Zalman CNPS8700 LED CPU Cooler: Update of a Classic

Cooling
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TESTING

Testing was done according to our unique heatsink testing methodology, and the reference fan was profiled using our standard fan testing methodology. A quick summary of the components, tools, and procedures follows below.

Key Components in Heatsink Test Platform:

Test Tools

  • Seasonic Power Angel for measuring AC power at the wall to ensure that the heat output remains consistent.
  • Custom-built, four-channel variable DC power supply, used to regulate the fan speed during the test.
  • Bruel & Kjaer (B&K) model 2203 Sound Level Meter. Used to accurately measure SPL (sound pressure level) down to 20 dBA and below.
  • Various other tools for testing fans, as documented in our standard fan testing methodology.

Software Tools

  • SpeedFan 4.32, used to monitor the on-chip thermal sensor. This sensor is not calibrated, so results are not universally applicable; however, results should be comparable with other results on this test bench.
  • CPUBurn P6, used to stress the CPU heavily, generating more heat that most realistic loads. Two instances are used to ensure that both cores are stressed.
  • Throttlewatch 2.01, used to monitor the throttling feature of the CPU to determine when overheating occurs.

Sound pressure level (SPL) measurements were made with the fan powered from the lab variable DC power supply with no other noise sources in the room. The ambient conditions during testing were 18 dBA and 22°C.

Load testing was accomplished using CPUBurn to stress the processor, and the graph function in SpeedFan was used to make sure that the load temperature was stable for at least ten minutes. The fan was tested at four voltages: 5V, 7V, 9V, and 12V, representing a full cross-section of its airflow and noise performance.

MEASURED TEST RESULTS

Zalman CNPS8700 LED
Fan Voltage
SPL
Temp
°C Rise
°C/W
12V
40 dBA
38°C
16
0.21
9V
33 dBA
39°C
17
0.22
7V
28 dBA
41°C
19
0.24
5V
24 dBA
45°C
23
0.29
Load Temp: CPUBurn for ~20 mins.
°C Rise: Temperature rise above ambient (22°C) at load.
°C/W: Temperature rise over ambient per Watt of CPU heat, based on the amount of heat dissipated by the CPU (measured power of 78W).
SPL: Noise measured in dBA@1m distance with high accuracy B & K SLM

@12V: Performance was superb with the CPU temperature rising only 16°C above ambient but at the cost of very turbulent and aggressive noise. Measuring 40 dBA@1m, it was a far cry from the maximum 33 dBA cited by Zalman... and completely unacceptable to SPCR.

@9V: The noise level dropped dramatically though it was still a curse on our sensitive ears. The temperature difference was barely measurable, which was a good sign.

@7V: The fan was much more bearable but still annoying with an evident buzz and slight rattle. Performance suffered by only two more degrees than at 9V.

@5V: The noise level finally crossed the border into what we would consider quiet territory. At 1m in our quiet lab it was audible but unintrusive.

For a 67mm tall heatsink, the CNPS8700's performance was commendable. With only a three degree difference between 12V and 7V, it's clear that Zalman could have easily used a quieter, slower fan with minimal negative effect on its cooling ability. There were no surprises with this fan. It's basically the one used in the 9700, and measures and sounds just about the same, within typical sample variance range. It's not a nice sounding fan except at the lowest speeds.

NOISE RECORDINGS IN MP3 FORMAT

Each of these recording starts with five seconds of "silence" to let you hear the ambient sound of the room, followed by 10 seconds of the fan's noise at 5V, 7V, 9V and 12V. The five seconds of "silence" is inserted between each 10 second stretch of fan noise to help you remember the reference ambient.

HOW TO LISTEN & COMPARE

These recordings were made with a high resolution, studio quality, digital recording system, then converted to LAME 128kbps encoded MP3s. We've listened long and hard to ensure there is no audible degradation from the original WAV files to these MP3s. They represent a quick snapshot of what we heard during the review. Two recordings of each noise level were made, one from a distance of one meter, and another from one foot away.

The one meter recording is intended to give you an idea of how the subject of this review sound in actual use — one meter is a reasonable typical distance between a computer or computer component and your ear. The recording contains stretches of ambient noise that you can use to judge the relative loudness of the subject. For best results, set your volume control so that the ambient noise is just barely audible. Be aware that very quiet subjects may not be audible — if we couldn't hear it from one meter, chances are we couldn't record it either!

The one foot recording is designed to bring out the fine details of the noise. Use this recording with caution! Although more detailed, it may not represent how the subject sounds in actual use. It is best to listen to this recording after you have listened to the one meter recording.

More details about how we make these recordings can be found in our short article: Audio Recording Methods Revised.



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