be quiet! Dark Rock 2 Tower Heatsink

Cooling
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STOCK FAN MEASUREMENTS

Specifications: be quiet! Dark Rock 2
Manufacturer
Power Rating
3.0 W
Model Number
BQT T13525-MF-PWM
Airflow Rating
57.9CFM
Bearing Type
?
Speed Rating
1,300 RPM
Corners
Open
Noise Rating
21.2 dBA
Frame Size
137 x 137 x 25 mm
Header Type
4-pin
Fan Blade Diameter
128 mm
Starting Voltage
< 5.0 V
Hub Size
47 mm
Weight
170 grams
Data in green cells provided by the manufacturer or observed; data in the blue cells were measured.

The Dark Rock 2's stock fan has a very interesting design. It's slightly smaller than a 140 mm model, its blades have ridges, and the circular frame has a soft, rubberized rim, possibly for dampening. The hub is unusually large, measuring 47 mm across; most 140 mm fans have a hub diameter of ~40 mm. The cable is short, measuring only 20 cm.

Stock Fan Measurements
Voltage
Speed
SPL@1m
12V
1280 RPM
24 dBA
10V
1020 RPM
19 dBA
9V
770 RPM
15 dBA
8.5V
630 RPM
13 dBA
8V
480 RPM
12 dBA
7V
350 RPM
<11 dBA
Measuring mic positioned 1m at diagonal angle from the center of the heatsink.
Ambient noise level: 10~11 dBA.

The stock fan is more finely controlled when PWM is used; with voltage control, the stock fan is only audible above 7V. Its motor produces a low pitched hum that increases in intensity almost proportionally with the fan speed. It's not particularly pleasant, but it's consistent, not developing any odd tones or quirks at different speed levels. At higher fan speeds, it generates more turbulent noise but this is true of all fans.


At 10V, the stock fan can be considered quiet, generating a noise level of 19 dBA@1m.

The fan has some tonal elements, particularly at ~350 Hz.

TEST RESULTS

be quiet! Dark Rock 2
Fan Voltage
SPL@1m
Temp
°C Rise
Stock Fan
12V
24 dBA
66°C
46
10V
19 dBA
68°C
48
9V
15 dBA
72°C
52
8.5V
13 dBA
75°C
55
8V
12 dBA
81°C
61
Reference Noctua 140mm Fan
12V
28 dBA
66°C
46
9V
21 dBA
69°C
49
7V
15 dBA
71°C
51
6V
12~13 dBA
73°C
53
Reference Nexus 120mm Fan
12V
15 dBA
68°C
48
9V
13 dBA
70°C
50
7V
11~12 dBA
72°C
52
°C Rise: Temperature rise above ambient (20°C) at load.

The Dark Rock 2's cooling proficiency is not great for a heatsink of its size. The better coolers we've tested over the years typically do not exceed a thermal rise above ambient of 50°C on our test platform, even at close to inaudible noise levels. The Dark Rock 2, with its stock fan at 8V measuring just 12 dBA@1m, exceeded 60°C above ambient, and the result at full speed was only 46°C.

Though the Dark Rock 2 doesn't have a mounting option for a standard 120/140 mm fan, we Jerry-rigged both our reference Noctua 140 mm and Nexus 120 mm fan to it anyway, to see if the stock fan was part of the reason for its poor performance. CPU cooling was fairly similar with the Noctua, except for a significant improvement at the 12~13 dBA@1m level. The smaller Nexus fan performed noticeably better (as it tends to do) but not enough to save the heatsink from being classified as subpar.


Thermal compound footprint.

Disappointed by the results, we checked the thermal compound footprint after testing and discovered the heatsink wasn't making very good contact with the processor, indicated by the noticeable "branching" pattern that was produced. There was also more excess TIM on the sides due to the base's uneven surface which we mentioned earlier.

In attempt to create more pressure, we re-tested the heatsink without the plastic spacers that were placed between the mounting clips and the motherboard PCB but the results were the same.



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