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Building an HTPC. Part 4: Cooling

June 12, 2007

Part 1, Part 2, Part 3.

So, what happened with the HTPC? Long time, no update? Well, what happened was that the power supply died, and I didn’t have the time to go and get it fixed for a week. But this saturday I went to Grosbill, and the happily… well, no, they grumpily, but quickly and with no fuss gave me a new power supply. So I spend another weekend with the HTPC, and it’s time for me to talk about cooling.

Things they don’t tell you

In my search for a processor, I ended up getting a boxed processor. The last few times I bought a processor I bought OEM versions, usually because when I asked for a processor that’s what I was handed. But this time they handed me a boxed version. It was a surprisingly heavy box. Because, it turned out, it included a fan. That’s interesting, because nowhere on any of the sites I have visited do the say things like “boxed version includes processor fan” or anything like that. If it had, I wouldn’t have bough a separate fan until after I knew if I needed one or not.

amd_processor_fan.jpgThe next thing they don’t tell you is how loud the included fan is. So the only way to know is to try it out. That’s annoying, because basically you have to guess how much more silent a separate “ultra-silent” fan is and if it’s going to be worth it for you before you buy one. You can of course also measure it, if you have a dB-meter that is good enough. I don’t. So first I tried out the AMD processor fan. Well, it makes quite a lot of noise. Not exactly what I had wanted in my “silent” system. In fact it was the noisest part of the system, and the harddisk is specified at 27db, so I’m guessing that the fan was around 35dB. I don’t know for sure, because my old cheap dB meter only goes down to 40dB. So it was time to put in the separate fan I bought.

zalman_and_fanmate.jpgGetting a separate fan sounds easy, but it isn’t. Most modern motherboards can control the speed of the processor fan. But most fans can not be controlled. Most fans to day have a three pin connection, and the third pin is known as “fan speed”. No, it does NOT control the fan speed, but is in fact a sensor to measure the fan speed. Fans whose speed can be controlled have four-pin connectors. These are not that common, and I couldn’t find a fan with that support and a profile low enough to fit in my case, so I got a Zalman CNSP75000-Cu because of it’s low profile. It noise is rated as 17db to 35db, so I put it in and turned on the computer, and was greeted with the noise of a small angry hairdryer. And in fact, it was one of the few things loud enough to actually get over my 40dB mark on my meter. It’s more like 45dB than 35dB, at least if measured from one meter away, which is pretty much standard. But it comes with a little controller you can use to control the speed, and I turned it down to the minimum, which should mean about 17db. The Zalman fan at that speed becomes less noisy than the hard disk, and it was in fact the chassis fans that was now the loudest parts.

There are two fans in the chassis, and also two in the power supply. But the temperature sensors in these configuration told me this was complete overkill for my configuration. The core temperature of my processor generally stays at only a couple of degrees over room temperature. That’s just silly. So I experimented with unplugging the chassis fans, and let the computer idle a while in this configuration. Without the chassis fans it is quite silent, and the processor temperature didn’t go over 50 when idle (and the max temperature is supposed to be around 90 for this processor). But even while idling, the motherboard temperature (whatever that means) got over 45 degrees, which I found a bit high for comfort (mostly because I have no idea what it actually is measuring). Also the power supply does run quite hot, so I don’t want the temperature inside the chassis to be too high, since the power supply draws it’s air from inside the chassis. The solution was obvious: Get another of the Zalman fanmates and try to lower the speed of the chassis fan as well. The Zalman fan is evidently complete overkill for AMDs Energy Efficient processors, but the airflow around the motherboard needs a bit of help, but not much, from a fan.

So, that’s what I did, and in the end, the complete computer ended up being around twice as noisy as my laptop, which is acceptable. I’m guessing it’s somewhere between 25 to 30dB in total (except when the DVD is spinning up, of course).

From → home theater pc, htpc

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