bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimizing Discrepancies of Intonation in Valve Instruments
Authors: Redfield John
Published: September 2005

If the crooks for the first, second, and third valves of a brass instrument are made of the proper lengths to produce respectively a tempered whole tone, a tempered half tone, and a tempered tone and a half, then the notes produced by the simultaneous use of any two or more valves are sharper than the corresponding tempered intervals. The problem of tempering the scale of a valve instrument thus becomes a matter of making each valve crook too long for tempered intervals when the valves are used singly, so that the sharpness of notes produced by the combined use of valves shall be reduced as much as possible. The precise lengths of the several valve crooks for minimizing discrepancies of intonation in a valve instrument appear to be unknown both to writers on acoustics and to makers of valve instruments. The paper presents the method of minimizing such discrepancies.
Open Pipes, Stopped Pipes and Double Stopped Pipes
Authors: Taylor John Bellamy
Published: September 2005

Air columns in rigid tubes reflect pulses (sound waves) at the ends. The classical sounding or vibrating air column is the organ pipe, broadly classed as either “open” or “stopped” and giving tones of different quality because lack of symmetry in stopped organ pipes suppresses the evenly numbered harmonic overtones. Pipes of both classes are usually considered to be so rigid that all of the “output” to free air occurs at two ends of open pipe or at single opening (mouth) of the stopped pipes. This rigidity assumption may not be justified.

If a pipe is stopped at both ends, symmetry is restored with opportunity for vibrations in the complete harmonic series. But with no free vent to outer air the double stopped pipes obviously may not be energized by the usual form of air stream; also confined vibrations will not be heard outside. These seemingly unworkable conditions are met by supplying energy and also withdrawing sound output at nodal points, rather than at loops (ventral segments). Such abstraction of energy at node of vibrating air column is useful in cases where the tone or vibration is to be transferred to a denser medium, e.g., to a liquid or to a solid such as a sounding board.
Further Studies on the Strike Note of Bells
Authors: Jones Arthur Taber , Alderman George W.
Published: September 2005

(1) Difference Tones.—The pitches of the first order difference tones from the fifth and seventh partials have been obtained for 24 bells, and from the seventh and tenth partials for 13 bells. These difference tones are probably not important in the production of the strike note.

(2) Relative Intensities of the Partial Tones.—Curves from bells have been obtained with a condenser transmitter, amplifiers, and an oscillograph. Analysis of the curves from four bells do not indicate the presence of the strike note. They do show that when a bell is first struck the fifth partial is the most prominent, and that this fifth partial is rapidly damped. The relative intensities of the partials fit well with the qualitative results which had already been obtained.

(3) Duration of Contact of Clapper.—296 records of the strokes of the clappers on four bells show that the duration of the contact increases with decreasing strength of blow, and that with increasing strength of blow the duration appears to approach a definite limit. This limiting duration of contact is about half the period of one vibration of the fifth partial, a fact which doubtless explains the early prominence of the fifth partial.
The Vibrations of a Metallic Plate
Authors: Colwell Robert Cameron
Published: September 2005

Hitherto a Chladni plate has been set in vibration by means of a violin bow. This procedure made it necessary to clamp the plate at some point. It has been found, however, that with a mechanical vibrator, a square (or round) metallic plate may be set in vibration while resting freely upon a rubber mat. In this way many new sand figures may be formed. The vibrations of such a plate is closely analogous to that of a membrane; so that some of the simpler figures permit a mathematical treatment. A brief mathematical theory will be given for several of these.
A Planetary Reduction Gear System for Turntables
Authors: Bedford A. V.
Published: September 2005

In the common synchronous gear drives for phonograph or talking picture turntables there is at least one driven gear which makes the same average revolutions as the turntable and which is driven by a higher speed gear (or worm). Commercial gears have slight but appreciable errors in both tooth spacing and shape, which necessitates a variation in the relative angular speeds of the two gears. These irregularities may introduce disturbances of frequencies corresponding to the frequency of revolution and its multiples.

The effect of the higher harmonics can be easily reduced by filtering, but to filter the lower frequencies the turntable must be prohibitively massive or the couplings must be so flexible as to put the table speed at the mercy of the irregularities of its bearings and endanger the synchronism of sound and picture.

The planetary gear system, to be described, increases the speed of the lowest-speed gear with respect to the gear meshing it, thereby increasing the frequency of the disturbance and greatly facilitating mechanical filtering.

The main turntable bearings are also run at higher speed with similar effect upon disturbances arising from frictional irregularities. Damping is also provided to dissipate transient disturbances of speed.
Experimental Judgments of Relative Loudness by a Number of Observers as Related to the Decibel Scale
Authors: Parkinson John S.
Published: September 2005

A large number of experiments were made, both on trained and untrained observers, to determine the factors which influenced individual judgments of the relative loudness of tones. These experiments included a considerable range of levels and a number of different frequencies. The results show a marked uniformity but do not appear to be related directly either to the intensity or the loudness levels as measured in decibels.
Differential Pitch Sensitivity of the Ear
Authors: Shower E. G. , Biddulph R.
Published: September 2005

Differential pitch sensitivity is defined as the minimum percentage change in frequency which can be detected by the ear. The value of this ratio was measured over a frequency range from 32 cycles to 11,600 cycles and from the thershold of audibility to a sensation level of 90 db. in the case of ten normal ears. A number of subsequent observations were made using binaural and bone conductions timuli. In a region above 1,000 cycles and above a 20 db. sensation level the minimum detectable variation Δ/f is approximately constant at a value of .003. Below 1,000 cycles the function Δf is approximately constant for any one sensation level. Binaural and bone conduction stimuli tend to increase the sensitivity of the ear to pitch changes in the general region below 500 cycles but above this region there is very little effect. The errors encountered in this type of measurement are discussed, together with the design and technique necessary to minimize such effects. A series of observations taken with modified apparatus show the effect of several such factors upon the results.
Acoustic Insulation and Cancellation Effects at the Basilar Membrane
Authors: Pohlman A. G.
Published: September 2005

The perceptive mechanism presents an apparatus of phenomenal sensitivity and of equally phenomenal capacity to withstand acoustic insult. The physiological requirement calls for a place of reasonable quiet in which the end organ may analyze the vibrations conducted to it. This is fulfilled by immersion of the end organ in the liquid of the internal ear, and the insulation (a factor of 40 db.) is overcome by the sound transmission apparatus which is about equally efficient throughout the audiorange. The auditory cells act as selective transformers and rest on the basilar membrane which is flanked by the two scalae. Vibrations pass into the internal ear through both windows and the basilar membrane is placed nearly edge-on to the advancing wave front. This would result in a cancellation effect at the basilar membrane and would present a shock absorber which is instantaneously operative at all frequencies. The interpretation is opposed to the generally accepted ideas both on transmission of vibrations to the internal ear and to the function of pitch analysis as dependent on mechanical factors which lie extrinsic to the auditory cells themselves. This is supported by both morphological and experimental evidence.
The History of the Microphone—Its Development and Use
Authors: Frederick H. A.
Published: September 2005

Most of the many possible types of microphones as they are now known to exist were tried during the few years immediately following Bell's original invention. The more important types are described, dated, and identified as to their inventor. During the last 15 years, the theoretical and experimental technique for the test, analysis and development of the microphone has advanced greatly with the result that many of the early types have again become of interest. The development of the vacuum tube amplifier during this period, moreover, has removed the old requirement of large electric output from the microphone and greatly altered the practical aspects of the situation. The refinement of the microphone during these 15 years is sketched and the characteristics of some of the more important recent instruments are given.
An Improved Form of Moving Coil Microphone
Authors: Wente E. C. , Thura A. L.
Published: September 2005

Microphones of the moving coil type have been previously used but difficulties have been encountered in attempts to cover a wide frequency range with uniform sensitivity. The paper describes an electrodynamic microphone of moderate size having incorporated in its design an acoustical network by means of which a uniform sensitivity is obtained from forty-five to ten thousand cycles per second. It is shown how by changes in dimensions the instrument may be given other forms of response curves. The sensitivity is such that ten millivolts per bar of sound pressure are impressed through a transformer on the grid of a vacuum tube.
Mass Controlled Electrodynamic Microphones: The Ribbon Microphone
Authors: Olson Harry F.
Published: September 2005

One of the requirements of a high quality microphone is uniform response over a wide frequency range. To attain this objective in an electro-dynamic microphone the ratio of the velocity of the mechanical system to the pressure or velocity in the acoustic system must be independent of the frequency. To maintain constant velocity in a mass controlled microphone the driving force actuating the mechanical system must be proportional to the frequency. This may be accomplished by the designing of the mechanical system so that the actuating force is derived from the pressure gradient of the sound wave. Provided the system is small compared to the wave-length of the incident sound wave the resultant pressure available for actuating the system is proportional to the frequency.

One example of this type is the ribbon microphone which consists of a light ribbon suspended in a magnetic field. The ribbon is driven from its position of equilibrium by the difference in pressure due to the difference in phase existing between the two sides. The acoustic impedance of the ribbon and air load is proportional to the frequency. The velocity of the ribbon (or the generated e.m.f.) is determined by the ratio of the resultant pressure and the acoustic impedance. In the case of the ribbon microphone this quantity is independent of the frequency.
A Theoretical Expression Relating Loudness and Intensity
Authors: Ham L. B. , Parkinson J. S.
Published: September 2005

Three series of experiments (see also abstract 8, Journal of Acoustical Society of America, 3, p. 7, July 1931) were performed with untrained observers as follows: (A) the sound energy was reduced by definite steps, (B) the loudness was reduced to definite fractional values of original, (C) the loudness was increased by definite multiple values of original.

The reciprocals of the remaining fractions of original loudness are plotted as ordinates y against reductions of sound energy in decibels as abscissae x, while in series C the multiple increases in loudness are plotted as ordinates y against increases of sound energy as abscissae x.

An analysis of these curves shows that they may be represented by the equation: y = enx.

A discussion of the curves as related to this equation is given. For the present, n = .076 is chosen as the best value for estimating loudness reductions.

If (y) is expressed as the percentage reduction, the equation takes the form: y = 100 − 100e−.076x.

The Weber-Fechner law of loudness is a first approximation to the theoretical considerations above.

A scale for noise measurement is suggested using multiple loudness units based on the above formulae.
The American Institute of Physics
Authors: Barton Henry A.
Published: September 2005

The American Institute of Physics has recently been organized through the cooperation of several scientific societies interested in the physical sciences, and the Acoustical Society of America is one of these organizing societies. By invitation of the officers of the Society, Dr. Barton, the Director of the Institute, will explain the organization, purposes, and methods of procedure.
The Application of the Norris-Andree Method of Reverberation Measurement to Measurements of Sound Absorption
Authors: Norris R. F. , Andree C. A.
Published: September 2005

Several methods of measuring sound absorption are in use but require rather large samples. The Norris-Andree method of reverberation measurement theoretically lends itself to sound absorption measurement, permitting relatively small samples to be used and necessitating no reference absorption material.

The paper outlines in detail the mechanical application of this method to sound absorption measurement and presents data collected over a year's time in making such measurements.
The Acoustic Design of Severance Hall
Authors: Miller Dayton C.
Published: September 2005

Severance Hall, the permanent home of the Cleveland Symphony Orchestra, was completed in February, 1931. From the very beginning of the plans, the donor, the Management of the Orchestra, the University and the Architects, have all been united in purpose that the acoustic condition should be as nearly perfect as is possible and that nothing should be allowed to interfere with this end. Calculations were made for proposed designs and treatments, and the architects were thus enabled to adjust and adapt plans and methods without any inconvenience, and were successful in choosing dimensions, shapes and materials which in connection with the furnishings and the audience would produce the desired acoustical effect. Perhaps this adjustment has been carried out more systematically and more effectively in Severance Hall than in any other auditorium of this type.

At the conclusion of one of the sessions of the Society there will be an opportunity for the members to visit Severance Hall.
The Weighting of Sound Insulation Data Against Frequency
Authors: Ross Ira G.
Published: September 2005

Any specification of the sound insulating efficiency of a partition or other building unit must express, in terms of normally generated sounds and human hearing, its insulating value over the whole range of normal sound. Attention is called to the fact that, in making such an evaluation of the insulating efficiency, the Reduction Factors over the normal frequency range should be weighted to take account of the manner of distribution through the frequency spectrum of the peak loudnesses of normal sounds, the acuity of hearing and the normally maintained level of incidental noise. Curves of uniform insulation efficiency in terms of Reduction Factor at each frequency are derived from the data on peak loudnesses, acuity of hearing and incidental noise.

It is frequently desirable to reduce the overall insulation value of a partition to expression in a single figure. This has been done in the use of “Average Reduction Factor.” It is suggested, in view of the considerations above, that a more representative expression might be made in terms of minimum insulation value referred to the uniform insulation levels as derived.
The Effect of Form on the Reverberation of Sound in Rooms
Authors: Knudsen Vern O.
Published: September 2005

Measurements of the mean free path p of sound in three dimensional models of eleven typical auditoriums—such as rectangular rooms (with and without balconies), fan shaped theatres, country and city churches, and rooms with gabled, barreled or domed ceilings—indicate that p varies from about 3.8 V/S (V=volume, S=interior surface) in a large rectangular room with a low ceiling to 4.3 V/S in a cruciform type of church auditorium. The reverberation formula for the impressed vibrations takes the form t=kV−rS loge (1−α)+4mV where k depends upon the shape of the room and has a value of .046 in the large room with the low ceiling, .053 in the cruciform type of church auditorium, and about .049 for the conventional type of room; r is a probability factor which depends upon the location of the absorptive material in a room; and m is the attenuation constant of the air. The more exact theory of reverberation must describe also the rate of decay of the free vibrations in a room. Some measurements of reverberation have been made in a small room which exhibit gross violations of the generally accepted reverberation formula. These measurements reveal the necessity of considering the free vibrations in reverberation theory.
Approximations in Determining the Total Absorption of a Room
Authors: Andree C. A.
Published: September 2005

In the formulae for the decay of sound in a room the total absorption is customarily taken equal to ΣiαiSi, where αi is the absorption coefficient for any uniform area Si. It is shown that this method of determining the total absorption is an approximation requiring the assumption “that sound which is reflected from material having a given reflection coefficient has a probability of encountering, on its next reflection, material with a like coefficient which probability is equal to the ratio of the area of that material to the total area present.” This assumption requires in many instances an amount of “mixing” of the sound in excess of what may normally be expected from dispersion phenomena. The author suggests a method of attack which permits one to account for varying degrees of dispersion and applies this method of attack to the simple case of a cubical room. Numerical values of, ᾱ, the average absorption coefficient are determined which shows the effect of assuming different degrees of dispersion, and the effect of altering the distribution of the absorbing material in the room.

The theory indicates that an error is introduced in determining the sound absorption coefficient of materials due to the uneven distribution of the materials in the average sound chamber.
The Noise Survey of the Rapid Transit Lines of New York City
Authors: Stanton G. T. , Tweeddale J. E.
Published: September 2005

The extension and increased operation of rapid transit facilities in the larger cities to keep pace with their growth creates a noise problem of the first magnitude. The reduction of existing noise conditions due to elevated and subway lines and the planning of future transportation facilities having a minimum of disturbance can only be effected after a complete and thorough investigation of all contributory noise sources and the various controlling factors.

In view of these considerations, this survey was initiated to study the noise conditions created by the operation of the rapid transit lines of New York City to provide information to guide in the planning of future extensions into outlying undeveloped areas, as well as to determine the effectiveness of proposed noise reduction measures on existing lines. The extensive nature of this survey involved a comprehensive study of all types of elevated and subway constructions—of the various types of cars and auxiliary equipment, roadbed, and the effect of the immediate surroundings, such as buildings and the contour of the land. Comparative data on the noise created for any given combination of conditions was obtained so that representative average results can be predicted showing the effect of the variable factors influencing the creation of noise. From the careful analysis of these results, very important conclusions, which in many cases were contrary to those generally held, were drawn which are of infinite aid in studying the economic feasibility of a constructive program of noise reduction.

General conclusions regarding elevated construction indicated that improvement of the elevated structure and roadbed as well as improved car construction and maintenance will effect a material reduction in noise. In addition, the combination of rapid transit and vehicular facilities in a comprehensive system of regional planning will aid materially in reducing the economic loss caused by these noise sources.
Direct Meaurement of Sound Energy Density and Sound Energy Flux in a Complex Sound Field
Authors: Wolff Irving , Massa Frana
Published: September 2005

Measurements were undertaken to determine whether advantageous results in the elimination of the effect of interference patterns in a room could be obtained by measuring either the energy density or energy flux in a sound field rather than the pressure or velocity. The measurements of energy density were made by determining, at the same point in space, the pressure and three velocity components at right angles to each other. By this means a calculation of the potential and kinetic energies and, therefore, the total energy density was made possible. In the course of these measurements an investigation was made of the distribution of pressure and velocity as well as energy at a series of points in the room and data are given to show the relative distributions of these quantities. A method is described for measuring the energy flux density. As a result of these measurements and others which have been made using a ventilated ribbon microphone, the conclusion was reached that the best conditions for minimizing the effect of interference pattern when measuring the output of a sound source in a specified direction are obtained by the use of a damped room and a directional microphone properly oriented so as to eliminate the most serious reflections.
Automatic Logarithmic Recorder for Frequency Response Measurements
Authors: Ballantine Stuart
Published: September 2005

This instrument was designed to facilitate obtaining records of frequency-response in cases, such as the investigation of electro-phones, where the response varies very irregularly with frequency and the point-by-point method becomes prohibitively tedious. The automatic registration is photographic and both the frequency and response coordinates are logarithmic. The logarithmic frequency scale (50–10,000 cycles) is obtained by the rotation of a special condenser connected to the platten carrying the photographic paper, the plates of the condenser being so shaped as to provide a logarithmic variation of frequency of the associated beat frequency audio oscillator. A logarithmic scale of ordinates is obtained by means of a new “logarithmic voltmeter” employing variable-mu exponential tubes which are automatically controlled. The response or sound-pressure range covered by the present instrument is 100x, although 1000x is obtainable if necessary. Specimen records will be shown and the application of this recorder to studies of the response of loud speakers in the actual reverberant surroundings of the average home will be described.
Related Nodal Lines on Chladni Plates
Authors: Colwell R. C.
Published: September 2005

No general solution of the differential equation of a square plate has ever been given; but Ritz has shown that an approximate solution may be developed. A particular case of his solution valid for the interior of the plate but not at the edges takes the form w = A cos mπxa cos nπya + B cos nπxa cos mπya. This equation is restricted to the cases in which the plate vibrates like a membrane. From it we may develop many curves which have the peculiarity that when two nodal lines cut one another, they must cut at right angles. By varying A and B, keeping m and n constant a series of nodal lines are found which resemble one another. This resemblance is due to the fact that the note of the plate is approximately the same for each figure. Some of these curves have been found experimentally with an electric valve oscillator.
A Reed Organ to Demonstrate the Just Scale
Authors: Jones A. T.
Published: September 2005

This is a “baby organ” which has been in use in the Department of Physics at Smith College for about a dozen years. There are two stops—one tuned to the equal temperament, and the other tuned in such a way that it is possible to play just scales in the four keys of c major, f major, g major, and a minor. On the special stop the white digitals give the key of c major, while the c♯, d♯,f♯, g♯, and a♯ digitals give respectively the d for the keys of f major and a minor, the g♯ for the key of a minor, the f♯ for the key of g major, the a for the key of g major;and the b♭ for the key of f major.

Since the d in the keys of f major and a minor is a comma flatter than the d in the key of c major, and the a in the key of g major is a comma sharper than the a in the key of c major, it is possible to give certain demonstrations of beats as well as to show the effects of certain chords and successions of chords.
Short Time Variations in the Sensitivity of Condenser Transmitters
Authors: Abbott E. J.
Published: September 2005

Although one decibel ordinarily represents a very minor change in loudness, it is often desirable to obtain an accuracy of measurement of a few tenths decibel. For example, in machine noise reduction it is often necessary to study the effect of a proposed change in the presence of several similar sounds. Hence the overall effect of a single change may be considerably less than a decibel, but if taken together with other similar changes the combined effect may be large.

Since the microphone represents the only part of the usual type of sound meter which cannot be calibrated fairly readily, it is usually depended upon to maintain its calibration over considerable periods of time. It appears that a microphone may maintain an average calibration, and still be subject to short time fluctuations in sensitivity which are liable to be serious in certain sound meter applications.

The literature on microphone calibration deals chiefly with the theory of various methods, and the effects of certain corrections. Little has been published concerning how well one might hope to determine the sensitivity of a particular microphone on the basis of an accepted method with accepted values for some of the uncertain constants. This paper presents data obtained in an attempt to obtain a reference standard for microphone calibration at our laboratory, and illustrates certain variations which are attributed largely to changes in microphone sensitivity. Although these variations are doubtless familiar to those who have worked with absolute microphone calibration, it is hoped that the material will be of interest to many others who use sound meters.
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 = fz I = EZ wherein velocity v is analogous to current I. It is incomplete in the following respects which lead to difficulty in its application.

The new analogy is derived from the similarity of the following equations: v = fz̄ E = IZ wherein force f is analogous to current I and 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 Variation of Hearing Acuity with Age
Authors: Kelly J. B. , Montgomery H. C.
Published: September 2005

Measurements were made of the threshold intensity, under soundproof conditions, of over 500 ears, at 8 octave steps, from 64 to 8192 cycles, for persons between the ages of 20 and 60. At frequencies below 1024 the variations of hearing acuity over the age range are relatively small. At higher frequencies differences are found from decade to decade, becoming very pronounced at 4096 and 8192 cycles.
The Estimation of Fractional Loudnesses
Authors: Geiger P. H. , Firestone F. A.
Published: September 2005

Considerable divergence exists in the results obtained by different investigators (see abstracts 4 and 3, Journal of Acoustical Society of America, 3, p. 311 and 315, January 1932) for the reductions in intensity which observers judge to correspond to reductions in loudness of one-half, one-fourth, or other fractions. In order to account for this divergence in results, experiments are being made wherein observers are asked to reduce the loudness of certain sounds to different fractional values of the original. Loudness levels corresponding to 1000 cycle sensation levels of 30, 55, and 80 decibels of three sounds were used as the original sounds from which the required reductions were made. The three sounds used were a 1000 cycle tone, a 60 cycle tone, and a complex tone with components from 60 cycles to above 3000 cycles. The preliminary data show that: (1) the observer's judgment can be easily influenced by the conditions of the test; (2) a given fractional change in loudness as judged by the observers does not correspond to the same fractional change in intensity for different loudness levels or for the different sounds.
Acoustic Pickup for Philadelphia Orchestra Broadcast
Authors: Maxfield J. P.
Published: September 2005

This paper describes the acoustic conditions surrounding the placement of the pickup microphones and the method of compressing the volume range to meet broadcast requirements in such a manner that the greatest possible motional value is retained.
Automatic Reverberation Meter for Sound Absorption
Authors: Chrisler V. L. , Snyder W. F.
Published: September 2005

During the past several years the Sound Section of the Bureau of Standards has been endeavoring to develop an electrical method to measure reverberation times as a tool in the determination of absorption coefficients of materials. Various methods have been tried, similar to those used by other investigators, such as measurements from oscillograms, determination of end points of a decay curve and the plotting of a decay curve from measured times taken at definitely spaced arbitrary thresholds. In the measurement of absorption coefficients, great accuracy is necessary in the measurement of the rate of decay of sound and a careful analysis shows that a number of points are necessary in plotting decay curve. Since sound does not die away uniformly in a closed. space, it is necessary to determine these points statistically. To make the operation of the equipment less tedious, automatic methods have been developed and the procedure is almost entirely self operating.
A New Reverberation Formula
Authors: Sette W. J.
Published: September 2005

The assumption is made that the probabilities are that any ray of energy, undergoing repeated reflection, will strike the individual surfaces of a room in proportion to the ratios of their areas to the total surface. The resulting expression for the reverberation time employs the logarithm of the geometric mean of the reflection coefficients.
Resonance in Rooms
Authors: Knudsen Vern O.
Published: September 2005

The observed characteristic frequencies (or eigentones) in a small room are shown to agree with the theoretical frequencies n for the vibrating volume of air in a six-sided rectangular room, namely n = c2p2l12 + q2l22 + r2l32 where c is the velocity of sound, l1, l2, and l3 the dimensions of the room, and p, q, and r are integers. One or more of these integers vanish when one or more surfaces in the room are covered with absorptive material. When a tone, which is nearly of the same frequency as the frequency of one of the eigentones, is sounded and then stopped in the room, the decay, especially during the latter stages, consists of the free rather than the impressed vibration. Thus, in a room in which the fundamental frequency was calculated to be 70 cycles, oscillograms revealed that impressed frequencies of 65, 68, 70, 72, or 75 cycles all decayed at the fundamental frequency of 70 cycles. The reverberation was about 50 percent longer for the resonant frequency (70 cycles) than it was for frequencies only 5 cycles lower or higher. Similar effects were observed in the vicinity of several of the overtones for the room. The results show conclusively that volume resonance must be considered in determining the absorptivity of materials by the reverberation method, and that resonance is an important factor in determining the acoustics of small rooms.
A Method of Measuring Acoustic Impedance
Authors: Flanders P. B.
Published: September 2005

An apparatus is 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 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.
Facts Developed in the Design and Construction of the Johns-Manville Acoustical Laboratory
Authors: Parkinson John S. , Young Paul O.
Published: September 2005

A brief description of the Johns-Manville Acoustical Laboratory is given, with test data on the efficacy of various constructions employed and a description of certain modifications in test procedure.
Effect of Rotating Vanes in a Reverberation Room
Authors: Chrisler V. L. , Miller Catherine E.
Published: September 2005

Rotating vanes have been installed in the reverberation room at the Bureau of Standards with the result that the rate of decay of sound is logarithmic even when a highly absorbent sample is in the room.

Since the vanes have been installed the change in the apparent coefficient with the size and shape of the sample is much smaller than has been previously measured. It is believed that this is due to the fact that the sound is kept more uniformly distributed by the rotating vanes.
The Dependence of Measured Absorption Coefficients upon Position and Quantity of Material
Authors: Wolf S. K. , Sette W. J.
Published: September 2005

Absorption coefficients obtained from reverberation chamber measurements are dependent not only on the amount of material present but also on the distribution of the material among the chamber surfaces. Curves obtained from experimental data are given to demonstrate the influence of these factors.
Electrically Produced Tone from String Vibration
Authors: Loar Lloyd
Published: September 2005

Several musical instruments will be demonstrated in which the small vibrations of strings are amplified to large volume.
Some Chemical Aspects of the Dispersion and Absorption of Sound
Authors: Richards W. T.
Published: September 2005

Modern acoustical interferometry promises to provide a quantitative answer to several questions of importance for the collision theory of chemical reaction rates. From the dispersion and absorption of sound in nitrogen tetroxide it is, for example, possible to obtain accurate and plausible values for the rate constant, the activation energy, and the effective molecular collision diameter of the dissociation reaction. Any other rapid chemical reaction should yield similar information from acoustical measurements. Since, according to current hypothesis reaction is closely analogous to the excitation of the vibrational heat capacity, the dispersion and absorption of sound in nondissociating gases has also direct chemical bearing. Measurements on the dispersion of sound in carbon dioxide, carbon disulfide, sulfur dioxide, and ethylene at various temperatures, pressures, and frequencies are discussed from this viewpoint. The velocity of sound in mixtures of ethylene with argon, nitrogen and hydrogen is also briefly considered. It is found that while collisions with argon and nitrogen are without influence on the vibrational heat capacity of ethylene, those with hydrogen are more effective than those with ethylene itself. This result has already been foreshadowed in the study of chemical reaction rates.
The Supersonic Interferometer and Absorption Measurements
Authors: Hershberger W. D.
Published: September 2005

The previously developed theory of the supersonic interferometer is extended with the particular view of utilizing it for absorption measurements in gases. It is shown that the mechanical impedance of the interferometer is Z = Z0 + Z(l) where Z0 = j(mω − s/ω) + r Z(l) = Acρtanh 2αl + Acρsinh 2αlejθ θ = −arctan sin 2Kl sinh 2αlcos 2Kl cosh 2αl − 1.

That is, if reactance is plotted against resistance we obtain an impedance spiral with center (Acρ/tanh 2αl, 0) and radius Acρ/sinh 2αl. The action of the interferometer is studied in terms of the properties of the spiral.

Absorption measurements are effected by compensating for the changes in the equivalent series electrical resistance due to changes in 1 by adjusting a shunt resistance in the circuit so the e.m.f. across the crystal is held constant, irrespective of 1. Absorption in the medium is calculated from the values of shunt resistance for the path lengths of interest. Measurements were taken at five frequencies in the range 298.6 k.c. to 2514 k.c. The quantity 2αλ2 a as measured by the interferometric method is not constant but shows a systematic change with frequency. The possible significance of that change is pointed out.
The Resonant Characteristics of Soft-Walled Cavities
Authors: Cotton J. C.
Published: September 2005

Resonance is undoubtedly of great importance in voice production, but little attention has been given to the resonant characteristics of such cavities as are found in the human vocal mechanism. A soft-walled cavity obviously must react quite differently to a complex tone than does the ordinary hard-walled resonator. X-ray photographs showing the human vocal cavities and motion pictures of the vocal cords indicate that more than simple resonant reenforcement must be responsible in creating voice differences. Without question, absorption plays an important part.

It is now possible to determine quantitatively the effect of soft-walled cavities on complex tones by means of an electro-acoustical set-up developed in the Phonetics Laboratories at Columbus. A beat-note oscillator, a sound source of the loudspeaker type, and a potentiometer arrangement serve to produce tones of constant intensity from 75 to 10,000 cycles. A condenser microphone, a resistance coupled amplifier, and a copper oxide voltmeter indicate the sound intensity.

The cavity under investigation is coupled to the sound source and the frequency slowly varied over any portion of the afore-mentioned frequency range. Deviations of the frequency-response curve from a straight line indicate directly the frequency characteristics of the cavity.
Vocal Chords Control Pitch Only and Not Vocal or Vowel Quality Demonstration
Authors: Taylor John Bellamy
Published: September 2005

Vibrating columns of air associated with wind instruments are seldom simple or even single. In a typical instrument, especially of the “reed” or “brass” classification, besides the air column that is usually considered, there is a second column or cavity on the air supply side of the “check-valve” or member which by opening and closing, releases air intermittently from bellows or lungs. This check-valve may be recognized as reed, tongue, lips, membranes or vocal cords. This air-column or cavity back of the check-valve has some control over the time of vibration, as was demonstrated by the author at Cleveland meeting of the Society, December 1st, 1931.

Usually the vibrations of the supply-side air column are heard not at all or but faintly, because of restricted opportunity for sound emission. But special devices may be employed (the stethoscope is an example) to hear sound in supply side air column and reduce or effectively suppress sound from external air column (the only one ordinarily considered).

With a microphone in close contact with an individual's chest, an amplifier and loudspeaker will make audible the sounds picked up from internal air column, and with sufficient amplification, the normal sounds of speech and singing are faint in comparison with the other. This set-up demonstrates that while the individual has pitch control on vibrations of the internal air column, he does not and cannot change the character or quality of the supply-side tone by any of the vocal speech or musical efforts.

This result is taken to indicate that the vocal cords have but one mode of opening and dosing (at a given pitch) and play no part in determining the character or quality of vowels and other “vocalized” sounds.
The Interference of Subjective Harmonics
Authors: Chapin Ernest K. , Firestone F. A.
Published: September 2005

The purpose of the work reviewed in this paper was to devise a techique for producing interference of subjective harmonics under controlled conditions and to investigate the nature of some of the effects of such interference.
A New Portable Meter for Noise Measurement and Analysis
Authors: Osbon W. O. , Oplinger K. A.
Published: September 2005

This article describes a new noise meter whose development is based upon several years experience in the field of industrial noise measurements. Care has been taken to make the instrument simple to operate and rugged enough for portable use.

The characteristics of noise and hearing which have been used as a basis for designing the meter are discussed. A superheterodyne analyzer attachment is described which permits analysis of noises with a high degree of selectivity.

The noise meter may also be used for vibration measurements with a moving coil type pick-up which is described.
Sound Measurements on Experimental Airplane Mufflers
Authors: Snyder W. F.
Published: September 2005

For the past few years the Sound Section of the Bureau of Standards has been cooperating with the Aeronautics Branch of the Department of Commerce in the development of practical methods of reducing the noise in airplanes. A part of this work has been the measurement in absolute intensities of the noise emitted by an airplane engine fitted with various types of experimental mufflers.

The propeller noise was eliminated by connecting the engine to a hydraulic dynamometer instead of the propeller. The dynamometer also served for the measurement of the horsepower. A muffler made of steel barrels placed in the ground allowed measurements to be made in the absence of exhaust noises.

The sound measuring equipment consisted of a calibrated condenser microphone, a sound meter and a set of band-pass filters. Measurements were made with no filter in the circuit and at the frequency bands 0–250, 250–500, 500–1500, 1500–3000 and 3000-etc. The microphone was placed at six different stations ranging in distances from 2 feet to 80 feet from the engine.

It is possible to reduce the exhaust noises by 15 or 20 decibels below that of the unsilenced engine without adding too much bulk or weight to the aircraft. The propeller noise, however, must be below that of the muffled engine for the muffler to become effective.
On Minimum Audible Sound Fields
Authors: Sivian L. J. , White S. D.
Published: September 2005

The minimum audible field (M.A.F.) has been determined from data taken on 14 ears over the frequency range from 100 to 15,000 c.p.s. The observer is placed in a sound field which is substantially that of a plane progressive wave, facing the source and listening monaurally. The M.A.F. is expressed as the intensity of the free field, measured prior to the insertion of the observer. Another type of threshold data refers to minimum audible pressures (M.A.P.) as measured at the observer's eardrum. The differences obviously to be expected between M.A.F. and M.A.P. values are due to wave motion in the ear canal and to diffraction caused by the head. The M.A.F. data are discussed in relation to the M.A.P. determinations available from several sources. Some possible causes of difference between the two, which are due to experimental procedure and may add to the causes already mentioned, are pointed out. At 1000 c.p.s. the average M.A.F. observed is 1.9×10−15 watts per cm2, corresponding to 2.8×10−4 bars or 71 db below 1 bar. Data are included to show the effect of observer's azimuth with respect to the wave front.
Transmission of Sound and Vibrations in Buildings
Authors: Meyer Erwin
Published: September 2005

Three problems are discussed: The insulation from air-borne sound by multiple walls. Structure-borne sound transmission. Measurements of vibrations by electrical apparatus.

It is known that a single wall vibrates almost as a mass, provided its lowest natural period is much lower than the sound frequencies. Therefore a series of single walls with air-spaces between them act as a mechanical low pass filter, with a cut-off frequency and sound dispersion. But these properties are only present, if the component vibrations in the air-space, parallel to the wall are damped. A multiple wall of this kind with a low cut-off frequency has a very large transmission loss.

Building materials propagate sound very well. Their small transmission losses (hysteresis) are investigated by a resonance method. To obtain a loss of 1 db material lengths from 10–100 m or more are required. Materials such as rubber or cork are used to avoid the sound propagation in buildings. Their dynamical properties (elasticity modulus and loss factor) are tested by a special electrodynamical vibrometer.

With a mechanical apparatus the displacement or the acceleration of the ground is determined. The method, which measures the velocity amplitude (obtained from a low resonance-frequency electrodynamical apparatus) is to be preferred. An easily portable apparatus of this kind has been constructed. The average value of the vibrations of buildings due to traffic is 3.10−3 cm/sec. The average vibration frequencies can also be determined. In the horizontal direction buildings oscillate mainly in two ways, as a whole or with one node.
Sound Analysis
Authors: Hall Harry H.
Published: September 2005

Instruments for sound analysis may be grouped into five classes—graphic, resonance, heterodyne, stroboscopic, and diffraction analyzers. The operation of each type of instrument is briefly described and examples of analyses performed by the various methods are presented.

From the point of view of analysis sounds may be classified roughly into four groups:

(1) Steady state sounds or sounds which may be maintained at constant fundamental frequency, constant intensity and unvarying quality for long enough to carry out the analysis.

(2) Sounds which are essentially transient in nature.

(3) Sounds which may be maintained constant on the average but whose frequency, intensity and wave form are modulated at a constant frequency.

(4) Noise, or sounds which are entirely random in form but which are continuously maintained.

The sound spectra corresponding to each group are described and the application of the various types of instruments to the analysis of these spectra is discussed.