bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of the Vibro-Tactile Senses as Means for Determining Direction
Authors: Gault Robert H. 
Published: September 2005

Earlier investigations in this field have left the factors of intensity, rate of transmission (and consequently time of stimulation) and phase without adequate control. In this investigation, as far as it has proceeded, we have attempted to supply this deficiency.
In the experimenter's room is a speaker that may be moved right or left upon the arc of a circle. Before it, in fixed positions, are two microphones. These microphones communicate with two vibrators, respectively, in the distant observer's room. The observer is seated with the index finger of the right hand upon one vibrator and that of the left hand upon the other. The situation is so arranged that he cannot hear the action of the vibrators. Before him, and covering the vibrators, is a sheet of cardboard on which the arc of a semicircle is described marked to designate degrees.
As the speaker, in action, is moved sufficiently to the right or left, thus varying its distance from the microphones, respectively, the intensity, time and phase of the stimulus upon the observer's fingers, respectively, are altered as in a corresponding situation in the sphere of audition. The observer “feels as if” a vibrating body before him were moving between right and left. On the semi-circumference before him he designates the degree of the apparent movement.
When, now, the speaker is kept in a constant middle position with reference to the microphones and when attenuators are introduced to control intensity in the vibrators, respectively, the time element is kept constant but the observer continues to experience the illusion of movement referred to. The degree of apparent movement corresponds to that that obtains in the auditory sphere in similar situations.
We have yet to complete the experiment by holding intensity constant while other factors are independently varied.
A Method of Eliminating Cavity Resonance, Extending Low-Frequency Response and Increasing Acoustic Damping in Cabinet Type Loudspeakers
Authors: Olney Benj. 
Published: September 2005

When a direct-radiator loudspeaker is mounted in a cabinet, as in the conventional radio receiver, response irregularities are introduced because of resonances in the space behind the loudspeaker. With a cabinet and speaker diaphragm of ordinary size, the acoustic load at low frequencies is highly reactive, the radiation efficiency is very low and diaphragm amplitudes become excessive.
In the method described, the rear of the loudspeaker diaphragm is tightly coupled to one end of a folded conduit lined with sound-absorbing material and terminating in an opening in the bottom of the cabinet. This arrangement is called an acoustical labyrinth. By suitable tuning of the conduit, an extension downward of the reproduced frequency range is secured. The acoustic impedance of the conduit is shown by measurement to offer a diaphragm load having desirable characteristics, it being predominantly resistive over virtually the entire measured low frequency range (40–350 cycles). Measurements of the acoustic impedance on the front of a diaphragm in a moderate sized baffle and of the impedance facing the back of a diaphragm in a conventional radio cabinet are also reported. The improvement in the frequency characteristic of a cabinet type loudspeaker afforded by the use of the acoustical labyrinth is shown by response curves.
A Modified Tube Method for the Measurement of Sound Absorption
Authors: Morrical Keron C. 
Published: September 2005

In a previous abstract a method was described for measuring the sound absorptivity of small specimens. Sound from a loudspeaker travels down a cast iron tube 8 inches in diameter, strikes the specimen under test at an angle of 45 degrees and is reflected down a side tube where it is measured. By measuring the sound reflected down the side tube from a thick glass plate, and by measuring the sound in the side tube when an exponential horn is substituted for the specimen, it is possible to arrive at the reflectivity and consequently the absorptivity of the specimen.
The earlier apparatus has been redesigned and measurements have been taken on a large number of materials. For the frequency of 500 c.p.s. the method has given absorptivities for commercial materials that are in satisfactory agreement with those determined by reverberation measurements. By means of a miniature condenser transmitter the actual pressure distribution in the tube is being investigated with the view of extending the usefulness of the apparatus to frequencies above and below 500 c.p.s.
Investigation of the Sound Absorptivity of Portland Cement Concretes
Authors: Watson F. R. 
Published: September 2005

Coefficients of absorption were determined by the reverberation method, both instrumentally and with the ear. The samples were special types of concretes, ranging from dense, heavy mixes using standard aggregates to light, porous ones having varying proportions of cement, sand and light weight aggregates, such as cinders and haydite.
The results show that porous materials absorb sound, but dense materials with small porosity are not efficient in absorbing sound. Haydite and cinder concrete constructions proved to possess effective sound-absorbing values; sandstone and limestone products were not so good, but most of the specimens are more sound absorbent than the usual hard plasters and cements so that these new products can be used advantageously in buildings to reduce noise.
NBC Studio Design
Authors: Morris R. M. , Nixon G. M. 
Published: September 2005

The factors influencing the acoustical requirements of broadcast studios are discussed with the relation of studios one to another and to appurtenant spaces. A method of procedure is outlined, showing the embodiment of certain principles and data obtained from 10 years' experience in the design, construction, and operation of studio groups of various sizes. Studio groups recently designed and constructed by the NBC are described as examples of the application of these principles. A portion of the paper is devoted to other details such as characteristics of various acoustical treatments; discoloration of treatments due to “breathing” and means of control; the sound control of air conditioning, plumbing, electrical and heating systems; and the sound isolation required between studios and the building structure.
Other essential empirical and experimental data are presented such as: optimum sizes and dimensions of studios for various numbers of occupants; optimum reverberation time and frequency characteristics; the arrangement and treatment of appurtenant spaces such as control and observation booths, vestibules, doors, windows, etc., fundamental requirements and recommended specifications for satisfactory acoustical performance.
Finite Acoustic Filters
Authors: Lindsay R. B. 
Published: September 2005

Most of the previous theoretical work on acoustic filtration has dealt with idealized infinite structures. The present paper is a theoretical study of finite filters such as are used in practice. Considering an acoustic structure with air as the medium with main line impedance Z and with n branch impedances Zb (pure reactances) equally spaced at intervals 2l, it develops that one can express the power transmission ratio for the structure in the simple form Pr = 1⧸(1 + Z24|Zb|2⋅sin2 nWsin2 W), (1) where cos W=cos 2kl+iZ/2Zb⋅sin 2kl, (2) the familiar parameter of the transmission theory of filtration (reference 2). The plot of Pr in (1) as a function of frequency shows the presence of transmission and attenuation bands which approach those of the corresponding ideal infinite case as n becomes large compared with unity. Comparison of (1) with the actual transmission measurements of Stewart (reference 2, pp. 170, 175) shows satisfactory agreement.
The phase change which occurs between successive sections in a filter is also computed and it is shown that unlike the situation in the infinite case the phase change is a function of the section. However, at relatively high frequencies and for large n this approximates to the total phase change along the structure divided by n. Comparison with such experimental results as are at present available yields reasonably satisfactory agreement.
An Adjustable Tuning Fork Frequency Standard
Authors: Hugo Schuck O. 
Published: September 2005

A portable tertiary frequency standard, adjustable over a small range, is described. The frequency determining element is a tube-maintained tuning fork, adjustment of whose frequency over a relatively small range is accomplished by changing the position of movable weights on the prongs. Calculations are simplified by the design of the fork, which permits the assumption of lumped constants.
The weights may be moved while the fork is running without interfering with its operation. Indication of their position is by means of a pointer reading on a scale graduated directly in frequency units. A precise method of calibration is given. Mechanical arrangements are described for obtaining a uniformly spaced scale, and the possibility of using such a scale in correcting for the temperature coefficient of the fork material is discussed.
The relative accuracy of such a fork is greater, the smaller the range of frequency adjustment. In the present development, adjustment may be made over a range of plus and minus three percent of the mean frequency, that is, a musical interval of one semitone, or 100 cents total change. Incorporation of this fork in the chromatic stroboscope has resulted in considerable simplification as well as an increase in the reliability of the instrument.
Effect of Physical Size on the Directional Response Characteristics of Unidirectional and Pressure Gradient Microphones
Authors: Massa Frank 
Published: September 2005

A quantitative theoretical analysis of the directional characteristics of a unidirectional microphone, taking into account (1) the finite separation between the pressure and pressure gradient actuated elements and (2) the acoustic path increase caused by the physical structure which must necessarily enclose the rear of the pressure actuated element, reveals two types of variation of the microphone characteristics at the higher audiofrequencies. For a balanced microphone, the directional characteristic is substantially a cardioid of revolution at the lower frequencies. As the frequency increases there are two distinct departures from the cardioid. First, there is a marked reduction in the angle of high attenuation which is caused by the physical separation between the microphone elements. Second, there is a shift in the axis of maximum attenuation at the higher frequencies which is caused by the size of the structure which surrounds the pressure element. Experimental data taken on a balanced unidirectional microphone are presented to show the general agreement with the theoretical characteristics. The methods for controlling the amount of angular shift at the high frequencies are described as is also the method of mounting the microphone with reference to the pressure actuated element so that the “shift” will occur in the most favorable direction.
Theoretical analysis of an idealized pressure gradient actuated microphone (velocity microphone) shows that the directional response characteristics get broader with increasing frequency. Experimental data are shown on an actual microphone which bear out the theory at the higher frequencies but not at the medium high frequencies. An explanation for the discrepancy is given in the text.
A General Theory of Passive Linear Electroacoustic Transducers and the Electroacoustic Reciprocity Theorem. II
Authors: Primakoff Henry , Foldy Leslie L. 
Published: September 2005

In Part I of this paper, it was shown that the reciprocity theorem for passive linear electroacoustic transducers could be established on the basis of a pair of general linear relations connecting the voltage and current at the electrical terminals of the transducer with the pressure and velocity distribution over the transducer surface provided certain “reciprocity relations” existed among the parameters entering these equations. In Part II it is now shown that on considering a transducer to be comprised of media characterized in the usual manner by appropriate linear constitutive relations between stress, strain, electric and magnetic polarization, charge and current density, and electric and magnetic field intensity, one can establish the validity of the linear relations and the “reciprocity relations” assumed in Part I, provided that certain sufficient conditions are met. These conditions are: (l) That the coefficients in the constitutive relations satisfy certain “symmetry conditions.” (2) That no magnetostrictive media and no static magnetic field are present in the transducer (that is, that the coupling is purely electrostatic or piezoelectric or both), or that no piezoelectric media and no static charge density are present in the transducer (that is, that the coupling is purely electromagnetic or magnetostrictive or both). (3) That the transducer does not radiate electromagnetic waves from its surface.
The validity of the “symmetry conditions” on the coefficients of the constitutive relations is established for frequencies sufficiently low that the harmonic changes in the variables can be regarded as adiabatic in the thermodynamic sense and under certain circumstances at higher frequencies by means of a general argument based on a principle of microscopic reversibility. One may, however, anticipate the possible breakdown of these conditions when appreciable losses due to “relaxation” phenomena in the transducer media are present. The conditions for the validity of the reciprocity theorem derived in this paper are only sufficient, but they may be considerably extended in their generality to include the presence of other phenomena (such as electrostrictive effects) by the application of the same general methods.
Attenuation and Scattering of High Frequency Sound Waves in Metals and Glasses
Authors: Mason W. P. , McSkimin H. J. 
Published: September 2005

By using a pulse method, attenuation and velocity measurements have been made for aluminum and glass rods in the frequency range from 2 to 15 megacycles. The sound pulses are generated by crystals waxed to the surface of the rod. This wax joint limits the band width of the transmitted pulse and measurements are made using long pulses which approach steady state conditions. The reflected pulses show evidence of several normal modes which can be minimized by using specially shaped electrodes. Longitudinal waves show delayed pulses of smaller magnitude that are caused by the longitudinal wave breaking up into reflected longitudinal and shear waves at the boundary. This effect is small if the diameter of the rod is 20 wave-lengths or more.
The measured losses for aluminum rods show a component proportional to the frequency and another component proportional to the fourth power of the frequency. The first component is the hysteresis loss found for most solid materials. The component proportional to the fourth power of the frequency is caused by Rayleigh scattering losses which are the result of differences in the elastic constants between adjacent grains caused by changes in orientation. Calculated scattering losses agree quite well with the measured values. The fourth-power scattering law holds quite well until the grain size is equal to one-third of a wave-length. For higher frequencies the scattering loss increases more nearly with the square of the frequency. Glasses and fused quartz have a loss directly proportional to the frequency, showing that any irregularities must be of very small size.
The Equivalent Circuit for a Bifurcated Cylindrical Tube
Authors: Miles John W. 
Published: September 2005

Using the impedance concepts developed in earlier papers, the problem of the diffraction of sound, caused by a bifurcation of a cylindrical tube, is solved. The equivalent circuit elements are shown to be related to the analogous changes of cross section. It is shown that the transmitted power is divided between the two tubes resulting from the bifurcation in proportion to their areas and without frequency distortion or reflection, and that the bifurcation may, therefore, be regarded as taking place in a virtual plane parallel to, but somewhat removed frown, the geometrical plane. A formula is given to locate this plane.
The results are applied to a concentric-circular bifurcation and to a rectangular-tube bifurcated parallel to one of its walls. Numerical results are given which may be applied both to the circular change of cross section and to the concentric bifurcation of a circular tube.
Construction and Calibration of an Improved Bone-Conduction Receiver for Audiometry
Authors: Carlisle R. W. , Pearson H. A. , Werner P. R. 
Published: September 2005

The construction of an acoustically shielded bone-conduction unit is described. The masses and springs have been proportioned for optimum purity of wave form at low frequency and for extension of the high frequency range to over 12,000 cycles.
The precautions taken in preparing an acoustical loudness-balance calibration are described, and the reproducibility of observations is considered. Methods of specifying the response of productions units are shown.
Broadened Criteria of Hearing Aid Performance
Authors: Mundel August B. , Carlisle Richard W. 
Published: September 2005

The requirements of hearing aid users include, besides adequate acoustic response, low reaction to “noise” excitation and other characteristics.
Methods used in reducing unwanted sensitivity are discussed. Other operational features of a hearing aid are considered, and a single chart method of presenting acoustic input-output characteristics, frequency response, and distortion is described.
Reflection and Transmission of Sound by Thin Curved Shells
Authors: Primakoff Henry , Keller Joseph B. 
Published: September 2005

In this paper the reflection and transmission of sound by thin curved shells, as well as several related problems, are treated mathematically. First, one derives an inhomogeneous integral equation for the sound field in an infinite medium containing a thin curved shell of different material. The solution of the integral equation is then reduced, approximately, to the evaluation of a surface integral not too different from that obtained in the usual Kirchhoff diffraction theory. The integral is evaluated approximately and gives expressions for the pressure waves reflected from and transmitted through a thin curved shell. The reflection and transmission coefficients of the shell are obtained from these expressions. It is found that the reflection coefficient can be expressed as the product of a geometrical factor, a phase-cancellation factor, and a reflectivity factor. When the reflection problem for a rigid obstacle is solved with the aid of the assumptions of the Kirchhoff diffraction theory, the reflection coefficient thus obtained is the product of the geometrical and phase factors of the previous solution. The geometrical factor alone is obtained as the reflection coefficient when the reflection problem is solved exactly by geometrical acoustics. The agreement among the various solutions may be considered as a partial justification for the Kirchhoff theory as well as for geometrical acoustics.
The Kirchhoff method is also applied to the problem of refraction at a curved surface. From the solutions of the reflection and refraction problems, the laws of reflection and refraction for curved surfaces are obtained. In addition, the mirror and lens laws, the conditions for point images, and the change of phase at a focus are obtained.
The Time Integral Basic to Optimum Reverberation Time
Authors: Maxfield J. P. 
Published: September 2005

Equations showing the relation between the volume, V, of an auditorium and its optimum reverberation time, T0, were published independently by MacNair and Liftschitz. MacNair's equation was derived from the following basic assumptions: ∫ 0T1 (logρ)dt = a const., (1) E = const., (2) where ρ = instantaneous value of the energy density of sound during decay. T1 = time of decay to minimum audibility. E = rate of supply of energy during the steady state condition.
This paper shows that an equation, relating T0 and V, can be deduced which more nearly fits all the empirical facts by basing the derivation on the following assumptions: ∫ 0T1 ρ⋅dt=a const., (1) E = GVn, (2) where G = a constant, n = a constant which should be less than unity.
The resulting equation, for n = 23, is T0 = 0.212 V1/6. This is in agreement with the empirical data and with the equation derived by Maxfield and Albersheim from acoustic “liveness” considerations.
The psychologists and physiologists studying the mechanism of hearing should be interested in these results, as they have a bearing on the manner in which the ear integrates the sound being perceived.
The Directional Characteristics of a Clamped-Edge Disk
Authors: Merrill Lynn L. , Slaymaker Frank H. 
Published: September 2005

It is well known that to obtain very small side lobe radiation, the amplitude distribution across a radiating surface should be such that the maximum amplitude is at the center and the minimum at the edges. The Gaussian distribution gives no side lobes but requires an infinitely large radiator. This paper gives the analysis of the clamped-edge disk vibrating in its first normal mode. It shows that the dynamic curve approximates the Gaussian form and that the sound pressure distribution has very small side lobes, the amplitude of the first side lobe being 33 db below that of the axial lobe.
For a disk of a given diameter the width of the axial lobe may be decreased by raising the frequency of the first normal mode, which requires a corresponding increase in the disk thickness. At very high frequencies the disk thickness may become prohibitive. In such cases a thin disk can be forced to vibrate in the shape of the first normal mode by a proper radial distribution of the driving force.
Measurement of Directivity Factor
Authors: Burbank Cecil J. 
Published: September 2005

The directivity factor, the ratio of the average sound intensity from an electroacoustic transducer to the sound intensity in the reference direction, both measured at the same separation, is measured directly using the device described.
The equipment is composed of a mechanical mounting which permits rotation of the unit about two mutually perpendicular axes and electronic equipment which integrates the power. The electronic circuits used are of two different types; one type, designed by D. H. Ransom and J. H. Martin, uses a thermocouple, a direct-current amplifier, a 60-cycle vibrator, a 60-cycle amplifier, and a modified watt-hour meter; the other type, designed by R. C. Fisher and C. J. Burbank, uses the potentiometer in a power level recorder into which 60-cycle alternating current has been introduced, a 60-cycle amplifier, and a regular watt-hour meter which has been modified to increase the dynamic range.
A measurement of the directivity factor and the input power to the transducer gives the over-all efficiency of the unit in question.
The design considerations and use of the instruments are discussed.