bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech Privacy Design Analyzer
Authors: Farrell W. R. , Watters B. G.
Published: September 2005

One of today's important acoustical problems is annoyance due to intruding speech sounds. The privacy analyzer is a design tool for solving this problem in spaces such as private offices and hotel rooms. Self-contained, with all required data, the analyzer offers increased accuracy of acoustic design and is simple enough to be used successfully by the layman. Increased accuracy is achieved, for example, by taking into account both the level and the tonal character of the background noise in the finished building. Also, data on the field values of transmission loss of partitions, suspended ceilings, doors, and interconnecting air passages are incorporated. The more critical privacy needs of the executive are recognized, as is the more stringent requirement on the isolation from conference rooms in which increased vocal effort may be expected. In spite of its increased accuracy, the analyzer is simple to use. This simplicity has been attained by carefully limiting the scope of its application and by expressing the ideas involved in the simplest possible terms. For example, the analyzer is limited to relatively small rooms. The frequency characteristics of the partition TL have been incorporated with the tonal character of the background noise to give a set of “one-number” ratings. Technical terms such as decibel and cycle-per-second have been avoided. The analyzer has been developed in collaboration with Owens-Corning Fiberglas. With the assistance of several other manufacturers, it is being prepared for distribution to architects and others interested in speech privacy.
On the Noise Attenuation Characteristics of Package Muffiers for Ventilating Systems
Authors: Doelling Norman
Published: September 2005

An experimental program has been carried out (1) to evaluate and compare several commonly used techniques for evaluating mufflers and (2) to measure, by a single uniform method, the noise attenuation characteristics of a wide variety of commercially available mufflers. Data are presented to illustrate how the attenuation characteristics depend on measurement procedure. Measured attenuation characteristics of muffllers manufactured by several companies are presented.
Acoustic Filters for Liquid Piping Systems
Authors: Mikeska E. E. , Hixson E. L. , Kahlbau J. V.
Published: September 2005

Acoustic filters are being developed for attenuating liquid-borne noise in piping systems. The filters investigated are analogous to RLC type electrical filters, using the series inertances of short lengths of piping together with lumped impedance shunt elements to produce low-pass filtering action. The construction of several 2- and 3-stage experimental models is shown, along with noise reduction data measured in a laboratory water pumping system using a centrifugal pump as the noise source. (This work was supported by the Bureau of Ships.)
Isolation of a Rigid Body on Resilient Supports from a Vibration Environment
Authors: Andrews G. J.
Published: September 2005

A rigid body on resilient supports, in general, has six degrees of freedom. Due to the complexity of the equations of motion and their solutions, simplifying assumptions are usually made regarding symmetry of the body, the orientation and/or dynamic properties of the supports, negligible product of inertia terms, etc. With the advent of the high-speed electronic digital computers, however, it is possible to set up a general program for predicting natural frequencies, and obtaining frequency response curves and static displacements due to inertia loading. The equations of motion of a rigid body supported by an arbitrary number of arbitrarily oriented and located resilient mounts with damping are developed with rigor and their steady-state solutions given for harmonic displacement excitation. A numerical example utilizing the preceding development is then presented.
Temporary Threshold Shifts from Tones and Noise Bands of Equivalent rms Sound Pressure Level
Authors: Thompson Paul O. , Gales Robert S.
Published: September 2005

For equivalent rms levels a narrow band of noise has a higher peak level than has a pure tone. One might hypothesize that the noise band would cause more temporary threshold shift (TTS) than a pure tone of equivalent rms level at the same frequency. On the other hand, if the stimulus is a band of noise wider than an aural critical band, one might hypothesize that the TTS would be determined by the level in the critical band only, in which case the TTS would be somewhat less than predicted from the level of the total band. To test these hypotheses, 8 ears (4 subjects) were exposed monaurally to pure tones at 500 and 3200 cps, and to noise bands of 5 cps, one-third octave and one octave widths, centered at these same frequencies. The exposures were for 5 min at an rms sound pressure level of 110 db. After exposure the subject tracked his 4000 cps threshold for 3 min and then his 500, 1000, 2000, 4000, and 6000 cps thresholds for the next 12 min. Threshold shifts produced by the tone, the narrow band, and the broader band were found to be essentially equal. The “bounce” phenomenon was prominent in most recovery curves (4000 cps), especially after exposures in the 500 cps region.
Auditory Vigilance by Experienced Listeners to a 1 kc Pip in White Noise
Authors: Pettie C. Robert
Published: September 2005

Thirty-four subjects monitored a 1000-cps tonal pip in 80 db of random noise for 1 hr. The tone was presented 12 times per 15 min period at four intensity levels re the 50% recognition threshold in noise. Percent instances of signal correctly reported is averaged. In contrast to the original threshold criterion, the same tonal intensity was heard 28–12% of the time in periods one to four, respectively; for a tone 6 db more intense percent correct varied from 89–68 from periods one through four, respectively. In general, there was a consistent decrease in percent of signals reported with respect to levels and duration: on the average better than 2 db appears necessary to maintain percent correct criterion from period one to period four. Some interaction between period and level is evident. Errors of commission decrease markedly from period one to period two continuing at a lesser rate through period four.
New Results Concerning Monaural Phase Sensitivity
Authors: Schroeder Manfred R.
Published: September 2005

A variety of subjective effects due to the phase spectra of complex stimuli have been observed. The stimuli were periodic wave forms of constant amplitude spectrum containing up to 31 coherent harmonics. Among the more striking effects are the following: Strong dependence of the “timbre” on the “peak factor” of the stimulus. Weaker, but still audible, effects occur for phase changes which lead to identical peak factors. Small or no subjective changes are produced by variations of the phase spectrum which leave the “envelope” of the stimulus invariant. Other manipulations of the phases produce distinct tones which permit one to play simple melodies by varying only the relative phases. The results of formal measurements of phase difference limen for periodic stimuli will also be presented.
Detection of a Pulsed Sinusoid of Uncertain Frequency
Authors: Green David M.
Published: September 2005

Two conditions were used in the experiments. In one condition the observer knew that a particular signal frequency would be used on all the trials of a sequence. In the other condition the observer knew only that the signal would always be some frequency in a given range. In this second condition the particular signal frequency used on any trial of the sequence was determined by a random process. The observer was therefore uncertain as to the signal frequency on any one trial but did know the range of possible signal frequencies. In both conditions the signals were adjusted in amplitude so that their detectability would be the same at all frequencies. The effect of frequency uncertainty was very small. In the most extreme condition, in which the signal ranged from 500 to 4000 cps, the decrement in detectability was approximately 3 db when compared with the condition where the signal frequency was fixed. The results are inconsistent with several models which have been proposed to explain the effects of signal uncertainty. The data also raise questions about the interpretation of the “critical-band” experiments.
Study of Speech Privacy
Authors: Farrell W. R. , Watters B. G.
Published: September 2005

Speech privacy—freedom from annoyance owing to intrusion of speech sounds—poses an important acoustical problem in the design of private offices, conference rooms, hotel rooms, and similar spaces. The provision of adequate speech privacy can be more difficult than reverberation control or the reduction of noise, especially in building construction of low cost and light weight. A study of factors relevant to speech privacy is reported in this paper. Psychophysical tests were conducted in which subjects performed simulated tasks in a private office in the presence of controlled background noise and of speech signals that were generated in an adjacent office. The subjects were instructed to respond when “… the speech reaches a level that you consider bothersome….” The experimental variables were: (1) signal-to-noise ratio as a function of frequency; (2) the frequency characteristic of the sound isolation between the rooms; and (3) the type of task. The subjective responses correlated closely with the calculated speech articulation index. Results of the study, including physical data on sound transmission and absorption characteristics of building components, form the basis of a self-contained procedure for designing speech privacy. [Written for use by architects and building designers, this procedure is being published by Owens-Corning Fiberglas Corporation (who sponsored this study) in cooperation with other interested manufacturers.]
Diffusion Principles for Suppressing Turbojet Exhaust Noise
Authors: Sobel J. A.
Published: September 2005

Diffusion may be described as a spontaneous process of equalization of physical states, as when one gas is liberated in another. This paper deals with the foregoing process as related to the control of turbojet exhaust noise; that is, the process of bringing the high velocity jet into equilibrium with the ambient with a minimum of disturbance. An equation has been derived which states noise reduction equals 60 log10V1/V2, where V1 and V2 are unsuppressed and diffused jet velocities, respectively. Measurements have shown that the predicted reductions are valid to a 40% reduction in velocity. Beyond this point, the noise reductions fall below the theoretical curve. Furthermore, from this point on, it was found that a family of curves could be measured, whose attenuations varied with the diffuser. Aerodynamic analysis led to the conclusion, that, due to the turbulence created by the diffuser, each element was capable of producing its own self-noise level. Further experimentation confirmed this to be the case. Indeed, full-scale and model data was collected for devices which exhibited generally the same losses, yet radically different self-noise levels. This became strikingly apparent when the same diffuser was merely reversed. Thus the discrepancy between observed and theoretical noise reduction was found to be due primarily to the self-noise level of the mechanical diffuser element which became the major noise source. In addition, general procedures for optimum diffuser design were established. Full scale data have been collected which verify these techniques.
Noise in Space Vehicles Due to Micro Meteorite Impact
Authors: Franken Peter A. , Ungar Eric E.
Published: September 2005

The great abundance of particulate matter outside the terrestrial atmosphere and the extremely high velocities associated with these particles would tend to lead one to be concerned about the noise levels to which the occupants of space craft vehicles would be subjected as a result of micrometeorite bombardment. Mean levels of momentum flux obtained from various available astronomical sources are used to estimate the magnitude of the impact noise problem, based on the assumption that the impacts are completely random in time and in position of occurrence on the vehicle. It is found that micrometeorite induced noise is negligible in comparison to noise from other sources. [Supported by Wright Air Development Center under Contract No. AF 33(616)-6217.]
Design of Equipment to Withstand Shock and Vibration
Authors: Morrow Charles T.
Published: September 2005

The straightforward motion and stress analysis that has been so successful in the design of airframes has seldom been applied to equipment and is not too effective there. On the other hand, the conventional application of vibration specifications to sub-assemblies leaves the resonances within the equipment very loosely controlled, so that the attainment of reliability is dependent primarily on testing the entire equipment and making design changes until the results are satisfactory. Furthermore, information on resonances of standard parts such as vacuum tubes and relays is not readily available. There is an urgent need for rules for controlling configuration and resonance in the course of design, so as to achieve something close to an optimum in the least possible time and decrease any amount of calculation, testing, or redesign required thereafter. Test procedures can be modified to assist such a design approach. Some complication results from consideration of mechanical impedance relationships, but not enough to prevent improvement of the development process.
Physics of Acoustic Cavitation
Authors: Flynn Hugh Guthrie
Published: September 2005

A vocabulary useful in describing cavitation in an acoustic field will be defined, and concepts will be introduced to facilitate the interpretation of complex, many-bubble phenomena in terms of single-bubble dynamics. A distinction between stable cavities and transient cavities will be made and the roles of these two limiting types of bubbles in “gaseous” and “vaporous” cavitation will be examined. Under the influence of an acoustic field, cavitation bubbles grow either slowly or explosively from small gas nuclei in a liquid. The conditions determining whether a gas nucleus will become an explosively growing, transient cavity or a slowly growing, stable cavity will be summarized, and the dynamics of the two types of cavities will be contrasted. In particular, a conceptual model of a transient cavity will be proposed, and calculations based on this model will be used to characterize the life history of such a cavity from its nucleation to its catastrophic end. The rationalization of specific cavitation phenomena (such as the erosion of solids and the acceleration of chemical reactions) in terms of the pulsations of a stable cavity or the violent collapse of a transient cavity will be considered. Finally, an attempt will be made to indicate where our understanding of the basic physical processes of cavitation needs to be deepened.
Study of the Application of Ultrasonic Energy to the Extraction of Belladonna Leaf U.S.P.
Authors: Wray Paul E. , Small LaVerne D.
Published: September 2005

Ultrasonic energy was applied to the extraction of belladonna leaf U.S.P. to demonstrate possible advantages over official extraction methods. The ultrasonic generator used operated at a frequency of 500 kc. It is composed of a radio frequency oscillator from which power is fed at high voltage to a quartz crystal immersed in an oil bath. The material to be treated was placed in the treatment vessel, attached to an adjustable support and lowered into the oil bath. Two types of treatment vessels were used: the first vessel was only partially submerged in the oil bath; while the other was designed for complete submersion in the oil bath. Subjection of the ammoniated ether, alcohol maceration mixture of the powdered leaf in the surface type vessel to ultrasonic energy for only twenty minutes gave results comparable to the official overnight (approximately 12 hr) maceration period. More efficient utilization of ultrasonic energy was possible by use of the totally submerged treatment vessel. The results indicate that complete extraction was obtained in twenty minutes with a 5-g sample, while a 10-g sample took approximately 90 min. These two times are in contrast with the overnight maceration and subsequent 3-hr Soxhlet extraction required by the U.S.P. method. The results obtained indicate a possible explanation of the beneficial effect observed. Increased agitation will speed extraction. Violent agitation was observed in these experiments. Heat will generally speed extraction. Acceleration of the powdered leaf particles would give rise to heating effects. Cavitation took place during performance of ultrasonic maceration in the open treatment vessel, and possibly occurred during extraction in the submerged vessel, but could not be observed. Collapse of the cavities formed during cavitation causes pressure to be built up locally and this, also, tends to accelerate partition. Reduction of particle size will normally speed extraction procedures. A particle size reduction occurred in submerged extraction. The contribution of each of these effects has not been firmly established and further investigation is necessary to determine the actual mechanism of ultrasonic extraction. [Paper abstracted from a thesis presented to the Faculty of the Graduate College of the University of Nebraska by Paul E. Wray, in partial fulfillment of the requirements for the degree of Master of Science. (Presented to the Scientific Section, A.Ph.A., Los Angeles, April, 1958.) Published in J. Am. Pharm. Assoc., Sci. Ed. 47, 823 (1958)].
Photographic Studies of Erythrocytes in Ultrasonic Fields
Authors: Binstock Leonard , Ackerman Eugene
Published: September 2005

A description is given of apparatus suitable for photographically observing the changes of mammalian erythrocytes in ultrasonic fields at frequencies from 250 to 1000 kc. These studies were undertaken to investigate the possibility of mechanical resonant modes of vibrations of the erythrocytes. The apparatus consists of an electronic generator, two barium titanite transducers, a microscope, a specimen exposure slide and holder, a camera, and photoflash unit. Photographs were taken of human, sheep, bovine, and rat erythrocytes showing the effects of frequency changes as well as changes in intensity level. Sensitivities were obtained by determining the percentage of red blood cells affected for various intensities at a given frequency. At this frequency, all the sensitivities for the four species were plotted as a function of intensity. Relative sensitivities were obtained by taking the ratios of the slopes of the best straight lines for three species with respect to the slope for the fourth species. These ratios were then plotted as a function of frequency. Results indicate the existence of several mechanical resonant modes in the frequency range investigated.
Effect of Phase on the Quality of a Two-Component, Unsymmetrical, Complex Tone
Authors: Craig James H. , Jeffress Lloyd A.
Published: September 2005

Carefully filtered 250 and 500 cps tones were mixed in various phase relations, producing wave forms which are not symmetrical about the time axis. By commutating the leads to an earphone it is possible to present the resulting complex tone to the ear with a given half either a condensation or a rarefaction. Subjects attempted to distinguish between the two presentations. The 250-cps fundamental ranged in SPL from 40 to 84 db and the 500 cps harmonic from below threshold to 73 db. For each combination of levels and phase, a random sequence of twenty presentations was used, half with the commutator in one position and half in the other. The one-second stimuli were separated by one second of silence. The results show that subjects can not only detect a difference between the phase-reversed signals but can identify one as “higher” or “louder” or “muffled.” The two subjects from whom most of the data were obtained responded under many conditions with 80 to 100% consistency. For some of these conditions the subjects agreed about which phase condition was higher (or louder); for others they disagreed although remaining self-consistent. The results will be shown to have some bearing on the “best-beat” controversy. [This work was partially supported by the Bureau of Ships.]
Psychoacoustic Study of the Mechanism of Binaural Fusion
Authors: Hall J. L.
Published: September 2005

The effect of masking noise on binaural interaction of disparate stimuli was studied. Stimuli were trains of pulses and trains of clicks. With continuous noise added monaurally to noise bursts, more noise was required to prevent fusion when the stimulus in the opposite ear was a noise burst than when it was a pulse. In neither case did the level of noise necessary to prevent fusion make the noise burst inaudible. In fusion of noise bursts and pulses, the level of noise added to pulses necessary to prevent fusion equalled the level which made the pulses indetectible. In another experiment, subjects were presented with trains of single pulses at one ear and closely-spaced pairs of pulses at the other. They were required to fuse the single pulse with the second of the pair of pulses. It was found that the addition of noise to the pair of pulses reduced the minimum interpulse interval at which this was possible. These results are interpreted in terms of a mechanism of binaural fusion which compares the strength of the short-term integrated neural response from the two sides. This model receives support from previous electrophysiological observations. [Work at MIT supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research), and the U. S. Navy (Office of Naval Research).]
Ultrasonic Absorption in Electrolytic Solutions
Authors: Stuehr John , Verma G. S. , Yeager Ernest , Hovorka Frank
Published: September 2005

Ultrasonic absorption has been measured in various electrolytic solutions which have not been reported upon previously in the literature. Specific electrolytes include potassium cyanide, cadmium sulfate, chromic sulfate, potassium ferro- and ferricyanides, and stannous sulfate. Measurements have been made by the reverberation-resonator method in both 12- and 50-liter spherical resonators at frequencies from 40 to 230 kc. Cadmium sulfate and potsssium cyanide show abnormal absorption with relaxation frequencies above the range of the present measurements. In addition results will be reported for magnesium sulfate solutions in which the ionic interactions associated with the ionic atmosphere concept have been buffered out in good part by the use of large concentrations of acoustically nonactive, uni-univalent electrolytes. The theoretical significances of these results will be discussed. [This research has been supported by the Office of Naval Research under Contract Nonr 1439(04).]
On the Effects of Diffraction in Ultrasonic Absorption Measurements
Authors: Carome E. F. , Burlage S. R. , Nichols W. H.
Published: September 2005

A study has been made of the propagation of ultrasonic waves in low absorbing liquids in the frequency range from 1 to 10 Mc to determine the effects of diffraction on attenuation measurements. Pulse techniques were employed and measurements were made in a variety of systems ranging from acoustic wave guides to effectively infinite diameter columns. The existing theories have been extended to treat the various systems which were studied and the experimental results compare well with the theoretical predictions. Some modifications appear to be required, however, to account for the differences between the idealized systems considered in the theory and the ones actually employed in practice. (This work was supported in part by the Office of Naval Research.)
Parameter of Nonlinearity in Fluids
Authors: Beyer R. T.
Published: September 2005

Increased interest in the nonlinear effects of finite amplitude sound makes imperative a better knowledge of the departure of fluids from a linear behavior. This nonlinearity is reflected in terms of the parameter 1 + ρ0/2c02(∂2β/∂ρ2)s. Values of this derivative for liquids have been almost wholly lacking in the literature. What data are available have now been used to compute the parameter for about a dozen liquids. Results are compared with those commonly cited in finite amplitude work. Discrepancies are also discussed. (Supported in part by the Office of Naval Research.)
Propagation of Shear Waves in Teflon
Authors: Leonard R. W.
Published: September 2005

A dynamic measurement of the shear modulus of Teflon has been obtained over a frequency range extending from 50 to 2000 cps. The shear modulus over this frequency range shows no anomalous behavior as indicated in the measurements of E. R. Fitzgerald. No dispersion or absorption anomaly was observable in the range between 200 and 1000 cps. The transmission loss in a circular Teflon rod is a monotonically increasing function with increasing frequency. Measurements have been made on a terminated rod permitting the propagation to be measured by continuously sweeping through the frequency range. The attenuation obtained from the terminated rod is in agreement with that obtained by standing wave measurements at closely spaced frequencies. (This work has received partial support from the Office of Naval Research.)
Absorption and Propagation Velocity of Sound in Argon
Authors: Feldstein Robert
Published: September 2005

Absorption of sound data for pure dry argon were obtained from measurements of the decay time of sound in a 66 inch spherical resonator. The measurements were made over the temperature range from −60°C to +20°C, from a pressure from 2 cm to 76 cm of mercury, and over the frequency range from 240 to 16 000 cps. The temperature was controlled to 0.15°C and measured to 0.04°C. The pressure was controlled to 0.1 mm of mercury. Over the frequency range from 240 cps to 1200 cps selected normal modes of vibration of the sphere were excited, and the decay time measured to high precision by a specially constructed digital system. Decay times as long as 50 sec were measured. Consistency of measurement within a single group of readings under optimum conditions was better than 0.01% and the individual measurements were repeatable to better than 0.1%. The decay time of white noise was measured for a one third octave band width at octave intervals from 1000 cps to 16 000 cps. The velocity of propagation was determined by measuring the exact resonant frequencies of the sphere for selected modes to within ±0.1 cps.
Acoustics of the Sidney Myer Music Bowl, Melbourne, Australia
Authors: Muncey R. W. , Nickson A. F. B.
Published: September 2005

The Sidney Myer Music Bowl, which has just been awarded the Reynolds prize of the American Institute of Architects, is an outdoor auditorium for speech, music, and drama. It is unique as the main structure or “canopy” covers both the stage and 2000 fixed seats, an area about one eighth of the bowl proper. The ground under the canopy was excavated to depths of up to 10 m and this allows an audience of 30 000 to view the entire stage. Overflow audiences of two or three times this number can listen in areas out of sight of the stage. The paper describes the sound reinforcement system and some measurements of reverberation time, transmission characteristics, pulse response, and insulation from unwanted noise. Subjective impressions as reported of music critics and others are included.
Acoustic Treatment of the Cleveland Public Auditorium
Authors: Hunter J. L. , Mull H. R.
Published: September 2005

The main arena of the Cleveland Public Auditorium is one of the largest listening chambers in the world. Built in the early 1920's, it has, since its opening, been the scene of important public functions, including presidential conventions. Criticism of its acoustic qualities had existed from its opening, but had increased rapidly since 1950, and in 1955 the city administration called for a thorough study of its acoustic qualities, and recommendations for improvement. This paper consists of a description of the initial acoustic study, including articulation testing and reverberation time measurements, the problems involved in the acoustic treatment, the actual application of the treatment, and opinions of users since completion.
Day-to-Day Stability of the Auditory Threshold in Noise-Exposed and Non-Noise-Exposed Air Force Personnel
Authors: Kopra Lennart L.
Published: September 2005

Individual pure-tone threshold tests were manually administered to three groups of men: Group I—27 flight-line personnel who were exposed to job noise during the test week; Group II—24 flight-line personnel who were not exposed to job noise during the test week; Group III—52 non-flight-line men. A modified psychophysical method of limits was used, and the intensity of the test tones was varied in 2-db steps. Thresholds for 250 cps through 6000 cps were established. Each man was tested daily, Monday through Friday, at approximately the same time each morning. The noise-exposed men were tested prior to daily noise exposure. Results are summarized as follows. (1) Most mean thresholds in the three groups on Tuesday through Friday were better than on Monday. The largest mean improvement in sensitivity was 2.2 db (Group II at 250 cps on Thursday), and the largest mean reduction in sensitivity was 1.7 db (Group I at 6000 cps on Friday). Improvement in measured auditory sensitivity during the test week is interpreted as indicative of a learning effect. (2) Intra-subject variability in thresholds at 4000 cps and at 6000 cps was not related to threshold sensitivity. (3) No cumulative short-term temporary threshold shift occurred in the noise-exposed men during the five-day test period. [This study was supported by funds provided under Contract AF 41 (657)-35 with the School of Aviation Medicine, USAF, Randolph Air Force Base, Texas.]
On “Latent” Auditory Fatigue
Authors: Ward W. Dixon
Published: September 2005

Some recent studies have indicated that noise exposures which do not, alone result in measurable TTS (temporary threshold shift) may nevertheless enhance the effect of a succeeding TTS-producing stimulus. The present experiments were designed to measure this “latent” effect in the case of the TTS at 3 and 4 kc produced by 1200–2400-cps octave-band noise. The TTS resulting from a 12-min (or longer) exposure to 100 db SPL was the same whether the exposure was preceded by 1 hr of (a) silence, (b) 60 db SPL, or (c) 70 db SPL. Apparently “latent” effects can be observed only when the principal (second) exposure is of short duration and high intensity. It is shown that this conclusion is in accord with present knowledge concerning the laws governing the growth and decay of TTS. (This study was supported by research grant B-1122 from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)
Residual Effects of Low Noise Levels on the Temporary Threshold Shift
Authors: Trittipoe W. J.
Published: September 2005

Can a sound level which itself is insufficient to produce a temporary threshold shift (TTS) modify the recovery threshold to a more intense sound? TTS measurements were obtained following two conditions of high-level noise exposure: (1) a control condition in which a period of silence followed a broad-band noise exposure; (2) an experimental condition in which the same exposure was followed by noise levels which alone produce no measurable TTS. A 3-min exposure to a noise level of 120 db SPL was followed: in the control condition, by a 3-min exposure to silence; and in the experimental condition, by a 3-min exposure to noise levels of 70 and 80 db SPL, which alone produced no measurable TTS. Threshold measurements were obtained for 16 ears at 4000 cps before and after noise exposure, for post-exposure durations from 1 to 10 mins. Statistical evaluation demonstrated highly significant differences between the results of the experimental and control conditions. We interpret this finding as answering the initial question affirmatively.
When Sonar was Called Submarine Signalling
Authors: Batchelder Laurence
Published: September 2005

In the decade preceding the conclusion of World War II, sonar advanced from an empirical art to a rational science. This important branch of applied acoustics was isolated from its brothers by a strong wall of security. That wall has been penetrated occasionally in the later years, but the section built before 1946 has only recently been removed by U. S. Department of Defense Directive 5200.9. Now that we are free to do so, it is amusing, and perhaps instructive, to recall the early developments of modern sonar, and the framework of comparative ignorance in which they were achieved. This historical review exemplifies the vital role of measurements in any technological advance.
Instrumentation and Techniques for Oceanographic Acoustic Surveys by Aircraft
Authors: Coop J. J.
Published: September 2005

Since two-thirds of the earth's surface is covered with water, surveys of variable oceanographic features such as propagation of sound, temperature variations, bottom scattering, bottom bounce, and ocean currents by use of aircraft would be highly desirable provided suitable instrumentation and techniques could be developed. The simultaneity of data would provide a picture impossible to obtain from ships. This paper describes instrumentation suitable for use by aircraft to obtain the following types of data: ambient noise, marine biological noise, acoustic propagation, bottom reflection, bottom scattering, ocean depth, bathythermograph (B.T.), and velocity gradient. Sonobuoys are used to provide contact with the water. The sound sources are explosive charges which provide a broad band of acoustic energy having a known spectral distribution and level. The frequency distribution of the bottom reflection as a function of time and ocean depth as well as the rate of decrease obtained from aircraft are shown. The vertical temperature gradients can be obtained by means of an acoustical telemetering bathythermograph (B.T.) unit which sinks at constant speed. It is estimated that an aircraft could measure the various acoustic parameters described in intervals of 25 miles along a 1500-mile flight path in one day. A discussion of data types and data analysis will be given.
Sound Transmission Characteristics of a Layered Wall Construction
Authors: Kurtze G. , Watters B. G.
Published: September 2005

It is well known that the transmission loss of most solid, isotropic walls is seriously limited by the high dynamic stiffness and the correspondingly fast speed of bending waves in a stiff wall. On the other hand, while a relatively limp wall will have a significantly higher transmission loss due to the lower bending wave speed, it may not be acceptable to the architect because of the low static rigidity. A new construction has been found which has high static stiffness but drastically lowered dynamic stiffness, thus permitting the simultaneous satisfaction of both acoustical and architectural requirements. The change in stiffness is effected by establishing a “shear-wave” motion of the core of a layered construction. A shear wave has a speed which is independent of frequency. Thus, the speed of transverse waves is constant over the frequency range in which this type of motion predominates. If the shear wave speed is chosen to be suitably low, the wall impedance is essentially massive in this frequency range. This construction is expected to have important applications especially in the field of architectural acoustics. Measured data on some particular embodiments of the idea will be presented.
Lightweight Walls Having High Transmission Loss
Authors: Kurtze Gunther , Farrell W. Ranger , Watters Bill G. , Hirtle Parker W.
Published: September 2005

This paper describes a single wall which, by proper distribution of massive elements on light, stiff plates, provides higher transmission loss than predicted by mass law for limp constructions. With sufficiently low damping, the masses and the unloaded plate areas will, at resonance, oscillate 180° out of phase. With uniform spacing of the masses, the average displacement of the wall would be zero, thus theoretically providing infinite TL at one frequency. A random mass distribution gives improved TL over a wider range of frequencies. At higher frequencies, mass law predictions will not be reached. The behavior of this construction can be represented by an inductance (mass) coupled in parallel with a capacitor (stiffness). Prototypes have been constructed and measured to corroborate the theory and the data are given.
Explanations from Theory for Differences between Laboratory and Field T. L. Data
Authors: Beranek Leo L.
Published: September 2005

A discussion of factors that influence the difference between laboratory and field transmission loss data is presented making use of recent theoretical information. Included will be a discussion of single-wall and double-wall constructions, both with and without damping and added sound-absorbing material.
On Signal Detection, Signal Perception, and Ideal Observers
Authors: Mathews M. V. , David E. E.
Published: September 2005

Recently a number of perception studies in which a subject is asked to determine whether a stimulus consists of noise or noise plus a sinusoid have been analyzed as statistical hypothesis tests. The subjective results are frequently compared with a mathematical model, called an ideal observer, which achieves the optimum detection based on 2TW samples of the stimulus, where T is the duration and W is the band width of the stimulus. A maximum-likelihood detection model is developed which utilizes more than 2TW samples and achieves better detection than the ideal observer. The implications of this result in signal perception experiments are considered.
Operating Characteristics Determined by Binary Decisions and by Ratings
Authors: Egan James P. , Schulman Arthur I. , Greenberg Gordon Z.
Published: September 2005

With the theory of signal detectability as a framework, two psychophysical experiments were conducted in which each observation interval was well defined for the listener. Each interval contained noise, and it either did or did not (p=0.5) contain a signal (1000 cps, 0.5 sec in duration). In separate sessions of the first experiment, either the listener gave a yes-no decision or he responded with a rating (1–4) after each observation interval. Operating characteristics were obtained with E/N0 equal to 15.8. It is clear from the data that the trained listener can perform as well when he adopts the multiple criteria necessary for the rating method as when he adopts the single criterion required by the binary-decision procedure. In the second experiment, only the rating method was used to determine the relation between d′ and E/N0. The resulting function, for d′ ⩽ 3.0, approximates a straight line which passes through the origin and which has nearly the same slope as that obtained in other laboratories. [This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, under Contract AF 19(604)-1962.]
Decay Characteristics of Piano Tones
Authors: Sabine Hale J.
Published: September 2005

Measurements have been made on a high-quality spinet piano to determine the initial amplitude and decay characteristics of the principal harmonic components of notes covering the entire scale. Decay rates of individual components varied from 1 to 100 db/sec as a function principally of frequency and string position in the scale rather than of harmonic number. An exception was noted in the third to fifth octaves, where the fundamental of a given string decayed at a considerably higher rate than the harmonics. This pattern appears to have a strong influence in determining typical piano tone in this region. Frequency spectra of the initial amplitudes of individual notes over the entire scale show, on the average, a sharp cutoff below 100 cps, a fairly flat region between 100 and 1000 cps, and a roll-off of at least 12 db per octave above 1000 cps, with negligible energy above 8000 cps.
Discrimination after Auditory Cortex Ablation
Authors: Goldberg Jay M. , Neff William D.
Published: September 2005

A neural model is proposed to describe the activity of subcortical auditory centers in the cat after auditory cortex removal. In the model it is assumed that, at any level of the auditory system, tones of different frequencies excite, at least in part, different neurons; and the higher the sound intensity of a tone, the more neurons it excites. It is also assumed that there is a decrement in response (habituation) to repeated stimulation such that the neural response to a tone shows a decrease in size when the tone is repeated once every few seconds for about a minute, but not for intervals much shorter than a minute. The habituation process is confined to those neurons stimulated by the tone. The events which take place during different discriminatory tasks can be reconstructed by means of the model. When this is done, it is found that all auditory discriminations which have been relearned after cortical ablation have the common property that the neural responses to negative and positive stimuli differ in size, and, moreover, this is a property not possessed by discriminations severely impaired by such a lesion. (This research was supported by the Office of Naval Research and the U. S. Air Force Office of Scientific Research.)
Closure of the Cochlear Windows: Its Effects upon Bone Conduction in Cats
Authors: Tonndorf Juergen , Tabor James R.
Published: September 2005

CM-responses were recorded in cats for seven frequencies between 150 cps and 7500 cps by means of differential electrodes in the basal cochlear turn. Both air- and bone-conducted signals were used. The cochlear windows were closed by means of dental cement (the round-window membrane being protected by silicone grease). A good seal was assured by (a) careful removal of the muco-periost under microscopic control and (b) by anchoring the cement plug against the walls of the bulla or middle-ear, respectively. Closure of either window resulted in a drop of BC responses of approximately 10–15 db. Additional closure of the other window had no noticeable effect unless the cochlear aqueduct had also been sealed off. In that latter case, additional response losses of approximately 5–8 db were observed. In no instance was it possible to abolish the response to BC sounds to the same degree (50–60 db) as was accomplished with respect to AC sounds by closure of the oval window alone.
Effect of Shock and Vibration Testing Techniques on Equipment Reliability for Aircraft and Missiles
Authors: Levy Samuel
Published: September 2005

This paper is a survey of present state of the art of obtaining high reliability by vibration and shock testing. Equipment for exciting a prescribed vibration or shock environment, and the instrumentation used to monitor the level of excitation, are important aspects. Examples of improvements in equipment reliability achieved by testing and redesigning are described. Current shock and vibration environmental specifications for different types of vehicles are discussed in relation to ground, airborne, and re-entry environments. Gross vehicle dynamics have an effect of modifying the component vibration and shock levels. The use of mechanical impedance concepts and the design of attachments are closely related to this change in levels. Typical components fragility curves are presented; reliability improvements are achievable by the proper “marriage” of these to structural resonance curves. The relationship between test duration and vibration amplitude for a given degree of fatigue damage is an important problem. The role of “operational assurance” and “qualification” testing in achieving flight reliability is evaluated.
Application of Impedance Methods to a Vibration Isolation Problem
Authors: Hixson Elmer L.
Published: September 2005

Three important factors in a vibration isolation problem are the characteristics of the vibrational source, the structure at the point of attachment, and the coupling element or isolator. The structure is considered a single port element and is represented by its driving point impedance. The source is considered an active single port element, and it is represented by a Thevenin or Norton equivalent circuit determined from measurements. Isolators are considered passive two ports and are represented by π or T equivalent circuits as determined from measured impedance or mobility parameters. The first step in isolating a small electric motor from a nonrigid structure was to determine the impedance representations by direct measurements at the points of connection. Then the motion of the structure was predicted and measured as a reference for isolator effectiveness. After considering the characteristics of the source and the structure, a simple isolator was designed. The effectiveness was predicted and then measured. The equivalent circuits of several other isolators, including commercial types, were determined and their effectiveness measured.
Analysis of Dynamic Systems Using the Mechanical Impedance Concept
Authors: Sperry William C.
Published: September 2005

The mechanical impedance concept is a powerful tool for the analysis of dynamical structural systems consisting of a single degree-of-freedom unit coupled to an infinite degree-of-freedom unit. Actual systems of interest that approximate this are (1) instrument components coupled through isolators to the vibrating shell of aircraft or missiles with the inherent problem of predetermining the dynamic forces acting upon the component, and (2) vibrating machinery coupled through isolators to the hulls of marine vessels with the inherent problem of minimizing the sound radiating into the sea. Formulas are presented for each case with damping included by rheological models. The quantities of the formulas can be measured if the continuous supporting unit is undefined. Simpler theoretical analyses result for defined continuous units than for the usual classical approaches. No approximations are made beyond those of classical linear continuum mechanics. (This research was supported by Armour Research Foundation.)
Suggested Sampling Procedure for Estimating Shallow Water Ambient Noise
Authors: Dietz F. T. , Kahn J. S.
Published: September 2005

On the basis of a 1-yr seasonal analysis of shallow water ambient noise, performed in Narragansett Bay, Rhode Island, and sponsored by the Office of Naval Research, estimates of the components of variance, associated with any random observation of shallow water ambient noise, were made for frequencies in the range 40–10 000 cps. For frequencies less than or equal to 150 cps, the variability associated with differences among days is not significantly different from zero, whereas the variability due to weeks is significant. On the other hand, for frequencies above 150 cps, the contribution to the ambient noise spectrum by weekly variability is considered not significantly different from zero, while the contribution due to days is. On the basis of the estimates of these components of variance, recommendations for future samplings of shallow water ambient sound are made based on the ratio of the variability of the specific variance component to the experimental error.
Building up of Flow Noise and Its Spectrum
Authors: Haddle G. P. , Skudrzyk E. J.
Published: September 2005

When a vehicle is set in motion, its flow noise level increases with the speed. If the surface is rough, flow noise level increases with speed and without any noticeable time lag. If the surface is highly polished, it takes a few seconds for the flow noise to build up. As a consequence, the level of the flow noise and its spectrum are dependent upon the history of the flow before the flow reaches the sound receiver. The amplitude distribution of the flow noise turns out to be very nearly Gaussian. However, in certain instances flow noise is emitted in bursts. Experimental results will be presented.