How to silence exhaust

**Silkadin** · 08-06-18, 01:20 PM

Hi all, been a lurker for a while but this is my first time posting. Basically after a little advice.

I've just finished building a soundproof box for my 4" rhino fan thinking it would cut down on the noise. Went way over the top... used green glue, acoustic sealant, 12mm mdf and 15mm acoustic drywall layers. Bungees in the box and flanges inside and out for the ducts. Now I'm scrapping that idea lol. Seems the fan's pretty quiet, it's the airflow through the CF and exhaust points that seem to kick out the noise. I'm setting up stealth and will have everything hidden along a 6 ft wall with a wall vent somewhere along the wall added. In front will be a fake wall situation.

I also tried a cheapie fan controller, but as expected, it makes the fan hum so won't be using it. The fan I have is way more than I need for the space so the CFM's more than is needed even on the slower speed.

I plan on perhaps upgrading the ducting I have to insulated (between CF (in the tent) and Fan (outside the tent), and then acoustic duct from the fan exhaust to the wall vent.... if I can find it in shorter lengths... most seems to be 5m minimum : /. May also buy "reducers" so I can use 6" ducting despite the CF and fan both being 4". My hope is that it slows the airflow a bit.

I am wondering however, if I should just build a simple 3' x 1' x 1' box to fill the gap alongside the tent (ten't also 3ft wide) to house the fan and exhaust ducting. Been looking at home made mufflers (chicken wire, bin, insulation etc) and now thinking on turning 2/3rds of the box into a muffler with an elbow bend in it to the wall vent. Would that work if I made sure the box was sealed well?

As I'm a newb and didn't want to go building something again that isn't fit for the purpose.

Welcome any feedback.

Once I have this worked out I'll move on to the CF mounting as I want it vertical in the tent but not hanging so as to protect the tent brackets from breaking.

Thanks all, looking forward to checking back every 2 mins for responses lol

Silkadin.

**MonsterEnergy** · 08-06-18, 01:29 PM

get some acoustic ducting, it will stop you hearing the air movement,
it's great stuff but make sure your fans off when installing it,

or you'll blow fiberglass everywhere lol

**Silkadin** · 08-06-18, 01:46 PM

Woohoo, a quick reply

Thanks for that, would I be correct in thinking the acoustic slows down the air flow... or does it just block the noise. The combi ducting I have isn't too loud, it's the cf and exhaust vent which is too loud. Cfm are higher than needed at the moment so I can afford less velocity as long as it doesn't hurt the fan itself.

Cheers,
Silkadin.

**WWBB** · 08-06-18, 01:56 PM

Mate

No loss of air flow as only the inner tube will connect just get the right size for your fan

Happy growing

**Silkadin** · 08-06-18, 02:06 PM

Lower air flow is kinda what I'm after. Fans pulling more air than it needs to which contributes to the noise being made at the cf and exhaust ends. So hoped larger ducting would slow it. Coupled with a kinda diy muffler box would slow it to a gentle push when it leaves the workshop instead of the jetting air I get currently.

Cheers again,
Silkadin.

**British green** · 08-06-18, 02:13 PM

Larger size ducting on the venting side of the fan will reduce the whoosh noise more than acoustic ducting. If you are using 100mm ducting move up to 150mm and ya will reduce the noise loads . If you can afford it use 150mm acoustic ducting and then you have the best of both worlds 😃🇬🇧

Sent from a green and pleasant land

**Silkadin** · 08-06-18, 02:20 PM

I also read 2 posts that lead be to believe that:

1. Acoustic ducting has holes in the inner layer so acts like a muffler in a sense, whereas insulated lining is solid. So would that kind of acoustic duct help reduce the air speed... was the poster correct in the difference?
2. Someone axhausted into a large foam lined cardboard box and then had the box connected to the wall vent.

Those were my 2 main sources of inspiration

Thanks for the feedback btw... loving this site