need some explaination for dba level

[rjiemamam]

i'm not sure if i understand this noise level concept.. i just removed 2 high power loud dba fans (i still have 2 in there) .. after i removed them.. the noise level isnt quite noticably lowered. it dont add up? cause removing those 2 fans yields the same noise level as with them in. .. i'm confused.. someone please explain :)

[It_The_Cow]

It's quite weird. The addition of fans doesn't add on it's rated decibal, instead it's added on logorithmitically. Here's something I got from a website somewhere

Total dB (sound level) =
dB rating of loudest fan + log(10^(dB fan_type1/10) + 10^(dB fan_type2/10) + ... + 10^(dB fan_typeN/10))


So, the setup I use is - 3 fans @30 dB, which gives: 30 + log(2 * 10^3) = 33.3 dB Which is much less then the Nidecs 38.7 dB. Thus more quiet. Cool, huh?

[rjiemamam]

awesome .. thanks for the tip! :)

[oc jason]

dunno if this will help, but to go up 1db you must double the sound, so unless you cut sound in half then you wont even get a 1db drop

[rjiemamam]

ok... so if i have 2 33dba fans pushing 35cfm each... it would still be more quiet than a 42dba fan pushing 50cfm?

[rjiemamam]

so in theory (again..) even 4 33dba fans would be more quiet than 1 42cfm ?

[It_The_Cow]

Yep. Two fans would give you about 37dba, and four fans would give you about 37dba as well. This depends on where you put your fans, though. If there are any obstructions, the noise levels will go up. Since they're probably used as intake and outtake fans, it probably won't fluctuate by much

[Legionnaire]

Is DBa decibles/10 or something?

[oc jason]

correct, id always use 3-4 80mm fans in a case and just use the cooler case to help cpu temps. Rather than not much case cooling and a screaming delta, i have a 80mm exhaust and a 120mm blohole in top with the Glaciator, and at idle i hit 35c at 1530mhz, i bet my whole puter is under 40db