Volume 59, Issue 3, March 1976
Index of content:
59(1976); http://dx.doi.org/10.1121/1.380907View Description Hide Description
Experiments are reported which pertain to the phenomenon of enhanced sonic booms or superbooms generated as a result of atmospheric refraction in threshold‐Mach‐number flights. Such ’’refraction superbooms’’ are created in a ballistic range by firing projectiles at low supersonic speeds into stratified medium of varying sound speed consisting of an inhomogeneous mixture of CO2 and air. The pressure signature recorded by a fast‐response transducer inserted in the flow field is studied in conjunction with sets of dual‐schlieren pictures obtained simultaneously during each run. The flow field observations indicate that the generated shocks are reflected near the sonic cutoff elevation, where the local sound speed equals the projectile speed, provided that such an elevation exists. The incident shock and its reflected portion join to form a Y‐shaped configuration near the cutoff region. Enhanced shock overpressures are detected near the ’’critical altitude’’ where the flow speed behind the shock becomes sonic. A maximum focus factor of 1.7 has been measured for the leading shock which, with some theoretical assumptions, leads to an estimated value of 1.3 for the constant which appears in the Guiraud–Thery scaling law. The same value is also deduced from field data taken during aircraft threshold Mach‐number flight by Haglund and Kane. The substantial agreement between the two experimentally derived values of the constant and the theoretical estimate of 1.4 given by Thery, Lecomte, and Reggiani seems to suggest the validity of the above‐mentioned scaling law. However, the discrepancy of these numbers with the value of 2.6 derived by Gill and Seebass indicates that further investigation is still needed.
Subject Classification: 25.20, 25.30; 28.55; 50.55.
59(1976); http://dx.doi.org/10.1121/1.380908View Description Hide Description
Ballistic range experiments for the study of the propagation of converging shocks are described and the similarity between the observed phenomenon and that expected for superbooms created by accelerating supersonic aircraft is discussed. For weak shocks (shock Mach numbers of about 1.03), a structure resembling that of a folded shock predicted by geometrical acoustics theory is observed while for stronger shocks, a concave front with enhanced overpressure is recorded. Other results are in general accord with the basic concepts of shock propagation and in conjunction with some theoretical scaling laws indicate that the peak magnification of sonic booms due to aircraft flight acceleration in the real atmosphere should be in the range of 6 to 13.
Subject Classification: 25.20, 25.30; 28.55; 50.55.
59(1976); http://dx.doi.org/10.1121/1.380909View Description Hide Description
In a previous paper, the author examined the bearing response pattern of a line array to a plane wave in a random medium. It was found that random effects are strongest when the source is broadside to the array. In this paper, the corresponding situation for a cylindrical wave is examined. A comparison is made with the plane‐wave case.
Subject Classification: 30.20, 30.40; 45.10; 20.15; 30.82.
59(1976); http://dx.doi.org/10.1121/1.380910View Description Hide Description
Recently published data on the attenuation of compressional (sound) waves in marine sediments and sedimentary rocks as a function of frequency and sediment porosity have been added to previously published figures. The revised figure illustrating attenuation as a function of frequency (5 Hz–1 MHz), and attendant discussion, continue to support the conclusion that attenuation is approximately related to the first power of frequency in sands, muds, and sedimentary rocks. The revised figure illustrating sediment porosity versus attenuation affirms that sediment porosity is an important index property which can be used to predict sound attenuation in surficial sediments. Data were collected and illustrated on sound attenuation as a function of depth in the sea floor. It is concluded that attenuation decreases with about the −1/6 power of depth in sands. As a silt–clay sediment (mud), or turbidite, is placed under increasing overburden pressure, there may be a progressive increase in attenuation due to reduction in sediment porosity, and a progressive decrease in attenuation due to increasing pressure on the sediment mineral frame. At about 200‐m depth a null point may be reached. Thereafter, pressure is the dominant effect, and attenuation decreases smoothly with depth and overburden pressure. The figure can be used to aid prediction of sound attenuation in sediment and rock layers in the sea floor.
Subject Classification: 30.20.
59(1976); http://dx.doi.org/10.1121/1.380911View Description Hide Description
A major purpose of this paper is to investigate the influence of mean sound‐speed structures on sound transmission in the presence of a single‐frequency internal wave. A cw signal is transmitted through a shallow ocean over a range that is small compared to the wavelength of the internal wave. A constant value of the Brunt–Vaisala frequency is assumed, and this value is taken as a parameter of the model. The total field associated with refracted/bottom‐reflected rays is studied, and the effect of the internal wave on total‐field phase and transmission loss is examined. Then, the maximum variation of the phase is investigated for different mean sound‐speed structures and internal‐wave amplitudes. This variation shows a general downward trend, as bottom sound speed increases, and an oscillatory behavior possibly due to rapid changes in the rate of change of phase with respect to mid‐depth sound speed. A simple mathematical model is constructed to explain the dominant decreasing trend. Phase variation is shown to vary linearly with bottom sound speed and to be proportional to wave amplitude, range, and acoustic frequency. It is inversely proportional to ocean depth.
Subject Classification: 30.20, 30.25.
59(1976); http://dx.doi.org/10.1121/1.380912View Description Hide Description
Calculations are made of the pulse shapes for sound waves reflected from a plane transducer. These show the effect of reflections from the two parallel surfaces and their relation to pulse width and transducer thickness. Illustrations are given for several representative combinations of samples and backing media, together with photographs of pulse shapes obtained experimentally.
Subject Classification: 35.80; 85.40; 20.30.
59(1976); http://dx.doi.org/10.1121/1.380898View Description Hide Description
The isothermal response of a bounded, three‐dimensional viscoelastic body, subject to arbitrary body forces, initial conditions, and boundary conditions, is considered within the linear theory of viscoelasticity. The viscoelastic properties of the body are assumed to be isotropic and homogeneous. The boundary surface areas over which the boundary conditions are specified are assumed to remain constant with time. The response is first found formally in terms of a causal Green’s function. It is then shown that when Poisson’s ratio is constant, the causal Green’s function can be expanded in a series of spatial eigenfunctions of an associated elasticeigenvalue problem. The resulting solution for the general problem is an eigenfunction series with Laplace transformed time‐dependent coefficients. The solution is inverted for two special cases, when the body forces and boundary conditions are separable in space and time, and when the relaxation function in simple shear has the form of a series of decaying exponentials.
Subject Classification: 40.20; 35.50.
59(1976); http://dx.doi.org/10.1121/1.380899View Description Hide Description
Longitudinal pulse propagation in slightly curved elastic rods is discussed in terms of an elementary theory due to Hsieh and Lee for which rotary inertia and radial shear are neglected. Moreover, the wavelength of motion is sufficiently long for practically all bending effects to be neglected. Three different approaches are presented. In the first, reduction of the Fourier transform of the governing equation to Bessel’s equation is sought. In the second, generalized Baecklund‐type transformations are utilized to reduce the characterizing equation to the conventional wave equation for certain radius of curvature variations. Finally, the formal Karal–Keller technique is used to solve certain impact problems. Numerical results are presented in graphical form.
Subject Classification: 40.22; 20.15, 20.20, 20.45.
59(1976); http://dx.doi.org/10.1121/1.380900View Description Hide Description
In a study of ways to reduce the sound power produced by propeller fans, the performance of various porous blades was compared with that of solid blades. It was found that a porous‐bladed fan could produce flow with characteristics similar to that produced with a solid‐bladed fan, with a reduction of about 5 dB in the sound at the cost of a slight reduction in static efficiency.
Subject Classification: 50.30, 50.40, 50.45.
59(1976); http://dx.doi.org/10.1121/1.380901View Description Hide Description
The diffuse sound field as used in standard measurements in reverberant enclosures has been analyzed in terms of two different models, the eigenmode and the free‐wave models. Recently the question has been raised as to the extent to which these models are consistent. To investigate these matters, the energy density as a function of position is calculated for axial, tangential, and oblique modes in a rectangular enclosure. The results show that, for a sound field consisting of several overlapping oblique modes, excited by a narrow band of noise, increases of mean sound pressure levels at the walls, edges, and corners of the enclosure are predicted that are in agreement with the results of the free‐wave analysis and experiment. It is concluded that the two models are consistent. The inplications of the models, regarding the spatial uniformity of energy, are discussed.
Subject Classification: 55.20; 20.30.
Covariance between Fourier coefficients representing the time waveforms observed from an array of sensors59(1976); http://dx.doi.org/10.1121/1.380902View Description Hide Description
Typically, the assumption of a long observation interval is made to achieve uncorrelatedness between Fourier coefficients at different frequency indicies. An explicit relationship between observation interval length and covariance between the Fourier coefficients is obtained to provide insight as to how long the observation interval should be to approximate this desirable condition.
Subject Classification: 60.20.
59(1976); http://dx.doi.org/10.1121/1.380903View Description Hide Description
With a tone‐on‐tone masking procedure the compound action potential (AP), elicited by brief tone bursts of set frequency and intensity, was decreased by a constant fraction. The frequency–intensity pairs formed by the masker that yield this decrease generate the AP tuning curve. It is demonstrated that such tuning curves are very similar to both psychophysical tuning curves and single VIIIth‐nerve‐fiber tuning curves. Changes in the properties of these curves are described as functions of stimulus frequency and level, mode of masking (simultaneous and forward), and parameters of the masker.
Subject Classification: 65.40, 65.42, 65.58.
59(1976); http://dx.doi.org/10.1121/1.380904View Description Hide Description
It is shown that any binaural detection model in either of two broad classes will, subject to certain approximations, correctly predict relative detection performance for tones masked by noise as a function of interaural tone parameters. A corollary of this result is that any model in either class gains little support by fitting this body of detection data. More meaningful support for any of these models is most likely to come from the adequacy of its predictions for performance as a function of other parameters, such as target frequency, interaural masker parameters, and masker spectrum. It appears that all binaural detection models in the literature are closely related to one of the two classes defined in this paper.
Subject Classification: 65.62, 65.58, 65.35.
59(1976); http://dx.doi.org/10.1121/1.380905View Description Hide Description
A series of sonar discrimination experiments has been performed using instrumented human divers wearing a helmet with a sending and two receiving transducers. Porpoiselike broad‐band clicks, with energy centered about 60 kHz, were projected and the returning echoes stretched electronically in time by a factor of 128 to enable the divers to hear them. Data were collected using metallic plate targets and targets of different geometrical shapes that were previously used in experiments with a porpoise. A comparison of scores indicated that the instrumented divers performed as well as, and in some cases better than, the porpoise.
Subject Classification: 65.62; 30.82.
Some preliminary observations on the interrelations between two‐tone suppression and combination‐tone driving in the anteroventral cochlear nucleus of the cat59(1976); http://dx.doi.org/10.1121/1.380906View Description Hide Description
For units of the anteroventral cochlear nucleus in the cat—as for primary units—response to a best‐frequency tone f 1 can be markedly reduced when a h i g h e r‐frequency suppressing tone f 2 of equal or greater intensity is presented simultaneously at a frequency separation corresponding, in the present experiments, to an optimal distance on the basilar membrane of about 0.5–0.8 mm. More data are needed, but this distance does not seem to vary systematically with best frequency and may be related to critical bandwidth. In further preliminary experiments, we have compared unit response to the combination tone, 2f 2−f 3, formed when f 1 is omitted and f 3 is added above f 2, with the unit’s response to a three‐tone stimulus. The three‐primary stimulus consists of tones with equispaced frequencies and controllable phase and amplitude relations. Primary tone f 1 and combination tone 2f 2−f 3 coincide at best frequency, while f 2 and f 3 lie above the tuning curve. The comparison of response to 2f 2−f 3 ’’alone’’ and of response to the r e s u l t a n t of f 1 and 2f 2−f 3, while f 1 phase is varied, allow relative amplitudes to be calculated. They are such that f 1 appears suppressed in amplitude by f 2 and f 3, while 2f 2−f 3 is correspondingly less than cancellation‐tone estimates. For constant f 2 level, 2f 2−f 3 amplitude reaches maximum when f 3 amplitude almost equals f 2 and decreases markedly as f 3 amplitude exceeds f 2. Lastly, when the combination tone resultant composed of 2f 1−f 2 and 3f 2−2f 3 lies at best frequency, variation in the phase of f 1 produces a marked variation in rate of response to the resultant, appearing to parallel psychophysical results obtained by J. L. Goldstein [’’Aural combination tones,’’ in F r e q u e n c y A n a l y s i s a n d P e r i o d i c i t y D e t e c t i o n i n H e a r i n g, edited by R. Plomp and G. F. Smoorenburg (Sijthoff, Leiden, Netherlands, 1969/1970)].
Subject Classification: 65.56, 65.42, 65.75.
59(1976); http://dx.doi.org/10.1121/1.380913View Description Hide Description
Sensitivity to interaural time differences at high frequencies is demonstrated in a number of experiments. Two types of waveforms are used—bands of noise and two‐tone complexes. Variables studied are rate and depth of fluctuation of the envelope, overall intensity, and additivity of interaural time information across frequency regions. In many conditions of listening, sensitivity to interaural time differences at high frequencies compares favorably with sensitivity at low frequencies—good performace requires only tens of microseconds of interaural time delay.
Subject Classification: 65.62, 65.68.
59(1976); http://dx.doi.org/10.1121/1.380914View Description Hide Description
A wide‐band noise having a deep notch with sharp edges was used to mask a tone. The notch was centered on the tone, and threshold was measured as the width of the notch was increased from 0.0 to 0.8 times the tone frequency (0.5, 1.0, or 2.0 kHz). The spectrum level of the noise was 40 dB SPL. If it is assumed that the auditory filter is reasonably symmetric at these intensities, then the shape of the filter centered on the tone can be estimated from the first derivative of the curve relating tone threshold to the width of the notch in the noise. The 3‐dB bandwidths of the filters obtained were about 0.13 of their center frequency. In the region of the passband, the Gaussian curve provides a good approximation to the shape of the derived filters. The equivalent rectangular bandwidths of the Gaussian approximations are about 0.20 of their center frequency, which is comparable to the critical‐band estimates of R. Zwicker, G. Flottorp, and S. S. Stevens [’’Critical bandwidth in loudness summation,’’ J. Acoust. Soc. Am. 29, 548–557 (1957)]. The Gaussian approximation cannot be used outside the passband, because the tails of the derived filters do not fall as fast as the Gaussian curve.
Subject Classification: 65.58, 65.35; 80.50.
59(1976); http://dx.doi.org/10.1121/1.380915View Description Hide Description
Ability to detect tones in noise was measured without defined observation intervals. Latency density functions were estimated for the first response following a signal and, separately, for the first response following randomly distributed instances of background noise. Detection performance was measured by the maximum separation between the cumulative latency density functions for signal‐plus‐noise and for noise alone. Values of d′, estimated by this procedure, were approximately those obtained with a 2‐dB weaker signal and defined observation intervals. Simulation of defined‐ and nondefined‐interval tasks with an energy detector showed that this device performs very similarly to the human listener in both cases.
Subject Classification: 65.58, 65.75, 65.50, 65.68.
59(1976); http://dx.doi.org/10.1121/1.380916View Description Hide Description
Laryngeal control in speech was studied by observing vertical laryngeal movements using the ’’thyrometer,’’ an optoelectric device. The thyrometer consists of a light source casting a narrow beam of light onto a small mirror stuck to the skin of the neck over the laryngeal cartilages and a special photocell which picks up the reflected light beam. Vertical movements of the laryngeal cartilages tilt the mirror and thus change the angle of reflection of the light beam onto the photocell which converts the change in the angle of the light into a voltage monotonically related to the original laryngeal movements. This method yields a highly sensitive recording of the vertical movements of the larynx in running speech without causing any significant impediment to normal articulation. Using this device investigations have been made of the laryngeal mechanisms employed in the production of the following: step‐function changes in pitch, word accents and sentence intonation in Japanese, and the four tones of Mandarin Chinese. The correlation between vertical larynx movement and the activity of the laryngealmuscles for pitch control is discussed based on some electromyographic data and the anatomical structure of the larynx.
Subject Classification: 70.60, 70.20.
59(1976); http://dx.doi.org/10.1121/1.380917View Description Hide Description
The purpose of this investigation was to determine the relative importance of the speaker’s laryngeal fundamental frequency and vocal tractresonancecharacteristics in speaker sex identification tasks. Six sustained isolated vowels (/i, ‐, ‐, a, o, u/) were recorded by 20 speakers, 10 males and 10 females, in a normal and whispered manner. A total of three master tapes (voiced, whispered, and filtered) were constructed from these recordings. The filtered tape involved 255 Hz low‐pass filtering of the voiced tape. The tapes were played to 15 listeners for speaker sex identification judgments and confidence ratings of their evaluations. Results of their judgments indicate that, of the 1800 identifications made for each tape (20 speakers × 6 vowels × 15 listeners), 96% were correct for the voiced tape, 91% were correct for the filtered tape, and 75% were correct for the whispered tape. Moreover, the listeners were most confident in their judgments on the voiced tape, followed by the filtered tape, and showed the least amount of confidence on the whispered tape. These findings indicate that the laryngeal fundamental frequency appears to be a more important acoustic cue in speaker sex identification tasks than the resonancecharacteristics of the speaker.
Subject Classification: 70.30.