bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil/structure interaction effects in geologic media
Authors: Isenberg J.
Published: October 2005

This paper treats soil/structure interaction under earthquakes and military explosions. The main purposes of the analyses described in the present paper are to determine the motions inside the structure at the attachment points of equipment and to evaluate structural integrity. The analytic techniques which are frequently applied include closed-form or transform techniques, lumped parameter methods, and finite-difference and finite-element methods. Closed-form methods, in which an idealized foundation is assumed to rest on the surface of an elastic half-space, are frequently applied to earthquake response of nuclear power plants and are the basis for choosing lumped stiffness and damping coefficients for lumped parameter methods. No such guidance is generally available for lumped interaction parameters for protective construction. Partly due to this gap in theoretical guidance and partly because protective structures and surrounding soil receive loads which require nonlinear soil properties to be considered, successive trials are needed for lumped parameter methods applied to protective structures. Partly to avoid this uncertainty, finite-element methods are increasingly being applied to soil/structure interaction. The two main types of structures being investigated in this way are near surface silos and partially exposed radar and power plant structures. The present paper gives analyses using the methods and for the structures described above. In addition, the concept of a soil island is discussed, along with nonlinear soil properties, methods of accounting for slip and debonding at interfaces between soil and structure, nonreflecting boundaries, gravity loading, and models of the structure or structural elements.
Rayleigh waves induced by a laser beam moving over a solid surface
Authors: Pierce Allan D.
Published: October 2005

In this study, directed towards assessing a suggested method of earth excavation, a laser beam is presumed to be moving across the surface of a solid at some speed greater than the Rayleigh speed. The principal function of the laser beam is to deposite energy (within a thin layer just below the surface) which raises the local temperature, such that a compressive stress is established, which in turn is relaxed by the emission of a stress wave. The analysis shows that, at moderate to large distances from the track of the moving spot, the Rayleigh wave appears as a V-shaped wave analogous to the sonic boom. When the Rayleigh wave passes, the surface is depressed downwards and particles move inwards, outwards, and then inwards again. Some numerical estimates of amplitudes of stresses, velocities, and displacements are given. A significant aspect of the analysis is that the surface wave does have two tensile phases in its signature. Whether or not these can lead to rock cracking or crack growth still remains to be answered. [Supported by U.S. Army, AMERDC.]
Cavity growth and collapse phase of hydraulic ram
Authors: Cardea G. C. , Torvik P. J.
Published: October 2005

Cavitation begins almost immediately after a liquid-filled container is penetrated by a projectile travelling at ballistic speeds. The cavity grows to a maximum size, at which time it is approximately spherical, and then collapses. This process of growth and collapse is repeated several times, with a pressure pulse being generated at each collapse, as in the underwater detonation of an explosive. It is shown that the formulas developed for analyzing underwater explosions can be adapted to projectile penetration and used to predict the relationships between the period of the cavity growth and collapse cycle, the energy required to produce the cavity, the maximum size of the cavity, and the peak pressures generated by its collapse. The predictions are then compared with the results of previously conducted experiments. Observed and predicted maximum cavity radii are found to be in agreement and the predicted energies are compatible with the energy deposited per unit length of projectile travel by drag. Indirect evidence suggests that the magnitude of the peak pressure is also predicted satisfactorily.
Dynamic response of structures with statistical uncertainties in their stiffnesses
Authors: Prasthofer P. H. , Beadle C. W.
Published: October 2005

A considerable amount of research has been done recently on the effect of uncertainties in the mathematical model of a structure on its response. These uncertainties may be due either to imperfections in the physical structure unknown to the analyst, or to his lack of ability to correctly model certain structural elements such as joints, for example. The bulk of this research has focused on developing the sensitivity of the model natural frequencies to random perturbation introduced into the structural elements. The perturbations are chosen to represent the uncertainty in that part of the structure. In the present paper, a technique is derived to compute the transient forced vibration response of an undamped N-degree-of-freedom structure to arbitrary driving functions when statistical uncertainties are allowed in the stiffnesses. The uncertainties can be either correlated or uncorrelated. For the case of impulsive input, simple bounds are derived showing the growth of response uncertainty with time as a function of the input parameters. In other words, how far in time can one look at the response of a structure and maintain a given level of confidence? Solutions are developed for perturbations of Gaussian as well as uniform distributions and the differences in their effect are discussed.
Electronic system for enhancement of reverberation at Kresge Auditorium, MIT, Cambridge, Massachusetts
Authors: Figwer J. Jacek
Published: October 2005

An electronic system for enhancement of reverberation was installed in the Kresge Auditorium, at MIT, in the Fall of 1970. The purpose of the system is to improve the acoustical environment for performance of music in an auditorium designed primarily for speech. The installation includes multiple microphones for pickup of sound close to the performers, a reverberation device employing a steel plate based on Kuhl's principle, and a system of concealed overhead loudspeakers distributing the delayed reverberated sound. An adjustment of reverberation time between 1.7 and 3.0 sec is possible at midfrequencies.
Assisted resonance
Authors: Berry G.
Published: October 2005

The concept of Assisted Resonance was developed by Parkin to meet the need for longer reverberation time at low frequencies in the Royal Festival Hall, London. The work of Schroeder and Kutruff influenced Parkin to believe that an ideal system would have frequency-selective positive feedback channels at a uniform 3-Hz interval. A more recent installation at the University of York, England, initially used a constant percentage spacing of 4%, i.e., 18 channels per octave. The final installation used a 2% spacing in the 1000-Hz band, but 72 channels sufficed to cover the frequency range from 70 to 921 Hz. The RT is increased from 1 to 2.2 sec in the 125-Hz octave and from 0.7 to 1.35 sec in the 1000-Hz octave. Experience has emphasised the importance of relating energy supplied by the system to the desired increase in RT. It has also demonstrated the importance of the 125- and 250-Hz bands in generating “warmth” and that of the 500- and 1000-Hz bands in generating roundness in the melodic line. The first installation in the U.S. will be in Concord, California, where a 3500-seat pavilion is in course of construction.
Sound architecture
Authors: Leitner Bernhard
Published: October 2005

Sound architecture is based on the kinetics of sound. Sound traveling between a multitude of loudspeakers describes and defines space. In my work, patterns of moving sound are used as a design element. Using the vocabulary of sound for architectural purposes opens up completely new dimensions for the design. Space is defined by the direction and speed of kinetic sound, and by its color, intensity, pitch, etc. Space itself becomes an event of time. Slowly swinging corridors, leading entrance ways, pulsating fields or rooms-relaxing, inspiring, soothing spaces. The emotional and psychological potential of the world of sound becomes part of the architectural statement. The implications of sound architecture are further defined through psychological, physiological, and medical research. Practical experience shows that spaces designed with kinetic sound can be objectivized. Since the beginning of my work in 1968, I have electronically programmed many examples and I have tested them with full-scale models. It is a new spatial experience with an equally new architectural meaning and message.
Response to tone-bursts of an electroacoustic feedback channel with a remote source or a remote receiver
Authors: Bradley J. S.
Published: October 2005

Although the in-channel response of an electroacoustic feedback channel is well known, the response when other sources or receivers are used has received little detailed attention. An investigation of the effects of these other paths was thought essential to a better understanding of reverberation-increasing systems, such as Assisted Resonance, which involve many such remote paths. Thus, the response of an electroacoustic feedback channel with a remote source or a remote receiver was investigated, paying great attention to transient phenomena and using both computer simulation and real measurements in a three-dimensional model. The effects of the natural pure-tone reverberation times and transmission maximum frequencies of the remote and channel paths were considered with varying-length tone-burst signals. The results are of particular interest in the study of feedback channel interactions.
Possibility of reducing reverberation time by negative electroacoustic feedback
Authors: Bradley J. S.
Published: October 2005

Although electroacoustic feedback channels have been very sucessfully used with positive feedback to increase reverberation times, the reduction of reverberation time by negative feedback has had only very limited experimental success. As part of a thorough investigation of tone-burst responses of electroacoustic feedback channels, the possibility of reverberation reduction was closely examined. Both computed results and measurements in a three-dimensional model showed that the resulting reverberation times were not accurately predicated by the normal feedback equations. The results were dependent on the reflection coefficient of the enclosure and the length of the source tone-burst, as well as the channel loop gain. In contradiction of other recent results, reverberation reduction by this method was not found to be of great practical utility, as in many cases the reverberation time was increased rather than decreased.
Magneplanar loudspeakers
Authors: Winey J. M.
Published: October 2005

An electromagnetic transducer is described utilizing one or more diaphragms, each carrying one or more conductors. The conductors are stacked upon each other on the diaphragm, and a flexible acoustically transparent sheet magnet is arranged to confront the diaphragm, being spaced from it and magnetized in a direction through its thinnest dimension in elongate zones, following the configuration of the conductors on the diaphragm. The sheet magnet lies against a panel of acoustically transparent ferromagnetic material. This design and variations of it are discussed. A demonstration will be given.
Effect of noise bandwidth on auditory intensity discrimination
Authors: Schacknow Paul N. , Raab David H.
Published: October 2005

Noise-intensity discrimination was studied as a function of both signal and masker bandwidth. Five bandwidths of noise-ranging from 100 to 10 000 Hz—were employed. Maskers were presented at each of three spectrum levels (5, 25, and 45 dB re 0. 0002 μ bar). Discrimination thresholds were relatively unaffected by changing noise bandwidth over a two-decade range when the signal and masker were filtered together with either continuous or gated presentation of the masker. When the masker bandwidth was greater than that of the signal, the reciprocity between signal power density and signal bandwidth was found to be 5 dB per log unit of bandwidth with continuous maskers and 5–10 dB (depending upon level) with gated maskers. Additionally, a “near-miss” to Weber's law was obtained with narrow-band noise, while discrimination with wide-band stimuli obeyed Weber's law.
Intensity discrimination of continuous noise in five paradigms
Authors: Macmillan Neil
Published: October 2005

Observers were presented monaurally with continuous wideband noise and were required to judge in which of two temporal intervals the noise was more intense. Threshold intensity differences at each of six signal durations (20–640 msec) were estimated for five conditions: (I) background alone in one interval, background-plus-increment in the other; (D) background versus background-plus-decrement; (II) background-plus-increment versus background-plus-larger-increment; (DD) background-plus-decrement versus background-plus-larger-decrement; and (ID) background-plus-increment versus background-plus-decrement. An energy-detection model would predict, for all these conditions, that a log unit change in duration should lead to a 5-dB change in threshold. Instead, the threshold-versus-duration curves ranged in average slope from 6.1 to 1.8 dB/log unit, being steepest for condition ID, and shallowest for conditions using decrements. In addition, the “pedestal” conditions, II and DD, yielded shallower curves than the corresponding detection conditions.
Effects of standard-tone range and intersignal interval on frequency discrimination
Authors: Jesteadt W. , Feigel L. J.
Published: October 2005

Psychometric functions and reaction times were obtained for four listeners in a pure-tone frequency-discrimination task using a same-different paradigm. In the fixed-standard conditions, each interval contained either a 1000-Hz tone (A) or a tone higher in frequency (B), such that all four combinations (AA, AB, BA, BB) were equally likely. In the roving-standard conditions, the value of A was randomly selected from a set of six logarithmically spaced frequencies ranging from 725 to 1378 Hz. In separate 60- or 120-trial runs, the duration of the interval separating the two tones was varied from 600 msec to 8 sec. The discrimination results can be interpreted in terms of the memory assumptions in the model of intensity resolution proposed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372–383 (1969)]. Increasing the intersignal interval had less effect in the fixed- than in the roving-standard conditions, presumably because context coding was possible. This interpretation is supported by the relative magnitudes of the RTs for decisions of same and different. [Research supported by a grant from NINDS.]
Discriminability of time-reversed click pairs: Intensity effects
Authors: Resnick S. B. , Feth L. L.
Published: October 2005

Determination of the minimum interclick interval which permits discrimination of time-reversed click pairs has been offered as a method for evaluating the temporal resolving power of the ear. This investigation examined the effects of interclick intensity ratio (ΔI) and signal level (I0) on estimates of temporal resolution thus obtained. Discriminability was assessed for five normal-hearing listeners at eight interclick intervals between 0.5 and 10.0 msec using a 2IFC procedure. The level of the more intense click (I0) was fixed at 75 or 45 dB SL. Within a click pair, the level of the more intense click exceeded that of the less intense click (ΔI) by 3, 6, 12, or 24 dB. Discriminability was altered systematically by changes in both I0 and ΔI. The interclick interval required for 75% correct discrimination ranged from less than 0.5 msec to 1.8 msec. The observed intensity effects suggest that discriminability of the time-reversed click pairs is predictable from temporal masking data. [Research supported in part by education and training funds from the Veterans Administration.]
Vocal pitch matching ability
Authors: Hanson Robert J. , MacNeilage Peter F.
Published: October 2005

Subjects were asked to match the pitch of their voice, presented in one ear, with the pitch of a sinusoid target tone, presented in the other ear, in 48 trials in each of the two stimulus/ear configurations. Each trial was measured for the mean and the standard deviation of the pitch produced, and for the absolute difference between the mean and the target (E). The results show that all subjects were able to match the target pitch in several trials with E less than 0.5% of target, while some subjects could perform consistently at this level of accuracy. Subjects were screened using the Edinburgh Handedness Inventory to be righthanders; but no significant difference in performance was noted between the two stimulus/ear configurations, a possible result of the high level of accuracy attained in performing the task. Other results indicate that (1) subjects were able to integrate their musical training and experience (all nonvocal) in performing this task; and (2) subjects tended to drift higher in frequency from trial to trial. The implications of these results for the integration of pitch production/perception are discussed.
Measurement of critical masking bands
Authors: Margolis R. H. , Small A. M.
Published: October 2005

Critical masking bands were measured at three signal frequencies (500, 1000, and 4000 Hz) and two signal levels (20 and 40 dB SL) in five normal-hearing listeners. Detectability index (d′) in a 2IFC paradigm was measured as a function of the cutoff frequency of a low-pass or high-pass computer-synthesized noise. With a fixed signal frequency and level, a continuous wide-band (100-–7000 Hz) masker was set to yield 60% correct detections (d′ = 0.36) of the 250-msec signal. Then d′ was measured as a function of the high or low cutoff frequency, keeping noise spectrum level constant. The range over which changes in d′ occur defines the critical band. These ranges were in close agreement with previously reported critical ratios [J. E. Hawkins Jr. and S. S. Stevens, J. Acoust. Soc. Am. 22, 6 (1950)]. There were no differences between the two signal levels investigated. There was some evidence of the influence of aural distortion products when the masker took the high-pass configuration. The data suggest that the critical band for low-level stimuli is symmetrical about the signal frequency.
Comparison of masking patterns for temporal and simultaneous masking
Authors: Leshowitz B. , Cudahy E.
Published: October 2005

Masking patterns were mapped under simultaneous and temporal masking conditions. In the first study, a 5-msec tonal signal was presented at various delays relative to onset of a 240-msec 80-dB tonal masker. Masked audiograms for the simultaneous (steady-state) masker conditions differed from temporal masking functions in two important respects. First, the classical upward-spread-of-masking effect was not observed in backward and forward masking. For example, at the secondary peak of the simultaneous masking function, the nonsimultaneous masker was nearly 30 dB less effective than the simultaneously presented masker. Second, for signal frequencies below the frequency of the masker, less masking was exhibited in the simultaneous masking condition. The temporal development of the masking pattern was investigated in a second study, in which the duration of the masker was varied. In the simultaneous-masker condition, in the region below the masker frequency, brief-duration maskers were as much as 20 dB more effective than long-duration maskers. In remote high-frequency regions, in both temporal and simultaneous masking, the brief-duration masker was as much as 15 dB less effective than the long-duration masker.
Underwater sound propagation in surface ducts
Authors: Bucker H. P.
Published: October 2005

Surface duct sound propagation models are compared against data collected on a Naval Undersea Center sea test. Models considered when there are no significant horizontal variations include a ray theory solution, the natural mode wave theory model, and a combination of the above that accounts for surface scattering. For runs that crossed a strong front in the surface water, more complicated models are used. These include a perturbation solution of the natural mode model and a numerical solution of the parabolic approximation to the wave equation.
Formulation of non-ray acoustics
Authors: Deavenport Roy L.
Published: October 2005

The resolvent Green's function technique of Marcuvitz (1951) is used to obtain a contour integral solution for the acoustic field due to a point source located in a vertically inhomogeneous ocean. The integrand of the contour integral is composed of the product of a depth-dependent Green's function and a range-dependent: Green's function. The contour must separate the singularities of the two Green's functions. Various representations are obtained by deforming the contour of the integration. The Fourier-Bessel integral representation is derived from the contour integral, and this derivation is compared with the work of Freehafer (1951), Brekhovskikh (1957), and Wait (1962). Evaluation of the various integral representations is accomplished by using Cauchy's residue theorem, stationary phase methods, and numerical integration techniques. The residue and stationary phase evaluations are then interpreted in terms of modes and rays.
Parabolic equation method in underwater acoustics
Authors: Tappert F. D.
Published: October 2005

A new theoretical-numerical method has been developed which enables one to accurately and efficiently compute the entire two-dimensional (depth and range) low-frequency underwater acoustic field in realistic ocean environments. The theoretical development is based on the parabolic equation approximation [V.A. Fock, Electromagnetic Diffracfion Problems (Pergamon, 1965)] which automatically includes diffraction and all other full-wave effects, as well as depth- and range-dependent sound speeds and volume losses, and variable bathymetry. This parabolic wave equation is solved numerically using the split-step Fourier algorithm [R. H. Hardin and F. D. Tappert, SIAM Rev. 15, 423 (1973)] which is accurate, efficient, unconditionally stable, and is readily implemented. Operational computer programs based on this method have been used to reliably predict long-range underwater propagation effects in areas of practical interest. Representative results are displayed in the form of detailed computer-drawn decibel contours which illustrates SOFAR, BSR, surface duct, bottom bounce, and other modes of propagation in the presence of horizontal thermoclines, sea-mounts, and sea-ridges, migrating sound channel axes, multiple channels, and so forth.
Comparisons of measured and predicted acoustic propagation
Authors: Spofford C. W.
Published: October 2005

The ultimate test of an acoustic model is its ability to accurately predict the results of measurements made at sea. Differences between predicted and measured values have traditionally been attributed to deficiences in the acoustic and environmental models. Improved model accuracy has increased the importance of measurement errors (system miscalibration or inaccuracies in the reported experimental geometry) and the need for the complete specification of the measured quantity including any averages represented by the processing. Models must then be exercised to simulate such averages as the finite frequency bandwidth used in shot processors or the range/time integration contained in CW measurements. These points are illustrated by concentrating on the comparison of low-frequency explosive transmission-loss measurements with predictions using ray and wave models. Within this admittedly restricted domain non-bottom-interacting energy can be modeled with an accuracy commensurate with measurement error using concurrently measured, or in many areas archival, oceanographic data. Present bottom-reflectivity models lack the environmental data necessary to predict even gross features of bottom-bounce transmission and lack the sophistication to predict its underlying detailed structure. Improvements in the environmental and acoustic components of bottom-reflectivity models require the development of specialized measurement techniques consistent with both the needs and current capabilities of acoustic models.
Propagation loss predictions: a summary
Authors: Bartberger Charles L.
Published: October 2005

This paper reviews briefly the material presented by the other speakers of the session and discusses the state-of-the-art in propagation loss modeling.
State of the art—gas turbine noise control
Authors: Wilson Craig A. , Carter John
Published: October 2005

The economic delivery of power often dictates that the location of a gas turbine peaking facility be in or near a residential community. To maintain the environmental and aesthetic qualities of these areas requires considerable emphasis on noise control. This paper discusses the development of a NEMA B silenced gas turbine peaking facility. Major noise sources were identified and sufficient silencing was provided each source to insure compliance with the system criteria. Design innovations in the turbine exhaust silencer resulted in efficient low frequency absorption and a significant reduction in silencer shell radiation. A vibration-isolated double-wall construction was designed to provide the necessary transmission loss required of the turbine enclosure and intake plenum. The architectural facade surrounding the facility was selected to provide additional silencing as a barrier. Sound pressure level measurements of the operational facility made at 400 ft were found to conform with a NEMA B criteria.
Use of prefabricated acoustical panels in the power plant industry
Authors: McAuliffe D. R. , Schiff M. I.
Published: October 2005

Since the passage of OSHA-1970, the power plant industry has taken substantial steps to reduce noise exposure. In particular, acoustical panels of the prefabricated type have found wide usage in such areas as fan rooms, machine tender stations, foreman offices, and boiler feed pump enclosures. A number of case histories are presented outlining the noise problem, the selection of equipment to reduce noise, and the results obtained.
Diesel engine-radiated noise as function of engine type, intake and exhaust restriction, and operating load-speed schedule
Authors: Trella Thomas J. , Mason Robert L.
Published: October 2005

The diesel engine itself is an important source of diesel-powered vehicle noise, and becomes dominant after proper treatment of intake/exhaust and cooling system noise at vehicle speeds below 50 miles per hour. An investigation was conducted to quantify the effects of intake and exhaust restrictions, and load-speed scheduling on the radiated noise from four diesel engines, i.e., four-cycle naturally aspirated, four-cycle turbocharged w/wo precombustion chamber, and two-cycle blower scavenged. All engines were inline six-cylinder and rated approximately 250 hp at 2100 rpm. Each engine was asymmetrically positioned in a reverberant chamber, and sound pressure measurements were obtained 3 ft from the engine. The noise associated with intake, exhaust, cooling, and their respective ducting systems was appropriately abated to permit quantification of engine-radiated noise. Dampers were placed in the intake and exhaust ducting systems for pressure regulation, and engine loads were applied with an electric dynamometer. Exhaust emission data including temperature were also monitored. The engine-radiated noise was not significantly affected by intake pressure restrictions up to 60 in H2O or exhaust restrictions up to 90 in. H2O, except with naturally aspirated engines. The precombustion chambered engine exhibited low sound output with respect to the mechanical power available under various load-speed conditions. The engine noise efficiency, defined as engine-radiated sound power/engine brake horsepower, has a minimum value for air-to-fuel ratios in the range 15:1 to 19:1, and its dependence on engine speed is most pronounced for turbocharged engines. The latter finding suggests the presence of noncombustion or mechanical-combustion related noise sources in turbocharged engines. Engine sound pressure level calculations, projected to 50 ft, were made from the engine noise data with the resulting A-weighted noise levels ranging from 74 to 85 dBA at rated engine speed.
Nonlinear effects in the radiation pattern of engine exhausts
Authors: Brammer A. J. , Piercy J. E. , Wong G. S. K.
Published: October 2005

The waveforms and spectra of the exhaust noise produced by a two-cycle engine have been recorded with a short 1-in. diameter pipe attached directly to the exhaust port. The waveform within the pipe is essentially a half-sinusoid pulse of 5-psi amplitude and 0.5-msec duration. The amplitude of the pulse radiated from the pipe decreases with increasing angle from the direction of efflux, reaching a factor of ∼ 3 by 140°. Spectral levels at frequencies below 1.5 kHz also progressively decrease leading to a maximum front-back difference ∼ 9 dB throughout this range. At higher frequencies, the directional characteristics resemble that predicted by linear theory for a piston source. The large deviations from linear theory at low frequencies appear to be associated with the momentum of the pulse, in the manner described by Ising for sirens. This effect can explain the otherwise surprising low-frequency directivity of many devices powered by small engines with rudimentary mufflers, such as lawn mowers.
Acoustical impact of cooling towers
Authors: Capano G. , Bradley W. E.
Published: October 2005

The rapid increase in the use of cooling towers for power plant condenser cooling in recent years has presented utilities with a potential community noise problem. Uncontrolled sound levels from large nuclear power station cooling towers may range as high as 60 dBA at 2000 ft, depending upon the type of towers used. This paper presents sound pressure level measurements of several large mechanical draft and natural cooling tower installations and compares the data with published methods of predicting tower noise. The importance of considering cooling tower noise in relation to noise codes and expected community response in site and tower selection is discussed.
Environmental noise impact of natural-draft hyperbolic cooling towers
Authors: Carlson J. P. , Teplitzky A. M.
Published: October 2005

Site planning and environmental regulations may require evaluation of the environmental impact of alternate cooling methods for electric power generating stations. One alternate cooling method utilizes natural draft hyperbolic cooling towers. A study of the noise emissions from both crossflow and counterflow natural-draft hyperbolic cooling towers was undertaken as the initial phase in evaluating the potential environmental noise impact. Measured data are in substantial agreement with published noise prediction schemes [R. M. Ellis, J. Sound Vib. 14, No. 2, 171–182 (1971)]. Results of this study suggest a simplified noise prediction scheme. Accuracy of this new scheme is verified by field data. This paper compares measured and estimated noise emissions from natural-draft hyperbolic cooling towers with typical residential community noise levels. The potential impact in surrounding communities from broad-band noise emitted by natural-draft hyperbolic cooling towers is evaluated by common indices such as environmental regulations and published psychoacoustic rating methods.
Noise environment of a typical school classroom due to the operation of utility helicopters
Authors: Hilton D. A. , Pegg R. J.
Published: October 2005

Municipal governments and other agencies are using light utility-type helicopters for police operations and other activities. These activities require that the machines be operated over populated areas at relatively low altitudes and low speeds for extended periods of time. Concern has been voiced as to the effects of these operations on the interior noise environment of institutional facilities such as schools, hospitals, public buildings, etc. Noise measurements under controlled conditions have been made inside and outside of a school building during flyover and orbit operations of four different helicopters. The helicopters utilized for this series of tests were the Bell 204, 206, and 47G2A and the Hughes 269A. This group of helicopters included both turbine- and reciprocating-engine-powered aircraft. The helicopters were operated at conditions considered typical for the police patrol mission. Flyovers were made at altitudes of 1000 and 500 ft, at 45 miles per hour. During these operations, the acoustic measurements were made inside and outside of the school building with the windows closed and then open. For the windows closed ease, the noise levels due to the operation of the helicopters ranged from 53 to 60 dBA with the normal ambient being approximately 45 dBA.
New York State Construction Noise Survey
Authors: Driscoll D. A. , Haag F. G. , Webster W. J. , Farinacci J. W.
Published: October 2005

This report is based on a survey of construction noise conducted by the New York State Department of Environmental Conservation, with the assistance and cooperation of the New York State Department of Transportation and New York State Chapter of Associated General Contractors. The survey was conducted during July–September 1973 at locations throughout New York State. The report summarizes the results of over 5000 sound level measurements taken at 60 locations on eight construction sites. The survey sampled the most significant noise–producing operations characteristic of the construction and renovation of highways and buildings. The operations measured included excavation, grading, paving, demolition, pile driving, and support operations. Questionnaires to determine the degree of annoyance and interference with normal activities resulting from the noise exposure were distributed in cases where noise-sensitive areas were near the construction sites (five of the eight sites). Ninety percent of the sound level measurements fell below a curve which passes through an Leq of 88 dBA at 50 ft and decreases 6 dB per doubling of the distance. Respondents in residential areas appeared to be intolerant of sound levels above 70 dBA.
Model studies of acoustic barriers
Authors: Masiak James E.
Published: October 2005

A model study was undertaken to investigate the diffraction of sound over barriers. Using the initial tests on simple barriers as a calibration, the study investigated the relation between the suggested procedure and experimental results for complex barriers of several shapes. In particular, the study investigated the propagation of a sound wave along the top of a barrier with a trapezoidal cress section in terms of an increased attenuation.
Numerical model of sound propagation in urban areas
Authors: Holmes D. Graham
Published: October 2005

A numerical technique has been developed for estimating the outdoor sound levels due to transportation noise sources moving through urban areas. A Monte Carlo method is used to account for the effects of reflection and scattering at building facades on the sound propagation. Inputs to the model are the geometry of the area, fitted to a rectangular grid, the source location and sound power level, and the absorption and scattering coefficients of the building facades. The user can then request the sound pressure level at any location in the area. This research has two objectives. The first is to develop a useful tool to assist in transportation planning in urban areas. The second is to further our basic understanding of multipath sound propagation in complex urban areas as part of a general program of noise propagation research at MIT.
Sound propagation near ground level in the vicinity of street intersections
Authors: Donavan P. R. , Lyon R. H. , Holmes D. G.
Published: October 2005

An investigation is in progress of the propagation of sound from ground level noise sources in complex urban areas. The first problem to be considered was sound propagation into side streets due to point or traffic flow line sources in a perpendicular arterial street. Experimentally, this topic was approached with a series of field and model studies employing calibrated noise sources. Model experiments included measurements of sound level distribution near an intersection, the delay of sound level down the side street, and a simulation of the field experiments. From this data base, prediction laws were formulated and judged. In the further investigations of sound propagation in urban areas, propagation through and around multiple intersections is considered. [Work supported by the U.S. Department of Transportation.]
Factors affecting the audibility of warning devices from inside automobiles
Authors: Quindry T. L. , Jones F. E.
Published: October 2005

Measurements of insertion loss and interior masking noise were conducted using a representative sampling of 23 1972–1973 automobiles. One-third octave-band insertion losses were determined for each car for different orientations with respect to the sound source. One-third octave-band interior masking noise levels were determined from tape recordings made during preselected portions of a test drive. An estimate of the sound level and frequency required of a warning device to be “heard” by the driver inside an automobile is given.
Acoustooptic diffraction of guided optical waves in LiNbO3
Authors: Schmidt R. V. , Kaminow I. P.
Published: October 2005

Recent experiments with surface-wave acoustooptic deflectors utilizing out-diffused LiNbO3 and ZnS thin-film guides on LiNbO3 are described. Some advantages of using guided optical waves and acoustic surface waves for acoustooptic deflectors and modulators are briefly discussed.
Measurements of acoustic surface waves by means of an acoustooptic probe
Authors: Miller R. L.
Published: October 2005

A laser probe is described which can measure amplitude, phase, and variation of phase velocity of surface waves on a acoustic surface-wave devices. The addition of a two-axis scanning system and signal processing electronics allows a simulated three-dimensional display of sound field information, in various display modes. Measurements shown include scattering loss, velocity variations, and attenuation of piezoelectric ceramics, surface and bulk wave reflections on LiNbO3 devices, sound fields in transducers, multistrip couplers and two-layer structures, and scattering of surface waves from various irregularities.
Comparison of an acoustooptic and radiation pressure method of measuring ultrasonic power
Authors: Haran Michael E. , Cook Bill D. , Stewart Harold F.
Published: October 2005

During the interim period while nationally acceptable methods of measurement of referential standards for ultrasonic power are being developed, comparisons are needed among measurement techniques currently used. This is particularly necessary for determining the acoustic power from ultrasonic medical devices. Such a comparison was made between an optical and a radiation pressure technique to measure the ultrasonic power output of a 1-MHz 1-in.-diameter PZT crystal from 70 mW to 2.3 W total acoustic power. The optical technique follows the theory of Raman and Nath, assaying the diffraction of monochromatic light by ultrasound. The radiation pressure technique relates the change of position of an air-backed, self-centering, reflecting float to the ultrasonic power. A linear regression analysis between the square of the voltage applied to the crystal and the measured power of each method is used. Results are given in detail and systematic differences are discussed.
Acoustooptic deflection
Authors: Knox J. D.
Published: October 2005

Acoustooptic light deflectors are finding their way into a wider range of applications by offering a viable means for fast and accurate beam scanning with sufficient resolution to make them very attractive for such applications as TV recording, laser-addressed light valves, large-bandwidth facsimile systems, and flying spot scanners and displays. There are a variety of materials available for light deflection, among these being Paratellurite (TeO2), which, by exploiting its birefringence to circularly polarized light, has emerged as a most attractive acoustooptic material for laser scanning in the visible range. Its high figure of merit (M2 = 525) and anomalously low shear wave velocity (vs = 0.0617 × 105 cm/sec) make possible light-deflector designs which offer high resolution and efficiency. The anisotropic Paratellurite also offers a substantially expanded angular range over which Bragg interaction can take place thus allowing operation deeper into the Bragg regime. For example, an anisotropic Paratellurite deflector with a 0.225-cm interaction length can achieve 70% deflection efficiency with 40 mW of rf drive power and is capable of 525 linearly resolvable spots with a 0.5-cm optical aperture. The assets and liabilities of using this material for light deflection are discussed in detail.
Survey of acoustooptic properties of new sulfosalt crystals
Authors: Feichtner J. D. , Gottlieb M. , Roland G. W. , Isaacs T. J.
Published: October 2005

We have prepared good-quality crystals of a large number of sulfosalt-type chalcogenide crystals. These include Tl3AsSe3, Tl3AsS4, Tl3PSe4, Tl3VS4, TlGaSe2, TlGaS2, and TlInSe2. The optical band edges range from 0.55 to 1.23 μm, and the transparency region typically extends to about 15 μm. The refractive indices range from 2.5 to 3.4. The acoustic velocities were determined for each crystal for the three acoustic modes along the principal axes, and fitted to the empirical Lindemann formula relating velocity, melting temperature, and molecular weight. These materials exhibit some of the lowest velocities recorded; a shear wave velocity of only 5 × 104 cm/sec was measured for Tl3PSe4, which is the lowest to be found in the literature for any solid or liquid, away from critical points. The optoacoustic figure of merit, M2, was measured relative to fused quartz. The highest relative figure of merit, 1370, was measured in Tl3PSe4. One of these new crystals, Tl3AsSe3, has a noncentric structure and is optically nonlinear. Its symmetry class, 3 m, is one for which the P41 photoelastic tensor component is theoretically nonzero, so that this crystal may be useful for collinear acoustooptic filters. [This research was sponsored in part by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Materials Laboratory, LP, under Contract No. F33615-72-C-1976.]
Short-latency averaged evoked responses to tones in hearing-impaired and suspected hearing-impaired subjects
Authors: Stillman Robert D. , Rupert Allen L. , Moushegian George
Published: October 2005

Brief tone-bursts evoke short-latency (5–12 msec) responses recorded from vertex-earlobe electrodes. At low frequencies, these responses characteristically exhibit “frequency-following” peaks which probably reflect neuroelectric activity in the brainstem. Use of the early tone-evoked response in clinical assessment has several advantages. It permits measurement of brainstem responses to both low and high frequencies, whereas clicks are primarily of high-frequency content. Tone-evoked responses are stable both with respect to stimulus rate and the subject's level of arousal. These responses have been obtained from normal, hearing-impaired, and deaf-blind children and adults. Preliminary results, particularly from “difficult to test” children, indicate that this technique is a useful addition to available means of assessing auditory functioning. [Supported by the South-Central Regional Center for Services to Deaf-Blind Children (BEH Grant OEG-0-9-536003-4093).]
Auditory reaction times as an index of functional hearing loss
Authors: Wood T. J. , Goshorn E. , Peters R. W.
Published: October 2005

The development and standardization of a new test for functional hearing loss will be discussed. This test is based upon differences in decision processes found between functional and nonfunctional individuals. Sensation level data are presented that reflect marked differences between the above individuals with regard to probability of response, and means of standard deviations of auditory reaction times. Group data show a much steeper slope when probability of response is plotted as a function of sensation level for nonfunctional subjects than for functional hearing loss subjects. Means and standard deviations of auditory reaction times for nonfunctionals are greatly reduced when compared with results for functionals. The above data reflect minimal overlap between individual scores for functional and nonfunctional subjects. The results of this study indicate that the preceding measures can be employed to determine the existence or nonexistence of functional hearing loss with considerable accuracy.
Effects of varying levels of interruption of temporary threshold shift
Authors: Schmidek M. E. , Margolis B. L. , Henderson T. L.
Published: October 2005

Intermittency is a noise exposure variable which must be considered in proposing standard limits. The Committee on Hearing, Bioacoustics, and Biomechanics (CHABA) defined a noise interruption as a period in the noise exposure when the level falls below 80 dBA for more than 5 min or for “20% of the duration of the preceding noise burst.” Our previous study indicated tlmt interruption levels below 80 dBA could have variable effects on resultant temporary threshold shifts. Thirty subjects, ten for each of the three conditions, were exposed to 45 min of broad-band noise (103 dBA). The noise bursts were interrupted twice for 5 min by levels of 57, 67, and 77 dBA. Corrected TTS2 measurements and uncorrected TTS30 measurements were taken. Subjects afforded the 67- and 77-dBA interruptions (1) had significantly more TTS2 and TTS30 at 4 and 6 kHz than those subjects afforded the 57-dBA interruptions, (2) demonstrated a slower recovery rate than the 57-dBA group, and (3) experienced seven times as many 40 dB+TTS2's as those afforded the 57-dBA interruptions These results imply that noise interruptions defined as 80 dBA or below afford significantly less protection than interruptions which approximate 60 dBA.
Effects of acoustical stimulation on equilibrium
Authors: Venderhei Sharon L. , Repko John D. , Loeb Michel
Published: October 2005

Effects of acoustical stimulation on human equilibrium were measured on a rail test developed by Graybiel and Fregly [Acta Otolaryngol. 61, 292–312 (1966)]. Two tasks were used—standing with eyes open on rails 114in. and 34in. wide and standing with eyes closed on rails 134in. and 114in. wide. Five noise conditions were used—bilateral and unilateral presentations of impact (135 dB) and continuous (110 dB), and a bilateral control (75 dB). Analyses revealed no significant effects of types of noise on rail performance. These findings appear somewhat at variance with earlier results [H. C. Sommer and C.S. Harris, Aerospace Med. Res. Lab. Rep. 70-26, Wright-Patterson AFB, Ohio (1970); C.W. Nixon, C.S. Harris, and H. E. von Gierke, Aerospace Med. Res. Lab. Rep. TR-66-85, Wright-Patterson AFB, Ohio (1966)] indicating that asymmetrical, free-field noise stimulation produced significant impairment on a similar test, but their asymmetrical conditions involved unequal protection of the ears, resulting in a much greater interaural intensity difference.