bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory Thresholds During Stroboscopic Visual Stimulation
Authors: Karlovich Raymond S.
Published: September 2005

Twelve experienced subjects participated in a Békésy-type tracking procedure and obtained their thresholds for a 25- and a 300-msec duration 1-kHz pulsing auditory stimulus in the absence and presence of time-locked stroboscopic visual stimulation. Six subjects obtained their thresholds in quiet, and the remainder tracked threshold in the presence of white noise. The data indicated that psychophysical sensory interaction between the auditory and visual systems does not occur when auditory thresholds are assessed in the presence of visual stimulation. Auditory thresholds were neither facilitated nor inhibited. These generalizations applied whether thresholds were obtained for short- or long-duration auditory stimuli in quiet or in the presence of a masking stimulus. Similar results were obtained for attenuator pen excursion size. A hypothesis is presented suggesting that the potential for psychophysical sensory interaction to occur between the visual and auditory modalities may increase as the magnitudes of sensory stimuli presented to them increase.
Comparison of Continuous and Pulsed Tones for Determining Békésy Threshold Measurements
Authors: McCommons R. Bruce , Hodge David C.
Published: September 2005

Two studies were performed to determine the parameters affecting the sensitivity and variability of Békésy thresholds. The first study was concerned with the effects of varying period, duty cycle, and frequency on threshold measurements obtained using pulsed tones and was done to derive an “optimal” pulsed tone. The second study compared thresholds taken using the optimized pulsed tone to those obtained with continuous tones. The effects of varying attenuation rate with both types of presentation were also investigated. Pulsed tones were found to yield superior threshold measurements both in terms of greater sensitivity and less intratest variability. Also, continuous tone thresholds were found to be susceptible to changes in attenuation rate whereas pulsed tone thresholds were not.
On the Discrimination of Frequency Transitions
Authors: Nabelek I. , Hirsh I. J.
Published: September 2005

Listeners attempted to discriminate sounds that differed in the rate at which frequency changed from an initial to a final value, in sound bursts that were much longer than the frequency transition itself. The results indicate that the rate of change of frequency for which the discriminability is optimum depends upon the extent of frequency change, from the initial and final frequencies. For small frequency differences, the optimum appears at small glide rates—i.e., at transition durations in the range of seconds; for large frequency differences, the optimum discriminability occurs at high glide rates, at transition durations of some tens of milliseconds. It seems that there are two mechanisms involved in hearing for perception of frequency transitions.
Envelope versus Microstructure in the Fusion of Dichotic Signals
Authors: Schubert Earl D. , Wernick Joel
Published: September 2005

An attempt was made to assess the effect of an imposed amplitude envelope on the binaural fusion of dichotic tone signals and noise signals. The envelope was imposed by an electronic switch at three rise/decay rates—10 msec, 25 msec, and 50 msec. The duration of the signals was such that there was no constant amplitude portion for any signal. The tonal signals covered a range from 250 to 2000 Hz. The noise was either high passed or low passed at 1000 Hz. Only the imposed envelope was delayed at one ear—not the microstructure of the signal. For tonal signals, the maximum envelope delay time for which the signal still yields a single stationary image is definitely a function of the envelope slope, being approximately 5–7 msec for the 10-msec slope; 10–12 msec for the 25-msec slope; and 15–20 msec for the 50-msec slope. For the two lesser slopes, there is also an envelope delay range for which the image moves across the head from leading ear to lagging ear. For the signals with noise microstructure, behavior of the image is more complex than for tones, but a number of tentative principles emerge, most of them amenable to further testing: (1) The position of the signal is predominantly determined by the interaural envelope delay. (2) Correlated microstructure (noise from the same noise generator) definitely increases the likelihood that a signal with large interaural envelope delay will fuse into a single image, even though the delay and the microstructure should yield different positions for the image. (3) Signals presented at higher sensation level tend to split into two at smaller envelope delays when microstructure information indicates the signals are different. (4) For the type of signal used here, maximum single-image envelope delays are greater for low-frequency microstructure than for high-frequency microstructure. For these signals, singleness of image and position of image appear to be analyzed separately, the information being combined later into a single perceptual impression.
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 taken through the open mouth, a method obviously limited to particular sounds. Running speech can be studied by a transillumination technique. A fiber-optics bundle or a miniature incandescent bulb introduced into the laryngeal vestibule through the nose illuminates 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 simultaneously recorded acoustic waveforms and intraoral air-pressure traces to determine how the voiced-voiceless distinction correlates with the closed-versus-open states of the larynx.
Comments on “Monaural Loudness Functions under Masking” [A. M. Richards, J. Acoust. Soc. Amer. 44, 599–605 (1968)]
Authors: Hellman Rhona P.
Published: September 2005

An explanation is given for the difference between the loudness functions of Richards [(1968). “Monaural Loudness Functions under Masking.” J. Acoust. Soc. Amer. 44, 599–605] and the experimental curves previously published by Hellman and Zwilocki [(1963). “Monaural Loudness Function of a 1000-cps Tone and Interaural Summation,” J. Acoust. Soc. Amer. 35, 856–865 (1964). “Loudness Functions of a 1000-cps Tone in the Presence of a Masking Noise,” J. Acoust. Soc. Amer. 36, 1618–1627]. It is shown that most of the difference can be attributed to two factors: a bias introduced by the method of magnitude halving and a misinterpretation of the method of numerical magnitude balance.
Design Methods for Minimization of Sonic-Boom Pressure-Field Disturbances
Authors: McLean F. Edward , Shrout Barrett L.
Published: September 2005

This paper reviews, through detailed consideration of airplane configuration, theoretically based techniques for minimization of sonic-boom pressure-field energy and overpressure. The discussion includes consideration of the recently discovered potential for overpressure minimization for large slender airplanes with extended nearfield characteristics. Use of the latter method is illustrated with correlations of theory and wind-tunnel measurements.
Instrumentation Techniques for Measurement of Sonic-Boom Signatures
Authors: Hilton David A. , Newman James W.
Published: September 2005

Special considerations are involved in the selection of instrumentation for meaningful sonic-boom measurements. Because of the nature of the sonic-boom pressure signature, the requirements include usable frequency response from nearly dc to several thousand cycles per second in the pressure range 0.1 to 10 lb/sq ft. A specially developed NASA instrument system is described along with techniques of measurement. The problems of vibration isolation, wind screening, long cable lengths, and field calibrations are discussed, and some sample data are presented.
A Pulse Technique for Sound Velocity Measurements in Solids and Liquids
Authors: Cedrone N. P. , Curran D. R.
Published: September 2005

A device developed to measure small changes in sound velocity is being redesigned to measure sound velocities in solids and liquids. A 10-megacycle pulse of approximately 2-microsecond width from a pulse generator is sent through the sample, amplified, rectified, and sent back into the pulse generator thus triggering the next pulse. The combined acoustical and electrical delay time is determined by counting the number of pulses which traverse the sample in an accurately determined time interval. The electrical delay time is eliminated by using another specimen of slightly different length. From the acoustical delay time and the measured dimensions of the sample, the sound velocity is then calculated.
A Phoneme Detector
Authors: Smith Caldwell P.
Published: September 2005

A speech analyzer is described which measures the degree of fit between the energy distribution of any speech signal and a set of “standard” energy distribution patterns stored in the machine. This technique is based on the assumption that a phoneme can be characterized, at least for a single speaker, by specifying the points of energy concentration in the frequency spectrum and by specifying the energy envelope, i.e., energy vs time characteristic, of selected portions of the spectrum. A set of contiguous-band filters covering the frequency range 100–7000 cps are used in combination with rectifiers and integrators to produce polarized signals which are functions of the energy distribution of the speech input signal. Improved selectivity and discrimination against noise and noiselike signals are obtained by combining the outputs from adjacent filters to measure the difference between signal levels, and further combining signals to measure the second difference between signals in adjacent filter bands. “Optimum filters” for phonemes are constructed by adding output signals corresponding to frequencies of energy concentration and subtracting signals corresponding to energy minima; this summation generates a signal proportional to the degree of “fit” between the speech signal and the specified pattern. Separate summations of the low and high frequency filter outputs provide measures of intensity, voiced-unvoiced detection, and pitch extraction signals. Some results will be presented.
Multiple Scattering by Two Parallel Cylinders
Authors: Twersky Vic
Published: September 2005

The wave scattered by two parallel cylinders (or two bosses on a rigid plane, or a single cylinder parallel to a rigid plane) is derived as an infinite sum of orders of scattering by specializing the results presented previously for an arbitrary configuration. A far field solution is obtained and all orders of scattering summed explicitly for separation large compared to wavelength to yield an expression essentially of the form obtained for multiple reflections within a thick plate. Certain “resonance wavelengths,” depending on the parameters, are found for which the effects of multiple scattering are maximal or give rise to the greatest departures from single scattering theory. These effects, which should be observed as intensity maxima and minima, result physically when either all orders of scattering are in phase and reinforce the first order, or when successive orders are completely out of phase and partially annul the first, the first order of scattering being the usual single scattering approximation. An analytic criterion for the range of validity of the single scattering hypothesis is also given.
The Use of Convex Plywood Paneling in Auditorium Design
Authors: Lane R. N.
Published: September 2005

A study has been made of four auditoriums of different sizes in which the principal acoustic treatment consisted of plywood paneling and upholstered seats. In general, the plywood was 14-inch thick built up of two 18-inch layers spot glued together and was installed in the room in cylindrical or splayed panels. The auditoriums studied varied in size from 1700 seats to 200 seats, but the panels were of similar construction in each case; the coefficient of absorption vs frequency for the paneling was calculated from reverberation time measurements in each room. These values are compared with coefficients obtained with identical measuring techniques on the same type of panel installed in the Defense Research Laboratory reverberation chamber.
The Propagation of Sound as Influenced by Terrain and Meteorological Conditions
Authors: Ingard K. Uno
Published: September 2005

The effect of wind and temperature gradients on the distribution of sound from a source, the influence of shielding by obstructions, and attenuation due to ground absorption are discussed. The relative importance of these factors is compared in special cases, particularly with regard to the problem of combating noise from airports.
Status of Research on Propeller Noise and Its Reduction
Authors: Regier A. A. , Hubbard H. H.
Published: September 2005

Fundamental concepts in the theory of noise from propellers are reviewed. Comparisons between experiment and theory are given for conditions of both subsonic and supersonic tip speeds. It is shown, for example, that the trend toward increasing sound energy in the higher harmonics with increased propeller tip speed is in accord with the theory. Noise of dual rotating propellers including blade interference and the associated directional effects is also discussed, and brief mention is made of tandem and shrouded configurations. Since the existence of intense oscillating pressure fields may be of importance both from acoustical and structural considerations, the sound field near the propeller in the vicinity of the wing and fuselage is discussed. The concluding section of the paper deals with some aspects of the propeller noise problem with reference to future high powered transport type aircraft. Results of recent analytical studies of acoustical and aerodynamic aspects of this problem are summarized. The noise intensity and spectrums of some proposed designs are compared with available tentative tolerance criteria.
Plane Wave Cavities for Pressure Response of Condenser Microphone above 10 kc
Authors: Biagi Fernando , Simmons Bernard D.
Published: September 2005

Low frequency calibration of condenser microphones by the reciprocity technique utilizes a reciprocity parameter, equal to the acoustic admittance of the cavity and valid with the conditions that the wavelength is small compared to the dimensions of the cavity and that the admittance of the microphone diaphragm is small compared to that of the cavity. The frequency range of calibration may be extended by (a) reducing the size of the cavity, (b) use of a gas with a higher sound velocity such as hydrogen, (c) proper dimensioning of the cavity. If the size of the cavity is reduced to extend the frequency range of calibration, the reciprocity parameter becomes dependent upon the unknown impedance of the microphone diaphragms. The frequency range may be extended somewhat by proper choice of cavity dimensions so that the effect of a radial mode cancels that of a longitudinal mode. A further extension of frequency range has been attempted using a cylindrical cavity having the radius of the microphone diaphragms. If plane waves are assumed and the diaphragm is effectively rigid with respect to the cavity, a reciprocity parameter can be calculated. Results up to 40 kc are compared with results obtained from theoretical calculations using electrical impedance data and with results obtained using an electrostatic actuator. Agreement within usual calibration error is obtained up to 20 kc.
The Near Field of a Spherical Resonator Exposed to a Plane Wave
Authors: Ingard Uno
Published: September 2005

The near field of a spherical resonator placed in a free field and exposed to a plane sound wave has been calculated and shown to be in good agreement with measurements. A discussion is included concerning the effect of velocity distribution in the resonator aperture on the scattered field.
The Acoustic Behavior of Induction Motors
Authors: Alger P. L.
Published: September 2005

The induction motor is the universally employed means for transforming electric power into mechanical work, in the home and the office, as well as the factory. As it is our daily companion at home and at work, experts in “Appearance Design” have been called in to give the motor an appearance that is pleasing, if not downright handsome. Now, there is a growing demand that the motor shall have good $ldquo;Sonance Design” as well. We want it to give out a pleasing steady hum, just loud enough to show that it is healthy and performing its functions properly, but not loud enough to disturb whatever we want to do in its neighborhood. This paper describes the acoustic behavior of the induction motor, and outlines the principles of good sonance design. Generally speaking, the stator of an induction motor comprises a laminated steel cylinder, supported in a steel or cast iron frame, and subjected to a series of radial and tangential magnetic forces, that vary at frequencies between 120 and two or three thousand cycles per second. The laminations can vibrate radially in elliptical or lobed patterns with 4, 6, or more nodes. The frame picks up the motions of the core through its supporting ribs, and translates them into a wide variety of “shivers,” depending on the degrees of freedom and resonant frequencies of the different parts. Each section of the frame surface acts as a loudspeaker diaphragm, sending out acoustic waves of intensities that depend on the ratio of the width of each vibrating surface to the wavelength in air of the sound frequency, as well as the amplitude and pattern of the motion. Besides these normal magnetic vibrations, the motor produces noise from resonant frequency shaft vibrations, from ball bearings, and from wind-age or fan effects. The varied problems encountered in calculating and controlling these different motor noises and in designing means for isolating, damping, or enclosing them in accordance with the requirements of each application pose a real challenge to engineers and scientists.
Responding to Both of Two Overlapping Messages
Authors: Webster J. C. , Thompson P. O.
Published: September 2005

The effects of overlapping messages was studied as one facet of a comprehensive laboratory study on factors affecting speech intelligibility in aircraft control towers. Speech intelligibility tests were constructed by including within the framework of standard airplane-tower phraseologies standard multiple-choice word lists. Air control tower operators listened to these test transmissions over four channels. Twenty percent of the time messages overlapped each other on two channels, and the degree of overlap was systematically varied. One quarter of the messages began simultaneously while the remaining messages lagged by either 2, 4, or 6 seconds. The task was to respond to both messages. The results show that the decrement in performance is related directly to the amount of overlap; that the leading message is understood better, unless the lead is so great that the two messages are sequential, and then the lagging message is understood better. Spatial separation of the sound sources did not improve intelligibility as long as both messages were to be responded to. However, separate experimentation showed that, if response to only one message is called for, spatial separation aids materially.
An Electronic Word-Recognizer
Authors: Baumann Roger H. , Licklider J. C. R. , Howland Bradford
Published: September 2005

Automatic devices that respond selectively to particular phonetic elements in the stream of speech have been built by Howland, Smith, and Davis, and an automatic digit-recognizer has been developed by Davis, Biddulph, and Belashek. The digit-recognizer responds accurately to spoken numerals, but mistakes other sounds for numerals. The word-recognizer described here is designed with the aim of responding always to a given word, never to any other word. It has the disadvantage of wording only on selected words, but this is not a disadvantage in the application for which it was intended: selecting telephone lines in response to key words from operators in information centers whose hands are too busy to push buttons. The word-recognizer combines Howland's phoneme-detector with a system of time delays and gates that is sensitive to a particular temporal sequence of speech sounds, For example, if the key word is “butterfat” (a particularly good word), a time delay is started every time an “uh” occurs. This delay lasts until the “er” is due and opens a gate to the “er” recognizer at that time. If the “er” comes on schedule, a second delay is started. It lasts until the “a” is due, etc. When all the contingencies are satisfied, the device connects the speaker to the appropriate communication line. The recognizer works best for the speaker for whom it was adjusted, but others can operate it with fair reliability.
Noneffect upon Speech Intelligibility of Phase Distortortion Produced by High-Pass and Low-Pass Filters
Authors: Smith S. L. , Licklider J. C. R.
Published: September 2005

Although it has long been the general belief that phase distortion produces no audible effect upon speech, it is easy to set up artificial phase distortions (time delays) that do affect both quality and intelligibility. In order to be sure that the effects of filters result from their selective action upon the amplitudes of the various frequency components, and not to the phase shifts they introduce, it is important, therefore, to have an empirical test. The test was made by playing each speech sample twice through each filter to obtain the effect of two filters in cascade. A recorded word list was played through a filter and re-recorded on a second tape. The second tape was then played through the same filter and presented through earphones to an articulation test crew of five. In half the tests, the tape was always run in the forward direction, and the phase shifts introduced by the filter and tape recorder were doubled. In the other half, the first run through the filter was made with the tape reversed end-for-end, and the phase shifts of the first run canceled those of the second. The two procedures were followed with high-pass and with low-pass commercial electronic filters set at the nominal cut-off frequency of 1800 cps. By cascading units, we obtained cut-off slopes of 48, 96, and 288 decibels per octave. In all, 288 articulation tests were run, each with five listeners. There was no difference at all attributable to phase distortion.
Heating of Haired and Hairless Mice in Sound Fields from 6 to 22 kc
Authors: Danner P. A. , Ackerman E. , Frings H.
Published: September 2005

Experiments have been conducted to provide a comparison of heat absorption by haired and hairless mice in high-intensity airborne sound fields. At 18–20 kc, threshold intensities for heating of the mice were found to be about 144±2 db for haired animals and 155±2 db for hairless animals. From 6–22 kc effectiveness of the sound in heating the mice increased with frequency. Absorption coefficients computed from the data were found to be higher at higher frequencies for both types of animals. Death time was found to be dependent upon intensity and frequency of the sound waves, external covering of the animals, and the portion of the animal exposed to the intense part of the soundffield. At frequencies of 18 and 22 kc localized burns were evident on hairless animals, and these were studied. The configuration of the sound field and its relation to the results is discussed. Measurements made with and without the presence of a hairless mouse demonstrated the effect of the animal body on the sound field at 162 db and 6, 12, 18, and 22 kc.
Ultrasonic Viscosity Measurements and Industrial Control
Authors: Roth Wilfred , Rich Stanley R.
Published: September 2005

The operating principles of the Ultra-Viscoson, an automatic viscosimeter that utilizes ultrasonic energy for the continuous measurement of viscosity, will be discussed. The viscosimeter comprises an ultrasonic probe approximately the size of a fountain pen and an electronic analog computer. The output of the computer is a meter and/or a continuous recorder/controller which are sensitive to the product of density and viscosity of the liquids being measured. Slides illustrating the use of the Ultra-Viscoson in industrial applications for automatic continuous control of processes are presented and discussed. Automatic temperature compensation equipment that permits the viscosity of a liquid to be referred to a particular reference temperature is described, and typical applications of the over-all system for the measurement of viscosity of liquids whose process temperature is varying are outlined.
Subjective Musical Pitch
Authors: Ward W. D.
Published: September 2005

The present Acoustical Society of America definition of “pitch” is “that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from low to high, such as a musical scale.” But since extant musical scales are based upon physical instead of subjective criteria, we are faced with the paradox of a subjective attribute with physical dimensions. Hence, experiments were performed to determine subjective musical scales for nine trained musicians. The assumption was made that, for a given observer, the subjective octave is an invariant relation between pitches, just as the physical octave is an invariant relation between frequencies. The observer adjusted one pure tone so that it appeared to be one octave above another (alternate presentation). Since the “error” (difference between subjective and physical octaves) for a given ear varied systematically with frequency, individual subjective scales of musical pitch could be derived. In agreement with the facts of binaural diplacusis, individual scales are fairly irregular, and scales for the two ears of a single observer are in some cases as different as those from different observers. The average (group) scale shows a gradual “stretching” relative to physical musical scales; i.e., the mean subjective octave corresponds to a frequency ratio of about 2.04:1.
The Frequency Dependence of Acoustic Cavitation
Authors: Laufer A. R. , Thomas G. L.
Published: September 2005

In the past it has been necessary to infer the frequency dependence of acoustic cavitation from the work of different investigators at different isolated frequencies, the experimental techniques and the condition of the liquid varying markedly from investigator to investigator. The results of such inference are open to considerable doubt. The present investigation has determined the dependence upon frequency of the acoustic pressure required for the onset of cavitation under conditions such that the only variable was the acoustic frequency. The method utilized a standing wave system set up between a quartz crystal projector and a calibrated barium titanate hydrophone used as a reflector. The liquid sample, protected by a polyethylene box with thin windows, was inserted in the standing wave system. The output of the quartz projector was raised until cavitation began, as evidenced by visible bubbles, non-linearity in the hydrophone response, or cavitation noise picked up by an auxiliary hydrophone. The variation with frequency of the acoustic pressure required for the onset of cavitation was determined in water and several other liquids through the range of 300 kc/sec to 5 mc/sec.
Use of Models in the Study of Seismic Phenomena
Authors: Silverman Daniel
Published: September 2005

In the shallow crustal volume of the earth which is of interest to the geophysicist, the seismic behavior of the earth is adversely affected by the complexity of the earth's structure. In order to study seismic phenomena in the earth, recourse has been had to the use of acoustic models. These models are simplified idealized structures, generally scaled down in time and dimension, with which the basic action of seismic waves in the earth can be studied. Different types of models have been built, including single-, two-, and three-dimensional solid models, multilayered liquid models, and optical models. All of these are essentially analog computers for solving the wave equations as applied to the specific structures. Model studies have been found quite useful in verifying theoretical analyses, in explaining observed phenomena in the field, and in suggesting additional field experiments. The use of scale models in the study of the seismic process is becoming widespread both in universities and in industrial laboratories.
The Frequency Characteristics of Colloidal Vibration Potentials
Authors: Yeager Ernest , Dereska Joseph , Hovorka Frank
Published: September 2005

Colloidal particles in a solution containing ionic components are usually charged with an ionic atmosphere of predominately opposite charge surrounding each particle. When ultrasonic waves are introduced into such a system, the distribution of the ionic atmosphere about each colloidal particle becomes periodically asymmetric because of differences in the reaction of the colloidal particles and ions to the sound waves. As a consequence, alternating potentials are developed between points separated by distances other than integral multiples of the wavelength in the direction of propagation. The frequency dependence of this effect has been determined in the range 105 to 106 cycles/sec with pulse-modulated ultrasonic waves. Colloidal silica suspensions of various concentrations and conductivities have been studied. In cases when the effective thickness of the ionic atmosphere is large compared to the colloidal particles, the response in volts per unit velocity amplitude is inversely proportional to the frequency. The experimental results compare favorably with theory.
Some Problems Associated with Finite Attenuating Structures
Authors: Dyer Ira
Published: September 2005

The reduction in sound pressure afforded by a finite attenuating structure located in a duct is often approximately determined from the attenuation of a plane wave in an infinite length of the structure. In many cases, this procedure is sufficiently precise, and its relative simplicity makes it attractive for engineering purposes. In other cases of practical interest, however, (for example in aircraft engine test cells) this procedure is often inadequate in explaining measured results. The possible influence of such factors as wave configuration scattering from the ends, radiation impedance of the ends, type of source and its distance to the attenuating structure, etc., is reviewed. Measurements and calculations which illustrate the influence of some of these factors in practical attenuating structures are presented and discussed.
Sound Propagation into a Wind-Created Shadow Zone above a Plane Boundary
Authors: Pridmore-Brown David C. , Ingard Uno
Published: September 2005

The presence of wind affects the propagation of sound in the open largely because of its ability to bring about the formation of acoustical shadow zones. The present paper is a study made of the sound field from a cylindrical source located above a plane boundary and driven at a single frequency in the presence of a wind. The wind velocity is considered to increase monotonically with height and to approach the sonic velocity at infinite heights. An expression is presented for the diffracted sound intensity in the shadow region which forms on the upwind side of the source.
Design of Cylindrical Microphone Windscreens
Authors: Dyer Ira
Published: September 2005

Measurements of the self-noise of finite circularly cylindrical microphone windscreens were reported at the last meeting. It has been possible to empirically correlate these measurements in such a way that the self-noise of other circularly cylindrical windscreens may be predicted. The correlation indicates the existence of an optimum diameter and flow resistance for a given wind velocity, frequency, and length. An example of the optimum design of a cylindrical windscreen is given.
Electrical Synthesizer of Continuous Speech
Authors: Stevens K. N. , Bastide R. P. , Smith C. P.
Published: September 2005

An electrical speech synthesizer controlled by teletype equipment is described. The basic components of the synthesizer are four simple tuned circuits each of which represents one of the resonances of the human vocal tract. The resonant frequencies of three of the tuned circuits are set by relay circuits that are controlled by data coded on punched tape. The punched tape also controls the intensity and pitch of a buzz generator that excites the variable tuned circuits, and modulates a noise generator that is filtered in various ways to generate fricative or stop consonants. The coded data are read from the tape at about the phonemic rate, with a rate of information transmission of about 35 bits per second. Smoothing circuits are incorporated in the synthesizer to provide smooth formant transitions between sounds. The generation of individual sounds, words, and sentences by the synthesizer is demonstrated.
Message Reception as a Function of the Time of Occurrence of Extraneous Messages
Authors: Peters Robert W.
Published: September 2005

The effect of extraneous messages upon the reception of messages was studied relative to the time of occurrence of the two messages and the content of the extraneous message. Criterion messages were multiple-choice intelligibility test word groupings or PB words. Six types of extraneous messages were presented with the multiple-choice words. Extraneous messages presented with PB words were other PB words. Extraneous messages either immediately preceded or followed the primary message. Individuals serving in panels participated as either experimental or control group listeners. The control group heard only primary messages; the experimental group, both primary and extraneous messages. Comparisons were made between reception values found for each group and among the values found for the experimental group relative to the type of extraneous messages. The results indicated that the presence of an extraneous message immediately preceding or following a primary message significantly interfered with reception. Extraneous messages following primary messages were more damaging to reception than were preceding messages. The amount of interference varied depending upon the type of extraneous message.
The Localization of the Sound from Two Sources in Phase Opposition
Authors: Feddersen William E.
Published: September 2005

Pairs of loudspeakers, one in front of the subject and one 40° to one side or the other and with one of the speakers of the pair reversed in phase relative to the other, provided phantom sources to be localized. For tones in frequency range from 600 to 1000 cps the phantom source was localized as predicted, on the side opposite the asymmetrically placed speaker of the pair used. Data will be presented showing the extent of the agreement between the predicted localization and the observed. At frequencies from 1250 to 2000 cps, where interaural time difference plays a diminishing role, individual differences become larger and the phantom source is localized in many cases on the side of the asymmetrically placed speaker, as would be predicted if the cue were intensity rather than time.
Acoustic Requirements of Music School Buildings
Authors: Lane R. N. , Mikeska E. E.
Published: September 2005

Acoustic measurements are presented on the recital halls, ensemble rooms, teaching studios, and practice rooms of several music buildings located in the Southwest. Minimum acceptable values for attenuation between the various types of rooms are suggested.
New Broadcast Studio Facilities for the Voice of America
Authors: Manhart J. Kenneth
Published: September 2005

A new and permanent broadcast plant for the Voice of America has been constructed in Washington, D. C. International broadcasts were initiated from these facilities on September 15, 1954. Unique features of this plant include a complete system design for equipment, which was fabricated to specification and requirement and a performance specification for all interior acoustical work. The equipment is comprised in part of a fully presettable, 100 input—50 output Master Control Desk and a 40-channel Recording Console. The Western Electric cross bar system is used for switching, and the recording functions are handled in a ten-cubicle recording room, each cubicle containing four disk or tape machines, the sets being completely interchangeable. Fourteen studios have been built which may be increased in number to thirty-six. A reference recording system of unusual application has been introduced. Five separate air-conditioning systems are used for the facilities area. Both tape and disk playback facilities are provided in every studio control room, all of which are indentical in size and layout to minimize operational problems. The studios are acoustically designed for speech reproduction suitable for the highest intelligibility of thirty-five different languages and are constructed to maintain an operational residual noise level of no greater than twenty-seven decibels. The acoustical performance specification demanded for the prescribed interior acoustical work is described. A variety of acoustical problems posed themselves during the plant design. A discussion is held concerning these problems and their practical solution.
Portable Masking Meter for Measuring Impact Noise in Industry
Authors: Hall H. H.
Published: September 2005

An instrument for evaluating loudness of industrial noises of the impact type must be portable, be convenient to use in the field, and yield results which may be interpreted in engineering terms. The development of such a device is described which enables an observer in the field to evaluate the magnitude of impact noise by finding the level of the masking threshold using an appropriate spectrum of masking noise. The instrument consists of a compact random noise generator, amplifier, filter set, attenuator, and mixer, and is normally used with a sound level meter and headphones. Six masking noise spectra of +9, +6, +3, 0, −3, −6 db per octave are available by means of a selector switch. The circuit is arranged so that the attenuator is calibrated in terms of phons. Metering circuits are provided for setting the output of the noise generator and the input from the sound level meter, as well as showing the condition of the batteries. In use, the microphone of a sound level meter is placed in the vicinity of an impact noise and the output of the sound level meter is connected to the masking unit. A spectrum of masking noise is selected which appears in the earphone simultaneously with the impact noise. The level of the masking noise is adjusted in the range of 70 to 110 db until the masking threshold is determined. This is repeated for each spectrum slope until the one with the lowest masking threshold is found. The attenuator dial then shows the level of the masking spectrum which most closely matched that of the impact noise. A demonstration using recorded industrial noises will show the operation of this equipment.
Probe Microphone Testing at High Temperatures and High Intensities
Authors: Goff Kenneth , Mercer Derwent
Published: September 2005

A microphone using a resistively terminated probe tube of the type described by R. W. Leonard [J. Acoust. Soc. Am. 24, 113(A) (1952)[ has been developed. This microphone was designed to facilitate the measurement of sound pressures at the wall surface of jet engine test cells and altitude wind tunnels and, therefore, attention was focused on the problems of obtaining satisfactory performance with the probe tip exposed to: (1) high temperature gases; (2) high sound pressure levels; (3) reduced static pressure of simulated altitude. Techniques have been worked out for measuring the flow resistance of the probe tube tip at temperatures up to 900°F. A resonant tube system has been used to obtain sound pressure levels up to 175 decibels for the purpose of rank ordering various probe tube tip materials according to their total harmonic distortion. A low pressure cavity enclosing a sound source and monitor microphone was used for measuring the mid-frequency sensitivity of the probe microphone system with static pressures from 1.0 to 0.2 atmosphere at the probe tip. An approximate electrical analog circuit of the probe tube microphone system provides a basis for using the results of these tests to predict the probable behavior of the microphone under simultaneous high temperature, high intensity, and low static pressure conditions. This work was supported by the U. S. Air Force under Contract No. AF33(600)-23807.
Corona-Type Loudspeaker
Authors: Oda Fujio , Ackerman Eugene
Published: September 2005

A corona-type loudspeaker was described by S. Klein [Acustica 4, 77–79 (1954)[ and called the ionophone. This loudspeaker differs from previous corona-type loudspeakers primarily in coupling the corona to a horn, which dramatically increases its efficiency. The frequency response of these loudspeakers is limited only by the horn shape. With a 50-w 27-mc rf generator intensities of the order of 120 db can be obtained in exposure chambers suitable for rats. By the introduction of a second point electrode inside the horn in place of a ring electrode outside the horn, the sonic output can be raised about 3 db. The horn near the corona must be made of Vycor or quartz because of the heat evolved in this region. By using higher powers and possibly several corona loudspeakers it is hoped to be able to expose rats to intensities of 135 db in the range of frequencies of 5–30 kc where their hearing sensitivity is believed to be a maximum. This work was supported in part by contract No. AF 33(616)-2505.
Detection of Ultrasound with Phosphorescent Materials
Authors: Petermann Lucien A.
Published: September 2005

Several authors have mentioned the possibility of studying ultrasonic beam patterns by using the influence of ultrasonic energy on the decay of luminescence of thermostimulable phosphors. A theoretical study of the effect was carried on by the author, assuming that the effect is purely thermal. A series of experiments have confirmed the theoretical prediction. The particular phosphor used for this study is a Ca—SrS activated by Ag and Y. Its electron trap distribution is found to be nearly exponential in the trap-depth range of 0.5 to 0.8 ev. The luminescence intensity as a function of time during exposure to ultrasound is derived theoretically. Theoretical and experimental results are shown on graphs and compared. A number of beam patterns obtained by this method have been studied, showing the great power of resolution attained and leading to some important observations concerning the ultrasonic intensity distribution in front of a circular disk transducer driven in thickness compressional mode.
Acoustic and Other Physical Properties of Shallow-Water Sediments off San Diego
Authors: Hamilton E. L. , Shumway George , Menard H. W. , Shipek C. J.
Published: September 2005

This paper reports on a continuing study of the mass physical properties of surficial, shallow-water marine sediments off San Diego, California. Sound velocity measurements in situ at 100 kc were made by pulsing between small transducers inserted into the bottom by diver. Density, porosity, and size analyses were determined on relatively undisturbed samples taken by diver. The following averaged representative values have been obtained:

Sediment type Density Porosity Med. diam Velocity in Impedance

(g/cc) (%) (mm) sediment at × 105g/cm2

60 deg F sec

(ft/sec)

Fine sand 1.93 46.2 0.19 5520 3.25

Very fine sand 1.92 47.7 0.12 5435 3.18

Silty very fine

sand 1.68 61.3 0.05 5075 2.60

Medium silt 1.69 60.9 0.03 4825 2.49

Clayey fine silt 1.60 65.6 0.02 4800 2.34

Laboratory measurements of velocity and attenuation at 25 to 35 kc were made by a resonant chamber method using diver taken samples; average attenuation values of about 0.5 db/ft (silt) to about 5 db/ft (fine sand) were obtained. Velocity measurements with both systems compared within 212%. At three stations the sediment sound velocity was less than the velocity in the bottom water.
Near Sound Field of Turbulence
Authors: Franz G. J.
Published: September 2005

The general expressions for the velocity potential, particle velocity, sound pressure, mean-square sound pressure, intensity, and sound power describing the sound field of a turbulent region are derived starting from Lighthill's fundamental relation for the density fluctuations in the medium outside the turbulent region. The mean-square sound pressure and intensity of the lateral and longitudinal quadrupole components of the near- and far-sound field are discussed in detail and for shear flows a correction to the sound pressure measured in the near field is given. These expressions should be useful in the interpretation of noise data taken close to jets and turbulent boundary layers.
Identification and Discrimination of Elementary Auditory Signals
Authors: Pollack Irwin
Published: September 2005

The absolute identification and differential discrimination of the sound level of tones were studied over a wide range of sound levels under comparable experimental conditions, and the results of the two experiments were compared in comparable units. Absolute identification improves and differential discrimination deteriorates as the range of sound levels examined increases. The net effect of these complementary changes is that the information associated with differential discrimination is roughly of the same magnitude as that associated with absolute identification.
Loudness Discrimination
Authors: Rawnsley A. I. , Harris J. D.
Published: September 2005

The persistent problem of DL for intensity has not heretofore been fully attacked with the resources of electronics plus the still-powerful analysis of judgmental behavior as exemplified by the classic techniques of psychophysics. Data are in sharp disagreement as to absolute values of DL, and as to effects of frequency and intensity upon DL. Seven experienced subjects repeated Riesz's intensity modulation at 1000 cps at sensation levels 5, 10, 20, 40, and 60. Results were very similar to his. These S's were also given the method of adjustments, at 1000 cps at the same sensation levels, and at 100 and 6000 cps at equivalent loudnesses. The results differ sharply from Riesz. Three of these subjects were used to explore 1000 cps most carefully by the method of constant stimulus differences. Two completed judgments also on 100 and 6000 cps. This method yielded finer DL's than either of the others, but in its conclusion that loudness level has relatively little effect it is allied much more closely with the method of adjustments than with intensity modulation. The correspondence of DL's for loudness discrimination between the classic methods of adjustments and of constants, and the dissimilarity of modulation, are leading to a search among tests not of loudness discrimination but of masking, auditory quantum tests, frequency modulation, etc., for auditory traits correlative with intensity modulation.
Recent Developments in the Use of Ultrasonic Attenuation Methods in Solid State Physics
Authors: Truell Rohn
Published: September 2005

This is a discussion of general methods of making ultrasonic attenuation measurements in the megacycle range (5–500 Mc/sec and higher). It includes some discussion of dislocation damping effects together with examples where ultrasonic attenuation measurements have led to new information. Work has been done on metals and alloys, semiconductors, and insulators; the work to be described will be mainly that of the Metals Research Laboratory at Brown University.