bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Characteristics of the Crash Victim—Comparison of Experimental Results on Anthropomorphic Dummies with a Three-Dimensional Computer Simulation
Authors: Bartz J. A. , Piziali R. A.
Published: October 2005

A mathematical model of the crash victim, either vehicle occupant or pedestrian, in a three-dimensional crash environment has been developed and validated at CAL. The result of this research is a functional engineering tool for parametric investigations of the dynamic behavior of the creash victim and for design of related experiments. The digital computer simulation includes a dynamics model with 40 degrees of freedom and a contact model that generates contact forces from vehicle surfaces and between body segments of the crash victim, and restraint forces from belts and inflatable restraints (air bags). Assumptions regarding the dynamic characteristics of the crash victim model are reviewed in detail. Experimental validation consisted of dummy response measurements in a series of accelerator sled tests simulating 20 and 30 mph barrier crashes. The experimental results include dummy kinematics, head and chest accelerations, and restraint forces. In another research effort, CAL had conducted an experimental program to assess the dynamic performance of the state-of-the-art anthropomorphic devices. Two dummies of each of two manufacturers were tested in each of five configurations on an accelerator sled simulating a 30 mph barrier crash. Three replications of each test were made to provide a measure of the reproducibility of the results. A brief summary of the results is made to indicate the variation in response between the dummies of the two manufacturers in the different configurations and the reproducibility of the results obtained.
Crashworthiness—in Perspective
Authors: Wilson Richard A.
Published: October 2005

Crashworthiness for automotive vehicles concerns more than how the fenders bend. The total system is involved from the vehicle's structure to the occupant's restraint. Field accident data must be used to establish the mix of variables required to provide an acceptable level of crashworthiness. Vehicle weight, structural stiffness, acceleration pulse, type of occupant restraint, degree of passenger compartment intrusion—all must be balanced and put into proper perspective. Experimental Safety Vehicles (ESVs) can be useful exercises in designing for arbitrarily set crashworthiness requirements, but they are not necessarily examples of designs that balance all vehicle requirements.
The Development and Use of a Long-Range Side-Scan Sonar
Authors: Rusby J. S. M.
Published: October 2005

The paper describes the construction and use of a long-range side-scan sonar, which was designed by the National Institute of Oceanography to view the ocean floor out to a maximum range of 12 miles. The sonar array is mounted in a stream-lined fiberglass vehicle towed at 300 ft at a speed of 7 kt. 6.5-kHz CW or FM pulses can be radiated at 50 kW in a beam 212° by 10° in the horizontal and vertical planes, respectively. The returned FM signals can be processed in real time on either a digital or analog correlator. The sonar has been in use since 1969; in 1971, it surveyed parts of the Mediterranean Ridge and the Azores-Gibraltar Ridge, and a region of deep trenches near the Mid-Atlantic Ridge, in all covering 35 000 square miles. During the year, an exploratory long-range survey was also made of a Scottish commercial fishery.
Spectrum Measurement in the Field of an Extended Source
Authors: Murphy Donald A.
Published: October 2005

The spectrum at points in the field of coherent line sources and coherent line arrays was calculated. Large fluctuations exist in the farfield due to the directivity pattern for a fixed length source except on the main lobe of the source directivity pattern. When the length of the source is inversely proportional to the frequency, the spectrum is undistorted at all points in the farfield. In the nearfield, however, the spectrum is distorted even for the on-axis case for a fixed length source. It is less distorted than in the farfield for points outside the main lobe of the source. For a source whose length is inversely proportional to frequency, the high frequencies are in the farfield and the low frequencies are in the nearfield. The spectrum contains a low-frequency peak whose frequency depends upon the distance from the source where the measurements are made. Errors of estimating radiated pressure levels by measuring in this nearfield and extrapolating by inverse distance spreading can be quite large.
Further Studies of the Aeroacoustics of Jets Perturbed by Screens
Authors: Arndt Roger E. A. , Tran Nam C. , Barefoot Galen L.
Published: October 2005

It is observed that the placement of a screen across the exit plane of a jet nozzle results in a substantial reduction in noise intensity over what would be realized with an equivalent unperturbed jet. In the past, the general features of this phenomenon were analyzed experimentally utilizing both farfield pressure measurements and velocity (hot-wire) measurements. This investigation has been extended to include the measurement of nearfield pressure along with a more extensive program of hot-wire measurements. Nearfield pressure measurements were made with a static pressure probe developed previously. These data were used to determine the distribution of sound sources in the screen perturbed jet. The results obtained from nearfield pressure measurements gave comparable information about the effect of the screen on the acoustics sources as was obtained with hot-wire measurements and theory. Extensive hot wire data indicate that there is a major change in the characteristics of the flow field of a screen perturbed jet. The potential core in the mixing region extends farther downstream and turbulent intensities are reduced to a lower level. The strength of the quadrupole sources (assumed proportional to Reynolds stresses) has changed from a maximum value of 0.011 to less than 0.008 near the center of the mixing region. Theory indicates that the acoustic power is also proportional to the fifth power of the longitudinal scale of the flow. Through correlation techniques, a reduction in the length scale of the perturbed jet is observed. The results of the nearfield study are correlated with farfield observations.
Predicted Vibration and Shock Environments for the Reusable Space Shuttle Orbiter
Authors: Himelblau H.
Published: October 2005

Structural vibration response to aeroacoustic noise, engine-induced mechanically transmitted vibration, and mechanical shock were predicted for various orbiter locations of the proposed shuttle vehicle. Aeroacoustic-induced random vibration was calculated using (a) predicted acoustic and aerodynamic noise environments defined in a companion paper; (b) the Condos-Butler scaling method; and (c) reference aeroacoustic and vibration data from Apollo and Saturn V flight and vibroacoustic tests. Random vibration envelopes of 17 g–18 g rms were derived for five zones of the orbiter fuselage, and 22 g rms and 81 g rms for the vertical stabilizer and wings, respectively. Mechanically transmitted random vibration of 22 g rms was estimated for the aft fuselage from the staged-combustion orbiter engines during orbiter burn, using Saturn S-II flight data as reference and the Barrett scaling relationship. Mechanical shock during booster—orbiter separation was calculated to be an initial peak sawtooth with a maximum of 1.8 g peak and a duration of 400 msec. Landing shock was not expected to exceed 1.5 g peak or 350 msec, using a maximum sink speed of 10 ft/sec.
Investigation of Propeller Vortex Noise Including the Effects of Boundary Layer Control
Authors: Healy Gerald J.
Published: October 2005

An experimental investigation has been conducted on the vortex noise produced by a two-bladed 4-ft diam model propeller capable of boundary layer removal. The propeller had a spinner comprising 70% of the total propeller radius. A porous section on both surfaces of the symmetric section airfoil allowed removal of the boundary layer. Free-field measurements were made in an anechoic chamber at three field points for three tip speeds (209.5, 314.2, and 366.5 ft/sec) and four blade angles (0°, 2.5°, 5°, and 10°) both without and with boundary layer control. Agreement with theory was good (within 2 dB) showing a sixth power of tip velocity relationship and a classical dipole radiation pattern for the over-all SPL of the vortex noise. Boundary layer removal primarily affected sound levels above 3150 Hz, with no ordered effect on the over-all level.
Rotor Noise Attenuation with Leading Edge Devices
Authors: Arndt Roger E. A. , Nagel Robert T.
Published: October 2005

The noise attenuation effects of leading edge serrations on rotors is studied in detail. Total radiated power, farfield SPL, directivity patterns, nearfield sound characteristics, and rotor slip stream and wake characteristics have been compared with rotors with and without leading edge devices. The data collected indicate that a substantial noise reduction is achieved with specific leading edge configurations and running conditions. A strong dependence on rotor speed and blade pitch angle was found. Spectral analysis of the total radiated power indicates that the attenuation occurs in both the pure tones and the broad-band component of the signal. The data also demonstrate that the broad-band attenuation is shifted to continuously higher frequencies as the rotor speed increases. Nearfield data were collected in a manner indicative of rotational noise com-components. A considerable noise reduction in the higher harmonics of rotational noise was detected. Thrust and torque data indicate that the addition of leading edge serrations results in a decrease in L/D. Hot-wire data show a strong decrease in the near-wake turbulence intensities. It appears that the rotor noise reduction phenomena encompasses both the rotational and vortex components of the noise signal. Reduction in the rotational components is traced to variations in the blade loading. Noise attenuation without performance penalty is therefore realized in the broad-band component only.
Proportion of Correct Detections of Rate Changes in Pulsed Stimuli
Authors: Warm J. , Decker Jo Ann , Smith R. P.
Published: October 2005

Two groups of 12 listeners each were required to detect and report—within a 5-sec interval—changes in the rate of ongoing square-wave pulses of 2 and 11 pulses/sec. One group was given preknowledge of the direction of rate change; the other was not. Blank trials, where no change in rate occurred, were inserted randomly into the trial sequences. High proportions of correct detections were associated with short reaction times and conversely. Preknowledge of the direction of rate change produced no significant effects. The proportion of correct detections was higher for accelerations than for decelerations only at a basal repetition rate of 11 pulses/sec. The percent-correct detection measure closely paralleled the reaction time measure previously employed by us. Performance efficiency was not affected by the 5-sec time limitation imposed.
Attenuation in Custom-Fitted Earplugs
Authors: Tobias Jerry V.
Published: October 2005

It seems obvious that personalized or custom-fitted earplugs should provide a better seal within the ear canal than should standard, over-the-counter earplugs. Tests of more than a dozen varieties of insert hearing protectors demonstrated that this reasoning leads to the wrong conclusion. The best earplugs tested were among the least expensive. Even wax-impregnated fiber is better (for most people) than most personalized earplugs. A few exceptions have been noted, and some discussion of them is provided, as is an attempt to specify the possible sources of ineffectiveness in specially made plugs.
Spatial Coherence of Sound Propagated in Deep-Water and Shallow-Water Geometries
Authors: Moldon J. C.
Published: October 2005

Scattering of sound from the sea surface and sea bottom causes losses in spatial coherence of the propagated sound field. Ocean measurements have been made of the wavefront coherence in both vertical and horizontal directions at frequencies of 2.4, 4.7, and 9.4 kHz in moderate sea-state conditions. Omnidirectional source and receivers were used, and results are presented for two geometries: (1) deep water in which only a single surface reflection is encountered and (2) shallow water where multiple surface and bottom reflections exist. Variations in coherence with source and receiver depths are described, and results are compared with theoretical estimates of the angular dispersion produced by scattering at the rough boundaries.
Pressure Dependence of High-Frequency Sound Attenuation in the Deep Pacific Ocean
Authors: Bezdek H. F.
Published: October 2005

Vertical and horizontal acoustic paths, located in the Pacific Ocean between depths of 910 and 3350 m have been utilized to determine the attenuation of sound at a nominal frequency of 75 kHz. Results from these two different geometries show that predicted values exceed the observed magnitudes of acoustic attenuation at this frequency and at these depths. At 3350 m, the predicted value is 22.7 dB/km vs a measured value of 13.3±0.5 dB/km, a discrepancy of more than 9 dB. Furthermore, increasing pressure reduces the attenuation, a fact which supports the work of Fisher [J. Acoust. Soc. Amer. 38, 805 (1965)] in contrast to that of Kester and Pytkowicz [Geochimica et Cosmochimica Acta 34, 1039 (1970)]. However, the amount of reduction is larger than previously suspected by more than 80% [This paper represents results of research sponsored by the Office of Naval Research.]
A Mathematical Model for Volume Reverberation. I. Experiment
Authors: Jobst W. J.
Published: October 2005

An experiment was conducted to measure parameters for a Poisson model for volume scattering. Using a stable platform suspended beneath a ship, echoes from discrete scatterers were observed and analyzed. A cumulative probability distribution of scatterer reflectivity (ratio of scattered to incident pressure) was obtained by examining more than 1200 individual echoes. The average number of scatterers per unit volume was estimated from experimental data. The envelopes of echoes from scatterers were similar to the envelope of the transmitted signal.
Relaxational Ultrasonic Absorption in Molten Selenium
Authors: Ring E. M. , Beyer R. T.
Published: October 2005

The temperature and frequency dependence of the ultrasonic attenuation in molten selenium have been studied in the range from 200° to 400°C, and from 30 MHz to 70 MHz. The data are consistent with the literature in the high temperature range from 350° to 600°C, but supersede previous results in the range from 200° to 350°C. Analysis of the data is complicated by the structure of molten selenium, which is thought to possess a double structure of rings and chains, in equilibrium at any temperature. The material has been treated as a polymer in the literature, and by comparing the observed relaxations in Se with those reported in other polymers the present data can be analyzed: the monomer-polymer structure gives rise to corresponding nonrelaxing and relaxing components, of which the monomer (rings) represents a nonrelaxing solvent, and the polymer (chains) a relaxing solute. Finally, once the frequency dependence of relaxations occurring at constant temperature has been mapped into the temperature dependence of relaxations occurring at constant frequency, the previously reported high-temperature data can be fitted by a single relaxation time model. [Supported by the O. N. R.]
Brillouin and Rayleigh Scattering Studies of Electrolyte Solutions
Authors: Maret Arthur , Yeager Ernest
Published: October 2005

Rayleigh and Brillouin scattering studies have been carried out in a number of electrolyte solutions at various concentrations up to 4M. The apparatus consisted of an argon laser operating in a single mode, a thermostated octagonal light scattering cell with provisions for scattering at precisely known angles, a piezoelectric scanning Fabry-Perot interferometer, and a photomultiplier-photon-counting system. Three types of results have been obtained: (1) hypersonic velocity data from the frequency shift of the Brillouin components; (2) hypersonic absorption coefficients from the line widths of the Brillouin components; and (3) Rayleigh-Brillouin intensity ratios. The first and second types of results have been found to compare very favorably with those from ultrasonic velocity and absorption data at lower frequencies. The theoretical Rayleigh-Brillouin intensity ratios have been calculated from concentration fluctuation theory and found to be in good agreement with experiment at concentrations up to several molal except for 2-2 electrolytes such as MnSO4 and MgSO4. [Research supported by the Office of Naval Research and a NATO grant.]
Noise Levels on Aircraft Carrier Flight Decks and Their Effects on Humans
Authors: Webster J. C.
Published: October 2005

Measurements were made of noise levels produced by four aircraft during pilot qualification exercises aboard the flight deck of USS KITTY HAWK. These measurements, on both the A- and C-weighting networks, were augmented by calculations of speech-interference levels made later from tape recordings. These data were compared to similar measurements made at the Naval Air Test Center at Pautuxent River, Maryland, and interpreted in terms of deafness risk and interference with speech communications. The levels measured on the carrier showed large amounts of low-frequency energy (at octaves centered at 62 and 125 Hz) not present in the data taken ashore; this variation is ascribed to the presence of blast deflectors on the carrier and to the effects of strong wind across the deck and the measuring microphone in its wind screen. The noise levels measured are shown to severely degrade speech communications and to present a risk of deafness to personnel. Measure the noise levels produced by aircraft landing on and taking off from flight decks of aircraft carriers. Assess these levels in terms of (1) the hearing hazards they present to personnel exposed to them for various periods of time, with varying degrees of ear protection, and (2) the extent to which they degrade speech communication. When noise exposures were extrapolated to a 12-h cyclic air operation, hearing hazards were predicted, even when current ear-protection devices were utilized. Direct observation together with calculation of speech-interference levels indicated significant decrement in voice communication under high-noise conditions.
Determination of Articulatory Parameters from the Speech Signal
Authors: Atal B. S. , Hartman J. E.
Published: October 2005

A speech analysis method is presented for obtaining a description of the vocal-tract shape in terms of articulatory parameters. A slightly modified version of the Stevens and House three-parameter articulatory model is used to specify the area function of the vocal tract. The area function is described by five parameters, namely, the area at the place of maximum constriction, the area of the lip opening, the length of the lip section, and the length of the vocal tract. Two additional parameters are used to characterize the source. Considering the vocal tract as a lossy acoustic tube, the parameters of a 12th order linear predictor for the synthetic speech signal at the output of the tube are obtained. The parameters so obtained are used to predict the current value of a speech sample by forming a linear combination of the preceding 12 samples of natural speech. The mean-squared difference between these predicted values and the actual sample values in natural speech is minimized by iteratively adjusting the seven vocal-tract and source parameters. The parameter values that minimize the error are finally used to describe the vocal-tract shape.
Contralateral Masking Effects on Auditory Thresholds
Authors: Stiffel Gail , Young I. M.
Published: October 2005

Thresholds and amplitude measurements of fixed-frequency Bekesy tracings were made in the presence of contralateral white-noise masking using bilateral normal-hearing subjects, and subjects with unilateral sensorineural hearing loss. In bilateral normal ears, the thresholds for both interrupted and continuous tones increased linearly as the cross masking effect increased. Amplitude remained unchanged. In some cases of unilateral sensorineural hearing loss, when the pathological ear was masked the noraml ear demonstrated threshold shift and reduction in amplitude for the continuous tone when the intensity level of the noise was too low to be attributed to cross masking. On the other hand, when the normal ear was masked, the first group showed the threshold shift and reduction in amplitude for continuous tones when the masking noise was less than the interaural attenuation. The second group demonstrated similar findings when noise levels were greater than the interaural attenuation. In both groups, these changes were either abrupt and plateaued or gradually increased with increased masking. There were insignificant changes for interrupted tones. The question still remains whether the shift in the threshold and amplitude of the continuous tones is due to (1) central masking, (2) cross masking, (3) pathological condition.
Real-Time Observation of Submicroscopic Vibration by Stroboscopic Holography
Authors: Khanna Shyam M. , Tonndorf Juergen
Published: October 2005

Time-averaged holography has been successfully employed for obtaining high-contrast vibratory patterns of the tympanic membrane [Khanna and Tonndorf, J. Acoust. Soc. Amer. 41, 1904 (1972)]. Nevertheless, this technique has two restrictions: (1) the time delay due to the photographic processing of the holographic plates and (2) its essential inability to give phase information. Attempts to employ real-time holography [Tonndorf et al., J. Acoust. Soc. Amer. 46, 106 (1969)] for the same purpose failed because of (a) its inherent low fringe contrast and (b) its sensitivity to slow, quasi-dc, membrane motions. Real-time holography that includes strobing [Archbold and Ennos, Nature 217, 942 0968)] markedly improves the image contrast, as will be demonstrated on an earphone diaphragm. It also gives both amplitude and phase information. Additional phase modulation [Aleksoff, Appl. Phys. Lett. 14, 23 (1969)], as will also be shown, permits removal of the 180° phase ambiguity. This latter combination holds good promise for application to measurements on biological membranes. [Supported by several NIH grants.]
Direct Determination of Input Impedance Singularities from Speech for Obtaining the Vocal Tract Area Function
Authors: Wakita H.
Published: October 2005

This method is based on the acoustic tube model of the vocal tract in which the tube is divided into a finite number of sections with equal lengths. The volume velocity is defined in each section. Input impedance at the front end of the tube (corresponding to the lips) can be computed as the ratio of the pressure and the volume velocity there, providing that the volume velocity and the pressure are continuous at each boundary between two adjacent sections. This input impedance is shown to be of the form D(z)/G(z), where D(z) and G(z) are polynomials in z−1. It is also shown that D(z) and G(z) are constructed as a difference and a sum, respectively, of two polynomials whose coefficients can be determined from the reflection coefficients of the acoustic tube model. Since a method for obtaining the reflection coefficients from the speech wave is already established [H. Wakita, SCRL Monogr. No. 9 (July 1972)], D(z) and G(z) can thus be obtained from the speech wave. Input impedance singularities obtained with area functions for five Russian vowels by Fant were in very good agreement with Mermelstein's results [J. Acoust. Soc. Amer. 41, 1283–1294 (1967)]. [The Office of Naval Research supported this work.]
Stop Consonant Voicing and Pharyngeal Cavity Size
Authors: Berti Fredericka B. , Hirose Hajime
Published: October 2005

Aerodynamic forces require a vocal tract volume increase subsequent to oral cavity occlusion if voicing is to proceed through stop consonant closure. Electromyographic recordings of pharyngeal musculature were obtained for three subjects during the production of the six stop consonants of English in controlled phonetic environments. In addition, simultaneous electromyographic recordings and fiberscopic motion pictures were obtained for one subject producing a subset of the total utterance set. Each subject shows differences in the pattern of cavity enlargement for the voiced stops. One subject shows increased levator palatini and sternohyoid activity, and demonstrates greater velar elevation (determined from the motion pictures) for voiced stops as compared with voiceless stops. A second shows decreased activity of the pharyngeal wall musculature along with increased activity of the sternohyoid for the voiced stop cognates. The third subject exhibits a composite of the activity patterns of the first two subjects. The data support earlier suggestions that pharyngeal expansion must be due, at least in part, to positive muscle activity. They also indicate that there may be intersubject variation of actuating mechanisms while the articulations are perceived as equal. [This research was supported by the National Institute of Dental Research, through an NIH grant.]
Intraoral Air Pressure Correlates of Lip Occlusion for Bilabial Stop Consonants
Authors: Shipp Thomas
Published: October 2005

The purpose of this procedural study was to determine if a one-to-one correspondence existed between the intraoral pressure curve and complete lip closing and opening for bilabial stop consonants. The faces of two subjects were photographed at high speed (250 fps) in simultaneous anteroposterior and lateral views as they produced a series of words with /p/ and /b/, the midvocalic consonants of interest. A timing signal synchronized the film with the physiologic-acoustic record. Results showed that the onset of the intraoral air pressure rise coincided with the moment of complete lip closure while initial lip opening was coincident with the steep fall in intraoral air pressure. These relationships obtained regardless of consonant voicing or stress position, or whether the intraoral catheter was partially obstructed.
Experimental Fatigue Results under Stationary and Nonstationary Random Vibration
Authors: Swanson S. R.
Published: October 2005

There is a steadily increasing supply of interesting fatigue test result for materials under the action of random processes, especially in the area of stationary random loading. In the strictest sense, nonstationary random processes in fatigue should be considered quasistationary processes since the fatigue loading is nominally stationary over the long run to failure. It is possible to imagine nonstationary loading s over a complete fatigue life (such as the action of wear or steadily increasing damping in a fatigue test), but actual tests of this nature are not yet available. This paper surveys the field of stationary and quasistationary random loading subsequent to the author's 1968 state of the art paper on this topic. One of the most significant findings from this survey is the widespread use of repeated random loading sequences by research groups and working professional committees in interlaboratory test programs. The necessity to analyze service loadings carefully, to separate random and nonrandom aspects, is also dealt with in detail.
Statistical Averages as Estimates for Acoustic Intensity
Authors: Palmer L. Bruce
Published: October 2005

Basic to the study of undersea sound propagation is the prediction of acoustic intensity at some fixed receiving point. In ray acoustics, the total intensity at a point is taken to be the sum of the individual intensities of the single ray, or ray-bundle, arrivals at that point. At the heart of the ray acoustics approach is the estimation of the geometric spreading loss suffered by a single arrival. The usual formulations of spreading loss require the evaluation of a derivative of either depth or range with respect to initial ray angle. The calculation of this derivative has proven to be tronblesome in practice, especially for long ranges from the sound source. By the representation of a single ray intensity at a point as a statistical average of the intensities of “neighboring” rays, the estimation of the derivative is avoided and smoothed intensity estimates are obtained that are particularly applicable at long ranges from the source. The statistical average can be formulated to be performed over either depth or range. In addition, these formulations can be applied in such a manner as to provide an adjustment to intensities near caustics.
The Design of a 360-Degree Symphonic Facility
Authors: Jaffe Christopher
Published: October 2005

In 1971 the first 360° concert facility for a major symphony orchestra was completed at Ontario Place, Canada, as a summer home for the Toronto Symphony. This paper describes the physical and electroacoustic criteria developed to meet the program requirements, discusses the degree to which the criteria fulfills design objectives, and the response of artists and audiences to this intimate, less formal performance environment.
On the Loudness of Music Rooms
Authors: Pirn Rein
Published: October 2005

Free-field measurements of instrumental music suggest close correlation between the A-scale loudness of music and the mid-frequency response of rooms in which it is played. Other measurements, utilizing a steady-state random noise source, establish a typically increasing order of loudness for spaces ranging from concert halls to practice rooms. While loudness consistently increases with decreasing absorption and cubage, often the number of musicians using the room does not correspondingly decrease. It is shown that rehearsal and ensemble rooms, in particular, are louder than preferred by most musicians and that reduced reverberance is accepted in preference to excessive loudness. Alternative solutions, with room volume and reverberation time as parameters, are discussed.
Design Practice Relating to Acoustics in Schools
Authors: Connor Williams K. , Benasutti Roger
Published: October 2005

A questionnaire survey of 401 architectural firms, completed in 1968, was designed to elicit information regarding usage of acoustical and other materials in schools, reasons for choice of materials, general design practice, and acoustical problems encountered. Of schools recently designed, 73% were of closed plan type and 27% of open plan type. Absorptive classroom ceilings, primarily of the acoustical board or tile type, were used in 94% of all schools. These were chosen for acoustical reasons, but also for economy and as part of integral ceiling systems. Carpeting was more prevalent in open-plan schools and was chosen for both acoustical and aesthetic reasons. Over half the schools were reported to have acoustical problems, predominant among which was sound transmission between class areas. This problem was associated with use of the open plan and also with inadequate wall and ceiling constructions. [Work supported by the Acoustical and Insulating Materials Association.]
Noise Control by Regulation
Authors: Cuadra Elizabeth
Published: October 2005

An overview is presented of the current and anticipated future roles of the Environmental Protection Agency in what is hoped will become a cooperative, nationwide noise abatement program. As background, a brief review is given of (a) the estimated current extent and severity of the “noise problem” outside the work place (based on work performed as input to EPA's “Report to the President and Congress on Noise”); (b) major existing federal statutes or regulations relating to noise abatement; and (c) the current general status of state and local government noise abatement programs. The EPA's anticipated future role (based on legislation pending before the Congress at the date of this abstract) is outlined, and the desirability of continued and increased noise abatement activities, especially at state and local levels, and also within other federal agencies, is emphasized. Clarifying examples are presented of the methods by which state and local governments can (and should) control environmental noise, even when sources of noise are involved for which preemptive federal noise emission regulations will have been promulgated under the (pending) Noise Control Act of 1972.
Computer Generated Airport Noise Contours
Authors: Spencer J. A. , Meyer T. H.
Published: October 2005

Existing airport noise prediction programs are incapable of dealing with complex flight paths and normal dispersion of flight paths due to variations in aircraft gross weight or pilot technique. A computer program that is capable of handling these problems has been developed, using an air traffic control simulation program as its base. The original air traffic control program is capable of very accurate simulation of aircraft motion in an airspace, including random deviations from assigned parameters and automatic metering of traffic using holds, delaying turns, etc. A grid of noise measuring points, of arbitrary extent, is superimposed on the airspace and constant recording of aircraft noise at each location is simulated. At the end of a “run,” a contour plot of noise levels in the grid area is produced. Variations in traffic density, controller technique, traffic patterns, and runway use can be simulated, and the results of such variations conpared directly.
Differential Reinforcement of High Responding Rate with Changes in Sound Intensity as the Reinforcer
Authors: Molino J. A.
Published: October 2005

Subjects (19 high school students) worked on a modified DRH schedule by tapping on a telegraph key to reduce the intensity of a continuous acoustic stimulus. The stimuli were three pure tones (125, 1000, 8000 Hz) and a white noise presented diotically through earphones. Every 20 responses falling within 200 msec of each other produced a 1-dB decrement in stimulus intensity. Failure to respond produced an intensity increase of 1 dB every 4 sec. One of the stimuli was chosen at random for each 10-min session until four sessions had been completed with each stimulus. The starting intensity level was always 70–74 dB(A). The average intensity curve as a function of time stabilized after about 4 min. The asymptotic levels achieved after 7 min were taken as a measure of equal averseness for the stimuli. Equal averseness levels were compared with other subjective weighting contours: equal loudness level, dB(A), and perceived noise level. The equal aversiveness levels fell between dB(A) and the other contours.
Measurement of Loudness Adaptation with a Monaural Procedure
Authors: Wiley T. L. , Small A. M. , Lilly D. J.
Published: October 2005

Monaural loudness-adaptation measurements were made at several suprathreshold levels for 500 and 4000 Hz with normal-hearing subjects. A unique procedure used the subject as a null device and adaptively varied the signal level over time until no change in loudness was indicated. Constant-loudness functions (SPL with time) were derived for each condition over a 30-sec interval. The results indicated no monaural loudness adaptation. This generalization held for all experimental conditions. These findings support similar data obtained by other investigators using delayed-balance procedures. It was concluded that the adaptation effects observed in experiments using some type of simultaneous binaural stimulation apparently are due to binaural interaction and may reflect central as well as peripheral influences.
Beats of a Sinusoidally Amplitude-Modulated Signal with a Tone near the Modulation Frequency
Authors: Kerr T. P. , Mikaelian H. H.
Published: October 2005

The “residue pitch” produced by a train of dc pulses will not beat with a search tone of similar frequency (Schouten, 1938). These results have been interpreted to mean that combination tones do not augment the residue pitch generated by low-amplitude periodic waveforms. This assumption was reexamined for the case of a sinusoidally amplitude-modulated (AM) signal synthesized from three inharmonic components—2050, 2400, and 2750 Hz. Acoustic energy at the modulation frequency (350 Hz) was 60 dB lower than the 2400-Hz component. The modulated signal was presented at 35, 45, 55, or 65 dB SPL, together with a 352-Hz search tone. Subjects adjusted the search tone amplitude for “best beats.” Two of the five subjects could detect beating at 350 Hz when the AM signal was less than 35 dB above threshold. When the search tone was set to 35 dB SL and above, all subjects heard a periodic sweeping pitch, located in the same approximate spectral region as the AM primary tones. This phenomenon, not previously described, will be discussed in relation to residue and place theories of pitch. [Experiments performed at Submarine Medical Research Laboratories, Groton, Connecticut, under ONR Contract with Connecticut College.]
Efficient Determination of Articulation Functions
Authors: Bode D. L.
Published: October 2005

Previous experiments using adaptive methodology to measure monosyllabic articulation functions were described at the 80th and 81st Meetings of the Society [Bode and Carhart, J. Acoust. Soc. Amer. 49, 95(A) (1971); Bode, J. Acoust. Soc. Amer. 50, 146(A) (1971)]. These data indicated that (1) the use of a large test vocabulary (100 CNC words) results in highly stable and accurate measurement of a specific point on a function, and (2) adaptive tests theoretically can be used to calculate a standard error for an individual listener based on a single test administration. Subsequent experiments reveal that the use of a small test vocabulary (50 words) also allows highly reliable and valid point estimation. Administration of two tests aiming for 29.3% and 70.7% points identifies both the shape and location of the rising portion of articulation functions. Tests were administered to 24 normal-hearing subjects in quiet and in 60 and 80 dB SPL white noise. Practice effects were minimal, in most conditions averaging less than 1 dB. Further, constant-level tests employed as validating criteria revealed that the adaptive measures were highly accurate (within a few percentage points) in identifying the preselected measurement objectives on normal functions. [Research supported by National Institute of Neurological Diseases and Stroke.]
Fundamentals Regarding Reduction of Noise Arising from Jet Interaction with Deployed Lift-Augmenting Flaps
Authors: Hayden Richard E.
Published: October 2005

Proposed lift-augmented STOL aircraft are expected to require noise reductions on the order of 20 dB to meet community noise goals, according to a number of recent model studies. A predominant source of noise associated with the concepts and configurations currently under consideration is the interaction of the exhaust stream with deployed flaps. This flow-surface interaction produces both large-scale aerodynamic force fluctuations, which radiate like point dipoles at low frequencies, and smaller-scale surface pressure fluctuations, which radiate only from the leading and trailing edges of these surfaces. The fundamentals of the relevant noise-producing processes are reviewed and basic noise reduction concepts developed using parametric source models. Experimentally observed noise reductions on a 1/15 scale externally blown flap (EBF) system are presented for two of the noise reduction concepts—modification of the acoustic transduction process using variable impedance surfaces, and modification of the incident flow field through introduction of high porosity mesh grids upstream of the flaps.
Wind-Tunnel Studies of Helicopter Rotational Noise in Forward Flight
Authors: Widnall Shelia
Published: October 2005

Some results of wind-tunnel studies of helicopter noise carried out on a model rotor operating in a large open-jet wind tunnel are described. The tunnel test section is surrounded by an anechoic chamber. Data processing techniques were used to obtain the average-repeated-transient signal per revolution and thus to extract the rotational noise from the total noise, which includes random components. Blade-vortex interaction is clearly visible in many of the repeated-transient signals and is felt to be an important contributor to rotational noise even outside of the brade-slap condition. Vortex noise can be identified in the spectra of the total signal. In addition to the vortex noise, a broad-band noise of lower frequency is evident. It is postulated that this lower-frequency noise is due either to vortex-wave unsteadiness or to local stall on the blades at certain azimuth locations.
A Comparative Study of Augmentor Wing, Ejector Nozzle, and Power Jet Flap Low-Noise STOL Concepts
Authors: O'Keefe J. V. , Nickson T. B. , True H. C.
Published: October 2005

A noise and performance comparison of these STOL airplane configurations is summarized. Aircraft were sized for a 2000-ft takeoff field length, 150 passengers, and a STOL range of 500 miles. A discussion of thrust augmentation ratios, airplane “thumb-print” sizing, thrust requirements, thrust lapse rates, static test configurations, 500-ft SL noise comparisons, and noise “footprints” is presented for each concept. Each concept originally showed approximately equal noise levels on a static test stand but more intensive test work shows that the augmentor holds superior potential for low noise.
Sound Transmission in Moving Media with Application to the BIFI Range
Authors: Stallworth L. A. , Jacobson M. J.
Published: October 2005

The effect of currents on sound transmission is examined for three ocean channel models: constant sound speed and spatially uniform current, linear depth-dependent sound speed and spatially uniform current, and constant sound speed and current of constant direction and linear depth-dependent magnitude. Ray theory is used to analyze the effect of current on ray path geometry, spreading loss, boundary loss and phase shift, and travel time of individual arrivals at a fixed receiver. The arrivals are summed to determine the effect of current on the acoustic field for each model. The results are applied to the BIFI range, a 33-km × 40-m channel. The theoretical calculations are compared with continuous observations of the received phase of an acoustic signal over a 48-h period when the first model is applicable and with intermittent measurements of propagation loss when the second model is applicable. In the third model, a tidal current is shown to produce the phase offset-amplitude fade phenomenon, as well as other acoustic fluctuations having a much shorter period than the tidal current.
Ray Propagation in Slowly Time-Varying Deep Ocean Channels. II
Authors: Clark J. G. , Weinberg N. L.
Published: October 2005

Results from the studies described in the two preceding abstracts have been combined in models that describe the effects of internal tides and surface tides upon multipath acoustic propagation. Deep ocean experimental data that motivated this analysis will be discussed briefly. Several examples of ray multipath propagation in deep ocean channels time-varying under the influence of internal and surface tides will be examined. Comparisons will be drawn with analogous results from shallow water studies.
A Technique to Verify Statistical Performance Requirements for Sonar Detection Systems
Authors: Buratti R. J. , Trezona G. E.
Published: October 2005

An automated forced-choice method of evaluating detection performance is employed instead of the familiar fixed-threshold technique. The latter method utilizes a number of preselected, constant thresholds to estimate both detection and false alarm probabilities, whereas, the former incorporates a variable threshold with a precise false alarm probability to estimate only the detection probability. The estimate is obtained by selecting the “greatest of” a number of alternatives—one containing signal plus noise and the remainder containing noise only—to determine the number of correct detections (selection of signal plus noise alternative). The advantages of the forced-choice technique are predetermined false alarm rate, a single parameter test, less required test time, and real time monitoring of test results by minimizing the amount of data reductions. A comparison of both techniques is presented for two sets of typical statistics encountered under test conditions. Because of the uncertainty associated with the variable threshold, the forced-choice results are slightly pessimistic, but are within 0.3 dB of the fixed-threshold results. However, the forced-choice technique can easily be made equivalent to the fixed-threshold procedure by incorporating a correction factor into the test procedure. [Work supported by Naval Ship Systems Command.]
The Principles Involved in Choosing an Explosive Source and Processing Filter for the Measurement of Transmission LOSS
Authors: Hanna J. S. , Parkins B. E.
Published: October 2005

Explosives are often used as a source of acoustic energy in transmission measurements in the ocean because of the broad-band spectra of underwater explosions and the wide range of levels that can be generated. At the same time, this broad-band spectrum can complicate a transmission loss measurement because the spectral character of the shock wave and subsequent bubble pulses of the shot can be very similar to the spectral character of the loss that is due to the multipath structure of the propagation. This complication can be avoided by the proper choice of the detonation depth and the charge weight. When these choices have been made, the properties of the analyzing filter of the data processing system must then be selected; this must be done with regard for the nature of that portion of the multipath structure to be resolved as well as the nature of the charge spectrum. This paper discusses the principles involved in making these choices and gives illustrations of both short- and long-range measurements.
Effect of the Ground on near Horizontal Sound Propagation
Authors: Piercy J. E. , Embleton T. F. W. , Olson N.
Published: October 2005

The propagation of sound from a point source over short grass on flat ground has been measured for the relatively small grazing angles (<20°) normally encountered in practice. The distances ranged from 1 to 1000 ft at several locations. Shadow zones caused by the ground impedance have been found in situations of importance to community noise problems. With the microphone 4 ft above the ground and 50 ft away from a source 1 ft above the ground, a configuration relevant to snowmobile legislation and also exhaust noise from vehicles in suburban settings, attenuation was ≃15 dB in excess of inverse square law for frequencies near 1 kHz. For longer distances, up to 30 dB of excess attenuation was observed at frequencies above 500 Hz. Two methods have been developed for determining the ground impedance at glancing angles. From these values, the attenuation in the shadow zones may be predicted using the theory developed by Rudnick (1947) and Ingard (1951). It is found that the concepts of ground and sky waves used for electromagnetic propagation are more helpful in predicting and understanding these phenomena than the inverse square law currently used for acoustic problems.