How to Silently Overclock with Air Cooling
Overclocking is a combination of gambling, engineering, and hardware hacking. There are many different approaches, and I've pretty much tried them all. I've done extreme air cooling, with something like 200 cubic feet per minute (CFM) rushing through my computer, I've done water-cooling in various forms, including my infamous four foot tall clear acrylic bong tower, and last year I gave it all up for silent cooling. With silence I backed off my heavy overclocks significantly, and lived with more modest increases over stock settings.
My latest nerd adventure is trying for a pretty heavy overclock with near silent cooling. I knew true silence wasn't possible, since true silence is typically considered a computer under 30dB. At ear level mine is probably more like 35dB - you can hear it, but only if you're listening for it. It's about as loud as a whisper from five feet away - typically it just blends into the usual background noise and is effectively silent, though not technically silent.
My Results
I started with this system as a base:
- AMD Opteron 146 @ 2000MHz w/ 1MB L2 cache
- 2x512MB of Buffalo RAM (generic, but uses the legendary Winbond BH-5 RAM chips)
*** RAM SPD (standard) settings are programmed to 166MHz, 2.5-3-3-7 timings
- ASRock Dual SATA-II Motherboard (semi-generic, $65)
- BFG 6800OC (nVidia 6000 non-ultra based card)
- 250GB Western Digital silent IDE-133 drive
- Seasonic S12 380W super-efficient Silent PSU
That's a pretty decent setup by most standards. Not a slow machine, but not a top performer either. But, as of 4/21/06, I've managed to take it much farther than spec:
- The Opteron runs at 2750MHz, and with the 1MB cache that makes it 98.2% as fast as an AMD FX-57, the fastest single-core chip available. FX-57's cost over $800 - my Opteron was $170.
- My RAM is currently at 230MHz with 2-2-2-5 timings. This is 30MHz over stock PC3200 (what most A64/Opteron machines use), and while the science behind RAM timings is mind numbingly boring, just take my word for it that 2-2-2-5 timings are basically as fast as you can get and are typically much better than stock. This required a 3.3v mod to the memory voltage on my motherboard by patching the 3.3v supply from the PSU to the vDimm supply. I put a silent fan over the RAM to keep the ram from frying. I've used Memtest86 to test the RAM up to 244MHz 2-2-2-5 stable, but due to divider issues I'm forced to use a slower 230MHz speed.
- My BFG 6800OC video card comes with a stock setting of 350MHz on the GPU and 350MHz DDR on the video memory. This is typically written out as 350/350. This card comes pre-overclocked - stock 6800nu cards come 325/325. With the addition of a near-silent Zalman cooler and ramsinks I was able to take the card to 400/430 which gives me about a 10% boost in speed.
All this was done with near silence, with the option of total silence. It's also verified as 100% stable by running the computer through a series of rigorous tests such as Memtest86 (9 hours stable), Prime95 (19 hours stable), and 3DMark. This can run all day, rock solid, and never crash, overheat, etc. How was it done?
How you can Overclock in Silence
It's all based on proper airflow. If you can manage the flow of air into and out of your case, you don't need loads of fans or whatnot to make up for a lack of planning. You can have hundreds of CFM flowing through the case and still have 'dead zones' without any significant flow. In my case the in/out CFM of the machine is only about 40 CFM. Inside the case I have additional fans for heatsinks and to help direct the airflow, but only about 40 CFM flows through the case.
First, take a look at the airflow diagram for my computer:
What makes this airflow plan work are these three elements:
1. Case Layout
As the picture shows, I keep the cables in my case very tidy. Don't waste your time packing your cables into Techflex or heatshrink - rounded cables don't make any difference if things are still a mess. If they're out of the way then it doesn't matter if they look messy - they won't affect airflow. Also think of where you place your drives. You want them out of the way of the fans, and you want them to allow for maximum passive airflow. You don't have to force air into and out of the case, let it do the work for you (and in silence).
2. Case choice
I chose a case that allows for maximum passive airflow, the Cooler Master Centurion for only $60 without a PSU. The entire front face of the case is a mesh with air filters behind it, which essentially provides a wide open design that still holds out the dust. The side panel has multiple passive vents, as does the back. If your case lacks these features you can still achieve them. Just remove the cover plates on the front panel, drill holes in the side of the case, etc.
3. Choice of Cooling Components
I use a Scythe Ninja cooler, which is one of the best coolers you can buy, with a silent 120mm ~40CFM fan. This fan is oriented to blow air upward, which aids in case airflow. For the video card I use a Zalman VF700-Cu near-silent 'flower' style cooler with 8 ramsinks for the BGA memory on the card. For case fans I use both 120mm and 80mm silent Cooler Master brand fans. The PSU is also silent yet effective at cooling. The Seasonic S12 series PSU uses a silent, variable speed 120mm fan and an open-airflow design to allow maximum cooling effect. Almost all my fans are hooked up to a Cooler Master Aerogate fan controller allowing me turn down the fans to achieve true silence if I want (music listening for example), though I usually leave them up at near-silent levels for the performance gain in games and other intensive apps.
Planning Case Airflow
In my case I knew that passive intake was the key to silence. I only have one active intake, a silent 80mm fan in the front. It helps to get cool air to an otherwise 'dead zone'. This air helps cool the hard drive and video card. When planning passive intakes, think about how the air will enter the case, and where it will be beneficial. Also, make sure you have negative case pressure, which means that you have more air being blown out of the case than there is being blown in. If more air is being sucked out of the case via fans, extra air will naturally flow in via your passive intakes to make up the pressure difference. This is the key to silent cooling in my opinion.
In the following pic, the passive intakes are marked blue and the exhaust is marked red. Both my PSU and lone exhaust fan use silent or near-silent 120mm fans. These two together pull a large amount of air out of the case, around 40CFM+. My lone intake fan, the silent 80mm mentioned earlier, only takes in about 15CFM. This creates substantial negative case pressure, which allows the passive intakes to function properly. Also I've left any unoccupied PCI slot cover open. This creates even more passive intakes for airflow.
The reason I covered the upper passive intake is because air takes the path of least resistance. If it were open, the exhaust fans simply suck air in through that hole and immediately blow it out of the case. By covering it, air is pulled in via the lower intakes and is then blown over the CPU heatsink before it is exhausted from the case. This dropped temps by 1C-2C.
Taking a look inside, you can see how the passive intakes help bring in air to the case. As you can see, my CPU heatsink, the Scythe Ninja cooler with a silent 120mm fan, has the fan pointing upward. This creates a strong upward flow. This takes all the cool air from the lower half of the case and blows it up through the heatsink, where it is then exhausted out the back. It also sucks away hot air from the video card, thus preventing it from stagnating and forming a dead zone around the video card.
Here's a low angle view of the heatsink fan showing the flow of air upward through the case. Once the air from the lower reaches of the case is pulled upward, it is exhausted out the back via the PSU and 120mm exhaust fan.
Next, see some detail of the front of the case viewed from the inside. On the left is the 5 1/4" bays, and you can clearly see the open-mesh design for the exterior covers which allow for passive air intake, and also allows some heat to escape from the RAM. On the right is the 80mm intake fan in the lower part of the case, which blows over the hard drive and then on to the video card.
And remember - rounded cables aren't always the best option! A flat ribbon cable used properly can actually provide more options for hiding the cables as shown here. Not only does it tuck neatly under the hard drive, it also helps cover the mess of other cables connecting to the motherboard.
And the last bit of detail is a silent 80mm fan zip-tied and wire-tied into the case to help cool the RAM. This fan breaks up a 'dead zone' near the 5 1/4" bays that was causing the RAM to overheat. This extra cooling is normally not necessary, but my 3.3v vDimm mod gives the RAM over 22% more voltage than stock - in this case the cooling was needed. Some of the heat from the RAM is sucked out through the PSU and case exhaust fans, while some simply escapes passively through the mesh 5 1/4" bays pictured above.
Conclusion
I hope this article can help provide you some guidance on how you can manage case cooling while maintaining a near-silent computer. With the right planning significant overclocks are achievable without the need for an 'extreme' cooling solution or significant cost. Please feel free to comment or email me if you have any questions on setting up a good cooling solution for yourself.
posted on 04.22.06
comments
While looking at your first airflow diagram I have to ask why do you have the lower back of the case open when the hot air is being expelled out right above it. Or does it not matter due to the fact that the air is hot enough that it simply rises away from the case.
posted by leonard on 05.01.06
Hi Leonard,
I've found that the exhaust fan blows the heat pretty far away from the back of the computer. Also the passive intakes are pretty weak overall - since there's so much surface area devoted to passive intake, no one spot really has any heavy suction. It's more of a slow-flow of air. Because of this there's not enough suction at the PCI slots to 'pull' the air from the exhaust downward. I'm sure there is *some* recycling of air, but I haven't found it to be much of a problem.
--Sean
posted by Sean on 05.01.06
hi liked your article. just a question doesn the PSU blow hotair onto the CPU? this way hotair ussing really being sucked in. by the PSU and out from the back.
posted by joshua on 08.23.06
The PSU fan is an exhaust, so it's doesn't blow anything onto the CPU, but rather helps exhaust air from the CPU.
--Sean
posted by Sean on 08.23.06
Surely mounting the HDD upside down can't be healthy?
posted by robaal on 10.31.06
Actually it doesn't really matter. You can even mount them sideways - many removable drives have orientations such as this. As long as the drive isn't being moved much during use it should be fine even at odd angles.
posted by Sean on 10.31.06
woldn't it be smart to take the top side panel vest inside rather than outside
posted by inf on 01.19.07
Liked the article. But I keep remembering my own cooling problems which didn't change at all even when removing the side cover of the tower. You'd think that would open up a lot of passive airflow. But my temps (cpu) stayed the same.
Steve
posted by Steve on 03.03.07
do you have any dusting problem with many opened slots for intake take air?
posted by intal on 03.10.07
nice ide....
posted by FList on 03.14.07
Hi,
I have a freezer 7 pro CPU heatsink/cooler.
I have checked multiple websites and all have the fan on the cooler facing the front of the case. This would cause air to be pulled over the ram and exahusted out the back of the case. Just wondered if you turned your cooler in a like fashion if that would eliminate the need for the extra fan.
Thanks,
Rob
posted by Rob on 11.20.07
Hi Rob,
Since I run 3.15V+ through my RAM I really need that 80mm blowing directly down on them...I actually used to have the config you mentioned but it overheated quite a bit :-)
--Sean
posted by Sean on 11.20.07
@ inf.
It wouldn't be smart to have air pulled in from the top, because hot air lighter than cooler air, therefore hot air always goes up faster than cooler air. It would be wiser to have cooler air pulled from the lower air of the case them have it pushed upwards on top for vetilation.
In addition, adding a fan at the bottom with a filter will also help lower temperatures at silent performance.
posted by Legend on 03.02.08
Adding a fan at the bottom helps, because it helps pus cooler air towards the top, giving the cpu fan to pull in cooler air to cool the heatsink, thus helping lower the processor cooler efficiently. Howerver, you need to have a fan on top (which i think is one most important fans) because it helps get rid of hot air. More hot air going out means more cool air in there.
posted by Legend on 03.02.08
now 1/3 coolers over ram only,
why not place taht cooler with some angle ?
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posted by sheshysep on 08.08.10