摘要:

In a comparison of tonal and narrow‐band signals, reported by the authors in 1964, the masking level differences (MLD's) for the two signals were the same for corresponding phase shifts. Earlier, Hirsh and Webster reported differences for similar conditions. In the authors' experiment, there was a random phase difference between the signal and masker since separate noise generators provided the signal and noise, while Hirsh and Webster's single noise generator gave a fixed phase difference between the signal and masker. In the present experiment, a single noise generator was used and the phase difference between the signal and masker was shifted in phase by 30° steps between 0° and 180°. For each signal‐masker phase difference, the signal was presented in phase at the ears and reversed in phase at one ear. Data are presented as MLD's relative to the signal‐in‐phase condition for each signal‐masker phase difference. The MLD's increase monotonically from 13 dB at 0° to 18.5 dB at 180°. [Work supported by USN Bureau of Ships contract NObsr‐72627 and under a grant from the National Aeronautics and Space Administration R‐129 through ONR contract 3579(04).]

ISSN:0001-4966    

DOI:10.1121/1.1939210

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The purpose of this work was to examine the effects of interaural time delay of the noise on the detection of tones. The noise was 1200‐cps bandwidth, white, Gaussian noise at a noise spectrum level of 57 dB/cycle (re0.0002 dyn/cm2). The noise level was the same in both ears and identical tones were presented to the two ears. The tone frequencies included 1040, 694, 500, 297, and 167 cps. The method used to measure masked thresholds was a modified Békésy technique in which the listener approached threshold from a condition where there was always signal present to use as a basis of judgment. The results of this experiment support previously reported results of Jeffress, Blodgett, and Deatherage. The curve of binaural masking‐level differences (BMLD) versus noise time delay (τn) shows cyclic behavior with a period identical to the period of the masked tone. These cycles are damped in that the maxima of the BMLD's decrease as τn, increases. The data at 297 and 167 cps indicate that the cycles flatten at low frequencies—the flattening first showing up at some frequency between 300 and 500 cps. Further results show that the flattening for low‐frequency tones begins at about 0.8 msec and the BMLD remains constant until a relatively long time later, at which point it decreases.

ISSN:0001-4966    

DOI:10.1121/1.1939217

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Using a deep source and deep receivers, measurements of the acoustic reflectivity of the ocean bottom at 1 kc/sec were made at an area in the Atlantic Ocean. The data, that is, the direct and the first‐order bottom‐reflected arrivals, were acquired digitally at sea and have been reduced via a computer program. The program computes the reflection coefficients based on peak pressure as well as the time‐integral square of the pressure. The computer analysis also furnishes the travel time of each arrival, horizontal range, and incident angle for each transmission. The total number of data points considered exceeds 4000. Computations based on velocities, densities, and attenuations that have been obtained from an analysis of cores taken in the general area of the acoustic tests have been performed, using a theoretical model of the bottom. This model consists of many absorbing liquid plane parallel layers over one absorbing semiinfinite solid. Comparisons of the experimentally derived reflection coefficient as a function of incident angle are made with those obtained from the model, and the relevance of the complicated layering structure and attenuation of the bottom is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1939226

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The continuous seismic‐profiling system now in use at the Woods Hole Oceanographic Institution employs an electrical‐spark sound source with a maximum stored energy of 100 000 J, a receiving system consisting of a streamlined, neutrally buoyant line‐hydrophone array and associated amplifiers having a bandpass of 20 to 10 000 cps, and a high‐quality tape recorder. When these received seismic signals are processed by a matched‐filter detector and displayed on a precision graphic recorder (PGR), an accurate quantitative measure of travel time through the subbottoms and a clear, qualitative picture of these layers results. It is now possible to obtain a quantitative measure of the reflectivity and absorption characteristics of the subbottom and bottom layers in the frequency ranges of 20–1000 cps. The received signals are first converted from analog to digital format and then processed through a series of digital‐computer programs: statistical techniques that improve signal‐to‐noise ratio, Fourier analysis, filtering, matched‐filter detection, and programs relating measured spectrum to original source spectrum. The detailed frequency and phase measurements of the information thus obtained allow new interpretations to be made of the substructures and give new acoustical signatures to the substrata. Results of data taken southeast of New England on the Continental Rise show that the energy spectrum of the first bottom reflection can be used to determine the original source depth to within 1‐ft accuracy. The original source spectrum including surface reflections can be determined to an accuracy of 3%. Knowing the source spectrum, the reflectivity and absorption coefficients for the bottom and of each subbottom have been computed as a function of frequency for the above area.

ISSN:0001-4966    

DOI:10.1121/1.1939228

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Vibration tests in support of manned space flight have been conducted by MSC since the origin of the Manned Spacecraft Center; this, of course, is ever increasing in both magnitude and scope and now embraces the field of acoustic testing. This paper discusses the sources of dynamic excitation in flight, whether vibration or acoustics, to the spacecraft or its occupants, and relates the resulting forces to the need for certain test facilities. Such facilities, either in existence or currently in construction, are described with regard to their physical make and environmental‐simulation potential and their use is illustrated by descriptive examples, experimental programs, test procedures, and technical results.

ISSN:0001-4966    

DOI:10.1121/1.1939236

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

At the last meeting of this Society, evidence was presented for intrafiber volleying by units in the superior‐olivary complex of cat. These results showed that an auditory unit could discharge during monaural tonal stimulation with interspike intervals that are equal to and multiples of the period of the stimulating tone up to about 2.0 kc/sec. Because these data were obtained with only a 20‐channel data processor, long interspike intervals were unobtainable and were lost, therefore, in an overflow basket. By utilizing a computer (CAT) with 400 memory addresses, it has been possible in recent studies to retrieve most of the data with a resolution of 78 μsec. These preliminary findings show that interspike intervals that are many multiples of the period of the tone occur during stimulation. At 1.0 kc/sec, for instance, spikes occur at time intervals of 1, 2, 3, 4, …, to 30 msec and at 0.5 kc/sec the intervals are 2, 4, 6, 8, …, to 16 msec. The intervals, in both instances, are multiples of the period of the tone. The periodicity upon stimulation evidenced by these units, which are at least two synapses from the periphery, suggests that temporal analysis of information is maintained to at least this level of the auditory pathway.

ISSN:0001-4966    

DOI:10.1121/1.1939238

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The hearing sensations stimulated by an audiofrequency current passed through various types of electrodes attached to different portions of the human head or body have been previously investigated and termed electrophonic hearing. More recently, modulated electromagnetic waves have been described to produce hearing sensations. The experiments reported in this paper investigated hearing phenomena in electrostatic fields when the whole head or parts of its surface are exposed to alternating electrostatic fields of audiofrequency. Threshold data obtained by this method are compared to the data reported by others for the different types of electrophonic stimulation mentioned above. Calculations show that all these types of auditory stimulation on the head surface of normal subjects can be explained quantitatively by mechanical tissue excitation by electrostatic forces. Application of this stimulation method for studying vibrotactile sensations on finger tips and other body areas, as well as research applications in psychoacoustics, are demonstrated and discussed.

ISSN:0001-4966    

DOI:10.1121/1.1939246

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The peak amplitudes ofSOFARsignals have been estimated by considering particular mathematical models for the acoustic speed‐versus‐depth profile of the ocean and for the explosion waveform. The souud speed was assumed to vary asc2 = c02(1 − α2z2)−1, wherec0is the speed at the channel axis,zis the vertical distance from the axis, and α specifies the width of the channel. The source waveform was assumed to be a finite wavetrain, typically a110‐secpulse of a 100‐cps sinusoid. It is found that the range dependence of the peak of the received pressure amplitude is the product of two terms. The first is the expected cylindrical spreading loss. The second term oscillates with range. The amplitude of the oscillation depends on the source waveform and the range; for the typical 100‐cps110‐secpulse at 400 nm, the amplitude is about 12 dB. The distance between successive maxima of the oscillation is about 6 nm, and is independent of range and source waveform. [Work supported by the Bnreau of Ships, U. S. Navy.]

ISSN:0001-4966    

DOI:10.1121/1.1939249

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In conventional transient thermal‐stress analyses, the heating rates are sufficiently slow so that the inertia terms in the equations of equilibrium are negligible and time enters as a parameter from the transient temperature in the body. Recently, one has encountered extremely high heating rates and it is necessary to reexamine the role of inertia. Such studies of extremely massive infinite and semiinfinite bodies and extremely slender bodies have been made by others. In the former, thermal‐stress wave propagation without reflection was examined; in the latter, thermally induced vibrations were considered. It is of interest now to examine the effect of inertia in a body whose dimensions lie be‐between these extremes. As an example, we consider a hollow sphere of arbitrary thickness subjected to a step change of temperature on its inner surface. In the solution, the propagation and reflection of thermal‐stress waves in the sphere are observed. For comparison, the results of the conventional analysis are obtained as a special case. After passing to appropriate limits, the results are compared to previous analyses of slender and massive spherical regions.

ISSN:0001-4966    

DOI:10.1121/1.1939261

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Experimental evidence establishing the existence of circumferential waves in a thin‐walled air‐filled cylinder with a finite discontinuity in the shell is presented. The discontinuity is a 0.062‐in.‐wide air gap extending the length of the cylinder and the full thickness of the shell. Evidence establishing that the principle portion of the circumferential wave travels within the shell and is reflected at the air gap is presented. [Work done under contract with the U. S. Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1939268

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP