The 4 case fans (2 front, 2 back) have been removed. The 6" inline fan is doing all the work. It has a manual speed dial which I have been tweaking while Braiins OS autotunes. Trying to keep the chip temps below 75°C. A little disappointing, but basically having to run the fan at full power to keep up, so a little noisier than I'd like (~59dB @ 1m). But still way better than the high-pitched case fans. The S9 power supply (APW3++) has its own small fan, but it doesn't contribute anything audible when the 6" is pushing this hard.

Thanks for the reply sir! Been a fan of your work for a long time. So your long term plan is to auto tune and set a specific hash-board voltage and then have the fan running at a constant rate unless manually adjusted? And if board temps ever get too high for that constant cooling rate, will the S19 automatically throttle?