I've been using the Sonic Tower from TT for about a year now, and I've been pretty happy with it as a passive cooler. It's worked well in my case, which has decent airflow (Tsunami Dream). I'd also tried using a fan mounted on the side of it, as the cooler comes with optional mounting brackets for a 120 mm fan. Unfortunately, on my motherboard I had to mount the cooler 90 degrees rotated from what it should be because of a conflict with some of the capacitors around the CPU. This means that the fan would be mounted below the heatsink, pointed upwards. In this position, the side of the fan covers the northbridge cooler, restricting airflow and raising temperatures, so I was forced to choose between cooler CPU and cooler NB temps.
On the basis of some other cooler designs, like the Tuniq 120, today I decided to jerry-rig the 120 mm fan so that it's now sandwiched between the two halves of the tower of fins. I've been so impressed with the improvement in cooling effectiveness I had to post here.
My CPU is a PD820, overclocked to 3.37 GHz at 1.33 Vcore. I do continuous folding at home on both cores, and with passive cooling I got a CPU temp at 35 +/-1 degrees above ambient (55C with 20C room temp and 50C at 15C room temp). Since I put the fan in sandwiched configuration, my temps have stabilised at 26C above room. I was amazed because this is a 9C improvement in temperature. With the fan on the outside of the cooler, I only saw a 2-3C temperature improvement, so I decided it wasn't worth it.
Now I'll be increasing my overclock another 10%. The extra bit might be enough to tide me over until the expected Q2 CPU price drop.
I also have a question for you posters: How does this performance compare to other OC'd PD820s with different coolers? Anyone here with a similar experience?
EDIT: I should note that the fan I installed is running at 1250 RPM.
UPDATE: I've experimented with some more overclocking. I tried FSB 266, but my computer would get through the initial boot and then freeze at GRUB. Next I lowered the FSB to 260 and I got through GRUB, only to reboot during booting Windows. Then I lowered further to 250, which is hardly much faster than I was running before, and Windows would run, but programs such as Firefox and FAH would randomly crash. This was especially annoying as the FAH crashes would cause me to lose the work I'd done, which was only hours away from completion. I should have waited to try new overclocking settings until after my WU's were handed in. I'll know better next time.
So I went back into the BIOS and I increased my Vcore to 1.37. This is a pretty mild overvoltage, but I have to say I'm a little disappointed that I couldn't push my CPU past 3.5 GHz without increasing the voltage. My temperatures are now running at 29C above ambient, and I would be comfortable running up to 6C hotter, so I might try some more overvolting and inch the FSB back towards 266.