Too Much Exhaust Noise! Help Needed

I have a 6 inch 400cfm centrifugal fan with a speed controller. Even with the speed turned all the way down it sounds like I have a dryer vent exhausting out of my bedroom. I have a carbon filter inside the tent with about 2 feet of rigid flex tubing connecting to the fan and another 3 feet of the same ducting connecting to the exhaust point. The noise is still noticeable from over 15 feet away.

It sounds like my best option are a duct muffler and insulated ducting. My question is, is this going to eliminate the "whooshing" sound or at least bring it to point where you have to be standing within a few feet? And, is it any help to increase the length of my ducting?

I want to maintain a quality air exchange, but stealth is definitely a gold key and right now there is just too much noise from the exhausting air.

Thanks!

Are my expectations unrealistic?

I had the same problem. Putting your fan into a cardboard box helps. Cut holes for the ducting and fill the empty spaces in the box with old clothes. Then put the fan in and tape the box shut. For stealth reasons i put a carbon filter at each end(one inside the tent drawing in, and one at the exhaust end blowing. The carbon filter on the exhaust side helps with the whooshing sound. Probably a 30% reduction in sound. You can also disguise the end carbon filter with a cardboard box with the top/side cut out. Im still going to get a silencer though. After that it'll be super quiet.

I have been able to eliminate the sound/vibration from the fan itself, it's just the air turbulence as it exits the room. I'm really focusing in the sound coming from the moving air as it's exhausted.

I want a muffler just don't like how long they are it's almost as long as my carbon filter when I build a larger room I might invest in one. I have used a wooden box and use actual insulation. You can mak sur your ducting is stretched out as tight as possible don't use reducers can wrap blankets around first two feet of ducting.

Yes, your exhaust ducting is too short. Double or triple the exhaust ducting or exhaust to a small box, cabinet, or crate lined with foam / fabric and exhaust holes. You can make this out of about anything to keep it stealth. After you are done check your air flow, because these additions will reduce your cfms.

As others have stated, you can also move the carbon scrubber to the outside of the tent inside the box described above to greatly reduce noise.

I'm going to start by re-positioning my ventilation setup so that the ducting will be longer and I picked up some insulation to put over my ducting. We'll see where that gets me and re-assess at that point. Thanks for the input, much appreciated.

Any other success stories out there?

DSchlepp21A said:

I have a 6 inch 400cfm centrifugal fan with a speed controller. Even with the speed turned all the way down it sounds like I have a dryer vent exhausting out of my bedroom. I have a carbon filter inside the tent with about 2 feet of rigid flex tubing connecting to the fan and another 3 feet of the same ducting connecting to the exhaust point. The noise is still noticeable from over 15 feet away.

It sounds like my best option are a duct muffler and insulated ducting. My question is, is this going to eliminate the "whooshing" sound or at least bring it to point where you have to be standing within a few feet? And, is it any help to increase the length of my ducting?

I want to maintain a quality air exchange, but stealth is definitely a gold key and right now there is just too much noise from the exhausting air.

Thanks!

Are my expectations unrealistic?

Click to expand...

Simple HVAC problem; Take your 6" duct and about 4 feet in put an 8" duct on the 6" then a couple more feet put a 10" duct on the 8" like reverse pressure momentum only it goes slower not faster, so no whooshing sound.

You should try the phat muffler mini. Its very small compared to most and does a great job at silencing the fan and any noise along with it

RIKNSTEIN said:

Simple HVAC problem; Take your 6" duct and about 4 feet in put an 8" duct on the 6" then a couple more feet put a 10" duct on the 8" like reverse pressure momentum only it goes slower not faster, so no whooshing sound.

Click to expand...

I definitely see where your coming from. The only issue with that is I have already mounted a 6" outlet onto the wall that goes out side. It's 6" diameter on one side and rectangular on the other. I would be required replace that, which would also require a number of other adjustments as well just to get that piece off. It's doable, just tricky! If my first adjustment isn't sufficient enough in lowering the sound, I think what you've recommended is the next best option. Thanks!

trueg115 said:

You should try the phat muffler mini. Its very small compared to most and does a great job at silencing the fan and any noise along with it

Click to expand...

The only part that concerns me with the muffler is its ability lower the sound of the moving air. This is only based of what other posts I've read but it sounds like it does a better job with fan noise than air velocity noise. But what I'm think is, if I end up doing what RIKNSTEIN recommended and still need a little extra love, I will strap on a muffler.

If using a combination of your ideas with a speed controller doesn't fix the problem I would be EXTREMELY surprised. Good lookin on the advice everyone! I will try and post some pics to give you a taste of what I got growing! Happy Harvests!

I have a silencer and it does nothing for the fan noise. It doesnt even make sense that a duct silencer would do anything for the sound of fan blades and a spinning motor. What it does is reduce the wooshing sound of any air passing through it so the wooshing sound is quieter on the exhaust side. It does nothing to quiet the fan and does nothing to quiet the air rushing through ducting before the silencer.

The longer your duct after the fan the quieter your exhaust but more resistance on your fan so less flow. Insulated ducting helps. I bought a phresh silencer and all it is is a 6" can filled with that black egg crate foam they use in sound studios with a 4" intake flange and 3" out. It works pretty decent but wont make it completely silent. But when stealth is mandatory I will take anything I can get. They say it reduces noise by 50% and I would say thats pretty accurate. Btw I have a 4" system.

The proper term is SOUND TRAP do a search on SOUND TRAP this is what you are looking for . HVAC equipment and supplies.

The muffler helps alot but does not eliminate the whooshing noise. You can't really hear mine from other rooms. I work in the same room as it and am on speakerphone all day with no issues.

So I've re-positioned my garden so that the ducting will be about 10' worth instead of 4'. The There's about 3' of 6" of semi-rigid ducting connecting the carbon filter to the fan. The rest will be insulated 8" flex ducting connected to the exhaust point. I still need to get the 8" ducting along with re-sizing my exhaust point, initially my exhaust point was only 6" port. I'm holding off on the duct muffler at the moment to see how it sounds after this set of adjustments.

I thought I would share a little bit of my set up. This is a personal medical grow. I'm doing an all organic grow, TLO Style, 600w mh/hps. Plan on vegging for about 6 weeks, until the plants are about 24-25" tall. All nine are Bubble Gum Strain. Thanks for all the help, and I hope you like the pics!