bluuebunny/crossref_metadata_2025 huggingface dataset:
Masked Differential Pitch Sensitivity of the Ear for Musical Intervals
Authors: Bolt R. H.
Published: September 2005

Discrimination experiments were performed with pairs of pure tones in simple frequency ratios corresponding to musical intervals, primarily major thirds. The detectability threshold for a frequency shift in one of the tones was determined statistically on the basis of fifty percent responses. Intensity levels of the two tones were controlled independently as experimental variables. The study involved intensity levels up to 85 db, frequencies from 600 to 1200 c.p.s., and two-ear headphone listening by several observers. The results suggest the following tentative conclusions. For low and intermediate intensity levels, discrimination Δν is determined by the varying tone, as if it were present alone, except that the low intensity rise of Δν is controlled by the masking threshold imposed by the fixed tone instead of by the threshold of hearing. At higher levels, the subjective difference tone becomes audible and determines the discrimination. At still higher levels, pitch discrimination as such becomes meaningless because subjective beats are heard and can be counted to any desired accuracy.
Thermodynamic and Viscous Absorption in Fibrous Acoustical Materials
Authors: Beranek Leo L.
Published: September 2005

Sound absorption in fibrous materials normally takes place because of viscous losses in the gas near the surface of the fibers. This paper describes a different process of absorption, namely, that caused by thermodynamic losses accompanying the exchange of heat between the gas and the fibers during a cycle of compression and rarefaction of the gas. At low frequencies this cycle takes place isothermally, while at high frequencies it occurs adiabatically. In the transition region between those extremes in frequency, the line integral of the pressure times the differential volume taken over a cycle does not equal zero and, hence, energy losses occur. By constructing a material from fibers laid uniformly in a two-dimensional lattice and then varying the lattice spacing, this cross-over region can be arbitrarily shifted along the frequency scale. In a narrow band the normal absorption coefficient of a sample of adequate thickness is found to be high. If the spacing of the lattice is made non-uniform, the band width can be broadened, but at a sacrifice of peak absorptivity. By constructing materials from layers of suitably spaced wire-mesh screen, acoustical band elimination. filters are possible.
Frequency Response Fluctuations in Rooms. II. An Approximate Theory
Authors: Bolt R. H. , Roop R. W.
Published: September 2005

Irregularities in the steady-state frequency response of rooms arise from the normal mode structure, and depend on the frequency spacing, the damping, and the relative excitation of the normal modes. A first approximation theory of transmission irregularity, Φ, has been developed on a simplified model. Uniformly spaced normal modes, equally excited and equally damped, are added to yield an average ratio of maximum to minimum response. The influence of non-uniform spacing is introduced in the form of a frequency spacing index, ψ, which has been calculated for certain cases. The influences of non-uniform excitation and non-uniform damping are introduced formally but explicit evaluation has been made only for certain simple conditions. The resulting equation has the form Φ = A V ν2 log[1 + Bψν4a2] db/c.p.s. where A and B are constants, V is volume of room, a is the room absorption factor (reducing to Σαs for Sabine conditions). There is a region of maximum roughness (irregularity per c.p.s.) at a frequency of the order of 104(T/V)12, where T is reverberation time and V is volume. Well above this region, Φ diminishes inversely with ν2 and A2. This result is compared with experimental data.
The Directivity Factor of an Acoustic Radiator
Authors: Burke T. F.
Published: September 2005

Let an acoustic radiator produce at large distance r in the direction of maximum response an r.m.s. acoustic pressure p in a medium having characteristic impedance ρc. Then the total power radiated is: P = 4πr2p2ρcD. The directivity factor D is defined by this expression. Knowledge of D and of the electrical impedance of a transducer allows one to calculate its electro-acoustic efficiency from a measurement of the pressure produced on the acoustic axis by a known applied voltage. Experimental determination of D is difficult and subject to large errors. Theoretical determination has been limited to those radiators for which a theoretical directivity pattern is known and is sufficiently tractable to allow integration over a sphere. In this paper the acoustic reciprocity principle is used to obtain a very general expression for D in terms of the geometry and velocity distribution of the radiating surface. The expression may be evaluated for many radiators of practical interest without recourse to integration. For example: in the particular case of a uniformly driven plane radiator having area A and all dimensions at least one wave-length λ across, D = λ24πA and D is independent of the shape of A.
Music as an Aid to Healing: Progress Report
Authors: Lewis R. C. , Burris-Meyer Harold , Cardinell R. L.
Published: September 2005

The gathering momentum and bulk of general interest, lay activity, and professional exploration, with music as a possible therapeutic adjunct for medicine, has created the need for some type of liaison at the national level. Moreover responsible identification, selection, allocation, supervision, and evaluation of a variety of projects is essential at this time in order to expedite and channel most opportunely energies and expenses in this area of work. Surveys show that in addition to work with music and medicine in this country a few foreign countries, notably Russia, England, and possibly Italy, are doing some exploratory work—music and industry, likewise. Within the armed forces, especially in the hospitals, whether under service auspices, Red Cross or volunteer civilian organizations, a considerable amount of circumstantial evidence has been accumulated testifying to potential values in music as a therapeutic aid. Also, the coordinated utilization of music and color, music, and drama, as additional possible tools of therapy, are areas within which enough initial investigation has been done to warrant the more intensive work necessary for research as the forerunner of scientifically establishing the procedure. The melding of music as an art, with acoustics as a science, to the advantage of medicine as a profession offers an entire area conducive to fruitful research, the results of which should provide the documentation respectively required for establishing the validity or non-validity of the tenet that music is a positive therapeuticz adjunct to medicine.
Music in Industry Today
Authors: Cardinell R. L. , Burris-Meyer Harold
Published: September 2005

During the past six years there has been phenomenal increase in the application of music to work processes. The number of people hearing music while they work has increased from a few hundred to an estimated 5,000,000. This rise is caused by demonstrable increases in productive efficiency or improved employer-employee relations in certain plants where music installations have been studied with great care. There is still considerable confusion as to the aims and methods of application of music in industry, due to the fact that a number of fundamental misconceptions are widespread. Many installations are supervised by individuals whose training and experience has been only in the field of personnel relations or the field of music as an art form. The establishment of a prescribed emotional atmosphere is not something for which these backgrounds alone are sufficient. The technique is a highly complex one, involving the correlation of a number of scientific studies. Since the last report on this subject to the Acoustical Society, investigations have established more precisely the form and pattern of music and the manner of its presentation particularized as to types of work. Music is now applied successfully in offices where the conditions, requirements and limitations are quite different from those of industry. Unfortunately, the whole concept of functional music may be jeopardized by haphazard approaches where scientific techniques are not used. Merely because an art form is involved does not preclude the necessity of employing the scientific method.
Imagery in Describing Tone Quality
Authors: Salmon Vincent
Published: September 2005

As with musical instruments, the final acceptance of a sound system is largely determined by its performance in a carefully conducted listening test before a sound jury. The judgments of the jury are usually expressed in terms suggestive of the subjective reactions produced by specific characteristics of the reproduced sound. Many of these terms are related to tactile sensations, while others may only be described by reference to the program material. Some of the terms will be discussed in the light of related objective characteristics, and tentative definitions will be offered as a preliminary to possible standardization.
Binaural Magnetic Recorder
Authors: Camras M. , Zenner R. E.
Published: September 2005

A system of binaural recording is described, utilizing two magnetically recorded tracks on a 14″ wide coated paper tape. The system provides automatic synchronization, freedom from cross-talk, erasure and re-use of the recording medium, and continuous recordings of half an hour or longer.
The Modes of Vibration of Quartz Plates
Authors: Hulsizer Robert I. , Van Dyke K. S.
Published: September 2005

Using the method proposed by Buchs and Muller and apparatus developed by Scott the amplitude of vibration over the areas of a number of quartz plates has been surveyed with a high power microscope, and for several different modes. The resulting lines of vibrational amplitude make vivid the coupling of shear flexural and extensional modes and serve to confirm Mason's analysis of the dependence of the frequency constant upon the ratio of dimensions as resulting from intermode coupling. The amplitude surveys are used as the basis for computing the distribution of strain throughout the crystal and this latter, when combined with the known piezoelectric constants of quartz, and graphically integrated over the crystal, predicts the current to the crystal in fair approximation to the measured current. Vibration surveys are shown for fundamental and overtones of rectangular plates of differing length-width ratios and orientation including a GT-cut plate. Some of the surveys were made by Scott.
The High Q of Quartz Resonators
Authors: Waltz Maynard , Van Dyke K. S.
Published: September 2005

An early report of very high Q's was given by one of the authors before limiting conditions of surface cleanliness had been attained. Later measurements found the Q of a Y-cut etched quartz ring supported in vacuum by the V-shaped inner wall of the ring resting on a glass rod to vary from 3 to 6 × 106 depending on the point of support. Q shows two maxima in a complete turn of the ring. Q is highly sensitive to surface contamination, falling to half value in a couple of days when vacuum sealing compounds are present in the container, and to 16 value in a few minutes when aluminum oxide is used as a drying agent. The mode which shows the highest Q is 123 kc while the principal mode is 100 kc. Other characteristics of this mode which has not been completely identified are its very weak piezoelectric coupling, the close proximity of a third more strongly excited mode at 122 kc, and its two-loop nature around the ring as against three and four for the 100- and 122-kc modes, respectively. The Q measurements were made by timing the rate of decay. No other reports of Q's within one order of magnitude of these is known.
Diffraction at a Step-Down
Authors: Polster Harry D. , Slaymaker Frank H.
Published: September 2005

The diffraction pattern of an ultrasonic wave from the top edge of a step-down was investigated experimentally, using a pulsed ultrasonic beam and a smooth, accurately formed step. The wave diffracted from the edge was separated from the reflected or scattered components by using techniques similar to those used in radar to distinguish between objects at different distances from the antenna: namely, to synchronize the horizontal sweep on an oscilloscope with the transmitted pulses so that all echoes received by the microphone appear in the scope as pips whose distance along the sweep line is a measure of the time between transmission and reception. Magnetostriction transducers were used as radiators, the signals being picked up by a Western Electric 640-AA microphone. The region from 0°–90° (from grazing angles along the top of the step to the normal) was explored and the data compared with the theoretical values derived by Sommerfeld in his paper on the diffraction at a half-plane.
The Effect of Sensation Level upon Pitch Discrimination in a Continuous Thermal Noise Mask
Authors: Harris J. Donald
Published: September 2005

The intensity of a thermal noise was adjusted until it just masked a 1000∼ tone of 40-db sensation level. The pure tone was then increased either 3, 5, 7, 10, or 15 db in intensity, and differential pitch threshold obtained by the method of constant stimuli. The same procedure was followed for 1000∼ tones of 30, 20, and 10-db sensation level. For each sensation level a plot was drawn relating the differential threshold to the intensity of the pure tone above its detection threshold in the mask. For the lower sensation levels, sensitivity was relatively worse as a function of pure tone intensity above the mask. Control tests with no mask were run to determine whether this effect was the result of the relation of tone to mask or simply to the poorer sensitivity found with lower sensation levels in quiet. It was concluded that the effect was largely caused by the tone-mask intensity ratio. A previous experiment had suggested that pitch discrimination was under certain masking conditions a function of log loudness, in sones. The present experiment indicates that at the lower sensation levels, discriminability may change even more rapidly as a function of loudness. Within the limits of this experiment a gradual transition occurs in the discriminability-loudness relationship.
The Growth of Auditory Sensation
Authors: Munson W. A.
Published: September 2005

The integration of sensation with respect to time was studied experimentally by means of tones of short duration. Loudness tests were made on sounds persisting from .005 to 0.2 second and covering a wide range of levels. The observed increase in magnitude of a sensation as the duration time is increased is attributed to the properties of nerve conduction in the central nervous system, and an equivalent electrical circuit is derived. The circuit analogy is then used in the computation of loudness as a function of the duration time of the stimulus.
A Theory as to the Function of the Scala Tympani in Hearing
Authors: De Rosa L. A.
Published: September 2005

The Scala Tympani canal is assumed to be coupled to the Scala Vestibuli of the cochlea throughout its length. If the mathematics are formulated for this premise, with appropriate boundary conditions, it is found that despite the absence of reflections and standing wave patterns, there is, nevertheless, an area of maximum stimulation of the basilar membrane as a function of frequency. Interpretation of various acoustical phenomena is simplified by reference to this analysis and a number of applications of this “2 canal theory” are presented. A model to show the probable mode of operation will be shown, this model comprising an electromagnetic transmission line network, suitably excited.
Phase Effects in Monaural Perception
Authors: Mathes R. C. , Miller R. L.
Published: September 2005

Experiments are reported demonstrating that the envelope wave shape of a complex steady-state tone is an important factor in audible perception. In particular, it strikingly influences sensations of roughness or smoothness and is related to a sensation of apparent pitch. As envelope wave shape depends on the phases as well as the amplitudes of the components, effects of this type can be produced by changes in the phase alone of but a single component or group of components. The results provide general verification of a limitation placed by Helmholtz on theoretical grounds as to the degree to which his phase rule might be expected to be true. The experiments were conducted at such levels that subjective tones produced by non-linearity in the ear are not believed to influence the results. It is suggested that these results emphasize the importance of time factors in the phenomena of aural perception.
Broadened Criteria of Hearing Aid Performance
Authors: Mundel August B. , Carlisle Richard W.
Published: September 2005

The requirements of hearing aid users include, besides adequate acoustic response, low reaction to “noise” excitation, and other characteristics. Methods used in reducing unwanted sensitivity are discussed. Other operational features of a hearing aid are considered and a single chart method of presenting acoustic input-output characteristics, frequency response, and distortion is described.
Construction and Calibration of an Improved Bone Conduction Receiver for Audiometry
Authors: Carlisle Richard W. , Werner Pierre R. , Pearson H. A.
Published: September 2005

The construction of an acoustically shielded bone conduction unit is described. The masses and springs have been proportioned for optimum purity of wave form at low frequency, and for extension of the high frequency range to over 12,000 cycles. The precautions taken in preparing an acoustical loudness-balance calibration are described, and the reproducibility of observations is considered. Methods of specifying the response of production units are shown.
Auditory Masking in Sonar Listening Systems
Authors: Gales Robert S.
Published: September 2005

An essential element in predicting the maximum range at which an underwater sound source (signal) may be heard over a given sonar listening system is the signal to noise ratio for a prescribed probability of recognition. This ratio, measured in the frequency band presented to the listener, and expressed in decibels, is termed the recognition differential. The usefulness of this quantity rests on the fact that with sonar equipment properly engineered and operated, signals ordinarily are masked by noise picked up by the hydrophone; thus both signal and noise receive the same amplification at each frequency, making their ratio independent of the gain of the system. Recognition differentials for many different combinations of underwater signals and background noises were measured experimentally by presenting recorded samples of the sounds to a crew of five observers. Although this method yielded a reliable value of the recognition differential for each pair of sounds tested, the wide variation in the value from signal to signal, and the observed dependence on the frequency band passed by the system led to a search for a more general measure of signal audibility. By making suitable spectrum analyses it was possible to interpret the observed phenomena in terms of current masking theory utilizing Fletcher's critical bands. This led to a useful criterion for predicting the threshold level for a signal masked by a background noise where the spectra of both are known. Application of this criterion is restricted to: (1) background noises having continuous spectra, (2) signal and noise spectra differing in shape, (3) receiving systems producing adequate loudness. This critical band criterion of recognition has been found useful in predicting the effects on sonar operation of such factors as: (1) system frequency response including filters, (2) system gain, (3) self-noise spectrum, (4) hydrophone directional characteristics, (5) frequency selective sound propagation. This represents one of the results of research carried out by the University of California Division of War Research under contract OEMsr-30 with the Office of Scientific Research and Development (Section 6.1 NDRC). This work is continuing under the Psychophysics Section of the U. S. Navy Electronics Laboratory.
The Type 310-A Z-Angle Meter, a New Instrument for Electrical and Electroacoustic Measurements
Authors: Packard L. E.
Published: September 2005

The importance of impedance and phase angle measurement over a wide range of frequencies of electrical and electro-acoustic apparatus such as amplifiers, microphones, loudspeakers, transmission lines, and other electrical networks having electrical or mechanical resonances, has long been recognized. Up to this time, engineers requiring such measurements have been forced to resort to hastily made laboratory set-ups using the two-voltmeter method of measuring impedance, to use a.c. bridge methods which inherently are not well adapted to this type of measurement, or to construct special apparatus designed around their own particular requirements. This paper describes the principle of operation of a new instrument, the Type 310-A Z-Angle Meter, which is designed specifically for these applications and which, in addition, because of its wide ranges of R, L, and C, is an extremely versatile general purpose laboratory instrument. Applications of specific interest to those concerned with electro-acoustic measurements, along with examples showing its applications to other types of measurement, are described.
Standard Lag Line for Phase Measurement
Authors: Schuck O. H.
Published: September 2005

Phase measurements are more difficult than current measurements, but are becoming more important as the art develops. In this paper the available methods for phase measurement are reviewed, and the usefulness of a method using a standard lag line as a reference is pointed out. Ways of using such a line for various types of measurements are discussed and the construction of two such lines is described. An investigation of errors indicates that accuracies to within 14° can be attained.
A New Logarithmic Electronic Indicator
Authors: Nolle A. Wilson
Published: September 2005

Acoustic measurements are often facilitated by the use of an electronic device with output consisting of a direct current which is proportional to the logarithm of the a.c. input voltage. A uniform decibel scale is obtained when such a device is used in conjunction with a linear indicator, such as a cathode-ray tube or a d.c. meter. The several circuits to perform this function which have been described previously have depended upon approximate logarithmic characteristics of vacuum tubes. The present paper outlines methods for securing from combinations of passive circuit elements a response which in principle is rigorously logarithmic. The logarithmic time-voltage characteristic of an impulse-excited resistance-capacity circuit is considered in particular. A brief description is given of a specific circuit which produces logarithmic indication over a 20–30 db range. The more important practical design limitations are mentioned.
Noise Reduction in Signal Corps Hand Generators. Part I: Internal Quieting of the Generators
Authors: Berg Sidney
Published: September 2005

During the war, the Signal Corps was faced with an urgent need for quiet portable hand generators for use near the front lines to power radio sets. Existing engineering practices used in quieting rotating equipment containing a high speed step-up ratio failed. Similar equipments of our allies and of the enemy were likewise noticeably noisy despite considerable effort to overcome this. A detailed investigation by the Signal Corps of silent drives and quiet machinery together with noise analysis of the equipment by means of the ERPI frequency analyzer and other conventional means resulted in the development of a silent drive heretofore unapplied for such a requirement. The drive developed was not only quiet but simultaneously met military requirements as to weight, size, efficiency, and life which, of necessity, are stringent. Comparisons are drawn of the relative merits of gears (types—internal, external, planetary, etc.; and materials—rawhide, copper, manganese, sintered powdered metal, laminated phenolics, etc.), hydraulic drives, belt drives, and chain drives.
Phase Effects in Monaural Perception
Authors: Mathes R. C. , Miller R. L.
Published: September 2005

Experiments are reported demonstrating that the enveloped-wave shape of a complex steady-state tone is an important factor in audible perception. In particular, it strikingly influences sensations of roughness or smoothness and is related to a sensation of apparent pitch. As envelope-wave shape depends on the phases as well as the amplitudes of the components, these differences of sensation can be produced by changes in the phase alone of but a single component or group of components. The results provide general verification of a limitation placed by Helmholtz, on theoretical grounds, as to the degree to which his phase rule might be expected to be true. The experiments were conducted at such levels that subjective tones produced by non-linearity in the ear are not believed to influence the results. It is suggested that these results emphasize the importance of time factors in the phenomena of aural perception.
The Effect of Frequency Spectrum on Temporal Integration of Energy in the Ear
Authors: Garner W. R.
Published: September 2005

These experiments are designed to test the following hypothesis. The rate of the temporal integration of energy in the ear (at threshold) is dependent on the width of the frequency band of the energy to be integrated. Duration is exactly equivalent to intensity only when all the energy to be integrated is in a narrow band of frequencies. The hypothesis tested by taking advantage of the spectral distribution of energy in short tones. As a tone becomes very short, the effective band width of the energy increases. The band width of energy is essentially defined by the reciprocal of the duration of the tone. Thus as the duration of a tone decreases, not only does the total energy in that tone decrease, but the band width of energy also increases. The intensity threshold, then, has to be increased (as duration is decreased) to compensate for both effects if the hypothesis is correct. The results are in line with the predictions of the hypothesis. The width of the band necessary for maximum integration is also related to frequency and the width of critical bands.
Reflection and Transmission of Sound by Thin Curved Shells
Authors: Primakoff Henry , Keller Joseph B.
Published: September 2005

In this paper the reflection and transmission of sound by thin curved shells, as well as several related problems, are treated mathematically. First, one derives an inhomogeneous integral equation for the sound field in an infinite medium containing a thin curved shell of different material. The solution of the integral equation is then reduced, approximately, to the evaluation of a surface integral not too different from that obtained in the usual Kirchhoff diffraction theory. The integral is evaluated approximately and gives expressions for the pressure waves reflected from and transmitted through a thin curved shell. The reflection and transmission coefficients of the shell are obtained from these expressions. It is found that the reflection coefficient can be expressed as the product of a geometrical factor, a phase-cancellation factor, and a reflectivity factor. When the reflection problem for a rigid obstacle is solved with the aid of the assumptions of the Kirchhoff diffraction theory, the reflection coefficient thus obtained is the product of the geometrical and phase factors of the previous solution. The geometrical factor alone is obtained as the reflection coefficient when the reflection problem is solved exactly by geometrical acoustics. The agreement among the various solutions may be considered as a partial justification for the Kirchhoff theory as well as for geometrical acoustics.

The Kirchhoff method is also applied to the problem of refraction at a curved surface. From the solutions of the reflection and refraction problems, the laws of reflection and refraction for curved surfaces are obtained. In addition, the mirror and lens laws, the conditions for point images, and the change of phase at a focus are obtained.
A Continuously Variable Acoustic Impedance
Authors: White J. E.
Published: September 2005

The mechanical impedance of an electromagnetic speaker is affected by current flowing in the electrical elements, just as the electrical impedance is influenced by the motion of the mechanical system. This paper gives the relation between mechanical impedance and electrical load impedance, making use of the three complex speaker constants evaluated by the motional impedance method presented earlier by R. D. Fay. Measurements are given showing that the mechanical impedance of a WE555 horn driver can be varied over a fairly wide range.
Measurement of Acoustic Impedances of Surfaces in Water
Authors: Fay R. D. , Brown R. L. , Fortier O. V.
Published: September 2005

An analytical and experimental investigation of the practicability of a water-filled acoustic impedance tube is described. It is shown that by proper choice of tube material, and of diameter and wall thickness with respect to wave-length, a satisfactory tube for measuring the impedance of underwater acoustic materials can be built. The phase velocity of sound in the tube is nearly constant in the useful frequency range but less than the velocity of sound in free water, and the variation in sound pressure along a radius of the tube is frequency dependent. Both rigorous and approximate formulae are given for the phase velocity and radial pressure dependence. These formulae are checked experimentally.
A Powerful High Frequency Siren
Authors: Allen C. H. , Rudnick I.
Published: September 2005

This paper describes the design, construction and performance of a high intensity, high frequency (3–34 kc) siren and some rather striking phenomena which occur in the intense sound field produced by it. The siren is of the usual type consisting of a rotor which interrupts the flow of air through orifices in a stator. The rotor consists of a disk, approximately 6 in. in diameter, with 100 equally spaced slots and is driven by a small 23s hp high speed motor whose speed is varied by changing the applied voltage. The 100 corresponding holes in the stator are circular in section. For better radiation at the lower frequencies a plywood horn is mounted on the siren. The siren itself is small, and may be operated in any orientation. In its initial form, operating with chamber pressures in the neighborhood of 0.2 atmosphere, its measured efficiency was between 17 percent and 34 percent in the frequency range 3 to 19 kc with an acoustic output between 84 and 176 watts. There is a fair amount of parasitic noise, but it is negligible compared to the signal. With recent modifications, chamber pressures of about 2 atmospheres were obtained, yielding acoustic outputs of approximately 2 kilowatts, and an efficiency of about 20 percent.
Plate Vibration of Stringed Instruments at the Wolfnote
Authors: Kessler John A.
Published: September 2005

The principal mode of belly vibration at the wolf note was determined by direct investigation of violins, violas, and cellos. The same mode was found to be common to all three types of instrument, corresponding to a marked peak in the response curves of the instruments. Chladni sand patterns were obtained on a flat brass plate shaped like a violin; typical patterns are presented, including the mode observed on instruments at the wolfnote. Requirements and methods for improving the wolfnote are discussed. Some functions of the f-holes, soundpost, bass-bar, and sides are noted.
An Electrical Method of Measuring the Intonation of Cup-Mouthpiece Instruments
Authors: Webster J. C.
Published: September 2005

An electrical driving system has been worked out for intonation tests on cup mouthpiece instruments. The system amounts to driving an acoustic transmission line from a closed end and measuring the resonant frequencies. It is shown experimentally that these resonant frequencies correspond quite precisely (within about 10 cents) to the frequencies normally played, except at the lower end of the scale where the player habitually corrects the defective intonation of the usual instrument. The experimental work includes tests on specially designed instruments that could not be played “in tune” with standard fingering.
Coordinates and the Reciprocity Theorem in Electromechanical Systems
Authors: Miles John W.
Published: September 2005

It is shown that the (force-voltage, velocity-current) mechanical-electrical analogy yields circuit equations for an electrostatic electromechanical transducer which satisfy the reciprocity theorem, while the (force-current, velocity-voltage) analogy acts similarly for a magnetic transducer. Reversing the two analogies between the two types of transducers yields (in both cases) equations which violate the reciprocity theorem in sign but not in magnitude. These conclusions indicate proper coordinate choices in applying Lagrange's equations to such systems. It is also shown that McMillan's “one-way” four-terminal network (see reference 1) is equivalent to a simple, class A vacuum-tube amplifier having an amplification factor of approximately two.
High Frequency Absorption in Air and Other Gases
Authors: Sivian L. J.
Published: September 2005

The absorption coefficients were measured for gases: (A) O2; (B) N2; (C) O2+N2 in normal air proportions; (D) O2+N2+CO2 in normal air proportions; (E) O2+N2+CO2 in normal air proportions, plus H2O vapor at 37 percent Rel. Hum. at 26.5°C; (F) O2+N2 in normal air proportions, plus a CO2-content varied from zero to 1.15 percent by volume. Let R denote the ratio of the measured absorption coefficient to that computed from the Stokes-Kirchhoff equation. For gases (A), (B), (C), and (D), R is roughly 1.5. For gas (E), R is of the order of 10 at 15 Kc.p.s., and approaches 1.5 with increasing frequency. For gas (F) at 89 Kc.p.s., R increases with rising CO2-content, attaining roughly R = 20 at 1.15 percent CO2-content.
On the Design of Perforated Facings for Acoustic Materials
Authors: Bolt Richard H.
Published: September 2005

An approximate analysis of the acoustic behavior of perforated facings for absorptive materials is outlined and is reduced to a design chart. Only the mass reactances of the holes and of the facing material are included in the analysis. This simplified picture is adequate for many practical problems, but breaks down for certain conditions which are discussed. If the acoustic impedance of the unfaced material is known, absorption coefficients for the material with perforated facing can be read directly from the chart.
Cones as Underwater Transducer Reflectors
Authors: Mueser Roland E.
Published: September 2005

Two conical reflectors have been constructed and used in conjunction with complete 90 tones. The result is a directional transducer in place of the non-directional pancake pattern resulting from a line source radiator. The change in peak sensitivity by focusing the beam is approximately equivalent to the change in directivity index.
A Recorder of Difference of Level
Authors: Lawther James M. , King John G.
Published: September 2005

Modifications have been made on a Sound Apparatus Company level recorder to permit its application to the measurement of difference in level between two sounds. The modified circuit explained with reference to simplified diagrams; anti-hunting devices are briefly noted; and the methods of pre-setting the instrument for level and differential operation are discussed.
The Application of Helmholtz Resonators to Sound-Absorbing Structures
Authors: Jordan Vilhelm L.
Published: September 2005

This paper intends to set forth some of the more important facts about sound-absorbing structures of the kind whose absorption may be explained as primarily due to resonance phenomena of the same kind as that occurring in Helmholtz resonators. It is believed that this kind of absorption has not been met with the general interest which it deserves, neither from the theoretical nor from the practical point of view. The theory is developed here only for the simple case of a single resonator. Special attention has been given to the question of the resistance of the resonator. It is pointed out, that the formula commonly used for the resistance of an aperture is not applicable in the case of resonance absorption, the actual values of the resistance being 3–6 times higher than the calculation predicts in the cases considered. Some examples of the practical applications of resonance-absorbing structures are mentioned.
Most Comfortable Listening Levels for Pure Tones
Authors: Watson Norman A.
Published: September 2005

By the most comfortable listening level for a pure tone is meant the level which the listener chooses as most comfortable for listening when he listens to a pure tone of which he can change the level at will. Ranges and mean values of most comfortable listening levels are given for pure tones in the range 128 to 8192 c.p.s. (at octave intervals) for listeners with normal hearing and listeners previously exposed to gunfire and airplane noise, with resultant marked hearing loss in some cases. Tentative most comfortable listening level contours are suggested. The use of a most comfortable level contour for specification of a hearing aid amplifier is discussed and an example given of the effectiveness of such an amplifier as compared to one specified by a most comfortable loudness level contour.
Bone Conduction Threshold Measurements
Authors: Frazier T. V. , Watson N. A.
Published: September 2005

Bone conduction thresholds were taken at frequencies from 1500 to 12,000 c.p.s., using the induction-type electrodynamic bone conductor and the air and bone conduction test assembly described in earlier papers. Stray air radiation from the bone conductor is an important factor at the frequencies considered; therefore, the bone conductor was enclosed by a sponge rubber jacket to minimize the air radiation, and the ears were covered by the test assembly boxes lined with absorbing material in order to protect them from the residual radiation. The present investigation is an extension of earlier work done at frequencies at which stray air radiation effects are negligible, and the results obtained are combined with those of the earlier study to yield a tentative bone conduction threshold from 80 to 12000 c.p.s.
The Time Integral Basic to Optimum Reverberation Time
Authors: Maxfield J. P.
Published: September 2005

Equations showing the relation between the volume, V, of an auditorium and its optimum reverberation time, T0, were published independently by MacNair and Liftschitz. MacNair's equation was derived from the following basic assumptions: ∫ 0T1 (logρ)dt = a const., (1) E = const., (2) where ρ = instantaneous value of the energy density of sound during decay. T1 = time of decay to minimum audibility. E = rate of supply of energy during the steady state condition.

This paper shows that an equation, relating T0 and V, can be deduced which more nearly fits all the empirical facts by basing the derivation on the following assumptions: ∫ 0T1 ρ⋅dt=a const., (1) E = GVn, (2) where G = a constant, n = a constant which should be less than unity.

The resulting equation, for n = 23, is T0 = 0.212 V1/6. This is in agreement with the empirical data and with the equation derived by Maxfield and Albersheim from acoustic “liveness” considerations.

The psychologists and physiologists studying the mechanism of hearing should be interested in these results, as they have a bearing on the manner in which the ear integrates the sound being perceived.
Some Biological Effects of Intense High Frequency Airborne Sound
Authors: Allen C. H. , Rudnick I. , Frings H.
Published: September 2005

Some experiments have been conducted to determine the effect of intense high frequency airborne sound on mice and a variety of insects. The sound source was a high frequency siren. The frequency used was about 20 kc, and its acoustic level, in the region where the subjects were placed, was between 160 and 165 db (relative to 10−16 watt/cm2). With sufficient exposure—from 10 seconds for flies and mosquitoes to 3 or 4 minutes for roaches and caterpillars—the sound proved lethal in all cases. More detailed work was performed on mice and the roach, Periplaneta americana. In both cases it was definitely established that the heating produced by sound absorption was sufficient to cause death. In addition to the heating there are other effects, notably tissue rupture, as evidenced by the almost complete distruction of the wings on flies and mosquitoes and the rapid deterioration and final disappearance of the external pinna of a mouse who had received a sublethal dose. During observations it has been impossible to completely avoid personal exposure to the sound field, and some of the effects observed under these conditions will be described. These included momentary dizziness, and heating of exposed parts of the hand.
Auditory Masking of Pairs of Tones by Random Noise
Authors: Schafer T. H. , Gales R. S.
Published: September 2005

Although a number of investigators have studied the summation of loudness of two or more tones heard simultaneously, there has been but little work on the summation of tones at or very near threshold. In the experiments here reported, summation effects at the masked thresholds for tones masked by random noise were investigated. The tones were studied in pairs, the separation of the two components being 25, 100, and 500 c.p.s., the frequencies being selected to maintain their geometric mean frequency at 800 c.p.s. The aural critical band width for binaural listening at this frequency is approximately 40 cycles; thus the tones selected were separated by slightly less than one critical band, slightly more than one critical band, and somewhat over ten critical band widths, respectively. The masked thresholds for the tones heard singly and in pairs were measured for five listeners for 60-db and 20-db masking. Addition of the second tone caused no significant improvement in recognition in any case except the one where the two tones were located within the same critical band. In this case a gain in recognition of approximately 1.7 db was obtained.
Audio Noise Reduction System
Authors: Olson Harry F.
Published: September 2005

A threshold type of noise reduction system has been developed for use in reducing the noise in sound reproducing systems. A non-linear element allows the useful signal to pass but discriminates against the noise. This system lowers the ground noise level and thereby increases the signal-to-noise ratio without discrimination against the useful part of the signal. The operation of the system is instantaneous. There is no frequency discrimination for any signal level above the threshold.
The Directional Characteristics of a Clamped-Edge Disk
Authors: Merrill Lynn L. , Slaymaker Frank H.
Published: September 2005

It is well known that to obtain very small side lobe radiation, the amplitude distribution across a radiating surface should be such that the maximum amplitude is at the center and the minimum at the edges. The Gaussian distribution gives no side lobes but requires an infinitely large radiator. This paper gives the analysis of the clamped-edge disk vibrating in its first normal mode. It shows that the dynamic curve approximates the Gaussian form and that the sound pressure distribution has very small side lobes, the amplitude of the first side lobe being 33 db below that of the axial lobe.

For a disk of a given diameter the width of the axial lobe may be decreased by raising the frequency of the first normal mode, which requires a corresponding increase in the disk thickness. At very high frequencies the disk thickness may become prohibitive. In such cases a thin disk can be forced to vibrate in the shape of the first normal mode by a proper radial distribution of the driving force.
Measurement of Directivity Factor
Authors: Burbank Cecil J.
Published: September 2005

The directivity factor, the ratio of the average sound intensity from an electroacoustic transducer to the sound intensity in the reference direction, both measured at the same separation, is measured directly using the device described.

The equipment is composed of a mechanical mounting which permits rotation of the unit about two mutually perpendicular axes and electronic equipment which integrates the power. The electronic circuits used are of two different types; one type, designed by D. H. Ransom and J. H. Martin, uses a thermocouple, a direct-current amplifier, a 60-cycle vibrator, a 60-cycle amplifier, and a modified watt-hour meter; the other type, designed by R. C. Fisher and C. J. Burbank, uses the potentiometer in a power level recorder into which 60-cycle alternating current has been introduced, a 60-cycle amplifier, and a regular watt-hour meter which has been modified to increase the dynamic range.

A measurement of the directivity factor and the input power to the transducer gives the over-all efficiency of the unit in question.

The design considerations and use of the instruments are discussed.
High Frequency Whistles; Edge Tones and Resonance
Authors: Nyborg W. L. , Schilling H. K.
Published: September 2005

A previous paper reported an experimental study of the dependence of the intensity and frequency of the output of ultrasonic whistles upon whistle dimensions and airflow, and suggested that the results could be explained qualitatively by assuming that the whistle is a system of two oscillators, the first being a cavity resonator and the second a jet-and-edge producing high frequency edge tones.

Since then the possibility of generating edge tones having frequencies exceeding 100 kc has been demonstrated. The resonance of small cavities has been studied, and it has been found that their first eigentones can be computed rather accurately on the basis of simple closed pipe theory. A “synthetic whistle” was constructed, consisting of a jet-and-edge and a small resonator, whose relative positions and orientations could be varied.

The properties of each of the two components of this whistle assembly were studied separately, as well as the results of their interaction upon each other. The findings for this synthetic whistle model are consistent with those for actual whistles and seem to verify the correctness of the assumption made earlier.
An Acoustic Screen for Making Underwater Noise Reduction Tests in Pearl Harbor
Authors: Loye Donald P. , Arndt William Fred
Published: September 2005

When the German submarine menace had been largely overcome during World War II, the attention of our Navy and scientists turned toward reducing the noise of our submarines in order to make them less readily detectable. To accomplish this required improvements in the submarine noise-measuring techniques.

In Pearl Harbor, where there often were eight hundred ships of all kinds, the underwater noise level was high. There was no place found where noise measurements could be made satisfactorily, and therefore special methods had to be developed. After extensive study it was decided that the best arrangement would be to insulate Auxiliary Repair Docks, and measure the noise of submarines while they were in the docks. This was done by the development of a suitable air-bubble screen across the open end of the dock. Such an acoustic barrier was comparatively easy to install, did not interfere with submarines entering and leaving, kept ocean surface oil out of the dock, insulated against low as well as high frequency noises as was required, and, after extensive experimentation, the noise of the screen was reduced to a level that did not interfere with the noise measurements. The insulation of the screen upon the noise of a nearby submarine-charging batteries is illustrated by a phonograph recording.