How size affect fan noise?

[Assafl]

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.

This was the quick answer I had already, apparently to quantify and get numbers it is not so easy.

True 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.

[Zucca]

BTW 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.

Could be all the design efforts were to minimize dB(A). Reliability was not the first priority.

[wraper]

BTW 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.

Could be all the design efforts were to minimize dB(A). Reliability was not the first priority.

They 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.

[Siwastaja]

How about same size, RPM and air flow. Do I expect again a "vastly different noise level"?
I would tend to disagree.

Still 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.

This 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 quieter and produces higher airflow. And a decent noise-optimized high end fan is dead silent still in comparison.

[nctnico]

BTW 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.

Could be all the design efforts were to minimize dB(A). Reliability was not the first priority.

They 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.

I agree. I have tried some EBM-PAPST fans in the past but they never where good where it comes to noise.

[3roomlab]

have you all seen that circular blade thingy ?
lotsa 3D printed tests on youtube




and the zipline

[Zucca]

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...

[BradTech94]

I’m surprised to see so many posts in this thread! I thought it was pretty straightforward—everything seems proportional to me

[wraper]

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...

Huh? 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.

[Zucca]

wraper you never like what I post here   

It seems people are installing NOCTUA in EE devices
https://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...

[Zucca]

This 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.

Probably the permanent magnet technology improvement is the reason behind it.

[Coordonnée_chromatique]

I’m surprised to see so many posts in this thread! I thought it was pretty straightforward—everything seems proportional to me

Because the motorized blades noises is a nightmare for everyone on earth.

[Zucca]

Because the motorized blades noises is a nightmare for everyone on earth.

AMEN!

[nctnico]

wraper you never like what I post here   

It seems people are installing NOCTUA in EE devices
https://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...

You 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.

[wraper]

wraper you never like what I post here   

It seems people are installing NOCTUA in EE devices
https://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...

I 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.

[Zucca]

Just slapping a Noctua fan in and calling it a day ain't gonna work. Not by a long shot.

I hope he knows, I never did it.

[Coordonnée_chromatique]

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.

[thm_w]

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.html
https://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.