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Process Engineering Equipment Handbook Episode 1 Part 2

Tham khảo tài liệu 'process engineering equipment handbook episode 1 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Acoustic Enclosures Turbine A-33 FIG. A-23 Predicted performance of flat and corrugated panels. Source Altair Filters International Limited. TABLE A-9 Predicted Sound Reduction Indices for Flat Corrugated Panels Panel Thickness of 2.5 mm Sound Reduction Index dB 63 125 250 500 1000 2000 4000 8000 Flat panel Corrugated panel 15 21 27 33 39 42 33 41 15 18 21 24 28 32 37 38 The attenuation of sound by absorptive linings Sound-absorbent linings are frequently fitted in acoustic enclosures to reduce the buildup of reverberant noise inside the enclosure. Typical reductions in the reverberant noise level may be between 3 and 10 dB depending on the application. An additional benefit is the increase in transmission loss of the enclosure panel which further reduces the noise level outside the enclosure. The increase in panel transmission loss arises because of several mechanisms. First if the absorbent lining is sufficiently heavy and the panel is relatively thin then the added layer may give sufficient additional weight to affect the mass-law performance and increase the damping of the panel. At high frequencies the absorbent may be relatively thick in comparison to the wavelength of the sound. The high-frequency sound may be attenuated not only because of the impedance mismatch between the air and the absorbent but as the sound wave passes through the added layer a significant amount of acoustic energy is converted into heat by viscous losses in the interstices. In practice the amount of heat generated is minute. It is possible to distinguish between three frequency regions in which different attenuating mechanisms are predominant. For convenience these are described as A-34 Acoustic Enclosures Turbine TABLE A-10 Comparison of Predicted and Measured Sound Reduction Indices of Three Lined Panels Measured or Predicted Sound Reduction Index dB 63 125 250 500 1000 2000 4000 8000 Panel 1 flat Predicted 14 22 31 39 48 47 65 63 Measured 20 21 27 38 48 58 67 66 Panel 2 flat .