Scythe Kamakiri CPU heatsink/fan

Cooling
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TESTING

Test Platform

  • Intel P4-2.8A The Thermal Design Power of this P4-2.8 (533 MHz bus) is 68.4 or 69.7W depending on the version. As the CPU is a demo model without normal markings, it's not clear which version it is, so we'll round the number off to ~69W. The Maximum Power, as calculated by CPUHeat & CPUMSR, is 79W.
  • AOpen AX4GE Max motherboard - Intel 845GE Chipset; built-in VGA. The on-die CPU thermal diode monitoring system reads 2°C too high, so all readings are compensated up by this amount.
  • OCZ DDRAM PC-3700, 512 MB
  • Seagate Barracuda IV 40G 1-platter drive (in Smart Drive from Silicon Acoustics)
  • Seasonic Super Tornado 300 (Rev. A1)
  • Arctic Silver Ceramique Thermal Compound
  • Two-level plywood platform with foam damping feet. Motherboard on top; most other components below. Eases heatsink changes and setup.

Measurement & Analysis Tools

The ambient temperature during testing was 20°C. Ambient noise level for testing and recording was 18 dBA/1m. Because the Kamakiri is intended for use with its manual fan controller, testing was performed using the stock fan. Three fan settings used: Maximum, minimum, and a level that we felt made the best compromise between fan speed and noise.

RESULTS

Scythe Kamakiri
Fan RPM
Load Temp
°C Rise
°C/W MP
°C/W TDP
Noise & MP3 files
5000
39°C
19
0.24
0.28
1700
52°C
32
0.41
0.47
1350
55°C
35
0.45
0.51
Fan RPM: 5000 = full speed, 1350 = min speed; 1700 is where we felt the fan ceased to be quiet.
Load Temp: CPUBurn for ~20 mins.
°C Rise: Temperature rise above ambient at load.
°C/W MP / TDP: Temperature rise per Watt, based on CPU's Maximum Power (79W) or Thermal Design Power (69W) rating
Noise: SPL measured in dBA at 1m distance with high accuracy B & K SLM
MP3 files: High resolution recording of fan on HS at 3" distance. Note that it is preferable to save these sound files to your hard drive, and then play them.

Full Speed, 5000 RPM: At full tilt, this fan ranks with some of the worst fans out there. The predominant noise is a loud whine that you could use to tune a piano. Turbulence noise is also a problem, although its broadband nature lacks the peculiar "bite" of the narrow-band whine. The 55 dBA/1m measurement and the corresponding MP3 should be enough to convince anybody that this fan should not be run at full speed, so I will say no more.

Minimum Speed, 1350 RPM: Once the fan controller is turned to minimum, the Kamakiri is reasonably quiet but far from silent. The whine that was so odious at full speed is still present, but it has dropped considerably in both pitch and volume. The turbulence noise has also dropped, although it is still noticeable. Unfortunately, these reductions in noise reveal a prominent buzz that does not change volume with fan speed. This buzz is now the main source of noise from the fan.

Cooling performance at this level at acceptable for our test setup, but there are definitely quieter ways to achieve this level of cooling. However, a hotter CPU might not be properly cooled at this fan speed, especially inside a case, where the ambient temperature can be expected to be at least 10°C higher.

Threshold, 1700 RPM: One final test was done at an intermediate fan speed to see how the Kamakiri performs with slightly higher airflow. The threshold fan speed was chosen based on what we thought would be the loudest the fan could get inside a case without becoming a major annoyance. Obviously this is a very subjective decision, so it should be taken as a guideline. Your threshold of annoyance may be different from ours!

The 3°C improvement over the minimum speed is not large, and reflects the small amount of headroom that this fan has before it crosses the line from background noise to foreground annoyance, at least from our listening perspective.

Below Minimum Speed: Although we did not perform thermal testing with the stock fan at anything other than the stock 12V, we did take the opportunity to listen to how it sounds when undervolted. With the fan controller set at minimum, the turbulence and the motor whine that make up the majority of the noise produced by this fan drops away at around 7V. At this level the only source of noise is the mechanical buzz that haunts most high airflow fans. This buzz never changes in volume, which means that further undervolting is useless.

The drop in airflow is considerable at this level, but it is doubtful that the Kamakiri would provide adequate cooling for any the desktop CPUs on the market today.

It is possible that the plastic shroud is another source of noise. Pressing the shroud to the fan to eliminate vibration made the sound smoother but no less loud. Removing the shroud altogether had a larger effect: The piercing whine of the motor dropped in pitch and seemed to become softer in character, if not in volume. It would appear that the shroud focusses the fan noise into a very narrow band of frequencies. Especially at lower levels, we preferred the character of the noise without the shroud.

Recordings of Comparable HSF:

MP3: Arctic Cooling Super Silent 4 Ultra TC MP3, 22 dBA/1m

MP3: Zalman 7000 - 5V - 22 dBA/1m

MP3: Panaflo 80L - 7V - 17 dBA/1m -- on most any heatsink

MP3: Coolermaster Hyper 48 - 9V - 21 dBA/1m

HOW TO LISTEN & COMPARE

These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings was 18 dBA or lower. It is best to download the sound files to your computer before listening.

To set the volume to a realistic level (similar to the original), try playing this Nexus 92mm case fan @ 5V (17 dBA/1m) recording and set the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, all tone controls and other effects should be turned off or set to neutral. For full details on how to calibrate your sound system playback level to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.

FINAL CONCLUSIONS

Despite its unusual design, the Kamakiri manages only average acoustic performance. Even at its lowest speed, the stock fan is not a good candidate for a silent computer. A fan swap could certainly improve the noise floor for this heatsink.

Unfortunately, the position of the fan may be the biggest acoustic flaw. No matter how good a fan is used with the Kamakiri, turbulence noise will be an issue. The fins of the heatsink surround the fan, which means that airflow impedance is high. This changes the noise character of any fan installed in the Kamakiri by increasing the pitch and volume compared to its noise in free air. It also contributes to an increase in turbulence noise. Furthermore, the plastic shroud is prone to resonating; even a quiet fan would find its noise performance degraded under the shroud

From a design point of view, the Kamakiri is quite efficient thermally. The total surface area of the fins is not all that large, especially considering that about a third of the fin space is lost to make room for the fan. This means that the heat dissipation per square centimeter is probably quite high. However, for best performance, it's pretty clear that fairly high CFM rates must be maintained.

Ultimately, the traits that make the Kamakiri a poor acoustic performer are responsible for its thermal efficiency. The maximal use of the fan's airflow, the large amount of turbulence, and the airflow shroud are all good for thermal performance. Unfortunately, all of these traits affect noise levels negatively.

Pros

* Wide range of fan speeds
* Universal mounting system ensures good compatibility
* Thermally efficient design
Cons

* Noisy fan
* Design inherently produces noise
* Mounting system required removing stock Intel retention module

Much thanks to Scythe USA for the Kamakiri sample.

* * *

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