bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow-Resistance Characteristics of Fibrous Acoustical Materials
Authors: Nichols R. H.
Published: September 2005

The flow resistance of a material is highly important as a factor in determining its acoustical performance in various applications, particularly in the blankets used for soundproofing of aircraft cabins. It is desirable, therefore, to know the manner in which the flow resistance of a lightweight acoustical material varies with such physical parameters as thickness, density, size and shape of fibers, and type of construction (“felting”) of the material.

From an experimental study of a large number of fibrous acoustical materials, the following empirical relation has been established for materials of high porosity (0.9 to 1.0): Flow resistance, R = KS(1+z)Tz 1r2 where K is a constant, characteristic of a particular material, S is the surface density of the blanket of material, T is the thickness, and r is the cross-sectional radius of the fibers. The type of construction of the material determines the value of x in the exponents. This value generally lies in the range from 0.3 to 1.0.
The Properties of Felt in the Reduction of Noise and Vibration
Authors: Tyzzer F. G. , Hardy H. C.
Published: September 2005

In order to provide engineering information for the use of felt in vibration isolation, the dynamic stiffness and damping of three widely different grades of felt were measured by means of resonance curves. The dynamic stiffness, which was much greater than the static stiffness, decreased with amplitude so that the resonance curves were unsymmetrical. Except for pressures below 6 p.s.i., the stiffness modulus of felt increased with static pressure at a rate which made their ratio nearly constant. The natural frequency of a mass supported by a felt pad is, therefore, nearly independent of the static pressure load on the felt. Curves are given showing natural frequencies for 1 inch thicknesses of soft, medium, and hard felt for a range of static pressure between 1.5 and 100 p.s.i. It is shown that, except at low pressures, there is little difference in the natural frequency of hard or soft felt, and that there is a low limit of about 20 c.p.s. for 1-inch felt.
A Slide Rule for the Study of Music and Musical Acoustics
Authors: Waddington L. F.
Published: September 2005

Musicians are seldom concerned with the mathematical background of their art, but an understanding of the underlying physical principles of music can be helpful in the study of music and in the considerations of problems related to musical instrument design. Musical data and numerical standards of the physics of music are readily adaptable to slide-rule presentation, since they involve relationships which are the same for any key. This rule adjusts relative vibration rates, degrees of scale, intervals, chord structures, scale indications, and transposition data, against a base of the piano keyboard. It employs and relates several standard systems of frequency level specification.
The Performance of Cup-Mouthpiece Instruments
Authors: Long T. H.
Published: September 2005

It is shown by a qualitative analysis that the playing of cup-mouthpiece instruments must be associated with the existence of a pressure antinode at or near the mouthpiece, and that harmonic production in such instruments can be adequately explained by the acoustic overload in the air column.

A quantitative analysis discloses the “mechanism” by which the odd series of modes of vibration occur at frequencies related to each other by the 1, 2, 3, 4 integers of the complete harmonic series.
The Influence of Body-Baffle Effects on the Performance of Hearing Aids
Authors: Nichols R. H. , Marquis R. J. , Wiklund W. G. , Filler A. S. , Hudgins C. V. , Peterson G. E.
Published: September 2005

The effect of the wearer's person as an acoustic baffle on the response of a hearing aid, under free-field and diffuse-field conditions, has been studied with a number of hearing aids and wearers. A characteristic effect is found for each model of hearing aid when it is worn at center-chest position in free field. The character of the effect does not appear to be strongly correlated with the size and shape of the wearer. In a sound field of “random” direction of incidence, the body-baffle effect appears to be negligible. Within the limits of linear amplification of a hearing aid, one of the most pronounced of the body-baffle effects had little or no influence on the intelligibility of speech, as determined with four hard-of-hearing subjects.
A Precision Ultrasonic Interferometer for Liquids and some Velocities in Heavy Water
Authors: McMillan D. R. , Lagemann R. T.
Published: September 2005

An acoustic interferometer of improved design and the associated electronic circuit for measurement of ultrasonic velocities in liquids are described. A beat frequency oscillator is used to generate the ultrasonic waves in the liquid, and a vacuum-tube voltmeter is employed as a detector of nodal positions. In order to secure adequate stability an electronically stabilized power supply is used. Measurements of velocities in acetone, benzene, and distilled water are compared with earlier workers and new measurements for heavy water at 5°, 10°, and 15°C are tabulated.
Self-Reciprocity Calibration of Electroacoustic Transducers
Authors: Carstensen Edwin L.
Published: September 2005

By an extension of the reciprocity principle for the absolute measurement of sound, it is demonstrated that a calibration may be obtained on a single transducer without the aid of auxiliary transducers. Measurements using the technique are described and shown to give satisfactory agreement with conventional calibrations.
Construction and Design of Parmly Sound Laboratory and Anechoic Chamber
Authors: Mills Peter J.
Published: September 2005

A description is given of the construction details of the Sound Laboratory recently completed by the Parmly Foundation at Technology Center, Chicago. The function of the laboratory is to carry out research in the prevention and alleviation of deafness. The chief feature of the laboratory is an echo free or “anechoic” chamber. The 40-ton chamber of concrete, steel, wood, and sheet-rock construction is suspended on Neoprene pads to have a natural frequency of about four and one-half cycles per second. Continuous ventilation through ducts of high sound attenuation, 90 db at 128 c.p.s., is provided. The inner surfaces are designed to have 99 percent absorption or better at 115 cycles per second or above. The Harvard treatment of wedge-shaped Fiberglas is used. The chamber is housed in a concrete block wing, the walls of which are lined with Fiberglas sheets. Costs in terms of man hours are given.
Performance of the Anechoic Room of the Parmly Sound Laboratory
Authors: Hardy H. C. , Tyzzer F. G. , Hall H. H.
Published: September 2005

The performance of the anechoic room of the Parmly Sound Laboratory has been measured to determine the characteristics of rooms of small volume with wedge-covered walls. The inverse square law holds to within ±1 db to 6.5 feet from 60 to 24,000 c.p.s., although the theoretical cut-off frequency of the room is 115 c.p.s. At 100 c.p.s., the radiation resistance of a loudspeaker placed near the walls was found to be 18 percent above the free-field value, and the radiation reactance was approximately 5 percent above the free-field value. The differences disappeared two feet from the wall. The wall transmission has been measured as a function of frequency, and the wedges themselves are found to act similarly to a thin plate in optics, having a maximum transmission at 110 c.p.s.
Acoustic Impedance of Sample from Motional Impedance Diagrams
Authors: Fay R. D. , White J. E.
Published: September 2005

If the electrical impedance of an electromagnetic speaker is plotted as a vector when the acoustic loading consists of an air column of variable length terminated by a rigid plug, a circle diagram results. If the air column is terminated instead by an acoustic sample, a second circle diagram results. Various relationships between the two circles have been worked out which yield the acoustic impedance of the sample with considerable precision. The method inherently averages many individual readings and automatically checks the self-consistency of the data. It is applicable to samples with little absorption since full advantage is taken of the possibility of coupling such a sample most effectively to the speaker by means of the air column. The method has been used to determine the acoustic impedance of commercial materials at low audiofrequencies, where the absorption is quite small.
A Method for Measuring Acoustic Source Impedance
Authors: White J. E.
Published: September 2005

The acoustic output impedance of a sound source can be determined from relative pressure measurements following a procedure which requires rather simple equipment and practically no time for processing data. The sound source must have a radiating area which is essentially a piston and which can be coupled to a closed tube of variable length. The tube is terminated by a rigid plug in which a pressure-measuring microphone is mounted flush with the surface. Thus the microphone measures the pressure at the terminating plug as the length of the air column is varied. These pressure measurements are related to the acoustic impedance of the source by the expression (P0/Pl)2 = sin2kl[R2 + (X − cotkl)2], where p0 is the zero length or blocked pressure, pl is the pressure at length, k is 2π divided by the wave-length, l is the length of the air column, R is the specific acoustic resistance ratio for the source, and X is the specific acoustic reactance ratio for the source.

The principal value of the method lies in the fact that for any chosen length, the possible values of the pressure ratio represent a family of circles on acoustic impedance coordinates. Thus a chart can be very easily prepared from which the source impedance can be read and recorded as the data are taken. The circles can be labeled in decibels so that the only data reduction required is the subtraction of the pressure at length l in decibels from the blocked pressure in decibels. The author used the method in the “cut and try” development of a sound source for an acoustic filter experiment, where the dozens of impedance determinations would have represented a prohibitive amount of work if even moderately complicated data processing had been required.
Attenuation of Sound by Light-Weight Multiple Structures
Authors: Beranek Leo L. , Work George A.
Published: September 2005

Nichols and Wallace et al. have described aircraft acoustical treatments and apparatus for measuring the attenuation provided by them. This paper presents a theory and charts for calculating the attenuation of sound by six different multiple structures as a function of dimensions, specific flow resistance, density, and frequency. Five of the structures are typical of those used in aircraft, and two are types used in lightweight office partitions.

The calculations are checked against experimental data taken on a modified form of the apparatus of reference 2. The agreement between experiment and theory is satisfactory. Differences between attenuations measured here and those described in reference 1 are explained.
Acoustic Impedance Measurement of Very Porous Screen
Authors: Harris Cyril M.
Published: September 2005

A new procedure is presented for the measurement of the normal specific acoustic impedance of extremely porous screen as a function of frequency. The method (based on a special application of the transmission-characteristic method of impedance measurement) is restricted to this case. Equations are derived which express the impedance of the screen in terms of the acoustical characteristics of a small enclosure, i.e., a rectangular chamber or a closed cylindrical pipe. Good accuracy can be obtained with relatively simple experimental equipment and with relatively little computation. Measured values of the impedance for samples of extremely porous cloth, determined by this procedure, are given.
Facilities of the Altec Lansing Corporation for the Measurement of Loudspeaker Performance
Authors: Veneklasen P. S.
Published: September 2005

Physical measurements of loudspeaker performance are becoming recognized increasingly as a reliable guide for the evaluation of loudspeaker excellence. The facilities of the Altec Lansing Corporation for the calibration of loudspeakers and microphones are described. The measurement techniques are illustrated with data describing a recent model loudspeaker showing the principal performance criteria, namely, frequency response, angular distribution, and distortion. Suggestions are given for a uniform presentation of performance data and specifications.
A New Instrument for Subsonic Frequency Measurements
Authors: Atanasoff J. V. , Snavely B. L. , Brown John
Published: September 2005

A new instrument was designed and built to record the subsonic atmospheric disturbances resulting from the explosive demolition of the German fortifications of Helgoland on April 18, 1947. Microbarometric disturbances flex the diaphragm of the microphone, altering one of two matched inductive circuits; the unbalance produces a signal voltage. This signal, the low frequency modulation of an audiofrequency carrier, is amplified and used to drive a modified Esterline-Angus graphic recorder. To provide wide dynamic range as well as high sensitivity to small signals, the amplifier has linear response to low level signals and logarithmic response to high level signals. Completely linear response is available by switching out the automatic volume-control circuit. Sensitivity may be reduced in steps to 1/5 or 1/125 to satisfy changing requirements, and at maximum sensitivity the recorder deflection is about 0.75 mm per microbar. As field equipment, the instrument system is necessarily battery operated. It is light and compact, and yet possesses high sensitivity and better stability characteristics than previous equipment of its type.
A Monitor Speaker
Authors: Carruthers Walter W. , Brettell George A.
Published: September 2005

The first portion of this paper is a discussion of the design philosophy of a monitor speaker. Attention is paid to the apparent inconsistency between pressure measurements and A-B tests with original material. Comment is made on the effects of change in directional pattern of the radiated sound. The performance of an experimental monitor loudspeaker is evaluated.

The second portion of the paper is a description of the experimental speaker. The configuration, significant dimensions, and motional impedance measurements are reviewed.
The U. S. Navy Underwater Sound Reference Laboratory, Orlando, Florida
Authors: English Bruce V.
Published: September 2005

A discussion will be given of the purpose and aims of the Laboratory with relationship to the other underwater sound laboratories in the country, and a description of the various acoustic measuring systems and measuring techniques employed in the Laboratory. Included in the discussion of systems and techniques will be the high frequency system from 50–3500 kc, the low frequency system from 0–100 cycles (0–100 lb. p.s.i. and 34–100°F), the two intermediate frequency systems, 0.02 to 150 kc, and the pressure system, 10–150 kc at 0–300 lb. p.s.i.

Emphasis will be placed on the high frequency system and the high pressure system, and the methods of measurement under each system.
Apparatus for Cavitation Studies
Authors: Blake F. G.
Published: September 2005

Cavitation in the body of a liquid, throughout a region well removed from all boundary surfaces, has been produced by means of a converging sound wave. The cavitation phenomenon can thus be studied as a function of the state and properties of the liquid, without regard to the possible effects of minute irregularities or adsorbed gases on the surface of the sound generator. The method employed is to bring one or more sound beams of moderate intensity to a common focus within the liquid by means of a parabolic mirror. At the sixty-kilocycle operating frequency of the magnetostriction transducers which serve as the projectors, attenuation in the liquid medium is small; nevertheless the use of a controlled resonant standing-wave system permits the experiments to be conducted in a tank of reasonable laboratory size not equipped with any special energy absorbing devices. Moreover, the necessary driving power is reduced. The apparatus provides for measurement of the cavitation threshold of various liquids as a function of temperature, hydrostatic pressure, and pulse length. This paper will describe the equipment and present some preliminary results.
Absorption of Sound in Fresh Water and in the Sea
Authors: Liebermann Leonard N.
Published: September 2005

Measurement of the variation of sound intensity with range in El Capitan reservoir has been used to calculate the absorption of sound in fresh water. At 500 kc and 1000 kc the absorption coefficient is proportional to the square of the frequency, and when extrapolated to much higher frequencies is in approximate agreement with the values of Fox, and Fox and Rock for distilled water. Absorption at 120 kc was found to be too low for measurement within the limited range (1100 yards) of the reservoir, but an upper limit is established. Measurements in the ocean at 120 kc give a value which is in approximate agreement with those of the University of California Division of War Research; this value is more than five times the fresh water upper limit, and more than ten times the extrapolated higher frequency values. Measurements at 500 kc and 1000 kc indicate that oceanic absorption is not proportional to the square of the frequency; oceanic absorption at 1000 kc is only slightly higher than fresh water. It is suggested that the oceanic absorption mechanism has a relaxation time lying between 10−5 and 10−6 sec.
The Attenuation of Ultrasonic Sound Waves in Water
Authors: Leonard R. W.
Published: September 2005

The attenuation of sound waves in distilled water has been measured in the frequency range from 50 to 450 kilocycles. The results are in good agreement with those of Fox and Rock in the range above 10 megacycles.

Measurements on filtered sea water from 50 to 180 kilocycles give values for the attenuation about 10 times as great as those obtained for distilled water. The measurements in sea water are in reasonable agreement with the measurements of other experimentors in the frequency range from 20 to 50 kilocycles.

The data to be presented were obtained by the reverberation method, using an improved spherical resonator.
Free Field Calibration of Transducers to 100 KC in Air
Authors: Rudnick I. , Stein M. N.
Published: September 2005

The feasibility of conducting reciprocity calibrations up to 100 kc in air, using W.E. 640 AA condenser microphones is pointed out, and the results of such calibrations will be presented. Curves of microphone sensitivity and the output of the unit when used as a sound source will be given for both a normal 640 AA unit and one whose diaphragm has been stretched to give increased high frequency response. In addition, curves for other transducers tested in this laboratory will be presented. All the calibrations were carried out in a small—6′×6′×6′—dead room.
Examples of Propagation of Underwater Sound by Bottom Reflection
Authors: Young Robert W.
Published: September 2005

From data obtained in an extended program of sound propagation measurements, eight examples at 200 cycles per second have been selected to illustrate long-range propagation of sound by reflection from the ocean bottom. The source was 14 feet below the water surface, the receiver was at a depth of either 16, 50, or 300 feet. With these transducer depths the surface-reflected and directly transmitted sound soon canceled each other. However, the sound from the non-directional source could travel four nearly identical paths (three of which involve surface reflection) and yet be reflected only once from the bottom. The interference among these four components, in a non-attenuating isovelocity medium, is represented by an equation put in a form such that a single curve can be utilized for any water depth. Interference maxima and minima such as predicted by the simple bottom reflection theory are indeed apparent, but the theory is not generally substantiated. The runs shown in this paper were obtained in water depths of 2000, 1000, and 52 fathoms, respectively. Essentially continuous sound measurements were made while the source moved from 100 yards to 60,000 yards or more away from the receiver. The difference in signal level at these two ranges was of the order of 50 db. Simultaneous observations at two receiver depths are illustrated for each of the three depth combinations. Two successive runs are given to demonstrate the change in propagation which may occur even from one set of observations to the next. Partly because in 2000 fathoms of water the distance to the reflecting bottom does not change rapidly with increasing horizontal range, the bottom-reflected signals were roughly constant to 10,000 yards. In an extreme case the bottom-reflected signal actually increased about 10 db in going from 250- to 1000-yard horizontal range, and then dropped back to the 250-yard value at 60,000 yards.
The Magnetrostrictive Radial Vibrator
Authors: Camp L. W.
Published: September 2005

A description of a radial vibrator for use in underwater sound signalling. A technique is presented for providing a plastic cast to protect the toroidal windings which serves to improve rather than decrease the potential efficiency. Data is presented to show the operating characteristics of these sound sources.
Theoretical Analysis of the Mercury Delay Line
Authors: McSkimin H. J.
Published: September 2005

Boundary conditions are set up for compressional waves traveling in a pipe filled with mercury. If the waves are generated by a quartz crystal having flat electrodes, the pressure at any point within the pipe may be analyzed by an infinite series having the form p = p0ΣnAnJ0(Sn(r/a))ε±θnz where a = radius of pipe, θ = propagation constant per unit length, Sn = root of the zero-order Bessel function. An expression is derived for the voltage developed on the plates of a receiving crystal as a function of distance from the radiator. Distortion effects caused by non-linear phase relationships can be studied for amplitude modulated waves provided the electrodes of the radiating crystal are so arranged as to give a single mode of vibration within the pipe. The entire analysis yields criteria for practical delay line construction.
Experimental Investigation of Non-Specular Reflection of Sound from Submerged Steel Plates
Authors: Finney W. J.
Published: September 2005

It has been found that an appreciable reflection occurs in the direction of the incident wave when high frequency underwater sound strikes a submerged steel plate at an oblique angle of incidence. The magnitude of this “non-specular” reflection, together with the associated transverse vibrations in the plate, has been studied experimentally as a function of frequency, plate dimensions, and angle of incidence. Significant non-specular reflection occurs from bounded plates between about one-quarter inch and two inches thick, when the product of thickness in inches and frequency in kilocycles per second lies between about 20 and 60 in-kc. Within this range, the angle of incidence for maximum non-specular reflection, n, is described by the empirical relation sinn = 2.16/((fb)13), where b is plate thickness in inches and f is frequency in kilocycles. The results of the present study are in excellent agreement with a theoretical analysis by Fay, which includes plate displacements due to shear strain as well as those due to bending. The results do not agree with an analysis which neglects displacements of the plate due to shear strain.
The Underwater Directional Characteristics of a Free-Edge Plate
Authors: Jaques A. T. , Tuck E. , VanZant R.
Published: September 2005

The problem of vibrating circular plates immersed in a fluid has a considerable interest in naval ordnance. A theoretical and experimental study of such plates vibrating in the second, third, and fourth normal axially symmetric modes has been made in the frequency range of 20 to 100 kc. The driving force, which is applied over a small area in the center of the plate, is produced by a vibrating magnetostrictive rod. Excellent experimental verification of theoretical directivity patterns has been obtained.
Scattering of Ultrasonic Waves in Water by Solid Cylinders
Authors: Bauer Louis , Tamarkin Paul , Lindsay R. B.
Published: September 2005

An x-cut quartz crystal with natural frequency about 1075 kc, placed at the center of one end of a water-filled steel tank (3′×3′×20′), was driven off resonance at 1145 kc. One side of the crystal vibrated in air. The driving circuit consisted of a Colpitts oscillator, buffer amplifier, and power amplifier. The crystal was matched to the output of the power amplifier by link coupling. The radiation in the water was received by a pick-up system consisting of an ammonium dihydrogen phosphate microphone connected to a tuned radiofrequency amplifier. The detected output was measured by means of an electronic voltmeter; readings were proportional to the maximum excess pressure. The obstacle used was a 14″ steel rod, placed in the beam where the latter's half-width was slightly greater than the diameter of the obstacle. Three types of measurements were made: (1) intensity distributions across the beam at different distances along the axis of the beam, (2) wave-front determinations at different distances along the axis, and (3) observations of the effect of moving the obstacle across the beam. The following results have been obtained: (1) The obstacle scatters the original beam into three major peaks flanked by a considerable number of subsidiary peaks. Any asymmetries in the original beam are magnified in the scattered beam. The peaks diverge along rays which appear to originate from a point somewhere between the crystal and obstacle. (2) The undiffracted wave front consists of two sides and a central portion, the three having roughly the same curvature. The obstacle flattens the central portion and steepens the sides. This steepening is to be expected since the velocity of sound is greater in steel than in water. (3) Moving the obstacle causes a continuous change in the scattering pattern. Actual splitting of the beam into three parts occurs only as the center of the beam is approached. Similar experiments are planned for rods of different sizes and for hollow rods of varying thicknesses and acoustic impedance
Ultrasonic Radiation from Curved Quartz Crystals
Authors: Fein Louis
Published: September 2005

From transmitting frequency responses in water, admittance measurements in air and water, and radiation patterns in water, calculations were made of the electroacoustic efficiencies at 1250 kc of four one-inch square x cut quartz crystals of practically equal thickness having radii of curvature of ∞, 25, 7, and 4 centimeters, respectively. Efficiency values calculated from acoustic measurements do not check as well with the calculated potential efficiencies as do those calculated from admittance. The latter values indicate that the radiation resistance is the same for the four crystals. Focusing measurements show agreement with Williams' prediction that the point of maximum acoustic intensity is not necessarily at the center of curvature. Resonance frequencies obtained from admittance measurements in air make plausible the deduction that the effective mass of a crystal decreases with increasing curvature.
Sonic True Air Speed and Mach Number Indicator
Authors: Corey Victor B.
Published: September 2005

A practical instrument has been developed which employs the convection refraction of high frequency sound waves to make accurate absolute measurements of both the true air speed and the Mach number of a moving vehicle. Mach number, which is the dimensionless ratio of true air speed to sound velocity, is indicated by a strictly proportional extension of a movable boom carrying an acoustic emitter, and requires no electronic computer or explicit transit time measurement. The true air speed, fundamentally involving the ratio of distance to time, is proportional to the ratio of boom extension to one experimentally measured acoustic transit time which remains constant excepting for changes in air temperature. There is no definite upper limit to values of Mach number or true air speed which can be measured by this method. The device is made automatic by servo-positioning the movable boom in response to an error signal obtained from an acoustic dual receiver in a fixed parallel boom. All transducers are flush mounted in plane surfaces intended to lie parallel to the air stream. The basic operating principles of this device, which has been given the name STAMNI (Sonic True Air speed and Mach Number Indicator), are applicable in general to velocity or Mach number measurements on a body which moves through any fluid medium of low viscosity.
The “Phangle” Meter
Authors: Corliss Edith L. R.
Published: September 2005

Based upon the idea of a phase-sensitive synchronous detector circuit, a meter has been constructed which permits simultaneous observation of the in-phase and quadrature components of an alternating current signal. With the arrangement to be described, it is possible to make observations on signals in which the phases are shifting too rapidly to be followed with the usual null-type instrument. The application of this circuit to acoustic measurements will be discussed.
Quantitative Amplitude Representation in Sound Spectrograms
Authors: Koenig W. , Ruppel A. E.
Published: September 2005

The sound spectrograph shows variations in signal intensity by varying shades of gray to black, which, because of the nature of the recording medium, are not susceptible to quantitative interpretation. Several methods are described in this paper for recording amplitude variations in measurable steps. These methods include contours, dot spacing, distinctive shadings, and variable area patterns.
Amplitude Cross Section Representation with the Sound Spectrograph
Authors: Kersta L. G.
Published: September 2005

Spectrograms as normally produced by the “Sound Spectrograph” are three-dimensional. Time is portrayed along the length of the spectrogram paper, frequency across it, and amplitude by the blackness of the marking. The time and frequency scales thus provided are adequate for most analysis purposes. The amplitude scale, however, is poorly defined, first because inherent characteristics of the spectrogram paper limit the amplitude portrayal to a highly non-linear 12-db range and, secondly, because reading degrees of blackness by eye is inaccurate. This inadequacy in determining amplitude led to the development of a method for portraying amplitude which was independent of the characteristics of the paper or of the ability of the eyes to delineate grades of blackness of marking. The device developed and herein described provides an auxiliary presentation which portrays, at any pre-selected point in time, a two-dimensional spectrogram with axes of amplitude and frequency. This device delineates a 35-db amplitude range with the scale in uniform logarithmic steps.
Rotational Absorption and Dispersion of Ultrasonics in Hydrogen
Authors: Stewart James L. , Stewart Ellen S.
Published: September 2005

The absorption and dispersion of the velocity of ultrasonic waves when the rotational degrees of freedom fail to follow the acoustic cycle were early predicted by Rayleigh, Jeans, and others. The anomalous absorption in hydrogen was first observed by Abello and carefully investigated by Van Itterbeck and his co-workers to yield a value of the relaxation time. The dispersion of the velocity was first reported by the authors together with a rough observation of the absorption peak and determinations of the relaxation time. Rhodes and Zartman have reported on more precise and extensive measurements of the dispersion and absorption curves. In this paper new data on these curves and some new developments in the theoretical interpretation of these data will be presented.
A Theory of Low Frequency Sound Absorption in Soda-Silica Glasses
Authors: Korn Granio A.
Published: September 2005

This paper deals with the theory of a class of relaxation mechanisms which may in part account for the absorption of sound in certain solids. The basic postulates of Eyring's theory of absolute reaction rates are applied to the development of general differential equations describing structural-chemical state changes. The macroscopic effects of a transition between the activated and unactivated states of complexes of atoms are discussed, and the results of the discussion are applied to the problem of sound absorption and mechanical relaxation due to structural-chemical changes in soda-silica glasses. It appears that the transition of alkali ions from holes in the glass lattice into the interstitial spaces, as in electrolytic conduction, is associated with the acquisition of a certain activation energy, so that the transition probabilities are finite. The process is thus of the nature of a relaxation mechanism which is capable of causing sound absorption. The functional dependence of absorption on frequency predicted by the theory as well as the predicted functional dependence of the relaxation time on temperature are found to agree with experimental results at low frequencies.
Energy Losses of Sound Waves in Metals Due to Scattering and Diffusion
Authors: Mason W. P. , McSkimin H. J.
Published: September 2005

When high frequency longitudinal and transverse sound waves are sent through a multicrystalline rod of metal, attenuation losses result due to scattering and diffusion of sound waves by the grains. When the grain size is less than one-third of the wave-length, these losses are due to Rayleigh fourth-power law scattering and are proportional to the grain volume. The scattering factor depends on the anisotropy of the elastic constants. Two different factors are obtained, one for shear waves and one for longitudinal waves. These factors have been evaluated for cubic and hexagonal metals. From the measured elastic constants the only metals with a low loss are aluminum, magnesium, and tungsten. The calculations indicate that the losses for aluminum and magnesium are about equal for longitudinal waves, but for shear waves magnesium has a very low shear loss. Experiments with higher frequencies show that when the wave-length is one-third of the grain size or less, the transmission process becomes a diffusion process similar to the propagation of a heat wave. The grain sizes determine the mean free path and the loss becomes inversely proportional to the grain diameter. An approximate formula for diffusion losses has been obtained which agrees closely with the experimental values.
Ultrasonic Measurement of the Elastic Properties of Polycrystalline Materials at High and Low Temperatures
Authors: Frederick Julian R.
Published: September 2005

Young's modulus, the modulus of rigidity, and Poisson's ratio have been determined at temperatures ranging from −195°C to 850°C for several different solids using pulses of longitudinal and transverse ultrasonic vibrations. The x- and y-cut crystals used as transducers were kept at room temperature and the velocities of the two types of waves were measured only over the heated or cooled regions. This was done by taking observations on echoes from different points in those regions. The elastic constants are computed from these data. Several pure metals, 28 different steel alloys, an aluminum alloy, and a specimen of lime glass were tested. The moduli of those steels that are non-magnetic decrease linearly with increasing temperature, while the ones that are magnetic show an increasing rate of decrease of the moduli as the α→γ transformation temperature is reached. Precipitation and agglomeration occurring at elevated temperatures in 24 ST aluminum and in a Cr-Ni steel containing 0.92 percent Be and 0.99 percent Wo (Turbaloy) increase the moduli. Poisson's ratio increases with increasing temperature in all the materials tested with the exception of the specimen of lime glass in which it decreases.
Ultrasonic Attention in Solutions of High Polymers
Authors: Hoopes Jean , Zallen Joseph
Published: September 2005

Using a pulsing technique, we have measured ultrasonic attenuation in various high polymer solutions over the range from 5 to 55 megacycles. In all cases measured the attenuation increases as the square of frequency. The attenuation in solutions of synthetic rubber in methyl-ethyl ketone increases rapidly with concentration. For example, at 50 mc a 7.8 percent solution absorbs 13.0 db/cm, a 5.5 percent solution 9.4 db/cm, and pure methyl-ethyl ketone absorbs 4.9 db/cm. We have measured a 3.5 percent solution of gelatin in water and find that attenuation increases sharply after the material has been gelled. Thus, at the same temperature, gelatin in the sol state absorbs 4.2 db/cm while the same sample in gel state absorbs 7 db/cm. The only physical change in the gelatin was a phase change. Further investigations are being carried out to determine the possibility of using ultrasonic attenuation as an index of phase changes and as a tool for studying structure of polymers in solution. A study is also being made to see whether attenuation correlates with molecular size.
The Attenuation of Longitudinal Waves in High Polymers
Authors: Smith J. C. , Ballou J. W.
Published: September 2005

The method of Ballou and Silverman for obtaining a dynamic modulus of elasticity in continuous filaments by measuring the velocity of longitudinal waves has been extended to include the measurement of attenuation of the wave along the sample. A theory of this method is presented in which special emphasis is placed on the measurement of the relatively low attenuations encountered in some polymeric materials, as compared to the higher attenuations in rubber-like materials reported by Nolle. The results of attenuation measurements on some polymers in filament form are presented to show the application of the method and theory. The use of attenuation measurements in characterizing some of the physical properties of high polymers is discussed.
Method for Determining Complex Compressional Modulus of Sheet Structures
Authors: Westervelt Peter J.
Published: September 2005

A method for measuring the compressibility and mechanical loss factor of compliant materials in sheet form is analyzed. An experimental model is described for measuring one-inch diameter samples from 1 to 50 mils thick over the frequency range 100 to 7000 c.p.s. The sample being tested is made a part of a simple resonant system which is excited by electrostatic forces set up across the sample. A piezoelectric crystal imbedded in the base of the resonant system measures force due to motion of the system. Three readings, one of frequency and two of audio voltage, suffice to determine the compressibility and loss at one frequency. Control is easily achieved over the static load to which the sample is subjected while being measured. Some measurements are reported on samples having a mechanical stiffness in the range 1010 to 108 dynes/cm and mechanical resistance in the range 104 to 106 dynes-sec./cm.
Mechanical Impedance Measurements
Authors: Kessler John A.
Published: September 2005

A method of measuring mechanical impedance at discrete frequencies is outlined; this method follows directly from Fay's telephone receiver analysis. The application of this method to the measurement of the mechanical transfer impedance at a violin bridge is discussed and some experimental results presented. Preliminary results of some other tests on violins are also discussed.
A Q-Machine for the Measurement of Mechanical Circuit Parameters
Authors: Tompkins Howard E.
Published: September 2005

The design and construction of a Q-Machine is discussed and its theory of operation is outlined. The Q-Machine to be described measures the mechanical resistance and reactance of small mechanical damping members in a frequency range near 100 cycles per second. The effect of the damping member under test on the resonant frequency and sharpness of resonance of a relatively high-Q, mechanical, tuned circuit is obtained by observing the amplitude of vibration of the mass in the Q-Machine's tuned circuit with capacitive pick-up probes. From this data, resistance and reactance can readily be computed. Application of the Q-Machine to the design of electromechanical transducers and to the testing of the properties of audio damping materials is discussed.
Audible Noise from a P-80 Jet Airplane
Authors: Wathen-Dunn Weiant
Published: September 2005

The polar distribution, in a horizontal plane, of the acoustic energy, generated in the 100-cycle to 10-kilocycle band by a P-80 jet airplane, running at full throttle on the ground, has been measured and analyzed on a constant band-width basis, and the results will be presented. As a check, the octave levels have been computed for the same frequency region, and from these, in turn, an over-all level has been calculated for each measuring position. Agreement between these values and the levels actually measured is within 2 db in all cases.
Trumpet Intonation Differences Due to Bell Taper
Authors: Webster John C.
Published: September 2005

A trumpet was made up so that a series of different bells could easily be alternately attached. Seven bells were made up such that there were six different tapers one of which was duplicated in different materials. The internal tuning differences due to these bells were determined for every chromatic pitch from F♯3 to C6 (written) by an electrical method and by five different players over five trials. These data were analyzed as to variance technique to determine the relative variability between players, trials, bells, and pitches. The analysis showed the statistical variance between players and bells to be highly significant whereas the trial and pitch variance was not significant. The results also indicate that the electrical measuring device is in the same statistical population with the five players. The conclusions indicate that the bell taper of a trumpet does appreciably alter the internal tuning of an instrument, and that although any one player is fairly consistent from trial to trial the differences between players is great.
The Problem of Novelty in Musical Instrument Design
Authors: Kent E. L.
Published: September 2005

Few instruments are found in today's symphony orchestras and concert bands that were not there 50 to 100 years ago. The instruments that have made a place for themselves have succeeded only after a long struggle. Many meritorious new and improved instruments have either dropped into oblivion or are still struggling for recognition. Novelty in musical instruments is up against the most formidable combination of conservatism confronting any product. Between the manufacturer of musical instruments and the consumer of his product lie five powerful conservative influences: the musician, the teacher, the composer, the music publisher, and the listening public.
Mathematics of Musical Scales
Authors: Gwynn M. H.
Published: September 2005

For each note of any octavic train of scales, the frequency, V/T, equals the product of the common scale term 2s and a typical note term, F. V/T = 2sF where S is an integer scale number, low for bass, higher for treble scales. F is a function of the note number within each scale. For any Just scale with 5 to 144 tones, as shown by E. S. Roeder, Fj = 2a3b/5c, where a, b, c, are integers, b and c each varying between 0 and 11. For any twelve tone Equal Tempered scale, Fe = 2m/12, where m is integer note number varying between 0 and 11. For any Sigma (Incremental) scale, FΣ = N_ + S + K, where FΣ, N_, S, and K are integers. N_ is the tone number varying between 0 and S + K. K is a series constant, variable for range rather than pitch. The serial number for any Sigma note or tone equals N_ + Σ(S + K). Both Just and Equal Tempered scales are repetitive, both their scale and note functions comprise a power of two. Sigma scales are freed from one of these two geometric and octavic restrictions, since FΣ is an arithmetic series. Sigma scales are non-repetitive, but are functionally coupled or coherent since the note as well as the scale term is a function of S. A Sigma train is an homology of scales with an added note in each higher scale to introduce new harmonic effects and to complete the octave within the scale. Chord rationality and the coincidence of partials with higher notes are least with Equal Tempered scales, most with Sigma scales. Sigma scales appear to possess Just tonality plus most of Equal Tempered simplicity and to excel in diversity and rationality.
Radio's Redefinitions of Voice Sounds
Authors: Benedict Claire
Published: September 2005

This is the third paper reporting researches carried on for more than thirty years in the arts and sciences pertaining to the human voice. The author's training in the arts has synchronized with developments in the sciences as they advanced from telephone to microphone to “talking pictures” the latter focuses instantly on the need in speech for those recognized technical and tonal standards previously associated solely with music. The magnifying effect of the microphone revealed coincidences in the source sounds of each that, in turn, revealed coincidences in their single natural source with those musical pipes of which it is the prototype. Preceding papers described essential redefinitions of physical-functional conditions in terms of a “voice pipe,” its natural “singing sound,” the technical controls underlying the sequence of sounds with which it “speaks.” A rare recording of these ideals in an unchanged but fully developed boy-voice will be presented. Thus, the Helmholtz theory that “the sensations can be explained on the basis of the laws of physics” arrives at Eddington's figure of speech for physiology of voice can be “explained away” in physics of music by the psychology involved.
Sound Pressure Measurement Equipment for the Range 50 Cycles to 250 kc
Authors: Massa Frank
Published: September 2005

This paper describes a newly developed acoustic instrument that is now commerically available for making absolute sound pressure measurements over the frequency range 50 cycles to 250 kc. The microphone standard is only 18″ diameter, and is therefore completely free of diffraction errors throughout the entire audible spectrum to beyond 20 kc. In order to maintain constant phase shift between the generated voltage and the actuating pressure, the vibrating system is stiffness controlled to beyond 250 kc, thus insuring accurate reproduction of pressure wave transients having extremely steep wave fronts. The tiny size of the microphone and its very high acoustic impedance will permit free field measurements throughout the entire audible range without diffraction errors, as well as making easily possible many special acoustic measurements extending well into the ultrasonic region, heretofore very difficult to make. One such application now in progress is the analysis of the sound spectrum from jet engines up to frequencies of 250 kc. A preamplifier and power supply unit makes the equipment readily portable.