r/sffpc • u/ElectronicInitial • 1d ago
Others/Miscellaneous Using 2 different fans to avoid beating resonance?
I have a 240mm AIO in a DanCase A4-H2O, and at moderate to high speed the fans create a resonance, called beating, because of their similar, but not identical blade frequencies. I've been looking at getting some new fans to improve cooling and noise, but wondering if people have used 2 different fan models with different blade frequencies?
An example would be the Phanteks T30 (7 blades) with a Noctua A12x25 G2 (9 blades), where at lets say 1800 rpm, they would have primary blade modes of 210 Hz, and 270 Hz, creating a 60 Hz beat frequency (high enough to not be noticeable).
Noctua does have a set of fans with offset rpm to avoid beating, but even with a 100 rpm offset, the modes are only separated by 15 Hz, and there is additional performance loss from not having equal fan performance.
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u/r98farmer 1d ago
You can buy 2 packs of the NF-A12x25 G2 that are offset in speed slightly to prevent what you are talking about.
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u/ElectronicInitial 1d ago
I mentioned that, but the beating frequency is still about 15 Hz, which is low enough to be noticeable to me. It also means some performance loss due to the difference in speed.
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u/HeroStrike3 18h ago
You lose virtually no performance by only increasing the fan speed by 100rpm. I have the Cooler Master 240 ATMOS ARGB In my A4-H2O and recently replaced the fans with the 2x Noctua G2 pack, and I saw the effect you mentioned, present in the old fans of my AIO, disappear. I no longer have them with the new Noctuas fans, in addition to being much quieter overall and lowering temperatures by about 3-5°C.
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u/mariano3113 2h ago
Coolermaster MasterFan A120 since static pressure use on radiator.
From Cybernetics comparison of PQ vs Phanteks T30 or Noctua NF-A12x25 G2 they are much higher static pressure ; this minimal loss of running 2 of them at different rpms (can separate them by 500-750 rpm or higher if willing to use the full 4000rpm mode.
Post with Cybernetic PQ links: https://www.reddit.com/r/coolermaster/s/LgBASvVe1O
I try to never have fans above 1100rpm, (usually between 650-1100rpm) so at 1800rpm they would have been too loud for my liking just on fan speed alone.
Desktop(Actually more of bedroom TV)SFFPC Iqunix ZX-1 Air with the 2-pack Sx2 PP Noctua NF-A14x25r G2 Chromax 640-900rpm as top exhaust; 2 Coolermaster MasterFan A120 at 900-1060rpm as bottom exhaust; & Noctua NF-A12x15 Chromax 1000-1115rpm on AXP120x67
-7600X with 4070 Super 1080p 60hz TV gaming
Travel SFFPC: Gemcase C9 2 Noctua NF-A9 Chromax as top exhaust 975-1050rpm, Noctua NF-A9x14 HS Chromax on AXP90x36 1000-1100rpm
-9600X with 5060 LP on Portable monitor 2560x1600 120hz or HDMI to hotel/cruise ship TV
(Enough for air to flow and keep thermals in-line with manual temp limit of 83C)
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u/HyperActiveNL 1d ago
You also get performance loss between 2 different fans on the same header. I actually way more loss because mixing 2000 and 2200 rpm fans will result in pretty big difference and they will also react differently on any voltage.
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u/Slyfer77 23h ago
Do you have a spare fan header on your mainboard?
Then just connect the fans of the AIO separately directly to the mainboard and use a program like "FanControl (Remo0)" to set the rpm of the fans individually.
Just create 2 different curves (well, "stairs" with 3-4 dedicated steps is better) with an offset to your liking.
If you are in principal content with your fans (noise, airflow, etc) then there's no need to waste any money on new fans.
When I had my big tower, I did a variant of this where I had 3 front intake fans that would "beat" quite a lot. I offset the middle fan and all was fine.