Thermalright AX-478

Very good performance for P4 CPUs though noisy, depending on the fan used — Joe

SUMMARY: Effective P4 cooling solution featuring easy mounting and top rank performance.

Thermalright AX-478

Size: Top 77x77x78 high; Bottom 83x77x78mm; Weight: 620gms.

The good guys at Thermalright were nice enough to send a sample of the Thermalright AX-478 – the P4 version of the AX7. The AX-478 is basically the same construction as the AX-7, although the cutouts are different and the base is longer to fit the P4 footprint. The base


is flat and nicely finished; it is also plated – perhaps to avoid discoloration and possible oxidation.

The clip is easy to use –


it mounts on the standard P4 retention bracket and holds the heatsink firmly in place. The tab is easily grasped – you slip it under the heatsink’s overhang and clip it into place.


The AX-478 was first tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences. I then tested it on an Lucky Star 4A845D with a modified P4 1500 to read CPU case temps, as an example of what users might see on their systems.

I used two fans in testing: a Delta FFB0812SHE, 68 cfm @ 4800rpm, 48.5 dBA and a Sanyo Denki DC Petit Ace 32, #109P0812A201, 54 cfm @ 4600rpm, 45 dBA. I concentrated on the Sanyo as it is less noisier than the Delta. I measured noise with a Radio Shack sound meter 8″ from the fan’s intake and normalized these readings to the fan’s spec. I then varied voltage to find performance at various rpms and noise levels.


Die Temp
Ambient Temp
AX-478, Delta 4800rpm, 49 dBA
41.6 C
21.0 C
20.6 C
AX-478, Sanyo 4725rpm, 45 dBA
45.6 C
20.8 C
24.8 C
AX-478, Sanyo 4320 rpm, 44 dBA
46.4 C
20.8 C
25.6 C
AX-478, Sanyo 3770 rpm, 40 dBA
47.6 C
20.6 C
27.0 C
AX-478, Sanyo 3240 rpm, 37 dBA
49.1 C
20.5 C
28.6 C

TEST RESULTS – Motherboard

CPU Die Temp

Ambient Temp




Lucky Star, P4 1500, Sanyo 4420 rpm

32.9 C

21.2 C



29 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 AX-478 in the top rank of heatsinks (Heatsink Ranking). The Sanyo fan delivers acceptable noise levels at around 3200 rpm.

Note that the performance difference from the Delta at 49 dBA to the Sanyo at 37 dBA is 11 C; whether this is too a high price to pay for sanity is up to each user to decide.


A very effective P4 cooling solution – depending on your noise tolerance, the AX-478 can deliver a wide range of cooling/noise options.

The AX-478 is available from The Heatsink Factory.

Email Joe

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