摘要:

The ultrasonic amplitude absorption coefficient has been determined in aqueous solutions of four molecular weights (73 000, 186 000, 370 000, and 2 000 000) of dextran, a linear α (1 → 6) anhydroglucose polysaccharide of biological origin, over the frequency range 3–69 Mc/sec at 22°C. It is found that the concentrationfree absorption spectrum exhibits a remarkable similarity to that of aqueous solutions of beef hemoglobin. The latter finding leads to the conclusion that ultrasonic absorption in tissues is not dominated exclusively by constituent proteins and that the contribution to such absorption by molecular structures lacking tertiary configurations may be considerable.

ISSN:0001-4966    

DOI:10.1121/1.1909733

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The articulation index used in telephone communication, the listening equation for sonar, and the acoustical‐privacy calculation of architectural acoustics are all founded on a computation of an excess of signal level over noise level just sufficient to permit some stated detectability. From this viewpoint, data compiled for “Speech Privacy in Buildings” by Cavanaugh, Farrell, Hirtle, and Watters [J. Acoust. Soc. Am.34, 475–492 (1962)] have been reviewed for possible simplications in their procedure for estimating acoustical privacy. Interrelations are demonstrated among various current methods for rating noise and sound insulation, and a general equation for acoustical privacy is derived. As an example, for the case of “confidential” privacy, 200‐ft2floor area, and raised voice, satisfactory acoustical privacy is to be expected ifD+NA= 85 dB, whereDis the sound isolation between the rooms (the reduction of sound from one room to the next) as rated by a procedure like that for the sound‐transmission class, andNAis the background‐noise level in the receiving room measured with a sound‐level meter on A‐weighting.

ISSN:0001-4966    

DOI:10.1121/1.1909735

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Reaction times were collected for three observers in aYES‐NOsignal detection experiment, for two different signal strengths, and threea prioriprobabilities of a signal occurrence—P(S): 0.2, 0.5, and 0.8. Each server gave 1800 responds under each of the six conditions. A trial ended only when the observer terminated it. Some of the major findings are (1) latencies have Pearson distributions, mainly Beta of the first and second kind; (2) there is an apparent genetic character to the distributions—that is, they resemble each other according to the response (YESorNO) rather than the stimulus (signal or noise alone); (3) atP(S) = 0.2, the mean latency of a false rejection of a signal is least, that of a correct detection greatest, but forP(S) = 0.5, and 0.8, mean latency is least for correct detection, and greatest for correctNO'S, and (4) generally, reaction times are inversely related to thea prioriprobability of their associated stimulus classes.

ISSN:0001-4966    

DOI:10.1121/1.1909737

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An experiment is reported on continuity effects produced in a longer‐duration, less‐intense noise signal alternating with a shorter‐duration, higher‐intensity tonal signal. The perceived continuity in the noise signal is demonstrated to be significantly affected by the following: (1) the frequency of the tonal signal (200, 400, 1000, 2000, and 4000 cps), (2) the duration of the noise signal (70, 250, and 950 msec), and (3) the manner of presentation (monaural versus dichotic). Monaural thresholds were found to be larger than dichotic continuity thresholds. Continuity effects were demonstrated under dichotic presentation. That is, the noise signal was reported as continuous when interrupted for periods of time that would be clearly perceived if no tonal signal were interpolated the interruptions of the noise. A two factor theory is forwarded to explain the dichotic and monaural continuity effects. The monaural effects are discussed in terms of rate of decay of auditory sensation. The dichotic effects are discussed in terms of facilitation of ongoing neural discharge somewhat more central than the first‐order neurons.

ISSN:0001-4966    

DOI:10.1121/1.1909739

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Firstly, theories are reviewed on the explanation of tonal consonance as the singular nature of tone intervals with frequency ratios corresponding with small integer numbers. An evaluation of these explanations in the light of some experimental studies supports the hypothesis, as promoted by von Helmholtz, that the difference between consonant and dissonant intervals is related to beats of adjacent partials. This relation was studied more fully by experiments in which subjects had to judge simple‐tone intervals as a function of test frequency and interval width. The results may be considered as a modification of von Helmholtz's conception and indicate that, as a function of frequency, the transition range between consonant and dissonant intervals is related to critical bandwidth. Simple‐tone intervals are evaluated as consonant for frequency differences exceeding this bandwidth. whereas the most dissonant intervals correspond with frequency differences of about a quarter of this bandwidth. On the base of these results, some properties of consonant intervals consisting of complex tones are explained. To answer the question whether critical bandwidth also plays a rôle in music, the chords of two compositions (parts of a trio sonata of J. S. Bach and of a string quartet of A. Dvořák) were analyzed by computing interval distributions as a function of frequency and number of harmonics taken into account. The results strongly suggest that, indeed, critical bandwidth plays an important rôle in music: for a number of harmonics representative for musical instruments, the “density” of simultaneous partials alters as a function of frequency in the same way as critical bandwidth does.

ISSN:0001-4966    

DOI:10.1121/1.1909741

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

An acoustic water tunnel has been constructed that can be used to study various solid‐liquid interface processes, such as heat transfer and scale formation, in the presence of intense sound. The tunnel, in modified form, can also be used to measure the acoustical impedance of various structures, such as porous metal plates, both in the presence and absence of convective flow.

ISSN:0001-4966    

DOI:10.1121/1.1909743

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In order to predict the performance of certain types of deeply submerged underwater transducers, measurements have been made of the properties of piezoelectric ceramics as a function of pressure, time, and electric field. Planar compressive stresses up to 35 000 psi were imposed on barium titanate and lead zirconate titanate ceramic by subjecting thin hollow spheres to uniform external pressure. With increasing stress, the dielectric constant, piezoelectric constant, coupling factor, and elastic compliance decreased by as much as 70%, part of the change being permanent but most of it reversible. The stability of the ceramic properties with duration and number of cycles of the imposed stress varied widely with ceramic composition. Large increases in high‐field dielectric loss were observed at high stress in ceramics usually considered suitable for high‐power projectors. The results indicate that transducers that utilize ceramic under planar stress may suffer significant degradation in performance when deeply submerged.

ISSN:0001-4966    

DOI:10.1121/1.1909745

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Two coupled modes of vibration are sometimes observed with piezoelectric‐ceramic resonators in which a single mode is expected. The coupling is inferred through the presence in the admittance characteristic of two close resonance peaks; it is also seen through a nonexponential decay of resonant vibrations. The effect is attributed to a perturbation of symmetry (such as a flaw in the material or imperfect geometry) that permits coupling of the principal piezoelectric mode to some other secondary mode whose resonance is close in frequency. To determine the requirements for obtaining coupling, a split‐electrode system was used on a thin, rectangular, ceramic plate to measure the resonant frequencies of the first three extensional modes (length, edge, radial) and first three face‐flexural modes, the dimensions being varied from a length/width of 6:1 to 1:1. Coupling between the length mode and second flexural mode was investigated in detail, using a plate of length/width 3.5:1, resonant at 45 kc/sec. Perturbations of symmetry were obtained by adding or removing mass at a corner; coupling could be produced by a change in mass of the order of 10−3of that of the whole resonator. The experiments show the modification of the electrical characteristics of the principal piezoelectric resonance as the coupling to a secondary mode of the same frequency is increased and, also, the effect of coupling two modes of different frequency. The results are discussed qualitatively in terms of an equivalent electrical circuit.

ISSN:0001-4966    

DOI:10.1121/1.1909748

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Errors in short‐term recall of six English vowels (I, ε, æ, U, ʌ, ɑ) were tabulated and related to several distinctive‐feature systems. Vowels were embedded in two contexts: /l[ ]k/ and /z[ ]k/. Subjects were instructed to copy items as they were presented, followed by recall of the entire list of (six) items. Perceptual errors were excluded from the recall error matrix by scoring for recall only correctly copied items. The rank‐order frequency of different intrusions in recall of each presented vowel was almost perfectly predicted by a conventional phonetic analysis in two dimensions: place of articulation (front, back) and openness of the vocal tract (narrow, medium, and wide). The error matrix also supported the assumptions that the values of openness are ordered in short‐term memory and that the correct value on the openness dimension is more likely to be forgotten than the correct value on the place dimension. The study suggests that a vowel is coded in short‐term memory, not as a unit, but as a set of two distinctive features, each of which may be forgotten independently.

ISSN:0001-4966    

DOI:10.1121/1.1909750

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Elementary high‐frequency approximations for scattering by an arbitrary body are specialized to ellipsoids and applied in detail for source and observation points at distances large compared to the scatterer's size. It is shown, for example, that, if the direction of observation is varied in a fixed plane containing the direction of incidence, then except for the near‐forward direction (“shadow region”) the first approximation for the far‐distant field for a given ellipsoid is specified by a “universal curve.” In particular, if the fixed plane contains an axis of the ellipsoid, then there is a unique curve for the intensity versus the angle measured from the reflection of the direction of incidence in the contained axis. For the special case of the spheroid, the field on the “axially specular” cone (the cone defined by the angle of incidence with the axis of rotation) remains constant until one gets near the shadow region, and the fields on adjacent cones (i.e., with generators at other than the specular angle with the axis) vary slowly with the azimuthal angle; for many practical purposes, we may neglect the slowly varying effects and approximate the reflected intensity pattern in the vicinity of the axially specular cone by a conical lobe of revolution. Numerical examples are given for a family of spheroids; e.g., we determine contours of constant intensity on a plane containing the source as functions of the spheroid's distance from the plane, etc.

ISSN:0001-4966    

DOI:10.1121/1.1909752

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP