I always wanted to get my hands on one of those R4's but could never manage to do so - is it really quiet enough to be in the same room with? I don't trust the videos I have seen lol
Get an old Canaan A741 - I first set one up a couple of years ago:
https://bitcointalk.org/index.php?topic=789369.msg19893916#msg19893916Under 50dB as a heater. You can make it slower (frequency) and quieter also.
I have that in my lounge room each winter.
This time I'll try an A851 and A921 to see if they can be as quiet on very low settings)
It is all to do with the fan speed and thus if the operational heat is lower, the fan speed will be lower.
Another angle to try--since my 921 still seems impervious to volt/freq changes :shrug:--is to set the default temp higher than default (e.g. 741 @ 95 instead of 90 = 75% fan, 921 @ 98 instead of 95 = 50% fan).
This helped in my case so the fan wouldn't try to fight as much at keeping the temps down. Maybe if Canaan comes out with a 921 firmware that actually responds to volt/freq changes, the above method may be used in conjunction with volt/freq changes too.
Edit: Oh, and the reason I'm hesitant to limit the fan directly is just in case some unforeseen heat wave causes it overheat since I didn't allow it to go up to 100% fan. That's just my personal preference, though.