I have this weird fascination with ATX-sized air handlers. Mesh air filters on ATX cases only stop the big stuff like hair. Years ago, ATX cases and some fan accessories used open-cell foam to act as a filter. The foam is a little better than the mesh, but it breaks down after a while, and you can't vacuum it clean more than 2 or 3 times before it starts to shred. So what is this engineer to do? Build his own.
One spring morning I was performing the yearly maintenance on my walk-behind lawn mower and noticed how the air filter is smaller than a 140mm fan; and the light bulb went on. Fast forward a year, and I have completed my project for a compact-ish air filter that fits inside an ATX case.
There is one problem with using a real filter on the intake of a computer, standard computer fans don't have enough static pressure to pull a sufficient volume of air through the filter to keep the electronics inside cool. We will combat this two ways.
- Use a pleated filter
- Use a fan with a high static pressure
Every filter will restrict air flow to some degree. But if you use a bigger filter, then the air flow restriction will be less. So how do you fit a very large filter into a smaller space? You add pleats.
A pleated filter folds the filter element many, many times:
Even though we have used a pleated filter, our standard 80mm and 120mm computer fans might not be capable of pulling enough air through the filter. Therefore, we need to look at stronger fans.
The best place I've found to shop for fans is DigiKey. Their web site allows you to search and sort according to fan properties. I selected three fans: 70mm, 80mm, and 92mm; all of which are 38mm thick. These are industrial-grade 12V fans with a tachometer output, PWM speed control input, and a static pressure rating of at least 1 inch H2O (25.4 mmH20). Why three different sized fans? I know that different sized fans will have a different sound profile. Each fan will have a different volume (SPL), base frequency (Hz), and harmonics. I've never heard any of these styles in person, so I decided to experiment. They might all be awful, or one of them might be perfect. And yes, they all have the capability of being "OH MY GAWD THATS LOUD", but with a PWM speed signal coming from my motherboard, I know they won't run flat out all the time.
I think I would like to experiment with some 120x38mm fans, too.