bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploration of Pressure Field Around the Human Head During Speech
Authors: Dunn H. K. , Farnsworth D. W.
Published: September 2005

A single speaker in a seated position repeated a fifteen-second sample of connected speech, while r.m.s. pressure measurements were made in thirteen frequency bands, and at seventy-six positions, in different directions and distances. The results are applicable to intelligibility and microphone placement problems. They show, in general, the greater variation with direction at higher frequencies. Directivity due to the size of the mouth opening appeared to enter above 5600 cycles per second, the axis at these frequencies being about 45° below the horizontal, in front. Frequencies below 1000 cycles per second were found strongest directly downward from the lips, or nearly so. The power radiated in different directions has been calculated, and a summation gives a spectrum of the total speech power emitted by the mouth. It is proposed that similar spectra for other speakers may be obtained from pressure measurements at a single point, using the relations discovered for this speaker. The necessity for protecting a microphone used close to the mouth, from the puffs of air accompanying the speech, is demonstrated and explained.
Apparatus for Acoustic and Audio-Measurements
Authors: Chinn H. A. , James Vir N.
Published: September 2005

A new automatic audiofrequency measuring assembly for reverberation and other acoustic measurements is described. In addition, the equipment provides a means for automatic response vs. frequency measurements of audio- and acoustic equipment components and of complete audio-systems. The assembly is completely a.c. operated and readily portable. It utilizes a high speed, power-level recorder recently introduced in this country and a new audiofrequency oscillator having exceptionally fine performance characteristics.
The Mechanism of Hearing by Electrical Stimulation
Authors: Stevens S. S. , Jones R. Clark
Published: September 2005

The harmonic components in the complex tone heard when a sinusoidal electric current is passed through the head were measured by the method of “best beats.” The relative intensity of these components was determined with and without a polarizing d.c. simultaneously applied. With no d.c. the observer hears only the second harmonic of the stimulating frequency, but in the presence of a d.c. he hears the fundamental as well. The quantitative relations between the perceived harmonic components and the polarizing current demonstrate that the response of the ear to electrical stimulation follows a square law. On the assumption that the eardrum is moved by electrostatic pressure whenever there is a difference of potential between the eardrum and the inner surface of the middle ear, it is possible to account for the square-law response, and for certain other aspects of the electrophonic effect. The middle ear appears, therefore, to behave as a condenser receiver. The large amount of distortion which normally prevents an observer from understanding a radio broadcast when the electrical output of a radio receiver is passed directly through his head can be reduced by the application of a polarizing d.c. Under this condition speech and music can be heard with great clarity.
The Multitone
Authors: Barrow W. L.
Published: September 2005

A new sound source, which has been termed a “multitone,” for space-acoustic measurements is described. It provides a plurality of equi-amplitude tones spaced equally in frequency over a given frequency band. A generator for it is described that employs shock excitation and has no vacuum tubes. Disk recordings are provided to secure a series of multitones of different mean frequencies but of constant ratio of band width to mean frequency.
Reversed Speech
Authors: Kellogg E. W.
Published: September 2005

Recording sound and then reproducing it with the rotation of the record reversed is not only a means of amusement, but serves to throw some light on our habits of speech, particularly if one tries reversing the order of the original pronunciation, so that the reproduced sound may be actual words. Some of the writer's observations are given in the paper.
Analysis of Sound Decay in Rectangular Rooms
Authors: Hunt F. V. , Beranek L. L. , Maa D. Y.
Published: September 2005

Sound decay in a rectangular room, each wall of which is uniform, is analyzed in terms of the damping of normal modes of aerial vibration, as influenced by the acoustical impedance of the boundary surfaces. From two to seven decay terms may be required in the complete decay equation under different circumstances, each term representing a group of the excited modes of vibration having common properties. The analysis is given in terms of r.m.s. pressure measured for specified locations of source and receiver and includes explicitly the relative dimensions of the room. The results of the mathematical analysis are presented in form to allow determination of the complex wall impedance from consideration of the initial and final slopes of the sound decay curve, and conversely. Experimental decay curves confirm both the detailed predictions of the theory and the sufficiency of the wall impedance as a unique characterization of the influence of the wall on the behavior of sound in the room.
Supersonic Dispersion in Vapors
Authors: Railston William
Published: September 2005

Measurements have been made of the velocity and absorption of supersonics in eleven vapors at several frequencies, using the Pierce method. Two of the vapors—carbon disulphide and benzene—showed change of velocity with frequency, but in the remaining nine no certain change of velocity could be established. All the vapors absorbed supersonic energy to a greater extent than the Stokes-Kirchhoff theory predicted.
Resonant Frequencies of Certain Pipe Combinations
Authors: Trimmer John D.
Published: September 2005

Calculated and measured values of impedance are given for certain combinations of closed and open pipes, with particular attention to the problem of computing resonant frequencies. Several of the combinations have interesting series of resonances, but the relative strength of harmonics in forced vibrations (e.g., as organ pipes) has not been determined experimentally and is hard to predict theoretically. One of the combinations is of particular interest for two reasons: first, although it includes no open pipes, its resonant frequencies are very closely those of a simple open pipe; and second, some of its resonances are much sharper than others, suggesting a method of designing acoustical elements of very sharp resonance.
Terminology for Logarithmic Frequency Units
Authors: Young Robert W.
Published: September 2005

Fletcher has proposed the use of a logarithmic frequency scale such that the frequency level equals the number of octaves, tones, or semitones that a given frequency lies above a reference frequency of 16.35 cycles/sec., a frequency which is in the neighborhood of that producing the lowest pitch audible to the average ear. The merits of such a scale are here briefly discussed, and arguments are presented in favor of this choice of reference frequency. Using frequency level as a count of octaves or semitones from the reference C0, a rational system of subscript notation follows logically for the designation of musical tones without the aid of staff notation. In addition to certain conveniences such as uniformity of characters and simplicity of subscripts (the eight C's of the piano, for example, are represented by C1 to C8) this method shows by a glance at the subscript the frequency level of a given tone counted in octaves from the reference C0 = 16.352 cycles/sec. From middle C4, frequency 261.63 cycles/sec., the interval is four octaves to the reference frequency, so that below C4 there are roughly four octaves of audible sound. Various subdivisions of the octave are considered in the light of their ease of calculation and significance, and the semitone, including its hundredth part, the cent, is shown to be particularly suitable. Consequently, for general use in which a unit smaller than the octave is necessary it is recommended that frequency level counted in semitones from the reference frequency be employed.
An Acoustic Transmission Line for Impedance Measurement
Authors: Hall William M.
Published: September 2005

A method and apparatus are described for rapid and accurate measurement of acoustic impedance in terms of the characteristic acoustic impedance of a tube. The measurement consists of the simple determination of the location and relative magnitude of the maximum and minimum sound pressures along the tube. The impedance of the termination of the tube can then be read directly from a slightly modified hyperbolic tangent chart. Two methods are given for measuring the impedance of acoustic elements with cross sections different from that of the measuring tube.
Remaking Speech
Authors: Dudley Homer
Published: September 2005

Speech has been remade automatically from a buzzer-like tone and a hiss-like noise corresponding to the cord-tone and the breath-tone of normal speech. Control of pitch and spectrum obtained from a talker's speech are applied to make the synthetic speech copy the original speech sufficiently for good intelligibility although the currents used in such controls contain only low syllabic frequencies of the order of 10 cycles per second as contrasted with frequencies of 100 to 3000 cycles in the remade speech. The isolation of these speech-defining signals of pitch and spectrum makes it possible to reconstruct the speech to a wide variety of specifications. Striking demonstrations upon altering the pitch of the remade speech stress the contribution of the pitch to the emotional content of speech. Similarly the spectrum is shown to contribute most of the intelligibility to the speech.
The Effect of Rotatory and Lateral Inertia on Flexural Vibration of Prismatic Bars
Authors: Thomson William T.
Published: September 2005

The problem of the flexural vibration of prismatic bars neglecting the rotatory and lateral inertia is treated in various texts on sound and vibrations. The effect of neglecting these two terms introduces no appreciable error when the cross section of the bar is small in comparison to its length. For bars of large cross section the error introduced in neglecting these terms is sufficient to warrant attention. In his text on sound Rayleigh offers an approximate solution introducing a correction term for the rotatory inertia, under certain boundary conditions. In a more recent paper Mason gives an exact solution for the frequency of vibration, where the rotatory and lateral inertia are taken into account. The disadvantage of this solution lies in the fact that his Eq. (14) for the eigenvalues of the frequency is extremely complicated, thereby throwing up a barrier to further analysis. Also no mention is made by previous investigators of the effect of the rotatory and lateral inertia on the node positions or the shape of the deflection curve. It is the purpose of this paper to present a simplified exact solution and to determine the effect of the two terms mentioned on the position of the nodes and the relative amplitude of vibration. Curves applicable to the solution of any type of constant cross section are included.
The Transmission of Sound Inside Pipes
Authors: Morse Philip M.
Published: September 2005

Methods developed in a previous paper are used to obtain an exact solution for the transmission of sound inside a rectangular pipe with absorbing material on its inner walls. Plots are given whereby it is possible to determine the phase velocity and attenuation of the simpler type waves in terms of the specific acoustic impedance of the walls and the frequency of the wave. Several examples are given of the effect of the absorbing surfaces on the distribution of the sound pressure amplitude over a plane perpendicular to the axis of the pipe. The effect of the reactive part of the material's acoustic impedance on the attenuation of the sound is also discussed. Formulas are developed for the transmission of sound in tubes of circular cross section. The plots for rectangular pipes can also be used in calculations of the acoustical properties of rectangular rooms.
A Design for a Keyboard Instrument in Just Intonation
Authors: Williamson Chas.
Published: September 2005

In a keyboard instrument, the just scale may be closely approximated by setting up two equally tempered scales, one on the basis of A440.0, the other on the basis of A436.3, and mechanically selecting from them those frequencies which most nearly satisfy the appropriate ratios. Within one octave above middle C, no scale-step is in error by more than 0.6 vibration per second. The keyboard is exactly the same as that now used, and the instrument is playable in equal temperament when the performer so desires.
Statistical Measurements on Conversational Speech
Authors: Dunn H. K. , White S. D.
Published: September 2005

Using apparatus designed to collect a large number of data in a short time, the following measurements have been made: peak and r.m.s. pressures in one-eighth-second intervals, and in various bands of frequencies up to 12,000 cycles per second, from the voices of six men and five women; comparison of r.m.s. pressures in one-eighth- and one-fourth-second intervals, from a single male voice; and distribution of the instantaneous pressures in whole speech, from a single voice. Derived from these data are peak factors in one-eighth-second intervals, and frequency distribution of speech energy in long intervals. Both the absolute value and the distribution of energy are found somewhat different from previously published results.
On the Theory of Fluctuations in the Decay of Sound
Authors: Jones R. Clark
Published: September 2005

A solution which is suitable for numerical computation is obtained for the classic problem of random flights in two dimensions with flights of unequal length. The solution is obtained by a development in series of the exact integral solution. The solution is applied to one aspect of the problem of the fluctuations present in the intensity of sound as it decays in a room. It is assumed that the room has reached a steady state of vibration under the excitation of a single frequency, and that the normal frequencies of the room are randomly distributed. The period of the decay is then broken into two sub-periods, in the first of which there is some degree of coherence in the phases of the normal vibrations. The treatment presented in this communication applies to the second part of the decay, comprising all but the first π/k seconds, for which the phases as well as the frequencies of the normal vibrations may be considered as distributed at random. It is found that the relative extent of the fluctuations which may be traced to beats between normal modes of vibration, does not depend appreciably on the number of characteristic vibrations excited unless the number is so small that statistical considerations are not helpful, nor does it depend significantly on the size or shape of the room.
Sound Diffraction and Absorption by a Strip of Absorbing Material
Authors: Pellam John R.
Published: September 2005

An exact solution for the sound energy absorbed by an absorbing panel set in the surface of a large, rigid, plane wall is obtained. The ability of the strip for absorbing sound is given by a “shape factor” A, defined as the ratio of the energy retained by the panel to the energy which would be absorbed, at normal incidence, by the same section of an infinite wall, covered uniformly with the same material. Curves of A are given for three angles of incidence, and for a wide range of wave-lengths and of normal acoustic impedance of the absorbing material. The “shape factor” reveals that a given material composing a panel absorbs most efficiently when the panel-width approximates, or slightly exceeds, a half-wave-length of the incident sound. For such widths, the factor is larger than two in the case of very “soft” materials, and reduces to unity for less and less absorbent panels.
The Acoustical Impedance of an Infinite Hyperbolic Horn
Authors: Freehafer J. E.
Published: September 2005

In discussing the acoustical properties of horns, it is in general a mathematical necessity to assume plane waves. In the case of a horn in the form of an hyperboloid of one sheet, however, it is possible to avoid this assumption and to obtain an exact solution to the problem. The analysis, carried through with the aid of the differential analyzer, leads to curves representing the acoustical resistance and reactance as functions of the ratio of the radius of the throat to the wave-length. Comparison with the conical horn shows that the hyperbolic is superior.
Attenuation of Sound in Tubes
Authors: Fay R. D.
Published: September 2005

Refinements in method and apparatus have made possible the precise measurement of attenuation of sound in tubes. Preliminary results check the tube wall effect predicted by Kirchhoff very closely. There is also found an unexpectedly large effect depending on the first power of the frequency. Further measurements are required to find whether this loss exists in free air or is due in part to the tube walls.
Power Transmission Loss in Exponential Horns and Pipes with Wall Absorption
Authors: Phelps William D.
Published: September 2005

The differential equation governing the propagation of sound in horns and pipes in general with wall absorption is formulated. Expressions for the pressure and power transmission loss in exponential horns and cylindrical pipes are given. Families of curves showing the power transmission loss in horns and pipes with various wall absorption coefficients are computed. Measurements on the power transmission loss in pine wood and fir wood horns, and the absorption coefficients of pine and fir are shown.
Starting Characteristics of Speech Sounds
Authors: Drew R. O. , Kellogg E. W.
Published: September 2005

In view of its bearing on the design of ground noise reduction systems, a study was undertaken, to determine how sudden or rapid are the increases in amplitude of the speech sounds that must be recorded in dialogue. A large number of oscillograms were taken, a number of which are reproduced herewith. The most important observation is that the human voice can start several of the vowel sounds in such a way that the first wave is from 40 to 80 percent of the final amplitude, or in other words with a suddenness comparable to that of keying an oscillator, but this is rare, being for all practical purposes confined to a few of the more open vowel sounds, when not preceded by any consonant, and only true of certain individuals, and depending on the manner of releasing the breath. Progressive build-up at rates which would carry the modulation from zero to 100 percent in 0.05 second are frequent, while the great majority of syllables start more gradually than this.
Sound Pressure on Spheres
Authors: Fox Francis E.
Published: September 2005

The theory of King for the radiation pressure exerted by plane progressive waves on spheres has been used to compute the constants for spheres of radii (r) of the order of a wave-length (λ) of the sound in the medium. These are given for integer values of α = 2πr/λ from 1 to 11, and for α = 15 and 20. For larger α the constants approach a limiting value so that one may use a simple approximation to obtain the constants for such spheres.
Sound Measurement Objectives and Sound Level Meter Performance
Authors: Barstow J. M.
Published: September 2005

The standardization of sound level meters is shown to have improved conditions in the field of sound measurement, although several characteristics thought to be desirable in visual indicating sound measuring devices are not fully realized in instruments conforming to the present standards. The extent to which certain sound measurement objectives have been realized in present sound level meters is discussed. Further work will undoubtedly be necessary before some of these objectives may be more completely realized. Present indications are that sound level meter limitations in regard to the approximation of sound jury loudness levels will be difficult to remove and at the same time retain reasonable apparatus simplicity. Some consideration is given to possible courses of action in regard to such limitations.
Propeller Rotation Noise Due to Torque and Thrust
Authors: Deming Arthur F.
Published: September 2005

Sound pressures of the first four harmonics of rotation noise from a full-scale two-blade propeller were measured and comparison is made with values calculated from theory. The comparison is made (1) for the space distribution at constant tip speed, and (2) for fixed space angles with variable tip speed. A relation for rotation noise from an element of radius due to Gutin is extended to cover the entire propeller disk. Curves are given showing the effect of number of blades on the rotation noise.
Transmission of Sound Through Parallel Conduits
Authors: Labaw L. W.
Published: September 2005

This paper is a theoretical study of the passage of sound through a series of similar sections composed of two parallel conduits. The infinite structure and the finite structure with finite termination are examined. The filter is low-pass and, by varying the cross sections and the lengths, practically as many or as few frequencies as desired, from 0 to 10,000 cycles, can be attenuated. The effect of cylindrical and conical finite terminations is calculated and plotted. The latter graphs indicate that by varying the length of the termination so that its anti-resonance frequencies fall within attenuation bands, the transmission is very approximately that predicted from the infinite structure study.
The Absorption of Sound in Five Triatomic Gases
Authors: Fricke Edwin F.
Published: September 2005

The sound absorption coefficients have been measured between 8 and 130 kilocycles for the five triatomic gases CO2, N2O, COS, CS2, and SO2. The frequencies of maximal absorption for these molecules were found to be at 20, 153, 287, 379, and 1040 kc, respectively. It was found that for the linear molecules CO2, N2O, COS, and CS2 a linear relationship exists between the maximal absorption coefficients and the frequencies at which these maxima occur. It was also found (1) that the lower the fundamental frequencies of vibration of the four linear molecules the higher are the acoustical frequencies of maximal absorption, i.e., the shorter are the lifetimes of the energy quanta; and (2) that the sonically activated fundamentals and harmonics of each of the above linear molecules commute and have the same lifetime, with the possible exception of CO2. From the experimental data it was possible to calculate the reaction rates, probabilities of removal of vibrational quanta, the numbers of collisions necessary to remove the quanta of energy, and the numbers of quantum transitions per second. In addition to the above data, a technique is presented which enables one to find the frequencies of maximal absorption for gases when these frequencies occur in a range beyond the scope of the apparatus.
The Absorption of Sound in CO2, N2O, COS, and in CS2, Containing Added Impurities
Authors: Knudsen V. O. , Fricke E.
Published: September 2005

We have investigated the absorptive characteristics of CO2, N2O, COS, and CS2 as influenced by the addition of certain gases, such as H2, H2O, H2S, CH3OH, etc., acting as “catalysts.” These catalysts shift the absorption bands to higher frequencies; the magnitudes of these shifts yield information respecting (1) the frequency at which each pure gas has its maximal absorption, and (2) the nature of the molecular collisions involved, and especially the effectiveness of these collisions in disturbing the vibrational states of the absorptive molecules. The results indicate that at atmospheric pressure and 23°C the absorption maxima for pure CO2, N2O, COS, and CS2 are shifted in each case by amounts proportional to the concentration of the added catalyst. The addition of one percent of H2O to CO2 shifts the absorption band for CO2 2250 kc; similarly, one percent of H2O shifts the CS2 band 2460 kc, the COS band 4200 kc, and the N2O band 427 kc. One percent of the other impurities produced shifts which varied from 20 to 1830 kc. Transition probabilities for the above gases have been calculated. These probabilities are characteristic of the colliding pair of molecules.
Symmetrical Sand Figures on Circular Plates
Authors: Colwell R. C. , Stewart J. K. , Arnett H. D.
Published: September 2005

It is shown that Kirchhoff's solution for a circular plate is a special case which gives circles and diameters only. If this solution is generalized, the very intricate figures actually found upon circular plates may be calculated mathematically. In particular, a few figures found by Chladni are computed from the new equations. The methods of computation from the curves of the Bessel functions are outlined briefly.
Three Mechanisms of Hearing by Electrical Stimulation
Authors: Jones R. Clark , Stevens S. S. , Lurie M. H.
Published: September 2005

It was previously shown that when an alternating electric current is passed through the head via a salt solution in the external ear canal, a normal observer hears a tone which is related to the stimulus by a square law, that is to say, if the sound heard is interpreted in terms of motion of the tympanic membrane, then the displacement of the membrane is proportional to the square of the instantaneous voltage. The writers suggested the hypothesis that the cavity formed by the middle ear acts as an electrostatic transducer. This hypothesis accounted for the square-law response and for certain quantitative aspects of the results. This hypothesis had to meet the objection, however, that persons without tympanic membranes are able to hear by electrical stimulation. In order to determine the relation between the hearing of normal and operated ears, twenty ears lacking tympanic membranes were stimulated electrically. Eleven ears heard pure tones corresponding in pitch to the frequency of the applied voltage; seven heard a buzzing noise whose character was roughly independent of the stimulating frequency. Examination showed that the pure-tone response in the operated ears was purely linear, in contradistinction to the quadratic response of normal ears. Hence, under electrical stimulation normal and operated ears hear by means of two distinctly different mechanisms. The square-law response in normal ears is apparently mediated by an electrostatic action in the middle ear. The linear response in operated ears may or may not be the inverse of the cochlear microphonic. Evidence is presented that direct stimulation of the auditory nerve occurs in those ears which bear a buzzing noise. This result is consistent with a “place theory” of hearing, and it suggests that the “frequency theory” of hearing is untenable even for low frequencies.
Noise Tremor Due to Traffic
Authors: Bernhard R. K.
Published: September 2005

This paper presents a study on noise and mechanical vibration abatement with respect to the field of structural engineering. Certain units of noise tremor are defined, and some psychological and physiological concepts outlined (sensation thresholds and bearable limits for the human body). Fundamental principles of the measuring instruments are given. In reporting the investigations in buildings and in the field, particular attention is given to the influence of: speed of vehicles, super- and substructure of roadbeds, operation and construction methods, and the damping capacities of soils. The combined effect of noise and mechanical vibrations is studied.
End Corrections of Organ Pipes
Authors: Jones Arthur Taber
Published: September 2005

This is an experimental study of the end corrections of two rectangular wooden pipes, each wide open at one end and partly closed in various ways at the other. The pipe to be examined was excited by a telephone receiver set into one side of the pipe, and the sound was picked up through a small bore brass listening tube screwed into another side of the pipe and connected by rubber tubing to the observer's ear. The telephone receiver was fed from an audiofrequency oscillator, the frequency of which was varied to obtain the maximum resonant response. Equations for the frequency of a partly closed pipe have been suggested by several investigators. The present experiments show that not more than one of these equations is satisfactory for any extended range of apertures. The one possible exception is an equation developed by Rayleigh and by Richardson, and for this equation the present experiments are not conclusive. Incidentally attention is drawn to the restriction which a wall near an opening imposes on the flow of air through the opening, and the consequent effect on the natural frequency of an adjacent cavity. It is also found that the fundamental resonant frequency of an organ pipe may be either above or below the frequency obtained by blowing.
Absolute Pressure Calibration of Microphones
Authors: Cook Richard K.
Published: September 2005

A tourmaline crystal disk was used both as a microphone (direct piezoelectric effect) and as a sound source (converse piezoelectric effect). Application of a principle of reciprocity to the acoustic measurements gave an absolute determination of the piezoelectric modulus d33 + 2d31 of tourmaline under hydrostatic pressure. A condenser microphone was calibrated by the tourmaline disk. The same principle was applied to data obtained by using a condenser microphone as both source and microphone to secure an absolute calibration of another condenser microphone. It was proved experimentally that the tourmaline disk and the condenser microphones satisfied the principle of reciprocity. The absolute acoustic determination of the piezoelectric modulus gave d33 + 2d31 = 2.22 × 10−17 coulomb/dyne. The “reciprocity” calibrations agreed with the results of electrostatic actuator, pistonphone, and “smoke particle” calibrations, but disagreed with thermophone calibrations of the condenser microphones.
Sound Level Meter Performance
Authors: Tweeddale J. E.
Published: September 2005

In the past decade, the increasing use of sound level meters in industry has fully demonstrated their value. However, with this increasing use, there has grown a more critical attitude with respect to their relative performance. A fundamental criticism, particularly in the case of noise acceptance measurements, has been the frequently observed lack of agreement among sound level meters of different manufacturers, though calibrated to the same reference level and otherwise fulfilling the performance requirements of the ASA. This paper discusses the factors responsible for this condition. Suggestions are advanced relative to the elimination of the tolerable deviations in frequency response of the standards that should aid materially in clarifying and improving the existing situation. In addition, the results of advances in the direction of improving the stability or constancy of performance of sound level meters are presented.
Sound Velocities in Gases Under Different Pressures
Authors: Colwell R. C. , Gibson L. H.
Published: September 2005

With a rapid succession of sound pulses and an oscilloscope, it is possible to measure the velocity of sound over short distances. A gas-tight metal container six feet long and twenty-two inches in diameter has within it a loudspeaker and movable microphone. The pulses sent out by the loudspeaker are received by the microphone and translated into a sine wave on the oscillograph. Measurements were made upon air, nitrogen and carbon dioxide at different pressures. The velocity did not vary with the pressure. The measured velocities gave for air, 331.42 meters/sec.; for carbon dioxide, 258.57 meters/sec.; for nitrogen, 337.12 meters/sec.
Ultrasonic Absorption and Velocity Measurements in Numerous Liquids
Authors: Willard Gerald W.
Published: September 2005

By means of ultrasonic light-diffraction phenomena the velocity and absorption of sound in some forty transparent liquids were measured in the frequency range of 6 to 30 Mc. Among the list of materials studied are mixtures of liquids in varying proportions, several solutions of solids in liquids, and a nonliquid jell. A novel-construction glass-to-metal-to-quartz cell made possible the study of highly solvent liquids. Velocity values were obtained from measurements of the diffraction spectra spacing. Absorption values were obtained by measurement of the sound radiator voltages required to produce certain color transmission effects at measured distances from the sound radiator. The use of a mercury arc light-source enhanced the necessary color effects. The relation between sound beam width (in the optical direction) and light transmission was studied. In general, the values of velocity obtained were found to be independent of frequency, and the absorption to be proportional to frequency squared and unrelated to calculated viscous and thermal losses. A simple calculation is proposed for estimating absorption errors caused by sound beam diffraction and spreading. These apply as well to absorption measured in other methods than here used.
Ultrasonic Absorption in Water
Authors: Fox Francis E. , Rock George D.
Published: September 2005

The coefficient of absorption (2αν−2) of ultrasonic waves was measured by a radiation pressure method at frequencies from 7 to 50 Mc. The average value is given for each frequency. These cluster closely around 43.1 × 10−17, and there is no indication of a drop in 2αν−2. Errors entering into absorption measurements are discussed.
The Propagation of Sound in Cylindrical Tubes
Authors: Rochester Nathaniel
Published: September 2005

The theory of the propagation of sound in cylindrical tubes is presented. Formulas are developed for the calculation of the attenuation factor for the first mode (“plane” waves), and these formulas take into account both the resistive and reactive components of the tube wall impedance. The nature of the higher modes of sound propagation in the tube is illustrated.
The Mode of Vibration of a Clarinet Reed
Authors: McGinnis C. S. , Gallagher C.
Published: September 2005

Theoretical explanations of the action of the vibrating clarinet reed have been based upon the assumption of the partial closing of the aperture under the reed. This assumption is not supported by experimental evidence. The motion of the reed was observed stroboscopically, with the tone produced by an artificial embouchure. The actual frequency of the reed has been determined and other details in the mode of vibration observed.
Theory of Conical Sound Radiators
Authors: Brown W. N.
Published: September 2005

An expression is derived for the sound pressure resulting from the vibration of a conical sound radiator and the sound field is compared to that generated by a plane piston.
Heat Conduction Effects in Sound Emission
Authors: Alleman Rav S.
Published: September 2005

This paper presents the mathematical formulation of the heat conduction phenomena occurring at the surface of a sound emitter, wherein the medium considered to be receiving the sound and impeding the motions of the source is a gas. The method employed is that previously used by Herzfeld to discuss reflection. The result is that due to the rapid, approximately adiabatic, compressions and rarefactions, an alternating temperature gradient and therefore temperature wave, is set up in the solid source and in the medium in such a manner as to cause a reduction in the total amount of sound energy radiated from the source. This effect is expressed in terms of two out-of-phase components of particle velocity amplitude. One is of the regular sound propagation, while one is a weak, slow, highly damped wave. The ratio of the regular wave amplitude to that of the source represents a complex coefficient of emission. This emission coefficient is compared with the reflection coefficient, and the losses are found to be just half as great as in the latter case. Such a complex emission coefficient implies the same form for the effective impedance of the medium on the source, i.e., the ratio of pressure to velocity, and accordingly this radiation impedance is partially reactive and partially resistive; each of these parts is given its explicit expression in terms of measurable physical characteristics of the medium. The results had previously been applied in the revision of Hubbard’s theory of the ultrasonic interferometer to take account of these heat conduction effects, and the experimental verification of the predicted reflection coefficients for several gases is taken as experimental justification of the theoretical synthesis given.
The Temperature and Frequency Effects on Ultrasonic Velocities in Carbon Dioxide
Authors: Overbeck C. J. , Kendall H. C.
Published: September 2005

Ultrasonic velocity measurements in pure carbon dioxide gas were made at temperatures ranging from 25° to 530°C with frequencies from 27 to 147 kilocycles. Experimental variations published in earlier reports are traced to gas contamination and temperature gradient effects. Data are presented showing that the velocity is a function of both temperature and frequency. The velocity dependence on frequency becomes greater as the temperature is increased. This is due to an increased probability of the excitation of vibrational energy states as the temperature is raised. The results seem to show that the relaxation time for a transfer of energy from translational to vibrational states is longer than that for the transfer from translational to rotational states.
The Origin of the Absorption of Ultrasonic Waves in Liquids
Authors: Herzfeld Karl F.
Published: September 2005

It seems now experimentally certain that the absorption of sound waves in water, benzene, carbon tetrachloride and methyl alcohol is strictly proportional to the square of the frequency up to 50 megacycles, but considerably larger than can be explained by viscosity and heat conduction. It is shown here that an explanation of this increased absorption by slowness of energy exchange between internal and external degrees of freedom is not in disagreement with the facts for the three last named liquids, while the absorption in water must have a different origin.
The Absorption of Ultrasonic Waves in Highly Viscous Liquids
Authors: Hunter Joseph Lawrence
Published: September 2005

The absorption of ultrasonic waves in glycerin, castor oil, linseed oil, and olive oil was studied at various temperatures and at two frequencies, 3.157 and 3.95 megacycles per second, respectively. These liquids were chosen because of their high viscosity and correspondingly high absorption coefficients. As the viscosity of the liquids used depends to a considerable degree on the temperatures, the experiment permitted the calculation of the temperature coefficient of absorption to a good measure of precision and the results thus obtained agreed within the experimental error with the theoretical values for the coefficient. The sonic resonator interferometer developed by Hubbard, and adapted by Fox for use with liquids in this laboratory, was used.
The Stereophonic Sound Film System—Pre- and Post-Equalization of Compandor Systems
Authors: Steinberg John C.
Published: September 2005

In order best to fit the volume range of the program material into the volume range available in sound film, it is generally advantageous to pre-equalize the program material before recording, and to compensate for the equalization by means of a complementary post-equalizer on reproduction. The type and amount of pre-equalization depends upon the properties of hearing and on the characteristics of the program material and the film noise. This paper discusses the relations between these quantities for systems using compandors, where the film noise varies up and down in level as the compandor gains vary. Ideally, different types of pre-equalization are needed for different types of program material, and a compromise must be made if a single type is to be used. The considerations leading to the choice of the pre-equalization used in the stereophonic recording and reproducing system are discussed.
Phase Distortion in Electroacoustic Systems
Authors: Wiener Francis M.
Published: September 2005

In the course of an investigation of phase distortion in electroacoustical systems the phase shift vs. frequency characteristic of a standard miniature condenser transmitter was measured by application of the principle of reciprocity. Measurements were made in a closed cavity and in free space. In analogy, to the free field response the phase of the pressure in the undisturbed sound wave was taken as reference. By application of a principle of similitude the phase shift due to diffraction and cavity resonance was determined experimentally and found to be in agreement with theory. The phase characteristics of a number of commercial microphones of representative types were investigated by comparison with the standard condenser microphone. Difficulties were encountered at wave-lengths comparable with the dimensions of the microphones due to the uncertainty of microphone position with respect to the source. Relative response curves were obtained as a supplement and general check on the experimental method. The phase characteristics of a number of electrodynamic loudspeakers are presented.
The Acoustic Wattmeter, an Instrument for Measuring Sound Energy Flow
Authors: Clapp C. W. , Firestone F. A.
Published: September 2005

An acoustic wattmeter has been constructed to measure sound energy flow. It consists of a crystal pressure microphone and a miniature ribbon velocity microphone mounted close together and connected through separate amplifiers and phase equalizing networks to a thermocouple-type audiofrequency wattmeter. Provision is made to measure sound pressure and velocity separately as well as the energy flow represented by their product. The normal acoustic mobility and absorption coefficient of a surface may be computed from measurements of sound energy flow into the surface and sound energy density at the surface. Measurements were made on samples of hairfelt and Type B Acousti-Celotex at normal incidence with the material mounted at the end of a tube, and at random incidence with the material on the floor of a large sound chamber. Referring all results to random incidence, the values of the absorption coefficients obtained by the two methods agree well with each other and are in fair agreement with results obtained by the reverberation-time method.
A Low Frequency Horn of Small Dimensions
Authors: Klipsch Paul W.
Published: September 2005

A new loudspeaker horn is described. It is a low frequency horn so folded as to utilize wall and floor reflections to improve the impedance match at the mouth. When operated in a room corner, the speaker is capable of reproducing sounds of wave-lengths over 8 times the actual apparatus dimensions with efficiency and smoothness of response comparable to theater “woofers” of several times the size of the device described. Since its size is approximately that of a console radio, it is applicable to living room use. Because of its high efficiency, its use for small theaters and recreation centers is indicated. With suitable modifications for one or more larger size driving units, it would be capable of delivering the large amounts of power required for large theaters. Units may be stacked or clustered for outdoor use. With a frequency range of 40 to 400 cycles it is capable of fine quality when used with a suitable high frequency unit, and since the high frequency unit needs to deliver power only down to 400 cycles it may be made quite small. The loading due to the horn offers a high real component of impedance for the diaphragm to work against, resulting in low diaphragm excursion and consequently the generation of negligible harmonic components compared with what would be generated by the same driving unit delivering the same sound output from a flat baffle. Motional impedance measurements show that the efficiency is good down to 40 cycles. The use of the corner, which is ordinarily waste space, and the arrangement of side baffles so that they, together with the room walls, form the terminal section of horn, results in a simple compact structure and a considerable saving in material. In spite of the small size there is no sacrifice in quality.
Resonance Characteristics of a Cornet
Authors: Woodward J. G.
Published: September 2005

The resonance of a B♭ cornet was measured over a wide range of frequencies and for all combinations of open and closed valves. An audiofrequency oscillator and headphone were used as the source of sound and a sound level meter was the indicating device. About twenty regions of resonance were found, all below 2500 v.p.s.
A Re-Examination of the Noise Reduction Coefficient
Authors: Parkinson J. S. , Jack W. A.
Published: September 2005

It is the present practice to call the average of the sound absorption coefficients at 256, 512, 1024 and 2048 cycles the noise reduction coefficient, in an effort to assign a single figure to an absorbing material which will be useful in judging its performance in a noise quieting problem. This is recognized as a makeshift, as no single figure can represent correctly the reduction obtained. Typical noise spectra are presented and analyzed for reductions that can be expected in each frequency band. It appears that if a single figure is to be assigned the absorption coefficient at 4096 should also be considered. This is particularly true of office quieting, which is an important field of commercial noise control. In factories where heavy machinery is operating, it appears advisable to give some weighting to 128 cycles.
The Flutter Echoes
Authors: Maa D. Y.
Published: September 2005

“Fluttering” is the transient vibration excited by short sound pulses between two parallel walls. To an observer near one of the walls, the flutter echoes always sound as if they originate from the farther wall. In this paper the phenomenon of fluttering is considered theoretically both by the normal mode technique and by the method of geometrical acoustics. Both methods predict a series of multiple echoes. This is verified experimentally by taking the oscillogram of the flutter echoes. The directional effect of the fluttering is explained by psychological reasons.
The Velocity of Sound in Air
Authors: Hardy H. C. , Telfair D. , Pielemeier W. H.
Published: September 2005

A rigorous equation is set up for the velocity of sound in gases. This is used to calculate the velocity of sound in dry air at standard conditions from data taken in independent measurements. The result of this calculation is 331.45±0.05 meters sec.−1 An extensive survey of previous reported measurements has been made. After proper corrections are taken into account, the weighted mean is 331.464±0.05 meters sec.−1 The results of very precise interferometer measurements by the authors give 331.44±0.05 meters sec.−1.
Properties of the Dulled Lacquer Cutting Stylus
Authors: LeBel C. J.
Published: September 2005

The recent improvement in disk recording standards is emphasized. The combined cutting and burnishing action of a standard lacquer cutting stylus is explained. It is emphasized that cutting and burnishing take place simultaneously (in terms of wavelength) at low frequencies; but that at higher frequencies the two operations are separated by a discrete wavelength fraction; phase shift and attenuation result. These depend upon circumferential velocity, hence are worst at low rotational speed and small distance from the center of the record. The experimental study, therefore, is confined to 3331 r.p.m. recordings at various diameters, and the recorded velocity as a function of frequency and diameter is determined for needles with different lengths of dulling. The effect of amount of dulling on surface noise is determined, and a technique for comparing the perfection of action of cutting and burnishing is given. It is emphasized that for modern quality standards the length of dulling must be restricted and that the resulting increase in surface noise is not of great importance.