[HN Gopher] Effects of grill patterns on fan performance/noise (...
___________________________________________________________________
Effects of grill patterns on fan performance/noise (2011)
Author : yread
Score : 308 points
Date : 2022-09-21 10:50 UTC (12 hours ago)
(HTM) web link (www.pugetsystems.com)
(TXT) w3m dump (www.pugetsystems.com)
| [deleted]
| timmahoney wrote:
| 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.
| [deleted]
| teekert wrote:
| 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).
| auxym wrote:
| I'm aware of some research from my department, though not the
| lab I work at:
|
| https://www.ingentaconnect.com/content/ince/ncej/2013/000000...
|
| https://www.sciencedirect.com/science/article/abs/pii/S00224...
|
| 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.
| 0xbadcafebee wrote:
| For passive noise cancellation you would need to add material
| that absorbs/dampens sound, or you would create a
| baffle/muffler of some sort. The only alternative I know of is
| ANC.
|
| This PC case fan (https://noctua.at/en/noctua_anc_project) is
| designed for ANC. It generates the inverted signal inside the
| fan.
| n4bz0r wrote:
| 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 (timestamp
| included)
| mannykannot wrote:
| 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.
| RobotToaster wrote:
| I was wondering if a honeycomb laminar flow grid would make it
| quieter.
| robmiller wrote:
| 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.
| roberthahn wrote:
| I would have expected that you'd _want_ to factor in air noise
| because humans don't only hear fan noise in their computers. Or
| am I misunderstanding?
| MengerSponge wrote:
| You know how someone blowing in your ear makes more sound
| than when you blow in someone else's ear? The airflow itself
| can make sound from eddies and whatnot.
|
| Most people don't put their ear next to a case fan to see if
| it's annoying or not. You experience its sound from several
| feet away, and the measurement should reflect that.
| ehnto wrote:
| I think they mean the excess noise of a volume of air moving
| past your ear, which is due to the turbulence created while
| air is passing over your ear and not the soundwaves being
| transmitted by said volume of air.
|
| Practically speaking no you wouldn't want to factor the
| turbulence generated at the microphone because the user of
| the computer wouldn't be hearing that.
| larrik wrote:
| They measured the intake side, though, so it was more of a
| vacuum effect. Would a windscreen still make a difference in
| that scenario?
| oliveshell wrote:
| I can't think of why not. The velocity might be lower, but
| moving air is moving air.
| robmiller wrote:
| Yes, I agree. Inlet side is quieter than discharge for most
| fan types (propeller, centrifugal, etc), but noise due to
| air movement are on both sides.
| joshuahutt wrote:
| What a cool and fascinating job you must have.
| robmiller wrote:
| 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.
| Darkphibre wrote:
| Thank you so much for what you do.
| nomel wrote:
| > signal-to-noise problem solved right.
|
| One evening, I was sitting alone in the eating area of a
| very high end office, and noticed a whooshing sound coming
| from the top edge of the room. I thought it was maybe some
| air vent, but there was no wind outside. I stuck my phone
| camera up behind the front lip of a shelf and saw a set of
| speakers. They were playing something close to brown noise!
|
| And, I learned about sound masking [1]. So, apparently
| there's two ends to be avoided, in the signal-to-noise
| problem!
|
| 1. https://cambridgesound.com/learn/sound-masking-101/
| robmiller wrote:
| There are various factors:
|
| 1. Partitions around workspaces create a modest barrier
| effect, not so much realizable for your nearest neighbors
| but those more distant. No one installs partitions up to
| 48" or 52" but you have to at least break line of sight
| to the noisemaker to realize any improvement. This
| reduces signal.
|
| 2. Acoustically absorptive ceilings avoid the overhead
| reflection that would be the next cue to an occupant. The
| partition comes first, but this is second. Another signal
| reducer.
|
| 3. Background noise, whether a consistent HVAC system or
| sound masking system raises the noise floor of the
| environment. We have a pretty good sense of what level is
| acceptable to most people, but there will always be those
| with sensitivities. The noise is usually pink noise with
| some EQ to sound like HVAC air distribution.
| Unfortunately there has to be some treble in the noise
| signal to reduce the consonants of speech, which can be
| more annoying.
|
| You won't make nearby co-workers inaudible, but the hope
| is that those 20 ft or so further will be less
| problematic. For inaudibility you have to get S/N to
| around -10 dB, that's a noise floor of 10 dB higher than
| the source, which is only realizable with walls at least
| to the ceiling.
| lelandfe wrote:
| I adore how diverse the HN audience is.
| whyoh wrote:
| Related: "How do different fan mesh patterns affect fan and
| chassis airflow?"
|
| https://www.silverstonetek.com/en/tech-talk/wh_chessis
| drgiggles wrote:
| 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 wrote:
| 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.
| Grimburger wrote:
| 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.
| somehnguy wrote:
| 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 wrote:
| zero harm to him or to the blade?
| jabroni_salad wrote:
| 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.
| Sarkie wrote:
| "It doesn't affect me, so it cannot be an issue"
| gigaflop wrote:
| 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.
| drgiggles wrote:
| 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 wrote:
| 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 wrote:
| No, I comment on posts about pc fan grills at 6am...I'm
| single :)
| wffurr wrote:
| 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.
| MichaelCollins wrote:
| 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 wrote:
| Sharp blades, hot radiator, equipped for cooking.
| sbierwagen wrote:
| >I can stop my plastic-bladed box fan by flicking my pinky
| finger between the blades and it doesn't even leave a bruise.
|
| I might be misreading this. Are you saying you can stop a
| running box fan, powered on, force being applied to the
| impeller by the electric motor, with your pinky?
| liminalsunset wrote:
| 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.
| kqr wrote:
| What can explain the case where there's more air moving out the
| exhaust side than being sucked up the intake side?
| mannykannot wrote:
| 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.
| danuker wrote:
| Coanda effects might drag air from somewhere else, not just
| from the intake.
|
| 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 wrote:
| It has to come from _somewhere_ , by conservation of mass.
| danuker wrote:
| 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 wrote:
| Evaporation and gas formation of the electrolytic capacitor
| goop comes to mind :)
| Neil44 wrote:
| 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.
| zh3 wrote:
| BSI standard for test finger appears to have been withdraw [0]
| in favour of EIC standards. You can still get test fingers on
| Amazon though [1].
|
| [0] https://knowledge.bsigroup.com/products/standard-test-
| finger...
|
| [1] https://www.amazon.co.uk/GOWE-IEC61032-IEC60529-Probe-
| Finger...
| auxym wrote:
| We often use stepped "reach gauges" for machine guards used in
| manufacturing and such:
| https://www.mcmaster.com/gauges/machine-guard-safety-gauges/
| Not too expensive though.
| Sohcahtoa82 wrote:
| ...
|
| Why was the "test finger" so expensive? What was it made of?
|
| Why not just use a $3 wooden dowel rod from Home Depot?
| Neil44 wrote:
| Maybe they just told me that to stop me loosing it all the
| time!
| JohnFen wrote:
| 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 wrote:
| I imagine they're small manufacturing runs as well. How
| many ISO-certified test fingers do they sell per year? Adds
| to the cost.
| queuebert wrote:
| You can buy small stainless steel cylindrical gauges accurate
| to 0.0001" for not much more than that.
| Kon-Peki wrote:
| All that cost savings goes out the window the first time you
| get sued ;)
|
| But also keep in mind that test fingers are used for more
| than just seeing if it can poke through a screen.
|
| Way way way back when I worked in the auto supplier industry,
| we needed to test to make sure the auto-up windows and auto-
| closing minivan doors would actually not cut your
| finger/hand/leg off. We always used pencils as a first try.
| They break a lot easier than a dowel rod of the same
| diameter. If we were happy with the results, we'd get out the
| test finger. If it looked a little iffy, we'd suggest that
| the engineers should use their own fingers if they were
| really confident in their work.
| once_inc wrote:
| 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_ wrote:
| 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 wrote:
| 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 wrote:
| 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
| nemacol wrote:
| 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.
| Sohcahtoa82 wrote:
| 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.
| flybrand wrote:
| 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.
| mannykannot wrote:
| 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.
| teekert wrote:
| 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.
| omega3 wrote:
| 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.
| jansan wrote:
| The difference of 5 to 15dbA is quite a big deal, as 10dBA higher
| values are roughly perceived as "twice as loud".
| donut wrote:
| 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 wrote:
| 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 wrote:
| It's not weird, and it's not a disclaimer! Many articles I
| come across online don't have a date on them.
| rtkwe wrote:
| You're comparing fundamental laws of physics to consumer
| product interactions. PC fan design is not static on the
| quiet end and neither are grill designs though they're less
| fluid. The interaction between them matters though for the
| kinds of changes and noise they're trying to measure.
| TehCorwiz wrote:
| 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?
| whyoh wrote:
| Anecdotal, but even with the new fans, stamped out grills
| still perform poorly in terms of noise. They're popular
| because they're cheap.
|
| I'd gladly pay $10 more for a PC case with a less noisy
| grill, but I can't find any that has this, not even ones
| that are advertised as "silent".
| rtkwe wrote:
| It's a pretty easy mod if you really want to swap to wire
| grills. 10 minutes with a dremel and 10 more to make it
| look ok again and you can have a completely open fan
| mount.
| npteljes wrote:
| 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 wrote:
| 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]
| hedora wrote:
| Well, for one thing, the once-excellent model of fan they
| picked aged as well as an avocado green Chevy Nova with a
| rusted out coffee can muffler:
|
| https://graphicscardhub.com/best-silent-pc-fans/
| elabajaba wrote:
| That list is terrible. They clearly didn't do any testing
| and just copied off the spec sheet, and ignored what
| enthusiasts actually recommend as good fans in 2022
| (Corsair fans are terrible, Arctic F12 instead of P12,
| etc).
| afterburner wrote:
| Weird, I remember Noctua fans being really good ten years
| ago too. Choosing Antec feels like a deliberately mid-range
| choice, but I don't remember how they were thought of back
| then.
| [deleted]
| SilasX wrote:
| Okay, but also keep proper perspective. 2011 is not some kind
| of ancient history in the domain of fluid mechanics and fan
| design.
|
| Reminds me of the time some Rust advocates insisted 2016 was an
| era before programmers were aware of the concepts of
| abstraction and separation of concerns:
|
| https://news.ycombinator.com/item?id=19109418
| NavinF wrote:
| Linked thread shows you getting schooled. You used a crappy
| library that died before it ever made it to version 1.0, a
| mistake that everyone makes at least once.
|
| On topic: This article was written by an SI (system
| integrator). 2011 is ancient history as far as PC hardware
| goes. Eg today's fans are a lot more efficient at the same
| price point and most enthusiasts need a lot more static
| pressure for radiators.
| anamexis wrote:
| The link seems to be you just constructing that straw man,
| with no one insisting on those things at all.
| SilasX wrote:
| I said the problem was that the function calls didn't obey
| well-understood practices for abstraction.[1]
|
| Responses defend it on the grounds that it was a long time
| ago, i.e. 2016.
|
| Where's the straw man?
|
| [1] https://news.ycombinator.com/item?id=19109093
| anamexis wrote:
| Where does anyone insist that "2016 was an era before
| programmers were aware of the concepts of abstraction and
| separation of concerns"?
| SilasX wrote:
| Like I just said, the part where they insist my
| expectations of that library where too high because it
| was 2016, and my expectation was that it obeyed proper
| abstraction.
| anamexis wrote:
| I don't see anyone insisting on that, either.
| 411111111111111 wrote:
| I don't think linking to that comment favours your point,
| honestly.
|
| > _Rust 1.0 was just released and the ecosystem was mostly
| maturing at that point. You 're talking about version 0.2.36
| of a library that had been in development for less than two
| years during a quite tempestuous time in Rust._
| SilasX wrote:
| And like I said at the time, that would excuse failure on
| some edge case. It wouldn't excuse the thing I was actually
| criticizing, that "the calls for common functions require
| you to specify low-level implementation details that don't
| matter to you". That's the kind of thing the typical
| software dev gets right when designing the function,
| because abstraction was _very well understood in 2016_.
|
| It's not something they would only figure out after fixing
| the thousandth bug.
| duskwuff wrote:
| > 2011 is not some kind of ancient history in the domain of
| fluid mechanics and fan design.
|
| But it is for most of the other articles this site publishes
| about consumer computer hardware, like the two that were
| published surrounding this one ([1], [2]). This article just
| happens to be an exception.
|
| [1]: https://www.pugetsystems.com/labs/articles/Product-
| Qualifica...
|
| [2]: https://www.pugetsystems.com/labs/articles/Product-
| Qualifica...
| AaronFriel wrote:
| Is Rust on topic here?
| Spooky23 wrote:
| 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.
| userbinator wrote:
| 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 wrote:
| At least the slightly upmarket ones still use a wire grill on
| the intake, where the fan resides.
| ehnto wrote:
| 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 wrote:
| 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).
| peanut_worm wrote:
| 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.
| londons_explore wrote:
| "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
| jongala wrote:
| 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 wrote:
| 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/phys221
| core/modules/m8/turbulence....
| Cthulhu_ wrote:
| 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).
| ridgered4 wrote:
| I seem to recall the wire covers being on the IBM XT power
| supply so I think they are the OG.
| londons_explore wrote:
| And 'stamped from flat metal' has a cross section of a
| cuboid... And a cuboid is also the shape of a brick... And
| there is that old expression... "As aerodynamic as a
| brick...".
| Darkphibre wrote:
| Ah yes, just like the space shuttle. ;)
|
| "They took a high-performance business jet, added extra
| drag, and ran the engines in reverse to simulate a flying
| manhole cover."
|
| https://youtu.be/pfNQW4jToHE?t=340
| carabiner wrote:
| The problem is you have very messy flow originating from the
| fan with a ton of swirl, so it is likely not like the top left
| diagram and more like the bottom two. It's totally unsteady
| flow, like in this CFD:
| https://www.automotivetestingtechnologyinternational.com/wp-...
|
| Wind tunnels use honeycomb flow straighteners to take care of
| this.
|
| A full blown analysis might use computational aeroacoustics
| software that can calculate the noise generated from solid
| geometry in a given flow. This field has advanced considerably
| since when the article was published due to newer methods like
| LBM. It'd be beyond the scope of journalism like this, but it
| is no doubt done by companies with resources like Apple.
| contravariant wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| So then wouldn't it basically be 142% louder?
| hinkley wrote:
| In that case 36 to 50 is well over twice as loud, right? So
| while 2500% is wrong, 42% is clearly wrong as well. It's
| closer to 130% (or 230% if you're not doing additive
| percentages).
| contravariant wrote:
| 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 wrote:
| 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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