I have a Corsair 400CX. It has the loudest fan in my system. (Not that fan the fan is very loud, but everything else is quieter so it by default becomes the loudest thing in my system.)
I would like to replace the fan, which is an ADDA, a AD1212MB-A71GL to be precise (http://www.mouser.com/search/ProductDetail.aspx?qs=OoDF8tjU0%2FOtPoFqQlgnYA%3D%3D
80.5CFM at 38 dBm which is a 2.12 air to noise ratio. However of course the fan does not run at 12v all the time, the PSU takes care of the voltage on the fan. (duh) I soldered 2 wires to the bottom of the power plug and ran the wires out the back of the PSU so I can monitor the fan speed while the PSU is "in action"
It currently is running at 4.22v and I have not seen it ever get to 5v from the little bit of watching I have done over the time I've had this setup.
So I am dealing with a decently low power system and a decently cool PSU. (right?)
So what fan would be the best replacement? I would doing a quick perusal at newegg and 2 Scythe's caught my eye.
The first one being an S-Flex getting 33.5CFM at 8.7 dBa, an impressive 3.85 air to noise ratio, and the second one being an 800rpm Slipstream, pushing 40CFM at 10.7 dBa, that's a 3.74 air to noise ratio.
Now I don't know how much airflow my PSU needs, lets say that the ADDA running at 5v is more than enough to cool my PSU, 5v is 41.7% of 12v, so 33.5CFM is 41.7% of 80.5CFM. Now of course I doubt that the math works out perfectly like that in the real world, but we can use those values as a ballpark. That is looking like the S-Flex at full 12v would be able to do the 5v of the ADDA, but I am concerned as I don't want my PSU to overheat, what if my PSU needs more than 5v of ADDA cooling, that would be more than 12v of the S-Flex could provide.
The Slipstream doesn't do much better, just doing simple math, it can only provide 50% of the ADDA, so that would be 6v, if my Corsair needs over 6v of ADDA cooling, the 12v Slipstream will fail to perform.
But that is just those 2 fans, I am not an expert in fans, so if you have any suggestions on the fan I should replace the ADDA with please chime in! I am not afraid of soldering, so I can solder this new fan right into the power connector of the old fan, or I can solder it directly to 12v, 9v (well, 8.7v) 7v, or 5v. So soldering and getting my hands dirty (so to speak) is not a problem.
My last concern is the sound difference I am going to achieve. Now I have said before that I doubt that math works like this in real life, but in a perfect world, where this fan is doing 1/3 of the rated voltage, it is doing 1/3 of the airflow and 1/3 of the noise level. What is 1/3 of 38 dBa you might ask? 12.7 dBa. So if I am replacing this 12.7 dBa fan with a 10.7 or a 8.7, how much of a noise decrease will there be?
So experts who know more than me, what is your take on my situation?