bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of Acoustic Pulses by a Solid Sphere in Air
Authors: Anderson Robert E.
Published: September 2005

The diffraction of an acoustical pulse in air by a solid sphere is studied by the use of a one cycle sine wave pulse. A generator was designed and built to produce pulses of this type. This generator delivered a gating pulse to an electronic gate to which the sinusoidal signal was applied. The gating pulse was adjustable in time position, width, and repetition frequency but was synchronized with the sinusoidal signal. Accordingly all pulses transmitted by the gate were identical, and could be separated in time by as much as 10 seconds. The gated pulse used was a single cycle of a 10 000-cycle sine wave, successive pulses being one second apart. The Fourier analysis of this pulsed sine wave was found. A speaker was built that would give a reasonable reproduction of this pulsed sine wave. A microphone with the necessary quality was available and was used together with necessary amplifiers and an oscilloscope to record the pulses. The pulsed sine wave was scattered by a one and one half inch diameter solid brass sphere and experimental data found every ten degrees about the sphere. Scattering by the sphere at one scattering angle was computed and compared to the experimental results.
Propagation of Sound Pulses in a Dispersive Medium
Authors: Kornhauser E. T. , Proud J. M. , Tamarkin P.
Published: September 2005

The dispersion of a rectangular pulse with many cycles of carrier frequency propagated along an acoustic wave guide of rectangular cross section has been observed experimentally. As expected, the main signal is propagated with the group velocity and is observed to separate from the initial and final transient portions which travel with the free medium velocity. In the dispersion process, the beating of the initial transient with the main signal causes fluctuations in the envelope of the carrier which compare favorably with the mathematical formulation given by J. D. Pearson [Quart. J. Mech. Appl. Math. 6, 313 (1953)[. This experiment serves, essentially, as a calibration of the wave guide so that it can be used qualitatively as a type of analog computer to predict the effects of similar dispersion on the transmission of pulses of other shapes that are not amenable to actual computation. This research was supported by ONR contracts.
A Method for the Calculation of the Distribution of Energy Reflected from a Periodic Surface
Authors: Meecham William C.
Published: September 2005

The problem consists of finding the amplitudes of the plane waves reflected from a periodic surface due to a plane wave incident upon the surface. Consider first the function formed by the value of the incident wave on the surface and likewise the functions formed from the values of the diffracted waves (consisting of both homogeneous and inhomogeneous plane waves) on the surface. A typical diffraction problem consists of expressing the incident function as a linear combination of the diffracted functions. Unfortunately the diffracted functions are not in general mutually orthogonal so that the problem remaining consists of inverting an infinite system of linear equations. In order to make progress on this inversion, an orthonormal system of functions has been formed from the non-orthogonal diffracted functions. One can then write out the successive approximations to the reflection coefficients of the periodic surface using any given number of diffracted waves. The method has the advantage that it secures the least square fit to the boundary condition using the given set of diffracted waves. The problem has been programmed for MIDAC (the University of Michigan digital computer) in the above form. Numerical results will be presented and compared with the results of experiment. This work has been supported in part by the Office of Naval Research.
Loudness Adaptation for Bands of Noise
Authors: Carterette Edward C.
Published: September 2005

Loudness adaptation is measured by a median plane localization of a dichotically presented acoustic stimulus. Two experiments were done on loudness adaptation for bands of noise. In Experiment 1 (36 subjects), loudness adaptation for a wide band thermal noise (100–5000 cps) was studied at five SPL's: 40, 70, 90, 100, and 105 db over-all. The mean maximum loudness adaptation obtained was 2.3, 9.9, 11.4, 14.4, and 16.3 db, respectively. The mean standard deviation for all measures was 6.1 db, and the distributions of the sets of measures tended to be skewed toward greater adaptation. In Experiment 2 (12 subjects), the loudness adaptation for a 1500 cps tone was compared with that for bands of noise whose centers (mel scale) were at 1500 cps, and whose over-all SPL's were equal to the SPL of the pure tone. The band limits in cps were 1280–1720, 1075–1950, 720–2600, and 100–4900. For each band, adaptation was measured for 50, 70, and 90 db SPL over-all. The essential results are: (1) Loudness adaptation for 1500 cps is about 8.5 db greater than the maximum adaptation for any noise band at any SPL; (2) Adaptation is small (4.5 db) at 50 db for bands of noise, is complete within one minute and is about equal for all band widths; (3) At 90 db a trend becomes clear: the wider the band, the greater the degree of adaptation and the longer the time required for maximum adaptation to be attained. This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, Air Research and Development Command, under Contract No. AF 18(600)-571.
Measurements of Interaural Time- and Intensity-Differences
Authors: Feddersen W. E. , Sandel T. T. , Teas D. C. , Jeffress L. A.
Published: September 2005

Measurements of interaural time-differences and of interaural intensity-differences have been made, employing five subjects and a variety of azimuth positions for the sound source. The time measurements were made using clicks from a movable loudspeaker. Microphones located at the entrances to the external auditory meatuses were used to actuate an electronic timer. Interaural intensity-differences were measured at a variety of pure-tone frequencies and source-positions. A high-speed level recorder was employed to record the output of a microphone located at the entrance to the external auditory meatus. The tape of the level-recorder was driven, during some of the measurements, to correspond to frequency-change for a particular source-position, and during other measurements, to correspond to source-position for a particular frequency. The results for the interaural time-difference measurements were in good agreement with expectation, but the results for the intensity measurements deviated widely from what has been commonly assumed. The largest interaural intensity-difference did not usually correspond to a source-position directly to one side, and the variation in interaural intensity-difference with azimuth position was markedly different for different frequencies and for different subjects. The question of how subjects localize high-frequency pure tones seems more obscure than ever. This work was performed under Bureau of Ships Research and Development Contract NObsr-52267.
Measurement of Elastic Stiffness and Dissipation for Solids at Ultrasonic Frequencies
Authors: McSkimin H. J.
Published: September 2005

A review is made of different experimental techniques for measuring the dynamic elastic behavior of solids at frequencies exceeding 20 kc/sec. Because of time limitations, only representative (and in general the more useful) techniques are described in any detail. The correlation between actual quantities measured and basic properties desired is discussed. At frequencies between 20 and 500 kc/sec, resonance, water immersion, and direct transmission techniques are of greatest interest. For frequencies exceeding 500 kc/sec, pulse techniques find wide application. Methods employing phase comparison for accurate velocity of propagation determination are stressed. For very dissipative materials a reflection technique is described. Illustrative data are presented for several of the methods considered, in both low- and high-frequency ranges.
Measurement of Dynamic Mechanical Properties Over an Extended Frequency and Temperature Range
Authors: Kline D. E. , Sauer J. A.
Published: September 2005

An apparatus is described for measuring internal friction and resonant frequency of materials as a function of temperature. A graph of the resonance curve of rodlike specimens is automatically plotted as these specimens are driven through a transverse mode. Data have been obtained for specimen temperatures ranging from 80°K to 400°K on a number of materials, mostly plastics. Results show widely varying behavior depending on the material. In many polymers, interesting relaxation peaks are observed. In instances where other investigators have tested the same material, results are in good agreement.
Change in Young's Modulus and Internal Friction of Sn and Pb at the Superconducting Transition
Authors: Welber Benjamin
Published: September 2005

A change in the elastic constants of Sn [B. Welber, Bull. Am. Phys. Soc. 30, No. 1, 57 (1955); J. K. Landauer, Phys. Rev. 96, 296 (1954)] and of the internal friction in Sn accompanying the transition from the superconducting to the normal state, has been reported recently. These changes have now been demonstrated to occur also in the case of polycrystalline Pb. For this purpose use was made of a 50 kc/sec composite oscillator [S. L. Quimby, Phys. Rev. 25, 558 (1925)] consisting of a quartz crystal cemented to a matched polycrystalline specimen of the metal. A measurement of the electric impedance of such a system at resonance, and in the neighborhood of resonance, is sufficient to determine the Young's modulus and the internal friction of the metal. It was observed that, as in the case of Sn, the internal friction coefficient increases by several percent when the superconducting state is destroyed by the application of a magnetic field. An increase in Young's modulus of the order of one part in 104 for Pb occurs at the same time, while in Sn the increase amounts to only about one part in 105. Increasing the magnetic field to several times the critical value produces no further change in the aforementioned properties of the metal.
Dislocation Relaxations and Anelasticity of Crystal Quartz at Low Temperatures
Authors: Mason W. P. , Bömmel H. E. , Warner A. W.
Published: September 2005

Recent measurements of the Q of well-mounted, contoured, etched, and evacuated quartz crystals show that Q−1 increases proportional to the frequency up to 100 megacycles indicating a relaxation process [A. W. Warner, Jr., Proc. Inst. Radio Engrs. 43, No. 3, 362 (March, 1955)]. Q−1's for crystals from 5 Mc to 80 Mc have been measured at temperatures down to 1.5°K, and two relaxation peaks have been discovered. The two peaks have different activation energies and satisfy equations for the relaxation frequencies fi = ωi/2π: ω1 = 1.3 × 109 e−155/RT; ω2 = 1013 e−1300/RT. (1) The first equation corresponds to a dislocation relaxation and the second to a process that has been interpreted as the sidewise vibrations of oxygen atoms in the Si–O–Si bonds. The dislocation relaxation causes the dissipation at room temperature. Using equations established for dislocations in metals [W. P. Mason, Phys. Rev. 98, 1136 (1955)], it can be shown that the relaxation is the result of pinned dislocations being displaced by one atomic spacing against the limiting shearing stress T130 of the crystal. From the measured results we find N̄, the number of dislocations per sq cm, ≐ 108, l, the loop length, ≐ 2 × 10−8 cm, and T130/μ (μ = shear elastic constant) ≐ 4.5 × 10−8. The number of dislocations is only 10−3 of those in a metal, which accounts for the higher Q and greater mechanical stability.
Transducer Calibration by Impedance Measurements
Authors: Sabin G. A.
Published: September 2005

A self-reciprocity free-field response calibration of a resonant electroacoustic transducer may be determined in a small water-filled tank by only two electrical impedance measurements at each discrete frequency point. The use of a pulsing technique permits the measurement of electrical impedance under two conditions: (1) free-field and (2) under the influence of a totally reflected signal. The vector difference between these two measurements together with the reciprocity parameter (J) establish the free-field response. No measurement of voltage, current, or power is required; the ratio of the hydrophone voltage to the projector current is measured as an impedance vector. This method is particularly applicable to ultrahigh-frequency calibration.
Directional Properties of Continuous Plane Radiators with Bizonal Amplitude Shading
Authors: Martin Gordon E. , Hickman John S.
Published: September 2005

The problem of reducing the levels of the minor lobes of linear, rectangular, and circular radiators is considered theoretically. The shading is accomplished by using equi-phase normal-velocity distributions limited to two discrete amplitudes. Relationships are derived for the sound-intensity directivity pattern and the directivity index of each radiator. An exhaustive study of various directional properties of such radiators is undertaken. This information is presented in terms of the behavior of the major-lobe width, minor-lobe levels, and directivity index as functions of (1) the ratio of the two normal-velocity amplitudes and (2) the fraction of the unit having the higher source amplitude. It is shown that linear and rectangular radiators with such source distributions can be designed so that all minor-lobe levels are at least 21 decibels lower than the major-lobe level; the corresponding value for the circular radiator is 28 decibels. The resultant increase in major-lobe width is approximately 20%. The results are presented so as to provide criteria for the effective use of this method in transducer design.
Comparison of Methods for Group Audiometry
Authors: Ward W. D. , Doehring D. G.
Published: September 2005

Studies were performed comparing various audiometric methods applicable to groups composed of men whose losses might range from 0 to 90 db. Interrupted tones and a 2-db-step attenuator were employed throughout. First, the following methods were compared, using enlisted Naval personnel: (1) simple intensity descent (S merely presses button “when beeps disappear”); (2) direct adjustment of attenuator by S (to “just barely heard”); (3) indirect adjustment (key controlling motor-drive of attenuator); (4) direct adjustment, but with alternate pulses separated by 6 db (in order to give S a “criterion”); (5) indirect adjustment with the 6-db difference in level. No important differences in reliability were found. Therefore, simple intensity descent is to be preferred, being independent of individual differences in adjustment time as well as requiring the least apparatus. Accordingly, a second study was run comparing different conditions of descent (pulse rates of 1.5 and 2.25 pps, rates of decline of 3 and 1.5 db/sec). Again there were no important differences in reliability, all conditions giving a mean standard deviation of about 1.5 db. Furthermore, there is good evidence that the thresholds thus obtained are fully as valid as the results of “standard” clinical audiometry. This work was supported by Office of Naval Research Contract No. Nonr-1151 and performed in collaboration with the U. S. Naval School of Aviation Medicine, Pensacola, Florida.
Effects of Listener Training on Differential Recognition of Monosyllables: Implication for Audiology and Intelligibility Testing
Authors: Dreher John J.
Published: September 2005

The effects of spaced training upon listeners' ability to recognize monosyllables in noise are considered in the light of previous studies and the predictions of information theory. Twenty-four American male listeners were alternately trained and tested at weekly intervals over several months on a sample of 600 English monosyllables which phonetically agglutinate on a given base. Differential recognition of these words according to the component number of speech sounds was charted. Correlations of stage-by-stage results with frequency of linguistic occurrence and number of words available within sound class are presented. Articulation scores of groups and individuals are shown to vary markedly on test and retest as a result of training and the number of phones in a test word. Both training and phonemic length of test words are seen as primary variables, optimum levels of which should be defined for all phases of audiological and intelligibility testing. The above work was carried out under contract with Operational Applications Laboratory, Washington, D. C.
Subjective Measures of Linearity in Ear Defenders
Authors: Harris J. Donald
Published: September 2005

With loudness matches under phones for speech, the threshold differences between a plugged vs a nonplugged ear may change with intensity [Harris et al., Arch. Otolaryngol. 55, 107–133 (1952), Fig. 2B]. This is true for pure tones as well, in about half our subjects. The departure from linearity may amount to 10 db, is related to the volume under the phone, and is not always a diminution of attenuation. This initial nonlinearity is confirmed by carefully noting the shape of the PB articulation function using an ear warden and headphone. A quick method, using ambient white noise and the separation of masked Békésy audiograms at successive noise intensities, has been worked out which determines whether the defender performs the same for medium and for high intensities. The method can be used for any cushion under which a phone can be mounted; or, using a bone conduction pathway, for any meatal plug. A more time-consuming method has been elaborated which directly compares threshold shift for any defender with its behavior in any sound field however intense. A family of recovery curves is drawn for an unprotected ear subjected to various sound intensities. A recovery curve for a protected ear will then identify the virtual SPL received. The attenuation at that noise level can readily be calculated. Extensive measures indicate this protection is not always predicted by the simple threshold-shift technique.
Noise Reduction in a Passenger Airplane
Authors: Beranek L. L. , Kerwin E. M.
Published: September 2005

This paper describes a noise reduction program for the Convair-Liner 340, a 44 passenger, 2 engine commercial passenger airplane. A systematic approach to the problem is outlined, involving: (1) the determination of the existing noise situation within the passenger cabin, including quantitative information on the identification of contributing sources; (2) the development of design criteria for aircraft passenger cabins, and (3) the specification of the amount of noise reduction required as a function of frequency and of position within the aircraft to achieve criterion levels. An exhaust muffler of special design, double windows, damping materials for the fuselage skin, and additional acoustical blankets as interior treatment, constituted the principal noise control measures specified. The distribution of these measures was based on the noise reduction required at the various positions within the cabin. Measured sound pressure levels are presented showing the effectiveness of the noise reduction measures. The results of this program are combined with results of earlier aircraft quieting studies [H. W. Rudmose and L. L. Beranek, J. Aeronaut. Sci. 14, 79–96 (February, 1947)] to produce modified design charts and procedures for the calculation of cabin noise levels.
Design and Operating Factors in the Noise Output of Turbojet Engines
Authors: Mercer Derwent M. A.
Published: September 2005

The noise output of turbojet engines has been shown [O. K. Mawardi and I. Dyer, J. Acoust. Soc. Am. 25, 389 (1953); D. M. A. Mercer and I. Dyer, Preprint 544, presented at the I. A. S. annual meeting, New York, 1954)] to correlate well with a dimensionless quantity containing the stream kinetic energy, temperature, and diameter of the jet. This paper extends these studies to include the effect on noise level of varying the operating parameters of a particular engine at a fixed rotational speed. An important cause of variation in operating parameters is change in atmospheric conditions. This paper presents charts, which, together with some details of engine performance, enable changes in noise level to be estimated. The acoustic output of an engine may vary by some 10 db, at a fixed rpm, over the range of atmospheric conditions encountered in the United States. A change of this magnitude is important when considering various problems of communication and hearing loss among engine operating personnel, and the reaction of a community to the noise stimulus. This work was supported by USAF Contract No. AF 33(616)-2151.
Noise from Centrifugal Fans
Authors: Goldman R. B. , Maling G. C.
Published: September 2005

The sound power radiated from the discharge of centrifugal fans of diameters between 3 and 612 inches has been measured as a function of fan dimensions and operating conditions. The measurements were made by arranging the fan under test to discharge into an 11 foot nonreflecting tube in which the static pressure could be controlled. Air was exhausted from the tube through a side port of high acoustic impedance located part way down the tube. The detecting microphone, which is located in the tube between the exit port and the acoustic termination, is out of the air stream and, therefore, not subject to wind noise. The total discharge noise power P in watts in the range 75 to 10 000 cps was found empirically to be given by P = 0.90 × 10−4(D/W) H3 + 5.2 × 10−10(Q5/W4D8), where D and W are the fan diameter and width respectively in inches, H is the static pressure in inches of water, and Q is the air flow in cubic feet per minute. The angular frequency of the fan wheel does not appear explicitly since this quantity is uniquely specified by H, Q, D, and W. Spectral analysis indicates that the power is concentrated primarily at low frequencies. Application of the results of this study to design problems will be discussed.
Surface Tension Bubble Vibrations
Authors: Proctor T.
Published: September 2005

Experimental verification of the various features described theoretically in the previous paper has been undertaken. A series of microphotographs have been taken of various bubbles while being excited by a small sound field. A movie demonstrating the type of motion as a function of frequency will be shown. Measured frequencies have been correlated with the theoretical modal frequency associated with the bubble's particular motion. Q values of the bubble system have been measured experimentally and found as predicted to be between 15 and 30 for air-water bubbles.
A Determination of the Dependence of Ultrasonic Machineability on Certain Physical Properties of Solids
Authors: Miller George E.
Published: September 2005

In order to gain a better understanding of the mechanism of ultrasonic machining, the ultrasonic machining rate has been measured on a number of solids having different physical properties. It has been found that a correlation exists between the measured machining rate and certain physical properties of the solid being machined. Two cases have been treated; namely, where the tool tip and workpiece are made of the same material, and where they are made of different materials. Empirical equations for the machining rate as a function of these physical properties have been obtained for both cases.
Effect of Vibration Amplitude and Abrasive Slurry on the Rate of Ultrasonic Machining in Tool Steel
Authors: Goetze D.
Published: September 2005

Results of experiments conducted to determine the dependence of the ultrasonic machining rate, V, in Ketos tool-steel on the peak-to-peak amplitude, PPA, of the vibrating tool-tip, on the frequency of vibration, f, of the tool-tip, on the geometric weight mean diameter, rw, of the abrasive particles used in the make-up of the slurry, and on the ratio, ma/mc, of the mass of abrasive to the mass of water vehicle used in compounding the slurry, are given. It is shown that the quotient V/rw PPA f is a constant of the ultrasonic machining process within the range under investigation, and that with its aid the contribution to the machining rate of a single abrasive particle can be calculated. On the basis of this investigation a possible model of the ultrasonic machining process is presented.
Ultrasonic Cutting of Quartz Wafers
Authors: Gibbs Norman E.
Published: September 2005

Apparatus has been designed and built which simultaneously cuts 20 or more quartz wafers, each of which may approximate 114×34×164 inch in dimension, by ultrasonic methods. The problems involved in the development of this equipment covered a wide range. Adequate amplitude of motion of the tool assembly was a prime requisite. One of the most stubborn problems lay in achieving stability in the cutting tool itself. The high acceleration involved created difficult bonding problems as well. Quartz must be cut into thin wafers the surface of which must lie within close limits, measured in minutes, of specified angles with the atomic planes of the quartz crystal. Basic elements of this problem are presented with a brief statement of the limitations and possibilities of the equipment as a tool This work was supported by the U. S. Signal Corps.
Limitations Encountered in the Design of Transducers for Ultrasonic Machining
Authors: Clark Neil
Published: September 2005

Since some data is now available on the acoustic power and vibration amplitude required for ultrasonic machining, design objectives can be formulated for transducers. Extrapolation of known data indicate definite limitations exist on the power required and a maximum power requirement can be predicted on the basis of transducer materials, frequency, active tool area, and material fatigue limit.
Output of a Sound Source in a Reverberation Chamber
Authors: Waterhouse Richard V.
Published: September 2005

Expressions are given for the sound power output of a simple source as a function of position in a rectangular reverberation chamber. The method of images is used in the derivation. The power output of the source near a single plane reflecting wall equals P[1 + (sin 2kx)/2kx], where P is the free-field power output, x is the distance of the source from the wall, and k is 2π f/c; f is the frequency and c the sound velocity. Similar but more complicated expressions hold near corners and edges of the chamber. Thus a simple source with given volume velocity can emit either more or less sound energy in a reverberation chamber than in a free field. When the source distance from the wall exceeds about one wavelength, the power output closely approaches the free-field value. The reverberation chamber can be considered as presenting an impedance which varies with source position. Experimental data are given which support the theory. The reverberation chamber method of measuring the power output of sources is considered in the light of these results. In the general case of an extended source emitting nonspherical waves near reflecting surfaces, the power output cannot be predicted in terms of the free-field output. It has to be measured experimentally.
Absorption Characteristics of Upholstered Theater Chairs and Carpet as Measured in Two Auditoriums
Authors: Lane R. N.
Published: September 2005

Data on the absorption of upholstered theater chairs as measured during the construction of a 496-seat auditorium and a 738-seat auditorium are presented. These data obtained on the seats after placement in each auditorium indicate a much lower absorption per seat over the entire audio-frequency band than has previously been reported. Before the seats were installed in the 496-seat auditorium, 1080 ft2 of Axminster carpet were laid on the floor of this room, and the absorption characteristics of this full-scale sample were determined. These data are also reported in this paper.
Insertion Loss of Side Branch Resonators
Authors: Ingard Uno
Published: September 2005

The effect of source and termination impedance on the insertion loss of a side branch resonator in a duct is calculated and compared with measurements. A graphical method is given which will aid insertion loss calculations when the duct is terminated with an arbitrary impedance.
Ultrasonic Attenuation and Velocities in Normal and Superconducting Metals
Authors: Mason W. P. , Bömmel H. E.
Published: September 2005

Measurements of the sound attenuation of metals at temperatures near absolute zero show that there is an attenuation which increases proportional to the square of the frequency if the metal is kept in the normal state. In the superconducting state this loss becomes very small. Measurements have been made for tin, lead, and copper. For lead and impure tin this loss is independent of the magnetic field, but for very pure tin this type of loss becomes very large and field-dependent. Most of the field dependence is the result of the magnetoresistance effect, but other variations occur which may be related to the size of the specimen. Theoretical calculations show that the increased loss in the normal state is the result of viscous damping of the lattice vibrations by the electrons. This viscosity increases enormously at low temperatures on account of the increase in the mean free path. For lead and tin the indicated number of free electrons is less than the number of atoms, but for copper the two are equal. Measurements in the kilocycle range [J. K. Landauer, Phys. Rev. 92, 296–302 (1954); B. Welber, J. Acoust. Soc. Am. 27, 1010(A) (1955)] have shown variations of velocity at the transition temperature, but no such large variations occur in the megacycle range. Hence it appears that this transition is not of the type predicted by thermodynamic theory.
Relaxation Processes in Shock Waves
Authors: Hornig Donald F.
Published: September 2005

Shock waves provide a convenient means for the study of relaxation processes. In a nonviscous fluid the shock front would be a discontinuity. In a real fluid its thickness depends on the mechanism of viscous dissipation. By studying, for example, the variation of density as fluid passes through a shock front one can study the simple compressional process in monatomic gases, rotational relaxation in diatomic and polyatomic gases, and vibrational relaxation. It has also been possible to gain information about bulk viscosity in liquids. Shock waves are readily generated in a simple apparatus, the shock tube. Processes occurring in a thickness of less than 10−5 cm in gases or 10−4 cm in liquids can be studied by the light-reflectivity technique. Results obtained with respect to all of the previous questions are presented, and some problems and difficulties in the interpretation discussed.
Ultrasonic Absorption Measurements in Some Electrolytes
Authors: Dill Melvin W. , Beyer Robert T.
Published: September 2005

The absorption coefficient α has been measured in aqueous solutions of potassium acetate and magnesium sulfate in the frequency range from 15 to 50 Mc using pulse equipment. The measurements were made at several concentrations in the potassium acetate solutions. These results show a decrease in the absorption below the pure water value for frequencies above 27 Mc. Water solutions of 0.2 molal magnesium sulfate were prepared with various mixtures of methyl alcohol and water as the solvent. It was found that the higher relaxational frequency (above 200 Mc) decreased, and the value of (2αλ)max increased as the dielectric constant decreased. This behavior is similar to that reported by Tamm, Kurtze, and Kaiser for the lower relaxational frequency. This work was supported in part by the Office of Naval Research.
Irradiation Changes of Acoustical and Mechanical Constants in Aluminum
Authors: Lefkowitz Isaai , Oncley Paul B.
Published: September 2005

Recent studies in the field of nuclear energy have shown that certain material properties are affected when materials are subjected to radiation. This paper deals with the results of such studies in relation to metal and more specifically with the irradiation changes of acoustical and mechanical constants in aluminum. A brief introduction highlights the basic theory of irradiation of metals, and is followed by a description of the mechanism of material damage in aluminum resulting from thermal neutron effects. The techniques of measurement after radiation are discussed and a final evaluation of the results and changes in acoustical and mechanical properties is then presented.
Sones, Spectra, and Summation
Authors: Stevens S. S.
Published: September 2005

The current assumption that the loudness in sones of a noise is the sum of the loudnesses in the separate octave bands is shown under direct test to be grossly wrong. These tests show that the loudnesses in octave bands can be combined according to the formula St = Sm + F(ΣS − Sm) where St is the loudness (in sones) of the total noise, Sm is the loudness of the loudest band, ΣS is the sum of the loudnesses of all the bands, and F is a factor that may vary between zero and one. It turns out that under a wide variety of conditions the factor F has the value of 0.27. Consequently, the rule for combining the loudnesses in octave bands is simply this: to the loudness in sones of the loudest band add 0.27 times the sum of the sones in the remaining bands. In order to facilitate the determination of the loudness level (in phons) of the octave bands, equal loudness contours for octave bands were measured in a diffuse sound field. These contours differ markedly from the well-known contours for pure tones. Since loudness in sones S is related to loudness level in phons P by the relation, log S = 0.03P − 1.2, a chart can be constructed from which the loudness of a noise can be computed under the foregoing rule of summation.
Apparatus for the Calibration of Hearing
Authors: Fleming Ethel R.
Published: September 2005

The specialized requirements of hearing tests on military personnel have led to the development of an audiometer which eliminates some of the psychological pressure on the subject. The device has a further advantage of producing results to a somewhat higher degree of accuracy than possible with conventional methods. The apparatus and some of its uses is described.
Attenuation of Ear Protectors by Loudness Balance Methods
Authors: Hershkowitz J. , Levine L.
Published: September 2005

The attenuation of several ear protectors has been measured by a loudness balance technique in which the subject, upon removal of the device, raised the ambient sound level to match loudness to that which existed while wearing the ear protectors. Results were obtained for half-octave bands of thermal noise in a diffuse sound field and for single frequency tones in free field. Attenuation measured by the former method was less at both low and high frequencies than for the latter. Both loudness balance methods gave lower values than had been anticipated from published data based on the absolute threshold method.
On Macronsonics and Periodic Shock Waves
Authors: Hudson G. E.
Published: September 2005

Since the time of Stokes, there has been an ever-increasing number of investigations of anomalies in sonic phenomena when the conditions of linear acoustics are not fulfilled. Some recent theoretical and experimental studies in this direction are discussed. For example, observations show the occurrence of periodic shocks in a Kundt's tube with a piston amplitude of only 18 inch. The laws which these satisfy are investigated as well as the use of such experiments to study the structure of shock fronts, collision of shocks, and ionization by shocks. A first-order description of the periodic flow pattern is obtained from elementary considerations.
Electronic Control of Noise, Vibration, and Reverberation
Authors: Olson Harry F.
Published: September 2005

Existing inactive materials are inadequate to cope with many problems in the control of noise, vibration, and reverberation. It is only within quite recent times that active systems have been given consideration for the control of sound. The electronic sound absorber [H. F. Olson and E. G. May, J. Acoust. Soc. Am. 25, 1130 (1953)] is an example of an active type sound absorber. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected in an inverse feedback manner. The electronic system reduces the effective acoustical impedance in the vicinity of the absorber. As a consequence, the electronic sound absorber may be used in the manner of a conventional sound absorber or as a zone-type sound reducer. The electronic vibration reducer consists of a sensor, amplifier, and driver connected either in negative or positive feedback fashion. The electronic vibration reducer may be used to isolate vibrating machines or to reduce the vibration of machines.
Transient Performance of Transducers for Ultrasonic Materials Inspection. Background
Authors: Van Valkenburg H. E.
Published: September 2005

A review of the development and scope of ultrasonic materials inspection by the method of pulsed wave trains; industrial applications of particular interest; brief description of instrumentation in widespread use today; problems relating to transient operation of transducers for Reflectoscope search units.
A Direct-Reading Acoustical Impedance Meter
Authors: Carrell R. M.
Published: September 2005

A device for the measurement of acoustical impedance is described which employs a high impedance source, monitored by a ribbon element acting as an acoustical ammeter. The output of the ribbon acts through an automatic volume control circuit to maintain constant the volume current injected into the impedance under test. The sound pressure so developed is proportional to the absolute acoustical impedance and is measured by a high impedance probe microphone. The ribbon element also serves as a phase angle reference for the unknown impedance. The total acoustical path length from the ribbon to the diaphragm of the probe microphone is kept to an absolute minimum.
Iron-Aluminum Alloys for Use in Magnetostrictive Transducers
Authors: Pigott M. T.
Published: September 2005

A systematic determination of the electromechanical coupling coefficient k has been made for Fe-Al alloys containing aluminum percentages between 12 and 14 by weight and annealed at temperatures between 600°C and 1100°C. For annealing temperatures in the neighborhood of 1000°C, k2 is about equal to 0.05 and is nearly independent of composition, a result in agreement with earlier measurements of Masumoto. For lower annealing temperatures, k2 becomes sensitive to composition, the highest value measured being equal to 0.12 for an alloy containing 12.3% Al and annealed at 650°C. In all cases eddy current losses are lower for Fe-Al than for soft annealed “A” nickel.
Effect of a Ground Layer on the Field within a Temperature-Created Shadow Zone
Authors: Pridmore-Brown David C.
Published: September 2005

The sound field from a point source located in an infinite half-space above a plane boundary has been studied for the case where the half-space is separated from the plane by a layer of a given thickness. The acoustic properties of the two regions are specified by their temperature gradients. The temperature gradient in the ground layer can be arbitrary, whereas that in the upper half-space is considered to diminish monotonically with the height. The source may be located either within the ground layer or above it. The purpose of this study was to determine to what extent the presence of such a layer might alter the sound field which one calculates when it is absent. In the absence of the ground layer the sound field in the shadow zone is approximately represented by the first mode in a Fourier Bessel expansion, which decays at a rate determined by the ground impedance. The analysis indicates that although the presence of the ground layer does not destroy this shadow region, it may alter the decay rate of the sound field within it. [Supported by Contract NAw-6405 with National Advisory Committee for Aeronautics.]
Instrumentation for Field Studies of Sound Propagation over Ground
Authors: Oleson Stanley K.
Published: September 2005

An instrumentation for sound propagation studies over ground is described. The sound field distribution over ground as well as vertical wind and temperature distribution is obtained. Four model pulsed jets are used as a sound generator, and the sound field is sampled by ten microphones placed over ground up to a distance of about one mile. Temperature and wind distribution up to a height of about 25 feet are measured by five thermistor anemometers and thermometers. The microphones, the anemometers, and the thermometers are sampled by means of a rotating switch, and the corresponding signals are displayed on an oscilloscope. [Supported by Contract NAw-6405 with National Advisory Committee for Aeronautics.]
Noise Spectrum of Acoustically Generated Cavitation
Authors: Holak William
Published: September 2005

Cavitating acoustic fields were generated at 9 kc, 210 kc, 440 kc, 800 kc, and 1080 kc. The noise due to cavitation has been analyzed over a continuous frequency range from 90 cps to 2 Mc. The receiving hydrophones used were a Massa 115 A and an Allen-Spencer probe microphone. The latter was calibrated by the Ordnance Research Laboratory of The Pennsylvania State University from 1 kc to 100 kc and by a pulse reciprocity system in the Physics Acoustics Laboratory from 100 kc to 2 Mc. Three different analyzers were used to cover the entire frequency range. Measurements were made both in the ORL anechoic tank and in the Physics Laboratory tank. In addition to the broad-band noise, harmonics as well as the subharmonic of the driving frequency have been observed. The broad-band spectrum exhibits two plateaus. An expression for the growth and decay of cavitating bubbles has been developed which is in accord with experimental results. More energy appeared at the driving frequency and its harmonics than in the broad-band spectrum. [This work was partially supported by the Ordnance Research Laboratory of The Pennsylvania State University.]
An Ultrasonic Velocimeter for Liquids
Authors: Tschiegg Carroll E. , Greenspan Martin
Published: September 2005

A device using the “Sing-Around Principle“ will be described. The instrument consists of a pair of barium-calcium-lead-titanate transducers and a hard rubber reflector to form a 10-cm sound path. The sending crystal is actuated by an 0.2-microsecond blocking-oscillator pulse. This pulse after passing through the liquid is received and reshaped by a high gain amplifier. It is then allowed to retrigger the blocking oscillator so that the system continually regenerates a sound pulse whose repetition rate depends upon the combined acoustical and electrical delays. Although not an absolute instrument, its high sensitivity and stability make it well suited for detecting small changes (1 part in 105) in the sound velocity. The effective path length and circuit delay are found by calibration against liquids of known sound velocity and having attenuation characteristics similar to those of the liquids to be measured.
A Speech Sound Coder
Authors: Smith Caldwell P.
Published: September 2005

An analyzer has been devised for the direct coding of speech sounds in terms of their characteristic spectral patterns. A conventional set of analyzing filters, with rectifiers and low-pass filters, transforms the voice signal to a set of dc voltages that vary at relatively slow rates. The analyzer transforms these voltages to a group of binary signals that specify the ratio of each filter voltage to the mean or average filter voltage from the set in a continuous measurement, thus providing normalization of the voice spectrum patterns with respect to the amplitude of the voice signal. The analyzer presents the measurement in a matrix having the dimensions of frequency and relative amplitude in decibels; the “occupied” matrix cells represent the spectral pattern of the voice signal at any moment. The transformed patterns are on a logarithmic scale of relative amplitude and are invariant with amplitude changes of the input voice signal over a wide dynamic range. Signals from the matrix “cells” can be summed in various pattern configurations to generate voltages that will serve to automatically detect the occurrence of particular spectral patterns, thus detecting speech sounds in terms of their spectra. A “many-to-one” relationship in the pattern output connections will identify a particular sound whether spoken by an adult or child, whether stressed or unstressed, etc. A thousand such patterns may provide “high-fidelity” voice coding, yet if sampled thirty times a second would require only 300 bits a second to specify the pattern sequences by a digital code. In addition to pattern matching uses, the matrix can drive an indicator matrix of neon bulbs, to generate a running visual display of the normalized spectrum of the voice signal, on a logarithmic scale of relative amplitude. The analyzer is not yet completed, but some of the novel circuit features will be discussed, and possible analogies of the system with the hearing mechanism will be conjectured.
Investigation of the Deep Scattering Layer with Impulsive Sound
Authors: Anderson Victor C.
Published: September 2005

The use of short, broad-band acoustic pulses to study the acoustic properties of the deep scattering layer is described. An underwater spark sound source, and a receiving hydrophone were lowered to the depth of the scattering layer to permit short range observations to be made. The received scattered sound was recorded oscillographically on a rotary drum camera in the ship. These records were subsequently reproduced in the laboratory with a flying spot reader, and a spectrum analysis covering the range of 1 to 10 kc was performed on the individual echoes. By the use of this technique, the frequency dependence of the scattering cross section of a number of individual scatterers was observed, permitting estimates of physical size to be made.
Noise Produced on the Ground by Jet Aircraft in Flight
Authors: Stevens K. N. , Galloway W. J. , Pietrasanta A. C.
Published: September 2005

Several types of jet aircraft with one and two engines were flown at specified altitudes and subsonic speeds directly over a recording microphone on the ground, and continuous recordings of the noise were made. The ranges of altitudes, speeds, and engine operating conditions included those normally used by jet aircraft operating within a few miles of air bases. From the recordings, sound pressure levels in octave bands of frequency were determined as a function of time. Typical results are presented, and comparisons are made between measurements of the noise generated by aircraft running up on the ground and by the same aircraft in flight. The effects of aircraft speed and altitude on the sound pressure levels and on the time patterns and spectra of the noise are evaluated, and some interpretation of the data is given. [This work was supported by the U. S. Air Force.]
Subjective Noise Ratings in Air Force Base Offices
Authors: Beranek Leo L.
Published: September 2005

Questionnaires were submitted to 200 Air Force base personnel located in executive, engineering, and shop foremen offices. The questionnaires asked for ratings of the noise conditions, effects of noise on telephone usage and conversation, sources of interfering noises, nature of the job and the activity most affected by the noise. Octave band sound levels and time variation patterns were measured over a period of two weeks for correlation with the subjective information. The results are compared to previously published data [Leo Beranek, Acoustics (McGraw-Hill Book Company, Inc., New York, 1954), pp. 423–425]. [This work was supported by the U. S. Air Force.]