bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Tone Envelope of Harmonic Components of Musical Sounds
Authors: Schmidt J. M.
Published: September 2005

A study was made of the relative intensities of the harmonic components of a musical tone during the build-up and decay periods of the tone. Tones from four musical instruments, clarinet, trombone, bassoon, and violoncello, were recorded so the same tone could be reproduced at will. The reproduced tones were separated into their various harmonic components by means of a wave analyzer. A complete oscillogram was obtained of each harmonic. From these separate oscillograms the harmonic content of the original tone could be determined for any time during its transient periods. All tones analyzed had a pitch of 220 vibrations per second. For the clarinet the 1st and 3rd harmonics appeared first and 0.03 second later the other harmonics also appeared, reaching their full intensity in 0.10 second. The 1st and 3rd harmonics also persisted the longest during the decay period. The tone of the trombone builds up rapidly. All harmonics appear simultaneously and reach their full intensity in 0.09 second. During the decay period the 4th, 5th, and 6th harmonics disappear all at about the same time. The 3rd, 2nd, and 1st harmonics disappear later and in the order named. For the violoncello the 2nd harmonic appeared long before the other harmonics and persisted even longer at the end of the tone than the 1st harmonic.
Laboratory Studies on the Violin and Other Bowed String Instruments
Authors: Small Arnold M.
Published: September 2005

Studies aimed at increasing the performer's understanding and control of his instrument have been carried out principally on the violin. Harmonic analyses have been made of tones over a wide range of fundamentals on the instrument with standard bowing and stopping of the string as well as of so-called natural and artificial harmonics. These are presented as specific spectra rather than statistically treated. The relationship between bowing factors and the relative intensity and overtone structure of the instrument's output were investigated by means of a controlled mechanical bowing mechanism. Additional work dealt with air-cavity resonance, effect of elimination of body resonance, effect of mutes, and analysis of viola, cello, and contrabass tones. An attempt will be made to correlate the results with the artistic demands placed upon the performer by music of the past and present and to relate them to the development of string playing over the last two hundred and fifty years.
The Barcroft Underwater Acoustic Facility of the Naval Ordnance Laboratory
Authors: Turner W. R.
Published: September 2005

The paper describes a new underwater acoustic measurement facility located on a raw-water storage reservoir in Fairfax County, Virginia. The reservoir contains a major basin approximately 1500 feet long and 350 feet wide. Water depth is 50 to 57 feet over an area 50 by 500 feet at the center of this basin. The bottom is covered by two feet of sound-absorbent silt. As a result, the basin is quite free of cavity resonances at frequencies above 200 cycles per second. Over-all ambient noise varies from 0.25 to 4.0 dynes/cm2 amplitude at the center of the basin. Construction work, just completed, has provided a 32- by 44-foot steel barge holding a 26- by 32-foot frame laboratory building, a 20- by 27-foot utility building on the shore, a pier, and a pontoon bridge connecting the barge and the pier. These structures were specially designed for the acoustic facility with particular attention to an adequate power supply and ground system, maximum utilization of the acoustic features of the basin, and operation by a minimum number of personnel. Electronic instrumentation is now being designed and constructed by a special project group. This equipment will cover an over-all frequency range of 10 cycles per second to 3.0 megacycles. Both continuous wave and pulse techniques will be employed. The signal measuring system will be in three channels. These can be employed for broad-band, or, utilizing a heterodyne system, for narrow-band reception. Measurements can be made of power, impedance, and phase angles as well as signal amplitudes.
A Quartz Crystal Hydrophone of Novel Design
Authors: Atanasoff John V. , Bobroff David L.
Published: September 2005

Early in 1944 a satisfactory secondary standard hydrophone for the audiofrequency range became essential for the testing of underwater sound devices at the Naval Ordnance Laboratory. The requisites were stability, low temperature coefficient, and a flat frequency response from 20 to 10,000 c.p.s. These were achieved by employing what appears to be a new way of mounting crystals for microphone purposes. A thin X-cut quartz crystal disk was cemented on the back of a steel diaphragm, the other side of which faced the water. Bending of the diaphragm by sound pressures in the water induced strains in the crystal which in turn induced an electric voltage between the two sides of the crystal. Further applications of this principle are pointed out, such as the determination of the circumferential extension of a gun barrel in firing and vibration studies.
Underwater Acoustical Measuring Facilities at the U. S. Navy Underwater Sound Laboratory
Authors: Hill A. M.
Published: September 2005

During the war the Underwater Sound Laboratory at New London carried on much of its acoustical test work on a sound barge located at the laboratory pier in the Thames River. Relatively shallow water and the high noise level resulting from rough water, passing ships, and manufacturing establishments located on the water front reduced the usefulness of this barge. A second sound barge was therefore installed on a small inland pond not far from the laboratory. It is intended to use this barge to satisfy the exacting demands of long-term tests of scanning sonar transducers and systems and to serve as a center for developmental research in measuring techniques. The barge is located at the end of a 300-foot pontoon pier in 48 feet of pure and practically noise-free water. It has a four-foot by twenty-foot well with one movable hoist column and one training hoist column. The electronic gear on the new barge is capable of measurements over a frequency range from two to 150 kc. Among the types of measurements made are: (1) frequency responses, receiving, and projecting; (2) directional patterns (polar or rectangular); (3) reciprocity calibrations; (4) admittance measurements; and (5) phase measurements. For frequency responses, a Leeds and Northrup “Speedomax” recorder is used. For directional patterns, the recorder is linked to a polar turntable by a mechanical linkage.
The German Use of Sonic Listening in World War II
Authors: Holt L. E.
Published: September 2005

The most successful German sonic listening device, the GHG Gruppenhorchgerät, is described in general terms. Reference is made to the types of ships using the equipment and to the arrangement and placement of the hydrophone arrays. A brief account is given of the steps taken by the Germans to improve the operation of the GHG by stream-lining the array and by altering its position on the hull. The simple but efficient electrical training device is explained and bearing accuracy and range data, as reported by the Germans, are presented. The paper is based on technical reports received from Germany and on subsequent investigations.
Problems in Sonar Data Research
Authors: Bergmann Peter G.
Published: September 2005

Sonar data research is that broad field of investigation concerned with the physical and psychological principles involved in the employment of underwater sound in naval weapons. It is proposed to sketch some of the problems involved in the propagation of sound in the sea. Almost all of the results obtained are now unclassified and are gradually being made available to the scientific public through publication by the individual authors as well as by the production of the Technical Summary Volumes of the NDRC, which in this field are mostly unclassified. The problems investigated may be briefly described as follows: (1) Transmission of sound in the ocean—(a) refraction of sound in the ocean, (b) attenuation of sound, (c) reflection from surface and bottom and Lloyd mirror effect, (d) signal fluctuation. (2) Scattering of sound in the ocean—(a) dependence on the properties of the sound source, (b) dependence on time, (c) distribution of the scatterers in the ocean, (d) frequency and coherence characteristics of the scattered sound. (3) The formation of echoes.
Acoustical Characteristics of Noise Produced by Snapping Shrimp
Authors: Everest F. A. , Young R. W. , Johnson M. W.
Published: September 2005

Some marine animals produce sounds which, under certain conditions, completely dominate the ambient noise in the sea. The snapping shrimp (not to be confused with the edible shrimp) is one of the most widely distributed of these animals; it is frequently less than 3 cm in length and produces the sound by snapping of the claw. Shrimp noise is likely to be found around the world in tropical and sub-tropical waters less than 55 meters deep wherever rock, coral, or other material on the bottom provides interstices in which shrimp thrive. This paper describing the acoustic output of the snapping shrimp (Crangon and Synalpheus) is based upon measurements made off the Southwestern and Southeastern coasts of the United States, the Hawaiian Islands, and several islands in the Southwest Pacific. Over a shrimp bed the noise spectrum is found to be roughly independent of frequency from 2 to 24 kc (the upper limit of measurement), whereas the ambient noise normally present in the deep sea decreases with frequency. There is a broad peak in the shrimp spectrum between 2 and 15 kc. Over a shrimp bed the noise at 20 kc is about 25 db above the ambient noise which accompanies a sea state of 2 (waves less than a meter high, not including swell). For low sea states shrimp noise is appreciable a mile or more from the boundary of the bed. The diurnal variation of shrimp noise is from 2 to 6 db, the noise being greater at night. Single snaps from isolated specimens have been subjected to a Fourier integral analysis which indicates a spectrum comparable to that measured over shrimp beds where the underwater sound consists of a multitude of snaps. A typical peak sound pressure at the distance of a meter from a single shrimp is of the order of 200 dynes/cm2.
Metronomic Tuning of Keyboard Instruments in the Tempered Scale
Authors: Mitchell William D.
Published: September 2005

This paper describes a practical method of tuning keyboard instruments in the tempered scale, based on the use of an ordinary metronome, and presents an extended table of beat frequencies for that purpose. The paper is intended to clarify the relationships between the beat frequencies corresponding to the various musical intervals, and to correct certain errors found in previously published material on this subject. A complete table of fundamental frequencies, based on A = 440, for the entire range generally found in a pipe organ, and accurate to four significant figures after the decimal point, is also included.
A Division of the Octave
Authors: Roeder Elwood S.
Published: September 2005

A low frequency as generator for the frequencies which divide the octave. 2. The three geometric progressions on which the frequencies are generated. 3. The twelve tones with their twelve intonations. 4. The divided octave as the background against which scales and chords are plotted. 5. The possible non-musical applications of this division of the octave.
Musical Tone Qualities as a Factor in Expressiveness
Authors: Pepinsky Abe
Published: September 2005

The adjective approach to tone quality has ever been a subject of interest to the musically minded person. One has but to review the great mass of musical criticisms and program notes to build up a meaningful vocabulary of expressive terminology. Although the average layman has been finely conditioned to the expressive values intended by the performers of music, it must be remembered that tone quality has taken on new meanings with the changing epochs of music history. This is clearly evidenced by the instruments in vogue during the development of the art of music. The technical advancement of the tonal synthesizers has made it possible to enter the psycho-physical laboratory for the study of hedonic responses to tone quality. The many variables involved can be held constant at will, thus obtaining objective measurement of the factors to be considered. Some of the findings thus far treated will be discussed and directions for continued research suggested.
Flow-Resistance Characteristics of Fibrous Acoustical Materials
Authors: Nichols R. H.
Published: September 2005

The flow-resistance of a material is highly important as a factor in determining its acoustical performance in various applications, particularly in the blankets used for sound-proofing of aircraft cabins. It is desirable, therefore, to know the manner in which the flow-resistance of a light-weight acoustical material varies with such physical parameters as thickness, density, size, and shape of fibers, and type of construction (“felting”) of the material. From an experimental study of a large number of fibrous acoustical materials, the following general empirical relation has been established: Flow-resistance, R = KS(1 + x)Tx(av)2 where K is a constant characteristic of a particular material, S is the surface density of the blanket of material, T is the thickness, and (a/v) is the ratio of surface area of the fibers to the volume of the fibers. The type of construction of the material determines the value of x in the exponents. This relation is compared with the theoretical relation derived by Fowler and Hertel for samples with randomly oriented fibers.
Frequency Response Fluctuations in Rooms. I. Experimental Investigation
Authors: Roop R. W.
Published: September 2005

The steady-state frequency response of a room is being studied in detail as part of a broad investigation of diffusion. Following Wente we define transmission irregularity as: Φ ≡  ∑ ν1ν2 (PL)max − (PL)minν2 − ν1 db/c.p.s. where (PL)max and (PL)min represent the values of the pressure level at individual maxima and minima in the frequency response curve in the frequency band ν2 − ν1.

For measurements of Φ, the requirements on the rate of frequency sweeping, (dνdt), and the writing speed of the recording instrument, R, are: (dνdt) < 2k2π∛ and R > 10π∛2.3⋅1k(dνdt) where k is the decay constant. Measurements of the transmission irregularity have been made as a function of frequency between 100 and 5000 c.p.s., with a source in one corner of a small rectangular room and a microphone in various standard positions. The resulting curves exhibit a rapid increase in Φ at low frequencies and a gradual decrease in Φ at frequencies above 1000 c.p.s.
Radiation of Sound by a Vibrating Absorber
Authors: Cook Richard K.
Published: September 2005

The rate of radiation of sound energy from a vibrating wall having a porous surface is lower than that for a solid wall vibrating at the same amplitude. The radiation is computed as a function of characteristic impedance and thickness of the porous layer. The theory can be regarded as applying to a porous material having a relatively rigid structure, in which sound is propagated mainly through the air in the pores. However, the theory can be regarded also as a purely phenomenological one in which no assumptions are made about the mechanism of the absorption process. From this point of view, the sound waves propagated through the material merely satisfy the “telegraph” equation. The results of the calculation are compared with the propagation of sound through the material when it is placed near (but not in contact with) a vibrating solid wall. Applications of the results to the reduction of sound energy transmitted through a partition, and the reduction of sound radiated by noisy machinery are discussed.
Velocity and Absorption of Sound in Suspensions and Emulsions
Authors: Urick R. J.
Published: September 2005

Measurements have been made of the velocity and absorption of sound in kaolin-water suspensions and in a number of emulsions. The size of the suspended particles was small compared to the wave-length of sound used. The data obtained do not substantiate a theory proposed by K. F. Herzfeld, which considers the effect on sound velocity of multiple scattering by spherical particles. Instead, the behavior of suspensions and emulsions with respect to sound velocity is as though they were homogeneous mixtures of the substances in suspension. Thus, the compressibility of a suspension is an additive function of the product of the compressibility and the concentration of the constituent materials, similar to its behavior in ideal solutions. These considerations have possible application to the determination of the compressibility of finely divided substances by means of sound velocity measurements.
A Continuously Variable Standard Acoustic Impedance
Authors: White J. E.
Published: September 2005

The mechanical impedance of an electro-mechanical device is affected by current flowing in the electrical elements, just as the electrical impedance is influenced by the motion of the mechanical system. The purpose of this paper is to determine over what limits the mechanical impedance of electro-magnetic loudspeakers and horn driver units can be varied by varying the load impedance across the terminals. A simple extension of the motional impedance analysis presented by R. D. Fay provides a means of calculating the mechanical impedance of an electro-magnetic speaker as a function of electrical load. The speaker when used in this way may be considered a continuously variable acoustic impedance. It is a secondary standard, since electrical measurements provide a means of calculating the impedance in terms of the surge impedance of a column of air. The calculated impedances were checked by direct measurement using the standing wave, or hyperbolic tangent, method. By means of a horn driver, the impedance of an area equal to approximately one square inch can be varied over fairly wide limits. The range of variation for cone speakers, with correspondingly larger areas, is much more restricted.
Musical Scales, Intonation, and Theory
Authors: Meyer M. F.
Published: September 2005

For a scientific theory of scales the traditional, medieval symbols of the musicians are worse than inadequate. Neither do the terms in “fractions” occasionally employed by physicists serve scientifically. A clear and simple numerical method of scale terminology is recommended. (2) The causality of musical experience can be no other than basic facts of neurological chemistry. (3) The mysticism of Rameau's distinction of “major” and “minor” is exposed, the distinction condemned. (4) Attempts at “pure” intonation are in general to be discouraged, although not rejected on principle. (5) The very limited possibility of “quarter-tones” is scientifically explained.
Musical Instruments in Nineteen-Tone Equal Temperament
Authors: Schafer Tillman H. , Piehl W. A.
Published: September 2005

Yasser has proposed a theory of evolving tonality to account for the structural relations of the pentatonic scales used by various primitive peoples to the seven-tone scales used in modern European music. He postulates a series of organically connected scales of increasing complexity and predicts a “supra-diatonic” scale as the logical next stage in tonal evolution. This scale has twelve regular degrees and seven intermediate auxiliaries. The intonation of this scale which appears most practical is nineteen-tone equal temperament. This temperament has been known for centuries as an intonation of the seven-tone scale. The fact that it serves for both scales is a consequence of their interrelations. In this paper, the theory of evolving tonality is sketched, instruments built for testing the theory are described, and both new and old scales and chords in nineteen-tone equal temperament are demonstrated aurally and compared with the nearest equivalents in the conventional twelve-tone equal temperament.
Stroboscopic Frequency Measurement
Authors: Kent Earle L.
Published: September 2005

A method is described for measuring a continuous spectrum of frequencies stroboscopically. The stroboscopic pattern is continuous along the frequency scale but has discontinuities with respect to time as it is viewed. The frequency scale may be linear or logarithmic.
Measurement and Calculation of Under-Signal Noise in Magnetic Recording
Authors: Chapin D. M.
Published: September 2005

The noise that appears with and as a result of a single frequency recording on Vicalloy tape and on coated tape is found to peak up very sharply at frequencies immediately adjacent to the recorded frequency. A method has been developed whereby this noise can be computed from the frequency response curve and the noise for direct current magnetizations. Computations have been made and curves plotted for noise appearing with 125-cycle, 250-cycle, and 1000-cycle recordings using both ring-type poles and offset type poles. Good agreement with measured values is obtained.
Study of the Admittance Spectra of Piezoelectric Plates in Thickness-Shear Vibration
Authors: Hok Gunnar , Van Dyke K. S.
Published: September 2005

A thin square plate vibrating in thickness shear has an infinite number of possible modes of vibration characterized by different standing-wave formation along the three major axes of the plate. When the plate is piezoelectric and connected into an electric circuit, the observed admittance spectrum may be further complicated by coupling between the thickness-shear modes and modes of other types of vibration, such as flexure or face-shear vibration. This paper describes observations made with a spectrum analyzer specially designed for the purpose. Two kinds of observations are made: (a) with the plate resing on a flat electrode, while the upper electrode is a small steel ball, which can be moved to any point of the surface of the plate, (b) with the plate mounted between electrodes of standard type. The first kind makes it possible to identify the modes and to determine their frequencies and their amplitude distribution over the surface. The second kind indicates to what extent the various modes are coupled to the electrical circuit in conventional operation. Some results are reported as to the effect of variation in thickness contour, ratio of width to thickness, and clamping conditions of the plate. The work is being done under a contract with U. S. Signal Corps.
High Frequency Siren
Authors: Allen C. H. , Rudnick I.
Published: September 2005

A siren has been constructed which has a useful frequency range from 3 to 33 kilocycles. Preliminary measurements indicate a relatively uniform power output of 125 watts and an efficiency of approximately 30 percent. It consists essentially of a small chamber from which air escapes through 100 orifices, shaped as conical horns, and equally spaced on a six-inch circle. The air flow (60 cu ft./min.) is interrupted by a rotor with 100 teeth driven by a 12 hp high speed motor integral with the siren. The unit is small (712 in. diameter, 1112 in. high) and easily portable. In operation it acts as a ring source with a directivity pattern closely duplicating that expected theoretically. The maximum over-all intensity in the central lobe, 8 cm from the siren, exceeds 160 db relative to .0002 dyne/cm2. The parasitic audible noise is at least 40 db below the signal intensity. Interesting phenomena associated with the intense sound field will be described.
Some Properties of Ultrasonic Fields
Authors: Slaymaker Frank H. , Polster Harry D. , Meeker Willard F.
Published: September 2005

The type of measurements described in the previous paper will be demonstrated and, in addition, there will be demonstrations of specular reflection, scattering from small obstacles, interference, frequency-modulation ranging techniques, and the Doppler effect.
Measurement of Impedance to Sound in Water
Authors: Fay R. D. , Brown R. L. , Fortier O. V.
Published: September 2005

The method of measuring acoustic impedance by means of the interference of plane waves in a cylinder is not directly applicable to sound in water since it is impractical to obtain sufficient rigidity in the cylindrical walls to insure plane waves. A successful modification of the method was developed at the Massachusetts Institute of Technology by using pulsed signals in a cylinder several wave-lengths in diameter. There is a low frequency limitation to this scheme, which in this case is about 10 kc. With a view to extending the frequency range downward by using continuous waves (which are not plane), a theoretical investigation has been made of the steady-state sound fields in a long steel cylinder in terms of the wall thickness and the radius. The theoretical results have been checked by measurements of the distribution of sound pressure over cross sections and of the wave-lengths at various frequencies and for various tube terminations. It appears from the results of these investigations that the acoustic impedance of samples of materials or structures used as a termination of the tube can be reliably computed over a reasonable frequency range with a tube of practical dimensions.
The Use of Resonant Rods to Determine High Frequency Dynamic Modulus of Rubber
Authors: Nolle A. W.
Published: September 2005

A previous paper described a method for determining the dynamic elastic and viscous coefficients of rubber-like materials from measurements of the phase velocity and attenuation of longitudinal waves in thin narrow strips. For a particular material at a given temperature, measurements were not feasible above some frequency at which either the attenuation became too large, or the wave-length became too small for ready measurement. The present paper describes a method which has been developed to circumvent these difficulties and to permit measurements between 10 and 100 kc for most rubber preparations. A small disk of rubber is placed in contact with the end of a freely suspended nickel rod and the effect of the specimen upon the resonant frequencies and upon the “Q” of the rod is determined. The elastic and viscous coefficients of the material are found from the measured quantities through mathematical relations which are described. An anti-resonant rod affords an effectively rigid backing for the sample. The resonant rod is driven magnetostrictively with the aid of a loosely coupled coil. The amplitude of vibration is determined from an electrostatic pick-up device.
The Radiation Pattern on an Ultrasonic Focusing Radiator
Authors: Willard G. W.
Published: September 2005

A focusing quartz radiator made in the form of a concave-convex lens of constant thickness (and being X-cut on the axis) should radiate spherical sound waves which focus at the center of curvature of the radiator surfaces. Because of wave diffraction, the focus should deviate from infinitely sharp in the same manner as is well known in the optical telescope. If R is the radius of curvature of the radiator, D the effective diameter of the radiator, and λ = v/f the ultrasonic wave-length, then the diameter of the central beam is δ1 = λR/D, of the first ring, δ2 = 2λR/D, of the second ring, δ3 = 3λR/D, etc. Using a 5-megacycle radiator (D = 29 mm, R = 63.5 mm) and radiating into water on the concave side, the pattern was studied by means of its light diffraction effects (of which slides will be shown). The radiation focused at the center of curvature and the diffraction at this point was as described above (δ2 = 1.5 mm). This is in agreement with the expectations and partial findings of J. G. Lynn, R. L. Zwemmer, A. J. Chick, and A. E. Miller, and is in disagreement with findings of L. W. Labaw. Variations of radiation efficiency about the periphery of the radiator are related to variations of the off-x-axis crystal constants, but do not affect the spatial distribution of the beam in the focal region.
The Audibility of Echoes Masked by Sea Reverberation and Noise
Authors: Small Arnold M.
Published: September 2005

For the purpose of predicting the maximum range at which a target may first be aurally detected with undersea echo-ranging gear, it is necessary to know the target-echo to background ratio which is required for perception of the echo. The value of this ratio in db for a particular recognition probability is known as the recognition differential. Experimental studies with a group of five observers were undertaken to determine such aural recognition differentials as a function of the emitted pulse length when the echo was masked (1) by sea reverberation and (2) by noise with a continuous spectrum. Pulse lengths from approximately 10 to 300 milliseconds were studied. Two conditions with reverberation masking were explored, namely, one in which the pitch of the echo and reverberation background were the same (no Doppler) and another in which they differed maximally by ±200 cycles per second due to Doppler effect. Results indicate that recognition differentials for 50 percent recognition probability vary from approximately +4 to +12 db over the range of pulse lengths studied (10 to 300 milliseconds, respectively) for the no Doppler case. Masking curves for the Dopplered echoes will be shown, from which it will be seen that, with a Doppler shift of 200 cycles per second, the recognition differential was reduced approximately 20 db compared to the no Doppler case (pulse lengths of about 40 and 100 milliseconds). Recognition differentials for the same echoes masked by thermal noise were very nearly the same as those for reverberation masking without Doppler, when the reference band is the appropriate critical band.
The Magnitude of the Physiological Noise Generated under Earphone Cushions
Authors: Brogden W. J. , Miller G. A.
Published: September 2005

When an earphone is held in the hand and placed tightly over the ear, a rumbling, low frequency noise can be heard. Since this sound is presumably caused by hand tremor, breathing, blood-circulation, etc., it is called physiological noise. It is possible, with a noise generator and low pass filters, to generate similar low frequency noises in an anechoic chamber, and to adjust the spectrum of the acoustical noise until a satisfactory qualitative match with the physiological noise is obtained. To make these matches, listeners used a circumaural cushion of the donut type which normally enclosed a volume of about 22 cc. Once a qualitative match was obtained, the listeners adjusted the intensity of the acoustical noise until it sounded just as loud as the physiological noise. These equal-loudness judgments indicated that the physiological noise was equivalent in loudness to an acoustical noise at a sensation level between 25 and 30 db. As the enclosed volume is increased, however, this level declines, and with volumes greater than about 1600 cc, physiological noise is seldom detected. This research was carried on under contract with the U. S. Navy, Office of Naval Research.
Effects of Noise on Radio Communication
Authors: Licklider J. C. R. , Goffard S. J.
Published: September 2005

In order to study the effects of noise upon radio communication, an amplitude-modulation radio system was set up in the laboratory and provision was made for generating electrical interference and introducing it, together with the speech-modulated carrier from the transmitter, into the receiver. In addition, arrangements were made for producing ambient noise at the talkers' and listeners' positions, so that the separate effects of acoustic noise and radio noise could be compared and their combined effects could be studied. By means of word articulation tests, the intelligibility of speech heard over the radio system was determined as a function of signal-to-noise ratio for each of a number of types of noise. Several principles of noise reduction were studied, and basic parameters of the radio link were varied systematically so that their influence upon the effects of noise could be determined. With regard to ambient noise, it was found that exclusion of noise at the microphone is even more important as a prerequisite for effective radio communication than it is for effective interphone communication, especially if either compression or premodulation clipping is employed in the radio transmitter. Noise exclusion at the listeners' end of the line is also important because, for optimal intelligibility under difficult conditions, it is necessary for the noise reaching the ear through or under the earphone cushions to be at least 10 decibels less intense than the noise coming through the earphones from the receiver. The deleterious effect of electrical interference was found to depend greatly upon the relation between certain characteristics of the noise and corresponding characteristics of the receiver circuits. In general, interferences with continuous spectra are more detrimental than those with line spectra, and non-impulsive types more detrimental than impulsive types. Noise-reducing circuits were ineffective against random fluctuation noise, but in the presence of certain types of impulse interference, limiters and cancelling circuits provided such great improvement in performance that it was possible to maintain satisfactory communication despite a 35-decibel reduction in carrier intensity. As a general principle, it appears that, whenever there is a characteristic difference between the wave forms or the spectra of the signal and the interference, the impairment of intelligibility by electrical interference may be reduced by employing amplitude-selective or frequency-selective circuits in the radio receiver.
The Difference between Monaural and Binaural Thresholds
Authors: Shaw W. A. , Newman E. B. , Hirsh I. J.
Published: September 2005

Although there is considerable agreement on the increase in apparent loudness of auditory stimuli presented binaurally as compared with monaural stimulation at supraliminal intensities, less agreement is found concerning binaural summation at liminal or subliminal intensities. Experimenters in the past have reported the binaural threshold to be (1) the same as that of the “better” ear, (2) lower than that of the “better” ear, or (3) lower than that of the “average” ear. The present paper shows the binaural threshold to be approximately 3 db lower than the “equated” monaural threshold for both pure tones and speech. “Normal” summation occurs when the stimuli presented to both ears are physically equal and the binaural threshold is 1.5 db lower than that of the “better” ear and 4 db lower than that of the “average” ear (average value of 14 frequencies tested). “Maximum” binaural summation occurs when the stimuli presented are functionally equal, i.e. when the stimulus intensities differ according to the difference between right and left monaural thresholds. For pure tones the “maximum” binaural threshold is 3.6 db below the thus equated monaural threshold (average of 14 frequencies tested). The comparable binaural threshold for speech intelligibility is approximately 3 db lower than the equated monaural threshold.
A Pulse-Tone Technic for Audiometric Threshold Measurements
Authors: Gardner Mark B.
Published: September 2005

The pulse-tone method of testing hearing, used as a basis for the 1939–1940 World's Fair tests in which over one million individuals voluntarily participated, has been adapted for clinical audiometric use. For this purpose, a tri-functional control has been utilized consisting of (1) an electronic method of producing the desired number of tone-pulses (normally one, two, three, or four) in a selected sequence under control of the operator, (2) a visual signal which occurs at the beginning of each pulse series to act as a warning to the observer, and (3) a visual signal which flashes in synchronism with the output tone-pulses to act as a counter for the operator. In threshold tests in which both the pulse-tone method and the standard audiometric method were used, approximately 90 percent of the observers expressed a preference for the pulse-tone procedure. This favorable preference rating was principally a result of the ability of the observer to relax between definite periods of concentration marked by the warning signal at the beginning of each series of pulses. The test, which lends itself to a high degree of standardization, was found to be of particular advantage for observers with tinnitus. For such observers, the regular on-off characteristic of the tone affords a better opportunity to differentiate between the audiometer signal and the auditory disturbances which are characteristic of this disorder.
Binaural Loudness Matching with Repeated Short Tones
Authors: Garner W. R.
Published: September 2005

Six experienced and 20 naive observers were tested to determine the effect of tone duration and repetition rate on the normal observer's ability to make a binaural loudness match. Durations from 1 to 200 milliseconds, and repetition rates from 1 to 100/second were used with various frequencies and intensities. The results show that binaural loudness matching is slightly more accurate with low repetition rates, and with either very short, or fairly long, durations. The differences are, however, small compared to the magnitude of the errors (as measured by the standard deviation), and any repeated tone is more accurately matched than a steady tone. Of considerable interest is the fact that differences between subjects in the matching are much greater than differences within subjects. These differences are so large that there is some doubt that intensity per se can operate as a cue for the localization of a sound source. If intensity is used as a cue, then the observers must have learned to compensate for an inherent difference in the loudness of tones in the two ears, since, in many cases, the difference in the match of two observers is greater than the maximum possible difference in intensity between the two ears with a single sound source.
Masking Effect of Periodic Pulses of Vibrations as a Function of Time and Frequency
Authors: Miller R. L.
Published: September 2005

Studies have been made of the masking effect of a periodically pulsed wave of vibrations upon a similar wave of the same or different vibrations. The occurrence in relative time of the masked wave was varied over the whole period of pulse repetition. The masking is greatest when the two pulses are near coincidence and approaches threshold as the pulse separation becomes greater. A small amount of fatigue effect was noticed when the masked pulse was in the region following the masking pulse. A totally unexpected result was that the maximum masking was generally obtained when the masked pulse preceded the masking pulse by 1 or 2 milliseconds. The amount of this time difference was found to be independent of the pulse repetition rate in the region explored of 30 to 100 pulses per second but is a function of the relative frequencies under the pulse envelopes.
Influence of Neural Degeneration upon Cochlear Interference
Authors: Lowy K.
Published: September 2005

Former experiments established that the electric cochlear response to watch ticks can be suppressed by simultaneous pure tones. The intact peripheral neural mechanism seemed to be required for this phenomenon. In the present series of experiments, the eighth nerve of cats was cut on one side and peripheral degeneration allowed to take place. A comparison of the cochlear response on the unimpaired and impaired side yielded uniformly a considerable decrease in the cochlear interference on the operated ear. Recent severing of the auditory nerve failed to yield this result. The bearing of these findings upon the theory of cochlear interference is discussed.
Construction and Design of Parmly Sound Laboratory and Anechoic Chamber
Authors: Mills Peter J.
Published: September 2005

A description is given of the construction details of the Sound Laboratory recently completed by the Parmly Foundation at Technology Center, Chicago. The function of the laboratory is to carry out research in the prevention and alleviation of deafness. The chief feature of the laboratory is an echo free or “anechoic” chamber. The 40-ton chamber of concrete, steel, wood, and sheet-rock construction is suspended on neoprene pads to have a natural frequency of about 5 cycles per second. Continuous ventilation through ducts of high sound attenuation, 90 db at 128 c.p.s., is provided. The inner surfaces are designed to have 99 percent absorption or better at 115 cycles per second or above. The Harvard treatment of wedge-shaped fiberglas is used. The chamber is housed in a concrete block wing, the walls of which are lined with fiberglas sheets. An audiometer room, workshop-laboratory, offices, and a reception room are housed in the same building.
Performance of the Anechoic Room in the Parmly Laboratory
Authors: Hardy H. C. , Tyzzer F. G. , Hall H. H.
Published: September 2005

The anechoic room of the Parmly Laboratory is being used by the Armour Research Foundation in its acoustic research. Performance of the room has been evaluated by the following means: 1. inverse-square-law measurements from 60 to 17,000 cycles per second; 2. measurements of the effect of nearness of the walls on the response curves and the acoustic impedance of loudspeakers; 3. ability to obtain consistent data with different geometrical arrangements. Results of these experiments will be presented and some of the techniques of measurement will be discussed. A method of measuring the wall attenuation will be described. It is estimated that it would be necessary to have a distant sound source produce an average intensity of 10−7 watts per square centimeter at the walls to be heard within the room.
Noise Reduction in Signal Corps Hand Generators. Part II: Acoustic Housings for the Generators
Authors: Sherard George W.
Published: September 2005

Paralleling the attempt to reduce the internal noise of the generators an effort was made to provide a modification consisting of a light-weight external acoustic housing which could satisfactorily reduce the noise. With a knowledge of the principle frequencies of the generator noise an experimental procedure was established by which hundreds of laminated panels of different fabrications were tested for attenuation characteristics. A very satisfactory construction was developed. With use of a modification kit consisting of the silent drive and the sound attenuation chest, noise reduction in excess of 25 db was achieved. Both design parameters have been incorporated in new models of Signal Corps hand generators to afford minimum noise. These same principles might be used by designers interested in minimum noise in similar apparatus. High efficiency of the specially constructed light-weight housing material suggests its use in many applications. Demonstrations of the equipments are to be given.
Methods of Measuring Speech Spectra
Authors: Stevens S. S. , Egan J. P. , Miller G. A.
Published: September 2005

A comparison was made of several alternative methods and devices for analyzing speech in terms of its acoustic spectrum (a time average of the sound-pressure level per cycle vs. frequency). A general procedure, applicable to a wide variety of analyzing instruments, consists of a comparison made between a known acoustic spectrum and an unknown spectrum (speech). For maximum convenience, the known spectrum should be a “white noise” whose spectrum level is a constant number of decibels per cycle. This spectrum is used as a standard to provide an over-all calibration of the entire recording and analyzing system. In practice, the shape of the speech spectrum is obtained directly as the difference in decibels, in each pass band of the analyzer, between the level obtained for the white noise and the level obtained for the speech.

In order to measure conveniently the spectrum of the noise used as the standard of reference, a graphic analyzer was devised as follows: A Hewlett-Packard wave analyzer, Type 300A, was modified to give access to the 20,000-cycle voltage al the input to the meter system. This voltage was used to drive either of two types of graphic recorders. Continuous analyses from 0 to 16,000 c.p.s. can be made with various constant band widths.

The procedure of comparing a known with an unknown spectrum eliminates the necessity of calibrating separately the recording, reproducing, and analyzing equipment. In the analysis of speech, only the calibration of the microphone need be considered as a final correction to the data. This procedure also makes it possible to obtain accurate analyses despite the use of voice recording and reproducing equipment having unknown frequency characteristics.

Although the choice of filter cut-off frequencies is arbitrary, it has been found most convenient to analyze speech by dividing it up into bands that stimulate equally wide regions on the basilar membrane. This is accomplished by choosing filter cut-offs at equal intervals along the mel scale of subjective pitch.

Within the limits of observational error the same answer is obtained when speech is analyzed by any of three different measuring systems: (a) square-law integrator (audio spectrometer), (b) linear integrator, (c) R.C.A. noise meter and Esterline Angus graphic recorder. When, with any of these systems, a speech spectrum is determined as the difference in decibels between the two analyses — that for white noise and that for speech — the speech spectrum can be stated in terms of sound-pressure level per cycle averaged over each of the nominal pass bands of the filters. Very narrow pass bands (5 c.p.s.) reveal details in the speech spectrum not disclosed by the wider filter bands.
Masking Effect of Periodically Pulsed Tones as a Function of Time and Frequency
Authors: Miller R. L.
Published: September 2005

Studies have been made of the masking effect of a periodically pulsed single-frequency tone upon a similar wave of the same or different tone. The occurrence in relative time of the masked wave was varied over the whole period of pulse repetition. The masking is greatest when the two pulses are near coincidence, and approaches threshold as the pulse separation becomes greater. A small amount of fatigue effect was noticed when the masked pulse was in the region following the masking pulse. A totally unexpected result was that the maximum masking was generally obtained when the masked pulse preceded the masking pulse by 1 or 2 milliseconds. The amount of this time difference was found to be independent of the pulse repetition rate in the region explored of 30 to 100 pulses per second but is a function of the relative frequencies under the pulse envelopes.
Microbarometric Pressures from Large High Explosive Blasts
Authors: Cox Everett F.
Published: September 2005

Charges detonated for Army-Navy Explosives Safety Board tests in Idaho, October 1946, produced pressure waves recorded by subsonic frequency microbarographs at distances 12.9 to 452 km. Observations showed both normal and abnormal signals at 182 and 292 km, no clear abnormal signals at 141 or 89 km, no signals of any kind at 872 km. In the zone of normal audibility, average wave velocity between blast point and receiving station decreases slightly with increasing distance, and may increase slightly with charge weight; it is substantially the same as sound velocity. No consistent travel-time differences for the abnormal signals resulted from changing charge weight between 3.2 and 250 tons TNT. Neither normal nor abnormal signal strengths were predictable from charge weight. The largest abnormal signal properly recorded was a 3-cycle wave train with peak-to-peak amplitude 220 microbars received 182 km from a 125-ton blast. Interpolated to apex pressure perturbation, this signal amplitude eliminates shock wave supersonic velocity as a logical explanation for abnormal audibility. Incident angles of abnormal rays are not calculable. However, if one assumes 182 km as the descent distance for rays starting out horizontally, neglects wind effects, and accepts the apex temperatures measured by balloons, rough calculations of lower stratosphere temperatures are possible. These establish 34 km as a minimum altitude at which ground temperature is reached.