bluuebunny/crossref_metadata_2025 huggingface dataset:
A Re-Examination of the Noise Reduction Coefficient
Authors: Parkinson J. S. , Jack W. A.
Published: September 2005

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

A demonstration of various parts of the ear during the act of sound transmission. Fresh human cadaver specimens were used. The method consists of: (1) Exposure of the ear drum, ossicular chain and cochlear windows without interference with their function. (2) Magnification of the anatomical structures. (3) Reduction of the speed of vibrations for the purpose of observation and analysis. This is accomplished by the use of sinusoidal air pressure changes of subacoustic frequencies and of slow motion pictures of acoustic frequencies. The vibrations of the ear drum, ossicles, and the round window membrane are demonstrated. Resonance phenomena on the ossicular chain. Changes of intensity and frequency the ossicular vibrations dependent on the physical characteristics of the tone. The acoustic reflexes of the middle ear muscles are shown as observed in patients with pathological ears.
Altered Acoustical Resonance of the External Auditory Canal as a Factor in the Transient Improvement of Hearing Obtained by Fenestration Operations in Chronic Progressive Deafness
Authors: Josephson Emanuel M.
Published: September 2005

Fenestration operations for progressive deafness widen and enlarge the external auditory canal. This results in altered acoustical resonance of the canal, which plays an important role in the apparent improvement in hearing that some of the cases show for a while. This factor is sufficient to explain the alterations of hearing which have been attributed to opening the inner ear and supposedly facilitating the entry of sound. This fact can be demonstrated by reconstructing the canal in operated subjects, with plastics. Altered acoustical resonance can be obtained without any of the great dangers inherent in the operation, by the use of the familiar, old-fashioned hearing tubes. Modern acoustical amplifiers are far more efficient aids to hearing. Fenestration operations severely impair the hearing in the majority of cases. There result frequently dangerous sequellae and complications, including low grade meningitis due to extension of inflammation along the tract for travel of infection to the brain which the operation creates, blindness, persistent vertigo and loss of equilibrium, painful injury to the jaw joint that interferes with chewing and nutrition, and unsightly paralysis of the face. Even when real or apparent improvement in hearing is obtained after the operation, it is usually lost eventually as the progressive deafness advances. The future of the prevention of loss of hearing by progressive deafness lies in the direction of medical treatment directed at discovered causes, such as correction of vitamin and glandular deficiencies that has proved so successful in many cases, rather than in dangerous operations on the ear that are irrationally undertaken to correct a disease of constitutional origin of which the deafness is only one local manifestation.
Electrical Response of the Auditory Nerve to Different Sound Intensities Under Pathological Conditions
Authors: Lowy K.
Published: September 2005

The method usually applied for practical hearing tests is the determination of threshold values. More recently, the importance of sound intensities above threshold has been stressed and they have been applied in human pathology. In a series of animal experiments an attempt was made to study the electrical response to liminal and supraliminal stimuli as recorded from the auditory nerve under normal conditions and after artificial interference with the conductive and perceptive mechanism of sound. The results are compared with human audiograms.
Evidences for a Neural Quantum in Auditory Discrimination
Authors: Stevens S. S. , Morgan C. T. , Volkmann J.
Published: September 2005

A quantal theory of the neural processes mediating auditory discrimination has been formulated and subjected to experimental test. The substance of the quantal theory is this: (1) a given tonal stimulus produces an all-or-none excitation of some number of neural units (quanta) and there is left a small surplus of stimulation subliminal to the excitation of one additional unit; (2) the number of units excited, as well as the amount of subliminal stimulation of the additional unit, fluctuates randomly during the presentation of a constant stimulus. Under experimental conditions in which human observers are required to react to an abrupt increment in the frequency (or the intensity) of a pure tone, the quantal theory predicts (1) a rectilinear relation between the size of the increment and the relative frequency with which it will be detected, and (2) that the slope of this rectilinear function will be such that the increment perceived 100 percent of the time is twice the largest increment which is never detected. Experiments with increments of intensity and of frequency gave results conforming to these predictions. Data from these experiments provide a precise measure of the size of the neural quantum. This was found to vary with individuals and to be related to the intensity of the stimulus.
Pitch and the Missing Fundamental
Authors: Lewis Don
Published: September 2005

Jeffress recently reported a study of the pitch of organ-pipe tones from which the fundamental component had been eliminated. His results, contrary to those of Fletcher, indicate that the average observer does not judge pitch to remain unchanged when the fundamental is eliminated. We have been making a further study of the problem as a part of a general investigation of subjective tones. Complex stimulus tones, produced with an electrostatic type multi-harmonic generator, have typically consisted of harmonics 2, 3 and 4 in combination, with values of Δf as follows: 268, 402 and 536 cycles. Intensity levels of 50, 70 and 90 db have been employed. Eight observers, seven of whom have had advanced musical training, were instructed to adjust the frequency of an oscillator tone until its pitch was judged to be the same as the pitch of the complex tone. On the whole, the results indicate that Fletcher was probably somewhat too optimistic in his original report. Far more often than not, the adjusted frequencies were around the frequency of harmonic 2 rather than the frequency of the missing fundamental. There were important individual differences—a fact which may indicate that the amount of distortion is greater in some ears than in others.
Experiments on Short Tones
Authors: Bouman H. D.
Published: September 2005

When the duration of a tone is shortened below a certain limit, there appears a sudden change in the character of the sound. Tones of shorter duration have a more click-like character. This limit is about 8 cycles for the medium frequency range. However, the clicks are still accompanied by a pitch sensation. Bürck, Kokowski and Lichte have explained similar results as due to the relative intensities of sine wave and transients. However, if the eight-cycle group is split into two four-cycle groups, the results remain the same even though there are twice as many transients as before, which proves their explanation to be wrong. The phenomenon is entirely comparable to nervous summation, the summation time is 0.1 sec. Further evidence of the importance of nervous phenomena is obtained when the frequencies of the groups differ. The result is a gliding tone, a perfect analogy of apparent movement in the visual field. Other evidence of nervous phenomena in hearing is obtained from strength-duration curves. They are typical of those obtained in nerves and are identical for different frequencies. The pitch difference-limen below the liminal duration is 40 cycles. This means that gross determination of frequency being a peripheral process, there is nevertheless evidence of a central process for the fine determination of pitch. Other evidence of neural phenomena is found in experiments on masking where a definite summation time can be established. Hartridge's experiments on phase reversal can be readily explained as being of nervous origin.
A Non-Cinching Film-Rewind Machine
Authors: Elmer L. A.
Published: September 2005

Cinching, or the sliding between layers of film within a reel, produces scratches and surface abrasions which increase the film noise level. Cinching is more apt to occur in rewinding than anywhere else in the normal usage of sound film. At the beginning of rewinding, when the supply reel is full and the take-up reel is empty, a small amount of torque is needed for rotating the take-up reel. Under this condition the film will be wound rather loosely. When the supply reel is nearly empty, relatively high film tension is required to produce a given torque on the supply reel. The torque to be applied to the take-up reel will then be high, on account of both the high film tension and the large radius arm of the film spiral on the reel. This high torque is almost certain to cause cinching in the loosely wound bottom portion of the reel. The conditions to be satisfied if cinching is to be avoided are analyzed. A power-driven rewind is described which meets these requirements. The film tension is controlled by the weight of the film on the supply reel at all times during the rewind.
Localization of Response in the Cochlea as Determined by Electrical Recording
Authors: Kemp E. H. , Johnson Parker
Published: September 2005

Electrical responses from the cochlea of the guinea pig were studied by means of an amplifier, a cathode-ray oscillograph and a wave-analyzer. The guinea pig was anesthetized with dial and urethane, put under artificial respiration and placed in a “sound-proof” room. A beat-frequency oscillator, attenuator and speaker provided tones which were delivered to the ear of the guinea pig through a rubber tube and a speculum which had been sewed into the external meatus. The cochlear response to frequencies of 100, 200, 400, 600, 1000, 2000, 4000, and 6000 cycles per second was recorded from selected positions on each turn of the cochlea. For each frequency a series of intensities was used and a log response log relative sound intensity curve obtained. From these curves the relative intensity of sound on each frequency necessary to elicit a response of three microvolts was determined for each recording position. The data obtained make it possible to construct a map of the cochlea which meets the requirements of the place theory of audition, and which confirms a map of the cochlea previously constructed by Culler from data obtained by a somewhat different method.
Contribution Offered Towards a Discussion of the Paper “Pitch and the Missing Fundamental.”
Authors: White William Braid
Published: September 2005

For several years we have used in this laboratory a set of steel bars, each mounted on a resonating box and respectively tuned to the frequencies 110, 220, 330, 440, 550, 660, 770, 880 and so on in the Fourier series, to and including 1760 c.p.s. This gives in effect it fundamental tone with the succeeding Fourier harmonics tip to the 16th inclusive. By repeated experiment with many students taking courses in the theory and practice of tuning pianos in equal temperament, during the last three years, we have found that, if we sound several of the bars simultaneously, choosing the members of the series in their regular succession, that is to say, such a series as 220, 330, 440, 550, 660, we always hear clearly and, as it were, beneath the simultaneous sounds, blended together into a chord, the fundamental tone 110. When again we take such a series as 440, 660, 880, 1100, we hear the fundamental 220. When we take 660, 990, 1320, 1560, we hear the fundamental 330. When again we have taken an irregular series, such as 330, 550, 660, 880 and 900, we have always heard a tone of pitch corresponding with the frequency of the smallest number of beats between any pair of the bars, namely 110. In the case above mentioned, the 110 is very distinct, with 220 existing simultaneously, and traces of 330 also. The most important fact however seems to be that the lowest frequency deducible, namely 110, is always, in the cases mentioned, definitely and distinctly heard. It should be understood that these bars are excited simply by blows delivered with felt-covered hammers, and that the beat-tones, as I shall call them, are therefore feebler than they would be if the bars were excited electrically at relatively large amplitudes, and were steadily sustained thereat. Phenomena such as these described have been explained by the Koenig theory of beat-tones, which states that when the number of beats between two frequency-generating units exceeds the minimum number of atmospheric pulses sufficing to arouse a sensation of sound (that is to say, when the number exceeds 16 or thereabouts), sensations of tone are aroused and identified, giving sensations of pitch corresponding to the beat-frequencies. Presumably such sensations may be described as having subjective origin, although it appears that the psycho-physiological foundation of any such theory has hardly yet been laid firmly. What seems more important for the moment is that our experiences corroborate the observations made, and conclusions reached, by Fletcher, as shown in his paper. We do not overlook the fact of Fletcher's experiments pointing to the fundamental tones being regarded as the actual pitch-sensation generators for the groups of simultaneous harmonic sounds used by him, while in our case we recognize the fundamental tones as forming weak but very distinct roots to the chords which are constituted by the simultaneous harmonic tones. The distinction however does not appear to be essential.
A Noise and Wear Reducing Phonograph Reproducer with Controlled Response
Authors: Goldsmith F. H.
Published: September 2005

A replaceable phonograph needle having a large radius stylus, a spring mounting and controlled damping has been developed in cooperation with Mr. John Reid. Improved results are obtained in record and stylus wear, reduction of acoustic radiation and the ability to reproduce complex passages of large amplitude. In addition, this new needle affords protection against accidental damage to the stylus point and to the surface of the record. It is shown that by proper choice of constants it is also possible to eliminate compensating networks and thereby effect an increase in reproducer output. This device is in current production by the Webster Electric Company of Racine, Wisconsin, and is used on the Crosley radio phonograph combinations. (The presentation of this paper will be accompanied by demonstrations of the benefits obtained with the new needle using sound reproduction, oscillographic illustration and slides.)
A Large Radius Stylus for the Reproduction of Lateral Cut Phonograph Records
Authors: Reid John D.
Published: September 2005

This paper shows that novel and unexpected benefits are obtained by use of a stylus of sufficiently large tip radius to contact only the upper portions of the side walls of a laterally cut phonograph record groove. The benefits are: (a) an increase in high frequency output; (b) a decrease in acoustic radiation from the surface of the record; (c) an increase in record life; (d) an increase in stylus life; (e) a decrease in picked up scratch frown both new and worn records; (f) a decrease in stylus point pressure required for proper tracking. A stylus tip which will give this performance for the case of standard commercial records has a radius on the order of 4.2 mils or nearly double the radius of 2.3 mils heretofore thought most desirable. This device is in commercial use in conjunction with the Crosley radio-phonograph combinations and is the subject of U. S. patent 2,251,204. In commercial use the large radius stylus is combined with a special spring mounting and drives a crystal cartridge. The spring mounted stylus was developed in conjunction with Mr. Frank Goldsmith and the additional benefits obtained thereby are explained in the preceding paper. (The presentation of this paper will be accompanied by demonstrations of the benefits obtained with the large radius stylus utilizing both sound reproduction and oscillographic illustration.)
A Discussion of Several Factors Contributing to Good Recording
Authors: Lynn R. A.
Published: September 2005

It is the desire, in using transcriptions, that the reproduced quality be a facsimile of the original program. The recording unit, the disk, and the reproducing unit play important parts in achieving the desired results. A discussion of the operating characteristics of these items is presented.
The Recording Laboratory in the Library of Congress
Authors: Wiesner Jerome B.
Published: September 2005

The work of the Recording Laboratory in the Library of Congress can be divided generally into two main divisions: the collecting, processing and preservation of records made elsewhere, and the making of field recordings to be stored in the Library. Included in the first category is the work of duplicating old cylinders on disks, of repairing broken cylinders and disks and processing all types of disks for storage when they come into the Library. In the other category fall such endeavors as developing and assembling field equipment, organizing expeditions, duplicating field records and so on. At the present time the Library has nine expeditions in the field collecting folk music and folk lore, to be preserved in the stacks of the Library. The equipment of the Library includes portable field sets, a recording truck, a large Laboratory, installation of recording machines, special cylinder and film machines and a machine under development at this time for playing broken disks.
History of Noise Abatement in New York City
Authors: Peabody Ernest H.
Published: September 2005

The history of early attempts to suppress noise in New York City is traced, including personalities involved, campaigns undertaken, political aspects of the movement and present status of noise abatement in New York.
Greater Chicago Noise Survey
Authors: Leedy H. A.
Published: September 2005

As a part of the program of the Noise Reduction Council of Greater Chicago, a survey of the magnitude of the noise in Chicago and suburbs has been undertaken. The purpose of this survey has been twofold: (1) To measure the magnitude of the noise at selected locations in Chicago and suburbs; (2) To determine from these measurements the most intense and most prevalent sources of noise. Most of the measurements to date have been made with a recording apparatus consisting of an ordinary sound-level meter, a logarithmic amplifier and a pen and ink recorder. At a given station the noise level was usually recorded for a ten-minute period and from the record thus obtained, the average maximum and minimum noise levels determined. In addition, whenever possible, the peak noise levels on the chart were identified with a particular source of noise. This portion of the Council's program has been very effective in producing an increased public interest in noise reduction, and it is hoped that the final results will be of value in making recommendations for noise reduction and in aiding the setting up of a city noise code.
What Can the Hospital Do about Noise?
Authors: Neergaard Charles F.
Published: September 2005

Noises which are disturbing to hospital patients are listed and methods are outlined for the control of such noises: minimum standards for sound insulation and acoustic treatment, and costs of adequate preventive measures.
Acoustic Experiments with an Electronic Switch
Authors: Wolf S. K.
Published: September 2005

Some recent experiments in the generation, transmission, and reproduction of segmented portions of continuously flowing electric sound currents indicate interesting auditory phenomena similar and perhaps as important in the field of acoustics as the phenomena known as the persistence of vision in the field of optics. These experiments have been made by means of an electronic switch capable of transferring at varying and equal or unequal rates the audio-electric currents from a common circuit to two or more independent circuits. The paper will discuss specific experiments performed and will suggest other experiments in the generation, reception, amplification, control, recording, and reproduction of sound or intelligence. The use of this system offers interesting possibilities in secret and confidential communications, more economical transmission, and stereophonic effects in radio and sound-picture reproduction by means of minor and inexpensive modifications of existing systems.
Acoustic Filtration by Membranes
Authors: Labaw Louis W.
Published: September 2005

The vibrations of single membranes have been studied both theoretically and experimentally, but no application has been made of these vibrations to acoustic filtration. Since one membrane executing forced vibrations will resonate in frequency intervals characteristic of the tension and surface density, a sequence of similar membranes spaced at equal intervals in an acoustic conduit should render the conduit an acoustic filter. A theoretical prediction of the transmission may be made by using the relationship between the exciting pressure and the normal displacement of the membrane, as one of the boundary conditions in the ordinary acoustic filtration theory, while still assuming plane waves. The experimental agreement is good up to 5000 cycles despite the approximations. A brief study of the filtering action of the above conduit when the membranes are pierced to make a small circular hole at the center has been carried out experimentally. This changes the filter from a high-pass to a low-pass type. Further studies on these annular membrane filters are in progress.
Some Aspects of the Transient and Steady State Tones of Organ Pipes and of Vibrating Strings
Authors: Nolle A. W. , Boner C. P.
Published: September 2005

An oscillographic study of the initial transients of a large number of organ pipes reveals characteristics of these transients peculiar to each organ tone family. The duration of these transients is measured and is found to vary with tone family and with pitch. The effects of certain factors upon the initial transients are studied. Inharmonic partials are observed in some of the transients. The relationships between the partials in the steady state tones of normally blown organ pipes are investigated by highly accurate methods of frequency comparison. The partials in this case are found to be harmonic to a high degree of accuracy. An oscilloscopic method of comparison between the frequencies of the partials of a vibrating string shows that the partials of the vibrating string may be inharmonic in the state of free vibration (transient state), but reveals only harmonic relations between the partials of the string in the state of steady (forced) vibration.
Some Characteristics of the Tuning of Valved Wind Instruments
Authors: Young Robert W.
Published: September 2005

Experimental evidence on the actual tuning of “brass” instruments demonstrates the magnitude of the discrepancies in tuning resulting from the dual use of valves singly and in combination. The effectiveness of the valve tubing in lowering the frequency varies somewhat with different modes of vibration. Moreover, the frequencies of the normal modes are shown to be not necessarily in the ratio of small integers. This refutes the explanation often given in treatises on the acoustics of wind instruments that the series of sounds elicited, for example from the cornet without the use of valves, forms the harmonic series. Actually the fifth, sixth and eighth modes are likely to be found sharper than the “harmonic” values. For a steady musical tone each mode of vibration has associated with it harmonic overtones whose frequencies are not in general those of the various normal modes. In order to obtain a clear understanding of the action of wind instruments, terms such as harmonic, partial, and overtone used in the description of tone quality should be distinguished carefully from the normal modes of vibration of an arbitrarily shaped air column whose frequencies may or may nor be in the ratios of small integers.
Polycylindrical Diffusers in Room Acoustic Design
Authors: Volkmann John E.
Published: September 2005

Recent acoustic design of studios, auditoria, and other enclosures has led to the use of polycylindrical wooden surfaces for obtaining a more uniform decay of sound and for minimizing the detrimental interference effects due to first reflections. A comment often made in first walking into a room with polycylindrical diffusing surfaces is that it “feels” or “sounds” larger than the ordinary room with parallelepiped construction. To obtain the maximum diffusing action in the direction of the three orthogonal planes, the axes of the polycylindrical surfaces should lie mutually perpendicular to each other. The major dimensions of the enclosure should preferably be in the ratio of the cube root of two or in even multiples thereof. Charts and illustrations of typical applications of the diffusers will be given.
An Acoustic Tube for Measuring the Sound Absorption Coefficients of Small Samples
Authors: Loye D. P. , Morgan R. L.
Published: September 2005

A brief resumé is given of two methods of using the acoustic tube for measuring the sound absorption coefficients of samples of acoustical materials. Following this, the authors describe a rapid method of using the acoustic tube to measure absorption coefficients on a commercial basis. The paper contains a description of a new, simplified acoustic tube built to take advantage of this method of measurement.
An Experiment on Middle Ear Deafness
Authors: Lowy Karl
Published: September 2005

If the chain of ossicles or the stapes foot-plate are immobilized, sound is supposed to reach the inner ear mainly through the round window. This causes reversal of phase, as Békésy tried to prove by experiments on sound localization. This explanation, however, leads to difficulties in interpreting deafness in otosclerosis, as has been shown by Pohlman. An animal experiment which permits us to study phase relations as affected by increased immobilization of the ossicles is described and discussed. It can be shown by direct observation that the change in phase is gradual. Considering that fact, the explanation of otosclerotic deafness seems possible without difficulty.
Relation of Audiogram Measurements to Hearing-Aid Characteristics Based on Commercial Experience
Authors: Kranz F. W. , Rudiger C. E.
Published: September 2005

This paper will review the significant classifications of audiograms taken in connection with the testing of hard-of-hearing people for the fitting of hearing aids and also the response characteristics of the hearing aids which have by experience been found to be suited to these various classes of hearing defects. The relative value of bone and air conduction will be mentioned as will also audiogram records of people whom it has been found difficult to fit satisfactorily with a hearing aid. Results reported in this paper will be based on commercial experience in the hearing-aid field.
Hearing Aids: Uniform and Selective: Monaural, Diotic and Binaural; Air and Bone Conduction
Authors: Watson Norman A.
Published: September 2005

Extensive articulation tests with laboratory equipment on an individual with a marked, primarily-conductive impairment have shown that for such an impairment for equal levels above threshold: (1) An amplifier prescribed according to the “most comfortable equal loudness curve” is superior to one prescribed according to a “most comfortable” curve, which in turn is better than a uniform amplifier; (2) Bone conduction is more satisfactory than air conduction if a high pass filter with cut-off frequency of 350 cycles is used in conjunction with the bone receiver; (3) Air and bone conduction together are superior to either alone; (4) When air conduction is used, frequencies up to 350 cycles and above 6500 cycles may be cut off without appreciably affecting the articulation. (Similar tests on an individual with monaural high frequency impairment have shown that low frequencies up to 350 cycles can be eliminated for either ear without markedly affecting the articulation.) Further tests with wearable vacuum tube aids on the individual with conductive impairment, have shown (1) the superiority of a binaural aid over a monaural aid, and the equivalence in articulation of a monaural and a diotic aid; (2) approximate equivalence of bone and air conduction, with crystal units being used in each case.
Some Considerations Relative to the Calibration of Bone-Conduction Receivers for Audiometers
Authors: Watson L. A.
Published: September 2005

In the past, confronted with the problem of establishing a normal zero reference level or threshold for bone-conduction calibration of an audiometer, some engineers set the zero point for the bone-conduction receiver on a basis of equal loudness or audibility as compared to the air-conduction receiver at threshold. The writer has observed that in every instance where an audiometer has been so calibrated that the bone-conduction receiver has equal loudness (sensation loudness to the normal human ear) with the air-conduction receiver at threshold of zero level, the bone-conduction receiver invariably appears to be excessively loud as compared to the air-conduction receiver at a level 30 or 40 decibels above threshold. Investigation reveals that there is a certain “non-linearity” of attenuation or sensitivity for normal human bone conduction as contrasted with normal human hearing by air conduction. This appears to be partially if not wholly due to the absorption of a certain amount of power by the mass or inertia of the heavy bones of the skull in contrast to the more delicate mechanism of the middle ear. With this “non-linearity” of attenuation by bone conduction in mind, an audiometer should be calibrated for accurate bone conduction on a basis of equal loudness with the air-conduction receiver at a level 30 or 40 decibels above the normal air-conduction threshold. An interesting phenomenon can be demonstrated here with two audiometers the bone- and air-conduction receivers of each of which are in perfect balance at 30 decibels of loss. Reduce the intensity of the air-conduction receiver by 25 decibels. To reach a comparable intensity level with the bone-conduction receiver only 15 decibels of attenuation is generally required. This will be demonstrated with audiometers.
The Laryngeal Ventricle Considered as an Acoustical Filter
Authors: Pepinsky Abe
Published: September 2005

The ventriculus laryngis is a pocket-shaped slit which extends laterally between the false and true vocal folds. It is deepest in the middle, and from its anterior half there projects vertically upward a blind sack called the appendix. Its physiological function is supposedly that of a lubricant for the vocal cords. The presence of fibrous tissue in the ventricular fold would seem to indicate the possibility of muscular control of the volume of the ventricle and the area of the orifice into the larynx, thus suggesting the possible action of the laryngeal ventricle as an acoustical filter. The necessary conditions are thus established for the consideration of a resonator of variable volume, neck, and orifice. Unique frequency resonance is obviously not to be expected from such a resonator with its highly damping walls. The theory of Stewart's Acoustic Filters is applied in consideration of the effect on tone quality of the human voice. Some of the practices in vocal training are discussed, bearing such possible effects in mind.
Ear Defenders
Authors: Watson Norman A.
Published: September 2005

Three types of ear defenders have been developed in this investigation. Two of them are improvements on earlier ear defenders as to comfort, durability, ease of insertion, and retention: the third is distinctly a new type. The first type is a single septum, double-fin ear defender. The second type is like the first except that a fine hole is molded into the septum and a small insert sealed into it. The insert is drilled in a special way and the hole packed with cotton to give a predetermined air-leak. It, therefore, provides protection from noise in circumstances where pressure equalization is necessary. The third type is a double-septum defender with outside shape like the other two, but with the space between the septa filled with a loaded plastic material and an insert sealed in the outer septum. It is valuable for use in unusual-shaped ears. The insulations for types one and three are approximately 30–40 db over the audible frequency range, and for type two, 30–40 db over the same frequency range. Strong indications have been found that types one and three approximate the maximum insulation possible with ear defenders and that the limiting factors are the shear compliance of the skin lining of the external ear canal and the enhanced occluded-ear bone-conduction threshold arising from sound impinging on the forehead and facial bones. A material suitable for use in making ear defenders has been developed.
Some Aspects of Model Larynx Function
Authors: Carhart Raymond
Published: September 2005

During the past six years an intensive study of the cushion-pipe variety of model larynx has been carried on in the Speech Laboratory at Northwestern University. The rationale for this research is that it allows conditions to be controlled and factors to be isolated in a manner impossible with the living speech mechanism. To the degree that it is a good analogy, the model larynx gives insight into the physical behavior of the human mechanism. Specifically, the following are among the experimental findings whose implications are challenging. First, the adjustment of the supply-tube exerts a critical influence on the frequency and amplitude of cushion-pipe vibration. Second, the mode of vibration is complex, being a combination of horizontal and vertical components. The pattern of vibration is affected by supply-tube adjustment. Third, the mechanism of sound initiation within the model larynx is of the puff tone variety rather than of the vortex tone variety. Fourth, the acoustic spectra of sounds emitted by the model larynx are of three kinds: harmonic, predominantly harmonic, and predominantly inharmonic.
Pitch Scales
Authors: Lewis Don
Published: September 2005

Experiments were conducted to secure data for constructing and comparing pitch scales. Eighteen advanced graduate students in psychology served as subjects. The following observational methods (all variations of the method of equal sense distances) were used: (1) bisection, (2) fractionation, and (3) equating supraliminal pitch extents. The extents involved in (3) were a little greater than a full tone. The scales derived from the various sets of data were compared not only with each other but also with the scales reported by Stevens and Volkmann and with a j.n.d. scale based on findings of Shower and Biddulph. The scales were not in satisfactory agreement, except in restricted cases; and the differences could not be attributed to experimental error. Any pitch scale apparently depends, in some measure, upon the group of persons who made the required judgments and upon the particular method of observation employed. A sort of “generalized scale” based on many experiments involving different groups of subjects and different methods of observation may be found to have scientific utility; but such a scale will have to be used with appropriate caution. The experiments are now being repeated with a group of sixteen trained amateur musicians participating as observers.
An Experimental Study of Trumpet Embouchure
Authors: Henderson Hayward W.
Published: September 2005

This paper is the result of a search for some way to facilitate the acquisition of trumpet lip-technique. A comparative study of players of various abilities, by means of photographs and stroboscopic observations of the lips in vibration, graphs of mouthpiece pressure against frequency, and readings of mouth-air pressure under various playing conditions, calls into question several of the currently held conceptions as to how trumpet tones are produced and controlled.
The Transmission of Sound Through a Temperature Sheet
Authors: Rudnick Isadore
Published: September 2005

Some experiments have been conducted on the transmission of sound through a heated sheet of air. This refracting plate is formed by the vertical convection current rising from a stretched, heated wire. Experiments were performed in which (1) the turbulence of the convective stream of warm air was suppressed by flanking it with cheesecloth, and (2) the convection current was allowed to rise freely and turbulently (i.e. with the cheese-cloth removed). The range of sound frequencies employed is from 2 to 16 kilocycles. The angles of incidence range from normal to grazing incidence. In the circumstance of the free convection current rather large fluctuations in sound amplitude occurred, the magnitude of these fluctuations being a function of the sound frequency and angle of incidence. Photographic records showing these variations are shown. The observed results are found to be reasonably consistent with the Rayleigh theory with regard to dependence on sound frequency and angle of incidence.
A Method for Measuring the Frequency of Vibration or Rotation
Authors: Kent E. L.
Published: September 2005

This method involves the operation of a synchronous motor whose speed is proportional to the frequency to be measured. The theory might be best given by briefly describing two instruments using this principle. A manufacturer of aircraft instruments desired to measure the r.p.m. of an air-driven gyroscope rotor. An instrument was constructed to pick up the sound created by the air jet striking the buckets on the rotor and the frequency of this sound was divided by the proper number to take care of the fact that there was a multiplicity of buckets on the rotor, and then a synchronous motor was driven with the resulting frequency. A sensitive tachometer was attached to the synchronous motor indicating the r.p.m. of the rotor. This method was used in an instrument for measuring pitch. An electric tachometer was used and the meter covered a range of one semitone. Push-buttons enabled the operator to pick the interval and its octave. An accuracy within 1/10 of 1 percent was maintained. The wave shape and amplitude of the input wave can vary over wide limits without any effect on the accuracy. The accuracy depends entirely upon the type of tachometer used.
A New Family of Horns
Authors: Salmon Vincent
Published: September 2005

An examination of the properties of practical horns indicates that the throat admittance of a horn with finite expansion cannot be a positive real at all frequencies. The nearest approach to this characteristic is a conductance (real part of the admittance) constant for all frequencies above a minimum or cut-off frequency. It is possible to generalize Webster's plane wave horn theory to yield a relation between horn shape and the conductance. When the condition that a constant value of this conductance be reached shortly above the cut-off frequency is specified a new family of horns results. With certain of these horns it is possible for the throat resistance to rise more rapidly to the asymptotic value than in the exponential type. As a result horns having optimum conductance and susceptance characteristics for practical electromechanical driving units may be readily selected.
Experiments with the Noise Analysis Method of Loudspeaker Measurement
Authors: Olney Benjamin
Published: September 2005

The determination of the frequency response of a loudspeaker by analysis of the acoustic output resulting from a continuous-frequency spectrum electrical input has been described in the literature. It has been claimed that this method obliterates errors due to standing waves, thus permitting the true response of a loudspeaker to be measured in almost any acoustic environment. The present paper compares measurements made by the above method in a room suitable for listening tests with measurements made by the warble-tone method in the same room, and with free-space measurements using an input of slowly gliding frequency. Automatic, continuous recording was employed in all cases. In the noise analysis measurements with the usual narrow-band heterodyne analyzer the recorded irregularities due to standing waves were of the order of 15 db, and below 1000 cycles the curve bore little resemblance to the free-space response. When the analyzer band-width was increased sufficiently to smooth the standing wave peaks, irregularities actually present in the loudspeaker response also were obliterated. It is concluded that the noise analysis method possesses no peculiar advantage over other time averaging artifices in discriminating against standing wave effects.
Electrical and Mechanical Analogies
Authors: Mason W. P.
Published: September 2005

Analogies between electrical and mechanical systems have been employed for many years, and have helped materially in the development of both electrical and mechanical theory. The outstanding example from the communication viewpoint is the influence of the theory of Lagrange for the vibrations of a string loaded with beads on the theory of electrical loading of transmission lines. In all of these early applications, electromagnetic energy was taken as the analogue of kinetic energy and electrostatic energy of potential energy. Recently Firestone and Hanle have shown that an equally consistent analogue is obtained by reversing this association. This results in a force being the analogue of a current and a velocity of a voltage. Although both analogies can be used equally well for a mechanical system, for electromechanical systems definite advantages result from using one or the other analogy depending on the type of coupling. It is shown that, for an electromagnetically or magnetostrictively coupled system, the use of the first system of analogies results in a violation of the reciprocity law whereas the second system of analogies satisfies the law. Using the second system a simple electromechanical circuit can be derived which describes the action of the electrical circuit, the mechanical circuit, and the associated coupling. On the other hand for electrostatically or piezoelectrically coupled systems, the first analogy satisfies the reciprocity law whereas the second analogy does not. By using the first analogy, a simple electromechanical circuit can be derived for electrostatically or piezoelectrically coupled systems. It is shown that the use of electromechanical equivalent circuits together with filter theory will determine the structure which can convert electrical into mechanical energy over the widest frequency range, and with the highest efficiency.
Improvements in the Acoustic Wattmeter
Authors: Enns J. H. , Firestone F. A.
Published: September 2005

In this work the acoustic wattmeter, an instrument for measuring the flow of acoustical energy, has been revised from its earlier form. The instrument has been rebuilt to transmit but a single narrow frequency band. Although in the original report the wattmeter was reported as limited to the frequency range of 100 to 2000 cycles, the variable phase shifting network and analyzer here introduced were designed to operate down to 65 cycles per second, thus increasing the usefulness of the instrument in the low frequency range. The principal error in the instrument, which was that of phase shift with a changing input level, was located and a considerable reduction in phase shift has been achieved. A method of adjusting and partial calibration of the instrument have been worked out.
A Siren of High Efficiency and Large Output
Authors: Jones R. Clark
Published: September 2005

A new high power siren has been developed by Bell Telephone Laboratories under the auspices of the National Defense Research Committee and in cooperation with the Army. Its release has been obtained by the Office of Civilian Defense for use in the study of air raid warning signals. The siren will be described with the aid of pictures, and some measurements of its performance will be presented. The air stream for the siren is supplied by a blower which is driven by a standard 95 horsepower automobile engine. The air stream represents a power of about 38 kilowatts. The flow of air is interrupted by a rotary valve at the rate of about 440 cycles per second, and then passes into an acoustic horn. The use of a suitable horn provides a certain amount of directionality, and contributes importantly to the high efficiency of the siren. The sound that emerges from the horn has a power of about 25 kilowatts in the fundamental. The siren is simple to construct and may be made entirely of iron and steel except for the small amounts of other materials which are used in the construction of the gasoline engine.
Field Measurements of Air Raid Warning Devices
Authors: Chrisler V. L. , Snyder W. F.
Published: September 2005

Total war has created the necessity of warning the civilian population of impending air attack. Acoustic signaling has proved to be an effective method of warning the people. The Office of Civilian Defense, which is charged with the protection of the civilian population, has sponsored a project to determine the characteristics of sound signaling devices for air raid warnings. As a criterion by which the sound output of a signaling device can be judged, sound levels have been taken at 100 feet from the source. Measurements have been made in a large open space with the device mounted about 20 feet above the ground. Frequency analyses of each device have been made. Distribution of energy has been determined both for the individual components and for frequency bands. Measurements have also been made at distances of 700, 1400 and 2800 feet from the source. Varying atmospheric conditions, such as wind, had considerable effect upon the attenuation of sound with distance; in fact, for most of the devices submitted, the effect of the wind seems to be as important or more so than the distribution of energy in the different frequency components. Measurements taken over city terrain show that the attenuation of sound is greater than when taken over open spaces. The results of these measurements can be obtained upon application to the National Bureau of Standdards in Letter Circular LC 685 and Letter Circular LC-685 Supplement.