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 Post subject: One or Two front intake fans?
PostPosted: Mon Aug 20, 2018 8:50 pm 
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Location: Calgary, AB, Canada
I was just wondering: is it better (i.e. quieter) to have one 140mm front intake case fan running at a higher rpm, or two 120mm fans running at lower rpm? (everything else being equal).

I'm assuming two 120mm fans would create more airflow, but not sure if the acoustics would be simply double the db/A of each fan?


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 Post subject: Re: One or Two front intake fans?
PostPosted: Tue Aug 21, 2018 3:53 am 
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The two 120mm fans would have roughly 50% more air flow, all else being equal, so they would be quieter. Two fans are slightly louder at the same RPM as the single fan, but they could be significantly slower RPM.

The other piece, though is whether the system would be close to balanced intake vs exhaust, or slightly negative or positive pressure. I prefer slightly negative pressure cases, as an exhaust fan is more efficient at pulling air, than an intake fan is at pushing air.

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 Post subject: Re: One or Two front intake fans?
PostPosted: Tue Aug 21, 2018 3:08 pm 
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So the noise of two fans would not be a simple linear doubling of a single fan, then? Great, that's good to know. Thanks.


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 Post subject: Re: One or Two front intake fans?
PostPosted: Wed Aug 22, 2018 4:24 am 
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No - I think the rule of thumb is if they are running exactly the same RPM, then there is about a 3dB increase of noise. If they are quiet fans - say 20dBA, together they would be 23dBA. Since they could be run at about 25-33% slower than the one 140mm fan, the pair of 120mm fans would likely be quieter.

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 Post subject: Re: One or Two front intake fans?
PostPosted: Thu Aug 23, 2018 5:17 am 
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Joined: Tue Nov 04, 2008 6:03 am
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Location: Sweden
NeilBlanchard wrote:
No - ... if they are running exactly the same RPM, then there is about a 3dB increase of noise.
+3 dB = double the SPL.
The main problem with running two (or more) fans is that there's a risk of interference that might lead to a low frequency variation or humming in the overall noise. Controlling the speeds of those fan independently can help minimising the problem but then require the fans to run at a constant speed independent of computer load and room temperature.


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 Post subject: Re: One or Two front intake fans?
PostPosted: Mon Aug 27, 2018 8:33 am 
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My mistake - I thought that 10dB was a doubling.

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 Post subject: Re: One or Two front intake fans?
PostPosted: Mon Aug 27, 2018 4:35 pm 
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It's messy...if dealing with SPL meters, 6dB is a doubling. Here's a fun read.

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