bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation over Underwater Obstructions
Authors: Koopman B. O.
Published: October 2005

The paper gives a geometrical construction showing the effect of absorbing geological obstructions (ridges, seamounts, etc.) in long-range propagation in a sound channel. It applies the general methods recently developed by G. Raisbeck and the author [cf. “Some Mathematical and Computational Contributions to Underwater Sound Propagation,” 78th Meeting of the Acoustical Society of America, paper 6H1; J. Acoust. Soc. Amer. 47, 100 (1970)]. The ray equations in Hamiltonian form are studied in their phase-space (manifold of positions-and-directions). The standard single-valued integral invariants of such a system are used to examine the power flux and, in the cases of the various types of spreading (e.g., cylindrical), to obtain a graphical representation. For this purpose, the set of rays (curves in phase-space) from the emitter are cut by a family of surfaces in this space, thus defining an area-preserving surface transformation on a prototype of the surface, the “surface of section” (introduced into dynamics by H. Poincaré and G. D. Birkhoff). The ergodic mixing produced by this transformation simplifies the distribution of power, particularly after partial removal by obstructions cutting some of the rays. [This work was supported by the Naval Ordnance Systems Command.]
Development of a Nonphonemic Feature in Child Speech—Differential Vowel Duration in English
Authors: Naeser M. A.
Published: October 2005

The development of differential vowel duration was observed in six subjects (Ss) who were tape recorded at one month intervals from age 2 yr 0 months to 3 yr 0 months. The three vowels chosen for study before one voiceless and one voiced stop, and one voiceless and one voiced fricative, were the close lax vowel /ɪ/, and the close tense vowels /i/ and /u/. Children named the pictures for: /stɪk bɪb kɪs hɪz/, /fit sid tiθ piz/, /but fud gus ∫uz/, thus producing a “pontaneous” response. They also repeated the /i/ series of words which had been prerecorded on tape, thus producing an “elicited” (mimicked) response. The Ss were placed in a sound-proof booth and tape recordings were made of their responses. Vowel durations were measured from duplex oscillograms of these recordings. The results show that all children at age 2 yr 0 months demonstrated correct differential vowel duration according to the adult model under both types stimulus presentation. Even children who could not yet articulate voiced consonants in word final position (and substituted voiceless consonants instead) showed increased vowel duration where it should normally be found. Although minimal pairs were not used in this study, these results indicate that the nonphonemic feature of differential vowel duration may assume phonemic status for children at this stage in speech development.
What is the Baseline for the Perception of Phoneme Duration?
Authors: Huggins A. W. F.
Published: October 2005

Changes of speaking rate affect both the total duration of an utterance and the relative durations of its component phonemes. An experiment was performed to see how these variables affect the duration that a phoneme should have, if it is to sound natural in context. Incremental and decremental just noticeable differences were measured for the stop closure of a /p/ embedded in a sentence spoken normally and spoken fast. The measurements were then repeated with the playback speed of the normally spoken stimuli increased by 8%, 16%, and 22%, and with that of the fast-spoken stimuli decreased by the same amounts. The optimal relative duration of the stop closure did not appear to change when the playback speed was changed, but was different for the normal- and fast-spoken versions when their total durations were equated. Some implications of this result are discussed. [This research was supported in part by the Science Research Council (U.K.), and in part by an NINDB grant.]
Pause Detection Thresholds in a Stop-Phoneme Environment
Authors: Ruder Kenneth F. , Rupp John A.
Published: October 2005

The minimum silent interval duration necessary to be perceived as an intrasentenee pause was investigated. The stimuli consisted of five recorded sentences within which the words “lost” and “contact” were manipulated so that their syntactic relation to one another varied in complexity from sentence to sentence. Thirty subjects, working individually, adjusted the silent interval duration between the words “lost” and “contact” to that point at which they just perceived a pause. Results indicated that complexity of syntactic structure had no effect on the obtained pause detection thresholds. Presence or absence of a plosive burst terminating the word “lost” did, however, have an effect on pause-detection thresholds. Presence of the plosive burst frequently resulted in negative pause durations, that is, the point at which the subject indicated he just detected a pause was in reality an overlap of the words “lost” and “contact.” Negative thresholds were not observed when the plosive burst was absent, thus indicating that the silent interval preceding the plosive burst may well have been perceived as part of the interword pause interval. [Supported by NIH Grant.]
Acoustic Intensity and Vocal Effort as Cues for the Loudness of Speech
Authors: Allen George
Published: October 2005

Lane maintains that speech loudness is most directly related to the acoustic intensity (SPL) of the speech signal, according to the sone scale. Ladefoged and McKinney argue, to the contrary, that listeners rate the loudness of speech more in terms of “vocal effort,” i.e., work done in producing the sound, which they showed was approximately proportional to the square of the speaker's subglottal pressure (SGP). This paper presents results showing that SPL and SGP are both about equally relevant correlates of speech loudness. The Ladefoged and McKinney experiment was replicated with 11 subjects, whose responses were analyzed for partial correlation between loudness and both SPL and SGP. The partial correlations for SPL were about the same size as those for SGP, showing that among syllables of equal SPL the ones produced with greater vocal effort were rated louder, whereas when SGP is the same the acoustically more intense syllables are louder. This shows that speech loudness is not simply a function of acoustic intensity but also depends upon cues that relate ultimately to the physiological force with which the speech was uttered.
Temporal Order Perception of a Reversible Phoneme Cluster
Authors: Day Ruth S.
Published: October 2005

The synthetic syllable /tæs/ was presented to one ear, while at the same time /tæk/ was presented to the other ear. On some trials, both syllables began at the same time, while on others /tæs/ led by 5, 10, 15,⋯, 100 msec, or /tæk/ led by these same intervals. When asked to report “what they heard,” subjects often reported /tæsk/ or /tæks/. Later, when asked to report “the last sound they heard,” subjects performed well on both /s/ and /k/. These results contrast with those of a previous study involving nonreversible clusters: when asked to report the first phoneme of the dichotic pair /bæek/-/læek/, subjects reported hearing /b/ first, independent of the lead conditions presented. A tentative model for temporal factors in speech perception is proposed. It incorporates considerations of the effects of both parallel and serial transmission of phonemic information. [This research was supported in part by a grant from NICHD to the Haskins Laboratories.]
Recovery from Temporary Threshold Shift in Monkeys Exposed to Impulse Noise: Evidence for a Diphasic Recovery Process
Authors: Luz George A.
Published: October 2005

In studying the recovery of rhesus monkeys from noise-induced temporary threshold shift, a consistent difference was noted between recovery from continuous 112-dB tank noise and electrically generated impulse noise (of 160–170 dB peak-to-peak SPL). Although recovery from tank noise proceeded linearly as a function of the logarithm of recovery time in all 10 monkeys studied, recovery from impulse noise was diphasic. There was a rapid logarithmic recovery during the first 10 min, and, for some monkeys, a secondary shift which was maximum at 30–40 min postexposure. (On occasion, animals showed more TTS at 30 min than they did at 10 min.) Some evidence for identifying the secondary shift as an indicant of permanent damage is discussed. Although this study was carried out with shuttle-box avoidance within an anechoic chamber, it mirrors previous findings of Romba and Gates, who presented stimuli through earphones and who used actual gun fire as exposure.
Validation of the Single-Impulse Correction Factor of the CHABA Impulse-Noise DRC
Authors: Hodge David C. , Garinther Georges R.
Published: October 2005

The 1968 CHABA criterion specifies peak pressure level and duration tradeoffs designed to prevent excessive TTS in all but 5% of exposed ears. The basic criterion assumes exposure to 100 impulses/day; a tentative trading relation (based on little empirical evidence) was proposed for exposures ranging from 1 to 1000 impulses/day. In this study, subjects were exposed to single impulses produced by two small rockets. Exposure conditions were chosen to approximate the CHABA limits for grazing-incidence exposure, viz., (1) peak level 161 dB, B-duration 12.6 msec, and (2) peak level 159 dB, B-duration 33 msec. At 6000 Hz (the worst frequency), exposure under these conditions produced TTS exceeding the CHABA limits in 7% and 4% of ears, respectively. Thus the CHABA correction for single impulses appears to afford an appropriate degree of prediction of TTS.
Technical Considerations in Applying High-Intensity Sound to Industrial Processes
Authors: Shoh Andrew
Published: October 2005

Application of high-frequency high-intensity vibration to industrial processes is discussed from the standpoint of mechanical energy transfer. Dependence of various sonic effects is shown as a function of basic physical parameters involved in the transfer of vibratory energy, stating quantitative relationships whenever possible. The discussion is limited to driving solid loads. Equipment for producing high acoustic power densities is discussed, including review of the present state of the art, the inherent limitations, and the potential developments in the future. An attempt is made to organize the information so that it could serve as a guide for potential users in considering an application of vibratory energy to a process, as well as to point out the inherent potential and the limitations of the process.
Atmospheric Absorption Values from Aircraft Flyover Noise Signals
Authors: Bishop Dwight E. , Simpson Myles A.
Published: October 2005

Experimental values of sound absorption were obtained from noise signals recorded at five ground positions during a series of 20 flyovers by two aircraft during a single day of field measurements. Differences in 13-oct band noise levels observed at the ground positions for the same angle of radiation from the aircraft were used to determine absorption values which are compared to calculated values of sound absorption based upon both surface and altitude measurements of temperature and humidity. The analysis did not assume uniformity of the sound source from flight to flight nor uniformity of sound power output or directivity characteristics for flights made at different altitudes. Experimental atomspheric absorption values based upon combined data for all flyovers showed good agreement (±0.8 dB per 1000 ft) with calculated absorption values for frequencies from 1250 to 6300 Hz. For the frequency range from 400 to 1000 Hz, experimental values (typically 2 dB per thousand feet) were significantly greater than calculated values. [Work supported by NASA.]
Effects of Signal Duration and Masker Duration on Detectability under Diotic and Dichotic Listening Conditions
Authors: Robinson Donald E. , Trahiotis Constantine
Published: October 2005

The detectability of a 500-Hz tone of either 32- or 256-msec duration in a broad-band 50-dB spectrum level noise was measured as a function of the duration of the noise. The noise was continuous or was gated 0, 125, or 250 msec before the onset of the signal. For the gated noise conditions, the noise was terminated approximately 5 msec after termination of the signal. With a homophasic condition (N0-S0), the three noise conditions led to approximately the same detectability as did the continuous masher. In an antiphasic condition (N0-Sπ), detectability was poorest when signal and masker began together and improved as the delay between noise onset and signal onset increased. The difference between the simultaneous onset and the continuous noise condition was about 9 dB for the 32-msec signal and about 3 dB for the 256-msec signal. These results will be compared to those reported by McFadden (1966) and discussed in terms of theories of binaural signal detectability. [Research supported by a grant from the National Science Foundation.]
Peripheral Transduction and Transient Centering
Authors: Zerlin S.
Published: October 2005

Peripheral transduction may involve the following: (1) the pressure waveform undergoes a first-derivative transform on the basilar membrane, and (2) the amplitude pattern on the membrane is isomorphically represented by the auditory fiber activity; i.e., the post-stimulus histogram maintains the shape of the stimulus. Psychoacoustic “centering” experiments should therefore give results consistent with a first-derivative analysis. Trained subjects listened to pairs of 1000-Hz low-pass transients whose members differed in polarity, amplitude, or both. Centering results were in the form of time separations between members of a dichotic pair. With these time separations preserved, stimulus waveforms were later differentiated (giving first-derivative transforms) and viewed on an oscilloscope and photographed. (These transformed pairs now represented the displacements on the two basilar membranes and the neural patterns that earlier yielded a judgement of center.) Only the rarefaction segments of the waveforms were considered, since these constitute the stimulating phase. When waveform pairs are viewed relative to their rarefactional areas, time separations between members are proportional to area differences, i.e., a form of time-intensity trade obtains.
Localization and Echo-Ranging from Complex Sounds
Authors: Stewart J. L.
Published: October 2005

An analog simulation for the ear responds to complex stimuli with time-space analog neural patterns having components to several hundred hertz. Photographs of such patterns deriving from the same sound received at spatially separated ears are compared to form a basis for a theory of binaural localization which does not require identical pattern shapes. A different process occurs when the analog ear is equipped with nonlinear mechanisms, ultrasonic echoes then being demodulated to yield complex cochlear patterns whose interpretation provides target quality data and ranging. These two analog mechanisms yield a plausible theory for the functioning of echo-ranging animals and for binaural localization in man.
The “Instant” of a Syllable
Authors: Boomsliter P. C. , Hastings G. S. , Creel Warren
Published: October 2005

The experience of rhythm in poetry indicates that the “beat” of a syllable is an important phenomenon in language. Investigators of metrical rhythm have assumed that the physical start of a syllable is the “instant” or its beat. In this study, subjects talked in strict time with a metronome “click.” Measurements were made from sound spectrographic recordings. The “instant” of the syllable is rarely at its start; it is much more usually at or within its vowel section. The evidence best fits the hypothesis that a tension peak in the speaker's vocal muscles is the timing point of a syllable.
Low-Frequency Fluctuations of a CW Signal in the Ocean
Authors: Stanford George E.
Published: October 2005

Amplitude and phase fluctuations, measured during a series of experiments in 1968, have been statistically analyzed towards obtaining a better understanding of long-range multipath interference phenomena. Measurement of these fluctuations utilized a projector and receiver which were stationary and separated by 711 NM. The amplitude fluctuations are almost Gaussian in distribution and exhibit a 51% coefficient of variation. Although possessing a different distribution, the phase fluctuations have a similar coefficient of variation, 52%. Power spectral density levels for both amplitude and phase fluctuations undergo their greatest change when the frequency F is between 5 cycles per hour and 20 cycles per hour. Here, the spectrum level for amplitude and phase fluctuations is proportional to (1/F)4 and (1/F)2, respectively. The spectrum level between 15 cycles per hour and 120 cycles per hour is subject to seasonal influences, showing a 9-dB difference in spectrum level between March and July.
Acoustic Rays in a Moving Inhomogeneous Medium
Authors: Uginčius Peter , Zondek Bernd
Published: October 2005

Two different formulations are presented in terms of ordinary second-order vector differential equations for acoustic rays in a three-dimensional medium moving with an arbitrary velocity (either subsonic or supersonic), and having an arbitrary index of refraction. The first formulation has the arc length of the ray as independent variable, while the second one is given in terms of a canonical variable and is equivalent to Keller's Hamiltonian formulation [J. B. Keller, J. Appl. Phys. 25, 938–947 (1954)]. An explicit Lagrangian is constructed for this problem, from which a generalized Fermat's principle is derived. An error in an earlier publication [P. Uginčius, J. Acoust. Soc. Amer. 37, 476–479 (1965)] is corrected, and it is shown that this error disappears when the velocity of the medium is small compared to the speed of sound.
Rays and Waves in an Arbitrarily Moving Medium
Authors: Zondek B. , Uginčius P.
Published: October 2005

A graphical method is given relating the ray, ray speed, wave normal, and wave speed at a point in an arbitrarily moving inhomogeneous isotropic medium. A distinction is made between “advancing” and “receding” wavelets. At a supersonic point, there are in any given permissible direction two rays, a fast and a slow one, and the angle between ray and velocity may not exceed the Mach angle. This paper explains the ambiguities mentioned in the preceding one.
Analog Method of Optimizing Duct-Lining Design
Authors: Shinaishin O. A.
Published: October 2005

The analytical results by Cremer and Morse on the attenuation of sound waves in rectangular ducts were used in the development of an electrical analog for the study of different lining designs for a jet engine fan duct. The analog was designed to give the optimum attenuation of a certain lining to sound waves grazing at the surface. The variables in the analog allow the variation of such parameters as the resistance and reactance of the lining material, the number of layers of lining, and the back spacing behind each layer, as well as the frequencies at which maximum attenuation is desired.
Attenuation of Sound in Ducts due to Acoustic Boundary Layers
Authors: Vaidya P. G.
Published: October 2005

Acoustic fields, set up in ducts carrying fluids, are modified owing to viscosity and heat conduction. These distortions are more prominent near the walls of the ducts. As a result, the field near a wall could be regarded as an acoustic boundary layer. In this paper, an account of the attenuation due to this boundary layer is presented. Included also is a discussion about the possible interacting influence of the flow boundary layer on the attenuation due to acoustic boundary layer.
Patterns of Human Electrocochleographic Responses—Normal and Pathological
Authors: Aran J.-M.
Published: October 2005

The electrocochleographic response is defined as the averaged electric signal recorded between the bony promontory of the cochlea and the earlobe, in response to repetitive acoustic stimuli (clicks and filtered clicks) of alternately reversing phases. Thus, the only averaged responses are the eighth-nerve action potential and the cochlear potentials which do not reverse when the phase of the stimulus is reversed (as with the summating potential). The cochlear-microphonic potential as well as other microphonics of different origin are canceled out. By now, more than 200 tests have been performed, covering a wide range of pathological conditions, both in adults and in children. Thus, different patterns have been observed. Four types of response can be clearly differentiated: the normal response, the recruiting response, the broad or prolonged response (vertigo, tinnitus, resonance), and the abnormal response (complex brain pathology), together with a few other types. The patterns of the normal response at each level of stimulation and during masking with white noise, as well as the different pathological patterns, are discussed with respect to the structure of the peripheral receptor, the mode of production of the whole-nerve action potential, the cochlear and brain pathology, and the psychophysiological audiometric findings.
A Quantification for the Desynchronization of Auditory-Nerve Discharges with Increasing Stimulus Frequency
Authors: Anderson D. J.
Published: October 2005

The upper-frequency limit for detectable synchronization of auditory-nerve discharges to a preferred half-cycle of sine-wave stimuli has been variously noted to be between 4 and 6 kHz. The steady decrease of synchronization with increasing stimulus frequency may be modelled if one assumes that (1) the probability of discharge versus time position within the period for very low frequencies has the shape of a half-wave-rectified sine wave, and (2) travel times for impulses traveling along the acoustic nerve have a Gaussian statistical distribution around a mean travel time. With these assumptions, the distribution of discharges with respect to time within the stimulus period may be predicted for any stimulation frequency. Records from squirrel monkey auditory-nerve fibers show that the deterioration of the half-sine-wave shape does progress with increasing frequency as predicted by the travel-time-jitter model. It is concluded that the standard deviation of the time jitter which predicts a given progression of desynchronization with increasing frequency may be a measurement which has general usefulness in auditory neurophysiology.
The First 20 Years of Acoustical Signal Processing
Authors: Anderson V. C.
Published: October 2005

The decade of the 1950's marks the beginning of acoustical signal processing as a subfield of underwater acoustics. The forerunner—signal recognition—gradually evolved into a unified class of spatial and temporal processing techniques and theory which came to stand on its own. The doctrines that emerged in that decade, such as spectrum analysis, correlation, and multiple beamforming, have continued to grow in sophistication, until now, we find methods such as the fast Fourier transform, sequential detection, and adaptive beamforming handed down to us from the 1960's. The milestones of signal processing over the past 20 years present a striking record of progress in that field.
Review of Underwater Acoustics: Noise
Authors: Wenz Gordon M.
Published: October 2005

The purposes, problems, and progress of radiated-noise, self-noise, and ambient-noise research are reviewed. Purposes are related primarily to national defense, but applications to fishery and to the utilization of other natural resources are also noted. Basic problems, most of which were recognized 20 years or more ago, involve ascertainment of properties of the noise, identification of noise sources and mechanisms of noise generation, and the discovery and definition of noise dependencies on environmental factors. Many radiated- and self-noise sources and mechanisms have been identified. Major problems are those of noise measurement, and noise reduction and prevention. In the field of ambient noise, most measurements have been of sound-pressure level. Some of the noise sources and environmental factors have been identified, and a capability for qualitative and gross prediction has been achieved. Recommended are further investigations of the variation of ambient noise with receiver depth, directionality of the noise field, statistics of both noise level and instantaneous noise values, additional work at frequencies below 10 Hz, and additional geographic coverage, making full use of current knowledge to fashion noise models for experimental guidance. Challenging problems exist in procedures and instrumentation for noise studies.
Descriptive Acoustics for Music and Speech Students
Authors: Strong William J. , Bassett Irvin G.
Published: October 2005

A descriptive acoustics course has been offered at Brigham Young University since the Spring semester of 1968. The course is primarily designed for students of music, speech, and hearing. The first 40% of each semester is concerned with fundamentals of physics and vibration and characteristics of sound. The remaining 60% of the semester is used to treat acoustical aspects of musical instruments, speech production, and hearing. Several books are used as texts and reference materials. These are supplemented with notes handed out during the term. A continuing effort is being made to produce demonstrations, tapes, and films that will be suited for the course. Apparent strengths and weaknesses of the course will be discussed. The philosophy and objectives of the course will be presented in the context of a course fulfilling general education requirements in the physical sciences, but will be tailored to support particular disciplines. Brief course outlines will be available.
An Experiment in the Design of an Acoustics Course for Technical and Non-Technical Students
Authors: Oslac Michael J.
Published: October 2005

Students in engineering acoustics at The Pennsylvania State University proposed a new basic acoustics course for prospective graduate students in acoustics. Owing to the large number of departments with a growing interest in acoustics, and to the varying backgrounds of graduate students interested in acoustics, the course material was expanded to accommodate both technical and non-technical backgrounds. Structurally, the course is divided into two groups. Those with a mathematical background are taught along more technical lines, while those in other disciplines receive the same fundamentals qualitatively. The groups meet either separately, with the same instructor, or, when appropriate, simultaneously. This eliminates needless duplication of courses, interchanges viewpoints of students from different field areas, and consolidates manpower. The course, entitled Introduction to Acoustics, is being given for the first time this fall and its progress is reported.
Acoustical Flanking in Structures
Authors: Shiner Allen H.
Published: October 2005

Many sound-control components are available today which have been designed and tested to provide the building occupant with satisfactory sound isolation. Tested under laboratory conditions, these assemblies provided an idealized rating which may or may not be representative of actual field preformance. Presented here are the first results of a research program undertaken by the United States Gypsum Company to study the acoustical performance of two typical wood frame structures and their influence on the sound isolation obtained between adjoining apartments. Various partition and floor-ceiling assemblies with known laboratory ratings were constructed and tested within these structures, with the resultant differences attributed to the flanking characteristic of the structure. Data are also presented on the proper treatment of partition perimeters and electrical-outlet-box penetrations. The results of this study show how effective partition performance can be obtained even when these boxes are placed back to back. Finally, the detrimental effect of single and double solid- and hollow-core door placement within an acoustically rated partition is discussed.
Noise Control in Home Heating and Air-Conditioning Systems
Authors: Bruce Robert D. , Hirtle Parker W.
Published: October 2005

The procedures for estimation of the noise generated by home heating and air-conditioning systems will be discussed. The discussion on heating systems will include forced hot-air and water systems. To be included in the air-conditioning systems discussion are window units and central air-conditioning systems. The primary noise generators for heating systems include the furnace, burner, blowers, and unit heaters. The primary sources of noise in air-conditioning systems are the compressor, condenser (evaporative, cooling tower, or air-cooled), and blowers. Other sources of noise within such systems include the piping, circulators, ductwork, registers, and diffusers. Noise-control techniques will include location of the equipment, dissipative silencers, enclosures, lining of the ductwork, sizing of the ductwork, and vibration isolation. In addition, problems associated with the location of diffusers and registers, such as crosstalk between rooms, will be presented as well as methods for eliminating these problems.
Inner Ear Impedance (Cat) Determined by Time-Averaged Holography of the Round Window
Authors: Khanna Shyam M. , Tonndorf Juergen
Published: October 2005

After amputation of the middle ear, a small closed system was built over the oval window, isolating it from the round window. Sound pressures applied to the stapes footplate were monitored by a probe microphone placed with its opening a few millimeters above the footplate. The round window was coated with a fine bronze powder to facilitate time-averaged holography. Vibration patterns of this window, obtained holographically, permitted calculating the volume displacement of the window for a given sound-pressure level and several frequencies between 300 and 6500 Hz. The small size of the window presented some initial technical difficulties. Inner-ear impedances were calculated on the assumption that the volume displacement of the round window should equal that of the oval window. Results are compared to those obtained in an earlier study [Tonndorf et. al., Ann. Otolaryng. 75, 752, (1966)] in which a capacitive probe has served for measuring round-window displacements, but the actual displacement pattern was unknown. [Supported by a number of HIH grants.]
Distortion due to the Electric Network Properties of the Cochlea
Authors: Haas G. F. , Strelioff D. , Honrubia V.
Published: October 2005

The production of microphonics and dc potentials in the cochlea has been investigated by means of a circuit model including a resistor at the hair cells that varies with acoustic stimulation. In this paper such a circuit model, augmented with capacitance expected across membranes, was analyzed with digital computer programs. These solve the time-varying differential equations by a numerical iteration procedure. Preliminary results using gradually rising and falling simulated tonebursts of high sound-pressure level show nonsinusoidal wave shapes of CM and of currents produced with sinusoidally varying resistance, sinusoidally varying conductance, and for both these cases with an inverse-sinusoidally varying capacitance added in parallel with the varying resistor. Both positive and negative summating potential can be produced at low frequency by choosing the proper combination of parameter variations. These results confirm that distortion and dc shift can be produced by the linear but time-varying electric resistance and capacitance elements alone. [Research supported by U. S. Public Health Service.]
Model for Generation of Cochlear Microphonics
Authors: Strelioff D.
Published: October 2005

The electrical properties of the anatomical elements of the cochlea were represented by a 100-section three-dimensional resistive network in order to study, by computer simulation, the generation of electrical potentials in the ear. Electrical currents were provided by network elements representing the biological batteries in the stria vascularis and the Organ of Corti. The resistances representing the hair cells were varied following Békésy-type wave functions, and comparisons were made between the space-time distributions of the cochlear potentials, the modulated electric currents, and the traveling wave functions. The model provides a quantitative approach to the study of the pathways of the excitatory electric currents in the cochlea during acoustic stimulation. It demonstrates that the length of the cochlea that is stimulated by the varying current is shorter than that stimulated by the mechanical traveling waves. Although only linear elements are used, nonlinear effects result which could give rise to sound pressure. Other properties of the model suggest mechanisms for inhibition.
Electrophysiological Correlates of Behavioral Temporary Threshold Shifts in Chinchilla
Authors: Benitez L. D. , Eldredge D. H. , Templer J. W.
Published: October 2005

Temporary threshold shifts (TTS) produced by long exposures to noise [Carder and Miller, J. Acoust. Soc. Amer. 45, 343(A) (1969)] recover so slowly and predictably that their physiological correlates can be conveniently measured. After exposure for 48–72 h to an octave-band noise centered at 500 Hz with a sound-pressure level of 95 dB, chinchillas have behavioral TTSs of about 48 dB. Recovery from these TTSs is slow and requires about 5 days. At 5, 24, and 48 h after termination of these same exposures, cochlear microphonics (CM) and whole-nerve action potential (AP) were measured in the cochleas of untrained chinchillas. Although the behavioral TTSs were approximately equal for test frequencies from 250–8000 Hz, the loss of sensitivity for CM increased significantly from first to third turn. Quantitatively, the average CM loss in the second turn was the best match to behavioral TTS at each time. At 5 h, synchronized AP could not be seen 90 dB above normal threshold. At 24 and 48 h, shifts of AP sensitivity were more than 30 dB greater than behavioral TTSs.
A Review of Reverberation, Scattering, and Echo Structure
Authors: Horton C. W.
Published: October 2005

The last twenty years have seen a tremendous amount of work in the area of reverberation and scattering. An effort is made to summarize with graphs and charts the amount and nature of this work. Comparisons are made between the results of measurements at sea, measurements with models, and theoretical calculations. Since theoretical solutions of scattering from randomly rough surfaces involve numerous approximations, these different solutions are classified with the aid of tree diagrams so that one can chart a path through the various approximations. Most of the unclassified work on echo structure has been devoted to intensive analyses for targets of relatively simple geometric shape. For example, the sphere and the cylinder (with and without internal structure) still present interesting problems.
Acoustics of Multipurpose Performance Facilities: An Evaluation of the Objective and Subjective Acoustical Characteristics of Several Recently Completed Halls
Authors: Kirkegaard R. Lawrence , McKay Ronald L. , Watters Bill G.
Published: October 2005

Multipurpose halls in the size range of 2000–2500 seats are discussed in terms of program uses as well as architectural and acoustical design considerations. Specific examples from several recently completed projects illustrate approaches to and results of acoustical variability either of sound-absorption or “sending-end” reflectivity or both. Particular emphasis is placed on the objective and subjective evaluation of the natural and electroacoustics characteristics of the completed facilities in relation to initial design criteria.
Dallas Brooks Hall, The Masonic Centre of Victoria, Melbourne, Australia
Authors: Figwer J. J. , Bruce R. D.
Published: October 2005

This paper discusses the room acoustics, sound-reinforcement system, and noise control of the Dallas Brooks Hall, a multipurpose hall utilized for Masonic functions, conferences, conventions, and exhibitions, in addition to its primary use as a concert hall. In the concert hall configuration, the hall, with a volume of 500 000 ft3, seats about 2000 people. Reverberation time is on the order of 2 sec at midfrequencies. The sound-reinforcement system employs a single cluster of low- and high-frequency loud-speakers. Supplementary cone-type loudspeakers are installed in the balcony soffits. The system is designed for even coverage and reinforcement with directional realism. A time-delay system is utilized with the underbalcony loudspeakers. Extensive noise-control treatments were incorporated in the air-handling systems to control the ambient-noise levels in the hall due to mechanical equipment. The actually measured ambient noise is below the NC-15 criterion curve. The noise-control treatment included dissipative silencers in the duct systems, low air speeds in the supply and return ducts, low slot velocities at the diffusers and return grilles, and vibration isolation of the machinery.
On the Tonal Dependence of Auditory Rhythmic Discrimination
Authors: Divenyi P. L.
Published: October 2005

Triplets of short tones, “micro-melodies,” were constructed by using sinusoidal pulses of frequencies f1−f1−f2, embedded in continuous broad-band white noise. Duration of the pulses was 100 msec. Their rise and fall times were, respectively, 10 and 20 msec. Pulses were either evenly spaced in time (i.e., leading edges of contiguous pulses were 300 msec apart) or a delay of some Δt was introduced before the third pulse. In a YES-NO-type signal-detection experiment where musical subjects were used, it was found that discriminability of a given delay was lower when (1) the separation between the two frequencies was small, (2) a given frequency pair outlined an ascending rather than a descending melodic interval, (3) the two frequencies were low-order contiguous harmonics of some common fundamental, or (4) the frequency pair belonged to a set of higher (675–1350 Hz) rather than to a set of lower (215–500 Hz) frequencies.
Aerodynamic Study of the Primary Female Register Transition in Singing
Authors: Large John , Iwata Shigenobu , von Leden Hans
Published: October 2005

The technique of “isoparametric tones” (tones of the same fundamental frequency, sound level, and phonemic category in different vocal registers), developed by Large (1968) for acoustic and perceptual studies of vocal registers, was utilized in an aerodynamic investigation of female chest and middle registers in singing. Air flow in each register was recorded by a pneumotachographic system. It was found that, for a given pair of isoparametric tones in which there was an audible difference in register timbre, more air was consumed in middle register than in chest register. The difference in air-flow rates between registers reached a high level of statistical significance. Marked variability occurred in the air-flow rates for both registers between subjects. Characteristic of most of the samples was a synchrony between the amplitude vibrato and the variation in the mean rate of air flow. The results of this study support the theory that the key to the register problem is primarily laryngeal, not pharyngeal. [This research was supported by a U. S. Public Health Service research grant from the National Institute of Neurological Diseases and Stroke.]
On Noise Generation of Air-Compressor Valves as Function of Flow Performance
Authors: Trella Tom J. , Soedel Werner
Published: October 2005

Earlier investigators showed the importance of location of circular orifices relative to beam-type valve reeds from the viewpoint of vibration response and dynamic stresses. By hypothesizing an acoustical analogy, valve porting locations, sizes, and shapes were varied in a random fashion. The valve reeds, in this case of the plate type, were left unchanged. Sound-pressure level spectrums were measured in an anechoic room with the compressor suspended from the ceiling and the suction valve exposed to the room environment. The measurement location was in line with the suction-valve direction. As expected, the sound output was affected by porting changes, along with the mass flow performance. By plotting A-scale readings as function of a flow-performance indicator, it was possible to show that a limiting bound existed on the degree of effectiveness of porting rearrangement with respect to a maximum flow performance and a minimum sound-power output. By examining frequency-spectrum data, it was found that two regions could be identified, one for lower flow performances where sound produced by the modulation of flow by the valve reed was dominated by other effects and one for higher flow performances where the sound output was dominated by the modulation effect. It is suggested that these experimental results are explainable by investigations of poppet-valve stability in literature.
Evidence Against Monaural Loudness Adaptation
Authors: Stokinger T. E. , Cooper W. A. , Meissner W. A. , Jones K. O.
Published: October 2005

Normal-hearing listeners were adapted for from 1–30 sec with pure tones of 0.25, 1, or 4 kHz presented at 30, 50, 80, or 100 dB SPL. Adaptation was measured with delayed or simultaneous single loudness balances using a method of constant stimuli for comparison-tone presentations. Delayed balances yielded essentially no adaptation. When simultaneous binaural stimulation occurred, a modest amount of adaptation was recorded. No apparent frequency or duration effects were present with either delayed or simultaneous balances. Intensity had a noticeable effect with the simultaneous-balance method only. Differences among subjects were great. The apparent absence of adaptation with the delayed-balance method and the lack of a duration effect with the simultaneous-balance method both suggest that the loudness of a steady tone does not change significantly over time. The “adaptation” measured by the simultaneous-balance method does not appear to fit the commonly accepted pattern of perstimulatory adaptation.
Preprocessing of an Already Noisy Speech Signal for Intelligibility Enhancement
Authors: Thomas Ian B. , Ravindran A.
Published: October 2005

A preprocessing technique which enhances speech intelligibility in noise when the noise enters after preprocessing has been described recently [I. B. Thomas and R. J. Niederjohn, “The Intelligibility of Filtered-Clipped Speech in Noise,” J. Audio Eng. Soc. 18, 299–303, (1970)]. The preprocessing technique involves high-pass filtering (cutoff 1100 Hz, slope 12 dB/oct) and infinite amplitude clipping. In the present experiments, we have determined the intelligibility of speech which has been passed through this same system but in which noise is added prior to filtering and clipping. Ten subjects took part; all signals were presented binaurally in phase through headphones. The noise signal was white noise, bandlimited from 250 to 6800 Hz. Intelligibility scores (percent) for Harvard PB words at signal-to-noise ratios of 0, 5, and 10 dB (measured at the microphone) were as follows: for unmodified speech, 40, 65, and 80; for filtered-clipped speech, 47, 82, and 96; for filtered-clipped-differentiated speech, 47, 74, and 95. [Work supported by NIH.]
Low-Bit-Rate Speech Transmission by Linear Prediction of Speech Signals
Authors: Atal B. S. , Hanauer Suzanne L.
Published: October 2005

A method of encoding speech for transmission at low bit rates is described. At the transmitter, the current sample of the speech wave digitized at 10 kHz is predicted as a linear combination of the 12 previous samples. The optimum linear combination is determined by minimizing the mean-squared error between the actual and the predicted values of the speech samples. The pitch period and a binary voiced-unvoiced parameter are determined by performing a short-time autocorrelation analysis of the speech wave. Fifteen parameters, namely, the 12 predictor coefficients, the pitch period, the rms value of the speech signal, and the binary voiced-unvoiced parameter are encoded into 72-bit frames and transmitted to the receiver at uniform intervals. Different transmission rates are obtained by varying the interval between adjacent frames. At the receiver, the decoded transmission parameters are used to control a speech synthesizer consisting of a linear recursive filter excited by a suitable combination of quasiperiodic pulses and white noise. Samples of speech synthesized at transmission rates between 1800 and 7200 bits per second will be demonstrated.
Applications and Limitations of Underwater Acoustic Telemetry
Authors: Riter S.
Published: October 2005

Underwater acoustic telemetry has the potential to increase substantially the volume and reliability of information transmitted between subsea work sites and remotely located monitor and control stations. In this paper, the applications and limitations of these techniques are discussed. The effects of the transmission media such as attenuation, dispersion, fading, and background noise are pointed out. This information is used to develop realistic design criteria for, and evaluate the performance of, a typical underwater telemetry system, which utilizes digital frequency-shift keying. Practical considerations such as complexity and reliability are then discussed. Finally, an outline of some of the problems which must be overcome if such systems are to gain widespread acceptance is given. [Partially supported by a National Science Foundation Sea Grant Program Institutional grant.]
A Small Anechoic Tank for Underwater Research
Authors: Willette J. G. , Muir T. G.
Published: October 2005

A small inexpensive anechoic tank (2.5 ft high, 3 ft wide, and 4.5 ft long) was designed, built, and tested for use in ultrasonic research. The tank is shaped like a pair of “butterfly wings” in all three principal planes passing through its center. This reduces the effects of standing waves and provides for a trapped mode of operation that forces reflected energy into the corners of the tank. The walls are lined with flexible polyurethane sheets, specially designed for maximum absorptivity in the frequency range 0.5–2.0 MHz. A simple manually operated transducer-positioning system allows for variable-range separation along a track and enables rotation and tilting of the transducers through their acoustic centers. Data on the acoustic properties of the tank are presented to demonstrate such design parameters as pressure reflectivity and absorption of the liner, reverberation time, and critical angles for trapped-mode operation. Some examples of its use as a research tool are given. [This work sponsored by the U. S. Navy Office of Naval Research.]
Microphone Characteristics at Various Depths in Helium-Oxygen Environments
Authors: Murry Thomas , Sergeant Russel L.
Published: October 2005

Speech and hearing testing in hyperbaric chambers have been criticized because of the lack of calibration data on test equipment. Advances in the reciprocity calibration technique provide evidence indicating that the characteristics of acoustic transducers vary as a function of the ambient pressures. The present study was procedurally a pilot investigation to compare the operating characteristics of three types of microphones (piezoelectric, ribbon, and condenser) to a reciprocity-calibrated microphone. A system was devised in which the microphones under test and the reciprocity-calibrated microphone were located within a sound-treated enclosure inside a hyperbaric chamber. Using a standard acoustic calibration technique, the frequency-response characteristics of the transducers were obtained. The reciprocity-calibrated microphone was then used to obtain the correction factors associated with the varying acoustical output of the system as a result of increasing the ambient pressure to 19 ata (600 ft). The results indicate that the ribbon and condenser microphones did not function as well as the standard. The data from this study are discussed in relationship to the problems associated with obtaining calibration data under high pressures and in relationship to the use of microphones in helium speech unscrambling systems.