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Engineered noise controls for miner safety and environmental responsibility 237

(A)

80 81 82 83 84 84 85 86 87 88
(B) (C)

73 74 75 76 77 75 76 77 78 79
(D) (E)

Fig. 12.21 Dominant noise sources at the tail section area (red box in (A)) covered by acoustic
maps at: (B) 500Hz, (C) 1000Hz, (D) 1600Hz, and (E) 2500Hz.

Overhead measurements revealed dominant noise sources located at the tail section
of the CMM—more specifically in the vicinity of the tail roller. Examination of
the acoustic maps suggests three different noise mechanisms: [1] chain-tail roller
interaction [2], flight tip-flexplate interaction, and [3] flight-upper deck interaction.
Fig. 12.21 shows these sources at four different frequencies. These noise sources were
previously suspected but not confirmed. It can be seen that not only do chain links
impacting the tail roller (TR) generate noise at the tail section, but that impacts from
flight tips on side boards and impacts from chain flights on the upper deck are also
significant noise radiators. Given this scenario, an effective noise control should atten-
uate noise generated in these locations.
Secondary sources were identified at the front end of the left flexplate guide at
1600Hz and 2000Hz as shown in Fig. 12.22. Flexplates provide confinement for