I have a 4 meter x 2 meter room, my ducting is 6 inch R1 insulated. approx six meters long.
My fan/muffler assembly is outside the room in a large cabinet with about a foot of insulation all around. The outlet air and fan motor noise is quiet like a whisper cant hear it at all. very happy.
There is a low frequency hum that appears to emanate from the trunking close to the fan inlet/outlet area. it gets worse as you walk away from it. i can also feel the vibration of this hum when i place my hand on the cabinet and even on the trunking. The hum isn’t consistent it kinda varies a few times each second. Its an air rushing hum. I’ve gotten rid of the air rushing woosh though (if that makes sense lolol )
i can even replicate the hum if i put my hand over the fan front or back as its running and not connected to anything. The air gets restricted by my hand and the hum begins.
I swapped from a v1 hyperfan 8" to a 6 inch v2 hyperfan.
Its the new 6 inch one thats causing the hum.
Im guessing i need to get a bigger fan. “use a bigger fan than you need at a lower speed” etc etc
Ive tried multiple mufflers, altering muffler positions, different lengths of duct, solid pipe duct,
its driving me crazy. maybe i just need a bigger fan.
The one thing i haven’t tried is ducting larger than fan size. i did try a larger short section on the inlet side of the fan, just seemed to amplify it more.
anyone got any good tricks?