bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic Ultrasonic Flaw Plotting
Authors: Erdman Donald C.
Published: September 2005

The interior of forgings as revealed by ultrasonic echo techniques is displayed as orthographic projections on cathode-ray tubes. The scanner, Snell's law computer, and display circuits are discussed and slides are presented showing correlation between the plotted ultrasonic images and defects in metal.
The Masking of Tones by White Noise as a Function of the Interaural Phases of Both Components
Authors: Jeffress Lloyd A. , Blodgett Hugh C. , Deatherage Bruce
Published: September 2005

Work by Hawkins, Hirsh, Licklider, Webster, and others has shown the considerable reduction in masking which occurs when the phase of either the signal or the noise is reversed, or when the phase of the signal is shifted by various amounts. The present paper extends this work by shifting the interaural phases of the masking component of the noise by various amounts between +180° and −180°. The interaural phases of both the noise and the tone are therefore parameters of this study. The results are in agreement with those already published, but show in addition large reductions in thresholds when the noise and tone differ in phase, even when neither has been reversed.
Observations on the Acoustic Impedance of Calibrating Couplers and Ears
Authors: Burkhard Mahlon D. , Corliss E. L. R.
Published: September 2005

The comparison of the performance of earphones on the ear and on closed calibrating couplers (reported in November, 1950 and May, 1951) has been extended to a study of the phase relationships involved. From these, the acoustic impedance that the ear presents to an earphone can be deduced. Using a direct recording meter (described by R. F. Brown), the real and reactive components of the pressure developed in the cavity or ear canal were observed. The results of the measurements will be discussed.
Avoidance of Crosstalk in Large Audio Systems Using Unshielded Wire
Authors: Tanner R. H. , Thompson G. B.
Published: September 2005

The master control system installed in Montreal headquarters of the Canadian Broadcasting Corporation, apart from being one of the largest on the North American Continent, is noteworthy for the fact that all the system wiring is carried out in unshielded telephone cable. It is estimated that nearly half a million feet of wire were used. In spite of this, the signal/crosstalk ratio has been kept better than 75 db for interfering signals (at full level) of frequencies up to about 4000 cycles and better than the RTMA specification figure of 65 db up to about 10,000 cycles. This paper describes the methods and precautions used throughout the installation to produce these results.
Phangle Meter
Authors: Brown R. F. , Mullen J. A. , Corliss E. L. R.
Published: September 2005

The phangle meter is an instrument for recording automatically the in-phase and quadrature components of the output of a four-terminal network with reference to its input. The present instrument operates over a range of 50 cps to 10,000 cps and consists of two cosine voltmeters and a phase splitter to give two signals 90° out of phase, and of equal magnitude. The phangle meter was developed to determine the impedance presented by an ear to an earphone.
Acoustics of the Remodelled Legislative Chambers of the National Capitol
Authors: Sabine Paul E.
Published: September 2005

It was the expressed opinion of the committees of the House and the Senate that “primary consideration should be given to the air conditioning, the lighting, and the acoustics of the remodelled Chambers.” This paper gives an account of the acoustical problems presented by the special requirements of rooms intended for deliberative assembly, together with the practical means used in the solution of these problems, and finally a summarized report of the acoustics of the two rooms as shown by tests made by Messrs. Wallace Waterfall and Hale J. Sabine.
Reverberation by Ultraspeed Recording
Authors: Dunbar James Y. , LeBel C. J.
Published: September 2005

Further study of decay characteristics in “dead” rooms with ultraspeed recording technique is made in several rooms using the method presented by the authors at the last meeting of the Society. The same studio is retested with the use of multiple tone sources consisting of semi-tone groups and chords. It is believed that the use of such sources saves the tedium of single tone explorations in locating peculiarities of decay.
Some Sounds from Marine Life in the Hawaiian Area
Authors: Schreiber O. W.
Published: September 2005

Sounds in the low audiofrequency region produced by marine life have been recorded at the U. S. Navy SOFAR Station, Kaneohe Bay. The SOFAR hydrophones are located at a depth of 2100 feet on the eastern underwater slope on the island of Oahu. These sounds have levels of the order of 1 microbar, and many have a rather musical quality. There is a marked seasonal variation in the production of these sounds, with the early spring months being the period of most frequent occurrence. This variation is coincident with the seasonal variation of whales in the area, and this feature, plus the characteristics of the sounds themselves, has led to the belief that they are produced by whales—with possibly an assist or two from porpoises. The sounds are described, and information is presented on their spectrum, sound level, and frequency of occurrence.
Noise Control in Aircraft Engine Testing
Authors: Lemmerman Richard D.
Published: September 2005

The development of larger and more powerful aircraft engines both of the reciprocating and gas turbine type has complicated acoustical design with many associated engineering problems. Sound spectrum analyses of reciprocating, gas turbine, ramjet, and rocket engines show the necessity for large attenuation over a wide frequency band. The associated problems of fluid mechanics and physical construction involved in quieting engine test facilities are often more difficult than the acoustic ones. A discussion of some existing and proposed test facilities in the light of these problems should be useful. This review is subdivided by engine types and covers engineering problems involved in the quieting of aircraft engine test facilities.
Quieting of the Jet Engine Testing Facilities in the Willgoos Turbine Laboratory
Authors: Potter S. M. , Hardy H. C.
Published: September 2005

The quieting of the Willgoos Turbine Laboratory, a jet engine development facility of the Pratt and Whitney Aircraft Company, presented very unusual acoustic design problems because there were residences within 200 feet of the proposed building. At the time of the design (early in 1948) there was little information available on the design goals, the expected noise levels in the operation areas, or practical methods of accomplishing the noise reduction. Altogether, 14 types of structures were designed to reduce various sources of noise emanating from this laboratory, including ventilation intake and exhaust ducts and atmospheric intake and exhaust systems for test cells, compressors, and exhaustors. The noise in control rooms and piping systems was also treated. The quantity of gases moved in some of these systems is nearly a million cubic feet per minute. A design goal was set at a sound level of 75 db in the 300–600 cps band in the immediate vicinity (approximately 50 feet) of the plant. The amount of sound reduction required for this band was 50 to 75 decibels. Various quieting constructions used on the project were baffle splitters, turns in the large acoustic ducts, lined plenums, and slotted exits. Some of the most important of these will be described in this paper. A limited number of measurements in the completed laboratory were made by using an air modulated horn driven by a broad-band noise source, from which a level up to 125 db could be obtained in the test areas. Measurements showed that, in all the installations except one, the attenuations obtained were within 5 db of those predicted before construction. The success of the project was such that none of the noisy operations inside the building can be heard at nearby residences.
Turbo-Jet Engine Noise
Authors: von Gierke H. E. , Patrick Horace O. , Gannon W. J. , Hansen R. G.
Published: September 2005

The noise fields generated by a standard turbo-jet aircraft engine have been measured for three different power settings. Measurements were made at points on a circle having a radius of fifty feet. The angular separation of the points was 22.5 degrees. The center of the circle coincided with the intersection of the longitudinal and transverse centerlines of the engine. The noise fields were analyzed using an octave band analyzer, starting at 37.5 cps. The over-all noise levels found (over 140 db at fifty feet) and the noise levels per band for the three low frequency bands (37.5–75 cps = 133 db; 75–150 cps = 137 db; 150–300 cps = 131 db) are significant in respect to the design of engine test facilities for adequate protection of personnel. They are equally important in respect to problems of noise control on an airport. The noise level data are presented graphically.
A Useful Theorem for the Testing of Isolation Mounts
Authors: Harrison Mark , Sykes A. O.
Published: September 2005

In the testing of isolation mounts, or more generally any vibrating system, it is often desired to know the ratio of forces at two points in the system. Since the measurement of dynamic forces is usually more difficult than the measurements of velocities of accelerations, it is useful to have a theorem relating the force ratio at two points in a system to the velocity ratio at the two points. A theorem relating the force ratio to the velocity ratio has been proven quite generally as a consequence of the reciprocity theorem. For lumped systems the theorem is equivalent to the ideas of duality in electrical circuits. The utility of the theorem is illustrated by examples drawn from actual practice.
On the Use of Metallic Noise Isolation Mounts
Authors: Sykes A. O. , Harrison Mark
Published: September 2005

Transmissibility data are presented for steel and copper manganese helical springs. It is shown that for frequencies 10 to 30 times the resonant frequency of the spring-mass system, wave phenomena are important and that due to the low damping of the metals, the isolation mount may amplify the force felt by the foundation at the standing wave resonances rather than reduce it. It is shown that several modes of vibration are possible and that a one degree of freedom treatment of the problem is inadequate. The effect of coupling between the modes is discussed. Improvement of the isolation properties by coating the springs with highly viscous materials is demonstrated. It is further demonstrated that if sufficient damping is added, the value of critical coupling exceeds the actual coupling between the modes and in this case the system resembles a one degree of freedom system.
Instrumentation and Techniques for Evaluation of Noise Reducing Components in Piping Systems
Authors: Callaway D. B. , Tyzzer F. G. , Hardy H. C.
Published: September 2005

In liquid-filled piping systems large coupling exists between water column vibrations and flexural pipe-wall vibrations. This fact and the difficulties associated with determination of sound pressure levels in the water suggested the evaluation of noise reducing components in terms of their reduction of flexural pipe-wall vibrations. A test setup was developed in which test components such as flexible couplings, isolating hangers, and various damping devices were mounted at the center of the test pipe. Broad-band noise was introduced into the water or the pipe wall at one end of the system. Pipe-wall vibrations were detected by accelerometers at points on opposite sides of the test components, and were analyzed by means of an octave filter set. The effect of entrapped air and other test conditions on the accuracy and repeatability of data was investigated. The test setup and techniques will be discussed and test results obtained for various types of noise reducing components will be presented.
Resonance in Barium Titanate Tubes
Authors: Haskins James F.
Published: September 2005

A study of resonance in circular barium titanate tubes is discussed, applying the theory of coupled circuits. A plot of resonant frequencies against length diameter ratio using the elastic coupling between radial and lengthwise vibrations shows close agreement with measured resonances over a large range of the ratio. Under the assumption that polarized barium titanate remains isotropic elastically a simple method is shown for measuring the Poisson ratio. A discussion is given of the energies at resonance associated with radial and longitudinal modes as the length diameter ratio is changed.
Measurement of Colloidal Vibration Potentials with Pulse-Modulated Ultrasonic Waves
Authors: Yeager Ernest , Dietrick Harry , Saunders Frank , Hovorka Frank
Published: September 2005

If ultrasonic waves are introduced into a colloidal suspension, alternating potentials of the same frequency are developed within the suspension between points separated by one-half wavelength. This phenomenon is associated with the distortion of the diffuse layer of ions surrounding each colloidal particle. The effect has been measured with pulse-modulated ultrasonic waves at carrier frequencies of 200 and 1000 kc/sec for several aqueous colloidal systems. For a 25-percent silical suspension with a specific conductance of 150 micromhos, the amplitude of the effect at 200 kc/sec has been found to be approximately 0.02 volt per atmos or −155 db re.: one volt per dyne/cm2. For such suspensions the alternating potentials appear to be directly dependent on the ratio of the colloid concentration to the specific conductance of the system. This effect offers an interesting method for the investigation of the physical properties of colloidal suspensions, particularly with respect to the electrokinetic characteristics.
Use of a Differential Phase-Delay Method for Study of Ultrasonic-Wave Propagation in Swollen Rubberlike Materials
Authors: Nolle A. W. , Mifsud J. F.
Published: September 2005

Velocity and attenuation of ultrasonic waves at 2, 5, and 10 mc, −90°C to 80°C, are measured in a buna-N vulcanizate immersed in liquid baths containing successively larger concentrations of the solvent methyl-ethyl ketone in mixture with ethyl alcohol or water. At constant frequency the temperature maximum of attenuation moves with increasing solvent concentration to lower temperatures, while the magnitude of the maximum decreases. Velocity dispersion regions move with the attenuation function. Results are discussed in terms of relaxation properties of the rubber-solvent system. The measurement method involves conventional liquid-path ultrasonic pulsed-signal reflection apparatus with precision synchroscope indicator. Phase velocity and attenuation are deduced from changes in echo arrival time and amplitude when the specimen is introduced. Large attenuation requires use of a sample only about three wavelengths thick. The random spread in velocity measurements is about ±10 percent for direct measurement of pulse-envelope arrival time. For additional information the operator measures, on an expanded sweep, the change in time-scale position of a single late peak of the signal-frequency sinusoid. The time difference, representing essentially steady state, indicates the amount by which the phase change due to sample insertion differs from a multiple of 2π. Resolution is about 10−8 sec. With coarse pulse-envelope observations as a guide, differential-method observations are adjusted to give velocity values with random spread of about ±1 percent.
On the Failure of Plane Wave Theory to Predict the Reflection of a Narrow Ultrasonic Beam from a Plane Surface
Authors: Weinstein M. S.
Published: September 2005

In past studies of the interaction of an ultrasonic beam with a solid plate immersed in water the general practice has been to assume that a narrow radiation pattern is a sufficiently close approximation to a plane wave to permit the use of plane wave theory to predict the results. Reflection measurements made in water with a three-degree radiation pattern at a frequency of 3.35 megacycles per second, using both air-backed aluminum plate of thicknesses ranging from 0.250 to 0.025 inch and a two-inch-thick aluminum slab to approximate a semi-infinite medium, indicate that under certain conditions this assumption is not valid. Experimentally, the excess pressure of the reflected wave is considerably lower than that predicted by plane wave theory when the angle of incidence is such that the change of phase of the wave upon reflection varies greatly with a small change of the angle of incidence. It is apparent that at these angles of incidence a divergent beam which is several degrees wide cannot be used to approximate a plane wave. The nature of the phenomenon indicates that it should be of equal importance in the study of transmission phenomena.
Radiation Loading of a Rigid Piston Source in a Finite Baffle
Authors: Watson Robert B.
Published: September 2005

Experimental data are presented for both the resistive and reactive parts of the radiation loading of a rigid piston source vibrating in a finite circular baffle, as a function of the size of the baffle. A qualitative explanation is given in terms of the direct radiated wave and the diffracted wave arising from the edge of the baffle.
Steady Torques and Streaming Associated with Crossed Plane Waves
Authors: Nyborg Wesley L.
Published: September 2005

Eckart has recently developed a formalism for calculating steady streaming velocities that often accompany intense sound fields in viscous fluids. From his results it may be shown that whenever steady flow takes place due to a sound field there will always be some region R where each included element of fluid is so acted upon by the sound field that a steady torque T(x, y, z) is needed in order to maintain dynamic equilibrium. It is the streaming motion which, in the steady state, provides this torque. By Eckart's method one essentially first calculates T(x, y, z) and then the streaming distribution which will yield that torque. In this paper a special procedure is described for calculating streaming and torque distributions due to sound fields consisting of superposed plane waves. The method is dependent on Eckart's theory, but differs from it in that effects of absorption due to causes other than viscosity may be taken into account. Solutions for simple situations are described. The streaming velocity is found to depend on the ratio α/μ, where α is the absorption coefficient and μ is the shear viscosity coefficient. For two crossed travelling waves the streamlines are essentially straight and parallel, whereas for two crossed sets of standing waves the sound field is under appropriate conditions filled with a checkerboard arrangement of vortices whirling in alternate directions.
Pulse Propagation in a Nonhomogeneous Medium
Authors: Garvin W. W.
Published: September 2005

This paper considers the propagation of a plane elastic pulse through a nonhomogeneous, elastic, and isotropic medium. The inhomogeneity is represented as a constant velocity gradient (caused by changes in the elastic properties) which is assumed to be parallel to the direction of propagation of the pulse. It is shown that it is impossible to transmit a “clean” pulse through such a medium—the disturbance will have a definite onset, but will be followed by a train of slowly decaying oscillations. The period of these oscillations is related to the existing velocity gradient. The case of a reflection from a free boundary normal to the velocity gradient is considered in detail and it is shown that the motion imparted to the boundary will not be a replica of the motion in the incident pulse.
Aerodynamic Noise and the Estimation of Noise in Aircraft
Authors: Rogers O. R. , Cook R. F.
Published: September 2005

Noise resulting from the flow of air over the fuselage of an airplane has been investigated and found to depend principally on approximately the fifth power of the indicated air speed. The resulting emperical relation of noise level to airspeed is found to be quite useful in estimating the noise in the frequency range above 600 cps, for airplanes varying widely in size, shape, and method of propulsion. From this relation a method has also been evolved for making rough estimates of the weight of acoustical insulation necessary to reduce the noise in airplanes to a predetermined level.
Preliminary Estimate of a Hearing Damage Risk Criterion for Steady State Noise
Authors: Hardy Howard C.
Published: September 2005

Much of the lack of correlation between noise level and hearing damage is because of unsatisfactory theories which express the effect of frequency. It is possible to get a simple damage risk criterion, if one makes the following assumptions: (1) that hearing damage for those who work in noisy environment is a progressive auditory fatigue phenomenon, (2) that the fatigue is the same function of the stimulus in the inner ear for all frequencies, and (3) the sensation level is a similar function of the stimulus in the inner ear for all frequencies. The damage is, on this hypothesis, simply a function of the sensation level and varies with frequency in the same manner. Fletcher's calculation of the energy levels in the fluid near the basilar membrane as a function of sound pressure and frequency supports this theory. This analysis leads to the setting up of equal loudness contours for broad-band noise which correspond to hearing damage contours. Such curves explain for the first time the 4000 cps “notch” in the audiograms of industrial workers. Research data taken from a survey of industrial noise serve to establish two octave band curves which tentatively appear to bracket the region for damage risk for daily exposure over many years to a steady state noise environment. When the noise exceeds 100 sones in any octave band, long exposure definitely appears to be damaging. When the noise does not exceed 50 sones in any octave band, there appears to be very little danger of hearing damage even after many years of working day exposure. These conclusions are supported by the few data available in the literature. Evaluation of clinical data, which have not yet been disclosed by industrial audiologists and otologists, should make it possible to confirm and more sharply define the damage risk levels.
Tentative Criteria for Noise Control Design
Authors: Rosenblith Walter , Beranek Leo L. , Bolt Richard H. , Newman Robert B. , Baruch Jordan J. , Labate Samuel
Published: September 2005

Presented in this paper is a set of criteria that have been developed and applied on numerous noise control problems. A wide range of confirmatory evidence and experiences has led us to view these criteria with some confidence, although we recognize that they are subject to modification on the basis of additional data which are continuing to accumulate. An essential feature of the criteria is that they incorporate a specification of frequency dependence (usually expressed by octave bands) as well as over-all sound pressure level. Tentative criterion curves are presented for: (a) risk of permanent damage to the hearing mechanism under habitual exposure to (i) continuous spectrum noises and (ii) single frequency components; (b) speech communication conditions in terms of percentage intelligibility, voice level, distance between talkers, and type of vocabulary; (c) risk of annoyance to residential areas as dependent on type and previous noise conditioning of the community, daytime vs nighttime exposure, and the time pattern of the exposure. Emphasis is laid on the importance of interpreting these criteria in the light of the inherent variability among individuals in their responses to noise stimuli.
The Space-Time Patterns of the Cochlear Microphonic in Guinea Pig
Authors: Tasaki I. , Davis H. , Legouix J.-P.
Published: September 2005

Two or three pairs of nichrome steel electrodes (20μ) are inserted into each of two or three turns of the cochlea of guinea pig. One electrode of each pair is in scala tympani, one is scala vestibuli. Such “differential” leads record nearly pure cochlear microphonics from segments of the cochlear partition only about 1 mm long. Low tones evoke microphonics from all four turns; but as the frequency is increased (holding the response from the basal turn constant by adjusting the intensity of sound), the microphonic ceases, first at the apical turn, then at the third turn, and finally at the second turn. The normal space pattern for each frequency as revealed by its cochlear microphonic is a long plateau rising slowly from the basal end but with a much more abrupt fall toward the apex. The locus of this abrupt fall is characteristic for each frequency. The space-time pattern of an acoustic signal is a decelerating traveling wave moving from base toward apex. The velocity of a 500-cycle wave falls from about 70 m/sec in the basal turn to about 2 m/sec near the helicotrema. These electrical patterns are in general agreement with the mechanical patterns described by Békésy.

The space and space-time patterns remain normal even when large sections have been removed from the bony shell of the second turn, over both scala vestibuli and scala tympani. The traveling wave still originates in the basal turn even when the cochlea is stimulated by sound transmitted through the fluid in a small pipette that enters scala vestibuli of the third turn through a hole in the bony shell.
Noise Audiometry
Authors: Tonndorf Juergen , Brogan F. A.
Published: September 2005

Audiometric tests (pure tones and speech) were conducted on deafened ears in quiet and at several levels of calibrated white noise. The cases were classed into six groups based upon results of their threshold audiograms. “Recession” describes the gradual approach toward normal levels with increasing noise of masking curves obtained from such ears. In cases displaying recruitment recession was relatively rapid, although not complete in some cases. A pure tone-to-speech perception ratio was established between the three audiometer frequencies within the speech range and the level of the 50 percent spondee score. Corrections were applied for (1) the type of loss and (2) the subject's unfamiliarity with the quietness of audiometric test rooms. This ratio is expected to differentiate speech losses as to their auditory or extra-auditory origin. From the results of speech tests, the “Social Adequacy Index for Hearing” in noise was evaluated in the same manner customarily used under quiet conditions. Adjustment of the test results was necessitated because of the narrowing of the “Useful Auditory Area” induced by noise. The SAI frequently increased but in some cases decreased with noise, indicating the relative hearing efficiency in noise of deafened subjects.
A Case of Tonal Uniaural Diplacusis
Authors: Ward W. D.
Published: September 2005

During a current investigation of ears with chronic high frequency tonal gaps, it was found that some sort of uniaural diplacusis is usually associated with this type of hearing abnormality. Generally this uniaural diplacusis takes the form of a “rough” or “noisy” sensation within certain frequency ranges. In one subject, however, the distortion is definitely tonal in character; in particular, frequencies from 2700 to 3300 and from 3900 to 4500 cps are heard as two or more separate tones. Extensive tests show that when an objective frequency F (within the above ranges and below 60 db SPL) is presented, one or more of the following tones is heard in addition to F: 2F-3600, 2(3600)-F, 3F-2(3600), 3(3600)-2F. (These tones represent the difference tones heard in a normal ear when F and an objective tone of 3600 cps are presented simultaneously.) Also, rough beats are heard at threshold for frequencies from 3500 to 3700, with a null point at 3600 cps. Finally, when the acoustic stimulation consists of alternate one-second tones and silence, the silent period is filled with a 3600-cps “after-clang.” These results suggest some basic instability of this ear at 3600 cps. There is, however, no persistent tinnitus. The similarity of the observed effects to the “personal tone” reported by Flottorp and to the “tinnitus beats” of Wegel is discussed.
Pitch Discrimination Data from Two Psychophysical Methods
Authors: Rosenblith W. A. , Stevens K. N.
Published: September 2005

Pitch discrimination data for pure tones have been obtained for two trained subjects at frequencies of 250, 1000, and 4000 cps. Two psychophysical procedures were used: In one method (Munson and Gardner's ABX procedure) the subject votes whether the third in a series of three tones sounds more like the first or the second of the series. In the second method (used extensively by Harris) the subject is presented with a standard tone followed by a test tone, and he judges whether the test tone is higher or lower than the standard. The difference limens measured by the second method are for both subjects smaller (by a factor of two or more) than those found by the ABX procedure. This fact gains in significance since one subject has small DLs while the other has rather large ones. Judgmental data obtained from a limited choice situation can provide at best an upper bound for so-called ultimate sensory capacity. Practically speaking, the second method not only yields smaller DLs, but is also easier on the subjects, who can form the discrimination relatively quickly.
The Perception of Vowel Formants
Authors: Stevens K. N.
Published: September 2005

Synthetic vowel sounds, formed by electrical excitation of resonant circuits by a regular series of impulses, have been used as stimuli in a group of psychophysical experiments. The experiments include measurements of just noticeable differences (JNDs) in formant frequency and in band width for the synthetic sounds with one and two resonances, and with resonance band widths comparable to those found in measured vowel spectra. Average JNDs in formant frequency and band width at 1000 cps are 17 cps and 25 cps, respectively. The results are used to establish a frequency scale for the representation of vowel formants. Equal distances on this scale correspond to an equal number of JNDs in formant frequency. The proposed scale is approximated more closely by a linear frequency scale than by a mel scale. The approximate number of JNDs between pairs of vowels (arranged on a scale from front to back vowels) is evaluated, and is in the range 15–20 on the average. In general, the data indicate that frequency analysis of vowels using a filter band width as narrow as 45 cps provides more information than the perceptual processes can resolve.
The Masking of Tones by White Noise as a Function of the Interaural Time Displacement of the Noise
Authors: Jeffress Lloyd A. , Blodgett Hugh C. , Deatherage Bruce H.
Published: September 2005

In a recent paper, the present authors described the effects upon masking of varying the interaural phase positions of a 500∼ tone and of the 500∼ masking component of a white noise. The present paper extends this work by displacing the masking noise in time. This is accomplished by moving one head of a binaural tape reproducer. The results are in agreement with those previously published on the masking of tones by noise, and support the idea of a “critical” band. They also furnish additional evidence of the importance for masking level difference, of the interaural noise correlation.
A New Automatic Screening Audiometer
Authors: Glorig Aram , Wilke Robert R.
Published: September 2005

A screening audiometer has been developed, which functions automatically. It has the following salient features: The subjects are required to make simple numerical choices as indicated by visual instructions. A single numerical choice for each frequency serves to evaluate the two ears separately. The stimuli consist of interrupted tones of pre-set levels. The operation of this instrument and the results of the field tests are presented.
The Transmission of Sound through Thin Cylindrical Pipe Walls
Authors: Bolt R. H. , Young J. E. , Lang H. C.
Published: September 2005

Measurements have been made on the transmission of sound through the walls (1/16 in. thick) of cylindrical steel pipes (9- and 15-in. diameter). Two source arrangements were used: (a) an approximately uniform distribution of small speakers along the axis, and (b) a speaker in one end, radiating into the pipe, with a ρc termination at the opposite end. The results from the two methods are qualitatively similar but exhibit significant differences in magnitude. The transmission loss (TL) behavior of thin-walled cylinders can be related to two principal resonances at f1≃(5400/d) cps and f2≃1.65 × 103(t/d2) cps; d = diam, ft; t = wall thickness, in. At f1 the walls stretch in a radial, axially symmetric mode of vibration. At f2 the walls bend in a mode of vibration that is symmetrical about a diameter. Above f1 the TL approaches that predicted by a “mass law,” rising with increasing frequency at about 6 db/octave. Below f2 the TL approaches that predicted by a “stiffness law,” rising with decreasing frequency at about 6 db/octave. At f1 and f2 the TL reaches minimum values that are controlled by internal resistance. Between f1 and f2 the TL rises to a broad maximum. These properties are illustrated by approximate agreement between the experiment and a first-order theory. The results are also compared with field measurements on pipes up to 10-ft diameter carrying high level broad-band noise.
Compound Direct Radiator Loudspeaker
Authors: Olson Harry F. , Preston John , May Everett G.
Published: September 2005

The closed cabinet, with or without a port, has become the standard mounting arrangement for a direct radiator loudspeaker mechanism for high fidelity sound reproducing systems. One of the objections to the cabinet for these systems is the large size required to obtain adequate low frequency response. The effective volume of a small cabinet may be increased by the use of an auxiliary loudspeaker mechanism which drives the radiating loudspeaker mechanism. This system has been termed a compound direct radiator loudspeaker. The use of the compound direct radiator loudspeaker makes it possible to obtain low frequency response comparable to that of the conventional wide range system but in a cabinet having only a fraction of the volume of the cabinet in the conventional system.
The Effect of Tube Noise on the Equivalent Noise Pressure of Transducer Systems
Authors: Byrnes Francis X.
Published: September 2005

In determining the equivalent noise pressure of transducer systems, the tube noise in the preamplifier is an important factor. Although adequate information on tube noise exists for the ultrasonic and higher audiofrequency range, it was found that there is very little quantitative data available on tube noise in the lower audio and infrasonic region. An experimental program to obtain quantitative data on tube noise in this frequency region down to 0.04 cps has been carried out. The usual increase in the tube noise spectrum level as the frequency went into the lower audio range, resulting from flicker effect, was observed. In addition, it was found that as the frequency was lowered into the infrasonic region, the slope of the noise spectrum became much steeper. Noise spectrums for a number of modern tubes will be presented.
Method for Measuring Normal and Tangential Forces and Accelerations with Barium Titanate Ceramics
Authors: Mason W. P.
Published: September 2005

Small pieces of barium titanate ceramic have been used in measuring normal and tangential forces and accelerations in telephone equipment. When these are poled in a direction normal to the electrodes these ceramics respond to normal forces, while if they are poled parallel to the electrode surfaces they respond to tangential forces along the direction of poling. Normal force responding ceramics have been used to measure forces in relays and accelerations in other systems. Tangential force responding ceramics have been used to investigate frictional forces and slide in mechanical systems and to measure tangential accelerations in various mechanical systems. These units are about 50 times as sensitive as quartz, the only other piezoelectric material with sufficient mechanical strength to be used in force measurements. Small ceramics pieces working into vacuum tubes with very high input resistances can measure forces and accelerations varying in time from 0.1 second to 1 microsecond. The voltage response for a given force and the stability with reversed voltages and time depend on the time and temperature of baking and on the effect of introduced additants. The response of the normal force responding ceramic depends on the distribution of stress over the surface, whereas the response of the tangential force responding ceramic is independent of the stress distribution.
An Experimental Study of Single Bubble Cavitation Noise
Authors: Harrison Mark
Published: September 2005

An experimental study of single bubble cavitation noise has been made. Single bubbles were produced either by a venturi nozzle or by a spark technique. The motion of the bubbles was studied photographically and simultaneously the noise measured. The noise consists principally of a shock wave associated with the collapse of the bubble. There are other sources of noise but they are of minor importance. The pressure versus time records permit the spectrum to be easily computed by Fourier transforms. Rayleigh treated the motion of an empty spherical bubble in an incompressible fluid. He showed that when the bubble collapses the radial velocity becomes infinite and an infinite pressure is developed. Incompressibility is clearly an untenable assumption. Also, the thermodynamics of the bubble contents must be considered. It was observed experimentally that the air content of the bubbles is the dominant factor in determining the magnitude of the pressure shock wave. When the air content becomes small compressibility becomes the dominant factor in determining the magnitude of the pressure shock wave. The venturi bubbles and the spark bubbles behave differently as might be expected since the thermodynamics of their contents are different.
Gaseous Cavitation in Liquids
Authors: Rosenberg M. D.
Published: September 2005

A focused standing-wave system of sound waves with a frequency of 60 kc/sec has been used to produce cavitation in gas-saturated liquids. The system consists of magneto-strictive transducers with appropriate paraboloidal and plane reflectors. A thin-walled flask holds the liquids to be studied at the focal point of the paraboloid. The liquid under study is saturated just before measurement with pre-dried air by means of mechanical agitation consisting of 1264 one-inch strokes per minute. A calibrated magnetostrictive probe, 18 inch in diameter is placed at the focal point of the system. The pressure at which cavitation bubbles (gas-filled) occur at the surface of the probe is plotted as a function of viscosity and pulse length. A new theory of sonically induced diffusion appears to offer an explanation for the experimental data.
Wave Propagation in Liquid-Filled Cylinders
Authors: Fay R. D.
Published: September 2005

Difficulties encountered in obtaining reliable measurements in a water-filled impedance tube over a reasonable range of frequencies have led to an investigation of the propagation of waves in a column of fluid bounded by a cylindrical shell of arbitrary thickness. The investigation has dealt chiefly with the phase velocity of free traveling waves in the shell, since the connection between such waves and the major measurement difficulties has been well established. The relation between these free waves and the dimension of the cylindrical shell will be presented graphically for typical cases.
Axially Symmetrical Vibrations of a Finite Isotropic Disk
Authors: Aggarwal R. R.
Published: September 2005

Using an approximate method similar to that of Love, some normal modes of a thick disk have been calculated. The boundary conditions have been exactly satisfied on the flat surfaces and approximately satisfied on the curved surface. It is found that two fundamental frequencies occur for each vibration pattern on the surface. The validity of the boundary conditions is tested by calculating the residual stresses on the curved surface and comparing these with the compressional stress at the center of the disk. Both compressional and shear vibrations will be discussed.
Sound Scattering by Thin Elastic Shells
Authors: Junger Miguel C.
Published: September 2005

The theory of scattering of plane waves of sound is extended to scatterers in the form of thin elastic shells of cylindrical and spherical shape. As for all elastic scatterers, the scattering action is the resultant of (1) “rigid body scattering,” i.e., the scattering which would be present if the scatterer were rigid and immovable; (2) “radiation scattering,” which represents the sound radiation from the shell undergoing forced vibrations under the influence of the incident wave pressure and which is determined by the dynamic characteristics of the submerged shell. Contrarily to solid scatterers whose dynamic characteristics are little different in vacuo and in the fluid medium, the characteristics of shells are profoundly altered by fluid reaction. When the shell is excited near resonance, the scattering pattern resembles the dynamic response of the shell in that it is highly frequency sensitive.
Absorption of Sound in Argon, Nitrogen, and Oxygen at Low Pressures
Authors: Parker J. G. , Stavseth R. M.
Published: September 2005

The amplitude absorption coefficient α for pulsed spherical sound waves in argon, nitrogen, and oxygen has been measured over a 1–10 mm Hg range of pressure p and a 60–70 kc range of frequency f for temperatures varying from 20° to 21.5°C, by means of apparatus described previously. For the three gases used, the following experimental values for pα/f2 × 107 were obtained: 1.86±0.05 (argon), 1.63±0.05 (nitrogen), 1.95±0.05 (oxygen) as compared with the respective classical theoretical values of 1.87, 1.31, and 1.61. Thus the absorption in argon is classical, while for nitrogen and oxygen there are fractional excesses of 0.24±0.04 and 0.21±0.03, respectively. If these excesses are attributed to rotational relaxation and the associated relaxation time τ is calculated for each gas in accordance with the thermal relaxation theory of Herzfeld and Rice, one obtains the values 4.85 × 10−10 and 4.95 × 10−10 second, respectively, for nitrogen and oxygen. Both of these values are significantly smaller than those which have been calculated in a similar manner by previous workers on the basis of data obtained at higher frequencies. We therefore have evidence that the aforementioned theory is unable to describe rotational relaxation processes adequately.
The Attenuation of Repeated Shock Waves
Authors: Rudnick Isadore , Leonard Robert W.
Published: September 2005

The sound waves generated by the siren described in an earlier paper on this program by the same authors develop shock fronts in a short distance of travel and their shape finally approximates the characteristic sawtooth form. The spatial attenuation rates of such waves have been measured as a function of the siren frequency in the range 30–100 cps. A typical datum shows that a 100-cps wave with a pressure ratio across the shock of 1.5 is reduced by a factor of 2 in a travel distance of 55 feet. A first-order theory using the Rankine Hugoniot shock conditions is developed for a sawtooth wave. This gives attenuation rates which are higher than those observed experimentally. For the datum given the ratio of theoretical to observed attenuation rate is 1.5. This discrepancy will be discussed.
Sound Propagation in Granular Media
Authors: Morse R. W.
Published: September 2005

The sound velocity and attenuation in a granular medium such as air- or water-saturated sand are discussed theoretically and conclusions are compared with experiments. A simplified theory based on the gross properties of the porous medium is shown to predict a square-root frequency dependent attenuation coefficient and a nondispersive velocity dependent only on the porosity of the sand and the sound velocity in the fluid (provided the frequency is high enough). Calculated values for the attenuation coefficient agree fairly well with reported measurements in air-sand mixtures. Predicted sound velocities are consistent with geophysical data. Comparisons are also made with results of theories based on viscous-wave scattering by the particles. The scattering theory of Epstein and others, though not intended to be applied to such a close-packed medium as sand, is shown to yield an expression for the attenuation coefficient which is very nearly the same as that given by the gross theory.
Surface Vibration Patterns of Ultrasonic Radiators. III
Authors: Nixon John D. , Rhodes Richard A. , Williams A. O.
Published: September 2005

Previous experimental work has been modified by placing an optically flat partially silvered quartz crystal between two optically flat plates of glass, partially silvered adjacent to the crystal (intervening air space 1 mm). The optical fringes, formed thus, indicate the behavior of both sides of the vibrating crystal. This modification prevents the study of acoustic radiation into liquids, but gives sharp fringes, and eases the problem of collimation and photography Two 1812° a X-cut and two X-cut quartz crystals, one of each at 0.5 mc and 1 mc, were investigated by this method and by a capacitance bridge. The 1812° crystals behaved more uniformly, but all displayed several modes corresponding to a particular localized vibration pattern in a small area; the sum of these areas approaches the surface area of the crystal. The phenomenon is tentatively attributed to crystalline inhomogeneity. Attempts to enhance the effect by reducing the acoustic loading through reduction of air pressure gave inconclusive results.
Some Vibration Patterns of Thick Barium Titanate Disks
Authors: Shaw E. A. G.
Published: September 2005

The forms of some resonant vibrations of thick polarized barium titanate disks have been examined by an optical method using multiple beam Fizeau fringes with stroboscopic illumination. The technique permits accurate determination of the distribution of displacement amplitude over the surface of the disk. Only modes having axial symmetry appear to be strongly excited, and more than one strong resonance is observed in a frequency range which should include the principal dilatational thickness mode. Each mode in this region has characteristics generally associated with both axial and radial resonances.
Diffraction and Reflection as Sources of Error in Ultrasonic Measurements
Authors: Hubbard J. C.
Published: September 2005

Current practise in ultrasonic intensity measurements and interferometry in gases favors the mounting of a source such as a piezoelectric crystal (1) flush with a plane surface, (2) behind an orifice, or (3) projecting into a chamber. Reflector and source in interferometers are usually mounted in a cylindrical or box-like chamber of greater lateral dimensions than source and reflector. It is well known that diffraction takes place under these conditions. Not much attention has been paid to the reflection of diffracted sound from side walls back into the main beam. Under such conditions measurements of intensity by probes or otherwise are subject to complicated variations with distance from the source and half-wave determinations by any method, especially near the source, show variations from the constancy which can otherwise be obtained. Errors due to these causes may largely be avoided if the measurements can be carried out in a tubular chamber of material having as large a value of ρc as may be obtained, the full cross section of which is covered at one end by the source. In the case of the interferometer the reflector should also completely fill the cross-section of the tube. Reflector and source should be plane and parallel and accurately perpendicular to the axis of the tube. Diffraction will then be practically absent, reflection is largely confined to the surfaces of source and reflector. Shadowgraph and schlieren pictures and numerical data will be presented in support of these statements. These precautions have been taken from the first by the writer and his students.