Modding the Zalman 9500 Heatsink

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TEST SETUP

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.
  • OCZ DDRAM PC-3200, 512 MB
  • Seagate Barracuda IV 40G 1-platter drive (in Smart Drive)
  • Seasonic Super Tornado 300 (Rev. A1)
  • Arctic Silver Ceramique Thermal Compound
  • Nexus 120 fan
  • Two-level plywood platform with foam damping feet. Motherboard on top; most other components below. Eases heatsink changes and setup.

Measurement & Analysis Tools

  • CPUBurn processor stress software
  • Speed Fan software to show CPU temperature
  • A custom-built fan controller that allows us to dial in the precise voltage to the fan
  • Electronic Anenometer (to measure fan air flow)

Noise measurements were made with the fan powered from the fan controller while the rest of the system was off to ensure that system noise did not skew the measurements.

The ambient conditions during testing were 17 dBA and 21°C.

TEST RESULTS

Acoustically, the salient fact of the comparison below is that even at the lowest setting of the Fanmate (5V), the stock fan is 2 dBA noisier than the Nexus fan at 12V. The Nexus 92 modded Zalman at 12V is probably quiet enough for most users. Other noise-producing components will likely prevent this fan from becoming an identifiable, audible source of noise.

At 9V, the Nexus fan becomes difficult to hear even from just a foot away. The smoothness of the sound is a huge improvement over the buzzy quality that dominates the stock Zalman fan when it is undervolted. Overall, there seems to be less turbulence noise with the Nexus 92 stripped of its frame and mounted in the Zalman 9500. The measured noise actually dropped a dBA or two.

Zalman 9500: Nexus 92mm Vs. Stock Fan
Fan Voltage
°C Rise
°C/W MP
Noise (dBA@1m)
Nexus92
Stock
Nexus92
Stock
Nexus92
Stock
12V
21
14
0.27
0.18
20
37
9V
25
15
0.32
0.19
18
32
7V
29
16
0.37
0.20
<17
27
5V
N.A.
18
N.A.
0.23
N.A.
22

Load Temp: CPUBurn for ~20 mins.
°C Rise: Temperature rise above ambient at load.
°C/W MP: Temperature rise per Watt, based on CPU's Maximum Power (79W)
Noise: SPL measured in dBA@1m with high accuracy B & K 2203 Sound Level Meter

The 21°C Rise (above ambient room temperature) of the Nexus-equipped 9500 at 12V is probably good enough to keep most AMD Athlon 64 and Sempron processors below 60°C at full load in a reasonably well designed system, even in 30°C room temperature. This probably holds true for Intel Prescott cores up to ~3.2 GHz. The cooling performance is still OK at 9V, but borderline. (These comments assume that the baseline temperature inside a PC typically runs ~10°C hotter than ambient room temperature. A better configured system could run cooler; others could run hotter.)

At lower voltages, the Nexus fan does not create enough airflow for useful cooling. Performance was not tested at 5V, considering the predictably poor cooling at 7V. There is little need to slow the Nexus fan below ~9V anyway. It's plenty quiet enough at that level.

CONCLUSIONS

The question is whether this Nexus 92mm fan swap mod is worth doing. If you're interested in the lowest possible noise and want to use the Zalman CNPS9500, then the answer is yes. The cost is not low, as the 9500 plus a Nexus 92 will probably set you back ~US$70 or more. The main advantages are:

  • Extremely low noise, typically 20 dBA@1m or lower at any drive voltage up to 12V.
  • Very good cooling at >9V.
  • Easy to direct the airflow towards the back exhaust fan.
  • Better cooling airflow across the voltage regulators on the motherboard than with most tall blow-across-the-motherboard heatsinks.
  • Sheer geek satisfaction.

As a parting shot, an alternative 120mm fan mod is shown in the photos below. It's the work of YHL, a friend who heard what I was doing and promptly sent over photos of his mod. Obviously, the goal was higher airflow with less noise. YHL says it is quieter than the stock 92mm fan; he refused to say which 120mm fan was used. With the fan blade area doubled, more effective cooling is achieved as well.

Link to our original Zalman CNPS9500 review

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