How do you cool 4 Cards, all bouble slot?

[IlbiStarz]

You should space each card with some foam or random stuff you find :O
If you are using a case, take the side panel off and get a fan (those standing square ones are best) and blow straight at the cards. Lowered the temps on my 6990 by 15C.
If you are going caseless, put 120mm fans on top of the cards, and other standing fans around it. Go look at the mining rig pic thread for more reference.
Make sure the room the rigs are in has good airflow. I put mine next to the window.

Good luck!

Here you go! LOL
http://www.newegg.com/Product/Product.aspx?Item=N82E16835706015
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Bearing Type:
    Ball Bearings
RPM:
    5500 RPM
Air Flow:
    252.85 CFM
Noise Level:
    66.5 dBA
Dimensions:
    120 x 120 x 38mm

66.5 dBa?! You have any idea how much noise is it going to generate???

Atleast i do, Yes, 66.5 dBa

In all seriousness tho:
http://www.gcaudio.com/resources/howtos/loudness.html
That is about as much as normal conversation.

Currently at my workstation the noise level is probably plenty above 66.5.

A 6990 at max load is like 70-80 decibels. :O

[Reckman]

 

Using two 12cm Fans, both lying right on top of the cards, blowing air into the gaps. I'm getting 56 - 74°C, all cards OC'ed from 800 to 950Mhz.

+1 just put two or three fans right on top

[toasty]

I'm really not trying to spam anyone, and I encourage anyone to grab these anywhere they can find them, but the tiny risers I found make about a 6C difference by staggering the heights of the cards. By letting more air move around the cards, and letting some of them directly suck in more air by being higher than their neighbors, it works really well. It's harder to use if you're using a traditional case because the cards can't be screwed down then, but it made a big difference for me.

[Jack of Diamonds]

66.5 dBa?! You have any idea how much noise is it going to generate???

Less than a 6990. I measured 88.6dB at 100% fan speed, lol.

It literally sounds like a jet takeoff.