Sound attenuation

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. 

It can easily be shown that an experimentally generated curve coincides with the synthetically generated DGS curve having applicable corrections (transfer loss and sound attenuation) with acceptable tolerances. However, our intention is not to replace the reference block method by the DGS method. In practical application you may encounter many cases, where only the reference block method can be applied, e.g. ... 

Since any DAC is defined by its coordinates P (Ai,S ) and the instrument sensitivity Gg f (reference gain) during DAC recording, any recalculation of the curve including the consideration of individual corrections (transfer loss, sound attenuation, etc.) is an easy task for modern PC based flaw detectors and does no longer burden the operator. 

Transfer loss, sound attenuation and other corrections may easily be considered and will again recalculate the curve, respectively. 

I oise Transmission Reduction in HVACSystems. One common use of sound-absorbing treatment is to reduce noise transmission in heating, ventilating, and air-conditioning (HVAC) systems (6). The treatments ate used to reduce the transmission of fan noise and air turbulence noise through ducts into occupied spaces. Noise transmission reduction in duct systems is described in terms of insertion loss, the difference in sound power level or sound pressure level measured at a given location before and after installation of the treatment or sound attenuation, the reduction in sound power between two locations affected by a sound source. The units ate decibels. 

The gas system did not inelude any storage other than pipeline paek and one relatively small high-pressure pipe-type holder. Therefore, pressures and flows in all areas of the system varied widely on a daily and seasonal basis. Several years of operating data were reviewed and analyzed to seleet a loeation that met the flow and pressure drop requirements for installation of an expander. Site seleetion also gave eonsideration to the requirements for eonneetion to the gas system, eonneetion to the eleetrie system, and sound attenuation measures neeessary to eliminate any impaet on the surrounding area. 

When the unit was initially plaeed in serviee, sound level measurement data were eolleeted. Within 3 ft of the expander ease, sound levels were measured at 92-99 dBA. At the property line 25 ft away from the ease, the levels were 68-85 dBA. At the time of installation, there were no stmetures near enough to the faeility to be impaeted by any noise. However, as the surrounding area eontinues to develop, it may be neeessary to install sound attenuation equipment. 

The installed eost is primarily determined by the size of the unit. However, other faetors may have a signifieant impaet on this eost. The eonneetion to the gas system eould be expensive if speeial hot tap fittings are required. If sound attenuation is neeessary for the ehosen loeation, this ean also have an impaet on the overall eost. The eonneetion to the eleetrieal system ean add signifieant eost if distanees are far or high-voltage switehgear is neeessary. Equipment manufaeturers are able to provide eost estimates for major equipment. The installation eosts are site speeifie and require individual studies and estimates. 

Figure 7-6. An integral geared compressor driven by a motor with an open drip-proof enclosure. The enclosure also includes 85dba sound attenuation. Courtesy of Elliott Company ...

Air terminals and functional factors affecting the air handling systems Some basic principles are presented in Chapter 8. However, more attention has to be paid to minimizing the leakages and to sound attenuation. 

Air terminal unit assembly The air terminal unit, consisting of casing, mixing section, flow control, heating, cooling, filters, fans, sound attenuators, etc. 

Since the Lindemann ratio dija 0.1 is empirically roughly the same for all substances, one expects the g value, as measured by sound attenuation, to be correlated with the glass transition temperature. Note that this relationship is independent of the details of the bead assignment. Equation (20), if rewritten as Tg di/a) g, is almost obvious, given the interaction of the form in Eq. (17) The typical lattice displacement, at Tg, is roughly A< ) j- dija. On the other hand, the typical structural excitations have the energy of about Tg, at the glass transition. 

Spontaneous locomotor activity (SLA) was measured in photocell activity cages isolated in light- and sound-attenuated boxes. 

Distance is a major factor in reducing nuisance noise and suitable spacing should be considered in the plant initial layout. The acceptable amount of noise generation should be specified on the purchase order for the equipment. Where sound levels cannot be alleviated by purchasing a different make of equipment, sound attenuation devices should be fitted (i.e., enclosures) as an alternative. 

In the preceeding section mention was made of ion association (ion-pairing) which, for the purposes of this paper, will refer to coulombic entities with or without cosphere overlap. Experimental support for ion-pairing has come from sound attenuation (2). Raman spectroscopy (2) and potentiometry (2, 2). Credibility has resulted from the model of Fuoss (2) applied by Kester and Pytkowicz (2). 

Sound attenuators should not be used in systems requiring sanitizing because the perforated face (interior) of the sound traps can collect dust and microorganisms. 

Sound attenuators are not used in systems requiring periodic sanitizing. 

Figure i. Records taken from a cat chronically prepared with electrodes to record the eye movements (EOG), the electroencephalogram from both sides of the skull (EEG), and the activity of the neck muscles (NMG). The animal was kept in an air-conditioned, sound-attenuated room supplied with a oneway mirror for observation. The records were taken while the animal was awake and active (top left), awake and resting (top right—note alpha waves), just dropped off to sleep (middle left —note "spindles"), in deeper sleep (middle right—note slow waves in EEG) in still sounder sleep (bottom left—note very slow waves), and in paradoxical sleep (bottom right—arousal pattern in EEG). (Note eye movements in awake animal and in paradoxical sleep). Note also reduced electrical muscle activity in paradoxical sleep. Calibrations vertical line at top middle = 100 microvolts (or o.oooi volt), horizontal line = l second. Original from author s laboratory. 

Another limitation on acoustic properties is expressed by the Kramers-Kronig (KK) relations, which are general relations between the real and imaginary parts of a complex function. These relations were originally derived for optics but can be applied in many other areas as well. The essence of the relations is that the real and imaginary parts of the function are not independent of each other but one may be calculated from an integral of the other. As applied to complex modulus, the specific form of the relations is given elsewhere in this book (J. Jarzynski, A Review of the Mechanisms of Sound Attenuation in Materials). 

Sound attenuation is defined as the decrease in intensity of the sound signal as it propagates from the source to the receiver. This definition does not, however, include the change in intensity due to geometrical spreading of the sound wave (such as, for example, the spherical spreading of the sound in the far field of a finite... 

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