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Nov 1967

Volume 42, Issue 5, pp. 947-1218

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Radiation Pressure on a Small Rigid Sphere

Wesley L. Nyborg

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 947-952 (1967); (6 pages) | Cited 14 times

Online Publication Date: 04 Aug 2005

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Simple expressions are derived for the acoustic radiation force F on a small rigid sphere of radius a, volume v and density ρ suspended In a liquid or gas of density ρ0. Effects of viscosity are neglected; use is made of methods developed by King and Embleton. Results are expressed in terms of the time‐averaged densities T̄a and V̄a of kinetic and potential energies, respectively, in the incident sound field. Letting β be ρ0/ρ it is found. as an approximation when a is much less than the sonic wavelength, that F  =  v[B∇matha − ∇matha]+Δ, B − 3 1 − β /(2+β), where Δ is given by a relatively complicated expression. The quantity Δ is important primarily in progressive waves of relatively uniform amplitude, as exist in the field of a large source; here ∇T̄a and ∇V̄a, may be relatively small while gradients of the phase exist. In a standing wave or in the neighborhood of a small source, Δ is negligible. When Δ = 0, the above expression for F agrees with one given previously by Gor′kov.

Reverberation‐Room Acoustics—Effects of Various Boundary Conditions

V. O. Knudsen, L. P. Delsasso, and R. W. Leonard

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 953-965 (1967); (13 pages)

Online Publication Date: 04 Aug 2005

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An investigation of the sound field in a large reverberation room as influenced by a 2 in. mineral wool floor covering and or an array or 96 suspended plywood panels yielded significant results. The panels do not increase the decay rates, that is, their absorption is negligible, for frequencies below about 250 cps; their added absorption to the room increased progressively at higher frequencies to 24 sabins at 4000 cps. Decay rates for low‐frequency single modes in the empty room were linear and ranged from 2.11 to 5.7 dB/sec; the decay rates when two contiguous modes were excited were very nonlinear; their contours were predicted in terms of the decay rates and the phase differences of the two modes. With the floor absorptive, the 96 panels reduced the maximal levels of impulsive sounds (pistol shots), at frequency below 250 cps.s, for all elevations above the floor; the average decrease was 4.6 dB. With the floor absorptive, the decay rate at 250 cps was only 6.2 dB/sec when source and microphone were in the upper part of the room, and 39.3 dB/sec when source and microphone were in lower part. The influence or these decay rates on the quality of recorded speech and music was shown to be large.

Underwater Hearing Thresholds in Man

John F. Brandt and Harry Hollien

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 966-971 (1967); (6 pages)

Online Publication Date: 04 Aug 2005

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The audibility threshold performance of the human ear submerged in water at ear depths of 12 and 35 ft was compared to its performance in air. Threshold SPL's at 125, 250, 500, 1000, 2000, 4000, and 8000 Hz from five male and three female divers wearing open‐circuit SCUBA equipment were obtained by the Békésy technique. Differences between water and air conduction thresholds ranged from 18 dB SPL re 0.0002 μbar at 125 Hz to 56 dB at 8000 Hz. Underwater thresholds ranged between 58 and 74 dB SPL, with maximum sensitivity around 500 Hz. Maximum sensitivity for air conduction thresholds was obtained at 2000 Hz. Slightly higher thresholds were obtained at the 35‐ft ear depth than at the 12‐ft depth. Tentatively, the data suggest the importance of bone‐conduction mechanisms in underwater hearing. However, it is apparent that further research must be carried out before it will be possible to predict the character and mechanism of the human ear submerged in water.

Masker Level and Sinusoidal‐Signal Detection

Richard A. Campbell and Elaine Z. Lasky

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 972-976 (1967); (5 pages) | Cited 2 times

Online Publication Date: 04 Aug 2005

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Threshold signal‐to‐masker ratios were obtained or a 1000‐Hz signal presented with either an identical frequency sinusoidal masker or a complex masker consisting of the same frequency as the signal plus two sidetones 300 Hz on either side of the central component. Data considered include signal durations of 20, 400, and 1000 msec with masker durations either equal to that of the signal or continuous for the block up‐and‐down, two‐interval, forced‐choice threshold run. The parameters of primary interest were the level of the masker and whether the masker was gated or continuous. The thresholds appear to indicate that when the excitation pattern of the masker is increased (by shortening its duration or adding sidetones) so as to equal or surpass that of the signal, masked thresholds tend toward an inverted‐N function, as related to masker level, rather than being independent of masker level. Also, differences between the gated and continuous masker thresholds do not appear to be related to changes in signal uncertainty as reflected in the slopes of psychometric functions.

Explanation of Masking‐Level Differences That Result from Interaural Intensive Disparities of Noise

Terrence R. Dolan and Donald E. Robinson

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 977-981 (1967); (5 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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The detectability of a monaurally presented 500‐cps signal was measured at each of several values of interaural correlation for a wide‐band noise masker. The results, when expressed in terms of masking‐level differences (MLD's), are in agreement with data reported by Whitmore and Wilbanks and show a function of similar form to that described by Robinson and Jeffress. Additionally, the detectability of a monaural signal was investigated as a function of the interaural intensive relations of a wide‐band noise masker. The data are in agreement with results originally shown by Hirsh, and since, replicated several times. That is, detectability is greatest when the level of the noise masker at the two ears is equal, and decreases as the level of the masker at the nonsignal ear is attenuated. The data are used to estimate parameters for a simple model that attempts to account for changes in detectability that occur when a monaural signal is presented with binaural, correlated noise having an interaural level difference. The model proposes that at low external noise levels, internal noise leads to a decrease in interaural‐noise correlation. Predictions from the model are in reasonable agreement with data reported previously.

Vibrational Displacement and Mode‐Shape Measurement by a Laser Interferometer

H. A. Deferrari, R. A. Darby, and F. A. Andrews

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 982-990 (1967); (9 pages) | Cited 5 times

Online Publication Date: 04 Aug 2005

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Four experimental methods are described in a tutorial way for use with a laser interferometer in measuring vibrational displacements and mode shapes of a transducer face. The relative merits and experimental difficulties of the methods are discussed. Quantitative data to show the type of experimental agreement that one might expect between the various methods and two illustrative mode shape measurements are given. In general, by proper choice of one or more of the methods, displacement measurements of magnitude 0.1–6000 Å at sonic and ultrasonic frequencies can be made at a point 0.1 mm in diameter. Mode shapes are determined simply by moving the laser beam a measured distance between points. Displacement data presented show a random error for all methods of 5% in the range 0.5–80 Å and less than 5% above 80 Å.

Instrumentational Rôle in the Observation of Geoacoustical Phenomena from Artificial Sources

Uri Fehr

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 991-1000 (1967); (10 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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Many physical principles have been applied to transform atmospheric pressure fluctuations of 1 sec and longer into electrical signals for the purpose of monitoring infrasonic signals. A survey of some infrasonic sensors is taken, with calibration and testing of several sensors at the UCLA calibration facility. An attempt was made to define the capabilities of each available sensor. Several experiments are described, which include the monitoring of static and dynamic firing of rockets, as well as the monitoring of explosions. The difficulties in interpretation of data are explained in relation to various instruments, taking into account wind effects, ground vibrations (observed by magnetometers), natural pressure fluctuations, and other phenomena producing noise at the frequency range of interest.

Analog Systems for Analyzing Infrasonic Signals Monitored in Field Experimentation

Uri Fehr and L. C. McGahan

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1001-1007 (1967); (7 pages)

Online Publication Date: 04 Aug 2005

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Large quantities of ultra low‐frequency acoustic data accumulated over long periods of time can be analyzed by several methods. Preliminary analysis of the analog waveform determines specific areas of primary interest prior to digital‐computer analysis. Data of no consequence can be discarded; or, the worth of such data may be graded, to scale their importance for computer processing. This technique also provides a means of expediting initial findings, and primary conclusions can be deduced. This study was conducted by the University of California, Los Angeles, and entitled, “Ionospheric Disturbance Experiment.” The raw tape‐recorded data are played back through an electronic system. Some important parts of this system are narrow bandpass filters and a Missilyzer (sound spectrograph). Some sample results are summarized.

Systems and Methods in Statistical Analysis and Reduction of Geoacoustical and Geomagnetic Data

Uri Fehr, Wallace F. Tolman, and Robert Crolene

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1008-1016 (1967); (9 pages)

Online Publication Date: 04 Aug 2005

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Geo‐acoustical and geomagnetic data gathered by an array of sensors for long periods of time were recorded on magnetic tape in frequency‐modulated form. A new digitizing system was worked out for an accurate study, then data were reduced and adjusted (or “recolored” in the time domain) using a numerical‐analysis technique, which corrects for frequency attenuation due to the frequency‐response characteristics of the sensor and field recording equipment. Wavelength and wave velocity depended on frequency and statistical error estimated from study of the F‐1 engine. The mathematical techniques involved in recoloring and filtering are explained, and the statistical techniques (autocovariance, cross covariance) used in the time‐series analysis are discussed.

Flush‐Mounted Pressure Transducer Systems as Spatial and Spectral Filters

G. Maidanik

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1017-1024 (1967); (8 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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Analysis of the responses of a flush‐mounted transducer system to the pressure field in a turbulent boundary layer and to the boundary pressure field induced by an incident plane acoustic wave is formulated and discussed. The transducer system is considered as a spatial and a spectral filter. The properties of the filters are defined and illustrated for the case where the system consists of nominally identical transducers. The analysis is limited to geometries where the centers of the transducers are regular y placed at the centers of a plane rectangular grid. Time delays between transducers are allowed for in this analysis.

Calculation of the Nearfield Pressure Induced by Vibrating Circular Plates

George W. Miner, II and Patricio A. Laura

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1025-1030 (1967); (6 pages)

Online Publication Date: 04 Aug 2005

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This paper deals with the determination of the nearfield pressure distribution induced by a circular radiator set in an infinite, plane, rigid baffle. Calculations are made in the present study for two deformable radiators (a clamped plate and a membrane or simply supported plate) and for a rigid piston. It is shown that the nearfield pressure distribution for the clamped and simply supported plate radiators differs greatly from the distribution obtained in the case of a rigid piston. In light of these considerations, the analysis and data presented in this paper could prove useful in the design of acoustic transducers.

Formant Frequency Regions of Polish Vowels

Wojciech Majewski and Harry Hollien

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1031-1037 (1967); (7 pages)

Online Publication Date: 04 Aug 2005

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Frequency regions of the first two formants of Polish vowels are given. The method included specification of these formants by spectral analysis of spoken vowels and by perceptual evaluation of synthetic vocalic stimuli.

Ultrasonic Absorption in Carbon Dioxide‐Water‐Vapor Mixtures

Roland W. Higgs and Ralph H. Torborg

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1038-1040 (1967); (3 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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The absorption of ultrasound in CO2‐H2O mixtures at 150° and 200°C was measured at frequencies of 1.25, 3.3, 4.8, 9.9, and 14.0 MHz for H2O vapor concentrations from 0.5% to 50%. The measured absorptions are compared with calculated results and agree reasonably well. The effect of H2O vapor on the relaxation frequency is linear at least up to 20% H2O vapor and a decrease in relaxation frequency is observed with increasing temperature.

Acoustic Absorption and Dynamic Viscosity in a Long‐Chain Polymer

J. L. Hunter and P. R. Derdul

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1041-1044 (1967); (4 pages) | Cited 2 times

Online Publication Date: 04 Aug 2005

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The acoustic absorption has been measured in the #200 series of silicones (linear polysiloxanes) over the frequency range 30–350 MHz, and the temperature range −30° to +30°C. The results are compared to measurements of dynamic viscosity made in the same fluids by Barlow, Harrison, and Lamb in approximately the same experimental region. It is found that a knowledge of the dynamic viscosity enables one to predict, quite precisely, the value of the acoustic absorption coefficient. The negligible volume viscosity and surprisingly low values of acoustic absorption and dynamic viscosity in this experimental range are discussed in terms of the theories of Rouse and Zimm for polymeric liquids of very long chain length.

Ultrasonic Phase Velocity by the Pulse‐Echo‐Overlap Method Incorporating Diffraction Phase Corrections

Emmanuel P. Papadakis

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1045-1051 (1967); (7 pages) | Cited 68 times

Online Publication Date: 04 Aug 2005

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The pulse‐echo‐overlap method for ultrasonic time‐delay measurements is reviewed. In this method, pairs of echoes are compared by driving the x axis of a viewing oscilloscope at a frequency equal to the reciprocal of the travel time between the echoes. A method for choosing the correct cyclic overlap for the rf within the echoes is given. Utilization of the proper cyclic overlap permits the accurate measurement of ultrasonic phase velocity. When corrections for the phase advance due to ultrasonic diffraction are applied to the travel times between various pairs of echoes, the accuracy of the average round‐trip travel time is improved. Experimental verification of this is presented for longitudinal waves in isotropic materials and in the pure mode directions in cubic crystals. Delay times are accurate to 0.2 nsec or better.

Influence of Attenuation upon the Frequency Content of a Stress Wave Packet in Graphite

Steven Serabian

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1052-1059 (1967); (8 pages)

Online Publication Date: 04 Aug 2005

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This paper presents experimental data concerning the distortion of the frequency spectrum of a stress wave packet as produced by attenuation effects in graphite.

Mutual Acoustic Impedance between Flexible Disks of Different Sizes in an Infinite Rigid Plane

Kwai‐Cheung Chan

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1060-1063 (1967); (4 pages)

Online Publication Date: 04 Aug 2005

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A direct method of analysis based on the “classical” Rayleigh formula is presented for calculating the mutual acoustic impedance between circular radiators of different sizes in an infinite rigid plane. The effects of the interactions between two radiators are considered in detail. The acoustic pressure on the plane baffle is described by a distribution of surface “sources” of known strength at the plane‐fluid boundary. As the sound‐pressure field produced by one radiator exerts a force on another radiator on the plane, the mutual radiation impedance can be defined by the force exerted by one radiator integrated over the surface of the other. This impedance is expressed by a series solution of products of Bessel functions. The results can be reduced to those found by Pritchard and Porter, who based their solutions of the problem as formulated by Bouwkamp. Numerical calculations for the series solutions of the pressure field and of the mutual impedance terms are not given. Attention is paid only to mathematical formulisms.

Reflection and Transmission of Oblique Plane Waves at a Plane Interface between Viscoelastic Media

Henry F. Cooper, Jr.

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1064-1069 (1967); (6 pages) | Cited 3 times

Online Publication Date: 04 Aug 2005

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The solution is obtained for the reflection and transmission of time harmonic plane dilatational or shear waves at a plane interface between two linearly viscoelastic materials. Except in special cases, the reflected and transmitted waves are general plane waves, i.e., plane waves whose amplitudes vary across their wave‐fronts. The angles of reflection and transmission depend on the incident angle in a more complicated way than in the limiting elastic case because the wave speeds of the reflected and transmitted waves are, in general, functions of the incident angle. Necessary and sufficient conditions for the existence of interface waves are obtained. It is found that no interface waves can exist for some materials. For another class of materials, interface waves exist for discrete angles of incidence. For still other materials, interface waves exist for all incident angles greater than some critical angle.

Multimode Response of Panels to Normal and to Traveling Sonic Booms

Malcolm J. Crocker

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1070-1079 (1967); (10 pages)

Online Publication Date: 04 Aug 2005

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A detailed theoretical study of the response of a uniform flat rectangular panel to a sonic boom (or “N” wave) is presented. Both cases, where the N wave arrives normal to the panel surface and where the shock front arrives at any angle of incidence and crosses the panel parallel to one side, are considered. Closed‐form solutions (for individual modes) are given for the cases of simply supported panel response to normal and traveling N waves; an approximate solution is presented for the response of a panel with fully fixed edges to a normal N wave. The Duhamel integral method used gives panel displacement‐, strain‐, and stress‐time histories for any point on the panel. The analyses derived have engineering applications in the computation of window or wall‐panel response to sonic boom. Some comparison made between theory and experiment. Good agreement is shown to exist between measured and predicted strain maxima and fair agreement to exist between the early parts of the strain‐time histories, despite some differences between the experimental and theoretical models. The necessity to include the contributions due to the higher modes is clearly borne out in theory and experiment, particularly for accuracy in strain‐time histories.

Spatial and Spectral Dependence of Acoustic Reverberation

Victor C. Anderson

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1080-1088 (1967); (9 pages) | Cited 1 time

Online Publication Date: 04 Aug 2005

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Reverberation data obtained in the latter part of 1966 at the northern end of the San Diego Trough are analyzed. Scattering coefficient distributions as a function of depth, horizontal displacement, and frequency are presented and compared with idealized normal distributions. Frequencies range from 8.0 to 9.5 kHz, depths from 100–3000 ft.

Detection of an Incoherent Finite Signal Using a Number of Sensors

Melvin J. Hinich

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1089-1094 (1967); (6 pages)

Online Publication Date: 04 Aug 2005

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Consider a collection of m sensors, immersed in an isotropic noise field, that is designed to detect the arrival of an unknown time‐limited signal of length T seconds. However, the power spectrum S(ω) of the signal is known. Asssume that the direction of the signal propagation is known approximately, but due to local perturbations of the medium or motions of the sensors, the precise arrival time of the signal at each sensor is unknown, and the signals cannot be added coherently. Time adjustments can be made for each sensor channel so that the signal is assumed to arrive during a sampling window of T seconds if some part or all of the signal is within the window for each sensor. If the noise is white, the weak‐signal optimal detection procedure is to compute
math
, where S(ω) is the observed power spectrum averaged over all the sensors and Δ is the interval between discrete observations, and then to compare U with a threshold. The signal is claimed to be present if U exceeds the threshold. This procedure is equivalent to a certain type of weighted power detection. It has a greater signal‐to‐noise ratio gain (called signal detectability) than that obtained by using simple power detection. The end effects due to loss of part of the signal in the finite window prohibit the use of power spectrum comparisons.
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On the Equivalent Circuit of a Plane Wave Confronting an Acoustical Device

Benjamin B. Bauer

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1095-1097 (1967); (3 pages)

Online Publication Date: 04 Aug 2005

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An approximate analog circuit of a plane wave confronting an acoustical device of aspect radius a is shown to comprise two in‐phase voltages, respectively, having magnitudes of 2p and p and driving the device through a resistance ρc/A, and inductance 0.5 ρa/A.

Addendum: Robust Two‐Input Correlators [J. Acoust. Soc. Am. 41, 1212–1219 (1967)]

S. S. Wolff and J. L. Gastwirth

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1097-1097 (1967); (1 page)

Online Publication Date: 04 Aug 2005

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Erratum: Mechanistic Aspects of Hearing [J. Acoust. Soc. Am. 41, 1500–1516 (1967)]

Edith L. R. Corliss

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1097-1097 (1967); (1 page)

Online Publication Date: 04 Aug 2005

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Abstract Unavailable

Erratum and Note: PEST: Efficient Estimates on Probability Functions [J. Acoust. Soc. Am. 41, 782–787 (1967)]

M. M. Taylor and C. D. Creelman

J. Acoust. Soc. Am. Volume 42, Issue 5, pp. 1097-1097 (1967); (1 page)

Online Publication Date: 04 Aug 2005

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Abstract Unavailable
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