摘要:

An ultrasonic pulse type apparatus was used to measure the speed of sound in distilled water over the pressure range 14.7 to 14 000 psia and the temperature range 0.9 to 91.2°C. The temperature where the maximum sound speed occurs shifts to a higher temperature when the pressure is increased. At atmospheric pressure the computed maximum speed was 1555.36 m/sec and occurred at a temperature of 74.164°C. The isotherms of sound speed, plotted as a function of pressure, are concave upward below 20°C, concave downward above 20°C, and are approximately linear near 20°C for the pressure range of 14.7 to 14 000 psia. These curvatures have a maximum value of 1 part in 300 compared to the estimated accuracy of measurement which is 1 part in 10 000. The results are presented in tables and also in the form of a fourth degree equation fitted to the experimental data by the method of least squares.

ISSN:0001-4966    

DOI:10.1121/1.1907828

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Thermal oscillations in molecular solids are of two distinct classes: lattice vibrations and atomic vibrations within each molecule. These two vibrational modes can overlap in frequency and “resonate.” This resonance leads to lengthy relaxation times manifested as unusually high acoustic absorption, a phenomenon termed resonance absorption. In order to study resonance absorption in solid benzene a method was developed for growing single benzene crystals of average linear dimension, 10 cm. At the acoustical frequency 10 mc, absorption in single benzene crystals is found to be 0.24 cm−1; at 6.4 mc the value is 0.09 cm−1. This excessively high absorption (104higher than in crystalline quartz) was quantitatively predicted from available molecular constants by a theory given previously. A partial list of compounds is given in which resonance absorption is predicted to be the dominant absorption mechanism.

ISSN:0001-4966    

DOI:10.1121/1.1907829

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The problem of the reflection and refraction of elastic waves at an interface of relative motion is solved. Total reflection of dilatational and rotational waves can occur for certain ranges of angles of incidence depending on the relative speed of the media. For very high relative speeds, resonance of the reflected and refracted waves occurs for certain angles of incidence, called angles of resonance. For a Poisson material and identical moving media, the relationship of the angle of resonance to the relative Mach number (based on the dilatational wave speed) is worked out and presented in the form of a curve.

ISSN:0001-4966    

DOI:10.1121/1.1907830

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The mechanisms of sound production by the splashes made by the gas‐to‐liquid entry of objects are discussed. The sound from the splash is considered to be associated with acoustic multipoles of all orders, the main ones being simple sources, dipoles, and quadrupoles. The orders of the multipoles that predominate during the various phases of the splash are estimated from the flow and boundary conditions. The sounds radiated into the water by the low‐velocity vertical entry of single water droplets, sprays of water droplets, and various other objects, such as spheres, cones, and wedges, have been measured and found to have the characteristics of acoustic dipoles. The extensive experimental data on the spectrum of the underwater sound from the splashes of droplets and sprays and the scaling laws for dipoles are used to estimate the spectrum levels of the underwater sound from the splashing of rain on the surface of a sea in terms of the rate of rainfall.

ISSN:0001-4966    

DOI:10.1121/1.1907831

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The resonant vibration of machinery and resiliently mounted equipment can be reduced with a dynamic absorber of suitable design. The necessary analytical and graphical information for an optimum design is presented in this paper. It is assumed that the absorber mass is attached resiliently to the vibrating item with a rubber‐like material, and not with a spring and dashpot in parallel as considered in the classical theory of Ormondroyd and Den Hartog. The dynamic absorber utilizing a material with a stiffness proportional to frequency and a constant damping factor can reduce the resonant vibration of machinery and equipment items considerably. Its performance is superior to that of the classical dynamic absorber.

ISSN:0001-4966    

DOI:10.1121/1.1907832

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The dynamic force measuring system for the measurement of machinery vibration is based on the use of four piezoelectric force transducers. These transducers are installed between the feet of the machine under test and a terminating foundation, preferably a large seismic mass. The four signals are combined in two ways: (1) as a phasor sum to provide a single vertical force measurement and (2) as a sum and difference with equivalent moment arms to provide torque measurements. These fundamental measurements are based on force and torque equations developed from the six motions of an assumed rigid body. At the fundamental frequency of machinery vibration the two combined signals provide a measure of static and dynamic unbalance. The force spectrum may be analyzed by conventional means to provide frequency and amplitude information.

ISSN:0001-4966    

DOI:10.1121/1.1907833

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Two experiments were carried out to determine how masking for frequencies either above or below one band of noise combine with the critical‐band type masking produced by a second band of noise. The results of both experiments indicate that at moderately high levels the combination of critical‐band masking with another type of masking results in a 6‐db increase in masking. The implications of this result are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907834

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Short duration auditory fatigue, i.e., the temporary shift in the threshold of hearing following the cessation of a masking source, may be termed “residual masking.” In this study, curves of residual maskingvsfrequency have been obtained in a free‐field in the low‐frequency range, for 250‐cps masking tones at sound pressure levels of 90 and 110 db, following the method of Munson and Gardner. These masking patterns were obtained 150 and 200 msec after the cessation of the masking tone. In addition, residual masking at 250 cps was measured as a function of the mel‐band intensity level of a “white noise” masking source. Plots of loudness densityvsfrequency were computed from residual masking patterns, and the loudness of the pure‐tone masking source was evaluated.

ISSN:0001-4966    

DOI:10.1121/1.1907835

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Monaural masking patterns were obtained for pure tones spaced by octaves from 250 cps to 8000 cps at 20–100 db SL on three listeners in an attempt to provide extensive data assessing the relative importance of aural harmonics and cochlear spread of masking tone activity in the extension of masking to frequencies above the masking tone. The masking patterns confirm and extend the results of others, but especially indicate that second peaks do not necessarily occur at the second harmonic of the masking tone. The masking patterns are explained in terms of (1) the activity pattern of the masking tone in the cochlea, (2) beats between signal and masking tones, (3) aural harmonics, and (4) suppression of cochlear response to the signal.

ISSN:0001-4966    

DOI:10.1121/1.1907836

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Earlier investigators of the free‐field bone‐conduction threshold occluded the auditory meatus with plugs and muffs and reasoned by various arguments that the real‐ear attenuation obtained was less than the attenuation provided for air‐conducted sound. The conclusion was that the sound perceived reaches the auditory system via bone conduction. The present experiments are a check on these conclusions for the frequencies from 1000 to 8000 cps. With the auditory canal occluded by plugs and muffs the whole skull, or sections of it, was covered with a 2‐in. layer of absorbent cotton. The muffs were not covered. A higher free‐field threshold with the cotton indicated that without cotton the sound was reaching the ear via bone. [The sound pressure level (SPL) at the surface of the muffs was not altered by the surrounding cotton.] Cotton over the entire head raised the bone‐conduction threshold by 10 to 18 db from 2000 to 8000 cps (8 subjects). Bone‐conduction thresholds determined previously were confirmed from 1000 to 8000 cps. The front and back of the head were approximately of equal sensitivity with respect to bone conduction. Covering only the side of the head facing the sound source raised the threshold more than covering the “shadow” side alone. The results suggest a possible method for improving the effectiveness of special noise‐attenuating devices.

ISSN:0001-4966    

DOI:10.1121/1.1907837

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP