Had some time to play with the build. I took out the gfx card, turned the fans off and set the HDD to idle after a minute. Here's some subjective data (HDD is idled unless otherwise noted). Also, while I might come across as picky, this is a very quiet build and I'm happy with the results.
MSI CPU Fan 2 header: Doesn't work with 2-pin Fractal fans, nor with 3-pin Antec True Quiet 140. (defaults to max rpm for True Quiet).
Active cooling: Mugen 4 fan only, hooked up to CPU fan control:
12.5% 450 rpm. Silent at 1m. Silent with ear to case.
25% 450 rpm. Silent at 1m. Silent with ear to case.
37.5% 600 rpm. Silent at 1m. Can barely hear it with ear to case.
Active cooling: Mugen @ 450 rpm, lower front and rear Fractal case fans @ 5V. Very quiet, but not silent. Low whoosh, hint of growl.
- turned off rear fan: Quieter, but still a low growl. Wouldn't notice with other sound in room. Had to turn off CFL room light as I could hear buzz from one of them.
- turned on rear fan and turned off front fan: A tad louder.
Antec True Quiet 140 as rear fan: I love the sound of this fan. No growl or other oddities in my measurement range. Just fan whoosh.
- Hooked up to system fan header (high fan switch setting), Mugen @ 450 rpm.
50% 460 rpm Pretty darn quiet, but not silent. Definately quieter than Fractal and with better signature.
60% 530 rpm
70% 610 rpm
80% 685 rpm
90% 760 rpm
- same set up except fan switch set to low.
50% 275 rpm. Dead silent. Unfortunately, fan needs somewhere between 400 and 460 rpm to start.
This contradicts what Lawrence saw in his review (192 rpm start up). 60% 340 rpm. Dead silent. Unfortunately, fan needs somewhere between 400 and 460 rpm to start.
70% 400 rpm. Dead silent. Unfortunately, fan needs somewhere between 400 and 460 rpm to start.
80% 465 rpm.
90% 520 rpm.
MSI GTX 760 Gaming. Mugen @ 450 rpm. Gfx card idles at ~1000rpm.
- gfx card fans are audible but very quiet. I need to bother MSI to see if there's a workaround to get Afterburner to run them below this speed.
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Adding Antec rear fan @ 460 rpm doesn't add noticable noise. - Adding Fractal lower front fan @ 5V adds a little growl.
WD Red 2TB: Quiet whoosh when spinning. Very quiet seek noise. When the HDD idles, the system goes from a subjective pretty quiet to really quiet.
I think I'll pick up a second True Quiet and just run the two of them instead of the Fractals. The gfx card is the dominant source at present (with HDD idled) and it's a very quiet system. If it turns out I can get the 760's fans to a lower rpm, I'll revisit the case fans.