IBM NeXtScale System Planning And Implementation Manual page 210

PSU Fan Speed tab
As shown in Figure 7-25, the PSU Fan speed tab shows the power supply fan
speeds and their healthy condition. PSU fan speed normally operates at 5,000 -
23,000 rpm and is considered faulty when the speed falls below 3,000 rpm.
Figure 7-25 PSU Fan speed information
Acoustic Mode tab
As shown in Figure 7-26, the Acoustic Mode is set in the Acoustic Mode tab and
is intended to reduce the noise of the IBM NeXtScale n1200 Enclosure. The
following acoustic levels (which are applied to the chassis as a whole) can be
selected:
None: no acoustic mode enabled
Mode 1: system fan speed is 28% (7.1 bels)
Mode 2: system fan speed is 34% (7.5 bels)
Mode 3: system fan speed is 40% (8.1 bels)
Note: These values might change in firmware releases at general availability
of the chassis.
Figure 7-26 Acoustic mode selection tab
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IBM NeXtScale System Planning and Implementation Guide