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Question External ATX-case Exhaust Fan Mounting -- what's your opinion?

BonzaiDuck

Lifer
Jun 30, 2004
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I suppose this seems like a slightly nutty idea, but I've done it before. I'm sure many -- AigoMorla, for instance -- have seen those "AeroCool" 120mm x 25mm fans with the fan frame/shroud built out of a solid aluminum block. Instead of mounting one inside a smallish ATX case, I chose to mount it outside -- bolting it to the exterior at the exhaust-fan mounting holes. Since it was metal, it really didn't seem so "hinky" exposed on the exterior of the rear case panel.

I always have this Rube-Goldberg impulse when I'm building something. Right now, I have this 120mm x38mm Sanyo-San-Ace fan I was considering as an exhaust fan alternative for a casual DIY computer building project. Ordinarily, a Noctua IPPC 3000 120mm x 25mm fan would be more than enough, and this latter option is just as likely to be my final choice.

The problem with the San-Ace is its 38mm width, and like the Bob Dylan "highway 61" song says, "it can [still] be very easily done". That is, mounting to the case exterior is a whole new ballgame for the case interior space prospects.

Of course, it will be noisier. But that's OK -- some Spire foam rubber and foam art-board, neatly increasing the fan's dimensions to 140mm -- and a few other "tricks" with the same materials -- can cancel some dBA's. I'd need to add one of those 120mm chrome fan guards with the concentric rings.

It's just extra trouble though. I can't make up my mind. The IPPC fan will push over 100 CFM as it is.

It's a trivial issue, but any casual comments will have my attention.
 

mindless1

Diamond Member
Aug 11, 2001
5,955
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I tend to avoid 38mm thick fans where humans are around, because they usually have high torque and can't be throttled back to an acceptably low noise level without starting to make a clicking noise, if they continue to spin at all. It's not how well they are mounted, rather the turbulent air noise.

I wouldn't hesitate to mount a fan on an exterior rear wall of a case if necessary to get it to fit. Front or sides of case no, don't want it sticking out in these areas, unless it is also something no human will be around, server in a closet or something.
 

BonzaiDuck

Lifer
Jun 30, 2004
14,905
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I tend to avoid 38mm thick fans where humans are around, because they usually have high torque and can't be throttled back to an acceptably low noise level without starting to make a clicking noise, if they continue to spin at all. It's not how well they are mounted, rather the turbulent air noise.

I wouldn't hesitate to mount a fan on an exterior rear wall of a case if necessary to get it to fit. Front or sides of case no, don't want it sticking out in these areas, unless it is also something no human will be around, server in a closet or something.
I'd had some experience with a DELTA 3-pin 120x38. If I were to do this -- with the 12v / 3A San Ace -- it would be PWM-controlled from the motherboard and powered directly from the PSU. Someone already recommended a splitter more likely to shoulder that amperage. I usually use Swiftech 8-way splitter/hubs -- $10 items, and have plans to use one or two on this project.

I'm just toying with the idea. A 120mm x 25mm Noctua ippc 3000 is currently deployed inside the case. It throws about 100+ CFM. The heatpipe cooler will be a Grand Macho RT. All the heatpipe coolers use limp fans. I checked it today, and I can put a Noctua 140mm IPPC 3000 on it as a pusher fan -- replacing the "round" fan that was bundled with the cooler. The 140x25mm fan throws almost 150 CFM. Since I'm already using these, and they seem noiseless to me, I'm starting to lean the other way against the 38mm San ACE.

I'm sealing the case so there are only three exhaust outlets, including the PSU. It probably won't matter at all if I were to use a fan throwing 230 CFM. Just more noise to manage.

If I were to use the San-Ace 120x38, as I may have said, I'd throw a chrome grill on it with the concentric rings. Otherwise, it would definitely be a hazard to any fingers coming in contact with it!
 

Paperdoc

Golden Member
Aug 17, 2006
1,952
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I had to do a similar job, but for different reasons. This is a small horizontal case holding a small-mobo system used as a DVR to feed a TV in the Living Room, so it's compact and sits on a shelf over the TV. The PSU supplied with that case failed and it was a little difficult to locate a replacement of the same size and capacity to fit in the odd space. What we got was a bit longer and encroached on the location of the cooling air intake fan in the side. (We replaced the fan at the same time.) So I drilled mounting holes around the fan slots in the case wall and used long bolts to mount the new fan outside the case, including a dust filter. So the parts sequence is: bolt (head) from inside the case through the case wall, nut and lockwasher to secure the bolt, fan, nut and lockwasher to fasten the fan, spiral fan grill, foam dust flter square, another spiral fan grille, and last nut to hold the filter and grilles into place. I can remove and clean / replace the dust filter easily without disturbing the fan. The fan's power wires feed through the narrow gap between it and the case wall to plug into the mobo header. It's a quiet Noctua unit, so no real noise issue. The fan sticks out from the side maybe 1½" altogether, but that space is just used for other items on that shelf like a PS/2 controller charging rack and a USB video camera, so they fit around the fan easily.
 

BonzaiDuck

Lifer
Jun 30, 2004
14,905
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I had to do a similar job, but for different reasons. This is a small horizontal case holding a small-mobo system used as a DVR to feed a TV in the Living Room, so it's compact and sits on a shelf over the TV. The PSU supplied with that case failed and it was a little difficult to locate a replacement of the same size and capacity to fit in the odd space. What we got was a bit longer and encroached on the location of the cooling air intake fan in the side. (We replaced the fan at the same time.) So I drilled mounting holes around the fan slots in the case wall and used long bolts to mount the new fan outside the case, including a dust filter. So the parts sequence is: bolt (head) from inside the case through the case wall, nut and lockwasher to secure the bolt, fan, nut and lockwasher to fasten the fan, spiral fan grill, foam dust flter square, another spiral fan grille, and last nut to hold the filter and grilles into place. I can remove and clean / replace the dust filter easily without disturbing the fan. The fan's power wires feed through the narrow gap between it and the case wall to plug into the mobo header. It's a quiet Noctua unit, so no real noise issue. The fan sticks out from the side maybe 1½" altogether, but that space is just used for other items on that shelf like a PS/2 controller charging rack and a USB video camera, so they fit around the fan easily.
I suppose I have time to think about this. I want to get the PSU and the mobo/CPU/RAM-&-Heatsink into the case and hooked up. The case has a slide-out motherboard tray, and the only issue about pulling it out to do the rest of the work is the cable connections. But I need to proceed with the exhaust fan either way, before I affix the motherboard to the aluminum tray once and for all.

What you describe is similar to what I did with the aluminum Aero-Cool, and since it was only a 25mm-thick 120mm fan and mostly metal, it didn't seem out of place bolted to the rear of the case.

I don't play around with mounting fans. I go through all sorts of hoops to obtain complete fan isolation pertaining to metal-to-metal and hard-plastic-to-metal contact. I've been known to wrap wire ties in rubberized hose bandage, locking a pair of them together so the buckles function like screw-heads or nuts/bolts, and I use rubber donuts from the electronics store as shock absorbers -- it works. Nylon machine screws are also in my toolbox, together with the Autozone roll of hose-bandage. I use those ready-made rubber fan mounts when I can! I cut gaskets from Spire Acoustic Foam-rubber. All that stuff comes in handy, I tell ya! Suffer enough tedium, it still all works as one would imagine.
 

BonzaiDuck

Lifer
Jun 30, 2004
14,905
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Here's an UPDATE on my prospective "fan experiments" with a 3.0A San-Ace 125x38mm -- the motive factor behind this thread.

Mounting the 38mm fan outside the case is not something I would shrink from, if the benefits could be proven. But it departs from the simplest configuration.

If I put the 120x38mm fan inside the case, then I have to modify the ThermalRight Le-Grand-Macho $10 accordion duct -- probably by cutting it and overlapping the ribs. But the ribs are not just "stacked" -- they are staggered, and with progressively differing size.

The solution is to either go forward as I'd planned with a Noctua 120x25mm iPPC 3000 exhaust fan, which pushes just over 100 CFM, or find a more powerful 120x25mm fan that matches the 150 CFM spec of my Noctua 140mm iPPC 3000 pusher fan. This all looks like picking fly-s*** out of pepper. I must have a "fan-boy" reputation. I am known here for being a noise-tolerant lover of extreme fans.

So I've decided to try a DELTA 120x25mm fan with a 150 CFM rating that brings the decibels close to 60dB. Having "tamed" a pair of Nidec-Servo Gentle Typhoon AP-30's in the matter of noise, I'm going to try one of these Delta's.

Let's just say I have a "fan fetish". I'm still confident that I can reduce the noise with "stuff" that I have in my parts-locker. I've got to see if I can!
 

UsandThem

Elite Member
Super Moderator
May 4, 2000
14,592
5,187
146
I too enjoy my computers sounding like vacuum cleaners. :p

I bought one Delta fan in like 2003-2004 or so to try and cool a Dell tower that kept overheating and crashing when gaming, and it ending up being used for about 30 seconds. Now I don't think I'd ever consider any fan that was over 25dB at max RPMs.
 

BonzaiDuck

Lifer
Jun 30, 2004
14,905
1,025
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I too enjoy my computers sounding like vacuum cleaners. :p

I bought one Delta fan in like 2003-2004 or so to try and cool a Dell tower that kept overheating and crashing when gaming, and it ending up being used for about 30 seconds. Now I don't think I'd ever consider any fan that was over 25dB at max RPMs.
This is what I argue. I freely offer up the fact that I went to my ear-doctor for a test in March, and shown to have "significant" hearing loss in my right ear. But I don't notice it. I wouldn't have been able to identify any difference left versus right.

I have a digital decibel meter -- very handy item. I was able to make a Nidec-Servo GT AP-30 acceptably quiet at about 3,400 RPM of its 4,000 maximum. IN all these fan endeavors, one must completely separate the plastic fan-frame from case metal with rubber. In extreme examples, you would laminate strips of adhesive Spire foam-rubber and wrap the fan. In the dead-spot of the exhaust-side fan-hub, you can install a "rubber nose" made of laminated Spire discs cut to size.

Delta made a "Tri-Blade" 125mm x 38mm which I had "Tri-ed" around 2005 for a CPU cooler. It was voltage-controlled from the motherboard, and I didn't do any of the wonderful things I just mentioned. I mean . . . it wasn't shrieking like a Vantec Tornado, and the computer just wasn't "noisy". Perhaps that experience explains why I'm not so shy about this current Delta prospect.

All the "quiet" fans I've seen, new, old, RGB -- any and all -- have RPMs below 2,000 and CFMs below 75. You can separate the noise components of intrinsic motor-whine, vibration amplified by contact with the computer case metal surfaces, and white-noise from air-turbulence. The white-noise is the component least susceptible to mitigation effort, unless you want to modify case surfaces or use a nibbler to remove the grill metal at the exhaust. You can kill the vibration with rubber mounts, rubber automotive hose-bandage and Spire. The whine can be reduced -- for instance -- by the use of Spire at the exhaust-side hub and by wrapping the fan.

The rest of it is simply a matter of defining fan-curves in the BIOS or fan-control software, preferably by PWM control but not less effectively with voltage control of the three-pin connection.

I've overclocked my systems and tuned the fan curves to meet the more extreme temperatures. But that primarily insures stability, and the CPU is not likely to reach the temperature extremes with normal use, or not so much with gaming. So even with a Delta, a GT AP-30 or something that hits the 59 dB threshold, you're not likely to see much of that noise. Maybe -- here or there -- for a few split seconds. Of course, when I use those fans, they don't generate as much noise as they would when installed by a lot of other users, and it's not because of my right ear.
 
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