Sound paths

Figure 3 Echo from 8 mm side-drilled hole at sound path 50 mm, before and after signal processing.

A corresponding composite probe with the same frequency and crystal size, however, detects the test flaw much better the echo has a 12 dB higher amplitude (see Fig. 4) and in addition, the noise level is much lower, resulting in an improved signal to noise ratio. This effect is especially observed at high sound attenuation. However, in materials with low attenuation or in case of shorter sound paths the standard probe yields a comparable good signal to noise ratio. 

Because of the double sound path involved in PE measurements of the back wall echo, we approximate the corresponding attenuation at a certain frequency to be twice as large as the attenuation that would be obtained by an ordinary TT measurement. We propose to use the logarithm of the absolute value of the Fourier transform of the back wall echo as input data, i.e... 

As stated previously, packing the chamber with an absorber may broaden the bandwidth, but this lowers efficiency. It may be overcome by using multiple absorbers in the sound path, and placing a perforated sheet some distance away from the rigid outer wall of the enclosure and filling the cavity with absorber can do this. It is not necessary to use cross walls between the chambers so formed. In this case the equation becomes ... 

The system was calibrated with water and the sound path (A) was found to increase slightly as the pressure is increased (assuming t is independent of pressure) (112). Since we are interested in measuring the relative speed of sound (Au) in aqueous solutions, we use the velocimeter in a differential mode. The value of t is not a function of pressure (or temperature), as the electronics are kept under ambient pressures. The values of Au were determined from... 

The image source A is a first order source, corresponding to a sound path with a single reflection. Higher order sources corresponding to sound paths with multiple... 

Figure 12.10. Direct and first order reflected sound paths from singer to listener in a simple room.

FIGURE 3.48 Effect of loudspeaker sound path differences on signal arrival times and intelligibility. Source Mapp. 1994. Sound reinforcement and public address. In Loudspeaker and Headphone Handbook, ed. J. Borwick, 2nd ed., p. 355. Focal.)... 

DP DIRECT SOUND PATH Onininj CZ -CONVERGENCE ZONE SOUND PATH... 

BB BOTTOM BOUNCE SOUND PATH - - - AREAASSUMED = MID NOPTH ATLANTIC OCEAN... 

FIGURE 17.40 Typical sound paths between source and receiver, in fathom unit of length or depth generally used for underwater measurements where 1 fethom = 6 ft. (Source Cox, A.W. 1974. Sonar and Underwater Sound, p. 25. Lexington Books, D.C. Heath and Co., Lexington, MA.)... 

Conventional ultrasonic methods include the pulse-echo, the pulse-transmission and the pulse-resonance techniques [104]. Depending on the incidence of the piezo transducer with respect to the structural surface as well as on their design, P-waves, S-waves or a combination of both can be generated within the structure. P-waves are best suited for the inspection of thick components, for through-the-thickness damage detection, and are quite effective for the detection of anomalies along the sound path. By the pulse-echo method, detects are detected in form of additional echoes. In the pulse-transmission method wave dispersion and attenuation due to diffused damage in the material indicate possible defects [103]. 

Oscillations travel through the structure to the cabin and reach pilots and passengers, as well as vibration sensitive navigation equipment some of this energy is radiated to the air inside the cabin. In addition to this structural sound path, there is the direct air sound path, see Gembler [79] for example... 

The virtual transducer can be placed in a specific location on the test object surface, it can be moved along a path (e.g. a robot scanning path generated off-line or a path resulting from a real inspection sequence) or it can be moved along the surface, dynamically updating the ultrasonic sound propagation in the material. 

The echo directivity for surface SH Wave probes and SH Wave angle probes was measured. The experiment was carried out by measuring the echo height from side drilled holes of different depths at a constant beam path length. The calculation of echo height was based on a point sound source on the test surface in different phases. The experiment and the calculation were compared. The effects of the frequency, height of... 

Environmental information is available extensively on the free Internet. Two main reasons aeeount for this. First, the freedom of environmental information law and, secondly, the fact that many environmental databases which used to be available only commercially are now accessible on the free Internet. This section focuses on environmental information which is available free of charge on the Internet. Three main paths are distinguished for searching environmental information effectively. In general, all three routes should be taken into consideration for achieving a sound search result for environmental information on chemical stibstances... 

At the present time there exist no flux relations wich a completely sound cheoretical basis, capable of describing transport in porous media over the whole range of pressures or pore sizes. All involve empiricism to a greater or less degree, or are based on a physically unrealistic representation of the structure of the porous medium. Existing models fall into two main classes in the first the medium is modeled as a network of interconnected capillaries, while in the second it is represented by an assembly of stationary obstacles dispersed in the gas on a molecular scale. The first type of model is closely related to the physical structure of the medium, but its development is hampered by the lack of a solution to the problem of transport in a capillary whose diameter is comparable to mean free path lengths in the gas mixture. The second type of model is more tenuously related to the real medium but more tractable theoretically. 

Extracted from U.S. Standard Atmosphere, 1976, National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration and tte U.S. Air Force, Washington, 1976. Z = geometric altitude, T = temperature, P = pressure, g = acceleration of gravity, M = molecular weight, a = velocity of sound, i = viscosity, k = thermal conductivity, X = mean free path, p = density, and H = geopotential altitude. The notation 1.79.—5 signifies 1.79 X 10 . ... 

In the second technique, the flowing liquid must contain scatters in the form of particles or bubbles that will reflect the sound waves. These scatters should be travehng at the velocity of the hquid. A Doppler method is applied by transmitting sound waves along the flow path and measuring the frequency shift in the returned signal from the scatters in the process fluid. This frequency shift is proportional to liquid velocity. 

There are two approaches to fluid-generated noise control—source or path treatment. Path treatment means absorbing or blocking the transmission of noise after it has been created. The pipe itself is a barrier. The sound pressure level inside a standard schedule pipe is roughly 40-60 dB higher than on the outside. Thicker walled pipe reduces levels some at more, and adding acoustical insulation on the outside of the pipe reduces ambient levels up to 10 dB per inch of thickness. Since noise propagates relatively unimpeded inside the... 

Deflagration to Detonation Transition A reaction front that starts out with velocities below the speed of sound and subsequently accelerates to velocities higher than the speed of sound in the unreacted material is said to have undergone a Deflagration to Detonation Transition. The possibility of transition is enhanced by confinement/turbulence generators in the path of the reaction front. 

Figure 4.21. Pressure-volume paths used to relate the slope of Hugoniot (dP/dV) to isentropic sound speed G (4.57).

Conductive hearing loss Hearing loss that is caused by blockage or other interference in the path by which sound energy is transferred to the inner ear. 

After the average crude oil price increased from 3.18 per barrel in 1970 to 21.59 in 1980, many analysts forecast skyrocketing energy prices for the remainder of the centuiy. The middle price path of the U.S. Energy Information Administration in 1979 projected a nominal price of 117.50 per barrel in 1995 Such forecasts seemed to be soundly based not only in recent experience but also in the economic theoiy of exhaustible resources. As a consequence, U.S. industries invested heavily in energy conseiwa-tion measures, with the result that industrial consumption of energy decreased from 31.5 quads in 1973 to 27.2 in 1985. Some of this investment was probably not warranted on economic efficiency gi ounds because prices ceased to rise after 1981, and even plummeted to 10 per barrel in 1986. 

When air in a room is disturbed by a person speaking the molecules of the air have movements that are along the path of the wave. If you were to draw a line from the speaker s mouth to your ear, the movement of the molecules would be along this line. This type of wave, called an acoustical wave, is said to be longitudinal. The pleasant sounds of music are produced by acoustical waves. On the other hand, destruction by a bomb blast also is caused by acoustical waves. Instead of oscillating up and down, molecules in the acoustical (or compression) wave bunch together as the wave passes. It is not a transverse wave. 

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