A cup, the USPS Priority packaging tape makes a good circle. I use a compass myself to draw out a top blowhole, since that way i can map where the center and exactly put it where i want it.
You want a slight overlap on your opening, you don't want it too small cause then you'll have excess noise from air brush against it. Sometimes its better to use a shape that looks like this:
o ____ o
/ \
| |
\____/
o o
Ya also wanna use finger grills as least as possible in intakes, cause that also causes air turbulance noise and screws with the airflow very so slightly, finger grills on outake ends of the fans doesn't make an noiticable noise. Just things to consider, usually doesn't matter with low rpm fans, but you will definatlly hear something when using a 120mm fan blowing 100cfm 🙂
Discussion Zen 5 Speculation (EPYC Turin and Strix Point/Granite Ridge - Ryzen 9000)
