MythTV Part 3: Getting Quiet Enough for the Living Room
Pages: 1, 2, 3

Killing the Noise

The six fans in my MythTV system are the main source of noise:

• Two 60mm exhaust fans. These are noisy if they are run at full speed from the 12V power supply output, so I run them at 5V.
• One 120mm exhaust fan in the power supply. The power supply has very sophisticated controls over the speed of the fan, and it generally runs low enough to be nearly silent.
• One 80mm case fan. The fan that I purchased with the case is so noisy that I disconnected it entirely.
• The CPU heat sink fan. This is the largest source of noise in the system, even at idle. The initial CPU heat sink came in the AMD retail box, so it is not surprising that its noise performance is not all that good. At idle, it runs at approximately 3,500 rpm, and goes to 4,700 rpm as the processor clock speed increases.
• The fan on the north bridge heat sink. This is the second-noisiest fan because it typically runs above 5,000 rpm.

Figure 1 shows the stock retail CPU heat sink and the north bridge fan before starting the project.

Figure 1: The existing major noise sources

The largest source of noise is the CPU heat sink fan, so that's where to start with noise reduction. The best way to reduce noise is to slow the fan down. Large fans move more air than small fans, so I went searching for a larger heat sink that still fit the motherboard. The best place to find information on quiet components is Silent PC Review. I started with their recommended list of CPU coolers and looked for the most effective heat sink that would fit on the MSI K8N Neo2 Platinum motherboard.

For an AMD64, there were four obvious choices to consider: the Zalman 7000 and 7700, and the Thermalright XP-90 and XP-120. Many manufacturers maintain compatibility lists of heat sinks with motherboards. The two heatsinks based on 120mm fans, the Zalman 7700 and Thermalright XP-120, are too large for the motherboard. In the end, my decision was made easy by the compatibility lists. Zalman's compatibility list stated that the 7000 is compatible with my motherboard, but the Thermalright compatibility list did not list a compatible unit.

The Zalman 7000 comes in two versions: an aluminum/copper hybrid, and a pure copper version. Aluminium is cheaper and lighter, but does not conduct heat as well. In a heat sink the size of the 7000, the extra weight can add up. AMD specifies a maximum heat sink weight of 450 grams, and the all-copper 7000 is a hefty 773 grams. While it might not present a problem in operation, it would be necessary to take care when moving the computer. Heat dissipation is not a problem, so the extra weight of the all-copper version is not necessary. I settled on the hybrid version.

As part of the same search, I looked for passive north bridge coolers. Zalman's NB-47J is a passive heat sink that attaches using the motherboard mounting holes. The mounting clips are fully adjustable, and easily fit a variety of motherboards, including mine.

Figure 2: The new coolers

Removing the old CPU heat sink was easy. Flip the clip holding it to the motherboard and pull it off. Looking at the old heat sink next to the new one, as in Figure 3, is a strong hint at the cooling power of the Zalman. With much more fin area, heat dissipation without the fan will be better, and the larger fan can move more air while rotating more slowly (and hence, quietly).

Figure 3: CPU heat sink comparison