How size affect fan noise? - Page 1
Forum section: electronics / general

author: Zucca
author_rank: Unknown
timestamp: August 22, 2024, 03:02:56 pm
content: Quick one, not 100% sure that's why I decided to ask here.I would like to understand better how fan noise is influenced by the fan size.Imagine you swap a fan with one double as deep as the original (theoretical example: 35mmx35mmx10mm with 35mmx35mmx20mm), RPM stays the same (again in theory).What is the expected noise level compared with the original fan?And what if the fan input voltage stays the same not the RPM?Many thanks in advance.

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 22, 2024, 05:23:33 pm
content: This might help,https://www.processingmagazine.com/home/article/15587087/understanding-fan-acoustics

author: thm_w
author_rank: Super Contributor
timestamp: August 22, 2024, 10:05:08 pm
content: Just changing the depth of the fan on its own, assuming everything else would stay the same, I can't see that having a significant effect on noise.But everything else would not stay the same. You'd lose a lot of airflow and static pressure. The lost airflow would mean lower noise.If you held airflow constant then expect more noise (since the fan has to spin faster).https://www.corsair.com/ca/en/explorer/gamer/accessories/fan-thickness-30mm-vs-25mm-vs-15mm/I don't know what you mean by "fan input voltage stays the same".

author: Postal2
author_rank: Frequent Contributor
timestamp: August 23, 2024, 01:38:57 am
content: QuoteYou just need to reduce the fan size to zero and get the result. Where it is necessary, for example in the bathroom, the fan should be on a rubber suspension. Although usually called "silent" fans, in fact, these are ordinary fans for the house, unless that house is a metal workshop.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 01:44:29 am
content: Blade profile means a lot. With thicker fan you can easily get more airflow/static pressure at the same noise level. On other hand with blade count/profile and RPM being about the same, thicker fan will be more noisy but also have higher performance. In general, larger fan means more performance per acceptable noise level. But of course you can make them more noisy than a small fan, something like 120x38mm fan at 10000 RPM is like a jet engine.

author: Postal2
author_rank: Frequent Contributor
timestamp: August 23, 2024, 01:55:38 am
content: Quote from: wraper on August 23, 2024, 01:44:29 amI've already been told I'm not blind enough. Now they're going to tell me I'm not deaf enough.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 02:34:20 am
content: Good links:https://blog.orientalmotor.com/fan-basics-air-flow-static-pressure-impedancehttps://www.cuidevices.com/blog/understanding-airflow-fundamentals-for-proper-dc-fan-selectionConsidering only the fan (and not the enclosure where it is moving air) it seems the noise level depends only on the fan RPM speed...To answer my questions:1) Doubling the depth and keeping the rpm constant the noise does not change (again not considering the enclosure and other variables like blade profile...)2) By keeping the voltage constant, the rpm in free air does not change (yeah I know, but a pretty good estimation). Doubling the depth double the air flow.Now putting a double air flow fan in the same enclosure, the rpm/static pressure and air flow will change according to the enclosure air impedance.So the rpm will be lower than the one in free air.. so the fan will be producing less noise than in free air.But the air flowing will be much more (in theory double more)... so the air hissing noise through the enclosure will be more (log(double)?).This is my best educated guess.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 02:35:15 am
content: Quote from: Postal2 on August 23, 2024, 01:38:57 amOf course if you turn off the light switch the room will be dark.

author: Postal2
author_rank: Frequent Contributor
timestamp: August 23, 2024, 02:43:15 am
content: Quote from: Zucca on August 23, 2024, 02:35:15 amYou are a master of metaphors. You can also close your eyes to this. And if you close the valve, the gas burner will go out. Or the flow of water will stop.I actually hate fans in computers and will never buy a computer with a fan again.

author: IanB
author_rank: Super Contributor
timestamp: August 23, 2024, 02:46:33 am
content: What kind of fan are you talking about?If you say 35 mm x 35 mm, that would be a case fan for a computer, for example? Not a room fan, nor a kitchen/bathroom extractor fan?Broadly speaking, fans with a larger diameter can move the same amount of air more quietly than smaller fans. So a 70 mm x 70 mm fan could be quieter than the 35 mm fan, because it can turn more slowly to achieve the same air flow. (But this implies that the speed should be regulated accordingly.)Most of the noise from fans comes from the speed of the blades, and the acceleration of the air moving over the blades.Secondary ways to reduce noise can include blade profile, bearings, mechanical vibration (balance) and mountings. All of these things are amenable to good design, so well-designed fans can be quieter than poorly designed fans.To some degree, you get what you pay for, which is why "quiet fans" tend to have a price premium.

author: Postal2
author_rank: Frequent Contributor
timestamp: August 23, 2024, 03:06:26 am
content: A professional artist records an audio book in his home, and in the background you can hear - guess what. Recordings from the 2000s.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 04:09:26 am
content: Quote from: Zucca on August 23, 2024, 02:34:20 amWrong, and can be easily figured out from fans of the same size and RPM having vastly different noise level.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 01:36:39 pm
content: Quote from: wraper on August 23, 2024, 04:09:26 amYou are correct wraper, my statement above was of course neglecting the blade profile, bearing type and so on.How about same size, RPMand air flow. Do I expect again a "vastly different noise level"?I would tend to disagree.That said this is also truth:QuoteNow if we double the depth, the blade profile change as well by definition so it is impossible to make a comparison.Now consider this:FAN A: 35mmx35mmx20mm 5000rpmFAN B: 35mmx35mmx10mm 10000rpmThe airflow should be almost the same in the two fans above, which one is expected to make more noise?Moreover:FAN A: 35mmx35mmx20mm 1rpmFAN B: 35mmx35mmx10mm 2rpmSame as above? Would a human hear notice the difference? I'm not so sure.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 01:37:46 pm
content: Quote from: IanB on August 23, 2024, 02:46:33 amLet's say DC brushless fan, since they should be the ones used the most in electronics.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 02:55:27 pm
content: Quote from: Zucca on August 23, 2024, 01:36:39 pmStill nope. Noise optimization is a thing. Otherwise everyone would be making cheap silent fans. Also beside noise from moving air, many brushless fans have annoying motor noise.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 23, 2024, 03:10:53 pm
content: Disregarding bearing squeals and other noises what causes fan noise is the same as other "whoosh" noise makers. Which is mainly the speed of the outermost tip of the blade. The other sides of the blade also make noise but much lower in intensity (ignored).That is why larger fans can move larger amounts of air at lower noise.The number of blades modulate the "whoosh" causing a low frequency beat. That is how SONAR operators know how many blades a submarine has.They make huge ceiling fans with many blades (I've seen 6 blades) that run at very low RPM. You can sleep under one, hardly hear it - yet catch a cold.So at a given CFM the larger fan has lower noise - ALWAYS (again - I know some bearing squeal and some have shot bearing that rattle - that is OT).And lower RPM is lower noise. But the same RPM for a larger fan means higher CFM AND higher noise (not because of the CFM - but because at the same RPM the velocity of the tip at greater radius is higher).With fans bigger is always better. Except when it doesn't fit. Then it isn't better.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 03:22:42 pm
content: Quote from: wraper on August 23, 2024, 02:55:27 pmhttps://www.digikey.com/en/products/filter/dc-brushless-fans-bldc/217?s=N4IgjCBcoCwGxVAYygMwIYBsDOBTANCAPZQDaIMADHAJwCslIAuoQA4AuUIAyuwE4BLAHYBzEAF9CYGhGggUkDDgLEyIAEwBmdTADs65m06Qe-YWMngamxPLRY8hEpHJw9ADkYsQHLr0GiEpYGLiAAJkgABBhCzOJAA35mmx35mmx10mm 5.5CFMmax-min noise level 3db(A) over 27 different fans.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 03:26:30 pm
content: ^AFAIK Delta never really cared about noise, also they're notorious for motor noise. I don't recall a single delta fan I've seen to not have it. Most of Sunon fans I've seen were pretty good though in this regard. Although expensive noise optimized PC fans I've used were more silent with other specs roughly equal.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 03:27:58 pm
content: Quote from: Assafl on August 23, 2024, 03:10:53 pmThis was the quick answer I had already, apparently to quantify and get numbers it is not so easy.

author: nctnico
author_rank: Super Contributor
timestamp: August 23, 2024, 03:34:26 pm
content: Quote from: Zucca on August 23, 2024, 03:22:42 pmIn my experience the noise specification doesn't say much about how a fan sounds when put into an enclosure. The noise depends highly on the pressure a fan needs to build up. See the attached datasheet for an ultra-low noise fan and what parts have been optimised to keep noise low. It is clear that there isn't a single aspect that dictates fan noise; it is the entire design.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 03:39:52 pm
content: ^BTW noise level by itself is not the whole story. Frequency distribution is important. Some frequencies sound/are noticeable way more than others.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 03:40:53 pm
content: Quote from: wraper on August 23, 2024, 03:26:30 pmTwo manufactures involved Delta and Wakefield-Wette.Let's see another example with ebm papsthttps://www.digikey.com/en/products/filter/dc-brushless-fans-bldc/217?s=N4IgjCBcoCwGxVAYygMwIYBsDOBTANCAPZQDaIMADHABwDMNIAuoQA4AuUIAyuwE4BLAHYBzEAF9CYAJwRoIFJAw4CxMiDgB2TWABMIQlu2bmbTpB79hYyeGl1ECtFjyESkcmBpw4dByxAOLl5BUQlbfQ8QABMkAAIMIVMNRwForjBKXQQzYKswwnYAT1ZcLnRsFHFxIA119mmx119mmx32mm 100CFM27fans at 45db(A),one fan at 30db(A)@ 72$.so half the noise by paying almost the double.So wraper is right if we consider those unicorns, generally speaking with the same budget, same dimension, same speed => same noise.

author: Zucca
author_rank: Unknown
timestamp: August 23, 2024, 03:42:05 pm
content: Quote from: wraper on August 23, 2024, 03:39:52 pmTrue, also old people does not hear high frequency as well anymore.

author: hans
author_rank: Super Contributor
timestamp: August 23, 2024, 04:50:57 pm
content: nctnico is right, the noise properties of a fan are so dependent on the environment. If the "impedance" changes, that will have a significant effect on the noise. If you ever try to "choke" a fan from air, you'll hear the noise pitch and volume change a lot.There are also other aspects. RPM, blade count, is one thing. Blade design of course as well. Blades are spinning airfoils with a certain angle of attack and rotation speed. As any airfoil will have, it will have a certain stall speed, turbulence on edges, etc. Consider that the rotational speed near the hub is much lower than at the edge tip of a blade, and there is a lot of art that goes into a fan design. Simply doubling the fan size and halving the RPM for a "lower noise fan" must mean that a blade redesign also must be reconsidered. Perhaps the airfoil near the hub are stalling and creating a bunch of turbulence.Then "noise" is often expressed in dBA, which is already a slightly subjective weighting of the pressure levels (Pa) that is produced. Nevertheless, if you take 2 fans and spin them together: the noise can completely fine or annoying as hell. I was watching a review/insight on a new Noctua CPU cooler by GamersNexus the other day that went into this. Basically their new CPU tower cooler will have a "faster" and "slower" fan because their modern PWM controller will regulate the fan speed to such a fine degree, that the mixing of frequency components of the blade frequency from both fans (which due to tight regulation may only differ by a few Hz) will make a very annoying "woop woop" sound.

author: wraper
author_rank: Unknown
timestamp: August 23, 2024, 05:04:58 pm
content: Quote from: Zucca on August 23, 2024, 03:40:53 pmBTW I don't get why people are so excited about overpriced ebm-papst. IME of seeing them in laboratory equipment working in the same equipment for many years, their reliability was much worse than of much cheaper Sunon.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 23, 2024, 05:17:37 pm
content: Quote from: Zucca on August 23, 2024, 03:27:58 pmTrue that. However - the physics does tell you that if noise annoys you: get a bigger fan or reduce the RPM. That will be the most ROI.If you cannot get a bigger fan or cannot reduce the RPM - only then start thinking about things such as using porous blades, blade vortex fins, etc. that will help reduce the noise.

author: Zucca
author_rank: Unknown
timestamp: August 25, 2024, 02:39:39 am
content: Quote from: wraper on August 23, 2024, 05:04:58 pmCould be all the design efforts were to minimize dB(A). Reliability was not the first priority.

author: wraper
author_rank: Unknown
timestamp: August 25, 2024, 03:28:01 am
content: Quote from: Zucca on August 25, 2024, 02:39:39 amThey were not even silent. Those were mostly 120x38mm 230V AC fans. But they had die cast metal blades (look almost the same as plastic, except weight). They had quite a bit of both motor failures and ball bearing seizures. Same spec (except much higher efficiency) Sunon fans with plastic blades (that were used by equipment manufacturer a bit less often) developed loud bearing a few times but never failed entirely IIRC. There were some other devices with EBM-papst DC fans but I did not find them particularly good either.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 25, 2024, 10:39:53 am
content: Quote from: wraper on August 23, 2024, 02:55:27 pmThis is obvious if you compare old vs. new fans. Even top-brand BLDC fans from 1990's (like Papst etc.) had this huge motor (and little room for the blades) so produced very little airflow and then the motor noise was just pure horror. A lot of torque ripple probably.Today even a cheap no-name fan is both quieterandproduces higher airflow. And a decent noise-optimized high end fan is dead silent still in comparison.

author: nctnico
author_rank: Super Contributor
timestamp: August 25, 2024, 10:43:47 am
content: Quote from: wraper on August 25, 2024, 03:28:01 amI agree. I have tried some EBM-PAPST fans in the past but they never where good where it comes to noise.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: August 25, 2024, 11:37:45 am
content: have you all seen that circular blade thingy ?lotsa 3D printed tests on youtubeand the zipline

author: Zucca
author_rank: Unknown
timestamp: August 26, 2024, 01:47:29 pm
content: wired things!Anyway if EBM-PAPST are like this the only alternative im my book are NOCTUA, anything else I should know here?Funny NOCTUA seems not to be for sale in DIGIKEY...

author: BradTech94
author_rank: Newbie
timestamp: August 26, 2024, 01:56:16 pm
content: I’m surprised to see so many posts in this thread! I thought it was pretty straightforward—everything seems proportional to me

author: wraper
author_rank: Unknown
timestamp: August 26, 2024, 02:06:35 pm
content: Quote from: Zucca on August 26, 2024, 01:47:29 pmHuh? It's strange to compare those. Noctua product range is almost entirely for PC enthusiasts. As I said, Sunon fans are of high quality and quite decent in regards to noise, also most of the models I've seen have balanced rotor (blades) to avoid vibration. If looking at PC market, Arctic cooling fans are quite good and much cheaper than Noctua.

author: Zucca
author_rank: Unknown
timestamp: August 26, 2024, 02:40:18 pm
content: wraper you never like what I post hereIt seems people are installing NOCTUA in EE deviceshttps://www.eevblog.com/forum/buysellwanted/fs-(usworld)-tonghui-th2830-upgraded-to-st2832-(200khz)-noctua-fan/and if it fits why not? Even if they are designed for PCs...

author: Zucca
author_rank: Unknown
timestamp: August 26, 2024, 02:42:00 pm
content: Quote from: Siwastaja on August 25, 2024, 10:39:53 amProbably the permanent magnet technology improvement is the reason behind it.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: August 26, 2024, 02:50:13 pm
content: Quote from: BradTech94 on August 26, 2024, 01:56:16 pmBecause the motorized blades noises is a nightmare for everyone on earth.

author: Zucca
author_rank: Unknown
timestamp: August 26, 2024, 02:57:00 pm
content: Quote from: Coordonnée_chromatique on August 26, 2024, 02:50:13 pmAMEN!

author: nctnico
author_rank: Super Contributor
timestamp: August 26, 2024, 03:43:46 pm
content: Quote from: Zucca on August 26, 2024, 02:40:18 pmYou might have to consider Noctua is overpriced for the quality you get. OTOH Noctua fans do have rubber mounts and so on which are convenient. However, typically I find myself using Sanyo San-Ace fans in test equipment as the choice of fans is wider so a precise replacement (static pressure and airflow) can be found to make sure the equipment remains cooled properly. Just slapping a Noctua fan in and calling it a day ain't gonna work. Not by a long shot.

author: wraper
author_rank: Unknown
timestamp: August 26, 2024, 03:45:08 pm
content: Quote from: Zucca on August 26, 2024, 02:40:18 pmI just pointed out that you somehow bypassed all ebm-papst competitors and gone straight to PC enthusiast range. Not to say PC fan range is limited to 12V only.

author: Zucca
author_rank: Unknown
timestamp: August 26, 2024, 03:59:31 pm
content: Quote from: nctnico on August 26, 2024, 03:43:46 pmI hope he knows, I never did it.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: August 26, 2024, 06:23:40 pm
content: Noctua is the safe choice for those who want a silent fan and don't want to select a fan rigourously and be scamed by the biased measurements of the manufacturers.

author: thm_w
author_rank: Super Contributor
timestamp: August 26, 2024, 08:46:09 pm
content: There are plenty of good Noctua alternatives that have similar performance for less than half the price. What you are getting for the money is a longer warranty, some guarantee that they've done reliability testing, and brand recognition.https://www.techpowerup.com/review/be-quiet-silent-wings-pro-4-120-mm-pwm-fan/4.htmlhttps://hwbusters.com/cooling/noctua-nf-a12x25-pwm-fan-review/5/Anyway this is kind of a pointless discussion without stating a use case, budget, restriction or static pressure requirements.In many cases test equipment (PSU, electric load, etc.) will have a lot of internal restriction, and using a typical PC fan is not ideal. In the case of the LCR meter, I doubt it needs enough cooling to really matter either way.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: November 15, 2024, 10:21:36 am
content: I remember some server blades in an enterprise the IT technician was wearing a big ear muffle each time he has to enter in the room because the blades were equipped with eight 12000RPM 40x40 square fans, it was impossible to enter in the room without a good pair of earmuffs and we were unable to communicate without yelling, even wthout the ear protectionsThe space contraint ...