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Originally Posted by gurdas
...using 3x 120mm slow moving fans that produce the same noise as a single silent on the pa160.
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You may not be able to make this trade-off:
When slowing down an axial fan that's moving air through a resistance there comes a point where the fan "stalls" in the sense that it isn't producing enough pressure to move much air through the resistance. Each of the three fans is going to "see" more resistance because it's moving air through a smaller aperture (and resistance is proportional to the
square of the velocity).
There's a formula for the increase in dB when adding equal-energy sound sources (which I don't remember, but I think it's add 3dB to double, add 2dB more for a third - maybe someone here can refresh me on this but for now I'm
guessing three fans are about 5dB louder than a single one). For comparison 10 dB is double the sound level (or half, depending on which way you're comparing).
So... you'd need to reduce the speed on all three fans so that each was about 5dB quieter than the single one on the PA160 in order to get the same noise level - which I'm not sure is possible without stalling the fans.