Quiet DIY OC'ed Pentium D 830 System, Part Two

Do-It-Yourself Systems
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SPCR member theyangster asked: Why don't you cut out the fan grills?

Not knowing why I would want to, I looked around and found this intriguing entry in the forums ("Case fan grills are evil..."), which convinced me that a grill close to a fan creates a lot of noise, and even if it isn't close it restricts airflow considerably. Since I want my system to be both finger and paw proof, as well as filtered, my options in this space were somewhat limited. I decided to remove the top case fan grill only. Here is a photo. The copper on the top left and at the top is the VRM heat sinks. The grey blob at the top right is the temperature sensor of the fan controller (described below).

top fan grill removed
Top fan after the grill is removed; note VRM heat sinks.

The original P180 spoiler provides safety, and fits without any mods over the soft-mount screws:

P180 spoiler provides safety for top fan
P180 top case fan spoiler in place: no fingers or paws can get to the fan.

The discussion of air flow restriction also led me to remove the front swing-out doors over the P180 dust filters. This is easy: just flip each one open, then press on the tab near the top hinge. Removing the top fan grill and front doors is a tiny incremental change, but when the goal is very low noise levels and fan speeds, every bit helps.

Maybe some day if I'm feeling both ambitious and destructive, I'll cut out most of the metal behind the dust filters. The Kama Bay would also work better with much larger holes.


The same Edwood thread in the SPCR forums that got me started on ducting also talks about the Noise Magic NMT-2 and NMT-3 fan controllers.

These handy little devices are designed to be mounted on a corner of an exhaust fan and control its voltage based on the air temperature. The NMT-2 and NMT-3 ramp smoothly between 5V and 12V, from 30ºC-50ºC, and 28ºC-42ºC, respectively. I bought one of each to try out on the top case fan. Unfortunately the NMT-2 didn't work (the sense signal never worked, and after a while every fan I tried would start but then slow to a halt). The NMT-3 worked fine. After some experiments, I ended up with it mounted on the front/far corner of the top case fan as shown in the above photo, where it is sampling a mix of VRM and motherboard warm air. This results in a speed of 720 RPM at idle, 810 RPM while folding, and 860 RPM running two copies of CPUBurn. I found this acceptably quiet, whereas other positions resulted in fan speeds that were noisier than I liked.

One feature of the NMT devices is that they spin up the fan at 12V then drop to the variable voltage. I noticed while experimenting with Nexus fan voltages and speeds that these fans do not always start at 5V, although once started they continue to run. Accordingly, I ordered another NMT-3 to control the power supply/hard disk fan in the lower chamber. This lets me run that fan at 5V which results in an inaudible 545 RPM. This gently wafting breeze is adequate to keep the disks below 38ºC and the power supply heat sink below 45ºC.

As shipped, the Nexus fan is designed to be run at 12V only, either from a 3-pin cable providing sensing, or from a 4-pin Molex without sensing. It didn't take me long to replace all that with a standard 3-pin connector that could be attached to a motherboard plug, an NMT, or an AcoustiFan voltage adjustor (of which I now had several). When used with an NMT, the wiring is quite tidy, as shown in this photo of the lower chamber fan. For the top case fan, I made the fan cable just long enough to reach the NMT so it wouldn't dangle into the system.

lower bay fan with NMT and cabling installed
Lower bay fan with NMT-3 installed and cabling tidied up.

I tried the CPU and motherboard fans for a while at 12V, and although the cooling was very good, I found it to be too loud. After a few experiments with the AcoustiFan adaptors I had lying around, I settled on 720 RPM for the CPU fan (103 ohms, 7.1V) and 840 RPM for the motherboard fan (78 ohms, 7.9V). With the case closed, the only fan I can hear is the top case fan, and it is about the same loudness as the buzzing of the desktop CRT.

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