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Very good performance, very loud noise — Joe

SUMMARY: Top rank performance with top rank noise.


Size: 83x70x70mm high; Weight: 500 gms.

The good guys at SIBAK were nice enough to send a sample of their copper core heatsink, the SIBAK AC-06-725TH. It features a copper core about 32mm in diameter surrounded by aluminum fins radiating out from the core. The copper core does not extend through to the top – it’s “buried” in the surrounding aluminum fins.

Removing the aluminum fan shroud


shows the fan bolted to the heatsink. Removing the fan and clip

Base Bare

shows the radial fin pattern; the groove is for the clip.

The fan is an Everflow model #T127025BU – a 70 x 25mm unit rated at 8.4 watts (do not use a motherboard fan header). At 12 volts, it spins at 6650 rpm with noise you would expect at this level – basically Delta 38 levels, although the fan’s noise includes a low whistling sound in addition to higher pitched sounds from the bearings.

I measured its noise at 69 dBA with a Radio Shack sound meter 8″ from the fan’s intake and normalized these readings. I then varied voltage to find performance at various rpms and noise levels.

The base


is flat and nicely polished – I could not feel any polishing marks on the copper core.

The clip is a little tricky – the rear clip is angled under the heatsink’s base, so you have to “feel” it into place. Once engaged, you have to use a screwdriver to mount the front clip. It’s fairly stiff and takes some pressure to engage the front clip.

In summary, an aluminum/copper cored heatsink with a very secure, though stiff, clip.


The SIBAK was first tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences. I then tested it on an Iwill KK266+, modified to read AMD’s on-die diode, as an example of what users might see on their systems.


Die Temp
Ambient Temp
SIBAK/7250rpm, 58 dBA
45.6 C
21.2 C
24.4 C
SIBAK/6650rpm (12v), 55 dBA
45.7 C
20.0 C
25.7 C
SIBAK/5700rpm, 52 dBA
48.1 C
21.0 C
27.1 C
SIBAK/3630rpm, 40 dBA
55.2 C
21.3 C
33.9 C

TEST RESULTS – Motherboard

CPU Die Temp

Ambient Temp



CPU Back Temp

Palomino 1200, Iwill KK266+, 6800 rpm

34.5 C

21.6 C



37.1 C

In-socket thermistor per MBM: 27 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 SIBAK, at 6650 rpm (12v) and high noise, in the top rank of heatsinks (Heatsink Ranking). Note that it takes a cutting fan speed almost in half from spec to get close to “acceptable” noise levels.


A very interesting design that turns in top rank performance, but once again, at the expense of your hearing.

Email Joe


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