bluuebunny/crossref_metadata_2025 huggingface dataset:
Absorption by Sound-Absorbent Spheres
Authors: Cook Richard K. , Chrzanowski Peter
Published: September 2005

The absorption of a plane wave of sound by a sphere is computed. The calculations are based on the assumption that the complex ratio of sound pressure at a point on the sphere's surface to the normal component of particle velocity is a constant independent of the direction of incidence (“normal impedance assumption”). Absorption measurements were made on hair felt-covered spheres placed in a reverberation room, and were compared with the computed absorption by means of the reverberation room statistics appropriate for spheres. The theory and measurements both show that absorbent spheres can have absorption coefficients greater than unity. The discrepancies between theoretical and experimental coefficients seem to indicate that the normal impedance assumption is not valid for the hair felt used in the experiments.
Ultrasonic Velocities and Absorption in Gases at Low Pressures
Authors: Zartman I. F.
Published: September 2005

Improvements to an ultrasonic interferometer are discussed. As a result a greater sensitivity to acoustic reactions is obtained and the reproducibility of the data is greatly improved. Velocity measurements in dried CO2-free air, dried N2, and dried H2 are given. Amplitude absorption coefficients for H2, N2, and CO2 are also included. Measurements are made over the temperature range from 9°C to 36.6°C and over the pressure range from 82.17 cm Hg to 0.45 cm Hg. The frequencies extend from approximately 500 kc to 2.16 mc. A maximum value for the absorption in H2, attributed to molecular absorption, is located at an f/p ratio of approximately 10 mc/atmos.
Supersonic Waves in Water-Alcohol-Sodium Chloride Mixture and Analysis of Its Intermolecular Action
Authors: Parshad R.
Published: September 2005

Supersonic velocities and adiabatic compressibilities of a series of mixtures of water-ethyl alcohol-sodium chloride have been found. In general, maxima of sound velocities and minima of adiabatic compressibilities were obtained. With increase of salt concentration, the depth of the minimum of compressibility decreased and shifted towards the value for alcohol free-salt water, and for 3N concentration of salt, no minimum at all remained. The phenomenon has been explained as caused by the depolymerization of water by sodium chloride. The explanation supports earlier results on the water alcohol system.
Motional Impedance Measurements on a Magnetostrictive System
Authors: Finlon Frank P.
Published: September 2005

The motional impedance of a magnetostrictive element is determined by a unique method involving embedding of the element in a block of Permafil, a non-magnetic plastic. The method used can be adapted to determine the motional impedance of any odd-shaped magnetostrictive element. The possible application of this method to the determination of magnetostrictive constants is pointed out.
Interactions between Microphones, Couplers and Earphones
Authors: Morrical Keron C. , Glaser John L. , Benson Robert W.
Published: September 2005

The earlier work on the comparison of the JRB and the Massa Artificial Ear couplers has been continued to seek the explanation of certain differences observed. The later work, for the most part, has been undertaken on couplers under active consideration for adoption by the American Standards Association.

The difference in pressure in 6-cc couplers as measured by the Western Electric 640-AA and the Massa M-101 microphones appears to be identified with the strong earphone coupler resonance peak rather than directly with the shape of the coupler. The effect is apparently associated with the diaphragm impedance of the microphone more closely when the microphone is in use as a measurement device than when merely present, but inactive, in the coupler, except in the case of the M-101 microphone whose presence gives rise to an unexplained increase in pressure.

For general earphone calibration work, the results obtained by means of any of the coupler systems will be satisfactory. For some physical purposes, however, the effects may lead to significant errors.
Internal Tuning Differences due to Players and the Taper of Trumpet Bells
Authors: Webster John C.
Published: September 2005

In order to isolate some of the factors affecting the internal tuning of brass instruments several differently tapered bells were made and a trumpet made up such that the different bells could be easily attached and detached. Tests were then run on the internal tuning using both a physical measure of the trumpet air column resonant frequency and a group of five players. The results were analyzed statistically and indicate that changes in the shape of the bell taper as great as those used for these tests caused significant changes in internal tuning, and that these changes were functionally related to the type of taper. Secondary results of the analysis gave measures of the magnitude of the differences among players and trials and showed the relationship between the player average and the physical measure of air column resonance.
A Composer's Music Box
Authors: Watson Robert B.
Published: September 2005

The Composer's Music Box is an electro-acoustic tone generator producing single tones. It is played in much the same way as a musical score is written. It has a pitch range of about an octave and an intensity range of about 40 db. Electrical circuits provide nearly constant tone structure independent of the fundamental frequency, and provide considerable variation in attack and decay times.
The Vibration of the Cochlear Partition in Anatomical Preparations and in Models of the Inner Ear
Authors: v. Békésy Georg
Published: September 2005

An experimental technique was developed to measure, for intact middle and inner ears, the volume displacement of the fluid in the cochlea produced by a given sound pressure on the eardrum. In order to determine whether it is possible to immobilize the stapes by increasing the static pressure in the cochlea, the transmission characteristics of the eardrum-to-round-window system were measured with the ear under the maximum static pressure that can be produced in the cochlea without bursting the blood vessels. Since no important change in transmission was observed, it was concluded that immobilization of the stapes cannot be produced by an increase in static pressure in the cochlea.

With the same technique the mechanical impedance of the movements of the stapes footplate, the round window, and the fluid in the cochlea were measured singly and combined as in the normal ear. Once the elastic properties of the cochlear partition were known, it was possible to construct an ear model that exhibited patterns of vibration similar to those found in the cochlear partition of the human ear. By changing the shape, the size, and the fluid viscosity in this ear model the relative importance of the different parts of the inner ear were studied.

These experiments made it plain that the pattern of vibration of the cochlear partition is determined primarily by the volume elasticity of the membrane and the fluid close to the membrane. Length, height, shape, and diameter of the cochlear canal do not influence the vibration pattern. A mathematical description of the hydrodynamic properties of the inner ear must take into consideration this independence of the physical dimensions of the cochlear canal.
On the Resonance Curve and the Decay Period at Various Points on the Cochlear Partition
Authors: v. Békésy Georg
Published: September 2005

In order to determine the way in which mechanical analysis of frequency occurs in the cochlea, a technique was developed for preparing anatomical specimens. This technique made it possible to measure the amplitude of vibrations along the cochlear partition when the stapes was driven with pure tones. It made it possible, further, to determine how the amplitude of vibration at any given place on the cochlear partition varies with the frequency. The relation of amplitude of vibration at a given place to frequency gives a curve very similar to a resonance curve. We can then calculate the logarithmic decrement characterizing the vibrations of the cochlear partition. This log decrement is almost independent of frequency and has a value of d = 1.3. The decay time of the vibrations of the cochlear partition was observed directly with a microscope, and the values obtained in this way agreed with those derived from the resonance curves. All the measurements have been made on preparations of the human ear.
The Effect of White Noise on the Loudness of Speech of Assigned Average Level
Authors: Pollack Irwin
Published: September 2005

Continuous recorded speech passages were presented against a background of white noise and against a quiet background. The effect of the noise on the loudness of speech was determined by having listeners adjust the level of speech heard in quiet to sound equal in loudness to an assigned average level of speech presented against selected levels of background noise. In general, it was found that (1) low noise levels produce a proportionately lower depression in the loudness level of speech than higher noise levels, (2) as a first approximation, however, the effect of noise on the loudness of speech is a function of the speech-to-noise ratio rather than of the level of the speech alone or of the noise alone, and (3) under none of the experimental conditions did white noise actually increase the loudness of speech (the “Egan effect”).

The assumption that a given level of noise subtracts a constant number of loudness units from speech (regardless of the level of the speech) was found to be fairly adequate in describing the experimental results.
The Sounds of Disease-Carrying Mosquitoes
Authors: Offenhauser Wm. H. , Kahn Morton C.
Published: September 2005

Some 40 or more years ago, there was evidence of interest among scientists in the sounds of mosquitoes. Despite very crude acoustical apparatus, significant conclusions had been reached by the early investigators. Although very little was done in the next three decades despite the growth in the field of acoustics, interest has recently been renewed because of the world-wide need to check the spread of mosquito-borne tropical diseases. Recent experiments have confirmed many early findings and have provided valuable new data.

Mosquito sounds are distinctive; gross differences occur that are readily detected both by listening and by wave analysis. All fundamental sounds occur in the center of the sonic range (200–1000 e.p.s.); all are rich in harmonics. All sounds are warble-modulated, some at a single low rate in the order of 5 c.p.s., others at a double rate with the same lower rate and a higher rate in the order 5 times the lower. In some tones, some harmonics are completely interrupted while the fundamental remains undisturbed. Warble amplitudes are quite large; 20 percent is not unusual. The fundamental pitch often drifts; in one case, for example, there was a 25 percent increase in as little as 0.05 sec. Male sounds seem higher pitched than female; sound spectrograms show this to be due more to the difference in harmonic emphasis than to the difference in fundamental pitch. Generally speaking, mosquitoes do not generate or respond to sine-wave tones.

Mosquito sounds are low in energy level; the total sound power output of a female Anopheles albimanus whose sound was used to bait a mosquito-killing trap in Cuba was in the order of 10−13 watt. With this low power level it is difficult to obtain recordings with the high signal-to-noise ratios customary in high quality commercial recording because of the relatively high noise levels. Despite this handicap, it has been possible to reduce the noise due to microphonics, hum induction, vibration, and airborne and other disturbances to the point where recordings with 40-db signal-to-noise ratio are made frequently.
A Proposed Loading of Piano Strings for Improved Tone
Authors: Miller Franklin
Published: September 2005

An ideally stiff string has overtones νn, which are sharper than multiples of the fundamental, the inharmonicity being proportional to (n2 − 1). This well known theoretical result has been verified by Schuck and Young [J. Acous. Soc. Am. 15, 1, (1943)] for typical strings. It is proposed to improve the tone of a piano string by attaching a small mass, thus lowering the frequency of each normal mode except those for which the mass is at a node. It turns out that for an ideally stiff string, approximate correction of a large number of overtones can be obtained with a single mass suitably located. In the limit of a large mass near the end of the string, the correction is exact for all overtones. A mass of the order of 0.1 g placed a few cm from the end of a typical string adjusts the first eight overtones to within a few hundredths of a semitone, a negligible inharmonicity. Improved tone is expected since the subjective fundamentals derived from difference tones between adjacent partials will show greatly reduced dispersion. The effect of the loading upon tuning would reduced the observed stretching of the octaves to a negligible amount. Deviations from ideal stiffness and the effect of adding two masses are also considered.
Generalized Solutions of Webster's Horn Theory
Authors: Mawardi Osman K.
Published: September 2005

Webster's equation for the approximate formulation of the propagation of sound waves in horns is solved using two methods of approach. The first method considers a transmission line with variable parameters as the electrical analogue of the horn. This approach is specially useful in yielding generalized solutions for horns of finite length. The second method, based on an investigation of the singularities of Webster's differential equation, leads to the discovery of a great number of new families of horns.
The Diffraction of Sound by Rigid Disks and Rigid Square Plates
Authors: Wiener Francis M.
Published: September 2005

A rigid circular plate was exposed to an essentially plane progressive sound wave, and the sound pressure p at various points on the surface measured relative to the free-field pressure p0 in the undisturbed incident wave by means of a small probe microphone. The diffraction effect |p/p0| was determined as a function of angle of incidence over a range of frequencies beginning with “long” wave-lengths and extending into the region where the radius a of the obstacle approximately equals the wave-length. Expressed in customary notation, 14 < ka < 8, where k is the wave number of the incident wave. Data were obtained for angles of incidence θ = 0, 45, 135, and 180 degrees, where θ is measured with respect to the axis of the obstacle. Similar measurements for θ = 0 and 180° were made for a rigid square plate with side 2a.

Approximate contour maps of the quantity |p/p0| in decibels have been prepared from the experimental data portraying the pressure distribution on the surface of the plates.

The experimental results are compared with computed values of |p/p0| obtained from an approximate theory in which an attempt is made to solve the problem in terms of a scattered potential calculated as if the face of the obstacle were surrounded by an infinite baffle. The agreement is quite good on the “illuminated” side of the plates, i.e., for θ = 0 and 45° and on the “shadow” side for θ = 180°. The agreement for 135 degree incidence is generally poor, although the computed values show the trends of the experimental data in many instances. At low frequencies the theory gives values which are somewhat too high on the illuminated side and too low on the shaded side.

The values of |p/p0| obtained from the exact expression of the diffraction of a plane wave by a disk of zero thickness and for perpendicular incidence are found to be in good agreement with experiment and the approximate theory on the illuminated side (θ = 0) and they agree reasonably well on the shaded side (θ = 180°) for 1⩽ka⩽5. The region near the edge shows discrepancies which are to be expected from the finite thickness of the circular plate (approx. a/12).

It is concluded that the approximate theory mentioned above is capable of predicting the diffraction effect |p/p0| on the illuminated side of the obstacles in the frequency range covered by this study for the angles of incidence investigated. On the shadow side the theory can be expected to yield usably approximate answers only for θ = 180°. There are reasonable grounds for the assumption that similar predictions can be made for points on or “near” the surface of “thin” plane obstacles of arbitrary shape and for other acute angles of incidence not too close to θ = 90°.
Theory of Ultrasonic Intensity Gain Due to Concave Reflectors
Authors: Griffing Virginia , Fox Francis E.
Published: September 2005

A concave reflector can be used to concentrate a beam of plane ultrasonic waves in the focal region, where the intensity If is much larger than the intensity Ii in the plane wave. When the sound wave-length is small compared to the dimensions of the beam and reflector, one can use the well-known Fraunhofer diffraction formulas to calculate the intensity gain, i.e., If/Ii. Expressions are derived for the maximum and average intensity gain in the zero-order image when the ultrasonic beam is circular or rectangular, together with formulas giving the total intensity falling upon circular or rectangular areas of arbitrary dimensions in the focal region.
Experimental Investigation of Ultrasonic Intensity Gain in Water Due to Concave Reflectors
Authors: Fox Francis E. , Griffing Virginia
Published: September 2005

This paper discusses a method of producing high intensity sound waves in liquids. A beam of ultrasonic waves (4.25 mc, 15 × 12 mm cross section, acoustic power≃2 watts) was focused with an ordinary watch glass (6.8 cm radius of curvature). The intensity in the focal region is large enough to raise an ultrasonic fountain 10 cm high accompanied by a spray of fog droplets. The distribution of intensity in the focal region was determined by measuring the screening effect of properly placed obstacles. The sound intensity in the focal region and in the plane wave was measured by the radiation pressure on beads of convenient size. The absolute intensity in the plane wave was also calculated from the driving potential and the measured mechanical Q of the crystal, and reasonable agreement was found with the direct measurement. A gain in intensity by a factor of about 70 was measured where simple diffraction theory predicts 74. For the highest voltages used the extrapolated negative peak pressure was 41 atmospheres. No cavitation was observed.
Focusing Ultrasonic Radiators
Authors: Willard G. W.
Published: September 2005

Piezoelectric ultrasonic radiators made in the form of a thin spherical shell radiate spherical sound waves which come to a focus at the center of curvature of the shell, thus enabling the production of much greater ultrasonic intensity in a small locality removed from the radiator than it is possible to obtain directly at the surface of a radiator. It is here shown by ultrasonic light diffraction pictures of the radiated sound field that the sharpness of focus is limited by wave diffraction in the manner well known in astronomical telescopes and may be calculated by optical diffraction formulas. By the same means the radiation efficiency of different areas of the curved surface is explored and the results compared with theory. The variation of efficiency is, of course, due to the variation of the effective elastic and piezoelectric constants of the differently oriented areas. Calculations are made of the radiation efficiency of a quartz radiator, and it is shown that a greatly improved focusing spherical radiator may be obtained by varying the thickness of the radiator to compensate for the varying frequency constant. Further, superior focusing cylindrical radiators may be obtained by special orientation or by thickness shaping or both.
Ultrasonic Lenses of Plastic Materials
Authors: Sette Daniele
Published: September 2005

The properties-of certain plastic substances have been examined with the idea of using them to construct solid lenses for focussing ultrasonic radiation. Some experiments are described which illustrate the advantages offered by such lenses. The use of a plano-cylindrical or a plano-spherical lens permits a reduction to 1/10 or 1/100 respectively of the energy which must be emitted by a quartz crystal to produce a given intensity of ultrasonic radiation over a given region.
A Low “Q” Directional Magnetostrictive Electroacoustic Transducer
Authors: Camp Leon , Wertz Francis D.
Published: September 2005

The description of a lamination design for the magnetostrictive motors of a directional transducer array. The design makes possible the efficient operation of the transducer with a “Q” of 6 under a full water load. Array patterns are presented to show that the laminated motors radiate as plane pistons into the medium.
Direct Reading Microdisplacement Meter
Authors: Arndt J. P.
Published: September 2005

Equipment has been built for measuring vibratory displacements of very small mechanical elements such as phonograph styli and piezoelectric crystals. It employs a probe of small dimensions so that virtually point measurements may be made. The probe does not contact the point under measurement and therefore imposes no mechanical load. The variation in capacitance between probe and vibrating surface is used to measure the displacement. Through the use of a built-in calibrator, the sensitivity may be adjusted electrically for direct meter reading of vibratory displacement without resorting to precise adjustment of condenser plate spacing. Displacement amplitudes of less than 10−6 cm may be measured. The output signal corresponds accurately to the displacement both in magnitude and in phase over a wide frequency range so that complex vibrations are portrayed accurately on a cathode-ray oscilloscope. The equipment has been calibrated by four independent methods, including a reciprocity method, with close agreement.
Auditory Masking of Multiple Tones by Random Noise
Authors: Schafer Tillman H. , Gales Robert S.
Published: September 2005

One, two, four, and eight simple tones were presented to listeners against a background of thermal noise. The masked thresholds for the single tones and the various combinations were determined, for different spacings of the tones. In the case of two tones, the improvement in threshold with respect to a single tone was slight or negligible unless the tones were within one critical band, when the improvement increased as the spacing decreased. In the case of four or eight tones all separated by more than a critical band, the improvement was slight (less than 3 db) or negligible, apparently depending on the combination of frequencies.
A Study of the Mechanism of the Middle Ear
Authors: Onchi Yutaka
Published: September 2005

I studied principally the mechanics of the middle ear, summarizing the anatomy and the physiology of the ear. I made Diagram I showing the anatomical structure of the ear, and translated it into physical terms of Diagram II, such as mass, spring, and frictional constant. etc. Thereafter I could get equations showing the mechanics of the middle ear through the Lagrangian equation. The complicated treatment for the kinetic, potential, and dissipation energies of the middle ear elements is for the purpose of expressing my opinion about the function of the middle ear which is partly different from the present contradictory medical views. By using the resultant equations of the motion of the ear and Diagram III (showing the electromechanical structure of the middle ear), I studied the mechanism of the middle ear under an assumption that the frequency characteristic curve of the inner ear is flat in a wide range. This assumption may be deduced from Luscher's experiment of the tympanic loading and hearing curves of men with complete defect of the tympanic membrane but with cochlear nerve intact. However, I do not explain it here, and it will be described in detail in further papers. From theoretical results thus obtained I made some experiments and calculation of the natural frequencies of the middle ear elements.

My conclusions are as follows: (a) The air vibration system of the ear which consists of the external auditory canal, the tympanic cavity, and the antrum can be shown electromechanically by Diagram III. (b) The middle ear has four main peaks of resonance on the hearing curves. (c) The middle ear and cochlea appear to be regarded as a displacement receiver and a pressure receiver, respectively. (d) The tympanic membrance has two important roles: (1) that of composing the vibration of the external auditory canala, of the antrum, and of the air cells of the mastoid process; and (2) that of propagating these vibrations to the ossicles. (e) The non-linear vibration of the tympanic membrane, the basilar membrane, and the secondary tympanic membrane, produce combination tones. (f) The air vibration system has an important role in understanding speech sounds. Its magnification of the sound intensity is above 50 db in a range from 700 or 800 cycles to 5000 cycles as in Fig. 5a. (g) This work offers a problem of design of a new audiometer, and is available for diagnosis of otological pathology.
The Lined Tube as an Element of Acoustic Circuits
Authors: Molloy Charles T.
Published: September 2005

This paper presents a method for calculating the performance of acoustic circuits containing lined ducts. The diameters of the ducts must be less than one-half the wave-length of sound in free air. The cases of long and short ducts are treated. For the latter, equivalent electrical circuits are given, and some discussion is given concerning the equivalent electrical circuits for long ducts. A brief list of formulas applicable to filters employing lined tubes is given.
Refracting Sound Waves
Authors: Kock Winston E. , Harvey F. K.
Published: September 2005

Structures are described which refract and focus sound waves. They are similar in principle to certain recently developed electromagnetic wave lenses in that they consist of arrays of obstacles which are small compared to the wave-length. These obstacles increase the effective density of the medium and thus effect a reduced propagation velocity of sound waves passing through the array. This reduced velocity is synonymous with refractive power so that lenses and prisms can be designed. When the obstacles approach a half wave-length in size, the refractive index varies with wave-length and prisms then cause a dispersion of the waves (sound spectrum analyzer). Path length delay type lenses for focusing sound waves are also described. A diverging lens is discussed which produces a more uniform angular distribution of high frequencies from a loud speaker.
On the Propagation of Sound Waves in Narrow Conduits
Authors: Mawardi Osman K.
Published: September 2005

The analysis of the propagation of sound waves in narrow tubes has usually been restricted to shapes yielding tractable mathematical expressions. A great number of practical applications do not fall within these categories and await a solution. An approximate solution of sufficient accuracy for narrow tubes of arbitrary shapes developed in this paper has been applied to a wire-filled tube. The theoretical predictions check satisfactorily with the experimental results. It is believed that this study will be useful in other similar applications.
Extraction and Portrayal of Pitch of Speech Sounds
Authors: Gruenz O. O. , Schott L. O.
Published: September 2005

An improved method for automatically extracting the pitch information of speech sounds has been devised. It employs a combination of gain control, double detection, voiced sound selection, unvoiced sound exclusion, and a means for counting the fundamental vibrations in the voiced sound intervals. Reliable indications of pitch have been obtained over a range corresponding to frequencies from 100 to 600 cycles for a wide variety of voices. The pitch-indicating signals have been applied, for study purposes, to a number of visual portrayal means for showing pitch changes, and descriptions of several of these systems are included.
Some Determinants of Interaural Phase Effects
Authors: Hirsh I. J. , Webster F. A.
Published: September 2005

It has recently been shown that the binaural threshold for a pure tone presented against a background of noise depends upon the interaural phase differences of the tone and the noise. For example, the threshold of a low frequency tone, in phase at the two ears, is low when it is heard against noise that is out of phase at the two ears, but is high when it is heard against noise that is in phase.

The masked threshold of a 250-cycle tone presented against a background of intense noise is in fact about 15 db lower under antiphasic conditions than it is under homophasic conditions. (Homophasic refers to the condition in which the tone and the noise have the same interaural phase difference. Antiphasic refers to the condition in which either tone or noise, but not both, is out of phase at the two ears.) When the tone is masked by another tone, fairly close in frequency but not so close that beats are detected, the dependence of masking on interaural phase does not appear. The present experiment attempts to determine what characteristics masking sound (“masker”) must have if it is to produce interaural phase effects.

A 250-cycle tone was presented against four different kinds of background. The masking sounds were (1) pure tones, (2) regular pulses (125 p.p.s.), (3) random pulses (average 125 p.p.s.) and (4) random noise. Combinations of filters permitted the presentation of these maskers in frequency bands that were varied in width and center frequency.

The results indicate that the threshold for the tone in the presence of a regular, periodic masker does not depend to any significant degree upon interaural phase relations. A necessary characteristic of the masker that produces interaural phase effects is randomness or irregularity. Both masking and the interaural phase effects increase as the frequency band of a random masker approaches the frequency of the tone. Band width alone does not contribute to the interaural phase effects except as widening a band tends to bring one cut-off nearer the frequency of the tone. Wide and narrow band maskers, both of which contain the frequency of the tone, produce the same effects.
Theory of Focusing Radiators
Authors: O'Neil H. T.
Published: September 2005

An approximate theory has been derived describing part of the sound field due to a concave spherical radiator, vibrating with uniform normal velocity; the radius a of the circular boundary is assumed to be large relative to the wave-length and large relative to the depth of the concave surface. The theory describes the distribution of pressure, particle velocity, and intensity along the axis of symmetry and in the vicinity of the focal plane, perpendicular to the axis at the center of curvature. It is shown that the ratio of the intensity at the center of curvature to the average intensity at the radiating surface is nearly equal to (2πh/λ)2 where h is the depth of the concave surface and λ is the wave-length. This ratio can be made very large by suitable choice of dimensions, and the focusing is then very sharp. The point of greatest intensity is not at the center of curvature but approaches it with increasing kh = 2πh/λ, and the greatest intensity is not much greater than the intensity at the center of curvature except when kh is small. In the central part of the focal plane, at angle θ from the axis, the pressure is approximately proportional to (2/ka sinθ)J1(ka sinθ), which is equivalent to the directivity function of a flat circular piston of radius a, for the region at large distance from the piston. The calculations are in reasonable agreement with G. W. Willard's experimental data for a 5-mc concave quartz crystal, when allowance is made for the non-uniform normal velocity of the crystal.
The Cathode-Ray Sound Spectroscope
Authors: Mathes R. C. , Norwine A. C. , Davis K. H.
Published: September 2005

This device provides for rapid analysis of short samples of speech and other sounds. It permits direct viewing of the energy-frequency distribution of the sound at instants of time in a two-dimensional pattern, and also over intervals of time as a three-dimensional pattern. Magnetically recorded on a disk at slow speed, and speeded up 200 times on playback, the sample of sound is analyzed rapidly by a broad band high frequency system.

The three-dimensional portrayal (in time, frequency and amplitude) shows the whole sound sample, including an interval of about 12 sec., on one cathode-ray tube, together with a movable indication of the point in time at which the “instantaneous” or two-dimensional frequency-amplitude section, appearing on another tube, is taken. This two-dimensional pattern displays amplitude on a decibel scale and covers about a 40 db range. The complete pattern is made up of 190 amplitude values for the 100 to 4000 cycle frequency range so that the pattern is formed by 190 vertical lines. The effective band width of the resolving filter is 45 cycles. The patterns are scanned at a rate of 2/sec. so that a slow phosphor screen is used for viewing. Successive sections approximately 212, 5, 10, 20, or 40 milliseconds apart may be established and photographed automatically. Or for direct viewing manual selection of any desired point of analysis is provided.
Theoretical Aspects of the Reciprocity Calibration of Electromechanical Transducers
Authors: Thompson Sanford P.
Published: September 2005

A unified theory of the reciprocity calibration of electromechanical transducers is presented in a form which facilitates the derivation of particular calibration theories. The theories of two types of calibration procedure are treated as special cases. One of the theories is shown to reduce, when lumped standards are used, to that of the original technique of Trent; the other is descriptive of a new procedure.

The application of calibration theories is discussed—particular attention being devoted to the use of distributed-constant standards and the consequent difficulties involved.
Musical Scales and Their Classification
Authors: Barbour J. Murray
Published: September 2005

A musical scale is a sequence of musical intervals in a certain range, such as an octave; a mode is a cyclic permutation of a scale; a key is a mode at a certain pitch-level; a raga is a melodic pattern of a key. There are 66 heptatonic scales, 462 heptatonic modes, and 5544 heptatonic keys. For each key there are thousands of possible ragas, or a total of many millions of ragas.

Most writers, confusing scales and modes, have listed comparatively few of the possible scales. The older writers were further limited by harmonic considerations. Slonimsky's scales and melodic patterns (1947) are mostly ragas, in which, as with Schillinger (1946), symmetry is paramount; Slonimsky's pentatonic and heptatonic scales are actually modes.

The inverse of a scale contains the same intervals in reverse order. The complement of a scale contains all the notes of an octave not in the scale itself. A scale may be measured by the total mean-square deviation of all its intervals.

The notation of a heptatonic scale as a harp scale (with seven letter names) agrees with the deviation index. However, the function of notes in the scale may often be expressed by fewer than seven letter names or by two different names for the same note. For the composer, the intensive study of individual scales will be more rewarding than the listing of thousands of keys or millions of ragas.
Theory of Passive Linear Electroacoustic Transducers with Fixed Velocity Distribution
Authors: Foldy Leslie L.
Published: September 2005

A general theory of passive linear electroacoustic transducers for which the surface velocity distribution is independent of the manner of excitation of the transducer is developed and applied to the calculation of important practical parameters of the transducer. A proof of the electroacoustic reciprocity theorem for such transducers is included. Another important theorem, the available acoustic power theorem, which states that the maximum power which can be absorbed by such a transducer from a plane wave sound field is given by the product of the intensity of the wave and the quantity λ2δR/4π where λ is the wave-length of the wave and δR is the receiving directivity factor of the transducer relative to the direction of incidence of the wave is also proved. The paper concludes with a discussion of the available power efficiency of a transducer and its relation to the threshold pressure of the transducer.
Method for Quieting Ram Jet Motor Test Stations
Authors: Snow William B. , Young C. J. T.
Published: September 2005

The Applied Physics Laboratory of Johns Hopkins University, operating under contract with the Bureau of Ordnance of the U.S. Navy, set up during the war a testing laboratory for ram jet motors at Forest Grove, Maryland, short distance outside of Washington, D. C., in a location surrounded by open country. Postwar building in the neighborhood made it necessary to quiet this installation if operation were to continue at the same location, and the Kellex Corporation undertook design of the revisions. Since very large volumes of air and hot gases had to enter and leave the test cells, it was necessary to design a duct system which offered extremely low resistance to gas flow, but high attenuation to sound. This paper gives a brief description of the resulting construction which has allowed the laboratory continue operation in the midst of a residential community.
The Plane Wave Reciprocity Parameter and Its Application to the Calibration of Electroacoustic Transducers at Close Distances
Authors: Simmons B. D. , Urick R. J.
Published: September 2005

The reciprocity parameter for a plane wave sound field is shown to be equal to 2A/ρc, where A is the area of the plane piston source and ρc the characteristic acoustic resistance of the medium. It is shown experimentally that the sound field in front of a plane piston source is effectively plane over a distance approximately equal to A/λ, and that in such a region the plane wave parameter may be used to obtain a free field calibration of the transducer by the reciprocity method.
THE APPROXIMATE NETWORKS OF ACOUSTIC FILTERS
Authors: Mason Warren P.
Published: September 2005

The approximate equivalent electrical networks of acoustic filters are developed in this paper, from the lumped-constant approximation networks for electric lines. In terms of this network, design formulae have been developed for all single band pass filters. It is possible, from these formulae, to determine the physical dimensions of an acoustic filter necessary to have a given attenuation and impedance characteristic.
THE MEASUREMENT OF SOUND ABSORPTION BY OSCILLOGRAPH RECORDS
Authors: Chrisler V. L.
Published: September 2005

This paper describes rather briefly some work which has been carried on at the Bureau of Standards in the attempt to use a recording instrument place of the ear in measurements of sound absorption. The reverberation method has now proved itself to be the most satisfactory way of measuring sound absorption. Possibly this term “satisfactory” should be modified because of the extent to which the personal element enters into the measurement. For this reason it has been considered desirable to have an instrumental method into which the personal element does not enter and yet which is as near like the reverberation measurement as possible.
Theory of Vibration of the Larynx
Authors: Wegel R. L.
Published: September 2005

The vibration in the larynx is caused by an automatic modulation by the vocal cords of the air stream from the lungs. Analytically the mechanism is the same, and physically, closely analogous to that of the vacuum tube oscillator. It depends principally on the resonance of the vocal cords, the modulation of air friction in the glottis by their motion and the attraction due to constriction of the air stream between them. When these forces exist in certain relative proportions and phases, sustained oscillation as in singing takes place. The whole mechanism may be represented analytically by force equations, from which conditions for accretion or subsidence of the vibration or for sustained oscillation may be easily deduced. These equations also show the analogy with other types of oscillating systems.
Part I. Noise Out-of-Doors
Authors: Galt Rogers H.
Published: September 2005

A summary is given of the results of noise surveys, including new measurements as well as certain material previously available. The report treats of noise out-of-doors, in buildings and in conveyances, and discusses noise levels and characteristics, noise sources, and noise reduction.
Part II. Noise in Buildings
Authors: Tucker Rexford S.
Published: September 2005

A summary is given of the results of noise surveys, including new measurements as well as certain material previously available. The report treats of noise out-of-doors, in buildings and in conveyances, and discusses noise levels and characteristics, noise sources, and noise reduction.
Part III. Noise Reduction
Authors: Parkinson John
Published: September 2005

A summary is given of the results of noise surveys, including new measurements as well as certain material previously available. The report treats of noise out-of-doors, in buildings and in conveyances, and discusses noise levels and characteristics, noise sources, and noise reduction.
The Objective Measurement of Machinery Noises
Authors: Firestone F. A.
Published: September 2005

The accurate measurement of the intensity of machinery noises, especially those of musical character, is very difficult under ordinary conditions on account of the presence of the interference pattern. The sound chamber method has been adapted to this problem, using a rotating reflector for securing uniform average distribution of sound intensity. A condenser microphone with tuned amplifier and slowly responding indicating meter is used for making the measurements which can be repeated on the same day with an accuracy of 0.5 decibel. In place of the tuned circuit in the amplifier, a “loudness circuit” is sometimes used which weights the various frequencies according to the sensitivity of the average ear at a loudness level 60 db. above the 700 cycle threshold. The loudness readings of six vacuum cleaners as taken with this apparatus checked against the average loudness estimate of twenty observers.
A Concatenated Cone Speaker which Behaves Essentially as a Point Source
Authors: Bedford A. V.
Published: September 2005

It is evident that if a speaker is to show great fidelity of reproduction of sound in all directions from the speaker, it must generate the same shaped waves for all frequencies. The generation of plane waves would require for the lower frequencies, a uniformly driven surface very much larger than is considered practicable for general use. (Dr. Hewlett's speaker is a good one of this type.)

The simplest means of generating a spherical wave apparently would be to use a piston whose diameter is smaller than the wave length of the highest frequency sound wave to be generated. However, a piston which is small enough to fill this requirement on 5000 cycles per second would have to move an absurdly great distance (several inches) at the lower audio frequencies to produce sufficient sound.

The present paper discusses and gives the results of tests on a new multiple cone structure speaker which changes its effective size so that it is practically a point source for all frequencies.

The transition from one effective size to another is made smoothly and in such a way that no major variations in response occur due to either interference or resonance.
Some High Scale Acoustic Phenomena
Authors: Bourne R. B.
Published: September 2005

A definition of “high scale” is given. Various phenomena encountered in the field are described, together with certain psychological considerations. Physical factors influencing silencer design are discussed. The Maxim Gun Silencer is described and demonstrated.
Some New Instruments in the Iowa Laboratory for the Psychology of Music
Authors: Seashore C. E.
Published: September 2005

This is a report describing briefly the following new instruments developed by the staff in the University of Iowa.

1. Piano camera: a camera which records the time and the force of the stroke for the entire keyboard in piano playing, under normal conditions of playing. (Tiffin and Seashore.)

2. Certain modifications of Metfessel's strobophotographic camera which graphs pitch and time of a solo instrument or voice, photographically. (Reger and Tiffin.)

3. The new synthetic vibrato apparatus: utilizes the photoelectric cell in controlling all the factors in the vibrato. (Tiffin.)

4. The rhythm meter: a graphic method of measuring precision in rhythm performance. (Seashore, C. E. and R. H.)

5. The tone dynometer: a means of measuring precision in musical “touch.” (Seashore.).

6. A new model of the tonoscope: portable and adaptable for general laboratory and studio use. (Seashore and Williams.)
The Reverberation Time Bridge—An Instrumental Method for Measuring Reverberation Time
Authors: Olson Harry F. , Kreuzer Barton
Published: September 2005

The analogy between the decay of the electrical energy in a capacitor shunted by a resistor and the decay of sound energy in a room with sound absorbing walls is the basis of this bridge.

The sound pressure is converted into a corresponding electrical voltage by a microphone and amplifier. This voltage is measured by a linear type v.t. voltmeter. The voltage across the resistor shunting the capacitor is measured by another similar v.t. voltmeter.

The room and capacitor are “charged” until steady state conditions are established, the capacitor charging voltage and the sound source are then cut off simultaneously. The bridge is balanced by adjustment of the variable discharge resistor, until the two voltages are equal during the decay period.

The value of “t” in the “time constant” of the electrical circuit is then the actual reverberaone time.
Incommensurability of the Octave Interval with any other Interval
Authors: Bartholomew Wilmer T.
Published: September 2005

Although it is common knowledge that the well-known tempered scale of twelve semitones is imperfect, relatively few musicians understand the necessary cause of that imperfection, which lies in the mathematical relations of the ratios involved.

In any method of tuning, the ear demands that at least the octaves must be true. It is demonstrated that if this is so, no other true interval, if successively stepped off from a starting tone, can ever arrive at an exact octave of the starting tone.

The mathematics, though elementary and obvious to the scientific musician, is important since it underlies all attempts at tempering scales.
I. Theory of the Electrostatic Loud Speaker
Authors: Hanna C. R.
Published: September 2005

In the electromagnetic driver the force per unit current has been shown to be a function of the inductance and the negative stiffness resulting from the presence of the steady magnetic field. In this paper it is proven that the force per unit voltage in the electrostatic device is a similar function of the capacity and the negative stiffness due to the steady electrostatic field.

A new concept called Motional Admittance is introduced for the electrostatic loud speaker and this is shown to be similar in its mathematical form to the Motional Impedance of the electromagnetic driver.

A calculation of the ultimate theoretical efficiency that may be obtained with an electrostatic speaker having a pure resistance radiator and covering a given frequency range is given. It appears that efficiencies between 5 and 10% may some day be obtainable with good fidelity of reproduction.
Directed Radiation of Sound from Loud Speakers
Authors: Wolff Irving , Malter Louis
Published: September 2005

A discussion of the importance of the directional characteristics of loud speakers from the standpoint of good reproduction of sound in small rooms and auditoriums. Calculated results will be shown for a number of ideal sound radiators and experimental measurements will be given in a number of typical cases.