The R4's aren't that loud. But there 19dba at 7volts. There closer to 30dba at full speed. I have a bunch of them in assorted colors. They have great static pressure, which is what you need to push air through the heat sink fins. They smoke the gentle typhoons. Those are better for system cooling.
If your looking for silence, Noctua NF-P12 (good static pressure, but low CFM ~60). If your looking for Max CFM (Panaflo L1BX) Install a Fan controller to turn down to 1000 RPMs when not Overclocking/Max load. They run at 2600 RPMs with about 42db. If you want a Average, Gentle Typhoons. They are about ~80 CFM at 35 db at 1800 RPMs.
Depending on your motherboard, you can set these things to spin down to about 700'ish RPM. I can't speak for every motherboard but on my Asus P6X58D-Premium they spun up to about 2065RPM just before 70*C
Also worth noting is that idle they are nearly silent. At full speed you can hear them without a doubt but they do an excellent job at top speed.
I have been doing a lot of reading and tinkering with dynamic fan control. If I have the main rig fired up just to browse or something I don't want to listen to high-RPM fans scream while at the same time I want the cooling power when I open the taps. The obvious choice would be a fan controller but there are a couple of problems:
1. I'm generally too lazy to become comfortable with having to adjust knobs every time I switch tasks.
2. Most motherboards, especially enthusiast models, have very good dynamic CPU fan control. Using the adapter I linked I'm thinking I can have the best of both worlds.
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