bluuebunny/crossref_metadata_2025 huggingface dataset:
Sonic Failure
Authors: Dyer Ira
Published: September 2005

Failures of substructures or equipments exposed to intense sound fields are inherently influenced by two general factors. First, failure depends upon the temporal properties of the sound field (as well as on its root-mean-square value). Second, failure is influenced by the spatial properties of the sound field and hence also by the properties of the main structure to which the substructures or equipments are attached. The temporal properties of sound fields pertinent to failure present special problems in the design of environmental tests. More formidable problems are presented, however, by the need to simulate the spatial properties of the sound field. The importance of these factors in the design of environmental sound tests, and in the interpretation of test and field results, will be discussed. [Supported by U. S. Air Force Contract No. AF 33(616)-5274.]
Structural Acoustic Proof Testing
Authors: Schjelderup H. C.
Published: September 2005

A series of acoustic proof tests conducted on aircraft structure and structural components is reviewed. The problem of simulating noise environments between an aircraft and an engine test cell is presented. Cell resonance and shift in spectrum frequency distribution are some of the problems mentioned. A method for determining test levels for accelerated testing is shown.
The Interaural Time Disparity Threshold as a Function of Interaural Correlation
Authors: Zerlin Stanley
Published: September 2005

A study of how the binaural system handles wave forms which are dissimilar at the two ears should yield information about the invariants of this system. We systematically varied the interaural correlation of a noncontextual wave form and noted the resulting changes in the interaural time disparity threshold. To get differing degrees of correlation we used an adaptation of Licklider's technique: narrow band noise common to both ears was mixed with similar noise of the same band width having independent wave forms at each ear. Varying the noise to noise ratio (common noise to independent noise) afforded a range of correlation values. The interaural time disparity threshold was used as our measure of binaural interaction because it reflects small changes of the stimulus, e.g., in frequency and duration. Indications are that the time disparity threshold is a positively accelerated function of the interaural correlation, where correlation is construed as the amount of variance common to both ears relative to the total variance. Some other interpretations of these data will be discussed.
Evaluation of a Modulated Air-Flow Loudspeaker
Authors: Webster J. C. , Klumpp R. G. , Witchey A. L.
Published: September 2005

As part of an over-all evaluation of the USNEL Flight Deck Communication System, an RCA Modulated Air-Flow Loudspeaker (air horn designed primarily as a high noise level reliability testing facility) was tried out as a speech and alarm signaling transducer on the flight deck of an aircraft carrier. Over-all levels of wide-band (200–6000 cps) noise reached 130 db at optimum points on the deck, as compared to 110 db for the present system. Speech intelligibility and alarm detection tests showed the air horn to be useable with jet aircraft at idle (30%) power while the present loudspeakers could not be heard. Neither loudspeaker system was adequate with jets at full power.
Ray Analysis of Low-Frequency Sound Propagation in Shallow Water
Authors: McLeroy E. G.
Published: September 2005

The problem of propagation of low-frequency sound in a system consisting of shallow water overlying several thin layers above a basement is approached through a ray theory in which the first two bottom layers are lumped together with the water layer. This effective structure is assumed on the basis of expected good transmission through a thin layer (less than one wavelength thick) of impedance not very different from those of its bounding media. The required reflection coefficient at the lower boundary of the lumped layer, expressed as a function of range and the order of the image source of a ray, is taken in the form given by Abeles for reflection of plane electromagnetic waves from a layered system. The theory yields calculated transmission curves whose rates of fall-off and fine structure agree reasonably well with experimental results.
Pressure Phone for Hydrophone Calibrations
Authors: Sims Claude C. , Bobber Robert J.
Published: September 2005

A small, closed system for an absolute calibration of a standard hydrophone is described. The method allows control of the static pressure and temperature and is applicable in the frequency range up to 5 kc. The system is designed so that the blocked or Thevenin pressure of the sound source is the same as the sound pressure acting on the hydrophone. The use of a hydrophone, calibrated with a pressure phone, as a standard in large closed-chamber systems is discussed.
A Voice Analog
Authors: Dersch W. C.
Published: September 2005

An artificial voice was constructed using novel and simple techniques. An outgrowth of an experiment in speech recognition, this voice analog was used to ascertain the efficiency of the information extraction techniques used in a speech recognition machine. The extracted information curves were reconstructed to full speech by means of this voice analog. Four voice-characterized noise generators were connected to four voltage-controlled bandpass filters. Each noise generator and filter pair operated within an assigned major subband. Four slowly varying frequency-describing information curves were connected, one to each of the filters. Each filter then passed a narrow minor subband of frequencies determined by the voltage of the frequency-describing curve at the same instant. Three additional power-describing information curves modulated the four filter outputs. The resulting curves were mixed, amplified, and connected to a loudspeaker. The voice analog speech was harsh and estimates of its intelligibility varied greatly. Plosive consonants were good and consonants in general were better than vowels. The complete system occupied only a few square feet of bench space. Although the voice analog was primarily an experiment which provided the desired data and was not fully refined at the time of its construction, its compactness and simplicity suggest the desirability of further development.
Pitch Synchronous Spectral Analysis of Vowel Sounds
Authors: Miller Joan E. , Mathews M. V. , David E. E.
Published: September 2005

Fourier analysis of individual periods of sustained vowel sounds has been carried out on a digital computer. The spectral data show two characteristics (1) a periodic oscillation in amplitude and (2) many rapid phase shifts, which cannot be explained by simple vocal tract resonances. A theory is developed to show that these spectral characteristics can be attributed to zeros of the glottal excitation function and that typically there is a large number of these zeros. Such a representation of the excitation is consistant with the glottal wave-form information from high-speed photography. A computer program has been developed to fit a spectrum with a pole-zero configuration and good agreement has been obtained between the observed spectrum and that computed from a pattern of glottal zeros and formant poles.
Tuning Preferences for Piano Unison Groups
Authors: Kirk Roger E.
Published: September 2005

Unison strings of a concert grand piano were tuned to five “unison” conditions. The conditions were “zero-beat” tuning and the upper string of three string unison groups tuned sharp and the lower string tuned flat by 12, 1, 2, and 3 cents relative to the center string. Magnetic tape recordings were made of the piano tuned under these conditions. These recordings in the form of a paired comparison preference test were presented to musically trained and untrained subjects. The most preferred tuning conditions for three string unison groups are 1 and 2 cents maximum deviation among strings. Musically trained subjects prefer less deviation in tuning among unison strings than do untrained subjects. Close agreement was found between the subject's tuning preferences and the way artist tuners actually tune piano unison strings. The results of this investigation are interpreted as supporting a “set” or learning hypothesis concerning the origin of preferences for piano unison tuning.
Electronic Music Synthesis
Authors: Olson H. F. , Belar H. , Timmens J.
Published: September 2005

The modern systems of communication have been applied to the electronic synthesis of music in the form of the electronic music synthesizer. The electronic music synthesizer is a machine which provides means for producing a tone with any frequency, intensity, growth, duration, decay, portamento, timbre, vibrato, and deviations. If these properties of a tone are specified, the tone can be produced by the synthesizer from a coded record. For implementing the electronic synthesis of music an improved and enlarged electronic music synthesizer Mark II has been developed and built. The new electronic music synthesizer and the use of the new synthesizer by professional musicians will be described.
Noise Due to Unsteady Flow
Authors: Harrison Mark
Published: September 2005

The area of knowledge under consideration is a composite of fluid dynamics and acoustics. In order to elucidate how noise is produced by unsteady flow, it is first necessary to discuss the various types of noise producing flows from the point of view of the hydrodynamicist. This will be done in a qualitative fashion that emphasizes the basic physical mechanism. It will then be possible to explain in terms of our usual acoustical concepts how certain types of flows generate noise. Some data, new and old, will be presented to illustrate this picture.
Scattering of Acoustic Energy by Solid and Air-Filled Cylinders in Water
Authors: Barnard G. R. , McKinney C. M.
Published: September 2005

This paper presents the results of an experimental investigation of the scattering of acoustic energy from finite circular cylinders in water. Solid and hollow brass cylinders were used as targets. Distribution-in-angle diagrams of acoustic energy scattered in the plane perpendicular to the longitudinal axis of the cylinders are shown for changes in finite cylinder length, changes in pulse length, and changes in frequency. Pulse photographs are presented to describe the echo structure of solid and hollow cylinders. Photographs are shown of the pulses scattered in the backward direction in the plane normal to the longitudinal axis of the cylinder and in the plane containing the longitudinal axis of the cylinder. The change in echo structure is presented as a function of pulse length and frequency. The echo structure exhibits characteristics dependent upon the sharp corners of the cylinder where there is a large change in slope and a discontinuity between brass and water. The photographs of pulses returned from the cylinders in the plane normal to the longitudinal axis describe the existence of surface waves which travel around the circumferences of the cylinders. (This work was partially supported by the Bureau of Ships.)
Flow-Noise Measurements with Buoyant Units
Authors: Haddle G. P. , Skudrzyk E. J.
Published: September 2005

Two buoyant units were equipped with six hydrophones and a seven-channel tape recorder. These units were sunk to a depth of 500 ft and released. The flow-noise spectrum was recorded in the frequency range 60 cps to 500 kc as a function of the position of the hydrophones and the roughness of the surface.
Vocoder Output and Whispered Speech in a Tone Language: Thai
Authors: Abramson Arthur S.
Published: September 2005

Phoneticians have tried in various ways to investigate the maintenance of tonal distinctions in whispering, where there is no variation of a fundamental frequency. In the present experiment it was found with whispered speech that native speakers of Thai, a language with five phonemic tones, could identify words minimally distinguished by tone, though with somewhat less accuracy than in normal speech. To determine whether such concomitant features as helped the subjects to make systematic distinctions in the whispered speech were also present in normal speech, the spoken words were passed through the Vocoder with the fundamental frequency of the buzz kept constant. No discriminations were made! With hiss alone, however, the results were better than in the natural whisper. We conclude that the features were present in the normal speech but that in the presence of the buzz, listeners were set to hear pitch variations. Inspection of spectrograms suggests that tonal oppositions in Thai whispering lean on such concomitant features as changes in intensity, relative durations of vowels, and small variations in formant frequencies.
Some Acoustic Correlates of Velarization in Lebanese Arabic
Authors: Obrecht Dean H.
Published: September 2005

A study is in progress to determine some acoustic correlates of the velarization associated with a group of consonants in modern Arabic. The problem is of interest in perception studies since it presents an opposition of a type unknown in the Indo-European languages, a set of consonants having a coarticulation of velarization in contrast with a set of nonvelarized “equivalent” consonants. Observation of spectrograms revealed rather sharp lowering of the second formant in the vicinity of the velarized phones. Synthetic speech was used to establish perceptual boundaries and optimum values for discrimination. Results to date show the second-formant transitions to be adequate cues for discrimination of velarized vs nonvelarized consonants by native speakers of Arabic. The data corroborate generalizations previously drawn concerning the role of second-formant transitions in English, while providing information on one more phonetic dimension. [This research was supported in party by the Carnegie Corporation of New York and in part by Lafayette College.]
Synthesis of Final /z/ without Voicing
Authors: Sholes George N.
Published: September 2005

American English often shows a tendency toward devoicing of “voiced” consonants, particularly in final position, without however losing the “voiced-voiceless” distinction. What simple pattern variables on a speech synthesizer, it was asked, would elicit consistent listener recognition of a “voiced” consonant without recourse to voicing? In an experimental study of this question a small group of listeners identified as “peas,” “peace,” “peed,” “peat,” or “pea,” a set of synthetic speech patterns in which the following features were varied: (1) the duration of a high-frequency final segment representing alveolar friction; (2) the duration of the total pattern (achieved by modifying the length of the steady-state formants representing the vowel); (3) point of buzz to hiss changeover; and (4) the presence or absence of an intensity drop at the end of the vowel formants. All the variables did in fact influence listener identification of the patterns in varying degrees and combinations. In particular, a number of patterns were consistently identified as “peas,” i.e., the word ending with “voiceless” /z/. There were noticeable differences among individual listeners in their sensitivity to the variables and in the ranges of maximum effectiveness. [This research was supported by the Department of Defense in connection with Contract DA 18-119-sc-260.]
Silent Interval as a Cue for the Distinction between Stops and Semivowels in Medial Position
Authors: Bastian Jarvis , Delattre Pierre , Liberman A. M.
Published: September 2005

Previous research with synthetic speech indicated that, in absolute initial position, the manner distinction between stop consonant and semivowel is cued by the starting frequencies and durations of the first- and second-formant transitions. In the present study it was found that an important cue for the same distinction in medial position is the presence or absence of a relatively brief interval of silence immediately preceding the onset of the transitions. This acoustic feature presumably signals the occurrence or nonoccurrence of articulatory closure. Its relative importance as a cue depends on the phonetic context; in some contexts the silent interval makes little if any contribution, while in others it effectively overrides all other cues combined. Preliminary findings on the discriminability of these silent intervals will also be presented. [This research was supported in part by the Prosthetic and Sensory Aids Service of the Veterans Administration under Contract V1005M-1253 and in part by the Department of Defense under Contract DA 18-119-sc-260.]
Some Characteristics of Stop Consonants
Authors: Fujimura Osamu
Published: September 2005

Stop-vowel syllables were synthesized by use of both the cascaded resonant circuit (POVO) and the dynamical vocal tract analog (DAVO). Variation of formant positions or of articulatory configurations, intensity envelope, and inflection of fundamental frequency were controlled. A noise source was used as excitation for unvoiced stop consonants. Unvoiced stops generated by DAVO are much superior to those generated by POVO when a noise source is inserted at the constriction point of the vocal tract. In comparing utterances produced by POVO with those produced by DAVO some interesting differences have been found. These will be discussed and an explanation will be offered. Methods involving both absolute judgments and paired comparisons have been used. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research); in part by Air Force Cambridge Research Center Contract AF 19(604)-2061; and in part by the National Science Foundation.]
Diphthongs, Glides, and Transitions
Authors: Peterson G. E. , Lehiste Ilse
Published: September 2005

The study deals with the formant movements associated with diphthongs, glides, and consonant transitions in spoken American English. The transitional characteristics associated with all initial and final consonant phonemes have been studied in a large sample of utterances. The rate of change of the transition from a consonant hub to the steady state vowel formant position and conversely has been investigated for vowels which are commonly considered monophthongs. It is assumed that such changes are cues for the perception of the consonants rather than linguistically significant components of the vocalic nucleus. The rate of change associated with syllable nuclei commonly perceived as diphthongs ([ɑɪ, ɔɪ, ɑᴜ]) is investigated and compared with the changes due to consonant transitions in monophthongs. An attenpt is made to establish criteria by which the formant movements due to transitions may be distinguished from movements that have linguistic signaling value within the syllable nucleus.
Intrinsic Duration of Syllable Nuclei in English
Authors: Lehiste Ilse , Peterson G. E.
Published: September 2005

The study deals with the influence of preceding and following consonants on the duration of vowels and diphthongs of American English that may occur in stressed position within a sentence. A set of 1263 CNC words, pronounced in an identical frame by the same speaker, has been analyzed spectrographically, and the influence of various classes of consonants on the duration of the preceding nucleus has been determined. The residual durational differences are analyzed as intrinsic durational characteristics, associated with each syllable nucleus. The theory is tested with a set of 30 minimal pairs of CNC words, uttered by five different speakers.
Effect of Learning on Perception: Discrimination of Relative Onset Time of the Formants in Certain Speech and Non-Speech Patterns
Authors: Harris Katherine S. , Liberman A. M. , Kinney Jo Ann , Lane Harlan
Published: September 2005

An experiment was made to determine if the discriminability of an acoustic difference between speech sounds depends on whether or not that difference cues a phonemic distinction. For comparison, discrimination data were also obtained for control stimuli in which analogous differences occurred in sounds that are not perceived as speech. The speech sounds, which were synthetic approximations to /do/ and /to/, differed only in the relative time of onset of the first and second formants. Discrimination of these sounds was found to be considerably better across the phoneme boundary than in the middle of the phoneme category. Indeed, this effect was so marked as to justify the assumption that the perception of these stimuli is essentially categorical. The control stimuli were produced by inverting the speech patterns on the frequency scale. There was, for these stimuli, no increase in discriminability in the region corresponding to the location of the phoneme boundary and, in general, their discriminability was poorer than that of the speech. To the extent that the inverted stimuli are an appropriate control, one may conclude that the effects obtained with the speech stimuli are a result of learning, and more specifically, that they represent a considerable amount of acquired distinctiveness. [This research was carried out in connection with Contract AF 19(604)-2285, monitored by Operational Applications Laboratory, AFCRC, Bedford, Massachusetts.]
Repetition and Confirmation of Messages Received by Ear and by Eye
Authors: Carterette Edward C. , Cole Michael
Published: September 2005

The rating method was used to obtain operating characteristics for sixty heterogeneous words. A single message was heard in noise, or seen briefly in a tachistoscope. It was repeated until it had been assigned to the highest accuracy category (“confirmed”) or sent a maximum of six trials. The comparisons showed that it matters little whether reception is by eye or by ear. Whether within a trial or over successive repetitions, accuracy of reception is a direct function of the confidence rating and is relatively independent of the intelligibility level. Neither do the accuracy of reception or the distributions of rating categories change markedly over trials. Although no direct test was made, it appears that accuracy of reception is not lessened by the task of rating. Both visual and auditory data are fitted reasonably well by predictions made from a simple stochastic model based on the assumptions that (1) intelligibility, (2) probability of a correct acceptance, and (3) probability of an incorrect acceptance remain constant over successive repetitions. The model fits the visual better than the auditory data, as might be expected, since conditions of reception are more homogeneous over trials for vision than for audition. [This research was supported by the Group Psychology Branch, Office of Naval Research under Contract No. Nonr 233 (58).]
Stability of Bruel and Kjaer Type 4131 Condenser Microphones
Authors: Embleton T. F. W. , Dagg I. R.
Published: September 2005

The absolute sensitivities of three type 4131 condenser microphones have been measured over a period of six months using a slightly modified form of the reciprocity technique. This method has been described in detail previously. The absolute accuracy of the method is ±0.08 db and changes in sensitivity can be measured to ±0.03 db. The cartridges have less rigid cases than other types tested previously and pressure on the casing can change the sensitivity by several decibels—this change is reversible. This effect is not present in normal use and has been eliminated during calibration by the use of an adaptor ring to transfer the forces to another part of the cartridge well removed from the diaphragm. The individual sensitivities show less random scatter than other types, the maximum deviation from the average being 0.05 db. All three microphones showed drift, being about 0.1 db in the first three months. The temperature coefficients between 10 and 25°C are −0.017 db/°C for two of the microphones and −0.01 db/°C for the third. The air cavity behind the diaphragm contributes 20% of the total stiffness acting on it.
Measuring the Free Field Correction for a New Condenser Microphone
Authors: Bruel Per V. , Rasmussen Gunnar , Morris Alan , Mowry Jack
Published: September 2005

In the development of the new Bruel & Kjaer Measurement Condenser Microphone, it was found necessary to thoroughly investigate the diffraction characteristics and to use several calibration techniques to establish the difference between the microphone's free field and pressure response. The techniques and results of these investigations are described as the following: (A) Measuring the pressure distribution around a model of the microphone placed in a free sound field and the sensitivity distribution over the microphone diaphram. In conjunction with measurements made with a specially designed concentric electrostatic actuator, the effective sound pressure increase on the diaphram is calculated. (B) Measuring the microphone sensitivity as a function of frequency according to the free-field reciprocity method, and comparing the results with the pressure response of the same microphones measured by means of the electrostatic actuator method. The free-field correction obtained by the two different methods (A) and (B) showed excellent agreement.
High Efficiency Transducer for Transmission to Air
Authors: Kritz Jack
Published: September 2005

The basic problems of transduction to low acoustic impedance media are considered. The advantages offered by flexure mode vibration of driving elements are shown. Selection of a driving element consisting of a free disk supported at the nodal circle is made. Fabrication in quartz and ceramic is described. Test results on transducers in the range 5 to 200 kc is given with transducer efficiencies of better than 90% obtained. Transducer mounting in parabolic reflectors and the resultant beam patterns are shown.
Instrumentation for Measurement of Sonic Boom
Authors: Taniguchi Harry H.
Published: September 2005

Instruments used to measure soniC boom disturbances produced by supersonic aircraft must have certain characteristics in order to reproduce accurately the pressure-time distribution of the pulse. Selection of a particular transducer system for these measurements was determined from theoretical analysis of the ideal N-shape wave which is characteristic of this disturbance. Measurements of sonic boom signals from a military aircraft are presented with comparative displays of the pulse recorded on both an oscilloscope and an oscillograph.
Digital Array Phasing
Authors: Anderson Victor C.
Published: September 2005

The extension of digital techniques to the problem of processing the output of an array of point receiving elements in an acoustic field has given rise to a method of phasing called DIMUS (Digital Multi-beam Steering). This digital technique incorporates the use of shift registers as delay line elements which results in a number of operational advantages. A description of the DIMUS technique is given. The effects of amplitude and time quantization imposed by the digital circuits are considered in the light of the relative signal processing gain of the array referred to an exact analog phasing network. The processing gain is computed as a function of sampling frequency for a number of types of signals. [This work represents one of the results of research carried out under Contract Nonr 2216 (10) with the Office of Naval Research.]
Optimum Fine Resolution Spectrum Analyzer
Authors: Vogel Reinhold , Bernstein Robert I.
Published: September 2005

A new technique is described for fine resolution spectral analysis possessing unique advantages in acoustic and vibration problems. The frequency resolution, data rate, and signal-to-noise ratio enhancement obtained are equal to the theoretically attainable optimum values permittted by linear signal processing. As an example of the technique, the performance of the Simoramic (trademark) (simultaneous panoramic) analyzer is described. This instrument performs Fourier analyses across a spectral band 500 cps wide with a frequency resolution of 1 cps at the rate of one complete analysis per second. This makes it possible to obtain a continuous series of “snapshots” of the spectra of temporally stationary or nonstationary signals. The output is presented as a deflection modulated oscilloscope display showing the amplitude of all Fourier components on a precisely calibrated frequency axis. The 500-cps coverage band can be positioned at any portion of the frequency spectrum, including the region starting at zero frequency (dc). The output noise bandwidth, for noise accompanying the input signal, is 1 cps, yielding a 27-db enhancement in signal-to-noise ratio throughout the entire 500-cps coverage band. The technique is based on the use of a delay line in a recirculation loop whose gain and phase are closely controlled. The phase of signals in the loop is adjusted continuously at a rate coherently related to the total loop delay. This causes re enforcement of signals in successive circulations in a manner that leads to a final output in which Fourier components are presented as pulses on a time base bearing a linear frequency calibration. After 1 sec of coherent integration within the recirculation loop, the frequency resolution is 1 cps. As soon as the display is presented the delay line loop is opened briefly, discharging its contents. Then a fresh processing cycle commences immediately.
Ultrasonic Doppler for Distance Measurement
Authors: Wachspress Melvin H.
Published: September 2005

An acoustic Doppler system can be used to provide true velocity information for distance traveled measurement. An ultrasonic system can be small, light in weight, and accurate. The Doppler equation is developed for a moving source in a moving medium. The results are applied to a Janus system and the error terms are separated. For an acoustic system propagation velocity variations must be considered, in addition to wind. A temperature compensated Janus arrangement will reduce errors in the acoustic system. The output of the velocity sensor is equivalent to noise passed through a narrow bandpass filter. Photographs of spectra obtained over various road surfaces are presented. The center frequency of the noise spectrum is proportional to the velocity of the sound source and provides input to a frequency tracker. Narrow band widths obtained with the acoustic system result in the synthesis of a sinusoidal current at the receiver output terminals such that a clear Doppler tone is audible if a loudspeaker is connected. Requirements on the frequency tracker are reduced in severity due to the narrow band width. A light weight sonic Doppler system is described which is comparable in size and weight to a modern autoradio. An experimental Janus system is discussed. Spectrum photographs for various road surfaces are presented.
Propagation of Low Frequency cw Signals in the Deep Ocean
Authors: Guthrie A. N. , Tolstoy I. , Shaffer J.
Published: September 2005

The acoustic field of a 10 cps cw source, towed at slow speeds at a depth of 24 m was measured by a stationary hydrophone out to ranges of about 75 km. The depth of the hydrophone was approximately 450 m. The records obtained are compared with theoretical calculations of the wave field, using a method developed by one of the authors. The degree of agreement is fair enough for one to feel that further work along these lines should leak to a quantitative understanding of long-range sound propagation in the ocean. (This work was supported by the Office of Naval Research.)
Some Effects of Velocity Structure on Low-Frequency Propagation in Shallow Water
Authors: Williams A. O.
Published: September 2005

Given conditions of “downward refraction,” low-frequency acoustic propagation in shallow water displays greater attenuation than it does in isovelocity water. Ray theory suggests this but is untrustworthy here. Since the main acoustic losses occur at the bottom, this attenuation should rise as does the intensity of the sound just at the bottom. When the bottom material acts practically like a fluid (Pekeris case), the increase of intensity is readily calculated by perturbation theory from the normal-mode solution for isovelocity water, provided at least a few modes are allowed. This increase depends on the fractional change in sound velocity, the detailed change with depth, and the square of H/λ (water depth/acoustic wavelength). Specific calculations for a linear velocity gradient and a bottom-limited sound channel show that the effect on attenuation can vary from negligible to large. Pertinent data are scanty and rough, but show the proper trend. The method is also applicable to “upward refraction,” which should lower the attenuation. A competing mechanism is the attenuative effect of a rough sea surface, which (relative to the isovelocity case) will play a larger or smaller role with upward or downward refraction, respectively.
Long-Range Sound Propagation in Shallow Water
Authors: Mackenzie K. V.
Published: September 2005

A theory is developed for sound propagation to ranges of 100 mi for water depths of more than several wavelengths. The directivity of the surface doublet is utilized to obtain the energy initially incident on the bottom. Random phase is assumed for the rays that are reflected many times from the imperfect bottom while traveling to the great ranges. The frequency is assumed to be high enough that reflections from subbottoms may be neglected. Rayleigh equations modified to allow for the attenuation in the bottom are used to compute the bottom reflection losses. Solutions are presented for the isovelocity case and for some typical arbitrary velocity profiles. The resulting long-range propagation losses are critically dependent on the attenuation in the bottom. For zero bottom attenuation, the reflection is perfect for grazing angles less than the critical angle and cylindrical spreading results. For real bottoms, which always have attenuation, the bottom reflection losses for small grazing angles control the propagation losses and the spreading behaves more like spherical spreading. Data taken in 1948 with omnidirectional sources and receivers are presented which show agreement between theory and experiment in 25-fathom water over ranges from 1 to 40 mi.
Long-Range Sound Reverberation in Shallow Water
Authors: Mackenzie K. V.
Published: September 2005

A theory is developed for computing the reverberation returning from great ranges for water depths of more than several wavelengths. The theory developed to compute long-range sound propagation is utilized. Two kinds of reverberation mechanisms are assumed. First, that the sound is scattered uniformly in all directions from the insonified reverberation surface; and, second, that the reverberation obeys Lambert's cosine law. The outgoing propagation depends on the doublet composed of the sound source and its surface image. The propagation of the returning reverberation depends upon the type of reverberation mechanism assumed. Solutions are presented for the isovelocity case and for some typical arbitrary velocity profiles. Computations indicate that the ratio of echo-to-reverberation, which is independent of the transmission losses, depends only a small amount on the velocity profile used.
Temporary and Persistent Threshold Shifts for the Cat
Authors: Miller J. D. , Watson C. S. , Anderson C. D. , Covell W. P.
Published: September 2005

The auditory sensitivity of the cat was measured by the method of behavioral audiometry before and at intervals after exposure to a broad band (about 200–4000 cps) of thermal noise. Temporary threshold shifts (TTS's) are reported for an exposure with duration of 15 min and an over-all level of 105 db. Although the cats show more loss than expected for man, TTS audiograms have the same general features as those for man. Persistent threshold shifts (PTS's) up to 55 db are induced in the cat by exposure to the noise at an over-all level of 115 db and durations of of 14, 12, and 2 hr. Over this range, PTS can be described as an increasing function of the logarithm of the noise duration. In these experiments, PTS and TTS audiograms have different shapes. PTS's appear at lower frequencies than TTS's. Histological findings that show the extent and severity of cochlear injuries after exposure at the 115-db level are described. There were slight to moderate injuries in the organ of Corti for the 15-min exposure, moderate for the 30-min exposure, and moderate to severe for the 2-hr exposure. [This research was supported by the U. S. Air Force under Contracts Nos. AF 33(616)-3844 and AF 33 (616)-3637, monitored by Aero Medical Laboratory, Directorate of Research, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio.]
Electrophysiologic Responses to Acoustic Transients. I. Cochlear Microphonics
Authors: Teas Don C. , Diamond Sidney P. , Davis Hallowell
Published: September 2005

Cochlear-microphonic responses to acoustic transients (clicks) were recorded with differential-electrode pairs placed at various positions along the cochlear partition of the guinea-pig ear. The acoustic stimuli were delivered through a PDR-8 earphone across which quasi-integrated square waves with variable rise times were impressed. The pattern of microphonic activity produced by several of these clicks was observed over a range of stimulus intensities. The spatial distribution and time course of these electrophysiologic responses will be described and some inferred properties of the cochlea will be discussed.
Electrophysiologic Responses to Acoustic Transients. II. Auditory-Nerve Action Potentials
Authors: Diamond Sidney P. , Teas Don C. , Davis Hallowell
Published: September 2005

Auditory-nerve action potentials evoked by acoustic transients were recorded and correlated with the space-time patterns of the associated cochlear microphonics. Of particular interest was the appearance, in some of these neural responses, of as many as six well-defined groups of action potentials after a single effective acoustic wave. The amplitude of successive peaks decreased with a time constant that appeared to be related to the slope of the final positive-going portion of the microphonic wave form. Attention will be given to the relation between neural latency and certain stimulus parameters in an attempt to clarify and extend the notion of time-intensity trading in the auditory system.
Cerebellar Acoustic Pathways in Unanesthetized Cats
Authors: Misrahy G. A. , Spradley J. F. , Beran A. V. , Garwood V. P.
Published: September 2005

Clicks evoke a complex, often “M” shaped, positive wave followed by a negative wave in the anterior lobe of the cerebellum. The first upward component of the “M” wave precedes the response from the auditory cortex by 3 to 6 msec. The latter, in turn, precedes the second upward component by 1.6 to 2.6 msec. This second component of the cerebellar response is suppressed by light anesthesia, and by either cooling or by destroying the temporal cortex. The first component of the cerebellar response is not affected by these procedures. These results strongly support Snider's hypothesis of a dual sensory projection system to the cerebellum. Electrical stimulation of the anterior lobe of the cerebellum will diminish the myoclonic response to clicks or tone-pips in Chloralosed cats. Electrodes placed at the round window, on the pyramids (above the decussation) and the medulla show that stimulation of the vermis has no effect on auditory nerve action potentials or evoked responses of the pyramidal system, but greatly depresses activity in the extrapyramidal system.
Shearing Motion within Scala Media of Cochlear Models
Authors: Tonndorf Juergen
Published: September 2005

In 1953, Bekesy reported the observation of shearing motion within the cochlear duct, specifically as occurring between the organ of Corti and the tectorial membrane. The direction of this alternating shear motion for any given frequency depended upon the location re the place of maximal transversal displacement of the cochlear duct as a whole. Proximally to the maximum the shear was radially, and distally it was longitudinally directed. This phenomenon was studied with the aid of cochlear models. Not only were Bekesy's original observations confirmed, but the model experiments lend themselves to a simple explanation. Although the displacement of the cochlear duct is commonly represented as a wave pattern with a varying longitudinal curvature only, in reality there are curvatures in both the longitudinal as well as the radial directions because of the fixation of the partition along both of its rims. The shear motion then follows the direction of the dominant curvature in each region which, with reference to the place of maximal transversal displacement, is radially in the proximal region, and longitudinal in the distal region, with a zone of transition at the place of the maximum itself. (Note—directional terms were used here as apply to actual cochleae.) [This work was supported in part by the U. S. Air Force under Contract No. AF 41(657)-148, monitored by the School of Aviation Medicine, U. S. Air Force, Randolph Air Force Base, Texas and by a National Institute of Health Grant No. B-1909.]
Forced Oscillation of a Spring-Mass System Having Combined Coulomb and Viscous Damping
Authors: Levitan Edwin S.
Published: September 2005

The solution for the response of a mass-excited spring-mass system influenced by both Coulomb and viscous damping has been presented by J. P. Den Hartog and by L. S. Jacobsen. However, there appears to be available no practical compilation of the results for the support-excited system, interest in which has been heightened by the demands of military installations of delicate electronic equipment. In the present paper, an analytic solution for the response of the support-excited system is presented. The solution to the equation of motion is developed through the application of a Fourier series to represent the frictional force opposing the relative motion between mass and supporting structure. It is assumed that no stops occur during any portion of the steady-state oscillation. The results are presented in a form convenient for observing the influence of system parameters.
Displacement, Resonant Frequencies, and Impedance Characteristics of a Free-End Cylindrical Shell
Authors: Borg Matthew F. , Brigham Gerald A.
Published: September 2005

Dynamic tests were made on an unstiffened stainless steel cylindrical shell, 36 in. long, 12 in. diam and 116 in. shell thickness. The shell had no end plates. It was freely supported such that its end boundary conditions were free free. Resonant frequencies of the inextensional deformation types of modes, and extentional modes were experimentally obtained. Point and transfer impedance values were obtained. Longitudinal and circumferential radial displacement patterns were mapped for all resonant frequencies. Comparison was made to standard theoretical methods.
Approximation of Source Strengths of Radiating Surfaces by Vibration Measurement
Authors: Lang William W.
Published: September 2005

A simple technique is described for estimating the power level of an extended source. The sound intensity near a plane radiating surface is proportional to the square of its velocity amplitude. The power radiated by the surface can be calculated from the velocity amplitude which is determined by standard techniques of vibration measurement. A correction factor is applied to the calculations when the smallest dimension of the radiating surface is less than a wavelength. Using standard methods of air-borne sound measurement, it is usually difficult to estimate the relative contributions to the sound intensity of several sources which cannot be operated independently. The method described here is particularly useful in these situations. Power levels calculated from the velocity amplitude are compared with those obtained by air-borne sound measurement under laboratory conditions for several experimental arrangements. Utilization of this method under field conditions to obtain the approximate power levels of radiating surfaces is also described.
Errors in Approximations to Maximum Transmissibility
Authors: Burgess John C.
Published: September 2005

The error in using transmissibility at the undamped natural frequency in place of the maximum transmissibility of a single-degree-of-freedom system is less than 4% for all values of the damping ratio. The error is a maximum for a damping ratio of about 0.6 and decreases with both increasing and decreasing values of the damping ratio. The error in using transmissibility at the undamped natural frequency is less than the error in using the Q of the system for all values of the damping ratio. [Research supported by the Electronic Components Laboratory, Wright Air Development Center, under Contract No. AF 33(616)-5752.]
Vibrations of Conical Shells
Authors: Saunders H. , Wisniewski E. J. , Paslay P. R.
Published: September 2005

A Rayleigh-Ritz procedure is used to determine the natural frequencies for a certain class of mode shapes of a thin conical shell built in on the edge with the smaller radius and either simply supported or free on the other edge. Both bending and extensional energies are included in the analysis. The results show that, for a sufficiently large number of circumferential nodes, the natural frequency predicted by this analysis is very close to the inextensional natural frequency for the same number of circumferential nodes and simply supported at the edge with the smaller radius. The comparison with inextensional theory predictions is consistent with what has already been found experimentally; i.e., boundary conditions for this type of shell are not as influential on the higher natural frequencies.
Frequency Discrimination as a Function of Interpresentation Interval
Authors: Creelman C. Douglas
Published: September 2005

In a two-alternative forced-choice frequency discrimination task observers were instructed to respond by indicating the presentation interval in which the higher of the two tones had appeared. The frequency difference between the two tones was fixed at 15 cps. The independent variable manipulated was the time between the two presentation intervals within each trial. Discrimination was measured at nine separation times from 30 msec to 9.6 sec. The data indicate a peak in discrimination, varying among the four observers, with about 1-sec separation. The data are accounted for by two “memory” mechanisms. A short-term effect causes the first of two closely spaced signals to interfere with the second. When the signals are separated by longer intervals a decaying memory of the frequency of the first makes comparison with the second signal less precise, lowering discrimination. [This work was supported by the U. S. Air Force under a contract monitored by the Air Force Office of Scientific Research.]
Effect of Painting on Transmission Loss of Lightweight Concrete Partitions
Authors: Sabine Hale J. , Huntley Ralph , Richards Roy L.
Published: September 2005

A program to determine the effect of painting on the transmission loss of concrete block partitions was carried out at Riverbank Acoustical Laboratories for the National Concrete Masonry Association. Blocks made from four types of aggregate were tested, with concrete densities ranging from 60 to 130 lb/cu ft. Airflow resistance measurements made on the unpainted blocks showed values ranging from 500 to 6500 rayls/sq cm. The transmission loss characteristics of all of the painted walls were similar to those of nonporous solid masonry. The reduction in average transmission loss for the unpainted vs the painted walls varied inversely with flow resistance from 1 to 16 db. For low flow resistance, the effect of painting was about the same at all frequenceis, but for high resistance the effect of painting appeared only at low frequencies. The data for the unpainted walls are compared with theoretical values based on the calculated propagation constants of the various blocks.