bluuebunny/crossref_metadata_2025 huggingface dataset:
Streak Camera in Shock Wave Experiments
Authors: Crosby John K.
Published: September 2005

The operation of a rotating mirror streak camera and its applications to various problems in explosive shock wave research are described. This instrument, which has a time resolution of a few hundredths of a microsecond, can be used to detect the arrival of a shock wave at the free surface of an opaque solid, to measure shock and free surface velocities and to observe detonation waves in various explosive configurations. Examples of its use in equation of state measurements for opaque solids, velocity measurements for explosively driven plates, and shock velocity measurements in transparent solids and fluids are given. These examples illustrate the techniques for shock detection by means of argon gaps and for generation of high intensity lighting which are necessary in this work and point out some of the procedures used for analysis of the film records. The streak camera is frequently supplemented by electronic or framing camera observations and these and the techniques connected with them are briefly described.
On the Reflection of Weak Shock Waves from Nozzles with No-Flow and Critical Flow through the Nozzle
Authors: Feiler Charles E.
Published: September 2005

High-frequency combustion instability in rocket engines is known to result from pressure waves traveling within the combustion chamber. For the longitudinal mode of instability, the pressure wave reflects directly from the rocket nozzle and this mode behaves acoustically as though the engine were an organ pipe closed at both ends. Very little is known about the reflective characteristics of the nozzle in terms of its geometry. The reflection of shock waves from nozzles having contraction ratios of 2, 4, and 16 and convergence half-angles of 15°, 30°, and 60° was studied in a shock tube. Two sets of experiments were conducted. In one, a series of no-flow tests were made and the results compared to a theoretical analysis (Otto Laporte, Los Alamos Scientific Laboratory of the University of California; Report LA 1740, August, 1954). In the other, a critical flow of air through the nozzle was supplied. This condition simulates more closely the condition of the rocket nozzle throat during combustion. For no-flow tests, the reflected pressure amplitude compared favorably with that predicted by the analysis. Nozzle convergence angle had no observable effect. Under critical flow conditions, reflected pressure amplitude was essentially that expected for a closed tube and was independent of nozzle contraction ratio and convergence angle.
Equipment and Procedures for Field Measurements of Aircraft Noise and Flight Paths
Authors: Keast D. N. , Clark W. E. , Galloway W. J.
Published: September 2005

Equipment and procedures that have been developed for observing aircraft flight paths and noise produced on the ground by aircraft in flight are described in this paper. The measurement system consists of a dual-channel tape recorder for sound recording and time synchronization, in conjunction with a 16-mm movie camera on a calibrated tracking mount. Azimuth and elevation of an aircraft are determined, on an incremental basis, from a series of small lamps mounted on a frame which bounds the field of view of the camera. Individual lamps are turned on or off by a pair of rotary switches located on the tracking mount. The range and altitude of the aircraft can be determined from analysis of the film record. Time synchronization between the tape recording of aircraft noise and the position data is maintained with a signal applied to one channel of the tape recorder and a timing lamp in the field of view of the camera. With this system, aircraft position information can be obtained from a number of filming intervals spaced throughout the noise recording of the aircraft passage. Data obtained with this equipment have enabled reconstruction of individual flight paths for analysis of the recorded noise data and of flight path distributions in space. [This work was sponsored by the U. S. Air Force under Contract No. AF 33(616)-3938.]
Procedures for the Measurement of Acoustical Effectiveness of Ground Runup Suppressors
Authors: Doelling Norman , Pietrasanta A. C.
Published: September 2005

A complete description of acoustical effectiveness of a ground runup suppressor would have to include the noise reduction as a function of frequency, angle, and distance from the suppressor. Such an involved description is impractical and generally unnecessary. As a result, various abbreviated measurement procedures have evolved. These abbreviated procedures vary in complexity depending on the amount and type of information required. Several measurement procedures for evaluating acoustical effectiveness are described and their advantages and limitations are discussed. Selected examples from field measurements are used to illustrate the application of these procedures. A simplified method for comparing the acoustical effectiveness of ground runup suppressors is suggested. [Supported in part by the U. S. Air Force under Contract Nos. AF 33(616)-2151, AF 33(616)-3335, and AF 33(616)-3938.]
Acoustic Factors Involved in Design of Non-coupled Jet-Engine Silencers
Authors: Gildard J. H. , Callaway D. B.
Published: September 2005

Lightweight jet engine exhaust silencers which require no physical connection to the engine under test are of considerable interest to the aircraft industry for both economic and operational reasons. The performance of some early design models has shown significant promise. Until recently, however, the practical acoustical limitation of such silencers due to inlet and coupling gap noise has not been definitively measured. To evaluate this limitation, a program of field measurement was undertaken using a prototype silencer with a military aircraft. From the data obtained it appears that noise due to the coupling gap and the engine inlet is somewhat lower than had been expected. It is concluded that a relatively high performance exhaust silencer can be justified without requirement for inlet and coupling gap silencing.
Shielding-Flap-Type Jet Noise Suppressor
Authors: Maglieri D. J.
Published: September 2005

Far-field noise measurements from model tests of a shielding-flap-type jet noise suppressor are presented in the form of radiation patterns and frequency spectra. The tests were conducted using a cold air jet issuing from the nozzle in such a manner as to attach to and flow along the surface of a shielding flap. Whereas other proposed noise suppressors provide generally symmetrical noise radiation patterns, the present device skews the pattern in a beneficial way such that large noise reductions are obtained in the downward direction. These large noise reductions are thought to result from both the acoustic shielding of the flap and the benefits of flow attachment.
Effects of Age and Sex on Pure-Tone Thresholds
Authors: Corso John F.
Published: September 2005

Recent developments have emphasized the need for an adequate reference level from which to assess the degree of noise-induced hearing loss. The purpose of the present study was to determine the threshold of hearing for pure tones on a large sample of subjects (N = 500) drawn from a population exposed to minimal levels of industrial noise. Four age groups were studied: 18 to 24, 26 to 32, 34 to 40, and 43 to 49 years, inclusive. Threshold measurements were made from 250 to 8000 cps on a Beltone audiometer provided with PDR-8 earphones calibrated in a National Bureau of Standards Coupler 9-A. The threshold data were analyzed by age groups, ear, and sex in terms of three types of distributions: (1) original distributions which contained the data for all subjects tested; (2) screened distributions which contained the data only for subjects who passed rigid screening criteria related to otological disorders and extent of noise exposure; and (3) truncated distributions which contained only data ±15 db from the mode of the screen distributions. The results of the study indicate that in general, only minor differences (less than 5 db) exist between ears, but that women have more sensitive and less variable hearing than men. The sex difference is independent of age and appears to be more marked at the higher frequencies. Although the effects of age are clearly evident for both men and women, there is limited agreement between the curves of presbycousis of the present study and those proposed by the American Standards Association. The suggestion is offered that future audiometric standards be specified independently for men and for women according to particular age levels. [This research was supported by the United States Air Force under Contract AF 33(616)-2626 monitored by the Bio-Acoustics Branch, Aero-Medical Laboratory, Wright Air Development Center, Ohio.]
Latent Effects of Low Noise Levels on the Temporary Threshold Shift (TTS)
Authors: Trittipoe William J.
Published: September 2005

Reasonable extrapolation of existing experimental data suggests that, while there may be no measurable change in the temporary threshold shift (TTS) following exposure to low noise levels, such exposure may have a sensitizing effect upon the hearing system. The present study measures the TTS following high-level noise exposure under two conditions: (1) a control condition where the high-level noise is preceded by a period of silence; (2) an experimental condition where the high-level noise is preceded by noise levels which alone are not associated with a measurable TTS. Four listeners were exposed to a series of noise conditions for 18 min per condition. The control condition consisted of 15 min of silence followed by a 3 min exposure to a noise level of 118 db SPL. The experimental condition consisted of a 15-min exposure to sensitizing noise levels ranging from 18 to 88 db followed by a 3-min exposure to 118 db. Threshold measurements were obtained at 4000 and 6000 cps for 5 min preceding the sensitizing exposure, and continuously for 10 min after cessation of the 18-min exposure duration. In general, when the sensitizing noise preceded the high-level noise, a significantly greater TTS resulted than when silence preceded the high-level noise. That is, a “sleeper effect” was generated by the sensitizing, low noise levels. This held for most of the listeners, and for most of the sensitizing levels employed. It is concluded, then, that (1) noise exposure levels which in themselves produce no TTS may have a sensitizing, or residual effect upon the hearing system and (2) that zero db of hearing loss following noise exposure does not necessarily constitute complete recovery of the auditory system.
Correlation between Thresholds of Hearing by Bone and by Air Conduction for Normal Individuals
Authors: Corliss Edith L. R. , Smith Ernest L.
Published: September 2005

On a group of young normal subjects for whom threshold of hearing by bone conduction was measured, threshold measurements by air conduction were made. Correlation of these results gives a limiting relationship for the difference between hearing by air and by bone conduction. Because of the lack of ear canal impedance data, absolute power threshold correlations could not be found, but empirical relationships to sound pressure threshold can be given.
Spectrum of Noise Passed through a Symmetrical Limiter (with Applications to Remote Masking)
Authors: Cox Jerome R.
Published: September 2005

A band of noise that is passed through a nonlinear device will generally have components throughout the frequency range below the original passband. Conventional techniques for calculating the strength of these components fail. The expansion in powers of the correlation function used by S. O. Rice [Bell System Tech. J. 25, 46 (1945)] converges too slowly in this frequency range. In addition the frequency characteristic of the assumed passband has skirts that do not vanish rapidly outside of the nominal passband. A new method has been developed that gives an analytic solution to this problem when the noise exceeds the linear range of the device only occasionally. Low-frequency spectra for several simple nonlinear devices will be discussed. The particular case of a symmetrical limiter will be presented with applications to the remote-masking phenomenon.
Excitation of Oscillations in the Shape of Pulsating Gas Bubbles; Experimental Work
Authors: Strasberg M. , Benjamin T. Brooke
Published: September 2005

When a gas bubble in a liquid responds to sound, the bubble surface can be excited into oscillatory departures from spherical shape. In the past it has been assumed that these shape oscillations occur only when the sound pressure varies over the surface of the bubble. It has now been observed that shave oscillations are excited even when the sound pressure is uniform, provided its amplitude exceeds a critical value. The excitation is associated with the inherent instability of a spherical surface when undergoing periodic radial pulsations in response to the sound. The critical sound pressure causing this instability has been measured for individual air bubbles trapped at the center of a water-filled sphere resonating acoustically in a radially-symmetric mode at 25 kc/sec. As the bubble radius increases from 2 to 7 × 10−3 cm, the measured critical peak sound pressure causing instability decreases from about 0.6 to 0.17 atmos.
Excitation of Oscillations in the Shape of Pulsating Gas Bubbles; Theoretical Work
Authors: Benjamin T. Brook , Strasberg M.
Published: September 2005

The theoretical model comprises a bubble undergoing radial pulsations of prescribed frequency ω and amplitude δ in response to a symmetrical sound pressure. To determine whether or not the spherical form of the bubble is stable, the behavior of a nonspherical perturbation is investigated; this is expressed as an(t)Sn, (n = 1, 2, 3 …), representing the general term in the expansion by surface harmonics Sn of an arbitrary perturbation. Account is taken of viscosity and surface tension. The coefficient an(t), which is a function of time only, is shown to satisfy a form of Mathieu's equation, and the theory of this equation gives the conditions under which an increases indefinitely and thus instability occurs. It appears that a given perturbation is unstable for certain combinations of ω and δ; in particular, quite small values of δ will cause instability when ω is approximately twice the frequency of free vibrations in the mode Sn. The main effect of viscosity is to suppress instabilities which might otherwise occur for large values of n.
Radiation and Absorption of Sound by Corrugated Pistons
Authors: Cook R. K.
Published: September 2005

Expressions for the radiated sound fields of vibrating strip pistons and circular pistons, on the surface of an infinite reflecting plane, have been obtained. The amplitude of the piston's surface vibration is a sinusoidal or Bessel function of location on the piston, so that the amplitude distribution is corrugated. The formulas are obtained by an integral equation technique. The expressions can be used to calculate absorption cross sections for sound incident on circular and strip patches of known admittance.
Noise Reduction in Vibrating Shells and Housings
Authors: Skudrzyk Eugen J.
Published: September 2005

A noise producer is usually pictured as a piece of rotating machinery mounted on a heavy base plate and insulated from the ground by means of an ideal spring. Such a model is too idealized to be of great value in many practical applications. The general case may be represented by a periodical force or statistical noise source that drives a point mass which, in its turn, excites a housing or shell with many natural vibrations. This case is dealt with in a rigid mathematical manner on the basis of the asymptotic laws of the natural modes of shells and membranes. The possibilities and methods of noise abatement for this general case in air and in water are discussed in detail.
Electromechanical Behavior of the Bender-Activated Tonpilz
Authors: Ehrlich S. L. , Parke N. Grier , Hueter T. F.
Published: September 2005

This paper relates to transducers using one or several bender elements that are clamped in a rigid structure of finite effective mass. Transducers of this type were first conceived by E. E. Turner of Raytheon (patent pending). The analysis of dynamic behavior of clamped-clamped benders is extended to the case where the damping structure partakes in the motion. The ratio of the effective mass of the clamps to the effective mass of the bender determines the location of the nodes, in close analogy to the case of the classical tonpilz. An equivalent circuit is found from which the Q and resonance frequency may be determined. From the stress distribution of the particular bending mode used optimal conditions may be specified for the attainment of a high electromechanical coupling coefficient.
Effect of Duration upon Vowel Identification
Authors: Stevens Kenneth N.
Published: September 2005

The purpose of this experiment is to determine the extent to which both duration and formant frequencies play a role in the identification of American English vowels. A resonance analog synthesizer was used to generate a number of cvc syllables in which the initial and final consonants were always /d/ and /s/, respectively. The durations of the vowels were given values from 20 to 500 msec. Two series of stimuli were recorded and were presented to listeners in random order. In the first test the frequencies of the first three formants of the vowel varied in several steps to encompass values appropriate for the front vowel series /iɪɛæ/, and the listeners were asked to identify the vowel as one of these; in the second test the back vowels /uᴜʌɑ/ were studied. The results indicated that the /iɪ/ and /uᴜ/ distinctions are affected only slightly by vowel duration whereas the distinctions /ɛæ/ and /ʌɑ/ are strongly influenced by duration. In a similar experiment in which the stimuli were mixed with noise, the influence of vowel duration was even more marked. The results are discussed in the light of existing data on vowel perception. (This research was supported in part by the National Science Foundation.)
Study of Perception of Phase Alterations in Speech Spectra
Authors: Miller Joan E. , Mathews Max V. , David E. E.
Published: September 2005

The extent to which the ear is sensitive to phase changes in the speech spectrum is uncertain. Evidence has been obtained previously to indicate that the ear does detect relative changes of phase in certain sinusoidal complexes, while on the other hand, many successful coding devices for speech ignore phase information. Therefore, it is the purpose of this study to obtain additional knowledge on phase sensitivity. A computer simulation is described in which speech samples have been modified so as to retain their original amplitude spectrum, but to have arbitrary phase spectrum. The study was carried out by sectioning the voiced portions of a speech sample into pitch periods, analyzing each pitch period to determine its harmonic components, and resynthesizing the pitch periods with various arbitrary phase patterns. The distribution of peak factors (ratio of range to average absolute amplitude for each pitch period) was computed to characterize the envelope for each phase pattern. The subjective effect of various phase patterns was evaluated by listening tests.
Fundamental Frequency and Absolute Vowel Identification
Authors: Wendahl Ronald W.
Published: September 2005

Five vowel-like sounds, /i/, /ɛ/, /æ/, /ɑ/, /ɔ/, and /u/, were recorded from a series vowel synthesizer with both male and female formant center frequencies and fundamental frequency varied in six steps from 100 to 800 cps. Each stimuli was inflected upward one semitone. Listeners, trained in phonetic transcription, were asked to identify which vowel sound was played. The data show interaction between formant frequency and vowel identification suggesting that information may be conveyed by the frequency spacing between the fundamental frequency and formants as well as the center frequencies of the formants.
Analysis of Vowels of Laryngectomized Speakers
Authors: Waldrop William F. , Toht Arthur E.
Published: September 2005

Three vowels, oo (u), ē (i), and ä (a), sustained, in isolation by laryngectomized speakers, using each of the recognized methods, buccal, pharangeal, and esophageal, of psuedo-phonation, and by a normal speaker, were analyzed for their harmonic content. Closed loops of magnetic tape presented a continuous, sustained sample to a standard sound analyzer and graphic recorder. The resulting harmonic analyses were compared to those of vowels of normal speakers. (This work was supported in part by the American Cancer Society, Illinois Division, with the technical assistance of Sears Roebuck and Company.)
Ultrasonic Absorption in Ethyl Acetate
Authors: Carome E. F. , Gutowski F. A. , Burlage S. R.
Published: September 2005

Measurements of the absorption of ultrasound in ethyl acetate have been made in the frequency range from 2 to 20 Mc. An interferometric method was used and comparative measurements in water were made in an attempt to eliminate errors produced by diffraction effects. As expected, these latter effects were evident especially at the lower frequencies; the sensitivity of the detection system employed was such that peaking effects due to diffraction, as predicted by other investigators [Seki, Granoto, and Truell, J. Acoust. Soc. Am. 28, 230 (1956)], were easily discernible. Though a steady increase in α/ν2 with decreasing frequency was found, the sharp rise reported by various workers in the vicinity of 6 Mc did not occur. (Supported in part by the Office of Naval Research.)
Measurement of Ultrasonic Wave Velocities and Elastic Moduli for Small Solid Specimens at High Temperatures
Authors: McSkimin H. J.
Published: September 2005

An improved buffer rod-specimen unit is described for measuring longitudinal wave velocities in solids at temperatures up to 350°C. The method is particularly useful in determining elastic moduli of single crystals since very small path lengths in any prescribed direction can be employed. The use of molten metals to provide coupling at still higher temperatures is discussed. Several high-temperature techniques involving mode conversion at an impedance discontinuity for generating shear waves will be detailed, with particular interest in application to crystalline media. The various methods are illustrated with data for fused silica and single crystal germanium.
Identification of Speech Sounds by Means of a Digital Computer
Authors: Hughes George W.
Published: September 2005

A digital computer (MIT Whirlwind I) has been programed to analyze speech. Present programs are capable of classifying different portions of the speech signal as vowel, fricative, nasal, or silence, and of tracking vowel formants with some accuracy. On the basis of these data procedures have been devised for identifying a number of words. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research); and in part by the National Science Foundation.]
Apparatus for the Generation of Psycho-Acoustic Stimuli Varying in Complexity from Noise Bursts to Syllables
Authors: Rosen George , Stevens Kenneth N.
Published: September 2005

Apparatus designed to control a speech synthesizer is described. The equipment is also useful for the generation of a large class of complex acoustic stimuli. It may be likened to a computer with both digital and analog elements. In the digital portion a system of counters and gates generates a 100-point time base. These points can be “picked off” as pulses to trigger flip-flops, relays, and functions generators in a large variety of possible temporal programs. In the analog portion, the function generators provide piece-wise-linear amplitude envelopes for buzz and noise sources and are also used in the synthesizer for programing changes in articulation or in formant frequencies as well as changes in fundamental frequency. The buzz and noise generators use novel diode amplitude control circuits to circumvent the shortcomings of balanced modulators. The logical design of the timing circuits is such that, in many cases, each experimental variable may be under the control of a single switch, so that tests may be recorded rapidly and accurately. Examples of the use of the apparatus in studies of the synthesis of speech and in the generation of stimuli for more general psychophysical experiments are given. [This research was supported in part by the United States Air Force under contract No. AF19(604)-2061.]
Self-Maintained Transverse Oscillations of a Jet; Edge Tones
Authors: Brackenridge J. B. , Nyborg W. L.
Published: September 2005

When a thin flat blade of fluid impinges upon a rigid wedge, transverse oscillations are set up, and, at high enough flows and sufficiently great amplitudes, sounds are generated, called edge tones. These phenomena have been fairly extensively studied in air but very little comparable information is available for operation in liquid. A report will be made here on observations in liquids, specifically, water-glycerine mixtures. For stream velocities up to 200 cm/sec jet configurations have been observed by means of stroboscopy and motion pictures have been taken, using camera speeds up to 3500 frames/sec. The jet was made visible by a special dye method originated by J. Bouyoucos. Three different modes of oscillation of the stream are found; these apparently correspond to similar modes previously observed in air, called stages by G. B. Brown. The onset of stage 1 and transitions between the various stages are studied as a function of viscosity, stream velocity, and other parameters of the system. At stream velocities greater than 200 cm/sec hydrophone measurements were made on the associated edge tones. Excerpts from the motion pictures will be shown. (This work was performed in part at Muskingum College, supported there by the Research Corporation, and in part at Brown University, supported there by the Office of Naval Research.)
Mode Coupling on a String—an Example of Magnetomechanics of Extended Systems
Authors: Ingard Uno
Published: September 2005

The motion of a stretched string, forming one part of an electric circuit, is studied as the string oscillates in a magnetic field. Special attention is paid to the mode coupling provided by the magnetic field, the rate of growth of higher modes as the string is released from its fundamental mode displacement, and the “equilibrium”-energy distribution on the various modes of the string. In addition to the study of the finite string, the scattering of a wave on an infinite string running through a magnetic field is discussed. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Air Research and Development Command), and the U. S. Navy (Office of Naval Research).].
Bending Wave Propagation in Multilayer Plates
Authors: Kurtze Günther
Published: September 2005

A simple method is described for the calculation of bending wave velocity and loss tangent in coupled plates using analog circuits. As special examples, the bending wave propagation is discussed in two parallel plates coupled once by a viscous liquid, and second by a layer of foamed plastic. A comparison between theory and experimental results shows satisfactory agreement. In both these cases, considerable damping can be achieved so that an application for structure-borne sound reduction seems promising. [Supported by ONR Contract Nonr-2321(00), Task NR 062-205.]
Method for Numerical Evaluation of the Coefficients of Fourier Series
Authors: Haase Kurt H.
Published: September 2005

The coefficients a0, am, and bm of a Fourier series f(x) = a0 + Σmam cosmx + bm sinmx, where m = 1,2,3,⋯, ∞ is the harmonic order, can be evaluated by a simple formula if f(x) is a sequential trace of n straight lines. The formula makes use of the slopes Ai and the intercepts Bi of the 1 ≦i≦n lines contained within the period. If the line crossings are equidistant in the direction of the x axis, the formula will not only be more simplified by the direct use of these n sample values but the coefficients can be taken as the products am = Cmam* and bm = Cmbm*. The factor Cm decreases with increasing values of the integers m. The discrete values Cm appear within an envelope that is the picture of an attenuated square cosine wave. The harmonic order m and the subdivision number n of the period range are parameters in a tabulation of Cm. The second factors are introduced as periodic Fourier coefficients am* and bm*. These coefficients are an infinite repetition of the finite range 1 ≦ m ≦ n, if m runs from 1 to infinity. Assuming n is a multiple of 4, only n/4 periodic coefficients have to be evaluated. Multiplication with the tabulated values Cm result in an arbitrary series of coefficients am and bm. So far as any periodic function f(x)—given by an experimental observation, for instance—can be approximated by a sequential trace of straight lines, f(x) can be approximated by the Fourier series of the straight-line trace. The numerical evaluation of the coefficients of the trace is not restricted to a certain number. in the harmonic order, such as to the first 6 or first 12 harmonics, for instance. It can easily be programed for desk machine calculators or for computers. A simple schematic calculation can be made to yield either an arbitrary series or any particular order of coefficients. The method can be extended to numerical evaluation of the Fourier integral as well.
Spatial Sampling and Processing
Authors: Stocklin Philip L.
Published: September 2005

Using the Dirichlet problem, it is shown that under certain general conditions, a complex monochromatic sound field may be completely specified by its amplitudes at points one-half wavelength apart in space. From this fact, an array space-field transform is built up analogous to existing Fourier array-pattern transforms. Discussion is given of the maximum order of spherical harmonic necessary to describe the sound field, and maximum necessary volume to describe the array-space transform of the field. Several fields and array-space transforms are given, including S/N examples. The manner in which spatial decision procedures (array design) may be based on the theory is indicated, and a time-frequency extension is introduced.
Comparison of Panel Sound Transmission Data with Noise Reduction Measurements of an Aircraft Fuselage Section
Authors: Bishop D. E.
Published: September 2005

Major differences often exist between the fuselage wall noise reduction estimated from flat panel sound transmission loss data, and that actually achieved with the completed aircraft. To determine the magnitude of these differences during the design of a jet transport aircraft, sound transmission loss measurements of 30- × 40-in. panels inserted in the walls between a reverberant source room and an anechoic receiver room were compared with the noise reduction achieved with a fuselage section 19 ft long, and approximately 12 ft in diameter. The noise reduction was measured with the section installed in a 33.5- × 26- × 21.5-ft reverberant room. The section interior was installed in steps, permitting evaluation of the intermediate stages of acoustical treatment. The panel transmission data represent idealized wall assemblies, while the section measurements introduce the influence of basic aircraft structure, important at frequencies below about 500 cps, and the limitations of practical installation details upon the noise reduction attainable at high frequencies. The section measurements also include the effects of the internal cabin environment, determined by cabin geometry and sound absorption, and the interaction of sound transmission paths of differing characteristics.
Noise Generation by Interacting Air Jets
Authors: Ingard Uno , Maling George C.
Published: September 2005

At a previous meeting of the Acoustical Society measurements of the noise produced as a result of the interaction of two air jets at angles of intersection between 0° and 180° were reported. The acoustic power from the jets was found to increase with the angle of intersection and reach a maximum when the angle is about 90°. In the present case (jet diameter 2 cm, Mach number M≅0.5) the maximum value of the interaction noise power is about 12 db larger than the power from the two jets separately. As an extension of this work measurements have been made as a function of the vertical separation of the jets, keeping the angle of intersection constant, equal to 90°. An attempt is made to explain the results from these experiments in terms of the effect of the mean gradients in the flow, which leads to a radiated sound power proportional to the integral of u′6|grad U|2 [Lighthill, 1952] where u′ and U are the local fluctuating and mean velocities of the jets, respectively. The experimental results can be satisfactorily explained on this basis since the noise from two interacting jets seems to be predominantly a result of mean shear. On the basis of these results the noise from a single jet is discussed as a sum of contributions proportional to u′8 and u′6|grad U|2, respectively, and the relative importance of these terms is discussed. [This work was supported in part by the U. S. Army (Signal Corps}, the U. S. Air Force (Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Measurement of Acoustic Definition in Several Large Auditoria
Authors: Anderson C. D. , Collins J. L. , Boner  , Lane
Published: September 2005

The acoustic definitions of several large auditoria and churches have been measured using the equipment described at the Fall, 1957, meeting of the Acoustical Society. The values obtained are discussed in relationship to the measured reverberation times and the sizes and shapes of the buildings. These included a city coliseum of over one million cubic feet, a church with a ceiling in the shape of a paraboloid of revolution, and other smaller churches and auditoria.
Pulse Technique Applied to Acoustical Testing
Authors: Cho Alfred C. F. , Watson Robert B.
Published: September 2005

The lack of validity of the diffusion assumption makes it desirable to search for further means of assessing the acoustical properties of a room rather than a criterion based solely upon reverberation time. A pulse technique is devised to study transient sound in a room. An electroacoustic system was constructed for generating sound pulses and for receiving and recording such pulses after transmission through a room. Sound pulses were introduced into a room and the resulting sound field was measured at a number of positions. Acoustical testing includes the transient response in a lecture room, the determination of absorption coefficient of a wall, and the trace of a sound path in a room. A pulse statistical analysis was made. A steady-state decay curve was constructed using known values of reverberation time. The deviations from this steady-state decay in transient pulse measurements (over the peaks and troughs) were measured for 35 terms. A “mean value” decay curve was constructed from the average of the deviations. From the transient curve and the “mean value” curve, a rms deviation was obtained. The rms deviations for several positions in a lecture room and at different frequencies were computed.
New Siren Design
Authors: Allen C. H. , Watters B. G.
Published: September 2005

On the assumption of the additivity of steady and acoustic flow characteristics, an equation was developed for the time variation of a siren port area required to produce a sinusoidal wave. For high efficiencies, the operating pressure must approach the peak acoustic pressure and under this condition the port area variation departs widely from a sinusoid if a sinusoidal wave is to be generated. A siren has been constructed incorporating the additivity assumption in the design of the aperture shaping. With this design a sinusoidal wave has been generated over a wide range of frequency and output power. The harmonic components are more than 15 db below the fundamental over a 40-db range of output power. Efficiencies ranged from 15 to 40% at full output. Amplitude modulation of the output signal was provided by the use of a fast acting shutter so shaped that it maintains a substantially sinusoidal output at all settings. [This work was supported in part by U. S. Air Force Contract AF 33(616)-5274.]
Cavitation Generated by Single Underpressure Pulses.
Authors: Kurtze Guänther
Published: September 2005

An experimental method is describe with which single underpressure pulses of two μsec duration and a maximum amplitude of −30 atmos can be generated. Recording of any cavitation event is ascertained by reducing the static pressure to about the vapor pressure of the liquid. The cavitation threshold for water, oil, and CCl4 turns out to be about −20 atmos independent of gas contents, impurities and surface tension of the liquid. Conclusions are drawn with respect to the nature of the cavitation nuclei. The apparent frequency response of the cavitation threshold for ultrasonic cavitation is discussed.
Sounds in the Rounds
Authors: Purcell Jack B. C.
Published: September 2005

Architects and engineers utilizing thin shell concrete domes, space frames of compound curvatures, and circular plan forms to enclose monumental spaces have created some of the most imaginative structures of our day. It would seem that the aesthetic possibilities and structural economies are unlimited. However, acoustical analyses performed on some of the structures indicate that serious acoustical defects can occur, if proper precautions are not taken. This paper presents a discussion of the fundamental problems inherent in these forms which give rise to the acoustical phenomena known as creep, focusing, and flutter echoes. For example, recordings in some of the recently completed structures indicate that prior to corrective acoustical treatment, flutter echoes may persist for periods in excess of eight seconds. The use of design studies to predict and control these phenomena is described and tape recordings are presented as an audio presentation. Experience gained from studies of these structures indicates that several basic techniques employing the use of sound reflecting and/or sound absorbing materials can produce aesthetically pleasing results as well as a satisfactory acoustical environment.
Rockefeller Institute for Medical Research Auditorium
Authors: Farrell William R.
Published: September 2005

This auditorium, designed principally for large conferences and lectures but also to be used for chamber music and other types of programs, is enclosed by a hemispherical dome. The solution involves the application of large convex sound reflecting surfaces to the interior combined with areas of sound absorbing treatment for reverberation control. Results of measurements and hearing tests are discussed.
Acoustic Treatment and Sound System for Coliseum, Corpus Christi, Texas
Authors: Lane R. N. , Boner  , Lane
Published: September 2005

The acoustic treatment of a large Quonset but shaped coliseum is described. Before treatment the building was judged to be “impossible” acoustically. Acoustic measurements of reverberation time, articulation index, and definition before and after treatment are presented. The design of a sound system for the coliseum is also described.
Procedure in Auditorium Design
Authors: Olney Benjamin
Published: September 2005

Discussion is confined to general-purpose auditoriums equipped with a stated number of fully upholstered chairs in a given floor area. Bounding surfaces of low absorptivity are stipulated. The design procedure is outlined as follows (1). The total absorption provided by the upholstered chairs, two-thirds audience, stage opening, and the hard room surfaces is estimated. From a chart that combines the Knudsen and Harris curve of optimum reverberation time with Beranek's curves of Sα as a function of volume and reverberation time there is found the volume that will yield optimum reverberation time with the total absorption estimated in the foregoing. (2) A ceiling profile that will, with the given floor area, yield the above optimum volume and, at the same time, give the most satisfactory distribution of reflected sound is developed by successive trials. A mathematical instrument that greatly facilitates the foregoing process is described. The rear wall is shaped to provide beneficial reflections to the rear seats. Optimum reverberation time and transmission efficiency are achieved in a minimum volume and without waste of sound energy in added absorption. Auditoriums designed according to the foregoing procedure have been found to provide excellent speech transmission and satisfactory hearing of music. No electrical amplification has been found necessary in auditoriums of upward of 1000 seats.
Sound-Absorbing Treatment for Large Auditoriums
Authors: Cavanaugh William J.
Published: September 2005

Currently available materials and methods for controlling echo and reverberation in large, arena-type spaces are discussed. Several recently completed domed and vaulted structures and their particular solutions are described. Experience has indicated that the architect and acoustician have available a wide range of materials from which to select a solution compatible with the ofttimes conflicting requirements of acoustics, aesthetics, and budget.
Latency of Action Potentials in the Cochlea of Guinea Pig
Authors: Deatherage Bruce H. , Eldredge Donald H. , Davis Hallowell
Published: September 2005

The latency of the well-synchronized whole-nerve action potential (AP) in the cochlea of the guinea pig includes both neural and traveling-wave delays. The latency varies with the intensity and with the frequency of the acoustic stimulus. Selective local interference with the response was produced by (1) selective masking, (2) local fatigue of sensory elements, and (3) local injection of drugs. Such interference in the basal turn prolonged the latency of the AP response. Interference in higher turns suppressed later portions of the response without changing the modal latency. Apparently nearly all of the well-synchronized AP is due to neurons that arise in the first turn of the cochlea, regardless of the frequency of stimulation. The traveling wave delay appears as a component of latency only in the smaller AP responses that remain after the impulses arising in the first turn are suppressed. Apparently information about the time of onset of an acoustic signal is delivered to the central nervous system primarily by the well-synchronized initial portion of the AP response. (Supported by the Office of Naval Research, Contract N6onr 272.)
Factor Analysis of Cochlear Injuries and Changes in the Electrophysiological Potentials Following Acoustic Trauma in the Guinea Pig
Authors: Eldredge Donald H. , Covell Walter P. , Bilger Robert C. , Davis Hallowell
Published: September 2005

Following acoustic trauma in the guinea pig the changes in “threshold” and maximum voltages which can be measured for action potentials (AP) and for cochlear microphonics (CM) in different turns of the cochlea and for different test frequencies differ quantitatively. Acoustic trauma was produced by exposure to 500-cps tones. Duration and SPL of the exposures were varied inversely and approximated exposures of equal energy. All changes in electrophysiological potentials were significantly correlated, some very highly. The anatomical ratings of cochlear injury were less well correlated. A factor analysis of all variables, including measures of the traumatic exposures, showed (1) changes in CM depend on the place of measurement, (2) changes in CM do not depend on the frequency of test signal, (3) changes in AP relate best to changes in CM measured in the basal turn regardless of frequency of test signal, and (4) the scale used for rating anatomical injury in these and prior experiments does not predict changes of CM when duration and SPL of traumatic exposure are varied widely. [Supported in part by Contract No. AF 33(616)-3637, Bio-Acoustic Branch of the Aero Medical Laboratory, Wright Air Development Center.]
“Steady-State” Auditory Nerve Potentials for Different Stimulus Repetition Rates
Authors: Peake W. T. , Goldstein M. H. , Kiang N. Y-S.
Published: September 2005

Two major difficulties encountered in recording auditory nerve potentials at high stimulus repetition rates are (1) the small amplitude of the responses, and (2) the possible contamination by aural microphonics. With the aid of an average response computer, we have studied the behavior of the N1 and N2 components to weak bursts of noise; the averages were computed for time intervals that start several seconds after the onset of the stimulus. Gross electrodes were placed either near the round window or in the vicinity of the internal auditory meatus of anesthetized cats. This procedure optimizes the detection of the neural components and the amplitudes of the “steady-state” neural responses can be measured as the repetition rate is changed. Above 10/sec the amplitude decreases continuously as the repetition rate increases. There are irregularities for rates near 600/sec, which may result from the interaction of N1 with the previous N2. The maximum rate at which synchronized activity is detectable lies around 3000/sec. The plot of amplitude vs rate does not exhibit plateaus as Derbyshire and Davis found in recording “maximal unequilibrated” responses at the onset of pure tone stimuli. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command) and the U. S. Navy (Office of Naval Research).]
Analysis of the Frequency Characteristic of the Ear below 1000 cps
Authors: Zwislocki J.
Published: September 2005

The available experimental data show that the mechanical system of the ear cannot fully account for the dependence of the threshold of audibility on sound frequency. Neural phenomena must be involved. Recently, a quantitative analysis of the threshold curve at frequencies below 1000 cps became possible, due to the determination of the effect of sound frequency on the temporal auditory integration. Such a determination is possible with the help of short pulses. As a consequence of the high damping of the ear, the pulse frequency can be varied in a wide range without noticeably affecting the transmission of the pusles to the sensory cells. It can be shown within the experimental error that three factors are responsible for the shape of the threshold curve at frequencies below 1000 cps. They are the sound transmission in the ear, the neural excitability, and the neural integration. (Investigation supported by a research grant PHS B-1559 from the National Institute of Neurological Diseases and Blindness, Public Health Service.)
Comparisons of Hearing Loss in General Population Groups and in Industrial Groups
Authors: Summerfield Anne , Nixon James , Glorig Aram
Published: September 2005

In reporting the hearing of large population samples it has been customary to use the hearing levels of males and females in the 20- to 29-year age decade as a reference zero. Because of the noise exposure and the noise-induced hearing loss sustained by men 20 to 29 years of age in many industrial samples it is not suitable to base comparisons of general population surveys and industrial surveys on the hearing levels of this decade age group. We have found the hearing of the 10- to 19-year old, and in some samples the 15- to 19-year old, females serves as a satisfactory reference zero. When population surveys and industrial surveys are compared on this basis two distinct types of curves appear. In general, the hearing losses of non-noise-exposed populations may be represented by a positive exponential function of age. The hearing of noise-exposed groups is, on the other hand, described by a negative exponential function of age. The differences in these functions lead to speculation about possible differences in cause of presbycusis and noise-induced hearing loss. These differences will be discussed in the light of information about other aging processes.