bluuebunny/crossref_metadata_2025 huggingface dataset:
Apparatus for Measuring the Total Sound Power Radiated by Small Sources
Authors: Hanson R. L. , Boardman E. M.
Published: September 2005

The measurement of the total power emitted by a sound source which does not radiate uniformly in all directions often presents a major problem. The simple method of measuring the power in terms of the energy level established in an enclosure involves factors which are detrimental to accuracy. The more reliable determination by means of the average intensity in all directions from the source usually requires an unreasonable amount of work. This paper describes equipment which by electrical and mechanical means integrates the intensity over a sphere about the source and gives a direct reading of the total sound power.
A Method of Measuring the Total Output of Speakers
Authors: Green Darrell B.
Published: September 2005

This paper presents a method of measuring the total output of speakers, which is analogous to the globe photometer method of measuring the total light flux from a lamp. The speaker is placed inside a hollow sphere with the measuring microphone located in a small hole in the wall of the sphere. A single measurement at the microphone window gives a value proportional to the total output of the speaker. In order to break up standing wave patterns which form in the sphere the frequency of the oscillator used to drive the speaker is wobbled above and below the steady value. Theory is developed to show that in order to smooth out standing waves a constant frequency deviation is required regardless of the fixed frequency instead of a certain percent of the frequency at which the measurement is made. Data are given comparing this method with measurements made out of doors on a speaker.
Absolute Sound Pressure Measurements with Tourmaline
Authors: Sivian L. J.
Published: September 2005

The crystal is cut as a thin circular disk, its faces normal to the optical axis. Except for two fine, very flexible electrodes by which it is suspended from the first stage of the measuring amplifier, the crystal is mechanically and acoustically free. The a.c. electric potential generated by the crystal under the action of the alternating sound pressure in a gas is shown to be the resultant of the piezoelectric and pyroelectric effects. A formula relating the magnitudes and phases of these two components as functions of frequency is derived. This gives the resultant absolute sensitivity of the crystal over the audiofrequency range, if the static or low frequency values of certain crystal constants are known. A practical procedure for the determination of these constants is described. Disks of 0.7 cm diameter and 0.07 cm thickness have been used for measurements up to 15,000 c.p.s. The frequency range is swept through continuously, and the crystal output is obtained as a continuous “level recorder” graph. The limitations of the method, particularly as to the signal-noise ratio, are pointed out.
An Approximate Theory of Tracing Distortion in Sound Reproduction from Phonograph Records
Authors: Lewis Willard D.
Published: September 2005

By means of a perturbation method a general formula is derived giving, as an expansion in powers of the amplitude, the motion of the center of a circle sliding on a warped surface representing any generalized recorded signal having a bounded spectrum. This formula must approach exactness for small amplitudes and is shown to agree substantially with the previous more exact analysis of Pierce and Hunt for a sinusoidal signal. The formula is then used to obtain general approximate expressions for tracing distortion in reproduction from both vertical and lateral cut records. The analytic expression for tracing distortion makes it possible to give a quantitative discussion of cross modulation products and permits a comparison between harmonic and cross modulation distortion for typical recorded signals. Rerecording as a method of reducing distortion is discussed, including the effect of the upper cut-off frequency to the recording channel.
Sound Measurement Objectives and Sound Level Meter Performance
Authors: Barstow J. M.
Published: September 2005

The standardization of sound level meters has considerably improved conditions in the field of sound measurement although several characteristics thought to be desirable in visual indicating sound measuring devices are not fully realized in instruments conforming to the present standards. The extent to which certain sound measurement objectives have been realized in present sound level meters is discussed. Further work will undoubtedly be necessary before some of these objectives may be more completely realized. Present indications are that sound level meter limitations in regard to the approximation of sound jury loudness levels will be difficult to remove and at the same time retain reasonable apparatus simplicity. Some consideration is given to possible courses of action in regard to such limitations.
Acoustical Work in Aircraft Engine Test Houses
Authors: Brennan Martin J. , Janke Frank H. , Jacobson Victor
Published: September 2005

Fifteen years ago saw the introduction of refinements in aircraft engine test equipment coincidental with growing production. It became necessary to build specially constructed houses for engine testing. As requirements of government and private specifications made continuous testing over periods of several days obligatory, incidental noise ranging up to one hundred forty decibels at the source became a growing nuisance in congested areas. Installation of sound absorbing materials presented real and unique problems because of the limitation inherent in the function of the building. Uninterrupted intake and exhaust airflows were necessary and passages had to be left open to the elements. Air velocities over one hundred miles an hour were involved. In addition, rigid fireproof requirements and maintainability were complicating factors. After early false starts with various absorbent media, porous and sound absorptive stone was found to be a practical material for the purpose. Arrangement of material has been approached in several ways, always with the requirement of uninterrupted airflow in mind. Honeycomb arrangement was first used, then ribbon walls of flat stone and later of beveled and perforated stone, as well as variations in the arrangement of the passages themselves, some being horizontal and some vertical. In the period of the last few years the aircraft engine manufacturers and the large users of engines such as the U. S. Army and Navy and the transport companies have become more conscious of the noise problem, partly due to complaints of nearby municipalities. The number of installations has grown and many noise readings have become available indicating the efficiency of various materials and arrangements of those materials. In many cases noise levels have been recorded in the test chamber itself, on top of the exhaust and intake passages, at various levels in these passages, as well as at varying distances from the test buildings and in varying weather conditions. Because of the variables such as engine horse power, propeller diameter, propeller tip speed and others, the results of comparative tests are indicatory rather than conclusive.
Acoustical Investigations of Joseph Henry as Viewed in 1940
Authors: Snyder Wilbert F.
Published: September 2005

Joseph Henry's investigations in the field of building acoustics published in the Reports of the Smithsonian Institution, 1856, have received only scanty attention. A versatile and resourceful man, Henry conducted experiments and expressed himself in such a manner that his writings show a clear concept of the basic principles of auditorium acoustics. A review of Henry's publication will be presented and a comparison made with our present knowledge of acoustics. Since these investigations were carried out in the locality of the Smithsonian Institution, reference made to them at a Washington meeting may be of interest to members of the Society.
Variable Boundary Impedance for Room Acoustics Investigations
Authors: Bolt R. H. , Brown R. L.
Published: September 2005

A method has been developed for obtaining a wide range of impedance values, both as to magnitude and phase angle. In one form, a variable impedance unit consists of (1) a steel face with perforations of variable area (obtained by overlapping identically drilled plates), (2) a “resistance element”—a layer of acoustic absorbent material with appropriate flow resistance, (3) a “mass element”—a solid board through which small channels are drilled at uniform spacing over the whole surface, and (4) a “stiffness element”—a cavity of variable depth backed by a rigid steel plate. The behavior can be predicted approximately by circuit theory, and is essentially that of a damped resonator. A unit with face 20×20 cm has been built and calibrated, for pure tones at several frequencies, using a straight acoustic impedance line of the same sectional area. The useful range appears to include phase angles from −45° to +45° and magnitudes of Z/ρ0c front 0.4 to 10, for frequencies between 250 and 850 c.p.s. Normal incidence “absorption coefficients” of 99 percent have been obtained. Modifications of the structure are being developed with a view to extending the frequency range and general applicability of controlled impedance. The variable impedance is being applied to a number of detailed experiments relating to the influence of boundary impedance on normal modes, and correlated with room acoustics theory.
The Dependence of Sound Transmission Measurements on Microphone Position
Authors: London Albert
Published: September 2005

In the customary method of determining the transmission loss of a wall or floor partition it is necessary to measure the difference in sound levels existing in two rooms which have the partition as a separating wall. Also, the ratio S/A2, where S is the transmitting area of the partition and A2 the total sound absorption of the receiving room, must be known. It was found that despite adequate precautions the sound energy density in both test rooms was not entirely uniform. In particular, on the quiet side a sharp drop in level occurred within a region of 2 or 3 feet from the panel face. The sound energy density existing at the panel face on the quiet side may be considered to consist of a direct component arising from energy radiated directly off the panel and a reverberant component arising from reverberant energy existing throughout the entire room. On this basis a formula was computed which allows one to determine transmission losses by restricting measurements on the quiet side to positions at the panel face. The formula was found to be in very good agreement with experimental results over a wide range of variation of A2. All of the above data were obtained with a pressure microphone. A number of similar measurements, using a pressure gradient (ribbon) microphone of special design, were also taken. The results so obtained were independent of the amount of absorption in the room and the area of the panel, although to secure the actual transmission loss a constant correction is required.
The Absorption of Noise in Ventilating Ducts
Authors: Sabine Hale J.
Published: September 2005

This paper describes an experimental study of noise in ventilating ducts and the quieting effect of a sound absorbing duct lining. The attenuation in decibels per foot length of duct was measured directly, using a loudspeaker as a sound source, for both lined and unlined rectangular ducts of various shapes and sizes, and for various frequencies. The relation of the attenuation to the cross-sectional dimensions of the duct and to the absorption coefficient of the lining was found to agree more closely with the formula derived theoretically by Sivian than with any of the other formulae which have been proposed. Measurements were also made of the noise of a fan of 5000 c.f.m. capacity connected to the system. It was found that the noise generated by the friction of the air against the inside walls of the duct, either lined or unlined, for velocities as high as 1500 f.p.m., was negligible in comparison with the noise created by the fan blades. Tests were made on the quieting effect and the resistance to air flow of a special baffle structure introduced in the system. The frictional resistance of the absorbent lined duct, as compared to that of the unlined duct, was also measured.
Effect of Painting on the Sound Absorption of Acoustic Materials
Authors: Chrisler V. L.
Published: September 2005

A brief discussion is given of the properties of a material which cause it to absorb sound. Photographs are shown and the results of sound absorption measurements before and after painting are given for a number of different types of material. A brief discussion is given of the kind of paint which can be used and how it should be applied.
Sono Radio Buoys
Authors: Dorsey Herbert Grove
Published: September 2005

When hydrographic surveying is carried beyond visual control it is necessary to have other methods to determine the ship's position. Radio acoustic ranging supplies the method and sono radio buoys, placed at known locations, emit radio signals when actuated by subaqueous sounds. Knowing the velocity of sound in water, a system of triangulation can be extended whereby the ship's position may be determined upwards of a hundred miles from shore. Sono radio buoys consist of one or two 50-gallon steel drums supporting a radio antenna above and a stabilizing counterweight below. A sound pick-up is suspended 30 to 80 feet below the buoy, inside of which there is an audioamplifier favoring low frequencies, connected to the pick-up. When the survey ship explodes a small bomb of TNT in the water a mark is made on a chronograph tape on the ship and the sound travels to the pick-up where it is amplified and actuates transmitters in the different buoys. Radio signals returning to the ship are recorded on the same chronograph tape. Measured to 0.01 second, these time intervals enable the plotting of the ship's position.
The Absorption of Sound in CO2, N2O, COS, and in CS2, Containing Added Impurities
Authors: Knudsen V. O. , Fricke E.
Published: September 2005

We have investigated the absorptive characteristics of CO2, N2O, COS, and CS2 as influenced by the addition of certain gases, such as H2, H2O, H2S, CH3OH, etc., acting as “catalysts.” These catalysts shift the absorption bands to higher frequencies; the magnitudes of these shifts yield information respecting (1) the frequency at which each pure gas has its maximal absorption, and (2) the nature of the molecular collisions involved, and especially the effectiveness of these collisions in disturbing the vibrational states of the absorptive molecules. The results indicate that at atmospheric pressure and 23°C the absorption maxima for pure CO2, N2O, COS, and CS2 are at 20 kc, 153 kc, 287 kc, and 379 kc, respectively. The shift in each case is proportional to the concentration of the added catalyst. The addition of one percent of H2O to CO2 shifts the absorption band for CO2 2250 kc; similarly, one percent of H2O shifts the CS2 band 2460 kc, the COS band 4200 kc, and the N2O band 427 kc. One percent of the other impurities produced shifts which varied from 6 to 1500 kc. Transition probabilities for the above gases have been calculated; the results will be discussed.
Ultrasonics and Elasticity
Authors: Ludloff H. F.
Published: September 2005

Previously a method of investigating elastic properties of solids has been devised. The method involves the piezoelectric excitation of spatial ultrasonic wave gratings and the irradiation of the solid with visible light. Interference patterns obtained in this way uniquely determine the elasticity and symmetry behavior of the solid. If the solid is transparent, the action on the light is that of a spatial grating. If the solid is opaque, the interference pattern appears in reflected light, the diffraction taking place on the oscillating surface. From our interference pictures one can determine simultaneously all the elastic constants of a solid with an accuracy hitherto unattained. By this method investigations on the temperature dependence of the elasticity are performed here. From the viewpoint of the solid state theory we can derive the general temperature law which the elastic parameters of solids must obey. By means of two thermodynamical identities and a quantum theoretical equation of state we get at low temperatures a T4 law, at high temperatures a T law for the elastic parameters; this is in satisfactory agreement with the modern measurements.
Ultrasonic Study of Phase Transition Near the Critical Point
Authors: Hubbard J. C. , Herget C. M.
Published: September 2005

The persistence of certain aspects of phase transition in the region above the critical point has been discussed from a thermodynamic point of view by A. Eucken, who pointed out the characteristics which might be expected of some of the differential coefficients, for example the isothermal modulus (∂p/∂V)T for p and T values in apparent continuation of the vapor pressure curve above the critical point. The continuity of p and T values through the critical point is strikingly brought out by measurements made by the junior author of the velocity of sound in CO2. The isothermal curves for sound velocity as a function of pressure show sharp minima both below and above the critical point. The p and T values for these minima below the critical point lie on the vapor pressure curve, while those above the critical point are on a continuation of the vapor pressure curve.
Problems in the Analysis of the Tone of an Open Organ Pipe
Authors: Northrop P. A.
Published: September 2005

An open organ pipe and a microphone are rotated about an axis making an angle of about 40 degrees with the vertical in a room acoustically treated essentially as described by Bedell. Using a General Radio Type 636-A wave analyzer, measurements of the first five partials are made in the following positions: (a) on the axis of the pipe, (b) on a line perpendicular to the axis at a point midway between the mouth and the end and (c) on a line parallel to the axis of the pipe at a distance of 112 inches from the body of the pipe. An interference pattern is obtained approximating that expected if the mouth and end are treated as point sources. It thus appears that even with negligible reflections there is no single location in which measurements can be made which will accurately represent the performance of the pipe. Possibly the most significant results may be obtained by rotating the microphone and pipe in a small room with highly reflecting surfaces. An experiment to test this is in progress.
Roaring Tinnitus and Deafness due to Vitamin E Deficiency
Authors: Josephson Emanuel M.
Published: September 2005

A type of progressive deafness associated with roaring ear noises occurs in persons suffering from vitamin E deficiency. It can be relieved permanently by the administration of vitamin E, wheat-germ oil or alpha-tocopherol together with a diet rich in substances from which the body can produce creatine. In the early stages of this condition transient relief can be obtained by the administration of prostigmine, but it soon recurs. Under the vitamin E treatment the tinnitus clears up completely and the deafness improves materially. The mechanism of action of this vitamin, which is popularly termed the fertility vitamin, is in these cases the same as that which I described last year in myasthenia gravis, progressive muscular dystrophy and in other neuro-muscular diseases, some phases of which were recently confirmed by Dr. Franklin Bicknell. The vitamin raises the kidney's threshold of excretion and stops the loss from the body of creatine, which is essential for muscular contraction, strength and tone. The action on the tensor tympani and stapedius muscles of the middle ear is responsible for the relief of the tinnitus and deafness. Incidentally there is evidence that the action of the vitamin on fertility is dependent on its action on the muscles involved in procreation. The variations in the excretion of creatine are a good index of the body's supply of the vitamin.
Relief of Conduction Deafness in Progressive Deafness
Authors: Josephson Emanuel M.
Published: September 2005

Data presented before this Society almost a decade ago made it clear that disease changes in the eardrum in progressive deafness contribute to the loss of hearing by increasing their resistance to the transmission of sound into the middle ear. This increased resistance can be eliminated by incision or excision of the eardrum. Further studies have shown that the results obtainable by the slight and simple operations on the eardrums fully equal those obtained by the grave and dangerous Sourdille “fenestration” operation or its various modifications. These operations do not effect a cure of the deafness but merely offer relief and temporary improvement of hearing. The disease process that causes the deafness continues to operate unless discovered and arrested. The effect of incision in various parts of the eardrum on the hearing raises the interesting acoustical problem of the exact mode of its transmission of sound. It raises the question whether the tympanic membrane may not be considered as consisting of several membranes resonating selectively to different frequencies; and poses the question of the modification of transmission by the action of the tensor tympani muscle. The inflation test and its influence on the transmission of low frequencies is described.
The Ultramicrometer as a Vibration Meter
Authors: Hubbard J. C. , Hambleton Philip
Published: September 2005

The L, C circuit of a radiofrequency oscillator of high frequency stability includes as part of its capacity a separate unit containing a reed condenser of variable inertia and resistance characteristics. When the oscillator is tuned to zero beat with another, preferably a Pierce oscillator, any shock or vibration reaching the reed throws the electrical tuning off zero beat. The resultant disturbance may be picked up by a tuned radiofrequency receiver and the output measured or heard by loudspeaker. The device has been used in the laboratory for testing the effectiveness of vibration insulation and “vibration free” mountings. The apparatus will be demonstrated.
The Absorption of Strips, Effects of Width and Location
Authors: Ramer L. G.
Published: September 2005

This paper presents the results of measurements, made by the reverberation method, of the absorption due to strips of various widths. Conclusion is drawn that, with diffusion agencies in the room, the narrowest practicable strip gives the greatest apparent absorption per unit area, with a continuous decrease as the strip width is increased. Further, for strips narrow with respect to the wave-length, the strip will be more effective if placed at the edge of a wall area, than if placed in the center of the same wall area.
Specific Normal Impedance and Sound Absorption Coefficients of Materials
Authors: Sabine Paul E.
Published: September 2005

This paper reports the results of comparison measurements of “reverberation coefficients” made on identical samples of materials in three reverberation chambers, having volumes ranging from 10,000 to 15,000 cubic feet. The results of these measurements indicate that, in rooms of comparable size, discrepancies in the measured values of the “reverberation coefficients” are not excessive at frequencies of 500 cycles and higher, and that disagreement at frequencies below 500 cycles are not sufficiently great to warrant the abandonment of reverberation methods. Reasons for the disagreements shown are considered. An attempt is made to correlate the results of acoustical impedance measurements made by the closed tube method reported by Beranek with room measurements of reverberation coefficients on eight commercial absorbents. It is shown that at frequencies below 500 cycles, the average values of the measured reverberation coefficients of the eight materials agrees very closely with the coefficient of absorption computed from the equation α = 1 −{|z/ρc| − 1|z/ρc| + 1}2, where z/ρc is the complex value of the normal specific acoustic impedance as given by tube measurements. For frequencies above 500 cycles the relation α = 1 −{|z/ρc| cos θ − 1|z/ρc| cos θ + 1}2 gives close agreement with the average value for the eight materials. Cos θ, the average value of cosine of the angle of incidence is 0.63, corresponding to an average angle of incidence of 51°, instead of the theoretical angle of 60° under the assumption of completely diffuse sound. Explanation is to be found in the arrangement of the diffusing agents used in the reverberation chamber which diffuse normal modes of vibration parallel to the absorbing surface more than the vertical modes.
Ideal Auditorium Acoustics
Authors: Watson F. R.
Published: September 2005

Some years ago, on reading a number of articles and comparing the results, the writer reached two conclusions; first, that practically all of the acoustical defects in auditoriums are due to reflected sound and second, that speakers and musicians are aided by nearby reflecting surfaces. These conclusions are not contradictory, since it was also shown that the reflections from the surfaces near the source of sound come quickly after the direct sound and are beneficial; the later reflected sounds cause the troubles. A combination of the two conclusions suggested the outdoor theater, which has almost no reflected sound except the acceptable portion coming from the rear wall of the stage, and which is generally commended for its excellent acoustics. On the basis of this study, the writer was led to propose a theory that good acoustics in auditoriums might be expected if the reflection of sound were reduced as in the outdoor theater, and if provision were made for nearby reflecting surfaces by which performers could “hear themselves.” Since this theory was advanced, various developments in the acoustic field appear to confirm the predictions. Auditoriums have been built without side walls, or with heavily padded walls, or with convex curved portions, etc., with a reduction of reflection in each case, and with resulting good acoustics. Furthermore, the use of special band shells, stage rooms and similar devices have furnished reflecting surfaces that have been welcomed by performers, with a consequent better production of music and speaking. Further developments in these two particulars are desirable if the ideal auditorium is to be found.
The Control of Acoustic Conditions on the Concert Stage
Authors: Burris-Meyer Harold
Published: September 2005

The control of acoustical conditions within a restricted zone has been undertaken by Mr. Paul Robeson as a means to recreating on the concert stage the acoustic characteristics of a small, highly reverberant room. The concert singer like all the rest of us sings with greater ease and assurance in the bath, or its acoustical equivalent, than anywhere else. In a large concert hall the effort to project the voice, which the singer doesn't hear as easily as in a small live room, may cause muscular tension, the use of an abnormally high key or faults in technique which militate against a good performance. To eliminate these hazards it is necessary only to reproduce the requisite acoustic conditions in a zone surrounding the singer but not touching the audience. The technique originally pioneered by Mr. Robeson has been analyzed and simplified, and special apparatus has been assembled for it. It seems to have a potentially large application to the public performance, recording and broadcasting of music.
Improved Techniques in the Study of Violins
Authors: Watson R. B. , Cunningham W. J. , Saunders F. A.
Published: September 2005

Frequency-response curves of violins are obtained by a modification of a method described by Backhaus and Weymann. A phosphor-bronze wire, properly damped to prevent the formation of standing waves, is substituted for one of the violin strings. Vibrations of the wire very near the violin bridge are produced by the interaction of a transverse magnetic field and an alternating current in the wire. The violin body responds at the frequency of the alternating current, variable from 30 to 20,000 cycles per second. The resulting sound is received by a microphone, whose output is amplified and automatically recorded by an audiograph on a logarithmic pressure versus frequency scale. This avoids the inconveniences of a previous method using harmonic analyses of steady tones produced by hand bowing. The similarity of frequency-response curves for old and new violins raises doubts as to the significance of the steady-tone results, and leads to a study of transient effects. The earlier attempts to study transients involved hand bowing, and failed because of the complexity of the tone. Pure-tone excitation, used to obtain growths and decays, allows the determination and comparison of the damping constants of the violins. The transient measurements are made using a cathode-ray tube and high speed camera.
Physical Properties of Wood for Violin Construction
Authors: Abbott R. B. , Purcell G. H.
Published: September 2005

Assuming that the best form of the characteristic response curve for a violin is one with the peaks and valleys flattened out to a minimum, and with the response at low frequencies augmented, it follows that one should know the properties of the materials which make up a violin in order to design one with any degree of accuracy. The following is a progress report of such an investigation. Specimens of wood in the form of rectangular bars 24″×38″×58″ were tested for their density, elasticity and internal resistance to motion. A method for separating the internal damping resistance from the air resistance was developed. Some of the effects produced on the properties of wood by coating them with oils, varnishes, paints, etc., were observed.
Trends in Acceptable Tone-Quality as Evidenced in Modern Musical Instruments
Authors: Pepinsky Abe
Published: September 2005

Taste in tone-quality, like style in dress and foods, is subject to fad and fancy. Past epochs evidence the influence of unique instrumental tone-color on vocal timbre. Instruments, in turn, were designed to imitate desirable vocal quality and that of other musical instruments. The last decade has revealed a number of electronic machines simulating other instruments, and generally using the pipe-organ as a prototype. Most organists resent such innovations because the “stops” representing various instrumental effects do not sound like those of their pipe-organ. Traditional organ-stops, however, offer themselves only a first approximation of the instruments they represent. Musicians and laymen have in general been greatly intrigued by the possibilities of these new music-makers. Psycho-physical data also indicate that these machines produce a nice approximation of steady-state tones. The trained ear, however, demands at least two refinements (thus far elusive) for a satisfactory reproduction of the characteristic effects of conventional instruments: (1) Differentiation of various instrumental registers, and (2) varied attack, typifying bowed, plucked or embouchure-controlled instruments. The infinite array of tonal effects produced by such modern musical instruments has further stimulated the composer's creative urge, although a predilection for well-defined regions of overtone structure is indicated.
Masking Effects in Practical Instrumentation and Orchestration
Authors: Pepinsky Abe
Published: September 2005

The relationship of one instrument to another within an ensemble and the quality of the composite tone produced have been empirically explored by the great composers of the past. Trial and error have played an important role here, however, and the reasons for the existence of intra- and inter-instrumental relationships within an ensemble which influence the tonal sensation have never been investigated. The effects of masking in the tone quality of one instrument in the presence of others are herein considered. The strong partials of one instrument influence other partials in the composite tone of that instrument as well as the partials comprising the combined tones of the other instruments. For illustration, an ensemble consisting of a cornet, French horn, trombone, baritone and E♭ tuba were selected to present a simple chord in varying settings and degrees of dynamics. The hypothesis is that masking in ensemble-playing consists of an accumulation of the masking effects produced by the components of the complex tones. The phono-photographic measurements obtained by Seashore and his associates were used to plot the strength and distribution of the partials within the tones produced by the various instruments. Total average pressures exerted by these instruments were adapted from the data given by Sivian, Dunn and White. The average reference intensity level of 40 db was used to signify a medium or mezzoforte tone level, and a sensation level of 20 db and 60 db were chosen for piano and forte tone levels, respectively, with resultant variation in the partial strength of each instrument in the spectral analysis. These results indicate that chords do not sound as they are written, and substantiate our hypothesis in that conductors alter the intensity which the composer has assigned to various instruments in combination to produce desirable effects. In many instances the notes of the chord must be reassigned to different instruments in order to secure good balance. Definite principles for the guidance of instrumental composition can thus be set up.
The Acoustical Bases of Music Theory and Composition
Authors: Loar Lloyd
Published: September 2005

This paper describes a scientific approach to chord and tone relationships that may explain their artistic use as media for esthetic expression.
Generalized Plane Wave Horn Theory
Authors: Salmon V.
Published: September 2005

Horns are primarily used with moving coil loudspeaker units to obtain sound radiators possessing satisfactory electro-acoustic energy transfer characteristics. The contribution of the horn to the over-all efficiency, as expressed by the acoustic driving point admittance, will be obtained by a generalized dimensionless treatment of Webster's equations. Numerical solution of the differential equation for the pressure may be effected by the Hartree method widely used in problems involving atomic wave functions, enabling an estimate of the behavior of any horn of reasonable flare. Some new types of horns suggested by certain solutions of the differential equation will be compared to the well-known exponential horn.
Uniphase Uni-Directional Microphones
Authors: Bauer Benjamin B.
Published: September 2005

The uni-directional microphone is treated as a generalized transducer and network which are subjected to sound waves at two points in space. Network relationships are derived to produce uni-directional operation. These relationships are fulfilled in the “uniphase” structure which has a single transducer and a phase-shifting network instead of the two transducers normally used in uni-directional microphones. Acoustical phase-shifting networks applied to a diaphragm-type piezoelectric microphone and to a moving coil dynamic microphone producing a cardioid-type polar pattern are described.
The Acoustic Wattmeter, an Instrument for Measuring Sound Energy Flow
Authors: Clapp C. W. , Firestone F. A.
Published: September 2005

An instrument called an “acoustic wattmeter” has been constructed to measure sound energy flow. It consists of a crystal pressure microphone and miniature ribbon velocity microphone mounted close together and connected through separate amplifiers and phase equalizing networks to a thermo-couple-type audiofrequency wattmeter. Provision is made to measure sound pressure and velocity separately as well as the energy flow represented by their product. The normal acoustic impedance and absorption coefficient of a surface may be computed front measurements of sound energy flow into the surface and energy density near the surface. Measurements were made on two representative absorbing materials at normal incidence with the material mounted at the end of a tube, and at random incidence with the material on the floor of a large sound chamber. Referring all results to random incidence, the values of the absorption coefficients obtained by the two methods agree well with each other and are in fair agreement with results obtained by the reverberation room method.
Phonograph Reproducer Design
Authors: Hunt F. V. , Pierce J. A.
Published: September 2005

After a brief review of the design objectives for a lateral-cut reproducer a suitable structural form for a dynamic unit will be described. A unitary metallic ribbon serves both as the mechanical support for the stylus mounting and as the electrical generating element. By proper conformation a suitable relation can be maintained between the lateral, vertical, and longitudinal compliances observed at the stylus. No viscous damping material is required when the pivoting axis determined by elasticity coincides with that due to inertia. Application of a principle of similitude allows the scale of the structure to be changed without altering significantly the sensitivity, thereby providing for any desired compromise between small bearing weight and ease of construction. Laboratory models of the reproducer exhibit uniform frequency response and an effective vibratory mass, referred to the stylus, of less than 1 milligram.
Tone Guard
Authors: Olson Harry F.
Published: September 2005

An acoustic network has been developed for attenuating the sound, generated and radiated directly into the air by the vibrating parts of the phonograph pick-up, which passes through the aperture between the door and the cabinet. The series elements are formed by the slit between the door and the cabinet. The shunt elements are formed by a wood strip fastened to the inside of the cabinet. The attenuation band extends from 1000 to 10,000 cycles. The attenuation is of the order of 15 decibels over that with the conventional door and cabinet. The network has been applied to both horizontal and vertical doors.
Some Acoustical Phenomena in the Antarctic
Authors: Poulter Thomas C.
Published: September 2005

In preparation for the geophysical measurements in the Antarctic during the Second Byrd Antarctic Expedition a rather extensive study was made of the sound transmission and absorption properties of the compacted snow and ice. Many strange and unexpected phenomena were observed such as snow tremors that were audible for as long as twenty minutes, multiple reflections between reflecting strata, reflections from clouds, and the location of hidden crevasses.
Application of Acoustical Analysis to Linguistic Problems
Authors: Cowan J. M.
Published: September 2005

An oscillographic record of a speech utterance can only be interpreted in the light of linguistic knowledge. The segregation of temporal portions of such a record into speech sounds is based upon phonetic observation. By careful auditory analysis the phonetician decides on the number of meaningful sound patterns which recur in essentially the same auditory form in a given language. These are called speech sounds or phonemes. After an objective record of an utterance has been divided into individual speech sounds, the physical characteristics of the sounds can be described. Much of this work has been done, but not as much as is desirable. Descriptions of certain consonantal sounds, especially, are inadequate. However, one further step of analysis is necessary. The linguist typically divides any utterance into two kinds of “sound-feature,” distinctive and non-distinctive. The distinctive features will be those structural features which give rise to the perception of the phonemes. All others, such as features of individual voice quality, are non-distinctive. We have some information on the structure of vowel phonemes, but practically none for consonantal phonemes.
Noise—Tremor due to Traffic
Authors: Bernhard R. K.
Published: September 2005

This paper presents a study on noise and mechanical vibration abatement with respect to the field of structural engineering. Certain units of noise-tremor are defined, and some psychological and physiological concepts outlined (sensation thresholds and bearable limits for the human body). Fundamental principles of the measuring instruments are given. In reporting the investigations in buildings and in the field, particular attention is given to the influence of: speed of vehicles, super and substructure of roadbeds, operation and construction methods, and the damping capacities of soils. The combined effect of noise and mechanical vibrations is studied.
Room Noise Spectra at Subscribers' Telephone Locations
Authors: Hoth D. F.
Published: September 2005

Information on the sound levels of room noise at subscribers' telephone locations has been presented before this Society by Mr. D. F. Seacord and was published in the July, 1940, issue of the Journal. The present paper contains information which permits the interpretation of the sound level data in terms of the distribution of sound as a function of frequency by presenting the results of physical measurements of sound spectra at telephone locations in and around Philadelphia. An average spectrum, giving the absolute sound pressure as a function of frequency is presented for a given sound level of room noise. In addition data are given for the results of similar measurements made in two Bell System office buildings in New York and the results are compared with the Philadelphia data.
Relation Between Acoustic Impedance and Flow Resistance of Porous Acoustic Materials
Authors: Morse P. M. , Bolt R. H. , Brown R. L.
Published: September 2005

A theory is developed for the penetration of sound waves into uniformly porous acoustic material. An expression is obtained giving the acoustic impedance at the front surface in terms of the porosity of the material, its flow resistance, and the effective density of air in the pores, taking into account reflection from the back surface. Curves will be shown of acoustic resistance and reactance as functions of frequency for different values of flow resistance, for uniformly porous material with rigid backing. Comparison of these curves with the experimental data of Beranek shows that for a number of commercial materials the effective values of flow resistance, porosity, and air density are constant over the frequency range 100 to 6000 c.p.s. It is indicated how other types of backing change the curves, and how computations can be made for non-uniform material. The static flow resistance or “d.c. resistance” of porous materials can be measured directly. A method is developed using a very slow steady stream of air flow through the material and determining the pressure drop across the material. The air flow is furnished by siphoning water at a known rate from a container mounted several feet above a control valve and outlet; air drawn into the container first passes through the porous material. The air velocities and pressures used are of the same order of magnitude as those obtaining in actual sound fields. Flow resistance values for several commercial materials are reported and correlated with the effective values indicated by impedance measurements.
Industrial Noises and Industrial Deafness
Authors: Rosenblith W. A.
Published: September 2005

During the years 1938 and 1939 a survey was conducted in France—on the behalf of Professor André Salmont—in order to determine the relationship between the intensity and the frequency distribution of industrial noises and the hearing loss which is commonly encountered in noisy professions such as boilermaking, etc. It was possible to show that there was some proportionality between the average noise level and the temporary as well as the permanent hearing loss for corresponding groups of workers. However, all attempts to relate the frequency spectrum of industrial noises to the corresponding hearing loss have failed so far, as the most important components of such noises are practically always below 1500 cycles while the hearing loss becomes severe for higher frequencies only. Thus for boilermakers having more than 15 years of employment the average hearing loss was found to be: 12.5 db at 1000 cycles, 39 at 1500, 64.5 at 4000, 77 at 6000 and 61.5 db at 8000 cycles. Certain other investigators also have reported this “high frequency deafness” after exposure to relatively “low frequency noises.” It therefore appears that further experiments under conditions where one would be able to control the intensity and the wave form of the noise might yield interesting results pertinent to an explanation and possible prevention of industrial deafness and also to the general theory of hearing.
A General Purpose Vibration Meter
Authors: Scott H. H.
Published: September 2005

The popularity and usefulness of the sound level meter have created a demand for a vibration-measuring device of similar character—easy to use, accurate, and adaptable to a wide range of applications. To provide such a general-purpose vibration-measuring device a new and unusual type of instrument has been developed. Based upon the experience gained in the manufacture of hundreds of sound level meters, a stable, high gain amplifying circuit has been developed, giving a satisfactory response at frequencies as low as 2 cycles per second. The use of an acceleration-type pick-up plus two stages of electrical integration provides the user with the choice of acceleration, velocity, or displacement characteristics, all in a single instrument. Among the many other features are a stable internal calibration system, instantaneous push-button control of the integrating circuits, a semilogarithmic meter with special damping characteristics, and a single-control dual attenuator providing a wide range of sensitivity. The factors involved in the choice of the various electrical and mechanical characteristics and some actual results obtained with the instrument will be described.
A Demonstration of the Chromatic Stroboscope as a General Purpose Frequency Meter
Authors: Schuck O. H. , Young R. W.
Published: September 2005

Experience has shown that the chromatic stroboscope is very useful as a general purpose frequency measuring instrument, even though it was originally developed for musical instruments. Its inherent accuracy of 1/20 percent can be made available above its nominal 4000-cycle upper limit by the use of easily constructed frequency dividers, one of which will be shown. A demonstration will be given illustrating important advantages of this method over the other available methods in range, accuracy and speed.
On the Perturbation of Normal Modes of Vibration
Authors: Bolt R. H. , Clogston A. M. , Feshbach H.
Published: September 2005

A recently developed boundary shape perturbation theory has been applied to the calculation of acoustic normal frequencies and wave patterns in enclosures which deviate somewhat from rectangularity. The method is quite general; it is applicable to any form of irregularity if the amount of distortion is “small,” provided solutions for the basic form are obtainable. Specific formulas have been derived for trapezoidal and parallelogram shapes. Calculated frequencies and wave patterns are found to agree closely with experimentally measured values reported previously. An experiment has been devised to test the range of validity of the perturbation calculations for one case. A small test chamber was built with walls which could be shifted continuously in plan to give trapezoids of constant area, but having any desired degree of deformity between a rectangle AB and an isosceles triangle of base 2A and height B. A number of normal frequencies were traced through the whole range of shapes. For wall angle shifts up to about 15° the perturbation calculations hold very well. The perturbation method promises to yield information bearing on the problem of sound diffusion in irregular rooms.