In an effort to make the BigBox quieter, I replaced the standard 50x50x10 mm fan with a 80x80x15 24V model, and let it run on half speed by placing a resistor of about 84 ohm. The designs in this post include the fan guard, the knob and the lid. You can find the hinges here. The stl files are on thingiverse. Replacing the fan with a bigger one certainly helps, the printer is completely silent now (when idle). I have a PWM on the case exit fan that is running on 2%. (see this post)
Nice. I got temp regulated fans for the lid and back. But still stock sizes. They only speed up when it's printing. Thinking of doing like you so I can have a bigger fan with a filter on the lid. Already getting dust on my rumba.