bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Acoustic-Feedback Stability by Frequency Shifting
Authors: Schroeder M. R.
Published: September 2005

The tendency of public-address systems to become unstable, when operated in reverberant spaces, can be reduced by shifting all frequency components of the audio signal by about 5 cps. Frequency shifts of this magnitude will raise the gain at which a public-address system remains stable by about 10 dB. However, heating the direct-sound signal and the frequency-shifted signals limits the usable additional gain to about 6 dB. Electronic devices for effecting frequency shifts of the desired magnitude and stability have been described previously and are now available commercially. In this paper, a theory of the stability of public-address systems with and without frequency shifting is presented and compared with experimental results obtained in rooms of various dimensions. Good agreement is found between theory and experiment. In addition, frequency responses of rooms are simulated by a Monte Carlo method on a digital computer and the permissible gains for stable operations of public-address systems are evaluated on the computer. The Monte Carlo results fall within 0.6 dB of the theory.
Coupling of Array Elements in a Nonrigid Baffle
Authors: Mangulis Visvaldis
Published: September 2005

It is pointed out that the coupling between two elements far apart in a nonrigid baffle will not have a simple 1/(distance) dependence.
Changes in the Cochlear-Microphonic Potential due to Resection of the Efferent Cochlear Fibers
Authors: Rossi G. , Voena G. , Cortesina G. , Buongiovanni S.
Published: September 2005

Resection of the direct efferent cochlear bundle in the guinea pig causes greater reduction in the cochlear microphonic potential than is caused by resection of the crossed efferent cochlear bundle. The findings of the present series of studies are thought to constitute physiological proof of the existence, in the guinea pig, of another component of direct efferent cochlear fibers, other than the direct olivo-cochlear fibers, which arises in cells of the reticular formation of the medulla.
Temporal Integration as a Function of Frequency
Authors: Sheeley Eugene C. , Bilger Robert C.
Published: September 2005

Temporal integration of acoustic power was investigated 250, 1000, and 4000 cps over a range of signal durations from 1 or 2 cps to 256 msec. Signals were presented in a background of low-level broad-band white noise. Breaks in the function relating performance to signal duration (assuming that bandwidth equals 1/t) were used to infer critical bandwidth and difference limen for frequency. The critical-bandwidth estimates are in agreement with most other data for the smaller set of critical-bandwidth values sometimes called critical ratios. The difference-limen estimates are in agreement with Shower and Biddulph's values obtained at a low sensation level.
Experiment with Speechlike Phase in a Spectrally Flattened Pitch-Excited Channel Vocoder
Authors: Gold Bernard
Published: September 2005

The pitch-excited vocoder invented by Dudley can be greatly improved and, it appears, made to produce very natural speech by the inclusion of (a) very precise pitch extraction and buzz-hiss indication, (b) pre-modulation spectral flattening of the exciting signal, and (c) more speechlike phase. This paper outlines a technique that induces more speechlike phase in a spectrally flattened pitch-excited vocoder. Results obtained thus far from a computer-simulated vocoder are quite hopeful.
Application of Ultrasonic Standing Waves to the Generation of Optical-Beam Scanning
Authors: Aas H. G. , Erf R. K.
Published: September 2005

The possibility of employing a time-varying refractive-index gradient, generated by an ultrasonic standing wave in solids and liquids, to provide nonmechanical optical-beam scanning has been investigated in detail. Heretofore-unobtained deflections of sufficiently large angles to be of practical value in active optical systems have been achieved. These angles range between 3° and 6° at frequencies below and above 200 kc/sec. respectively. Standard slit and photomultiplier techniques were employed to study the effects of stress-induced birefringence in crystal quartz on the attainable angular movement of two collinearly deflected light beams that were orthogonally plane polarized. High-speed streak photography was used to measure the fidelity of the light beam as it emerged from a tetrachloroethylene ultrasonic cell. The photographic technique was utilized to evaluate effects of (1) light-beam diameter/sonic-wavelength ratio, (2) light-beam transit position relative to the sonic-pressure nodal point, and (3) light-beam angular-deflection amplitude.
Radial Deformation of a Composite Piezoelectric Annular Disk
Authors: Sinha D. K.
Published: September 2005

In the present paper, the equations of elasticity and equations of electricity, together with the constitutive relations of a piezoelectric quartz, have been used to solve the problem set forth in the title.
Thermoelastic Dissipation in Thickness-Shear and Flexural Vibrations of AT-Cut Quartz Plates
Authors: Tasi J.
Published: September 2005

Approximate equations are used to study the thermoelastic dissipation present in the thickness shear and flexural vibrations of a finite AT-cut quartz plate with tractionfree edges. The dimensionless measure of energy dissipation Q−1 is found to be of the order of 10−8 near the thickness shear frequency.
Fine Structure and Stability of the Sound Channel in the Ocean
Authors: Piip Ants T.
Published: September 2005

The sound-channel region in the ocean is traditionally assumed to be stable and uniform over large areas, although indications of rapid and appreciable variations have been observed. To improve understanding of the true situation, a study of the fine structure and short-term temporal and spatial variations in this region has been undertaken. The instrumentation and method developed for this purpose are described briefly. An underwater package containing two independent velocimeters, an FM pressure gauge, and auxiliary circuitry is repeatedly lowered and raised on a single-conductor armored cable through the channel region. Sensor information is telemetered to the ship and recorded. Results from three stations south of Bermuda in the Fall of 1963 are described and analyzed. A surprising amount of activity is found, proving that the sound-channel region, at the base of the main thermocline, is subject to much larger rapid changes than generally recognized. Considerable fine structure, evidence of internal waves, layers, and cells of “strange” waters have been observed. Sound-velocity changes of several meters per second in a few hours, at the same depth, are common. From August to October, the average sound velocity on the axis has decreased from 1494.5 to 1491 m/sec, the axis depth from 1300 to 1150 m.
Two Transientfree Switches
Authors: Philips Charles M. , Cutt Roger A.
Published: September 2005

Two transientfree switches are described. One is manually controlled and has fixed rise and decay times of 125 and 135 msec, respectively. The second switch can be triggered either repetitively or manually and the rise times can be adjusted for 0.25, 0.5, or 1.0 msec.
Note on the Variability Hypothesis in Category Scaling
Authors: Schneider B. A. , Lane H. L.
Published: September 2005

The “variability hypothesis” attributes the nonlinear relation between category and magnitude scales to the growth of variability along the psychological continuum. The findings of some earlier research seemed to contradict the hypothesis. Now, an alternative interpretation of these findings is presented.
Frequency Multiplex System for a 10-Spectrum-Channel Voice-Excited Vocoder
Authors: Golden Roger M. , MacLean D. J. , Prestigiacomo A. J.
Published: September 2005

An experimental frequency multiplex system has been completed for with a 10-channel voice-excited vocoder. This system reduces the band width required for speech transmission from 3 to 1.4 kcps, thereby achieving a bandwidth reduction of better than 2:1.
Restrictions in Pachner's Analyses for Determination of the Farfield Directivity Function from Nearfield Measurements
Authors: Smith P. W.
Published: September 2005

The implicit restrictions of Pachner's analyses, for the determination of the farfield directivity function from nearfield measurements [J. Acoust. Soc. Am. 28, 86–92 (1956)] are discussed, with extension and clarification of recent comments [J. Acoust. Soc. Am. 35, 1666–1667 (1963)]. Pachner's analyses appear inadequate to describe radiation from even cophasal vibration of a finite surface, except as an engineering approximation for flat surfaces with large rigid baffles.
Acoustics and People
Authors: Meyer Harold Burris
Published: September 2005

This paper postulates as a worthy, but often overlooked, objective of acoustical research the discovery, definition, and development of means to achieve an acoustical environment that shall be most conducive to man's welfare, his health, his enjoyment of the arts, his means of self-expression. The ways in which much acoustical research and the applications thereof to architectural and psychological problems deviate from or ignore this ideal are cited. Means to achieve it are proposed.
Low-Frequency Approximations for Scattering by Penetrable Elliptic Cylinders
Authors: Burke James E.
Published: September 2005

The Mathieu function-series solution for the scattering of a plane wave by a penetrable elliptic cylinder is used to obtain explicit low-frequency (long-wavelength) approximations in powers of the frequency. The far-field scattering amplitude is given to the sixth power of the frequency, and the external and internal fields are given to the third power. We consider arbitrary angles of incidence and observation, and arbitrary eccentricity.
High-Frequency Acoustical Reverberation from a Rough-Sea Surface
Authors: Clay C. S. , Medwin H.
Published: September 2005

The scattering of high frequency underwater sound (λ < < waveheight) from the sea surface is described in terms of two mechanisms: conventional scattering theory for a rough surface with normally distributed slopes appears to adequately predict the backscattering at incidence near normal; a rather low population of near-surface resonant bubbles would suffice to explain the behavior at angles near grazing. The two effects are used to interpret the experimental surface scattering data at high frequencies for all angles of incidence.
Acoustic Wave Motion along a Periodic Surface
Authors: Miller M. K.
Published: September 2005

An analysis is made of a surface wave traveling axially along the boundary of au infinitely long cylindrical surface that has small periodic variations superimposed upon it. By the application of Floquet's theorem, the acoustic pressure is expressed in terms of an infinite series. For waveguides that have acoustic reactances that are periodic with period L in the axial direction, an infinite system of equations is obtained. Unknown amplitude coefficients are determined by a method of infinite determinants. After the amplitude coefficients are known in terms of one coefficient, the phase variation for the surface wave along the cylindrical axis is calculated by Φ (z) = arctan (ImP/ReP). The general method is illustrated by considering a waveguide with a variable reactance given by χ = χ0 + x cos (2πz/L), where x≪χ0 and z is the axial coordinate. The effects of small changes in the parameters x, χ0, and L are analyzed for an arbitrary surface wave. It is shown that for a surface wave with wave number given by h = 2π/;λg, as hL → π with hL < π, the phase variation is quite rapid in the vicinity of z = nL, where n is a positive integer and is very small over the remainder of the waveguide.
Vertical Coherence of Explosive Reverberation
Authors: Urick R. J. , Lund G. R.
Published: September 2005

Time-delay correlograms of the reverberation, following an explosion in the sea, received on pairs of vertically separated hydrophones show the direction of arrival in the vertical and the degree of coherence of reverberation of various origins in deep water. The clipped correlation coefficient is found to be highest for the bottom return near normal incidence and least for the volume reverberation just preceding it. The correlograms show evidence of a deep scattering layer of scatterers resonant at 1.6 kc/sec. The direction of arrival of the reverberation at various times after the shot is consistent with existing knowledge about the sources of deep-water reverberation.
Analysis of Spreading Loss for Refracted/Reflected Rays in Constant-Velocity-Gradient Media
Authors: Jacobson M. J.
Published: September 2005

The analytical properties of existing spreading-loss formulas are not well-known in the case where a ray experiences multiple boundary reflections. This paper investigates spreading loss in detail for refracted/bottom-reflected rays when the velocity gradient is a negative constant and the bottom is horizontal. Expressions for the spreading loss are derived, special cases are examined, and upper bounds are obtained. It is shown that there are some points on every ray at which the spreading loss is less than inverse-square loss and some points on some rays at which the loss exceeds inverse-square loss. The loss behavior is examined as a ray path is traversed, and is found to be markedly dependent upon initial ray inclination, the ray lobe being considered, and velocity structure. The problem of multiple arrivals at a fixed receiver is also studied. Relationships are given between the number of arrivals and their intensity, travel time, initial inclination, and number of reflections. Two examples are presented. The results in this paper apply not only to refracted/bottom-reflected transmissions, but also to surface-channel and deep-sound-channel transmissions.
Influence of Sound upon Local Heat Transfer from a Cylinder
Authors: Richardson P. D.
Published: September 2005

Measurements far local heat transfer on a horizontal heated circular cylinder in a horizontal transverse standing sound field are reported. Observations were made by Schmidt's method, which makes use of optical properties of thermal boundary layers and requires no correction for thermal conduction or radiation. Significant local effects are found at intensities well below the “critical” sound-pressure level. The “critical” level determined from average heat-transfer measurements is found to have no intrinsic fluid-mechanical significance.
Ohm's Acoustical Law and Short-Term Auditory Memory
Authors: Pollack Irwin
Published: September 2005

The ability of listeners to “hear out” individual components of a tone combination was examined under a variety of experimental procedures. Contrary to the expectation of Ohm's acoustical law, listeners were relatively unable to accurately “extract” components from nonharmonically related tone combinations.
Effect of Noise on Listening Levels in Conference Telephony
Authors: Gardner Mark B.
Published: September 2005

The present study outlines the effects of background noise on requested loudspeaker levels of incoming speech signals at the conference table for four basic listening assessments. Two general classes of loudspeaker systems were employed proximity units in the “wings” of individual high-back chairs and a loudspeaker display above the long axis of the conference table. In addition, a brief outline of the effect of noise on vocal output has been included. The results show that for either loudspeaker system the preferred listening level under relatively quiet conditions (NC-23) was 63 dB (A+B)/2 as measured at the ears of the observers. This is approximately the level of so called conversational speech at a meter. For a 37-dB increase in the noise level (to NC-60), the participants requested a 15.5 dB increase in the preferred listening level. This compares with a 13.5-dB increase in the vocal output of the participants for the same 37-dB increase in noise level. The range between the strain level (threshold of message intelligibility) and the maximum acceptable listening level for conference purposes was about 50 dB under quiet conditions but only about 20 dB at NC-60. This rather rapid convergence stresses the importance of operating at a relatively low noise level in order to insure good intelligibility of all incoming voice signals.
Absorption of Sound in Air below 1000 cps
Authors: Harris Cyril M. , Tempest W.
Published: September 2005

For many acoustic problems, it is of importance to have accurate data of absorption of sound in air as a function of humidity. Such information has not been available below 2000 cps. This paper presents data at lower frequencies in the range from about 125 to 1000 cps. The intensity attenuation coefficient m is given as a function of relative humidity at 20°, 0°, and −20°C for normal atmospheric pressure. Similar data are given at pressures of 400 and 200 mm Hg for a temperature of 20°C. The experimental results are compared with the theoretical values predicted by Kneser.
“Negative Afterimage” in Hearing
Authors: Zwicker Eberhard
Published: September 2005

If a white noise with a half-octave-band suppression placed anywhere from 300 to 7000 Hz is presented at an over-all sound-pressure level of about 60 dB for 1 min and then switched off, a decaying, poststimulatory sound similar to a pure tone is heard for about 10 sec. The pitch of the post-stimulatory tone corresponds to a frequency within the suppressed band.
Absorption of Sound in Oxygen/Water Mixtures
Authors: Harris Cyril M. , Tempest W.
Published: September 2005

Data have been obtained of the absorption of sound in oxygen and water mixtures. These data agree very well with previous measurements by Clark and Henderson, supporting the view that the frequency dependence of the absorption peak on moisture content contains a quadratic term.
Genesis off Absolute Pitch in the Audio Spectrum
Authors: Pikler Andrew G.
Published: September 2005

Current theories of hearing silently imply universal absolute pitch. To evade the paradox, psychoacousticians prefer to deny the true difference between the absolute and relativistic ways of frequency resolution. The writer, on the basis of his own absolute pitch experiences, refers to about 24 specific aspects which confirm the true difference. Only the digital power-spectrum analyzer model of hearing can account for the relativistic effect. Audio quanta are encoded by the Corti organ in the form of time series (based on the two code symbols, discharge and silent interval), then decoded in the acoustical area of the cortex. A biological clock is needed to count code frequencies in the decoding process. Clock beats of the flow of auditory microtime could be identified with the eighth nerve's spontaneous firings. In the light of relativity of time, both neural time and sound source's time (e.g., a reference oscillation), represent local time flows. Generally, these two time flows are asynchroneous. From spectroscopy it is understood that in hyperfine spectrum analysis drifting must emerge. The fundamental equations of audio spectral drift are derived as functions of asynchrony. In the special case of absolute pitch, a fair synchrony exists. Explanation of 24 crucial manifestations is offered. Moreover, absolute pitch implies absolute Doppler preception, i.e., a kind of continuous orientation in observer's space. Finally, diplacusis in the normal is explained as interaural drift due to interaural asynchrony existing between the two reference oscillations in the two branches of the eighth nerve.
The Effect of Acoustic Loading on the Vibration Patterns of Barium Titanate and Quartz Disks
Authors: Sujir R. J. , Shaw E. A. G.
Published: September 2005

In previous work, the normal surface displacement patterns of thick barium titanate disks vibrating in various normal modes have been obtained using multiple-beam optical interference. This technique has now been used to determine the effect of loading the disk with a liquid in contact with one plane surface. It is found that the discrete modes observed with an unloaded disk begin to merge so that the vibration patterns show a continuous transition with changing frequency as one passes from one mode to the next in the “thickness resonance” region. In the case of a quartz disk, two modes with a frequency separation of 0.5 percent merge fairly completely when the disk is loaded, and the vibration patterns appear to indicate composite motion of a more uniform character than that of either mode alone.
Progress in Accelerometer Calibration
Authors: Jones Earle , Edelman Seymour , Smith Ernest R.
Published: September 2005

This paper reports progress in the measurement of vibration since the work described at the San Diego meeting of the Acoustical Society. Improvements have been made in the design of cemented piezoelectric accelerometers, in piezoelectric ceramic vibration exciters, and in methods of calibration. Stroboscopic and interferometric methods of calibration are described.
Free-Field Measurements on Jet Engines
Authors: Mercer D. M. A.
Published: September 2005

Directivity patterns of American and British jet engines have been measured, by our group and others, for several operating conditions and at a number of distances. Variations of the frequency spectrum with engine power may be used, for instance, to indicate the noise output and directivity of the compressor. For different measurement distances, apparent deviations from the inverse square law are considerable; these may be partially resolved by considering the different elements in the engine and jet stream which produce the noise.
A Survey of Background and Aircraft Noise in Communities near Airports
Authors: Stevens K. N. , Bolt R. H.
Published: September 2005

An extensive survey has been made of noise levels in residential communities in eight cities having major airports. Some 25 000 readings of background noise, in the absence of recognizable aircraft noise, were obtained. The measurements were equally divided between night and day, and were taken in about 20 areas in each city, each area being about two blocks on a side. The areas were selected at distances of about 0–2, 4–6, and 8–12 miles from the airport and were chosen to be under regularly used aircraft flight paths. The readings of background noise were obtained primarily in the octave bands 75–150, 300–600, and 1200–2400 cps, about 25 such spectra being taken in each area. In addition, octave band spectra were obtained from magnetic tape recordings of the noise of about 250 aircraft in flight, representing substantially all commercial types, at distances up to 12 miles from the airports. The results have been analyzed to yield a statistical description of the background noise in various types of communities and of aircraft noise spectra at various locations with respect to airports and flight paths.
The Propagation of Sound Through Natural Fogs
Authors: Delsasso L. P.
Published: September 2005

Measurements of the velocity and attenuation of audio-frequency sounds in natural fogs have been found to be in general agreement with measurements made in the laboratory. The slow fluctuations in both velocity and attenuation observed in the field can be accounted for by the observed meteorological factors. The rapid fluctuations remain to be explained.
Electromagnetic Analogy to Sound Propagation in Moving Media
Authors: Kraichnan Robert H.
Published: September 2005

An analogy is developed between the paths of sound rays in fluids undergoing shear flow and electron trajectories in magnetic fields. If the Mach number of the flow is small, and the characteristic eddy size large compared to the sound wavelength, the ray paths coincide with electron trajectories in a magnetic field everywhere parallel and proportional to the vorticity vector. The ratio of the magnitude of the magnetic field to the electron momentum is determined by eH/Pc0 = Ψ/c, where H = magnetic field, P = electron momentum, e = electron charge, c0, c = velocities of light and sound, Ψ = vorticity. Mathematically the analogy is based on the similarity between the eikonal equation for the sound rays and the Hamilton-Jacobi equation for the electrons. Simple illustrations of the correspondence will be given.
The Effect of Envelope Shape on the Masked Threshold of Short Bursts of Tone
Authors: Gales R. S. , Wilcott R. C.
Published: September 2005

Earlier work by Garner and Miller and others has established the temporal integration property of the ear for the masked threshold of pulses of tone in the range of duration between 10 and 500 msec. This paper reports two studies of the temporal integration at the masked threshold for various envelope shapes over the same range of durations. A photoformer is used to generate the envelope voltage which modulates a sine wave of selected frequency to produce the shaped tone pulses. These are masked by noise from a gas-tube noise generator. In experiment I frequencies of 800 and 3200 cps, with two different envelope shapes, rectangular and Gaussian, were used at seven different durations ranging from 10 to 1000 milliseconds. The masked threshold at each frequency with each envelope shape at the different durations was obtained at masking levels approximating 30, 50, and 70 db. In experiment II a frequency of 800 cps was used with four envelope shapes, ranging from rectangular to cusp, and presented at six durations from 10 to 750 milliseconds. The masking level was maintained at about 50 db. Experiment I demonstrated temporal integration of acoustical energy as a function of pulse length for both frequencies and both envelope shapes at each level in general agreement with published data. This was further supported by experiment II for other envelope shapes.
Effect of Arrival Time on Stereophonic Localization
Authors: Snow William B.
Published: September 2005

Exploratory tests under a variety of conditions were made during Bell Telephone Laboratories' studies on stereophonic reproduction to determine the effect of arrival time as a factor in localization. The recent rapid rise of interest in stereophony appears to warrant a summary of these old results (1934), for which the Laboratories has granted permission. It is shown that arrival time differences have essentially the same effect whether they are generated in the pickup room, listening room, or in the electrical system. They can therefore be made to add or compensate. Small differences (0–3 milliseconds) cause large shifts of localization angle, but the effect becomes relatively constant for larger differences. Time differences can be compensated by level differences. The results of two other experimenters are given for comparison. It is concluded that reasonable agreement is attained, considering the small total amount of data, but that more experiment is required to establish accurate quantitative relationships for practical stereophonic reproduction.
“Periodicity” Pitch and “Place” Pitch
Authors: Licklider J. C. R.
Published: September 2005

In the year of the founding of the Acoustical Society of America, Wever and Bray observed periodic “volleys” of impulses in the auditory nerve. Since that time, the theory of pitch perception—particularly, whether pitch depends upon the frequency of the discharges or upon the locus of the active neural tissue—has been one of the most active issues in physiological and psychological acoustics. The most recently reported observations, those of Hoogland, 1953, support the place theory and the conclusion that “Schouten's residue theory [a form of the volley theory] seems to be improbable.” The present paper contains a demonstration to the contrary, that one can, in fact, hear low pitch with the high-frequency channels of the auditory system—with the part of the system that, according to place theory, should give rise to high pitch. This demonstration is one of Schouten's, but with the low-frequency auditory channels saturated with low-frequency masking noise. The pitch that is heard is correlated with volley frequency but not with Fourier frequency. However, the paper then shows that a pitch-like attribute is associated also with Fourier frequency, and therefore with the place dimension. These demonstrations support a theory that distinguishes two pitch-like attributes. This duplex theory reconciles place and frequency theories in the sense that both appear as partly correct. It makes clear the futility of trying to disprove one by proving the other.
The Method of Reproduction and the Identification of Elementary Auditory Displays
Authors: Pollack Irwin
Published: September 2005

The present study considers all experimental procedure designed to take advantage of the acute differential discrimination of the human observer in identifying dimensions of elementary auditory displays. This procedure, suggested by Dr. Miles Rogers of the Harvard Psycho-Acoustic Laboratory, is a combination of the method of identification and of reproduction. The essential feature is that the stimulus step identified by the subject is, in turn, reproduced for him. He can then compare the original stimulus presentation with the reproduced presentation and presumably sharpen his identification. Experimental tests, employing this procedure in identifying the sound level of a tone, indicate that identification may be appreciably sharpened this way. The major portion of the improvement, however, occurs after the first reproduction with little additional gain thereafter.
Noise Characteristics of Cathode-Follower Input Stages
Authors: Byrnes Francis X.
Published: September 2005

Cathode followers are frequently used as the input stage for transducers with capacitive impedances; condenser microphones, crystal or ceramic microphones, and hydrophones are examples. The primary purpose of the cathode-follower-type connection rather than the plate-loaded connection for the input stage is to present a higher load impedance to the transducer, thus extending its low-frequency response. An additional advantage which is sometimes claimed for this circuit is that the signal-to-noise ratio is improved. This is supposed to be due to the greatly increased effective value of the input resistor, which in turn means a smaller resistive component and therefore smaller thermal noise of the input impedance. It will be shown both analytically and experimentally that this signal-to-noise ratio does not improve with the cathode-loaded connection and, in fact, in most cases is poorer than with the plate-loaded connection. A comparison of the signal-to-noise ratio for each of these connections with other factors held fixed will be shown. Other circuits which combine both the better noise characteristics of the plate-loaded circuit and the high input impedance of the cathode follower will be shown.
New Developments in Stereophonic Sound
Authors: Paulson B.
Published: September 2005

Stereophonic sound represents the latest and most promising effort in audio technology towards achieving realistic reproduction of recorded sound. A summary of the developments in stereophonic recording from its inception will be presented. Present-day status of the art will be analyzed, emphasizing new fields for the use of stereophonic recording techniques. The technical details of the Ampex 3-channel stereophonic recorder will be described, and this equipment will then be utilized in a demonstration of various stereophonic recording techniques.
The Application of Correlation Techniques to Some Acoustic Measurements
Authors: Goff K. W.
Published: September 2005

This paper discusses the application of an analog correlator, computing the crosscorrelation function between two sound pressures, to such measurement problems as the localization of noise sources, the determination of transmission loss, and the measurement of room transient response. The crosscorrelation function φ21(τ) between two nonperiodic signals will have a peak in amplitude if a component of each signal originates from a common source. The value of time delay τ for which this peak occurs equals the difference in time required for the individual components to propagate from the common source to the two points under study. An analog electronic correlator has been constructed which, by employing the above-mentioned property, can separate the acoustic signal at a given point into components according to: (1) their points of origin (assuming independent sources), and (2) the transit time from source to the point in question. Preliminary experimental results substantiate methods for determining the amount of sound contributed to a given point by each of several sources and for measuring transmission loss using the correlator to separate the signal transmitted directly through the structure from the flanking signal on the basis of arrival time.
Impedance of a Rigid Piston in an Infinite Rectangular Array of Pistons
Authors: Hudimac Albert A.
Published: September 2005

A general solution is obtained for the velocity potential due to an infinite rectangular array of rigid pistons in a plane, rigid baffle. It is formed by a superposition of a double infinity of plane waves. For a given wave, corresponding to index (m. n). the mass reaction of the fluid increases monotonically with frequency to an infinite value at a critical frequency; the wave is propagated parallel to the plane of the array. Above the critical frequency the reaction of the fluid is resistive and decreases monotonically with frequency from infinity at the critical frequency; the direction of propagation has a component, which increases with frequency, perpendicular to the plane. The pressure due to each wave is integrated over any piston, and the total impedance is obtained by summing for all waves. Results are graphed for impedance versus frequency for a class of piston sizes and spacings.
Solubility as a Factor in Sonochemical Reactions
Authors: Weissler Alfred , Pickard Hugh B.
Published: September 2005

Previous work on the chemical reactions caused by intense ultrasound waves in aqueous systems had raised the following question. Is the obtainable amount of chemical change of a slightly-soluble reactant (such as carbon tetrachloride) limited by the circumstance that at any given time only a small portion can be dissolved in the cavitating water? In the present work, an answer was sought through study of the ultrasonic splitting of carbon-halogen bonds in selected pairs of compounds. The two members of each pair were of similar molecular size, but one was soluble and the other was relatively insoluble; a typical pair was chloroacetic acid and chlorobutane. It was found experimentally that the soluble compound showed actually less chemical change than its insoluble analog upon irradiation in dilute aqueous systems under parallel conditions. Solubility, therefore, does not seem to be the limiting factor in determining the quantitative yield of a sonochemical reaction.
Thermal Relaxation in Vapors of Chlorinate Methanes
Authors: Hubbard J. C. , Busala A. , Sette D.
Published: September 2005

Ultrasonic velocity has been measured as a function of frequency over pressure at 30°C in the four chlorinate methanes. Dispersion of velocity has been found in each case, the relaxation frequency/pressure ratios being in CH3Cl, CHCl3, and CCl4, respectively, 1.13, 27.3, and 23.3 Mc sec−1 atmos−1. In CH2Cl2, two relaxations have been found with respective relaxation frequency/pressure ratios of 2.27 and 105 Mc sec−1. The experimental velocity values, corrected for deviation from the ideal gas law, are in good agreement with those obtained from spectroscopic indication showing that the dispersion is due to thermal relaxation of the vibrational modes of the molecules. The results seem to corroborate the idea that in many polyatomic molecules the energy exchange translation-vibration occurs mainly as a series process.
The Absorption of Sound in Air at Low Pressures
Authors: Goldman R. B. , Bohn J. L. , Nadig F. H.
Published: September 2005

Measurements of absorption coefficients for 25-kc sound waves in air at low pressures using a pulse method are described. One-millisecond pulses emitted by a ribbon loudspeaker in a large low-pressure tank are detected by a condenser microphone mounted on a movable trolley. The usual procedure is to observe the decay of the wave amplitude as the microphone recedes from the source, the pressure being held constant. It is shown that absorption coefficients may be inferred also from observations of the amplitude as a function of ambient pressure at a fixed distance from the loudspeaker. Results obtained in the range 2–10 mm Hg are shown.
Rate and Duration of Change in Formant Frequency as Cues for the Identification of Speech Sounds
Authors: Gerstman L. J. , Liberman A. M. , Delattre P. C. , Cooper F. S.
Published: September 2005

Earlier experiments have shown that the direction and extent of the frequency changes in the formants of synthetic speech sounds can serve as effective cues for the identification of certain phones according to place of production. Examination of spectrograms and exploratory work with synthetic speech has suggested that the temporal course of these changes may provide a basis for distinguishing among some classes of speech sounds that differ in manner of production. It was found in the present experiment that the tempo of the change between two fixed formant frequencies is, in fact, sufficient to enable naive listeners to distinguish rather reliably among stop-consonant-plus-vowel (e.g., ba), semi-vowel-plus-vowel (e.g., wa), and a sound of shifting vowel color (e.g., ua). Further experiments suggest that the duration of the frequency changes are more important than the rate at which the changes occur.
Optical Method for Ultrasonic Velocity Measurements at Liquid-Solid Boundaries
Authors: Mayer Walter G. , Kelsey John F.
Published: September 2005

An optical method is used to measure the energy ratio of reflected and incident ultrasonic waves at a liquid-solid interface. The ultrasonic velocities in the solid are calculated from the angles of maximum reflection in the liquid.
Active Load Impedance
Authors: Bobber Robert J.
Published: September 2005

The load impedance of a generator or the radiation impedance of a transducer can be controlled by a second active generator coupled to the first generator by a transmission line. The primary control variables are the relative magnitude and phase of the signals in each generator. A load impedance of any magnitude and phase, including negative resistance, can be obtained. The second generator is used as an active reflector and absorber. The theory is applicable to the case where the generators are underwater sound transducers and the line is a water-filled tube.
Effect of Rough Surfaces on the Resolution of Acoustic Rays in the Ocean
Authors: Berman Alan
Published: September 2005

In the frequency region below 1 kc, the effect of velocity inhomogeneities on acoustic propagation in the ocean will be negligible. In this frequency region, fluctuations in travel time and ray direction will be caused by scattering from rough boundaries. In this paper, the effect of boundary scattering on the resolution of ray paths is investigated. Using a simplified model of the process, a rough estimate of the spatial line broadening of a low-frequency ray in the ocean is obtained.
Preloading of Acoustic Transducers for High-Pressure Operation
Authors: Brickman Arthur D.
Published: September 2005

The characteristics of a piston-type transducer that must withstand varying hydrostatic pressures can be improved by mechanically preloading the assembled transducer prior to operation and by carefully matching the axial compliances of the individual elements. A simple analysis and some tests of an experimental preloaded transducer are described, and the particular advantages of conical disk springs as transducer isolators are discussed.
Problems Associated with the Measurement of Ambient-Noise Directivity by Means of Linear Additive Arrays
Authors: Stone Julian
Published: September 2005

The problems associated with determining the angular distribution of continuous and discrete noise sources by means of a linear additive array are discussed. A spatial frequency analysis shows that an array acts as a low-pass filter in the spatial frequency domain and hence cannot distinguish between spatial-noise distributions whose spatial spectra differ outside the spatial bandwidth of the array. It is shown that smoothing due to side-lobe response results in a large reduction in the ability of an array to measure accurately peaks in the angular distribution.
Theory of a Passive, Reversible, Distributed-Coupling Transducer
Authors: Trott W. James
Published: September 2005

Equations are derived to describe an underwater sound transducer consisting of an acoustical transmission line coupled to a low-pass electrical transmission line. If the two transmission lines have the same phase velocity, the energy of a wave is transferred cyclically from one line to the other as a function of line length; a reversible transducer with a low Q, high efficiency, and essentially constant resistive impedance is thereby achieved. Theory and four proposed designs are described.
Remarks on the Paper by Montague and Strickland
Authors: Bennett G. S.
Published: September 2005

It is suggested that the hearing threshold shift found in underwater subjects indicates that the human ear is basically a velocity-sensitive device.
Vibrational Relaxation in Nitrogen and Other Gases
Authors: Henderson Malcolm C.
Published: September 2005

The vibrational relaxation in nitrogen and oxygen, both pure and with admixtures, has been measured with a high-pressure Kundt's tube. Pure nitrogen relaxes at f0/p of 1 cps/atm, at 203°C; oxygen at 90 cps/sec at 50°C.
Generalization of a Method of Potentials for the Vector Wave Equation of Elasticity for Inhomogeneous Media
Authors: Hook Joseph F.
Published: September 2005

In a recent paper, the Helmholtz method of potentials was generalized for application to the vector wave equation of elasticity for certain types of inhomogeneous media. Only the cases of three-dimensional axially symmetric waves and two-dimensional waves were treated. It is shown in this letter that these restrictions on wave symmetry can be removed, so that the method is applicable for waves of general spatial variation.
Automatic Recognition of Spoken Digits
Authors: Forgie Carma , Groves M. L. , Frick F. C.
Published: September 2005

No necessary-and-sufficient stimulus, or stimuli, has been discovered for the identification of any given word, yet people can reliably recognize speech under a wide variety of conditions One implication of this fact might be that speech recognition involves a complex data processing which takes advantage of linguistic redundancy. Such a system could make possible a reliable identification on the basis of a number of discriminating conditions, no one of which was in itself dependable. An attempt was made to realize such a data processing system in a program written for an experimental computer at Lincoln Laboratory. The program input consisted of the spoken digits processed through the Haskins Laboratories' resonance vocoder. Ninety-eight percent recognition was achieved on a sample of ten voices, mixed male and female. [The research reported in this talk was supported jointly by the U. S. Army, Navy, and Air Force under contract with the Massachusetts Institute of Technology.]
Intelligibility of Words in Sentences
Authors: Rubenstein Herbert , Pickett J. M.
Published: September 2005

Acoustical and nonacoustical factors have been observed which suggest that words in one position in a sentence may be more intelligible than words in other positions. An experiment was undertaken to determine the effect of some of these factors upon word intelligibility in sentences heard in noise. One-hundred six-word sentences, drawn from magazines, were read to 10 listeners The intelligibility of words in the first, fourth, and sixth positions was determined and their acoustic characteristics were measured. Measurements of intensity, duration, and total energy were obtained for each word. The words in final position were lowest in intelligibility despite the fact that they were highest in average intensity, duration, and energy. This apparent contradiction was resolved by a grammatical analysis of the words. The words in the final position included a larger proportion of content words (Nouns, verbs, adjectives, adverbs) than words in the other positions. The content words are less predictable, less intelligible, and contain more information per word than pronouns and function words (articles, prepositions, conjunctions). The intelligibility observed at each position was approximately equal to the intelligibility calculated from (1) the intelligibilities of content and function words, irrespective of position, and (2) the relative proportions of content and function words.
Sound Propagation in a Fluid Flowing through an Attenuating Duct
Authors: Pridmore-Brown D. C.
Published: September 2005

Undesired sound is frequently attenuated by having it pass through ducts with absorbing side walls. If the absorptive properties of the walls are described by a normal impedance, and if there is no air flow in the duct, the resulting attenuation is easily predicted on the basis of existing theory. In many cases, however (e.g., in ventilating ducts or the exhaust ducts in certain wind tunnels or jet-engine test cells), there is also a flow of air through the duct which may affect the rate of sound attenuation. In order to investigate this phenomenon a study is made of the propagation of sound in both constant gradient shear flow and a turbulent shear flow above a flat surface. Curves are presented showing how, in the case of downstream propagation, the flow gradient tends to channel the sound energy into a narrow layer next to the wall. These results are used in estimating the effect of a flow on the attenuation of sound in a duct with absorbing side walls.
Creation of Sound Absorption by dc Airflow
Authors: Sanders Guy J.
Published: September 2005

Studies have indicated that dc airflow through an orifice creates acoustic resistance. The creation of this resistance has been investigated by the measurement of the impedance of a perforated plate in an impedance tube. A method of calculating the acoustic resistance due to dc airflow has been prepared. The close agreement of theory and measurements points the way toward the use of this phenomenon for the improvement of all types of silencers where airflow is present.
Acoustic Wave Propagation in a Wedge
Authors: Runge Richard J.
Published: September 2005

A method is developed for solving the scalar wave equation in a wedge in which the specified sources and boundary conditions yield two-dimensional wave propagation. The pressure field in the wedge interior is expressed as the sum of a Fourier expansion which vanishes on the boundaries and another term which satisfies the boundary conditions. The Fourier coefficients are obtained by using the theory of Hankel transforms, and the formal solution is given. An application of the method is given for a free acoustic wedge excited initially by a uniform pressure impulse on one boundary. The ray solution and the diffracted wave are then developed from the formal solution. Modifications of the formal solution to solve the diffusion equation and Poisson's equation are considered.
Variations in Audio Oscillations Amplitude
Authors: McPherson R. R.
Published: September 2005

Amplitude variations in commercial audio oscillators have been found to be of the order of 50 to 60 db below the amplitude of the oscillator fundamental output. In a companion paper these variations are considered with respect to their effect on psychophysical experiments, as in audition. This paper presents a summary of the sources of variation in amplitude and discusses their relative magnitudes and differences in spectra. The quantity N0, noise power per unit band width of white noise, is related to the amplitude spectra of the variations in oscillator output, and the spectral value at the oscillator average frequency is shown to be important as an equivalent noise power per unit band width in psychophysical experiments. Results of typical approximate measurement of this quantity are given. (This work was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center.)