Honestly this is the best way to reduce noise of the antminer s9 if you don't have a cooled server room : r/Bitcoin
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Antminer noise reduction ideas. Just printed this part and added to the output fans, and now I am thinking to add also the same part to the intake fans with a quiet
Killers” of the mining equipment — getting rid of noise and dust | by BiXBiT | Medium
Antminer S9 noise level? - The most accurate Antminer noise level - like a Train - YouTube