The Silent Shoebox: An inaudible 6.88L VR-ready system

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
Hello SFF Forum!

I travel very frequently, and needed an ultra-portable system. It also needed to be powerful enough to handle development and gaming in VR, and performing demos in VR. Those two requirements alone can be a tough bill to fill, but on top of that, I needed it to be inaudible, even under a 3D load. I need to be able to code and run 3D apps simultaneously while maintaining silence, and to me that means that I shouldn't have any indication of the system being on unless I put my ears within 6 inches of it. My goal was to have it fit comfortably in a backpack. That way, no suitcase or briefcase would be a challenge.


tl;dr - The finished result pictured next to its namesake

I started out looking for any store-bought case which I could cut up to meet my requirements, as none stood a chance out-of-the-box, but pretty much none of them were of an appropriate size even with hacking. Some community-built options, such as the DAN case, the Diesel Engine, the NFC S4, are interesting, but are tailored more towards extreme space savings, rather than silent computing. Mainstream mini ITX cases tend to have one or two fans left to fend with the entire system, which usually means they end up running fast under load, which means they get loud. Small and silent don't mix easily.

So I had to start from scratch. The plan has been to begin with a very rough cardboard model, a less rough plastic model, and a final model in aluminum. What you see here is the completion of step 2. I'm a terrible craftsman, and I'm embarrassed posting here TBH. I wasn't aware of this forum till a few days ago, and the projects you guys are working on are on a totally different level. Not to mention that the aforementioned cases are now commercial products...

I don't have any knowledge of CAD tools, just basic hand tools at home, and I'm no good with them, so, at the end of the day, this is still just a sloppy proof-of-concept, though it works great from a functionality standpoint. I didn't really know what the exact dimensions would need to be until I had all the parts in hand and starting experimenting, so there was a lot of trial-and-error and cutting as I went. I got sheets of ABS plastic from mcmaster.com, as they were inexpensive and purportedly easy to machine. I've had a lot of problems in the past with acrylic melting and cracking, and wanted to avoid it. For the short-term, it does the job. I'm going to look into getting something more professional constructed down the road.

From the getgo, I knew that I had to give ample room for fans. Good ventilation is necessary to achieve high performance in conjunction with low noise, and its an area where the run-of-the-mill micro ATX/HTPC case is sorely lacking. The goal was to have as many extremely slow-running fans as possible, and the largest ones at that. I picked up the following parts, and proceeded to unscientifically cram them together in different orientations in an effort to find out what made the most sense.

The parts:

i7-6700k - Overkill, but I got a deal on one, and why not? Any 6xxx would've done well, but the HT was a nice-to-have, as was the high clock out of the box.
ASUS Z170i Pro Gaming- Reasonably priced board with a good suite of features.
Gigabyte GeForce GTX 1070 Mini ITX - By far the best option here, and an excellent one at that. Unfortunately, though, its coil whine sometimes makes it the loudest part of the system.
Samsung 950 Pro 512GB- My excuse to splurge on it was the space savings from forgoing a traditional SSD, and the space savings are significant.
2x8GB Crucical Ballistix Sport 2400- The cheapest 16GB set of DDR4 I could find.
FSP Group 400W Flex ATX PSU FSP400-60FGGBA - One of the beefiest PSU's in this form factor, from my favorite brand. The version on Amazon conveniently comes with 8 pin connectors for the GPU and motherboard. (Other versions may or may not)

It also needed extender cables both for the 8-pin EPS connector on the mobo, and the 8-pin PCI-E connector on the GPU, and of course, a PCI-E riser cable for the video card.


CPU+heatsink, motherboard, memory, and PSU, with the fan removed, and a 3-pin fan adapter

Because I wanted it to be backpack-sized and with some oomph in regards to cooling, I opted to place the video card on top of the motherboard, rather than directly next to it, as that would make it undesirably long. Putting it directly on top would've saved a lot of volume, but resulted in bad ventilation and limited cooling for the CPU. Offsetting the video card such that the socket area remained clear allowed for a heatsink to extend into that space. This allowed for the CPU cooler to be taller than a typical low-profile one such as the Noctua L9i. The CPU cooler lined up (almost) flush with the GPU heatsink, so that each could have a fan blowing ambient air directly onto it. This also provided the interesting benefit of space underneath the video card for a flex ATX power supply. I had originally planned to place it to the side for better thermals, but this ended up working out nicely.

The only CPU heatsink that I could find which fit the bill is the Coolermaster Vortex Plus. Unremarkable performance, but it has 4 heatpipes, and the size was just right. Better than most if not all low profile heatsinks, though definitely worse than most if not all towers. Unfortunately I don't have better pictures to demonstrate how the GPU and CPU heatsinks are almost flush. The GPU heatsink is a quite a bit shorter, and the CPU heatsink sticks out by enough to line up with it.


Video card added on top of the PSU

I had originally planned to use 4 120mm fans in a square, but as it turned out, two 140mm fans were almost a perfect fit with the orientation that I was playing with, and allowed the case to get much narrower. In retrospect, an 11"x11" square (which is what I was thinking of) would've been unnecessarily large.

One 140mm fan blowing onto the GPU heatsink, and one blowing onto the CPU with decent airflow onto the memory and power management MOSFETs. That brought the total system height to just below 4" or 100mm, and making it (barely) possible to fit three 92mm fans on the side also nearly matching the length of the rest of the components, including the two 140mm fans. Set one of them as an intake directly behind the PSU, enabling me to dump its obnoxious 40mm stock fan entirely, and the remaining two as exhaust to provide decent ventilation.


CPU and GPU fans added

The fans:

2x Noctua NF-P14s Redux 1200 - One for cooling the GPU, and one for cooling the GPU. They had to have PWM headers, and standard 140mm mounting, not 150mm with 120mm holes, and have a width of 25mm, not 26mm, not 27mm, which narrowed the choices significantly. The P14's have a very pleasant noise profile even when they do make noise, just a woosh without any clicking or buzzing.

2x Arctic F9 PWM PST for exhaust. - The F9's are quiet, but have an annoying buzzing noise if you get close enough to them, or run them at high enough RPM. Running one off the PSU header seemed to make things worse, perhaps because of the way it undervolts, so I replaced it with the Nexus. Still, at below 700 RPM they are effectively inaudible as long as your ear is a couple of inches away.
1x Nexus Real Silent DF1209SL-03 for the power supply, no PWM header, not needed, since I have it wired to the PSU directly. Its name doesn't lie. It truly is a real, silent fan, and is distinctly superior to the F9 IMHO. Silent 92mm fans are indeed a thing.

The final dimensions ended up being 12"x8"x4.375" or 6.88L, slightly larger than an Xbox 360, though I'm cheating a little and have the ports barely sticking out. Also very similar in size to the DAN case. Rather than allowing for a full-size GPU, however, my design devotes over 1.6L to fans alone, which is completely worth it for me personally. With the advent of the mini-ITX GTX 1070, I don't really have any need for a full-size GPU or SFX PSU, but I do value ventilation. Silence and good cooling performance are two sides of the same coin. This level of ventilation allows for quietness under a heavy a load, but it can also allow for much better performance at medium noise levels. Much higher potential for overclocking, if needed.

I have the fan curves set up to run at 300-600 RPM in most cases. I consider anything past 700 or so annoying, and try to avoid anything past 1000 . My noise requirements are unusually stringent. Even at such slow speeds, the CPU and GPU rarely go beyond the mid 60's. The SSD idles at 45-50, and reaches 55-60 under load. I probed one of the power supply's "heatsinks" (really just a slab of metal in the center), and it maxed out at 75C with the stock fan, and reaches a few degrees lower with the Nexus, so it is completely safe to remove the stock fan as long as you manage to get the PSU enough airflow. The heaviest load I managed to place on it was running Furmark and Prime95 small FFT simultaneously (which I'm never doing again), which had it drawing about 305W from the wall. Still comfortably below the PSU's max rating of 400W. The main 12V rail stayed at 12.2v without budging as measured with a multimeter. All completely in line with the quality I expect from FSP products, at least their industrial ones.

Overclocking:

For now, I'm not overclocking at all for my daily usage. This is just to demonstrate what is possible, because, as I wrote earlier, good cooling performance and silence are two sides of the same coin. I can turn my silent system into a high performing one by letting the fans stretch out their legs. I ran two quick OCCT small data tests, once at 4.4GHz with HT enabled, and once at 4.5GHz with HT disabled. Both at 1.25v, both barely touch 90C at certain occasions, which is why I stopped there. I didn't feel comfortable running for much longer than 15 minutes, so its not a comprehensive test, just a demo of what's possible. Even with the fans maxed, they run at "only" 1200 RPM, which is too high for me, but still qualifies in the slow category. A faster fan for the CPU would allow for more headroom, but even as it is, its a solid overclock.

The GPU is power limit bound. The memory seems significantly worse than what I've read full-size GTX 1070's to be capable of, but that's a non-issue to me. I went with +150MHz for the GPU and +200MHz for the memory. Paired with the CPU at 4.5GHz with HT enabled, it scored 16480 in 3DMark Firestrike, 97.8 FPS in Unigine Heaven, and a SteamVR performance score of 11. All numbers are competitive with any high-end desktop, at least one with a single GPU.

Firestrike
Heaven
OCCT 4.4GHz HT on
OCCT 4.5GHz HT off
Conclusion:

So far, this system has shaped up to be even better than I expected. The amount of performance it offers given the space and noise level is almost hard to believe. My requirements are pretty niche, but I'm far from the only one who needs a portable VR system, and I think we'll see more people and manufacturers experimenting with laying the GPU out parallel with the motherboard. If you think about it, the standard ATX layout doesn't make perfect sense for today's systems. It was designed back when video cards were just another small peripheral with similar size and power draw as an Ethernet card or RAID controller. Now all of that is integrated on the motherboard, if not the CPU itself. Video cards, on the other hand, have just gotten bigger and hungrier, to the point where they have similar power draw to CPU's, and have PCB's of a similar size to motherboards. It's only sensible to cool them similarly.

Next step: Get through TSA at Boston Logan...


With an Oculus Rift for scale

imgur album
 

jeshikat

Jessica. Wayward SFF.n Founder
Silver Supporter
Feb 22, 2015
4,969
4,780
Welcome to the forum!

I'm a terrible craftsman, and I'm embarrassed posting here TBH. I wasn't aware of this forum till a few days ago, and the projects you guys are working on are on a totally different level.

Eh, don't be embarrassed. If anything, I'm jealous of those who can craft things with their own hands. Usually I get lazy and just get other people to do it for me.

I probed one of the power supply's "heatsinks" (really just a slab of metal in the center), and it maxed out at 75C with the stock fan, and reaches a few degrees lower with the Nexus, so it is completely safe to remove the stock fan as long as you manage to get the PSU enough airflow.

That's good to know. I'm sure our resident FlexATX fanboy will be interested in your data, paging @iFreilicht

Next step: Get through TSA at Boston Logan...

...small, homemade plastic box crammed full of metal, wires, and electronics, good luck with that :p

Though I have heard of people hooking up their custom carry-on PC and turning it on to show it's a working computer to pacify the TSA agent.
 
  • Like
Reactions: Soul_Est and Gautam

BirdofPrey

Standards Guru
Sep 3, 2015
797
493
Yeah, I recommend putting a PC in checked luggage, less questions asked, though if you fly a lot, it is probably best to make sure it's as obvious as possible what it is, since they also xray checked bags, and I've seen all sorts of electronics torn out of their box and inspected.

Anyways. Nice work. looks pretty good, and don't feel inadequate about not being able to compete with people working with specialists.
Anyone can work with protocase. it's much tougher to build it yourself
 
  • Like
Reactions: Soul_Est and Gautam

jtd871

SFF Guru
Jun 22, 2015
1,166
851
Gautam,

Welcome to the forum.

If I could offer 1 minor nitpick, it would be that the CPU heatsink fins are not oriented in line with the airflow from the 92mm fans. I realize that there are probably interferences on the motherboard that prevent it being installed in the other orientation.

Jeff
 
  • Like
Reactions: Soul_Est and Gautam

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
Welcome to the forum!

Eh, don't be embarrassed. If anything, I'm jealous of those who can craft things with their own hands. Usually I get lazy and just get other people to do it for me.

That's good to know. I'm sure our resident FlexATX fanboy will be interested in your data, paging @iFreilicht
Thank you, great corner of the net you've got here! It seems to me that flex ATX PSUs and mini ITX cards are somewhat underused. Hopefully that starts changing. Though admittedly I wouldn't be able to tolerate it with the stock fan.
Yeah, I recommend putting a PC in checked luggage, less questions asked, though if you fly a lot, it is probably best to make sure it's as obvious as possible what it is, since they also xray checked bags, and I've seen all sorts of electronics torn out of their box and inspected.
Believe it or not, I was carrying the parts through in a cookie box in my backpack before this, though I guess in some ways that could be less suspicious. :p It raised a few eyebrows, and I'd have to wait as they swabbed everything, but it was ok. Prior to that, I was using a Rajintek Metis, which also got through every time, but whose size forced me to use a suitcase that (barely) broke the guidelines of some European carriers. I usually have to wait and answer questions, but I prefer that to check-in and potentially damaged hardware. I've checked in plenty as well, and haven't had deaths, but definitely had stuff dinged up pretty noticeably, so I avoid it. I always get those little slips that tell me that they went through my stuff. :p

I just checked out protocase and their stuff looks good. I obviously have a lot more reading up to do, but if I were to get them to build a cleaner of version of this, what ballpark would it run in? One of their reps apparently quoted $200-$400 in an earlier thread here. Is that realistic? Sounds too good to be true...
Gautam,

Welcome to the forum.

If I could offer 1 minor nitpick, it would be that the CPU heatsink fins are not oriented in line with the airflow from the 92mm fans. I realize that there are probably interferences on the motherboard that prevent it being installed in the other orientation.

Jeff
Thank you! That's a great insight. I thought that I'd thought of everything, but the orientation didn't cross my mind. It might be possible for me to orient it such that a part of the heatsink sticks out on top of the motherboard (the side which is over the RAM). It will be a (very) tight squeeze, with the heatpipes from the CPU heatsink touching those from the GPU, but its probably a worth a try. Hmm...I wonder how much I'm hurting myself with this orientation...
 
  • Like
Reactions: Soul_Est

Phuncz

Lord of the Boards
SFFn Staff
May 9, 2015
5,827
4,902
Welcome to the forum ! An interesting project too, did you use acrylic or plexiglass panels for the prototype ? Well done, I'm looking forward towards the end goal !

I'm wondering though, if the amount space the fans occupy in regards to the case volume isn't too much.

I'd atleast look up the airflow properties of both types of fans (disregarding the PSU fan for a moment) and try to find the points where both intake and exhaust are at an equal amount of airflow. Because looking at the arrangement of two 140mm and one 92mm as intake and two 92mm as exhaust, there's most likely a serious difference in intake and exhaust volume. This means air is forced out of every gap the case has, but it also changes the role from the intake fans from moving air freely (airflow optimized fans) to pushing air (pressure optimized fans) out. So it might perform close to the current state wif you remove the two 92mm exhaust fans altogether, because I'm suspecting these are working partially as a restriction..

If you want a silent build, two good starting points are the largest heatsinks you can fit (GPU and CPU) along with the least amount of fans to reach the needed airflow (dependant on TDP).
 
  • Like
Reactions: Gautam

jeshikat

Jessica. Wayward SFF.n Founder
Silver Supporter
Feb 22, 2015
4,969
4,780
I just checked out protocase and their stuff looks good. I obviously have a lot more reading up to do, but if I were to get them to build a cleaner of version of this, what ballpark would it run in? One of their reps apparently quoted $200-$400 in an earlier thread here. Is that realistic? Sounds too good to be true...

It really depends on the complexity of the design and how much of the CAD work you can do yourself, it could be anywhere from $300-$3000.

If you provide a ready CAD file that doesn't need much tweaking on their end, I'd estimate around $400 for your design (if kept simple) from Protocase.

Sometime this week I'll have a post on my STX160.0 build log talking about how to find a manufacturer and getting quotes.
 
  • Like
Reactions: Soul_Est and Gautam

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
Thank you. I'm using ABS plastic. I've used polycarbonate/Lexan on past projects and it was a little bit too hard. Acrylic melts and cracks very easily. I can crack it badly even with my bare hands.

I tested the fans to make sure. I ran Project Cars, which heavily loads both the CPU and GPU, with them at max RPM and completely off. (And in a typical case, but I didn't manage to capture it of all things...)

Exhaust max
Exhaust off
With the exhaust fans off, the CPU temperature actually was rising and getting hotter after I snapped it. It went up to 64C and then I stopped. The GPU went to 77C and was rising. With them at maximum speed, the CPU held at 55C, and the GPU at 70C, though the screenshots make it hard to tell, since I have to alt-tab in order to take them, which immediately removes the load...:-/ It was very unscientific, and just a quick check to see what was what, but the results were pretty apparent. My typical case of 600RPM had the CPU at around 58C and the GPU at around 73.

You might say that having the fans not moving at all would be worse than having them not exist and instead having empty holes, and you'd be right, but this was the best I could do in a pinch.

Regarding the fans, first of all, the space is pretty much necessary thanks to the power supply cables. Even if I didn't put fans there, there would be some dead space, though I could possibly shave half an inch of width or so. Putting the biggest fans that I could simply made good use of it.

You're correct that I have positive case pressure on the net. I would argue that most cases in the real world, especially mini-ITX and micro ATX ones, have an imbalance of pressure in one direction or the other, often massive. SFF cases usually tend to have 0 or 1 case fans. (Not the M1, of course, which is partly why its exceptional) It's not strictly optimal to have fan more air flowing in than out, but it works fine in practice anyways. Trying to nail zero pressure is difficult even in full-size ATX cases, and you probably won't find many systems in the real world that have. As for which way is better, you can google the topic "positive vs negative pressure" and get literally pages of forum debates on it. I've usually found positive to be superior personally, though most of the systems I've built are liquid cooled which skews things, and this one isn't.

The CPU and GPU fans are Noctua P14's which are more towards the pressure-optimized side. They are well suited to be heatsink fans, which is effectively what I'm using them for. The Arctic F9's likewise are lower pressure case fans.

The number of fans isn't cut and dry. In practice, I've usually found it better to add more and run them slower. My full-tower system has no less than 15 120mm Yate Loons, and its also unusually quiet. By the numbers, doubling the number of fans theoretically increases the dB rating by 3. Taking a chart like this for example, you can see that even increasing airflow by a factor of 1.5x typically requires adding around 10 dB. Adding fans helps until it doesn't, but with the small, crammed cases we're dealing with, it will usually help. There's also more than the CPU (and GPU) TDP to consider. Without additional fans, my 950 Pro would also be in far worse shape.

It really depends on the complexity of the design and how much of the CAD work you can do yourself, it could be anywhere from $300-$3000.

If you provide a ready CAD file that doesn't need much tweaking on their end, I'd estimate around $400 for your design (if kept simple) from Protocase.

Sometime this week I'll have a post on my STX160.0 build log talking about how to find a manufacturer and getting quotes.

Thanks, that estimate makes it seem worth my while to get a detailed quote. Building this case from hand wasn't exactly cheap either.
 
Last edited:
  • Like
Reactions: Soul_Est and Phuncz

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
Took me a while to see it, great build! Good to know that the FlexATX PSU is running well on that fan, did you use any ducting for that at all?
Oooh...Mr. FSP500 group buy. :D I'm waiting...:D

No ducting, its very sub-optimal. No modification to the PSU at all other than just removing the fan. Ideally, I'd've probably sliced the back panel of the PSU off completely, so that the 92mm fan could sit in the place of the 40mm one, which would result in much better airflow. But I don't want to physically mod the PSU yet. Especially not if it can be replaced by a 500W version. ;)
 

jeshikat

Jessica. Wayward SFF.n Founder
Silver Supporter
Feb 22, 2015
4,969
4,780
Thanks, that estimate makes it seem worth my while to get a detailed quote. Building this case from hand wasn't exactly cheap either.

If you're not in a hurry, I may be able to do the CAD model for you since I'll want a fresh example when I rewrite my STX160.0 build log into a more formal "How to design a SFF case" guide. We're probably talking 2-3 months away at least though.
 
  • Like
Reactions: Soul_Est and Gautam

Necere

Shrink Ray Wielder
NCASE
Feb 22, 2015
1,719
3,281
This is very similar to a layout I've considered for a sub-10L case, the main difference in mine being having just the front 92mm fans (no side fans/vents), and flipping the GPU so a hard PCIe riser could be used. A lot of people seem to overlook the importance of good system airflow in the pursuit of ever-smaller SFF systems, but it's really one area where you don't want to compromise too much. That your system performs virtually silently is an impressive feat for that much performance in such a small volume, and underscores the importance of proper airflow design.
 
  • Like
Reactions: Phuncz and K888D

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
If you're not in a hurry, I may be able to do the CAD model for you since I'll want a fresh example when I rewrite my STX160.0 build log into a more formal "How to design a SFF case" guide. We're probably talking 2-3 months away at least though.
I think I might take you up on that, as that's a pretty awesome offer. I don't know how far I'll get in that timeframe, but it sounds cool.
This is very similar to a layout I've considered for a sub-10L case, the main difference in mine being having just the front 92mm fans (no side fans/vents), and flipping the GPU so a hard PCIe riser could be used. A lot of people seem to overlook the importance of good system airflow in the pursuit of ever-smaller SFF systems, but it's really one area where you don't want to compromise too much. That your system performs virtually silently is an impressive feat for that much performance in such a small volume, and underscores the importance of proper airflow design.
Thank you, that means a lot coming from you. That's an interesting idea, and definitely a lot more mass-market friendly than essentially requiring a single specific heatsink and the removal of the stock GPU fan. :) I toyed around with having the GPU folded on top of the mobo. I'd guess a design like that could hit right around 4L if you went for 80mm fans instead...sounds alluring.

I guess you have to compromise something no matter what. More performance, more volume, less volume, less performance.
 
  • Like
Reactions: Soul_Est

Gautam

Cable-Tie Ninja
Original poster
Sep 5, 2016
148
123
Pretty sure that's impossible, the Hutzy XS is 4L already and there is absolutely no space for fans there. 5L should be doable, though.
I think it's possible, but it's only a thought experiment of mine, so something probably messes it up. It's probably also too sloppy to be marketable. I think it's possible to go much narrower than 100mm in width, cramming the GPU directly on top of the mobo rather than cleanly placing it on the other side like the Hutzy and DAN. No space for 2.5mm drives etc. My setup here is 111mm in total but 9.5mm of that is plastic. Steel/aluminum would be ~3mm. I'm also spending 25mm on fans. In short, I think 80mm thickness would be possible. If I removed fans and went to the stock cooler with a 40mm CPU heatsink, I'd be down to 86. Switching to metal would probably bring that to just below 80. I'm figuring something like 205mm*85mm*225mm should be possible, even yielding a few mm on each dimension to spare, but it might be too messy to be practical.
 
Last edited:
  • Like
Reactions: Soul_Est

jeshikat

Jessica. Wayward SFF.n Founder
Silver Supporter
Feb 22, 2015
4,969
4,780
I'm figuring something like 205mm*85mm*225mm should be possible, even yielding a few mm on each dimension to spare, but it might be too messy to be practical.

It's doable, STX160.0 is 86mm thick with the motherboard and GPU back to back. But it's a very tight fit.

The screws for the heatsink sticking out the back of the card are almost touch in the backplate for the CPU heatsink, the vertical SODIMM RAM on the Mini-STX mobo are almost touching the chassis, I have to use the 23mm tall SilverStone NT07, etc.
 

EdZ

Virtual Realist
May 11, 2015
1,578
2,107
A facing-PCB shared-heatsink layout with fans through-ventilating a 'thermal tunnel' would cut down on volume even further (particularly if you used the PSU boards to form the 'top' and 'bottom' of the tunnel), but with the caveat that your unified heatsink would only really work with a very limited selection of components. a set of touching-but-not-unitary heatsinks would benefit from the shared fans and could be swapped for component changes, but the heatsinks themselves would need to be larger.
 

Minefoxi

Cable-Tie Ninja
Jul 8, 2015
146
68
www.youtube.com
A facing-PCB shared-heatsink layout with fans through-ventilating a 'thermal tunnel' would cut down on volume even further (particularly if you used the PSU boards to form the 'top' and 'bottom' of the tunnel), but with the caveat that your unified heatsink would only really work with a very limited selection of components. a set of touching-but-not-unitary heatsinks would benefit from the shared fans and could be swapped for component changes, but the heatsinks themselves would need to be larger.

That sounds like a rectangle shaped Mac Pro with all the components layed out arround a "heatsink tunnel", an interesting idea though.