fan noise

I'm building a new system soon and there's one question that's been bothering me. If I have a fan that's running at 40 dba and 2 that are running at 30 dba, does that mean I hear 100 dba of noise, or just 40? The #s are arbitrary, but basically do the volumes add up or does only the loudest one count?.

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I'm building a new system soon and there's one question that's been bothering me. If I have a fan that's running at 40 dba and 2 that are running at 30 dba, does that mean I hear 100 dba of noise, or just 40? The #s are arbitrary, but basically do the volumes add up or does only the loudest one count?

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it probly adds to some extent but it certianly would not double the noise or anything like that

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I have plenty of fans in my case, so my system sounds like a jet all the time. You'll get used to it...what are you saying, speak up, dammit!
It will be kinda loud, but it depends on how many youve got.

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The dba is a ratio
xdba = 10Log(Pout/atto watt)
to get the new db add the total power (just use some ohms law) then divide by an atto watt, log that, then multiply by 10.
So from what i calculated you should hear 40.79 dba.

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Decibels are log-based, which means that for every increase of 10 dB the loudness is multiplied by 10. The math behind this is nasty, but 40 dB + 30 dB + 30 dB = about 41 dB, which isn't much of a difference to the human ear above 40 dB.
 
If you're really concerned, PC Power & Cooling sells some really quiet fans. When they say they're silent, they mean it. I can't tell they're on unless I press my ear to the case.

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OP
Thank you all for the quick responses! I am now a much better informed shopper.

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Plus, from what I remember in Physics, the dB halves for every doubling of distance from the sound source. So, just get a wireless KB/Mouse and a longer VGA cable if it gets too obnoxious.
 

 
------------------
Regards,
 
clutch

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Are there any wireless mice out there that don't suck. I have used them before but they always seemed laggy and inaccurate. Are there any out there that would compare to the smoothness and accuracy of my intelli mouse explorer.

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There will be some very loud fans or HSF like the Global Wins are supposedly loud.
Also, Swiftech has some gigantic coolers that are 50dB, so if you want a quiet pc, those ones are to be avoided. Tom's hardware guide has a good article on HSFs that includes the best cooling, the noise level, and some estimates of HSF prices.
Also, as Ive found out today, some HSFs will only run around their spec'd rpm if they are plugged into one of the PSU power connectors, and you'll have to get a cpu fan header to PSU power connection. I will be snagging one tomorrow, so that way my cpu can enjoy the cooling that every other component is enjoying.