Quiet PC for Torrid Thailand

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IN THE MAIN CHAMBER


Before the duct: Innards don't look so different from an ordinary PC... or do they?

There's a lot to look at in the above picture. Let's start at the back of the case.

Antec 120mm Tricool fan for Case Exhaust

The standard stock one is black; this one is a clear retail version that has a more convenient 3-pin plug that goes into standard motherboard fan headers. I would have left the stock one in place, but during testing, it developed a nasty buzz that I attribute to a manufacturing variance. I could have replaced it with a Nexus 120 fan, which is quieter, but it's limited to ~40 CFM airflow at full speed, which may not be enough in hot weather. The retail Tricool has the same airflow characteristics as the stock black one, which we measured in the lab to have 75, 47 and 28 CFM airflow at the three switchable speeds. At the top speed, it's loud, but should an emergency thermal situation arise, the extra cooling power could be very helpful.

The fan itself was mounted using soft silicone rubber grommets from a fan mounting kit by AcoustiProducts, which we reviewed last year. Using AcoustiProducts' metal screws proved to be counterproductive here. The screws themselves make contact with the edge of the panel mounting holes; enough so that vibration noise is not much reduced. I came up with a way of securing the fan without using screws. A picture is sometimes worth many words:


Two short pieces of clothing elastic hold the fan in place.

Clothing elastic is one of my favorite quiet PC building materials. I get it from a nearby warehouse-style textiles store for around a dollar a meter. It's the kind of elastic string used in jackets as a waist-cinch with a spring-loaded lock. It has multi-core rubber strands in the core with a stretchy woven material around it; it's extremely durable. Great for hard drive suspensions and all kinds of other vibration reduction applications... like mounting fans. It makes for more effective vibration reduction than the screws provided in the AcoustiProducts fan grommet kit.

At the minimum speed the Tricool 120 is pretty quiet, measuring 20 dBA@1m in free air. But mounted on the back panel of the P150, even with the damped mounting, I didn't think it was quiet enough. The speed is just a bit too high, and some still vibration gets transferred to the back panel, which resonates just enough to add a low frequency hum that further increases overall noise. The system measured 24~25 dBA@1m from the back with this Tricool fan set on low.

My solution was to add a couple of zener diodes in-line (series) to reduce the voltage going into the Tricool fan, so that it would run at even slower speed. (For more information on zener diodes, see Cpemma's excellent web site on fan noise control.) The input voltage is dropped from 12V to around 10V. With the zener diodes, when the Tricool fan switch is set to low, it's now slightly under 23 dBA@1m from the back. The dangling 3-position switch was pushed through a small lockhole to the outside of the case so that it is accessible without opening the side cover.

Scythe NCU-2000 heatsink with Nexus 120 fan

This innovative big heatpipe heatsink is marketed as fanless model. We tested it a while ago, and found it to be usable in a typical system with some airflow from peripheral fans, but there's no way I'd ship a fanless PC to Thailand. I fastened a Nexus 120 fan on the NCU-2000 using enamel solid-core wire. (Clothing elastic is not wise here due to the stress of high temperature.) It is set up to blow the air through the HS fins towards the back of the case. It's a basic straight through push-pull arrangement: The CPU heat is pushed by the Nexus 120 fan towards the Tricool 120 fan, which pulls it out of the case.

One thing to note in the picture below: The fan is actually mounted slightly off center, and it occupies the memory slot closest to the CPU. Yes, it is actually jammed right up against the memory slot. This was done to get the fan's airflow as close to the surface of the motherboard as possible. Why? To make sure the the board-mounted components, particularly the voltage regulators, get adequate cooling. This is an issue with most of these tower-style heatsinks. The older style of heatsink where the fan blows straight own does have a major advantage: There is always some airflow across the motherboard components. Allowing these components to run too hot lower reliability, longevity and power efficiency.


Nexus 120 fan on the Scythe NCU-2000 heatsink mounted as close to the motherboard as possible.


The fan mounting also ensures decent airflow for the heatpiped heatsink that pulls the heat from the chipsets.
Some of the voltage regulation components are visible on either side of the chipset heatsink.

The Nexus fan is plugged into the CPU fan header of the Asus board. The output of this fan header is thermally controlled by the motherboard. Q-fan is what Asus calls their board-embedded thermal fan speed controller, which is accessible in the BIOS under Hardware Monitor. It's a simple on/off switch, with a manual selection for the target CPU temperature at which the fan get the maximum 12V. The range is 51°C to 82°C ¬ó the latter number seems absurdly high. During the testing, this setting was at 66°C, and the CPU fan never ramped up, which is perfectly logical, given that the CPU never hit higher than 47°C. Just out of curiosity, I lowered the setting to 51°C and stressed the CPU with two instances of CPUBurn, bringing the CPU temperature up to 47°C. Again, there was no change in fan speed.

This suggests that Q-fan will bring the CPU fan speed up only when the trigger temperature is reached, but it may take it from minimum to maximum speed as soon as it's triggered. If so, this ramp-up in fan speed will definitely be audible. It is not quite as bad as it sounds, as the Nexus 120 is still very quiet even at 12V, measuring just 22 dBA@1m in free air. I changed the trigger temp to 60°C in the final build. Frank may want to re adjust this after he has had some time to work with the machine in his environment.

EVGA eGeForce 6800GS graphics card with Arctic Cooling NV Silencer 5 (Rev 3)

The vidcard is visible in the above photos. The main heatsink and the fan are on the underside (of the video card) but there's also a passive memory heatsink on the trace side of the board, which benefits from peripheral airflow of the case exhaust and CPU fans. Revision 3 of the NV Silencer is compatible with nVidia 7800 models, and it has a much better-behaved fan. The first revision had some nasty ticking/buzzing effects which made them considerably louder than the original VGA Silencer. The improvement to the fan was apparently implemented in all AC VGA cooler models in Rev.2. The AC VGA coolers remain the only ones on the market to evacuate the heat of the GPU rather than just recirculate it inside the case. The AC VGA coolers help to lower not only GPU temperatures, but system and CPU temperatures as well.


After cooling the GPU, the air from the Arctic Cooling heatsink gets blown out the back panel through the next PCI slot.
Photo shows the exhaust duct of the AC cooler.

A Zalman Fanmate1 is used to control the speed of the AC NV Silencer's fan. At full speed, this fan is too loud for a quiet computer. The fan speed setting was chosen on the basis of noise (quiet enough not to be identifiable as a discrete noise source) and cooling (which you'll see later). It turned out to be a very slow speed; I would guess the fan is not getting more than 7V. Still it is plenty cool enough, even at very high, extended loads. The Fanmate1 is mounted on the back panel in such a way so that its little knob protrudes through one of the grill holes, and can be adjusted from the outside. Because the knob is so small, it may require smaller fingers than Frank's to turn... but that shouldn't pose much of a challenge.


Externally accessible fan speed controls. Arrow points to knob on Zalman Fanmate1 controller.


Finally, a shot of the back panel.
Note exhaust grill below VGA slot for the Arctic Cooling VGA cooler to exhaust hot air.



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