Advice needed on 12mm fans.

I have a full tower and want to get two 120mm fans. one blowing in at the bottom and one blowing out at the top. right now i have 2 80mm plus the PSU fan. My question is what is the best way to balance the 2 120s and the PSU? i have read i the forum that positive air flow is best and i am going to put a filter on the bottom intake which will limit air flow in. will this allow to much negative airflow? i dont want to use the 80mm's because thay are old and loud.

Also i was looking at these fans at 2cooltek:
Panaflo 120mm L1A 68.9 cfm - 30.0 dBa
Sunon Quiet 120mm by 25mm Fan, 4 pin 69 CFM - 35.5 dba
Sunon 120mm 3 Pin Fan 84 cfm - 35 dba
Sunon 120mm 4 Pin Fan 108 cfm - 42 decibels
YS Tech 120mm 3 Pin Fan 131.5cfm - 45.0decibels

Panaflo seems to be what most here on the forum prefer. but how much lowder will the 84cfm sunon be? does 5dba make a big differance for 15 more cfm(will that make a noticable differance). as usual i am probably over analising everything. i just want a good deal on a lot of cfm with little noise. I would appreciate any input. thanks

Its unlikely that you will get positive airflow with one 120 mm inlet and a 120mm exhaust as you have to take into consideration what the PSU fan is doing. Assuming that both fans move the same amount of air, you will at least take the same amount out as you put in. Although there is a prefrence towards 'positive' pressure it does not always obtain the best results. On my system the main advantage I find of positive pressure is that it reduces dust intake a little which obviously's matters a great deal a a layer of dust insulates the components and creates more heat, but as I regularly clean my case and components.. I use slight negative pressure as my tempratures clearly show this has better results for my system

Tip of the day.. A CD is 120mm disk and a useful tool for marking out placement of a 120mm fan
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Full Tower with 5 (120 mm) case fans with seperate PSU

Use a Sanyo Denki 92x32mm 55cfm on the exhaust. They're quiet yet powerful. The 120mm 86cfm Panaflo is an excellent choise for the intake. You can get both at Millisec.com

Hoot

so a 92 and 80mm for exhaust and 120mm intake with a filter sould give positive air flow. i am trying to reduce dust thats why i want positive airflow and intake filter. what if i got a 108cfm sunon with filter for intake and the panaflo for exhaust. how much does a filter reduce airflow? what about the noise? that is important to me too. i dont want it to sound like a 747 on takeoff. sorry to pester but i dont have the money to spend on a dosen fans and try every combo. i want to get it right the first time. thanks.

Filters will reduce airflow considerably as axial fans are poor performers when they have a pressure gradient across them ( trying to suck or blow against resistance) The higher the fan rpm and the thicker the fan mounting the less you will see this effect. Make sure you have a high performance fan on the filtered intake and you should have no problems. Although this kinda craps on your idea of low noise you can't have everything

Slain (May 30, 2001 01:18 a.m.):
Filters will reduce airflow considerably as axial fans are poor performers when they have a pressure gradient across them ( trying to suck or blow against resistance) The higher the fan rpm and the thicker the fan mounting the less you will see this effect. Make sure you have a high performance fan on the filtered intake and you should have no problems. Although this kinda craps on your idea of low noise you can't have everything

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What would yo recommend for a high performance fan?

the difference between 30dB and 35dB is huge. The way the dB scale was created, They(I say they cuz I can't remember the guys first name) took a sound, and then a sound twice as loud, and said that sound was 1 dB higher than the previous sound. This sound also happened to put out 10x as much energy into the air. So in theory, it would take 10 30dB fans to reach 31dB, although that's probably not right(due to air interference, extra turbulence etc), but it's pretty close. With that said, this means that a 35dB fan will be 32 times as loud as a 30dB fan. However, you probably won't find it that loud, because if 35dB was loud, then those 42dB fans would blow the windows out of your house

get one 120mm ys-tech 135CMF fan for the front and a 108 for the back, that should ballence it out

most deaf (May 30, 2001 08:02 a.m.):
get one 120mm ys-tech 135CMF fan for the front and a 108 for the back, that should ballence it out

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i had thought about that but was concerned about the ys-tech sounding like a turboprop.