bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological Acoustics; Loudness
Authors: Stevens S. S. , Davis H.
Published: September 2005

Functional relationships obtained from studies of the electrophysiology of the auditory mechanism in animals may be used to determine the physical basis of the psychological aspects of hearing. Thus equal magnitudes of electrical potential are generated by the hair-cells of the inner ear when subjected to tones (of different frequency and intensity) which sound equally loud to the human observer, i.e., equal potential contours correspond to equal loudness contours. Therefore, loudness appears to be proportional to cochlear potential. Since end-organ stimulation can reach the brain only via afferent nerves which conduct series of discrete action potentials, loudness must also depend upon the number of fibers involved in the transmission of a volley of action potentials.

The relation of the size of the cochlear potential to the intensity of sound deviates from the Weber-Fechner relationship in the same manner as do the psychological functions. However, at about 60–80 db above threshold the cochlear potential begins to decrease, and a reversible depression of the response, due to overload, is shown by a “hysteresis” effect. If the overload is prolonged, microscopic degeneration of the hair-cells occurs, or if overload is too great the organ of Corti is shaken loose from the basilar membrane.

For a given tone the potential recorded from the scala vestibuli is out of phase by 180° with that recorded from the scala tympani. Therefore the potential drop is across the membrane, or from end to end of the hair-cells. The potential at the round window is in phase with that in the scala tympani, but the potential at the apex differs from the potential in the scala vestibuli by an angle which increases with the frequency of the stimulus. By moving the grid electrode along the outside of the cochlea, a point is found where the potentials which leak out of the two ends (round window and apex) cancel each other by interference.
The Position of Pure Tone Stimulation of the Basilar Membrane
Authors: Steinberg John C.
Published: September 2005

The relation between tone frequency and position of stimulation on the basilar membrane has been calculated from data on differential pitch sensitivity and on the density of innervation of the membrane. The calculations involve assumptions concerning the choice of the upper and lower pitch limits of hearing and the choice of tone levels which should be used in obtaining differential pitch sensitivity data. It is shown that for quite different assumptions the positions of stimulation for tones in the range from 1000 to 4000 cycles are not greatly affected. Outside this range the positions depend on the assumptions. It appears that tones of 1000, 2000 and 4000 cycles stimulate, respectively, portions of the membrane about 1/3, 1/2 and 2/3 of its length away from the helicotrema.

Calculations made several years ago by Wegel and Lane from the differential sensitivity data reported by Knudsen gave the positions of a 1000-cycle tone in the middle of the membrane. The differences between the present positions and the earlier ones are due in part to taking account of the density of innervation of the membrane and in part to differences between the low frequency tone data on differential sensitivity reported by Knudsen and that reported later by Shower and Biddulph and used here. The latter data are believed to be more characteristic for low frequency tones.
A Method for Obtaining Natural Directional Effects in a Public Address System
Authors: Fay R. D.
Published: September 2005

In studying the effects produced by two or more source simultaneously emitting the same sounds, it has frequently been noticed that all of the sound appears to come from the nearest source provided the difference in distances between the observer and the sources lies between fairly definite limits. A group address system was set up to utilize this effect in making it appear to the audience that the amplified sound of the speaker's voice came directly from his mouth. Excellent results were obtained, even with relatively great amplification, when the sound reproducing units were about 20 feet behind and 45 feet above the speaker.
A Method for Maintaining in a Public Address System the Illusion that the Sound Comes from the Speaker's Mouth
Authors: Hall W. M.
Published: September 2005

As described in the paper by Professor Fay, it is possible to maintain the illusion that the sound comes from the speaker's mouth by arranging the reproducing system so that the original sound reaches the listener's ear before the reproduced. A study has been made of this effect to determine some of its limitations and possibilities.
Sound Reenforcing Systems
Authors: Olson Harry F.
Published: September 2005

The inadequate speech power of the human voice in theaters and auditoriums is one of the most serious limitations to good hearing. The type of theater which suffers most from inadequate loudness of speech is, of course, the very large enclosed theater and the open air theater. Further in some instances the music furnished by an orchestra is of inadequate volume range to render full artistic interpretation. In these cases means are required for augmenting the intensity of the original sound. The systems for accomplishing this objective are termed sound reenforcing or public address systems. This paper describes the arrangement of the microphones, microphone mixing system and the loudspeakers for increasing the level of the original sound as well as obtaining uniform sound intensity in all parts of the theater. The use of directional microphones and loudspeakers minimizes difficulties due to feed-back. Arrangements for outdoor sound reenforcing systems for various applications are discussed. Announce and call systems are discussed with respect to the arrangement of loudspeakers and microphone locations.
Sound Reenforcement—An Acoustic Problem
Authors: Wolf S. K. , Stanton G. T.
Published: September 2005

This paper discusses the approach to the subject of public address as an acoustic problem.

The primary function of a public address system is to faithfully produce, at all points in the listening area, sound of adequate loudness as heard close to its origin. The attainment of this objective is discussed in terms of the acoustic factors involved and their relation to the physical design of the apparatus.

The first of the factors is the directional-frequency characteristic of the loudspeakers involved, in terms of their relationship to the acoustic transmission of the auditorium. The tremendous complexity of computation of acoustic transmission requires, in the present state of the art, empirical determination of this factor by instrumental means. Since design limitations in the loudspeaker are such as to seldom permit securing exactly the frequency-directional characteristic required, a modification in the characteristic of electrical energy input to the speaker must be made. The requirement of attaining adequate loudness may be limited by acoustic regeneration or “feedback.” A brief discussion of the controlling factors is included.
The Performance of a Public Address System as a Function of Auditorium Absorption
Authors: Boner C. P.
Published: September 2005

This paper summarizes the work done in connection with public address systems at the University of Texas, particularly in Gregory Gymnasium, an auditorium of one million cubic feet capacity, seating eight thousand people. The results of sound pressure measurements are given, as they show the nature of absorption in the auditorium and the resulting effect on acoustic regeneration and the frequencies at which “singing” takes place. Methods of reducing acoustic regeneration are discussed, which, in the case of Gregory Gymnasium, permit the public address system to establish a sound pressure of approximately twenty bars in the rear of the room, with microphone on the stage and a small orchestra playing.
Measurement of Speed Fluctuations in Sound Recording and Reproducing Equipment
Authors: Kellogg Edward W. , Morgan Adolph R.
Published: September 2005

High quality reproduction of recorded music is possible only if the speeds of recording and reproducing machines are maintained constant within very narrow limits. As improvements are made in these machines greater refinement in measurement of the variations is required in order that the progress may continue. The development of an improved “Wow-meter” for such measurements is described, and various alternative schemes are discussed. The securing of a standard record, itself sufficiently free from imperfections, presents one of the most serious difficulties. For testing turntables a toothed steel wheel was built, in which special precautions were taken to minimize indexing and other possible errors. The current generated by means of this wheel is supplied to an electric circuit so arranged that variations in frequency cause deflections of a galvanometer, which are registered on a photographic film. The principle employed, namely, a resonant circuit slightly off tune, has been used in earlier devices. In the meter described a push-pull arrangement has been adopted to reduce the likelihood of errors due to variations in voltage. A frequency meter of this type has certain inherent limitations in its ability to register very rapid fluctuations. Certain measures have been adopted to make the meter satisfactory in this respect, and the possibility of going further in this direction if necessary is given consideration.
Psychophysiological Acoustics: Pitch and Loudness
Authors: Stevens S. S. , Davis H.
Published: September 2005

The problem of psychophysiological acoustics is to determine the characteristics of auditory sensation in terms of the physical dimensions of the stimulus and the relation of physiological phenomena (in animals) to the same stimuli, and by comparison to infer the relation of the psychological function to the physiological. Four such correlations have been examined. (1) Data previously reported show a fairly good correspondence of the threshold function of electric response and the psychological thresholds. (2) Pitch perception depends upon selective resonance of different portions of the basilar membrane, although an intense tone activates a large area. The positions of maximal sensitivity were determined by the effect of localized lesions of the cochlea upon the threshold for electric response. The resulting map was compared with the map derived from the integration of Shower and Biddulph's data on pitch discrimination. The correspondence is very close (Fig. 1). (3) The equal loudness contours of Fletcher and Munson were compared with the corresponding contours of intensity required to produce equal electric responses from the cochlea. The correspondence is satisfactory. (4) The loudness function of Churcher was compared with the relation between the intensity of a 1000-cycle tone and the magnitude of the electric response of the cochlea. The functions are similar as a first approximation, except at high intensities. The deviations are partly random, partly systematic. Theoretical explanations of the deviations are suggested. The size of the electric response of the auditory nerve, representing the total number of active fibers, also corresponds approximately to the loudness function. The loudness function does not correspond to the function obtained by integration of the difference limens for loudness (data of Riesz). A DL at high intensity involves the addition of more loudness and therefore the activation of more nerve fibers than a DL at low intensity. As a first approximation, the size of a DL in sones (units of loudness) is expressed by DL = KN1.2, where N is the number of DL's above threshold.
Studies of the Vibro-Tactile Senses as Means for Determining Direction
Authors: Gault Robert H.
Published: September 2005

Earlier investigations in this field have left the factors of intensity, rate of transmission (and consequently time of stimulation) and phase without adequate control. In this investigation, as far as it has proceeded, we have attempted to supply this deficiency.

In the experimenter's room is a speaker that may be moved right or left upon the arc of a circle. Before it, in fixed positions, are two microphones. These microphones communicate with two vibrators, respectively, in the distant observer's room. The observer is seated with the index finger of the right hand upon one vibrator and that of the left hand upon the other. The situation is so arranged that he cannot hear the action of the vibrators. Before him, and covering the vibrators, is a sheet of cardboard on which the arc of a semicircle is described marked to designate degrees.

As the speaker, in action, is moved sufficiently to the right or left, thus varying its distance from the microphones, respectively, the intensity, time and phase of the stimulus upon the observer's fingers, respectively, are altered as in a corresponding situation in the sphere of audition. The observer “feels as if” a vibrating body before him were moving between right and left. On the semi-circumference before him he designates the degree of the apparent movement.

When, now, the speaker is kept in a constant middle position with reference to the microphones and when attenuators are introduced to control intensity in the vibrators, respectively, the time element is kept constant but the observer continues to experience the illusion of movement referred to. The degree of apparent movement corresponds to that that obtains in the auditory sphere in similar situations.

We have yet to complete the experiment by holding intensity constant while other factors are independently varied.
Articulation Testing by Bone Conduction
Authors: Watson N. A.
Published: September 2005

The paper describes briefly the apparatus used for transmitting the recorded articulation lists to the bone-conduction vibrator, and the construction of the induction type electrodynamic vibrator itself. Results of articulation tests on normal-hearing persons are given which indicate that, with high quality apparatus and sufficient power, articulations can be obtained by bone conduction as high as those by air conduction. 100 percent often being attained. The variation of percent syllable articulation with increasing level is given for bone conduction for open ear canals and for partially blocked canals. The effects of the following factors on percent syllable articulation are also discussed: (1) Variation of total force and pressure of the vibrator against the observer's head; (2) frequency and nonlinear distortion in the amplifier system; (3) use of multiple vibrators; and (4) clenching of teeth and other variations of the condition of the observer's head.
The Influence of Intensity on the Pitch of Violin and 'Cello Tones
Authors: Cowan Milton , Lewis Don
Published: September 2005

Three independent investigators (Zurmühl, Stevens and Fletcher) have recently shown that significant changes in the pitch of certain pure tones accompany changes in their intensity, the amount of change depending upon both frequency and intensity. The question naturally arises as to whether the pitch of complex musical tones is similarly related to intensity. The present paper is the report of an investigation which was undertaken to answer this question insofar as it relates to violin and 'cello tones. The results are not entirely unequivocal, but they tend to show that intensity has no measurable effect on the pitch of the tones studied. Intensity may affect the pitch of these tones but, if it does, the pitch-intensity relationship here is basically different from that operative in the case of pure tones; and this is unlikely.
Automotive Quieting
Authors: Norris R. F.
Published: September 2005

Intake roar, exhaust noise and body resonance are discussed. Methods by which these noises are attacked are explained and data showing their relative importance are given.
A Method of Eliminating Cavity Resonance, Extending Low-Frequency Response and Increasing Acoustic Damping in Cabinet Type Loudspeakers
Authors: Olney Benj.
Published: September 2005

When a direct-radiator loudspeaker is mounted in a cabinet, as in the conventional radio receiver, response irregularities are introduced because of resonances in the space behind the loudspeaker. With a cabinet and speaker diaphragm of ordinary size, the acoustic load at low frequencies is highly reactive, the radiation efficiency is very low and diaphragm amplitudes become excessive.

In the method described, the rear of the loudspeaker diaphragm is tightly coupled to one end of a folded conduit lined with sound-absorbing material and terminating in an opening in the bottom of the cabinet. This arrangement is called an acoustical labyrinth. By suitable tuning of the conduit, an extension downward of the reproduced frequency range is secured. The acoustic impedance of the conduit is shown by measurement to offer a diaphragm load having desirable characteristics, it being predominantly resistive over virtually the entire measured low frequency range (40–350 cycles). Measurements of the acoustic impedance on the front of a diaphragm in a moderate sized baffle and of the impedance facing the back of a diaphragm in a conventional radio cabinet are also reported. The improvement in the frequency characteristic of a cabinet type loudspeaker afforded by the use of the acoustical labyrinth is shown by response curves.
A Modified Tube Method for the Measurement of Sound Absorption
Authors: Morrical Keron C.
Published: September 2005

In a previous abstract a method was described for measuring the sound absorptivity of small specimens. Sound from a loudspeaker travels down a cast iron tube 8 inches in diameter, strikes the specimen under test at an angle of 45 degrees and is reflected down a side tube where it is measured. By measuring the sound reflected down the side tube from a thick glass plate, and by measuring the sound in the side tube when an exponential horn is substituted for the specimen, it is possible to arrive at the reflectivity and consequently the absorptivity of the specimen.

The earlier apparatus has been redesigned and measurements have been taken on a large number of materials. For the frequency of 500 c.p.s. the method has given absorptivities for commercial materials that are in satisfactory agreement with those determined by reverberation measurements. By means of a miniature condenser transmitter the actual pressure distribution in the tube is being investigated with the view of extending the usefulness of the apparatus to frequencies above and below 500 c.p.s.
Investigation of the Sound Absorptivity of Portland Cement Concretes
Authors: Watson F. R.
Published: September 2005

Coefficients of absorption were determined by the reverberation method, both instrumentally and with the ear. The samples were special types of concretes, ranging from dense, heavy mixes using standard aggregates to light, porous ones having varying proportions of cement, sand and light weight aggregates, such as cinders and haydite.

The results show that porous materials absorb sound, but dense materials with small porosity are not efficient in absorbing sound. Haydite and cinder concrete constructions proved to possess effective sound-absorbing values; sandstone and limestone products were not so good, but most of the specimens are more sound absorbent than the usual hard plasters and cements so that these new products can be used advantageously in buildings to reduce noise.
Steady-State and Transient Aspects of Vowel Production
Authors: Lewis Don
Published: September 2005

At first, to clarify concepts and to facilitate later presentation of experimental data, the steady-state (or harmonic) theory of vowel production is differentiated from the transient (or inharmonic) theory, and each is given definite formulation. It is shown that the two theories are not, as is sometimes supposed, merely two ways of viewing the same phenomenon, but are quite different in their physiological and acoustical implications. Recent experimental data are then summarized. These data, taken from the writer's work on vocal resonance and from the reported work on vowels of Trendelenburg, Wolf, Stanley and Sette, and others, indicate that vowel production is primarily a steady-state process. In other words, the data show beyond much doubt (1) that the vocal cords give rise to a cord-tone which consists of a fundamental component and a large number of its overtones; (2) that the vocal cavities, on which the cord-tone acts as a force, constitute a number of singly-resonant systems and thus serve to modify the spectrum of the energy flowing from the cords; and (3) that vowel sounds, as radiated from the mouth, are composed mainly of a harmonic series of simple motions, each of which has a determinable magnitude. The limitations of this somewhat idealized picture are set forth, with stress on the transient aspects of the process.
NBC Studio Design
Authors: Morris R. M. , Nixon G. M.
Published: September 2005

The factors influencing the acoustical requirements of broadcast studios are discussed with the relation of studios one to another and to appurtenant spaces. A method of procedure is outlined, showing the embodiment of certain principles and data obtained from 10 years' experience in the design, construction, and operation of studio groups of various sizes. Studio groups recently designed and constructed by the NBC are described as examples of the application of these principles. A portion of the paper is devoted to other details such as characteristics of various acoustical treatments; discoloration of treatments due to “breathing” and means of control; the sound control of air conditioning, plumbing, electrical and heating systems; and the sound isolation required between studios and the building structure.

Other essential empirical and experimental data are presented such as: optimum sizes and dimensions of studios for various numbers of occupants; optimum reverberation time and frequency characteristics; the arrangement and treatment of appurtenant spaces such as control and observation booths, vestibules, doors, windows, etc., fundamental requirements and recommended specifications for satisfactory acoustical performance.
Deviations in the Loudness Judgments of 100 People
Authors: Steinberg J. C. , Munson W. A.
Published: September 2005

Distributions of loudness judgments are shown for a large group of observers comparing 100- and 5000-cycle tones with a 1000-cycle reference tone. The tests were made with automatic equipment for conducting the constant stimuli type of test. Additional tests show how experience, hearing acuity, time variations, and other factors affect deviations of loudness judgments.
A Method of Eliminating Cavity Resonance, Extending Low Frequency Response and Increasing Acoustic Damping in Cabinet Type Loudspeakers
Authors: Olney Benjamin
Published: September 2005

When a direct-radiator loudspeaker is mounted in a cabinet, as in the conventional radio receiver, response irregularities are introduced because of resonances in the space behind the loudspeaker. With a cabinet and a speaker diaphragm of ordinary size, the acoustic load at low frequencies is highly reactive, the radiation efficiency is very low and diaphragm amplitudes become excessive. In the method described, the rear of the loudspeaker diaphragm is tightly coupled to one end of a folded conduit lined with sound-absorbing material and terminating in an opening in the bottom of the cabinet. This arrangement is called an acoustical labyrinth. By suitably proportioning the conduit, an extension downward of the reproduced frequency range is secured. The acoustic impedance of the conduit is shown by measurement to offer a diaphragm load having desirable characteristics, it being predominantly resistive over nearly the entire measured low frequency range (40–350 cycles). Measurements of the important acoustic and electrical impedances of a conventional and a labyrinth loudspeaker system also are reported. The improvement in the frequency characteristic of a cabinet type loudspeaker afforded by the use of the acoustical labyrinth is shown by response curves.
Some Data on a Room Designed for Free Field Measurements
Authors: Bedell E. H.
Published: September 2005

This paper gives some data on the absorbing material used in a room recently completed and intended for acoustical measurements under essentially free field conditions. The absorbing material, which consists of a number of layers of cloth separated by air spaces, is shown to have an absorption coefficient of the order of 98 to 99 percent over a wide frequency range. Some data are also given showing the degree of departures of the sound field in the room from the field to be expected in free space. It is shown that it may not be possible to duplicate a free field in an enclosed room, regardless of the freedom from interference obtained, because of the fact that the pressure may decrease more rapidly than the inverse distance law applying to a free field.
Loudspeakers for High-Fidelity Large Scale Reproduction of Sound
Authors: Massa Frank
Published: September 2005

The extension of both frequency and volume range in large scale sound reproduction has imposed severe limitations on the performance characteristics of loudspeakers employed in these applications. This paper discusses some of the problems that arise under such conditions and what means have been taken for their solution. The limitations of single speakers to cover the entire frequency range are mentioned and the advantages of multispeaker systems are pointed out.
Finite Acoustic Filters
Authors: Lindsay R. B.
Published: September 2005

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

The phase change which occurs between successive sections in a filter is also computed and it is shown that unlike the situation in the infinite case the phase change is a function of the section. However, at relatively high frequencies and for large n this approximates to the total phase change along the structure divided by n. Comparison with such experimental results as are at present available yields reasonably satisfactory agreement.
Detection and Location of Laminations in Steel Plates
Authors: Hayes Harvey C.
Published: September 2005

Laminations in the plating and other members of fabricated steel structures cause weaknesses and failures in present welded junctions that did not occur in the case of riveted joints. Thus the need has arisen for some effective method and means for detecting such flaws in structural steel material. Simple theoretical considerations predict that the presence and location of such laminations can be determined by the distortion which they produce in sand patterns formed on the plates when they are thrown into various types of mechanical resonance. Practical tests have substantiated these predictions in the case of plates of different form and thickness.
The Vibrating String Considered as an Electrical Transmission Line
Authors: Kock Winston E.
Published: September 2005

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

This paper discusses the measurement of hearing loss for levels of sound that were well above the deafened threshold and hence were audible to the deafened person. In the tests, observers having unilateral deafness, i.e., one impaired and one normal ear, balanced a tone heard with the deafened ear against the tone heard with the normal ear. For some people, the impaired ear heard less well than the normal ear for all sound levels. For others, tones which were well above the deafened threshold were heard about equally well with either ear. In other words, such deafened ears tended to hear loud sounds with normal loudness. It was found that this type of deafness could be represented quantitatively on the assumption that it was due to nerve atrophy. Loudness judgments for a normal ear in the presence of noise were found to be similar to judgments by a nerve deafened ear. Relations, based on the loudness properties of normal ears, have been extended to represent the loudness heard by deafened ears.
A Study of the Effect of Frequency and Temperature on the Velocity of Ultrasonic Waves in Gases
Authors: Warner Glen W.
Published: September 2005

Measurements of the velocities of ultrasonic waves were made in carbon dioxide, nitrous oxide, and sulphur dioxide at temperatures from 30°C to 150°C. The fundamentals of seven quartz oscillators were used to obtain frequencies from 40 kc/sec. to 105 kc/sec. The gases were heated by passing them through a coil of copper tubing surrounded by a heating unit, both being wound around the gas chamber in which wave-length measurements were made. This chamber was a modified Kundt's tube with movable reflector for producing standing waves. The reflector was carried by a screw with a pitch of one millimeter and a dial graduated in hundredths of a millimeter. As the reflector passed through the nodes and loops the varying amount of energy reabsorbed by the electric circuit made it possible to determine the wave-length by the reaction of a radiofrequency milliammeter in the energizing circuit. The frequencies of the oscillators were determined by a frequency meter constructed for this work and calibrated by beating with WLW. The velocities thus obtained were reduced to 0°C and plotted against temperature at which the measurements were taken. In all three gases the velocity increases with increasing frequency but the increase is greater in carbon dioxide than in the other two gases. The velocity (V0) at any frequency is practically constant at all temperatures in N2O and SO2, but in CO2 the curve is flat for the lower temperatures, decreases rapidly by from six to ten meters per second in the temperature range from 50° to 130°, and again becomes constant at the higher temperatures.
Hearing of Speech by Bone Conduction
Authors: Watson N. A.
Published: September 2005

A method for testing hearing of speech by bone conduction has been developed on the basis of Fletcher and Steinberg's articulation testing methods. High quality recordings of the articulation lists were substituted for callers. A special induction type electrodynamic bone conduction vibrator was developed from the original Barany-Schwarz Knochentelefon. It is linear over a wide intensity range for all speech frequencies and has a frequency response characteristic which allows clear transmission of speech. The method and apparatus have been tested by a comprehensive series of measurements on an individual with hearing slightly above normal. The force of application of the vibrator necessary for best understanding of speech was found to be approximately 350–400 grams-weight. The best area of vibrator button varied with conditions; for open ear canals a button of 0.7 sq. cm area gave higher articulations than larger ones and as high scores as smaller, less comfortable ones; for closed ear canals a larger button gave better results. Speech was heard best by bone conduction when the observer's mouth was closed, his teeth touching but not clenched, and his ear canals occluded. The variation of percent articulation with level-above-threshold was studied for bone conduction with both open and occluded canals and for air conduction with one ear and two. The curves obtained were coincident within observational error, indicating the same functional relation in all four cases. (The intensity levels at threshold varied for the four cases, being greater for bone conduction than for air conduction and greater for open-canal bone conduction than closed-canal.) A large amount of frequency distortion was tolerable without seriously affecting the articulation as long as there was no nonlinear distortion. Finally, all the results have revealed that the hearing of speech by bone conduction may attain as high a degree of perfection as that attained by the more usual method of air conduction.
Factors in the Production of Aural Harmonics and Combination Tones
Authors: Newman E. B. , Stevens S. S. , Davis H.
Published: September 2005

The magnitudes of the aural harmonics and combination tones produced in the ears of cats and guinea pigs in response to pure tonal stimuli were measured electrically. The cochlear potentials were sampled by an electrode applied to the round window and thence conducted through suitable amplifiers to an electrical wave analyzer (General Radio). The wave analyzer measured the energy present at any frequency in the cochlear response. The functions relating the magnitudes of the first five harmonics to the intensity of the pure tonal stimulus were determined. The harmonics first appear at about 50 db above the threshold and thereafter grow more rapidly than the fundamental as a function of intensity. Several differences in the behavior of the odd and even harmonics reveal the characteristics of the constraining mechanisms responsible for the production of the aural harmonics. Simultaneous stimulation of the ear by two tones (700 and 1200 cycles) produces a cochlear potential out of which not only the several harmonics of these two tones, but also the sum and difference tones, representing combinations of these harmonics, can be analyzed. Nearly all of the combination tones up to the seventh order have been observed. As a function of intensity, the different combination tones grow in characteristic manners and disclose interesting aspects of the auditory mechanism.
Sound Waves in a Moving Medium
Authors: Trimmer John D.
Published: September 2005

A theoretical approach is made to the problem of the behavior of sound waves in a pipe through which the medium is moving in a unidirectional flow with uniform velocity V. Calculation indicates the resonances of pipes to be affected by the steady flow so that the resonance peaks are flattened, while the separation between nodal points is reduced by the factor 1 − (V/c)2.
Acoustical Detection of Electrically Weak Vibrations in Quartz Plates
Authors: Pielemeier W. H.
Published: September 2005

Correlation of extensive results obtained from Y-cut plates with those obtained from X-cut and other plates leads to the conclusion that some thickness vibrations may produce a considerable acoustical effect while their electrical effect may be absent or at least difficult to detect by ordinary methods. The cause of this condition is thought to be the relatively strong electrical effect of the shear vibration or of certain length vibrations (harmonics) that happen to be quite near the mechanical thickness frequency responsible for the detected sound waves. Obviously the latter is more effective in producing sound waves traveling normal to the plate. The effect of humidity on the wave velocity was also studied. Two dispersion regions in air were discovered.
Limits of Audition for Bone Conduction
Authors: Watson Norman A.
Published: September 2005

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

An analysis is made of a standing wave resonance system consisting of an eight-foot iron pipe with an eight-inch dynamic speaker at one end and a movable iron piston at the other. Considering the speaker both as a source and as an impedance, expressions are derived for the phase shift, φ1, of the pressure wave at the speaker, and for the pressure amplitude in the tube. The relation connecting l and λ at resonance is found to be l = (n + φ/2π)λ/2, placing the speaker at a distance (φ/4π)λ from the first particle velocity node. (Contrast this equation with the relation l = nλ/2 for a tube rigidly closed at both ends.) Initial resonance frequencies and a pressure-frequency curve are computed for comparison with experimental data. The possibility of using the resonance conditions for measuring the impedance of diaphragms is pointed out.
Tones Produced by a Wire Placed in an Ignited Gas Jet
Authors: Coop J. J.
Published: September 2005

It was found that a wire placed in an ignited gas jet would produce a tone when the velocity of the gas reached a critical value. The tone was amplified by use of a second wire and by use of a photoelectric cell. The relation between the diameter D of the wire, the diameter O of the orifice, the distance d of the wire from the orifice and the critical velocity Ui for the initiation of the tone was found to be of the form OUi = kd/D + C, where k and C are constants. This equation is not linear for values of d less than one centimeter. It appears that a similar relation exists for the critical velocity Uf at which “flaring” starts. The products OUi/ν, where ν is the kinematic viscosity, were found to be nearly the same for the two gases used. At any distance of a wire from the orifice the frequency of the tone was found to be a linear function of the efflux velocity of the gas. The expression for the frequency was found to be of the form N = k/D(U − U0), where k is a constant and U0 is the velocity intercept. The quantity D(dN/dU) has an average value of about 0.047 for wire diameters between 0.04 and 0.1 cm. For a constant frequency the relation between the orifice velocity and the distance was found to be of the form U = Kdn, where n is approximately 12; nO12 is a constant and KO12 nearly constant. An approximate relation between frequency, velocity, and distance is given by N = kU/d12 + C, where k and C are constants. A thin metallic sheet placed against the wire on the downstream side prevents the production of the tone. As the distance between this sheet and the wire is varied the tone ceases at a critical distance, which is a function of the velocity and the diameter of the wire. For a fixed velocity this critical distance is proportional to the square root of the diameter of the wire. It was concluded that the tone is an Aeolian tone modified by the flow of one stream into a similar fluid at rest. An equation of the form N = kU/D was derived on the basis of the Bernard-Karman vortex theory. By comparing experimental with theoretical results it was concluded that for an ignited jet the density varies inversely as the distance from the orifice.
An Operational Treatment of Nonlinear Dynamical Systems
Authors: Pipes Louis A.
Published: September 2005

When a mechanical system is undergoing vibrations whose amplitudes are small but not infinitely small, then the Lagrangian equations of motion are of a nonlinear character and the phenomenon is most complex. The Laplacian transform, or operational treatment of linear dynamical systems is being more and more widely employed in the treatment of linear systems leading to a set of ordinary differential equations or to partial differential equations of the linear type. The use of the operational method in nonlinear cases here presented appears to be new. For purposes of illustration, a system of acoustical interest will be considered although the method is general and yields interesting results in a wide variety of cases.
The Absorption of Sound in Carbon Dioxide and Other Gases
Authors: Knudsen Vern O. , Fricke Edwin F.
Published: September 2005

Sound absorption measurements in pure CO2 at atmospheric pressure and 22°C have been conducted which, together with measurements by others, confirm the collision theory of anomalous absorption as developed by Einstein, Kneser, and others. The absorption coefficient is appreciable at frequencies as low as 2000 cycles, and increases to a maximum of 0.317 per wave-length at 77,000 cycles. This maximum is higher than values obtained by previous workers, and indicates that both the deformation and symmetrical valence vibrations participate in the exchanges between translational and vibrational energy. Small impurities, as water or alcohol vapors, affect the absorption greatly; the entire absorption band is shifted to higher frequencies. Measurements in mixtures of CO2 in O2 and CO2 in N2 indicate that neither the O2 nor N2 is appreciably excited by collisions with CO2. Measurements in CS2 reveal an absorption similar to that for CO2 except that the absorption begins at about 10,000 cycles. In mixtures of CS2 and O2, the observed absorption at frequencies below 10,000 cycles is accounted for by assuming that only the vibration of O2 molecules is excited by collisions with CS2 molecules; at higher frequencies the CS2 molecules also are excited, principally by collisions with other CS2 molecules.
Absolute Sound Measurements in Liquids
Authors: Klein Elias
Published: September 2005

The fundamental problem of absolute sound measurements in liquids is discussed. Regarding acoustic determinations, reference is made to certain inherent differences between air and water. An outline is presented of three methods now available for sound determination. A modified radiation pressure apparatus is described which permits a dual check of the basic measurements involved, and at the same time makes possible microphone calibration for secondary standards.
An Adjustable Tuning Fork Frequency Standard
Authors: Hugo Schuck O.
Published: September 2005

A portable tertiary frequency standard, adjustable over a small range, is described. The frequency determining element is a tube-maintained tuning fork, adjustment of whose frequency over a relatively small range is accomplished by changing the position of movable weights on the prongs. Calculations are simplified by the design of the fork, which permits the assumption of lumped constants.

The weights may be moved while the fork is running without interfering with its operation. Indication of their position is by means of a pointer reading on a scale graduated directly in frequency units. A precise method of calibration is given. Mechanical arrangements are described for obtaining a uniformly spaced scale, and the possibility of using such a scale in correcting for the temperature coefficient of the fork material is discussed.

The relative accuracy of such a fork is greater, the smaller the range of frequency adjustment. In the present development, adjustment may be made over a range of plus and minus three percent of the mean frequency, that is, a musical interval of one semitone, or 100 cents total change. Incorporation of this fork in the chromatic stroboscope has resulted in considerable simplification as well as an increase in the reliability of the instrument.
Effect of Physical Size on the Directional Response Characteristics of Unidirectional and Pressure Gradient Microphones
Authors: Massa Frank
Published: September 2005

A quantitative theoretical analysis of the directional characteristics of a unidirectional microphone, taking into account (1) the finite separation between the pressure and pressure gradient actuated elements and (2) the acoustic path increase caused by the physical structure which must necessarily enclose the rear of the pressure actuated element, reveals two types of variation of the microphone characteristics at the higher audiofrequencies. For a balanced microphone, the directional characteristic is substantially a cardioid of revolution at the lower frequencies. As the frequency increases there are two distinct departures from the cardioid. First, there is a marked reduction in the angle of high attenuation which is caused by the physical separation between the microphone elements. Second, there is a shift in the axis of maximum attenuation at the higher frequencies which is caused by the size of the structure which surrounds the pressure element. Experimental data taken on a balanced unidirectional microphone are presented to show the general agreement with the theoretical characteristics. The methods for controlling the amount of angular shift at the high frequencies are described as is also the method of mounting the microphone with reference to the pressure actuated element so that the “shift” will occur in the most favorable direction.

Theoretical analysis of an idealized pressure gradient actuated microphone (velocity microphone) shows that the directional response characteristics get broader with increasing frequency. Experimental data are shown on an actual microphone which bear out the theory at the higher frequencies but not at the medium high frequencies. An explanation for the discrepancy is given in the text.