Silverstone Fortress FT01: Positive Pressure Case

Cases|Damping
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TESTING

System Configuration:

Measurement and Analysis Tools

  • CPUBurn K7 processor stress software.
  • FurMark stability test to stress the integrated GPU.
  • GPU-Z to monitor GPU temperatures and fan speed.
  • SpeedFan to monitor system temperatures and fan speeds.
  • Seasonic Power Angel AC power meter, used to measure the power consumption of the system.

Stock Fan Measurements

Stock Fan Noise Level (Individual)
Fan Voltage
Rear Fan (Exhaust)
Top Fan (Intake)
Front Fan (Intake)
Speed
SPL @1m
Speed
SPL @1m
Speed
SPL @1m
12V
1040 RPM
20 dBA
700 RPM
24 dBA
720 RPM
26 dBA†
9V
840 RPM
17 dBA
570 RPM
19 dBA
600 RPM
22 dBA
7V
690 RPM
12 dBA
470 RPM
14 dBA
500 RPM
17 dBA
6V
not tested
not tested
420 RPM
13 dBA
440 RPM
15 dBA
5V
510 RPM
11 dBA
n/a*
n/a*
n/a*
n/a*
Noise level from the front fan rose by 2 dBA and became noticeably rougher when the front filter was removed.
* Fan did not spin at this voltage.

The stock fans are pleasantly slow and quiet. The fastest is the smaller exhaust fan, which tops out at a leisurely 1,040 RPM (it's rated at 900 RPM). It's not the smoothest fan, but it quickly disappears when undervolted because of its low speed. At full speed it added a touch of buzz to the noise character of the case, but it wouldn't take much undervolting for even that to disappear under the noise floor of a real-world environment.

The larger intakes are even slower — about 700 RPM at full speed. But, with more than double the surface area of a convention 120mm fan, they can afford to be undervolted even from this low speed. Although their measured SPL was higher than the exhaust fan, their tonal balance was more toward the lower end of the spectrum, allowing them to blend more easily into the background. Like the exhaust fan, the motors had a tough of buzz, except their deeper voice made the sound more of a growl than a buzz.

One word of caution: Because the intake fans are already so slow, they did not start at 5V, although they could reliably be turned down this low once started. They did start — barely — at 6V, and this level was used as a minimum voltage instead of our usual 5V. At this level, the fans turned at just over 400 RPM and produced a rumble that was just barely audible in our anechoic chamber. They would not be heard in the real world.

Perhaps because of its location and impeded surroundings, the front fan was noticeably louder than the top fan at the same rotation speed. The difference was measurable — generally it was 2~3 dBA above the top fan. On a whim, we pulled out the front filter to see if its impedance. was causing the problem, but this did nothing but bump up the SPL by 2 dBA and introduce an annoying warbling into the noise character. We quickly put it back.

Stock Fan Noise Level (Combined)
Fan Voltage
All Fans
Front Fan Off
SPL @1m
SPL @1m
12V
28 dBA
25 dBA
9V
24 dBA
21 dBA
7V
18 dBA
15 dBA
6V
16 dBA
13 dBA

Turning on all the fans together didn't produce any new surprise. Noise character didn't change appreciably; if anything, it became more broadband as the multiple noise sources blended together. It did get noticeably louder, however, as is bourne out by the SPL measurements.

One thing we did find a little annoying was the interaction between the various fans at full speed. With the two 180mm fans spinning at almost but not quite the same speed, the effect was a distinct "train whistle" effect as the two resonant frequencies blended dissonantly. This effect was not noticeable once the fans were dialed down below 12V.

Disabling the front fan confirmed our subjective opinion that this was the dominant source of noise. The measured SPL dropped by 3 dBA across all speed levels without the front fan. While it is probably not a good idea to abandon the fan entirely, it might be wise to run this fan slower than the others — the hard drives that it cools need only a minimum of airflow to stay cool.



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