摘要:

A solution for the transient response of a thin elastic shell that rests on a viscoelastic foundation is found by means of the mode‐acceleration method. For a uniform load, this solution is compared with a similar solution obtained by means of the mode displacement method. A numerical example for a hemispherical shell illustrates that the mode acceleration method converges slightly more rapidly that the mode‐displacement method during the time of application of the transient pulse.

ISSN:0001-4966    

DOI:10.1121/1.1909968

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The problem of long range propagation in a continuously stratified medium is considered for those cases where the stratification is such that a region of slow sound velocity is found to be embedded in a region of relatively faster sound velocity. It is then possible to explain the guiding mechanism of the medium in terms of surface‐wave theory. The technique employed utilizes an equivalent integral‐equation representation for the differential equations describing the boundary‐valve problem, and yields information concerning the dispersive character of the medium. As a means of illustrating the mechanics of this technique and demonstrating its application, dispersion curves are obtained for the particular case of propagation in the sofar sound channel.

ISSN:0001-4966    

DOI:10.1121/1.1909969

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A series of standard U. S. Navy explosive charges was dropped by an aircraft en route from Bermuda to Brazil, and recordings were made at various hydrophone locations of the missile impact locating system in the Atlantic. Data from the Bermuda station have yielded attenuation coefficients between 10 and 480 cps for deep‐sea propagation over a total pathlength of 2600 miles. The results are compared with the compilation made by Thorp [J. Acoust. Soc. Am. 38, 648–654 (1965)]. The data suggest a low‐frequency relaxation process as one of a number of possible attenuation processes of sound transmission in the deep sea.

ISSN:0001-4966    

DOI:10.1121/1.1909970

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Field noise reduction measurements in 21 school, motel, and residential rooms during flyovers of jet and propeller aircraft are described. The measured noise reduction for most rooms was found to lie within or near the range of moderate noise‐reduction values observed in previous measurements of houses and wood‐frame air‐base buildings. Sizeable differences in room noise reduction values were observed during successive aircraft flyovers. For jet‐aircraft flyovers, the root‐mean‐square value of the standard deviations for noise‐reduction measurements in school and motel rooms was 2.7 PNdB. For the four residential rooms studied, a root mean‐square value for the standard deviations of 3.4 PNdB was observed.

ISSN:0001-4966    

DOI:10.1121/1.1909971

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Amplitude measurements of threshold fixed‐frequency Békésy tracings were made for interrupted and continuous tones on normal and pathological ears. Comparison of four attenuation rates (1, 2, 4, and 8 dB/sec) on the same subjects indicates that bottoms of spikes were at similar sound‐pressure levels (SPL) foe different attenuation rates both for interrupted and continuous tones, while the tops and midpoint of spikes were at significantly different levels as attenuation rate varied. Standard audiometry thresholds related best with the SPL of bottoms of spikes of pulsed‐tone tracings in both normal and pathological ears. Doubling the attenuation rate changes amplitude in the ratio of about 1 to 1.62 and increases pen reversals per unit time in the ratio of approximately 1 to 1.23. This is true for both interrupted‐ and continuous‐tone tracings for all frequencies in both normal and pathological ears. Separation between interrupted‐ and continuous‐tone tracings in pathological ears is not significantly different for various attenuation rates when measured between bottoms of spikes for different attenuation rates.

ISSN:0001-4966    

DOI:10.1121/1.1909972

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Listeners are presented with pulse‐train stimulus pairs and asked to judge whether they can hear a difference between them. The interval between pulses is a random variable, identically and independently distributed for each stimulus of a pair. Two distributions are observed: one, nominally Gaussian, and the other, nominally the distribution of the amplitude of a sinusoidal wave whose phase is uniformly distributed. The principal experimental parameters are the mean interval between pulses and root‐mean‐square deviation or jitter about this interval. The stimuli of each pair are identical in other respects—pulse shape (50‐μsec pulse width), loudness (30 or 35 dB sensation level)—but differ in polarity pattern. Two pattern combinations are observed. For the range of mean pulse intervals investigated, 5–15 msec, the stimuli of each pair are generally discriminable when unjittered. However, the results indicate that, when jittered in amounts greater than 1 or 1.5 msec, the stimuli may be rendered nondiscriminable. This critical amount of jitter coincides with a flattening of the power‐density spectra of the stimuli for frequencies greater than 250 or 200 cps. On the basis of this result and the results of other investigations, it is hypothesized that the correlates of discrimination for unjittered or lightly jittered stimuli are distinct neural volley patterns associated with basilar‐membrane activity in the 300‐ to 1000‐cps region.

ISSN:0001-4966    

DOI:10.1121/1.1909973

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The length variation of the thickness‐shear and thickness‐flexure modes in rectangularATquartz plates are computed from Mindlin's first order theory, which assumes particular thickness variation. These curves are compared with the mode shapes determined experimentally by measuring the x‐ray intensity diffracted from vibrating quartz plates. The diffracted x‐ray intensity is proportional to the curvature, a combination of strain‐gradient terms of the Bragg planes, which may be approximated from the first‐order theory. The approximation for the curvature is quite good for modes that are essentially thickness shear. When the mode has a large flexure component, the approximation used to determine the curvature of the Bragg planes is not as accurate.

ISSN:0001-4966    

DOI:10.1121/1.1909974

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The question of the effect of wall vibrations on the tone of an organ flue pipe is examined theoretically and experimentally. The effect of nonrigid walls is calculated and it is shown that, if they do not affect the pipe frequency, they do not radiate appreciably. For pipes as ordinarily constructed of circular or nearly circular cross section, the lack of rigidity of the walls will have negligible effect. The wall vibrations actually occurring in sounding organ pipes were investigated experimentally and found to be owing to the vibrating air stream from the flue impinging on the lip. By artificially vibrating pipes to the same acceleration levels as when blown, it was found that the sound radiated from the vibrating walls is negligible. By surrounding pipes with a jacket and filling the space between with water, it was determined that the wall vibrations do not affect the internal standing wave in the pipe. Measurements of pipes in other organs confirmed the laboratory findings. It is concluded that the steady tones of organ pipes are not affected by wall vibrations.

ISSN:0001-4966    

DOI:10.1121/1.1909975

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Preference tests used in the evaluation of speech‐communication systems typically employ as reference conditions different levels of one type of distortion, produced by a single reference system. A new preference test has been developed to explore the possible advantages of using several reference systems that represent fundamentally different types of distortions. The new test was experimentally compared with the more conventional test, and it was found that the preference judgments obtained with the new test exhibited a significantly smaller variance among the listeners. This finding suggests that, by using several reference systems that represent an appropriate variety of distortions, preference tests can be constructed that are more efficient than those developed to date.

ISSN:0001-4966    

DOI:10.1121/1.1909976

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The purpose was to evaluate ways of predicting the onset frequency of the second vowel formant (F2) following consonant constrictions. Spectrograms of 604 constrictions were measured to obtain the frequency and slope of F2 offset just prior to each constriction, the duration of the constriction, and the frequency of F2 onset after the constriction. Three types of F2 onset prediction were applied to each constriction: (1) holding the F2 offset frequency, (2) linear extrapolation of F2 offset slope, and (3) exponential extrapolation of the offset slope. Statistical analyses of these data indicated that linear extrapolation gave poor results, that holding predictions were superior to predicting merely the modal onset, and that exponential extrapolations were better than holding offsets under certain conditions of offset slope and frequency region. Articulatory place and complexity of consonant constriction were found to be related to prediction error.

ISSN:0001-4966    

DOI:10.1121/1.1909977

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP