摘要:

When a sound beam travels through the sea, it is scattered in all directions by inhomogeneities of various sorts in the sea and on its boundaries. In the backward direction, the aggregate of all the scattered contributions is called “reverberation.” In other directions, the “side‐scattering” can be studied by using two directional transducers, oriented so that the beams cross each other, to measure the sound scattered out of one beam and received on the other. This method was employed in an off‐shore area in the Gulf of Mexico having a particularly uniform bottom. Using two‐bottomed transducers a mile and a half apart, the intensity of scattering was measured at 22 kc for different angular orientations of the two beams. The measurements were reduced to the coefficient, scattering strength, without requiring either transducer calibrations or direct measurements of transmission loss. The results indicate a bottom scattering strength between −30 and −40 db having no appreciable dependence on angle between the two beams. Within the angular range from the backward direction around to 150° in the forward direction, the scattering appears isotropic. This indicates that isotropic bottom scattering may be safely assumed in applications utilizing separated transmitting and receiving transducers at kilocycle frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1930279

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Auditory‐nerve action potentials evoked by acoustic transients were recorded and correlated with the space‐time patterns of the associated cochlear microphonics. Of particular interest was the appearance, in some of these neural responses, of as many as six well‐defined groups of action potentials after a single effective acoustic wave. The amplitude of successive peaks decreased with a time constant that appeared to be related to the slope of the final positive‐going portion of the microphonic wave form. Attention will be given to the relation between neural latency and certain stimulus parameters in an attempt to clarify and extend the notion of time‐intensity trading in the auditory system.

ISSN:0001-4966    

DOI:10.1121/1.1930287

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

After complete bilateral section of the brachium of the inferior colliculus, cats cannot relearn an auditory frequency discrimination, a task which can be easily relearned after ablation of all known auditory neocortical areas and the subsequent degeneration of the thalamic auditory nuclei (the medial geniculate body and the posterior nucleus). The problem can be relearned when a small part of the brachium remains intact; the rate of relearning depends upon the anatomical locus of the remaining fibers. These results suggest that the brachium may contain fibers that do not end in the medial geniculate body and that these fibers, which probably come from the inferior colliculus and/or the nucleus of the lateral lemniscus, play an important role in the neural mechanisms underlying frequency discrimination. (This research was supported by the Office of Naval Research and the Air Force Office of Scientific Research.)

ISSN:0001-4966    

DOI:10.1121/1.1930290

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The error in using transmissibility at the undamped natural frequency in place of the maximum transmissibility of a single‐degree‐of‐freedom system is less than 4% for all values of the damping ratio. The error is a maximum for a damping ratio of about 0.6 and decreases with both increasing and decreasing values of the damping ratio. The error in using transmissibility at the undamped natural frequency is less than the error in using theQof the system for all values of the damping ratio. [Research supported by the Electronic Components Laboratory, Wright Air Development Center, under Contract No. AF 33(616)‐5752.]

ISSN:0001-4966    

DOI:10.1121/1.1930299

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In a two‐alternative forced‐choice frequency discrimination task observers were instructed to respond by indicating the presentation interval in which the higher of the two tones had appeared. The frequency difference between the two tones was fixed at 15 cps. The independent variable manipulated was the time between the two presentation intervals within each trial. Discrimination was measured at nine separation times from 30 msec to 9.6 sec. The data indicate a peak in discrimination, varying among the four observers, with about 1‐sec separation. The data are accounted for by two “memory” mechanisms. A short‐term effect causes the first of two closely spaced signals to interfere with the second. When the signals are separated by longer intervals a decaying memory of the frequency of the first makes comparison with the second signal less precise, lowering discrimination. [This work was supported by the U. S. Air Force under a contract monitored by the Air Force Office of Scientific Research.]

ISSN:0001-4966    

DOI:10.1121/1.1930302

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The multidimensional scaling model of successive intervals was applied to investigate the dimensionality of auditory perception of pure tones. The stimuli consisted of 16 pure tones. Thirty‐nine observers made distance judgments of similarity between stimuli. These interstimuli distances were analyzed mathematically to reveal the minimum number of dimensions necessary to account for the distances between stimuli. The results of the analysis indicated that two factors, pitch and loudness, were fairly well defined. A third factor, not as well defined, appeared to relate to pitch. The purpose of the study was to evaluate the multidimensional scaling method for use in auditory areas where the dimensions are not well known, and, since the anticipated dimensions, pitch, and loudness, were revealed, proposed use of the model in other auditory areas is supported. [This research was supported in whole by the U. S. Air Force under Contract No. AF 33(616)‐3644, monitored by the Aero Medical Laboratory, Wright Air Development Center.]

ISSN:0001-4966    

DOI:10.1121/1.1930312

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

For equivalent rms levels a narrow band of noise has a higher peak level than has a pure tone. One might hypothesize that the noise band would cause more temporary threshold shift (TTS) than a pure tone of equivalent rms level at the same frequency. On the other hand, if the stimulus is a band of noise wider than an aural critical band, one might hypothesize that the TTS would be determined by the level in the critical band only, in which case the TTS would be somewhat less than predicted from the level of the total band. To test these hypotheses, 8 ears (4 subjects) were exposed monaurally to pure tones at 500 and 3200 cps, and to noise bands of 5 cps, one‐third octave and one octave widths, centered at these same frequencies. The exposures were for 5 min at an rms sound pressure level of 110 db. After exposure the subject tracked his 4000 cps threshold for 3 min and then his 500, 1000, 2000, 4000, and 6000 cps thresholds for the next 12 min. Threshold shifts produced by the tone, the narrow band, and the broader band were found to be essentially equal. The “bounce” phenomenon was prominent in most recovery curves (4000 cps), especially after exposures in the 500 cps region.

ISSN:0001-4966    

DOI:10.1121/1.1930313

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Speech privacy—freedom from annoyance owing to intrusion of speech sounds—poses an important acoustical problem in the design of private offices, conference rooms, hotel rooms, and similar spaces. The provision of adequate speech privacy can be more difficult than reverberation control or the reduction of noise, especially in building construction of low cost and light weight. A study of factors relevant to speech privacy is reported in this paper. Psychophysical tests were conducted in which subjects performed simulated tasks in a private office in the presence of controlled background noise and of speech signals that were generated in an adjacent office. The subjects were instructed to respond when “… the speech reaches a level that you consider bothersome….” The experimental variables were: (1) signal‐to‐noise ratio as a function of frequency; (2) the frequency characteristic of the sound isolation between the rooms; and (3) the type of task. The subjective responses correlated closely with the calculated speech articulation index. Results of the study, including physical data on sound transmission and absorption characteristics of building components, form the basis of a self‐contained procedure for designing speech privacy. [Written for use by architects and building designers, this procedure is being published by Owens‐Corning Fiberglas Corporation (who sponsored this study) in cooperation with other interested manufacturers.]

ISSN:0001-4966    

DOI:10.1121/1.1930319

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The straightforward motion and stress analysis that has been so successful in the design of airframes has seldom been applied to equipment and is not too effective there. On the other hand, the conventional application of vibration specifications to sub‐assemblies leaves the resonances within the equipment very loosely controlled, so that the attainment of reliability is dependent primarily on testing the entire equipment and making design changes until the results are satisfactory. Furthermore, information on resonances of standard parts such as vacuum tubes and relays is not readily available. There is an urgent need for rules for controlling configuration and resonance in the course of design, so as to achieve something close to an optimum in the least possible time and decrease any amount of calculation, testing, or redesign required thereafter. Test procedures can be modified to assist such a design approach. Some complication results from consideration of mechanical impedance relationships, but not enough to prevent improvement of the development process.

ISSN:0001-4966    

DOI:10.1121/1.1930330

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The problem of mount bottoming of resiliently‐mounted equipment and its collision with adjacent structure when both are subjected to random vibration is solved in terms of probability of occurrence and the mean time between occurrences. The system is represented by two simple mechanical oscillators (with damping) whose relative motion is determined. A complete solution is obtained for white Gaussian excitation. This solution can also be applied to other structural problems, such as the mechanical design of electronic components, when the same representation can be used.

ISSN:0001-4966    

DOI:10.1121/1.1930331

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP