摘要:

Discussed theoretically is the manner in which the transmissibility of a vibrating item may be reduced by the attachment of a dynamic absorber, or by the attachment of three absorbers of staggered natural frequencies. It is demonstrated that the dynamic absorbers can provide significant isolation at frequencies of concern; yet the presence of the “compensating” resonant peaks normally associated with the use of a dynamic absorber may be avoided by employing small absorber damping and by damping heavily the resilient elements that support the vibrating item.

ISSN:0001-4966    

DOI:10.1121/1.1919171

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The nature of sonar echoes from a hollow metallic sphere in water is investigated theoretically in relation to the thickness of the shell and the contents of the hollow region. Steady‐state solutions are presented for iron and aluminum spheres filled with water and for iron spheres with a vacuum inside. Calculated results for pulsed sound suggest that part of the echo originates from a type of flexural wave moving around the shell, which changes into a surface wave as the shell thickness increases. Significant differences in echo structure occur when the interior region is changed from water to a vacuum.

ISSN:0001-4966    

DOI:10.1121/1.1919173

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Investigations of the underwater sound produced by shooting bullets into water indicated that the principal mechanism of sound production might be the oscillatory collapse of an air bubble near the surface. High‐speed motion pictures taken of a .38‐caliber‐pistol bullet's entry into a tank confirmed this idea. The main features of the acoustic signature can be explained and correlated with the motion pictures. On the order of 1% of the available kinetic energy was converted to acoustic energy. Most of the energy was transferred to a single bubble during the first 2 ft of travel in the water.

ISSN:0001-4966    

DOI:10.1121/1.1919174

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The transient pressure produced by explosive sources in a two‐layered liquid half space has been evaluated in terms of definite integrals, using Cagniard's method of inversion of the Laplace transforms involved.

ISSN:0001-4966    

DOI:10.1121/1.1919175

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

It is hypothesized that the backscatter of wave radiation from a rough boundary is the result of reflections from a large number of “facets” having random distributions of size and slope. This hypothesis developed into a mathematical model from which curves are computed for a number of values of mean size and rms slope. An explanation is offered for the lack of frequency dependence in reported backscatter measurements. The model is also fitted to some previously reported measurements of the backscatter of sound from the deep‐ocean bottom.

ISSN:0001-4966    

DOI:10.1121/1.1919176

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Expressions are given for the nearfield pressure on a flexural disk in an infinite, rigid, plane baffle. This pressure is then integrated over the disk to obtain finite series expressions for self‐radiation impedance, which is referred to average surface velocity, as are all impedances in this article. Expressions are derived for the far field directionality factor of a flexural disk. The Bouwkamp integral method is used to obtain infinite series expressions for mutual radiation impedance between flexural disks by integrating the farfield directionality factor of two identical flexural disks, vibrating in phase, over a set of complex angles. It is shown that as the relative radius (ka) of the disk approaches zero and the element spacing becomes large as compared to the radius of the disk, the equations for mutual‐radiation resistance and reactance and self‐radiation resistance for flexural disks are the same as for circular pistons. However, aska→ 0, the self‐radiation reactance is larger for disks than pistons, being 0.849kafor pistons, 1.060kafor supported‐edge disks, and 1.204kafor clamped‐edge disks.

ISSN:0001-4966    

DOI:10.1121/1.1919177

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Nine subjects with normal hearing were exposed for 3 min to 50‐ and 100‐dB‐SPL, 4‐kc/sec tones during the performance of a task. Three tasks were used: long division, light tracking, and reverie. Each subject received 3 replications of every task/level‐of‐exposure combination. Performance of task during exposure was found to have no significant effect on the magnitude of TTS. Repeat‐reliability measures showed the subjects to be reasonably consistant in their responses.

ISSN:0001-4966    

DOI:10.1121/1.1919178

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Temporary hearing losses were observed for 20‐min exposures to pure‐tone frequencies (500, 1000, 2000, 4000 cps), which were independently mixed in various strengths with a broad‐band noise to create different exposure conditions involving a strong tonal component in a noise field. The over‐all (combined pure‐tone/noise) SPL for all conditions was fixed at 105 dB and the resultant losses were compared to those caused by equivalent exposures to just the broad band noise (referred to as the continuous‐spectrum‐noise condition). The pure‐tone/noise combinations produced greater threshold losses than the continuous‐spectrum noise primarily when the pure tone was of low frequency (below 2000 cps) and contained most of the available energy in the sound field. These more prominent pure‐tone exposures exceeded the criteria set forth by the U. S. Air Force 160‐3 Noise Regulation for identifying those conditions of strong pure‐tone energy in noise that are believed more hazardous to hearing. However, other pronounced pure‐tone conditions in this study also met these criteria even though they gave no evidence for increased hazard to hearing when their postexposure losses were compared with those of the continuous‐spectrum noise. The findings were discussed with regard to the action of the acoustic reflex that has been proposed to account for the differences in the ability of pure tones and noise to cause hearing loss.

ISSN:0001-4966    

DOI:10.1121/1.1919179

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Auditory density refers to the apparent compactness, concentration, or hardness of a sound. An attempt was made to determine directly the form of the density surface by the method of magnitude estimation with both pure tones and bands of noise (quarter‐octave). For both tones and noises, density grows as a power function of sound pressure. The values of the exponents decrease with frequency, and the two families of power functions converge toward a common point near about 150 dB SPL. The equal‐density contours turn out to be straight lines in a plot of SPL vs log frequency. The general slope of the equal‐density contours for pure tones was verified by a direct‐matching procedure.

ISSN:0001-4966    

DOI:10.1121/1.1919180

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In this paper, the covariance function of noise at two points in a sound‐carrying medium is derived for an arbitrary distribution of noise generators when the noise suffers attenuation and spreading loss. The analysis is then applied to the cases of a volume and a plane distribution of omnidirectional sources. It is shown that the effect of attenuation on covariance is generally negligible in the volume case but is ordinarily important in the plane case. For the plane distribution, an asymptotic expansion is derived that holds for small values of an attenuation parameter. This expansion is then used to study the effect of attenuation on covariance as a function of receiver separation, receiver‐line orientation, and time delay.

ISSN:0001-4966    

DOI:10.1121/1.1919181

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP