11 ms·

Effects of grill patterns on fan performance/noise (2011)

360 points by yread 4y ago

jansan 4y ago
The difference of 5 to 15dbA is quite a big deal, as 10dBA higher values are roughly perceived as "twice as loud".
Spooky23 4y ago
This is really cool! Measuring something as that nobody even thinks about or realizes is there, and finding an actual big difference in performance is always a delightful discovery to me.
peanut_worm 4y ago
Didn’t think it would make such a big difference. I am also surprised the mesh was so quiet, I would have assumed it would have been the loudest.
drgiggles 4y ago
The point of a grill is to block dust and debris, which presumably I want. Otherwise I would just not use one and my fans would be the quietest and cool most effectively. What is the trade-off between the two metrics sited and effectiveness of each type of grill at its intended purpose?
- kqr 4y ago
  I think the purpose of the grill on a computer is not so much about dust and smaller debris as it is about (a) protecting user fingers against fan bites, and (b) protecting the fan against bigger pokey things that could damage the fan blades or jam the fan.
  - drgiggles 4y ago
    hmm, I always assumed there was some other benefit. I'm taking all mine off. Seems pretty easy to not ram my finger in it.
    - zamadatix 4y ago
      No roaming pets or children I take it :p. Debris are usually covered by a foam filter in front of the fans (if at all). I’ll usually take that off though and just clean it every once in a while.
      - drgiggles 4y ago
        No, I comment on posts about pc fan grills at 6am...I'm single :)
        wffurr 4y ago
        That's exactly the kind of thing I do in the morning over coffee in those quiet few minutes before the children are up. Rest assured that you can still continue to comment on obscure tech minutiae at odd hours of the morning.
  - Grimburger 4y ago
    I have a large fan at home that I remove the front protector from because it gets dirty often and is quieter. My young nephew shoves his hand it in all the time for fun with zero harm.
    - Sarkie 4y ago
      "It doesn't affect me, so it cannot be an issue"
    - somehnguy 4y ago
      On the flip side, a few of my hobbies include devices where the fans are usually exposed - and I've cut myself a handful of times because of it. It's very size/shape/rpm dependent.
    - mellavora 4y ago
      zero harm to him or to the blade?
    - jabroni_salad 4y ago
      Big fans are at a relatively low RPM, and household fans might be made with kids sticking their fingers in them in mind. I've got a little noisy desk fan with metal blades in it that I would prefer not to take my chances with. I've also cut myself on my RC Plane's props a few times.
  - gigaflop 4y ago
    In super small form factor PCs, sometimes you use a fan grille on the inside, to make sure that wires, etc on the interior don't get caught in the fan.
kqr 4y ago
What can explain the case where there's more air moving out the exhaust side than being sucked up the intake side?
- danuker 4y ago
  Coandă effects might drag air from somewhere else, not just from the intake. https://en.wikipedia.org/wiki/Coand%C4%83_effect https://en.wikipedia.org/wiki/Coand%C4%83_effect Edit: I see the tester used an anemometer, which measures just the air moving THROUGH the anemometer. If the exhaust is smaller than the intake, then air will move at a higher speed through the exhaust. Thus the anemometer will show a higher reading.
  - lupire 4y ago
    It has to come from somewhere, by conservation of mass.
    - danuker 4y ago
      Indeed. I was thinking it's from some other holes of a non-airtight case. But actually, the mass conservation happens through air around the anemometer (i.e. air not getting measured, but still moving).
    - Scoundreller 4y ago
      Évaporation and gas formation of the electrolytic capacitor goop comes to mind :)
- mannykannot 4y ago
  The airflow into a fan is in response to the low pressure created by the blades, an so will approach over a wide angle. The outflow, however, is initially strongly biased to a direction perpendicular to the plane of the blades (together with some swirl imparted by the blades.) Because of this, the anemometer shown is likely to intercept a larger fraction of outflow than the inflow. Maybe the swirl will also have an effect, depending on whether the fan blades and anemometer blades rotate in the same or opposite directions.
londons_explore 4y ago
"Wire" is effectively the air passing around a cylinder. There is a lot of information about airflow around cylinders. Eg [1]. The top left diagram should be the one that applies with small diameters and the kind of airflow rates in a PC fan. I would guess that all the other shapes have micro-scale sharp edges that leave vortexes which both slow the flow down and make noise. [1]: https://i.ytimg.com/vi/pW0JfEBE9h8/maxresdefault.jpg https://i.ytimg.com/vi/pW0JfEBE9h8/maxresdefault.jpg
- jongala 4y ago
  I agree, it feels like a missed opportunity to not explore this. I'd love to see an analysis of the swirl design (or other commonly used manufacturer patterns), with the edges rounded or beveled on the intake face, exhaust face, or both. Like, even on cut or stamped grills, how much could performance be improved by e.g. sandblasting the finished piece from one or both sides and taking down the edges a bit?
  - londons_explore 4y ago
    The wire is only just laminar flow... I found a random PC fan and assumed a 1mm wire diameter, 2.3m/s airflow, and the reynolds number comes out at 36. That tells me if you were to get a 1000x really powerful fan, then the grille would start giving turbulent flow, and might no longer perform the best. Page with lots of details: http://labman.phys.utk.edu/phys221core/modules/m8/turbulence.html#:~:text=The%20air%20behind%20the%20cylinder,of%20approximately%202000%20to%20100000 http://labman.phys.utk.edu/phys221core/modules/m8/turbulence....
    - simne 4y ago
      This is 10 years ago article, coolers tech changed a lot since that. I even remember, when in mac clones used ultra-high-speed coolers, which now used only in rack devices. And yes, ultra-high-speed coolers, has much higher speed and make turbulence.
- Cthulhu_ 4y ago
  I mean that's the main difference between the wire and all the others, really; the wire is round metal, the others are shapes stamped from flat metal. That said, my current PC has plastic "angled slats" at the back (outlet) and a honeycomb and mesh (filter) at the front, so it could be quieter. I'll keep it in mind if I ever buy a new one. I believe the wire one was the most common on older PCs (90's / 2000's).
once_inc 4y ago
I just realized that my Synology DS218play NAS is so loud because of the fan grill at the back. Too bad I can't easily remove it...
- Cthulhu_ 4y ago
  Looks like it's nothing some pliers or a dremel can't handle. Also if it's the one I'm seeing on an image search, it looks like the grill at the back is of the mesh variant - it's plastic, molded in a rounded-off fashion. There's probably some tweaks you can do, if it stays cool enough, lower the fan speed or make it dynamic depending on temperature.
  - neilv 4y ago
    Additionally, replacing the fan itself with a quieter one can also help. Image search for "synology noctua" shows this is a thing (and looks like some of them are just removing the grills altogether).
  - n4bz0r 4y ago
    Not quite sure you'd have to get down and dirty like that. Here is a video of a (seemingly) similar model where a guy simply unscrews the grill without even opening the case: https://youtube.com/watch?v=lBaeK5ry-aM&t=30s https://youtube.com/watch?v=lBaeK5ry-aM&t=30s
nemacol 4y ago
https://www.youtube.com/watch?v=1L2ef1CP-yw https://www.youtube.com/watch?v=1L2ef1CP-yw Matthias has an interesting video that is tangentially related talking about the distance of a fan to a window and air flow. While watching I was wondering how this interacts with PC case fans and if they are losing a lot of performance by being directly against the case.
omega3 4y ago
I think a more interesting question would be whether the design actually makes any difference or if the airflow just depends on the free/unobstructed area.
contravariant 4y ago
Going from 36 to 50.2 dBa is not a 41.4% increase, you can't use percentages with a relative scale. Technically it's a 2530% increase, but that's silly because it doesn't correspond to how people experience sound.
- dwringer 4y ago
  Sorry if this is a nitpick, but by design, sound doubles in perceived loudness (roughly) every 10dB, and dBa is a calibrated version of dB which is intended to correspond to how people experience sound, so that increase is only around a tenth of the figure you gave (although you're absolutely right that it's a lot higher than 41%).
  - martincmartin 4y ago
    Yes, but the zero point is arbitrary, so a percentage of dBa is meaningless. You can say it's 14.2 dB louder, or 10^(1.42) more energy, neither of which is very meaningful to the average person.
    - mckirk 4y ago
      So then wouldn't it basically be 142% louder?
  - contravariant 4y ago
    I don't mind being nitpicked when I'm being pedantic. Indeed you can (roughly) approximate perceived loudness that way, but only the absolute difference in dBa is meaningful, looking at a relative difference in dB is meaningless.
    - LeifCarrotson 4y ago
      Rather than using percentages under the noise readings, it would be much more useful to show the delta. If the unguarded fan is at 35.5 dBa, and the turbine guard is at 50.2 dBa, the delta is 14.7 dB. This is the same increase in perceived noise as an unguarded 60 dBa fan and a guard that raised the noise level to 74.7 dBa, not a relative difference of 41% and 24.5%.
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flybrand 4y ago
The author doesn’t consider % void volume / aka ‘open-ness’ of the grill. (Or if they did, I missed it.) I’d predict the most open to Have the least resistance, which would give the least noise.
- teekert 4y ago
  I predict that is a large impact of laminar vs turbulent flow, which is not really an intuitive thing to reason about. But it could be that a more closed but weirdly shaped grill is better than a more open configuration? I'm not an expert, just have some experience with microfluidics, back in the day.
- mannykannot 4y ago
  An engineer wishing to design a quieter or more efficient fan may be interested in developing a model in which 'open-ness' is a factor, but as a user, I am primarily interested in firstly creating the required airflow quietly, and secondly efficiently. For my concerns, direct measurements are more valuable than indirect ones. The author did not compare the grills at specific airflows, but the information is still useful.
donut 4y ago
Love this: > Always look at the date when you read a hardware article. Some of the content in this article is most likely out of date, as it was written on September 19, 2011. Not only do they have a date on the article (and many posts in recent years simply don't), but they draw your attention to it because it's long ago. It's such a small but important detail. Instantly increases my trust for the company.
- jeffbee 4y ago
  I actually came to complain about that warning. Why does it exist? These are just experimental observations. They are valid forever. Many of the thermodynamics texts I needed at university traced their first editions to the 19th century. They didn’t come with weird disclaimers.
  - robertlagrant 4y ago
    It's not weird, and it's not a disclaimer! Many articles I come across online don't have a date on them.
  - npteljes 4y ago
    I suspect it's the feature of the website engine. I have seen it on other websites as well - it just appends this disclaimer, after a preset amount of time.
    - Karliss 4y ago
      Yes few clicks looking at other articles on that website confirm that they show that warning for all posts older than ~1 year. Makes sense for a blog focusing mostly on latest computer hardware and software benchmarks which can get outdated quit quickly.
  - deleted 4y ago
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  - TehCorwiz 4y ago
    While this is broadly true it does ignore some interesting developments in CPU fans. Ten years ago fan sizes were smaller and blade designs less differentiated. Now, there are fans optimized for air flow for air cooled systems and fans optimized for static pressure for cooling radiators in water cooled systems. This opens up a whole bunch of questions which may obsolete these results. Does the change and differentiation in fan blade design have implications for grill interference noise with regards to this data? Do fans that are optimized for flow versus those for pressure behave the same? Do 80mm, 120mm, and 140mm all have the same grill noise characteristics?
teekert 4y ago
Interesting that "no grill" is always the most quiet, is there no configuration possible (or has never been explored) where the air flows in such a way that sound waves cancel each other out? I.e., even holes emit noise 1/2 phase changed from the uneven ones? Would be a nice area of research. Perhaps it exists, I'm lazy (some 5 mins of searching gave me nothing).
- n4bz0r 4y ago
  Not what you describe, but that reminds me. There are panels that 'cancel' (some of) the noise by guiding the air through foam channels. Had never heard of such thing before, personally. [0]: https://youtube.com/watch?v=tMLIzedVvH8&t=1031 https://youtube.com/watch?v=tMLIzedVvH8&t=1031 (timestamp included)
- auxym 4y ago
  I'm aware of some research from my department, though not the lab I work at: https://www.ingentaconnect.com/content/ince/ncej/2013/00000061/00000004/art00001 https://www.ingentaconnect.com/content/ince/ncej/2013/000000... https://www.sciencedirect.com/science/article/abs/pii/S0022460X15004848?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S00224... https://www.sciencedirect.com/science/article/abs/pii/S0022460X13002824?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S00224... They place specially shaped "obstructors" in fan ducts which create destructive interference with some of the prominent noise tones.
- mannykannot 4y ago
  I'm just speculating here, but the grill is the source of the additional noise, rather than something that attenuates noise already present in the airflow. Therefore, to get two holes to emit sound out of phase, the mechanism by which they generate sound must be synchronized somehow. One way that such synchronization can occur is by the blades passing the holes, and I suppose that the high noise of the 'turbine' grill is caused or exacerbated by the blades alternately aligning with the holes and the ribs. I recently learned that tire treads are made with a pseudo-randomized block size, as with a same size all around the sounds each makes as it contacts the road would be periodic, producing a siren-like sound with a definite pitch. The swirl pattern presumably mitigates this effect by having little variation in the overall blade/rib alignment through one revolution. There are also tire treads like this. The difficulties of using interference in reducing fan noise are that it becomes less effective the whiter the noise is, and that destructive interference somewhere usually creates constructive interference elsewhere else.
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Neil44 4y ago
I remember back in 2000 ish I worked in R&D of a PC manufacturer and had to check the new PSUs and cases with a 'Test Finger' to make sure all the holes were small enough. The test finger was really expensive IIRC. I also had to strap a full CRT PC to a table that rotated through various axies to measure the EMI/RFI coming from the complete setup while it was running and every now and then the straps would slip and the whole thing would crash down and make a big bang and a mess. Good times.
- auxym 4y ago
  We often use stepped "reach gauges" for machine guards used in manufacturing and such: https://www.mcmaster.com/gauges/machine-guard-safety-gauges/ https://www.mcmaster.com/gauges/machine-guard-safety-gauges/ Not too expensive though.
- Sohcahtoa82 4y ago
  ... Why was the "test finger" so expensive? What was it made of? Why not just use a $3 wooden dowel rod from Home Depot?
  - JohnFen 4y ago
    Very likely they just wanted or needed certification-level accuracy. A wooden dowel would be very inaccurate for a bunch of reasons, including that its dimensions will change with humidity. Test fingers and the like are very expensive because of the serious precision they have to be machined to, and are made of expensive materials to minimize dimensional changes the result from environmental variations and use.
    - JohnBooty 4y ago
      I imagine they're small manufacturing runs as well. How many ISO-certified test fingers do they sell per year? Adds to the cost.
  - Neil44 4y ago
    Maybe they just told me that to stop me loosing it all the time!
userbinator 4y ago
Interesting to see the classic wire grill at the top. All PC PSUs used to have them, but I guess cost reduction took over.
- layer8 4y ago
  At least the slightly upmarket ones still use a wire grill on the intake, where the fan resides.
robmiller 4y ago
Acoustics consultant here. Its too bad there's no mention of using a windscreen on the sound level meter, especially at 2 inch distance. It would make sense if the mesh performed best, while airflow was restricted nearly most if air rushing by the microphone element was contributing to the level measured, and not the noise of the fan itself.
- joshuahutt 4y ago
  What a cool and fascinating job you must have.
  - robmiller 4y ago
    Hey thanks. Yes, esoteric enough to keep it interesting day to day. I mostly work with architects and design engineers to coordinate quiet building systems and good interior acoustics--projects anywhere from K-12 to major performing arts centers to commercial offices, including some of your US offices... On that point, I feel everyone's collective pain on the situation with open offices. I don't have the power to avoid them, so the best I can do is advocate for getting the signal-to-noise problem solved right.
    - robomartin 4y ago
      A couple of decades back I was very involved with work that required paying attention to acoustics. I remember building this room with walls lined with 1 foot thick Helmholtz resonators tuned to a range of frequencies. The same with portions of the ceiling. And, of course, there were broken-up and angled surfaces to help diffuse sound, avoid creating standing waves and stimulation of room modes. Back then I even wrote a bunch of software to run acoustics analysis and evaluate room characteristics based on a range of parameters, including construction materials, etc. Here are a couple of screen shots: https://i.imgur.com/sXQmc8d.png https://i.imgur.com/sXQmc8d.png https://i.imgur.com/q0kHVbQ.png https://i.imgur.com/q0kHVbQ.png Since then I have always been very aware of acoustics in every environment. Restaurants are particularly horrendous. Nearly all of them seem to be reverberation chambers designed to destroy sound. Most would benefit greatly by deploying a few very simple tools to control sound and allow patrons to have conversations in a reasonable environment.
Sohcahtoa82 4y ago
As someone with three long-haired cats, Mesh is my only option unless I want to take on a monthly task of removing fur from all the fans.
MichaelCollins 4y ago
I think grills on plastic bladed fans are an anachronism. Most fan blades used to be metal (some still are) and those can likely hurt you badly if you stick your finger in the blades. Plastic fan blades came later, but by that time people expected fans to come with blade guards so they do, even though they now serve no practical purpose. I can stop my plastic-bladed box fan by flicking my pinky finger between the blades and it doesn't even leave a bruise. But I leave the fan guard on my metal bladed lasko, I think that fan might cut my finger off if I tried the same trick. Those metal fan blades are fairly sharp and have a lot more momentum.
- Heyso 4y ago
  Sharp blades, hot radiator, equipped for cooking.
- liminalsunset 4y ago
  I think it's always a good practice to exercise caution and respect for mechanical and electrical devices, no matter how low the perceived risk may be. While standards exist for e.g. voltage or current under which the relative risk is reduced, careless operation of even low-energy systems may at best damage the equipment, or at worst result in injury. It also tends to lead to the normalization of dangerous practices, which transfer to dangerous situations. PC fans are surprisingly dangerous. So much so, that Dell and HP are forced to put a little triangle "warning!! fan!" sticker next to the fan in a laptop. Okay, maybe not. In the case of the blower fans, you are more of a danger to the fan than it is to you. Touching the thin blades while operating is often enough to snap some or all of them off the hub. On normal axial fans, DIY PC market fans are often underpowered, at 0.1-0.2A at 12 volts. This isn't a lot of power, and the rotation speed is low and as you have found, not very dangerous. However, outside of the DIY PC market, even in any PSU, fans are often rated at 0.3 A, and the average graphics card fan is rated 0.6 A. Once you get into the several watts territory, the fan is capable of operating at 3000+ RPM. On OEM PCs, 80-90mm CPU fans are rated at like 0.9-2.5A. In servers, fans up to 4A are common. These operate at 10,000 RPM or more. The reason you do not hear about this is because most systems oversize the fan and run it at a low speed to reduce noise, but keep that machine that is choking in dust running at full speed so the factory floor doesn't halt or something. I have seen Dells in these kinds of situations where nobody will clean the PC in 20 years, but it has to, and does, keep trucking. These kinds of fans produce robot vacuum cleaner territory of static pressure, up to many inches of water column at 250 CFM. These kinds of fans are extremely dangerous. China/AliExpress calls them "high speed violence fans" for a reason. The motor hubs are usually made of steel in higher powered ones, and the stall torque is high. The blades have a swept, sharpened tip made of glass fiber reinforced plastic, and the blade assembly carries several hundred grams to kilograms of inertial force. These fans will mangle fingers. When I was very young and inexperienced, [warning graphic], I caught my finger on the sharp tip of a 90mm fan from a Dell while it was spinning down. In a separate incident, I also managed to touch a Intel stock cooler on full speed, and the blade got caught under my fingernail. Always use a suitable fan guard or safety equipment when testing cooling fans or working around them. The more powerful fans will take off chunks of your fingers, and even a tame seeming fan can quickly speed up to dangerous power levels without notice when the system controller senses a case open, fan failure, or high ambient situation.
ehnto 4y ago
The real secret to a quiet PC is not running the fans until absolutely necessary. My PC is silent 95% of the the time, because of massive heatsinks, good venting, and a lack of silicon sympathy, I can tune the fans to only come on at 90th percentile temps.
- whyoh 4y ago
  The other main source of PC noise nowadays is coil whine. That one is harder to deal with, because it's often down to just luck (and that's because companies apparently don't care enough to solve this problem during production).
  - ehnto 4y ago
    I hate coil whine so much! It really is luck of the draw. Even if you RMA you could just get another one thst whines.
timmahoney 4y ago
I put together a silent pc earlier this year and I'll never go back. I had a Dell "new" XPS with 16 cores and 32GB on it, and the fan for the laptop itself runs 80% of the time, and even the docking station for it has a fan that runs pretty often. This thing in contrast never makes a single sound.
whyoh 4y ago
Related: "How do different fan mesh patterns affect fan and chassis airflow?" https://www.silverstonetek.com/en/tech-talk/wh_chessis https://www.silverstonetek.com/en/tech-talk/wh_chessis
simne 4y ago
If close eyes for article date, I seen at least one defect. 20 years ago where known, that place instead of grille deflector tube (like lens hood), will make cooler significantly quieter, just because tube absorb some sound and vibrations. I don't know, why this variant does not shown in this research.
danielodievich 4y ago
As a household with two Puget Systems workstations, i can attest that this article is very representative of their attention to detail. The workstation built in 2015ish was their Serenity series (nod to Firefly), designed to be as quiet as possible. It does so amazingly well by using large fans and lots of acoustic filtering. My 2022 gaming machine is bigger than that but still very quiet in almost all circumstances. Great place to have a custom build. Not the cheapest though.

360 points by yread 4y ago

The difference of 5 to 15dbA is quite a big deal, as 10dBA higher values are roughly perceived as "twice as loud".

This is really cool! Measuring something as that nobody even thinks about or realizes is there, and finding an actual big difference in performance is always a delightful discovery to me.

peanut_worm 4y ago

Didn’t think it would make such a big difference. I am also surprised the mesh was so quiet, I would have assumed it would have been the loudest.

drgiggles 4y ago

The point of a grill is to block dust and debris, which presumably I want. Otherwise I would just not use one and my fans would be the quietest and cool most effectively. What is the trade-off between the two metrics sited and effectiveness of each type of grill at its intended purpose?

kqr 4y ago
I think the purpose of the grill on a computer is not so much about dust and smaller debris as it is about (a) protecting user fingers against fan bites, and (b) protecting the fan against bigger pokey things that could damage the fan blades or jam the fan.
- drgiggles 4y ago
  hmm, I always assumed there was some other benefit. I'm taking all mine off. Seems pretty easy to not ram my finger in it.
  - zamadatix 4y ago
    No roaming pets or children I take it :p. Debris are usually covered by a foam filter in front of the fans (if at all). I’ll usually take that off though and just clean it every once in a while.
    - drgiggles 4y ago
      No, I comment on posts about pc fan grills at 6am...I'm single :)
      - wffurr 4y ago
        That's exactly the kind of thing I do in the morning over coffee in those quiet few minutes before the children are up. Rest assured that you can still continue to comment on obscure tech minutiae at odd hours of the morning.
- Grimburger 4y ago
  I have a large fan at home that I remove the front protector from because it gets dirty often and is quieter. My young nephew shoves his hand it in all the time for fun with zero harm.
  - Sarkie 4y ago
    "It doesn't affect me, so it cannot be an issue"
  - somehnguy 4y ago
    On the flip side, a few of my hobbies include devices where the fans are usually exposed - and I've cut myself a handful of times because of it. It's very size/shape/rpm dependent.
  - mellavora 4y ago
    zero harm to him or to the blade?
  - jabroni_salad 4y ago
    Big fans are at a relatively low RPM, and household fans might be made with kids sticking their fingers in them in mind. I've got a little noisy desk fan with metal blades in it that I would prefer not to take my chances with. I've also cut myself on my RC Plane's props a few times.
- gigaflop 4y ago
  In super small form factor PCs, sometimes you use a fan grille on the inside, to make sure that wires, etc on the interior don't get caught in the fan.

kqr 4y ago

What can explain the case where there's more air moving out the exhaust side than being sucked up the intake side?

danuker 4y ago
Coandă effects might drag air from somewhere else, not just from the intake. https://en.wikipedia.org/wiki/Coand%C4%83_effect https://en.wikipedia.org/wiki/Coand%C4%83_effect Edit: I see the tester used an anemometer, which measures just the air moving THROUGH the anemometer. If the exhaust is smaller than the intake, then air will move at a higher speed through the exhaust. Thus the anemometer will show a higher reading.
- lupire 4y ago
  It has to come from somewhere, by conservation of mass.
  - danuker 4y ago
    Indeed. I was thinking it's from some other holes of a non-airtight case. But actually, the mass conservation happens through air around the anemometer (i.e. air not getting measured, but still moving).
  - Scoundreller 4y ago
    Évaporation and gas formation of the electrolytic capacitor goop comes to mind :)
mannykannot 4y ago
The airflow into a fan is in response to the low pressure created by the blades, an so will approach over a wide angle. The outflow, however, is initially strongly biased to a direction perpendicular to the plane of the blades (together with some swirl imparted by the blades.) Because of this, the anemometer shown is likely to intercept a larger fraction of outflow than the inflow. Maybe the swirl will also have an effect, depending on whether the fan blades and anemometer blades rotate in the same or opposite directions.

londons_explore 4y ago

"Wire" is effectively the air passing around a cylinder. There is a lot of information about airflow around cylinders. Eg [1]. The top left diagram should be the one that applies with small diameters and the kind of airflow rates in a PC fan. I would guess that all the other shapes have micro-scale sharp edges that leave vortexes which both slow the flow down and make noise. [1]: https://i.ytimg.com/vi/pW0JfEBE9h8/maxresdefault.jpg https://i.ytimg.com/vi/pW0JfEBE9h8/maxresdefault.jpg

jongala 4y ago
I agree, it feels like a missed opportunity to not explore this. I'd love to see an analysis of the swirl design (or other commonly used manufacturer patterns), with the edges rounded or beveled on the intake face, exhaust face, or both. Like, even on cut or stamped grills, how much could performance be improved by e.g. sandblasting the finished piece from one or both sides and taking down the edges a bit?
- londons_explore 4y ago
  The wire is only just laminar flow... I found a random PC fan and assumed a 1mm wire diameter, 2.3m/s airflow, and the reynolds number comes out at 36. That tells me if you were to get a 1000x really powerful fan, then the grille would start giving turbulent flow, and might no longer perform the best. Page with lots of details: http://labman.phys.utk.edu/phys221core/modules/m8/turbulence.html#:~:text=The%20air%20behind%20the%20cylinder,of%20approximately%202000%20to%20100000 http://labman.phys.utk.edu/phys221core/modules/m8/turbulence....
  - simne 4y ago
    This is 10 years ago article, coolers tech changed a lot since that. I even remember, when in mac clones used ultra-high-speed coolers, which now used only in rack devices. And yes, ultra-high-speed coolers, has much higher speed and make turbulence.
Cthulhu_ 4y ago
I mean that's the main difference between the wire and all the others, really; the wire is round metal, the others are shapes stamped from flat metal. That said, my current PC has plastic "angled slats" at the back (outlet) and a honeycomb and mesh (filter) at the front, so it could be quieter. I'll keep it in mind if I ever buy a new one. I believe the wire one was the most common on older PCs (90's / 2000's).

once_inc 4y ago

I just realized that my Synology DS218play NAS is so loud because of the fan grill at the back. Too bad I can't easily remove it...

Cthulhu_ 4y ago
Looks like it's nothing some pliers or a dremel can't handle. Also if it's the one I'm seeing on an image search, it looks like the grill at the back is of the mesh variant - it's plastic, molded in a rounded-off fashion. There's probably some tweaks you can do, if it stays cool enough, lower the fan speed or make it dynamic depending on temperature.
- neilv 4y ago
  Additionally, replacing the fan itself with a quieter one can also help. Image search for "synology noctua" shows this is a thing (and looks like some of them are just removing the grills altogether).
- n4bz0r 4y ago
  Not quite sure you'd have to get down and dirty like that. Here is a video of a (seemingly) similar model where a guy simply unscrews the grill without even opening the case: https://youtube.com/watch?v=lBaeK5ry-aM&t=30s https://youtube.com/watch?v=lBaeK5ry-aM&t=30s

nemacol 4y ago

https://www.youtube.com/watch?v=1L2ef1CP-yw https://www.youtube.com/watch?v=1L2ef1CP-yw Matthias has an interesting video that is tangentially related talking about the distance of a fan to a window and air flow. While watching I was wondering how this interacts with PC case fans and if they are losing a lot of performance by being directly against the case.

omega3 4y ago

I think a more interesting question would be whether the design actually makes any difference or if the airflow just depends on the free/unobstructed area.

contravariant 4y ago

Going from 36 to 50.2 dBa is not a 41.4% increase, you can't use percentages with a relative scale. Technically it's a 2530% increase, but that's silly because it doesn't correspond to how people experience sound.

dwringer 4y ago
Sorry if this is a nitpick, but by design, sound doubles in perceived loudness (roughly) every 10dB, and dBa is a calibrated version of dB which is intended to correspond to how people experience sound, so that increase is only around a tenth of the figure you gave (although you're absolutely right that it's a lot higher than 41%).
- martincmartin 4y ago
  Yes, but the zero point is arbitrary, so a percentage of dBa is meaningless. You can say it's 14.2 dB louder, or 10^(1.42) more energy, neither of which is very meaningful to the average person.
  - mckirk 4y ago
    So then wouldn't it basically be 142% louder?
- contravariant 4y ago
  I don't mind being nitpicked when I'm being pedantic. Indeed you can (roughly) approximate perceived loudness that way, but only the absolute difference in dBa is meaningful, looking at a relative difference in dB is meaningless.
  - LeifCarrotson 4y ago
    Rather than using percentages under the noise readings, it would be much more useful to show the delta. If the unguarded fan is at 35.5 dBa, and the turbine guard is at 50.2 dBa, the delta is 14.7 dB. This is the same increase in perceived noise as an unguarded 60 dBa fan and a guard that raised the noise level to 74.7 dBa, not a relative difference of 41% and 24.5%.

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flybrand 4y ago

The author doesn’t consider % void volume / aka ‘open-ness’ of the grill. (Or if they did, I missed it.) I’d predict the most open to Have the least resistance, which would give the least noise.

teekert 4y ago
I predict that is a large impact of laminar vs turbulent flow, which is not really an intuitive thing to reason about. But it could be that a more closed but weirdly shaped grill is better than a more open configuration? I'm not an expert, just have some experience with microfluidics, back in the day.
mannykannot 4y ago
An engineer wishing to design a quieter or more efficient fan may be interested in developing a model in which 'open-ness' is a factor, but as a user, I am primarily interested in firstly creating the required airflow quietly, and secondly efficiently. For my concerns, direct measurements are more valuable than indirect ones. The author did not compare the grills at specific airflows, but the information is still useful.

donut 4y ago

Love this: > Always look at the date when you read a hardware article. Some of the content in this article is most likely out of date, as it was written on September 19, 2011. Not only do they have a date on the article (and many posts in recent years simply don't), but they draw your attention to it because it's long ago. It's such a small but important detail. Instantly increases my trust for the company.

jeffbee 4y ago
I actually came to complain about that warning. Why does it exist? These are just experimental observations. They are valid forever. Many of the thermodynamics texts I needed at university traced their first editions to the 19th century. They didn’t come with weird disclaimers.
- robertlagrant 4y ago
  It's not weird, and it's not a disclaimer! Many articles I come across online don't have a date on them.
- npteljes 4y ago
  I suspect it's the feature of the website engine. I have seen it on other websites as well - it just appends this disclaimer, after a preset amount of time.
  - Karliss 4y ago
    Yes few clicks looking at other articles on that website confirm that they show that warning for all posts older than ~1 year. Makes sense for a blog focusing mostly on latest computer hardware and software benchmarks which can get outdated quit quickly.
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- TehCorwiz 4y ago
  While this is broadly true it does ignore some interesting developments in CPU fans. Ten years ago fan sizes were smaller and blade designs less differentiated. Now, there are fans optimized for air flow for air cooled systems and fans optimized for static pressure for cooling radiators in water cooled systems. This opens up a whole bunch of questions which may obsolete these results. Does the change and differentiation in fan blade design have implications for grill interference noise with regards to this data? Do fans that are optimized for flow versus those for pressure behave the same? Do 80mm, 120mm, and 140mm all have the same grill noise characteristics?

teekert 4y ago

Interesting that "no grill" is always the most quiet, is there no configuration possible (or has never been explored) where the air flows in such a way that sound waves cancel each other out? I.e., even holes emit noise 1/2 phase changed from the uneven ones? Would be a nice area of research. Perhaps it exists, I'm lazy (some 5 mins of searching gave me nothing).

n4bz0r 4y ago
Not what you describe, but that reminds me. There are panels that 'cancel' (some of) the noise by guiding the air through foam channels. Had never heard of such thing before, personally. [0]: https://youtube.com/watch?v=tMLIzedVvH8&t=1031 https://youtube.com/watch?v=tMLIzedVvH8&t=1031 (timestamp included)
auxym 4y ago
I'm aware of some research from my department, though not the lab I work at: https://www.ingentaconnect.com/content/ince/ncej/2013/00000061/00000004/art00001 https://www.ingentaconnect.com/content/ince/ncej/2013/000000... https://www.sciencedirect.com/science/article/abs/pii/S0022460X15004848?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S00224... https://www.sciencedirect.com/science/article/abs/pii/S0022460X13002824?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S00224... They place specially shaped "obstructors" in fan ducts which create destructive interference with some of the prominent noise tones.
mannykannot 4y ago
I'm just speculating here, but the grill is the source of the additional noise, rather than something that attenuates noise already present in the airflow. Therefore, to get two holes to emit sound out of phase, the mechanism by which they generate sound must be synchronized somehow. One way that such synchronization can occur is by the blades passing the holes, and I suppose that the high noise of the 'turbine' grill is caused or exacerbated by the blades alternately aligning with the holes and the ribs. I recently learned that tire treads are made with a pseudo-randomized block size, as with a same size all around the sounds each makes as it contacts the road would be periodic, producing a siren-like sound with a definite pitch. The swirl pattern presumably mitigates this effect by having little variation in the overall blade/rib alignment through one revolution. There are also tire treads like this. The difficulties of using interference in reducing fan noise are that it becomes less effective the whiter the noise is, and that destructive interference somewhere usually creates constructive interference elsewhere else.

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Neil44 4y ago

I remember back in 2000 ish I worked in R&D of a PC manufacturer and had to check the new PSUs and cases with a 'Test Finger' to make sure all the holes were small enough. The test finger was really expensive IIRC. I also had to strap a full CRT PC to a table that rotated through various axies to measure the EMI/RFI coming from the complete setup while it was running and every now and then the straps would slip and the whole thing would crash down and make a big bang and a mess. Good times.

auxym 4y ago
We often use stepped "reach gauges" for machine guards used in manufacturing and such: https://www.mcmaster.com/gauges/machine-guard-safety-gauges/ https://www.mcmaster.com/gauges/machine-guard-safety-gauges/ Not too expensive though.
Sohcahtoa82 4y ago
... Why was the "test finger" so expensive? What was it made of? Why not just use a $3 wooden dowel rod from Home Depot?
- JohnFen 4y ago
  Very likely they just wanted or needed certification-level accuracy. A wooden dowel would be very inaccurate for a bunch of reasons, including that its dimensions will change with humidity. Test fingers and the like are very expensive because of the serious precision they have to be machined to, and are made of expensive materials to minimize dimensional changes the result from environmental variations and use.
  - JohnBooty 4y ago
    I imagine they're small manufacturing runs as well. How many ISO-certified test fingers do they sell per year? Adds to the cost.
- Neil44 4y ago
  Maybe they just told me that to stop me loosing it all the time!

userbinator 4y ago

Interesting to see the classic wire grill at the top. All PC PSUs used to have them, but I guess cost reduction took over.

layer8 4y ago
At least the slightly upmarket ones still use a wire grill on the intake, where the fan resides.

robmiller 4y ago

Acoustics consultant here. Its too bad there's no mention of using a windscreen on the sound level meter, especially at 2 inch distance. It would make sense if the mesh performed best, while airflow was restricted nearly most if air rushing by the microphone element was contributing to the level measured, and not the noise of the fan itself.

joshuahutt 4y ago
What a cool and fascinating job you must have.
- robmiller 4y ago
  Hey thanks. Yes, esoteric enough to keep it interesting day to day. I mostly work with architects and design engineers to coordinate quiet building systems and good interior acoustics--projects anywhere from K-12 to major performing arts centers to commercial offices, including some of your US offices... On that point, I feel everyone's collective pain on the situation with open offices. I don't have the power to avoid them, so the best I can do is advocate for getting the signal-to-noise problem solved right.
  - robomartin 4y ago
    A couple of decades back I was very involved with work that required paying attention to acoustics. I remember building this room with walls lined with 1 foot thick Helmholtz resonators tuned to a range of frequencies. The same with portions of the ceiling. And, of course, there were broken-up and angled surfaces to help diffuse sound, avoid creating standing waves and stimulation of room modes. Back then I even wrote a bunch of software to run acoustics analysis and evaluate room characteristics based on a range of parameters, including construction materials, etc. Here are a couple of screen shots: https://i.imgur.com/sXQmc8d.png https://i.imgur.com/sXQmc8d.png https://i.imgur.com/q0kHVbQ.png https://i.imgur.com/q0kHVbQ.png Since then I have always been very aware of acoustics in every environment. Restaurants are particularly horrendous. Nearly all of them seem to be reverberation chambers designed to destroy sound. Most would benefit greatly by deploying a few very simple tools to control sound and allow patrons to have conversations in a reasonable environment.

Sohcahtoa82 4y ago

As someone with three long-haired cats, Mesh is my only option unless I want to take on a monthly task of removing fur from all the fans.

MichaelCollins 4y ago

I think grills on plastic bladed fans are an anachronism. Most fan blades used to be metal (some still are) and those can likely hurt you badly if you stick your finger in the blades. Plastic fan blades came later, but by that time people expected fans to come with blade guards so they do, even though they now serve no practical purpose. I can stop my plastic-bladed box fan by flicking my pinky finger between the blades and it doesn't even leave a bruise. But I leave the fan guard on my metal bladed lasko, I think that fan might cut my finger off if I tried the same trick. Those metal fan blades are fairly sharp and have a lot more momentum.

Heyso 4y ago
Sharp blades, hot radiator, equipped for cooking.
liminalsunset 4y ago
I think it's always a good practice to exercise caution and respect for mechanical and electrical devices, no matter how low the perceived risk may be. While standards exist for e.g. voltage or current under which the relative risk is reduced, careless operation of even low-energy systems may at best damage the equipment, or at worst result in injury. It also tends to lead to the normalization of dangerous practices, which transfer to dangerous situations. PC fans are surprisingly dangerous. So much so, that Dell and HP are forced to put a little triangle "warning!! fan!" sticker next to the fan in a laptop. Okay, maybe not. In the case of the blower fans, you are more of a danger to the fan than it is to you. Touching the thin blades while operating is often enough to snap some or all of them off the hub. On normal axial fans, DIY PC market fans are often underpowered, at 0.1-0.2A at 12 volts. This isn't a lot of power, and the rotation speed is low and as you have found, not very dangerous. However, outside of the DIY PC market, even in any PSU, fans are often rated at 0.3 A, and the average graphics card fan is rated 0.6 A. Once you get into the several watts territory, the fan is capable of operating at 3000+ RPM. On OEM PCs, 80-90mm CPU fans are rated at like 0.9-2.5A. In servers, fans up to 4A are common. These operate at 10,000 RPM or more. The reason you do not hear about this is because most systems oversize the fan and run it at a low speed to reduce noise, but keep that machine that is choking in dust running at full speed so the factory floor doesn't halt or something. I have seen Dells in these kinds of situations where nobody will clean the PC in 20 years, but it has to, and does, keep trucking. These kinds of fans produce robot vacuum cleaner territory of static pressure, up to many inches of water column at 250 CFM. These kinds of fans are extremely dangerous. China/AliExpress calls them "high speed violence fans" for a reason. The motor hubs are usually made of steel in higher powered ones, and the stall torque is high. The blades have a swept, sharpened tip made of glass fiber reinforced plastic, and the blade assembly carries several hundred grams to kilograms of inertial force. These fans will mangle fingers. When I was very young and inexperienced, [warning graphic], I caught my finger on the sharp tip of a 90mm fan from a Dell while it was spinning down. In a separate incident, I also managed to touch a Intel stock cooler on full speed, and the blade got caught under my fingernail. Always use a suitable fan guard or safety equipment when testing cooling fans or working around them. The more powerful fans will take off chunks of your fingers, and even a tame seeming fan can quickly speed up to dangerous power levels without notice when the system controller senses a case open, fan failure, or high ambient situation.

ehnto 4y ago

The real secret to a quiet PC is not running the fans until absolutely necessary. My PC is silent 95% of the the time, because of massive heatsinks, good venting, and a lack of silicon sympathy, I can tune the fans to only come on at 90th percentile temps.

whyoh 4y ago
The other main source of PC noise nowadays is coil whine. That one is harder to deal with, because it's often down to just luck (and that's because companies apparently don't care enough to solve this problem during production).
- ehnto 4y ago
  I hate coil whine so much! It really is luck of the draw. Even if you RMA you could just get another one thst whines.

timmahoney 4y ago

I put together a silent pc earlier this year and I'll never go back. I had a Dell "new" XPS with 16 cores and 32GB on it, and the fan for the laptop itself runs 80% of the time, and even the docking station for it has a fan that runs pretty often. This thing in contrast never makes a single sound.

whyoh 4y ago

Related: "How do different fan mesh patterns affect fan and chassis airflow?" https://www.silverstonetek.com/en/tech-talk/wh_chessis https://www.silverstonetek.com/en/tech-talk/wh_chessis

simne 4y ago

If close eyes for article date, I seen at least one defect. 20 years ago where known, that place instead of grille deflector tube (like lens hood), will make cooler significantly quieter, just because tube absorb some sound and vibrations. I don't know, why this variant does not shown in this research.

danielodievich 4y ago

As a household with two Puget Systems workstations, i can attest that this article is very representative of their attention to detail. The workstation built in 2015ish was their Serenity series (nod to Firefly), designed to be as quiet as possible. It does so amazingly well by using large fans and lots of acoustic filtering. My 2022 gaming machine is bigger than that but still very quiet in almost all circumstances. Great place to have a custom build. Not the cheapest though.