bluuebunny/crossref_metadata_2025 huggingface dataset:
A Note on Supersonic Methods
Authors: Richardson E. G.
Published: September 2005

In collaboration with two research students, I have in hand an experimental investigation of the dispersion and absorption of supersonic waves in gases, O2, CO2, SO2, N2O, etc., with particular reference to the effects of pressure and temperature of the gases on absorption. Besides the now familiar Pierce method (for the velocity) and torsionvane method (for the absorption), methods employing hot-wires have been developed. It has been found, for instance, that the steady resistance of a heated filament placed near a piezoelectric quartz oscillator varies with the amplitude of the supersonic waves to which it is exposed. The instrument is calibrated by keeping the filament at a fixed point relative to the quartz, and applying different alternating differences of potential to the latter. After this, the wire may be used, while the quartz is driven at constant potential, to plot the amplitude in its neighborhood, and hence the absorption coefficient for the gas may be calculated. If the velocity is required the wave-length of the radiation is measured by means of two heated filaments, each connected to one of two primaries of a transformer, the induced current in the secondary, due to fluctuations in the two primary circuits, being measured by a thermoelement and sensitive galvanometer. If the two wires are spaced at one wave-length apart, the two trains of fluctuations are in phase. Having determined the wave-length by keeping one filament still, and moving the other relative to it, until maximum response of the galvanometer is attained, the frequency is measured on a wave meter, and so the average velocity of the radiation over this small space is obtained. At present, the latter method has not proved practicable above 200 kilocycles, owing to the limited response on the part of the hot wires, but with improved technique, it is hoped to use the method at higher frequencies. Further details will be published in due course.
Direct Recording and Reproducing Materials for Disk Recording
Authors: Keller A. C.
Published: September 2005

Recently materials for direct recording and reproducing work have been improved so that they are now suitable for many uses. These materials, as they are available on the market, are classified chemically into five groups and measurements are given of frequency characteristic, surface noise, life, distortion, etc. These data have been taken with both lateral and vertical recording. A short aural demonstration will be given of typical recording of materials of each group.
Violin Intonation
Authors: Greene Paul C.
Published: September 2005

The purpose of the study was to determine whether violinists, in unaccompanied performance, typically play in either the natural or the equally tempered musical scale, and if not, whether they tend systematically to expand or contract musical intervals as compared with their theoretical magnitudes. Six professional violinists participated in the investigation. Unaccompanied performances of three standard violin selections were recorded by an oscillographic technique. The average fundamental frequency of the main body of each of the tones was measured, and interval extents then were computed. The major part of the study was limited to an analysis of five intervals—major and minor seconds, major and minor thirds and perfect fourths. Tests of reliability of measurement showed that the largest expected error of measurement (±3 SDs) for any given frequency was approximately 0.03 tone, but in at least 78 percent of the cases, measurements were statistically significant to 0.01 tone.

The major findings were: (1) The six violinists typically performed in neither the natural nor the equally tempered scale. (2) As compared with both natural and equally tempered intonation, major seconds and major thirds tended to be expanded, minor seconds and minor thirds on the average were contracted, and perfect fourths tended to approximate the theoretical scale values for that interval. (3) The average extent of each of the five intervals approximated its theoretical magnitude in Pythagorean intonation.
The Nature and Origin of Aural Harmonics
Authors: Newman E. B. , Stevens S. S.
Published: September 2005

Problems as to the nature and origin of the aural (subjective) harmonics, tones which are heard, but which are not present in the sound wave outside of the ear, have concerned musicians and scientists for many years. It is customary to assume that these harmonics arise because of non-linearity in the functioning of the middle ear. Their magnitudes have been measured by indirect means, such as the method of best beats, but there has been no adequate direct study.

We have used several means to attack this problem. (1) The minimum amount of distortion (2nd harmonic) which the ear can detect in a tone was studied by determining the thresholds for the second harmonic when it is added, outside the ear, to a pure fundamental in various phase relations. (2) Since it is possible to pick up from the cochlea an electrical potential which gives a good indication of the functioning of the auditory mechanism, we made an analysis and measurement of the harmonic components present in the cochlear response of animals under normal and certain abnormal conditions. (3) The phase relations of the harmonics in the cochlear response were determined with the aid of a cathode-ray oscillograph. (4) Externally generated harmonics were added to the fundamental in various phase relations both for human and animal subjects.

The results show that, for purposes of analysis, we can distinguish two sources of aural harmonics. The odd harmonics arise, from non-linearity, when the amplitude of vibration approaches the elastic limit of the ear. The even harmonics are due to an asymmetry produced by tension of the muscles of the middle ear, and consequently, their magnitudes can be experimentally controlled.

Professor Hallowell Davis aided in the work on animals.
A Scale for the Measurement of the Psychological Magnitude Pitch
Authors: Volkmann J. , Stevens S. S. , Newman E. B.
Published: September 2005

A subjective scale for the measurement of pitch was constructed from determinations of the half-value of pitches at various frequencies. This scale differs from both the musical scale and the frequency scale, neither of which is subjective. Five observers fractionated tones of 10 different frequencies at a loudness level of 60 db. From these fractionations a numerical scale was constructed which is proportional to the perceived magnitude of subjective pitch. In numbering the scale the 1000-cycle tone was assigned the pitch of 1000 subjective units (mels).

The close agreement of the pitch scale with an integration of the differential thresholds (DL's) shows that, unlike the DL's for loudness, all DL's for pitch are of uniform subjective magnitude. The agreement further implies that pitch and differential sensitivity to pitch are both rectilinear functions of extent on the basilar membrane.

The correspondence of the pitch scale and the experimentally determined location of the resonant areas of the basilar membrane suggests that, in cutting a pitch in half, the observer adjusts the tone until it stimulates a position halfway from the original locus to the apical end of the membrane.

Measurement of the subjective size of musical intervals (such as octaves) in terms of the pitch scale shows that the intervals become larger as the frequency of the mid-point of the interval increases (except in the two highest audible octaves). This result confirms earlier judgments as to the relative size of octaves in different parts of the frequency range.
Reverberation and Absorption
Authors: Meyer Erwin
Published: September 2005

We distinguish between geometrical and dynamical acoustics of rooms, which both have to be considered to obtain good quality of speech and music. Using a simple automatic method of recording the sound decay on an instrument with a logarithmic scale, concert and auditory rooms with and without audience are acoustically investigated.

Generally the sound absorption materials are tested in reverberation chambers. The results of different laboratories are not in agreement, the reasons being probably, that the rooms are small and that geometrical instead of diffuse sound reflection occurs. Comparison tests therefore have been made in the reverberation chamber of the Institute and in the intake chamber (Wasserschloss) of a big hydroelectric power station: this chamber had a size of 13,000 m3 and an average reverberation time (60 db) of 40 sec. The results are discussed. It is interesting to make similar experiments in optics with “Ulbricht” balls. These experiments show that it is only possible to measure absorption coefficients of light in boxes with scattering walls. Therefore a model reverberation chamber was built with interchangeable walls reflecting either geometrically or diffusely. Under “diffuse” conditions the results were more in agreement with theory. For practical measurements it seems best to standardize the measuring device.

Finally special kinds of nonporous flexible sound absorbing materials are discussed. It is shown, that these materials in connection with an air space very strongly absorb the low and middle-pitched tones.
Theory of the Haskell Organ Pipe
Authors: Jones Arthur Taber
Published: September 2005

Some twenty-five years ago William E. Haskell patented an organ pipe which has the characteristics of an open pipe of the usual form but is considerably shorter. The pipe is similar to an ordinary open pipe with a smaller tube, closed at the top, mounted inside of it. The pipe gives the same overtones that are obtained from an ordinary open pipe of length equal to the sum of the lengths of the main pipe and the inserted tube. No theory of the Haskell pipe appears ever to have been published.

The pipe is here regarded as made up of three parts: (1) The main pipe up to the bottom of the inserted tube, (2) the inserted tube, (3) the part of the main pipe that surrounds the inserted tube. Suitable boundary conditions are introduced, and a general equation for the frequencies of the normal modes of vibration is obtained. If the inserted tube ends at the top of the main pipe, and if the cross-sectional area of the inserted tube is half that of the main pipe, the equation reduces to that for an open pipe of the length stated above.
Combination Horn and Direct Radiator Loudspeaker
Authors: Olson H. F. , Hackley R. A.
Published: September 2005

A loudspeaker is described consisting of a long horn coupled to one side of a small dynamically driven cone for the reproduction of low frequencies and an acoustic filter for changing the output from the horn to the open side of the cone for the reproduction of the mid and high frequency range. A theoretical analysis shows the action of the system. Experimental data substantiates the theory.
Spherical Torsion Pendulum as Supersonic Radiation Pressure Meter in Liquids
Authors: Klein Elias
Published: September 2005

Following King's theoretical work, a series of measurements has been carried out with bronze spheres varying in diameter from 14 to 112 inches. In plane stationary waves in water at frequencies between 100 and 200 kc. King's predicted dependence of radiation pressure on the location of the spheres relative to the position of nodes and loops is verified. Neglecting the viscosity of the medium and the compressibility of the spheres, it was found that the radiation pressure approximates inverse variation with the radius a of the sphere when the latter's size is such as to make 2πa/λ greater than unity and less than four.

Considering the spherical torsion balance a likely laboratory acoustic standard in liquids, it is possible to calibrate as secondary standards any pressure microphone for subaqueous use in the supersonic range. Such calibration was effected upon tourmaline crystal microphones by the usual resonance tube method. The piston source was telescopically fitted into the end of a horizontal rigid cylinder about 6 in. in diameter and 15 in. long. The other end was machined and covered either by a blank quarter wave plate which acted as a perfect reflector or a quarter wave plate in the reflecting face of which the tourmaline crystal was inserted. The spherical torsion balance was suspended over the center of the cylinder so as always to maintain the sphere on the axis of the cylinder. The whole suspended system was provided with horizontal motion by means of a micrometer screw of 4 in. travel.

The results obtained by this calibration compare favorably with other methods and check roughly with the pressures calculated from the static piezoelectric constant of the tourmaline crystals.
Demonstration of Dorsey Fathometer
Authors: Dorsey H. G.
Published: September 2005

This instrument was recently developed at the U. S. Coast and Geodetic Survey Hydrosonic Laboratory as a precision instrument for visually measuring ocean depths by echoes. It has been regularly used on the surveying ships in place of the lead and line and gives 20 echoes per second, or a measurement about every foot. No moving contacts are used, the signals being sent by light reflected to a photoelectric tube. The speed is accurately controlled by operating the indicator with a synchronous motor, driven from a tuning fork. Results are so accurate that phenomena of surveying are discovered which were never revealed by the hand lead methods. The demonstration will show echoes in air at distances of a few feet by high pitched sounds, results considered impossible with sounds of ordinary frequencies.
Loudness Factors of Sound-in-Air Fog Signal Units
Authors: Gill Irving L.
Published: September 2005

The Bureau of Light-houses of the U. S. Department of Commerce has established a fog signal testing laboratory at Cape Henry Light Station, Virginia. Field tests of reciprocating piston type and diaphragm type air horn signals were made during the Fall of 1936, and this paper presents data with slides showing a loudness-distance curve for a diaphone signal, pressure-air consumption and pressure-loudness curves for a diaphragm air horn, and tables showing frequency structures of reciprocating piston and diaphragm types of fog signal units. The analysis of frequency structure was accomplished with a General Radio Co. type 636-A Wave Analyzer. It is shown that these signals have a large number of harmonics and that the reciprocating piston type unit (diaphone) produces the major energies in the harmonic structure. The fundamental frequency does not apparently contain the greatest energy. Data are also presented showing the frequency of the diaphone piston for comparison with the frequency of the sound signal from this same instrument. Loudness curves showing field patterns of various sound signal units around the horizon are presented, as well as data indicating that frequencies above the range of about 300 cycles per second may be propagated with less loss of energy over an increasing distance range than lower frequencies.
Requirements of the Bureau of Marine Inspection and Navigation for Emergency Announcer Systems
Authors: Hoelzle F. C.
Published: September 2005

To replace the use of megaphones to give orders to crew and passengers in times of disaster and other emergencies, Congress has passed certain laws requiring the use of sound amplifying systems on American ocean vessels. Such a system would be used in times of emergency to summon the crew, direct passengers to embarkation deck and life boats, and to avert panic. Necessarily, such a system must be extremely reliable and equipped with stand-by apparatus for use in case of breakdown. The system must be rugged to withstand shock, salt water and other abuses. The acoustical power radiated by the loudspeakers must be sufficient to “over-ride” the noise of storms and the general turmoil of any type of disaster.
Complex Elastic Wave Patterns in the Earth and Their Directional Analysis
Authors: Rieber Frank
Published: September 2005

Geophysical prospecting by the so-called reflection shooting method encounters many difficulties in certain regions, due to the fact that the impulse from an explosion near the surface may be returned as a complex group of reflected waves, arriving from various directions at the same time. A new method for recording and analyzing such complex wave groups is described. It consists in detecting the arriving waves at a number of points on the earth's surface by a properly placed group of pick-up devices. The vibrations at each of these pick-up points are recorded as a sound track, ten such tracks being conveniently placed side by side on a single piece of motion picture film. This sound track record may then be passed through a photoelectric analyzer which is adapted to select and separate the waves arriving from different directions. The analyzing apparatus records its findings in the form of an ink record on paper which may then be used as a basis for constructing the geophysical section. By the use of this new method work has been carried on with great success in many regions where the confusion in wave patterns was so great as to preclude the use of other types of reflection equipment.
Vibration Instruments
Authors: Greentree C. D.
Published: September 2005

The accuracy and usefulness of portable electrical vibration measuring instruments depend to a great extent upon the excellence of the mechanical system employed to create a stationary body relative to which a measurement can be made. For example, changes or modifications which tend to increase the responsive frequency range may disturb the vibration amplitude of the body itself, or decrease the sensitivity of the device. In addition, certain types of signal generation and amplification seem to be best suited to the specific measurement of vibration amplitude, velocity or acceleration. Electrical vibration signals permit the use of easily portable high gain vacuum tube amplifiers and the direct visualization of frequency, wave shape, etc., by means of magnetic or cathode ray oscilloscopes. They also make it easier to adapt the instrument for telemetered indicating or recording. The means developed for testing vibration instruments of different kinds and varying ranges has helped to improve the design of the instruments.
Vibration Problems in Buildings
Authors: Young L. H.
Published: September 2005

A study was made of the vibrations set up in a school building by pupils exercising in the gymnasium. The frequency of the disturbing vibration was near enough to the natural frequency of the girder system to cause disturbance. The possibility of operating at resonant speed was present. Measurements were made of the magnitude of the disturbance and from these the disturbance at resonance was calculated. The results of the analysis and corrective methods are discussed. Vibration records are given as illustration.
Finite Solid Acoustic Filters
Authors: Lindsay R. B. , Focke A. 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 solid filters together with an experimental check of the results obtained from the theoretical discussion. Two types of filters are considered. The first consists of a solid rod loaded at equal intervals with heavy masses; the second consists of a structure in which rods of one material are alternated with rods of a second material, each pair of rods being similar to the next pair. Expressions are derived for the power transmission ratios and for the phase changes which occur between successive sections of the filters. Experimental filters, which were designed to approximate the theoretical considerations, are tested for their transmission characteristics. The acoustical system is set into vibration by a modified dynamic speaker unit. The vibrations in the system are detected by phonograph pickups. Satisfactory agreement of theory and experiment is obtained.
Variations in Absorption Coefficients as Obtained by the Reverberation Chamber Method
Authors: Morris R. M. , Nixon G. M. , Parkinson J. S.
Published: September 2005

Absorption coefficients determined by the reverberation chamber method on the same material in different laboratories are not in agreement. The discrepancies were noted with several materials tested in both the NBC and J-M laboratories. An investigation, involving comparative measurements on materials of different absorbing efficiencies, was undertaken to determine the reasons for the variations. The results indicate that the order of agreement depends on frequency and the absorptivity and size of the sample under test. Various reverberation time formulas have been proposed and of these the Millington formula tends to give the best agreement and most reasonable results under the test conditions. An attempt is made to define the limiting assumptions of the formula empirically from absorption vs. sample area data obtained during the investigation.
Sound Propagation in Ducts Lined with Absorbing Materials
Authors: Sivian L. J.
Published: September 2005

In ventilator and exhaust systems it is desirable to provide a high degree of attenuation for audio frequency sound waves while offering low resistance to continuous or slowly pulsating air flow. For that purpose ducts lined with absorbing materials frequently are used. This paper deals with sound propagation, particularly with its attenuation constant, in such ducts. A method for computing the propagation constant in terms of the acoustic constants of the lining and of the duct dimensions, is given. Two types of lining are considered, nonvibratile and vibratile, the former admitting of no wave motion propagated in the direction of the duct axis within the lining itself. Experimental data are presented for a duct lined with rockwool, and are compared with computed attenuations. It is concluded that the computational procedure is fairly valid up to a frequency at which the sound wave-length is about twice the internal duct diameter.
The Amplification of Sound Received by Horns
Authors: Bloomenthal S.
Published: September 2005

1. The known equations for the amplification of sound received by conical, exponential, hyperbolic and parabolic horns are deduced on the basis of Webster's theory using a more direct method than is generally employed. 2. Representative theoretical and experimental amplification curves are given for each type of horn. 3. The variation with frequency of the ratio of sound pressure at the closed end to that just inside the mouth for the various type short horns having the same length, throat and mouth areas is calculated to show the superiority of the exponential horn. 4. The amplification of a short conical horn with exponential listening pipe is also considered.
The Acoustics of the Telephone Receiver with a New Earcap
Authors: Jarnak Poul
Published: September 2005

The invention of a new earcap for the telephone receiver is described incorporating a resonatory body which consists of a channel-formed room made up of a number of tubes open at both ends. The development of this invention has been based on investigations of the actions from the resonatory body of the violin and through studies on a new type of an organ pipe. It has been found by subjective tests that this new earcap compared to the standard earcap, now in general use, reproduces sounds with less “singing” mechanical vibrations from resonance in the diaphragm. Consequently an improvement in making speech clearer and music more mellow has been accomplished. It is believed that the acoustical improvement obtained by the new earcap is due to the interaction between the vibrations excited in the diaphragm and the interfering standing waves generated thereby in the tubes. This action reaches an optimum by the formation of a differential wave which is one octave below the excited fundamental if the tubes have such dimensions in relation to one another that their resonance frequencies build a series of numbers, the terms of which have the proportion 2 : 3. The aural impression of a more true reproduction of sound with the new earcap has been confirmed by tests supplying electric currents of a single sine wave and of combined waves to the same telephone receiver alternatively equipped with the two different types of an earcap, the standard one and the new earcap, the sound intensity produced accordingly being measured and recorded with an oscillograph.
Magnetic Recording and Reproducing
Authors: Hickman C. N.
Published: September 2005

This paper describes an improved method of recording sound magnetically on steel tape, similar in principle to that of the Poulsen telegraphone. By making use of perpendicular instead of longitudinal magnetization, the speed of the tape may be reduced as low as 8 inches per second for recording speech. The low tape speed eliminates many of the difficulties encountered with those systems which made use of longitudinal magnetization. The ratio of the signal to the background noise has been substantially reduced. The recording medium is a steel tape having a thickness of about 2 mils and a width of about 50 mils. A small recording and reproducing machine will be demonstrated.
Relation Between Loudness and Masking
Authors: Fletcher Harvey , Munson W. A.
Published: September 2005

A functional relationship between the loudness of a sound and the degree to which it masks single frequency tones, that is, the masking audiogram of the sound, is developed. A loudness masking function is determined experimentally. From this loudness masking relationship the loudness of a sound can be computed by simply integrating the area under the masking audiogram plotted on a special chart. Comparisons of computed and observed loudness levels are shown for a number of sounds and serve to illustrate the precision to be expected from the method. Finally, the results of a large number of masking tests are given in the form of masking contours, which enable one to predict the masking audiogram of a sound from measurements of its intensity spectrum.
The Harmonic Structure of the Violin Tone as a Function of Bow Speed and Bow Pressure
Authors: Small Arnold
Published: September 2005

Two factors in bowing, speed and pressure, have been varied independently by means of a mechanical bow. The results of harmonic analysis indicate that both variables may operate significantly to alter harmonic structure; that the degree of change and relative effectiveness of the two factors varies markedly with frequency; that increase in speed results in relative decrease in energy in the upper partials, while increase in pressure results in relative increase in energy in the upper partials.
An Improved Method for Obtaining Photographs of Ripple Wave Actions
Authors: Raquet M. E. , Watson F. R.
Published: September 2005

The use of ripple waves to show reflection, diffraction, etc., of waves is well known. Light shining upward through the glass bottom of a tank containing a shallow layer of water will be modified by waves on the water surface and will show a pattern of the waves when striking a frosted glass surface, of which photographs may be taken. One of the difficulties experienced in ripple wave photography is the optical distortion of the waves set up by surface tension at the edges of obstacles placed in the water. For example, when a miniature model of an auditorium is used the boundaries of the model appear distorted because of the passage of the light through surface tension modifications of the level water surface; furthermore, these irregularities set up by the surface tension affect the regularity of the reflected waves. To reduce this distortion, the reflecting obstacles were made plane parallel, placed on the glass bottom of the tank which had been carefully leveled; then the water level was lowered slowly by a siphon until the layer of water over the obstacle was so thin that the waves were completely reflected (a suggestion made to F. R. W. by Dr. F. V. Hunt). A series of photographs were made while the water was being lowered to secure the best result—too much water or too little water gave distorted photographs. It was necessary to have the tank clean (no oil), to use distilled water, and to make the obstacles scrupulously clean by application of acid-alcohol (95 percent alcohol, 5 percent glacial acetic acid) wiped with a clean cloth and not touched by the oily fingers, again washed with plain alcohol and dried with a clean cloth. Photographs show the resulting clear patterns of waves.
A Horn Consisting of Manifold Exponential Sections
Authors: Olson Harry F.
Published: September 2005

The expressions for the throat impedance of a horn with two rates of exponential flare have been derived. This expression is applicable to any number of sections by considering two sections at a time. The impedance frequency characteristic of specific multiple horns shows the possibility of obtaining a large variety of impedance characteristics suitable for improving the efficiency characteristic over that possible with a single rate of flare. The efficiency of a horn type loudspeaker having a horn with three rates of flare shows an efficiency within a few percent of the ultimate efficiency.
Acoustic Networks in Loudspeaker Cabinets
Authors: Knowles Hugh
Published: September 2005

Hornless loudspeakers used in conventional speaker cabinets and baffles have appreciable transient and nonlinear distortion and are relatively inefficient at low frequencies. Acoustic networks which couple the speaker to one or more auxiliary sources of sound may be used to reduce this distortion. By proper choice of the circuit elements in this network, the combined radiation from all sources may be made to exceed that obtained from a given speaker in an infinite baffle at low frequencies. Some aspects of the general theory of compound sources are discussed, after which the detailed application of the theory to one type of unit is outlined.
Pressures of Sound Waves Measured by a Condenser Microphone and Oscilloscope for Continuously Varying Frequency
Authors: Rogers Robert , Willig F. J.
Published: September 2005

Sound waves were generated by a 555 Western Electric loudspeaker and attached exponential horn when actuated by a Clough-Brengle beat frequency oscillator. The sound pressures were received by a miniature condenser microphone, 34 inch in diameter, and were then amplified and led to a cathode-ray oscilloscope which gave a visible straight line response on its fluorescent screen. When the frequency of the source was continuously varied, the line on the oscilloscope varied in length according to the reception of sound pressures by the condenser microphone. Photographs of the action were taken on a moving film. The apparatus was used to explore the resonating response of boxes filled with air when sound waves impinged on the flexible membranes used to cover the box tops.
Muffler and Silencer Design
Authors: Nelson C. E.
Published: September 2005

The reduction of machinery noises—whether industrial or automotive—can best be accomplished by an attack on the most important source of noise. In the case of engines, compressors and the like, the first attack usually centers on exhaust and intake noise. This paper will present the method used to design special silencers as well as those intended for general service, together with data on specific applications.
Are Automobiles Not Quiet?
Authors: Norris R. F.
Published: September 2005

The quieting of automobiles has progressed from the early days to the present through a number of steps, the greatest quieting having been done when mufflers were attached to the engines. Present day automobiles, with the exception of windage, are exceptionally quiet, which is the goal that has been striven for.
Absorption Effects in Sound Transmission Measurements
Authors: Sabine Paul E. , Ramer L. G.
Published: September 2005

Transmission of sound between adjacent rooms by way of an intervening wall is essentially the relative intensities of vibration of two bodies of air dynamically coupled by a solid septum. The transmission loss of a partition has been defined by the equation T.L. = 10 log (E0/E2)(A/a2), in which E0/E2 is the ratio of the intensities on the two sides of the partition, and A/a2 is the ratio of the transmitting area to the total equivalent absorption of the receiving room. Varying a2, the equivalent absorption, from a value of 7.1 to 131 sabins it is shown experimentally that the transmission loss as defined is constant over this range of variation in a2. The bearing of these results on the proposed definition of “transmittivity” is considered.
Recent Progress in Supersonics
Authors: Richards William T.
Published: September 2005

A summary of recent contributions to several branches of acoustics which have been useful to physics and to chemistry. The theory of the propagation of sound in dispersive gases is first discussed from a standpoint which it is hoped may be intelligible to those who have no special knowledge of the subject. There follows a description of the various types of apparatus which have been devised to measure the velocity of sound and the attenuation coefficient. The direct photography of sound using Töpler's “Schlieren-methode” is stressed as promising to obviate difficulties inherent in the interferometric technique. The experimental results are then summarized with particular attention to the effects of pressure, temperature, and traces of foreign substances on the dispersive behavior of gases. The collision theory has received strong support from the majority of these measurements. Finally, the effects of intense sonic and supersonic radiation are briefly reviewed. Since most of these have been found to depend upon cavitation, the role of cavitation is examined. A ballo-electrical explanation of the phenomena is considered the most promising, although it is difficult to prove.
Absorption of Sound in Carbon Dioxide—Effects of Impurities
Authors: Knudsen V. O. , Fricke E.
Published: September 2005

Further measurements on the absorption of sound in CO2 reveal that the nonclassical (or collision) absorption begins at about 3000 cycles and increases rapidly for higher frequencies (to 34,000 cycles). This is probably a portion of the absorption band which has its maximum at about 105 cycles. The addition of small impurities, such as H2O and various alcohols, greatly reduces the absorption in the frequency range investigated, namely that corresponding to the ascending branch of the absorption band. This is explained on the assumption that the effect of such impurities is to shorten the lifetime of the vibration of the CO2 molecule, that is, the absorption maximum is shifted to higher frequencies. A similar shift of the dispersion band has been observed in the velocity measurements of Eucken, Becker, and others. Although the absorption in CO2 at 8000 cycles is quite large (of the order of 2 db/ft.), the addition of a small impurity of water vapor (less than 0.5 percent) reduces the absorption to less than that for pure N2. This is consistent with the classical theory, and probably means that at such frequencies there is very little, if any, nonclassical absorption in CO2 containing small impurities of H2O. This also is the case for certain other impurities.
The Application of Negative Feedback to Electromechanical Devices
Authors: Wiebusch C. F. , Vieth L.
Published: September 2005

The elementary theory of feedback as applied to electromechanical transducers is discussed. Provided the conditions for stability are met, the feedback will produce a flat velocity vs. frequency characteristic; reduce the phase shift, noise, and nonlinear distortion normally introduced in the amplifier and the transducer; and will increase the output mechanical impedance of the transducer. A disk recorder embodying this principle is described. The new recorder is capable of recording on wax or direct recording material without appreciable effect on its characteristics which include a uniform response from 30 to 12,000 cycles and exceptional freedom from distortion products.
Resonant Frequencies and Damping Constants of Vocal Resonators
Authors: Lewis Don , Tuthill Curtis
Published: September 2005

In a recent paper by Lewis, a method was developed for determining the resonance frequencies and damping constants of the principal resonators typically involved in the production of sustained vocal tones. The method has been used in further research; and the present report deals with data secured on the vowels “O” and “AH”. Generalized values are presented. In addition, some of the effects on vowel structure of variations in pitch and loudness level are shown. It is evident, for example, that the magnitude of high frequency components, relative to the magnitude of low frequency components, varies with loudness level. The effects of pitch variation are, on the whole, neither clear-cut nor consistent.
Limits of Audition for Bone Conduction
Authors: Watson Norma A.
Published: September 2005

The laboratory facilities and apparatus described in an earlier paper were used to study the normal intensity and frequency limits of audition for bone conduction. The condition of the observer's head to give greatest acuity for pure tones, and the optimal total force of application and area of the vibrator button were found to be essentially the same as for speech sounds. Acuity was found to vary with the position of application of the vibrator; for example, the maximum variation with position of the 1000-cycle threshold was 18 db. A threshold for open canals was determined for the frequency range 80–2000 cycles, without interference from stray air radiation (18 normal observers). Above 2000 cycles air radiation interfered with open canal tests to such an extent that a special technique was devised to obviate its effects. The occluded threshold curve, for a single normal individual, lay below his open canal curve over the range 80–2000 cycles, and also at 10,000 cycles. The usable intensity range for open canals was tentatively determined; it is a maximum of 80–90 db at 1000–2000 cycles. The total audible frequency range for open canals was found to be at least 25–17,000 cycles.
On the Phase and Magnitude of Subjective Tones
Authors: Lewis Don
Published: September 2005

It has been shown by Lewis and Larsen that the phase and the magnitude of a subjective tone heard monaurally may differ significantly for two different observers with normal hearing. This paper deals with a study of the two ears of the same observer. Differences as well as similarities in both phase and magnitude are indicated, differences in magnitude being more common than differences in phase. Further investigation seems necessary before a satisfactory explanation of the findings can be offered.
On Sound Localization
Authors: Wallach Hans
Published: September 2005

The binaural cues for sound localization are effective only in determining the angle between a given direction of sound and the axis of the ears (lateral angle). Since there is localization in the median plane, a second factor should be found which determines the direction of sound in this dimension.

Head movement during sound localization might yield such a factor. With head movement the lateral angle of the sound changes giving a sequence of lateral angles characterizing the direction of sound geometrically in both dimensions.

That sound localization actually works on this principle is proved by experiments in which directions of sound are synthetically produced. The sequence of lateral angles which a certain elevated direction of sound would yield with a certain head movement was determined. While the observer performed this head movement a sound was shifted in the horizontal plane in a way to present the same sequence of lateral angles. The observer perceived the sound in the direction from which the presented sequence of lateral angles was derived instead of in the actually given shifting position.
An Analysis of Perceptible Overtones in the Voice
Authors: Lewis Don , Lichte William H.
Published: September 2005

Both oscillographic and phonographic recordings were made of a vocal sound in which five successively prominent partials were produced, in a few seconds, by a singer who meanwhile maintained the sound at a specified pitch level. Representative waves from the period of prominence of each partial were subjected to harmonic analysis, the results showing the physical bases for corresponding auditory experiences. Detailed investigation of the periods of transition from a given perceptibly prominent partial to the succeeding one revealed significant changes in energy distribution. For example, during the transition from the 4th to the 5th partial, there was found to be a 5 db decrease in the intensity level of the 4th, a 20 db increase in the level of the 5th, and a 10 db increase in the level of the 6th, with all other partials remaining essentially constant. The changes were gradual but rapid, and were apparently dependent upon resonance factors. The crucial importance of a given transition in attracting attention to a particular partial and, consequently, in shaping perception has been determined by psychological analysis.
The Mobility Method of Computing the Vibration of Linear Mechanical and Acoustical Systems
Authors: Firestone F. A.
Published: September 2005

It is shown that the conventional mechanical-electrical analogy (velocity across→current through; force through→voltage across) has grave defects which have hindered its general adoption as a method of solving vibration problems. The new analogy however (velocity across→voltage across; force through→current through) can be safely applied in such a natural intuitive manner that it becomes unnecessary to distinguish between the mechanical system and the analogous electrical circuit. The problem solving techniques of electricity are taken over bodily into mechanics with the aid of the following devices: The mechanical systems are diagrammed with the aid of a set of conventionalized two-terminal symbols which picture the springs, mechanical resistors, and masses comprising the system. The letter symbols for velocity, force and mass are changed from the usual v, f and m to e, i, and c, respectively. A complex constant called the “mobility” (ease of motion) is defined as z = e/i = velocity/force and it is found that the mobility of the mechanical elements is of a familiar form (ze = jωl, zr = r, zc = −j/ωc) while series and parallel combinations of z's are made by the familiar rules. The solution of the mechanical problem is thus reduced to a determination of the mobilities at different points in the system and the application of the equation e = iz. The problem remains a problem in mechanics and there is no reference to electricity.

Not only can forced vibration be computed in this manner, but the normal frequencies and normal modes of free vibration of resistanceless systems can be found. The concept of “acoustical mobility,” Z = E/I = volume velocity/sound pressure, permits the calculation of mechanical-acoustical systems.
A New Acceleration Meter (With Demonstration)
Authors: Hayes Harvey C. , Curtis W. F.
Published: September 2005

Problems involving the lessening or elimination of vibrations in machines and associated mechanical structures call for methods and means of measuring their amplitude and frequency. Several devices have been developed for this purpose which serve well over some limited range of frequencies and amplitude but they offer little or no aid in solving many problems having to do with ships where extremes in both frequency and amplitude are encountered such as shaft and blade vibrations of super-audible frequency and problems involving roll where the period may exceed 10 seconds. To meet these problems a new type of acceleration meter has been developed. It utilizes the change of electrical impedance of a coil of fine wire wound as a solenoid around a wire of magnetostrictive material when tension in the wire is changed. In practice a known mass is anchored to the moving or vibrating member by such a wire and the accelerating forces acting on this mass are measured in terms of change of electrical impedance of the coil which forms one arm of an impedance bridge. The bridge is energized at high frequency and its output can be amplified to give almost any desired degree of sensitivity.
Tracing Distortion in Sound Reproduction from Phonograph Records
Authors: Pierce J. A. , Hunt F. V.
Published: September 2005

When the spherical tip of an ideal reproducer stylus slides over a warped groove surface having a sinusoidal profile, the traced curve is not exactly sinusoidal. An analysis of the harmonic content of the traced curve, similar to that given by Di Toro but avoiding his approximations, is directly applicable to reproduction from vertical-cut records. These results may be applied to reproduction from lateral-cut records by taking the original groove surface as inclined approximately 45° from the horizontal, projecting the traced curve on the horizontal and vertical planes, and adding in proper phase the guidance of the stylus tip by both sidewalls. It is shown that there is a residual vertical component of stylus motion (“pinch” effect) and complete cancellation of all even harmonics in the tracing distortion. Computation of the remaining odd harmonics indicates that, when the ideal lateral-cut reproducer characteristics include ideal “following” for vertical motion at signal frequencies, a lateral-cut record may be reproduced with 4 to 10 times less r.m.s. distortion than a similarly recorded vertical-cut record. These results are displayed for convenient reference by contours of constant distortion on a universal chart whose dimensionless coordinates characterize any recording condition, and allow the immediate specification of the maximum permissible recorded amplitude, maximum permissible predistortion of the frequency characteristic, and the required clearance angle of the recording stylus.
Optical Analogy of a Loudspeaker in a Reverberant Room
Authors: Watson F. R.
Published: September 2005

When a speaker talks in a large, reverberant room, the numerous reflections from the various surfaces fill the room with sound that may be regarded as an acoustic “fog.” The speaker thus has difficulty in making himself “seen” (heard) through this “fog” by distant auditors. By analogy with an auto in a real fog, he turns on his “acoustic headlights” (loudspeakers) to make his speech “visible” (understood) by auditors. Care must be taken to avoid “acoustic glare” (excessive loudness), which is also likely to produce a “reflection” (echo) from distant walls. This optical analogy has been found helpful in explaining the acoustic effects set up by reverberation in rooms.
A Method of Observing Sound Decay and Measuring Reverberation Time
Authors: Tuttle W. N. , Lamson Horatio W.
Published: September 2005

The shape of the transconductance versus grid bias characteristics of certain vacuum tubes is such that, by employing a discharging capacitor to bias these grids in an audio-amplifier, it is possible to have the over-all gain of the amplifier increase exponentially with time over a wide range to a very close approximation. This known rate of gain increase can be adjusted to match the average rate of decay of reverberant sound so that deviations from a true exponential decay can be observed directly on a meter or cathode-ray oscillograph as decibel differences. The time constant of the discharging capacitor may then be calibrated directly in reverberation time.