bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedance Tube for Underwater Sound Transducer Evaluation
Authors: Bobber Robert J. , Beatty Louis G.
Published: September 2005

A new method of making acoustical evaluation measurements on small underwater sound transducers at high static pressures is described. The method is applicable to small resonant transducers, or elements from a transducer array, in the mid-audio-frequency range at static pressures as high as 10 000 pounds per square inch. The transducer being evaluated radiates into an acoustical transmission line whose terminal impedance is adjustable. The transmission line consists of a water-filled tube that is several wavelengths long and a small fraction of a wavelength in diameter. The tube is terminated with a second transducer that can be made to act like any acoustical impedance, including the characteristic impedance of the tube or transmission line. The tube and terminal transducer together is called an impedance tube, and is an adjustable acoustic load on the transducer being evaluated. For a given acoustic load, the output pressure and input current, voltage, or electrical impedance can be measured as a function of frequency or static pressure. The theory of the method will be discussed, experimental results will be presented, and plans for a permanent 10 000 psig facility using 16-in. naval gun barrels will be described.
Sound Attenuating Gaps
Authors: Veneklasen Paul S.
Published: September 2005

Essential gaps or slots in architectural structures can be provided with improved sound attenuation by including a simple acoustic filter. This device relieves the requirement for careful fitting and sealing, and is especially useful in demountable structures. Simple design formulas are given with experimental verification.
Field Testing for Sound Transmission
Authors: Hardy Howard C.
Published: September 2005

Accurate sound transmission tests in the field have been made with portable equipment which will be described. A method of test of STL using recorded half octaves of broad band noise has been found to agree with the more conventional laboratory tests. Simple methods will also be given for tracing vibration-borne sound energy and measuring impact sound transmission. Emphasis has been placed on convenience and portability without sacrificing accuracy. Examples will be given from a large number of field experiences.
Interpreting Laboratory Sound Transmission Loss Data for Design Use
Authors: Bonvallet George L.
Published: September 2005

When designing a facility, the user and his architect are interested in adequate noise control at lowest cost. Not being acoustical experts, they depend on them or on component manufacturers for noise reduction information. Among these problems, it is necessary to translate STL data from recognized laboratories into terms of noise control. A number of important considerations prevent this from being a simple matter. Some involving expense in space as well as money will be discussed.
Proportion of Correct Responses as a Function of the Number of Stimulus-Response Alternatives
Authors: Clarke Frank R.
Published: September 2005

The effect of the number of stimulus-response alternatives on the human observer's probability of making a correct response was predicted by three models: a simple threshold model; the constant-ratio rule with simplifying assumptions; and the theory of signal detectability with simplifying assumptions. Four types of signal ensembles were used in these experiments: (a) speech signals; (b) a sinusoidal signal occurring in one of n intervals in time; (c) sinusoidal signals of varying amplitude; and (d) sinusoidal signals of varying frequency. In all of these experiments the listeners had complete knowledge of the set of stimuli under test and limited their responses accordingly. The simple threshold model failed to account for any of the data. The simplified version of the constant-ratio rule and the simplified version of the theory of signal detectability were both compatible with the data obtained in the speech experiments. Also, over the small range tested, both handled data obtained when a sinusoidal signal occurred in one of n intervals. No model tested was sufficiently complex to account for data when the sinusoidal signals varied only in amplitude or only in frequency. (Work under sponsorship of Operational Applications Laboratory, Air Force Cambridge Research Center, and U. S. Army, Signal Corps Engineering Laboratories, Fort Monmouth.)
Study of the Comparative Spectra of the Tones Produced by Pipe and Electronic Organs
Authors: Culver C. A.
Published: September 2005

Although it is recognized that the acoustical environment has an important bearing on the sound spectrum of any musical instrument as heard by a listener, it has seemed to be worthwhile to make a study of the tone color of certain basic organ stops of several electronic organs when compared with the corresponding voices of several conventional pipe organs. So far as possible the two types of instruments were studied under similar environmental conditions. The harmonic content of two tones in the middle register of each instrument was determined by means of the author's wave analyzer and the resulting data graphically presented. The characteristics of the various spectra are discussed.
Psychoacoustics Applied to Music Listening and Music Appreciation
Authors: Martin Francis F.
Published: September 2005

The gap between the science of acoustics and the art of music narrows as the two disciplines mutually exchange resources and ideas. An application of psychoacoustics is made to the art of music listening and music appreciation. The functional process is treated chronologically as follows: sound production, sound transmission, sound reception, sound perception. Subjective listening is the emotional and physiological response in the hearing process to the acoustic elements of musical sounds. Objective listening is the intellectual evaluation of the acoustic elements of musical sounds. Music appreciation is a result of the synthesis of subjective and objective listening.
Studies on the Endolymphatic DC Potentials of the Guinea Pig's Cochlea
Authors: Rice E. A. , Shinabarger E. W.
Published: September 2005

The effect of loud sound on the endolymphatic DC potential was studied in both normal and hypoxic animals. When the integrity of the cochlear wall was maintained, the endolymphatic DC potential decreased 5 mv with the onset of sound (1000 cps at below 140 db) and recovered immediately when the sound was terminated. At intensities of 140 db and above, the DC potential irreversibly decreased. The effect of sound on the DC potential was the same for both normal and hypoxic animals. A negative DC potential was found in the scala media of hypoxic and dead animals. This potential survived the life span of the post-mortem microphonics. The positive DC potential returned on terminating hypoxia. Oxygen deprivation resulted in the DC potential decreasing before the microphonics. The possible significance of these findings to the physiology of hearing is discussed.
Optical Calibration of Vibration Pickups at Small Amplitudes
Authors: Schmidt V. A. , Edelman S. , Jones E. , Smith E. R.
Published: September 2005

A method for measuring the amplitude of small sinusoidal vibrations, originally propounded by Bershstein and Gorelick in the USSR, is developed for use in the accurate calibration of accelerometers throughout the entire range of audio-frequencies. The apparatus employs a Fizeau interferometer with one of the reflectors mounted on a piezoelectric shaker table. A photomultiplier examines the fringe pattern, and auxiliary electronic equipment converts its output into a form from which the amplitude of the motion of the shaker table may be calculated as a fraction of the wavelength of the monochromatic light used. The detection apparatus is effective over an extremely wide range of frequencies and amplitudes. Amplitudes as small as 2 A have been detected and measurements carried out at 10 A. The accuracy of the method is checked against the fringe-disappearance method. The method described here allows calibrations to be performed at much smaller amplitudes than the fringe-disappearance method, and it is not restricted to discrete amplitudes as is the fringe-disappearance method. Potentially, it is capable of greater accuracy than the fringe-disappearance method.
Calibration of Vibration Pickups at Large Amplitudes
Authors: Jones E. , Edelman S. , Sizemore K.
Published: September 2005

The use of the axial resonances of long rods and tubes makes it possible to calibrate vibration pickups accurately over a wide range of frequency and acceleration. Levels of several hundred g at a few hundred cps up to 12 kg at 22 kcps have been attained (1 g = acceleration of gravity taken as 9.81 msec−2). The rods and tubes are driven at one end by piezoelectric ceramic shakers chosen to give good motion at the frequency of vibration. Electrically, the shakers are capacitors and are tuned by inductors to resonance at the frequency of mechanical resonance of the rod. By using great care in tuning the shaker-conductor system and in the mechanical details of supporting the shaker, in coupling the rod to the shaker, and in supporting the pickup cable it has been possible to perform calibrations whose errors are estimated to be no greater than 2%. The motion of the surface to which the pickup was attached was measured by direct viewing with a high-powered microscope using stroboscopic light and by the method of interference fringe disappearance. More than fifty disappearances were necessary at some frequencies to provide adequate overlap between the methods. A number of peculiar phenomena occurring at high acceleration levels are described.
Random Response of Two Coupled Resonators
Authors: Morrow C. T. , Troesch B. A. , Spence H. R.
Published: September 2005

The root-mean-square response of a simple mechanical resonator mounted on another, which is excited by vibration of a flat motional power spectrum, is investigated theoretically for the case of no loading effect between resonators. While the solutions are not general, the condition of zero loading is of particular interest, as it leads to extreme vulnerability of electronic and electromechanical equipment to shock and vibration when there is a coincidence of resonance frequencies of coupled resonators. Approximate formulas are obtained and computed by hand. The exact equation is solved on a digital computer to yield a series of curves for comparison. The approximate formulas hold surprisingly well, except when the resonators are close in frequency and highly damped. Curves of the derivative of the rms response, as one resonance frequency or the other is varied, are obtained by use of the digital computer. They illustrate the importance of mechanical tolerances in relation to detuning and the importance of detuning as a factor in design changes for improved reliability.
Measurement of Mechanical Impedance
Authors: Schloss Fred
Published: September 2005

Two devices for measuring mechanical impedance have been developed, one for heavy structures capable of measuring a stiffness of 140 × 106 lb/in. over the frequency range of 5 to 4000 cps, and the other for lighter structures capable of measuring a stiffness of 1 × 106 lb/in. over the frequency range of 5 to 15 000 cps. Phase angles are measured in the presence of noncorrelated vibrational and electrical noise and distortion. Each device uses two piezoelectric ceramics to sense the applied force and the acceleration response of the structure. The mass associated with the coupling between the impedance transducer and the structure is canceled electronically. Novel details of the design are discussed, such as the elimination of magnetic pickup by the piezoelectric transducers and the reduction of mechanical “crosstalk” between transducers.
Theoretical Model for a Seasonal Study of Shallow Water Ambient Sound
Authors: Kahn J. S. , Dietz F. T.
Published: September 2005

The Narragansett Marine Laboratory, sponsored by the Office of Naval Research, undertook a systematic seasonal study of shallow water ambient sound, commencing in October, 1958. With a general lack of information on average values and the variabilities associated with these average values, it was decided to base the experimental work on a theoretical model, which would elicit systematic seasonal differences, if they existed, as well as suggest procedures for further sampling of shallow water ambient sound. The model selected was a mixed-model, one-way analysis of variance experimental design, constructed to determine the existence of significant seasonal differences among months of the year, specific hours in a day, as well as to determine the contribution made to any ambient noise spectrum by variability due to weeks of the month, days of the week, and minutes within any sampling hour.
Empirical Studies in Ultrasonic Cleaning
Authors: Larson L. G.
Published: September 2005

A study of ultrasonic cleaning is presented. The parameters which affect the cleaning system are examined, and the parameters which play a critical role in ultrasonic cleaning are handled in detail. The relationship between cleaning and gas content in the medium is shown. This effect of various commercial detergents and certain basic chemicals in an ultrasonic cleaning system is also examined. The results of these experiments are compared to the existing theory of cavitation in an attempt to define the relationship between cavitation and cleaning. Instrumentation is discussed in detail. A method of quantifying cleaning is shown. An integral part of the quantification concerns the use of a cleaning index. which the author proposes. Problems in controlling variables are identified and discussed. A simple and unique method of detecting cavitation is also shown.
Ultrasonic Polymerization
Authors: Fox Robert , Yeager Ernest , Hovorka Frank
Published: September 2005

Although extensive studies of ultrasonic polymerization have been carried out in homogeneous systems (solutions), no research appears to have been reported in which ultrasonic waves are used to induce emulsion polymerization in the absence of a chemical source of free radicals. In the present work, ultrasonically produced cavitation has been used as a source of free radicals for the emulsion polymerization of styrene in water. At the same time, the ultrasonic waves have provided a convenient means for dispersing the styrene in the water phase without the need for an emulsion stabilizer. The polymerization has been carried out at 300 and 600 kc with the liquids saturated with helium and with extensive precautions to preclude atmospheric oxygen from the system. The rate of polymerization and the molecular weight of the resulting polymer have been examined as functions of the acoustical intensity, time of sonoration, temperature, and monomer-to-water ratio. Ultrasonic techniques for promoting free radical emulsion polymerization do not appear to be commercially feasible at present from an economic point of view. (This research has been supported by the Office of Naval Research.)
Progressive Wave System with Electro-Pneumatic Transducer
Authors: Hilliard John K. , Fiala Walter T.
Published: September 2005

This paper describes a Progressive Wave System, 1 in. × 1 in. in cross section, employing one electro-pneumatic transducer in the frequency range 37.5–1200 cps. The unit is capable of generating sound pressure levels in excess of 160 db over-all sound pressure level. High-frequency energy is generated by conventional compression-type dynamic transducers. The high-frequency energy is combined with the low-frequency energy in a mixing unit which consists essentially of a 45° acoustic mirror. By means of appropriate slots, the mirror is made transparent in the low-frequency range and reflective at the higher frequencies. Design data on the acoustic mirror and measurements of over-all and octave band sound pressure levels, as well as variations in sound pressure over the cross section of the tube, particularly in the transition range from the plane to the progressive wave condition, are presented. The capability of the system when four electro-pneumatic transducers are employed also is discussed.
Parametric Artificial Talking Device
Authors: Lawrence Walter
Published: September 2005

The Parametric Artificial Talking device is described. Earlier forms of this apparatus for speech synthesis were demonstrated to this Society in 1953 and 1956. The speech synthesis circuits are designed as analog computers and can be set up to simulate various mathematical models for the system function and the excitation. The parameters of these functions can be varied by changing the values of control voltages, and, when these are suitably varied, complete words and phrases can be synthesized. A new controller has been developed which allows up to 12 separate parameter control functions to be generated simultaneously. This instrument is described in a companion paper. In one mode of operation the outputs of the formant generators are combined in parallel. In this form the device has been used to synthesize speech from spectrographic analysis and to show intelligible speech can be synthesized from a phonemic input by rules. This work is described in a companion paper. In another mode of operation the formant generating circuits are connected in tandem, conforming to the pole-zero mathematical model developed by Fant. The positions of the poles and zeros can be related by acoustic theory to the shape of the vocal tract, and the excitation can be related to vocal cord movements, enabling intelligible speech to be synthesized from a knowledge of the details of articulation.
Study of Vowel Classification
Authors: Houde Robert A.
Published: September 2005

It is generally accepted that the voiced portions of speech may be idealized into time variations of the first three formant frequencies and the fundamental frequency. The influence of these parameters upon the classification of short steady-state vowel segments was determined. The mechanism by which a listener quantizes the voiced portions of speech into units subjectively equal to the steady-state vowel segments is presented. The application of this method of vowel classification to an automatic speech recognition process is discussed.
Effects of Harmonic and Intermodulation Distortion on Speech Intelligibility
Authors: Zerlin Stanley , Burnett Edwin D.
Published: September 2005

Although the effects of peak clipping on speech intelligibility have been investigated, the influence of other forms of nonlinear distortion are not as well known. In the present study, we introduced specified amounts of second-order distortion into PB word lists. A square law circuit generated the distortion products. The playback of the previously recorded PB word lists was split into two channels which fed a dual-track tape recorder. One channel contained the distortion generator. Thus, while the original clean speech was simply dubbed onto one track, the other track recorded only the second-order distortion products of that same speech. On playing back the dual-track tape, any degree of distortion could be obtained by varying the relative amplitudes of the two channels. Intelligibility score (percent of words correct) was investigated as a function of four degrees of distortion, nominally termed 0, 30, 50, and 100% distortion. Findings showed that normals and conductive losses withstood the effects of distortion far better than those with sensori-neural impairments and that the intelligibility score of the sensori-neural was a decreasing monotonic function of the degree of neural impairment.
Radiation of Sound by Earthquake Waves
Authors: Chrzanowski Peter , Cook Richard K.
Published: September 2005

Earthquake waves as they proceed over the earth's surface radiate sound waves into the atmosphere. Several instances of such sound waves have been observed at Washington, D. C. A notable instance was the great Montana earthquake of August 18, 1959 (UT). Calibrated microphones responding to very low frequencies measured the amount of the radiated sound pressure and the time delays between sound pressures at several geographic locations. From these have been deduced the vertical amplitudes of the seismic waves and their speed of transit through the Washington area. Recordings of the waves will be presented. Results of the acoustical measurements will be compared with seismological observations. With respect to one of the Chilean earthquakes, sound radiated at the epicenter was apparently propagated through the atmosphere to Washington.
Large-Amplitude Pressure Pulse Propagation in Oil Contained in a Narrow Bore Pipe
Authors: Karplus Henry B.
Published: September 2005

The velocity and attenuation of sound in an oil contained in a narrow bore thick wall pipe (6.4 mm i.d., 21.4 mm o.d.) have been measured as a function of pressure amplitude. Oscillatory pulses of 15 kc lasting 1 msec were generated with a magnetostrictor. A barium titanate cylinder was used for low level pulses up to 150 kc. Alternatively. pressure step functions were generated by means of an air-driven piston hitting a piston sliding in the oil-filled pipe. Pressure amplitudes were varied by changing the air pressure and the acceleration time of the driving piston. Pressures up to 300 bars having rise times of 20 μsec were obtained readily. Pulses were terminated by limiting the travel of the driven piston either by means of a rigid stop or by the reflection of the pulse from the end of the pipe. Rectangular pulses of 1-msec duration were attenuated 0.6 db/m in oil having a viscosity of 25 centistokes. Velocity increased with pulse amplitude rising from 1365 m/sec to 1400 m/sec for an amplitude increase from 2 to 200 bars. (This research was supported by the International Business Machines Corporation, Endicott, New York.)
Operating Characteristics and a Priori Probability of the Signal
Authors: Schulman Arthur I. , Greenberg Gordon Z.
Published: September 2005

Two fixed-interval observation experiments were conducted to determine the effect of a priori probability of signal occurrence [p(SN)] on signal detectability. The signal was a “pure tone” of 1000 cps, presented for 250 msec against a continuous background of white gaussian noise. (1) Three values of p(SN) (0.25, 0.50, and 0.75) were paired with each of three values of E/N0 (6.3, 12.6, and 20.0). (2) With E/N0 fixed at 12.6, p(SN) was assigned values of 0.10, 0.25, 0.50, 0.75, and 0.90. Listeners employed a four-point rating scale to indicate their confidence that a signal had been presented. Operating characteristics were fitted to the data on normal probability paper. An obtained operating characteristic indicates the detectability of the signal for the listener and may be specified completely by its two parameters, slope and √de. The results indicate that √de is independent of p(SN), as predicted by the Theory of Signal Detectability. The slope of the operating characteristic, on the other hand, appears to be a joint function of p(SN) and E/N0. With E/N0 = 20.0, slope increased markedly as p(SN) increased; with E/N0 = 12.6, slope was a nondecreasing function of p(SN), ranging from about 0.70 for p(SN) = 0.10 to about 1.00 for p(SN) = 0.90; and with E/N0 = 6.3, slope was independent of p(SN). (This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center.)
Pitch in Gated Random Noise
Authors: Harris Gerard G.
Published: September 2005

Gated random noise was used as a stimulus in a psychophysical experiment to determine whether a timing signal was present for certain conditions of gating frequency, gating duration, and noise spectrum. The stimulus was presented via earphones as all pass or 2400 cps high pass. The subjects controlled the gating frequency matching it to a 0.1-msec click, and the standard deviation of the match was measured. All stimuli had sensation levels near 40 db. Ungated noise was added to the gated noise to mask any switching transients. For a DF (% of time noise was gated on) of 20% and 50%, some timing signal in the noise could be matched to a click of 750 cps. All-pass clicks were easier to match than high-pass clicks. For a DF of 80%, there was no timing signal above a frequency of 200 cps. This also checked that there was little information given to the subject through the frequency controlling dial. In an auxiliary experiment subjects could fuse gated, random, binaurally incoherent, noise on some but not all of the conditions for which a pitch match was obtained.
A Note on Low-Pass Filters for Retrieving Sampled Speech Signals
Authors: McDonald Henry S.
Published: September 2005

In the case of retrieving a sampled speech signal using a nonideal low-pass filter, some loss of quality is observed due to passing energy grouped as side bands about the sampling frequency. This paper describes a series of experiments designed to relate the filter characteristic to the speech quality. By subjective matching of signals using filters with variable out-of-band transmission, it was found that the transmission in the vicinity of the sampling rate was the most important correlate to signal distortion. The transmission in the frequency region adjacent to the base band was found to be relatively unimportant. An explanation in terms of the spectral characteristic of speech signals is offered. Presampling low-pass filtering was also investigated and found to be much less important than accurate post sampling filtering.
Underwater Noise in a Semireverberant Environment
Authors: Saltus D. W.
Published: September 2005

Many investigators have studied the airborne noise radiated from machines or groups of machines operating in a semireverberant space. The similar situation for the noise levels produced in a water-filled, semireverberant space has received little consideration. Recently, broad-band measurements were made of the noise radiated by the main and auxiliary machinery of a naval vessel anchored in a floating drydock. The characteristics of the noise field produced in this test will be described and some comparisons made with the analogous airborne case.
Ambient Noise Levels in a Deep Inland Lake Under Exceptionally Calm Surface Conditions
Authors: Lomask Morton R. , Saenger R. Alfred
Published: September 2005

A preliminary attempt has been made to determine to what extent ambient noise levels in a relatively large isolated body of water are accounted for by seismic disturbances communicated to the water through the land-water boundary. Using the Naval Electronics Laboratory barge facility at Lake Pend Orielle, measurements of ambient noise pressure levels in the frequency range from 11 to 250 cps have been made under various surface conditions, in water of 750-ft depth. Of particular interest is the lowness of the levels recorded during a rare period when wind and surface waves were absent: e.g., at a depth of 147 ft, using a half-octave filter with a center frequency of 63 cps, the mean of four individual 1-min averages of the pressure level taken over an 11-min interval was 2.8×10−3 dyne/cm2/cycle band width, about a factor of ten smaller than corresponding typical levels in the ocean for low sea states. The results suggest the possibility that for remote inland water bodies under average weather conditions, contributions to the ambient noise levels from the earth together with those conceivably associated with the medium itself are relatively minor, in comparison with those contributions arising from wind-wave interaction at the surface. (This work has been supported by the Office of Naval Research.)
Acoustic Lloyd Mirror Effect in Deep Ocean Water
Authors: Steinberger R. L.
Published: September 2005

Measurement of acoustic signal transmission between source and receiver suspended from surface ships on the deep ocean is described. The four sources suspended at a chosen depth (maximum 225 ft) beneath the sending ship were keyed in sequence by 0.5-sec cw pulses. The pulses were received by a hydrophone suspended at chosen depths (maximum 400 ft) beneath the receiving ship. Sources and hydrophones are nondirectional. Signal strengths are presented graphically; one figure for each day of operation. Each figure contains four charts; one for each of the four signal frequencies used. Bathythermograph data are presented. The data are discussed in the light of the Lloyd mirror effect. Correlation with sea state is suggested.
Correlation of Some SOFAR Arrivals in the Western North Atlantic
Authors: Northrop J. , Berman A.
Published: September 2005

During a sound transmission experiment in the western North Atlantic, background noise was continuously recorded at four stations from hydrophones located on the bottom approximately in the SOFAR channel. Separations between stations were as great as 1100 miles. During the five-day period during which this monitoring was accomplished, forty strong arrivals correlated well between stations and were plotted on a great circle chart by delay time positioning. Four main types of signals were noted in addition to SOFAR shots detonated by Hudson Laboratories for navigational purposes: (1) groups of SOFAR-like pulses with small geographic scatter; (2) isolated short pulses with large geographic scatter; {3) earthquake T-phases; and (4) T-phase arrivals that do not correlate with known earthquakes. It is pointed out that the method of correlating and plotting has applications in navigation, earthquake epicenter location and in the detection of bomb explosions. (This work was sponsored by the Office of Naval Research.)
Synthesis of Sound on Film
Authors: McLaren Norman
Published: September 2005

This paper discusses techniques for the construction of hand-made sound tracks on films. A simple and direct technique is to draw or engrave patterns on the film itself. This is most effective for producing special sound effects such as percussion. A more elaborate procedure is to draw large scale patterns on cards which can be photographed down by means of an animation camera. This permits much greater control of the pitch and wave form of the sounds, and the production of musical tones. The film sound track is thus put together frame by frame to produce the aural equivalent of a mosaic. Examples of sounds and music produced in this way will be demonstrated.
Mechanistic Aspects of Hearing
Authors: Corliss Edith L. R.
Published: September 2005

Despite the ear's physical complexity, its performance may be described in terms of a set of simple analyzers. Considerable work on the analogous properties of the ear has already been presented by Fletcher and Munson, among others. Work on the analysis of transients leads to equations permitting further extension of the earlier work. Experiments requiring a subject to make quantitative estimates of magnitude indicate the sensory behavior of the ear. Experiments yielding the limits of a subject's discrimination are likely to lead to a mechanistic analog. (This work is supported by the Office of Naval Research.)
Electrostatic Transducers
Authors: Schultz T. J.
Published: September 2005

An approximate theoretical treatment extends the results of experimental work on electrostatic loudspeakers to predict that, in addition to the advantages of small size and light weight, certain features of the acoustical performance represent improvement over conventional communications transducers.
Instrumentation Precision as Affected by Vibrational Environment
Authors: White C. E.
Published: September 2005

The rapidly expanding increase in employment of indicating instruments in newly-constructed laboratories points up a problem of great importance—the deleterious effect of vibration upon the operation and precision of the instrumentation. Few, if any, manufacturers make known to the purchaser the fact that many instruments have a critical minima of vibration. Engineering skill and constructional care are wasted if the scientist or research worker establishes operation in a new area which is susceptible to transmitted vibrations considered as unimportant by the final inspection team. An analysis is presented of several commonly employed instruments whose functions are reduced or destroyed by the presence of transmitted vibration, normally considered in-consequential. Case histories of troublesome incidents are outlined; corrective measures are mentioned. A plea is made for a more detailed study of the problem with the hope that the manufacturers will establish a criteria of maximum allowable vibration wherever sensitive instrumentation is employed.
Some of the Current Research Efforts in Japan in the Field of Speech Science
Authors: Fujimura Osamu
Published: September 2005

A review will be given of activities in speech research in Japan, referring particularly to the original contributions which have recently been published in Japanese [e.g., “Symposium on speech analysis and their applications,” J. Acoust. Soc. Japan 14, No. 2 (1958)]. The fields to be covered in this paper are analysis, synthesis, and automatic recognition of speech sounds, band-compression systems, and some observations and data on speech sounds of Japanese. Some earlier work which is considered to be relatively less known abroad will be also discussed. Recorded samples of Japanese sentences which have been synthesized by the author's synthesizer with optical control pattern will be demonstrated.
Acoustical Clues to Word Boundaries
Authors: Lehiste Ilse
Published: September 2005

One of the unsolved problems in automatic speech recognition involves the determination of word boundaries. In English, a sequence of segmental phonemes may represent utterances of different meanings, depending on contrastive placement of the word boundary. For example, the phonemic sequence /kipstɪkɪŋ/ is ambiguous, since it may refer to either keep sticking or keeps ticking: the phonemic transcription is insufficient, if the word boundary is not indicated. In linguistic terminology, such a boundary is called internal open juncture. The present study is concerned with a search for possible acoustical clues to indicate the position of word boundaries in such ambiguous sequences. Results of an extensive spectrographic study are reported. involving three speakers and 139 contrastive sets of utterances, Various kinds of internal open juncture are described and illustrated.
On the Determination of Sound Power in Semi-reverberant Spaces
Authors: Wiener Francis M.
Published: September 2005

The principles and limitations of determining the radiated acoustic power of sources of sound in reverberation chambers and in anechoic rooms are reasonably well understood. By necessity, the practicing acoustician must frequently carry out sound power determinations in ordinary spaces such as factory or office areas. The limitations governing sound power measurements in such semireverberant spaces [R. J. Wells, Power App. and Systems No. 21 (1955)] are less well understood at present. To obtain a better estimate of the accuracies obtainable in practice in such spaces the results of a series of sound power determinations on two small sound sources in several semireverberant spaces are presented and compared with the results obtained outdoors. One of the sound sources is in the process of being tested at other laboratories for further cross comparison.
Anechoic Chamber of the National Research Council of Canada
Authors: Olson N. , Thiessen G. J. , Shaw E. A. G. , Embleton T. F. W.
Published: September 2005

The anechoic chamber built recently by the National Research Council (approximately 24×17×17 ft) incorporates a number of design features which reduce substantially the cost of the structure with no sacrifice in performance. An appreciable part of the saving was achieved by a simplification in the preparation and mounting of the wedges. (The cost of treatment was $3.53 per square foot.) The wedges were sprayed with three coats of lacquer to improve the binding of the Fiberglas and thus facilitate handling and avoid shedding. The only appreciable effect on the absorption coefficient for normal incidence was to lower the cutoff frequency from 85 cps to 80 cps. The wedges were wrapped in cheese cloth which was then “stitched” by means of hot paraffin. Instead of pre-mounting the wedges on a base individual holders were stamped out of sheet metal and stapled to the furring strips. The wedges could then be mounted in about 8 sec each. The inner room is of frame construction with a removable catwalk hung from the ceiling. The performance of the completed chamber was measured by the standard inverse square law method.
New Approach to Time Domain Analysis and Synthesis of Speech
Authors: Schroeder M. R.
Published: September 2005

In order to avoid some of the inherent difficulties of frequency channel vocoders, time domain methods of analyzing and synthesizing speech have been studied. Autocorrelation analysis has the desirable property of eliminating phase and lends itself to synthesis with complete control over phases. Also, it avoids the problems caused by the use of filter banks in frequency channel vocoders, Unfortunately, the sysnthesis of a time wave which has a given autocorrelation function is cumbersome: samples of the autocorrelation function have to be Fourier-transformed to obtain samples of the power spectrum. Square root devices are required to yield the amplitude spectrum. After another discrete Fourier inversion and a scanning and band-limiting operation, the desired signal is obtained. A new approach to time domain analysis/synthesis will be described. It eliminates the necessity of going through the frequency domain and, as a result, is much simpler to implement while preserving the desirable characteristics of autocorrelation analysis and time domain synthesis. Bandwidth savings are identical to those of channel vocoders (approx 10:1 before multiplexing). A tape-recorded demonstration of speech samples analyzed and synthesized according to the new method is planned.
Factorial Study of Speech Perception
Authors: Solomon L. N. , Webster J. C. , Curtis J. F.
Published: September 2005

A battery of speech and tonal tests was administered to 90 male Navy recruits between the ages of 17 and 24. This battery included verbal facility tests and intelligibility tests of (1) distorted (clipped, interrupted, and reverberant) speech; (2) noise-masked speech; (3) filtered speech; (4) speech at threshold; and (5) speech in the presence of distracting speech (limericks, stuttering). Also included were individual and group pure tone audiometer tests and the Seashore Tests of Musical Talent. Pearson Product-Moment Correlation Coefficients were computed for all possible pairs of tests in the battery. The resulting intercorrelation matrix was factor-analyzed by means of the complete centroid method and rotated to orthogonal simple structure by means of the Varimax method. The more important of the 8 factors that were extracted were: “Resistance to Distortion,” “Distraction,” “Acuity,” “Individual Audiometry,” “4000 cps Hearing Loss,” and “Verbal Facility-Seashore.” Differences between the results of this and other factor analysis studies will be discussed in terms of different populations (recruits vs college students) and analysis methods (oblique vs orthogonal factor rotations).
Comparison of the Reception of Heterogeneous and Relatively Homogeneous Messages under Repetition in Noise
Authors: Carterette Edward C. , Cole Michael
Published: September 2005

Receivers listened to sets of 60 messages, words from the Thorndike-Lorge list. The words were of different syllabic length, of several mean frequencies of occurrence (20 each at frequencies of occurrence of 64, 128, and 256 per 4.5 million words). Messages were sent at three speech-to-noise ratios. For each word presented the receiver recorded a message and, immediately following, gave a confidence rating of his accuracy of reception. Each message was repeated until confirmed or until six presentations had occurred. The main purpose of the experiments was to test a simple stochastic model relating the probabilities of correct reception, correct and incorrect categorization of confidence ratings of repeated messages in noise. The data are in excellent agreement with predictions of the total number of message events required before the entire set of N messages is confirmed, and of the total numbers of correct and incorrect identifications confirmed. An earlier finding was that the model gives a good description of the process for homogeneous messages. The description is shown here to be nearly as good for the heterogeneous messages used in these experiments. In addition, a stimulus-sampling model is tentatively proposed to account for confusions among messages. [Supported by Research Committee of University of California and Office of Naval Research Contract Nonr 233 (58).]
Multimode Ceramic Transducers
Authors: Ehrlich S. L. , Serotta N. , Kleinschmidt K.
Published: September 2005

Cylindrical transducers of poled piezoelectric ceramic, magnetostrictive, and similar materials can be excited electrically or mechanically in any one of the modes of the cylinder or a special combination of modes. Plane wave signals which can be expressed as the mathematical sum of an infinite series of cylindrical waves with their origin at the center of the cylinder and a reference axis at 0° azimuth provide multimode mechanical excitation. The multimode ceramic transducer is designed to respond to the conventional fundamental radial mode and also to the two orthogonal components of the first-order circumferential mode simultaneously. These three modal components with beam patterns described by the functions P=const, P=sinθ, and P=cosθ are sufficient to determine unambiguously the direction of propagation of the plane wave signal. These signals can be combined in a manner similar to that used for the radio direction finder. Measurements were made in the Raytheon test tank using cathode follower summing circuitry and an oscilloscope to indicate azimuth. Over the entire 360° rotation of the transducer the bearing measured on the oscilloscope was within ±7° of the mechanical orientation of the transducer.
Magnetostrictive Ferrites for Transducer Applications
Authors: Brady L. J.
Published: September 2005

Prior to the end of World War II echo-ranging equipment was largely confined to the military, and little or no ferrite transducers were employed. Now, magnetostrictive transducers find applications in military equipment as well as in echo-ranging devices for detecting fish shoals and are used for ultrasonic drilling, cleaning, degreasing, and electromechanical filters. Ferrites used in electromechanical filters are characterized by mechanical Q's of 3000–5000, electromechanical coupling coefficients under 0.25, Young's modulus of 1.4–1.7×1012 dynes/cm2, high effective permeability, and low-temperature coefficients relating change of permeability with temperature and change of resonant frequency with temperature. Ferrites for power transducer applications are notable in that they can be operated at temperatures exceeding 450°C. These ferrites have electromechanical coupling coefficients ranging from 0.15 to over 0.40 and are characterized by the following physical properties: have low porosity; show little or no fatigue effects; can handle up to 10 or 12 watts per cm2 radiating surface; cavitation erodes the radiating surface slowly; Young's modulus varies from 1.4–1.7×1012 dynes/cm2 depending on the supplier; mechanical Q varies from 40 to 6000 depending on the supplier; temperature coefficients are generally greater than the corresponding coefficients used in filters. Ferrites for power transducers can be obtained in a wide variety of shapes ranging from thin-walled cylinders to large complex shapes.
A Geometrical Acoustical Extension of the Theory of Arrays
Authors: Lubell Alan H.
Published: September 2005

The foundations of the theory of electromagnetic arrays are reviewed, and it is shown that an equivalent theory is valid for an array of acoustic sources provided that the sources are sufficiently small that diffraction of the field produced by each source by its companion sources can be neglected. The extension of array theory to an inhomogeneous medium is considered. The difficulties of a formal solution of the wave equation lead one to consideration of an approximate theory based on geometric acoustics. The validity of geometric acoustics for a constant gradient region is discussed.
Array Steering in a Layered Waveguide
Authors: Clay C. S.
Published: September 2005

The usual way to determine the direction of a radiating source using an array is to steer the array for maximum output. The steering can be done with time delays or by mechanically turning the array. The output of the array can be expressed as the sum of the time average of the products of the pressure 〈PmPn〉 observed at detectors m and n. The values of 〈Pm(τm)Pn(τn)〉 can be maximized by a proper choice of time delays τm,τn. This procedure is straightforward in an infinite homogeneous medium. If the medium is a layered waveguide, there are many more possibilities for submaxima of the 〈PmPn〉 terms. The normal-mode solution of the radiation field of a band-limited noise point source in a waveguide is used in the calculations [C. S. Clay, J. Acoust. Soc. Am. 31, 1473–1479 (1959)]. Values of 〈Pm(τm)Pn(τn)〉 are calculated for time delay steering and mechanical steering. If the array steering is done with time delays, the number of maxima are related to the number of modes propagating in the waveguide. Mechanical steering yields a maximum that corresponds to the source direction. For these calculations, the source is assumed to have a bandwidth of 1/15 of the center frequency, and the depth of the water is assumed to be about 2 λ over a thick layer of unconsolidated sediments. (This work was supported by the Office of Naval Research.)
Bilinear Gradient Approximation to Convergence Prediction
Authors: Maunsell C. D.
Published: September 2005

As is well known, sound propagation in a medium where the velocity structure is essentially a function of depth alone, showing a minimum at some depth, leads to a prediction of convergence zones of high intensity. A simple model showing this behavior consists of a layer with a linear negative velocity gradient overlaying a layer with a linear positive velocity gradient. Algebraic expressions have been derived for the various caustics producing convergence structure for arbitrary source and receiver depths in the upper layer. If source and receiver are at different depths, five convergences are predicted, two for refracted rays and three rays that are surface-reflected but refracted at depth. Minimum water depths required for the convergence also can be derived from the model. Numerical results have been calculated for several values of the parameters involved. These indicate a considerable spreading in range of the convergence structure for source and receiver depths near the velocity minimum.
Acoustical Design for the Santa Fe Festival of the Opera
Authors: Purcell Jack B. C.
Published: September 2005

The presentation of opera out-of-doors poses unique acoustical problems. Aside from expected considerations of stage enclosure, orchestra pit, and seating arrangement, unexpected difficulties were encountered in the form of echoes from mountains ringing the site. This paper describes the techniques employed in locating the image sources and minimizing their effect. The design of the performing and auditing areas to permit adequate performance of opera in an open space also is discussed.