mabey im missing somthing, and please feel free to inform me if i have.

but ive noticed alot of ppl talking and posting pics with an exhaust 120mm fan AND an exhaust 120mm fan in their psu.

and then i see further talk of ducting cool air to your psu.


why would you not instead just lose your main exhaust 120mm fan completely, and rely on your 120mm fan in your PSU to exhaust the hot air from the system?

i assume most of you have just 1x 120mm intake fan, so having 2 exhaust fans gives you a negative internal case pressure. and if you just dropped your main exhaust this would elieviate this problem, and remove a noise maker from your system.

is their a reason why you want to drop your PSU temps a few C degrees cooler?

right now i have 3x 120mm papst sleeve syntec fans in my system all running at 7volts. 1 for cool air intake at front/bottom of case. 1 in the psu for hot air exhaust from the case. and 1 on my xp-120 cpu cooler. zalman passive sinks on video and northbridge. my 6600gt runs around 50c and my A64 3200+ winchester runs around 40c idle. which imo is very good for a quiet (stock speed) system. right now my pc is sitting on top of my desk about 1foot away from my face. and it is completely inaudible. i have to put my ear up next to the front bezel to hear it at all.

hot air going through psu's should be avoided where possible. as an approximate rule, for every increase of 10 degrees celcius (over 40 degrees) you half the lifetime of a capacitor, so venting air from a hot cpu could shave a lot off your psu's lifetime, not to mention speed up its thermistor-controlled fan. it depends on how much you value the psu.

for a low-power system though, sure. i'm planning to pair this case with a winchester as so:

- 120mm psu fan exhausting
- 92mm fan ducted to cpu, intake from the case's side panel
- 80mm/92mm fan ducted to gfx card, intake also from case's side panel
- no rear or front intake/exhaust fans

i'm hoping the two 92mm fans will give me positive pressure, the psu's fan could be undervolted i suppose. the only problem will be hdd cooling, but i could get creative. perhaps have the gfx card and suspended hdd in the same duct, with the fan drawing from the front intake and exhausting to the lower side-panel grill.

the temps in the psu never exceed the manufacturers defined thermal limits.

sure colder always means longer lasting. but their warrented for like 3-5 years at their specified temp ranges.

think about what you had in your computer 5 years ago. i guarentee just about everyone in here has gone through at least 2 or 3 upgrades since then.

plus 40c is pretty darn hot for an internal case temp. i dont think my internal case temp ever gets above 35c under heavy load.

someone would have to be running a hot system, in a poor ventalated case to be running 40+ C in their psu's.

i thought we were all about quiet operation, not the lowest temp we can possibly get. [H]ardocp's forum is where you wanna go for stuff like that.

i wouldnt worry about the HD, i keep my barracuda V SATA in a smartdrive 2002 with no airflow over it at all, and it runs just fine, never gets over manufacterers specified thermal limit. unless your runnin a 10k drive or somthin. then you may need active cooling on it.

Actually there's some merit to this idea. Yesterday, playing around in my Sonata, I realised that improving the airflow through the PSU ended up rendering the rear 120mm exhaust COUNTERPRODUCTIVE !!!

I'll do further experimentation and post my results

oh, and heres a tip for all you guys that i noticed helps ALOT with keeping dust out of your system, and helps with noise (sort of)

go buy an air purifier. i use one that uses a hepa air filter, washable standard filter, and the ionized bar thingys.

it makes a soft wooshing noise. for me, i like the noise it makes. its like a blanket of air sorta noise. idunno about you, but if im trying to sleep and i cant hear anything at all, i start imagining sounds, and ringings in my ear n stuff. i usually have music playing all day and night also.

also this soft air noise will mask the noise from a computer.

but it does help ALOT with dust, in the room and in the case.

i never really thought it would help as much as it does before i got one.

mine was only like 50 bucks at walmart. its a small one rated for 1 room (cause im living in a dorm room)

The sticky Core Info about PSUs contains some links. One of them is Does "Evacuate the heat" role for the PSU work?

If you read that discussion, then you'll see that there are people who tried a setup similar to yours and ended up with PSU fans that spun to fast (=loud) and others for who it worked. So the answer to the question in the title of that thread is not a straight yes or no answer. It greatly depends on the rest of the system. This just leaves us with several valid cooling strategies.

Now I have the impression that you are mixing up what people do with the various stategies. People who duct fresh air to the PSU almost never use a 120mm fan / angled airflow PSU. They use a 80mm fan / straight airflow PSU.

Most PSU fans are temperature controlled. If you can keep the PSU at a lower temp, then the fan will spin slower and thus be quieter.

depends on the manufacturer - i think we've all had some experience with the $3-in-bulk rebadged psu's that go poof within a couple months. plus, i just don't like the inconvenience of being without a psu when it finally does die, which all psus eventually do.



true, but i'm talking more about the temperature delta - if a psu normally has 20c air incoming and exhausts it as 32-33c, increasing the 20c air to say 35 or 40c (thanks to the cpu) bumps up your internal psu temp to 45-50c.



ah, but there are often thermistors that are outside our (reasonable) control. plus, i'm very cheap, and i know the effect heat has on parts that i can't be bothered paying to replace - some of my components are pushing 3 years now (hdd, tv tuner, audio).

i dont have that problem because i hard mod every PSU i get with a 120mm papst and hard volt it to 7volts or less. i never leave any fan in my system stock.

if its not a papst 120mm fan it doesnt belong in my system.

also ive never used a stock psu that came with a case. i havnt bought an enclosure that has come with psu in a long time. but when i did i always replaced them. im using a Seasonic Supertornado 400w right now

i guess i can see if your poor, or cheep. and are looking for inexpensive ways. but ive seen other ppl spend alot of time and money on sysytems and still make this mistake. so this isnt always the case. but i can see how this would be the case for some.

still, i think its a valid question to bring up to those that do have the time/money and want the best results no matter the cost like i do. just like burcakb. who just noticed this issue recently. ive also seen other ppl who obviously have the time and money make this mistake, but i dont wanna call anyone out unless they have already spoken up about this.

There are plenty of ways to skin a cat, and whatever works for you is fine, but generally dropping the intake fan makes more sense than dropping the exhaust.

Having a second exhaust helps keeps a stock PSU from ramping up, the increased CFM also reduces the recirculation of the CPU HSF air, keeping the cpu cooler, and thus allowing a slower fan for that purpos. Having a 120mm intake does nothing except make noise. (unless you've got 4 HDD's or something. A single drive is easily cooled by passing intake air)

Running a case with negative pressure isn't a problem so long as you've got proper open intake area.

having negative case pressure increases dust buildup in the case overall, especially in things like optical drives

it also creates hot pockets of air inside the case because you dont have a good directional flow of air from an intake to an exhaust. it just comes in from anywhere it can, path of least resisistance, which may or may not be where you need circulation to flow past.

dropping your intake fan is the worst thing you could do for proper circulation and case ventalation.

a case with a good directional flow pattern will keep your hot components cooler which means you can run fans slower

idealy, you want even internal case pressure, for the best internal flow pattern possible. but if you have to choose one or the other, positive case pressure is better than negative.

The only mistake I see is your attitude.

You have found a way to silence your computers. That is fine for you. Other people have found other ways to silence their computers. That is fine for them. Why are you on a crusade to convince other people your way is the only right way?

I see a big problem with your solution. For it to work, you have to modify your PSU. A lot of people don't want to do that because they either lack the skills or don't want to void the warranty or both. This doesn't mean your solution is bad. Just that it won't work for everybody.

The discussion about positive, negative or neutral pressure has raged often enough on a lot of different forums all over the internet. I don't think you will find a lot of people on this board who follow the neutral pressure way. Simply because in most designs neutral pressure means more fans, means more noise. Especially intake fans are avoided by a lot of people here, because they are positioned so close to the user. Plus in a well designed case layout the path of least air resistance is there where you want it.

P.S. If you are that concerned about dust in your optical drives, then buy Asus QuieTrack drives. They have a rubber seal that prevents dust from entering the drive and noise from leaving it.

no need to flame dude. ive been trying to keep this thread and my replies as objective as possible.

i found some things that work that i noticed some ppl that have spent alot of time and money on the quest for silence might wanna know, and wanted to discuss it with them. if its not for you, then dont participate.

i cant wait to hear from burcakb and see his results.

please try to stay on topic and keep the conversation positive.

Can you explain to me where I went off topic

The fact that you have modded your PSU and restricted the max voltage of its fan to 7V is what makes this method of silencing and cooling very unattractive to me as I'm just not willing to do that.

Additionally, I prefer a negative pressure system with extraneous holes in my front panel carefully taped. This allows for carefully designed airflow paths that provide cooling where needed. The only additional issue is dust where the only additional work is to clean the front filter every few months - no big deal.

My system is only 6-7 months old in its current configuration, so I'm not really certain that dust won't be a problem with the optical drive. I don't really think that is much of an issue, though, because the system breathes pretty well through the front intake and I just don't think much dust will be filtering through the drives. I could be wrong about this, but I won't really be able test this theory for another 6 months or so of dust buildup.

This contradicts itself. Look at the picture below. It is a simplified model of a typical tower case. Left with neutral pressure; right with negative pressure. The grey rectangles are fans. The blue lines the paths of the airflow. The orange ovals are hot air pockets. The breaks in the line on the top right are gaps in / through the optical drives. The breaks in the line on the bottom left are gaps around the PCI slot covers.

With the neutral pressure setup the ammount of air coming through the front fan equals that going out of the back fan. The small holes have a large resistance to airflow, so there is no air flowing in the corners of the case.

With the negative pressure setup, the air "just comes in from anywhere it can". This includes the gaps in the corners of the case.

Note that I wouldn't use either model. My personal preference is a positive pressure setup, with a bottom filtered intake. No dust problems at all.

thx to imageshake for hosting the pic, got it from tibors pic

i think this is more likely to be the reaction in a typical case than what you depicted.

for the negative air pressure pic you described to be correct, it would take carefull case planning and case modification to create inlets for air where its needed most, and to also seal up any crevices where you would rather not have air come in at. i could see it working well with good planning, but then you'd still have probelms with dust.

as for your even air pressure pic. theirs nothing stopping the air from moving all the way over to your vid/pci cards, then rising with heat to the psu exhaust. your seal, and your air pressure wouldnt be great enough to cause it to bypass the bottom back of your case like you showed. it would leave a hotspot where your drive cages are though i agree. but i dont believe this to be a major problem as optical drives dont run all the time, and 7200rpm hard drives rarely require active cooling. and even if you had a hd you wanted activly cooled you could always place it in front of your intake fan.

the way i was describing to keep even air pressure, wouldnt require any case mods at all as long as you had a case with a 120mm front intake stock on your case, which many ppl here do have. it would, however, require a psu fan mod, which i can see why some ppl would like to avoid. but other than that it would be fairly simple to produce

how come you made your true opinion so small if you argue its devil's advocate?

I have noticed over a long term there is definitely problem with dust in optical drives in negative pressure cases (2 optical drives dead in about 3 years). Since my case has a door with some slits, I sealed the door with some foam where the optical drive is. Then I removed two drive bay covers to give the PSU some fresh cool air from up top. This is a non issue if your case has sealed doors or if your case has "stealth" drive covers. Many cases come with one or the other these days.

Negative/positive pressure works great if you can seal up useless openings. I personally always run with negative or slightly negative pressure in different systems. Dust is cured by canned air once every 4 months or so.

WRT removing the fan below the PSU, I havent tried it but following the discussions on it doesnt really make me want to try either. Unless of course the whole system was ducted like a couple of bluefronts designs.

In the bottom back of the case there usually are PCI/AGP cards. These hindrances to airflow are the reason I think your neutral pressure model is not right. One hint in that direction is that removing one or two PCI slot covers usually improves the temp of passive graphics card coolers. Another hint is the effectiveness of the "bird-house" mod, which forces air into that area. (Invented by Bluefront and copied many times.)


Do you have any reasoning for your negative pressure model? I can't see why all the air would come through small gaps (with high flow resistance) while there is a wide open path for the air from the bottom front of the case. The model as I depicted it is used succesfully many times. Just look around these forums.

Even if the neutral pressure would result in slightly lower temps, then this would be at the cost of adding a noise source very close to the user. The common experience on this forum is that you can't win that back at the noise sources enclosed inside the case.

-----------
As to why I don't recommend the method I think is best to everyone. It's simple. Not everyone needs/wants dust filtering. Plus it is more work. Just as with your 7V Papst PSU mod. Not everybody wants or is able to cut out 3/4th of the bottom of a computer case and build a filter chamber. (Plus my current project can't be depicted in a 2D model. )

Thanks to ImageShack for Free Image Hosting

EDIT: Hey don't change your post, while I am replying. That makes arguing very difficult.

the "bird house" or ducting of the front intake fan decreases card temps because the velocity of the air from the fan isnt disapated nearly as quicly and thus hits your cards with more force increasing cooling performance.

ive actually been thinking of a proffesional looking way to do this cause i have a window mod and neon light, so i want it to look good, and work well at the same time.

the reason removing back pci slot covers reduces temps is simple. air flow follows path of least resistance. if you open a path right next to the cards to flow right past, it will move quicker and with less restriction, reducing temps for the cards. but it'll increase temps above the cards in the cpu/psu region.

as for my negative air pressure model, air is going to come in from everywhere, it'll even come in from around the case fan blowing air out the back. direction of airflow is very chaotic in a negative pressure environment, especially so with no intake directional flow whatsoever like your picture indicated. unless you completely sealed all possible paths for air to go, it would be very difficult for you to pull cool air from, the absolute furthest spot in the case, the front lower intake position. also because you have negative pressure the fans will have to work extra hard to pull what air it has available to it out of the case. (think of putting your hand over the suction hose on a vacume) same effect will happen in a negative air pressure environment in your case. this will increase the amprage they pull and the noise they create because of increased turbulance. the sevarity of which would depend on the amount of negative pressure. a slight negative pressure prolly wouldnt be so bad.

as for the front fan making your system louder cause it would be closer to you. get a quite fan to begin with, 7volt it, and put a dust filter in front of it and i guarentee you, you wont hear it. mabey if you put your ear up to the front of the case, but definatly not if its under your desk.


i didnt start this thread in hopes of moving everyone in this forum to do what i describe. i was more hoping to grab the attention of ppl like you and burcakb. ppl who spend lots of time and money trying to get the absolute best results from their computers. sound and performance wise.



its like race cars and ultra high end video cards. 99% of the population will never own one. but whoever holds the title is going to sell more budget cards.

not everyone is going to want to do what i do, or what you do. but mabey we can discuss it, and ppl can take what they are comfortable with from it, and use it to help them in their own way.

Aris,

It's time for you to do your homework:

First, read this: Fan configurations compared. I'll paraphrase the results for you: Exhaust fans only outperformed having both intake and exhaust every, single time

Second: Unplug your intake fan. Yes, right now. And see what happens to your temps.
Third: Move your intake fan to the rear, and run it at the same speed you were when it was the intake. And see what happens to your temps.

If your case has decent airflow, your temps will be lower, or the same, with the intake moved to the exhaust position.


I don't particularly care what setup you run. Whatever works for you is great. But its another thing to wrap your ego around an idea thats been disproven so completely, so often.

"Negative" and "positive" case pressure debate is hugely over-rated. Yes, for some people there's a trivial dust issue, but in terms of cooling (and thus silencing) its pretty clear that exhaust plus a free-flowing bezel is the simplest method. Having an exhaust supplemental to the PSU means you can run the PSU at a lower speed as well, even with a hard-wired mod like your's.

Bluefront's positive-pressure setups work because he carefully controls the airflow paths. In a normal case setup, there's no benefit of striving for neutral or positive pressure, in regards to temps or noise.

Your little diagram of how you think the airflow works in an exhaust-only case is wildly contradictory to the known laws of physics. The incoming air will enter through the available openings in a volume proportional to the resistance at each opening. In other words, it takes the path of least resistance. With an open bezel, the vast majority of the air will enter there, at the same location your intake fan is now. And it will enter at the same volume, only without the help of a fan there. The amount of air that does come in through other cracks is so small as to have no impact on temps.

rusty:

i dont have to try it. i know your right. my temp would drop. and i know exactly why. CFM would increase cause the fans would be running in parallel instead of in series like i have them now.

but i dont want to have to grab my can of air every month or replace optical drives like tay has had to do.


EDIT: as for the positive case pressure, i dont believe i covered that at all. but since you brought it up....

i would support positive much more than negative if you had the choise. one for the dust issue, which is more than just clenlisness. when your components get dusty, they lose their ability to dissapate their heat as well. the dust acts as an insolator. also it would be alot easier to predict your flow patterns in a positive case pressure scenario than the opposite situation.

Aris, I fail to understand what it is you're arguing then. If you agree that your current method is inferior in terms of both temps and silence....


...sorry, I just don't get what your purpose in this entire thread is then. You started off asking why people didn't do it like you do, and you popped an attitude when the reasons why were pointed out. And now you say that you knew you were wrong to begin with? The only logical conclusion is that you're arguing just for sake of arguing. Find somewhere else to do that.



To finish off the matter at hand: I have machines that have run "negative pressure" only for literally years, and have never had to blow dust out of them, nor have I ever replaced an optical drive. And even if occasional (ie every 6 months) dust removal were necessary, that's a 30 second task compared to months of quieter operation. This is SilentPCReview, not Dust-bunny-freePCReview.

i never said it was inferior. you did. (please dont flame cause you dont agree with me, its ok for us to not agree)

i also already stated that with the proper case preperation and good planning negative air pressure would work well.


as far as the dust issue, your the first person, out of hundreds, ive talked to and read reviews on that had zero issues with dust in a negative pressure case over the long term. id guess its because you've spent more time than most with case preperation and good planning like i said earlier.


i did go back and read that review. it didnt really suprise me too much.
i knew with 2 exhaust fans you'd get lower temps cause your CFM would incrase.

i also liked the "front and top" configuration results. quickest time to idle. not as good in lowest temp though cause your CFM is lower cause only 1 fan is really moving air through the system (fans in series work with each other but dont improve CFM) instead of 2 like in the dual exhaust scenario (in which the fans are in parellel).

i guess in a technical sense your right, my question was answered. but i still like to discuss possibilites. i didnt think that was so bad.


i think if ive learned anything with this its this. positive, even, or negative. if you plan it out, and make the proper selections when it comes to components/case/mods as it pertains to how you want the system to work. it will work well.

you have a negative pressure system that runs well
i have a neutral pressure system that runs well
and tibors has a positive pressure system that runs well.

they are all within our thermal/acoustic and asthetic requirments for each of us.

i still think it was worthwhile to explore the options though. even if you do not.

i think the biggest stumbling block here is a lack of objective measurements from the same starting points. this is one thing i learned very early from hydrogenaudio - without repeatable objective facts, any argument will meet resitance.

what we need is this - identical case/cpu/ram/vga/fan/hdd configurations which test the following:

- 0 fan intake, 1 psu exhaust (negative pressure)
- 0 fan intake, 2 exhaust (psu+case = very negative pressure)
- 1 fan intake, 1 psu exhaust (neutral pressure)
- 1 fan intake, 2 exhaust (psu+case = negative pressure)
- 2 fan intake, 1 psu exhaust (positive pressure)
- 2 fan intake, 2 exhaust (psu+case = neutral pressure)
- 2 fan intake, 0 exhaust (psu disconnected/ducted? = very positive pressure)

and for each, run for at least 2 months to gauge temperatures, dust buildup, and most importantly the dBA required to keep the cpu/vga/hdd at a given temperature.

this is obviously a very large undertaking, so it isn't too surprising that i haven't read about anyone doing it. and of course, any results from such a test are only applicable to someone that has the same case/cpu/psu/etc. configuration.

here - like many other fields - there are no black and white answers, only shades of gray. maybe some day when we all have identical components we can settle the issue, but until then pressure and air-flow are definitely a case-by-case problem.

I think the main reason there are very few examples of setups without a rear exhaust fan in the usual place, and using the PSU fans as the only exhaust, boils down to the amount of work involved.

There are only a few stock cases setup for this sort of cooling. If you want to try such a setup, you will have to do extensive modification to keep the case cool as well as quiet. If you eliminate the rear exhaust fan, you probably can cut the noise level of the whole system by 30% or more. Of course the PSU fan will have to spin faster to keep the temps down, but the overall noise reduction is worth the effort.

Here's an example of a setup that can operate with one fan (at the expence of elevated HD temps), totally negative pressure, completely filtered, the one 120mm fan between the CPU heatsink and the PSU.

In this album you'll see the final setup without a rear exhaust fan, using the PSU fan to evacuate all the heat, another 120mm intake fan (birdhouse mod) that renders the setup neutral pressure, and completely filtered.

In my current project (not quite finished), you'll see another example of using the stock rear exhaust fan opening as an intake instead.

I'm completely sold on the concept.....although it does take much modification to pull it off successfully. Don't expect to find much sympathy around here for such setups. Too much work involved.

thx for the post blue, i heard so much about you i was kinda hoping you'd show up


i like work, this is my only fun all day, working on my computer case mods.

I'm working on a project with another guy and we went all exhaust,but with a V-Tech mesh case. The V-Tech has a LOT of mesh area,all backed by filter material. Our plan is to construct baffles that will allow ample inflow of air while obstructing any straightline path for soundwaves. As there is so much potential inflow area,some will get fully blocked leaving flow where we want it,and tending to minimize front openings. Having a lot of inflow,all filtered should mean the exhaust fans don't work hard and dust won't be much of a hassle. The CPU and (2) exhausts will be Artic Cooling 80mm TC type which are thermal types with a 1000-1800 rpm range. We may mount an additional fan inside on a"L" bracket to pull air across the HD's,sending that heat toward the rear exhaust. With luck we hope to be able to skip one of the fans or perhaps undervolt one to get even lower rpms. Sensor placement should have some effect on actual fan speeds. It is going to be an Athlon64 3000 Winchester on an ECS FN-1 Extreme NF4-Ultra with a 37gb Raptor and 1 or 2 160gb SATA Spinrights. This case is the opposite of a thick,padded wood case where the case blocks plenty of noise,the aim is to have quiet running stuff inside with rather free airflow and baffles to reduce escaping sound

So it's 1:35am... what else to do but wade into a debate!

This is relevant to the very first post of this threead:

I assembled system as a lab utlity PC and decided it should be encased rather than on an open platform like most of the stuff in the lab. Just to keep it a little safer from accidents. It needed to be as quiet as possible so acoustic measurements and recordings of super quiet stuff could be made in the room.

The system is a heavily modded study steel mid tower. There are 2 fans: A Nexus 120 on the back panel as an exhaust, and the Yate Loon 120 in a Seasonic Super Tornado 300.

There are two large holes in the front:
1) A 120mm hole at the tradition front bottom with a very open hole in the bottom edge of the bezel. A Samsung HDD sits on foam on the floor of the case directly behind this hole.
2) The two top CD bays are completely open. The 3rd bay holds a CD drive.

The HS for the Athlon XP 2500+ (?) is a Thermalright SI-97. Its fins run up and down. It is fanless. The Nexus 120 spins at ~5.5V -- the min it will run. The PSU was left stock -- it never ramps up, I think its rpm is no higher than the Nexus. I think the system measures ~18 dBA/1m. It's under a desk so you have to put your head under it to really hear the PC at all.

The airflow in this system is not huge; each fan is probably not moving more than 15 cfm tops. The system is constantly loaded with folding@home running 24/7.

When the case side is off, the CPU temp hits around 60C. Put it back on and it gradually drops over about a 10-15 minutes down to 52-53C. Put your hand in the CD bay hole at the top and it feels cool because of the air tunneling in. Put your hand at the bottom front edge of the bezel, and again, your fingers feel cool because of the airflow.

The air flows from the front holes to the 2 fans perpendicular and so close to each other. From behind the case, the PSU exhaust feels a slightly warmer than the case fan and has less pressure; the airflow is obviously a lot more blocked by the PSU innards.

Turning the back case fan up to full does improve CPU temps a bit, but much less than you would expect; the two fans spinning slowly together are very efficient at pulling the air in from the front of the case without any conflict which each other.

My thought about this dual-fan-at-right-angles set up is that it works fine as long as neither fan is spinning real fast, and if the intake vent/s are unrestricted enough to allow the air to come in and get to the fans. If the intake vents are too small, then yes, the two fans could fight each other. With the CPU/HS right at the "crossroad" in tront of the 2 fans, the concentration of directed airflow is high despite the low fan speeds. The air simply has to go across the HS fins to get to either fan.

Dust has not been a problem but it's only been running 2-3 months.

The airflow in the setup MikeC just described, is exactly what I am trying to avoid in those three computers I just linked to. In MikeC's setup you have two fans, both fighting to get air out of the same space. The fanless CPU heatsink sits in the middle of this "airfight"......and somehow gets enough airflow to run at a safe temp.

Well of course this airflow setup works, and it mimics most of the setups seen around here. But IMHO, it does not provide optimal airflow for the CPU, and unnecessarily opens up the front of the case for noise leaks. I've tried to avoid both those problems in my recent projects, and at the same time providing air filtration.

Getting that last bit of noise reduction is becoming more and more difficult for me.....and providing quite a challange.

The way you describe it is just not the way it works. There is no fight for air because of the open venting and there is no noise to get out. Maybe you didn't read what I wrote: It measures 18 dBA/1m and cannot be heard till you stick you head within a foot! I can also guarantee that a single 120mm fan moving anywhere close to the ~30cfm these fans are moving is noisier, at least 20-21 dBA/1m.