bluuebunny/crossref_metadata_2025 huggingface dataset:
Sounding Systems for Public Air Raid Warning
Authors: Abbott E. J.
Published: September 2005

One of the essential parts of the United States Air Raid Warning System is an outdoor sound-signal system for public warning. These sound signals are intended to reach people who are out of doors or are in the external rooms of buildings at the time the warning is sounded. It is anticipated that additional supplementary signals will be required for stores, theaters, factories, public buildings, etc. It is common experience that whistles and other noises from trains, boats, etc., are heard for miles under favorable conditions such as exist on quiet summer nights. It is equally common experience that under more usual conditions, loud sounds are seldom heard for more than a few blocks. In fact, this experience is so common that it is usually forgotten. When sounding systems for air raid warnings were first contemplated a few months ago, it was thought that adequate coverage could be obtained by means of a few horns, sirens, or whistles. Initial tests with such equipment were uniformly disappointing. Accordingly, the United States Office of Civilian Defense undertook to determine what would be required for a practical air raid sounding system, and to make this information available to the communities responsible for installing such equipment. A number of organizations have participated in this work, and the technical information obtained will be presented by representatives of these organizations. The present paper describes how these various efforts were correlated.
A Survey on Air Raid Alarm Signals
Authors: Volkmann John E. , Graham Max L.
Published: September 2005

This paper will deal with tests and investigations using electroacoustic transducers fed by several electronic signal generators having characteristics suitable for air raid warning purposes and with the results of a survey on the audibility of warning signals and speech in a residential area of Indianapolis. Sound level requirements and the use of indoor and mobile sound systems as a supplement to outdoor and other basic air raid warning systems will also be discussed.
Air Raid Siren Tests in Detroit
Authors: Ball Laurence M.
Published: September 2005

Noise measurements and listening tests are reported.
The Vibration Characteristics of “Free-Free” Circularly Curved Bars
Authors: Bundy F. P. , Pliskin W. A. , Edwards J. E.
Published: September 2005

The positions of the nodal points and the values of the frequencies of vibration have been determined for the first five or six modes of parallel and transverse vibration of circularly curved bars of uniform cross section with central angles ranging from 356° to 60°. For vibration in the plane of curvature (parallel) the relative positions of the nodal points are the same for the same central angles, regardless of the type of cross section. Also, for the parallel vibration the frequency in the nth mode is given by the expression, fn = θ2K(n, θ)L2(Bm)12 where θ is the half central angle in radians, L is the length, B is the bending stiffness of the cross section about an axis perpendicular to the plane of the ring, m is the mass per unit length, and K is a “frequency constant” which depends upon n and θ. For n > 1 or 2, K may be expressed accurately as, K(n, θ) = S2(θ)[n − g(θ)]2K(1, θ). Graphs of S(θ), g(θ), and K(1, θ) are presented. For vibrations transverse to the plane of curvature the relative positions of the nodal points depend only upon the central angle. The frequency in the nth mode of transverse vibration is given by the expression, fn = θ2ψ(n, θ, A/C)L2(Am)12 where θ, L, and m are the same as defined above, A is the bending stiffness of the cross section about an axis in the radial direction, and ψ is a “frequency constant” which depends upon n, θ, and the A/C ratio. For n > 2, ψ may be expressed quite accurately as, ψ(n, θ, A/C) = Q2(θ, A/C)[n − q(θ, A/C)]2ψ(1, θ, A/C). Graphs of Q(θ, A/C), q(θ, A/C), and ψ(1, θ, A/C) are presented.
The Overblowing of Organ Pipes
Authors: Boner C. P. , Newman R. B.
Published: September 2005

This paper reports preliminary results of research on beating phenomena observed when organ pipes are blown at pressures substantially above normal. Various investigators have suggested that the obnoxious beating resulting from overblowing comes from inharmonic partials, vibration of pipe walls, and the like. The results of the present research indicate that during overblowing each partial of the pipe may be broken down into “component partials” of different frequencies, and that the strong beats observed are beats between members of the same “partial family.” For increasing pressure the partials often occur as triplets, whereas on reduction of pressure a hysteresis-like effect occurs in which partials often appear as quintuplets.
Criteria of Excellence in Violins
Authors: Saunders F. A.
Published: September 2005

This report continues a series from the Harvard Laboratories of which the last was published in our Journal in January, 1941 (Watson, Cunningham, and Saunders). Recent work has produced the response curves of several excellent old and new violins, and also the rates of decay of a few of their tones. Some of these results will be shown. They disclose considerable differences in decay constants among both old and new instruments. Low damping implies greater volume of sound and an easier though slower response. Loudness (without deterioration of quality) is considered very desirable. This was demonstrated in a test conducted by two of the best violinists in this country on a large group of new instruments. The best of these were later measured by us, and showed relatively high emission in the lowest octave, and more uniformity than usual up to 4000 c.p.s. Experiments are now in progress in several places on the effects of varnish, etc., on the damping of vibrations in wood. The Chladni figures in a violin-shaped plate recently studied by J. A. Kessler (not yet published) make it clear that vibrations across the grain of the wood (whose damping is known to be very high) are as important as those across the grain. Lowering the damping of the wood by special treatment should increase the sound emission as a whole at the risk of increasing the unpleasant weakness of tones occurring between resonant peaks; but the experiment is decidedly worth trying.
Estimation of Percentage Loss of Hearing
Authors: Carter Howard A.
Published: September 2005

The Council on Physical Therapy of the American Medical Association, assisted by its Consultants on Audiometers and Hearing Aids, has formulated a method for determining the percentage loss of useful hearing for medico-legal purposes. The method has been endorsed by several leading medical societies specializing in diseases of the ear. The paper describes briefly the reasons leading up to the selection of the method and also explains how to use the audiogram charts to arrive at a percentage loss of hearing. There is a brief discussion of some of the methods that have been used prior to the formulation and adoption of the method under discussion.
A Reinvestigation of the Relation Between Pitch and Intensity
Authors: Morgan Clifford T. , Galambos Robert
Published: September 2005

Pure tones were presented monaurally at octave frequencies from 125 to 8000 c.p.s. For each frequency, the pitch at different intensities was measured relative to the pitch of a standard tone of 40-db sensation level by varying the frequency until a pitch-match was obtained. Six ears (four observers) were studied. These ears differed considerably as to the direction and magnitude of change of pitch with intensity as well as to the frequencies at which the change was most prominent. With increasing intensity, the change of pitch was slight at all frequencies (maximum 3 percentage) and almost entirely absent at high frequencies (4000 and 8000 c.p.s.). The greatest changes of pitch with intensity (maximum 20 percentage) occurred in ears suffering from temporary hearing loss in part of the spectrum. These results suggest that the change of pitch with intensity is more closely related to irregularities in auditory sensitivity than to the over-all properties of the ear. This possibility may account in part for differences between these data and previous findings based upon fewer ears.
Effect of Music on Accident Reduction
Authors: Hough Edith
Published: September 2005

The effect of music on the reduction of accidents will be shown. This effect is in part due to lessening of fatigue and greater application on the part of the employees noticed since the introduction of music. An additional effect of the music program has been an increase in the workers' efficiency.
Attitudes toward Types of Industrial Music
Authors: Kerr W. A.
Published: September 2005

Attitudes of four groups representing various types of occupations and backgrounds are measured and reported. Response comparisons are made and practical implications of the psychological measurements are pointed out. The procedure of scientific management of plant broadcasting is discussed.
Exhibition of Force at the Entrance of a Resonator
Authors: Leadbetter R. L.
Published: September 2005

It was about the year 1876 that Dvorak suggested an acoustic motor. He had discovered that some repelling force caused a resonator to back away from a sound source, pitched to resonator frequency. In an effort to explain this phenomenon it was necessary to assume that radiation of energy outward from the resonator opening caused a reactive force in the opposite direction. It was then necessary to assume that at any instant the absolute internal pressure on the back wall of the resonator was greater than the absolute pressure on the front wall. This really required imagination. This reactive force is easily demonstrated by attaching a number of resonators to the ends of spokes of a wheel, and mounting the hub of the wheel on a spindle. The wheel spins when placed in front of a loudspeaker generating a tone pitched to the frequency of the resonators. With the aid of titanium tetrachloride vapor it can be observed that the air flows into the opening, around the perifery, and out again in the form of a jet. On the positive half of the cycle air ejected through the entrance continues to flow outward causing air around the perifery to flow (by aspiration) toward the entrance. Obviously then, on the negative half of the resonator cycle, air flows in from the edges. In effect, this is a pulsating self-charging rocket. There is, however, a phenomenon more difficult to explain. When a light weight spherical resonator is set in a horizontal ring, smaller in diameter than the resonator, and the assembly placed in front of a loudspeaker, a tone at resonator frequency causes the sphere to roll around in the ring from any position and so orient itself that the opening is pointed directly at the most intense region of sound. This turning force is greatest when a neck-type resonator is used, as though the neck exerted a leverage on the sphere.
Conditions for Wide Angle Radiation from Conical Sound Radiators
Authors: Carlisle R. W.
Published: September 2005

The steps leading up to the general use of corrugated loudspeaker cones are briefly enumerated. The correlation between the wide-angle radiation of a hemisphere and that desired from a loudspeaker cone is considered. The mathematics of the directional pattern of a cone is developed by considering the latter to be constituted by a progression of rings of increasing size, each ring being different in phase of vibration. The directional pattern of these rings is then approximately calculated by considering a cross section through the cone as an array of pairs of point sources. This shows that wide angle radiation may be secured if there is a proper phase retardation between the center and the rim. The mathematics of a cone as an iterative network is then considered, and the conditions estimated for propagation of vibrations within a desired frequency band. The correlation between the phase retardation occurring in an iterative network and that required for wide angle radiation is demonstrated, and characteristics of experimental cones presented.
A New Frequency Selective Vibrometer
Authors: Kent Earle L.
Published: September 2005

This paper gives the theory and practice involved in the design of a small instrument which is useful in measuring the frequency, direction, and amplitude of vibration. The instrument obtains its frequency selectivity and high sensitivity by mechanical resonance. A novel method of tuning is employed which also produces variable damping in such a manner as to produce an essentially flat frequency response. The direct indicating model shown in the accompanying photographs covers an amplitude range up to 0.010″ double amplitude and a frequency range from 800 c.p.m. to 2000 c.p.m. Other ranges have been covered by other models and models have been produced using a photoelectric pick-up which made it possible to read the vibration amplitude on a meter with greater precision than on the direct indicating model.
An Acoustic Impedance Meter for Rapid Field Measurements
Authors: Bolt R. H. , Petrauskas A. A.
Published: September 2005

A method is developed for rapid, direct measurement of acoustic impedance. It is applicable to large panels and to materials already installed for use, and therefore offers a means of investigating effects of panel vibration and mounting conditions. The pressure and pressure gradient are measured by two microphones near the surface, in a line normal to it. If p1 and p2 are the sound pressures (time phase vectors) at the microphones; d their spacing; λ the wave-length; and θ the phase angle of the impedance; then the complex acoustic impedance ratio is given by zρc≃πdλ|p1+p2p1−p2|ei(θ−π/2). This approximation is reasonably good for λ/d greater than 10 or 15, depending somewhat on the impedance value. The microphone output voltages e1 and e2 are fed into an electronic circuit which gives voltages proportional to (e1+e2) and (e1−e2). These combination voltages are then mixed, and adjusted in relative phase and magnitude to give a null indication. The impedance magnitude and phase angle are determined from the dial settings. Null methods are also used for calibration and alignment, which must be performed with great precision to obtain reasonably accurate results. Preliminary tests with the instrument, using commercial dynamic microphones, appear to yield satisfactory results for frequencies from 50 to 500 c.p.s. and for impedance magnitudes up to 10 ρc.
A Mechanical Impedance Bridge
Authors: Wiggins A. M.
Published: September 2005

The mechanical impedance bridge consists of two identical cantilever reeds clamped to a driving mechanism which can be driven electrically at various frequencies. Conventional condenser microphone amplifiers are used to measure the relative displacements of the reeds from their neutral positions. From the values of the relative displacements of the reeds, with one reed loaded with an unknown mechanical impedance, the value of the mechanical impedance may be calculated.
The Application of Sound Absorption to Factory Noise Problems
Authors: Sabine Hale J. , Wilson R. Allen
Published: September 2005

This paper presents the results of experience in attacking factory noise problems by the use of sound absorbing materials. It has been borne out that the harmful effects of noise as well as the degree of relief obtainable depend not as much on the magnitudes of the noise levels as on the character of the noise. Space and time distribution of noise sources and of the resulting sound field are important factors, as are the effects of reverberation. The conventional method of calculating the reduction in average noise level due to the addition of absorption is found invalid when applied to large factory areas. Instead, results are expressed more accurately in terms of the rate of attenuation of noise level with respect to distance from the source.
Materials and Construction for Speech Broadcasting Studios
Authors: Green Lonsdale
Published: September 2005

This paper describes the types of materials used in correcting broadcasting studios, and shows graphs of the calculated time frequency curves for studios, and also graphs showing the actual time frequency curve as determined with a high speed level recorder. This paper explains the method of testing with the high speed level recorder and also the discrepancies which occur between the calculated and actual graphs. It explains the method by which the standing waves in the room are broken up to such an extent as not to be objectionable.
Acoustics for Broadcasting Studios for Speech Versus Music
Authors: Content Edward J.
Published: September 2005

WOR, New York City, has recently completed three small speech studios. The factors taken into consideration are: (1) the reverberation time, (2) the shape of the reverbation time versus frequency curve, and (3) the reduction of the standing sound waves in the studio. This paper describes how a studio designed for good music conditions will not give the best conditions for speech; particularly speech of the news broadcast type. By lowering the reverberation at the low frequencies and allowing it to rise at the high frequencies, the effect is achieved of putting the speaker in the studio directly in the room in the home where he is being heard.
Acoustic Laboratory in the New RCA Laboratories
Authors: Olson Harry F.
Published: September 2005

Modern facilities for development and research in all branches of acoustics are provided in the new RCA Laboratories. The new Acoustic Laboratories include the following: a free field sound room, a large sound stage, a standard living room, a soundproof room for life tests, dust-free rooms, magnetizing facilities, a live room, a field laboratory and towers, and conventional communication laboratories. The free field sound room is designed to combine acoustical conditions as obtained in free space outdoors with ideal and normal test conditions. The large sound stage is designed for tests of sound pick-up in standard conventional settings. By a change in “acoustics” the sound stage may be converted into a small theater for sound reproduction tests. The living room laboratory is designed to be the acoustical equal of the ideal living room in which sound instruments such as radios and phonographs may be developed and tested for normal home use. The soundproof room is provided with special walls and doors for testing loudspeakers at high levels without annoyance to adjoining rooms. The dust-free rooms are used for assembling magnetic structures. The live room is designed for testing of sound absorbing materials. The conventional laboratory bays include all types of measuring equipment: oscillators, amplifiers, recorders, bridges, etc. Multiple audiofrequency lines are provided so that laboratories may be interconnected. A remotely located field laboratory is used for conducting free field response, power and life tests.
Curved Quartz Crystals as Supersonic Generators
Authors: Labaw L. W.
Published: September 2005

The supersonic beam radiated from a one-centimeter radius quartz disk has been examined as a function of the curvature of the crystal. The large curvature crystals produce a definite focusing action as has been reported from an earlier investigation. Experimental curves show that it is possible to obtain a much greater amplitude close to the generator than is possible from a flat crystal of comparable dimensions using the same input energy. The plates of smaller curvature do not produce as marked a focusing action but give a greater supersonic amplitude than a quartz plate of zero curvature having the same thickness and excited by an equal crystal current at the same frequency, at any given distance from the generator. The beam spread for the crystals of small curvature is no greater than that for the flat crystal, indicating a transition from the wide angle to be expected in the case of a crystal which focuses the energy to the small angle predicted for the flat crystal.
A Theorem on Directivity Patterns
Authors: Jones R. Clark , MacColl L. A.
Published: September 2005

The directivity pattern p(φ) of a surface distribution of acoustic sources at a single frequency and at a great distance from the source, is a function only of the angle φ between the direction and the normal to the surface, provided that the surface distribution possesses circular symmetry. Similarly the corresponding directivity pattern q(θ) of acoustic sources distributed along a line is a function of the angle θ between the direction and the plane normal to the line. Given now the complex function A(r) which specifies the amplitude and phase of the circularly symmetric surface distribution, it is elementary to determine the linear distribution B(x) which will have the same directivity pattern—that is to say, which will make q(ξ) = p(ξ). The converse problem is also of interest: given B(x), to determine A(r) so that p(ξ) = q(ξ). It will be shown that the solution of this converse problem involves an integral equation which may be reduced to Abel's canonical form. Accordingly, the solution may be given in closed form as the derivative of an improper integral which involves the variable of differention both in the limits and in the integrand.
Analyses of Tones of Wind Instruments and of Resonating Strings
Authors: Saunders F. A.
Published: September 2005

In the course of studies of violins, it became of interest to find out how much their tone analyses differed from those of certain wind instruments. Analyses were made of flute, clarinet, oboe, English horn, and French horn, rather softly blown, over their whole range. The results show no such violent variations in volume of tone as in violins, though a weak spot appears in the oboe and the clarinet. For low tones in oboe, English horn, and French horn the upper partials are strongest. These die off progressively on the way up the scale until at the top the order of prominence is the order of the partials, as in high violin tones. The order of appearance of the even-numbered partials in the clarinet is interesting; 6, 4, and 2 are absent in the lowest tones, and they appear progressively, in that order. The second passes the third one octave below the top; the fundamental is nearly always loudest.

The violin family includes the viola d'amore, in which seven or more extra wires which are not fingered are added for resonance. Some writers and many musicians believe that the extra wires increase the loudness, though wires were once supposed to kill the sound in an auditorium. To test the matter, analyses were made of A-440 tones from each of two violins played on the D string, with or without allowing the open A string to resonate. The results show no effect unless the tuning is exact, but clearly show that the resonating string weakens the output of the fundamental without appreciably affecting the upper partials. If the energy supply given to the bowed string is constant, it is clear that the roundabout process of producing sound from the violin box by way of the resonating string must involve a loss of energy. The peculiar quality of the viola d'amore, if it exists, must be due to some cause other than the presence of the extra wires.
Ear and Closed Coupler Acoustic Impedance
Authors: Cook G. S. , Chrzanowski P.
Published: September 2005

The Flanders method for measurement of acoustic impedance has been adapted to the measurement of ear impedance. The results of measurement of ear impedance as seen through the caps of several types of audiometer receivers are reported. These are compared with similar measurements on a standard closed coupler used for receiver calibration. The suitability of present couplers for receiver calibration is discussed.
A Wide-Range Adjustable Acoustic Impedance
Authors: Meeker Willard F. , Slaymaker Frank H.
Published: September 2005

A method for obtaining a wide range of calculable impedance values has been developed. Three telescoping tubes are used, one being acoustically “infinite” in length. This “infinite” tube is used as a convenient, calculable impedance terminating the device. The effective lengths of the remaining two sections are varied to adjust the input impedance, whose value may then be calculated in terms of that of the “infinite” section. A unit having an input section 1 inch in diameter and an “infinite” section 0.130 inch in diameter has been constructed. The range of impedance values obtainable is best described in terms of a resistance-reactance plot. On such a plot the range at 800 c.p.s. for the 1-inch diameter unit includes the impedance values enclosed by a circle having its diameter on the resistance axis and determined by the points R = 0.194 acoustic ohm, X = 0 and R = 342 acoustic ohms, X = 0. The theory is developed, and measured and calculated impedance values for several conditions are compared.
The Physics of Hearing Measurements
Authors: Steinberg John C.
Published: September 2005

This paper discusses some of the physical considerations involved in the measurement and correction of hearing impairment, and briefly reviews work which has been done in the past.
Air- and Bone-Conduction Audio-Testing Assembly
Authors: Watson Norman A.
Published: September 2005

An assembly of apparatus for the testing of hearing by air conduction and bone conduction is proposed which is designed to obviate the use of the soundproofed booth, to eliminate errors common in present techniques, and to provide more comprehensive and accurate tests of hearing than is possible with the usual audiometer. It consists of an adjustable chair and insulated chin rest; a pair of large, adjustable, acoustically-treated air-conduction source-boxes to be placed one over each ear; and an adjustable bone-conduction vibrator, mounted so as to impinge on the center of the forehead of the person being tested. If used in a quiet room, the air-conduction source-boxes would obviate the use of a soundproofed booth and insulate against air radiation from the bone-conduction vibrator without causing false enhanced bone-conduction thresholds. Air-conduction masking should always be used on one ear while testing the other by bone conduction and should be used on the better ear when testing the poorer ear by air conduction. Such an assembly, with an appropriate set of microphones, phonograph pick-up and turn table, oscillators, amplifiers, attenuators, equalizers and filters, would provide the possibility for equal-loudness as well as threshold measurements and for articulation testing with selective amplifiers by diotic as well as by monaural listening, and by various combinations of air- and bone-conduction receivers. Thus it would provide, at relatively small expense and without a soundproofed room or booth, the extensive and intensive tests of hearing for diagnosis of hearing impairment and prescription of hearing amplifiers previously available only in specialized acoustical laboratories.
Evidence for the Existence of Peripheral Auditory Masking
Authors: Lowy Karl
Published: September 2005

In the course of experiments involving the response of single auditory nerve-fibers, it was found that watch ticks elicit synchronized potentials which can be recorded from a great number of fibers. An almost identical response is easily obtained from the round window. Both can be suppressed by pure tones, a frequency around 4050 c.p.s. being most effective for a particular watch. There is experimental evidence that the tick-response, also if recorded from the fenestra rotunda, consists almost entirely of nerve potentials (aural microphonics being negligibly small in this case). Thus, it is possible to record a practically pure nerve-response from the cochlea. This opportunity was used to determine the locus of suppression of the click-potential by the masking pure tone. It is found that damage to the auditory nerve does not abolish the masking effect. One would therefore conclude that it takes place within the cochlea. This is in agreement with an assumption made by Galambos in his report on suppression of a single nerve-fiber response by a second pure tone.
The Consideration of Hearing Aids and Audiometers by the Council on Physical Therapy
Authors: Carter Howard A.
Published: September 2005

This paper consists of a brief account of the activities of the Council on Physical Therapy of the American Medical Association in its investigation of hearing aids and audiometers, the problems encountered in its attempt to advise on the accuracy of advertising and the methods by which evidence is considered.
Acoustic Amplification of Hearing Aids
Authors: Sabine Paul E.
Published: September 2005

This paper gives the results of measurements of the over-all acoustic gain shown by six commercial hearing aids. The input level was 50 db above the reference level of a General Radio sound level meter. The measurements covered the frequency range from 200 to 4096 c.p.s. A steady sound field was set up in an absorbent lined booth. A Western Electric 640A condenser transmitter was fitted into a hole at the center of a small baffle, with its diaphragm in the plane of the baffle face. The field was monitored by the sound level meter, with its microphone in a fixed position close to the edge of the baffle. The output of the condenser transmitter was fed into a measuring system consisting of an attenuator, amplifier, and indicating meter. The attenuation needed to produce a given reading on the meter was determined. The condenser transmitter was then replaced by the microphone of the hearing aid, with its diaphragm in the same position the transmitter diaphragm had occupied. The hearing aid receiver was coupled through a 2 cc closed coupler to the condenser transmitter and the attenuation required to give the same reading as before on the indicating meter was noted. The difference between the attenuations in the two cases was taken as a measure of the over-all acoustical gain afforded by the hearing aid. All of the instruments tested, except one, showed maximum amplification in the 1000 to 2000 c.p.s. range. Among the different instruments, this maximum was between 45 and 68 db. The one exception showed a maximum gain of 42 db at 700 c.p.s. At 300 c.p.s., the spread between the different instruments was from 12 to 55 db, while at 4096 c.p.s. it was from 18 to 52 db. Only one of the instruments tested showed any significant change in frequency response with change in the “tone control setting” of the instrument. In this instrument a change of 25 db in the amplification of tones below 512 c.p.s. was possible with a change of only 4 to 8 db at the higher frequencies.
The Vibratron
Authors: Rieber Frank
Published: September 2005

A continuously adjustable high Q electromechanical resonator, which may be used in the control of oscillators, pass-band amplifiers, and the like. Applications of the device to laboratory apparatus, and to the telemetering and signaling fields, are described.
Transmission, Reflection, and Guiding of an Exponential Pulse by a Steel Plate in Water
Authors: Osborne M. F. M. , Hart S. D.
Published: September 2005

The problem of the action of an underwater explosion—a pulse of the form pmaxe−t/τ—on an elastic plate in water can be divided into two parts. In the first, the plate is considered as an infinite slab with the explosion wave as an incident plane wave transient. In the second, the plate is considered as a wave guide, with the explosion wave setting the initial conditions at the edge of the plate. The first is an inhomogeneous boundary value problem, the second a homogeneous one. The inhomogeneous case has been solved in the literature, for continuous waves, and the results of the theory are in qualitative agreement with the experiments on transients. The homogeneous problem forms the principal part of this paper. The phase velocity curves, as functions of frequency, for the principal normal modes of a plate in water, are closely related to the corresponding curves for a plate in a vacuum. The effect of the water on the principal symmetric mode of the plate is not to change the real part of the phase velocity from its value for a plate in a vacuum, but to add a small imaginary component, or attenuation due to radiation loss into the water. The principal antisymmetric mode is slightly attenuated at high frequencies, and strongly attenuated at low frequencies. The cut-off comes at that frequency where the phase velocity along the plate equals the velocity of sound in water. In addition to these two modes, which correspond closely to the principal modes for a plate in a vacuum, the presence of the water introduces two additional modes, one symmetric and one antisymmetric. At high frequencies, their phase velocities are very close to, but a constant fraction of, the velocity of sound in water. At low frequencies, the phase velocity of the symmetric mode approaches the velocity of sound in water, the phase velocity of the antisymmetric mode approaches zero. Both these modes are unattenuated, i.e., their phase velocities are all real. The problem of the propagation of a transient in a wave guide presents the interesting mathematical problem, as yet unsolved rigorously, of the contour integral of a function of a complex variable defined implicitly. Brief comparison of the theory with experiment shows that the pure real antisymmetric mode accounts for most of the properties of the precursor. This is an oscillation which precedes the explosion wave along the plate, at a velocity slightly greater than that of sound in water, but less than that of rotational or dilational waves in the plate.
The Driving-Point Impedance of an Infinite Solid Plate
Authors: Jones R. Clark
Published: September 2005

In the design of mechanical filters whose function it is to prevent the transmission of vibration from one structure to another, it is necessary to know the impedances of the structures between which the filter is to be connected. In many of the cases which arise in practice, the impedance may be estimated from a knowledge of the driving-point impedance of an infinite plate. An equation is presented for the impedance of an infinite plate of constant thickness when connection is made to the plate at a single point. The impedance may be written in the form 8ρh2v, where ρ is the density, h the thickness of the plate, and v a velocity approximately equal to the velocity of shear waves in the material. It is shown that the driving point impedance is equal, except for a constant factor, to the impedance of a mass equal to the mass of a disk cut from the plate whose radius is the mean proportional of the thickness and the wave-length which corresponds to v. The results are exemplified by applying them to the case of a steel plate.
Theory of the Effect of Wall Irregularities on the Distribution of Sound in a Room
Authors: Morse P. M.
Published: September 2005

The perturbation theory of Feshback and Clogston can be applied to determine the amount of wall irregularity required to produce adequate “randomness” in the sound waves in a room. When the second-order terms in the perturbation series are as large as the first-order terms, then each standing wave is a complete mixture of all the types of simple waves, and the decay rate approaches that predicted by the Sabine formula. From this criterion one can obtain an “index of randomness,” which is a measure of the ability of the room to “mix” sound of a given frequency adequately. If the index is much smaller than unity, the sound will not be well mixed, and the decay curve will be a curved line (Sabine formula will not hold). If the index is much larger than unity, the Sabine formula will hold. Approximate formulas for the index show that irregularies in wall shape are usually more effective (in mixing the sound) than irregular patches of absorbing material, that patches (or bumps) of the order of size of a half-wave-length are more effective than larger or smaller ones, and that rooms large compared to the wave-length are easier to “randomize” than smaller rooms. It is quite difficult to treat a room of dimensions smaller than ten wave-lengths so that the index of randomness comes out larger than unity.
Detection of Resonances in Vibratile Members by Measurement of Electro-Magnetically Induced Voltages
Authors: Carlisle R. W. , Koren H. W.
Published: September 2005

An instrument is described by which the velocity versus frequency characteristics of a conducting filament or similar vibratile member may be detected, regardless of the inaccessibility of the member. The assembly to be studied is submerged in a known magnetic field and subjected to vibration over the audio range. The voltage generated in the vibratile member is amplified and this indicates the integrated vibration velocity of the member.
Basic Measurements on the Physical Characteristics of Speech Transmission Systems
Authors: Beranek L. L.
Published: September 2005

This paper discusses proposed American standardization of basic tests on the physical characteristics of speech transmission systems.
Acoustic Pulse Testing
Authors: Shrader E. F.
Published: September 2005

In the testing of electro-acoustic transducers such as microphones one desires to find the generated electrical signal in the presence of an incident plane wave sound field. Likewise, in testing loudspeakers, one wishes to measure the generated sound field. In practical testing systems, reflections which interfere with the measurement are in general present even in the best of “dead” rooms. The pulse testing procedure has been successful in acoustic measurements in eliminating the effects of reflections from the boundaries of the medium. The method consists of generating in the medium a short finite train of sinusoidal waves whose wave-length corresponds to the frequency at which the measurement is desired. The directly transmitted pulse is measured before any reflected signal reaches the sound pickup. The reverberation level is allowed to become negligible before the next pulse is generated and measured. Electronic circuits for generating the applied electrical signal and for continuously recording the received signal level will be described. The system also has been designed so that the direct signal may be discriminated against and any reflection measured, thus providing a means of measuring reflection coefficients of acoustic materials. The limitations of the pulse method will be discussed and compared with those of frequency warble and noise methods of vitiating reflections.
Schlieren Photography of Sound Waves
Authors: Carlson F. D. , Clark K. C. , Eisenstein J. C.
Published: September 2005

This paper summarizes the historical background of the schlieren detection technique and gives a qualitative and quantitative description of its operation. The optical and electronic features of a working schlieren apparatus with high speed illumination are described. The equipment provides visual or photographic observation of an acoustic wave, conveniently generated by a spark gap, at a precisely adjustable time after its formation. Typical measurements of photographic density across wave fronts are shown and discussed. Applications of the schlieren technique in certain acoustical problems are mentioned, including the reflection, diffraction and refraction of sound and the variation of propagation velocity and wave form in sound waves of finite amplitude.
A General Proof of the Reciprocity Theorem for Electroacoustic Transducers
Authors: Foldy Leslie L. , Primakoff Henry
Published: September 2005

On the basis of a general theory of the operation of passive linear transducers developed by the authors, a proof of the reciprocity theorem for electroacoustic transducers is presented together with the conditions necessary for its validity. The reciprocity theorem states that the ratio of the microphone response to the speaker response for an electroacoustic transducer is a quantity which, under certain general conditions, is independent of the specific nature and construction of the transducer. This quantity is 2d/ρf where ρ is the density of the medium, f is the frequency, and d is the distance from the center of the transducer to the point where the pressure is measured in obtaining the speaker response. The center of the transducer is defined as the point where the incident pressure is measured, in the absence of the transducer, when obtaining the microphone response. The general theory referred to above assumes a pair of the most general equations (in this case, integral equations), relating the pressure and normal velocity at each point on the surface of the transducer and the voltage and current at its terminals. These, together with the appropriate solutions of the wave equation derived by the use of Green's functions and relating the pressure at any point in the medium to the normal velocity distribution on the transducer surface, completely characterize the behavior of the transducer and allow explicit calculation of the responses. The validity of the reciprocity theorem then requires certain symmetry conditions on the parameters entering into the equations. The relation between these symmetry conditions and the physical characteristics of the transducer allow the limits of validity of the reciprocity theorem to be delineated.
Measurement of Acoustic Impedance by the Room Transmission-Characteristic Method
Authors: Harris Cyril M.
Published: September 2005

The value of the decay constant and frequency of a normal mode of vibration of a rectangular room with uniform boundaries of known impedance can be predicted from the wave theory of room acoustics. Conversely, from measurements of these quantities from the room's transmission-characteristic, i.e., from the width of the resonance peak and the frequency of the peak's maximum, the boundary impedance may be determined. This value of the impedance is checked by comparing the pressure distribution for the mode obtained theoretically (with the use of the determined impedance value) with the pressure distribution experimentally obtained. With this method, one can determine the acoustic impedance at all angles of incidence, at very low frequencies, for large samples, and under actual mounting conditions.
Frequency Response Preference Tests for Record Reproduction
Authors: Bauer B. B.
Published: September 2005

The design of a sound-reproducing system often involves a number of compromises which can be resolved only by resorting to listening tests. Some of the principles involved in administering and interpreting such tests are considered. Equipment designed to test frequency-response preference of listeners for recorded music is described. Tests given to technical and to non-technical audiences showed that the former give preference to a more extended frequency range than the latter, despite increased audibility of surface noise and distortion. These factors must be kept in mind by the engineers who design equipment for use by the general public.
Practical Considerations of “Higher Fidelity” in Sound Transmission and Reproduction
Authors: Nixon George M.
Published: September 2005

The paper discusses the various factors which influence the performance of a sound system and which must be considered in the provision of a “higher fidelity” service. The effects of loudness, noise, hearing, sound absorption etc., are included in the discussion.
Relation Between the Theory of Hearing and the Interpretation of Speech Sounds
Authors: Munson W. A.
Published: September 2005

The theory that the interpretation of speech sounds is largely dependent upon differential sensitivity, i.e., the ability of the ear to detect small changes of pitch and intensity, is used as a basis for predicting the results of intelligibility tests. By use of empirical methods, a functional relation is obtained between the energy distribution of speech, the differential sensitivity of the ear, the masking properties of sounds, and the number of correctly perceived syllables in an articulation test. A comparison is made of the empirical functions and the corresponding fundamental speech and hearing characteristics. It was found that in most instances computed intelligibility compares favorably with experimental results, but in a few cases large discrepancies were noted.
The Place of Music in Healing
Authors: Burris-Meyer Harold , Cardinell R. L.
Published: September 2005

The current vogue for employing music in hospitals, convalescent and rehabilitation centers, and the publicity attendant thereon, has bred a popular belief that music is a well-understood and essential element in therapy. This paper undertakes to survey and evaluate current practice, to define the scope of what can safely be undertaken in the light of existing knowledge, and to outline an analytical approach to the problem of finding out what music can do toward the alleviation of human ills. Studies in the effect of music on men, the control of emotion by auditory means, and music in industry are cited as examples of techniques and indications of the direction in which progress may be anticipated.
Incremental Coupled Musical Scales
Authors: Gwynn M. H.
Published: September 2005

The equation V/T = 2SN represents a family of preferred number series. S and N are of integer value, V is a rational number. One particular type series, which is both incremental and coupled, is defined by the following proportion for the terminal terms, i.e., extreme notes, of each scale, Nmax/Nmin = 2(S+C)/(S+C). C is an integer constant for each series of the type. Each of several incremental coupled series is an homologous train of scales whose notes are interpreted as frequencies, the ratios thereof being rational. Each scale possesses one more note than the preceding scale, and the highest frequency in each scale is an overlapping member of two arithmetic progressions. An octave is spanned within each scale. The lower scales of these series are separated in four groups. The several lowest scales compose two primitive and subsonic groups relating to tone quality. The next or sonic group consists of nine audible scales. Harmonic potentialities with respect to a new pure tone music are tabulated. One half of the sonic group notes are members of at least one major chord. Composition and rendition should be extraordinarily simple, since bass scales contain relatively few notes conforming to the recent findings that aural sensitivity to pitch progresses with sonic frequency.
Patents from the Viewpoint of the Applied Physicist
Authors: Knowles H. S.
Published: September 2005

Negligible attention is given to patents in most colleges because of the crowded curriculum and the widespread feeling that inventions should be treated in the same manner as scientific discoveries. As a consequence, many physicists and engineers are insufficiently instructed in the basic patent knowledge required in the academic and industrial fields and are not prepared to properly influence pending and future legislation on this subject. The journal of the Society has devoted an increasing amount of space to the publication of its review of acoustical patents. It therefore appears desirable to summarize some of the principal aspects of patents and their management from the viewpoint of the applied physicists. Stress is placed on sources of patent information, the selection of patent counsel, industrial patent practices and judicial and legislative trends.