bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Time Integration in the Discrimination of Frequency Response Patterns
Authors: Hunt F. V.
Published: September 2005

It is impertinent—but fair—to ask why we should care whether the frequency response of a loudspeaker is flat or not when the point-to-point steady-state transfer function of an ordinary listening room is sure to introduce a much greater degree of frequency-response irregularity in the over-all chain of transduction leading from electrical signal to perception. Of course, we do care; so we are led to the hypothesis that a time-invariant pattern of frequency response (such as that of the loudspeaker) can be discriminated in the presence of a variable pattern of frequency-response irregularity (such as the room response when the listener keeps moving slightly) when, but only when, the listening interval is of sufficient duration to allow the variable part of the total response pattern to be averaged out. Qualitative evidence seems to support the hypothesis, but quantitative evaluation of the needed integration times is still wanting. If the effect is real, however, it may have an important bearing on the interpretation of the conventional A-B tests used for the assessment of sound-reproducing systems.
Condenser Earphone with Solid Dielectric
Authors: Sessler G. M. , West J. E.
Published: September 2005

A high-quality condenser earphone will be described in this paper. It consists of a solid backplate and a metallized Mylar foil which is stretched across the backplate. Its frequency response is within ±1.5 db between 25 and 14 000 cps and within ±3 db between 20 and 16 500 cps. In this frequency range the harmonic distortion is less than 1%, and the intermodulation distortion is less than 3% at 100 db SPL. The earphone shows an impulse response which is an almost true image of the applied voltage. The high quality of this earphone makes it useful for many purposes particularly in psycho-acoustic experiments.
Depletion Layer High-Frequency Transducers
Authors: White D. L.
Published: September 2005

The depletion layer transducer is a new ultrasonic transducer made from piezoelectric semiconductors, such as gallium arsenide, and is best suited for use at microwave frequencies. The electromechanically active region is a thin, flat, high-resistance depletion layer such as a p-n junction or the surface barrier at a metal semiconductor contact. Since the transducer is a thin piezoelectric layer, its behavior is more like that of a flat piezoelectric transducer plate used at low frequencies than other microwave transducers. Advantages expected when the thickness is comparable to a half wavelength of sound are large electromechanical coupling and large bandwidth. The major difficulty is the low impedance due to the extreme thinness. It is also possible to change the thickness, hence the resonant frequency, by a dc bias. The first models utilized metal semiconductor contacts to form the depletion layers. Frequencies above 1000 Mc were generated and detected, and bandwidths of 5% were observed. The insertion loss was much higher than theoretically predicted. Current efforts are directed toward transducers formed by p-n junctions. It is anticipated that improvements in fabrication techniques and circuitry will extend the frequency range and lower the insertion loss.
Esaki Diode Pressure Transducer
Authors: Sikorski M. E.
Published: September 2005

Studies of the effect of point as well as hydrostatic pressures on the switching current-voltage characteristics of tunnel diodes have been reported earlier [L. Esaki and Y. Miyahara, Solid-State Electronics 1, 13 (1960); S. L. Miller, M. I. Nathan and A. C. Smith, Phys. Rev. Letters 4, 60 (1960)]. In the present work diodes were subjected to hydrostatic pressure. The transducer consists, essentially of a tunnel diode shunted by a resistor which satisfies the stability conditions for operation in the negative resistance region of the I-V characteristic. The pressure range as well as the pressure sensitivity in a chosen pressure interval can be varied by adjusting the values of the shunt resistor and the current through the diode-resistor combination. A very sensitive hydrostatic pressure transducer was made using a silicon tunnel diode. Gauge factors obtained ranged from about 2000 to 30 000, depending on the value of the shunt resistor. Pressure and temperature effects were compared for tunnel diodes made of silicon, germanium and gallium arsenide. Results show that the change in the I-V characteristics with pressure was smallest for silicon and larger for the other materials in the order listed. The order is reversed as far as the temperature effects are concerned. The advantages of the tunnel-diode transducers are (1) small size, (2) sensitivity, and (3) versatility.
An Energy Detection Model for Monaural Auditory Detection
Authors: Pfafflin S. M. , Mathews M. V.
Published: September 2005

In the presence auditory detection of a sinusoidal signal in the presence of random noise, it has previously been demonstrated that the presence of a “pedestal” or background sinusoidal of the same frequency and phase as the signal increases detectability. This increase was confirmed in a two interval forced choice experiment in which a 1000-cps sinusoid was present in our of two 0.1-sec intervals, and the noise plus pedestal were present in both intervals. Pedestals of moderate intensity in phase with the signal increased detectability. Pedestals 90° out of phase with the signal did not improve detectability. Very large pedestals decreased detectability regardless of phase. A simple energy detection model was developed and its performance compared with the experimental results. The model consists of a bandpass filter, a rectifier or square-law element, and an integrator. The probability of correct detection varies with signal in a manner similar to the auditory results. Detectability is improved by an inphase pedestal and approaches that of a correlation detector in the limit of infinite pedestal. Detectability is not improved by 90° out-of-phase pedestals. However, the model does not predict decreasing detectability with large pedestals.
Experimentally Induced Shifts in Apparent Pitch
Authors: Christman R. J.
Published: September 2005

The influence of prolonged antecedent pure tone stimulation on the apparent pitch of an immediately subsequent tone is described as a phenomenon warranting future investigative effort. Past history of research on the effect is discussed, along with a suggested explanation in terms of satiation effect, similar to that postulated by Prof. Wolfgang Köhler for visual figural after-effects. Current research effort is described and recently completed work is discussed briefly.
Eliminating Stimulus Bias in Category Scaling
Authors: Pollack Irwin
Published: September 2005

Category scaling provides a listener with a fixed set of numbers, or ratings, for assignment to sounds under test. Unfortunately, category scales are sensitive to stimulus bias—that is, to the specific distribution of sounds arbitrarily selected for testing. Stimulus bias may, however, be reduced by an iterative procedure suggested by Stevens. A series of experiments is successively performed in which the results of the first experiment provide the stimuli for the second, etc. It is demonstrated that the procedure eliminates stimulus bias over a wide range of conditions for auditory frequency and intensity, as well as for several nonauditory variables. (Research performed at the Applied Psychology Research Unit, Cambridge, England, under a National Science Foundation Fellowship.)
Low-Loss Wide-Band Delay Line Using Multielement Ceramic Transducers
Authors: Bieling C. A. , Hixenbaugh R.
Published: September 2005

This paper describes a means of obtaining reasonable values of transducer impedance through the use of multielement transducers whose individual elements are connected electrically in series. This facilitates impedance matching, which reduces end reflection and insertion loss. The electrical characteristics of a 700-μsec, 20-Mc, fused-silica, polygon delay line using sectioned barium titanate transducers is compared with a conventional line using quartz transducers. When the line is properly matched into 10 ohms, the new design provides an 8-Mc band with a total loss including beam spreading and wave attenuation of 32 db at 20 Mc. In comparison, a line with quartz transducers has a 7-Mc band at 30 Mc and an insertion loss of 42 db when highly mismatched into 75 ohms.
Resonant Vibrations of Ceramic Rectangular Bar Transducers
Authors: Fabian E. Larry
Published: September 2005

Electrical admittances have been measured for rectangular bars of barium titanate, lead zirconate-titanate, and sodium potassium niobate which were poled in a direction normal to the driving electrodes. Resonant frequencies for the first eight modes of vibration have been determined from these measurements. A comprehensive survey has been made of 50 or more transducers of each material in a width-to-thickness (w/t) range from 0.2 to 100. The velocities for longitudinal waves in a thin rod and dilatational waves in an extended body have been determined from the value of frequency-thickness (fRt) product at the limiting values of w/t. Graphs show the dependence of electromechanical coupling and fRt on w/t over a range from 0.2 to 6. The results are compared to those for resonant vibrations in circular disks reported by Shaw. Graphical results show the optimum values of width and thickness dimensions for transducer design in the first mode and a technique for determining optimum dimensions for resonance in other modes is outlined. A normalizing parameter is introduced which is determined for a given material from a measurement of fR in the first mode for a single transducer. For materials with Poisson's ratio between 0.2 and 0.4, this parameter permits the design of transducers to a frequency within ±3% in the first mode.
Long-Range CW Sound Transmission
Authors: Berman A. , Lord N. W. , Sherry H. B.
Published: September 2005

An attempt was made to propagate pulsed CW sound coherently over thousand-mile distances in the mid-Atlantic using the focusing properties of the sound channel. The sound field emanating from a 440-cps lumped source at the sound channel depth off Barbados was studied at stations 159 and 975 mi. away in the NNE direction. This field was probed in depth with a 3-dimensional array of hydrophones with the source on for 8- and 9-min periods followed by 2- or 1-min silent periods. While a moderately coherent field existed at 159 mi., inter-hydrophone correlation measurements indicated a sharply rippled wave front which was not at all stable in time. Individual hydrophone records showed large random instabilities with variation of intensity by a factor of 3 occurring within periods of a few minutes. At 975 mi. no coherent signal at all was detected on individual hydrophones although the source strength was eight times greater. A barely detectable inter-hydrophone correlation was observed. The negative results of this attempt are at least in part due to the irregular sound velocity structure of the sound channel as described in the accompanying abstract (F1), (This work was supported by the Office of Naval Research.)
Convergence Zone Propagation in the North-East Pacific
Authors: Maunsell C. D. , Scrimger J. A.
Published: September 2005

Oceanographic factors cause the sound velocity minimum in the Gulf of Alaska and the neighboring portions of the North-East Pacific to occur at a much shallower depth than in more southerly waters. As a result it is fairly easy to make experimental measurements with hydrophones at depths near the vertex. Measurements using pulsed CW signals of sound level against range have been made at several locations with arrays including hydrophones at various depths. These measurements have been compared with predictions based on ray tracing assuming a series of layers each with constant velocity gradient. Use of the Kuwahara sound-velocity relationship predicts too short a range for the convergence. Work is in progress to utilize predictions based on the work of Wilson. The pulse-to-pulse amplitude fluctuation is small, indicating at least short-term stability in the acoustic path without much effect from surface or internal waves.
Ray-Tracing Program for High Speed Digital Computers
Authors: Norris A. B.
Published: September 2005

A ray-tracing program which has been developed for the IBM 704 and 7090 computers yields results which show excellent agreement with experimental data. The program permits ray computations for arbitrary source and receiver depths, bottom profiles, and velocity structures. The tabulated results give actual ray trajectories as well as the geometrical spreading associated with each path. Realistic curves of transmission loss as a function of range can be determined by adding individual ray intensities, once reflection loss values have been introduced. Theoretical results were compared with a 100-cps transmission loss curve obtained using a CW projector and a bottomed hydrophone in a deep ocean area of the North Atlantic. Good agreement was observed at moderate to long ranges. Significant errors at short ranges were attributable in part to the lack of refinement of the methods used. (This work was supported by the Bureau of Ships, U. S. Navy Department.)
Noise Models for the Calculation of Spacial Correlation
Authors: Cron Benjamin F. , Sherman Charles H.
Published: September 2005

Observations indicate that noise in the ocean is a superposition of an isotropic noise field and an anisotropic noise field originating at the surface. Models are described which produce such noise fields, and the spatial correlation functions are obtained. The volume noise model, which produces an isotropic noise field, consists of noise sources uniformly distributed within a sphere. Each noise source emits one frequency, the frequency and mean-square output of each are the same, the relative phases are random, and inverse spreading occurs. It is shown that for a very large sphere the spatial correlation is the same as that given by the Faran and Hills noise model which consists of noise sources on the surface of a large sphere. The surface noise model consists of noise sources uniformly distributed on a large circular area of a plane. The noise sources are assumed to be directional in addition to having the properties listed above. The spatial correlation is obtained as a function of the directionality of the noise sources, the spacing of the receivers and their orientation with respect to the surface, and the electrical delay. Results for the two noise models are compared in relation to signal-to-noise gain of hydrophone arrays.
General Design and Performance Characteristics of a Military Voice Communication System. State of the Art Appraisal
Authors: Snow William B.
Published: September 2005

The general requirements, plan, and equipment for on-board voice communication in military aircraft are described. The characteristics and functions of essential components, including speech projectors, receptors, and intervening electronic equipment, are illustrated by conventional current and improved equipment. This equipment and its design problems are demonstrated in relation to requirements dictated by personnel protection, respiration, and altitude provisions. The electrical, mechanical, and acoustical characteristics of prospective transducers, conventional and unusual, including microphones, earphones, loudspeakers, and accelerometers, are reviewed as part of a morphological study of speech projection and reception techniques. Evaluation is based upon standard electrical and acoustical ratings and newly devised ratings appropriate to the problem, as well as engineering judgment regarding adaptability to flight systems, including wearability. The comparisons show great promise for the electrostatic transducer as an earphone or loudspeaker.
Noise Environment and Control—Present and Prospects; Evaluation of Speech Projection and Reception Systems
Authors: Veneklasen Paul S.
Published: September 2005

The noise spectra in present military aircraft are reviewed, describing the characteristic sources. Objectives for noise control based upon communications, aural damage risk, and comfort are proposed. The probable maximum increases in noise exposure are described, and the prospects for control in future aircraft and space vehicles are discussed. Requirements for personal protection are deduced. Latest methods of evaluation of speech projection and reception systems are based both or physical measurements and intelligibility testing. Highly efficient articulation testing is based upon most difficult consonant sounds and upon simulated flight command sentences. Results permit rating of systems in terms of noise tolerance as a function of speaking effort.
Vibration Damping Materials with Optimum Efficiency in Temperature Bands of Prescribed Position and Width
Authors: Oberst Hermann
Published: September 2005

Highly effective vibration damping materials for metal sheet structures can be obtained by making use of amorphous high polymers in the viscoelastic state. Materials of this kind can be adjusted to provide optimum damping at given frequencies in temperature bands of prescribed position and width. This can be done by mixing high polymers having different glass transition temperatures in suitable distribution or by copolymerizing suitable monomers. Plastification and addition of filling materia[s can play a part in obtaining the desired results. The larger the temperature bandwidth of high internal energy losses the larger is the frequency bandwidth. However, the maximum damping will be diminished when the bandwidth is increased; this follows from the laws which govern the molecular behavior of high polymers. Damping materials have been developed for different combined systems, such as metal sheets with a single damping layer at one side or sandwich systems, according to special technical demands with respect to frequency and temperature dependence. Experimental results obtained with these combined systems will illustrate the damping efficiencies which can be attained in optimum cases.
Low Bit Rate Digital Speech Communication
Authors: Stead L. G. , Jones E. T. , Weston R. C.
Published: September 2005

Preliminary results and experience with a two-way analysis/synthesis formant tracking speech system are reported. Parametric information from the analyzer is coded into binary digital form at rates in the range 600 to 1200 bits per sec and transmitted over audio channels by high-speed voice-frequency telegraph equipment. (Paper presented by Walter Lawrence.)
Design vs Performance Factors for Some Speech Compression Systems
Authors: Smith Caldwell P.
Published: September 2005

In selecting the design parameters for a speech compression system, perhaps one of the most difficult problems involved is that of deciding what compromise to make between the projected data rate of the system and the performance to be achieved by the system (in terms of such factors as intelligibility achieved with words, syllables, and connected speech; voice quality factors; ability to recognize a familiar talker over the system; interactions of rate of talking with other performance factors, and so on). Some aspects of this problem are discussed and illustrated with data.
Analog Multiplexing of a Telephone Semi-Vocoder
Authors: Howell A. S. , Schneider G. O. K. , Stump T. M.
Published: September 2005

Narrow-band analog multiplexing means accommodating three telephone semi-vocoders, each comprising 500 cps of unvocoded baseband and 250 cps of vocoded spectrum information, within a nominal 3-kc bandwidth are discussed. Developed under Air Force contract, the plan involves analog level companding of the vocoded and time-sampled spectrum energy. Transmission of the latter information is accomplished by negative modulation in conjunction with vestigial sideband techniques. The unvocoded baseband content is transmitted by single sideband. A compatible synchronizing system constitutes an essential part of this plan. Design problems accentuated by narrow-band confinement of the multiplexed information are pointed out. It is shown that severe response requirements are imposed upon the vestigial filters. Associated sampling techniques are necessary in order to minimize inter-channel spectrum cross-talk. A TDM control system providing the necessary freedom from mutual interference between the transmitted spectrum intelligence and the receiver synchronizing information is described.
Phonetic Typewriter
Authors: Sakai T. , Doshita S.
Published: September 2005

We have constructed a research model of phonetic typewriter named Sonotype since 1960. This equipment was designed based upon our research results of these several years, aiming at both universal and flexible ability in the processing of speech sound. The basic equipment was a device for one hundred Japanese monosyllables in which about 3000 transistors and about 5000 diodes were used. For the purpose of treatment of Japanese conversational speech, some parts of control system have been added considering the data obtained from the basic equipment; however, the experimental result has not yet been obtained. This equipment has several peculiarities together with some features similar to those reported in other papers. (a) All the control pulses are derived from the input speech sound wave itself. (b) Distinctive features of speech sound are obtained by using not only the results of ordinary spectrum analysis but also various kinds of features necessary for the recognition of phonemes: for instance, voiced, unvoiced, fricative, nasal, contracted, and so on. (c) Discrimination is made by digital technique such as order pulse, AND gate, OR gate and binary circuit. Of course it is necessary to convert analog quantity to digital one and vice versa.
Performance of the Articulatory Analog of the Speech Mechanism: A Status Report
Authors: Hecker M. H. L. , House A. S. , Stevens K. N.
Published: September 2005

During the past few years an electrical dynamic analog of the vocal tract and various experiments performed with this equipment have been reported. The control system of the synthesizer specifies articulatory parameters such as the configuration of the vocal tract, glottal excitation, fundamental frequency, noise excitation, and velopharyngeal coupling as piece-wise linear functions of time. Previous reports have described the synthesis of some fricative, stop, and nasal consonants in a few vowel environments, usually in consonant-vowel syllables. The vocabulary has now been extended to include a larger number of consonants and vowels arranged in a variety of one- and two-syllable structures. Advantages and limitations of the present synthesizer and control system are discussed. The acoustic output of the device is demonstrated by means of a tape recording of samples of syllabic utterances and of short sentences constructed from groups of these utterances. (This work was supported in part by the U. S. Army Signal Corps, the Air Force Office of Scientific Research, and the Office of Naval Research; and in part by the Air Force Cambridge Research Laboratories and the National Science Foundation.)
A Comparison of Five Articulation Tests
Authors: Nickerson James F. , Miller Adam W. , Shyne N. A.
Published: September 2005

It is difficult to make direct comparisons between estimates of intelligibility afforded by experimental studies employing different articulation tests. Articulation testing is at best rather slow and tedious for the experimenter and the subject. This study sought a comparison of intelligibility estimates of five different articulation tests which have been used in a number of research laboratories. From the performance on these five tests a better comparison of intelligibility level from test to test is available. The Fairbanks Rhyme test as recorded for this study (50 words, administered at the rate of one word every 2 sec, for a total of 100 sec per test) is shown to yield a representative measure of intelligibility with half or less of the experimental time required by the other tests employed. (This work was supported by Rome Air Development Center, Rome, New York.)
Reflection of Pulses from the Ocean Bottom
Authors: Blaik Maurice
Published: September 2005

The macroscopic physical properties of the ocean bottom have received considerable attention in recent years. Two important points of view which serve as motivation for such studies are acoustical and geological in nature. Experimental records of explosion pulses were obtained before and after reflection from the relatively smooth and level Hatteras Abyssal Plain. The amplitude (pulse height) and phase (pulse shape) characteristics show significant changes as the angle of incidence is varied from about 12 to 60 deg. The pulses were electrically filtered to restrict the information band to 10–500 cps. The theory of reflection of pulses provides three simple models that can be applied to the ocean bottom problem. These are the (a) low speed homogeneous elastic bottom, (b) high speed homogeneous elastic bottom, and (c) the inhomogeneous bottom. The results of the present experiment definitely exclude cases (a) and (b) and may lead to a layered model in which the first bottom layer is characterized by sound speed less than water. (This work was supported by the Office of Naval Research.)
Application of Electrically Powered Sound Pulses to Problems of Submarine Seismology and Hydroacoustics
Authors: Hersey J. B. , Knott S. T. , Edgerton H. E.
Published: September 2005

Acoustical and seismological research from ships at sea have long made common use of high explosive charges as sound sources. Their principal advantages are intense radiation, broad spectrum, and the highly identifiable features of the waveform, the shock front, and the bubble pulses. In recent years far weaker electrical, and electromechanical impulse sources have been brought to a useful state for many problems of acoustical and seismic research. These sources share the advantages of high explosive except that they are far weaker. However, they have the distinct advantage over explosives that they can readily be repeated at a rapid rate. Very recently two electrical sources called the Sparker and the Thumper have been operated at sea with electrical inputs of 5000 watt sec and higher. With such electrical inputs subbottom reflections have been detected above noise level by a hydrophone towed from the same ship at speeds of two and a half knots in water 3000 fathoms deep. In the acoustical field experimental transmissions have been measured over very weak paths from the same sources. The early bottom reflections have provided new limits about the history of sea mounts and oceanic sediments while the new acoustical research demonstrates how these sources greatly facilitate path identification in sound and seismic P-wave transmission.
Continuous Geophysical Profiling in Shallow Water
Authors: Clay C. S. , Liang William
Published: September 2005

Experiments to study continuous subbottom reflection profiling techniques were made in Long Island Sound. The data were taken with a ship-towed source and hydrophone. The electromagnetic source was tuned to 150 cps and had a Q of about 15. The 50-ft long hydrophone was towed behind the ship on a single cable. The hydrophone consists of 28 spaced barium titanate elements inside of an oil-filled hose. The elements are tied in parallel. The source transmits a plug or coded pings. The receiver includes a shift register time delay type of matched filter. Subbottom profiles were taken to compare coded pulse-matched filter data with the simple ping system. The seismic profiles in Long Island Sound indicated a “basement” reflection to about 800-ft depth in about 50-ft water depth. In addition to the “basement” reflection, subbottom “hills” were observed. The subbottom topography changes considerably in a profile that was a few miles long.(This work was supported by the Office of Naval Research.)
Short-Period Seismic Waves along Oceanic Paths from East Pacific Shocks
Authors: Sykes Lynn
Published: September 2005

Short-period oceanic surface waves have been studied for shocks on the East Pacific Rise recorded at Huancayo, Peru, and Hallett, Antarctica. The steep part of the group velocity curves for these waves is highly sensitive to the thickness and shear velocity of the sediment. For periods greater than 10 sec, mantle structure has an important effect upon the group and phase velocity curves. Shear-coupled waves were also recorded from one of these earthquakes. Computations are given for the amplitude of free surface displacement due to SH waves incident upon a layered oceanic crust.
Spectrum Analysis of Earthquake T Phases and Large Underwater Shots
Authors: Northrop John
Published: September 2005

Spectrum analysis of T phases recorded in the Atlantic for oceanic paths up to 3500 nautical miles are compared with similar recordings of large (up to 10 tons) underwater shots. In one case the T-phase energy was propagated across the Mid-Atlantic Ridge without excessive attenuation, but islands near the source or receiver do attenuate the signal. The T phases show dispersion, in the 0–35 cps range, which is proportional to the signals' duration (up to 7 min). The mid-depth shots which do not excite such low modes show comparatively little dispersion. It is possible, therefore, to establish the following criteria for differentiating shots from T phases:

Shots T-Phases

Sharp onset in the 0–150 cps Early low-frequency forerunners

range Poor reflections

Good reflections from bottom Foreshocks and aftershocks

topography P and S arrivals ahead of T

No foreshocks or aftershocks Gradual onset and decay

No early ground arrivals

Rapid onset and decay

These data are compared with those obtained from analysis of bottomed shots in the Gulf of Maine. (This work was supported by the Office of Naval Research.)
Real Time Spectral Analysis of Seismic Body Waves and Microseisms
Authors: Bogert B. P. , Menard J. Z. , Walker R. A.
Published: September 2005

Application of apparatus to make continuous real time spectral analysis of seismic body waves has shown that the spectra of teleseisms, in the 0.3 to 2 cps range, have a complex fine structure, containing many narrow lines of width reciprocal of the length of the seismic signal. No conclusive relation between the spectral fine structure of a seismic body phase and depth, epicentral distance, or arrival azimuth has yet been found, but detailed studies are now underway. The spectra of short period microseismic noise recorded at Chester, New Jersey, and at Palisades, New York, have been examined and show the gradual shift of the maxima of the spectra as cold fronts pass out to sea off the Atlantic Coast. A number of spectral lines, almost stationary in frequency near 1 cps, appear continuously, for which no explanation has been found. These lines appear at Chester but not at Palisades and do not appear to be due to the instrumentation. (This work was supported in part by ARPA via BuShips contract.)
Explosion Measurements of Crustal Structure in Maine and the Gulf of Maine
Authors: Steinhart J. S. , Aldrich L. T. , Meyer R. P. , Howell B. F. , Fahlquist D. A. , Bonini W. E.
Published: September 2005

A series of 61 explosions were fired in the Gulf of Maine during June and July, 1961, by the U. S. Navy and the U. S. Coast Guard, forming a detailed line of shot points along an azimuth 129° true from Thomaston, Maine. These shots were recorded by a line of portable seismic stations 70 km long on the landward extension of the shot line. Shots were continued to the edge of the continental shelf. Additional recordings were made on Matinicus Rock and Texas Tower number 2. The research vessel Bear recorded some of the shots at the edge of the continental shelf. The principal advantages of this technique are that a reverse profile may be obtained from one set of shots and that the effects of large scale crustal inhomogeneities may be separated from the average picture of crustal structure. A preliminary analysis based only on first arrivals shows that the M discontinuity dips flown from the edge of the shelf at about 4° and that the crustal thickness near the coast of Maine is about 35 km.
Active Electroacoustic Networks and the Synthetic Absorber
Authors: Parvulescu Antares
Published: September 2005

H. F. Olson has initiated the use of an amplifier and projector to cancel the acoustic pressure in the vicinity of a control microphone. His method could be described as connecting the microphone with an active electroacoustic network so chosen that the microphone impedance appears zero to incoming sound waves. This approach can be extended to impose other impedance conditions at the microphone, an obvious example being the infinitely rigid case, or infinite impedance. The more interesting case is that where the system appears to have the characteristic impedance of free space. Two methods of synthesis for such a matching network will be presented, and laboratory experiments will be described. This method offers considerable promise in the construction of anechoic rooms for operation at frequencies lower than practicable with passive, viscosity absorbers. (This work was supported by the Office of Naval Research.)
Estimation of Structural Response to Reverberant Sound Fields
Authors: Lyon Richard H. , Maidanik Gideon
Published: September 2005

A method of estimating vibrational levels in skin-stringer structures is presented. The method is a development of a statistical approach described previously [R. H. Lyon, J. Acoust. Soc. Am. 33, 860 (A) (1961)]. The mechanical behavior is separated into two ranges, one below and one above the frequency of significant modal overlap. The importance of the relative magnitude of radiation and internal damping is discussed, and the estimated behavior of radiation resistance for these structures is presented. Other important quantities in the estimation scheme are internal damping, modal density, and coincidence frequencies. The manner in which these are estimated theoretically or determined empirically will be presented. Possibilities of vibration reduction by radiation resistance control are discussed. (Supported by Aeronautical Systems Division, Air Force Systems Command, USAF.)
Estimation of Structural Response to Reverberant Sound Fields; Experimental Results
Authors: Maidanik G. , Lyon R. H.
Published: September 2005

Some preliminary experiments were carried out in order to test some of the ideas expressed in the previous presentation. In particular, two mechanical systems were examined: a simply supported baffled beam and a ribbed panel. The experimental procedure consisted of (a) exciting the structure mechanically and measuring the rms velocity of the structure and the rms pressure field in the reverberant room, and (b) exciting the room to a given rms pressure and measuring the resulting rms velocity of the structure. The reverberation time of the structure was also measured. From these measurements the following quantities were determined: (a) the radiation resistance, (b) the ratio between the modal energy of the structure to that of the room, and (c) the radiation resistance plus the mechanical resistance. The relevant relationships between these quantities and their magnitudes were found to be in fair agreement with the theoretical predictions. (Supported by Aeronautical Systems Division, Air Force Systems Command, USAF.)
Novel Uses of Digital Computers in Room Acoustics
Authors: Schroeder M. R.
Published: September 2005

The advent of large, high-speed digital computers has opened up new approaches to the study of complex problems in room acoustics. Digital computers can simulate the transmission of sound in rooms using speech and music as signals. Thus, it is possible to subjectively evaluate and redesign proposed concert halls and theaters prior to construction. More basic problems such as, for example, the influence of delays and intensities of the first reflections on subjective quality can likewise be studied without restriction to the limited choice offered by existing rooms. Other interesting applications of digital computers result from the simulation of frequency and space responses of rooms. By generating and evaluating these responses on the computer according to a Monte Carlo method, many difficult analytical problems have been solved. Among the questions which have been answered by this method are the following: What is the permissible maximum gain of a public address system in a room of given reverberation time to avoid instability (howling)? By how much can the gain be raised if an electronic frequency shifter is inserted between microphone and loudspeaker? How does frequency irregularity depend on reverberation time and the ratio of direct-to-reverberant sound intensity? What is the relation between space irregularity and sound diffusion? Examples of both Monte Carlo computation and simulation of actual sound transmission in rooms will be discussed to illustrate the application of digital computers in room acoustics.
A Very Hard Reverberant Room
Authors: D'Eustachio D.
Published: September 2005

A 6000-cu ft reverberant room has been built as part of a new acoustic research facility. Interesting features are (1) a construction technique whereby uniform distribution of load on the resilient mounts was achieved without the use of temporary blocking, and (2) treatment of the walls to obtain low absorption and high damping. The finished room has a decay time of approximately 27 sec at 160 cps and it falls smoothly to 4 sec at 4000 cps. The transmission loss of the walls exceeds 60 db at 125 cps and appears to have no resonance dips. Construction details and performance data will be presented.
Further Studies on Contralateral Remote Masking
Authors: Ward W. Dixon
Published: September 2005

The elevation of threshold for low-frequency tones in one ear caused by presentation of a high-frequency band of noise to the other, called contralateral remote masking (CRM), has been shown to be due mainly to bilateral arousal of the acoustic reflex. Some aspects of the adaptation of reflex activation in time have been studied by the CRM technique. Implications of the following conclusions will be discussed: (1) In contrast to what would be predicted from the literature, a mere change in the frequency of the arousal noise is not sufficient to restore full contractile strength after adaptation has occurred. (2) A slight but consistent “residual CRM” (persistence of threshold elevation upon cessation of the inducing noise) may be due to post-tetanic potentiation. (3) The CRM produced by the (air-conducted) noise is the same whether the test tone arrives at the contralateral ear by air or by bone conduction.
Post-Stimulatory Shift of the Preyer Reflex Threshold in Rats
Authors: Herman P. N. , Clack T. D. , Harris J. D.
Published: September 2005

The Preyer reflex is a quick, transient front-to-back retraction of the pinna, occurring in certain animals in response to sudden relatively loud sounds. This reflex has been used to study the effects of several experimental variables including the presence or absence of hearing. The purpose of this study is to quantify the Preyer reflex threshold shift, after varying amounts of exposure to intense white noise. Preyer reflex thresholds based on two observations for each kilocycle from one to twenty were obtained for ten albino male rats. The animals were then subjected to exposure of white noise from 90 to 120 dbSPL in 10-db steps at durations of 10, 20, and 30 min. Post-stimulatory thresholds were obtained. Threshold decrements were obtained for each animal at intervals up to one week following exposure, or until recovery was complete, i.e., recovery to within one standard error of average pre-exposure levels. Preliminary analysis of results indicates: (1) The post-exposure threshold is positively related to intensity with duration held constant, and to duration with intensity held constant. Study of the post-exposure threshold in terms of the intensity-duration function is in progress. (2) More significant decrements occur for the higher than for the middle or low frequencies. (This work was supported by the U. S. Public Health Service.)
Temporary Depression in VIIIth Nerve Output Following 90–110 SPL in the Nonanesthetized Cat
Authors: Harris J. Donald
Published: September 2005

Attempts to predict human auditory fatigue and permanent auditory damage by recourse to the animal have often suffered from two procedures used for expedience only, namely, the use of the cochlear microphonic as an index of hearing, and the use of anesthesia with its destruction of the protective acoustic reflexes. Chronic implantation of a round window electrode in the cat and recording N1 and N2 potentials help to diminish the blurring the earlier compromise procedures create. In one and the same cat it is possible to go from short durations and low SPL's to conditions approaching those giving rise to permanent damage, with or without anesthesia at random. Onset curves of N1 − N2 depression can be drawn, and recovery curves. For example, 105 db SPL at 2 kc/sec reduces the N1 − N2 potentials in negatively accelerated fashion to about 110 original in about 20 min, with recovery complete within about 5 min. At 100 db SPL, the reduction is about 13; and so on. Intensity-time relationships will be drawn and the effects indicated of the protective reflexes at various SPL's.
Quantitative Evaluation of Inertial and Compressional Components of Bone Conduction in Cats
Authors: Tonndorf Juergen , Campbell R. A. , Bernstein L. , Reneau J. P.
Published: September 2005

The effect of occlusion of the two cochlear windows and of other structural alterations within the middle ear upon transmission of sound by bone conduction had been the subject of an earlier study [cf. J. Acoust. Soc. Am. 32, 1494 (1960)]. At that time, only changes in amplitude had been registered using the alterations of CM responses as an indicator (diff. electrodes in the basal turn). After considerable technical difficulties were overcome, a procedure was developed permitting the simultaneous measurement of amplitude and phase alterations. Measurements were taken under different conditions and their various combinations: with both cochlear windows open or closed, either one at a time or both simultaneously; with the ossicular chain intact or interrupted; and also with the cochlear aqueduct open or closed. The amplitude and phase shifts resulting from each structural alteration permitted to calculate the magnitude and phase of the component thus eliminated, i.e., to present quantitatively inertial and compressional components of bone conduction. (This research was supported by a grant from the National Institutes of Health.)
Monaural Double Click Interactions at the Round Window, Eighth Nerve, and Inferior Colliculus of Cat
Authors: Finck Alfred , Ruben Robert J.
Published: September 2005

These experiments study the interactions between successive, supra-threshold stimuli in the auditory nervous system of the anesthetized cat. Experiments have been carried out using two clicks to stimulate the ear of the anesthetized cat. The clicks were varied as to intensity and intra-click interval (delta interval). The effect of the first click upon the response to the second click was studied by measuring the electrophysiological response at the round window, eighth nerve, and inferior colliculus. The results obtained at the round window were different for the two components of the potential observed there. A smooth, monotonic recovery was found for the N1, whereas the recovery of the N2 between cats showed a depression for low-intensity click-pairs for delta intervals of 5 to 20 msec. Measurement of recovery at the inferior colliculus demonstrated three characteristics. An oscillatory component was observed. There was a difference in the relative recovery amplitudes of the evoked potentials which was related to the click intensity at short delta intervals. Finally a depression in recovery was observed which depended upon click intensity for delta intervals between 6 and 20 msec. (This work is supported by the Alfred P. Sloan Foundation and the National Institutes of Neurological Diseases and Blindness.)
Measurement of the Displacements and Non-Linearities of the Guinea Pig Tympanum
Authors: Hoeft Lothar O. , Ackerman Eugene , Anthony Adam
Published: September 2005

Direct measurements were made of the displacement of the guinea pig eardrum when acted upon by acoustic pressures (200–6000 cps). The mechanical nonlinearities of the ear were studied by introducing a static pressure (0 to ±3000 dynes/cm2) in the middle ear cavity. Below 1000 cps, the ratio of the tympanum displacement to the sound pressure was frequency independent with a value of about 4×10−7 cm3/dyne. Above 1000 cps, this ratio exhibited a series of maxima and minima. A static pressure difference across the tympanum changed the frequency at which the maximum occurred and generally decreased the displacement/pressure ratio. It was concluded: (1) For low frequencies, the lumped parameter description of the ear as a cavity was valid. (2) The tympanum acts like a flexible, conical plate under slight tension. (3) Hysteresis as well as a nonlinearity of the elastic properties was suggested.
On the Motion Induced by Vorticity in a Slightly Compressible Fluid
Authors: Powell Allan
Published: September 2005

In classical hydrodynamics, the velocity u of an incompressible fluid is expressible in terms of the vorticity ζ=curl u, the governing differential equation being ∇2u = −curlζ. The counterpart to this equation is developed for a slightly compressible fluid, it being shown how the motion of the vorticity itself is modified and how the sound field arises, the far field depending on the Lamb vector ζ ∧ u. The hydrodynamic flow field differs slightly from the corresponding uncompressible one, and a consequence of the sound radiation is a spreading out of the vorticity. (This work also supported by the Office of Naval Research).
Some Measurements on Heat-Maintained Oscillations
Authors: Maling George C. , Ingard Uno
Published: September 2005

The Rijke tube is a well-known example of a device in which oscillations are maintained by the presence of a heat source in a medium. The onset of oscillation of a Rijke tube, as well as the intensity of oscillation, have been studied as a function of the acoustic damping in the tube and the air velocity through the tube. The results of the measurements are compared with theoretical analysis. (This work was supported in part by the U. S. Army Signal Corps, the Air Force Office of Scientific Research, and the Office of Naval Research.)
Measurements of the Acoustic Properties of Sediments. II. Acoustic Attenuation
Authors: Williams J. D. , Hampton L. D.
Published: September 2005

In conjunction with the velocity measurements reported in the previous paper, measurements of the acoustic attenuation in sediments have also been made. This paper describes some of the preliminary measurements of acoustic attenuation for several artificial sediments containing a wide range of particle sizes and for sediments composed of relatively pure day minerals. Measurements are reported for the frequency range from 50 to 200 kc/sec. The attenuation was measured as a function of frequency and as a function of particle concentration. The attenuation displays a marked dependence on frequency, sediment composition and particle concentration for a given sediment. (This work is supported by the Bureau of Ships.)
A Seasonal Variation of Propagation on the Scotian Shelf
Authors: Fothergill N. O. , Macpherson J. D.
Published: September 2005

From 1957 to 1960 a series of propagation experiments were carried out on the Scotian Shelf. In the summer and fall of each year a large seasonal systematic variation of attenuation was observed. This variation was apparently caused by a change in the vertical temperature structure. A ray theory is presented which successfully predicts this variation and also gives information about the bottom reflection coefficient.