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The Silence of the Fans

“When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence.”
    Ansel Adams

Off-topic alert: This article is outside the bounds of my usual writing on photography and related travel/photo locations, subjects, technologies, and similar topics. Next month I'll return to more familiar territory.

In my December, 2019 article I wrote about replacing an ancient Mac Pro with a tiny new Mac Mini. I described the peripheral boxes and cables necessary to give the Mini a port count and storage capacity and flexibility to which I'd become accustomed with the old, user-expandable tower Mac. The Mini is not user-expandable, so any extra stufff one might want to add must be via external chunks of hardware.

One of those external boxes is an Oyen Digital Mobius Pro 2-bay RAID System (link active as I write this in February, 2020). As the name indicates, the Mobius has two bays to hold 3.5 inch hard drives. These can be configured as RAID 0 or RAID 1, which combines drives in different ways, or as independent separate drives, the mode I chose. I started with a 500Gb solid state drive (SSD) in the top bay (via a 3.5-inch adapter bracket), and a 1Tb spinning-platter hard disk drive (HD) in the bottom. I've since changed both of those drives; more on that later.

The Mobius is small, nice-looking (although mine's located out of sight), and as I'd learn later, very well-made.

(Un)Truth in Advertising

If you look at the specifications on the Oyen page linked above, you'll see this bullet point:

Like much of what our 45th president tweets, Oyen makes the “quiet fan” statement without evidence. The truth is that the fan in the Mobius is so freaking loud I can't concentrate on my work when the fan is running, which is most of the time. When it starts up it's like a physical slap. Perhaps “quiet” is relative, but you'd have to be a hundred feet (30 m) away from the thing to not hear it. Seriously.

I work in silence or listen to music when seated at my monitor. I've a decent hi-fi system with a nice pair of speakers in my work area, but the roar of the Mobius made listening impossible. I found myself using my headphones, which helped quiet the fan's gale, but also muted things like my wife calling down from upstairs or the telephone (in order of importance, of course). I like the old Sennheisers, but they aren't always the best solution. Something had to be done about that damned fan.

How To Void a Warranty

1 / 4
The Mobius Pro 2C chassis base after removal of the case, fan, and front panel. The power supply is to the left of the motherboard. The cable at bottom connects to the front panel (not shown).
2 / 4
The Mobius 'exploaded:' the main chassis is at center, the other sheet metal parts at far left and right. The power supply is under the black insulating cover, the motherboard to the right. The (new) fan and front panel complete the picture.
3 / 4
Beginning reassembly: my speed control board, with the DIP switch on the back, is next to the fan.
4 / 4
The rear panel of the Mobius, showing my crude cut-out for switch access, and the 'truth table' defining the fan voltages for the four possible switch settings.

As mentioned in other articles, I'm an compulsive tinkerer, rarely averse to taking things apart to see how they work (or why they don't). I'd either have to return the Mobius or find a way to silence it. A quick inspection showed the case would be easy enough to remove. The Mobius had to come apart.

The case, of course, was just the beginning, starting with the simple removal of the first six of what would become, an hour later, a pile of over 30 small screws. The first task was to gain access to the fan so it could be measured. As always O'Toole's Corollary rules; the fan appeared to be the very first component placed in the Mobius's chassis, with all remaining parts installed around and in the way of it. I had to completely disassemble the box, keeping track of the aforementioned 30+ screws and a growing stack of sheet metal parts. The four pictures here tell the story.

After measuring the OEM fan I ordered a Gelid Solutions Silent Series Case Fan. As usual I did my research before buying, and concluded this would be as quiet as any other 70mm fan. The company's advertising says it is “Designed for Silent enthusiasts” (who knew that's a thing?) and its “precisely balanced fan blades and long life Hydro Dynamic bearing guarantee ultra low noise.” A longer-life bearing than the OEM fan's would be fine. The rest turned out to be politician-level BS.

I had to remove the OEM fan's two-wire connector and solder it to the new fan, ignoring the new fan's speed-control third wire. Not a problem, as the Oyen's motherboard doesn't support speed control—the fan's either on or off. With the new fan in place and connected I reassembled the box, connected the external cables, and fired it up. And discovered it's at least as loud as the OEM fan, if not perhaps a bit worse. But at least I had to work for it.

Levels of Crazy: Obsession Driven by Compulsion Driven by Noise Sensitivity

Speaking from experience I know that crazy people are rarely deterred from their goals. I lived with the noise for a couple of weeks. As I knew it would, the annoyance factor grew every day until I simply had to do something about it. The fan is small, has lots of blades, and rotates at a high speed, a perfect recipe for loud. Larger fans with fewer blades and slower speeds can be quieter. But I could do nothing about the size, and none of the fans I found when researching had a significantly lower decibel (sound level) rating. But I could reduce the fan speed by lowering the voltage from the nominal 12 volts supplied by the Mobius's motherboard. The easy way to do that would be to place a resistor in the fan's power wire. A little math applied as directed by Georg Ohm (Ohm's Law) showed that to reduce the fan's voltage to 8 volts at the fan's rated current I'd need a 27 ohm resistor rated for a little under one watt. In my electronics junk box I had a 33-ohm 1-watt resistor; it'd slow the fan a bit more, but also generate some heat; not an ideal solution.

The Oyen Mobius Pro 2C reassembled

The Oyen Mobius Pro 2C, proving that it really did go back together.

Never make two solder joints when you can make several dozen (solder is my favorite programming language). A typical diode has a forward voltage drop of .8 volts. My junk box contained a handful of old 1N4001 diodes and several small switches (known as DIP, or dual-inline-package switches). Six diodes would drop the voltage by 4.8 volts, and the diodes are rated at 1 amp, several times more than necessary. With only those parts I could make a little circuit board that would allow me to vary the fan speed based on switch settings. I'd have to drill some holes in the rear case of the Mobius, adding to the fun.

Short version: I built the circuit on a little piece of prototyping board (again, from the junk box), tested it with a bench power supply and the new fan, laid out the hole pattern and did the drilling of the Mobius chassis, and installed it. See the series of photos above for the breakdown. I will be monitoring the case temperature of the Mobius in case my slowing of the fan lowers airflow to the point where it's not adequately cooling the box's little power supply. I've replaced the two drives mentioned above with a pair of 1Tb SSDs, which draw much less current and generate less heat than the spinning HD I'd used earlier. This will lower the load (and the heat) on the power supply. And unlike the spinning HD, the SSDs are silent. So far all's well, although the fan runs almost continuously now.

Crazy? No doubt. Would I buy another Oyen drive box? Tough question. I'm impressed by the quality of the design and construction. It does exactly what it's supposed to do, although I can't address its RAID capabilities since I'm not using them. I think I'd look for a fanless design, if those exist. I have a NAS (network-attached storage) RAID system located in another room, making the noise from its fan and four spinning HDs a non-issue, but networked storage is much slower than the SSDs in a box connected to USB 3.1 Gen 2 port (10Gbps) on the Mac, that speed being the point of getting the Oyen in the first place.

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I'm now once again enjoying the quiet (or music) of my photographic work time without the auditory abuse of the Oyen, and it only took about 20 hours of design and assembly work to get there.

February, 2020

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