Quiet MP Dual-CPU Workstation

Do-It-Yourself Systems
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PAUSE: Materials Analysis

In all the previous versions of HDD silencers, I kept running into 2 issues:

1) sound leaks through wherever there is no sound barrier, and

2) sound leaks though the sound barrier itself.

Issue 1) could be easily observed with a close ear-listening test. I decided to test issue 2) using my alarm clock radio as a noise source. Just by simply placing the different materials over top the speaker, I could get an idea of how well each blocked the sound.

In addition to the materials used in the previous attempts, I also included a high-performance acoustic ceiling tile (as mentioned by Melchior on the SPCR Forums) and block print carving rubber (inspired by the ideas on http://www.geocities.jp/numano3).

This is what I found when I measured from 5" above my radio speaker. It was tuned in to an unused AM radio band that contained a lot of broadband noise, essentially a type of pink or white noise.

Sound level (dBA)
Noise Reduction (dBA)
None (reference)
1" camera foam
1" rebond foam
1/2" EVA closed-cell foam
3/4" acoustic ceiling tile (NRC: 0.85)
3/8" block print carving rubber

The block print carving rubber for artists was by far the best. So, I decided to build V5 from the rubber. It can be found at good art supply stores. It is the same material I used to make the rubber noise reduction gasket for the door that closes over the CD drives.

VERSION 5: 3/8" Rubber Enclosure, foam feet decouplers. Best acoustic performance so far, just-bearable thermal performance

One rubber enclosure was built for each of the two drives. Each box measures 4.75 x 1.75 x 7 inches. The pieces were cut up with a utility knife and super-glued together. A cover allows the IDE cables and power wires to be fitted snugly for minimal noise escape. The boxes are sized so that the drive fits tightly, ensuring maximum heat transfer by direct conduction. Before the drives were inserted, I applied thermal grease liberally on the top, sides and front surfaces of the drive. The boxes were placed one on top of the other at the bottom front of the case on a bed of foam to decouple them from the case. The cost of each box was approximately US$10.

Here are the results:

V4: 3/8" rubber enclosure
Front of case (0.5" from case at HDD height)
Hard drives (inside case between 2 hard drives)
Exhaust fans (outside case, corner closest to fans)
CPU fans (between sides of 2 cpu fans)
CPU 0/CPU 1 (with BurnK7)
66 / 61
+15 / +13
+1 / +3
40GB/80GB HD (Dtemp)
55 / 55
+17 / +21
+10 / +6

*ChangeB = Change from Baseline; ChangeP = Change from Previous

The dBA readings really are not very useful; they fell below the scale of the sound level meter, the bottom limit of which is 50 dBA. There is no question this is the best HDD silencer so far. The 20 dBA measured reduction from the hard drives seem consistent with the noise reduction from the alarm clock radio test. The rubber seems to conduct some heat away from the hard drives too because they perform comparably to the sidesinked, foam-sandwiched hard drives.

The noise of the HDD was greatly reduced, and high pitch whine was mostly eliminated. I could live with this.

With this rubber box mod, the PC became the quietest noise producer in my space - quieter than the forced-air heating, quieter than the refridgerator in the next room. Although much hotter than before - between 13C - 21C hotter - the components were still within maximum temperature specs. But the borderline high temperature of the Maxtor hard drives worried me.

Back to the drawing board.

VERSION 5A: Add sidesink and front fan to V5.

Again, the sidesinks are based on the SPCR article Effective Passive Hard Drive Cooling. Several small holes were drilled through the rubber to expose the mounting holes on one side of each of the drives. Metal grommets and bolts were used to tightly secure the aluminum u-channel pieces, with heatsink grease at the interface. Between the hard drive and the inside of the rubber enclosures, I also put a generous amount of heatsink grease. A 6V Panaflo at the front of the case is blowing onto it.

  • Old Temps: peak at 60C / 60C (for deach drive, vertical position)
  • New Temps: peak at 39C / 42C

Although the drives are much cooler, perfectly safe, in fact, the noise went up substantially. There was considerably more whine than before. Perhaps the aluminum channels were transferring the vibrations out or the small gaps were allowing the high pitched sound to escape more. I needed to quiet them down more again.So...

VERSION 5B: Remove sidesinks from drives, leave Panaflo fan

The side HS were removed and the holes in the rubber boxes plugged up tightly with foam. The noise level returned to what I had achieved with VERSION 5, the rubber boxes alone, because the extra Panaflo fan at 6V is pretty much inaduible.

  • My new max HDD temps are now 44C and 45C!

This is a good stop on the HDD silencing road for me, at least for now. (Editor's Note: With the amount of time, money(?) and energy put into HDD silencing, we know Leo could have got quiet Barracuda drives and transferred the data without any problems. But he wouldn't have had nearly as much fun, and we would not have a new quieting solution for loud hard drives.)


Yet another Mod: Better Fan Control with Diodes

The 6V supplied to the HDD fan above comes from a a circuit I built using diodes and a 6-way rotary switch (see schematic). The circuit is similar to the Diobus at http://www.cpemma.co.uk/sdiodes.html, but rather than soldering diodes directly to the rotary switch, I created mine on a circuit board. This allowed me to more easily solder extra headers to connect my heatsink and case fans.

I used diodes becaused they are a good way to control voltage. The voltage drop of a single 1N4001 diode is fairly constant at about 0.75 volts and only increases slightly with high current draw (eg: 1 amp). This allowed me to control the voltage in fairly small and predictable increments. Diodes also do not require heatsinks because they give off little heat (1 watt for a 1 amp load).

I wired 4 diodes in front of the rotary switch to give me 9 volts at the first step. I added a diode at each step to give me voltages all the way down to 5.25 volts. My fans are normally at 6 volts, but my machine is stable down to 5.25 volts.


Conclusions and Future Mods?

Living with a quieter computer has been very rewarding. It's now subjectively the quietest noise producer in my space - quieter than the forced-air heating, quieter than the refridgerator in the next room. It's even beginning to act like a half-decent HTPC. Although much hotter than before -- between 13C - 21C hotter -- the components are still safely below maximum specified temperatures.

Because of the progress I've achieved with my computer, some new components are becoming the greatest noise producers, while other previously quieted components are becoming "noisy" again. Like other SPCR forum members, I'm getting annoyed by the buzzing of my monitor. Also, my newly undervolted fans are now audible. And the PSU fan, even though it is a quiet fan running at 10.5V, calls for still more noise reduction.

I know it is a subjective thing but it is very real: my hearing sensitivity seems to go up with every step closer to silence. Sigh... A single CPU system or one with quieter drives would have been easier to deal with, but after getting used to the power of my dual MPs, there is no going back.

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Discuss this article in the SPCR Forums.

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