Sound amplitude

The use of acoustic resonances for increasing sound amplitude from an OA cell was first described by A. G. Bell, Phil. Mag., 11, 510 (1881). Recent experiments with resonant OA cells are described by C. F. Dewey, Jr., R. D. Kamm, and C. E. Hackett, Appl. Phys. Lett. 23, 633 (1973). 

The absorption is commonly recorded as the difference in the logarithms of the sound amplitudes at two points a wavelength apart. The absorption per wavelength turns out to be... 

It should be mentioned that the data of Chynoweth and Schneider have been taken in Fig. 8 to measure the attenuation of the sound amplitude rather than the sound intensity. The theory of their experimental method is extremely intricate, and the authors were not able to apply it fully. However, the simplest interpretation of their method makes their numbers refer to intensity attenuation, and the values of a in Fig. 8 should be halved. The optimum parameters are then I = 5 A, /S = 3.4 X 10 sec i. 

Amplitude Modulation (AM). With AM radio, the amphtude (height) of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone. The transmitted frequency remains constant. AM transmission is degraded by static and interference because sources of electromagnetic transmission such as lightning and automobile ignitions, which are at the same frequency, add their amplitudes to that of the transmitted signal. AM radio stations in the United States and Canada are limited to 50 kilowatts (kW). Early twentieth century, U.S. stations had powers up to 500 kW, some of which could be heard worldwide. 

Fig. 3 First laser-induced sound waveforms of various tissues. The samples exhibit different sound amplitudes and waveforms...

Schuchmann, H.P.,andTavman, S. (2008) Influence of hydrostatic pressure and sound amplitude on the ultrasoimd induced dispersion and de-agglomeration of nanoparticles. Ultrasonics Sonochemistry,... 

Some of the problems often encountered during ultrasonic inspection of plane specimens are also found on cylindrical specimens. For example, problems associated with the directional characteristic of the ultrasonic transducer. Furthermore, the discontinuity influences the shape and propagation direction of a reflected pulse, causing wave mode transformation. In addition, the specimen influences the shape and amplitude of the reflected pulse by sound absorption. 

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. 

DAC DAC (distance amplitude control) up to 40 dB optimized for material with high sound damping 0.1 to 20 MHz (-3 dB)... 

During the attenuation measurements. Transducer 1 was excited with a narrowband tone burst with center frequency 18 MHz, see Figure 1 for a schematic setup. The amplitude of the sound pressure was measured at Tranducer 2 by means of an amplitude peak detector. A reference amplitude, Are/, was measured outside the object as shown at the right hand side of Figure 1. The object was scanned in the j y-plane and for every position, (x, y), the attenuation, a x, y), was calculated as the quotient (in db) between the amplitude at Transducer 2, A[x, y), and Are/, i.e., a(x,y) = lOlogm Pulse echo measurements and preprocessing... 

The previous subsection described single-experiment perturbations by J-jumps or P-jumps. By contrast, sound and ultrasound may be used to induce small periodic perturbations of an equilibrium system that are equivalent to periodic pressure and temperature changes. A temperature amplitude 0.002 K and a pressure amplitude 5 P ss 30 mbar are typical in experiments with high-frequency ultrasound. Fignre B2.5.4 illustrates the situation for different rates of chemical relaxation with the angular frequency of the sound wave... 

For sufficiently long times (index n ), the exponential can be neglected, leaving an oscillation of the turnover variable phase shifted with respect to the sound wave and with its amplitude reduced by the finite relaxation... 

Noise Control Sound is a fluctuation of air pressure that can be detected by the human ear. Sound travels through any fluid (e.g., the air) as a compression/expansion wave. This wave travels radially outward in all directions from the sound source. The pressure wave induces an oscillating motion in the transmitting medium that is superimposed on any other net motion it may have. These waves are reflec ted, refracted, scattered, and absorbed as they encounter solid objects. Sound is transmitted through sohds in a complex array of types of elastic waves. Sound is charac terized by its amplitude, frequency, phase, and direction of propagation. 

For airborne sound, the reference pressure is 2 X 10" Pa (29 X psi), which is nominally the human threshold of hearing at 1000 Hz. The corresponding sound pressure level is 0 dB. Conversation is about 50 dB, ana a Jackhammer operator is subject to 100 dB. Extreme levels such as a jet engine at takeoff might produce 140 dB at a distance of 3 m, which is a pressure amplitude oi 200 Pa (29 X 10" psi). These examples demonstrate both the sensitivity and wide dynamic range of the human ear. 

McQueen et al. (1982) demonstrated that by placing a series of high-impedance transparent fluids (called optical analyzers) over the sample at a series of thicknesses less than d in the target that the overtaking rarefaction (sound) velocity can be accurately obtained. Arrival of rarefaction waves rapidly reduce the shock pressure. These wave arrivals could be very readily detected by the change in light radiance caused by the onset of a decrease in shock amplitude when the rarefaction wave caught up to the shock front. The... 

When the elastic shock-front speed U departs significantly from longitudinal elastic sound speed c, immediately behind the elastic shock front, the decaying elastic wave amplitude is governed by (Appendix)... 

Hugoniot. At low-stress amplitudes pot /o C S c,o, where c,o is the adiabatic longitudinal elastic sound speed at p = pg. 

If we accept the assumption that the elastic wave can be treated to good aproximation as a mathematical discontinuity, then the stress decay at the elastic wave front is given by (A. 15) and (A. 16) in terms of the material-dependent and amplitude-dependent wave speeds c, (the isentropic longitudinal elastic sound speed), U (the finite-amplitude elastic shock velocity), and Cfi [(A.9)]. In general, all three wave velocities are different. We know, for example, that... 

EiTatic high-frequency vibration amplitude and possibly an audible sound. Rotor mb Labyrinth mbs generally self-comect Disc mbs due to thrust bearing failure often self-comect temporarily through wean steel on steel shrill noise during wear Rotor deflection is critical speed... 

If sound vibrations are applied to an electrode being in contact with a solution, a variable electrode potential component AE is generated. Its amplitude depends on the electrode potential E. It shows a maximum at the Epzc Further details have been provided elsewhere [66Kuk2]. (Data obtained with this method are labelled AE). 

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