported by NIH Grant NS10414-01.]
Real-Time Cross-Correlation Analysis of VIIIth Nerve Afferent Responses to Pseudorandom Binary White Noise
Authors: O'Leary D. P.
Published: October 2005

Filter characteristics of labyrinthine receptors can be determined on-line by cross-correlating VIIIth nerve spike trains with pseudorandom binary inputs. The technique was applied initially to the semicircular canal. Isolated labyrinths of the ray Rhinobatos productus, centered on a servocontrolled rotating table, were stimulated by pseudorandom binary sequences (PRBS) of angular acceleration: 100°/sec/sec clockwise and counterclockwise. Spike trains from lateral canal afferents were recorded and FM telemetered. A PDP-11 program generated the PRBS, relay-controlled the table acceleration direction, cross-correlated spike time outputs with PRBS inputs, and displayed 255 lags. All computations and display were done during interspike intervals to obtain real-time displays. The program included corrections for known non-ideal input transducer responses of the rotating table. Resulting cross-correlograms from this initial study were fitted, to a good approximation, with theoretical linear system impulse responses. The technique has certain advantages: (1) noise that is uncorrelated with the input does not affect the cross-correlogram and (2) nonlinear responses could be fit by a Wiener-Volterra functional expansion.
Noise Abatement Program
Authors: Miller Maurice H.
Published: October 2005

Baseline threshold audiometry is performed in the sound-isolated test area of the specially constructed mobile van. The van is moved to the power generation site where four men are tested simultaneously with a discrete-frequency automatic audiometer. The program functions as part of the Medical Department under supervision of the Medical Director. An audiological case history is obtained including information on past industrial and nonindustrial noise exposure and potentially significant medical conditions. Testing is performed by students majoring in audiology and speech pathology under the supervision of an audiologist certified by the American Speech and Hearing Association. The Con Ed audiological consultant reviews all audiometric records. Workers whose initial automatic tests are unsatisfactory are retested on the automatic audiometer with additional individual supervision. If the second test remains unsatisfactory, a manual audiometric test is performed. Criteria for referral of the worker for additional audiologic testing and otological examination will be presented. A variety of audiological procedures are performed both in the trailer and in the home office as well as at several comprehensive audiological facilities in the community with which Con Ed is affiliated. Statistical data will be presented showing the numbers of workers at different plants requiring audiometric retesting and complete audiological evaluations of various types.
Design Considerations for Power-Plant Pump Noise Reduction
Authors: Meyerson Norman L.
Published: October 2005

Reduction in vibration, pressure pulsations, and noise in power-plant centrifugal pumps can be achieved by increased impeller to volute tongue distances, improved geometric relationship between the tongue and impeller to minimize the shock of sudden fluid deceleration, control of impeller suction and discharge recirculation effects, and the elimination of hydraulic whirl set up in wearing ring annuli. In addition to the benefits of lower noise and vibration, less destruction of the surfaces of the impeller and volute by cavitation erosion is experienced.
Theory and Construction of Multivariate Gaussian Surfaces
Authors: Schuetz L. S. , Zipfel G. G.
Published: October 2005

Theories concerning the scattering of acoustic waves from random rough surfaces usually assume the surfaces to have a Gaussian height distribution. In order to compare experiment and theory, additional approximations in the theory are generally made. To determine the validity of these approximations, random rough surfaces with multivariate Gaussian distributions and specified directional spectrums have to be constructed. The necessary surfaces have been constructed. These surfaces are generated numerically using a random phase process, which is implemented via a fast Fourier transform. The construction of the surfaces is accomplished via a numerically controlled milling machine. A computer program package is available which generates the surfaces, numerically evaluates their statistics, and produces a paper tape to control a milling machine. The resulting surfaces are periodically continuable and can be used to produce tiles which can be combined to form a periodic mosaic, random over one tile.
Frequency Smearing of Forward-Scattered Sound from the Ocean Surface
Authors: Brown M. V. , Frisk G. V.
Published: October 2005

An open sea experiment was performed in which forward-scattered CW acoustic signals of 100, 180, 250, 400, and 500 Hz were measured with surface grazing angles in the range 35°–60°. At the same time, the vertical acceleration and orthogonal slopes of a typical patch of ocean surface were measured by a float system which was sensitive to gravity wave components with frequencies of up to about 1 Hz. The acoustic and ocean wave data were digitized and fast-Fourier-transformed with frequency resolutions of 0.01 and 0.02 Hz, respectively. The results of the experiment show good agreement with existing theoretical and experimental results [e.g., W. I. Roderick and B. F. Cron, J. Acoust. Soc. Amer. 48, 759–766 (1970)]. Theory predicts that sound which is forward-scattered by the ocean surface is phase modulated and the resulting power spectrum contains the discrete carrier frequency component with sidebands symmetrically positioned about the carrier. The sidebands are displaced from the carrier by multiples of the ocean wave spectrum. Note, however, that the energy may be asymmetrically disposed. Typical measured surface spectra have prominent peaks at 0.10 and 0.15 Hz. The measured acoustic spectra have prominent first-order sidebands close to these frequencies, although a slight asymmetry is evident. Less prominent second-order sidebands are also identifiable at the theoretically predicted frequencies. A comparison of measurements made at the various acoustic frequencies indicates that the location of the sidebands for this frequency range is independent of the acoustic frequency and that more energy is concentrated in the sidebands (relative to the carrier) as the acoustic frequency is increased.
Technical Considerations in the Design of a Precision Vibration Isolation System for Extremely Sensitive Bio-Engineering Experiments
Authors: Jhaveri Arun G.
Published: October 2005

A wide variety of diseases and fractures impair the ability of a patient's leg to bear weight, or nonuniform fractures in which the bone fails to knit properly, may weaken the leg for a considerable time. In order to heal properly, the leg must be protected from the forces exerted on it during walking after the cast is removed. This protection is frequently attempted by means of an ischial weight-bearing leg brace, a device which attaches to the injured leg, to transmit the forces generated during walking directly to the pelvis, thus bypassing the leg itself. It is of interest to investigate the distribution of the load between the brace and the patient's leg during a normal walking cycle. In this investigation the force carried by the leg and brace together and the force carried by the brace alone were measured separately. Forces carried by the leg and brace combined were determined by measuring the reaction forces on the floor. The proposed vibration-isolation system design was to isolate three floor-mounted transducers from disturbing building vibrations as well as vibrations in the floor below, while maintaining a high degree of rigidity in the isolated portion under dynamic loading from above.
Hair-Cell Transduction Mechanisms
Authors: Strelioff D. , Honrubia V.
Published: October 2005

The simple structure of the lateral-line organ of the toad Xenopus laevis makes it ideal for the study of sensory transduction in hair-cell systems. When mounted in a specially designed chamber, the end organ is readily accessible for precisely controlled mechanical, electrical, or chemical stimulation and the afferent fibers are available for recording neural activity. In addition, the chamber prevents movement of the preparation during stimulation consisting of either fluid flow past the cupula or fluid pressure variation. There was no response to constant or alternating pressure and only a transient response to a constant laminar flow of water. Sinusoidal movements of water past the cupula resulted in an increase in the mean firing rate and in a sinusoidal modulation of the spontaneous activity over a stimulus frequency range of 0.25 to 40 Hz. These results not only imply that a displacement of the cupula (and the hair-cell cilia) is the necessary stimulus for neural excitation but also suggest that the transduction process is dependent upon a continuously varying rather than constant displacement of the cilia.
Energy Losses from Large- and Small-Amplitude Underwater Gas Bubble Oscillations Compared
Authors: Epstein D.
Published: October 2005

It is an experimental fact that the period of oscillation of successive bubbles from an underwater explosion decreases. In a typical sequence, the bubble starts out as a large-amplitude nonlinear pulsation and ends up as a small-amplitude linear oscillation about the equilibrium radius. This effect is attributed to the bubble energy losses since in the incompressible no-loss treatment, successive pulsations have the same period. Thus losses cause a decrease in the period of large-amplitude pulsations; but, conversely, analysis reveals that when losses are taken into account, the small-amplitude oscillation period shows an increase relative to the lossless case. Hence it appears that the loss mechanism has an opposite effect on the bubble pulse period in the cases of nonlinear and linear bubble pulse oscillations, respectively.
Investigation of Critical-Angle Ultrasonic Phenomena by Bragg Diffraction of Laser Light
Authors: Powers J. P. , Brown R. D.
Published: October 2005

Detection and measurement of ultrasonic waves have been made above and below a liquid-liquid interface where ultrasound can undergo total internal reflection. Using laser-beam probes above and below the interface, the properties of the incident, reflected, and transmitted waves can be monitored as the angle of sound incidence is varied. In particular, as the angle of incidence exceeds the critical angle, scalar wave theory predicts that evanescent waves occur below the interface with shorter wavelengths than propagating waves and with exponentially decreasing amplitude in a direction away from the interface. Results of experimentation verify the critical-angle phenomena and, in particular, quantitatively produce the proper wavelength and decay of the evanescent waves, thereby verifying their existence.
Design and Preliminary Results of an Acoustic Parametric Source in Air
Authors: Shealy William P. , Eller Anthony I.
Published: October 2005

An acoustic parametric source for use in air was constructed and tested. The source uses a modified St. Clair resonator (a solid aluminum cylinder driven by a ceramic disk at one end) to generate the two high-frequency primary signals. The resonator is excited simultaneously in two resonant modes at frequencies from 20 to 40 kHz and radiates primary signals at levels that typically exceed 130 dB re 0.0002 dyn/cm2 in the nearfield. The two high-frequency primaries mix within the air to generate narrow-beam waves at the difference frequency, ranging typically from 3 to 10 kHz. This paper describes the radiation properties of the modified St. Clair resonator and presents measurements of the beam width and source level of the difference-frequency signal for a variety of primary wave combinations.
Decision Processes in Speech Discrimination as Revealed by Confidence Ratings
Authors: Glanzman David L. , Pisoni D. B.
Published: October 2005

Standard speech discrimination tests require the listener to make a decision about a given sequence of stimuli. For example, with the ABX test the listener is required to determine whether the third stimulus is most like the first or most like the second. This test along with several other forced-choice procedures has the excellent property that the E need not specify the dimension along which the stimuli differ, e.g., select the stimulus with the higher pitch. The typical measure of the listener's performance is the percentage of stimuli correctly discriminated. However, in recent attempts to examine the processes underlying the identification and discrimination of speech sounds, it has become apparent that the listener's task, i.e., providing just a single response, may not accurately reflect all the information that the listener may have available to him about the stimuli. For example, sometimes a listener may be quite certain that his response was correct whereas other times the listener may be very uncertain about his response. In this study we examined how listeners assign confidence ratings to discrimination judgments for a set of synthetic stop consonants and a set of steady-state vowels. The confidence ratings obtained with both ABX and 4IAX discrimination procedures carry additional information about the stimulus properties of consonants and vowels and provide some insight into the decision processes employed in the discrimination of these two classes of speech sounds.
Attentional Control in Speech Perception
Authors: Shiffrin R. M. , Pisoni D. B. , Castaneda-Mendez K.
Published: October 2005

Does the ability to identify speech stimuli entering an ear depend on the number of ears being monitored simultaneously for these stimuli? Two tests of this question were carried out to examine the operation of attentional control during auditory perceptual processing. Condition 1 involved simultaneous monitoring of both ears for the presence on one of four consonant-vowel syllables. Condition 2 involved successive monitoring of the ears in a known order, 500 msec apart, for the same stimuli. In the simultaneous condition, O must split his attention among both ears. In the successive condition, O can give all his attention to each ear in turn. Thus, models proposing limitations of capacity and attentional control during perceptual processing predict an advantage for successive presentation. Experiment I presented only one of the four target stimuli on any trial. Experiment II always presented, in addition, a non-confusable syllable on the non-target ear. In both cases the near equality of performance in the simultaneous and successive conditions suggests that only minimal attentional control could have been present.
On the Identification and Discrimination of Very Brief Vowels
Authors: Pisoni D. B.
Published: October 2005

The distinction between categorical and continuous modes of speech perception has played an important role in theoretical accounts of the speech perception process. Certain classes of speech sounds, such as stop consonants, are usually perceived in a categorical or phonetic mode. Listeners can discriminate two sounds only to the extent that they have identified these stimuli as different phonetic segments. Discrimination functions are not monotonic with changes in the physical scale but show marked discontinuities at points along the continuum that are correlated with changes in identification. Recently, several findings have suggested that vowels, which are usually perceived in a continuous mode, may also be perceived categorically, although this outcome may be dependent upon various experimental manipulations. This paper reports the results of a series of experiments which examined the identification and discrimination of brief 50-msec vowels and longer 300-msec vowels under a variety of experimental conditions. The type of discrimination test, the duration of the stimuli, the range and spacing of the stimuli, and the context of the stimuli all contribute in various ways to the observed differences in shape and relative level of discrimination in vowel perception. Although under some circumstances vowels may be perceived in a categorical-like mode, quantitative differences still exist in the perception of stop consonants and vowels.
Intelligibility of Temporally Interrupted Speech with and without Intervening Noise
Authors: Powers Gerald L.
Published: October 2005

A previous investigation [G. R. Miller and J. C. R. Licklider, J. Acoust. Soc. Amer. 22, 167–173 (1950)] reported that intelligibility of interrupted monosyllabic words was essentially equal in the presence and absence of intervening noise when speech-time fraction was 0.5 and switching rates were approximately below five interruptions per second (ips). Two experiments investigated the effect upon intelligibility of temporally interrupted C. I. D. sentences [S. R. Silverman and I. J. Hirsh, Ann. Otol. Rhinol. Laryngol. 64, 1234–1245 (1955)] when noise was introduced during the speech-free interval. In study 1, listeners received the test material under two conditions at five interruption rates ranging from 0.77 to 3.85 ips. In one instance the speech-free interval was silent; in the other it was switched to white noise of the same average level as the speech. Speech-time fraction was 0.5. Study 2 examined the intelligibility of the interrupted sentences as a function of noise level present during the speech-free interval. The switching condition was held constant and signal-to-noise ratio varied from +9 to −15 dB. Results indicate that for the particular interruption conditions selected, speech switched to noise was significantly more intelligible than speech interrupted in the silence. In addition, listener performance depends upon the level of noise present during the speech-free interval.
Noise Characteristics of Several Power-Plant Boiler Feed Pumps
Authors: Wood E. W. , Hoover R. M.
Published: October 2005

Boiler feed pumps are potential major noise sources in power plants. The noise levels of several auxiliary and shaft-driven boiler feed pumps have been measured. Octave-band and narrow-band data measured at close and remote locations are presented. The effects of these noise levels on employee noise exposure are discussed.
Modulated Reverberation—A New Method for Measurement of Absorption and Sound Power
Authors: Cook Richard K.
Published: October 2005

In a reverberation chamber having a diffuse sound field, a source of sound power modulated in amplitude (100%) at a very low sinusoidal frequency is introduced. The total acoustical energy in the sound field will have an amplitude modulation at the same frequency F but differing in phase by φ. We obtain (1) the absolute cross section A for absorption, and (2) the time-averaged absolute sound power W0 of the source, from measurement of F, φ, and the modulation amplitude |q| of the sound intensity: A = 4ΩVccotφ, and W0 = ΩVc|q|cscφ, where V = volume of the reverberation chamber, c = speed of sound, and Ω = 2πF. The sound intensity |q| is obtained from the time-averaged squared sound pressure |p2| of the audio (signal) frequency by |q| = |p2|/ρc. Pilot measurements of A and W0 have been made in the 425-m3 reverberation chamber of the Bureau. The modulated source of sound power was an array of four loudspeakers, with the audio input voltage amplitude-modulated at F's in the range 0.1–1.0 Hz. The sound pressure |p2| was measured with an array of four microphones, and the phase φ was obtained from oscilloscope photographs. The principle of modulated reverberation is applicable to standing-wave (impedance) tubes. Analogously to the case of the reverberation chamber, the absorption in an impedance tube can be determined from a measurement of the phase angle between the modulated envelope of the signal-frequency voltage applied to the loudspeaker sound source, and the envelope of the sound pressure sampled at one or more locations in the tube.
Control of Noise in Power Station Cooling Tower Systems
Authors: Goodfriend Lewis S.
Published: October 2005

Power-station cooling tower systems must handle large volumes of water and air with large potential energy in the water flows and the requirement for large fans. To minimize the noise generated at power station sites, use is made of efficient tower fill materials, dual low-speed fans (which shifts the spectrum and lowers mid-frequency noise level), and barrier effects in tower location and orientation. Conventional noise control measures such as mufflers are avoided because of the required increase in pressure across the fan and the high initial cost for quieting large towers. The use of natural draft towers is discussed and it is shown that although the low-frequency noise may be reduced, the noise levels at typical property line locations are of the same order of magnitude as that for conventional mechanical cooling towers. Since cooling towers at power stations are required as an environmental (thermal) pollution control measure, a trade-off between temperature rise of local water supplies versus increases in community noise becomes a critical factor.
F. V. Hunt and the Disk Recording Arts
Authors: Bauer Benjamin B.
Published: October 2005

If necessity is the mother of invention, F. V. Hunt surely was its father. Confronted with the need to play some delicate recordings of the Harvard Tercentenary in 1936, Ted invented the first phonograph pickup capable of operation with five-gram bearing forces—a 10:1 advance in the state of the art—thereby ushering in the era of high-fidelity sound reproduction. This was followed in rapid succession by a definitive study of tracing distortion with Pierce and Lewis, including an uncanny prediction of the feasible parameters of a long-playing record. In 1941 and 1945 he received patents on inventions related to pickup and stylus structures, and in 1962 he again reduced the pickup bearing weights by an order of magnitude, producing successful 110th-gram models which are yet to be commercialized. But Ted's favorite saying was that he would receive most accolades for the work done through and by his students. Two among them, Frank G. Miller (1950) and James V. White (1970), made significant contributions to the understanding of stylus-groove contact, thus laying a new theoretical basis for continued leadership of the disk record as a means of high-fidelity sound reproduction in the home.
Hydroacoustic Transduction
Authors: Bouyoucos John V.
Published: October 2005

Professor Hunt once asked, “Can you ‘blow’ a whistle under water?” This question was perhaps the first of a series of events that has led to the emergence of a new power-conversion technology for the efficient conversion of hydraulic power to acoustic or vibratory power. This hydroacoustic power-conversion process embodies flow switching techniques that are analogous to switching methods that are employed in electronic dc to ac power-conversion practice. The hydroacoustic technology has been developed for the generation of high-power underwater sound for communication and echo location, and for such industrial uses as high-frequency, rotary-percussion rock drilling and pile driving. The origins of the power conversion technology will be reviewed, analytical models used in predicting equipment performance will be described, and illustrations of specific applications will be shown. Professor Hunt had significant influence on the early phases of the technology development. Illustrations of this influence will be provided and the continuing impact on the program of his general attitudes will be traced.