bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Earphone Enclosure for Communications in Noise
Authors: Bauer Benjamin B. , DiMattia Alfred L.
Published: October 2005

In this paper, earphone enclosures are described embodying an improved acoustical network for enhanced noise reduction and efficient performance for an earphone. The network uses two chambers; one adjacent to the ear and the other contained in a re-entrant expanded portion of the enclosure. The two chambers are connected by parallel passages defining predominantly a resistance and an inertance. It is shown that this form of network is more effective than an arrangement of inertance and resistance in series. Cushions filled with nonfluid gel provide high wall impedance for good noise attenuation and good conformance with circumaural contours of the bead. Values of noise attenuation are given, measured by artificial head and by psychoacoustic methods. Performance of a typical earphone in the enclosure is shown.
Wide-Range Calibration System for Pressure Gradient Hydrophones
Authors: Bauer Benjamin B. , Abbagnaro Louis A. , Schumann Juergen
Published: October 2005

A gradient hydrophone calibrator consists of a precisely made water-filled tank with ports to receive the hydrophones to be calibrated and the reference pressure hydrophones, which is set into axial oscillation with suitable drivers to develop a standing wave of sound in the water [“Laboratory Calibrator for Gradient Hydrophones,” J. Acoust. Soc. Amer. 39, 585–586 (1966)]. An improved calibrator is described, which, by using a very rigid tank, covers a range of 3 to 2500 Hz. Measurements are simplified through use of electrical feedback, which maintains a constant pressure-gradient versus frequency function. The applications and limitations of this system to the measurement of sensitivity, frequency response, phase response, and polar pattern of gradient hydrophones are described.
Ambient Pressure Independent Acoustic Capacitor for Use at Infrasonic Frequencies
Authors: Bedard A. J. , Hubbard E. K.
Published: October 2005

Acoustic capacitors are frequently used as components in filter networks of infrasonic microphones. Since this capacitance is normally pressure dependent, the filter time-constant characteristics are a function of ambient pressure. A technique is described for compensating for the pressure dependence and the theory is compared with experimental test results. It is shown that it is quite possible to make an ambient pressure independent acoustic filter for use at infrasonic frequencies. This technique should be applicable to infrasonic microphones used at the earth's surface.
Focusing of Shockwaves at Caustics
Authors: Sachs D. A.
Published: October 2005

As a result of the depth dependence of the speed of sound in the ocean, the sound energy of a shockwave produced by an underwater detonation focuses in some regions, producing pressures much greater than would be observed if the ocean were uniform. In addition, the initial waveform is drastically distorted. A theory to describe the amplification of shockwaves in these focusing regions, usually called caustics, was recently proposed by Silbiger [A. Silbiger, Cambridge Acoustical Associates, Inc., Tech. Rep. U-286-188 (June 1968)]. A comparison of theoretical predictions with the experimental results of Barash and Goertner [R. M. Barash and J. A. Goertner, U. S. Naval Ordnance Lab., Tech. Rep. 67-9 (19 April 1967)] shows fair agreement: order-of-magnitude predictions of peak overpressures are achieved along with a qualitative description of the waveform's distortion. Sources of error include the neglect of finite amplitude effects and the effects of the experimental equipment as well as inaccuracies inherent in the use of the asymptotic methods employed in the theory. [Research sponsored by the Field Projects Branch of the Office of Naval Research.]
Anomalous Sound Absorption below 10 kHz in the Ocean and Lake Superior: Another Chemical Relaxation?
Authors: Fisher F. H.
Published: October 2005

Quantitative calculations have been made which show that dissociation of the [HCO3−] ion could explain the magnitude of sound absorption below 10 kHz in sea water, which is not accounted for by the MgSO4 absorption [W. H. Thorp, J. Acoust. Soc. Amer. 38, 644–654 (1965)]. The applicability to the absorption observed in Lake Superior rests on the accuracy of the data [D. G. Browning, E. N. Jones, R. H. Mellen, and W. H. Thorp, Science 162, 1120–1121 (1968)]. To verify the proposed explanation, the relaxation time needs to be measured, probably by a pressure jump technique in actual samples of sea water and of Lake Superior or artificially synthesized samples.
Reverberation-Derived Scattering Strength of the Shallow Sea Bed
Authors: Urick R. J.
Published: October 2005

Measurements of explosive reverberation level and transmission loss have been made at a location off the west coast of Florida in water 200 ft deep. The measurements were reduced to scattering strength by means of a simple formula that ignores the details of the propagation paths to and from the scatterers. These reverberation-derived scattering strengths are found to be comparable to those previously measured for the deep sea bed. In addition, the reverberation tails of off-set sources, displaced by distance up to 5 miles from the receiving hydrophone, are found to be identical to the reverberation tail of a nearly source when time-shifted by the travel time from source to hydrophone. Although no direct scattering measurements on the shallow sea bed were made, the agreement of the reverberation-derived scattering strengths with the known scattering strength of the deep sea bed suggests the validity of the simplified model and its possible value for reverberation prediction, so as to make it analogous to the various existing prediction models for shallow water transmission.
Helium Speech Translation Using Homomorphic Deconvolution
Authors: Quick R. F.
Published: October 2005

Previous research by Oppenheim has established the applicability of homomorphic deconvolution to speech analysis-synthesis systems. The present research is an application of homomorphic methods to the problem of correcting divers' speech in pressurized helium-oxygen atmospheres. The vocal tract impulse response of such speech was extracted by the homomorphic deconvolution technique, and its frequency components were moved downward in frequency according to correction formulas given in a study by Gerstman. Both linear and nonlinear frequency corrections were used. Speech samples taken at 800 ft pressure depth in a 96% helium, 4% oxygen atmosphere were processed in this way, using a digital simulation of Oppenheim's analysis-synthesis system. Results indicate considerable promise for the technique as a tool for further study of helium speech, and perhaps as a future on-line translation method. [This work was done at the Air Force Cambridge Research Laboratories while the author was enrolled in the Electrical Engineering Department cooperative program.]
Voice Pitch Rate Patterns on an Analog Ear
Authors: Stewart J. L.
Published: October 2005

In response to stimulation by a voiced speech sound, a point on the basilar membrane of an electric analog cochlea executes motions in the manner of a comparatively high-frequency carrier with envelope fluctuations at the fundamental voice pitch rate and/or at the second or third harmonic of this rate. Perception of a sound is based collectively on the pattern of such motions over the entire cochlea. These motions have been observed and photographed using a two-dimensional oscilloscope display wherein distance along the cochlea is one dimension, time is another (2 msec/cm). and light spot intensity represents magnitude. A form of inhibiting detection was used to improve contrast and achieve amplitude range compression. Patterns for a number of different speech sounds as produced by several different speakers are presented and discussed. Some pattern features appear to relate mostly to the sound and others to the speaker. Localization along the cochlea is not as important as is the general pattern arrangement. Speech sounds synthesized by pattern matching retain some quality characteristics; and synthesis permits pattern features of little importance to be identified by experiment. The analog cochlea reveals comparatively high-speed envelope fluctuations, even in parts of the cochlea responsive to frequencies below 1 kHz; comparable patterns are not readily obtained from a spectrum analyzer because of limited channel bandwidths, especially at low frequencies.
Application of Speech Recognition to Automatic Intelligibility Testing Procedures
Authors: Teacher Charles F. , Richards Jerry R. , Hewitt Hollis
Published: October 2005

Although most automatic intelligibility testing procedures are based on the articulation index principle, speech recognition techniques offer an attractive alternative to existing procedures. In essence, recognition provides a mechanism by which the communication system can be tested with realistic speech samples rather than sine or square waves. Since formatted test samples can be used, segmentation and time normalization problems are circumvented. A recognition process, which makes use of statistical decision theory to imitate the results of a listening jury, is discussed. Data on the ability of the system to extrapolate learning data automatically to predict the results of new degradations on the same listening jury is presented. Details on the advantages and disadvantages of such techniques are discussed. [This work was supported by the Air Force Systems Command at the Rome Air Development Center, Rome, New York.]
Models for Predicting Intelligibility of Pattern-Matching Vocoder
Authors: Smith Caldwell P.
Published: October 2005

An experimental pattern-matching vocoder was utilized with various combinations of tables of stored spectrum-pattern events in processing 31 lists of the 448-word Diagnostic Rhyme Test of Voiers et al. Responses of eight naïve listeners were analyzed to determine intelligibility scores for the features voicing, nasality, sustention, sibilation, graveness, and compactness, as well as total intelligibility. These scores were used for computation of models for assessing the relative importance of the processing parameters for the voiced and the unvoiced spectrum samples (as labeled by the vocoder voicing decision) as determinants of speech intelligibility, for three cases: (a) intelligibility as a function of the mean “spectrum error” measured during processing the voiced and unvoiced spectrum samples from the analyzer; (b) in relation to calculated “information” estimates for the tables of voiced and unvoiced pattern stereotypes used in synthesizing speech; and (c) as a function of total number of stored voiced and unvoiced patterns. It was ascertained that the “spectrum error” measurements provided the best prediction of over-all intelligibility, and that the fidelity of “voiced” samples was approximately four times as critical for intelligibility as that of “unvoiced” samples.
Measurement of the Two-Click Threshold
Authors: Leshowitz Barry
Published: October 2005

Observers were asked to discriminate between a pair of 10-μsec pulses and a single 20-μsec pulse having the same total energy. The independent variable was the time, ΔT, between the two 10-μsec pulses. The stimuli were also presented as elements in a periodic pulse train. The ΔT required for resolution of two clicks (two-click threshold) was 10-μsec. This value is in the same range as the separation needed to lateralize clicks delivered to the two ears and is about three orders smaller than the temporal separation needed to hear two clicks as distinctly separate. Whereas the addition of a steady background noise produced a remarkably small change in the magnitude of the two-click threshold, performance deteriorated markedly when the pulses were lowpass filtered. It appears that discrimination of slight changes in the power spectrum of the two transient signals. especially in the high-frequency region (8000 Hz and above) underlies the ear's sensitivity to a temporal discontinuity. [Research supported by the National Institute of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to the Center for Human Information Processing.]
Discrimination of the Envelope Curve for Tone and Noise Bursts
Authors: Nábĕlek Igor V. , Rozsypal Anton J.
Published: October 2005

A critical duration was found, below which two acoustic bursts differing in their envelope curves are indiscriminable, and above which they sound different. The method of limits was used. Both bursts to be compared had the same energy, the same peak intensity, and the same carrier signal. The influence of the type of the carrier signal (tone or noise of different bandwidths), of its central frequency (250, 1000, and 4000 Hz), and of the shape of bursts on the critical duration was determined. Three shapes—Gaussian, divergent triangle (ramp up), and convergent triangle (ramp down)—were compared. With one exception the influence of factors mentioned above is small. The critical duration, expressed as the duration of a rectangular burst of the same energy and peak intensity, was found to be about 2 msec, except for the ramp up-ramp down combination with the carrier at 4 kHz, for which the critical duration is 1 msec.
Decision Criteria in Mentally Retarded Adults
Authors: Main Dana B.
Published: October 2005

Likelihood ratio cutoff measures, β, were obtained on six mentally retarded adults (I.Q. 42–65) who participated in an extensive YES-NO psychoacoustical study. Experiments were designed within the framework of the theory of signal detectability and conducted under different values of optimum β by (1) systematically changing monetary values and costs associated with the decision outcomes and (2) changing prior probabilities of input occurrence. Of those observers yielding nonchance d′ measures, the observers who changed decision criteria in the direction of optimum β had higher I.Q. than those who did not. Of those observers who changed decision criteria, the change most often took place on the first day of the new condition. Measures of β on the second and third day were comparable to measures after several days. Indeed, later measures occasionally indicated that the observer was moving away from an optimum criterion.
Loudness Summation of Pairs of Short Sounds
Authors: Cannon M. W. , Zwislocki J. J.
Published: October 2005

The loudness summation of a pair of 12-msec 1000-Hz tone bursts was investigated as a function of the interburst time interval. The listeners were asked to match the loudness of a third burst to that of the burst pair or of the second burst. Both instructions yielded similar results. In an additional series of experiments, the first tone burst was replaced by a burst of broad-band noise without materially changing the results. The loudness level plotted as a function of the time interval shows a minimum in the vicinity of 50 msec. At longer time intervals, it increases to a maximum at about 150 msec, then declines asymptotically to zero. The results may be accounted for by a combination of two processes: a linear summation with a time constant of 200 msec and an exponential poststimulatory recovery of neural sensitivity.
Electrotactile Sensitivity under Different Intensities of Simultaneous Auditory Stimulation
Authors: Gibson R. H. , Prichep Leslie S.
Published: October 2005

Direct electrical stimulation of the skin can arouse sensations similar to those from brief mechanical contact. In this study, tactile thresholds were obtained with brief pulses of direct current, under four different intensities of simultaneous broad-band continuous noise ranging from 54 dB (estimated ambient noise) to 92 dB SL. Stimulation site was the right thenar eminence, the palmar base of the thumb. Electrical touch stimuli were 100-msec-long trains of 0.5-msec anodal rectangular pulses, delivered by constant current stimulator at a pulse repetition rate of 100 pps. Thresholds were obtained from 12 subjects by means of a two-alternative forced-choice procedure. Stimulus intensity was varied by changing pulse amplitude alone. Electrotactile thresholds were highest under moderately intense noise, 66 and 79 dB SL. The magnitude of the threshold shift was small, less than 1.0 (tactile) dB, and statistically significant. Thresholds were lowest at both extremes of the sound intensity range, 54 and 92 dB SL. Variability around threshold was greatest under moderate intensity noise, least under ambient noise, where tactile thresholds were lowest. Electrotactile intensity discrimination, as it presumably involves stimulation behind the receptor, should measure limits for the touch sense. ΔI/I was most acute where absolute thresholds were worst, under moderate noise intensity. Conservative estimates of ΔI/I using run length are at worst 0.05/with ambient noise, a value in line with vibratory tactile measures.
Comparison of Information Obtained with Various Test Methods and Procedures Applied to the Violin and Parts Thereof
Authors: Hutchins Carleen M.
Published: October 2005

The variables in the violin, as well as its extreme sensitivity, make it imperative for the experimenter to understand and control as far as possible the conditions under which tests are made. Comparisons will be given between: (1) several types and positions of electroacoustical driving transducers, keeping the pickup constant as well as ambient conditions; (2) several positions of the pickup microphone, keeping the driver constant; (3) displacement measurements using the “Foto Sensor” as compared to those made with a microphone in various positions; (4) tests of a completed violin with strings damped and undamped. These factors are discussed in relation to the directional output of the violin and the environmental conditions under which it is tested.
Pressure Fluctuation Characteristics on Swept Wings under Stall Conditions
Authors: Heller Hanno H. , Bliss Donald B. , Widnal Sheila E.
Published: October 2005

To establish the feasibility of detecting incipient stall on aerodynamic lifting surfaces by measuring fluctuating pressures at strategic surface locations, a wind tunnel study was performed on models of a 45° swept and a 70° Delta wing. The experiments served to determine gross flow patterns and associated lift characteristics, and to relate these to surface pressure spectra. Several typical flow patterns were identified as the angle of attack was changed through the flow regimes where the wings experience maximum lift and approach lift loss, and related to observed pressure spectra, indicating the likelihood that such pressure spectra measurements may be useful for the detection of incipient stall. [This study has been sponsored by the Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio.]
Radiation of Sound From an Unflanged Circular Duct With Flow
Authors: Lansing D. L. , Drischler J. A. , Pusey C. G.
Published: October 2005

The problem of calculating the radiation of sound from an unflanged circular waveguide is a classical acoustical problem, which received considerable discussion in Rayleigh's treatise on the theory of sound. However, the exact solution of this problem was obtained only two decades ago by Levine, Schwinger, and Carrier for a plane wave and by Vajnshtejn for the higher modes. Owing to the complexity of the formulas obtained, numerical results have been very limited. Using modern high-speed computers, the authors bare greatly extended the previous calculations so that the theory is now useful in problems involving high-frequency sound sources operating within waveguides with flow. The proposed paper will review the exact solution for the unflanged circular waveguide and present a generalization of Vajnshtejn's results that includes flow. The effects of mode number, source frequency, and flow Mach number on reflection coefficients, radiated power, and directivity patterns will be discussed. Comparisons are made with several approximate methods now in use and the range of validity of these methods indicated.
Investigation of the Effects of Flow and Intensity on the Acoustic Impedance of Orifices
Authors: Bies D. A. , Hersh A. S.
Published: October 2005

The possibility of constructing acoustic linings for noise control by making use of the nonlinear resistance of orifices offers great promise in terms of durability and economy of construction. Such devices are particularly attractive for application in the inlet ducts of turbomachinery, where both flow velocities and sound pressure levels are generally quite high. An investigation is reported of the sensitivity of orifice impedance to adjacent orifices or walls and to tangential flow at various sound pressure levels. The sensitivity of orifice impedance to adjacent orifices or walls was found to be very much less than the sensitivity to tangential flow even for relatively modest air flow speeds. These results imply that flow effects may dominate the absorption characteristics of nonlinear orifices in ducts. [This work was sponsored by the Aircraft Division, Douglas Aircraft Company, McDonnell Douglas Corporation, Long Beach, California.]
On the Identification of Acoustic and Turbulent Fluctuating Motion in a Moving Ideal Fluid
Authors: Doak P. E.
Published: October 2005

In a moving turbulent ideal fluid, there is not necessarily a clear distinction between acoustic motion and turbulent motion. The possibilities of making unambiguous and conceptually satisfactory definitions of acoustic and turbulent components, respectively, of the fluctuating motion of an ideal fluid have been investigated. The results of the investigation have fundamental implications for a number of problems. Among these are: (a) propagation and radiation of acoustic disturbances in a sheared, heated turbulent fluid flow; (b) origins of “aerodynamically generated” sound; (c) energy density and energy flow in an acoustically radiating turbulent fluid.
On the Propagation and Radiation of Sound in Finite-Length Acoustically Lined Ducts Carrying Heated, Sheared Flows
Authors: Vaidya P. G. , Doak P. E.
Published: October 2005

A unified mathematical analysis has been developed for describing acoustic propagation in, and radiation from, finite-length acoustically lined ducts carrying heated, sheared flows, such as inlet and exhaust ducts of jet and turbojet engines. It is shown that simplified models of the complete theoretical description can be used in a number of important practical situations for prediction of radiation efficiency and of propagation effects of both thermal and viscous gradients. The theory also can be applied to problems of prediction of mode excitation amplitudes at frequencies near cut-on, where the reaction of the field back on to the source can be important.
Calculation of Eigenvalues of the Finite Difference Equations Describing Sound Propagation in a Duct Carrying Sheared Flow
Authors: Wynne G. A. , Plumblee H. E.
Published: October 2005

A finite difference technique for solving the associated differential equation and boundary conditions is described. The technique used is comprised of a reduction of the problem to an algebraic eigenvalue problem and its subsequent solution through a modified L-U algorithm. Solutions found by this technique were verified by comparison with those obtained earlier [see P. Mungur and H. E. Plumblee, “Propagation and Attenuation of Sound in a Soft-Walled Annular Duct Containing a Sheared Flow,” NASA Basic Noise Res. Conf. (July 1969)], using repeated Runge-Kutta integration. A reduction in machine time by a factor of 10 or 15 over the earlier method was obtained. Convergence and numerical stability of the process are discussed.
Psychometric Functions Obtained with Band Limited Noise
Authors: Bourbon W. T. , Nicholas T. W. , Todd G. E.
Published: October 2005

The relations between noise spectrum level, S/N ratio, and critical band width were determined for 500-Hz signals. With wide-band noise at spectral levels of 15 and 45 dB SPL, psychometric functions were obtained in a 2AFC task. Signal intensities that produced P(c) values of 0.50, 0.60, 0.70, and 0.80 in wide-band noise were presented in band-limited noise. The resulting critical-band patterns differed from those often predicted in the masking literature: they were highly dependent on spectrum level but were less influenced by S/N ratio.
Masking by Double-Sideband Suppressed Carrier Amplitude-Modulated Sinusoids
Authors: Booth Joan C. , Brandt John F.
Published: October 2005

A variation of the two-tone masking technique was employed in an experiment designed to investigate the effects of stimulus intensity upon the critical band. The masker consisted of the upper and lower sidebands of an AM signal with the carrier signal suppressed. The test signal was a pulsed sinusoid equal to the carrier frequency and located midway between the two maskers. The spacing between the sidebands (Δf) of the masker, the masker SPL and the location of the masker (carrier/test frequency) were parametrically varied. As the test frequency increased, a peak (increase) in the masking audiogram occurred that was dependent upon Δf and SPL. As Δf increased, this peak occurred at a higher test frequency. With Δf held constant, the peak migrated to a lower frequency with increases in masker SPL. While the traditional two-tone masking technique generally results in critical band estimates that are dependent only upon frequency, the variation used in the present study leads to results that are dependent upon frequency and SPL.
Detection of Signals in Brief Maskers
Authors: Patterson James H.
Published: October 2005

A class of brief waveforms (10 msec) having identical energy spectra and different phase spectra (Huffman sequences) were used in a series of masking experiments. The peak factor of these waveforms can be systematically varied, thus changing the distribution of the energy over the duration of the waveforms. When these waveforms are used as signals, they are equally detectable in white Gaussian noise. However, when these waveforms are used as maskers of sinusoidal signals, they do not produce equal masking. The masked threshold for the sinusoids changes as much as 30 dB as a function of the peak factor of the maskers. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to the Center for Human Information Processing.]
Distribution of Multidimensional Random Sinusoids
Authors: Lyon Richard H.
Published: October 2005

The probability density of sums of the form y =  ∑ i=1N  ∏ j=1n sinψij are of interest in the statistics of structural and room response. The ψij's are assumed statistically independent, the value of N is arbitrary, and n may vary from 1 to 6 for problems of interest. Success in obtaining the probability functions for y using various methods will be reviewed.
Effect of the Modal Damping on the Statistical Properties of the Sound Field in Reverberant Chambers
Authors: Tichy J.
Published: October 2005

The spatial distribution of the sound pressure was investigated in a model reverberant chamber at discrete frequencies. Results of the measurements were evaluated in terms of cumulative distribution of sound pressure squared, variance, autocorrelation function and phase relations of the sound field as a function of modal damping. Statistical distributions of the maximum, minimum, and zero crossings of the spatial sound-pressure distribution are presented. The conclusions concerning applications on sound power measurements in reverberant chambers are discussed.
Use of Mean Squared Pressure along a Reverberant Room Diagonal for Sound Power Measurement
Authors: Ingalls Douglas J. , Ebbing Charles E.
Published: October 2005

The mean of the squared pressure along part of a room diagonal is frequently used to determine the sound power using the reverberant room technique. The spatial pressure along a room diagonal has been evaluated experimentally and theoretically for a source located in the corner of a 300-m3 and a 150-m3 reverberant room. For frequencies between 100 and 2000 Hz, the average number of maxima in the mean squared pressure 〈p2〉 is given by N=4L/πλ, where L is the length along the diagonal and is independent of absorption, room size, and stationary diffusers. The variation of 〈p2〉 at a maxima is given by 〈p2〉=An cos(πkx/4), where the An possesses a gamma probability distribution that depends on absorption. It is shown that the value of the mean of 〈p2〉 for white noise with a 6-Hz bandwidth depends on the traverse length selected and is independent of damping while the standard deviation is improved by adding damping. Experimental results substantiate this conclusion.
Techniques for Improving the Low-Frequency Performance of Small Reverberation Chambers
Authors: Scharton T. D.
Published: October 2005

An experimental study of two small reverberation chambers (135 ft3 and 107 ft3) with different shapes indicates that the performance of the chambers evaluated primarily on the basis of small spatial variations in mean-square pressure is good when the modal overlap index is greater than one-third. Two techniques for reducing the spatial variations in the low-frequency regime are investigated. The first technique involves suspending honeycomb panels in the chamber to enrich the acoustic modal density. The results of the study indicate that the panels did increase the apparent acoustic modal density and decrease the spatial variations in the low-frequency regime. The second technique consists of increasing the low-frequency absorption to lower the frequency at which the modal overlap index equals one-third. The results show that increasing the absorption also reduces the spatial variations at low frequencies.
Using a Simulator to Study Subjective Rating Scales for the Acoustics of Music Halls
Authors: Anderson G. S. , Horrall T. R. , Watters B. G.
Published: October 2005

An auditorium acoustics simulator can be used in constructing rating scales for the subjective characteristics of hall acoustics. It is also helpful in determining the relationships between various objective hall parameters and the resulting subjective characteristics. For example, we can use a simulator to establish a calibrated set of symphonic music sound fields where the over-all loudness is varied in equal steps. The set then becomes a useful scale, which can be used to describe loudness judgments for a particular hall to anyone who is familiar with the set. A simulator can also be used in psychoacoustic experiments. For example, it can help determine whether judgments of the over-all loudness of constant intensity symphonic music are affected by changes in the relative arrival time of sound components (related to reverberance) or the spread of direction of arrival (related to envelopment). We present preliminary results of experiments where a simulator was used to study rating scales for musical acoustics.
Development of Speech Acoustics Criteria Using an Auditorium Acoustics Simulator
Authors: Bruce R. D. , Watters B. G.
Published: October 2005

A prime requirement for the acoustical design of theaters and multipurpose auditoria is adequate speech clarity. We have reported earlier a reasonably good correlation between the subjective evaluation of clarity for live drama in several theaters and the articulation index derived from the omnidirectional hall impulse response using the computational scheme of Lochner and Burger [“The Influence of Reflections on Auditorium Acoustics,” J. Sound Vibration 1, No. 4, 426–454 (1964)]. However, since their study was done using a restricted number of echoes and directions of echo arrival, we have performed further experiments utilizing an auditorium acoustics simulator. Reverberant sound fields were generated having an echo density and range of arrival directions comparable to those in typical multipurpose auditoria.
Sound Absorption of Curtains
Authors: Peutz V. M. A.
Published: October 2005

The absorption of normal incident sound by a curtain hung flat before a wall depends on the flow resistivity and the weight of the material and the distance to the wall, as has been found experimentally and could be deduced theoretically. The same theory allows one to calculate the absorption for oblique incident and, also therefore, for statistical omnidirectional incident sound. The sound absorption thus calculated for many curtains with different flow resistivity, weight, and distance to the wall has been compared with the sound absorption as measured for these curtains hung flat at the mentioned distances to the wall in a reverberation chamber. An excellent agreement has been obtained. If the curtain is draped, the absorption also depends on the draping. If the “draping degree” is defined as the ratio of the apparent surface to the total undraped surface, it has been found experimentally that the amount of acoustical absorption introduced by the curtain into a reverberation chamber is for the midfrequencies inverse proportional to the fourth root of this “draping degree.”
Acoustic Tests of a Flexible Spacecraft Model
Authors: Noonan W. E. , Daiber J. R. , Schoenster J.
Published: October 2005

An acoustic test program has been conducted with a dynamically scaled model of a representative space-craft structure to investigate the effectiveness of producing vibration response over a wide frequency range. The model was a 110 scaled Voyager Spacecraft and Shroud Assembly supplied by NASA Langley Research Center. Specific objectives of the program were to determine: (1) the capability to produce dynamic response of a scaled model over a wide frequency range; (2) the linearity of the response with changes in the acoustic levels; (3) the sensitivity of the test article to unsymmetrical mounting in the acoustic field; (4) the effects of the dynamic response resulting from variations in the structural configuration. The acoustic test facility utilized four air stream modulators and a laminated fiberglass progressive wavetube. Model configuration and position were varied during testing. Acclerometers, strain gauges, and displacement probes were used to measure the acoustic field external and internal to the model. Acoustic noise levels to 140–146 dB were produced in the progressive-wave tube. The results of this program indicated that acoustic testing using a simple fiberglass enclosure is an effective means of producing broad-band dynamic response of flexible vehicles. In addition, minor variations in structural configuration and variations in structural configuration and variations of model position in the test facility indicated minor effects on the test results.
Seismic Waves Generated by Sonic Booms
Authors: Posey Joe W.
Published: October 2005

Seismic waves produced by sonic booms striking the earth's surface have been observed and reported by several investigators. The incident N wave of sound pressure emanating from a supersonic aircraft in level flight moves across the ground at a speed below the speeds of seismic waves. Thus, all of the boom energy is reflected and the seismic disturbance decays exponentially with depth. R. K. Cook has solved the problem of the penetration of a sonic boom into water. Cook's technique is applied to the generation of seismic waves, and similar results are found. The pressure at the interface has a positive singularity at both the leading and trailing edges of the N wave and includes a precursor and a tail, each being weak and positive. Strains and displacements are small and pose little threat to structures.
Similitude Approximations for Vibrating Thin Shells
Authors: Soedel W.
Published: October 2005

True dynamic similitude in the Newtonian sense proves often to be too restrictive in experimental investigations of dynamic characteristics of large shell structures by use of smaller models. Also, design information yielded by true similitude considerations is limited because of the usual requirement of total geometrical scaling. Thus, approximate similitude relationships were derived starting with Love's equations of motion for thin shells. Depending on the relative dominance of bending and membrane stress influences, selection is made betwen two similitude expressions. This allows the introduction of shell thickness as a parameter independent of the scaled surface geometry. Free as well as forced vibrations are examined. Some of the implications of approximate similitude are illustrated using as example a simply supported circular cylindrical shell.
Operational Methods in Determining the Exact Eigenvalues of ∇4φ+K2(∂2φ/∂t2)=0, in Rectangular Coordinates
Authors: Selvaggi J. A. , Schmitt J. A.
Published: October 2005

The rules of the LaPlace transforms are invoked in the determination of the eigenvalues of the above equation. The boundary conditions, although physically realistic, were arbitrarily chosen. The method is independent of the set considered. The solution applies to the natural modes of rectangular plates. Previous solutions have only given approximate results. The above technique results in closed-form solutions. The method of separation of variables is not needed. The boundary conditions chosen were: φ(x,ly) = φ(lx,y) = φ(0,y) = 0 ∂2φ∂y2|y=0 = ∂2φ∂y2|y=ly = ∂2φ∂x2|x=lx = ∂2φ∂x2|x=0 = ∂3φ∂y3|y=0 = 0 The initial conditions were also zero.
Variational Finite-Element Calculation of the Acoustic Response of a Rectangular Panel
Authors: Gladwell G. M. L.
Published: October 2005

The problem of the acoustic response of a structure falls into three parts. (1) The response of the structure to given acoustic excitation, when the effect on the vibration of the resultant acoustic radiation is ignored. This part of the problem is usually solved by using a normal-mode approach, and has usually therefore been carried out only for simply supported plates, for which the normal modes are simple functions. (2) The determination of the acoustic radiation from a given structural vibration. Numerous workers have calculated the total radiated energy and/or the radiation-intensity-distribution pattern for different vibrating surfaces. (3) The effect of the radiation on the response of the plate. This aspect is usually ignored, and when the acoustic medium is air, it is in any case, an effect that is usually negligible. When it is included, the problem is closed (in the sense that it has a feedback loop) and its theoretical analysis involves the use of integral equations. Morse has recently solved the complete problem for the case of a circular membrane set in an infinite plane rigid baffle. In this paper, a variational principle derived in an earlier paper [J. Sound Vibration 4, 233 (1966)] is used in conjunction with a finite element method to calculate the response of a rectangular panel set in an infinite plane rigid baffle. The method can be applied with equal ease to plates with different boundary conditions, and the effect of the acoustic radiation on the plate vibration is considered in full.
Children's Perception of Stress Contrasts
Authors: Atkinson-King Kay
Published: October 2005

Children are believed to perceive and produce stress at an early age, but we have little knowledge of what they actually know about the rules of stress in a language at various ages. In an attempt to determine children's competence in regard to one aspect of English stress, children of different ages were asked to identify two types of noun phrases that were minimal pairs with respect to stress. One type of noun phrase was a compound noun with a primary-secondary stress pattern (e.g., gréenhouse), and the other was an adjective followed by a noun with a secondary-primary stress pattern (e.g., green hóuse). Children listened to the complete set of items in an irregular order and were asked to identify what they heard each time by choosing between two pictures corresponding to the terminal pair. The percentage of correct identifications increased with age and grade, reaching almost 100% by the sixth grade. Individual variation and sex differences also played a role and are discussed. [This work was supported by a NINDB grant.]
Natural-Speech Experiment on American English Intonation
Authors: Greenberg S. R.
Published: October 2005

A number of potential intonation contrasts were elicited from 12 speakers, who were subdivided into a “sophisticated” group, consisting of male and female graduate students in speech, English, and linguistics, and an age-matched “naïve” group of six undergraduates. Their excised stimuli were played for 50 listeners, including the 12 speakers, who categorized them on a forced-choice basis. There were eight “syntactic” categories (including such contrasts as statement/repetitive question and unemphatic/emphatic) and five “emotional” categories (including bored/interested and calm/angry/contained anger). In all but one category, the speakers communicated far more effectively than had been predicted by previous investigators such as Hultzén (1964) and Bolinger (1958). The significant differences in performance among the speakers provide partial corroboration for Gleitman's (1967) contention that competence is not necessarily universal and equal. Furthermore, differences in performance of the same subjects as speakers and as listeners suggest that competence might best be viewed on a continuum from “active” to “latent.”
Coarticulation and Phonetic Competence
Authors: Tatham Marcel A. A.
Published: October 2005

This paper examines possible criteria for establishing competence/performance distinctions in phonetic theory. It is emphasized that for the competence aspect, rules should take a form compatible with those of the phonological component, and question of whether the coarticulation phenomenon can be handled adequately in the phonetic competence model is also discussed. Recent electromyographic data are referred to, and the problem of the relative roles of active and passive (voluntary and involuntary) programming of the muscles associated with articulation re-examined. It is argued that the area is by no means exhausted and that there are even yet questions to be asked.
Preliminary Evidence for a Universal Feature Detector System—Perception of the Repeating Word
Authors: Naeser M. A. , Lilly J. C.
Published: October 2005

The phenomenon of perceiving alternate word forms upon repeated hearings of the same word has been described by psychologists variously as the repeating word effect or the verbal transformation effect. The purpose of this investigation was to describe the phone-type substitutions occurring in the alternates perceived by linguists and nonlinguists, native (N) and nonnative (NN) speakers of English during repeated presentations of the word “cogitate” [khadȝɪtheyt]. The stimulus word was recorded once every 0.75 sec onto a 15-min master tape from a single recording of the word on a sound spectrograph drum. A total of 159 linguists (27 NN, representing 12 different tonal and atonal languages) wrote their perceived alternates to the stimulus word in broad IPA transcription. The 60 nonlinguists (2 NN) wrote their alternates in traditional American orthography; these were later converted to “best-guessed” IPA by a trained phonetician. The linguists heard an average of 15 different alternates in 15 min; the nonlinguists heard 11. The alternates were coded by the trained phonetician and analyzed by a computer, showing phone substitution and alternate type. Five different alternate types were perceived: nondictionary, dictionary, phrase, clause, and foreign. The stimulus word was considered to contain the 11 phone segments as transcirbed above. The subjects' (Ss) phonetic alternates were coded by feature substitutions for these 11 segments. Evidence for a universal feature detector system is seen in the overwhelming regularity of phone-type substitutions in alternates of N and NN speakers. All Ss tended to use 11, 12, or 13 phone segments in each alternate. For all Ss, the average alternate contained 50% of the original stimulus phone segments in correct temporal order. The study thus speaks to both a universal feature detector system and to redundancy in speech.
Simulation of the Localization of Distant Sound Sources by Earphones
Authors: Molino J. A.
Published: October 2005

Subjects made forced choices to either side of a reference direction (0°, 30°, 60°, 75°) to locate the image of pure tones presented through earphones. Various combinations of interaural intensity differences (IIDs) and interaural time differences (ITDs) were used, including some combinations that do not occur in nature. Psychometric functions confirmed the expected apparent azimuth of IID/ITD combinations based on free-field diffraction theory and microphone measurements. The relative dominance of the intensive and temporal cues was examined at each frequency (500, 1000, 8000 Hz). The shape of the psychometric plane for the bidimensional matrix of IID/ITD combinations centered around 30° azimuth showed possible nonlinearities in the trading relation for 1 kHz. Data were also collected from the same subjects using the same signals presented by means of distant loudspeakers in an open field. When the free-field data were compared with the data from earphone simulated sounds, they showed similar angular acuities, being approximately the size of those reported in the literature. Equations are presented for computing the IID/ITD combinations necessary at any frequency for any apparent frontal azimuth. [This research was partially supported by the Office of Naval Research and Columbia University.]
Binaural Threshold and Interaural Phase Angle Differences
Authors: Gerber Sanford E. , Jaffe Phyllis G. , Alford Brownyn J.
Published: October 2005

The relation between interaural phase angle differences and the binural threshold of hearing was investigated using Békésy audiometry and a Grason-Stadler phase shifter. The literature on the subject has been contradictory and limited in most cases to only one or two phase differences. Threshold tests were administered to 27 subjects at 0°, 45°, 90°, and 180° at each half-octave from 500 to 4000 Hz. Thresholds at 45°, 90°, and 180° were subtracted from thresholds at 0°, and t tests were done on the differences. The interactions among interaural phase-angle differences and the binaural thresholds were limited to frequencies of 1500 Hz and lower. This finding is consonant with some of the extant literature. Moreover, the significant interactions were limited to 45° and 90°. There were no significant interactions at any frequency for 180°.
Monotic and Homophasic Detection of Pure Tones in White and Pink Gaussian Noise
Authors: Sonn Martin
Published: October 2005

This study compares aural detectability for pure tones in white and pink Gaussian noise for a monotic (NmSm) and three homophasic (N0S0, Nπ/2Sπ/2, and NπSπ) listening conditions. Pure-tone signals from 125 to 4000 Hz masked by a 5000 Hz-wide noise band with band pressure levels of 70 and 90 dB re 20 μN/m2 served as stimuli. Subjects used a method of tracking to obtain masked threshold contours. MLDs (re N0S0) for the homophasic conditions did not show a consistent trend at all frequencies and levels but appeared to be dependent on the interaction of these variables as well as the slope of the noise spectrum. The most consistent improvements observed occurred with Nπ/2Sπ/2 for the 70 dB white-noise condition with MLDs of about 0.8 dB (at 355 Hz), 0.4 dB (at 500 Hz), 1.2 dB (at 710 Hz), and 0.2 dB (at 1000 Hz). Monotic results were consistently poorer than for any of the homophasic conditions. These results showed a minimum MLD of −0.1 dB (at 2000 Hz, 70 dB, white) and a maximum of −3.2 dB (at 2000 Hz, 70 dB, pink). At frequencies below about 1000 Hz, detection was better with white noise masking and at higher frequencies with pink noise masking. For the results obtained, the standard error of measurement was 0.2 dB or less.