bluuebunny/crossref_metadata_2025 huggingface dataset:
Second-Order Calculation of Transit Time in a Medium with a Velocity Variation in One Dimension
Authors: Potter David S.
Published: September 2005

The transit time along a ray path in a medium with a one-dimensional sound-velocity variation has been calculated to the second order. The calculation makes use of the first and second moments of the velocity variation. Define the velocity (a function of the Z coordinate only) as C = C0/1 + μ(Z). Define μl¯ = 1Z2 − Z1  ∫ Z1Z2 μldZ. The transit time from a point P1(ρ1 = 0, Z1) to a second point P2(ρ2,Z2) is found to be t = (R/C0)[1 + μ̄ − 12(μ2¯ − μ̄2) ctn2β], where R2 = ρ22 + (Z2 − Z1)2; ctn2β = ρ2/(Z2 − Z1). The solution is useful for situations where β is large enough so that 12(μ2¯ − μ̄2) ctn2β≪μ̄ holds and has been verified to second order with known eikonal solutions.
Pressure-Gradient Microphone for Sonic-Field Measurements
Authors: Heiserman R. L. , Thurston G. B.
Published: September 2005

A pressure-gradient microphone has been developed for sonic-field measurements in air. The microphone consists of two closely spaced probe tubes which communicate to the air volumes adjacent to either side of the metal diaphragm of a condenser element. The characteristics of this condenser-type gradient microphone have been studied both in a free field and with a small coupling chamber. The calibration characteristics thus obtained are presented along with the results of the study of the radiation field of a simple source. (This work was supported by the Office of Naval Research.)
Periodicity Pitch and Masking in Pathologic Ears
Authors: Voots Richard J.
Published: September 2005

The locus of the periodicity-pitch sensation within the auditory system continues to be a subject of controversy. A recent paper by Small and Campbell supports the thesis that the low-pitch sensation is the result of a periodic neural activity in high-frequency perceptual channels (2000 cps in their experiment). In the present experiment, the methods of Small and Campbell have been used to further investigate this phenomenon by examining the responses of several subjects with severe high-frequency losses (presumably due to cochlear or neural pathology) to a similar pulsed signal. The filter range has been shifted to 4000 cps to coincide with the loss. Narrow-band random noise was used as the masker. Results are compared with normal ears under the same conditions. The data indicate that a narrow-band noise centered at 250 cps, covering the repetition rate, is a more effective musket for the low-pitch sensation than either a similar 2000- or 4000-cps noise.
Analog Simulation of the Basilar Membrane
Authors: Hemdal John F. , Hughes George W.
Published: September 2005

An analog-computer simulation of the mechanical action of the basilar membrane has been performed which results in a closer approximation to the Békésy experimental data than is feasible by a numerical evaluation approach. Confirmation of the results of Flanagan pertaining to pitch perception has been obtained. The analog model has been utilized in testing several hypotheses concerning the phenomenon of the “residue” in hearing.
Two-Dimensional Green's Function for a Thin Plate
Authors: Pilant Walter L.
Published: September 2005

The two-dimensional Green's function for an infinite free elastic plate is calculated for an arbitrary time harmonic line force parallel to the surfaces of the plate. This force may act on the surface of the plate or within the plate. Using this two-dimensional Greens' function, representation theorems are derived for a terminated plate. For “mixed” boundary conditions at the termination of the plate, explicit solutions are derived for the reflections of waves and for the excitation of the plate at the terminating end.
Tapering a Bar for Uniform Stress in Longitudinal Oscillation
Authors: Bies David A.
Published: September 2005

A new kind of cross-sectional taper is described which provides a bar with the possibility of uniform stress in longitudinal oscillation, provided that the ends of the bar be properly terminated. A theory which describes the behavior of the bar in longitudinal motion is presented and compared with the results of experiment.
Flexural Vibration of Shallow Orthotropic Spherical Shells
Authors: Hoppmann W. H. , Miller C. E.
Published: September 2005

The paper presents the theoretical development of the equations of motion for the flexural vibrations of a shallow spherical shell of orthotropic material. For symmetrical vibrations, the motion is described by two ordinary sixth-order differential equations with variable coefficients. Factorization of the sixth-order operators into second-order operators is discussed, and the details of solution are worked out for the case in which the equations are reduced to those for the isotropic shell. It is shown that equations for the latter case agree exactly with those derived previously by Reissner [Eric Reissner, “On Vibrations of Shallow Spherical Shells,” J. Appl. Phys. 17, 1038–1042 (1946)]. A table of calculated frequencies is given along with some experimental results for steel shells. (This investigation was conducted under Contract No. DA-30-115-509-ORD-912, Department of Army Ordnance Corps, Ballistic Research Laboratory, Aberdeen, Maryland.)
Loss Factors of Viscoelastic Systems in Terms of Energy Concepts
Authors: Ungar Eric E. , Kerwin Edward M.
Published: September 2005

The definition of loss factor in terms of energy quantities is re-examined, particularly as it applies to composite viscoelastic systems. A restatement of this definition in terms of a corresponding viscoelastic spring is used to show that this definition is extremely useful for massless (ideal viscoelastic spring) systems, but may be applied unambiguously to spring systems with a single attached mass only at resonance. Simple relations are presented which express the loss factors of series-parallel arrays of massless viscoelastic springs in terms of properties of the individual components. Implications of these relations in damping of composite structures are discussed. (This work was supported in part by the Aeronautical Systems Division, U. S. Air Force.)
Effect of Transducer Velocity on the Structure of Signals Reflected from the Ocean Bottom
Authors: Hurdle Burton G. , Ferris Raymond H.
Published: September 2005

The time history of acoustic signals scattered from the bottom displays a beat or interference characteristic when the source and/or receiver are in motion. Beat rates obtained statistically from observed data are shown to vary with velocity of source and receiver, as well as with transmitted frequency and acoustic geometry. These data obtained with a conical beam at 19.5 kc/sec are compared with a simple physical model. Experimental results of a method for controlling the beat rate by frequency modulation of the transmitted signal are illustrated. Implications of the observations relative to reflection and scattering theory are discussed.
Backward Scattering of Acoustic Energy from Objects of Simple Geometric Shape for Low Values of ka
Authors: Diercks K. J.
Published: September 2005

Measurements have been made of the backward-scattered energy from spheres, spheroids, and cylinders at values of ka ⩽ 10 (0.5 ⩽ ka ⩽ 10). Echo levels (reported as Target Strength) have been obtained for 5-in. o.d. solid and air-filled aluminum spheres and cylinders, for a 1-in. o.d. solid aluminum sphere and cylinder, and for 5- and 1-in. interfocal distance (fineness ratio 5/3) solid-aluminum prolate spheroids. Pulses of 1-msec duration over the frequency range 5–60 kc were employed for all measurements. For each target used, two curves were obtained. The first is a plot of the average value of the echo measured at the back-scattering point; the second is of the peak value of the energy contained in the first 50–100 μsec of the echo. The latter analysis is an attempt to resolve that portion of the echo which is due only to reflection from the surface of the target and is not confounded by the interference effects of, e.g., reradiation. Agreement between predicted and obtained values is in general good, with the major differences occurring with the thin-walled targets.
Scattering of Sound by a Cylinder Having a Reactive Surface Impedance
Authors: Horton C. W. , Diercks K. J.
Published: September 2005

A solid metal cylinder was transformed into a corrugated surface by cutting deep, narrow grooves parallel to the axis. These grooves were designed so that the impedance of the surface would approximate a pure reactance. The structure of echoes scattered by this cylinder is measured and compared with the theoretical prediction of W. Franz [Z. Naturforsch. 9a, 705 (1954)].
Electromyographic and Acoustical Study of the Production of Certain Final Clusters
Authors: MacNeilage Peter
Published: September 2005

This study attempted to answer the question: What is the difference, if any in the acoustical and articulatory characteristics of /f/ in utterance final position and /f/ embedded in final clusters. Spectrographic analysis of acoustical records was made. An index of articulation was provided by electromyograms recorded from muscles concerned with the production of /f/. The acoustic representation of /f/ was found to be different depending on its context. In particular, the duration of /f/ was greatest when /f/ was in final position, and varied, depending on context, in other positions. On the other hand, the muscle-potential patterns were similar for all positions of /f/. Electromyograms taken from the corner of the lip showed a peak at the onset of /f/ friction, similar rise times and decay periods for the muscle-potential burst, and similar amplitudes. The change in duration of /f/ from final to prefinal position, therefore, seems to involve merely a change in timing of the production of other phonemes in relation to /f/, rather than reorganization of the articulatory gesture of /f/ itself.
Development of a Water-Cooled Ground Run-Up Suppressor
Authors: Hirschorn Martin , Morgan James A. , Oran Frederic M.
Published: September 2005

High-powered afterburning jet engines have made it evident that effective ground run-up suppressors are required for personnel protection as well as for good community relations. This need exists particularly in the military services. Efforts to satisfy military requirements for durable, portable high-performance ground run-up suppressors were initiated by Industrial Acoustics Company, Inc., in 1958 under the sponsorship of the U. S. Navy. The primary component of the first prototype built was a MULTI-JET, essentially a perforated colander, which had been tried and proven in many installations throughout the U.S.A. The MULTI-JET, however, in its original design concept was not applicable to the extreme operating conditions to which it was subjected during afterburner tests. Therefore, major changes in type of material and thicknesses, supporting structure, and over-all design had to be made. These changes, however, were not adequate to permit afterburner operation without the use of coolant. At the same time that durability problems were experienced, the acoustic performance of the MULTI-JET deteriorated. This occurred due to mismatching of the diameter of the MULTI-JET and exhaust of the engine. Unavoidable changes in the diameter of the perforations due to the changes in thicknesses of the material also affected the acoustic performance. The oversized MULTI-JET resulted in backflow during military operation and a “boom” or pressure wave during afterburner operation. Substantial development work in the laboratory and the field yielded a design for a universal aerodynamic and acoustic coupling. This coupling, or flow diffuser, alleviated some of the problems. Field experience and test data with this flow diffuser are reported. The remaining problem, that of adequate cooling or efficient utilization of water during afterburner, was solved by utilizing the same flow diffuser as a water-injection device. Details of the design and acoustical, aerodynamic, and structural considerations are discussed. The suppressor evolved from the combination of the MULTI-JET and flow diffuser, however, did not meet the ultimate acoustic-performance goal set by the U. S. Navy. Continued development on all-steel type of silencers resulted in a new type of packless dissipative panel. This panel was called the Q panel. Test data and design considerations are discussed. A review of the performance of the various prototypes manufactured, including the accepted water-cooled ground run-up suppressor consisting of flow diffuser, MULTI-JET, and Q panels, is presented.
Response of a Disk to Rigid-Body Motions of Its Boundaries
Authors: Jones J. P. , Bhuta P. G.
Published: September 2005

The dynamic response of a homogeneous, isotropic, elastic disk due to rigid-body motion of its boundary is treated. Asymptotic values of the displacements and stresses are obtained for small times. The specific problem of impulsive applied accelerations is treated numerically and analytically; more-general motions can be built up from this by integration. This problem has applications to propellant-grain stress analysis and to other problems of interest to machine designers.
Source-System Interaction in the Vocal Tract
Authors: Flanagan J. L. , Meinhart D. I. S.
Published: September 2005

Acoustic analyses of the vocal system conventionally assume separability of the voiced-sound source and the system. That is, the tract configuration and its driving-point impedance are assumed to influence the acoustic volume flow at the glottis negligibly. Some interaction between the glottal source and the tract is known to occur, however. Toward estimating this interaction and its potential importance to speech naturalness, a computer simulation is made of glottal-source operation. The nonlinear (flow-dependent) properties of the glottal impedance are used to calculate the acoustic volume velocities at the glottis and mouth for a simple vocal configuration. Glottal-area functions, obtained from high-speed photography, are supplied as parameters to nonlinear difference equations with non-constant coefficients. From known initial conditions, the equations are iterated to reach steady-state solutions. The calculated glottal velocities are compared for negligible vocal-tract input impedance and for a low-frequency approximation to a realistic load. The influence of physiological parameters such as subglottal pressure and vocal-cord thickness are also considered.
Duality Principle for Horns
Authors: Pyle Robert W.
Published: September 2005

The concept of duality often encountered in electrical network theory may be extended to acoustic horn theory. For “plane” waves in two horns whose cross-sectional areas vary as S1(z) and S2(z), one can show that if S1(z)S2(z)=const, then the horns are acoustic duals. That is, the axial distribution of pressure in one horn is the same as the distribution of volume velocity in the other. As a result, input, output, and transfer acoustic impedances of one horn have the same form as the corresponding acoustic admittances of the other. A solution of the Webster horn equation for the pressure and volume velocity corresponding to a given horn contour thus yields the solution for the reciprocal contour as well. Whereas the exponential horn and its limiting case, the uniform tube, are their own duals, the dual of the conical horn is generated by revolving a rectangular hyperbola about its asymptote. Consideration of the latter pair of duals contributes to the understanding of brass wind instruments. [Work supported in part by the U. S. Office of Naval Research.]
Determination of Smoothed Cross-Sectional-Area Functions of the Vocal Tract from Formant Frequencies
Authors: Mermelstein Paul , Schroeder M. R.
Published: September 2005

Approximate formant frequencies for a given vocal-tract configuration can be calculated by integrating Webster's horn equation. No general methods are available for the solution of the inverse problem, that of determining the cross-sectional area from the formant frequencies. Previous attempts involved approximations of the tract shape in terms of a small number of parameters of a given model based on the physical constraints acting on the vocal tract [see, for example, K. N. Stevens and A. S. House, J. Acoust. Soc. Am. 27, 484–493 (1955)]. The procedure presented here elimininates the necessity for such a priori assumptions. The logarithm of the area function is represented by a spatial Fourier cosine series of a symmetrical tract of length twice that of the original tract. Starting with a uniform tract closed at one end, a steepest-descent search in the multidimensional space of Fourier coefficient is found to converge rapidly to a configuration yielding low-order formant frequencies nearly identical to those specified. Results are presented for articulations of sustained vowels calculated from the first three formant frequencies and represented by 3 Fourier coefficients. The area functions so obtained are found to be good smoothed approximations to those derived from x-ray data.
Subjective Judgments of Footstep Transmission through Floors
Authors: Olynyk D. , Northwood T. D.
Published: September 2005

The ISO procedure for assessing impact transmission through floors involves comparing the spectra of transmitted noise produced by a standard tapping machine. An obvious weakness in the method is that it does not really simulate footsteps. One is more interested, however, in how well the method rank-orders floor structures as compared to the impressions of an apartment dweller listening to his upstairs neighbor. This project was intended to provide a partial answer to this complex question. Subjective comparisons were made of the “loudnesses” of footsteps on a concrete-slab floor with various surface layers. The main procedure was to make pairs of tape recordings, involving two different floors, on a 2-channel recorder. Observers listened to a tape loop on which the two sets of footsteps were presented alternately, and adjusted gains of the two channels until the two sets sounded equally loud. Then the difference in over-all gain was used as a measure of relative loudness of the two sets of footsteps. Comparison with ISO ratings shows that they exaggerate the differences between unacceptable floors, but that there is a reasonable degree of correlation among floors that might be deemed acceptable.
Anatomical Dimensions and Electrical Potentials of the Chinchilla Cochlea
Authors: Eldredge Donald H.
Published: September 2005

The chinchilla cochlea has three spiral turns above a round-window segment. Total length of the basilar membrane under the tunnel of Corti is about 17.5 mm, with about 4.5 mm in the round-window segment. Corresponding dimensions in guinea pig are 18.8 and about 1.5 mm. Width of the basilar membrane measured from the foot of innermost tunnel rod to spiral ligament changes from 0.10 mm at the round window to 0.35 mm near the apex. Corresponding dimensions in guinea pig are 0.06–0.25 mm. Frequency-response characteristics for cochlear-microphonic potentials measured with differential electrodes in 1st, 2nd, and 3rd turns clearly reflect a basilar-membrane response “tuned” to lower frequencies than at corresponding locations in guinea pig, but maximum voltages available are essentially the same. Cancellation of cochlear microphonic in the whole-nerve action potential electrode configuration is poor. Apparently, the long round-window segment introduces asymmetry in the electrical fields. Partial masking and a LINC computer reveal reasonable action potentials. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Computer Study of Violin Tones
Authors: Mathews M. V. , Miller Joan E. , Pierce J. R. , Tenney James
Published: September 2005

Recordings were made of tones played by a professional violinist in an anechoic chamber. The sounds were digitized at 10 000 samples/sec and a frequency analysis made by computer. The amplitude of each harmonic was plotted at each pitch period. Two features of the spectrum were noted. The spectral envelope is essentially constant throughout the tone. The spectrum possesses zeros at regular spacing—typically every third harmonic. To explain the zeros, a theory was developed that involves the nature of the excitation by the bow. A computer program was written to synthesize tones with zeros. Tones with zeros characteristic of the violin were judged to have a very stringlike sound. It is hypothesized that these zeros, produced by the bow excitation, may be as important in determining string timbre as resonances introduced by the violin body.
Head-Baffle Effect for Different Hearing-Aid Microphone Locations
Authors: Lybarger Samuel F. , Barron Fred E.
Published: September 2005

Using a small magnetic microphone, the response at four selected microphone sound-entrance locations in the vicinity of the ear was compared with the freefield response at the center head position. The four positions of the microphone sound entrance were immediately behind the ear, at the top of the ear, immediately in front of the ear, and at a point some 212 in. forward of the last-mentioned position. Response curves were made for sound-incidence angles of 0°, 90°, 180°, and 270° over the frequency range 200–7000 cps. While baffle effects are materially different for different angles of incidence, results indicate only minor differences due to microphone location, except for sound approaching the head from the opposite side. For this situation, the top and forward locations appear to reduce the head-shadow effect some 6 or 8 dB compared to the behind-ear location. Direction of the microphone opening, checked at the top-of-ear position, had no significant effect on response, as would be expected.
Experiments on Stimulated Brillouin Emission in Liquids
Authors: Brewer Richard G.
Published: September 2005

The characteristics of stimulated Brillouin emission in liquids are discussed. Special attention is given to multiple-scattering events, gain behavior, second-harmonic acoustic waves, and acoustic frequency detection by optical beats. The influence of stimulated Rayleigh scattering and the self-focusing of optical beams on Brillouin-scattering measurements are considered.
Diffraction of Waves at the Boundary of a Shadow Zone
Authors: Hudimac A. A.
Published: September 2005

In ray-theory solutions of propagation problems, one often determines a geometric boundary between an ensonified region and a shadow zone. It is desirable to be able to investigate the diffraction of sound into the shadow zone by a method of comparative simplicity. It is shown that the pressure discontinuity and the discontinuity of the normal derivative of the pressure determine the densities of a distribution of dipoles and of simple sources, respectively, such that there is a mutual annihilation of the geometric wave discontinuities and the distribution singularities. The radiation from the distributions (into both the ensonified region and the shadow zone) can be obtained by ray theory or by approximate wave-theoretic techniques. In the case of a classical problem (for a homogeneous medium), there was agreement between the results of the above method and the classical results.
Ray Transmission in a Sound Channel with a Pseudorandom Boundary
Authors: Seifer A. D. , Jacobson M. J.
Published: September 2005

An isovelocity underwater acoustic channel having a flat surface and a pseudorandom bottom is considered. The two-dimensional problem (range-depth) is investigated, where the bottom is assumed to consist of piecewise-connected, linear segments having small random slopes about a zero mean and small random deviations in depth about a constant mean value. Ray theory and specular reflection are assumed, and rays experiencing at most one bottom reflection between source and receiving point are considered. Under appropriate conditions on the bottom and the initial ray inclination, existence and uniqueness of bottom-reflected ray arrivals can be proved. Statistical properties of travel time and geometrical spreading loss are investigated for each ray. In addition, the superposition of the six possible arrivals, experiencing at most one bottom reflection, is examined; the statistical properties of the resulting amplitude and phase are determined assuming Rayleigh's reflection theory. In certain cases, the above results are applicable to the problem of a horizontal bottom and a random sea surface. [Work supported in part by the U. S. Office of Naval Research.]
Transillumination of the Larynx in Running Speech
Authors: Lisker Leigh , Abramson Arthur S. , Cooper Franklin S. , Schvey Malcolm H.
Published: September 2005

A fundamental distinction between speech sounds depends on whether the excitation is a noise source or a quasiperiodic one. The noisy or voiceless sounds are presumably produced with an opened and quiescent larynx, while for voiced sounds the larynx is closed down and in rapid oscillation. Direct evidence of this has come from motion pictures recorded through the open mouth, a method obviously limited to particular sounds. Running speech requires different methods, and is being studied by a transillumination technique. A fiber-optics bundle introduced into the laryngeal vestibule through the nose is used to illuminate the glottis, while a photocell placed below the thyroid cartilage registers the variable light transmitted through the glottis and the tissues of the neck. The “glottograms” so obtained are compared with acoustic waveforms simultaneously recorded with air and throat microphones to determine how the voiced-voiceless distinction correlates with closed versus open states of the larynx.
Further Experiments Using a Larynx Model
Authors: Crystal Thomas H.
Published: September 2005

Research has continued on the model of the larynx described at a previous meeting of the society. [T. H. Crystal, “Model of Larynx Activity during Phonation,” J. Acoust. Soc. Am. 33, 93(A) (1965)]. The model has been adjusted to exhibit the same trends in subglottal pressure, average flow rate, and vocal intensity measured by Isshiki in experiments on human subjects [N. Isshiki, “Regulatory Mechanism of Voice Intensity Variation,” J. Speech Hearing Res. 7, 17–29 (1964).] This is achieved by adjusting spring tension and rest position of the simple-harmonic oscillator that is used to model the mechanical facets of vocal-fold activity. Additional data have been gathered on the loading effect of simple vocal-tract models on the operation of the larynx model. The model also has been used to demonstrate the waveform changes that might be expected when a talker breathes helium-rich air. [Work supported in part by the National Institutes of Health, U. S. Department of Health. Education, and Welfare, by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, by Project MAC, an MIT research program sponsored by the U. S. Department of Defense.]
Articulatory Analysis of Speech by On-Line Computing
Authors: Mermelstein Paul
Published: September 2005

An on-line interactive computer program is described for calculating the parameters of an articulatory model of the human vocal tract corresponding to measured amplitude spectra of speech sounds. The computational procedure comprises two stages: (1) determination of the poles and zeroes of the amplitude spectrum; (2) calculation of a vocal-tract shape having the computed pole-zero pattern. In the first stage, a match to the input spectrum is synthesized from a predetermined number of resonance curves of individual pole or zero pairs having adjustable frequency and bandwidth values. In the second stage of the computation, the cross-sectional area of the vocal tract and the degree of nasal coupling are iteratively adjusted until a satisfactory match to the pole-zero pattern of the input spectrum is achieved. Specification of the vocal-tract shape in terms of the Fourier coefficients of the logarithmic area function leads to a rapidly converging matching strategy. Results for the analysis of vowel-consonant-vowel sequences are given.
Linguistic Basis of Research on Speech
Authors: Fry D. B.
Published: September 2005

Communication by speech is based on the linguistic structure of the message and is possible only between language users who hold a common store of linguistic information. The message wave that modulates the speech carrier wave at syllabic rates is one expression of a control function or program organized in the speaker's brain; the decoding of the message by the listener is in effect the retrieval of this program. There is at present no means of isolating the program at the brain level but experimental research of the past 20 years has produced a body of evidence gained from the behavior of language users that shows some of the main features of the linguistic organization of speech. The paper reviews the major contributions to the study of speech processing in the human being, in particular those concerned with phonemic categories, rhythm and intonation patterns, syntax and lexis, with redundancy and with processing times in speech. All experiments on speech are founded, whether explicitly or implicitly, on the assumption that speech communication is language-based; the paper suggests that future advances in our understanding of the speech process are most likely to come from experiments specifically designed to reveal the main lines of this linguistic organization.
Baffled Piston Radiator; Potential in the Far, Paraxial Field
Authors: Greenspan Martin
Published: September 2005

King's integral for the velocity potential of a baffled piston radiator is expanded in powers of l/z with coefficients that depend on r and a. (Cylindrical coordinates, r, θ, z; a is piston radius.) For a radially symmetrical, but otherwise arbitrary, distribution of particle velocity on the radiator, the leading term depends only on the volume velocity at the source. For a known distribution, the remaining terms can be calculated; for unknown distribution, limits can be set. Special cases are treated. [Work supported in part by U. S. Office of Naval Research.]
Adiabatic PiezoOptic Coefficients of Liquids
Authors: Riley W. A.
Published: September 2005

Knowledge of variations in the optical properties of liquids with pressure is required in ultrasonic-light interaction studies. One parameter used to describe these variations is the piezooptic coefficient, defined as the change in refractive index produced by a unit change in the applied pressure. The relative adiabatic piezooptic coefficients of numerous pure liquids and alcohol-water mixtures were determined from measurements made on light diffracted by pulsed ultrasonic waves. Absolute values of this parameter for the liquids tested were calculated from a consideration of experimental values previously determined and the results compared with the theoretical and empirical formulas presently used to compute this parameter. [Research sponsored by the Office of Naval Research.]
Acoustic Absorption and Dynamic Viscosity in Polymers
Authors: Hunter Joseph L. , Dardy Henry D. , Derdul P. R.
Published: September 2005

We have obtained results that show that acoustic absorption in linear polysiloxanes varies with viscosity and frequency in a unique manner. At any constant temperature, a significant relaxation is found, with a broad spectrum of relaxation frequencies. On the other hand, the absorption shows a monotonic rise with increasing viscosity up to very high viscosities. For this reason, there is some doubt as to how to treat the data by means of reduced variables. Shear impedance has recently been measured in the same liquids over a wide range of frequency and viscosity, and dynamic viscosities have been computed. We have also attempted to show that there exists in general a simple relaxation between the acoustic absorption and the dynamic viscosity. It is not clear, however, that the two are uniquely related. [Work sponsored by the Acoustics Branch, U. S. Office of Naval Research.]
Effect of Water Impurity on the Napier (Relaxation) Time of Methane
Authors: Monkewicz Alan A.
Published: September 2005

Using a modified Hubbard low-pressure acoustic interferometer, the velocity-dispersion region of methane/water-vapor mixtures was measured as a function of (f/p). From this, it was possible to obtain the shift in the Napier time of the mixtures as a function of the mole percent of water vapor present. The results were subjected to an analysis similar to that of Tuesday and Boudart, an analysis that is based on two postulates: a “resonance” between methane and water vapor and rapid deexcitation of water vapor with itself. Numerical solution of the resulting equation kTτp = K10+(K20−K10)X+K30X[K50+(K40−K50)X(K03+K50)+(K40−K03−K50)X] yielded a quadratic dependence of the Napier time on the mole fraction of water vapor. Reaction rates for the five possible reactions in a binary gas mixture were obtained. Since these reaction rates are the reciprocals of the Napier times, the collisions numbers were also obtained. When the collisions numbers obtained are compared with those of other investigators, the agreement is found to be very good.
Sabines and Sabins—Some Historical Notes on Room Acoustics
Authors: Northwood T. D.
Published: September 2005

The science of room acoustics is concerned with the process of production, propagation, and perception of sounds in rooms. Its development as a science began with the work of Wallace Clement Sabine, about 60 years ago, and during the next few decades there ensued an enthusiastic exploration of especially the purely physical portion of the subject. By the late thirties, the job seemed to be done, at least to the satisfaction of the mathematical physicists. Today's renaissance in room acoustics, exemplified by the other papers in this session, makes it clear that the job was not done. Today, we can see that insufficient attention was given to the listener, to his processes of perception, and to the transient nature of the sounds he was interested in hearing. It is proposed, with these aspects in mind, to take a second look at the early history of room acoustics.
Reverberation Time: Definition, Theory, and Measurement
Authors: Schroeder M. R.
Published: September 2005

Various definitions of reverberation time and their significance are reviewed. The relations of reverberation time to mode theory (decay rates of the normal modes) and ray theory (time intervals between successive reflections and distribution of absorptive materials within the enclosure) are discussed. Different methods of measuring reverberation time are described and expressions for their accuracy and reproducibility are derived. Variations of reverberation time with location within an enclosure is considered. The subjective significance of different definitions of reverberation time and experimental results for nonexponential decays are discussed. The paper concludes with a brief description of new methods of subjective multidimensional scaling and its relevance to the general problem of acoustic quality.
Absorption of Audiences Seated in Upholstered Chairs
Authors: Beranek Leo L.
Published: September 2005

Several papers have appeared in recent years dealing with the absorption of sound by seated audiences. This paper compares the results of those studies with reverberation data taken in completed halls. Suggestions for further investigations are made.
Spectra and Waveforms of Bottom-Reflected Pulses
Authors: Eby Edward S.
Published: September 2005

A mathematical model considering reflection as a reradiation phenomenon has been constructed. The model allows computation of the spectrum and waveform of a reflected pulse in terms of the incident plane-wave pulse or its spectrum, the reradiation characteristics of the reflector, the incident direction, and the reradiation direction. Bottom reflection of sonic pulses in an isovelocity medium has been considered in terms of this model and temporal and spectral distortions have been calculated. The theory of Cron and Nuttall [J. Acoust. Soc. Am. 37, 486–492 (1965)] is shown to be a special case of the present theory.
Frequency Discrimination as Measured by AB and ABX Procedures
Authors: Saslow Michael G.
Published: September 2005

Rosenblith and Stevens reported in 1953 that difference thresholds for frequency measured by an ABX procedure were at least twice as great as those measured by an AX procedure. Their report is consistent with the great bulk of the literature. The relationship has always been rationalized in terms of the greater physical and judgmental complexity of the ABX procedure. The present experiment was performed at 120 cps, 70 dB SPL, with two practiced subjects. For frequency differences of plus or minus 0.3 cps, or one-fourth of 1%, responses were 95% correct for ABX and 82% correct for AB. This result contradicts the usual finding, and suggests a need for an experimental analysis of frequency-judgment mechanisms. The experimental data were collected at the Massachusetts Institute of Technology Research Laboratory of Electronics.
Hydroacoustic Impulse Generator
Authors: Bouyoucos J. V. , Selsam R. L. , McLaucghlin J. K.
Published: September 2005

A repeatable generator of unidirectional strong underwater acoustic transients is described. The method of transient generation involves a three-step process in which (1) sea-pressure energy is converted to kinetic energy of fluid adjacent to a moving (sea pressure driven) piston; (2) the kinetic energy is converted to an acoustic shock upon near-instantaneous impact of the piston upon an anvil; and (3) the acoustic shock propagates backwards along the piston axis with a pressure-time history and directional pattern that is dependent upon the geometry of the piston and its adjacent baffle. The results of measurements on a small-model impulse source are described and are compared with theoretical predictions. This model source embodies a 3-in.-diam piston and produces peak acoustic pressures on axis of magnitude greater than 130 dB re 1 μbar at 1 yd at depths of the order of 14 ft. It is shown how the shape of the piston contour can affect the shape of the pressure-time history on axis, the shape of the transmitted spectrum, and directivity of the peak radiated signal. Theoretical scaling predictions suggest that it should be possible to produce peak acoustic pressures of the order of 170 dB re 1 μbar at 1 yd with an energy spectrum centered in the low kilohertz range. [Work supported in part by the U. S. Office of Naval Research.]
Sensitivity of Single Auditory-Nerve Fibers to Acoustic Stimuli
Authors: Kiang N.-Y. S. , Shipley J. W. , Sachs Murray B.
Published: September 2005

The responses of single auditory-nerve fibers in anesthetized cats to tonal stimuli were recorded with microelectrodes. Sound-pressure levels were measured at the eardrum. After correcting for the effects of the middle ear, we were able to compare sensitivities of fibers with different characteristic frequencies. It is difficult to find a single response criterion that will serve as a satisfactory measure of sensitivity for all fibers. Data are presented to show the results of using several sensitivity measures for fibers with different rates of spontaneous activity and characteristic frequencies. The effects of previous stimulation and choice of stimulus parameters on the responses of these fibers are discussed. [Work supported in part by the Joint Services Electronics Program, by the National Science Foundation, by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the National Aeronautics and Space Administration.]
Study of Wall-Pressure Fluctuations in a Supersonic-Engine Inlet Duet
Authors: Shulman A. , Parry H. J. , Shapiro N.
Published: September 2005

Necessarily idealized assumptions have been used in preliminary estimates of boundary-layer noise to be expected in an engine inlet designed for use on a supersonic transport. Confirming measurements of turbulent wall pressures have been made in wind-tunnel tests of a scale model. The purpose of this study was to determine if the presssure fluctuations would be sufficiently great to be a factor in the structural design of the inlet. The inlet is a 2-dimensional mixed-compression type; its geometry will be varied to optimize performance over the flight régime. Boundary-layer bleed will be provided at the transonic throat to minimize the severity of the shock-wave/boundary-layer interaction. The testing was done in the NASA-Ames 11×11-ft transonic and 9×7-ft supersonic wind tunnels using flush-mounted 14-in.-diam miniature capacitive microphones. Data are presented of spectra of boundary-layer pressure fluctuations for a number of inlet operating conditions, and comparisons are made with the previously made predictions. Preliminary analysis of the data indicates that sonic induced vibration will not provide a serious design limitatlon for the inlet and duct.
Noise Reduction in a Cylindrical Shell
Authors: Manning Jerome E.
Published: September 2005

A theoretical study of the transmission of acoustic energy from a diffuse sound field through a thin cylindrical shell is described. This study is part of a larger investigation of the acoustic and vibratory energy transmission in a shroud-mounting truss-spacecraft assembly. The results are presented as average noise reduction (NR) in 13-oct bands of frequency. It is assumed that the frequencies under consideration are above the first resonant frequency of the shell and of the interior acoustic space and are in the multimode region. It is further assumed that the critical frequency of the shell lies above its ring frequency. The transmitted acoustic energy is considered in two parts. First, energy transmitted by resonant shell modes (which may or may not be well coupled to the acoustic field) is computed. Second, the energy transmitted by forced (mass-law) shell modes that are well coupled to the acoustic field is calculated. It is found, for a representative example, that the energy transmitted by resonant shell modes dominates that transmitted by forced (mass-law) modes, except for frequencies between the ring frequency and the critical frequency. Relative minima in NR are found at the ring frequency and the critical frequency. These result from shell modes that are both resonant and well coupled to the acoustic field. [Research supported by the National Aeronautics and Space Administration.]
Aural Perception of Sentences of Different Syntactic Structures and Lengths
Authors: Compton Arthur J.
Published: September 2005

Eleven sets of 16 sentences, previously rated as natural English statements, were presented to two groups of listeners. Each set of sentences differed in syntactic structure and contained four sentences of each of four lengths: 8, 10, 12, and 14 words. The listeners heard the sentences either under a fixed condition of filtering or without filtering; their task was to write as much of each sentence as possible immediately after it was presented. The sentences were scored for the number of words correctly reproduced, and differences in aural perception among the various sentence types and lengths were tested on the basis of the derived intelligibility scores. The results of the study indicated that (1) perception of the sentences was affected by their syntactic structure and varied, depending upon the grammatical complexity of the statements as specified by a generative grammar; (2) the sentences of 12 words were more easily perceived than were the sentences of the other lengths; (3) no relationship was established between the relative perception of the various sentence structures and their degree of naturalhess.
Perception of Visual Transforms of Speech Stimuli: A Preliminary Experiment
Authors: House Arthur S. , Hughes George W. , Goldstein D. P.
Published: September 2005

A preliminary experiment has measured the effect on word intelligibility of a visual transform of the speech signal. Articulation-test materials were mixed with noise and presented under earphones at a signal-to-noise ratio yielding correct response scores close to 50%. In some listening sessions, the speech materials also were displayed instantaneously, without added none, art the face of the output CRT of a visible-speech translator. During the experiment two rotational speeds of the CRT were used, providing two different sizes of visual displays. Subjects experienced with sound spectrograms provided the responses. Improvement in intelligibility scores with the addition of visual stimuli was demonstrated. The influence on response score of various experimental variables, such as display aspect ratio, permitted subject latencies, prior knowledge of response sets, etc., is discussed. An analysis in terms of linguistic feature is presented. [Research supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare. The visible-speech translator was furnished by the Bell Telephone Laboratories, Inc., Murray Hill, New Jersey.]
Effects of Listener Criteria on Speech Identification
Authors: Speaks Charles , Jerger James
Published: September 2005

A series of experiments was undertaken to determine whether the theory of signal detectability could be applied meaningfully to the task of synthetic sentence identification. The observers were four normal-hearing listeners. Results suggested that observers generated ROC curves consistent with the theory and that one can derive a measure of performance in this listening task that is independent of changes in the listener's criterion.
Criterion under which the Standard Detector is Optimal
Authors: Shapiro Arthur
Published: September 2005

This paper is concerned with the detection of a narrow-band signal using two hydrophones. Specifically, it addresses itself to the problem of finding the “optimal” linear combination of sample spectra, cospectrum, and quadrature spectrum to use as a detection test criterion. The “optimal” detector is defined here to be the one that maximizes the average probability of detection for given probability of false alarm and given observation time, where the average is taken over all possible noise-phase difference conditions. It is shown that under not unrealistic conditions, the “optimal” detector, among all those that are linear in the sample spectra, co-, and quadspectrum, is the one that adds the outputs of the detectors and squares the result. However, if one is willing to consider detectors that are not linear combinations of the various spectra, there are detectors that offer significant improvements over the sum and square one and that require no additional information. [Work supported by the Bureau of Ships, U. S. Navy.]
Limit on Signal Design against Reverberation
Authors: Stewart James L.
Published: September 2005

In the situation where the unwanted scatterers are uniformly distributed in range and have a Doppler distribution that is independent of range, the reverberation power spectrum is completely determined by the energy spectrum of the signal transmitted. The optimum detector of an echo in noise plus reverberation is the colored-noise type of matched filter the output signal-to-noise ratio of which depends only upon the energy spectrum of the echo and the power spectra of the noise plus reverberation. It is significant that this output does not depend upon the phase spectrum of the signal and hence upon its waveform. This limitation of signal design to energy spectral design does not take into account the possible effects of the angular distribution of the unwanted scatterers. The optimal energy spectrum design of signals is discussed for low and high Doppler targets, indicating the limiting values of the output of the colored-noise filter as a function of available bandwidth. The special cases of the Urkowitz filter and MTI signals and processing are discussed.