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PRELIMINARY ACOUSTIC TESTING
First, the fans were left in the case, powered up with a fanless DC power supply, and measured for sound pressure level (SPL) in various settings and combinations from a distance of one meter with our standard B & K 2203 sound level meter (SLM). The SLM was positioned 35cm above and one meter from the top front edge of the case. This was the same setup used for acoustic measurements and recordings after a test system was installed in the case.
Not an ideal acoustic test setup, but it had to do.
The ambient level in the lab was 19 dBA. The results are shown in the table below.
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Antec Mini P180 Fan SPL (dBA@1m)
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Speed Setting
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low
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mid
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high
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|
200mm fan
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23
|
28
|
35
|
|
120mm fan
|
22
|
33
|
41
|
|
|
24
|
37
|
44
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The 200mm fan is clearly quieter than the 120mm fan at any setting other than low. The actual sound character of the larger fan is more pleasant, as it consists mostly of wind noise (whooosh) and a bit of low level clacking or chatter at the low speed. Most of its noise is low in frequency, which makes it less audible, in general. (Note: It sounds much worse in the recording than live, especially if you set the playback volume too high.) The 120mm fan sounds reasonably pleasant at the low setting but at the mid and high speeds, it is much louder, with unpleasant high frequency overtones.
Other fan speed combinations were tried. Here are the results, ordered from quietest to loudest:
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Antec Mini P180 Fan Noise (dBA@1m)
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200mm
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120mm
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SPL
|
|
off
|
low
|
22
|
|
low
|
off
|
23
|
|
low
|
low
|
24
|
|
med
|
off
|
28
|
|
med
|
low
|
29
|
|
low
|
med
|
34
|
|
high
|
off
|
35
|
|
high
|
med
|
36
|
|
med
|
med
|
37
|
|
med
|
high
|
42
|
|
high
|
high
|
44
|
Despite the closeness of the SPL readings, the 23 dBA@1m of the 200mm fan alone on low is subjectively more pleasant than the 22dBA of the 120mm fan or the 24 dBA of both fans on low. Personally, I would not be willing to run either fan on medium, with or without the other fan on; it's just too much higher than the ambient acoustics of my environment.
For the record, the big fan was removed and examined closely. Its basic design is sound, with struts probably no bigger than they have to be, and positioned correctly to be more or less perpendicular to the trailing edges of the blades to minimize tonal and turbulence effects. From the overall acoustic signature, I'd guess that it has ball bearings; a sleeve bearing might be too short lived in this large a fan. Holding and listening to it at the low speed setting, I have to say it's pretty dang quiet, especially for the amount of air it moves. We have no way of measuring the airflow as our fan test rig is set up for maximum 120mm diameter fans. Its SPL measures around 20~21 dBA@1m without load in free air
It measures 22.5 x 20 x 3 cm. The hub (motor, really) measures 6.5cm across.
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