It is currently Wed Dec 11, 2019 10:08 am

All times are UTC - 8 hours




Post new topic Reply to topic  [ 4 posts ] 
Author Message
 Post subject: The "Fix-ATX" Quiet Case Design
PostPosted: Sun Mar 08, 2015 11:41 am 
Offline

Joined: Sun Feb 22, 2015 11:57 am
Posts: 59
Hi guys! For job-search reasons I need to put more stuff on my blog, and I haven't posted this yet. I would appreciate criticism of the writeup as well as the case design itself. Thanks!

I recently decided that my computer was powerful enough. That's an odd thing to think, especially considering that the only things in my computer that are less than 3 years old are the small SSDs. The reality is, however, that typical users have very little to gain from upgrading any reasonably modern hardware. Everyday tasks such as web browsing and document editing are bottlenecked by network and storage speeds, and even as those components are improved I doubt that there are any perceptible gains to be made from improved chip design. What is a computer geek to do? I want to tweak!

While the performance gains to be made are minimal, improved chip design (and particularly increased focus on mobile processors) has dramatically improved the potential for efficient computing. While it's difficult to compare processors across architectures, consider that the legendary Q6600(*1) has a Thermal Design Power of 105 Watts, a good indication of both power consumption and heat generation. In comparison, Intel's hottest 4th generation i7 has a TDP of 88W, while possessing exponentially more processing power. Many i5s have TDPS of 45W.

Over the past few weeks, I have been focusing my tweaking efforts on harnessing these cooler processors to make my computer quiet and power efficient. There is a superb website called silentpcreview.com dedicated to this practice, which has been an excellent resource for both theory and assistance. I've used their advice, as well as forum discussion and articles on other sites, to bring my computer near ambient volume while maintaining GPU and CPU temperatures 20C° less at full processing load than when I started. The only hardware changes I made were swapping a few fans and a cooler!

This all got me thinking about airflow, which is the second most important element of maintaining a cool PC, the first being contact between the CPU and heatsink. The most common design for motherboards and computer cases is called ATX and it celebrates its 20th anniversary this year. I've read a few articles in which people have complained about it being a dated design over the last few years, but none of them mentioned airflow. Back in 1995, graphics cards didn't have fans. Often CPUS didn't either. The Pentium 1, released in 1993, had a TDP of 8W. Further, HDDs were so loud that they would drown out case fans to some extent, meaning that those fans could be run faster without being noticed. Perhaps most telling of all, Intel originally intended for airflow in an ATX case to go in the opposite direction it does now(*2)!

Nowadays we have graphics cards with massive cooling requirements, and CPUs that demand meaningful air cooling. My Radeon 7970 has a TDP of 250W...before overclocking. While CPUs have gotten generally cooler, GPUs have been on an upward trend. Fortunately our heatsink and fan design have improved along with those requirements, and we can get that heat away from the chip quickly and quietly. The problem is that the air then needs to go somewhere. That's where ATX falls flat on its face.

Image
This is the case I have, a Corsair Obsidian 550D. Of course this isn't mine (I wish mine looked so neat), but it's a very typical setup for newer cases. Air is sucked by two fans in the bottom right and flows through to the top left where another fan blows it out. On the way it needs to collect as much heat as possible and then get out immediately. The problem is that middle bit. In ATX, the CPU sits above the expansion slots which hold (in this example) a pair of very hot graphics cards which can only expel a fraction of the air they process out to the left. This means that any air sucked in is being heated up before it gets to the CPU. It is impossible to reduce the temperature of a chip below the temperature of the air flowing over it. This means that the bottom graphics card is making the card above it hotter, which in turn is making the CPU hotter still. This problem is compounded if, as I do, you have a cooler which blows all of its air upwards rather than flowing as much as possible directly outside. It would be better, though not perfect, if the airflow order were reversed because the CPU has a lower operating temperature than the GPUs, meaning that the air would be cooler moving through the case, even though it would ultimately exit the system at the same temperature. Unfortunately the exhaust fan needs to be higher than the intake fan (because hot air rises), so it is not possible to simply reverse the fans on a standard case. Remember that the original specification had the fans placed in the same places, but with reversed airflow. Then it would have been PSU->CPU->GPU->exhaust, which is a much better order.

I could go on, but I think you get the point. ATX cases have somewhat poor airflow. All of this has gotten me thinking about improved case designs that would allow better airflow, giving us more efficient cooling and therefore quieter systems. I've come up with a design for a case which is compatible with ATX motherboards. It would work even better it that were changed as well, but by keeping it I am able to ensure that this could be theoretically be made and sold. Though probably not cheaply.


Meet Negative Nelly!


Image
The case layout above is a representation of NNs layout as viewed from the front. It is broken into 3 compartments, each of which is partially isolated from the others. The green line on the far right is a standard ATX motherboard. The CPU is housed in compartment A, the GPU in compartment B, and everything else in compartment C.

Note that there are two sets of lines defining the case. The inner lines are actually a tray that sits on roller bearings and can be pulled out to build and modify the PC. This is necessary because the external "shell" must be airtight in order to benefit from the cooling effect of negative pressure. See where the name comes from?

Positive pressure is when the intake fans are blowing more air into the case than is being exhausted, negative pressure is the inverse. Since very few cases are perfectly balanced, all PCs have either positive or negative pressure. There is much debate about which is better, and the argument for negative pressure is as follows:

Noise is caused by more fans running at higher RPMs.

When a fan pulls air, it creates a vacuum behind it which will fill with more air almost instantly.

if the case is exhausting more air than it is pulling in, the vacuum effect will pull air through more quickly without requiring more fans or higher RPMs.

Therefore: Negative pressure = quieter!


I was in this camp until I read an article on the Silverstone website(*3) on the topic. As a component manufacturer they have the time and equipment to properly test airflow, so heed their words (unless they are trying to sell you something of course). Additionally, every case I have ever owned came set up for positive pressure, as do laptops, so there seems to be consensus among those who should know. The crux of the problem is that negative pressure does not direct airflow. Just like water and electricity, the air filling the vacuum is going to come from the place which has the easiest access (following the path of least resistance), and in a typical ATX case that place is very close to the exhausting fan. This means that the hot air being expelled is being sucked right back into the case, and not even passing over the components we want to cool!

Image
This is the motherboard side of NN(*4) . Here you can see the single MASSIVE 400mm case fan exhausting air from the case. Because it's so big, this fan can pull huge amounts of air at low speeds, meaning very quiet operation. Because the shell housing the fan is airtight, all of the air being sucked in must come from the front of the case, where all the cool air is. There will be some exchange of heat between compartments, but that is unavoidable and not concerning.

The next detail you should note is the line between the case and the CPU, sitting approximately where most mobos have a PCI-e 1x slot. In the actual setup I have here this isn't actually necessary, but it prevents air from interchanging between compartments A and B. Because many GPU coolers blow their air upwards, this blockage exists to prevent as much GPU air as possible from approaching the CPU. Since it will interfere with some motherboards and GPUs, I would make this panel removable in a retail design (note that it does not need to be airtight).

The reason we don't need it here is that the GPU cooler I used, to my knowledge, doesn't actually exist. While impractical in a dual GPU setup (which very few people have or need), what I've done is planned a frankly ridiculous tower cooler of the type normally used on CPUs. Weight would be an issue and the contact between the GPU and cooler would have to be perfect in order to fully utilize it. However, it does represent an ideal cooling situation.

The last point of interest is cabling. In the layout picture you can see a thick central line in the removable tray. That houses permanent wiring that connects anything which needs to sit between the three compartments. IO panels inside the case link the sections as required, as well as to a front panel which houses this like headphone and USB ports. Once again, in a retail design this wouldn't be flexible enough, because it locks the user into certain types of cabling which become obsolete or otherwise insufficient. It would also increase cost substantially. Replacing the panels with holes would allow custom cabling with a minimal impact on airflow, though extension cables may be required for some components. Anything at needs to exit the case (such as video cables) can be sent out a hole in the front as seen in the layout

Image
In compartment C we have all the remaining gubbins. Because they are connected by cables, we have much more flexibility with respect to their configuration. Starting from the top:

The IO panel is directly connected to the wiring passage in the tray, and has all of the USB ports, headphone cables, and whatever else you might want. A disc drive sits below it, with room to add more if desired.

HDDs are mounted right in the middle where they will get more than enough cooling. In my experience they need none at all, so this is like Christmas for them! Because they have lots of room to play with, they can be suspended elastically from the middle of the case. This has been demonstrated to reduce drive noise substantially. With a specially designed frame this will be no less convenient than in a typical ATX case. This suspension system is the only reason for the leftmost panel in the tray as seen in the layout, so if it were eliminated that would make installation of components on this side slightly easier.

I am of two minds regarding the power supply. I have put it on little feet so that it can be placed with the intake fan down without compromising air tightness of the shell, but in this drawing I have it upside down. Testing would be required to determine the best method, so I left both in to represent both options.

This concludes exploration of the case. The only other point that I wish to address is the notion that the exhaust fan could be exchanged for an intake fan on the other side, creating a positive pressure case which would move a similar amount of air by pushing it out quickly. There are a few reasons this wouldn't be as good:

1. That would compromise your ability to have disc drive and IO panels on the front of the case where they are needed. Putting an intake fan on the back to resolve this means blowing hot air out the front, which is usually not what people want.
2. Airflow from an intake fan is shaped, and according to Silverstone (who are admittedly trying to sell us something in this case) it moves outward from the fan, meaning that most of the airflow would be on the edges of the case where it isn't needed. Further, there is a hole at the hub of the fan which has no airflow at all, again taking air from where it is needed most. A negative pressure situation should provide a much smoother distribution of airflow.
3. Positive pressure can create pockets of "standing air" which don't move out as quickly and heat up the case.
4. Intake fans need dust filters which block airflow. This case will still need a dust filter in the front, but because it is behind the fan it shouldn't create any blockage.


Of course it would still work, and I believe better than a standard ATX case. I just don't see any reason to do it.

The PC component industry has given open air cases and computers built into desks...

Could Negative Nelly be the next big thing?



*1 - In furtherance of my argument about computers being "good enough", consider that there are still people using Q6600s to play games. I expect that with the new consoles out, we will be finally start seeing games which render that 10 year old chip obsolete.
*2 - http://www.intel.com/support/processors ... 011025.htm
*3 - http://silverstonetek.com/techtalk_cont ... ve&area=en
*4 - Note that I have left out representation of the removable tray for clarity.
*5 - http://silverstonetek.com/techtalk_cont ... =wh10_0061


Top
 Profile  
 
 Post subject: Re: The "Fix-ATX" Quiet Case Design
PostPosted: Sun Mar 08, 2015 9:34 pm 
Offline

Joined: Thu Jul 28, 2011 10:35 pm
Posts: 19
Interesting post.

I think it is necessary to first of all figure out whom exactly one is designing a layout and case for. Going through a design process like this will require some compromises, and making the right ones is all about knowing who you are designing for.

If current performance is good enough, as you say, for web browsing and the like, then we are probably not looking at a multi-gpu solution - which is great, as cooling such can be quite difficult without water cooling. Although the recent SPCR article does show that we've come a long way in this regard.

Then we get to such decisions as whether an optical drive is really necessary. Are HDD's even? I doubt it. And at most one. If you need more, set up some NAS solution. The power requirements can be handled by a 400-500W unit. That's either SFX or passive ATX PSU territory, hopefully soon we'll see a passive 400+ Watt SFX unit. Semi-passive exists already I think and 300W may even by enough. And we might as well jump to mini-ITX if we have no use for the extra expansion slots.

These components fit in a volume quite a bit smaller than what you have drawn up. And I don't think it will produce worse noise and temperature results for that reason. A big heatsink on both the CPU and GPU, and a 140mm fan on each idling at 300 RPM and possibly approaching 800 at load. If the inlets are close by and not obfuscated by layers upon layers of plastic grills, metal grills and dust filters of various flavors, that should do the trick.

My general philosophy when it comes to cooling PC's is "point the blowey thingy at the hot bits". I don't really see the point of creating airflow in a case, when it is to make up for badly placed inlets. Bring the inlet to the heatsink.

When it comes to the compromise between noise and cooling, I haven't seen a single case do a better job than the open air testbed. Go read a review of a "silent" case (not SPCR). They will of course claim it to be more quiet than more open cases at the cost of higher temperatures - and they will happily give it an award. But why not just tune those fans, so the open case produces the same amount of noise? I bet they would getter better temperatures too. This naturally requires that we have the option of controlling those fans - which we fortunately often do have today.

Most of the time a case usually acts a terrible one-setting fan controller. Stick your components in it, the temperatures go up, the noise goes down. Like tuning a fan. The problem with "silent" cases is that the tradeoff happens at a generally terrible exchange rate. I should say that this perspective ignores electronic noise, coil whine and the like, and HDD's. These may very well benefit from a well insulated case, but should hopefully be a distant concern to fan noise.

Anyway - I'm rambling! I guess my point is that your design proposal tackles a very different heat load than the one you are describing initially. And even with a multi-gpu setup, I think a future layout will gravitate more towards something akin to the Mac Pro. One heatsink, one fan.


Top
 Profile  
 
 Post subject: Re: The "Fix-ATX" Quiet Case Design
PostPosted: Thu Mar 12, 2015 8:40 am 
Offline

Joined: Fri Jan 20, 2006 10:12 am
Posts: 566
Location: UK
nintendoeats wrote:
...Unfortunately the exhaust fan needs to be higher than the intake fan (because hot air rises), so it is not possible to simply reverse the fans on a standard case...

This has to be taken into account it you're relying on natural convection alone, but even a slow fan can completely overpower gravity, so blowing hot air down is just as good in practice.

nintendoeats wrote:
...everything else in compartment C...

Ren0ir already addressed this, but compartment C is a huge volume which for most people will contain nothing but a PSU. There is a trend towards smaller PCs, so if you want to actually sell these then you're going to have to trim away any unnecessary size.

nintendoeats wrote:
...the external "shell" must be airtight...

One of the disadvatages of negative pressure is that it sucks dust in through every tiny little gap in the case, including around the front panel connectors, which is the last place you want to fill with dust. Airtight connectors are available, but be prepared to pay a lot.

_________________
https://mrevil.asvachin.eu/


Top
 Profile  
 
 Post subject: Re: The "Fix-ATX" Quiet Case Design
PostPosted: Fri Mar 13, 2015 10:18 am 
Offline

Joined: Sun Feb 22, 2015 11:57 am
Posts: 59
Mr Evil wrote:
nintendoeats wrote:
...Unfortunately the exhaust fan needs to be higher than the intake fan (because hot air rises), so it is not possible to simply reverse the fans on a standard case...

This has to be taken into account it you're relying on natural convection alone, but even a slow fan can completely overpower gravity, so blowing hot air down is just as good in practice.

I concede that "needs" is not the correct word, that's a fair point. For maximum efficiency it is desirable, but if one was able to adapt on their graphics card I agree that the difference would be minor.

Mr Evil wrote:
nintendoeats wrote:
...everything else in compartment C...

Ren0ir already addressed this, but compartment C is a huge volume which for most people will contain nothing but a PSU. There is a trend towards smaller PCs, so if you want to actually sell these then you're going to have to trim away any unnecessary size.

A: The size of the case is defined by the size of the fan, so this is a part of the concept that cannot be helped unless we somehow design oval fans. You could save a bit by triming the fan down to the exact height of the motherboard, but losing that headroom would be down to the individual's preference.
B: I haven't calculated it, but I believe that with the reduction in height and depth this case has similar volume to a typical mid tower.
C: The quiestest and coolest cases tend to be full size towers and my hope is that this would have comparable performance in a much smaller package.

nintendoeats wrote:
...the external "shell" must be airtight...

One of the disadvatages of negative pressure is that it sucks dust in through every tiny little gap in the case, including around the front panel connectors, which is the last place you want to fill with dust. Airtight connectors are available, but be prepared to pay a lot.[/quote]
Hey, I did say it would be expensive :P. BMW designed a case that retails for over a grand which people have bought. I think this could be sold much cheaper than that. Of course, I am well below this price bracket.

Thankyou for the input.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 8 hours


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group