In the previous issue, I mentioned my gear rack that’s the control-room equivalent of a kitchen island. I wanted active cooling for the rack, but routing an air-conditioner duct to that location was impossible, so I opted for the simpler solution of utilizing vent panels as intakes with exhaust fans in the three upper rear sections of the island to pull out hot air. Scott McChane wrote a favorable review of an AC Infinity USB fan [Tape Op #129], so I purchased an AC Infinity CLOUDPLATE T7 rackmount cooler <acinfinity.com> for $139 from Amazon after reading many five-star reviews. Its anodized-aluminum chassis holds four 80 mm muffin fans and a programmable thermostatic controller for managing fan speed. It looks beautiful in my rack, and its build quality is top notch; internal components are precisely mounted with well-placed fasteners, and the wiring inside is neatly tucked away. Why do I know this? Because I took it apart to replace its fans. Even when running at their lowest speed, I could hear them whirring while I was downstairs in my kitchen. (My control room is directly above my kitchen via an open staircase – an intentional layout decision that’s a story for another day.) For replacements, I purchased be quiet! Pure Wings 2 (BL044) fans <bequiet.com> for $11 each, because of their impressive performance in my DIY computer builds. These Pure Wings fans have an SPL noise rating of 18.2 dBA. I also bought a set of Coolerguys CG08025L12B2-3Y fans <coolerguys.com> for $7 each, and these are rated even quieter at 17 dBA. Unfortunately, a single SPL rating isn’t as meaningful as an analysis of spectral energy. Therefore, I measured SPL across the frequency spectrum, running these fans at their maximum speed as well as at various lower RPMs (using a PWM [pulse width modulation] controller). In summary, the AC Infinity fan is 0 to 5 dB higher in SPL than the other two fans up to their half-RPM frequencies, and 10 to 20 dB higher at frequencies above that. Meanwhile, the Coolerguys fan is roughly 3 dB lower in SPL than the Pure Wings fan across most of the spectrum. But the Pure Wings fan is much quieter to my ears. Why? Because each of these fans has a mechanical resonance peak that corresponds in frequency to half its rotational speed, and that resonance is way more noticeable to the ear than the fan’s “white noise.” I consistently measured the half-RPM resonance of the Coolerguys fan to be 3 to 5 dB louder than the Pure Wings’ resonance. Additionally, the Coolerguys fan had harmonic resonances that were significantly greater in number and amplitude. Moreover, when two or more fans with audible resonance peaks are spinning at slightly different speeds, “beating frequencies” will stand out even more than the individual resonances. Long story short – if you buy an AC Infinity rackmount cooler because you appreciate its aesthetic design, you should replace its annoyingly loud fans with truly quiet Pure Wings 2 fans. Unfortunately, AC Infinity terminates its neatly tucked fan cables with JST XH connectors instead of the standard Molex KK 254 series connectors, so I just cut away the shrouds of the JST headers on the AC Infinity controller board and hot-glued the Pure Wings’ Molex connectors down. Too much effort? I also purchased a Procool SP480XT-E rackmount fan <rackfans.com> for $200. It has four 80 mm fans that are managed by a central controller in conjunction with individual thermistors on each fan. Unlike the stock AC Infinity, my Procool is near silent without mods – although it doesn’t look as cool. If $200 seems too high, you can buy all its components for $110 from Coolerguys (including the Procool-branded thermistor fans). I did this too, and assembly took less than half an hour.
-AH