Thermalright ALX-800

Excellent choice for aggressive air-cooling, but at very high noise levels – Joe

SUMMARY: Excellent choice for aggressive air-cooling, but at very high noise levels.


The good guys at Thermalright were nice enough to send the ALX-800 for a test spin. This unit is squarely targeted for the performance user. This heatsink is a little different from other Thermalright products in that the fins are aluminum with a copper base; note that the fins are thicker than the usual thin copper plates used on others:

ALX-800 bare

Thermalright sent me a Delta fan (FFB0812EHE) to test the ALX-800 – a 80 x 38mm unit rated 80 cfm @ 5700 rpm, 53 dBA¹. I found it to be about the noisiest fan I’ve ever tested – I measured its noise at 76 dBA with a Radio Shack sound meter 8″ from the fan’s intake – very loud. It uses almost 11 watts; it comes with a four pin power plug and a separate tach plug for rpm monitoring.

The base is fairly well finished:


When I ran my nail over it, I could just about feel small ridges – lapping might improve performance a tad, but it would have to be a real fine job.


The ALX-800 was tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences.


Die Temp
Ambient Temp
ALX-800, 6868 rpm
37.9 C
22.5 C
15.3 C

Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt (CPUw) that the CPU
consumes, the HSF will limit the CPU’s temperature rise to (C/W x CPUw)
plus the temperature at the HSF’s fan inlet. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that CPU temp will increase 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Die Simulator results place the ALX-800 in the top rank of heatsinks tested to date (Heatsink Ranking), although with top rank noise as well.


Thermalright’s ALX-800 is a fine choice for aggressive Socket A cooling when used with a very aggressive fan, such as a high-energy Delta 80. However, there is no doubt that the noise that goes with this performance borders on the absurd. The ALX-800, I think, is an excellent example of the limits of air cooling and what lengths users must go to extract the last bit of performance.

Barring radically different materials, IMHO air cooled solutions appear to have hit a wall at a C/W of about 0.20.

Thanks again to Thermalright for sending this our way.

¹Note that manufacturers measure fan noise usually 3 feet from the fan.

Email Joe