Noise reduction for exterior vent for dust collector

[Szymon Balasz]

Hello,

Need some advice. Just converted my old 3HP twin bag dust collector to a Bill Pentz inspired cyclone system. Put up ducting and I'm mostly happy with performance. My unexpected problem manifested with the vent from the cyclone going outside. I have one of those gravity flaps on my garage exterior with a PVC pipe through the brick wall. The plan was to vent the fine dust outside as I don't really have access to high quality filters and it's considerably cheaper.

However, all the noise from the motor carries outside and it's actually louder outside the garage than inside. My vent faces my neighbours and it's definitely too loud when the DC is running. I don't really have another option for vent location. My garage is insulated and the noise from inside is... still tolerable.

So the way I see it, I have two options.

1) Get the best kind of filter available here. Same as this one (http://www.woodworkingsuppliesqld.com.au/FM-300CF). Importing a clearvue wynn filter isn't an option at this point. I can then jury rig this up somehow to the cyclone exhaust.
2) Try and muffle the sound with one or more duct silencers. After some research I think I can take a page out of the HVAC book and try build some type of duct silencer. Like this (https://s3.amazonaws.com/media.hydroponics.net/pi/136765-250.jpg)and/or like this (https://i.pinimg.com/originals/6a/cb/4e/6acb4e06ebb201254d28aa36d69c541b.jpg). For this I would probably get larger diameter ducting hose (https://images-na.ssl-images-amazon.com/images/I/31Y3hLeF05L.jpg)and maybe even insulate it?

I'm already way over budget and neither option is cheap. I'd prefer to still be able to vent outside as the filtration option doesn't really perform as well as I'd hoped when setting out for this project. I just don't know if the muffler will even work, or if it'll restrict airflow too much.

Any thoughts?

[Mike Heidrick]

In-line Mufflers dont work very well.

A couple long sweep 90s will get the sound back into your shed.

[Roy Petersen]

In-line Mufflers dont work very well.
Agreed. I have a canister filter from Oneida that has an internal one which is supposed to reduce the noise 3-6db, and it frankly does little in that regard.

A couple long sweep 90s will get the sound back into your shed.
To exhaust the fines into the shop? Can you explain?

[Bradley Gray]

Through the roof?

[Mike Hollingsworth]

I vented my Oneida to the outside a few years ago. Incredible Upgrade.
Let me know if you want my old filters.
376278

[Peter Christensen]

Your second "this" is probably the way to go. If your neighbours can't see the exhaust and muffler (behind trees or fence) then making it from weather proof plywood and lining it will be enough. If they can see it then you may have to make it match the building. Having the exhaust opening near the ground will be better than high up. You'll want a critter screen over that opening too. ;)

There is more information on the Woodwork Forums in Australia, Hand Tools and Machinery section, under Dust Extraction. I won't put the link up as I am not sure if it is allowed.

[Jim Becker]

You can partially mitigate directly transmitted sound from the machine out the vent be making sure it doesn't follow a straight path outside. Since you mention using the "flapper" type outlet, it sounds like you are providing a straight path for sound transmission. Put a nice bend on that vent downward toward the ground and see if that helps...this is in addition to any in-line muffle that you might consider.

This is exactly the same issue as exists for folks who vent back to their shops from a sound deadened closet for their DC...the return must be "bent" and take an indirect path. My return to the shop provides for two 90º bends and is up-sized to account for the extra restriction that the bends create so that air flow isn't impinged.

[Szymon Balasz]

Thanks all for the tips.

I'll definitely add in a few bends.

@Mike Hollingsworth appreciate it, but Californee is a long way from the ****hole I call home :p

@Peter thanks I'll look for it. Critters aren't the problem. Too many snakes around for that to ever become a problem.

@Jim ok so bends, muffling, up-sized ducting. Got it. Thanks.

[Brian Henderson]

MTMWood recently upgraded his dust collection and put a silencer on his outdoor exhaust that might help. He did a video about it here:

https://www.youtube.com/watch?v=cvPzRdd5EBU

[Bill Dufour]

Ask around about big trucks/bulldozers and what they use for air filters. People here in the USA use the truck air filters because they are cheaper then the official wood dust filters. I would be surprised if you do not have bigger and better truck filters then most of the USA.
Maybe you could get a few used ones to try from a shop. Also look at all the nice molded rubber air fittings/ducting that could be adapted for your use. I used to use an Audi air intake duct to conenect my shop vac to my shaper
Bill D.
Modesto, CA USA

A quick google search found this about truck filters.

http://lumberjocks.com/topics/237697

[Bill Dufour]

One idea I read about for a gas engine is to run the exhaust down into the ground into a large barrel then a vent pipe up out of the ground.

[kevin tompsett]

My dust collecter is in attached shed. Oulet expands to 10” flexible insulated hvac dust $25. And makes a sweeping 180 degree turn before exit. Outside noise is barely 50db at outlet. And barely noticeable at property line.

[glenn bradley]

I have an inline muffler on mine between the cyclone exhaust and the hole in the wall where I vent to the outside. The muffler does pretty much diddly but, once I exit I hit a pair of adjustable 90's. I twisted them this way and that while measuring db's. Once I had them optimized I shot in a few screws. No complaints from the neighbors and I start early and run late.

[Bill Dufour]

How big is this vent? To me it sounds like a much smaller diameter then I am expecting for a DC system. In the USA like 150mm is normal size. How hard is your ground? I would dig a hole 3 meters deep 250mm diameter and drop the exhaust pipe down the hole at least one meter. I assume you do not care about pumping the shop air outside and drawing in fresh outside air. No air conditioning is there.
BilL D

[Aaron Inami]

I have found that a Fantech duct silencer works very well in blocking a lot of the higher frequency noise. I have a Fantech LD8 in addition to the Oneida inline filter muffler. At the filter exhaust, I pretty much only get the low frequency rumble of air. It's very effective.

You can get the Fantech in various duct sizes (LD8, LD10, LD12, etc.). Or you can make your own.

The MTMWood video shows kind of a duct muffler, but he is using the wrong type of insulation. I guess he chose Technonicol XPS Carbon which is a hard/solid extruded polystyrene foam. While this may work for thermal insulation, it does very little for sound absorption. If you are making your own, you need to get some sort of fiber based insulation such as Owens fiberglass, rockwool, cotton, etc.

The insluated duct you mentioned can help reduce sound, but keep in mind that it also restricts airflow. The Fantech duct silencers are engineered to allow the most airflow while doing a good job at silencing the harsher/louder higher frequencies.

As a note, I can definitely see where the Oneida filter muffler doesn't perform that well. They just shove some open cell foam into the insides in addition to some fiber pads. Not as good as a fiberous-based insulation, but it does do some sound reduction.

[Stephen Bandirola]

I second the oversized flexible insulated HVAC duct. Mine has 2 90 degree curves, it works great, quiet and cheap.