Fan noise driving me crazy

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?

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Hello mate. Can you post a couple of pics of your acoustic enclosure and duct in & out of the fan?

It seems that the fan/ enclosure needs to be isolated from any structure or frame/ base. Ideally, mount the fan enclosure on some waffle pad or foam rubber (styrofoam works - but not as well). Hang your dust as straight/ stretched as you can. Use packing tape or rope to hang the duct (again isolating it).
It definitely seems to a transmitted frequency rather than one heard.

Hope that helps mate. Moving up to the 8" would just get you noise/ flow issues - even at low speed - if the 6" is doing enough air at the moment. :v:t2: :sunglasses:


You could try an ac infinity fan they are super quiet.


I second AC Infinity. I run them in all of my tents and have no complaints. I expect that an 8" would do what you need it to do.


hey guys, thanks heaps.
yep, fan cabinet is about 2 meters high and sits on acoustic foam stuff. each penetration of ducting has a foam insulator as it travels through walls/partitions etc.
i just swapped back to the 8 inch v1 and things are settled again. The 8" v1 has a whine…and is pushing some ok air at its lowest setting (35% i think).
it makes an air rushing noise that i can dampen down to nothing easily. but it doesn’t make the deadly hum.
The v2 is super quiet. zero jet engine noise. and a powerful little beast. But that resonance is killing me. it only happens when i restrict its flow in some way.
Im just gunna go buy the 8 " version on Monday i think.
ah well. has to be done. Ill report back with how it goes.
if you’re interested im cooking about 120 monster cropped northern lights. and running out of room, They are very bushy… but i have two rooms to use, so it should be ok… i let them veg a week too long i think. zero training so far. might have to tie them up as i go. Their roots are quite large too.
My last shot was sea of green feminised seeds. Learnt a lot last time.
One thing i noticed is that MC clones can come straight out of the dome and grow really well with normal nutes (ec 1.0-1.4) and light. No hardening needed. It kinda makes up for some lost time swapping from bloom to veg. im getting a bit of stretch between nodes which im not happy about too.

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Definitely interested in your monster grow.
Tag me when you get a journal going - I will be doing a run of little monsters off the back of my current grow. In the process of a Week 3 clean out - and taking clones as I go. :sunglasses:

If I had to guess you are just hitting a spot with your settings where static load is creating just the wrong amount of air turbulence. When you were trying different lengths of duct did you have any success? As quiet as the new mixed flow fans are, can you ditch the acoustical cabinet and get your fan back into groe room where you could run shortest amount of duct possible and try it?


yeah me too. im pretty keen to see how this goes.
i didn’t keep mothers. god knows why. So i took clones really late… about week 7 or 8. Ive got mothers now, but they are in some crappy hot as fuck soil which they dont appreciate lol :slight_smile:
it didn’t matter , 100 percent rooted. 90 percent re-vegged. the others just stayed in a dormant kinda flower phase. they grew lots of roots but maybe they were full of flower hormones or something and couldn’t get going again. poor things.
Monster cropped clones seem stronger/hardened but take longer and need zero training during veg. (you could if you wanted to screen/trellis them)
The main thing i can see is that the plants have multiple equally thick stems instead of one. (obviously there is a large single stem above the roots).
Will energy be spread and flowers smaller? Who knows.
I know that keeping nodes shorter and limiting stem growth is a bonus. That’s not happening here. But i have half a dozen (prob more) really thick “main size” stems on each plant.

100% this.
You hit the nail on the head.
I tried shorter duct runs where the fan wouldn’t labour (or have such a load on it etc)
And it worked much better.
But…its a fair bit of work to re-jigg everything.


I understand. Have fought with stuff like this in the past.

I kinda sorted it all out by increasing my insulation level. And realising I can only go so far with fan speed. ( Should have gotten oversized fans etc )

Now I’m fiddling with cutting all the thin branches off. The pop corny ultra thin ones that pop out everywhere. All over the plants top and bottom. Not kidding some of these tiny things are 40-50 cm long.
It’s a major effort. Time consuming anyway. And i have to kinda swim through the leaves to get around as the room is extended now. Out to 6m long. Or crawl up the middle pathway. Clothes stink afterwards. Getting tired of that smell. Annoying. Not going near an airport or sniffy dog training facility for the next year.

Not sure how to attack. Might just go by gut feel. Surely if I trim all the little branches off and leave the main stems intact it’s going to be better than a bush full of thin bizzo.
These things get bushy. Madness.
All stem. Not a good ratio. Probably my abilities at fault aswell.