bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Substitution Method of Measuring the Open Circuit Voltage Generated by a Microphone
Authors: Hawley M. S. 
Published: September 2005

An analysis of the substitution method of measuring the open circuit voltage generated by a microphone is given which shows that the “normal” substitution voltage equals the open circuit voltage for all types of acoustic measurements and for any value of electric impedance loading the microphone. It is shown that the method recently proposed by some authors of removing the acoustic load from the microphone when applying the substitution voltage results in a substitution voltage which does not equal the open circuit voltage. It is also shown that a formula for the response of a transducer derived for a system in which the microphones are open-circuited may be used when the microphones are terminated by finite electrical impedances, by replacing the generated open circuit voltages in the formula by the corresponding “normal” substitution voltages.
Consideration is given to the restriction in the definition of the pressure response of a transducer made necessary by the fact that the pressure on a microphone diaphragm is a function of the electrical impedance terminating the microphone.
An experiment is described which involves a microphone coupled to a chamber, the acoustical impedance of which is high relative to that of the microphone. The results of this experiment agree with the conclusions of the analysis.
Application of Activated Ceramics to Transducers
Authors: Koren H. W. 
Published: September 2005

The conditions under which titanate ceramics may be made to have piezoelectric properties suitable for application to transducers are described. These conditions involve a selection of the titanate material to give a Curie point well above the working temperature, polarization from an external voltage source within certain limits of potential gradient and time duration, and mechanical structure. Most common transducers have a mechanical impedance far below that of a solid block of ceramic. Multilamellar strips have been developed to provide the mechanical impedance required in a phonograph pick-up, microphone, or the like. These consist, in general, of a metal strip with a thin plate of ceramic soldered to one side or with thin plates soldered to both sides. As the multilamellar strip cools below the solidification point of the solder, the ceramic becomes pre-stressed in compression. This strip is then used in flexure in a transducer. It has many unique properties, especially for applications involving extreme conditions of humidity.
Applications of this strip for a phonograph pick-up and to a microphone are shown.
Precautions involved in controlling production of a pick-up are discussed.
Non-Linear Distortion in Dynamic Loudspeakers due to Magnetic Effects
Authors: Cunningham W. J. 
Published: September 2005

Two sources of non-linear distortion in a dynamic loudspeaker are considered in this discussion; both are related to the magnetic characteristics of the driving mechanism The first type of distortion arises because of a force of attraction between the voice coil, carrying a current, and the iron of the field structure. This force varies as the square of the current and produces second harmonic distortion. The force may be related to the space rate of change of self-inductance of the voice coil as it moves in the air gap. The magnitude of the distortion produced in this way may be several tenths of one percent, and is greater for low frequencies and large currents. This distortion may be reduced by proper proportioning of the voice coil and field structure and by using a short-circuited winding on the field structure.
The second type of distortion arises due to non-uniformity of the magnetic field in which the voice coil moves. This effect is well known qualitatively, but equations are given here for its quantitative evaluation. These equations indicate that the distortion characteristically is less than one percent, and is greater for large amplitudes of motion. If the voice coil is centered in a symmetrical field, only odd-order distortion is produced. If the field is not symmetrical about the voice coil, even-order distortion is also present. This distortion may be reduced by proportioning the voice coil and field structure so that the mean field in which the coil moves remains as constant as possible.
Building to the Acoustical Optimum New Mutual-Don Lee Broadcasting Studios
Authors: Carruthers Walter W. , Love Donald P. 
Published: September 2005

The acoustical design and construction of the new Mutual-Don Lee Broadcasting Studios in Hollywood were done under novel and very favorable arrangements. First, a careful check was made of the optimum acoustical characteristics to which it was decided to design the studios. Some of the best auditoriums for broadcasting were measured, and from these data as well as comments regarding the excellence and shortcomings of these auditoriums, the optimum characteristics for the new studios were determined.
During the course of construction, acoustical measurements were made several times for the purpose of “tailor-making” the acoustical characteristics of the studios. On the basis of the measurements, it was found that only a few minor modifications in acoustic treatment were necessary, such as changing the mountings of the Acousti-Celotex materials in order to change the low frequency absorption characteristics as desired, and the areas used of these materials.
The results are, close agreement between optimum and finally measured acoustical characteristics, and very satisfactory broadcast programs.
Aural Microphonics in the Cochlea of the Guinea Pig
Authors: Davis H. , Gernandt B. E. , Riesco-MacClure J. S. , Covell W. P. 
Published: September 2005

Electro-acoustic equipment and methods for the study of aural microphonics and action potentials of laboratory animals are described. A new feature is the placement of electrodes not only on the round window but also in one or more very small holes drilled into the cochlea of the guinea pig.
Analysis of the aural microphonics so recorded confirm the conclusions of Wever and Lawrence, of Békésy, and others. The microphonics generated at the apex by low tones or near the round window by high tones axe conducted electrically to the other end of the cochlea with an attenuation of at least 10 db. The effects of the local injury caused by the small holes are described, and their relation to anatomical position confirms the earlier data of Stevens, Davis, and Lurie. Detailed comparisons of phase relations, wave form, etc., at different positions did not prove feasible because of electrical leakage of the aural microphonic from one turn to the next through the bony partitions.
At high intensities the microphonic for a tone of 3000 c.p.s. or higher may show a very strong “sub-harmonic” at the apex although the sub-harmonic component is very small at the round window. The threshold for appearance of the sub-harmonic is very sharp.
Intonation of Solo and Ensemble Performance of the Same Melody
Authors: Nickerson James F. 
Published: September 2005

A study was made of solo and ensemble performance of the same musical material as related to systems of intonation postulated by certain acoustical, musical, and psychological theories. In particular, it was desired to check earlier findings that unaccompanied performance and listener preferences approximate Pythagorean intonation and to extend a similar line of investigation to ensemble performance.
Solo and ensemble performances by 24 well-trained string quartet players were recorded from which stratified random samples of tones were obtained for frequency analysis. This analysis was made through the use of 16-mm sound-on-film loops with a chromatic stroboscope (Stroboconn).
The results confirm earlier findings for unaccompanied melodies and indicate that Pythagorean intonation is also most typical of ensemble performance. This tendency appears to dominate any “cultural conditioning” which may exist for equi-tempered intonation.
The Effect of Sound on Laminar Propane-Air Flames
Authors: Loshaek S. , Fein R. S. , Olsen H. L. 
Published: September 2005

The application of sound of known intensity and a frequency of 12.7 kc to a laminar propane-air flame is found to produce a shift in the stability limits of the flame. The sound alters the flashback limit so that the flame becomes more stable and the blowoff limit so that the flame becomes less stable. It is shown that the normal burning velocity is not changed with the application of sound and that the flow-velocity profile in the tube is likewise unchanged. From the Lewis and von Elbe theory of flame stabilization it is then concluded that the “penetration distance” must be increased. The “penetration distances” are calculated from the flow-velocity distribution and the normal burning velocity and, near stoichiometric, are found to increase about 20 percent at the maximum sound intensity of 10 milliwatts/cm2. Sound at a frequency of 18.3 kc is found to affect the blow-off limit in a similar manner as the lower frequency but no appreciable effect is noted on the flashback limit.
It is concluded that these results in combination with further experimental studies should yield useful information about the nature of the “penetration distance” and flame holding in general, but that sound at these low frequencies does not offer a useful tool for studying flame propagation. It is recommended that the effects of sound on practical burners be given careful study because the results presented indicate that the maximum quantity of energy that can be released in a given burner volume may be limited by the sound level in the combustion chamber.
The Binaural Localization of Pure Tones
Authors: Wightman E. R. , Firestone F. A. 
Published: September 2005

Measurements of phase difference and amplitude ratio of the sound entering the ears of a man-shaped wax dummy were taken with the source at varying azimuths around the head; at 256, 1024 and 1944 cycles per second; and at distances of 20, 50, 100 and 400 cm. from the head. The measurements at the two frequencies agree with the values published by Hartley and Fry computed on the assumption that the head is a rigid sphere in free space, except that the observed values of amplitude ratio are about 13 per cent. less than the computed values on account of the interference of the neck. The observed values at 1944 cycles are quite different from the computed values.
As a converse experiment, pure tones of frequency 256 cycles were presented binaurally to eight different observers, the phase difference and amplitude ratio of the acoustical pressures at the two ears being known and adjustable. The observers were asked to state the direction and distance of the apparent source of sound. Only three of the eight observers were influenced in their judgment of direction by the phase difference and even they were rather inaccurate. All were influenced more or less in judging direction by the amplitude ratio. None was able to tell the distance of the source by the amplitude ratio.
The Two Points of View in Teaching the Control of the Human Voice in Speech and Song
Authors: Simmions Louis 
Published: September 2005

First: The School of the control of the vowels. This includes the teaching of the Bell Canto. The Old Italian School where the human voice is treated purely as an instrument where beautiful sound predominates.
Second: The Consonantal School of dramatic recitation in speech and in song where beautiful sound in voice development is not a prime consideration. This school belongs to the German and French.
The speaker, through practical demonstration, believes he can prove that the constant struggle between these two schools can be eliminated and coordinated through scientific investigation of the action of the Ventricles of Morgagni—two air spaces situated in the throat between the true and false vocal chords. According to some authorities and the speaker's own investigation these two ventricles or air pockets act as a valve and control the air pressure above the oscillation of the vocal chords, consequently controlling the binding of the two elements in speech and in song.
II. Theory of the Horn Type Loud Speaker
Authors: Hanna C. R. 
Published: September 2005

In the electromagnetic driver the force per unit current has been shown to be a function of the inductance and the negative stiffness resulting from the presence of the steady magnetic field. In this paper it is proven that the force per unit voltage in the electrostatic device is a similar function of the capacity and the negative stiffness due to the steady electrostatic field.
A new concept called Motional Admittance is introduced for the electrostatic loud speaker and this is shown to be similar in its mathematical form to the Motional Impedance of the electromagnetic driver.
A calculation of the ultimate theoretical efficiency that may be obtained with an electrostatic speaker having a pure resistance radiator and covering a given frequency range is given. It appears that efficiencies between 5 and 10% may some day be obtainable with good fidelity of reproduction.
Area and Pattern Effects in Absorption Measurements
Authors: Parkinson John S. 
Published: September 2005

The coefficient of absorption of an acoustical material as obtained by the reverberation chamber method varies with the area tested and the shape of the sample. A theoretical explanation of this phenomenon is outlined, showing that the results cannot be attributed entirely to edge affects, and explaining the discrepancies which appeared when the diffraction theory was applied to the tests.
Test results show the efficiency of various patterns and arrangements of treatment. It can be shown that the absorption coefficient isproportional to K(p/A)where p is the perimeter of the individual sample and A the area. It can be shown also that the absorption per square foot of total pattern area is always proportional to the ratio of treated to untreated area, regardless of the pattern arrangement. This relation is formed to hold good for all frequencies with the same material, but not for different materials. Typical questions of construction and design can be answered as a result of the data.
Recent Advances in Sound Absorption Measurements
Authors: Chrisler V. L. , Snyder W. F. 
Published: September 2005

Part I. Measurement of Sound Absorption by Oscillograph Records. The method is much the same as that described in the previous paper except the decay is measured through as much as 50 decibels. The results agree very closely with those obtained by the ear using the usual reverberation method. The coefficients for a few materials are given as determined by both methods.
Part II. Absorption of an audience. The absorption of an audience has been determined when seated in different kinds of chairs. The results of these measurements are given with the suggestion that they should be checked by other observers.
PLANE SOUND WAVES OF FINITE AMPLITUDE
Authors: Fay R. D. 
Published: September 2005

The principal object of the analysis is to find the change in type of periodic plane waves of sound of finite amplitude propagated in free air.
A solution of the exact equation of motion is obtained as a Fourier series. Due to the nonlinear relation between pressure and specific volume there is found to be a gradual transfer of energy from components of lower frequency to those of higher frequency. Since the effect of viscosity is to attenuate the higher frequency components more than the lower, there is always a wave form having the harmonic components in a stable relation such that the decrease in relative magnitude of any component due to viscosity is compensated by the relative increase due to nonlinearity. The conditions for stability vary with intensity. There is therefore no permanent wave form, but the stable wave will change its form more gradually than any other wave of the same intensity and wave length. The change in type of any wave is toward this stable form. There is a marked departure from the sinusoidal in the stable type even for waves of very moderate amplitude.
A Method of Measuring Acoustic Impedance
Authors: Flanders P. B. 
Published: September 2005

An apparatus s described whereby acoustic impedances may be measured in terms of a known acoustic impedance and the complex ratios of two electrical potentiometer readings to a third. As a known impedance, there is chosen the reactance of a closed tube of uniform bore which is an eighth wave-length long. The electrical readings are obtained by balancing the amplified output of a condenser transmitter against the electrical input of the source of sound. The condenser transmitter picks up the acoustic pressure at the junction of the sound-source and the attached impedance. A balance is made for each of three successively attached impedances: (1) a closed tube an eighth wave-length long, (2) a rigid closure of the sound-source, and (3) the impedance to be measured. The unknown acoustic impedance Z is then calculated in terms of the known acoustic impedance Z0 by means of the equation Z = 'Z0 z1 − z2z3 − z2, where z1, z2 and z3 are, respectively, the three electrical impedance settings of the potentiometer. As indicated by this equation, the constants of the electrical circuit are involved only as ratios, so that the response characteristics of the source of the sound, condenser transmitter and amplifiers (provided they are invariable) do not affect the measurement.
Illustrations are given of impedance measurements on a closed tube of uniform bore, a conical horn, an exponential horn, an “ infinite ” tube, and a hole in an “ infinite ” wall.
A NEW ANALOGY BETWEEN MECHANICAL AND ELECTRICAL SYSTEMS
Authors: Firestone F. A. 
Published: September 2005

By considering each mass in a linear mechanical system as having two terminals, one fixed in the mass and one fixed to the frame of reference, every linear mechanical system is reduced to a multiplicity of closed mechanical circuits to which force and velocity relations similar to Kirchhoff's laws, may be applied. The conventional mechanical-electrical analogy is derived from the similarity of the equations v = f/z and I = E/Z. It is incomplete the following respects which lead to difficulty in its application.
I. There is a lack of analogy in the use of the words “through” and “across” which indicates a fundamental difference in the nature of the analogous quantities, for instance, force through and e.m.f. across.
II. Mechanical elements in series must be represented by electrical elements in parallel, and vice versa.
III. Mechanical impedances in series must be combined as the reciprocal of the sum of the reciprocals while electrical impedances in series are additive.
IV. There is an incompleteness the mechanical analogues of Kirchhoff's laws.
The new analogy is derived from the similarity of the following equations: v = fz̄ and E = IZ where z̄ is the reciprocal of the mechanical impedance as usually defined. This new analogy is complete in all of the above-mentioned respects in which the old analogy failed. It leads to analogous relations of a simple sort and permits an equivalent electrical circuit to be drawn in an easy intuitive manner.
The Ventricular Bands and the Physiology of the Voice
Authors: Josephson E. M. , Simmions Louis 
Published: September 2005

Recent studies in the anatomy of the ventricular bands and of the thyro-arytenoid muscles, and physiologic researches in the mechanics of the larynx have compelled changes in concept of voice formation.
These studies have revealed the presence of structures which have been overlooked which impart to the false vocal cords an independent motility and an action antagonistic to that of the thyro-arytenoid muscles; and which actively alter the conformation of the Sinus Morgagni. These studies stress the hitherto unemphasized importance of the function of the suspensory mechanism of the larynx, and the interrelation of the motor mechanisms of respiration and voice formation.
Clinical studies prove that ventricles of the larynx play an important rôle in the formation of the human voice. Filling of the ventricles by disease processes which do not in any wise impair the motility of the true vocal cords or their freedom to vibrate, nevertheless results in complete or high-grade aphonia and dysphonia. Similar disorders are associated with disease of the ventricular bands. These studies indicate the need of extensive researches in the mechanism of the voice; for they contradict much that has been written and dogmatically taught on the subject of the voice.
On Frequency Modulated Signals in Reverberation Measurements
Authors: Hunt F. V. 
Published: September 2005

A point-by-point curve tracer, similar to that described by Norris and Andree [J.A.S. 1, 366 (1930)] but permitting a longer period of decay to be traced, is employed to study the reverberant decay of pure tones and tones having various degrees of frequency modulation (so called “warble” tones). Straight lines (db vs. time) are fitted to the decay curves by the assumption that the slope determined by every pair of points should be weighted in the average according to the decay time included between the two points. This leads to a simple numerical procedure when the points are equally spaced on the time axis.
The deviations of individual points from the best straight line are computed and found to fall into regular and consistent time patterns, from which large group deviations can be seen to gradually disappear as the degree of warble is increased. These time patterns differ from point to point in the sound chamber but the magnitude of the deviations and the slope of the decay curves (within a limit of accuracy consistent with the deviations) is practically independent of position.
Conclusions are drawn regarding the accuracy with which decay rates can be determined using pure and warble tones.
Experimental Evidence of Nonlogarithmic Sound Decay
Authors: Chrisler V. L. , Miller Catherine 
Published: September 2005

In this paper experimental data are presented showing that in a room containing the average acoustical installation the distribution of sound energy does not remain uniform as the sound decays. In consequence the decay of the sound energy is not logarithmic. As one of the fundamental assumptions in all reverberation theories is that the sound energy does decay logarithmically and that it remains uniformly distributed during the decay, it is evident that the reverberation formulae as now given do not apply in most cases. The error introduced in computing the reverberation time where there is a ceiling treatment only may be as much as 30 percent.
It should be possible by further study of this problem to introduce some form of a correction factor in the present formulae so as to take care of most cases encountered in practice.