Doug's Quiet Wood Case PC

Do-It-Yourself Systems
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THE RESULTS

Yes, you say, it looks very nice. But how well does it work?

Upon firing it up the first time, I immediately noticed that I hadn't been successful in eliminating resonance. The case was emitting quite a noticeable hum. A little experimentation (consisting of pressing my ear against the case and stopping the CPU fan with my finger) showed the vibrations were coming from the CPU fan. This wasn't terribly surprising, since it wasn't isolated from the case. There had been no good way to mount the motherboard tray besides screwing it in solidly. So, I pulled the Arctic Cooling fan off the heatsink, and replaced it with a Panaflo 80L held on with elastic cords and isolated from the heatsink with foam standoffs.


CPU HS fan mechanically decoupled with foam and elastic cord.

As an aside, the little black cube seen at the bottom left between the CPU and the two small heatsinks is the source of the motherboard's hissing. I imagine it's an induction coil of some sort involved in powering the CPU. In any event, decoupling the CPU fan improved the resonance issue immediately.

Somewhat oddly, the Panaflo was keeping the CPU substantially cooler than the Arctic Cooling fan had been. I say oddly because the Panaflo's rated airflow is lower than that of the stock fan. I've concluded that the difference was likely due to a combination of a better thermal interface (i.e., the right amount of thermal goop) and washing the dust off the heatsink while I had it off. In any event, I was able to undervolt both the Panaflo and the Nexus. Since I didn't have my fan switch finished, I used the 7V difference trick on both fans, and recorded some temperatures. Case temperature was taken by means of placing a thermometer inside near the top. I think it shows a little high, since it always says my apartment is 24-25 degrees but it never feels that warm, but anyway. System temperature is that reported by the motherboard. I have no idea where that probe is.

Wood Case System Temps in °C
Activity
Case
System
CPU
Idle
29
38
47
CPUBurn
31
42
55
Ambient temp was 24°C

As you can see, the temps are quite acceptable. I tried dropping the Panaflo 80L to 5V, which resulted in CPU temps of 52°C idle and 64°C under load, but since I couldn't hear the fan at either speed, I moved it back up to 7V.

NOISE

With the exhaust and CPU fans at 7V, the new case is dramatically quieter than the old case. From my chair, the fans are essentially inaudible, and I can only just make out the chatter of HDD seeks and the motherboard hiss when I load the CPU. In the old case, simple flash banner ads would be enough to drive me bonkers, as they'd load the CPU enough to induce the dreaded hissing. Ironically, this used to mean that I'd rarely keep the SPCR front page open since a few of the frequent advertisers love their flash. Now it's just not an issue. The case appears to work exactly as intended. It's virtually inaudible from the sides and front. If you stick your ear right down at the bottom, you can just make out a bit of sound leaking through the intake ports. There is a fair bit of sound coming off the back of the case, though. The motherboard (when it's hissing) and the hard drive are predominant, but the gentle whirring of the Nexus can also be heard. This sound can be heard from my chair, as it tends to bounce off the walls and come back to me.

But enough of these subjective descriptions, let's see some objective data. My employer was kind enough to allow me to borrow his SPL meter, a B&K 2237. Unfortunately (or fortunately, depending on how you look at it), it wasn't sufficiently sensitive to register a reading at the standard 1m distance, having a minimum sensitivity of 30 dBA. So, we'll have to do some extrapolation of the data I did manage to gather.

The difference between idle and load is strictly the addition of the motherboard hiss. The fans were turning at a constant rate the whole time. I couldn't get a reading until I was right up against the case, except for at the back or with the side door open. I couldn't get any reading from the front at all.

A weighted SPL Readings w/ 30 dBA limit Sound Level Meter
Position
Distance
Idle
Load
Front
Any
n/a
n/a
Side
0.01 m
31
32
Rear
1 m
n/a
30
0.5 m
31
35
0.01 m
40
44
Side Open
1 m
33
37
0.5 m
36
42
0.01 m
46
52

There's a fair bit of guesswork involved in estimating what the SPL at 1m at the front and sides might be. We could just duplicate the difference between the 1m and 0.01m readings seen in the rear and open measurements, but this is problematic in that the close up readings were highly variable depending on where precisely the meter was held. Still, a difference of around 10 dBA seems reasonable, which would put the 1m figure at ~21 dBA for the side and a couple dBA lower for the front. I think that this is quite remarkable, since as the readings with the open side show, that WD hard drive is a noisy little thing, and yet it simply can't be heard most of the time. [Editor's Note: Any measurement device used at the limit of its capability is usually subject to higher than normal error. This SLM was definitely at the limits trying to read below, say, 33 dBA.]

I tried readings on a few noteworthy variations. Removing the absorbing panel from the side door resulted in levels 1-2 dBA higher all around. The subjective difference is rather greater than this, and I'm sure a graph showing sound level by frequency would show a much greater difference in high frequencies.

Spinning the fans up to 12V results in a substantial hum, substantial enough that readings at 1m became possible: 31 dBA front, 33 dBA side, and 35 dBA rear. This is due to the fact that the right side door begins resonating as the Nexus is brought near to full speed. I had thought my foam block/elastic strap mounting technique provided good isolation, but apparently it doesn't, since the resonance drops off if the fan is pulled away from the foam. Since my temperatures are fine with the fans spinning slower, this isn't much of an issue, but it's clearly something I'll have to deal with if I should ever need a lot more airflow for some upgraded components in the future.

COSTS

Parts
Cost in CA$
1x12 (10')
$29.82
1x8 (12')
$15.84
1x4 (12')
$8.64
Hinges
$11.94
Catches
$8.45
Other hardware
$3.24
Switches
$11.99
Felt, elastic
$3.99
Abrasives
$15.14
Total
$109.05
W/Taxes
$124.32

The total includes a set of sanding drums for use with a drill that are nowhere near used up, and some sandpaper I didn't use. However, that's counterbalanced by the fact that I didn't have to buy screws or any finish, as I had both left over from previous projects. If the switch category looks a bit high, it's because two thirds of it is for the rotary switch and diodes for my rudimentary fan control.

  • Time spent: ~30 hours
  • Dimensions: 21"(H) x 11"(W) x 20.75"(D). For comparison, an SLK3700 is 18.3"(H) x 8.25"(W) x 18.6"(D)

CONCLUSIONS

My computer is now below ambient noise levels most of the time. Most of what little sound it was producing I wiped out by propping that acoustic panel I promised to tell you about behind the case. It's far enough back to allow the exhaust to escape freely, but absorbs the great majority of sound coming through the rear ports.

During the design process, I encountered all kinds of worries about building a case from wood. Questions about EMI/RFI, resonance, and cooling came up. Incidentally, some playing with an AM radio demonstrates that the computer is indeed radiating some RF noise, but my LCD monitor generates more. I tried sticking my cordless phone and my cell both right next to the case, but didn't get any static on either. I consider that case closed. Cooling, as I think those who frequent SPCR know, isn't really dependent on case material. As the debunking of the aluminum case cooling myth shows, what matters for cooling is airflow, and this case has very adequate airflow.

The resonance of wood is an issue, but it's manageable. Even with fans and hard drives decoupled from the case, some resonant frequencies can be amplified. I have not found it difficult to work around that so far, though, and the advantages of wood in sound blocking relative to sheetmetal more than compensate. This last is important, as it has allowed me to effectively silence my machine even though it still contains a couple of loud components.

Would I do anything differently if I had it to do over again? Well, yes, I would. I'd make the power led visible from the outside without opening the front door, because I can't tell when the computer is on. Other than that, I'm pretty happy.

Many thanks to those who contributed to my design thread in the forums, even if I did ignore some of the advice.

* * *

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