bluuebunny/crossref_metadata_2025 huggingface dataset:
The Coincidence Wall: A New Design for High Transmission Loss or High Structural Damping
Authors: Holmer Curtis I.
Published: October 2005

A recent paper by this author presented a theory of the transmission loss of sandwich panels. This paper presents a design concept for a high transmission-loss barrier operating above its critical frequency following this theory. Calculations indicate that this panel can exceed mass-law performance over an extended frequency range when certain parametric requirements are exceeded. This concept may be applied to damping of very stiff structures to achieve high composite-loss factors. Experimental verification of these results is presented and discussed.
High-Resolution Cassegrain Sonar Antenna
Authors: Foster Harold E.
Published: October 2005

A sonar acoustic antenna operating at 1 MHz and producing a 0.3° beamwidth is described. High angular resolution is obtained from a compact structure by using a two-reflector Cassegrain collimator for the transducer. The two reflectors are offset to avoid aperture blockage and thereby achieve a sidelobe level of −30 dB. The reflector contours are hyperboloidal and prolate spheroidal, so that the aperture phase distribution focuses the acoustic beam to a point in the antenna's Fresnel region. Analytic design procedures and computer predictions of acoustic performance are included.
Generation of Subharmonic Frequency Pairs in Nonlinear Systems
Authors: Eller Anthony
Published: October 2005

Under the proper conditions, the response of two coupled, nonlinear oscillators driven by a sinusoidal input will contain a pair of subharmonic frequency components. The frequencies f1 and f2 of these subharmonic components correspond approximately to the resonance frequencies of the linearized system, and their sum f1+f2 is equal to the driving frequency f. The occurrence of subharmonic pairs requires that the driving force exceed a threshold value. This threshold is determined by an analysis that relates the existence of the subharmonics to the properties of a pair of coupled Mathieu equations. Finally, results are presented of an experimental study of subharmonic-pair generation in a nonlinear circuit that was constructed to illustrate this phenomenon.
Profile of Weak Shock Waves in a Shock Tube
Authors: Magerlein John H. , Wright Wayne M.
Published: October 2005

It is commonly assumed that pressure will undergo a discontinuity at a shock front, and then remain steady or slowly decrease with time. In his work with finite-amplitude tone bursts in an air-filled tube, however, McKittrick [J. Acoust. Soc. Amer. 42, 1153(A) (1967)] observed a rounded top for each shock front, rather than the expected perfect sawtooth shape. Shock amplitudes 10 to 100 times as great have been obtained for the present work with a 2-in.-i.d. shock tube, which uses a compressed-air driver and Cellophane diaphragm. The pressure profile is observed at normal incidence with a wide-band capacitor microphone (0.3 μsec rise time), which was constructed as an integral part of the tube termination. For 0.1–0.4-atm shock waves, the initial pressure jump is followed by a further exponential rise of perhaps one-tenth the shock amplitude, with a rise time of about 0.5 msec. Preliminary results with a 1.25-in. tube indicate a similar profile but shorter rise time. [Work supported in part by ONR and NSF.]
Simplified Adaptive Psychophysical Procedure
Authors: Bilger Robert C. , Conn Frank W.
Published: October 2005

Recently much interest has been shown in psychophysical methods, so-called adaptive methods, that combine the convenience of traditional methods with the rigor of decision theory. None of the existing adaptive procedures is appropriate for our interest, which involves the need for rapid testing of listeners during their first visit to the laboratory. We have found that, if we adpot 4IFC and try to measure the signal level for which the probability of a correct response is 0.75, then we can justify a very simple decision rule that requires only two trials at a given level to permit us to (1) accept the hypothesis that S heard the signal with P(C)=0.75, (2) reject that hypothesis, or (3) defer the decision and take two more observations. In addition to the development of this decision rule and comparison with other adaptive procedures, results from this simplified procedure will be contrasted with the psychometric function for 4IFC and with results from other traditional methods. [Supported by a grant from NINDB, National Institutes of Health.]
Monte Carlo Simulation of Adaptive Psychophysical Procedures
Authors: Creelman C. Douglas
Published: October 2005

In an adaptive procedure the level of an independent variable is adjusted on a trial-by-trial basis, depending on observer performance. PEST (Parameter Estimation by Sequential Testing), BUDTIF (Binary Up-Down Two-Interval Forced-Choice), and UDTR (Up-Down Transformed Response) adaptive procedures have been investigated through simulation with regard to their bias, robustness in lack of sensitivity to selection of parameters, and efficiency. In general, techniques that use fixed step size seem to yield a consistent bias that is a function of the step size chosen, while PEST shows bias only with target probabilities thate are relatively low, independent of a wide range of initial parameters. When the rules are properly applied, there is no difficulty with “bumping zero,” as alleged by Pollack for discrimination measurement using PEST. Empirical results in an attempt to validate the PEST simulations yield some differences at low target probabilities between human data and the simulations: Bias seems not to be as large in human observers as it is with simulated observers.
Oral and Nasal Sound-Pressure Levels as Related to Presence or Absence of Velopharyngeal Closure
Authors: Massengili Raymond , Royster L. H. , Walker Thomas , Maxwell Susan
Published: October 2005

In this study, a comparison is made between oral and nasal sound-pressure levels for subjects with normal oral structures and complete velopharyngeal closure, for subjects who had undergone surgical repair of the palatal clefts and had complete velopharyngeal closure, and for subjects with repaired cleft palates but who lacked velopharyngeal closure as determined by cinefluorographic analysis. The study is also concerend with the relationship between SPL measures obtained for the right nostril as opposed to the SPL for the left nostril for all subjects. Statistically significant differences were found between the normal group and the cleft-palate group that lacked velopharyngeal closure and between the normal subjects and the cleft-palate group with no velopharyngeal gap. Other aspects of this study are presented.
Pitch is Voicing; Manner is Place
Authors: Haggard Mark P.
Published: October 2005

In intervocalic voiced stop consonants, pitch decreases then increases; in voiceless stops it decreases, skips up during silence, then falls back again. Here pitch depends upon glottal pressure drop, hence upon supraglottal constriction, glottal opening, and intervening cavity volume. An experiment is reported showing that these pitch contours can cue the voicing distinction in stops. Down-up-down contours can occur with voiced fricatives; as supraglottal pressure mounts (i) closure formants fade, (ii) voice-modulated friction onsets, and (iii) pure friction takes over. Oscillograph experiments show that occurence of down-up-down contours depends upon whether Phase (iii) is reached. This varies with place of articulation, and freely. Thus, pitch changes could not rival closure formants before or during friction as chief voicing cue in fricatives. As friction amplitude varies directly, and pitch and voice amplitude vary inversely, with supraglottal pressure, all segmental excitation data can be derived from time course of supraglottal pressure, and hence from glottal and supraglottal constriction parameters. In articulatory synthesis by rule, therefore, only these parameters need be specified for each phoneme; an algorithm to generate excitation data is outlined.
Generation of Harmonics in the Trumpet
Authors: Backus John , Hundley T. C.
Published: October 2005

The sound produced by the trumpet is quite complex, being characterized by a highly peaked waveform having strong harmonic components near 1500 Hz. How this complex waveform is generated has hitherto not been satisfactorily explained. Highly nonlinear lip motion is not the cause, since it has been shown that the area of the lip opening varies nearly sinusoidally [J. Acoust. Soc. Amer. 13, 305 (1942)]. Measurements in this laboratory now show that over a small fraction of the lip-motion cycle, the impedance of the lip opening is much greater than the input impedance of the trumpet, while over the remainder of the cycle, the converse is true. A sinusoidal lip-opening variation then produces a strongly nonsinusoidal air flow into the instrument; this accounts for the harmonic generation. Mouthpiece pressure waveforms have been calculated for a simple model based on this idea, using measured values of the impedance of a mechanical “lip” together with values of trumpet input impedance. The curves obtained closely resemble those observed with a blown trumpet. [Research supported by the National Science Foundation.]
Effect of Velocity on Subjective Noise Levels
Authors: Vogel J. W. , Blakney D. F.
Published: October 2005

In this paper, the effects of the Doppler shift on the acoustic waves emitted by a moving aircraft are discussed, and it is shown how this velocity results in spectrum changes of the sound as measured on the ground. Further, the Doppler-influenced data are analyzed in terms of perceived noise levels, and the results and implications are discussed.
Performance of Foam Wedges in a New Semianechoic Room
Authors: Jelinek R. E. , Brehm L. W.
Published: October 2005

Polyurethane-polyether foam wedges used for sound absorption in new 18 ft × 22 ft × 11 ft semianechoic chamber. Details of the wedge installation and an evaluation of chamber performance with the wedges installed are discussed. The development of the wedges is described in another paper by Gardinier et al., Abstract 6G9. The 36-in. long wedges were designed to achieve a cutoff frequency of 100 Hz when installed. This objective has been met
Some Mathematical and Computational Contributions to Underwater Sound Propagation
Authors: Koopman B. O. , Raisbeck G.
Published: October 2005

This study of underwater acoustic propagation seeks, first, to determine just what can be known concerning the medium (velocity as a function of position and time, conditions of bottom and surface, etc.), so that the mathematical inferences therefrom can be realistic; second, to apply to this purpose the most powerful modern mathematical tools; third, to implement the results by efficient methods of numerical computation. Starting with the standard wave equation and energy-flux vector, specializations are made for traveling waves of high frequency, in which the energy flux is along the bi-characteristics (rays). To the latter are applied Hamiltonian methods: perturbation theory, integral, invariants and statistical information theory, etc. The wave is also treated directly by modern mathematical methods. The numerical methodology takes advantage of these analytic results, and is further simplified by avoiding levels of detail inconsistent with the levels of knowledge. Relatively simple and powerful computer programs are developed when sound speed depends on depth only; they are extended by perturbation methods to a more general case, including small but not negligible horizontal gradients. The statistical effects of fluctuations of actual from average profiles are examined. [Work was supported by the Naval Ordnance System Command.]
Underwater Sound Propagation across the Hawaiian Arch
Authors: Northrop J.
Published: October 2005

Recordings of sounds of 300 small explosive charges were made from SOFAR depth hydrophones off Midway and Wake Islands. The charges were detonated at various depths north of Hawaii. Underwater sound signals from selected shots were analyzed for signal duration, peak pressure level, and frequency content. The effect of the Hawaiian Arch on the signals received was measured by comparing data from events whose travel path to Wake crossed the Arch with those at Midway that traveled unobstructed paths. When travel paths to Wake crossed the Arch between the longitude of Oahu (157°30′W) and the longitude of Midway (176°W), the signals were 5–25 dB below those at Midway and 4–6 sec shorter than expected in duration. Complete blocking of the signal at Wake occurred when both of the following conditions were met: (1) when travel paths across the Arch made angles of <35° with the trend of the Arch and (2) when water depths less than 2000 fm were encountered. For angles >35°, diffraction of sound partially ensonified the shadow zones behind shoals atop the Arch. Atolls near the western end of the Arch (Kure, Midway) completely blocked the signal at Wake. Isolated seamounts caused little shadowing unless their minimum depth was near 850 fm or less.
Temporal Relations in Pure-Tone Ipsilateral Masking
Authors: Lankford J. E. , Stokinger T. E.
Published: October 2005

Masking efficiency of a 50 dB SPL, 1000-msec, 1000-Hz pure tone was determined on nine masked frequencies (ranging from 500 to 1500 Hz). Ipsilateral masking was sampled near the onset, at the midpoint, and near the offset of the masker for four normal-hearing subjects. Masking efficiency was greater near onset of the masker than at either of the other two temporal delays. Although masking near offset was less than that near onset, offset masking was greater than at the midpoint of the masker. This increase in masking near onset and offset is called overshoot. Onset overshoot was related to the initial threshold shift at the test frequencies. The experiment revealed that both onset and offset masking overshoot occur for maskers and maskees with similar frequency spectra (pure tones). A follow-up study compared ipsilateral masking at the midpoint with steady-state masking. [This study was part of Lankford's dissertation completed at the University of Oklahoma Medical Center and was supported by the Oklahoma City VA Hospital.]
Off-Frequency Tonal Masking
Authors: Wightman Frederic L. , Leshowitz Barry
Published: October 2005

The results of several experiments suggest that when an observer is asked to detect a burst of a sinusoid, he will often listen for signal level at frequencies far removed from that of the signal. For example, in one experiment, observers were asked to detect a 10-msec sinusoid, masked by wide-band noise and a continuous sinusoid 300 Hz lower in frequency than that of the signal. In one condition, the signal was high-pass filtered, and in another condition no filter was used. The filter was such that it reduced the total level of the signal by 23 dB. At low noise levels, despite the 23-dB signal-level reduction, detectability was only 8 dB poorer in the filtered condition. This result suggests that observers were detecting the signal by listening for off-frequency energy, probably high-frequency energy. In a second experiment observers detected a 10-msec sinusoid masked by an off-frequency continuous tone and by a 10-msec gated tone at the same frequency as the continuous tone. The gated masker was added either in phase or in quadrature with the continuous masker. Masking functions relating threshold signal level and gated masker level were identical for the in-phase and quadrature conditons. This result suggests that the effective masker in these conditions is the energy off the frequency of the masker. This energy, which is produced by the gated masker, is nearly the same for the in-phase and quadrature conditions. [Research supported by the National Institutes of Health, U. S. Public Health Service, Department of Health, Education, and Welfare.]
Experimental Determination of Auditory-Filter Shape for Tones Masked by Bands of Noise
Authors: Patterson Roy D.
Published: October 2005

The detectability of a pulsed sinusoid was measured as a function of its distance, in frequency, from a broad band of noise having very sharp skirts. In contrast to the procedure used by Greenwood, the frequency of the sinusoid was held constant while the position of the noise band was varied. If we assume (1) that the center frequency of the auditory filter is set equal to the frequency of the sinusoid, and (2) that the power of the just-audible sinusoid is some constant multiple (not necessarily unity) of the noise power passing through the auditory filter, then the shape of the auditory filter can be determined to within a constant. The general form of the auditory filter obtained under these assumptions is very well approximated by the equation: |H(w)|2 = (a2/Δf2+a2)2, where Δf is the distance between the sinusoid and the edge of the noise, and 1.29a is the 3-dB bandwidth of the auditory filter at that signal frequency. At 1000 Hz, we estimate the 3-dB bandwidth to be 65 Hz. [This research was supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Aural Harmonics: Measurements at f3 When f1 = 500 Hz
Authors: Clack T. D.
Published: October 2005

The amplitude of the harmonic-distortion components produced within the normal auditory system can be inferred from measurements of tone-on-tone masking. Over-all masking levels (A1), interference (A2), and aural-harmonic (AH) estimates at f2 (where f2 = 2f1) have been presented previously for f1 = 500 Hz. Comparable measurements at f3(= 3×500 Hz) have been obtained from 10 normal listeners for sound-pressure levels at f3 separated by 5-dB intervals from 50 to 75 dB. The averaged results indicate that while A1 grows in a similar curvilinear manner at f2 and f3, it is 3–10 dB greater at f2. Second, A2 is less for f3 than f2 at lower f1 intensities but increases rapidly to near equality as the SPL for f1 approaches 70–75 dB. Finally, estimations of AH (SPL) indicate that the third AH remains about 65 dB below the level at f1 and increases about 1 dB for each decibel increment in the SPL f1 until about 65 dB SPL. Then there is a sharp increase in growth rate to about 3 dB/dB. Relative to the level at f1, the second AH is about 50 dB down and has a growth rate approximating 1 dB/dB up to 65 dB SPL. At this level, there is some indication of an increase to 2 dB/dB. These tentative findings have implications for frequency as well as amplitude distortion.
Monaural Masking Patterns in Normal and Abnormal Listeners
Authors: Bess F. H. , Clack T. D.
Published: October 2005

The purpose of this study was two fold: to determine (1) is pure-tone monaural masking patterns in abnormal ears differed from normals; and (2) if a relationship exists between the spread of masking and speech intelligibility. Using 125-, 250- and 500-Hz maskers at three intensities, thresholds were measured at octave intervals in seven normals and 18 sensorineural impaired listeners. Articulation functions for each ear were obtained with the Rush Hughes List. The masking results from normals are consistent with previous findings. Patterns for abnormals, however, display wide individual differences, especially at frequencies above the masker. Some abnormals displayed extensive masking (20–30 dB) at 3 and 4 oct above the masker, while exhibiting a minimum degree of masking nearer the masker. An attempt is made to establish a relationship between speech intelligibility scores and the spread of masking. The data are discussed under the hypothesis that low-formant energy masks higher-frequency cues in the speech signal.
High-Speed Movie Films of Visible Cavitation in Liquid Helium
Authors: Mossé A. , Chu M. L. , Finch R. D.
Published: October 2005

High-speed movie pictures, at up to 3200 frames/sec, were made of visible cavitation in liquid helium. Cavitation was generated by a PZT 4 cylindrical transducer at about 52 kHz. The bubbles were found to occur in the form of streaks or streamers consisting of several individual bubbles. Individual bubbles appeared to persist for 10–100 sound cycles. The streamers lasted much longer than the component bubbles and were frequently paired, apparently having a common point of origin. It is unclear if the mechanism of streamer formation in normal liquids is applicable in this case or whether the bubbles originate on vortex filaments.
Nonlinear Transmission Loss of Acoustic Waves of Finite Amplitude
Authors: Lee Tsin N. , Liu C. K.
Published: October 2005

From the solution of the nonlinear differential equations that govern the transmission of acoustic waves of finite amplitude, it has been found that the attenuation coefficient of waves of finite amplitude is proportional to the product of the frequency and the pressure amplitude. With the assumption that the attenuation coefficient is proportional to the product of the frequency and the rms value of the acoustic pressure, the differential equations for the transmission (level) loss in decibels for both plane waves and spherical waves are established and subsequently solved. Simple formulas capable of calculating the transmission losses are derived for both simple waves and the over-all level of complex waves. The only coefficient in the fomulas has been determined from the physical properties of the medium and test data. The coefficient for simple waves is in order of 8×10−3/cps/in. and that for complex waves is 8×10−2/in. The formulas have been applied to both the nearfield and farfield of the space rocket booster noise. The computed results show excellent agreement with the measured data.
Prediction of Infrasonic Waves from Thermonuclear Explosions Using Cagniard's Integral Transform Method
Authors: Pierce Allan D. , Posey Joe W.
Published: October 2005

The acoustic disturbance at horizontal distances of the order of 1000 km from an atmospheric nuclear blast is composed primarily of small-amplitude infrasonic waves with periods of 1 min or longer. Present methods for predicting the ground-level waveforms produce fair agreement with empirical data for most of the wavetrain; however, these methods are generally inapplicable for predicting the very early (first few cycles) portion of the waveform. If the vertical acceleration term in the equations of hydrodynamics is omitted, Cagniard's integral transform method can be used to find exact transient solutions to low-frequency wave propagation problems in atmospheres with arbitrary temperature profiles. To demonstrate the technique, solutions are derived for line and point sources in an isothermal atmosphere above a rigid ground. The results for the point source are compared with the results of Row and those of Cole and Greifinger and with the predictionsof the guided normal-mode approximation.
Segmented Stator Blades to Reduce Noise in Axial Compressors
Authors: Embleton T. F. W.
Published: October 2005

The edges of rotor and stator blades are essentially straight and radial in axial-flow compressors. The acoustic strength of each source can be reduced by setting the edge of the stator blades in a nonradial direction, though this is undesirable because it results in radial forces being applied to the fluid flow. More noise reduction, with less adverse effect on the efficiency of the compressor, is obtained by dividing each stator blade into 2, 3, or 4 segments and displacing the leading edge of some parts relative to the others, so that the edge of the blade is stepped rather than a straight line. Thin webs at the junctions of segments prevent flow between the front and back of a blade. Theoretical calculations of farfield radiation patterns show that some blade designs can give up to 8 dB reduction of radiated power, compared with straight blades. Measurements show reductions of up to 6 dB and with certain three-segment blades this may be obtained with equal or marginally improved mechanical efficiency.
Acoustic Spectra of Specular and Near-Specular Scattering from a Three-Dimensional Traveling Sinusoidal Surface
Authors: Roderick William I.
Published: October 2005

A model tank experiment has been conducted that investigated the spectral characteristics of surface reflected and scattered underwater sound. The major experimental objectives were to determine the frequency spectrum of specular and near specular scattering from a traveling sinusoidal surface. The spectral characteristics were investigated for various directions of surface wave propagation and also for a two frequency surface. A narrow-beamed 500-kHz CW signal was projected at the surface and the reflected and scattered sound was received, bandshifted, and recorded on magnetic tape for spectral analysis. A vibration generator produced gravity waves: wavelength and wave-height measurements were made over the insonified area. A scattering integral developed in the literature was evaluated for a traveling sinusoidal surface to compare the experimental results. Experimental and theoretical results show that for large surface-to-acoustic wavelength ratios, the specularly reflected signal is amplitude- and phase-modulated by the near-specular scattering regardless of the surface directionality. The frequency spectrum is symmetrical about the carrier in both amplitude and frequency. This symmetry holds for a multifrequency surface if the surface frequencies are not commensurable. The spectrum of off-specular scattering is Doppler shifted and is a function of surface wave directionality.
Measured Time and Frequency Spreading of Acoustic Signals Reflected from the Sea Surface
Authors: Thomas R. S.
Published: October 2005

Measurements have been made of time and frequency spreading of acoustic signals propagated by means of a surface reflection. Pure tones and short pulses at 4.75 and 9.5 kHz were transmitted between relatively stable transmitting and receiving platforms in the deep ocean. Results were obtained for grazing angles between a fraction of a degree and 60° and for sea states 12 and 3. Time and frequency spreading are both functions of sea surface statistics, and the data show the increasing frequency spreading with grazing angle and wind speed, and the variation in time spreading with grazing angle, wind speed, and wind direction. Continuing experiments in which surface wave statistics are collected along with acoustic data are being carried out.
Sonic Fatigue of Aircraft Structures Due to Fan Noise
Authors: Holehouse I.
Published: October 2005

The current generation of high bypass ratio turbofan engines are noted for their reduced broad-band noise output at the expense of high-frequency, intense, discrete tones. Such tones have been considered to be of too high a frequency (3–4 kHz at high engine-power settings) to represent a serious sonic fatigue threat; 0.1–1 kHz is considered the usual frequency range over which sonic fatigue failures occur, this being the frequency range encompassing maximum broad-band noise and most fundamental natural frequencies of the structural components. Structural vibrations in the range 3–4 kHz will probably be either force or, if resonant, 4th or 5th harmonics. Both cases require considerable acoustical energy if they are to occur with sufficient intensity to cause fatigue failures. It has been found that such failures have occurred, and that they have not always been correctly identified. This paper presents details of an investigation into such a failure problem, highlighting some of the considerations essential to a proper diagnosis, shows how the problem was solved (achieving stress reductions of up to 1/18), and suggests precautionary measures for future design efforts.
An Optical Heterodyne System for Measurement and Analysis of Vibration
Authors: Eberhardt F. J. , Andrews F. A.
Published: October 2005

Calibration and use of an optical heterodyne system for nonsinusoidal vibration measurements is described. A low-power ultrasonic cell produces Raman-Nath diffraction of a 6328Å laser beam to give an 11-MHz frequency shift. The frequency shifted beam is heterodyned in a photomultiplier with the unshifted central light beam, which has been phase modulated by motion of a reflecting surface. The output of the phototube is an rf phase-modulated signal, which is amplified and passed to a limiter-discriminator receiver. The detected signal is integrated and is a linear reproduction of the surface vibration as long as the frequency-amplitude product is within limits. The linearity and a calibration technique have been tested out to a product of 13 kHz×4700 Å. At lower frequencies, higher vibration amplitudes can be measured. The average calibration accuracy is witin 5% of laser homodyne measurements used for comparison. A minimum amplitude measurement of 3.5Å was obtained. Measurement of time delay or spatial cross-correlation functions is domonstrated using two heterodyne detectors.
Multiple Noise Sources in an Enclosure
Authors: George Ballard W.
Published: October 2005

An expression is derived for the sound field in a room resulting from multiple sources that includes the effect of statistical dependence (correlation) between them. The room response is analyzed in terms of the normal modes. Resulting expressions are analogous to these that describe the excitation and response of a structure (e.g., beam or plate) acted on by a set of input forces. The formulation is extended to three dimensions to include the most general case in the room acoustics problem. Applications to the achievement of a diffuse sound field and to noise control by cancellation are discussed. Noise-source arrays of concern could include, for example, equipment in a machine shop or computer equipment room. Comparisons with source arrays in the free field and with sound fields due to a single source in the room are shown.
Pitch Perception of Two Types of Frequency Change: Glides and Jumps
Authors: Nabelek A. , Nabelek I. , Hirsh I. J.
Published: October 2005

Listeners attempted to match the pitch of two types of tone bursts: continuous and discontinuous. Continuous bursts had two parts of constant frequency connected by a linear transition while discontinuous bursts consisted of two successive parts separated only by a pause. Both types of bursts were matched with a single pitch (fusion) for small frequency changes or with two pitches (separation) for larger frequency changes. Fusion and separation as a function of burst duration were established. For short transitions (5% of burst duration) or a pause equal to zero, the region of fusion and separation for both types of bursts was similar. Prolongation of the transition obscured the separation while the prolongation of the pause made separation easier. In fusion, prolongation of the transition changed the pitch, but prolongation of the pause influenced the pitch very little. The results indicate that bursts are perceived in pitch similarly when the change (either transition or pause) occurs in a short time (abour 10 msec). The longer changes (30 msec) are differentiated by the hearing system.
Reciprocal Spreading Effects on Frequency Discrimination
Authors: Ronken Don A.
Published: October 2005

The reciprocal spreading phenomenon tells us that short-duration signals are poorly defined in the frequency domain, while line spectra exist only for signals of infinite duration. Formally, ΔfΔt = CONST describes how “effective” bandwidth and “effective” duration are constrained by a reciprocal relation. The value of the constant is unique to the envelope of the signal and varies considerably for the types of signal envelopes that occur in actual waveforms. Only a few studies have examined frequency discrimination at short durations where reciprocal spreading effects might be important. Liang and Chistovich found that for durations less than about 40 msec, the difference limen for frequency is proportional to signal bandwidth. To investigate this bandwidth hypothesis in more detail, several different waveforms were selected as envelopes for short-duration sinusoids. These included a rectangular, a Gaussian, two exponentials, and a gamma function, which were equated for “effective” bandwidth. From the ΔtΔf = CONST relation, it can be seen that sinusoids with these different envelopes have different “effective” durations, and we might expect that this would have some effectjon the ability to detect frequency differences. The experimental results indicate that such is indeed the case: wide differences are observed for these signals that are nominally equivalent in bandwidth. [This research was supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and an NIMH—Postdoctoral Fellowship.]
Physiology of Vocal Registers in Singers and Nonsingers
Authors: Hollien Harry , Colton Raymond
Published: October 2005

The focus of this presentation includes only three registers (vocal fry, modal, and falsetto) even though it is recognized that other registers and/or subregisters probably do exist. In this regard, data from four studies are presented in order to establish the f0 boundaries in these three registers for large numbers of nonsingers and smaller groups of singers. Secondly, perceptual and acoustical data from five studies is discussed in which the registers are compared to each other and to other types of phonatory signals. Special emphasis is given to a set of investigations in which perceptual and acoustical differences between modal and falsetto registers (for fundamental frequencies where they overlapped) were studied in a group of singers and a matched group of nonsingers. Finally, a substantial number of published and unpublished studies will be utilized in order to contrast the three specified registers with respect to the underlying physiology of each. Of special emphasis here will be vocal-fold length, vocal-fold thickness, vibratory patterns, subglottic pressure, and air flow.
Investigation of a Noise Problem in the Cockpit of a Fighter Airplane
Authors: Bies David Alan , Carmichael Richard F.
Published: October 2005

The noise levels during operation in the cockpit of the Fδ fighter plane are controlled primarily by the operation of the air-conditioning unit that operates on bleed air from the engine compressors. In one version of the airplane, low-frequency noise in narrow bands at about 135 and 180 Hz was found to be associated with severe pilot complaint about the cockpit acoustical environment. The paper briefly reviews the procedures by which the source of troublesome low-frequency noise was discovered and corrected. The paper also reviews procedures by which the most likely sources of remaining high-frequency noise have been identified and indicates the direction that should be taken to improve further the cockpit environment.
Noise Control for Induced-Draft Fan Installations
Authors: Hoover R. M. , Wood C. O.
Published: October 2005

Noise-level data on a number of induced-draft centrifugal fans with flat radial blades are presented with emphasis on the level of the normal low-frequency blade-passage tone. Data taken near the fans at ground level, at the top of fan discharge stacks, and in far field community areas are included for installations with and without noise-control treatment.
Pressure Fields inside Rooms with Open Windows Due to Airborne Sounds, with Particular Application to the Sonic-Boom Problem
Authors: Doak P. E. , Vaidya P. G.
Published: October 2005

Expressions are obtained for the pressure field inside a room due to a harmonic wave incident on the window. The room is visualized as a terminated duct. A solution is obtained as a combination of two elementary solutions, which together satisfy the boundary conditions at the end wall. A revised version of this formulation, using Green's functions, is also presented. A Laplace transform of the steady-state solution is obtained in a form that is particularly useful for the earlier part of the time history. A Helmholtz-resonator analogy is used to obtain an alternative form of the time domain solution. This solution is more representative of the actual problem when the later part of the time history is required. Particular forms of this solution, relevant to sonic-boom-type excitation, are presented along with the comparison with experimental results carried out by using simulated sonic booms.
Multidelay Model Relating Tide Height to Underwater Acoustic Phase
Authors: Yacoub Kamal , Almeida Jose
Published: October 2005

Observed relationships between environmental parameters and underwater acoustic phase were earlier reported and a multi-input nonrealizable model was analyzed showing that, among several parameters, tide height has the strongest coherence with measured phase fluctuations. This work is concerned with a special case of the above model, where the system is single input, with a realizable impulse response consisting of few delays. Several cases are considered such as a single delay, two or more delays. Among these, a special case is found where one of the delays is fixed at zero time (in phase, no delay component). Two kinds of results are reported—one where optimization is carried out on all energy bands, another where optimization is carried out on selected bands that are least corrupted by noise and the effect of other parameters. The resulting transfer function is calculated and errors from measured values are given individually for each band and also collectively as a figure of merit for that solution. [Work supported by Office of Naval Research Code 468.]
Performance of Bearing Estimators Subject to Nonideal Inputs
Authors: Richter R. J. , Schalow R. D.
Published: October 2005

The practical case of computing the bearing θ to an object given N noisy measurements of the orthogonal components of the direction vector (X, Y) by using either θ̂ = arctan (〈Y/X〉) (1) or θ̂ = 〈arctan〉 (Y/X) (2) has been previously studied and reported for ideal descriptions of the noise associated with X and Y; namely, equal variance (σx2 = σy2) and zero correlation (ρxy = 0). Further analysis removes these restrictions. It is shown that both methods are asymptotically efficient but only Eq. 1 remains asymptotically unbiased for ρxy≠0 (in fact, Eq. 1 is a maximum likelihood estimator). For finite N, nonideal inputs cause bias with either method. Performance curves relating bias and estimation variance to signal-to-noise ratio, σx/σy, ρxy, N, and θ are developed which show that, as before, Eq. 1 is the preferable estimator in virtually all practical situations.
Existence and Stability of Periodic Motions of a Harmonically Forced Impacting System
Authors: Senator M.
Published: October 2005

A simple idealization of a vibratory plow that is impacting against an immovable, relatively rigid obstruction is analyzed to determine possible periodic motions and the stability of these motions. The plow is idealized as a translating rigid body with an applied harmonic force and viscous damping. It is pushed against a wall by an applied-bias force with the resulting impacts characterized by a coefficient of restitution. Necessary conditions are found for the existence of periodic motions with one impact per motion cycle. The infinitesimal stability of these periodic motions is investigated, and it is found that either a motion with the highest number of crank revolutions per cycle is stable, or none are stable. Some cases are investigated numerically, and it is found that the infinitesimally stable solutions are approached even for large departures from the periodic initial conditions. For unstable cases, the two dependent variables of greatest interest, average number of force cycles per impact and average impact velocity, can be approximated by using the formulas developed for the one impact per cycle motions analyzed.
Effects of a Bar Stiffener on the Flexural Response of a Reinforced Circular Ring
Authors: Shivaram M. , Mitchell W. S.
Published: October 2005

In seeking to understand the mechanics of underwater radiation from a submarine, a study was made on a reinforced circular ring section, the analog of a submarine structure, in which the effect of a stiffening bar on the flexural vibration of the ring was studied both analytically and experimentally. The stiffening bar, which is a chordal member whose cross section is identical to that of the circular ring, is the analog of an equipment deck on a submarine to which deck loading is applied. The method of attaching the bar to the ring is assumed to represent a fixed-fixed end condition. Results are compared with an analysis for incomplete rings subjected to time-dependent boundary conditions. They are also compared with the analytical and experimental results for rings without stiffeners. It was found that the stiffener makes significant changes in the vibrational response of the ring. The ring resonated at multiples of the forcing frequency. Moreover, upper and lower segments of the ring responded in independent modes.
Method for Analyzing Perceptual Confusions of Consonant Phonemes
Authors: Murray Thomas
Published: October 2005

A method for analyzing listener's phonemic confusions of monosyllabic words was developed in order to determine the type as well as the number of consonant errors made in certain speech-intelligibility testing situations. This method, which deals exclusively with consonants, allows for the listeners' responses to be written in phonetics or traditional orthography. Therefore, it can be used with experienced listeners or with naïve listeners, which, in some cases, is desired or necessary. From the listeners' responses, the errors are grouped into simple consonant-for-consonant substitutions, substitutions involving consonant clusters, omissions, and additions. The results of the analyses are presented in terms of the percent correct for each phoneme relative to the total possible number of correct phonemes at a certain condition. In this way, the relative intelligibility of each phoneme may be obtained and compared with other phonemes in the same test or with the same phoneme in various testing situations. Preliminary data indicate that the reliability of transforming the orthographic responses to phonemes ranges from 87% to 93% Some results of the application of this procedure to the phonemic confusions of divers' speech at various depths and breathing mixtures are presented.
Acoustic Analysis of Speech Produced in Air Compressed from 14.7 to 147 psia
Authors: Sergeant R. L. , Duffy J. R.
Published: October 2005

Confusions in studies of speech in the deep undersea environment are caused by variations in the response of microphones under abnormal ambient pressures as well as an interactive effect upon vocal production caused by increases in ambient pressure and changes in gas mixture make up. In the present study, speech was analyzed when the gas mixture, normal air, was held constant, and reciprocity calibrations were made at those pressures under study of the microphone used in the recording of speech samples. Taped recordings were collected of the speech of six Navy divers reading lists of words and a paragraph inside a pressure chamber at normal atmospheric pressure and at pressures found 50, 100, 150, 200, 250, and 300 ft underwater (equivalent to 14.7 to 147 psia). The mean time required to read the paragraph increased 17% from 14.7 to 147 psia. Spectrographic analysis below 4 kHz showed an upward shift of formant centers of about 175 cycles, regardless of vowel, formant frequency, or speaker. The effect of a lower limiting frequency of resonance for the human vocal mechanism is discussed in light of the above results.
Binaural Interaction in Backward Masking
Authors: Dolan Terrence R. , Trahiotis Constantine
Published: October 2005

The binaural auditory system exhibits certain advantages over the monaural system when detecting a tonal signal in a background of masking noise. These advantages have been described in detail and are referred to as masking-level differences (MLD). It has recently been suggested that these same advantages may be demonstrated in a binaural-masking experiment in which the signal and masker are not presented simultaneously. This suggestion is particularly puzzling since most explanations of MLD require addition or some other simple interaction of the signal and masker. In the present investigation, the size of the binaural advantage was measured in a backward-masking experiment in which the signal termination preceded the onset of the masker by 0, 4, 8, 12, or 20 msec. The results indicate that simultaneity of signal and masker is not required to show binaural improvement over monaural performance. [Research partially supported by the National Science Foundation and the National Institute of Mental Health.]
Application of Holographic Interferometry to Vibrations of the Bodies of String Instruments
Authors: Reinicke W. , Cremer L.
Published: October 2005

Some eigenmodes of both the top and back plates of the bodies of string instruments are known from measurements with capacitance transducers. But this method has been rather tiresome. It seems adequate, therefore, to apply holographic interferometry. Unfortunately, it was not possible to make use of real-time holographic interferometry because even the short time needed for the photographic developing process for the hologram is large enough that the wooden body changes its surface, maybe on account of small moisture changes. On the other hand, the time-average holograms give satisfying holographic pictures. Examples are given of those at low, middle, and high frequencies and also for excitation over the sound post and over the bassbar. The results are discussed in connection with measurements of the point impedances at both places of excitation.
Chords from Tones Having Stretched Partials
Authors: Slaymaker F. H.
Published: October 2005

Helmholtz pointed out that dissonance results when the upper partials of tones in a chord produce beats. If the musical scale and the partial structure of the tones are consistent, chords could be formed from tones having inharmonic partials, which would not produce beats. Tones have been generated on a computer, converted to analog form, and used to form chords. The tones contained partials having frequency ratios of NS, when S is the “stretch” exponent and N is the partial number. Such tones, in general, are not periodic. Scales were also constructed in which the ratio between “half steps” was (21/12)S. Chords analogous to the tonic, subdominant, and dominant, will be demonstrated for S varying from 1.001302, comparable to the smallest amount of stretch in the middle of the piano range, to 1.261859, which makes the ratio of the frequencies of the third and first partials equal to four instead of three. The sensation produced by the stretched chords is consistent with Helmholtz's criterion for dissonance. The quality of the individual tones, however, becomes more and more strange as the value of S increases. The stretch exponent may serve as a new parameter that can be manipulated by avant-garde composers.
Numerical Calculation of Farfield of Transducer Array near Critical Frequency
Authors: Chertock George
Published: October 2005

For the case of a simple box-shaped transducer array, operating near a frequency at which the interior space of the box has a standing-wave solution with p = 0 at the surface, one method of calculating the external radiation field has been developed and demonstrated by Schenck [J. Acoust. Soc. Amer. 44, 41–58 (1968)]. An alternative method of solution to this same problem is demonstrated, based on an approximation to the sound pressure at the surface of the array.