bluuebunny/crossref_metadata_2025 huggingface dataset:
The Harmonic Structure of Violin Tones
Authors: Small Arnold
Published: September 2005

Violin tones covering the greater part of the playing range of the instrument have been subjected to harmonic analysis. The analyses included normal tones and “harmonics,” which were studied with a variety of technical playing conditions obtaining, for example, variable point of contact between bow, and string, sympathetic vibration of unstopped strings, constant pitch but with change of string, variable pitch on each string, and recording in a music studio and a “dead” room. The results show (1) that change in point of contact between bow and string effects a characteristic variation in harmonic structure; (2) that harmonic constitution varies with the introduction of sympathetic vibration of open strings; (3) that not only do tones of the same pitch played on different strings vary in harmonic structure but also different pitches played on the same string; (4) that the lower natural harmonics are not essentially different in structure from fully-stopped tones of the same pitch and same string; (5) that the higher natural and artificial harmonics are not pure tones but approach a much greater degree of purity than do most normal tones.
The Dependence of Hearing Impairment on Sound Intensity
Authors: Steinberg John C. , Gardner M. B.
Published: September 2005

Although hearing impairment is ordinarily measured for tones of threshold intensity, attention has recently been turned to the measurement of impairment for tone levels above threshold. It has been found that some people may have an appreciable hearing impairment for threshold sounds yet hear normally for loud tones. Others show the same hearing impairment at all levels of sound intensity.

Loudness studies indicate that the variable or recovery type impairment should occur if the impairment is due to an atrophy of nerve fibers, and hearing losses calculated on this assumption are quite similar to observed losses. From this viewpoint the hearing loss caused by the presence of a masking noise should be of the variable type which was found to be the case.

Thus the often made statement that deafened people hear better in noisy places turns out to be true when the deafness is of the variable or recovery type. The implication of the statement that the noise as such improves the hearing however, is wrong.
An Investigation of Subjective Tones by Means of the Steady Tone Phase Effect
Authors: Trimmer J. D. , Firestone F. A.
Published: September 2005

An observer listens with one ear to a combination of two pure tones. One is a loud 100-cycle tone, the other is a weaker 200-cycle tone. A phase relation between the two tones can be found such that the loudness of the two tones together is about one decibel less than the loudness of the fundamental alone. This is an example of the steady tone phase effect, in which a fundamental and one of its harmonics are heard together, the phase relation between the tones, as well as the pressure level of the harmonic, being subject to arbitrary control by the observer.

This effect was studied with a fundamental of 100 cycles kept at a sound pressure level of 104 db above 0.0002 dyne/cm2. Harmonics up to the fifth were used, with particular emphasis on the second and third. Measurements of the phase of the harmonic sound pressure giving minimum loudness averaged approximately 180° for the second harmonic and 0° for the third (epoch angle of cosine functions relative to fundamental). Loudness measurements at these phase settings showed the loudness of the combined fundamental and harmonic to be about 1 db less than that of the fundamental alone. 180° from the phase of minimum loudness the loudness of the combined tones was about 1 db greater than that of the fundamental alone. The variation of quality with phase relation was also studied.

Interesting variations between observers were investigated and attributed partly to psychological and physiological differences in individuals. But consideration of all the data obtained points to the conclusion, supported by theory, that the phase effect is a more complicated phenomenon than has commonly been assumed. Since this effect has been the basis for many studies of subjective tones, the concept of subjective tones is analyzed and interpreted in a new light.
On Hearing by Electrical Stimulation
Authors: Stevens S. S.
Published: September 2005

The well-known fact that the ear generates an electric potential in response to stimulation by a sound wave has its counterpart in the fact that, when an alternating current is passed through the head, an auditory sensation results. The observer hears a tone whose pitch is determined by the frequency of the alternating current.

Measurements were made of the power needed to elicit a sensation using currents of various frequencies. The power, rather than the simple voltage or current was measured, because the body presents a complex impedance to the current. The total impedance, when the electrodes are applied in a standard manner, decreases with increasing frequency. The power factor varies slightly with frequency. When the power is increased about 20 db above the threshold value, the threshold of electric shock—a stinging sensation—is reached. This effect severely limits the size of the auditory area under electrical stimulation.

The amount of distortion present makes it difficult to understand speech when the observer is connected directly to the output circuit of a radio set, but music can be readily identified. The rectification producing this distortion appears to be largely electrical.

It is probable that the alternating current sets up vibrations in the inner ear due, perhaps, to a residual charge on the basilar membrane which makes it behave as a condenser microphone.
Finite Acoustic Filters
Authors: Lindsay R. B.
Published: September 2005

Most of the previous theoretical work on acoustic filtration has dealt with idealized infinite structures. The present paper is a theoretical study of finite filters such as are used in practice. Considering an acoustic structure with air as the medium with main line impedance Z and with n branch impedances Zb (pure reactantes) equally spaced at intervals 2l, it develops that one can express the power transmission ratio for the structure in the simple form Pr = 1 ⧸ (1 + Z24|Zb|2⋅sin2 nWsin2 W). (1) where cos W = cos 2kl+iZ/2Zb⋅sin 2kl, (2) the familiar parameter of the transmission theory of filtration. The plot of Pr in (1) as a function of frequency shows the presence of transmission and attenuation bands which approach those of the corresponding ideal infinite case as n becomes large compared with unity. Comparison of (1) with the actual transmission measurements of Stewart and Lindsay (ibid., pp. 170, 175) shows satisfactory agreement.

The phase change which occurs between successive sections in a filter is also computed and it is shown that unlike the situation in the infinite case the phase change is a function of the section. However, at relatively high frequencies and for large n this approximates to the total phase change along the structure divided by n. Comparison with such experimental results as are at present available yields reasonably satisfactory agreement.
The Vibrating String Considered as an Electrical Transmission Line
Authors: Kock Winston E.
Published: September 2005

An analogy is drawn between the piano string and an electrical transmission line, utilizing a different correlation than is customary in usual electro-acoustical analogs. The current in the line is compared with the displacement and the voltage is compared with the momentum. With this correspondence the highly developed treatment of transmission lines becomes applicable to the piano string. The various cases discussed include: Open circuited line with and without attenuation (i.e., ideal and actual string with ends rigidly fixed), terminated line (string affixed to bridge of sound board), electrical impulse introduced (impact of piano hammer). A relation is derived giving the optimum position of striking point for a given ratio of hammer mass to string mass, and this is shown to agree with the results of George and Beckett. The appearance of the nth harmonic when the string is struck at 1/nth of its length is explained, likewise the advantages of the modern practice of high string tensions. Conclusions are drawn concerning impedance matching (string to soundboard) and the velocity of propagation for different frequencies.
The Effect of High Intensity Sound on Smokes and Other Aerosols
Authors: Tatum G. R.
Published: September 2005

When smoke or other aerosols are placed in a resonance tube driven by a strongly vibrating source the particles are aggregated rapidly. In the investigation reported at this time magnetostrictive sources of frequencies 11.3 to 22 kilocycles per second were placed at the lower end of a vertical resonance tube into which either water vapor, cigarette smoke, or titanium tetrachloride smoke was introduced. The aggregated particles which are suspended at certain stationary positions in the tube, form large “disks” and “thimbles.” Some of the “disks” are oriented horizontally, while others have vertical orientation. The vertical “disks” are formed in sets of three equally spaced about the axis of the resonance tube. The process of aggregation is illustrated by means of motion pictures.
A Sensitive Method of Measuring Magnetic Flux in Small Areas
Authors: Thuras A. L.
Published: September 2005

Most acoustical measuring and sound reproducing instruments at the present time make use of magnetic circuits in which the concentrated flux in an air gap is utilized. To design efficient magnetic circuits it is necessary to know the magnitude of the leakage flux. Mapping of leakage flux is made by measuring the voltage generated by a vibrating wire as it is moved throughout a magnetic field. By amplifying the generated voltage it is possible to measure low intensity magnetic fields in very small areas. The method is remarkably accurate in measuring a nonuniform magnetic field.
Acoustic Signaling along the Plane Boundary between Two Media
Authors: Pierce G. W. , Noyes Atherton
Published: September 2005

The paper presents an experimental and theoretical discussion of acoustic signaling between a sending station and a receiving station near a plane reflecting surface, and is applicable to fog horn and submarine signaling. The experiments were made with a small scale apparatus employing supersonic waves of a frequency of 67.5 kilocycles per second. It is shown that at grazing incidence the direct and reflected waves cancel, or partially cancel, as predicted by theory. The cancellation for propagation in air near a water surface, or other surface of high sound velocity and high density, is found to be restricted to angles very near to grazing incidence. On the other hand, theory predicts cancellation for much larger departures from grazing incidence if the reflecting surface has high density but low velocity; experimental curves for transmission over beach sand and certain other substances resemble such theoretical results very closely. Acoustic mirages caused by temperature gradients were studied experimentally, and their effects are shown to be of striking importance in modifying the above results.
Radiation Pressure by Torsion Pendulum and by “Weighing” on Spring Balance (With Demonstration)
Authors: Klein Elias
Published: September 2005

Spherical radiometers were utilized to measure the steady pressures existing in a sound field. Similar determinations were made with a special helical spring. Comparative data as obtained by the two methods in liquids at supersonic frequencies are presented. The possibilities of these devices to serve as standard acoustical receivers in liquids are discussed and a plan for such a standard is briefly outlined.
Coordinated Treatment of Automobile Noise and Vibration
Authors: Janeway R. N.
Published: September 2005

The object of this paper is, first, to consider the various sources of mechanical vibration and noise in the automobile together with their respective characteristics and treatment; and, second, to attempt by analysis of available data to show a fundamental coordination in human reaction to noise and vibration. For the most part, noise and vibration have always been treated as independent problems both as to their origin and effect. Actually, they are so closely related in both respects that intelligent approach to the job of promoting passenger comfort in automobiles requires broad visualization of noise and vibration as coordinated phenomena. In outlining the various sources of mechanical vibration and noise, they are to be treated both in their independent and interrelated aspects. The vibration sources are subdivided into external disturbance to vehicle, engine dynamics and unbalance in drive members: independent noise sources to be considered are road surface factors, tire characteristics and those directly excited by engine operation. In each case, the method of treatment will be discussed from the standpoint of practical necessity for obtaining maximum results at minimum cost. The available data with regard to human annoyance factors, while meagre, are sufficient for developing an analytical method of coordinating noise and vibration reactions. Using Professor Jocklin's data on human vibration tolerance, and Hale Sabine's data on equal annoyance noise levels, it will be shown that when both types of disturbance are expressed in the same dimensional units, a similar characteristic variation of tolerance with frequency is indicated. The hypothesis is advanced that noise, having been generated by mechanical vibration, is reconverted by the mechanism of hearing into analogous disturbance of the human organism to that set-up by directly transmitted vibration. Much further research is essential to establish a definite quantitative relation between the two types of excitation. Eventually, it should be possible to integrate both the noise and vibration present in a given environment to obtain a single resultant human discomfort factor.
A Method for Evaluating Compliant Materials in Terms of Their Ability to Isolate Vibrations
Authors: Jack William , Parkinson John S.
Published: September 2005

A method is given for evaluating by dynamic means the stiffness and resistance of a vibrating system. By using this method, compliant materials not readily evaluated by static means may be investigated. The actual efficiencies of isolating systems are compared with the efficiencies predicted from a theoretical one-degree-of-freedom treatment. The comparison is favorable, but certain limitations of the theoretical treatment are discussed.
The Kansas City Municipal Auditorium Acoustics and Sound Reinforcement
Authors: Stanton G. T. , Potwin C. C.
Published: September 2005

The Kansas City Municipal Auditorium, with an enclosed volume of more than 4,500,000 cubic feet, presents an outstanding example of excellent acoustic design. The ultimate success of this project was made possible through architectural consideration of acoustic requirements in the original design stage. In this paper, the various phases of the acoustic design of the auditorium will be discussed. Experience has proved that the theoretical formulae commonly used in making acoustic analysis of enclosures do not hold for auditoria having extremely large volumes. Reverberation measurements made in existing large auditoria have proved of invaluable aid in establishing the actual requirements for new design. With respect to surface treatment, particular emphasis will be placed on the value of acoustic specifications and job sample testing in guaranteeing complete fulfilment of the sound absorption requirements. The public address system was specially designed to coordinate with the acoustic characteristics of the auditorium and to ensure the best distribution of amplified sound with a minimum of wall and ceiling reflections. The features of this system, in their relationship to the acoustic and esthetic qualities of the auditorium, will be discussed.
Sound Frequencies from an Airplane Exhaust System
Authors: Bruderlin Henry H.
Published: September 2005

Noise from a typical aircraft exhaust system consists chiefly of a combination of pitched tones, which have been considered by past publications to be the firing frequency and its harmonics. Investigation has shown that such frequencies may be nearly or completely absent and may be replaced by a number of fundamentals and their harmonics, which may not be harmonically related to the firing frequency, and that this frequency shift may be readily determined from the configuration of the exhaust system, the firing order and the density of the exhaust gas.
The Dynamics of the Auditory Ossicles
Authors: Stuhlman Otto
Published: September 2005

Ossicles model, 24 magnification, was constructed with accurate scale reproduction of articulating surfaces. Model mounted on a turntable with anterior process of Malleus in axis of rotation, and articulating surface up, that of Incus down. Contact lubricated with petroleum jelly. Incus' short crus pointed upward about 80° with rotating plane, supported at this end by a small depression simulating the fossa incudis. Axis of rotation, vertically down, without passing through Incus, passing through center of gravity of Malleus and terminating in its anterior process. Lever arms with locked Malleus-Incus joint, 1.27 to 1.00. Helmholtz's articulation 3 to 2. Manubrium of Malleus given deflections to 10° in horizontal plane. Motion communicated to lenticular process of Incus recorded with a 1/100 mm displacement gauge. The articulating surfaces turn this motion 39°. Resulting undistorted motion makes 57° angle with axis of long crus of Incus in an anterior direction. Corrugations of articulating surfaces exist but no locking of “Sperrzähne” determinable. A second displacement component exists at right angles to the axis of the long crus of Incus. Head of Stapes when attached to Incus, contact at inferior side, thrust up and anterior or down and posterior. Arch of Stapes found to tilt 23° down from perpendicular to foot plate and 7° forward. Resulting thrust gives a maximum displacement to a point on the margin of the foot plate located 33° superior to the anterior margin. Resulting foot plate motion is rotation around an axis at the posterior margin, with increased displacement; the rotation around the inferior margin becomes more dominant. Verifies Bekesy's recent optical analysis.
Vocal Resonance and Puff Oscillations
Authors: Cotton Jack C.
Published: September 2005

Experiments indicate that chest or tracheal resonance has little effect on sounds emitted from the mouth. Sound transmitted through the chest wall during phonation has an intensity level 30 decibels or more below the oral sound. Artificial alterations of the oral cavity volume prove that any vowel may be produced without loss of vowel character while the oral cavity dimensions are those characteristic of the vowel (i) as in “machine.” “Nasal resonance” can occur only when the mouth and nose are coupled together (lowered velum). Louder phonation is possible with the velum raised. Sound passing through the velum is attenuated from 20 to 30 decibels. Accessory nasal sinus resonance can affect only nasal sounds, and these negligibly. The glottal puff is an efficient complex sound generator. The abruptness of this puff determines the brilliance or “resonance” of the sound. A sudden puff from any source causes a 2800∼ oscillation of the air. This “atmospheric natural frequency” is responsible for brilliance in good voices. It is the limit approached by a resonator's natural frequency as the orifice is progressively enlarged. It is a function of the effective inertia and elasticity of the air in the region of the puff.
Pedagogical Hearing Tests of Large Groups
Authors: Russell G. Oscar
Published: September 2005

At Ohio State University over 4000 students are examined yearly at 90 per hour. The 4-A test was found inadequate and indeed misleading. So the following were developed. First, a push-button for each student, recording on a compound kymograf synchronized with another recorder which simultaneously indicated the pitch and intensity of the tone at the instant it was passed into the head-set. Too slow and cumbersome, though very accurate. Second, the student indicated by marks on a paper how many times he heard a 2-A audiometer tone interrupted from one to five times. This modification of the 4-A technique proved entirely unsatisfactory. Third, six sound-proof booths, with push-button operating flash light on the operator's desk. These are arranged in groups of three to five, superimposed one above the other. One operator follows six to ten lights quite efficiently. This is now modified by a “weeding out” test. Essentially the same, except that only two tones are tested—256 c.p.s. and 8192 c.p.s. Fifteen students tested every three minutes. All failing to respond at 15 sensation units above threshold are then sent in for complete test. Including latter, 1000 students are tested daily Freshman Week of the Autumn Quarter.
The Mechanical Action of Violins of High Quality
Authors: Saunders F. A.
Published: September 2005

Continuing work reported two years ago, we have studied the mechanical action of about ten excellent violins, five of which were made by Stradivarius. These studies consisted of (a) measurements of the quality of over 60 tones as produced by each instrument, analyzed by H. H. Hall's harmonic analyzer, and (b) measurements with a noise meter yielding the total intensity of the same tones. The two methods agree in disclosing many resonant points in each instrument, mainly due to vibrations of the wood of the violin. “Response” (or “frequency”) curves showing these peaks will be presented, together with such deductions as can be made from them as to the characteristics common to violins from the same maker, the existence of frequency-regions (formants) of high response, etc. Minor matters to be discussed are the vibrations of the air inside the instrument, the effects of different sorts of bowing, the influence of the bow pressure on the loudness of the note emitted, etc.
An Improved Chromatic Stroboscope
Authors: Young Robert W. , Loomis Allen
Published: September 2005

A multiple-disk stroboscope is described which permits direct measurement of audio-frequencies from 32 to 4070 cycles/sec. The light source is controlled by the sound whose frequency is to be measured. Twelve disks are permanently interconnected by suitable gearing to rotate at speeds corresponding very closely to the frequencies of the twelve chromatic notes within an octave of the equally tempered scale, the disk pattern having a separate sector ring for each of the seven octaves of the range. The basic driving speed of the stroboscope disks is controlled by an electrically maintained tuning fork. In addition, accurately measurable variation of the basic speed over a small range is provided to permit measurement of any frequency in terms of cents deviation from some note of the equally tempered scale based on A =440 cycles/sec. (One cent represents a frequency difference less than 0.06%.) Applications of the device are described illustrating its usefulness in musical problems of tuning and intonation. Its special value is pointed out for cases in which effects of an audible comparison tone are undesirable.
Pitch Variations Arising from Certain Types of Frequency Modulation
Authors: Lewis Don , Cowan Milton , Fairbanks Grant
Published: September 2005

This report deals with an investigation of the pitch of sounds characterized by frequency modulation. It has to do mainly with the perceived extent of pitch glides. By means of a specially-designed variable condenser the frequency of an oscillator could be modulated, intensity of output remaining essentially constant. Either sinusoidal or linear modulation could be obtained, and the amount and rate of modulation were both subject to control. It was possible to secure, among others, the following types of variation: (a) isolated frequency sweeps, either upward or downward in direction; (b) upward-downward or downward-upward sweeps; (c) sweeps, either upward or downward, at the beginning or end of a steady-state sound; (d) periodic modulation, that is, frequency vibrato. Sounds with vibrato were studied only casually. The experimental data, which reveal the relationship between perceived extent of glide and both the amount and the rate of frequency modulation, are interpreted to indicate their bearing on problems of pitch perception in speech and music. The results are further shown to have a significant bearing on auditory theory in that they reveal the great rapidity with which the ear responds to sounds of continuously varying frequency.
Resonance in Two Types of Non-Uniform Tubes
Authors: Jones Arthur Taber
Published: September 2005

The first tube considered consists of two open cylinders of different diameters joined end to end. The theoretical expression for the frequencies of standing waves in such tubes is not new, but it leads to a rather surprising result which is now tested experimentally. The second tube considered consists of two open cylinders of different diameters joined by a conical connecting tube. A theoretical expression for the frequencies of standing waves in such a tube is developed. For the one tube examined experimentally the agreement between theory and experiment is satisfactory.
Sound Measuring Instruments as Applied to Noise Reduction
Authors: Stanton G. T.
Published: September 2005

The measurement of noise by the use of sound level meters has been accepted by the aeronautic and automotive industries. Such measurements may be of comparative value for reasonably continuous composite noise. This is particularly true when the types of noise produced by the objects under comparison are similar in nature. Under properly controlled conditions, such measurements are of value in determining the relative success of various attempts or methods of noise reduction. In attacking noise reduction from an engineering standpoint, it is generally desirable to consider the individual physical characteristics of noise. Some of these characteristics and their effect on methods of instrumentation are discussed.
On the Noise Inspection and Noise Rating of Mechanical Equipment
Authors: Abbott E. J.
Published: September 2005

In the August issue of Refrigerating Engineering, W. W. Soroka outlines the drawbacks of present methods of noise rating, and proposes “a rational method which can be successfully worked out for machinery”. Briefly, his suggestion is to take account of differences in acoustical absorption when a machine is operated in different locations. If a given machine is operated in a room with small absorption, it will obviously produce a higher sound level than in a room of large absorption and suitable corrections can be made along the lines which Mr. Soroka indicates. On the other hand, experience has shown that noise ratings of actual machinery involve many factors which are of greater importance than differences in acoustical absorption. Hence, correction for absorption cannot be the solution for all our difficulties, as one might infer from reading the proposal. In the present paper, the author proposes to outline some of the practical aspects of noise inspection and noise rating of mechanical equipment.
Some Acoustic Problems of the Automotive Fan
Authors: Cary B.
Published: September 2005

The method of testing the fan on a car is discussed. The effect of spacing fan blades is shown to give the greatest change in the noise spectrum. Some extreme designs of spacing are presented.
The Effects of Cylindrical Pillars in a Reverberation Chamber
Authors: Sabine Paul E.
Published: September 2005

It is recognized that the fundamental assumption of the reverberation theory, namely, that there is a diffuse distribution of sound within a room during the decay period, is not fulfilled in rooms whose dimensions are not great in comparison with the wave-length. This departure from theoretical assumption has led to discordant results in the measurement of the coefficients of absorption of materials by the reverberation method in different laboratories. The present paper presents the results of a series of investigations to determine the effects of the presence of 193 feet of cylindrical pillars made of plaster, 12 inches in diameter, upon the character of the decay in a reverberation chamber whose volume is 10,000 cubic feet. The following effects were noted. (a) At frequencies below 512 cycles, the presence of the pillars produced a marked decrease in the deviations of single measurements of the time of decay from the mean of a large number of observations. At higher frequencies this effect was nil. (b) Below 512 cycles, the presence of the pillars produced an appreciable reduction in the spread of the measured values of absorption coefficients between large and small absorbent areas. (c) The presence of the pillars materially reduced the variation in the effect of a highly absorbent sample on the rate of decay with varying sample position. (d) Measurements of absorption coefficients of a number of samples of fixed size showed that the presence of the pillars produced negligible effects upon the measured values. The conclusion is drawn that the diffuse reflection from the pillars improves conditions for absorption measurements at frequencies below 512 cycles.
High Speed Motion Pictures of the Vocal Cords
Authors: Herriott W. , Farnsworth D. W.
Published: September 2005

Bell Telephone Laboratories has for several years made use of high speed motion picture photography as a visual aid in the study of problems associated with the design, manufacture and performance of telephone apparatus. This presentation is concerned with its application to problems relating to the functioning of the vocal cords in speech production. Vocal cord pictures taken at several different camera speeds up to 4000 frames per second are shown. These pictures, projected at a rate of sixteen or twenty-four frames per second, permit detailed observation of the motion of the cords vibrating at voice frequencies. Adequate illumination was secured by directly imaging a tungsten light source on the vocal cords. Harmful heat and ultraviolet radiation were absorbed by a liquid filter.
Preliminary Report on a High Fidelity Reproducer for Lateral Cut Disk Records
Authors: Hunt F. V. , Pierce J. A.
Published: September 2005

The moving element of the reproducer is a horizontal, single-turn, elongated loop of phosphor bronze ribbon which is driven by an inverted conical shell whose base is attached to the free end of the loop and whose apex bears a sapphire stylus. In the front half of the loop, which passes through a concentrated magnetic field, the ribbon lies in the vertical plane and is bent into a channel to increase its rigidity. In the remainder of the loop the ribbon is twisted into the horizontal plane and its ends are clamped between insulating blocks. This provides a light structure which is relatively stiff for lateral displacement but quite flexible in torsion, so that a lateral vibration of the stylus is converted into an oscillation of the stiffened portion of the loop about its longitudinal axis. Damping is provided by a membrane of Pyralin connecting the free end of the loop with the adjacent magnetic structure. The mass of the entire moving system is approximately 50 milligrams and the unbalanced weight on the stylus is less than six grams. The electrical output is approximately 50 db below that of a standard transcription reproducer, but the response is proportional to the recorded velocity amplitude within ±3 db from 30 to 18,000 cycles.
Scale Temperament as Applied to Piano Tuning
Authors: Railsback O. L.
Published: September 2005

A number of pianos were tested immediately after tuning to determine whether the actual tuning follows that of the “equal temperament” as defined in physics, within the limits of the ability of the tuner to set the strings, or whether there is a systematic deviation from the equally tempered scale and what the nature of such a systematic deviation is. The method for testing the tuning was by means of the chromatic stroboscope as described in a previous paper. The stroboscope used was an improved model of the type described in the last paper. Tests were made with several tuners and where possible with several pianos of each tuner. This gave an opportunity to determine whether different tuners have individual “styles” of tuning or whether there are marked general trends of a definite character. The results are plotted on graphs showing the deviations of each tone as read from the corresponding tone of the equally tempered scale. Comparisons of charts are made and averages are taken to show trends. In addition to accidental deviations there is a marked trend in the “stretching” of octaves. This stretching tends to be more marked at the upper and lower ends of the piano keyboard. Possible explanations are suggested and further investigation planned.
Exploration of Pressure Field Around the Human Head During Speech
Authors: Dunn H. K. , Farnsworth D. W.
Published: September 2005

The pressure spectrum of average speech has been measured at 80 different positions about the head of a speaker, thus showing the directional properties of the mouth and head as a sound radiator. The direction of strongest radiation was found to the front, but varying from somewhat above the horizontal, to 45° below, depending upon the frequency region studied. The results are directly applicable to problems of microphone placement, and of speech intelligibility in different directions. They also permit a more accurate estimate of the spectrum of total speech power than has been possible by older methods. Pressure measurements close to the lips were found to require special precautions, due to extraneous frequencies introduced when the air-stream from the lips strikes the microphone. For the same reason, reproduction from a close pick-up will sound unnatural, unless similar precautions are observed.
Measurement of Absorption in Rooms with Sound Absorbing Ceilings
Authors: Power J. R.
Published: September 2005

Serious difficulties have been encountered in attempts to measure the absorption coefficients of sound absorbing ceilings in large offices. An analysis of the sound field is made and it is concluded (1) that the reverberation time formula is usually invalid if the absorption is concentrated on one surface of the room, (2) that the energy density formula is not subject to such a restriction and (3) that under such conditions there is no apparent field method of determining the absorption coefficient that will serve as an accurate check on laboratory measurements.
Effect of Physical Size on the Directional Characteristics of Uni-Directional and Pressure Gradient Microphones
Authors: Massa Frank
Published: September 2005

Theoretical and experimental data are presented showing the effect of finite structural size in modifying the directional characteristics of a uni-directional microphone. When the separation between the pressure and pressure gradient actuated sections is increased beyond a small fraction of a wavelength, there is an appreciable reduction in the solid angle in which the attenuation is very high. The effect of the finite enclosure which terminates the pressure actuated element is to shift the axis of maximum attenuation from an axis of symmetry between the microphone elements at low frequencies to one inclined toward the pressure element at the high frequencies. Computed directional characteristics for an idealized pressure gradient microphone indicate a progressive broadening with increasing frequency. For an actual structure, carefully obtained experimental characteristics show a sharpening effect at medium frequencies and eventually a broadening at high frequencies. The intermediate sharpening is explained by the diffraction of sound which causes a pressure increase at normal incidence to the microphone when its dimensions become equal to a sizable fraction of a wave-length.
A Miniature Directional Condenser Microphone for Acoustic Measurements
Authors: Willig F. J.
Published: September 2005

Miniature pressure gradient condenser microphones similar to the type described by Braunmuhl and Weber have been developed to measure various acoustic quantities. They are especially useful because of their directional qualities and small size, some being only a centimeter in diameter and a millimeter thick. They are thus small enough to avoid disturbing the sound field, and are advantageous in experiments where the direction of the sound is important. For example, they can be used to map the sound field in an organ pipe. Preliminary experiments have been made to obtain approximate sound absorption coefficients of small samples of materials, by measuring the sound that is incident and the sound that is reflected from the material. Other obvious applications of the microphone are contemplated.
Field Calibration of Microphones
Authors: Cook G. S.
Published: September 2005

The first requirement for the making of field calibration of microphones is a space in which free field conditions are realized as nearly as possible. A room has been constructed 16′×16′×12′. The treatment of the room is the same as that used in a similar room constructed at the Bell Telephone Laboratories with the exception that there is a four-inch layer of rock wool outside the layers of cloth. Exploration of the room shows a marked pattern as was found in the room at the Bell Telephone Laboratories. However, fair conditions are to be had when both the sound source and receiver are near the center of the room. The results of microphone calibration show fair agreement with those of other laboratories. When observations are made at short frequency intervals there are variations in the apparent sensitivity of a microphone sometimes greater than 1 db. These are evidently due to interference. Such variations are to be expected even with walls having a reflecting power of about one percent. It seems desirable to make a group of observations over a short frequency range rather than several observations at the same frequency.
A Study of the Tuning of Pianos
Authors: Railsback O. L.
Published: September 2005

Measurements of the pitch of each note on the piano were made immediately after tuning by means of the chromatic stroboscope. Sixteen grand pianos and twelve upright pianos were included in this study. Different makes of pianos were used and the tuning was done by different tuners. Averages were computed for each of four tuners, using three grand pianos by each tuner, to discover whether or not different tuners follow different patterns of tuning. The conclusion is that they follow, on the average, about the same pattern with individual differences on the extreme ends. With this established the average was then taken of sixteen grand pianos to determine the slope of average deviation from the equally tempered scale. A line drawn to true fifths much more nearly coincides with the line of averages than does the line of true octaves and is very close for the middle five octaves. At the ends the departure is considerably greater. For the twelve upright pianos the departure is still greater.

A variety of causes seem to contribute to the “stretching” of octaves. In harmonic overtones in the bass and over compensating to avoid “flatting” are probably most significant.
Recent Advances in the Use of Acoustic Instruments for Routine Production Testing
Authors: Foulds Blair
Published: September 2005

Early attempts to use sound level meters for routine inspection purposes were not generally satisfactory. Subsequent experience in such applications has uncovered the basic reasons for early failures. These reasons are discussed and solutions reached in certain projects described. Practical considerations in the use of such equipment under factory conditions are discussed.
Acoustic Effects of Humidity in Gases
Authors: Pielemeier W. H.
Published: September 2005

Small anomalous absorption and velocity variations in air produced by water vapor were reported last year. Since then, Kendig has investigated oxygen in a similar way in our laboratory. The anomalous velocity effect was likewise small but absorption peaks were found at approximately the humidity predicted by extrapolating to 98 and 284 kc/sec. on Knudsen's curve. Extensive work has now been done with CO2. At 528 kc/sec. (T = 300°A) the partial vapor pressure (p) was changed by 55 steps. The absorption per cm (m) rose rapidly in the water vapor pressure region 1 mm to 4.2 mm. The velocity went through an inverted S-curve for which the steepest portion came at p=4.2 mm as it should. The total decrease was about 9 m/sec. A second frequency (1080 kc/sec.) yielded similar curves. The peak absorption is at p=7.5 mm. The two peak values are proportional within 1 percent to the respective frequencies, in accordance with the theory. The data show a great effect of water vapor on the average life time of a quantum of vibrational energy in the CO2 molecules and suggest slight traces of water vapor as the cause of the variously reported critical frequency (45 to 200 kc/sec.) in “dry” CO2.
Theory of Acoustic Effects of Humidity in CO2
Authors: Saxton Harold L.
Published: September 2005

Letting h represent the ratio of water vapor molecules to total number of molecules in a mixture of CO2 with water vapor, the collision constant, S, is given by S = a0+a1h+a2h2. At an absorption peak, S can be calculated from a theoretical formula and h measured. By using principally the data of Pielemeier at 528 and 1080 kc/sec. the constants have been determined. When S is thus expressed in terms of h, the velocity versus h curve, with frequency and temperature held constant, can be predicted with considerable precision. The complete data of Pielemeier at either frequency afford an excellent check on the theory.
The Crevasse Phenomenon in Piezoelectric Quartz and its Application in Physical Measurements
Authors: Hubbard J. C.
Published: September 2005

Piezoelectric quartz resonators, because of their mechanical durability and their small decrement, have found many well-known uses, particularly in frequency stabilization and in the construction of electric filters for high frequency channels, but their possibilities in connection with general laboratory use have not been realized. A piezoelectric ultramicrometer has been described permitting linear displacements to be measured to 10 9cm under ordinary laboratory conditions. Work has been continued on the application of this method to the precise measurement of the thermal coefficients of expansion of fine wires, the diameter of fibers, the effect of small temperature and pressure changes on the dielectric constants of gases, the estimation of moisture content in thin solid films, and the dielectric constants of thin solid and liquid films.
Acoustic Absorption and Reflection Coefficients in Gases by Supersonic Interferometry
Authors: Alleman Ray S.
Published: September 2005

The necessary experimental requirements of acoustic interferometry in gases have been examined by optical and electrical methods with the object of evaluating the influence of the boundary of the acoustic field, and the effect of departure from parallelism of the reflector with the source upon the experimentally determined attenuation and reflection coefficients. The results show that the requirements of parallelism of the reflector are as rigorous as in optical interferometry and are best met by adjustment for maximum height of peaks rather than by optical or mechanical methods. Recently determined values of reflection coefficients at 1237 kc are found to be in much better agreement among themselves and with the theoretical predictions of the theory (in press) of K. F. Herzfeld for dissipative reflection coefficients than most of those heretofore obtained with the resonator interferometer. Schlieren photographs of modes of vibration of X-cut piezoelectric quartz plates and of the acoustic radiation from them will be shown.
On the Auditory Significance of the Term Hearing Loss
Authors: Steinberg J. C. , Gardner M. B.
Published: September 2005

For a number of years hearing impairment has been expressed by the audiogram, which is a measure of the hearing loss for sounds which are just audible to the deafened ear, with the implication that impairment for threshold sounds indicates the impairment for sounds above threshold in the range of interest to the deafened. It is shown that the audiogram is not an accurate indication of hearing impairment for above threshold sounds in cases involving nerve deafness, when the loss in loudness sensation is taken as the criterion; but when the capacity to interpret speech sounds, as indicated by articulation tests, is the criterion, the audiogram does give an approximately correct indication of the hearing impairment. The relation of the audiogram to experiences in interpreting the speech of everyday life and the relation of hearing loss to absolute ear sensitivity are given.
A Study of the Pure Cochlear Microphonic in the Cat
Authors: Rawdon-Smith A. F. , Hawkins J. E. , Lurie M. H.
Published: September 2005

The cochlear response was studied in a cat whose cochlea has been denervated by an operation in which the auditory nerve was crushed intracranially. Five weeks were allowed for degeneration of the nerve fibers. By means of suitable tests those components of the electrical response to auditory stimuli which in the normal animal are due to action potentials of the auditory nerve were shown to be absent. The response was otherwise unaffected: the threshold contour (“electrical audiogram”) corresponded closely to that of the normal animal over a range of frequencies from 50 to 10,000 cycles, and the maximal voltage developed as a result of stimulation at high intensity was normal Four equal-response contours were obtained, showing the intensity of stimulation required to produce responses of constant voltage at different frequencies. These are approximately parallel to one another and to the threshold curve. Complete elimination of nerve action potentials enabled us to make for the first time an analysis of the harmonic content of the pure cochlear microphonic in response to stimulation at low frequency. The increase in the intensity of the harmonic components with increasing intensity of stimulation at frequencies of 200 and 1000 cycles was recorded. On the basis of these observations the influence of the action potentials of the auditory nerve on the harmonic content of the response in the normal animal is discussed. The results of microscopic study of the denervated cochlea are reported.
An Investigation of Auditory Fatigue, Especially as Applied to the Determination of Subjective Harmonics
Authors: Nichols R. H. , Firestone F. A.
Published: September 2005

An investigation has been made of the pattern of fatigue effect (shift in minimum audible threshold) against frequency for a very pure 202 c.p.s. fatiguing tone, for three observers. The fatiguing tone was sounded for about 2 seconds at levels of from 85 db to 116 db about 0.0002 dyne/cm2, and a short test tone was used to determine the threshold at various frequencies, within from 0.15 sec. to about 0.7 sec. after cutting off the fatiguing tone. Special attention was paid to the frequency region around 404 c.p.s. in an effort to determine whether excess fatigue might be caused by the subjective second harmonic. Considerable variability of results among the three observers was found, although each of the three was consistent in his own results. Two observers gave essentially a constant fatigue effect for the fatiguing frequency and higher frequencies over the range tested. The third observer shows a pronounced peak in fatigue effect at the fatiguing frequency (202 c.p.s.), and some indication of a peak at the second harmonic of the fatiguing frequency (404 c.p.s.). This observer is being tested further to determine whether the peak at 404 c.p.s. is due to subjective harmonic or to his minimum audible threshold characteristic.