Re: Quiet fan advice

The message <dN6dnc0M_cOWkl_ZnZ2dnUVZ8qWdnZ2d@xxxxxxxxxxxxxx>
from "Alex Fraser" <me@xxxxxxxxxxx> contains these words:

My main computer as a whole is virtually silent while idle in comfortable
ambient temperatures. In a quiet room, I have to be quite close (say,
within
a metre) and listen carefully to hear it. Under sustained load (gaming) or
in higher ambient temperatures, the processor fan (speed controlled by Asus
Q-Fan) becomes audible.

Yes, that's a really serious defect in thermostatic control of fan
speeds. :-(

There are three fans in the system: a 120mm fan in the PSU (Seasonic S12

I now have my doubts about using a nice large 120mm fan in a PSU. In
theory, it should provide very quiet and ample cooling flow. The
practice, rather sadly, can be _very_ different, as I proved recently.
The problem seems to be along the lines of trying to squeeze a quart
into a pint pot, it just can't be done!

430W), a 120x25mm fan running at ~6V below the PSU, and the 70mm(?) Athlon

Presumably, the 120x25mm case fan is providing additional exhaust
capacity. If so, it will be in competition for what might be a limited
supply of intake air.

64 retail fan on the processor heatsink. The graphics card [1] and

Are you sure it isn't the standard 80mm? 70mm seems rather mean (and
non-standard, or at least unusual and not so easily sourced as a
replacement).

motherboard [2] chipset are passively cooled using heatpipes. (In the case
of the motherboard, the radiator also seems to double as a heatsink for the
Vcore regulator bits.)

[1] http://uk.asus.com/products4.aspx?l1=2&l2=8&l3=0&model=961&modelmenu=1
[2]
http://uk.asus.com/products4.aspx?l1=3&l2=15&l3=148&model=539&modelmenu=1

The hard drives run a little hot; they reached 45C in a room at 32C. The
hard drives bays are at the front and bottom of the case, next to the main
air inlet (the only inlet, save "leakage") where I can mount a second
120x25mm fan.

I wouldn't bother actually blocking this intake aperture with a fan.
:-) Far better to take a pair of tin snips to the rather pretentious
"grillework" most cases seem to be curesd with.

You can mount a 7 volted ex cpu cooling fan on a bracket to direct
airflow over the drives if need be. I used a 7 volted ex-cpu heatsink
60mm slimline fan for this job.

Provided there is at least 15mm clear space top and bottom of each
drive, a gentle flow of air to prevent a layer of stagnent hot
insulating air building up should suffice.

I am thinking of fitting a fan by the hard drives - what would you
recommend
given my desire to keep noise down?

I could also replace the fan below the PSU, and perhaps cut out the
(hexagonal) stamped grilles. Are either of these likely to be worthwhile?

As Dorothy would confirm, removing such grillework will make a
considerable improvement.

Cutting out the grilles is a lot of effort since I am reluctant to do it
without emptying the case, to ensure I don't get shards of metal in bad
places.

A decent pair of tin snips should make short work of the job. It's only
when the results of such hacking are visible or accessable to handling
that you need to tidy up any sharp edges.

Although I am not concerned over the CPU temperature (which I have never
seen at more than 50C), I wondered if a larger processor heatsink,
taking an
80mm or 92mm fan, would give more airflow over the motherboard
heatsink/radiator (which gets too hot to hold with the system under
load and
high room temperature) and thus reduce temperatures without increasing the
noise level. Does this sound reasonable? Should I see what effect improving
the case airflow has first?

I'm using a case that must be some 7 or 8 years old. It's of the
wideline Midi ATX tower form factor with the PSU mounted "over the cpu
area". This was fine for the slot 1 P2/350 I was overclocking to 467MHz
and nice and quiet considering the pair of 12 volted cooling fans on the
cpu heatsink.

The (almost) origional 300 watt 'Noisekiller'(tm) PSU never sped it's
fan up until I fitted a socket A MoBo and Barton cored XP2500+ cpu. When
it did prove itself, it was rather late at night and gave me a bit of a
fright as a new, unheard of noise (a whine that kept increasing in
pitch) suddenly manifest itself.

The PSU had the conventionally mounted rear panel 80mm fan and vent
grilles on the opposite panel. I'd had difficulty finding a suitable fan
cooler for the cpu on account a decent sized one would place the top of
the fan within 5mm of the unvented PSU case panel.

I was about to give up on the case and rebuild in a newer one when it
occurred to me that all I had to do was to rebuild the PSU into a
discarded psu case which had the vent grilles in the correct place, i.e
on that large panel facing the top of the CPU area, and reverse the fan
on the cpu heatsink so it sucked the air from the heatsink and dumped
it's warm exhaust straight into the PSU vent slots (which I'd twisted
into alignment with the airflow to reduce turbulence and maximise
effective CSA). Whilst modding the PSU case I took the sensible
precaution of entirely removing the 'grillework' that was choking the
PSU fan's exhaust airflow.

I tried fitting a 7 volted 80mm fan on the front panel intake of the
case but all this did was allow the MoBo sensor to recieve more fresh
air and show a 4 deg cooler reading whilst leaving the CPU temp
untouched. That was when I got the tin snips out and hacked away this
grille work and opened out the 42 x 3mm diameter holes on the plastic
facia immediately in front of this grille work to 10mm diameter (I'd
already opened out the inadequate vent slots on the underside of the
plastic facia some years back and fitted taller feet to reduce the
intake restriction).

The system is entirely dependent for ventillation on the PSU fan alone
(with some slight assistance from the CPU fan) and is very quiet. The
MoBo components around the CPU now recieve cool case air rather than
warmed up air from the CPU exhaust and the almost total absence of the
'Hot Air Recirculation Effect' inherent with the usual fan/heatsink
airflow arrangement means much lower case temperatures.

Even so, I had to seperate the two hard drives by fitting a drive cage
taken from a scrapped system and bolted to the bottom of the case and
fit a small 60mm slimline 7 volted fan to direct airflow over the drives
which typically run around 9 deg above ambient (The CPU runs 17.5 deg
above ambient idle and goes up another 5 deg under Prime95's stress test
(or another half deg under CPUBurn)). Mind you, I have the CPU
undervolted by 0.3v to reduce dissipation somewhat (about a 20 watt
saving, AFAICR), but even at stock voltage, this is still, by far and
away, the most optimum cooling solution.

Unless you have generously large CSA of intake vents, adding an extra
case exhaust cooling fan puts the PSU at risk of ventillation
starvation. Not a good idea if you don't want the PSU to go bang.

HTH

--
Regards, John.

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