Index of content:
Volume 36, Issue 5, May 1964
- PROGRAM OF THE SIXTY‐SEVENTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session A. Psychological and Physiological Acoustics I
- Contributed Papers
36(1964); http://dx.doi.org/10.1121/1.1919149View Description Hide Description
The generation of airborne sonic emissions by Tursiops was described by Aristotle (384 to 322 BC). In modern times, only passing notes are found in the literature (Tomilin, etc.). The first sonic spectrograms are published [Proc. Am. Phil. Soc. 106, 520 (1962)]. During the first few days in confinement, the usual large underwater sonic repertoire of Tursiops can be recorded; airborne emissions are rare [Science 134, 1873 (1961); Handbook of Physiology, p. 741; Am. Physiol Soc. (1964)]. (During the first day or two of confinement, some individuals (3 out of 40 observed) produce in air sounds usually heard under water, and then become “air‐silent.” In many cases, after 8 to 24 weeks in confinement, the airborne emissions start. These complex sounds in air are specified by their amplitude patterns, basic repetition rates, frequency spectra, time courses, and relations to underwater sounds produced concurrently and/or alternatively. Oscillograms and spectrograms are presented. Some recorded evidence for some degree of apparent time‐course coupling of trains of some of these emissions to similar missions from other sources is presented. [Work supported in part by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, by the U. S. Air Force Office of Scientific Research, and by the National Aeronautics and Space Administration.]
36(1964); http://dx.doi.org/10.1121/1.2143143View Description Hide Description
Using various conditioning procedures, three species of monkeys have been conditioned in order to determine their audiograms. Squirrel monkeys have been conditioned in a double‐grill cage, using shock as the reinforcement, while squirrel monkeys, Rhesus monkeys, and Cynamolgus monkeys have been conditioned in a single‐bar reward and a single‐bar avoidance situation. In general, the audiograms obtained for the various species, and using the various conditioning procedures, agreed quite well. The audiograms of the individual animals, as well as the average performance for each species, are reported.
36(1964); http://dx.doi.org/10.1121/1.2143144View Description Hide Description
Eleven cats were exposed to pure‐tone stimulation intended to produce moderate hair‐cell damage. Behaviorally defined pre‐ and post‐stimulation intensity‐difference thresholds were then compared to see whether recruitment would be evident. Following this, the animals were sacrificed and their ears sectioned and examined to determine the extent of the damage. While varying degrees of damage were evident from the animals' behavioral audiogram and from the histopathological data, there was no evidence of a decrement in their intensity‐difference thresholds. This lack of relationship between the discrimination and the histopathological data is discussed.
36(1964); http://dx.doi.org/10.1121/1.2143145View Description Hide Description
Development of a method of using a class of short‐duration tonal stimuli for exploring auditory perception indicates that the method measures some factors not measured by conventional audiometry. While a normal listener perceives tonal quality in a pure‐tone stimulus of 10 msec duration, impaired subjects require much longer (in this study, up to a full second), perceiving the shorter duration stimuli as clicks. Additional dimensions, such as the size of the gap between ascending and descending test scores, also appear significant. On humans and dogs, the test has shown that adequacy of blood supply to the brain stem relates to these dimensions. Surgical relief of stenotic arterial lesions limiting brain‐stem circulation in humans improves these scores, independent of pure‐tone audiograms. Four dogs trained to respond only to a sensation of tone were subjected to ligation of the basilar artery. A 5‐fold increase of the stimulus duration necessary to elicit the response was seen in three animals.
36(1964); http://dx.doi.org/10.1121/1.2143146View Description Hide Description
Masked thresholds in rats were measured with an operant tracking method [Science 131, 1046 (1960)] at four frequencies between 1000 and 8000 cps and at three to five levels of wide‐band noise. Critical ratios calculated from the masked thresholds were found to be greater than those found in cat and in man. The mathematical function derived by Greenwood [J. Acoust. Soc. Am. 33, 1344 (1961)] relating critical bandwidths to position on the basilar membrane was shown to fit reasonably well the data collected in this experiment. [Work supported by grants from the National Institutes of Health, U. S. Department of Health, Education, and Welfare (NB‐02484), and from the Alfred P. Sloan Foundation, Inc.]
36(1964); http://dx.doi.org/10.1121/1.2143147View Description Hide Description
Intra‐primate temporal integration is examined for differences in both the rate and upper critical duration (t 0) as a function of frequency. The thresholds of five women and two Rhesus monkeys were obtained monauarally and/or binaurally (MAF) for pure‐tone stimuli at 0.25, 0.5, 1, 2, 4, and 8 kcps. The signal durations were in log units from 10 to 1500 msec. The single‐lever, go/no‐go procedure was similar for humans and monkeys, allowing comparison of responses for possible influences of the decisional behavior upon the obtained thresholds. As in humans, the absolute limens of monkeys show linear changes as a function of log signal duration within the range of sampled time intervals. The t0 values are also similar for humans and monkeys. The slope of the temporal integration function is frequency‐dependent, with monkeys showing the greater effect below 1 kcps. Differences in absolute sensitivity, plus the frequency dependence, raise problems for current hypotheses concerning temporal integration. [Work supported by a grant from the Public Health Service, U. S. Department of Health, Education, and Welfare.]
36(1964); http://dx.doi.org/10.1121/1.2143148View Description Hide Description
There have been relatively few studies concerning the auditory capacities of the lizard. Because of its intermediate structural complexity, however, the saurian ear offers the opportunity for a number of interesting comparisons with the more highly developed avian and mammalian ears. The present paper describes the results of several investigations in this area performed at the Auditory Research Laboratory, Princeton University. 14 species representing 6 families were studied. Inner‐ear potentials, recorded from the round‐window membrane, were used as an index of hearing. In relation to the mammalian ear, these ears were generally found to (a) be rather insensitive within a narrow frequency range, (b) have a very narrow dynamic range, and (c) be nonlinear at even low stimulus intensities. It was found, however, that the best individuals of a few species rivaled the sensitivity of mammalian ears in the middle frequencies. The role of the middle‐ear mechanisms in sound conduction and sound control was also studied.
36(1964); http://dx.doi.org/10.1121/1.2143149View Description Hide Description
The morphological kinship of the lateral‐line organ and the various maculae of the inner ear has long been recognized. Recent investigations of the ultrastructure of the sensory cells in the organs and maculae have strongly reinforced the belief that the acoustico‐lateralis system should be considered a unitary sensory system. Its several subsystems have special peripheral adaptations to deal with particular forms of mechanical stimulation, but use the same fundamental sensecell, the hair cell. Since the lateral line has been shown to be a displacement detector that responds to acoustic stimulation in the near field only, the question arises how the farfield, pressure‐sensitive ear has evolved. It is proposed that the middle ear be regarded as a pressure‐to‐displacement transformer. Its earliest evolutionary form is the fish's swimbladder, which generates a local near field inside the fish in response to pressure waves. This local near field is then transmitted to the inner ear, through the body tissues in primitive forms, or via special links in higher forms. In terrestrial vertebrates, the eardrum evolves; it is always linked by special ossicles to the inner ear. In frogs, both forms of the middle ear are found in the tadpole and adult stages, respectively; in metamorphosis, the aquatic middle ear(lung) is replaced by the terrestrial form (drum membrane).
36(1964); http://dx.doi.org/10.1121/1.2143150View Description Hide Description
Fishes apparently employ the lateral‐line organ as an underwater nearfield acoustic detector and their swimbladder‐ear system as a farfield detector. It can be shown, however, that the latter system is not directionally sensitive. Since the terrestrial ear evolves from this latter system, directional sensitivity is somehow acquired in the course of evolution. In the underwater near field, time‐of‐arrival differences are negligible for average‐size fish, but the intensity gradient is very steep. The directional sensitivity of the lateral line is, therefore, probably based exclusively on intensity clues. For “zero‐difference” azimuth localization, only two neurons (such as the Mauthner neurons) are sufficient. In the terrestrial animal, arrival‐time difference between the two ears is significant, while intensity differences may be relatively minor. In view of the time constants of the nervous system, a single cell pair cannot accurately resolve small time differences, and a multiple‐cell system, such as the superior olive, is necessary. It is interesting to speculate on the fact that fishes do not have a superior olive but a pair of Mauthner neurons, and that frog tadpoles have Mauthner neurons, which are replaced by a superior olive at metamorphosis.
- Session B. Physical Acoustics I
36(1964); http://dx.doi.org/10.1121/1.2143151View Description Hide Description
Cavitation thresholds in water have been measured as a function of frequency, dissolved gas, ambient pressure, and suspended‐particle size. The apparatus used comprises a 2‐1 volume of water enclosed by a spherical glass shell driven at its radially symmetric resonance frequencies by 8 multiresonant piezoelectric transducers. Large acoustic pressures can be produced, ranging from 10 bar at 27 kc/sec to 200 bar at 1.16 Mc/sec. The threshold data can be divided into three regions: In region A—defined by f<200 kc/sec, acoustic pressurePa <3 bar, and air saturation presure Ps >600 mm Hg—small air bubbles grow by rectified diffusion and stabilize at the pressure nodes. In region B—defined by f<200 kc/sec, Pa >3 bar, and Ps <500 mm Hg—transient cavities are formed that can be detected visually and aurally. In region C—where f>200 kc/sec, Pa >5 bar, for any value of Ps —transient cavities are formed, but their presence can be detected acoustically only. The threshold tends to a slope of 12 dB/octave for frequencies above 1 Mc/sec. Experiments on cavitation at pressures larger than the threshold indicate that only a finite number of cavitation events can be produced in a given sample of water when it is isolated from contamination by airborne motes. In this way, water can be “strengthened” by a factor of at least 8 by repeated cavitation.
36(1964); http://dx.doi.org/10.1121/1.2143152View Description Hide Description
Experiments were made with bubbles, under various different conditions, using a microscope and a high‐speed (Fastax) camera for applied sound frequencies in the range 100–5000 cps and also at 20 kc/sec. In commencing an experiment, a single air bubble of measured volume was placed just under the lower face of a solid bar dipping into a liquid. A number of interesting events were observed as the bar was set into vibration and its amplitude increased up to the threshold for collapse cavitation. These include surface‐wave phenomena and microbubble throwoff, as noted by Willard, as well as fragmentation, coalescence, migration, and other time‐dependent effects. The motion of a bubble depends on the proximity of its size to resonance. Measurements of the resonant frequency for bubbles in the lower frequency range gave values higher than those prediceted by Strasberg for a bubble near a rigid boundary but lower than those for the case of an isolated bubble. Under certain conditions, when a macroscopic bubble is present, effects such as erosion, usually associated only with collapse cavitation, were seen to occur at relatively low sound amplitudes. Photographs of damage done to prepolished solid specimens placed near to the bubble were taken with an interference microscope. [Work supported in part by U. S. Air Force Office of Scientific Research grant AF 62–63 and National Institutes of Health, U. S. Department of Health, Education, and Welfare, grant GM‐08209.]
36(1964); http://dx.doi.org/10.1121/1.2143153View Description Hide Description
The superfluidproperties and the restrictions on possible types of nuclei make liquid helium especially interesting for cavitation studies. Previous measurements of the tensile strength of liquid helium, using static techniques, have led to values of 0.1 to 0.3 atm, which are considerably lower than theoretical estimates, as made for instance from the Van der Waals equation. This paper reports the production of ultrasoniccavitation in liquid helium over the temperature range 1.2° to 2.3°K. Visible bubbles were observed only at power levels much greater than threshold. A pair of identical transducers, resonant at 90 kc/sec, were used to generate cavitation, listen to the accompanying noise, and simultaneously measure the threshold of acoustic pressure, using a reciprocity technique. The onset of noise was used as a criterion of the threshold. Determined this way, the threshold is even lower than indicated by the static techniques, being very close to the liquid pressure head, except near the λ point where it rises sharply to values not exceeding 0.01 atm. This λ‐point behavior is similar to that of other properties of the superfluid, such as the specific heat, with which it is possible that some correlation exists. [Work supported by the U. S. Office of Naval Research.]
36(1964); http://dx.doi.org/10.1121/1.2143154View Description Hide Description
As evidence has increased that microbubbles reside in natural waters, a number of investigators have speculated as to the stabilization mechanism. Two independent conditions must be satisfied: (a) the interchange of gas by diffusion between the bubble and the surrounding liquid must be equalized; (b) the positive buoyancy of the bubble must be neutralized. The modelmicrobubble is hypothesized as being stabilized by minute particles picked up on the bubble surface, which compress upon outdiffusion of gas to form a wall capable of supporting the hydrostaticpressure. This permits the internal pressure to drop to that of the gas dissolved in the liquid, thus satisfying condition (a). The particulate mass neutralizes the buoyancy, thus satisfying condition (b). Recent experimental evidence suggests that microbubble stabilization may be critically affected by trace chemicals, such as detergent. Further, the stiffness added by the compressed wall appears to raise the resonant frequency of the bubbles and modify the damping constant, and the wall's elasticity may affect the cavitation threshold. [Work sponsored by the U. S. Office of Naval Research.]
36(1964); http://dx.doi.org/10.1121/1.2143155View Description Hide Description
A spherical cavity in an infinite homogeneous and isotropic elastic medium is enveloped by a plane compressional shock wave whose front propagates with a constant velocity. The displacement and stress fields produced by the diffraction of the wave by the cavity are formally determined by means of an integral transform technique. Expressions for the transforms of the various components of the displacements and stresses are derived. The rigid‐body component motion of the cavity boundary is also extracted. The problem is considered for compressional waves with a step distribution in time. The results may be used as influence coefficients to determine by means of Duhamel integrals the displacement and stress fields produced by stress waves with time‐varying intensity. [Work performed under contract No. AF29(601)‐5132 (Project No. 1080, Task No. 108007) for the U. S. Air Force Special Weapons Center, Kirtland AFB, New Mexico.]
36(1964); http://dx.doi.org/10.1121/1.2143156View Description Hide Description
Experimental investigations of the Rijke‐tube phenomenon have used the same basic apparatus as that used by its discoverer in 1859—an open‐ended vertical pipe containing a heated gauze in its lower half. Difficulties arise when this configuration is used for quantitative tests since the standing‐wave distributions of the tube and its environment interact unless elaborate precautions are taken; consequently, the acoustic output of an experimental assembly of this form varies with its location. To vitiate this acoustic coupling, an inversion of the classical configuration was designed in which a water‐cooled horizontal tube containing an electrically heated grid was terminated at each end by sliding pistons. A metered airstream passed through narrow annular ports in the piston heads, one of which housed a calibrated microphone. Thus, an assembly was obtained in which all the parameters connected with this thermoacoustic phenomenon could be continuously varied with no interruption of the test procedure. Maximum and minimum limiting airflows and thermal inputs for the resonant condition were established for all heater locations. Measurements were made of the oscillation amplitude and the data are shown to be consistent with existing theories, within the scope of necessary assumptions relating to the heat‐transfer mechanism at the grid.
36(1964); http://dx.doi.org/10.1121/1.2143157View Description Hide Description
Theoretical expressions due to Twersky [New York Univ. Rept. EM‐59 (1953)] for waves multiply scattered by an array of cylinders have been recast in a form suitable for numerical calculation and, hence, comparison with experiment. This theory affords sufficient explanation of the magnitude of the attenuation observed in forests, 7 dB/100 ft [T. F. W. Embleton, J. Acoust. Soc. Am. 35, 1119 (1963)], provided that the scattering cylinders are assumed to have surfaces of finite impedance. The resistive component of the bark on trunks and branches at 500 cps needs to be about 10 ρc to obtain agreement; values close to this have been obtained from impedance‐tube measurements. The S‐shaped curve of attenuation vs frequency, observed in certain parts of the forests, may be related to the “resonance” of the cylindrical surfaces as their reactive impedance changes sign.
36(1964); http://dx.doi.org/10.1121/1.2143158View Description Hide Description
A previous paper described amplitude measurements, made with a probe microphone, of the acoustic field of a plane wavescattered by obstacles of finite dimensions. A new 8‐channel recording system has now been set up, which includes among its data not only the amplitude of the output of a moving probe microphone, but also the output of a phase metermeasuring the phase angle between the output of the probe microphone and that of a reference microphone. The phase meter covers the full 360° and provides means of marking on the trace whether the phase angle is lead or lag. First tests were run at the surface of a single cylinder and a single sphere to check the accuracy of the equipment. The results for the area surrounding a single infinite cylinder were compared with scattering of electromagnetic waves by King and Wu. The multiple scattering of two parallel cylinders was investigated and the results were compared with predictions of theory for forward, backward, and 90° scattering for various kb (where b is the spacing between cylinder axes). Predictions were made for two spheres and verified, and the same techniques were applied to multiple arrays. [Research supported by the U. S. Office of Naval Research.]
- Session C. Architectural Acoustics I
36(1964); http://dx.doi.org/10.1121/1.2143159View Description Hide Description
New information is added relative to the author's multiaxial reverberation formula, originally presented as an invited paper at the 56th Meeting of the ASA in 1958 and later published [D. Fitzroy, J. Acoust. Soc. Am. 31, 893 (1959)]. It includes experiences with off‐parallel boundaries and the allocations of sound absorption contributed by an audience where such absorption is effective along different axes. This paper also includes further results of field experience.
36(1964); http://dx.doi.org/10.1121/1.2143160View Description Hide Description
Progressive measurements of the reverberation times were obtained during the construction of three similar lecture rooms. Two of these rooms have identical shape. Each has 106 seats. The third differs only in its width and has 158 seats. The three rooms have essentially flat reverberation characteristics of slightly less than 1 sec. The reverberation characteristics were measured just after the rooms had been plastered, when the acoustical treatment had been placed on the walls, and then progressively as the seats were added. The rows of seats were installed in the following sequence: 1st, 3rd, 5th, 2nd, 4th, 6th, and 7th. From these observations, the absorption per seat and per unit area are calculated for the different configurations. These values are compared with values measured on identical seats in a reverberation room.
36(1964); http://dx.doi.org/10.1121/1.2143161View Description Hide Description
An investigation of the diffraction of sound by rectangular panels, similar to those that have been used for acoustical purposes in concert halls and other auditoriums, confirms certain expectations based on well‐known properties of both optical and acoustical diffraction: namely that, for wavelengths that are (1) large as compared to the dimensions of the panels and the spacing between them, the incident sound on the panels is essentially all transmitted; (2) small, the panels reflect nearly all the sound incident upon them; and (3) of the same order of magnitude as the dimensions of the panels and spacings, there are complex diffractioneffects that are manifest both in the transient and steady‐state properties of the surrounding sound field. For example, a horizontal array of sixteen 2×4‐ft panels with spacings of 14×18 in. in a room 15.6×25×13 ft introduced a prominent nonlinear decay in the reverberant sound for frequencies between about 500 and 2000 cps. Thus, whereas the rate of decay at 1000 cps was about 136 dB/sec with or without the panels in the room for the initial 25 dB of decay, for the subsequent decay the effect of the panels was to prolong the sound—with the panels in, the average rate of decay for the next 20 dB was reduced to 52 dB/sec, whereas with the panels out it was 62 dB/sec.