Helpful ReplyFan Noise?

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Bristol_Jonesey
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2016/02/23 10:56:14 (permalink)

Fan Noise?

Ever since I purchased my new box a couple of years ago I've been concerned about the level of noise coming from the computer.
 
It's not enough to trouble a non-audio guy, but it's enough to trouble me!
 
I sent the pc back to Carillon who did the original build and they encased my HDD's in acoustic sleeves, saying this fixed the problem.
 
Well, when I got it back, to my ears there was no improvement.
 
Later last year, I sent it back again and they replaced my original system drive with a 1Tb SSD, but again, the noise levels didn't go down at all. All this leads me to think it's either the CPU fan or PSU fan.
 
Last weekend, I replaced the graphics card and took the opportunity to run it for several hours whilst it was out of the rack and with the covers off.
At first I thought it wasn't working because there was no appreciable noise whatsoever coming from it.
But, as soon as I put the cover back on, I could hear it again.
 
The noise doesn't start when booting up from cold, but gets louder over the course of an hour or so.
 
The cover itself is a fairly massive structure being made from 2mm steel - quite unlike what you'd get from an off the shelf computer, so I think this rules out vibration.
 
So, dear people, any ideas?

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#1
BobF
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Re: Fan Noise? 2016/02/23 11:16:05 (permalink)
I'm trying to find a way to put up a shield that works.  My PC is in prolly the worst possible position for noise, but it's the best position for access to connection, etc.
 
Not the same as what you're doing exactly, but maybe there will be some good info.

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Bristol_Jonesey
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Re: Fan Noise? 2016/02/23 11:22:57 (permalink)
Hopefully Bob!

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mettelus
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Re: Fan Noise? 2016/02/23 11:24:30 (permalink)
I am not sure of your setup, but wondering if a portion of this is coming from resonance in the case itself. I have noticed the most noise comes from the case fans on my machine, but is easily blocked/isolated because it sits in a cabinet-like enclosure. That is probably the most helpful, but a very important note with this is to also make sure the machine can breathe so it doesn't overheat and cause more fan noise.
 
In a nutshell, dust can cause a fan to imbalance, so that is probably #1. Next the fan mounting should be snug (but not tight enough to strip screws) so the case/MB is mitigating any "wobble" further. From there, the case should be on rubber mounts or similar to dampen the vibration it is seeing; and lastly, the surface it is sitting on should also be devoid from possible resonance issues (either hard as a rock, or dampening like a carpet).
 
If fans blades are clean, you can do a quick check of fan mounting mounting screws, then test by putting the computer on a folded towel to check if it is passing vibration to the surface it is sitting on (or simply lift the computer while running if applicable).
 
Two side notes with "fans themselves" - If they have wobbled from dust imbalance and damaged bearings, cleaning them will help, but not solve the damage (they can still wobble). Also, fans have inherent noise based on speed (power consumption, hence noise, is 2^x the fan speed - double is 4 times more, triple fan speed is 8 times more). "Normal" fan speed is based on two things - how much heat it needs to remove (legitimate issue), and how the fans are set in BIOS. Some fans have a "Silent" BIOS setting, but be careful with this one, as you will want some active monitoring in place until you know how the system performs (mine are set to "standard").
 
Quick edit: If the computer breathes through the bottom (such as a laptop), do not leave it sitting on a towel which can plug the holes.
post edited by mettelus - 2016/02/23 11:40:23

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#4
Starise
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Re: Fan Noise? 2016/02/23 11:37:58 (permalink)
I would look at replacing the fan with fans advertised as "quiet" or " low noise". Over time blades might get slightly warped and start to vibrate which causes noise. Bearings can wear. Dust can be an issue too, but I can't imagine that Carillon wouldn't have cleaned the blades (maybe not).Manufacturers have several ways to get a lower noise with a fan. One way is to use a larger fan running at a lower rpm..this is highly effective. Another way is through bios. If you have a bios that supports fan speed you can have the fan ramp up or down according to cpu temp. Yet another way manufacturers get a lower speed is they add more blades which can move more air at less speed and in this way lower the noise.

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Bristol_Jonesey
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Re: Fan Noise? 2016/02/23 11:45:19 (permalink)
Just some more information.
 
The entire computer is a rack mount affair which sits inside my rack.
There are vents on each side with about an inch clearance between the case and the side of the rack, and 2 more rear facing vents.
 
All fans are clean and free of dust.
 
I also have an earlier, more or less identical machine (my old XP32 box) which emits practically zero noise.
 
I'll have another play with it tonight and report back.
 
Thank you gents for your musings.

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tlw
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Re: Fan Noise? 2016/02/23 16:58:27 (permalink)
Damped or heavy cases don't prevent fan and drive noise getting out because the case has holes in it, though they will prevent case vibrations.

I've been building very quiet PCs since the mid 1990s. The ine in my sig has two fans, never overheats and my decibel meter often can't tell it from room background noise at one metre.

I suggest you look at Noctua's website for a big cooler that fits your cpu.

After that cooling is all about getting enough airflow to prevent overheating while keeping noise down.

Then look for quiet fans, the bigger the better. Noctua again are pretty good. However you also need to be running them at low voltage to keep the speed, therefore noise, down. There are a variety of fan speed controllers on the market, or cables which convert the usual 12v fan power points to 5 or 7v.

Your next problem is the video card fan. These can be incredibly noisy. I use a fanless card, but there are editors about for gpu card's BIOS settings which allow you to adjust the pre-set fan speed vs temperature curve. Lots of cards fan the fan up to full speed as soon as the card is doing more than idle. By adjusting the fan speed settings you can delay fan acceleration to when the card temperature actually calls for more cooling.

Finally there's the power supply fan. Another source of noise. Seagate make good fanless power supplies so long as you watch the total power drain. A case that puts the psu at the bottom can help keep the psu cool. Heat rises, and a psu at the top of a case is usually sitting in the hottest spot.

Then you need to test everything to find the lowest possible amount of fan noise. I do this by loading the cpu to 100% and keeping it there (prime95 is a useful tool for that) while I keep an eye on cpu temperature. So long as it stabilises for 15 minutes while below the cpu's maximum thermal rating I'm happy. This makes the cpu a bit hotter than normal at idle, but really pays off sound-wise. It's very rare for a cpu to hit a sustained 100% capacity, so running closer to the chip's rated temperature doesn't seem to cause a problem.

I do a similar thing with the gpu. I also check drive temperatures, though that's not an issue with SSDs. Suspending an HDD so it's isolated from the case, or even putting it in the case bottom on a layer of foam can do wonders for quieting them.

It's also worth trying case fans in different locations and voltages. The PC before this one had a single case fan which I found gave greatest cooling at lowest rpm when placed at the back of the case (where air usually exits) blowing into the case, with the top front 5.25" bay left empty and open for hot air to get out.

www.silentpcreview.com is a useful resource, especially the forums.

http://www.quietpc.com are a UK supplier of quiet parts, as are https://www.overclockers.co.uk. (no connection with either other than as a customer).
post edited by tlw - 2016/02/23 17:19:23

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LaszloZoltan
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Re: Fan Noise? 2016/02/23 17:44:09 (permalink)
another option not yet mentioned is watercooling. I use 3 wc systems with longer tubing that allows me to place my rads where ever and easy cleaning. Sure made a difference from perpetual vacuum cleaner "On" mode to a much more tolerable ambience ( I still have a case fan for my hard drives- there are wc solutions for those too). There used to be in fact a passive wc system you could buy too, no fans. Heat build up on the rads with fans off just from the cpu is interesting imho. Complete self contained wc systems are available now, fairly reasonably priced with great longevity ( put those in the kids pcs a few years ago, no need to muck around with them since). Maybe worth looking into.
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Re: Fan Noise? 2016/02/23 18:26:37 (permalink)
I have a Cooler Master Comos 1000. I choose it because it has sound insulation as well as 120 mm fans 4 of them. These are low noise fans yet move a lot air. The CPU fan is the loudest fan but is well contained by the case. This is not a inexpensive case but well worth the cost.
 
The overall noise from it is very low. A whisper. 

Best
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mettelus
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Re: Fan Noise? 2016/02/23 18:34:50 (permalink)
Out of curiosity Jonesey, have you done an SPL check? Noise unto itself is subjective, so is difficult to understand the situation.

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Bristol_Jonesey
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Re: Fan Noise? 2016/02/24 06:13:01 (permalink)
mettelus
Out of curiosity Jonesey, have you done an SPL check? Noise unto itself is subjective, so is difficult to understand the situation.

No, but I can do
 
Thanks for all the ideas so far chaps, didn't get chance last night to investigate further but intend to tonight.
 
FYI: graphics card is passive - no fan!

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ston
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Re: Fan Noise? 2016/02/24 08:32:21 (permalink)
www.quietpc.com ftw!  I get my CPU and case fans from those guys.
 
Make sure your PC's internals are being sufficiently cooled by the case fans (i.e. ensure you have sufficient case fans fitted), otherwise the CPU fan will ramp up more than it'd otherwise have to which is possibly why your computer gets louder over time.  Do you have any (temperature) monitor software which you can run to investigate this?
 
Also, what is below the PC in the rack?  Anything that can generate much heat?
 
[edited re: gfx card is fanless]
post edited by ston - 2016/02/24 08:47:46
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King_Windom
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Re: Fan Noise? 2016/02/24 10:18:33 (permalink)
 
I have also used Noctura cooling and fans. They work very well and are quiet
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Jim Roseberry
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Re: Fan Noise? 2016/02/24 10:20:03 (permalink) ☄ Helpfulby tlw 2016/02/25 19:37:15
Note that mounted HDs (even when mounted via anti-vibration mechanisms) can cause a case to resonate.
If you have a case with many 3.5" drive bays (and you notice this type of noise), try moving the HD/s to different tray slots.  Essentially, you're "tuning" the vibration... so that its source is in a less sympathetic position (won't resonate).
 
You'll also notice this type of issue with mounted toms (drums)... albeit in reverse.
Even with higher-end drum kits, where you place the tom on the tom-mounting arm is critical.
At one spot, the tom will sound completely dead... as the vibration/resonance cancels out (similar to a dead-spot on a bass neck).  Move the tom to a different place on that same tom mount... and the tom's sustain is long/clean (unimpeded).
 
Back on topic...   
 
Once you are used to a quiet PC, the genie is out of the bottle.  There's no going back.
post edited by Jim Roseberry - 2016/02/24 10:35:28

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#14
ston
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Re: Fan Noise? 2016/02/24 10:38:25 (permalink)
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Bristol_Jonesey
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Re: Fan Noise? 2016/02/24 11:18:31 (permalink)
Jim Roseberry
Note that mounted HDs (even when mounted via anti-vibration mechanisms) can cause a case to resonate.
If you have a case with many 3.5" drive bays (and you notice this type of noise), try moving the HD/s to different tray slots.  Essentially, you're "tuning" the vibration... so that its source is in a less sympathetic position (won't resonate).
 
You'll also notice this type of issue with mounted toms (drums)... albeit in reverse.
Even with higher-end drum kits, where you place the tom on the tom-mounting arm is critical.
At one spot, the tom will sound completely dead... as the vibration/resonance cancels out (similar to a dead-spot on a bass neck).  Move the tom to a different place on that same tom mount... and the tom's sustain is long/clean (unimpeded).
 
Back on topic...   
 
Once you are used to a quiet PC, the genie is out of the bottle.  There's no going back.


Hi Jim, thanks for chipping in.
 
There are now only 2 HDD's (used to be 3) and yep, my old machine was nigh on silent so I was expecting the same from this box.
 
Home time soon....

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Re: Fan Noise? 2016/02/24 12:22:39 (permalink)
A case that's intended to be low-noise is going to have variable-speed fans. If the fans are always running at high speed it could be an indication of inadequate airflow. This would not surprise me in a rack-mounted device, wherein larger, slower-moving fans might not be practical.
 
If possible, I'd situate the computer at the bottom of the rack so there's nothing producing heat below it, and leave a 1U gap above it. You can get rack filler panels that are vented. I suppose you could test this by measuring noise levels immediately after turning the computer on, and comparing that to a couple hours later. This could be accomplished by mounting your SPL meter on a mike stand so it's locked in a fixed position.
 
This is assuming the problem is really fan noise, rather than hard drives. The difference is that fans produce broadband semi-white noise that can be mitigated with acoustical absorption, whereas case rattles, resonances and hard drive spindles have to be treated mechanically rather than acoustically.
 
All of this could be moot, though. If the noise level as seen at your microphone is 30 dB or more below the ambient room noise, it's probably not affecting your recordings anyway. My computer is only 3 feet from my microphone and with 5 fans is by no means a "quiet" computer. But it's on the dead side of the mike and there is acoustical absorption between them. Even with the mike gain cranked, the fan noise picked up is down -60 dB or more, so I don't worry about it.


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slartabartfast
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Re: Fan Noise? 2016/02/24 12:48:04 (permalink)
If I am reading you correctly, the noise diminished or disappeared when the case was removed. If so, then it is not so much an issue with the noise source as with the enclosure. But if removing the case also removes the fans, then the issue is less clear, and if it also involves removing the unit from the rack, then rack vibration is still in the differential. The full test is to assemble/disassemble the unit on a noise absorbing pad, and unplug the case fans if they are attached to the removable section. You can also examine the questionable components using a poor man's stethoscope, your ear at one end of a piece of pvc or other handy pipe and the other end close to the component in question.
 
Assuming that the problem is isolated to the case environment there are a couple of possible issues. Vibration is one possible mechanism, something in the case is picking up a frequency from the root problem component, and that is setting up a sympathetic vibration that either magnifies the sound or re-radiates it at a more annoying frequency. That problem can be less with a heavy case (imagine replacing the paper of a speaker cone with plywood) but there are still possibilities that have to do with connections of the case components like a loose screw. The other issue is acoustic reinforcement, sounds inside the case can be bounced around in such a way that there is positive reinforcement of the waves, like the chamber of a violin. A 2mm sheet is about 13 or 14 gauge, and may not by itself be enough to completely kill vibration, especially if the natural resonance of the sheet reinforces the noise. Attaching a mass to an off center location on the (usually largest) sheet could alter or eliminate that resonance. Rubber grommets or fiber or plastic washers or tape along the joins and screws may help. In a rack mount there is very little room inside the case, but a noise absorbing material there would be most effective at killing echo/reinforcement (you put the bass traps inside the room). Wrapping a noise reducer around the outside of the case is not going to prevent sound from getting out via the vents. The traditional way of handling that kind of escape is with baffles in a duct connecting to the vents, but that takes a lot of space, albeit external to the unit, and the fans that are designed to move air a short distance may not be up to the task. Adding a large fan inside the duct creates another potential noise source. I do very little recording, and I grew up on vinyl and AM radio, so my brain easily filters out the low level crap when I am listening. If I have to record, I do it in a closet packed with clothes and bedding (not created specifically for this purpose) and run a mic cord to the room downstairs where my computer lives. 
 
 
#18
mettelus
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Re: Fan Noise? 2016/02/24 13:59:06 (permalink)
bitflipper
All of this could be moot, though. If the noise level as seen at your microphone is 30 dB or more below the ambient room noise, it's probably not affecting your recordings anyway. My computer is only 3 feet from my microphone and with 5 fans is by no means a "quiet" computer. But it's on the dead side of the mike and there is acoustical absorption between them. Even with the mike gain cranked, the fan noise picked up is down -60 dB or more, so I don't worry about it.




I agree with this, and is a good "practical" point. Because of this thread I checked my machine's SPL (simple phone app) and was 21dB with the machine off and 26dB with the machine running with the meter at "normal mic location." Simply rubbing my fingers together spiked it into the 35dB range (or even thing like shifting in chair (40dB), picking up/rubbing a piece of paper, etc.). It is easy to get fixated on something that we notice. With the same app my vocals exceed 70dB consistently, so the S/N ratio is pretty big and easily managed.
post edited by mettelus - 2016/02/24 14:13:25

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slartabartfast
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Re: Fan Noise? 2016/02/24 15:57:11 (permalink)
mettelus
bitflipper
All of this could be moot, though. If the noise level as seen at your microphone is 30 dB or more below the ambient room noise, it's probably not affecting your recordings anyway. My computer is only 3 feet from my microphone and with 5 fans is by no means a "quiet" computer. But it's on the dead side of the mike and there is acoustical absorption between them. Even with the mike gain cranked, the fan noise picked up is down -60 dB or more, so I don't worry about it.




I agree with this, and is a good "practical" point. Because of this thread I checked my machine's SPL (simple phone app) and was 21dB with the machine off and 26dB with the machine running with the meter at "normal mic location." Simply rubbing my fingers together spiked it into the 35dB range (or even thing like shifting in chair (40dB), picking up/rubbing a piece of paper, etc.). It is easy to get fixated on something that we notice. With the same app my vocals exceed 70dB consistently, so the S/N ratio is pretty big and easily managed.




An excellent point, and reason enough I think to come out of the closet, except for the fact that my computer lives in a room full of file cabinets and the wife's trousseau makes for a cheap anechoic chamber.
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rebel007
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Re: Fan Noise? 2016/02/24 20:34:45 (permalink)
Agree with Jim, if the noise is increasing when you add the case, then there is probably some kind of sympathetic resonance happening. i.e. The case is amplifying whatever is causing the initial vibration.
Swapping out fans for different types/sizes/rotation speeds will help if it's a fan. Moving HDD's to a different mount will help if it's those that are causing the initial vibration. Placing a sound absorber between the computer and your recording position may also reduce the noise to an acceptable level.
Removing the case during recording would be a quick and dirty solution till you find out what's really going on.
Let us know what you end up doing as this is an issue for many home recordists and all efforts to reduce this kind of problem is always of interest.
Good luck.

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Bristol_Jonesey
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Re: Fan Noise? 2016/02/25 05:10:56 (permalink)
Yeah I think you guys are onto something here.
 
I ran a good long session last night with the covers off and the computer sat on a chair next to me.
Yes I could hear the fans but the noise was at such a low level that one would assume putting the covers off would kill it completely.
That clearly isn't happening so there's probably some sort of acoustic bounce around happening, but it's still odd that with the pc coverdd and in the rack, the noise only build up after an hour or so of use.
 
My SPL meter only goes down to 50dB so I'll download the app mentioned by mettelus and try again.
 
There are only 2 fans inside the case - 1 for the CPU and 1 for the PSU. See picture
 

 
If I am reading you correctly, the noise diminished or disappeared when the case was removed. If so, then it is not so much an issue with the noise source as with the enclosure.

 
This seems to be where we're headed.
 
if removing the case also removes the fans, then the issue is less clear, and if it also involves removing the unit from the rack, then rack vibration is still in the differential

 
As you can see, no fans are removed when taking the covers off.
 
The next thing to try (apart from a more sensitive SPL meter/app) is to put it back in the rack without the covers. This should help to narrow down the source
 
 
Thanks guys, we'll get there!!

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#22
ston
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Re: Fan Noise? 2016/02/25 06:09:55 (permalink)
The two things that look like fans at the top of the picture, are they not fans, but where case fans would fit?
 
If you have no case fans, I would suggest to fit some.  They're important to ensure good airflow within the case whilst the case is fitted.  I think you have a lack of airflow inside the case when it is fitted and temperature (and hence CPU fan speed) is building up over time.
 
[edit] If that's the OEM CPU fan, ditch it and fit a quiet one.  Also, a 500W PSU is perhaps a bit on the low side for the machine spec in your signature (assuming that spec is for the machine under discussion).
post edited by ston - 2016/02/25 06:28:08
#23
mettelus
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Re: Fan Noise? 2016/02/25 06:30:25 (permalink)
+1 to adding case fans, since they drastically improve heat transfer out of the box.

I am not sure if that cheapo foam weatherstripping will compress enough to isolate the case edge from the cover and still let you get screws in, but something similar would also mitigate the cover transferring vibration to the case. Wait on that idea till you better understand the source though.

FYI, the app I used was "Sound Meter" by Smart Tools, Co. I should have mentioned that earlier, sorry.

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#24
bitflipper
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Re: Fan Noise? 2016/02/25 11:21:28 (permalink)
Running the computer with skins off can be risky because it can actually lead to overheating (as non-intuitive as that seems) by defeating the internal airflow design. (I say this even though my own machine has had its side panels off since day one.)
 
I once studied this phenomenon by monitoring heat sensors at critical points with skins off and on. This was in a server room where noise was not an issue but heat was. The machines ran cooler with fewer airflow paths, because the air could be directed over the heat-producing components rather than being dispersed.
 
The easiest solution, I think, is quieter replacement fans. They're relatively inexpensive ($20-30) and fit right into the space the old fans occupied.
 
 
 
 


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#25
Jeff Evans
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Re: Fan Noise? 2016/02/25 13:14:28 (permalink)
The size of the internal case fans is important.  Smaller fans spin faster and hence make more noise.  One of my computers started to get quite loud.  I removed the smaller case fans and replaced them with larger bladed ones. (yes I had to modify the case a little with the mounting holes) Now they are super quiet and move more air in the process and spin slower.
 
Also nothing beats putting the computer inside a rack that has a door on the front.  I have had a smallish rack case now for years that just fits two computers inside and sits under my main table.  There is a front steel door with a large dark perspex window and the whole door seals tight and literally shuts in all the sound.  There is a rear door with mine too but I have it open slightly.  The cabinte is also well vented too at the top and the bottom of the sides.  It is under a table and you don't hear any sound coming from the back of it.  I also lined mine with acoustic foam on all surfaces except the bottom surface.  Foam about 1" thick that has smaller wedge shapes on it.  This quietens things down a bit as well.
 
With the front door closed I hear nothing at all.  I can record close to it and still not hear it.  Once you experience this as they say you will never go back.  For me the sealed rack case is the only way really.  Sure you have to open it to burn a CD etc but it is no big deal.  The benefits far outweigh any problems.
 
I picked up mine in a second hand office furniture type place. I see Bristol you are running a rack mounted computer but in a way they can be noisier. Simply by the fact they are higher up and you are closer to their front panel. I have got one or two rack samplers that have even quiet fans on the rear panel but they are audible because they are rack mounted. You could still put a rack mounted computer into an even smaller server cabinet with a smaller door on the front perhaps. Its positioning may require you to rethink some of your cables and connections though.
 
This type of thing:
 
http://www.ebay.com.au/itm/6U-6RU-19-19-Inch-Network-Wall-Mount-Server-Data-Rack-Cabinet-450mm-Deep-/221942882487?hash=item33acd3a0b7:g:~BMAAOSwJkJWjGDi
 
 
post edited by Jeff Evans - 2016/02/26 00:00:59

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#26
tlw
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Re: Fan Noise? 2016/02/25 19:49:07 (permalink)
Is that picture of the open case looking down on it as it is in the rack or sideways on? In other words, is the cpu cooler fan horizontal or vertical when it's in the rack? I'm just trying to get a mental picture of where the hot air naturally wants to go.

My gut thought is that a big, slow fan pushing air into the case might be helpful, so long as it's in the right place if it allows the cpu fan to be slower and prevents the psu fan kicking in. A similar cpu fan might help, depending on how noisy the one fitted at the moment is. Trouble is, not all fans and hardware advertised as "quiet" actually is, it's just a bit quieter than the small Intel and similar OEM fans that sound like vacuum cleaners when their speed ramps up. Gigabyte used to use a tiny fixed-speed fan on the m/b North Bridge chip which could be heard a few yards away.

The two HDD silencers look very much like ones I've used in the past. I found them a help with some HDD noise but not particularly effective at silencing seek noise and clicks or preventing a slow build up of initially low volume resonances from the motors that eventually could get quite noticeable. The most effective solution I found was to decouple the drives from the case by mount the boxes very loosely, either suspended by silicon bands with no screws directly linking them to the drive bay or placed on acoustic foam in the bottom of the case.

Another possibility for case resonance creation might be the fans creating beats between themselves which get magnified as they reinforce the resonance over time in a feedback loop. I had a problem last year when after an hour or two of running I'd start to get a regular slowly building "buzz.......buzz......buzz......buzz....." which was quite noticable in the room below the PC via the floorboards. The case side (a well-padded Fractal Design) could be felt vibrating.

The source turned out to be the case fan's bearing going a little rough and noisy (a long screwdriver makes an excellent stethoscope for isolating noise as any good mechanic will tell you, just keep hair, jewelry, sleeves etc. away from anything going round). The noise was so little at first I decided it couldn't be the cause of the problem, so ignored it and spent hours trying to isolate the source of the noise until in desperation I tried swapping the fan out, which cured the buzz immediately.

Poor fan mountings transmitting fan vibrations into the case or something connected to the case might be another thing to look at.

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#27
Bristol_Jonesey
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Re: Fan Noise? 2016/02/26 05:02:08 (permalink)
Further update.
 
I reinstalled the computer in the rack, minus the cover, ran it for a few hours and noise levels were absolutely minimal, so it's nothing to do with the rack, but definitely something to do with the case and/or other resonances echoing around once the cover is in place.
 
@tlw - that shot is looking downwards and the back of the pc is at the top of the picture, so the cpu fan sits horizontally within the case.
 
Interesting thoughts about the lack of case fans (only in this industry could a solution to noise be to add more fans heh he)
 
@mettelus - thanks for the, downloaded & installed on my phone
 
@jeff - it should be perfectly possible to fit a door on the front of the rack so if no other solution presents itself I'll have a look at making one
 
Another possibility for case resonance creation might be the fans creating beats between themselves which get magnified as they reinforce the resonance over time in a feedback loop

 
This has got me thinking.
 
Time to get the stethoscope out to try and identify which fan, or both, are causing the issue.
 
One other option would be to replace the exiting psu for a fanless model. These aren't cheap (what is with this hobby?)
 
More musings please and thanks to all.

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#28
tlw
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Re: Fan Noise? 2016/02/26 08:34:35 (permalink)
Not sure how well a fanless psu would handle that psu position. They usually have most vents in the top to let the rising hot air out. I'm using a Seasonic 460W one which handles the sig PC's requirements OK. It hase vents in the back (where the mains cable fits) and the top is a grille. It sits at the bottom rear of the case with the case fan extracting at the top rear.

A fanless psu also makes a case fan pretty indispensable I would think. One way or another adequate cool air has to be encouraged into the case or the hot air sucked out or allowed to escape.

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#29
mettelus
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Re: Fan Noise? 2016/02/26 10:40:57 (permalink)
+1 to this. Bear in mind that heat transfer is proportional to flow rate of the coolant over the surface. The "cooling fin" design of fanless gear is pretty reliant on external airflow being provided (or open to the general atmosphere like air-cooled motorcycles, or when you pulled the cover off). As soon as a cover is installed, air is trapped except for where it leaks out and the PSU/CPU fans are then acting more like a blender - just making the inside of the box "hot" and the air slowly seeping out the ports. Case fans are ideal to pull hot air from the CPU and get it into the room and allow cooler room air to flow in.
 
A utility to monitor your motherboard (temps, fan speeds, etc.) would be recommended. If this noise occurs over time, it is highly likely the blender phenomenon is occurring (and you can simply put your hand on the case to tell if it is hot or not). TBH, I would be less concerned of noise over CPU heat, and I worry the CPU/PSU fans are ramping up speed to stay cool creating the noise you are hearing. Again, a utility to check these will let you know better.
 
A case fan will not run at high speed if the system is running cool. Other options are to leave the cover off, put holes into the upper portion of the lid (to enhance natural convection), or mount the system so it has holes as the bottom and top (and will function naturally like a chimney). I honestly would go the case fan route first and foremost though.

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#30
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