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The best air pressure inside a case
Overpressure 43%  43%  [ 6 ]
No pressure 14%  14%  [ 2 ]
Underpressure 43%  43%  [ 6 ]
Total votes : 14
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 Post subject: Overpressured build with P182
PostPosted: Wed May 28, 2008 5:31 pm 
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Hello to you and all the others too. I'm a new user to this forum - with some odd ideas. My nature denies me to do things same way with others, even thou they have made it better :) Eternal seeker of a new way.

My components (all laying on a table so far):
Quote:
CASE: Antec P182
MB: Abit X38 quadGT (question 1)
CPU: Intel core2 duo E8400 3.0Ghz
CPU heatsink: Noctua NH-U12 "brick" (question 2)
MEM: 2 * OCZ DDR2 1GB PC2-8500 with heatsinks
GPU1: Asus EN7300 GT Silent 256Mb
GPU2: (will be added later) (question 3)
GPU heatsink: stock model or accelero S1 rev.2 (question 4)
PSU1: Seasonic S12II-380
PSU2: Seasonic S12-430 (question 5)
HDD1: 500Gt WD5000AAKS
HDD2: 500Gt WD5000AACS (question 6)
FAN1: Noctua 120 x 120 x 25 NF-P12-1300
FAN2: Noctua 120 x 120 x 25 NF-P12-1300
FAN3: Noctua 120 x 120 x 25 NF-P12-1300
FAN4: Noctua 120 x 120 x 25 NF-P12-1300
FAN5: Noctua 120 x 120 x 25 NF-S12-1200 (question 7)

Price of all the component's above (couple of them were used) was all together 750€ here in Finland


The goal: PC as silent as possible, even with possible underclocking of the hottest parts. I'm trying to build a system to last for years and i've chosen few of the component thinking about the future demands. I have no need to push everything out of them yet (overclocked memory, another PSU, extra fans and crossfire with two GPU's are all future options)

The idea: I'd like to try to cool the computer with overpressure instead of underpressure (please arque that a lot) by putting the needed amount of fans to blow cool air towards the hot components from down / front / back, and to leave the P182 top hole open (without a fan) letting the hot air breethe out free. I really don't know if this is a good idea at all, but that's why i'm writing here. I will probably need some channeling / tubing inside the case to get the cool air exactly where it's needed most, and to get it to blow all the component from right direction (mostly from down).

Base of the idea:
- Installing fans deep inside the case is vanishing a bit of their sound
- Overpressured air is capable of moving more heat than underpressured
- ABit quadGT has automatic rpm reduction for several fans
- Heat rises up, i'm just helping it out with a little pushing

Problems to solve:
- Possible turbulence inside the case
- Overpressured air is also moving more sound waves
- Aiming the cool air to blow where it's needed

The questions:
1. Which parts of the motherboard need direct cool air, and how it could be aimed for them?
2. Is it possible to put a noctua fan under the NH-U12 heatsink and blow the heat away upwards aiming the top hole? And how do I get the cool air under the heatsink?
3. Which pair of GPU's would be best (price/cooling/performance) for a crossfire system in the future?
4. I already have two of those very good accelero heatsinks, but I don't know if I need one yet in this system. Would you recommend to replace the stock sink of my old EN7300 GT, or do I really win any dB:s by doing so?
4b. How should I direct the blowing of cool air for the GPU? Should I divide the case to have a totally own wind tunnel for GPU (in future two of them)?
5. If I need the extra power in the future, how would you install two PSU's in P182 (note: P190 has two), or should I get a bigger PSU then?
6. Which one of the HDD's should be prime, or does it matter at all in sound level? Should I just use the faster AAKS model?
7. How many fan's should be used (5V / 7V) and where? There are a lot of possibilities in the front panel, and it might be even possible to use the empty backside cardholes to get the cool air in. I don't know if there's any room for 12cm fan thou.

More interesting question
8. Has anyone ever thought if certain fan rpm's or HDD rpm's resonate inside the case to make the sound louder? What frequency levels would a P182 have to be avoided?
9. I will probably get some disturbing turbulence inside the case if i need to use air-tubes, but if it all goes well, i might find all the sounds mixed to a very nice and steady humming. What size and what material should i use in these tubes? Is the "wired pipe" best option? (At least it's easiest to bend)
10. Is this all worth trying at all, or is the traditional underpressure system just better?

(I'll add some pictures here later)


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 Post subject:
PostPosted: Wed May 28, 2008 6:38 pm 
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Many people here have done many experiments, and AFAIK, the only one who advocates an overpressured case is Bluefront.

The basic concept is to get cool air where it is needed, and get rid of hot air as quietly as possible. My experience (and lots of others too) is that this is best done with fans inside the system that blow cool air directly over heat sinks, combined with ducts that direct the heated air out of the case with no recirculation.

If you haven't read it yet, take a look at my "superquiet superclocked" article in the DIY section of SPCR. You'll discover that a few very slow fans that direct airflow into some ducts surrounding heat-pipe-based coolers works extremely well.

By contrast, an overpressured case relies on passive airflow to remove heat from the case with no control over recirculation; with ducts you can be very selective about the airflow, and select exactly the speed/noise level needed to let the heat sinks do their job.

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 Post subject:
PostPosted: Wed May 28, 2008 8:34 pm 
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Thanks, I read your article right away. Dividing the whole chamber with a single duct seems great, making two wind tunnels from front to back. Does your system actually need that top hole at all? And your way of using a fan in the PSU chamber (putting it in the middle of it) seems also great.

I'm still thinking about tunneling more from down to up. I wonder if I could use the top hole to exhaust the motherboard and processor heat, and the upper backside hole to get rid of GPU heat with some different kind of ducting? Your article and pictures gave a lot of ideas. Isolating the GPU heat in different wind tunnel seems like a MUST, but in your system the heat must first come downwards from the GPU to it's massive heat sink, leaving the GPU still quite hot.

First idea that popped into my mind is to duct the processor heat sink to exchaust only from the top hole. That way there would be room for another wind tunnel to exhaust from the upper back hole. I would probably need some bending material to make that wind tunnel, or at least lift the dividing plate to an angle, ending it to down-back corner of the processor heatsink. How does it sound to you?

Noctua NH-U12 should be about as good as Scythe Ninja, so that shouldn't be a problem. Accelero S1 should also be good enough. I'm not, however, intend to buy a scythe kama bay, and i'm hoping i don't need to use 5.25 bays for air intake either. So i would need another intake method. Any ideas for that? Does the middle front fan provide alone enough fresh air for both subchambers (p182 has a fan place there), or should I consider some other intake route?


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 Post subject:
PostPosted: Thu May 29, 2008 1:03 am 
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FWIW.....Terminology/translation. The term "positive pressure" is usually used instead of "over-pressure" on English computer forums. Likewise "negative pressure" means "under-pressure".

There have been endless discussions on this subject over the years....on SPCR and other places. There is no "best" way. Each airflow method has advantages. Most people end up with a mostly negative pressure case because of one reason...... almost all cases are designed to be mostly negative pressure. And that includes the Antec P-180 series. In fact with the PSU taking up most of the bottom of the case, I would not attempt to build a true positive pressure case using this Antec product.

My opinion..... the easiest and best true positive pressure setup, has the intake fans on the bottom of the case blowing upward, with no exhaust fans at all. The exhaust consists of passive vents mostly on the top of the case. As you said.... heated air always goes upward. This is assisted by fans on the bottom also blowing upward. Is this the best airflow method and the quietest? Debatable. But IMHO.....it's the best positive pressure method.

As you can see, the Antec case puts the PSU right where the main intake fans should be located. I suppose you could design positive airflow around this problem.....but not easily. I prefer a different location for the PSU. Check out my current positive pressure project in the General Gallery..... Dual MB...Rocketfish/Lian Li. This is a true positive pressure case.... no exhaust fans, two mother-boards, two power supplies, three 140mm intake fans on auto-control, and a built-in effective air filtration system. This particular design could have been constructed using no intake fans, and exhaust fans on the top blowing upward. IMHO.....it would not run as quietly or cleanly being built as a negative pressure case.

You can construct cases using neutral pressure..... I used to do it that way. But no more. Do a search under my name and positive pressure and you'll find dozens of links.....maybe hundreds. :lol:

Good luck with your project.

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PostPosted: Thu May 29, 2008 1:26 am 
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Quote:
By contrast, an overpressured case relies on passive airflow to remove heat from the case with no control over recirculation


i'm surprised BF didn't respond to this, from what i can tell in his builds there is control over recirculation, and sometimes it can be more efficient to use cooling air more than once (ie "recycle" it), so "smart" recirculation if you will.

from the OP:
Quote:
Overpressured air is capable of moving more heat than underpressured


if there is any difference at all, it is likely to be infinitesimally small. air is air, cooling rate is dependent on mass flow and temperature differentials.

Quote:
Problems to solve:
- Possible turbulence inside the case


turbulence is good for cooling, but may cause additional noise.

Quote:
Overpressured air is also moving more sound waves


again, I don't think the physics of this stack up. the main thing is what barriers are in the way of the sound waves, and the travel paths to the user's ears.

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PostPosted: Thu May 29, 2008 2:04 am 
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jaganath...... I'm not sure if I'm getting everything in his posts, perhaps through a translation problem. Without a doubt, the airflow in a positive pressure case can be completely managed. In that Rocketfish/Lian Li setup there is no re-circulation effect at all. The airflow from the "blow-down" CPU heatsink is instantly blown upward and out of the case by the intake fan's airflow.

That setup doesn't really use any real "ducts". There are airflow deflectors in there, a louvered plate at the exhaust opening.....but no real ducts. Ducting certainly can be of benefit is some setups, but adds complication.

Check out this I-Star setup. It's mostly positive pressure, using a somewhat complicated mass of ductwork to cool everything without any possibility of re-circulation.

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PostPosted: Thu May 29, 2008 5:44 am 
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Quote:
FWIW.....Terminology/translation. The term "positive pressure" is usually used instead of "over-pressure" on English computer forums. Likewise "negative pressure" means "under-pressure".

Quote:
I'm not sure if I'm getting everything in his posts, perhaps through a translation problem.

Translating finnish to computer terminology is new for me, sorry about that. I'll talk about positive pressure from now on, and please feel free to ask what i mean if there are other misses.
Quote:
almost all cases are designed to be mostly negative pressure. And that includes the Antec P-180 series. In fact with the PSU taking up most of the bottom of the case, I would not attempt to build a true positive pressure case using this Antec product.

The P182 case is not a best possible case for a positive pressure setup, i did have some consideration about it before I bought it. The room it gives for different kind of solutions was probably a reason to choose it, and the silence of course. Well... i'm trying to make it a good positive pressure case :) It probably needs some moding.
Quote:
if there is any difference at all, it is likely to be infinitesimally small. air is air, cooling rate is dependent on mass flow and temperature differentials.

Has anyone made any testing for the absolute air pressure inside a case in positive and negative pressured systems? If the difference is small anyway, there really is no meaningful difference in air moving the heat nor the sound. Double pressure (0,75 -> 1.5) would have a double amount of particles in the airspace to move the heat and sound waves, but if the actual difference is somewhere around 0,98 -> 1.02 we can forget those problems / benefits totally.

Nice to see my thread have started a discussion, I hope i'll get some answer's to the rest of the questions as well soon. I'm anxious to start the building, all the components are still untouched. But as they say, don't rush. Giving a few days for interesting ideas might end up with a better build here. Keep it coming :)


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PostPosted: Thu May 29, 2008 8:27 am 
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Recommendation..... take your time, particularly when doing mods that cannot be undone. Building the quietest possible setup takes planning, and consideration before you start cutting and modding.

The absolute pressure (either negative or positive) means very little, and no sense worrying about it. It's airflow that is meaningful.....exactly how it flows through the computer, and how much airflow there is (CFM). I use positive pressure because the intakes can be filtered much easier than negative pressure cases. Links to a bunch of positive pressure setups

There's no reason a P-180 case couldn't be turned into a good positive pressure setup. I only remember seeing a few examples however. I've never owned that case..... so no specific recommendations from me. I do think it could be done. Try it. :)

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PostPosted: Thu May 29, 2008 8:43 am 
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Hello,

This is a post that I wrote earlier:

I'm of the opinion (based on my observations) that pulling air is much easier/more efficient than pushing it. Because nature "abhors a vacuum", and this principle causes the low pressure area to be "filled in" easily, and the air is put into motion farther away from the fan.

Pushing air into a case and increasing the pressure inside the case causes the air to "try" to go back out through the fan itself, since it is closer than the exhaust. This is basic fluid dynamics.

What it really comes down to is: your choice about how you want to deal with the dust, that is inevitably in the air. in order to cool the computer, you must move enough air through it -- and that air will contain dust, no matter how you configure the air flow.

With negative pressure, you can either:

:arrow: Clean it regularly, including any filter.

:arrow: Or limit/control the intake as much as possible, to force air to pass through a filter -- by covering as many openings in the case as possible, except through the filter. If you want this to be quiet, you must provide enough filter area, and the filter must be low enough restriction to not force the fan to run faster, but still be effective at stopping dust.

With positive pressure you can either:

:arrow: Clean it regularly, including any filter.

:arrow: Construct a larger filter that can pass enough air, even after some dust accumulates. If you want this to be quiet, you must provide enough filter area, and the filter must be low enough restriction to not force the fan to run faster, but still be effective at stopping dust.

Negative pressure can move air through multiple openings with one fan: some in the front (over the HD's) and some through the side/back onto the video card. It also often concentrates the air flow past the CPU heatsink.

Positive pressure is less able to cause air to move through multiple openings (see above), because of the way a higher pressure zone will dissipate outward in all directions -- and it will take the shortest path.

Another way to think about it: a negative pressure case is moving air into the whole room, where it easily dissipates; and therefore the fan only has to work against negligible pressure. A positive pressure case is moving air into the case, which is not going to dissipate as easily, and therefore makes the fan work against a little greater pressure, all else being equal.

In order to take full advantage of a filter, in either arrangement, you must run the fan a little faster -- because by definition, the filter will restrict air flow somewhat. This will be a little noisier, no matter what.

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PostPosted: Thu May 29, 2008 9:01 am 
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NeilBlanchard wrote:
Pushing air into a case and increasing the pressure inside the case causes the air to "try" to go back out through the fan itself, since it is closer than the exhaust. This is basic fluid dynamics.

And so does pushing air out of the case. Vacuum is created inside, so air wants to go back the same way it came in, through the fan. This is basic fluid dynamics back at ya. ;)

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PostPosted: Thu May 29, 2008 9:40 am 
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Modo wrote:
And so does pushing air out of the case. Vacuum is created inside, so air wants to go back the same way it came in, through the fan. This is basic fluid dynamics back at ya. ;)


vacuum is a bit of a misnomer, we're probably talking about a pressure differential of less than 5mmAq (axial fans at typical SPCR speeds almost impossible to produce more than this) between the intake and exhaust sides, but yes either way there will be some degree of recirculation through the space between the blades and blade tips/rotor housing.

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PostPosted: Thu May 29, 2008 11:36 am 
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I've given a deep thought for this positive or negative now... and i have finally given it my own vote too.

For gaining something like 1 dB I'm not going to choose underpressure + regular cleaning or almost impossible sealing. And you might also loose that 1 dB if you forget the cleaning :)

I also think that either solution would actually affect at all on recirculation of the air, since between different sides of the fan there's always negative pressure on the intake side and positive pressure on the exhaust side of the fan (air very close to the fan). So there's some recirculation (impossible to avoid) anyway.

I'm very thankful for all your links and posts. Keep up the good work debating here, it doesn't matter if I made up my mind with this upcoming system already. My system is going to be positive pressured and pretty much ducted, all vents will have proper filters.

Update to my question list:
1. So I'm ducting the heatsink on the processor - how do I secure that other hot parts of the motherboard will be provided with enough cool air
2. Is it possible to mount a fan downside an NH-U12 heatsink pushing the heat away from the top vent of P182?
3. Which pair of GPU's would be best (price/cooling/performance in that order) for a crossfire system in the future? Both of them will have Accelero S1 rev.2 on them.
4. (To be tested by myself)
5. If I need the extra power in the future, how would you install two PSU's in P182 (note: P190 has two), or should I get a bigger PSU then?
6. Which one of my HDD's should be prime, or does it matter at all in sound level? Should I just use the faster AAKS model?
7. I think i'll amount 1 fan to middle front with 5V-7V, 1 under the CPU heatsink with 3,5V-7V, 1 to PSU chamber with 3,5-5V and 0 fans to top/upper back vents. Opinion?
8. Has anyone ever thought if certain fan rpm's or HDD rpm's resonate inside the case to make the sound louder? What frequency levels would a P182 have to be avoided?
9. solved
10. solved
11. Most of the air will be provided by Noctua 120 x 120 x 25 NF-P12-1300 pushing from middle front. I'm thinking about cooling the MB+CPU heat via top vent and GPU heat via upper back vent. Do you have ideas for ducting / dividing the main chamber and possible second air intake?


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PostPosted: Thu May 29, 2008 12:40 pm 
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First picture of the idea
Image
(fans placed in blue arrows, not in red. White lines are plating/ducting)
What would you do to get it better?


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PostPosted: Thu May 29, 2008 1:05 pm 
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Sorry... I can't answer any of those questions, but I can reply to Neil's post. With the normal small flat filter you see for sale here and there, you'll be cleaning it all the time, and since it clogs quickly, the fans will need to spin faster, and dust no doubt will be sucked in through every small opening.

With a large filter such as some of those in my links, you need to clean it very infrequently. The fans don't spin faster except after a long time, and all the air entering the computer has to go through the filter......something a negative pressure case cannot accomplish, no matter how careful you are with sealing.

The noise factor.....IMHO, a fan blowing into a case (positive pressure), will be quieter than the same fan at the same location, blowing out of a case. Sit close to a fan opening and test it out....

Filters cause increased fan noise? Not necessarily. A big filter inside an acoustically dampened housing, can decrease the intake noise. I've done it in quite a few setups. The same housing in a negative pressure setup, would also decrease fan noise. This isn't something you can buy.....it's DIY.

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PostPosted: Thu May 29, 2008 5:41 pm 
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Hello,

Modo wrote:
NeilBlanchard wrote:
Pushing air into a case and increasing the pressure inside the case causes the air to "try" to go back out through the fan itself, since it is closer than the exhaust. This is basic fluid dynamics.

And so does pushing air out of the case. Vacuum is created inside, so air wants to go back the same way it came in, through the fan. This is basic fluid dynamics back at ya. ;)


No, I think the dynamics are a little different, because of the much greater volume of air in the room -- it doesn't pressurize very much at all, and so it won't flow back into the case. Conversely, the case is relatively small, and so the pressure will be relatively higher inside the case if the fan is blowing into the case; all else being equal.

Here's an example that I am basing my theory on: I use exhaust fans in my attic during the summer, and if I close all the windows on the second floor and on the first floor -- and I open a couple of basement windows, I can feel air flow on the basement stairs, and I can feel the cooler air in the basement being drawn up into the first floor.

The same thing can be done in one room with at least two windows. If you blow air into the room from one of the windows, it never seems as effective at cooling the whole room; or at least it takes longer.

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PostPosted: Thu May 29, 2008 7:38 pm 
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maalitehdas wrote:
Thanks, I read your article right away. Dividing the whole chamber with a single duct seems great, making two wind tunnels from front to back. Does your system actually need that top hole at all? And your way of using a fan in the PSU chamber (putting it in the middle of it) seems also great.

I'm still thinking about tunneling more from down to up. I wonder if I could use the top hole to exhaust the motherboard and processor heat, and the upper backside hole to get rid of GPU heat with some different kind of ducting? Your article and pictures gave a lot of ideas. Isolating the GPU heat in different wind tunnel seems like a MUST, but in your system the heat must first come downwards from the GPU to it's massive heat sink, leaving the GPU still quite hot.

My CPU uses much more power than yours will (an overclocked 6600 consumes about 95W), so I needed to isolate the CPU heat from everything else. That's why the duct over the Ninja runs straight out of the box. The top fan exhausts the heat from the rest of the motherboard, mostly the north bridge, but other components as well. A newer system probably doesn't need this.

As for the GPU, first of all the Condor was the best heat sink at the time, but the Accelero is much better. Second, heat pipes don't care about gravity, so "pulling heat down" is not an issue, although of course it is true that having the radiators below the heat source is not optimal. If I were building a system today, I'd use an Accelero. Third, the exhaust path for the GPU heat is straight out the back through some open vents in the PCI slots.

Quote:
First idea that popped into my mind is to duct the processor heat sink to exhaust only from the top hole. That way there would be room for another wind tunnel to exhaust from the upper back hole. I would probably need some bending material to make that wind tunnel, or at least lift the dividing plate to an angle, ending it to down-back corner of the processor heatsink. How does it sound to you?

The ducting from a square heat sink (such as the Ninja or HR-01) is much simpler to the back hole, since everything lines up. Ducting to the top is harder, and really won't work significantly better.

Quote:
Noctua NH-U12 should be about as good as Scythe Ninja, so that shouldn't be a problem. Accelero S1 should also be good enough. I'm not, however, intend to buy a scythe kama bay, and i'm hoping i don't need to use 5.25 bays for air intake either. So i would need another intake method. Any ideas for that? Does the middle front fan provide alone enough fresh air for both subchambers (p182 has a fan place there), or should I consider some other intake route?

There are lots of CPU heat sinks that work very well at today's CPU power levels. Scythe, Noctua, ThermalTake, ThermalRight, Xigmatek, etc.

For the GPU, an Accelero is the best choice.

Whether you need a Kama Bay (or other filtered inlet) depends entirely on your airflow/noise tradeoffs. For my system, the 2:1 outlet:inlet ratio of the stock P180 was entirely inappropriate. A lower-wattage system might be able to get by with the small inlet cross section.

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PostPosted: Mon Jun 23, 2008 12:22 pm 
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I was on a long vacation, very very nice... after my holidays i finally got my silent build ready. I took the photos like i promised while doing it, but I can't remember where are they... I'll add them when I find them.

Overpressured build seems to work very nice:
Image
Picture is from a beta version of SpeedFan, not yet able to control fans in this mobo (abit IX38 quadGT). I took it after 10h of normal use.

You can all guess that noctua fans are almost noiseless with these speeds. Only sound I hear is the PSU and HDD. I managed to run 3Dmark03 getting 10655 points (which is very good with one overclocked 7300GT GPU), temperatures went up about 10 degrees during the test ending up to PWM max 70C. GPU didn't reach even 50C. Accelero RULES!

My fans are situated
- CPU fan (ninja's own fan) attached under Scythe NINJA blowing upwards
- SYS fan (Noctua NF-P12) in lower chamber (HDD + PSU)
- AUX1 fan (Noctua NF-P12) to intake from middle front
- AUX2 fan (Noctua NF-P12) to intake from back down (through free card slots) aiming GPU
- AUX3 (Noctua NF-P12) fan to exhaust from back upper hole (not very necessary...)
- P182 case top hole is without fan

Fans speeds are controlled with abit uGuru microprocessor and voltages are also reduced with L.N.A adapters. It gives me a chance to vary the voltages between 4.5V-9V (CPU fan is without L.N.A and it should vary between 3.6V-12.0V, doesn't seem to work perfectly however...)

What next?
I'm going to run few tests with different fan positioning / fan amount
I'm going to try some ducting to see if it really affects or not

If anyone knows a link about making Seasonic S12 PSU fanless, please put it here


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PostPosted: Mon Jun 23, 2008 1:30 pm 
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Joined: Fri Jan 23, 2004 7:50 am
Posts: 1705
Location: Baton Rouge, Louisiana
Old thread, but I'll chime in anyway--I also advocate positive pressure setups. Some of my rigs are positive pressure; some are negative pressure. The latter tend to be minor modifications of normal ATX layouts, with low power old CPUs so the heat of the CPU can acceptably be flushed out through the PSU.

However, most of my more powerful rigs are positive pressure. I've settled on a sort of "standard" layout--air gets sucked into the case via a flipped undervolted 80mm PSU fan; the PSU is mounted at the bottom of the case. The air exhausts behind a fanless tower CPU heatsink. The PSU gets the coolest freshest air, and air warmed by the CPU immediately leaves the case without warming anything else.

For my next build, I'm probably going to use a cheapo ATX case and simply flip the entire case upside-down. The potential downside to this is that AGP/PCI cards are exposed to air warmed by the CPU, but my next build won't have any expansion cards.

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Isaac Kuo


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