bluuebunny/crossref_metadata_2025 huggingface dataset:
Young's Modulus of Elasticity of Fibers and Films by Sound Velocity Measurements
Authors: Ballou J. W. , Silverman S.
Published: September 2005

A method for measuring the modulus of elasticity of fibers and films by sonic means is described and the results of an exploratory study of this modulus in various natural and synthetic fibers and films are given. The method is based on the equation for the propagation of longitudinal waves in elastic materials, which expresses the velocity of propagation in terms of the elastic modulus and density of the medium. The procedure involves measuring the sound velocity and calculating the modulus, using the proper density value. The modulus so calculated is characteristic of a dynamic, short period measurement, since a sound frequency of approximately 10 kilocycles per second was used. The range of moduli found was from 1×1010 to 50×1010 dynes per square centimeter. Correlations of moduli with other physical properties are given.
The Action of a Direct Radiator Loudspeaker with a Nonlinear Cone Suspension System
Authors: Olson Harry F.
Published: September 2005

During the past few years a number of mathematical investigators have directed their efforts toward the solution of differential equations with variable coefficients. These analyses are useful in explaining some of the phenomena which occur in electroacoustic vibrating systems with nonlinear elements. In particular, this mathematics may be used to explain the various phenomena exhibited by a direct radiator loudspeaker with a nonlinear cone suspension system. One of the effects is a jump phenomenon in the response frequency characteristic. Another effect is the production of harmonics and subharmonics.
A Precision Method for the Determination of the Velocity of Sound in Air
Authors: Leonard R. W.
Published: September 2005

A method has been developed and refined in the laboratory at U.C.L.A. for the measurement of the velocity of free progressive sound waves in air. The method involves wave-length measurements in a free sound field of known frequency. A directional source radiating “spherical” waves is placed at one end of the free field room. Measurements of positions of equal phase along the axis of the source are made with a movable microphone. The phase measurements are made on the screen of an oscilloscope. The amplified voltage developed by the microphone is applied to the vertical plates of the oscilloscope and a voltage derived from the source oscillator is applied to the horizontal plates. Closure of the ellipse on the oscilloscope screen is used to determine position of equal phase. The microphone is moved away from the source on a steel track, the position of the microphone being remotely controlled by Selsin motors. The positions of equal phase are recorded by photographing a reference scale against a steel tape stretched parallel to the axis of the source. The camera and reference scale move with the microphone. Wave-length measurements are made over an interval of 10 meters. The source frequency is determined by beating one of its harmonics with the carrier frequency of a commercial broadcasting station. Harmonics of the order of the 100th are generated in a suitable diode circuit. Temperature measurements are made by means of thermocouples distributed along the line of measurement. Humidity is determined by a gravimetric method. A sample of air of known volume is passed through a drying tube and the change in weight of the tube determined. Since it is unnecessary for the operator to enter the room during or immediately previous to making the measurements temperature gradients and turbulence are at a minimum.
Some Problems for Post-War Musical Acoustics
Authors: Young Robert W.
Published: September 2005

Problems of musical acoustics worthy of study may be found in at least three categories: basic studies of the vibrating media, techniques and criteria, and new devices. As an example of the first category, the velocity of sound within wind instruments should be investigated for various ambient conditions. The internal air temperature and humidity distribution resulting from the breath of the player are involved as well as external temperature, the openings in the instrument its material, and its shape. This information in turn is needed for a problem in the second category, namely a criterion of standard pitch suitable for a wind band. The pitch of different wind instruments in general increases with ambient temperature, but by varying amounts. Can a “variable” standard pitch dependent upon ambient temperature be found which will permit all the instruments of a wind band to remain relatively in tune with each other under varying climatic conditions better than is possible with the nominal fixed standard now in use? In addition to new instruments, a need falling in the third category is that of a sound analyzer capable of operation during normal musical performance, but which gives the results of its analysis in a form easily comprehended and not requiring prohibitive labor of interpretation. High speed operation is clearly indicated to delineate change of tone quality with time.
The Clang Tone of the Pianoforte
Authors: Knoblaugh Armand F.
Published: September 2005

This phenomenon occurs in the bass section of all pianofortes and is termed a “clang” or “wolf” tone by piano makers. It comprises a distinctly audible, high pitched sound, emitted with the bass tone when the string is struck in the usual manner. Its pitch, varying from 500 to 3000 c.p.s. throughout a piano, is constant for any one string but varies with string dimensions, being higher for the shorter, lighter bass wires. The fundamental tones of the corresponding bass strings range from 30 to 100 c.p.s. With the aid of a tone analyzer and other apparatus, the effect has been shown to be due to a longitudinal vibration of the bass string. The velocity along the string has been found to be (AE/M)12 where A = the cross-sectional area of the core wire, E = the modulus of elasticity of the core wire material, and M = the total mass (core+wrapping) per unit length of the string. Dividing the velocity by twice the length of the string yields the frequency of the clang, confirmed by observation and experiment. The clang has its own system of partials, substantially harmonic. The component of hammer motion tangential to the string is probably an exciting cause and the complex motion of the bass bridge probably permits transfer of energy to the soundboard.
The Dipole Microphone
Authors: Olney Benjamin , Slaymaker Frank H. , Meeker Willard F.
Published: September 2005

A dipole microphone is defined as a microphone whose response is a function of the pressure difference between two distinct acoustic terminals. One application takes the form of a wearable, close-talking microphone in which only the acoustic dipole element need be located near the mouth of the wearer. The sound is conducted through small tubes and is applied to opposite sides of a diaphragm housed with the remainder of the microphone elements in a case attached to the head or body of the wearer. Such a microphone exhibits strong discrimination against ambient noise. Tube resonances are avoided by correct termination of the tubes at the dipole ends, and without intermediate damping. Expressions are developed for the acoustic pick-up characteristics of a dipole close to a small source; for the over-all frequency response of the microphone; and for the random energy efficiency of a dipole as compared with that of one of its poles. Measured and computed characteristics of an experimental microphone are given.
Sound Wave Fields Within Cavities
Authors: Cook Richard K.
Published: September 2005

Cylindrical cavities of circular cross section are extensively used in acoustics in the calibration of microphones and receivers. Such a cavity having plane ends is assumed to be driven by motion of one of the plane ends. Solutions of the wave equation in the form of Fourier-Bessel expansions for the distribution of pressure and particle velocity (as a function of frequency) within the cavity are obtained. The theoretical results are compared with experimental measurements of amplitude and phase of sound pressure within cylindrical cavities.
Propagation of Sound in Lined Ducts
Authors: Molloy Charles T.
Published: September 2005

This paper presents the theory of the propagation of sound in lined ducts, developed from a uni-dimensional wave equation. This approach was first used by Sivian. Differential equations are derived for ducts with similar linings on all walls and for ducts having different linings on each wall. A general formula is given for the attenuation constant and various special cases are discussed. Graphs are given which make the practical calculation of attenuation in ducts convenient. The variation of attenuation constant with duct size is discussed and methods for calculation of acoustical impedance from attenuation measurements given.
The Baffle Effect of the Human Body on the Response of a Hearing Aid
Authors: Hansen Wilbur W.
Published: September 2005

Theoretical and experimental curves are presented to show the change in response of an electronic hearing aid produced when it is worn by a person. Effects produced by placing the aid in different positions on the person and by aids and persons of different sizes are shown and discussed. The effects shown are large enough to warrant their consideration in describing the response of a hearing aid.
The Role of the College and University Hearing Clinic
Authors: Pauls Miriam D.
Published: September 2005

The introductory discussion will deal with the factors that have led to the growth of hearing conservation programs in our public schools, and the establishment of broad rehabilitation facilities for military and civilian personnel with a hearing impairment. The role of the college and the university hearing clinic will be pointed out. It would seem logical that these clinics with their broad affiliations and scientifically trained staffs can serve as the clearing house to utilize the research and facilities of the interrelated fields and thus develop sound therapeutic procedures for the rehabilitation of the acoustically handicapped. The major part of the paper will present in some detail the possible scope of such a hearing program, by discussing the actual program of the clinic with which the speaker is affiliated. The nine clinical services that are available to the hard-of-hearing individual will be described and illustrated with pertinent case material. Implications for future growth and development in the field will be touched upon.
Acoustic Sound Filtration and Hearing Aids
Authors: Grossman Frederick M. , Molloy Charles T.
Published: September 2005

The receiver of a hearing aid is usually connected with the ear by means of an ear mold made from a plastic material. It has been clinical experience that the dimensions of the mold canal influence the acoustical performance of hearing aids. Molds having different canal diameters are connected with a microphone in front of which is a tube approximating the external auditory canal. The other end of each mold is connected to a hearing aid receiver. The acoustical out-put of the receiver through the coupling system is registered by a high speed level recorder. The frequency response curves thus produced are found to be distinctly different for the various molds tested. The behavior of an acoustical high frequency pass filter, inserted between the receiver and the mold is also investigated. A mathematical analysis is made and sound pressures in front of normal ear drums are calculated. It is confirmed by laboratory proof that the acoustic line between receiver and drum is one of the determining factors in the performance of hearing aids. It is consequently an important consideration in the clinical fitting of hearing aids.
Pressure and Field Response of the Ear In Hearing Aid Performance Determination
Authors: LeBel C. J.
Published: September 2005

Since hearing aid receiver acoustical output is commonly measured by an artificial ear wherein a microphone replaces the ear drum, a correction factor must be applied to the artificial ear out-put to relate it to the free field performance of the ear (which is the norm). In other words, substituting pressure operation for free field operation of the human ear changes its frequency response, and this change must be allowed for in determining the corrective characteristics of a hearing aid. The correction is computed and is then compared with subjective determinations. The sum of this correction and one for the baffle effect of the human body wearing the hearing aid transmitter is then computed and it is concluded that such an over-all correction is rather great. In fact, the over-all correction is so great that it cannot safely be neglected in determining or comparing hearing aid characteristics.
Practical Hearing Aid Measurements
Authors: Carlisle R. W. , Mundel A. B.
Published: September 2005

The application of an inertia-controlled sound generator or artificial voice to free-field measurements of hearing aids is described. The distribution of pressure over the person, in the usual places that a hearing aid is worn, is shown, together with data on a simple baffle or artificial body which has been used to simulate the person in pressure measurements of hearing aids. A simple oscilloscopic method of simultaneously observing undue distortion while taking frequency characteristics is described. The construction of a simple artificial mastoid is described, together with its calibration. The testing of individual hearing aids in production is described. A rapidly-sweeping variable-frequency oscillator is electronically controlled and its output applied to each hearing aid. The frequency response of the instrument appears on an oscilloscope screen continuously while the volume and tone controls are varied. Acoustic coupling to the hearing aid is provided by dynamically driven sound sources, close coupled to the hearing aid and compensated to approximate speech-band free-field characteristics.
Measurements of Elastic and Dissipative Properties of Solids by Supersonic Methods
Authors: Siegel Sidney
Published: September 2005

A number of methods used to excite mechanical vibrations of supersonic frequency in solid bars will be described. Among these are the piezoelectric, magnetostrictive, magnetic, and eddy current methods. A large variety of investigations has been carried out with these, and the results, in fields where these methods are particularly suited, will be described. Elastic and dissipative properties of single crystals, and the variation of such properties with temperature, degree of order, magnetic state, etc. will be described.
Absorption and Scattering by Absorbent Cylinders
Authors: Cook Richard K.
Published: September 2005

The absorption and scattering of a plane wave by an infinitely, long circular cylinder, whose axis is perpendicular to the direction of propagation of the wave, are calculated. The surface of the cylinder is assumed to have a known normal acoustic impedance. Absorption measurements made on long cylinders placed in a reverberation room (where the incident wave directions are at all angles to the axes of the cylinders) are comparedz with the computed values.
Influence of Room Proportions on Normal Frequency Spacing
Authors: Bolt Richard H.
Published: September 2005

Proportioning of rectangular rooms to give smooth low frequency response has been guided by an empirical rule: dimensions should be related by ratios of 213 or its powers. An analytical basis for a criterion is being explored. Normal frequencies and their distributions are expressed in generalized terms, using dimensions L, pL, qL, and a dimensionless frequency parameter μ. Distributions of μ can be investigated as a function of proportions (p, q) alone, holding volume constant. A frequency spacing index Ψ is obtained by averaging the ratio of actual to average spaces, weighted by the width of each space. The index Ψ increases with increasing fluctuation from uniform spacing; Ψ = 1 for uniform spacing; Ψ = 2 for random (Poisson) distribution. The index has been evaluated numerically over arbitrary frequency intervals, for a number of room proportions. As expected, Ψ is large (>2) for a cube and other proportions with simple ratios. The index has a small value (<1.5) over ranges of incommensurate p, q values. The “213 rule” gives results in the low region, but is apparently not a unique measure of optimum smoothness. These calculations are approximately correct for basically rectangular rooms having irregularities (e.g., polycylindrical diffusers) appreciably smaller than wave-lengths involved. Room proportions, and the Ψ-criterion, are probably not important when room dimensions are longer than about 10 wave-lengths, as adequate diffusion can then be obtained by shape irregularities and absorption.
Headphone Measurements and Their Interpretation
Authors: Martin Daniel W. , Anderson Leslie J.
Published: September 2005

Methods of acoustical measurement and of data presentation are reviewed, with emphasis on relating headphone data to the requirements of the communication and monitoring fields of application. The conditions of headphone listening are compared to standard and typical listening conditions, as an aid to the interpretation of headphone measurements. Data are shown to demonstrate the importance of statistical analyses of the performance of headphones on different wearers. Some effects of presenting too “artificial” an acoustical load to the receiver during measurement are illustrated. An experiment in artificial ear development is described. The requirements for an improved artificial ear are outlined, based in part upon the experimental work.
A Working Standard for Sound Pressure Measurements
Authors: Massa Frank
Published: September 2005

This paper discusses the necessary requirements to be met in an ideal sound pressure measurement standard. It also describes the design and shows the characteristics of a new microphone that meets these requirements to a greater degree than do existing units which are generally available for use as laboratory standards.
The Absolute Calibration of Condenser Microphones by the Reciprocity Method. A Review.
Authors: Wiener Francis M.
Published: September 2005

The reciprocity method of securing absolute calibrations of condenser microphones offers several important advantages over the thermophone and other methods, which it has effectively displaced in recent years. Both pressure and free-field calibrations can be obtained by this method. Through cooperation between the Bell Telephone Laboratories, the National Bureau of Standards, and the Electro-Acoustic Laboratory, Harvard University, the technique of obtaining absolute pressure calibrations of condenser microphones by the reciprocity method has been perfected and standardized to a gratifying degree of accuracy. Work on absolute free-field calibrations has, in general, progressed at a somewhat slower rate. A review of the work of the past several years is given together with a discussion of some of the problems encountered.
The Problem of Frequency Range in Speech and Music Reproduction
Authors: Glover Ralph P.
Published: September 2005

The specification of a frequency range for a speech or music reproducing system is a complicated matter, with immediate implications as to quality, efficiency, cost, and bulk. The boundaries of the spectra of speech and music are well established but the cost of reproducing these extreme ranges in a near-ideal manner is prohibitive for all ordinary applications. Studies of masking by noise and of hearing ability in the population indicate that statistically there is no real loss in restricting the band width to the order of half that of the original spectrum. Furthermore, it is the opinion of many experienced observers that something less than the complete spectrum yields optimum listening enjoyment and satisfaction. Further restriction of the frequency range entails loss of quality for essentially distortion-free sources with low noise content. The situation is examined for both speech and music with the aid of frequency diagrams for the audio frequency range which show the relationships between cut-off frequencies, band widths and the various criteria of quality and intelligibility. A rational system for departing from the complete frequency range can be developed in the form of a preferred series of reproduction bands based on the liminal intervals of Gannett and Kearney and aural balance relationships. This provides a practical approach to a system of bands with definite but just-perceptible quality differences between them, which is a most useful concept and one which would greatly aid in the engineering of sound systems. In the case of amplified speech communication, where the emphasis shifts from quality to effectiveness from a communications viewpoint, articulation, power economy, directivity and similar considerations, different bands are necessary and possible frequency ranges are discussed.
Factors Governing the Intelligibility of Speech Sounds
Authors: French N. R. , Steinberg J. C.
Published: September 2005

This paper discusses the factors which govern the intelligibility of speech sounds and presents relationships which have been developed for expressing quantitatively, in terms of the fundamental characteristics of speech and hearing, the capability of the ear in recognizing these sounds. The success of the listener in recognizing and interpreting speech sounds depends on their intensity in the ear and the intensity of unwanted sounds that may be present. The relationships presented in this paper deal with the intelligibility of speech sounds as a function of these intensities in the different frequency ranges of speech. Results calculated from these relationships are compared with observed results for a variety of systems.
The Musical Scale of Just Intonation
Authors: Urquhart Noel
Published: September 2005

The musical scale of Just Intonation in one tonality (key) as evolved since early Greek times, may be defined as consisting of four tonal notes: subdominant, tonic, dominant and supertonic at intervals of fifths (3/2) apart with four major notes, each an interval of the major third (5/4) above these tonal notes and with four minor notes, each an interval of the major third (5/4) below these tonal notes, all brought within the limits of an octave (2/1). Assuming the frequency of the keynote of C equals 260.74 cycles per second, we obtain the following scale of frequencies:

Frequency Frequency

Note Name of Interval Ratio to Prime Cycles/Second

C Prime (Tonic) 1/1 1.0000 260.74

D♭ Subdominant Minor Sixth 16/15 1.0667 278.13

D Second (Supertonic) 9/8 1.1250 293.33

E♭ Minor Third 6/5 1.2000 312.89

E Major Third 5/4 1.2500 325.93

F Fourth (Subdominant) 4/3 1.3333 347.65

F♯ Dominant Major Seventh 45/32 1.4063 366.69

G Fifth (Dominant) 3/2 1.5000 391.11

A♭ Minor Sixth 8/5 1.6000 417.18

A Major Sixth 5/3 1.6667 434.57

B♭ Minor Seventh 9/5 1.8000 469.33

B Major Seventh 15/8 1.8750 488.89

C Octave (Tonic) 2/1 2.0000 521.48

In connection with research and experimental work on an electronic type piano, the writer devised the Electronichord as described in the American Physics Teacher, February, 1934. Using two Electronichords, it was possible to study the relations that exist between the harmonic overtones of two string tones tuned any harmonic or tempered interval apart. These experiments, among other things, audibly demonstrated the importance of the harmonic intervals to satisfy the discriminating musical ear. The purpose of this paper is to offer a mathematical approach in demonstrating that the musical scale of just intonation is a fundamental acoustical measurement.
Aero-Otitis Media in Submarine Personnel
Authors: Haines Henry
Published: September 2005

Careful pre- and post-examination of several thousand men passing through the Submarine Escape Training tank at New London reveals that about 30 percent have aero-otitis media as a result of exposure to the high pressure chamber. This agrees rather well with Fowler's figure of 22 percent among fliers in England. We believe the cause of the condition in most instances to be blockage of the Eustachian tube by hyperplastic adenoid tissue. A description of some of the effects of pressure on the ear is given from extensive data collected with the otoscope and with the nasopharyngoscope. A description is given of the effects of various types of treatment, principally radium applied to adenoids, x-ray, astringent nose drops, and psychological prescription.
Musicology, the Stepchild of the Sciences
Authors: Pepinsky Abe
Published: September 2005

The musicologist wants the respect of both the musician and the scientist, but the musician frowns upon him because, although he is supposed to know all about music, he seems to derive no sensory pleasure from it, and the scientist looks askance at the sort of stuff the musicologist busies himself with and his methods of approach. The question might well be asked: “What is Musicology?” Briefly, it purports to be the scientific study of music. Musicology reaches into many fields and someone facetiously remarked that it includes practically everything that lies outside of the personality of the performer and the purely technical aspects of his performance. But why exclude the personality of the performer or even the consideration of the technical aspects of the performance? Surely the personality of the performer plays an important role in presenting the musical thought to an auditor Likewise, the technical aspects of performance lend conviction to the meaning of the music. It would seem therefore, in considering music, that every possible phase of the art should be subjected to scrutiny and, if this be accomplished by utilizing acceptable scientific procedures, the musicologist need not be apologetic for his field of endeavor. Some of the areas explored will be reviewed together with the tools at the musicologist's command. New fields to conquer and the advantages of novel treatment will also be suggested.
Sound Conduction in the Head and in the Adjacent Regions
Authors: Jellinek Agusta
Published: September 2005

Sound conduction through bone and tissues varies according to the point of sound transmission. Every region of the head as well as neck and upper part of thorax has a conduction optimum for a certain pitch range, while other tones require greater intensities to be transmitted. Not only bony structures but also other tissues transmit sound at comparable intensities (for instance, throat and cheeks). The mastoids are not always the optimal regions of transmission, some people show better transmission from the temporal or occipital bones. Bone conduction varies far more with time than air conduction. For practical purposes these findings have some bearing on the use of hearing aids. Testing the bone conduction of the mastoids only gives an incomplete picture of the patient's possibilities. He may be able to hear better from another point. In some cases the hearing aid might be worn invisibly (on the skull, throat, occipital prominence). The acoustic selectivity of the head should be used in fitting a hearing aid.
Clinical Phenomena in Conductive Media: The Individual Earpiece
Authors: Schier Mayer B. A.
Published: September 2005

A hearing aid may be well designed and produced, acoustically and mechanically, but its optimum efficiency will depend upon delivery of instrument characteristics to the drum or middle ear structures by an earpiece. The initiated practice of fitting every air conduction hearing aid with an individual earpiece is an acceptable and generalized practice. This paper is concerned with clinical and experimental experiences on the effects produced by auditory prosthesis or the individually made earpiece as acoustic couplings and conductive medias; with divisional considerations of the many factors involved which may favorably or adversely induce maximum correlation between instrument and deafened ear.
The Cathode-Ray Translator
Authors: Riesz R. R. , Schott L.
Published: September 2005

A system has been developed whereby speech analysis patterns are made continuously visible on the moving luminescent screen of a special cathode-ray tube. The screen is a cylindrical band that rotates with the tube about a vertical axis. The electron beam always excites the screen in the same vertical plane. Because of the persistence of the screen phosphor and the rotation of the tube, the impressed patterns are spread out along a horizontal time axis so that speech over an interval of a second or more is always visible. The upper portion of the screen portrays a spectrum analysis and the lower portion a pitch analysis of the speech sounds. The frequency band up to 3500 cycles is divided into 12 contiguous sub-bands by filters. The average speech energy in the sub-bands is scanned and made to control the excitation of the screen by the electron beam which is swept synchronously across the screen in the vertical direction. A pitch detector produces a d.c. voltage proportional to the instantaneous fundamental frequency of the speech and this controls the width of a band of luminescence that the electron beam produces in the lower part of the screen. The translator has been used in a training program to study the readability of visible speech patterns.
Basic Phonetic Principles of Visible Speech
Authors: Kopp G. A. , Green H. C.
Published: September 2005

The phonetic principles basic to the legibility and interpretation of visible speech are discussed in this paper along with the unique characteristics which differentiate the patterns of individual sounds and sound groups. The visible patterns are interpreted in terms of physiological phonetics and the types of modulation used by the speaker in producing the sounds. A threefold comparative classification is developed, including physiological, audible, and visible descriptions of the sounds used in American speech. From the analysis and interpretation of the visible patterns, suggestions are made concerning the inclusion of several sound variations that heretofore have not been of interest generally to phoneticians, and a reconsideration of the classification of some sound units. In analyzing or reading speech patterns, problems arise from the innumerable and varied patterns formed by sound combinations. A key and system for the recognition and interpretation of these varied patterns which result from the transitional movements between sounds are presented in some detail. Similarities and differences apparent in the audible speech of different individuals are portrayed in the present visible patterns to a limited extent. While the limitations in the translation of the range and variation of frequency and intensity, and of vocal quality, simplify the patterns, they also tend to obscure the phonetic factors which are essential in differentiating individual speakers. The terminology developed for visible speech is introduced as it is required in the course of this discussion of the basic phonetic principles of visible speech.
The Attenuation of Sound in Fogs and Clouds
Authors: Knudsen Vern O.
Published: September 2005

The absorption of sound in artificial fogs or clouds has been determined by measuring the rates of decay of sound in a reverberation room, first when there is no fog in the room (with the relative humidity nearly 100 percent) and then when an artificial fog of known density and particle size is in the room. For a fog containing 2.0×10−6 g/cm−3 of water and a mean droplet diameter of 0.0012 cm the attenuation owing to the fog increased from 0.018 db/m at 512 cycles to 0.032 db/m at 8 kc. For a fog of larger droplet size the attenuation was somewhat less. The attenuation is, to a first approximation, in agreement with the value predicted by a theoretical formula developed by Sewell, and independently by Epstein. It is possible therefore to predict approximately the attenuation of sound in fogs or clouds if the density (or visibility) and the particle size of the fog or cloud are known. Conversely, the composition of fogs and clouds can be investigated by measurements of audibility.
Ultrasonic Propagation in a Uniform Atmosphere
Authors: Givens M. P. , Nyborg W. L. , Pielemeier W. H. , Saby John S.
Published: September 2005

The atmosphere is referred to as being “uniform” when there are in it no large scale temperature or wind gradients. Usually under these conditions the variation of the ultrasonic intensity with distance from a small source, such as a whistle, can be explained simply in terms of the inverse square law, together with a negative exponential law which accounts for losses due to absorption. This is indicated by the rectilinearity of so-called Δ curves, obtained by subtracting the loss due to assumed spherical divergence from the total transmission loss and plotting the difference Δ in decibels against distance in rectangular coordinates. The slope of such a curve, when it is rectilinear, equals the absorption coefficient in db/ft. At times in unforested areas Δ curves are not rectilinear, and in dense forests they never are. This may be explained in terms of scattering. A theory of propagation in scattering media has been developed which yields a method of computing the separate effects of scattering and absorption. Values obtained for absorption coefficients are consistent with those reported by other workers.
The Design of Anechoic Sound Chambers
Authors: Beranek Leo L. , Sleeper H. P.
Published: September 2005

Generalized specifications for the optimum design of highly efficient linings for free-field (anechoic) sound chambers assuming the use of Fiberglas PF insulating board formed into wedges are presented in terms of either (a) lowest frequency at which 99 percent or better absorption is desired or (b) maximum depth of treatment which may be installed in the room. The application of these specifications to the construction of two rectangular rooms is shown and inverse square law measurements performed in two completed chambers, one large and one small, are presented. In the larger chamber, the deviations from inverse square law are within ±0.3 db out to 10 feet and ±1.0 db out to 30 feet from a point source of sound. In the smaller, the deviations are within ±1.0 db out to 10 feet.
Measurement of the Transmission of Sound through Lightweight Structures
Authors: Wallace R. L. , Dienel H. F. , Beranek Leo L.
Published: September 2005

This paper discusses a method for measuring the effectiveness of lightweight wall structures and thin windows in attenuating transmitted sound. Samples approximately 18 inches square are used. The results of measurements on airplane side wall structures (including acoustical treatment) are mentioned briefly.
The Effect of Non-Uniform Wall Distributions of Absorbing Material on the Acoustics of Rooms
Authors: Feshbach Herman , Harris Cyril M.
Published: September 2005

The acoustics of rectangular rooms whose walls have been covered by the non-uniform application of absorbing materials is treated theoretically. Using appropriate Green's functions a general integral equation for the pressure distribution on the walls is derived. These equations show immediately that it is necessary to know only the pressure distribution on the treated surfaces to predict completely the acoustical properties of the room, such as the resonant frequencies, the decay constants, and the spatial pressure distribution. It was found useful to introduce a new concept, that of “effective admittance,” to express the results for the resonant frequency and absorption for then the amount of computation is reduced and the accuracy of the results are increased. The absorption of a patch of material was found as a function of the position of the absorbing material and was checked experimentally for a convenient case, an absorbing strip mounted on the otherwise hard walls of a rectangular room. Particular attention is given to the case where the acoustic material is applied in the form of strips. Approximate formulas are obtained which permit estimates of the diffusion of sound in a non-uniformly covered room. In agreement with experience, these equations show that diffusion increases with frequency and with the number of nodes on the treated walls. The “interaction effect” of one strip on another is shown to decrease with an increase of the number of nodes.
The Acoustics of Coupled Rooms
Authors: Harris Cyril M. , Feshbach Herman
Published: September 2005

There are many examples of acoustically coupled rooms where ordinary reverberation formulas do not apply, for example: theaters, auditoriums, or churches connected to foyers, anterooms, hallways, or organ chambers. The theory of coupled rooms has been given by Davis and by Eyring based on the assumptions usually made in deriving reverberation-time formulas: diffuse distribution of the flow of sound in the room and continuous absorption at the boundaries. Eyring showed experimentally that these conditions are not always fulfilled, indicating that the problem should then be considered from the wave point of view. Experimental data are presented showing how the frequency and damping constant (a measure of the absorption) for a number of normal modes of vibration of a model room vary with the size and position of a coupling window between two chambers. These results are then correlated with wave theory, treating the acoustics of coupled rooms as a boundary value problem.
Underwater Noises Due to Marine Life
Authors: Loye Donald P. , Proudfoot Don A.
Published: September 2005

The widespread use of underwater acoustical devices during the recent war made it necessary to obtain precise information concerning ambient noise conditions in the sea. Investigations of this subject soon led to the discovery that fish and other marine life, hitherto generally classified with the voiceless giraffe in noisemaking ability, have long been given credit for a virtue which they by no means always practice. Certain species, most notably the croaker and the snapping-shrimp, are capable of producing noise which, in air, would compare favorably with that of a moderately busy boiler factory. This paper describes some of the experiments which traced these noises to their sources and presents acoustical data on the character and magnitude of the disturbances.
Effects of Conditions of Use upon Performance of Hearing Aids
Authors: Nichols R. H.
Published: September 2005

Because of the extreme variety of conditions under which a hearing aid may operate when in use, it is desirable to determine the character and ranges of magnitude of differences between the performance of an instrument when worn and its performance as measured by the conventional laboratory procedures. The principal differences are due to the following factors: (1) differences between the 2-cc coupler and human ears, (2) the snugness of fit of the molded earpiece, (3) the size and shape of the acoustical channel of the earpiece, (4) the acoustic baffle effect of the wearer's person, (5) clothing covering the hearing aid, and (6) the nature of the sound field. These effects have been investigated by techniques described in an earlier paper. In the order listed, it is found that, (1) in many cases the 2-cc coupler does not represent the ear as well as might be desired, (2) a loosely fitting earpiece will reduce the response at low frequencies and will allow some earphones to distort low frequency signals, (3) differences among about 40 commercial earpieces from several manufacturers did not cause important differences in the response, (4) the body-baffle effect consists of several characteristic peaks and valleys in the response, the effect being less marked in a random field than in free field, (5) the effect of clothing over the instrument is to reduce the response in the frequency range 800–3000 c.p.s. and (6) differences between field and pressure sensitivities of the ear are of sufficient magnitude to be considered when comparing performance of aided and unaided ears.
Low Impedance Ear Shields for Explosive Pulses
Authors: Pielemeier W. H.
Published: September 2005

Early in 1941 the writer designed an ear shield which should enable soldiers to hear conversation and commands about as usual but which should stop sudden pressure or suction pulses. Occasional improvements were made and more than a year ago a patent application was made. The first models of the ear shield had a hard plastic shell containing a thin stiff plate floating between two valve seats, so as to permit alternating air flow of small amplitude around its edges. A sudden pulse forced the plate against the appropriate valve seat, thus protecting the ear drum. About 1942 the rigid shell was modified to fit into a soft adapter similar to the present N.D.R.C. Type V-51R Ear Warden. Other soft models had a very small spot made quite thin at the middle of a thicker closing septum. The thin spot kept the attenuation low for sounds of low intensity. The decrement ranged from 5 to 10 db for frequencies below 1000 c.p.s. Beyond this frequency it reached a maximum of 20 db in the range up to 12,000 c.p.s. Most other ear protectors impede all sounds as much as possible.
A Standard Scale of Speech Sounds Defined in Radio
Authors: Benedict Claire
Published: September 2005

In a previous paper (1943), on “a new anatomy of the human voice,” this member described analogies to structure and action in certain types of musical pipes, which will be concluded in this paper with a new technique: comparable to “blowing and fingering” and the preliminary process of “voicing.” The last involves a specific aspect of hearing aroused in this instance by radio: confirming the “feel” of structure and action by sight as well as “by ear”; identifying the so-called singing voice in the natural mechanics of speaking; and defining these sounds in sequences comparable to a standard scale to which all voices, all languages, conform, as will be shown by simple alphabetic rearrangements. It seems significant, too, that this advance in the cultural arts has come through “coordinated research” in the natural sciences: although unknown as such until the war made a name for it.
Correlation of the Audio Characteristics of Communication Systems with Measured Articulation Scores
Authors: Beranek Leo L.
Published: September 2005

Based on a procedure advanced by Steinberg and French, a method for calculating the ability of a communication system to transmit speech intelligibly has been devised. The method has been applied to the calculation of the performance of seventeen different communication systems for which articulation data are available. The results indicate that it is possible to estimate from physical data the performance of a system in an assumed ambient noise field, and to determine how to modify the characteristics of the system to achieve better results.
Training Personnel for Voice Communication
Authors: Black John W. , Mason Harry
Published: September 2005

A research program was conducted to discover the feasibility of improving effectiveness in AAF voice communication through training. The results indicated marked improvement in message transmission and led to setting up systematic instruction in voice. The topics and procedures of the training were ones that yielded improvement in intelligibility when studied in isolation with AAF flying personnel as experimental subjects. This paper summarizes the rationale of the training program and the effects of the training.
Effects of Distortion on the Intelligibility of Speech at High Altitudes
Authors: Miller G. A. , Mitchell S.
Published: September 2005

Sounds spoken into the closed cavity of an oxygen mask at high altitudes differ substantially in quality and intensity from normal speech at sea level. The mask imparts a low, “booming” quality to the speech. Tests with a wide variety of frequency response characteristics show that low-frequency attenuation improves the apparent quality without modifying appreciably the intelligibility of the speech. Also, the intensity of the speech signal varies considerably as a function of altitude, and talkers exhibit large individual differences in their ability to compensate for altitude effects. The range of speech levels under all conditions of altitude and talker differences is between 20 and 30 db, and for most installations some form of compression should be used to reduce this range. Sharp, symmetrical limiting (“peak clipping”) is the most satisfactory method, since it combines the advantages of compression with the advantages of premodulation peak clipping for AM radio-telephony.
The Effects of High Altitude on Speech and Hearing
Authors: Rudmose H. W. , Clark K. C. , Carlson F. D. , Eisenstein J. C. , Walker R. A.
Published: September 2005

Speech energy in twelve contiguous frequency bands, each 250 mels wide, has been measured at simulated altitudes ranging from sea level to 40,000 feet in intervals of 5000 feet. Measurement of speech energy at 35,000 feet was also made with the subject talking into the open air of the altitude chamber. In any frequency band, the energy decrement of vowels and semi-vowels, expressed in decibels, varies uniformly with altitude; however, there is little or no change in the energy of unvoiced consonants with altitude. The number of words per breath which a subject can say while maintaining constant sound pressure output is proportional to air density. The threshold of hearing was measured at sea level and 35,000 feet, and no shift in threshold sensitivity was observed.
The Directional Characteristics of a Free-Edge Disk Mounted in a Flat Baffle or in a Parabolic Horn
Authors: Slaymaker Frank H. , Meeker Willard F. , Merrill Lynn L.
Published: September 2005

In the attempt to obtain a sharp beam of supersonic sound from a parabolic horn, it became apparent that the sharpness of the beam was a function of the mode of vibration of the diaphragm exciting the horn. Experiments showed that the sharpest beams with the smallest side lobes were obtained when the diaphragm was radiating most of the energy toward the side walls of the horn rather than toward the mouth. Experiments with a free-edge disk for a diaphragm connected the wide angle radiation with the two nodal circle mode of vibration of the disk. Comparison between directional patterns measured with the disk in a flat baffle and calculated patterns confirmed the correlation between the wide angle radiation and the two nodal circle mode. Further analysis indicated that similar radiation patterns could also be obtained from one and three nodal circle modes of vibration. In the analysis, the differential equation for the vibration of a thin plate is solved for a free-edge circular disk assuming circular symmetry and considering a driving force applied at an arbitrary circle concentric with the disk. The dynamic curve of the disk is given for any frequency in the form of a series of the normal modes of the disk, and the directional pattern of the radiation from the disk mounted in an infinite baffle is calculated. The calculations have been so systematized and tabulated that the dynamic curve and directional pattern for any disk and frequency can be calculated quite readily. The analysis is sufficient to predict the disk diameter and thickness required for the one, two, or three nodal circle modes and for any frequency, when the disk is mounted in a flat baffle and when the maximum radiation is placed at an arbitrary angle from the axis. On the basis of the analytical predictions, a disk has been made to give the wide angle radiation required with the disk vibrating with one nodal circle instead of two nodal circles as discovered experimentally.