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 Post subject: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 11:39 am 
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Hello everyone.
I have a issue that keeps constantly remind me of its presence.
I have this humming sound coming from my computer in pulses. I have read up on it and i have tried several methods.

unplugged all mechincal hdd's (running os on a ssd)
used rubber grommets on the fans, hardened and loosened the screws.
Unplugged fans.
Tried new fans.

The humming gets louder the faster rpm fans i have and gets a little quieter the lower rpm i have.

Im using an Obsidian 550d with:
Front: 2 120mm quiet edition
back and bottom: 140mm quiet edition with the voltage step down adapter.
On the H100 cooler: 2 120mm quiet edition.
and an ax850 power supply.

When i open the side panel the sound seems to disappear and when i put my hand over the top fan grills the sound also disappears.
I suspect its the h100+the fan grills that makes the noise.
So im thinking of removing the top fan grill but wanted to ask here first if anyone suspects something else before i proceed or have any ideas.


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 1:45 pm 
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Torwald wrote:
When i open the side panel the sound seems to disappear and when i put my hand over the top fan grills the sound also disappears.

Two separate solutions remove the noise..hmm. Maybe the source is the h100+fan and the side panel is just loose enough to enhance the vibration. When you touch the fan grills you dampen it and when you remove the side panel you dampen it.

What happens if you press against the side panel? (is it the side with the fan/covers? is that loose?) If that works, maybe you can just add a shim or two between the side panel and case.

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 2:08 pm 
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It could also be cavity resonance - the interior volume of air inside the case can sometimes resonate because of the fans. Is there one intake and one exhaust fan? Have you tried running the system with just an exhaust fan, or with a faster fan on one or the other position?

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 3:05 pm 
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CA_Steve wrote:
Two separate solutions remove the noise..hmm. Maybe the source is the h100+fan and the side panel is just loose enough to enhance the vibration. When you touch the fan grills you dampen it and when you remove the side panel you dampen it.

What happens if you press against the side panel? (is it the side with the fan/covers? is that loose?) If that works, maybe you can just add a shim or two between the side panel and case.


I haven't tried the shim yet, i did try and press both panels but it didnt change anything, i ducktaped the grill on the side panel also but without sucess, when i remove the side fan panel, the pulsating sound changes to a faster speed.

I did notice though that i havent noticed before is that without the side panel the sound is still there but so faint its barely noticeable.


NeilBlanchard wrote:
It could also be cavity resonance - the interior volume of air inside the case can sometimes resonate because of the fans. Is there one intake and one exhaust fan? Have you tried running the system with just an exhaust fan, or with a faster fan on one or the other position?


Yeah i tried all kinda combinations and used different speeds.
i tried the fans mounted between the h100 and the case also.
Im using 3 intake and 3 exhaust at the moment with some positive pressure. i also tried more exhaust but its the same.


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 4:25 pm 
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So, does the sound go away if you unplug the h100's fans?

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 5:32 pm 
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Yeah i tried to stop them, but its hard to hear when the side panel is open.
Tomorrow im gonna try and get a hold of an air cooler. That way i can test with sidepanel on.
I'll report back after i tested and thank you both of you for your help so far :)


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Mon Mar 04, 2013 7:28 pm 
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Before you swap out the h100,

At idle, your setup can probably handle running without the fans on at all. Turn em all off and then turn them on one at a time to find the culprit. With side panel on.

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Tue Mar 05, 2013 2:55 pm 
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CA_Steve wrote:
Before you swap out the h100,

At idle, your setup can probably handle running without the fans on at all. Turn em all off and then turn them on one at a time to find the culprit. With side panel on.


I installed an air cooler and using the same fan setup in the case.
When i stop the top case fan the humming disappears, also when i press the mesh down so it touches the fan its a constant humming without pulsing. So i guess its the fan that makes the mesh vibrate? i do use rubber grommets but that doesnt seem to help.


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Tue Mar 05, 2013 4:00 pm 
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From SPCR's review:
"Putting a fan on top makes it slightly louder as the top panel lacks structural integrity; it hangs from a large, unsupported honeycomb grill making it susceptible to vibration. "

Without the top mounted radiator, the good news is you can just remove the top fans and put the cover back on. You shouldn't need the extra cooling and the noise will go away.

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Tue Mar 05, 2013 4:20 pm 
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Ok that makes sense since it doesnt have a "support beam" between the 2 fan slots, just one big mesh.
I guess the case is closed :)
Thank you so much for your help CA_Steve.


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Tue Mar 05, 2013 7:17 pm 
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Enjoy your quieter case :)

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Tue Mar 26, 2013 7:40 pm 
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So ive noticed another type of sound and ive been testing for quite a while now.
I can't really describe the sound..its quite irregular in its tone, not the humming type of sound.
So just recently i started thinking about acoustic in the room, like when i stand in a corner it seems louder and when i moved an old empty case underneath the desk (the running computer is standing next to the desk) the overall sound from the running computer changed tone.

I noticed the other day something i havent payed attention too is that it seems that the house ventilation is making that same sound, more or less in every room but not as loud. So i thought maybe for some reason it get enhanced when the computer is on, would that be possible or are im way off?


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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Wed Mar 27, 2013 3:26 am 
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Hi,
don't you wish you had a loud computer ? That would explain the noise !! :mrgreen: just kidding...
Yes, it's possible. Turn off the computer and listen to what happens. You could also move the case to the other side of the desk if it's possible, and listen... Think about where you are when using the room most of the time (desk, couch, bed...) and make it quiet from that position if you can.
Where to stop when trying to make something more quiet it up to you : at some point, your house can be so quiet you can hear your breathing, your heart beating, then what do you do :roll: ?

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 Post subject: Re: Humming pulsating sound, suspecting fan grills.
PostPosted: Wed Mar 27, 2013 7:24 am 
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Could be the natural frequency of the room. Adding/subtracting/moving stuff around can tweak the resonant amplitude :)

This could either be a fun project to dampen/minimize, or drive you crazy.

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