SPCR

I just bought an Antec Three Hundred for my next computer build but I have some other parts to order and I plan to put it together in a couple weeks. There are two front panel spots for 120mm fans and I was thinking about putting a pair of very quiet fans there trying to get positive pressure or at least less negative pressure. I'm not sure how much it would add to noise, especially with them in the front, but what do you think?

I definitely value quiet with my computer components but I'm not a near complete silence guy anymore for practical reasons. Plus there is a fish tank nearby the computer spot with filter and bubble noises But I do sit right next to the computer with it below the desk.

I was also thinking about the rear fans - one 120mm rear fan and the 140mm top-rear fan that are really right next to each other. They might be fighting each other a bit for air sucking I imagine. The front fans would prevent that. Plus I could possibly get rid of one of them with the additional incoming air forcing it out the back anyway. There is a side panel fan spot too so maybe I'd need another incoming fan there or I could just close it off.

Just looking for opinions. What do you think?

By the way I'll be getting maybe a Phenom II X4 and a Radeon 68xx or 69xx video card which could be hot and noisy. I'm really thinking about putting an aftermarket HSF on that.

Why do you need a positive pressure setup? Negative pressure is does slightly better at keeping temps cool.

Air will find the fastest way free- removing the rear fan and leaving the top in place may bring air in the rear vent, and out the top.

My suggestion would be to block the side vent to prevent noise from escaping and disruption of airflow, undervolt/softmount the top 140mm fan, replace the rear fan with something of better quality, and experiment with one intake fan in the front to cool the video card.

Close off the side and add some dampening material wherever you can. If you'd like you could well close off part of the front as well, and then a slow moving fan or two could be worthwhile. Otherwise the front is so open that fans are largely unnecessary. The parts you are going for are easily cooled in such a roomy case.

I don't think you'll need the top fan at all. The rear 120mm should be enough to force air out and any hot air that it "misses" will rise and find its way out of the case anyway.

In the front, you'll only need one fan to supply air to the GPU.
For comparison: I have a GTX460, which sits between the 68x0 and 6950 in terms of power consumption. My case is the Silverstone TJ08, which has a front 120mm fan roughly where the top 120mm fan of the Antec sits.
I use a Thermalright airduct to move this front fan closer to the graphics card. At first, I had it blowing fresh air from the front the case onto the GPU. Standard setup. It didn't accomplish much. In Furmark (which produced seriously unrealistic temps) I was hitting 95°C (and climbing) when I stopped it. Then I turned the fan around and it's now sucking cold air through the PCI-slot covers and through the side panel vent (your Antec has that too) and out of the front. That made Furmark top out at 87°C.
But in Metro 2033, which is probably the most stressing actual game out there, I'm only hitting ~72°C.

All in all, I have a total negative pressure case. The front fan exhausts, the rear fan (ducted to the CPU cooler) exhausts and so does the Power Supply. The only fan not exhausting is the one on the GPU.
And it's the quietest setup I have ever had. In non-gaming usage, the front fan is off, the GPU and CPU fan spin ~400 rpm while keeping their chips well below 40°C.

Great, thanks for the feedback. Yeah I'll stick with negative pressure then which is what I've always had. I don't know, something mystical about positive pressure or something Thanks for the info about the front fans not helping the video card. This will affect my secondary gaming computer as well.

I read in another thread that there are some good quiet 140mm fans from Fractal Designs. So I may pick one of those to replace the top fan as well so I can run both rear fans slower.

Maybe I’ll do a some cereal box duct work if needed.