Ok, I did it: tested the "cpu fan perpendicular to mobo way"! Thanks Pangit for the idea and encouragements!
- Here is the initial set up: what matter here is the cpu fan and Heatsink: Taisol Aqua HS, with 60mm fan replaced by 80mm Noiseblocker S4 on 60->80 adpater:
- As you can see, the cpu is located pretty close to the rear of the case, so that the 120 exhaust fan and the 80 cpu fan are competing against eachother. This is bad because it requires to have both fans rev higher (=louder) than needed to get the same flow.
- To solve this competition issue, I already tried ducting (see above in this trend), but was not happy with it (resonates, obstrusive vs exhaust fan, and... well, uh... ugly!)
So my objective was to somehow have the 2 fans (cpu and exhaust) blowing in the same direction, ie toward the rear exhaust hole (from right to left on the pic).
First, I started with some modding of the heatsink:
My Athlon 1.4 ("Toasterbird") has a Taisol Aqua heatsink (80x60mm Al/Cu base, Al fins), with a 80 mm Noiseblocker S4 blowing thru a 80->60 adapter.
The Taisol Aqua HS was designed to have a fan facing it, not being perpedicular to it. So I decided to help it a little bit with a popular mod of the rad fins.
The idea is to allow for more space between the rad fins, by bending them toward the outer of the rad. Bending each of the 120 Aluminium fins without breaking any is a bit touchy... and doing it leaving the HS on the cpu is not recommended... But somehow both the fins and the cpu seemed to survive it.
The result is an increase in the height of the heatsink, which is nos 80X90mm, versus its initial 80X60mm dimensions (stock fan was a 60mm whiny one).
The benefit is much more space between the fins, allowing for more air to pass thru more easily.
Positioning the cpu fan
I used some strong electric wire to suspend the fan to the case bar. This is as cheap as can be, but actually is very handy to quickly experiment several orientations ( both vertically and horizontally speaking).
First, to test the modded rad and the effect of getting rid of the 80-60 adapter, I started by hanging the fan just face to face with the rad, almost in his standard position.
- noise improved radically: I guess due to the fact that air is no more smashed thru the adapter and against the HS. Also the fan does not generates any more vibrations that resonate in the HS).
- temperature did not moved a bit, so I decided to carry on the test.
So here is the real test: I started gradually turning the cpu fan, until his final position right of the HS, in a almost perpendicular angle to the mobo.
- as the fan was moving to the right, cpu fan rpm went up, showing that there was less and less competition with the exhaust 120 fan,
- cpu temperature went down 3 degrees (idle: 51 to 48, load: 57 to 55), from the initial position to the perpendicular position. I was happy with this but decided to "re-invest" this temperature benefit in reducing both fans revs.
- the MAJOR improvement is that it allowed me to decrease the cpu S4 fan speed from 2700 rpm down to 2290 rpm: made a huge noise improvement because this brought the fan back to its "quiet" range of operation.
- I was able to also reduce exhaust fan speed ( from 2100 to 1600 rpm), reducing engine and turbulence noise. Due to reduced competition, note that this did not impact case temperature!
- Testing several angles/positions also confirmed that moving the fan away from the HS certainly reduced turbulences, but there is a compromise here when the fan is too far from the HS to ensure proper cooling.
Here is my final setup, with the 80mm cpu fan perpendicular to the mobo. Note that it is blowing slightly upward for a couple of reasons:
1/ when the fan is blowing, air pressure makes it move backward a bit, so its working position is actually more vertical;
2/ this position allows some fresh air to be pushed into the PSU fan, reducing its need for revs, and so cutting PSU noise as well.
Another view more from the front of the case: no doubt: the 2 fans are blowing in the same direction!
So overall, it works, and yes, it is much more silent than before!
I now plan to take it a bit further (too far?) by applying a second round of fin bending to the HS. But i promise this time I will remove the HS from the CPU for the extra bending... and apply some Artic ceramique as well...