bluuebunny/crossref_metadata_2025 huggingface dataset:
In-duct fan sound power measurement systems
Authors: Crocker Malcolm J. , Wang John S. P.
Published: October 2005

The sound power from ducted and nonducted fans is still mainly measured in reverberant rooms. However, much work has recently been complete on developing in-duct standard measurement methods. Such methods are very desirable, owing to reduced cost and increased convenience. All the main measurement problems—flow noise, duct-end reflections, and cross modes—have now been sufficiently overcome so that it is anticipated that the proposed in-duct standards ISO/TC/43/SC1 and ASHRAE 68 P can soon be adopted. Based on the work of Wang and Crocker—and of Neise in Berlin-the Brüel & Kjær Company has built a microphone wind-screen (sampling tube) for the suppression of flow noise for use in these standards. This paper discusses the performance of this Brüel & Kjær sampling tube and the problems which are involved in in-duct sound power measurements. Some results are also given which compare the sound power of the same fan measured using AMCA Bulletin 300-67, “Reverberant Room Method,” and the ASHRAE 68 P In-Duct Proposed Standard. [Work supported by the Air Conditioning and Refrigeration Institute and the Air Moving and Conditioning Association.]
Behavioral audiometry in the guinea pig: implementation of shiver audiometry
Authors: Crockett R. S.
Published: October 2005

The guinea pig, like its more costly relative the chinchilla, has been widely utilized in anatomical and electrophysiological studies of the normal and pathologically altered auditory system. However, attempts to assess hearing in this species through behavioral audiometric techniques 'have met with limited success. One notable exception to this tradition is the “shiver audiometric” procedure originated by Anderson and Wedenberg [Acta Otolaryngol. 60, 375 (1965)]. This paper describes the technique, critical variables, and limitations associated with its use, and modifications to enable automatic data recording and reduction. The audibility curve and its reliability obtained through shiver audiometry on a normal guinea pig population are presented and compared with those derived from other techniques.
Asymptotic temporary threshold shift in chinchilla measured by the auditory evoked response
Authors: Woodford C. M. , Henderson D. , Hamernik R. P.
Published: October 2005

Monaural chinchilla were exposed to octave-band noise (4 kHz center frequency) at 80 dB SPL for 96 hours. Quiet thresholds at 1, 2, 4, and 8 kHz were estimated before, during, and after the noise exposure using the auditory evoked response technique. The greatest threshold shift that was measured occurred at 24 hours after noise onset; then hearing level recovered by approximately 5 dB to an asymptotic level. After cessation of the noise, hearing returned to normal by 72 hours. The results agree with previous behavioral studies of asymptotic TTS [Mills, “Threshold Shifts Produced by Exposure to Noise in Chinchillas with Noise-Induced Hearing Losses,” (in press)] in showing comparable levels of TTS, and also that the hearing level during the noise exposure is determined by the level of the noise rather than the animal's preexposure threshold. [Study supported by Grant No. 1RO1 OH 00364-01, National Institute for Occupational Safety and Health, Public Health Service, Department of Health, Education and Welfare.]
Variations in bone-conduction responses with contact area and contact pressure
Authors: Khanna Shyam M. , Tonndorf Juergen , Queller Judith
Published: October 2005

A magnetostrictive vibrator was used that was described earlier [J. Acoust. Soc. Am. 51, 124 (1972)]. It has wide frequency and intensity ranges. BC thresholds as well as sound pressure readings in the ear canal (to assess vibratory skull responses) were taken with reference to acceleration measured at the input, i.e., at the forehead. Response variations were reduced by a number of improvements in the suspension of the subject's head in relation to the vibrator. In terms of acceleration at the forehead, BC thresholds and sound pressures in the ear canal still varied considerably and systematically with changes in contact area and, to a lesser degree, with contact pressure. The latter kind of variation was reduced, and overall sensitivity improved, when a relatively stiff grease was applied between vibrator and skin in an effort to improve coupling. The results indicate once more that monitoring acceleration at the contact point is not a reliable way of predicting BC responses. [Supported by NIH and DRF grants.]
Considerations of the pathophysiology and histopathology of deafness associated with decompression sickness and absence of middle-ear barotrauma
Authors: McCormick J. G. , Holland W. , Holleman I. , Brauer R.
Published: October 2005

Dr. J. Donald Harris has previously speculated in the literature that, based on clinical impressions, a group of Navy Divers with post-dive deafness and/or vestibular attacks may have suffered inner-ear hemorrhage. We have found hemorrhage in the inner ear of a guinea pig sacrificed 16 days after a post-dive vestibular attack with cochlear potential function loss. In terms of potential treatment for human divers it is important to determine how soon after the onset of an attack inner-ear hemorrhage can occur. We now have an additional guinea pig with a severe post-dive cochlear potential loss which was sacrificed for histology at 21 hours post-dive. This animal shows a plasma exudate in the inner ear, but no red cells are present. The similarity of these two pathology cases to the results of sympathetic nervous system stimulation by Seymour and Tappin reported in 1953 is discussed. We also consider the possibility that hypercoagulation, embolic, and thrombotic problems may be involved in the etiology of the diving-deafness syndrome. Preliminary results of post-diving deafness treatment with urokinase and urokinase plus heparin are also discussed.
Optical-lever measuring laser microscope
Authors: Jako G. J. , Cook Reginald O.
Published: October 2005

Measurement of peak amplitudes, waveform shape, slope, frequency sensitivity, and phase differences along the ossicular chain and basilar membrane have long been sought by auditory physiologists investigating cochlear hydrodynamics and neural encoding. Since reports by one of the authors in 1966 and 1967 on the use of noncontact optic-lever systems for making microdisplacement measurements in the ear, advances in laser, solid-state electro-optic, fiber optic, and longer-working-distance lens technology have made possible more sensitive and practical recording optic-lever systems. This paper describes design and use of an optical-lever system utilizing single or multiple laser beams and photodetectors capable of simultaneously resolving vibration of points only 100 μ separated. Micropositioning and optical scanning devices allow x, y scanning along the basilar membrane. Advantages and disadvantages of optic-lever systems versus laser interferometers for noncontacting microdisplacements are discussed.
Language communication skills of deaf children
Authors: Carp J. , McGarr N. , Levitt H.
Published: October 2005

One hundred and twenty 10-year-old deaf children received a comprehensive battery of tests to measure speech and language skills. The test battery included measures of syntatic comprehension (as developed by S. Quigley and associates, Illinois Institute for Exceptional Children), written language samples, tests of speech reception, speech production, and speech reading of words, sentences, and phrases. An analysis of proximities showed a high degree of clustering between all the language measures and a moderate degree of clustering between the communication measures. Of the latter, speech reading of sentences and phrases showed the highest correlation with the language measures, [Research supported by New York State Education Department, CREED Project ED 73-001DC.]
Computer simulation as a diagnostic tool in language evaluation
Authors: Levitt H. , Stromberg H. , McGarr N. , Carp J.
Published: October 2005

The language of congenitally deaf children is generally less advanced and contains many more errors than that of hearing children. Because of the complex structure of language and the many types of errors that can occur, it is not always clear which errors or syntactic forms should receive special attention in teaching for the most rapid improvements in language. An attempt was made to obtain such information by means of computer simulation. Samples of the written language of several deaf children were entered into the computer together with syntactic corrections, suitably coded, whenever an error occurred. The computer then reproduced each child's written sample several times, systematically eliminating various errors and combinations of errors. The modified versions of each written sample, which covered the range from original to a completely corrected sample, were then rank ordered in terms of overall quality. From these rankings it was possible to determine on a child-by-child basis which errors, if eliminated, would produce the greatest improvements in the child's language. In addition, statistical analyses can be performed to determine the most common error types both between and within children. [Supported, in part, by New York State Education Department, CREED Project ED 73-001DC.]
Prosodic feature reception and production in deaf children
Authors: Stark R. E. , Levitt H.
Published: October 2005

Errors in prosodic features are particularly severe in the speech of deaf children. However, significant information on prosodic features is contained in the lower frequencies which may be within the deaf child's range of residual hearing. This study examined the interrelationship between the reception and production of stress, intonation for yes-no questions, and location of pausal juncture. Performance was poor both in reception and production, the highest error rates occurring with intonation. There was some evidence of a systematic relationship between prosodic errors in reception and production.
Interjected sounds in deaf children's speech
Authors: Smith Clarissa R.
Published: October 2005

Recordings and phonetic transcriptions of deaf children's speech were examined for nonstandard interjected elements associated with consonant production. Vowel release of both stop consonants and fricatives is found in word-final position and between abutting or normally blended sounds, particularly where assimilation ordinarily occurs, such as between stops or between a stop and fricative. A lateral /1/ is also used as a release. Stop positions are arrived at too slowly, introducing a fricative of similar place and voice. A stop released with overeffort produces an affricate. A fricative may be preceded by a stop of similar place and voice. Cessation of nasality without movement from a position produces a plosive following the nasal sound. Extra nasals are inserted before or after a stop in the same place. The substitutions in deaf children's speech often result from undershoot of the articulatory target. Some interjected elements apparently represent overshoot, which may be due to conscious effort at articulatory placement, while others stem from slowness of movement of the articulators.
Preliminary research with a three-channel vibrotactile speech-reception aid for the deaf
Authors: Miller James D. , Engebretson A. Maynard , DeFilippo Carol L.
Published: October 2005

Envelopes of signals from (1) an accelerometer attached to the talker's nose, (2) a microphone near his mouth, and (3) an accelerometer attached to his throat (see Nickerson and Stevens) were multiplied by a 100-Hz square wave and the products were used to drive three vibrators. Normally hearing subjects with simulated total loss of hearing for speech felt signals on vibrator 1 proportional to the amplitude of vibration in the talker's nose, on vibrator 2 proportional to the amplitude of sound near the talker's mouth, and on vibrator 3 proportional to the amplitude of vibration in the talker's larynx. The vibrators were on separate fingers of the same hand or on a single finger. When the three-channel aid is used with lipreading, scores on syllable and word tests are better (sometimes dramatically) than with lipreading alone. Improvement is demonstrated for nasal/oral, voiced/voiceless, and continuant/interrupted discriminations. Variations in vowel duration as with voiced and voiceless final consonants are clearly felt. [Supported by Grant No. 03856, National Institute of Neurological Diseases and Stroke, Department of Health, Education and Welfare.]
Signal processing for perceptive deafness: improving speech intelligibility in the presence of interference
Authors: Villchur E.
Published: October 2005

The frequency/amplitude coordinates of amplified speech, plotted against the average frequency/amplitude span of residual hearing of six deaf subjects with recruitment, are projected to proportionate positions in the corresponding normal span of hearing. Speech with and without interference has been processed to conform to the projection, using a bank of expanders followed by a treble attenuator, to simulate for normal listeners the abnormal loudness relationships in speech perceived by the deaf subjects. The lack of redundant recognition cues in this processed speech (and by implication, in speech as perceived by deaf subjects) decreases the resistance of the intelligibility to interference: If the number of recognition cues available to the listener is insufficient or barely sufficient for intelligibility under ideal conditions, he cannot afford to lose further cues to destructive influences. When the processed speech is corrected by amplitude compression plus frequency equalization, the intelligibility becomes less vulnerable to the interference, even though compression has reduced the signal-to-interference ratio. Such processing has increased deaf-subject tolerance to interference. Validation of the analogy by deaf subjects is described. The simulation of recruitment, and of hearing-aid processing, will be demonstrated.
Solution of an integral equation in random rough surface scattering theory
Authors: DeSanto John A. , Shisha Oved
Published: October 2005

A one-dimensional singular integral equation which appeared in a previous paper on random rough surface scattering theory [J. Math. Phys. 13, 1903 (1972)] is solved numerically using quadratic splines. Its solution yields an approximation to the coherent (specular) scattered intensity for plane wave incidence on the surface. This approximate scattered intensity is plotted versus the Rayleigh factor Σ = k0σcosθi, where k0 is the wavenumber of the incident plane wave, σ is the surface root-mean-square height, and θi is the angle of the incident plane wave. For values of Σ > 1 this approximation yields more coherent intensity than the Kirchhoff approximation.
Theoretical modeling of reflection loss from ridged sea ice
Authors: Diachok O. I.
Published: October 2005

A theoretical model of underwater acoustic reflection loss from ridged sea ice has been developed using the method of Twersky [J. Acoust. Soc. Am. 29, 209–255 (1957)]. Ridges are represented by a distribution of randomly spaced elliptical half-cylinders. An approximate solution for reflectivity as a function of grazing angle and ridge depth, width, and number per unit distance has been obtained for the case where the average ridge spacing, the average ridge depth, and the average plate thickness are large compared to wavelength. Using this frequency-independent equation, reflection loss was computed over the measurable range of ridge characteristics for comparison with the results of coincident measurements of reflection loss and ridge parameters. Good agreement between the theoretical computations and experimental measurements demonstrates the applicability of this theory to model under-ice reflection loss. Some of the limitations of this model, and the problems involved in experimental determinations of sea ice ridge characteristics and acoustic reflection loss are discussed. Theoretical modeling of under-ice reflection loss for the case where wavelengths are large compared to average ridge depth and the average plate thickness is also considered.
Geographic patterns in volume reverberation spectra in the North Atlantic between 33°N and 63°N
Authors: McElroy P. T.
Published: October 2005

Volume reverberation observations were made at 34 stations on Cruise 105 of R/V CHAIN during its passage from Newfoundland to the Azores, and thence to Portugal and Ireland. The acoustic returns at each station were analyzed in 16 1/3-octave bands extending from 1 to 31.5 kHz to yield column strength spectra. Representative spectra are given. Using a measure we have called the cross-standard deviation, we found evidence that the spectra for nearby stations were similar and thus could be classed in geographically based groups called pelagic regions. This is reasonable, since much volume reverberation is sound scattered from animals which in turn are distributed in pelagic faunal regions. We present a matrix showing the similarity of each pair of stations; a small number indicates similarity, while a large number indicates difference in the two spectra. We have identified many of these regions on the basis of physical-oceanographic features such as the polar front. These features are used in defining boundaries for the regions.
Prevalence of impaired hearing versus age and sound level at work
Authors: Botsford James H.
Published: October 2005

An equation relating prevalence of impaired hearing to age and sound level at work has been derived. It is based on the assumption that the probability of developing impaired hearing at any age is proportional to the fraction of the population of that age which has already developed impaired hearing. In other words, the stress on the auditory system of living to any age is indicated by the prevalence of impaired hearing at that age. If there is also exposure to dangerous noise, the probability of impairment occurring increases with severity of exposure. The solution of the differential equation resulting from these assumptions reveals a complex relationship among age, noise exposure, and impairment. The effects of age and noise are shown not to be simply additive, as is often assumed. Also, the prevalence of impaired hearing in the working population is shown to increase 0.8% with each dBA rise in sound level at work.
The advantages of using four octaves versus three octaves for calculating speech interference levels (SIL)
Authors: Webster J. C. , Cluff G. L.
Published: October 2005

Three sets of preferred frequency octaves have been proposed to replace the old 600–4800-Hz SIL calculation; 500, 1000, 2000 (3L); 500, 1000, 2000, 4000 (4); and 1000, 2000, 4000 (3H). Similarly, sets of frequency weighting contours have been proposed as substitute weighting networks (for A-level) for sound level meters. One hundred twelve environmental noises were adjusted in level to get equal articulation indices (AIs) of 0.1, 0.2, … 0.9. For each of six C − A groupings of noises 3L, 4, 3H SIL, and SI-50, 60, 70, 80, A and D weighting measures were calculated at each AI level. Standard deviations of calculated levels show that except for C − A ⩾ 15 dB (1) the 4-band SIL is the best estimate of AIs between 0.3 and 0.6; (2) the 3H SIL is generally best for higher AIs and the 3L for lower ones (and when C − A ⩾ 15 dB). When averaged over all AIs and over all C − A levels the 4-band SIL gives the best estimate of AI (av SD = 1.2 dB) followed by 3H (1.5 dB), SI-60 (1.9), 3L (2.1), and A (2.2). No speech intelligibility tests were run to verify the validity of these findings.
Effects of a traffic noise background on judgments of aircraft noise
Authors: Powell C. A. , Rice C. G.
Published: October 2005

Subjects were asked to rate their annoyance to recorded aircraft noises when combined with several levels of road traffic noise in two sets of numerical category scaling tests. The aircraft and traffic noise levels were typical of a closed-window indoor environment. For one set of tests, the mean background noise level was continuous, whereas for the other set of tests the mean background noise level was changed between each aircraft noise. Under the continuous background noise conditions, the rated annoyance was found to decrease consistently with increasing background noise level. For example, when the aircraft and traffic noise levels were of equal Intensity, the reduction in annoyance was the equivalent of a 5-dB reduction in aircraft noise. For the discontinuous background tests, no consistent change was noted. Regression analyses of the subjective annoyance ratings showed high correlation with the incremental noise pollution level, LNP, developed by D. W. Robinson [NPL Acre Report AC49 (1971)].
Community response to elimination of nighttime aircraft noise
Authors: Smith H. G. , Meecham W. C.
Published: October 2005

About a year ago night flight patterns were changed at Los Angeles International Airport so that approach and takeoff operations were carried out largely over the ocean, relieving hundreds of thousands of residents in the vicinity of the airport of nighttime jet noise. We undertook a sample telephone survey of the approximately 100 000 residents within the 90-dBA contour about the airport to determine their reactions to this change. On the question “How do you feel about returning to the old night flight patterns?” we found 71% in favor of present patterns, 15% wishing to switch back, and the remainder with no opinion. On the question “Has your home seemed quieter at night?” we found 52% answered yes, 37% answered no, and 11% with no opinion. Many of those answering no remarked, in effect, that the noise was so intense during the day that the night changes made little difference. These findings are in keeping, qualitatively, with widespread public community approval of the removal of (at least) nighttime jet noise from those areas. Fidell and Jones in a similar study [J. Aconst. Soc. Am. 53, 446(A) (1974)] reported, “No appreciable effects were noticed in terms of reduction of annoyance,” a result substantially negated by our study. We believe their surprising findings may be caused by sample-content errors and perhaps less-than-incisive questioning.
Nonlinear Aspects of Wind Instrument Regeneration
Authors: Benade A. H.
Published: October 2005

During the past decade considerable progress has been made in following up observations by Bouasse on the coupling of air column modes of a musical instrument by the nonlinear reed flow-control characteristic. For brasses and single-reed woodwinds, the internally generated pp-mf spectrum is of the form pn ∼ p1nZn, where Z is the air column impedance at the frequency of the nth component. The transformation to the radiated spectrum is mediated by the tone hole (or bell) cutoff frequency. Harmonically related air column resonances promote prompt attack, stable pitch, full tone, and good dynamic range. Slightly inharmonic resonances can lead to pitch changes with dynamic level, as in the clarinet low register. The action of register keys is explained in terms of properly arranged impedance peaks and dips. Register change criteria are different for pianissimo and forte playing levels, and can be demonstrated separately. The trimming-up of good wind instruments to make them excellent has been ak matter for craftsman's skill and intuition. He has unconsciously used criteria which are coming to have a scientific explanation.
New low sound velocity magnetostrictive transducer
Authors: Sinsky J. A. , Huston E. L.
Published: October 2005

The magnetic and magnetostrictive properties of a magnetostrictive scroll wound ring transducer made from “cube textured” nickel developed by Inco were measured and compared to the corresponding properties of a conventional nickel ring transducer. The conventional ring was fabricated by the Naval Underwater Systems Center and the “cube textured” ring; with nearly identical dimensions, by Inco. Both transducers were separately excited in air under identical conditions and their electrical input impedances measured with a pulse vector immittance meter. Using Butterworth and Smith and NDRC analyses of a magnetostrictive ring transducer, the following parameters were obtained as a function of the bias induction (1 ⩽ B ⩽ 5kG): sound velocity, Young's modulus, reversible permeability, effective coupling coefficient, magnetostrictive and stress sensitivity constants. The Young's modulus of the “cube textured” ring was 40% lower than that of the conventional nickel ring, resulting in a 20% lower sound velocity and radial resonance frequency. This reduction was obtained without any appreciable sacrifice of electrochemical coupling coefficient or magnetostrictive constant. The “cube textured” ring also exhibited a much lower loss angle.
Acoustic slow waveguide antenna
Authors: Rogers Peter H. , Trott W. James
Published: October 2005

The acoustic analog of the dielectric rod antenna for electromagnetic radiation is investigated both theoretically and experimentally. In acoustics, a cylinder of silicone rubber (whose bulk sound speed is about two-thirds that of water) is analogous to the dielectric rod. An acoustic wave in the direction parallel to the axis of the waveguide is concentrated within the guide by progressive refraction. A hydrophone (whose free-field sensitivity is omnidirectional) is attached near one end of the waveguide and detects this concentrated radiation as a gain in signal for this direction relative to any other direction. Similarly, if the slow waveguide is attached to an acoustic source, it will enhance the source level in the direction of the waveguide. The antenna is mathematically modeled by coupling the surface Helmholtz integral equation appropriate to the region within the silicone waveguide to a similar equation for the water region exterior to the cylinder (which includes the point hydrophone) by requiring continuity of acoustic pressure and normal velocity on the common surface. The coupled integral equations are solved numerically. Predicted beam patterns and directivity gains are in excellent agreement with experiment.
Synthesizing of tilted beams using phase-symmetric and phase-antisymmetric directivity patterns
Authors: Hughes W. J. , Thompson W.
Published: October 2005

It can be shown that by combining particular amplitude shaded phase-symmetric and phase-antisymmetric directivity patterns, one can obtain a tilted beam without delay lines or numerous phase shift networks. Experimental verification of this concept has been obtained where both sum and difference directivity patterns were tilted to various angles off axis. The phase-symmetric and phase-antisymmetric directivity patterns must be combined in phase to form a tilted beam. Consequently, because they are inherently in phase quadrature with one another, one of the pattern signals must be phase shifted by 90° before the two signals are combined. This concept is analogous to the formation of a tilted beam using numerous, phase shift networks in that the angle of tilt varies with frequency. Analysis of the data indicates that low sidelobe levels can be maintained only over restricted tilt angles. The dependency of the tilted beams on variations in frequency and in the 90° phase shifter are also investigated. [Supported by Naval Ordnance Systems Command.]
Portable anechoic shield for measuring transducer vibration sensitivity
Authors: Marciniak R. D. , Reeser F. D. , Thompson W.
Published: October 2005

A unique facility at the Applied Research Laboratory (The Pennsylvania State University) is the Machinery Quieting Laboratory (MQL), where various measurements may be made on submerged, tethered, powered experimental underwater vehicles with simulated propulsor shaft loading. In the present application, it was desired to evaluate the contribution to vehicle self-noise generated by the power plant which propagates to the transducer via structural paths rather than through the water path. To obtain valid results, it was therefore necessary to blind the transducer to water-borne sound while, at the same time, insuring that the transducer elements remained acoustically loaded by an anechoic medium. To fulfill these requirements, a large floodable wooden chamber was fabricated which measured 16 × 16 × 12 wavelengths at the frequency of interest. Additional interior absorption in the form of wooden wedges was incorporated and the exterior was completely covered with cell tire neoprene rubber to form a pressure-release reflecting surface. The design, evaluation, and use of this anechoic shield in the MQL are described. [Supported by Naval Ordnance System Command.]
Jet propulsion for quiet aircraft
Authors: Bossler F. Bert , Smith D. L.
Published: October 2005

A novel method of jet noise reduction has been subjected to bench and wind tunnel tests. This patented method uses very small nozzles arranged on struts protuding from the upper surface of an aircraft wing. Bench tests included various arrangements of nozzles on each strut; tests with heated air; tests of noise power and directivity versus number of struts, strut spacing, and location of struts on a simulated wing; and tests of discharge coefficients and velocity coefficients. Wind tunnel tests included induced aerodynamic effects of upper-surface blowing, effects of tunnel flow on discharge and velocity coefficients of the nozzles, acoustic effects of tunnel flow on the jet noise, and effects of jet flow on aerodynamic noise. A full-scale test of aerodynamic noise was made using dummy struts on a sailplane. Preliminary design of a quiet research test vehicle was prepared and its aural detectability was predicted (on the basis of the test data) to be significantly superior to other approaches. Predicted noise levels for 1500-ft flyover were shown to be less than 25 dB (1/3-octave-band SPL) and were dominated by aerodynamic noise of the aircraft wing. [This work was supported by USAFFDL and USAFAPL.]
Noise due to jet motion caused by internal unsteadiness
Authors: Plett E. G. , Summerfield M.
Published: October 2005

The flowfield surrounding a jet is analyzed to determine the noise levels caused by the oscillations of the jet boundary. The jet boundary oscillations are assumed to be a function of pressure oscillations in the chamber upstream of the exit nozzle. A pressure wave is observed to propagate outward from the jet, due to a sudden jet expansion, and a rarefaction follows as the jet surface acceleration decreases. It is concluded that large-scale motion of the jet, observed in some cases, may be responsible for a substantial fraction of the observed noise. Available data are discussed in connection with this noise-generation mechanism, and the expected levels are compared with observed levels. [Supported by ONR Contract N00014-67-A-0151-0029.]
Analysis of noise produced by jet impact near the trailing edge of a flat plate
Authors: McKinzie D. J. , Burns R. J.
Published: October 2005

The sound field produced by the interaction of a subsonic cold gas jet with the trailing edge of a large flat plate is analyzed. The jet issuing from a 2-in.-diameter convergent nozzle impacted the plate seven nozzle diameters downstream from the nozzle exit and one diameter from the plate's trailing edge. The plane of the plate intersected the nozzle axis at 60°. Data analysis was performed to obtain a better understanding of the dominant noise source and the mechanism governing the peak frequency of the broad-band spectra. Results indicate that noise from the plate emanates from two principal sources: first, the impact of the jet on the plate and, second, the flow over the plate's trailing edge. Above a jet Mach number of 0.5, the dominant noise as detected on the impingement side of the plate results from the jet impact (eighth power of the velocity dependence) rather than a trailing edge disturbance (fifth or sixth power of the velocity dependence), which is generally assumed dominant. Also, the frequency of the peak SPL may be governed by a feedback phenomenon, resulting in periodic formation and shedding of ring vortices from the nozzle.
Acoustic loads on an externally blown flap system due to impingement of a TF-34 jet engine exhaust
Authors: Schoenster James A.
Published: October 2005

One of the techniques being investigated in the studies of powered-lift augmentation of aircraft is the use of externally blown flaps. When the flaps deploy, the exhaust of the engine directly impinges on them and is directed downward, providing additional lift. Because of this direct impingement on the flap surface, severe dynamic loads may be induced on the flap elements. To obtain data on these surface loads, a section of a wing and triple-slotted flap system was mounted behind a TF-34 jet engine (nominal thrust of 7000 lb). Fluctuating pressure in the range from 20 to 10 000 Hz, temperature, and static pressure measurements were made at several locations over the span and chord of the second and third flap elements for a typical takeoff flap angle setting—0°, 20°, 40°—and a typical landing flap angle setting—15°, 35°, 55°. The effect of engine power setting was also investigated. The wing and flap sections were of boiler plate construction to minimize the effect of the structural response on the loads measurements. Data are presented showing the overall fluctuating pressure levels and power spectral densities as a function of engine performance. The maximum fluctuating pressures reached levels of 165 dB on the flaps. The spatial distributions of the loads are also presented and discussed. Some comparisons with previous results are discussed.
On the calculation of aerodynamic noise generated by large aircraft at landing approach
Authors: Revell J. D.
Published: October 2005

This paper calculates the aerodynamic noise of large aircraft at landing approach with several motives: (1) to estimate the “noise floor” associated with non-power plant (airframe) noise; (2) to estimate the relative contributions of the various components of the aircraft configuration; and (3) to indicate possible means of noise reduction. Various noise mechanisms are considered, and dipole radiation is found to dominate with both fluctuating Lift and drag forces. The prediction method is semi-empirical, using previously measured gliding flyover noise data as reported by Healy [NASA CR-2377 (to be published)]. In the present theory, the sound power generated by each component is expressed as a fraction of the mechanical power absorbed by the components of drag associated with the major components of the airframe. The prediction method employs a unique approach to defining the spectral peak frequency for the spectrum of each component, and the composite spectrum for the entire airframe is obtained by antilogarithmic summation of component spectra.
Radiation of higher-order acoustic modes into a moving fluid in a duet
Authors: Ingard Uno , Singhal Vijay K.
Published: October 2005

A study of the influence of fluid motion of the radiation of higher-order acoustic modes from a stationary source in a duct is presented. In particular, the ratio between the upstream and downstream higher-order mode amplitudes is calculated. This ratio has been measured for the (1, 0) mode in a rectangular duct at flow velocities from zero to 0.25 times the sound speed. An observed irregularity in the Mach number dependence of the pressure ratio is interpreted as a result of a flow transition which, in effect, alters the boundary conditions at the source. The frequency dependence has also been measured at a fixed-flow Math number of 0.1. [This work was supported by the U.S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-0019.]
Propagation of plane waves in a variable-area duct carrying a compressible subsonic flow
Authors: Davis Sanford S. , Johnson Margaret L.
Published: October 2005

A complete numerical solution is obtained for plane wave propagation in a variable-area duct which carries a mean compressible flow. The equation solved is a matrix formulation of the equation first derived by Tsien in 1952. The solution is uniformly valid in the sense that waves of all frequencies are allowed for in the calculations. Solutions for the two extreme cases of very low frequency (compact element theory) and very high frequency (geometrical acoustics) are computed and compared with analytical predictions. Sample calculations are presented for two particular applications pertaining to aircraft engine silencing technology: the sonic inlet problem and the core noise exhaust problem. For the sonic inlet, the effect of various convergent-divergent nozzle geometries and throat Mach numbers on the acoustic power transferred to the surrounding medium is examined. For the exhaust nozzle, the effect of nozzle geometry and flow on the acoustic power output is calculated. These latter calculations represent an extension of a previous analytic solution [J. Acoust. Soc. Am. 55, 425(A) (1974)] for compact nozzles.
Survey of successive stages of flow noise generation
Authors: Peter Abraham C.
Published: October 2005

A qualitative survey of the successive stages of flow noise generation is presented within the framework of dissipative fluid dynamics. First, the generation of progressive waves, by initially imparting potential and kinetic energies to the acoustic medium, is compared to the formation of convected frictional disturbances by means of removal of the kinetic energy from the fluid (due to the conversion of the energy of motion into heat through friction). The resultant convection of these frictional disturbances, at a velocity which is less than that of the fluid particles, is then related to the relevant thermal processes taking place in the fluid. Finally, the perpetual steepening of the entropy gradients of these convected frictional disturbances causing their collapse and mixing are deduced to be the prime generators of flow noise.
Sound propagation in a nonreacting binary fluid mixture using a generalized Fick's law
Authors: Schwarz W. H. , Huang M. N.
Published: October 2005

Sound absorption and dispersion have been calculated for several binary mixtures of nonreactive gases (monatomic) using a hydrodynamical theory with a generalized form of Fick's law that includes an inertial-diffusive term and viscous-diffusive terms. Three propagating waves are possible, of which type-I corresponds to the classical wave at low frequencies. The absorption coefficients of the type-II and type-III waves are relatively large at these frequencies, so as to make their observation difficult. However, at larger frequencies these waves are shown to attenuate at about the same rate as the type-I wave and, in fact, there is an indication that the experimental results of Prangsma, Jonkman, and Beenakker in argon-helium mixtures were influenced by these waves. The theoretical results were also compared to the two-fluid theory of Goldman and the kinetic theory of Foch, Uhlenbeck, and Losa.
Acoustic gravity wave propagation past the antipode
Authors: Kinney Wayne A. , Kapper Christopher Y. , Pierce Allan D.
Published: October 2005

The previous theoretical formulations and numerical computations of pressure waveforms (such as described by Harkrider, Pierce, and Posey, and others) apply only to atmospheric traveling waves which have traveled less than 12 the distance around the earth. In the present paper, a technique resembling that previously introduced by Brune, Nafe, and Alsop [Bull. Seismol. Soc. Am. 51, 247–257 (1961)] for elastic surface waves on the earth is discussed and applied to the acoustic-gravity wave propagation past the antipode problem. The principal modification to the older theory is a shift in phase of π/2 to the Fourier transform of the wave after it has traveled over halfway round the globe from the source. The source of the wave is presumed to be a nuclear explosion of given energy E. Numerically synthesized waveforms of antipodal arrivals are exhibited and compared with those for direct arrivals. The necessary modifications to the Lamb-mode model theory of Pierce and Posey [Geophys. J. Roy. Astron. Soc. 26, 341–368 (1971)] are also described.
Acoustical analysis of thunder signatures
Authors: Losey R. E. , Bass H. E.
Published: October 2005

Seven thunder signatures resulting from cloud-to-ground lightning strokes have been analyzed in third-octave bands spanning the frequency range from 25 to 500 Hz. Atmospheric absorption was found to contribute significantly to the change in the signature from source to receiver. Although atmospheric absorption is not large, it is frequency dependent, and hence can not be ignored when attempting to reconstruct the source spectrum from measurements taken several thousand feet away. A program has been developed which converts received sound pressure level (SPL) to initial power level (IPL) for given frequency bands. No attempt was made to determine an absolute measure of the acoustic energy released during each event. These initial results indicate that the spectra of different thunder events are sufficiently consistent to allow thunder to be used as a source for studying low-frequency absorption and atmospheric effects which lead to absorption.
Radiation pressure
Authors: Joyce W. B.
Published: October 2005

Simple physical arguments based on adiabatic invariance, energy conservation, and energy quantization are used to describe radiation pressure in a formalism that applies equally to all types of waves and particles. The experimental situation is reviewed, showing that Brillouin's widely accepted acoustical expression (pressure = energy density) is inconsistent with this theory and with analogous measurements on light beams and material-particle beams. Acoustical experiments which appear to confirm Brillouin's expression are shown in every case to have been performed in media where any error in his formula is probably too small for detection, and other media are suggested.
Sound waves through a laminate composite medium
Authors: Rentzepis G. M.
Published: October 2005

The propagation of sound through a laminated composite medium is discussed here. The composite medium itself is characterized by periodicity of material properties in a three-dimensional rectangular lattice, and consists of alternating layers of uniform thickness. The constituents of the composite are elastic homogeneous isotropic bodies. Subsequently, the long-wave equivalent homogeneous elastic medium is constructed. Then influence of geometric and physical distribution of the constituents of the actual composite on the properties of sound propagation are determined.
Gravitational wave analog to the parametric acoustic array
Authors: Westervelt Peter J.
Published: October 2005

The gravitational intensity radiated by a 100% modulated well-collimated and truncated laser beam has been shown by me [JETP Letters 4, 225 (1966)] to be S = (kc−5)PE2(4πR02)−1 {1 − cos[kmL (1 − cosφ)]}[(1 − cosφ)−2sin4φ]n. The crucial nature of this expression is the fact that S vanishes in the forward direction as a consequence of the sin4φ term characteristic of tensor waves. For vector waves and for scalar waves the sin4φ term is replaced by sin2φ and by 1, respectively, and then resonant interaction leads to a Rutherford-like peaking in the forward direction which corresponds, in the scalar case, to the parmetric acoustic array. It is clear that gravitational radiation from ultrarelativistic particles will not exhibit the forward peaking characteristic of electromagnetic radiation from ultrarelativistic charged particles which corresponds to the vector case. [This work was supported by the U. S. Navy Office of Naval Research.]
Source of negative potentials in the organ of Corti
Authors: Bobbin R. P. , Gondra M. I.
Published: October 2005

The organ of Corti of the guinea pig was penetrated by microelectrodes filled with Niagara Sky Blue 6B dye (8%). Negative dc potentials in the organ of Corti were recorded and an attempt was made to determine the source of these potentials by iontophoretically ejecting dye. Evidence that the potentials are recorded from within cells (including hair cells) is presented.
Receptor potentials from the noctuid acoustic receptor
Authors: Adams William B. , Belcher Edward O.
Published: October 2005

A slow potential that is related to the stimulus can be recorded from the surface of the scoloparium of the noctuid acoustic receptor. Evidence of several kinds indicates that the potential is a true receptor potential, corresponding to generator potential activity of the receptor cell. At low stimulus intensities, the receptor potential reflects activity of a single receptor cell. The receptor potential is negative in polarity, consistent with a depolarizing generator potential that is produced by an increase in conductance of the ciliary or dendritic membrane.
Audiometric and histological effects of exposure to three levels of reverberant impulse noise
Authors: Hamernik R. P. , Henderson D. , Woodford C. M.
Published: October 2005

Monaural chinchillas were exposed to 140, 150, or 155 dB peak SPL impulses with 200-msec B-duration. Each animal received 50 impulses, 1/min. Thresholds were estimated by the auditory evoked response technique at 0.5, 1, 2, 4, and 8 kHz before and after exposure. Animals were sacrificed at 30 days postexposure for surface preparation. The 140-dB group sustained no permanent hearing losses and had normal cochleas. The cochleas of the 150-dB group ranged from normal to severe losses of both OHC and IHC. The 155-dB group had consistently large cochlear lesions. The magnitude of cochlear lesions is not always completely reflected in the audiograms. The cocklear lesions induced by the reverberant impulse are compared to the lesions caused by 1-msec and 40-μsec A-duration impulses. Finally, the data are discussed in terms of the present impulse noise damage risk criteria. [Study supported by Grant No. 1RO1 OH 00364-01, National Institute for Occupational Safety and Health, Public Health Service, Department of Health, Education and Welfare.]
Mechanism for continuing degeneration in the organ of Corti
Authors: Bohne Barbara A.
Published: October 2005

Fluid within the organ of Corti is generally believed to be completely separated from endolymph in the scala media by tight junctions which join sensory and supporting cells at the reticular lamina. Damage to the reticular lamina may result in entrance of endolymph into the fluid spaces of the organ of Corti. Because of its unusual ionic composition, endolymph may be detrimental to cell membranes not normally exposed to it. A number of chinchilla ears which had been exposed to noise and allowed to recover for various intervals were examined as whole mounts by phase contrast microscopy for evidence of breaks in the reticular lamina. Scattered areas were found in which the junctions between outer pillar heads appeared to have separated and then partly reformed. Several hair cells were always found to be absent at the same locations. In one ear perfused within an hour after termination of the exposure, the reticular lamina was found broken and the adjacent hair cells were in the process of degenerating. Other cases were seen in which OHC had degenerated and had not yet been replaced by phalangeal scars. Signs of degeneration were noted in the tunnel spiral fibers at these loci. Damage to the continuity of the reticular lamina may result in severe injury to cells not appreciably affected during the noise exposure and, thus, may be responsible for some of the continuing cell loss which occurs after noise exposure.