PC case fan noise reduction - which method - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: February 27, 2021, 08:34:28 am
content: Hi! I have a new PC case which supports up to 6 fans (3 front fans - for intake, 1 in the back and 2 on the upper side).I want to use 3 x 120mm, 12V fans in front of the case for intake and I need to reduce the noise made by those fans. I don't know what type of motor they use, so I need an universal solution.I connected those 3 fans in parallel, and by powering them at 7V, I can se on the Amp meter 0.13A, and the noise made by them is barely audible.I would like to know what is best: using a resistor for reducing the voltage by a few volts, using a few diodes (1N4007) in series to reduce the voltage or by using a simple voltage regulator, which can be adjusted using a trimmer (for example LM317) ?Also, it is correct to use a DIY solution for reducing the noise in a PC ?

author: kjr18
author_rank: Regular Contributor
timestamp: February 27, 2021, 09:14:19 am
content: If you can accept less air flow, then you can do that. Are those fans are with three of four pin plugs? Four pin fans can be easily controlled with pwm, those with 3 pins not really (well you can, but it's not recommended).

author: Twoflower
author_rank: Frequent Contributor
timestamp: February 27, 2021, 10:27:39 am
content: From my experience don't use the 7V adapters anymore. They might be useful when the mainboards did not regulate the fans. Today: Let the mainboard control the fans. For example in my case the fans have actually trouble to spin up if the case is cold :-)You should check your mainboard specifications how many fans the board support. Usually the minimum is 1x CPU and at least 2x Case (sometimes 1x aux and 1x case). Some mainboards don't support PWM on all fan connectors. If possible use PWM fans (four wires). If the board supports directly enough fans: You're a winner! If not there are solutions.But from the beginning: Use silent fans. And spend some € in the CPU cooler as the boxed coolers require the CPU fan to spin up a lot.To provide a bit more specific help, you should provider more info: Lots of informations are missing. At least the CPU, GPU and case-size (MIDI-Tower, ITX-Case...) is important. And the used mainboard.

author: mike_mike
author_rank: Super Contributor
timestamp: February 27, 2021, 11:25:16 am
content: @Twoflower I want to install at least 4 fans into the case. The motherboard can control up to 3 PWM (4 pin) fans, except the CPU cooler fan (also 4 pin). The fans have 3 pin connector, but I have already connected them in parallel and I cannot revert this operation. The fans are not new, they were used in a old computer, but they seems to work silently. The 3rd pin of the connector was left unconnected for all 3 fans.The fans are made by Deepcool, and the case is a Deepcool Matrexx 55. The CPU is a i5 10400F, the GPU is a MSI GTX1660 6GB, the case size is MIDI-Tower, the mainboard is a MSI MAG B460M Mortar. The CPU cooler is a Cooler Mater Hyper 212 LED, which I think that is not the best, but I hope it will do the job correctly.One of the fans, the one at the back of the case will be a 4 pin one, and it will be directly connected on the motherboard, but the rest (the intake ones) are only 3 pin, and I want to power them directly from the PSU, but I need to reduce the voltage because they make some noise (not very high) but it could be a little bit disturbing.

author: Twoflower
author_rank: Frequent Contributor
timestamp: February 27, 2021, 12:11:50 pm
content: That's some nice equipment. But if you want to run it quiet (like I like my box as well). You might have too many fans in there to reach a quiet setup. My setup has similar power dissipation in the case and runs nicely cool with two 120mm fans nearly at 200RPM. And for a silent system you might not set the target temperature too low (bigger delta T is easier to cool). You should probably try that by blocking the airflow of one or two fans (not the fans itself!) to see how the temperatures behave.I'm not sure if you want to get below the 7V or if you wan to use the 12V to go down to 7V. You can connect you fans between 12V and the 5V rail to run them at 7V. That's the approach I saw several times.In case you want to go from 12V to 7V: The way you use to reduce the supply voltage doesn't matter much. But the startup current might change the behavior during startup. The regulator (as long as not in the current limit) provides all time the set voltage. The resistor approach will reduce the voltage for the fans more; so a slower start. That could be a possible problem if the fans don't reliable start under that condition.As all these options 'burning' the excessive voltage away (7V * .013A = 0.91W). As said, the way you're doing that doesn't matter as long as the Resistor/Regulator is cooled enough. In case you're using the LM317 you need a heatsink for the regulator. In case using a resistor use at least a 2W type to get some headroom. Both ways they might get hot. Using diodes: As you need several diodes: You might be OK as each of them dissipate about 100mW. And use 1A diodes is most likely required as the spin up current might be higher than the 130mA you measure in steady state.And you might still consider to use the mainboard: It is able to drive up to 1A on the SYS fan outputs. And it is limited to regulate the supply voltage of the fans (even if it is a 4-pin connector, no PWM regulation). No additional HW required, either controlled by the on-board controller (with customizable temp/RPM curves). And you can connect one(!) of the tacho signal (the third wire) to the sys-fan connector to read the PWM of that fan (don't do this in case you use the 12V-5V adapter approach).And the board seems to be able to use the pump-connector for fans as well.

author: antenna
author_rank: Frequent Contributor
timestamp: February 27, 2021, 04:25:18 pm
content: Most computer manufacturers make their case a negative pressure by putting internal fans that blow out. Make sure they draw air inwards to raise the pressure in the case, not draw a vacuum on it. Then, using a sheet of paper, check for cavitation. The paper should be held tight to the fan input, if it vibrates and falls off, you have a cavitation issue.It might be worth checking out BBi on youtube. He builds/repairs larger HF amplifiers and fans are something he is passionate about. He explains the cavitation thing and why you pressurize (not draw a vacuum on) the case you are cooling. Consider what happens when you draw a vacuum on air, it gets hotter. You are not only pre-heating the air as it enters the case, you are reducing the amount of it. On the other hand, if the fans draw air in to the case, the air is being pressurized (and thus cooled ~ that's physics) and has a higher mass.The quality of fan is also critical. There is a science to properly cooling a case with fans and the PC industry has seriously dropped the ball there.

author: nightfire
author_rank: Frequent Contributor
timestamp: February 27, 2021, 11:03:15 pm
content: Other option: Check if the case supports 140mm fans, and exchange them. Bigger fans usually run slower whilst moving the same amount of air, therefore running quieter.

author: wraper
author_rank: Unknown
timestamp: February 27, 2021, 11:09:41 pm
content: Quote from: mike_mike on February 27, 2021, 08:34:28 amJust why??? As if motherboard cannot regulate fan speed by itself.QuoteMotherboard with 99% probability can regulate both types of fans. And if there is not enough connectors, connect 2 fans in parallel except leave one yellow/RPM sense wire unconnected. Also often there is "CPU OPT" fan or water pump connector which usually can be repurposed as case fan in bios settings.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 28, 2021, 06:12:20 am
content: Quote from: mike_mike on February 27, 2021, 08:34:28 amResistor solution is the simplest and so the most popular. A voltage regulatror is good when you don't know power consumption of your fan.

author: amyk
author_rank: Super Contributor
timestamp: February 28, 2021, 06:53:42 am
content: Quote from: mike_mike on February 27, 2021, 11:25:16 amI'm surprised to read that name - they've been selling that model for over a decade now. I have one from around 2009, and the fan it came with was definitely on the loud side; unfortunately it failed within a year or so, and I've since replaced the fan with a much quieter yet just as effectiveGentleTyphoon(the spindown takes close to a minute - they have extremely low-friction bearings and a heavy rotor.)

author: Raj
author_rank: Frequent Contributor
timestamp: March 04, 2021, 10:35:38 am
content: I saw someone on the internet use a custom "cupboard" with serpentine air intakes to keep the case inside to kill noise completely while having fans even at full speed.Don't know how he'd keep it clean though.Maybe some audio engineer here can discuss the viability of noise cancelling.I would rather buy long cables and have the computer in a different room and if asked how i'd manage to switch it on or off remotely. I'd say i'd replace my power push button with optocoupler and remote system of my own design.

author: jmelson
author_rank: Super Contributor
timestamp: March 04, 2021, 03:54:46 pm
content: Quote from: mike_mike on February 27, 2021, 08:34:28 amDo not use series resistors, the fans will not start reliably. I have used series diodes in the past, this has worked for years on those units.There are also fans with integral airflow sensors and with external PWM speed control inputs.Jon

author: Raj
author_rank: Frequent Contributor
timestamp: March 04, 2021, 04:52:49 pm
content: Quote from: jmelson on March 04, 2021, 03:54:46 pmI guess 555 will do for this or he can use a microcontroller based solution if he wans smaller footprint. A microcontroller can also help sense the rpm and have it fixed to a certain rpm and depending on the code, one can send full power if fan is stalled to kickstart it easily.Also,Tip: if you want to lower your noise, have all fans spin at same rpm, preferably at CPU fan rpm.

author: Renate
author_rank: Super Contributor
timestamp: March 04, 2021, 07:52:49 pm
content: Jeez, never put a load between +12 V and +5 V.What if the load on the +5 V is less than the load between +12 V and +5 V?Ok, not so likely, but just don't do it.The fans you have are PWM controlled, so control them that way.My television was too loud so I put it on a light dimmer.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: March 05, 2021, 09:45:39 am
content: diodes in series or a voltage regulator are the best for this. Resistors are ok but if you add/remove/change fans they will be too fast/slow.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 05, 2021, 11:04:29 am
content: Its funny that you mention 7V.I've done that for years by sticking a fan between +12V and +5V.I think I later replaced that with an LM317, or even a BJT with two resistors. Voltage level is not very critical.

author: magic
author_rank: Super Contributor
timestamp: March 05, 2021, 12:27:24 pm
content: Quote from: Renate on March 04, 2021, 07:52:49 pmIt can be likely if the fan craps out and shorts out. I haven't seen it happen yet, but why tempt Murphy?

author: SmokedComponent
author_rank: Regular Contributor
timestamp: March 05, 2021, 02:08:40 pm
content: Sorry for posting non-electronic solution here (which you may have already tried), but:Besides reducing speed, I found that using "rubber baby buggy bumpers" helps reducing fan noise significantly - by preventing vibration being transferred to and amplified by the case.Basically having a soft rubber gasket between a fan and the case. Computer stores sell these solutions (including rubber pegs to fasten the fan instead of screws) buy you can DIY something by using self-adhesive rubber seal. That's what I did.

author: madires
author_rank: Super Contributor
timestamp: March 05, 2021, 02:15:51 pm
content: Besides larger fans and lowering rpm values have a look at the case's airflow design and where heat is generated. A part of the noise is created by the airflow itself, especially at sharp edges (e.g. intake holes or slots). Dust can have an impact too. Some cases have a poorly designed airflow and you won't be able to reduce the noise significantly while keeping the cooling reasonable. The best approach is to have a defined airflow through the case which is able to cool anything hot.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 05, 2021, 04:58:28 pm
content: Quote from: Renate on March 04, 2021, 07:52:49 pm- I guess nothing will happen.

author: magic
author_rank: Super Contributor
timestamp: March 05, 2021, 05:24:24 pm
content: O rly?Then connect a 12V/100W lightbulb between the rails of your computer and report back.

author: Marco
author_rank: Super Contributor
timestamp: March 05, 2021, 05:36:37 pm
content: IME a good fan at 800 rpm is quiet, at 600 rpm silent ... if you need more rpm than 800, put the PC somewhere you can't hear it and get longer cables.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: March 11, 2021, 08:50:44 pm
content: Decided to bodge up my own based on the lm317. It reads 7.14v under load with the voltmeter which is close enough to the 6.91v I calculated my resistors to supply(they're +-5% smd resistors). I think it could easily handle 5 fans or maybe more, though it would get pretty hot at that point. Supplying 0.35A with 12.1v input to a 20 ohm dummy load I measured 75c after 15min.

author: Raj
author_rank: Frequent Contributor
timestamp: March 12, 2021, 04:02:14 am
content: @bobbydazzlerYou had 4 pin fans?you could have slowed them down in software

author: bobbydazzler
author_rank: Regular Contributor
timestamp: March 12, 2021, 06:54:31 am
content: No I wanted to reduce the minimum rpm of my fans down to 150rpm(noise and dust control), I know I can easily reduce the max speed in software. 7.1v can easily start up any of my pc fans from 0rpm and with PWM control that lets you go well below the minimum pwm rpm the manufacturer has set for their fans.

author: antenna
author_rank: Frequent Contributor
timestamp: March 13, 2021, 05:13:47 am
content: junk dunk that machine in oil and be done then lol