bluuebunny/crossref_metadata_2025 huggingface dataset:
Review of Flight and Wind-Tunnel Measurements of Boundary-Layer Pressure Fluctuations
Authors: Bies David Alan
Published: September 2005

A review is presented of available data on boundary-layer pressure fluctuations from flight and wind-tunnel investigations. The wind-tunnel data include flatplate pressure-fluctuation spectra and space-time correlations. The flight data include pressure-fluctuation spectra and “equivalent acoustic spectra,” the acoustic fields that would produce the same response as the aerodynamic fields. General trends are indicated by the results, and good agreement is found between flight and wind-tunnel measurements. Of particular interest is the fact that wind-tunnel measurements show the same scatter as flight measurements, in spite of the fact that wind-tunnel flow conditions are much better controlled and boundary-layer parameters are generally measured rather than estimated. For intercomparison purposes, the same normalization procedure has been used with all of the data. This has required the development of engineering curves by which boundary-layer parameters may be estimated. [Work sponsored by NASA-Langley.]
Measurements of Sonic Boom with Limited Frequency-Response Instrumentation—A Theoretical Study
Authors: Crocker Malcolm J. , Sutherland Louis C.
Published: September 2005

The modifications to an ideal sonic boom caused by various measuring systems with different frequency-response limitations are determined analytically. Measurement systems with lowpass, high-pass, and bandpass frequency-response characteristics are considered. The approach adopted is to obtain the Fourier transform of an ideal sonic boom and by using the system frequency-response function to predict the measured time history of the sonic boom. The measured time histories for each system are computed for various system cutoff frequencies. The computations indicate the effects upon the measured peak overpressure and upon the length of the positive and negative phases owing to limitations in frequency response of the measuring system. Some comparison is made with experimental measurements. Similar analyses have been computed for system response to idealized blast waves and step pulses and are reviewed briefly. This work has useful applications in evaluating the accuracy of measurements made of sonic boom, blast, and shock-tube pressure pulses.
Circuit Model for Transfer Characteristics of the Cat's Middle Ear
Authors: Peakes William T. , Guinan John J.
Published: September 2005

Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts From measurements of ossicular displacement and cochlear-microphonic potential in response to tones, we have determined amplitude and phase of the following transfer ratios in anesthetized cats: (1) incus displacement/malleus displacement; (2) stapes displacement/sound pressure at the drum membrane; (3) middle-ear transfer function with the bulla closed/middle-ear transfer function with the bulla and bony septum open [J. Acoust. Soc. Am. 37, 1201(A) (1965)]. A 10-element equivalent circuit duplicates all of the major features of these measured transfer ratios. The model predicts the middle-ear transfer function with bulla open and bony septum intact. For some elements, anatomical measurements predict values that approximate those obtained by fitting the transfer-ratio data. However, the transfer function of the model is insensitive to the values of other elements for which we have no independent measurements. Hence, one must be cautious in equating these particular elements to physical properties of particular anatomical structures. [Work supported in part by the Joint Services Electronics Program, by the National Science Foundation, by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the National Aeronautics and Space Administration.]
Iso-Rate Contours for Single Auditory-Nerve Fibers
Authors: Sachs Murray B. , Kiang N.-Y. S.
Published: September 2005

Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts The rate of spike discharges is one commonly used measure of the activity in single auditory-nerve fibers. We have constructed iso-rate contours in the frequency-intensity plane for one tone presented alone and two tones presented together. Data are presented for fibers having different characteristic frequencies and rates of spontaneous activity. We have not found maintained inhibition of spontaneous activity by either one- or two-tone stimuli. However, responses to one tone may be inhibited by the simultaneous presentation of a second tone. The iso-rate contours permit one to define “excitatory” and “inhibitory” response areas. Certain features of these areas are found consistently in 350 units and are discussed. [Work supported in part by the Joint Services Electronics Program, by the National Science Foundation, by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the National Aeronautics and Space Administration.]
Neural Responses to Diotic and Dichotic Clicks
Authors: Langford Ted L. , Rupert Allen , Moushegian George
Published: September 2005

Interaural times and intensities of click stimuli were varied while recording from single neurons in the medulla of cat. Both time and intensity were referred to the N1 action potentials recorded at the round windows. Probability and latency of response were determined for each stimulus condition. Probability functions show that, for some cells, binaural interaction occurs over a relatively narrow range of interaural time conditions, while for others interaction takes place over a wide range. Maximum interaction was produced by zero interaural time in some cells and in other cells by a time lead at one ear. Data are also presented for interaural intensity differences. [Work supported by the National Science Foundation.]
Transduction of Boundary-Layer Noise by a Rectangular Panel
Authors: White Pritchard H.
Published: September 2005

The response and consequent sound radiation of a thin rectangular panel excited by convected boundary-layer turbulence has been examined. By taking averages over a frequency band, and including many modes in this average, the detailed characteristics of the system are bypassed and only gross features such as panel modal density, ratio of radiation to total resistance, and the boundary-layer characteriqtics are of interest. A large proportion of the sound power is transmitted in the region of the hydrodynamic coincidence conditions. The hydrodynamic coincidence frequency is the most important feature in determining the shape of the transmitted acoustic-power spectrum and the power laws for the total radiated power. The change in power-law dependence with the flow velocity and the panel thickness is satisfactorily explained. Excellent agreement between theory and experiment serves to verify the basic assumptions of the theory.
Effect of Duration on Perceived Noisiness
Authors: Pearson K. S.
Published: September 2005

Recent experiments have been conducted investigating the effect of the duration of a sound on its judged noisiness. For these tests, duration is defined as the amount of time that the sound was within 10 dB of its maximum level. The tests were conducted using two different time patterns and three spectra including a simulated jet spectra, a 1000-Hz pure tone, and a 13-oct band of noise centered at 1000 Hz. The range of durations tested extended from 4 to 60 sec. The results are compared with those of earlier tests, which were conducted over a range from 112 to 12 sec. The current tests indicate that, for the longer durations, the relative effect on judged noisiness is not as great as that found for the shorter durations. [Work supported by the Aircraft Development Service. Federal Aviation Agency.]
Land-Use Planning and Industrial Noise
Authors: Gordon Colin G.
Published: September 2005

The prediction of neighborhood reaction to industrial noise can be a complex problem, particularly when the noise sources are intermittent in time and distributed spatially throughout the industrial plant area. In a recent study, such a situation was examined and solved using the method of “composite noise rating,” developed some years ago for application to the aircraft- and airport-noise problems. By this technique, the various parameters relating to the source, the transmission path, and the exposed community are combined to produce contours of equal subjective exposure around the source area. By correlating these contours with different levels of community reaction, we may then differentiate between land areas which will or will not be suited to future development.
Control of Community Noise of a Supersonic Transport
Authors: Shapiro N. , Shulman A. L. , Schulert J. F.
Published: September 2005

Control of airplane noise by means of engine-suppression devices is accompanied generally by undesirable airplane-performance penalties. The unusual cruise requirements of a supersonic transport result in versatile engine- and airplane-performance characteristics at takeoff and landing approach; advantage is taken of these to moderate the noise environment in the community around an airport. The airplane's performance capability allows for the selection of operating conditions for low-thrust requirements, and the large range of thrusts available from the engines permits tradeoffs between airport and community noise. Consequently, in spite of the tremendous sound-power output capability of the SST engines, on the order of 1 000 000 acoustic watts, community noise is expected to be substantially lower than that experienced with current subsonic transports. Investigations on ejector nozzles, effect of secondary cooling air, choked inlets, acoustical treatment of inlets, and fan-discharge ducts are being pursued in an effort to achieve additional noise reduction.
Cockpit Noise in Small Aircraft
Authors: Tobias Jerry V.
Published: September 2005

In cooperation with several of the major manufacturers of light, general-aviation aircraft, carefully calibrated magnetic-tape recordings were made of the noise levels in the cockpits of their most popular models. Straight and level flight (with constant power) at 2000, 6000, and 10 000 ft was recorded as were takeoff and landing. Each recording was made twice—once with the vents open and once with the vents closed. A 13-oct band analysis was made and compared with the data reported by Wick, Roberts, and Ashe [Aerospace Med. 34, 1133–1137 (1963)]. A further comparison was made with several damage-risk-criterion curves. According to these curves, the noise levels found are not likely to be productive of measurable acoustic trauma, even for the pilot who flies every day.
Damping Experiments on Rapid-Transit Wheels and Squeals
Authors: Kirschner Francis , Teplitzky Allan
Published: September 2005

The so-called “screech”-type noise generated by railroad wheels on sharp curves was investigated. Laboratory tests confirmed by field trials have shown noise reductions of up to 15 dB in the noise radiated by excited resonant modes of vibration. Noise reductions were obtained by an application of a homogeneous damping treatment in selected areas of the wheel. Laboratory tests were performed to establish if damping by homogeneous layers was feasible and economical. Tests were performed on a resiliently suspended 550-lb forged-steel rapid-transit car wheel identical to those used in the field. Applications of homogeneous damping material with a weight ratio of damping material to steeI of 3.6% reduced the resonant amplification “Q” by a factor of 10. Field trials were conducted on electric-driven two-car-unit rapid-transit vehicles well known for their quietness. Sound measurements were conducted on the same section of curved track for a series of speeds for vehicles with and without damping material applied to the wheels.
Rocket-Noise Monitoring System
Authors: Sawyer G. Norman
Published: September 2005

This report describes the performance of a system designed to meet the specific requirements of monitoring rocket noise in communities located miles from the test site. The pole-mounted remote stations were designed to transmit their signal via normal telephone voice channel. This was done to provide maximum economy, availability of transmission lines at many locations, and reliability through redundancy of other voice channels available from the telephone company. The microphone signal is transmitted via frequency modulated carrier over the telephone channel from the remote station to the base station. Performance of the system, including the microphone, is within the required frequency range of 0.7–350 cps, 50-dB signal-to-noise ratio, and accuracy of plus or minus 1 dB.
Consonant-Vowel Ratio and Speaker Intelligibility
Authors: Williams Carl E. , Woods B. , Hecker Michael H. L. , Stevens Kenneth N.
Published: September 2005

Since voiced and voiceless speech sounds are generated by different mechanisms, it might be hypothesized that differences in speaker intelligibility are due in part to differences in the production of these sounds, and, in particular, are related to the consonant-vowel (C/V) ratio for voiceless consonants. To explore this question, eight selected male speakers recorded lists of the Modified Rhyme Test; two of the speakers made recordings at three levels of vocal effort. Initial and final /s/-vowel and /t/-vowel ratios were obtained from graphic-level tracings of the recorded utterances. The lists were presented to listeners at two signal-to-noise ratios. Significant correlations were found between speaker intelligibility and final C/V ratios for the consonants examined. There were monotonic relations between vocal effort and /s/-vowel ratio and between /s/-vowel ratio and intelligibility. [Work supported by Decision Sciences Laboratory, Electronic Systems Division, U. S. Air Force Systems Command, Bedford, Massachusetts.]
Some Factors That Influence Judgments of Circuit Quality
Authors: McDermott B. J.
Published: September 2005

Similarity, preference, and loudness judgments were obtained for all possible pairs of 22 voice-communication circuits, including both linear and nonlinear distortions. Each set of judgments was analyzed, using multidimensional techniques. The analyses indicate that each type of judgment has some factors in common. The interrelationship of these factors and their influence on judgments of circuit quality is discussed.
Crosslanguage Study of Perceptual Confusion of Plosive Phonemes in Two Conditions of Distortion
Authors: Singh Sadanand
Published: September 2005

The intelligibility of /p t k d b g/ as spoken and heard by native speakers and listeners of Hindi and English and the relationship of this intelligibility to the transitions of consonants to vowels in CV monosyllables was investigated. Phoneme boundaries were determined. A measure of intelligibility was obtained in terms of information transmitted per stimulus for four and two separate channels and a composite channel. The separate channels represented distinctive linguistic features. Through a comparison of the information transmitted by these systems, redundancy was quantified. There was uniformity among the four speaking-listening groups in information transmitted at six points of temporal segmentation and in 20 different bandwidths, as well as similarity in the importance of channels. Models of linearity were set to assess information as a function of (1) time, (2) width of the frequency band, and (3) lower frequency of the frequency band. Multiple correlations of 0.83 in the case of 1, 2, and 3, of 0.83 in the case of 1 and 2, and 0.77 in the case of 1 and 3 were found.
Adaptive Beamforming for Sonar Signal Processing
Authors: Kennedy Robert M. , O'Neill Robert J.
Published: September 2005

The detection of weak sonar signals in a system exhibiting interchannel noise correlation may be enhanced by a beam-forming technique first introduced hy Mermoz, which maximizes the output signal-to-noise ratio. Such a system has been implemented, using an analog computer, for the case of two input channels. The system automatically adjusts to slowly varying values in the noisecorrelation matrix. The output S/N, as a function of bandwidth and interchannel correlation magnitude and time delay, is compared to that of conventional processors employing simple delay and summation of inputs. In addition, the sensitivity of the technique to component tolerances is discussed.
Creeping-Wave Description in Sound Scattering from Elastic Cylinders
Authors: Doolittle R. D. , McNicholas J. V. , Überall H.
Published: September 2005

Plane-wave sound scattering from infinite cylinders results in creeping waves for a rigid or pressure release surface, and in circumferential waves for elastic cylinders (which may include creeping waves altered by elastic effects). Calculations such as backscattering cross sections for rigid or soft cylinders are greatly facilitated by the creeping-wave method, which involves transforming the normal-mode solution by the Sommerfeld-Watson transformation. The physical interpretation in terms of surface waves made possible by this method suggests that the method yields a meaningful description of circumferential waves in elastic shells. The search for such waves is reduced by the creeping-wave method to the location of roots of a 6×6 determinant or, for a solid cylinder, a 3×3 determinant, involving cylindrical functions of complex order.
Preferential Excitation of High-Order Modes in Strips
Authors: Fabian E. L.
Published: September 2005

High-order propagating modes have been excited preferentially in strips at ultrasonic frequencies by utilizing the displacement configuration of the modes. A single propagating mode is excited by using a transducer exciter that approximates the displacement profile of the desired mode of propagation. The technique has been used experimentally to excite longitudinal and flexural modes in fused silica and aluminum strips. Results are presented for a 3-Mcps aluminum strip propagating the 2nd flexural mode, and a 15-Mcps fused silica strip propagating the 5th longitudinal mode. Discriminations of at least 20 dB to spurious modes are reported. The calculations of displacement profile and construction of the transducer exciter are discussed. A wide range of dispersive characteristics is available with the higher modes, which extends the useful frequency and delay range in device applications. [A portion of this work was performed at the Bell Telephone Laboratories, Inc., Allentown, Pennsylvania.]
Simple Algorithm for Determining the Location of a Focus in Atmospheric Sound Propagation
Authors: Fox H. L. , Wiener Francis M.
Published: September 2005

There exist methods for computation of a focus that require a computer. These are based on ray acoustics in a horizontally stratified atmosphere. However, often a quick judgment must be made relative to the focal area of a high-intensity sound source, and quick estimates are desirable. It is then adequate to determine the existence of a focus and its approximate location. The algorithm discussed here results in a simple technique for predictivg the existence and location of a focus for a common type of effective sound-velocity profile.
Long-Range Atmospheric Infrasonic Propagation
Authors: Richie William C. , Chick D. R.
Published: September 2005

A surface explosion of 500 tons of TNT at the Suffield Experiment Station, Alberta, Canada, was monitored with a solion infrasonic microphone at a horizontal distance of 299 km to the southwest. The frequency response of the infrasonic microphone extended from 0.01 to 50 Hz. Statistical analysis using the power spectra and deterministic analysis using the amplitude spectra show a primary signal component at 0.26 Hz. Additional examination of the autocorrelation function and the spectra indicate that an atmospheric modulation of pressure waves may have been encountered. [Work sponsored by the U. S. Army Electronics Research and Development Activity, White Sands Missile Range, New Mexico.]
Internal Pressure Waves and Troposphere Dynamics
Authors: Young Jessie M. , Bowman Howard S.
Published: September 2005

Certain spatially coherent, traveling, atmospheric pressure waves observed at the surface of the earth appear to be related to the dynamic behavior of the upper tropospbere. The waves have periods greater than about 4 min and horizontal speeds between 15 and 100 m/sec. Experimental data are presented as evidence that these waves are related to tropospheric jet-stream behavior. The properties of these waves are compared with properties of experimentally observed pressure fluctuations from other sources.
Geometrical Acoustics' Theory of Waves from a Point Source in a Temperature- and Wind-Stratified Atmosphere
Authors: Pierce Allan D.
Published: September 2005

This paper is concerned with the development of practical numerical methods of estimating the amplitude and travel times of received pulses generated by a small source in a temperature- and wind-stratified atmosphere. The basic theory of Blokhintzev [J. Acoust. Soc. Am. 18, 322–334 (1946)] is shown to hold for propagation in the atmosphere even when gravitational forces are included, if wave periods are sufficiently short. The “ray-tracing” equations are derived from Blokhintzev's eikonal equation using Cauchy's method of characteristics and the boundary conditions on these equations appropriate to a point source are discussed. The numerical solution of the ray-tracing equations by integration over height is discussed and an integration approximation is introduced for handling the singularities at ray turning points. The method is illustrated by numerical examples.
Subjective and Objective Measurement of the Loudness Level of Single and Repeated Impulses
Authors: Reichardt W.
Published: September 2005

In the subjective measurement of impulses, the 1-kHz comparison tones must be of the same duration and must recur at the same repetition rate as the impulses being measured. The loudness levels of the short 1-kHz tones and tone bursts can be taken from the nomograms presented. Objective measurement of impulses requires an impulse sound-level meter with an RC integrating network following the squaring device. The RC time constant must simulate the inertia of the human ear. The ringing and ringing time constant must be the same. Then the effective value is indicated with a continuous transition from steady noise to rapidly repeated impulses. The ringing time constant must correspond to the rate of decrease in loudness after the sound has stopped. This can be described as τ=0.25 msec or as 60-dB reverberation time of 0.35 sec. The reading of such an impulse sound-level meter with A weighting is designated LΔI. Loudness calculation by Niese's method, for either single or repeated impulses, requires a spectrum correction ΔLSP to be taken from a nomogram. LNI=LΔI+ΔLSP. Stevens' and Zwicker's methods, for single impulses or impulses repeated less frequently than 2 per second, require the dynamic impulse level LCI to be measured in 1- or 13-oct bands. For comparison, impulses repeated more frequently than 2 per second are measured in 1- or 13-oct bands with the slow setting LCS. After calculating the loudness level, we then obtain another impulse correction ΔLI=LΔI−LAS.
Temporary Threshold Shifts from Dichotic Exposures
Authors: Ward W. Dixon
Published: September 2005

Previous research has shown that the TTS produced by dichotic low-frequency stimulation is significantly less than the TTS from monotic exposures, but that the difference is not significant for high-frequency exposures (above 2000 cps). Also, attenuation by the middle-ear muscles has been found to be great at low frequencies, negligible at high. These results suggest that the middle-ear muscles may be responsible for the monotic-diotic difference. If so, simultaneous (dichotic) presentation of a low-frequency tone to the right ear and a high-frequency noise to the left might be expected to reduce the TTS in the right ear but not in the left, relative to the monotic condition. This hypothesis was tested on 17 listeners using 5-min exposures of 700-cps tone at 115 dB SPL and 2400 to 4800-cps noise at 112 dB SPL, respectively. The prediction was not confirmed: instead, the TTS in the dichotic condition was less than in the monotic for both stimuli. Alternative explanations must therefore be advanced, such as the possible action of the efferent system. [Research supported by the Public Health Service, U. S. Department of Health, Education, and Welfare.]
Relationship of Induced Tinnitus to Physical Characteristics of the Inducing Stimulus
Authors: Loeb M. , Smith R. P.
Published: September 2005

Volunteer subjects were exposed to 500-, 1000-, 2000-, and 3000-cps tones and to white noise at intensities up to 120 dB for 5 min. Subsequently, the subjects' temporary threshold shift (TTS) was measured at selected frequencies and they were asked to manipulate the controls of an oscillator to match their tinnitus, if any. Contrary to previously reported findings, most subjects reported tonal rather than noise tinnitus. There was a significant and positive relationship between the frequency of the elicited stimulus and that of the reported tinnitus, but considerable variability was noted. There was not a simple relationship between the frequency of the reported tinnitus and the point of maximum TTS.
Poststimulatory Auditory Fatigue of Masked and Quiet Threshold
Authors: Smith J. H. , Anderson C. V.
Published: September 2005

The effects of the presence or absence of background noise during exposure were investigated for masked and quiet temporary threshold shift. The threshold for a 1400-cps signal was measured prior to and following exposure to a 1000-cps signal at 110 dB SPL for a period of 4 min. These measures were taken in the presence of bandlimited (150–4000 cps) random noise at an over-all sound-pressure level of 60 dB and in quiet. No consistent effects upon either masked or quiet temporary threshold shift were noted as a result of exposure in the presence of the noise. Other results were in agreement with previous investigations.
Tonal Signal Detection under Various Light Stimulation Conditions
Authors: Watkins William H. , Schjelderup John R.
Published: September 2005

Using forced-choice, a tonal signal was presented under several photic conditions. In one experiment, binocular exposure to a strong light had 0.25 sec duration as had 4 white-noise bursts (60 dB SPL) per trial—one burst coincident with the signal. Onset times of light exposures were 0.50 or 0.25 sec before noise bursts, concurrent with them, or immediately following. One run of 48 consecutive trials under each photic condition along with a control run comprised an experimental set. A later experiment, similar except for shortened periods (0.20 sec) and for maintenance of white noise at 60 dB, provided light onsets 0.20 sec before, coincident with, or immediately following the possible signal periods. A two-level light intensity variable was also included. With noise bursts, all condition means (48 sets) fell within a range of 5.3 in percentage correct responses. Here, the small advantage favored light coincident with possible signal periods (3 of 6 subjects conforming). Detectability of the signal in steady noise was significantly lower when light followed possible signals. Detectabilities were independent of light intensity variable. Results were discussed in relation to findings of Child and Wendt [J. Exptl. Psychol. 23, 109–127 (1938)1 and others.
Artificial Voice
Authors: Olson Harry F.
Published: September 2005

An artificial voice has been developed in which a two-way loudspeaker system is located in an enclosure with the dimensions of the average human head. The entire artificial voice consists of a simulated head, neck, and chest. The frequency response of the artificial voice is within ±3 dB from 62.5 to 12 000 Hz. The directivity patterns of the artificial voice are practically the same as those of the human voice [H. K. Dunn and D. W. Farnsworth, J. Acoust. Soc. Am. 10, 184–199 (1939)] throughout the frequency range of 62.5–12 000 Hz. There are many applications for an artificial voice of this type for tests of microphones and studio and room acoustics for pickup conditions and distances of the kind and magnitude employed in speech reproduction in radio, television, sound motion picture and phonograph recording, sound-reenforcing, etc.
Some Improvements in Ear Enclosures
Authors: DiMattia A.
Published: September 2005

Attenuation of ear enclosures suffers limitations owing to resonance between earcup mass and compliance of cushions and the circumaural flesh. Worthwhile improvements in attenuation at this frequency and below are obtained by selectively coupled volumes (Helmholtz/Absorbers) tuned to this resonance. If the unwanted resonance falls below the communication spectrum of interest, then the added volumes produce no lowering of acoustical impedance load to the headphone transducers. A jel-filled cushion is described. Since the jel does not escape through small holes or tears, it may be contained in an envelope of thin, limp plastic material. A special cross-sectional configuration permits the cushion to conform to the circumaural region with little or no stretching of the envelope material, thus retaining the soft jel properties. [Work supported by the U. S. Army Electronics Command.]
Tubular Shield for Enhancing Noise Cancellation of Pressure-Gradient Microphones
Authors: DiMattia A. , Rosenheck A.
Published: September 2005

The object of this research was the development of a shield whose noise-cancellation properties would effectively complement those of a pressure-gradient microphone, thus providing substantial cancellation at high frequencies where the pressure-gradient microphone alone has little or no cancellation. In contrast to the normal vented-cavity type, the new shield is tubular in shape with the microphone and mouthpiece at one (closed) end, and the other end open for breath expulsion. The intended microphone has a cosine directional pattern and is positioned so that its null plane coincides with the tube axis. Therefore, unwanted noise arrives at both sides of the exposed diaphragm in phase, producing no output. Further enhancement of noise cancellation is provided by lining the tube with acoustical absorption along the inner wall. The mouthpiece is located on the side of the tube, directly above the microphone. Thus, speech is effectively received as a result of proximity to the microphone and because of the large pressure gradient of the speech wave. With the tubular shield, noise reduction is enhanced, by 15 dB or more, above 1 kHz. [Work supported by the U. S. Army Electronics Command.]
Moving-Coil Pressure-Gradient Hydrophone
Authors: Bauer B. B. , DiMattia A.
Published: September 2005

A pressure-gradient hydrophone exhibiting uniform response and precise polar pattern has been developed based on the moving-coil principle. The coil, under mass control, closely matches the impedance of the medium contributing to high sensitivity. Equivalent-circuit analysis demonstrates how to select the electrical-termination resistance for any desired degree of damping and for proper phase-shift control. Theoretical performance is compared with measurements using a CBS Laboratories gradient hydrophone calibrator, and in free field. [Work supported by U. S. Naval Air Development Center, Johnsville, Pennsylvania, under subcontract from Sanders Associates, Nashua, New Hampshire.]
Calibration of Infrasonic Microphones at WSMR
Authors: Harmon James A. , Leinbach Henry J. , Prince Nicholas
Published: September 2005

This paper describes a technique for the rapid calibration of high-sensitivity, low-frequency microphones in the presence of relatively high ambient noise. Because of the uncertain volume displacement and the physical configuration of the microphones, normal pistonphone calibrations cannot be made. This technique entails calibration of a reference microphone in an electrodynamically driven pistonphone, comparison of the test microphone with this reference to determine the sensitivity magnitude, and the use of an electrostatic actuator to determine the relative response at ambient pressure. All voltage comparisons made are instantaneous amplitude and phase balances of single-frequency components referenced to the dc voltage input of the displacement control in the pistonphone calibration. This method minimizes the error contributions from voltage-transfer (dc to ac) distortion and noise. Microphone circuit modifications are described that allow field system calibration from a remote location. The estimated uncertainty of the calibration is 0.75 dB. Plans for the improvement of the method are presented.
Horn-Type Moving-Coil Driver-Unit Development
Authors: Renkus J. A. , Hilliard J. K.
Published: September 2005

This paper reviews various types of driver units for size, frequency response, and efficiency. A 4-in. moving-coil driver of high efficiency is described. The unit achieves high power (20 acoustic watts) and utilizes nexv materials and techniques for the compliance and coil supports. The mass of the moving system is reduced to increase the frequency response. High flux density is utilized with smaller magnets by controlled leakage.
Dissipative Mechanisms in the Operation of the Electropneumatic Acoustic Generator
Authors: Van Houten John J. , Kaplan R. E.
Published: September 2005

The construction, performance, and method of evaluation of the electropneumatic acoustic generator utilized to produce extremely high controllable sonic energy has been previously discussed [J. Acoust. Soc. Am. 38, 956–964 (1965)]. Current work includes the analysis of the flow system and the mechanism of energy dissipation in the conversion from pneumatic to acoustic energy. The observed loss of total pressure through the transducer suggests the existence of two separate dissipative mechanisms, each dominating in different regions of pneumatic supply pressure. These are described as (a) unsteady separated flow caused by the sharp-edged modulating orifice; and (b) a shock system that interacts with the unsteady flow at higher reservoir pressures. The flow system is qualitatively described with reference to these two dissipative mechanisms. The relationship between transducer geometry and supply pressure is discussed, and an experimental program that complements the analysis is described.
Spectral Contour Plotter—An Improved Instrument for Spectral Analysis
Authors: Ide Kenton J.
Published: September 2005

An improved form of spectrograph utilizing a contour representation of amplitude is described. Detailed consideration is given to the novel features incorporated in the instrument such as variable sample length, fully adjustable frequency-scan limits, and a quasistationary display. The use of contours to extend the dynamic range of the display medium is described, together with a versatile digital technique for obtaining any practical amplitude contour spacing. Finally, samples of typical plots are shown, indicating the versatility and wide application of the spectral contour plotter to acoustical signal analysis.
Acoustics of the Mid-South Coliseum, Memphis, Tennessee
Authors: McCandless David
Published: September 2005

The Mid-South Coliseum, the new municipal coliseum in Memphis, Tennessee, is a circular hall with a domed roof enclosing 3 760 000 cu ft. It has over 9000 permanent seats and an additional 4000 temporary seats that can be set up on the the alcua floor. The coliseum was planned for the usual sports events, conventions, religious functions, circusses, etc. Two loudspeaker clusters were designed to accommodate the two possible areas of activity on the arena floor. The paper discusses the various factors considered in the acoustical design of the coliseum, including the suspended acoustical ceiling for which there were no published absorption coefficients. The predicted reverberation time is compared to the measured reverberation time in the finished building. A general comparison is made of this coliseum and several others of similar use and volume, with observations on present trends in coliseum design in the United States of America.
Sound Field in Very Wide and Long Rooms
Authors: Gober Hans J. , Lübcke Erns
Published: September 2005

The sound-pressure level versus distance from a single point source was measured in many factory halls and similar rooms. These rooms were either flat—ten times wider and longer than high—or long—ten times longer than high or wide. The sound field is not diffuse in these rooms and the simple statistical theory could not be applied. In flat rooms for distances greater than several meters from the source, the sound-pressure level decreased a fixed amount for each doubling of distance. This amount was proportional to the average sound absorption coefficient α in the room. In long rooms, the sound-pressure level decreased directly proportional to the distance from the source for distances over 30 m from the source. Details of the measurement techniques were given in a previous paper [E. Lübcke and H. Gober, “Schallausbreitung in Fabrikhallen,” Forschuugsher. No. 1364 des Landes Nordrbein-Westfalen (Westdeutscher Verlag, Opladen, Germany, 1964) ].
Effect of Wood Strip Facings on Sound Absorption
Authors: Goodfriend Lewis S.
Published: September 2005

The sound-absorption coefficients of 2-in.-thick glass-fiber blanket and 2-in.-thick paper-wrapped thermal blanket faced with several arrangements of 2×4-in. lumber are presented. With the 2×4's flat and with spacings of 14, 12, and 1 in. the absorption peaks in the 250- to 500-Hz range. Increased spacing improves the high-frequency absorption. Setting every third 2×4 vertical, 1-in. spacing results in a broader peak and a higher, smoother high-frequency absorption. All measurements were made in accordance with ASTM Designation; C423-65 T in the reverberation room of Cedar Knolls Acoustical Laboratories.
Sound-Insulation Ratings from Third-Octave-Versus Octave-Band Measurements
Authors: Young Robert W.
Published: September 2005

Methods proposed internationally for the rating of impact-sound and of airborne-sound insulation allow use of measurements made with either 12- or 1-oct bands of noise; observed values are compared with a standard sequence conveniently described by a curve that is shifted until there is an average unfavorable deviation between 1 and 2 dB; the value of the shifted reference curve at 500 Hz is then the single-number rating. Peaks and valleys are delineated nmch less clearly by 1-oct-band measurements than by 13-oct-band measurements, and in recognition of this fact the proposed international standard allows a maximum deviation from the rating curve of 8 dB for 13-oct bands but only 5 dB for 1-oct bands. Ratings obtained with the two different bandwidths were investigated with a variety of source spectra and families of sound-insulation curves having coincidence dips at different frequencies. Extreme examples of impact-sound produced by the standard tapping machine were selected for calculation. In general, a rating obtained from 1-oct-band data was like that obtained from the corresponding 14-oct-band data within 1 dB. Moreover, the analysis showed that nearly the same rating of sound insulation could also be obtained simply as the difference between the sound level A in the source and receiving rooms.
Analog Computer Solutions for the Sound Pressure from a Line Source with Time-Varying Source Strength
Authors: Remillard W. J.
Published: September 2005

An integral relationship between the time variations of the strength of a line source and the time variations of the resulting pressure wave was derived by Levi-Civita in 1897. In general, this integral cannot be evaluated by analytical means. An analog-computer set-up is shown that uses Levi-Civita's integral to simulate a line source and generate functions that describe the resulting pressure disturbances. A number of examples are given. [Research supported in part by the Weather Radar Branch, Meteorology Laboratory, U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research.]
Question of Consistency as between the Eulerian Viewpoint and the Lagrangian Viewpoint
Authors: Kline Herbert , Westervelt P. J.
Published: September 2005

Considered in this paper is the problem, in one dimension, of forced oscillations and standing waves of sound in a cube-shaped resonator, the vibrating wall of the resonator being represented as a delta-function source that is then expanded in the normal modes of the resonator. Calculations are carried out first from the Eulerian point of view and then, secondly, from the Lagrangian point of view. The uncovering of a discrepancy in this connection, i.e., as between the Eulerian and Lagrangian points of view, necessitates modification of the usual Lagrangian equation of continuity so that it be consistent with the Eulerian equation of continuity in the presence of sources, upon which modification the two viewpoints, Eulerian and Lagrangian, are found to be consistent. Obtained also, in connection with this question of consistency, is the wave equation for the Lagrangian particle displacement in the presence of sources, once sources have been specified from the Eulerian point of view. [Work supported by the U. S. Air Force Systems Command.]
Thermoelastic Vibrations of a Thick Hollow Elastic Sphere
Authors: Cinelli G.
Published: September 2005

A new finite Hankel transform [G. Cinelli, Intern. J. Eng. Sci. 3, 5 (Oct. 1965)] is used to find the transient radial displacement and corresponding stresses in a thick hollow elastic sphere when the surfaces are subjected to the simultaneous occurrence of dynamic loads and very high heating rates, which in turn are arbitrary functions of time. Employing the general solution obtained for the arbitrary loads and temperature inputs, the time variation is specialized to standard forms such as an impulse, step function, etc., and the corresponding motion and stresses found. The propagation and reflection of the thermal and elastic waves in these cases are evident. Next the solutions to the problems of (1) the solid sphere, (2) a thin spherical shell, and (3) spherical cavity in an infinite medium are obtained from the general solution as limiting cases. Finally, it is shown how the corresponding viscoelastic case can be solved using the same techniques.
Development of Nodal Patterns in the Forced Vibration of Thin Shells of Revolution
Authors: Goldberg John G. , Alspaugh Dale W.
Published: September 2005

The steady-state response of an arbitrary shell of revolution to an arbitrarily specified harmonic forcing function is determined. By carrying out a series of analyses at various frequencies of the forcing function, the mechanism of transition from one nodal pattern to another is investigated. The method is applicable to a shell of revolution with an arbitrarily specified generator. The shell properties, including thickness, may vary in the direction of the generator. The shell may be initially prestressed and may contain branches. Any physically plausible boundary conditions may be imposed. The method is applied to an illustrative example and some results of interest are presented. The example shows the shifting of the nodal pattern and the accession of additional nodal lines.
Effect of Boundary Conditions of Flexural Vibrations of Thin Orthogonally Stiffened Cylindrical Shells
Authors: Penzes Leslie E.
Published: September 2005

The flexural vibrations of thin orthogonally stiffened cylindrical shells are discussed considering the effect of different boundary conditions. The orthotropic shell theory of W. H. Hoppmann, II, was usect to derive the orthotropic stress-strain law, and the equations of motion were formulated for the shell element in three partial differential equations. The equations were reduced to a single eighth-order ordinary differential equation. This equation yielded a fourth-order frequency equation by considering a relatively long cylinder. The following three boundary conditions were applied: clamped-clamped, clamped-simply supported, and both edges simply supported. The author's theory was compared with Hoppmann's theory and test results for the case of simple supports. The errors are about the same for both theories. The author's theory shows that the clamped-clamped and clamped-simply supported boundary conditions can affect the frequencies seriously in the case of longitudinal stiffeners; however, the effect is smaller with radial stiffeners. For the isotropic case, the theory simplifies to the solution of Yi Yuan Yu.
Effect of Curvature on Response and Fatigue Resistance of Simple Panels
Authors: Ballentine J. R.
Published: September 2005

Experimental investigations to determine the effect of curvature on dynamic response and fatigue resistance of simple panels exposed to broad-band and discrete frequency acoustical excitation are presented in detail. Descriptions of (a) modes-shape studies, (b) response to discrete frequency and broad-band excitation, and (c) fatigue tests are given. Particular emphasis is placed on evaluating the role that panel curvature plays in resisting broad-band acoustically induced fatigue. [Research was sponsored by the U. S. Air Force.]
Acoustic Radiation from Locally Driven Infinite Plates with Fluid Loading
Authors: Maidanik Gideon , Kerwin Edward M.
Published: September 2005

Fluid loading influences the total acoustic power and the directivity of the radiation from a large flat plate driven by localized forces. The frequency range considered here is that below the “critical” frequency. In this range, the in vacuo speed of plate flexural waves is less than the speed of sound in the adjacent fluid medium. For a point force, the directivity of the radiation field is that of a monopole for light fluid loading, but changes to that of a dipole for heavy fluid loading. Analogous behavior occcurs in the case of a line force. An equivalent acoustic dipole source can be specified, and one can apply this equivalent source formalism to calculate the power radiated by point and line moment excitations under conditions of heavy fluid loading. The radiated power for a point moment excitation computed by this approach agrees with the earlier results of Thompson and Rattayya [J. Acoust. Soc. Am. 36, 1488–1490 (1964)]. [Work supported by the Ship Silencing Branch of the U.S.N. Bureau of Ships.]
Properties of Fiber Metal Acoustically Resistive Materials
Authors: Fisher James I.
Published: September 2005

Fiber-metal materials are available which can provide virtually any acoustical resistance in the form of thin, strong, formable and joinable sheets. Manufacturing procedures are described briefly. The mechanical, thermal, and fatigue properties of the materials, in both aluminum and stainless steel, are described insofar as these properties are known. Also, the tradeoffs relating to weight, strength, and cost are presented, along with a discussion of material design options and limitations. Within the acoustical-flow resistance range of 10–60 cgs Rayl, produceability limitations are reviewed statistically in terms of sheet thickness and flow-resistance tolerances. The effect of particle velocity on flow resistance is described, showing that the resistance increases owing to turbulent flow at equivalent sound-pressure levels (SPL) above 140 dB. Finally, the effect of flow-resistance variations on impedance-tube absorption characteristics is discussed, considering again the range of 10–60 cgs Rayl. The major unresolved question is the effect of very high SPL's on absorption characteristics.
Sound Output for Gas-Turbine Power Plants
Authors: Audette R. R.
Published: September 2005

The nearfield and farfield sound-pressure level measurements are given for a number of gas-turbine power plants in the 5000- to 105 000-kW size range. In addition, sound measurements are given for various auxiliaries, such as starting devices, generators, cooling fans, etc.