Volume 29, Issue 11, November 1957
Index of content:
29(1957); http://dx.doi.org/10.1121/1.1908727View Description Hide Description
Observations on models of the tectorial membrane in the basilar papilla of the frog are described. The model membranes constitute a series of increasing complexity, and are studied with sinusoidal stimulation and stroboscopic illumination. It is found that traveling waves occur on these models, and that frequency‐dependent maxima are formed. By arrangements of fibers and small masses on the membranes the direction of wave travel and location of maxima can be altered. Measurements of the elastic gradients on the membranes show that waves tend to follow a path defined by the smallest change in elastic properties per unit distance. It is concluded that the frog's basilar papilla is capable of performing frequency analysis according to the place principle.
29(1957); http://dx.doi.org/10.1121/1.1908729View Description Hide Description
Twenty subjects, working individually, monitored a simple vigilance task, a modified “Mackworth Clock Test,” for in noise (112.5 db SPL) and for in quiet (79 db SPL). No difference in efficiency attributable to noise level was found. This result is in conflict with previous reports from this and other laboratories which ascribed decrement in performance on vigilance tasks to noise levels. Vigilance tasks in which performance decrements due to noise were found, differed from the present task in that they required subjects to scan a series of displays in addition to maintaining vigil over each display. It is, therefore, suggested that flexibility of attention may be affected by noise, whereas vigilance without the requirement for flexibility may be unaffected.
29(1957); http://dx.doi.org/10.1121/1.1908731View Description Hide Description
Recording, by means of a sonagraph, the sound pressuregenerated by a turning loudspeaker, fed by white noise, one can give a synthetic representation of the directional behavior of the loudspeaker. One can study the behavior of reflecting surfaces and the directivity of a microphone by the same method.
Comparison of the Take‐Off Noise Characteristics of the Caravelle Jet Airliner and of Conventional Propeller‐Driven Airliners29(1957); http://dx.doi.org/10.1121/1.1908733View Description Hide Description
Based upon earlier published information concerning the factors that influence neighborhood response to noise exposure, it is assumed that there are three principal characteristics of noise which must be considered in comparing community response to jet take‐offs with that due to propeller aircraft take‐offs. These three noise factors are: (1) relative noise levels; (2) duration of noise; and (3) frequency distribution of noise. This paper is devoted to a comparison of the noise produced by the French jet aircraft, the Caravelle, with that produced by conventional propeller‐driven airliners in terms of these three factors. Noise level measurements were made under the take‐off path at various distances from the beginning of the take‐off run‐way. The conclusion is drawn that the comparative noise levels of the Caravelle, when considered in terms of probable response of listeners to the spectrum distribution of the noise, are approximately equal to those of large propeller aircraft for similar climb rates when heard out‐of‐doors. Second, the Caravelle noise levels, based on relative listener response, are somewhat lower than those of propeller aircraft when heard in‐doors or when the Caravelle is permitted to take off under steep climb conditions. Third, the Caravelle noise persists for longer time intervals than does propeller aircraft noise by a factor of between 1.5 and 3.5, depending upon the distance from the runway.
29(1957); http://dx.doi.org/10.1121/1.1908735View Description Hide Description
In “Kneser” liquids the mechanism of excess ultrasonic absorption is the slow exchange of energy between internal and external degrees of freedom, just as in gases. Eight such liquids are selected; in two the relaxation time in the liquid is known from measurements, in the others it is calculated from low‐frequency absorption. In comparing the relaxation time for the liquids with that in the vapors of the same substances, the latter is found to be 100 to 600 times that in the liquid. This is related to the ratio of the collision times.
29(1957); http://dx.doi.org/10.1121/1.1908737View Description Hide Description
When the continuous ultrasonic wave is sent forth towards the heart from the surface of the chest wall, the cardiac motion causes the Doppler effect upon the partial wave reflected from it. Therefore, an apparatus suitably constructed for sending and receiving ultrasounds is quite useful for the investigation of the movements of theatrium, ventricle, or valves, etc., through the analysis of the particular Doppler signals developed from the motion of the respective part.
The author developed a method for the inspection of cardiac functions by recording these Doppler signals simultaneously with the electro‐ and phonocardiographs the oscillograph paper. This method made it possible not only to obtain direct informations for the valvular movement which could not have been ascertained up to present, but also to examine the transitional aspects of the myocardial excitation which is utterly uudetectable by the electrocardiograph alone.
Ultrasonic Pulse Technique for Measuring Acoustic Losses and Velocities of Propagation in Liquids as a Function of Temperature and Hydrostatic Pressure29(1957); http://dx.doi.org/10.1121/1.1908739View Description Hide Description
A fixed path ultrasonic unit operating in the frequency range of 20–200 mcps is described which can be used for measuringacoustic wave velocities and losses in liquids as a function of temperature and hydrostaticpressure. A simple phase balance technique insures a high order of accuracy for velocity determinations,
Illustrative data for carbon tetrachloride, Dow Corning DC‐703 and DC‐200 silicone fluids, and water are shown. Determination of freezing points of liquids using ultrasonic waves for indication is also discussed briefly.
29(1957); http://dx.doi.org/10.1121/1.1908741View Description Hide Description
A simple solution is developed for the reflected waves on a rough surface from a simple harmonic point source. It is assumed that the roughness is represented by a distribution of hemispherical bosses whose size and mutual distance are small relative to the wavelength. It is shown that under these conditions the effect of the roughness is equivalent to a boundary condition for the wave equation. This boundary condition embodies the surface polarization and the mutual interaction of the bosses. If the generating source lies above the reflecting surface the reflected wave is found to be equivalent to that originating from concentrated and distributed image sources on a line situated below the specular image with a magnitude decreasing exponentially with depth. The case of vanishingly small roughness is discussed along with the field intensity at large distance and grazing incidence. The effect of fluid viscosity is also evaluated.
29(1957); http://dx.doi.org/10.1121/1.1908743View Description Hide Description
The analysis is carried out in terms of particle velocities expressed as Mach numbers. In general, the pertinent quantities are expressed in relation to the infinitesimal values by a power series of these Mach numbers ha which two powers are retained. To this order of approximation, the particle velocity is the vector sum of the particle velocities of the isolated component waves and the speed of propagation in each direction has an increment proportional to the vector difference of these particle velocities. The general behavior of the sound field may be predicted from these two relations.
29(1957); http://dx.doi.org/10.1121/1.1908745View Description Hide Description
29(1957); http://dx.doi.org/10.1121/1.1908747View Description Hide Description
There is described, in this paper, a detailed study of Ekstein's solution of the equations of elasticity for the case of the coupled vibrational modes of an infinite, monoclinic, crystal plate with traction‐free faces. It is shown how the spectrum of frequencies and the character of the modes may be deduced by tracing the development of coupling from a simple solution in which the modes are uncoupled and by taking into account the asymptotic behavior at long and short wavelengths and high and low frequencies. The results of computations are given for the AT cut of quartz. The purpose of the investigation is to obtain some of the qualitative and quantitative information which is needed for the formulation of approximate equations of motion which may be solved for plates of finite dimensions.
29(1957); http://dx.doi.org/10.1121/1.1908749View Description Hide Description
A representation of the field of a sound source of arbitrary shape and size as a series of multipole fields of increasing order is derived. This series is convergent for sources of any size if the surface is sufficiently regular, but its main advantage is for sources small compared to the wavelength. In this case the source has, in general, the directivity pattern of a multipole, the order and strength of which can be determined from the formula.
Although the representation is not unique, certain coefficients have physical significance. The presently used definition of “strength of a sound source” is discussed and a modified definition suggested.
29(1957); http://dx.doi.org/10.1121/1.1908751View Description Hide Description
The rigorous determination of the field of a spatially extended sound source moving with subsonic speed in a viscous compressible gas is formulated as an initial‐boundary value problem of a system of linear partial differential equations. This system reduces to a single equation of the second order with variable coefficients if the medium is a perfect gas and the motion of the gas around the source a potential flow. For steady motions and harmonic sources the equation becomes elliptic if time is eliminated.
Generalizations of Green's identity and Helmholtz's formula for this partial differential equation allow the representation of the sound field as a series of generalized multipoles. The field of a sufficiently small source of arbitrary shape with boundary conditions appropriate for the acoustic case and its relation to the concept of a moving simple source, dipole, etc., is investigated.
29(1957); http://dx.doi.org/10.1121/1.1908753View Description Hide Description
An exact solution is obtained for the motion of the surface of a uniform elastic half‐space due to the application at a depth H below the surface of a concentrated vertical force. The time‐variation of the applied force is assumed to be represented by the Heaviside unit function. The solution for the horizontal and vertical components of displacement cast in the form of single integrals over a fixed range, and these have been evaluated on the electronic computer of the Weizmann Institute (WEIZAC). The assumed source emits both S waves and P waves. Beyond a distance r 1 from the epicenter, which is equal to H/√ in the case λ = μ, the original S wave is converted on reaching the surface into a diffracted SP wave traveling along the surface. At large ranges, the SP phase is more pronounced than the P phase. The S phase is marked by a finite jump for r<r 1, and by a logarithmic infinity for r>r 1. The coefficient of the logarithmic term is zero both at r=r 1 and at large ranges, having a sharp maximum at r=1.004r 1. There is no Rayleigh wave at r<r 1. At large ranges (r/H≫1) the solution, as a function of the reduced time τ = ct/R, approaches the form of the solution for the surface pulse.
29(1957); http://dx.doi.org/10.1121/1.1908755View Description Hide Description
- PROGRAM OF THE FIFTY‐FOURTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session B. Hearing I
- Contributed Papers
29(1957); http://dx.doi.org/10.1121/1.1918983View Description Hide Description
It would be reasonable to expect that temporary threshold shift (TTS) following exposure to higher sound levels would be an increasing function of the exposure level. However, numerous investigators have observed that when duration of exposure is held constant, a greater TTS may occur after exposure to a less intense level than after a more intense level. This is frequently observed when the TTS is measured soon after exposure, but less frequently observed when the TTS is measured 3 min or longer after exposure. Thus, Miller found that 3 min of white noise at 115 db produced more TTS than at 120 db (measured 6 min later at 4000 cps). In the present study TTS was measured by the Békésy method at 4000 and 6000 cy for 10 min following exposure to 3 min durations of thermal noise. Five different noise levels were used. They ranged, in 5 db steps, from 108 to 128 db. Each of 9 ears was run twice on each noise condition. Only 1 ear showed a definite pattern of decreasing TTS with increasing intensity.
29(1957); http://dx.doi.org/10.1121/1.1918985View Description Hide Description
Theoretical considerations regarding the interaction between the two ears suggest the possibility that the amount of auditory fatigue (threshold elevation) in one ear following exposure to sound will depend, in part, upon whether the exposure was directed at that ear only or at both ears. Exposures to noise and to tone were directed at either ear and at both ears of five observers, and continuous threshold recording of the absolute threshold for one ear was made following each exposure. The results indicate no significant difference in the fatiguing effect in one ear between exposures on that ear and exposures to both ears. (This research was supported in whole or in part by the U. S. Air Force under Contract No. AF33(616)‐3505, monitored by Aero Medical Laboratory.)
29(1957); http://dx.doi.org/10.1121/1.1918987View Description Hide Description
In physiological experiments on the cat's auditory system clicks have often been used because of their ability to produce synchronized neural firings. In this study the class of impulsive stimuli has been extended. The electrical signals fed to the earphone are close approximations to members of the family of singularity functions. In the present experiments doublets, impulses, step, and ramp functions have been used. Each of these functions is the time integral of the previous one, with a conversion factor involving the time dimension. The actual wave form of the acoustic stimulus at the animal's eardrum could not be observed. The above‐mentioned integral relation, however, holds for what may be thought of as the linear part of the system. As a typical result, it has been found that the peripheral neural response, N 1, to the step is equal to that of the pulse provided the pulse has the same height as the step, and a length of 20 μsec. This holds over a fairly large range of amplitudes (20–40 db). Similar results have been found for the other signals. Preliminary results will also be reported with respect to both microphonic and cortical responses to the above‐mentioned stimuli. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
29(1957); http://dx.doi.org/10.1121/1.1918989View Description Hide Description
In a previous report (November, 1956, 52nd meeting of the Acoustical Society) we concluded that cortical off‐responses observed in cats under barbiturate anesthesia are in fact responses to acoustic transients that appear in the signal as it is turned off. We have since found in unanesthetized cats with high spinal sections off‐responses that seem to occur in the absence of such acoustic transients. This conclusion is based on the following considerations; first, these off‐responses are observed when bursts of noise are turned off and are abolished by injections of barbiturates: secondly, the latencies of these off‐responses are 6–8 msec longer than the latencies of the previously reported off‐responses to acoustic transients: and thirdly, these off‐responses occur also under stimulus conditions which produce no off‐responses in the anesthetized animal (burst durations shorter than 60 msec and fall times longer than 10 msec). These findings suggest that these off‐responses in unanesthetized animals may involve neurons other than those which give rise to on‐responses; the possibility that inhibitory neuronal links at levels below the auditory cortex are involved will be discussed. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
29(1957); http://dx.doi.org/10.1121/1.1918991View Description Hide Description
The envelope over the train of waves traveling along the cochlear partition is asymmetrical: the distal slope being steeper than the proximal one [G. von Békésy, J. Acoust. Soc. Am. 19, 452 (1947)]. In experiments on models, this asymmetry was seen to increase with intensity. Since the mean revolving velocity of Békésy's “eddies” also varies with intensity, artificial “eddies” were introduced into the model while the intensity remained constant. Thereby the asymmetry of the envelope was also increased. Propulsion of the “perilymphatic” fluids by the “eddies” converts particle motion (ordinarily in closed orbits) [Juergen Tonndorf, J. Acoust. Soc. Am. 5, 558 (1957)] into cycloids. As the eddiesaccelerate along the partition (see the paper by Tonndorf), the cycloids expand with distance, its velocity attaining a sawtooth‐like pattern. The asymmetry of the envelope can be explained satisfactorily by the combined effect upon the partition of the distorted cycloids in both “perilymphatic scalae.” However, the same theoretical considerations lead to asymmetry of the displacement pattern of the partition and to an effect similar to peak clipping, both of which increase with distance. This distorted displacement pattern in the distal region of the partition in turn affects particle motion in the adjacent fluids, whence the distortion is propagated proximally by the eddies to be resolved in the usual way (see the paper by Tonndorf) along the cochlear partition. [This research was supported in whole or in part by the U. S. Air Force, under Contract No. AF‐41 (657)148, monitored by the School of Aviation Medicine, UASF, Randolph Air Force Base, Texas.]