DIY sound muffler for outdoors dust collector exhaust

[Staffan Hamala]

I've now finished building my Thien baffle dust collector with outdoor exhaust. I also replaced my blower with a new 3 hp blower. Separation seems to work as expected, but I was a bit startled by the sound where the exhaust blows. It's almost like listening to a jet engine starting up. I first thought I needed insulation around the pipe. But it turns out not to be the motor that is loud, but the air turbulence from the pipe.

My design has the blower mounted as high up as possible, with the exhaust pipe leading through the outer wall:
dust_collector_outlet1.png


Worried that the neighbors would complain, or that their horses would panic when I start the dust collector (there's a horse pasture about 10 yards from the exhaust pipe). The horses were further away when I tested today, and they didn't seem to mind the noise.

However, in an attempt to deflect the noise, I made a small "house", with an opening downwards, around the exhaust pipe. The walls were 2" thick with insulation, and hard board on the inside. In an attempt not to add too much resistance to the system, I made the "house" about three times as wide as the pipe (6"). This seems to have worked in deflecting the sound. It's not as noticeable from a distance, but it's still roaring like a jet engine when you stand near the wall:
dust_collector_outlet2.png

I'm now thinking of making a muffler. Any ideas on how to do this?

I thought about drilling holes through the hard board on the inside, into the insulation. Not sure if this will help.

Another idea is to make an extension to the "house", so that the air needs do go further downwards before escaping.
But maybe it would be better to make a real muffler, with a pipe within a pipe and padding in between.

[Andy Giddings]

Stefan, if you go to the ClearVue forum, there are a few designs of mufflers there with quite a lot of detail. As I recall, there's a link to a Woodworking Club in Oz that has a very detailed breakdown of how they made theirs

[andy bessette]

I would create a voluminous labyrinth lined with "egg crate" foam.

[John K Jordan]

Staffan,

I know my cyclone is a demonic screamer so I put the whole thing in a sound-insulated closet. But I read that a large part of the sound comes from the exhaust duct. Some people have had success with just insulating the exhaust duct between the cyclone and the inside filters with HVAC duct insulation. The longer the exhaust duct, the more effective the insulation.

Are you going to collect the dust/chips or let it all go into a pile? One thing I might do is put a big 90 on the outlet with a duct running down the outside of the building. If worried about back pressure, just use a larger duct. (The duct can even be built rectangular - there is nothing magic about round if the area is large enough.) Build a sealed wooden chase to cover it and pack it full of insulation. A vented box at the bottom could house a bin or simply collect the chips with a door on the front to empty or just clean out. This might also keep clouds of fine dust from blowing across the property line.

The neighbors are one thing, but if it is just the horse you are concerned about you can train it to ignore almost anything. Blip the DC and watch the horse's reaction. He might react then go back to munching grass. Repeat with short then increasing lengths of sound. Pretty soon the horse will ignore it completely. This may only take a few minutes for some horses. We train our riding horses to accept some very scary things that way, including whip cracks, firearm shots, brushed all over with branches full of leaves, waving and flapping things in the air, gentle slaps with plastic bags, and to even stand still and calm while pulling a big tarp over their body and head. It helps to have someone with a lead rope there to calm and reassure the horse. You might discuss this with the neighbors (if you get along well with them - if you don't know them very well, take them gift you made in your shop!). If their house is far enough away that the noise won't bother them and they are cooperative and knowledgeable about horse training, they may even help since desensitizing a horse is a very good thing.

JKJ

[glenn bradley]

I bought the commercial muffler with my unit. They were about $30 at that time. Honestly, I can't tell much difference but, I would think you could make one easily enough. It is a tube, larger than the diameter of the air path so as not to provide resistance, with "egg crate" foam around the inside walls.

[Chris Parks]

I made a soundproof box to run the exhaust into then I put in the box a vertical duct to exhaust it through. The duct has the exhaust from it exiting through the bottom of the box and the entry into the duct is very close to the top of it. This reduced the noise from 92db to 65db at the exhaust. I'll see if I can find a photo.

[Bill Dufour]

Run the duct into an under ground cavern then have some large vents at the far end of the cavern. that is how some mines stored their compressed air.
If you do not have an existing cavern hire some miners to dig one for you. Be prepared Y3K is coming soon.

[James Biddle]

Here's the offerings from Oneida...
https://www.oneida-air.com/inventoryD.asp?selectedItemNumber=BSS103600&rowId= &item_no=SCOLLECT34

We've got a leftover 10" silencer from our install we'd give you a great price on.

[Jerome Sidley]

A 3-6db reduction is not much, for the price.

[Mike Kreinhop]

We use a produce similar to this for a completely different purpose (not dust collection), and it does a fairly good job of attenuating the noise when combined with the other measures incorporated. We realize about 20 dBA attenuation across the audible spectrum.

My concern with using such a silencer for a dust control system is the degradation over time when the silencer starts filling up with the fine dust particles. I agree that the meager reduction is not worth the price.

[Mike Heidrick]

A 3-6db reduction is not much, for the price.

From an audio site...

Doubling of the volume (loudness) should be sensed as a level difference of +10 dB − acousticians say. Doubling of sound intensity (acoustic energy) belongs to a calculated level change of +3 dB. +10 dB is the level of twice the perceived volume or twice as loud (loudness) in psychoacoustics − mostly sensed.

[Chris Parks]

Stefan, if you go to the ClearVue forum, there are a few designs of mufflers there with quite a lot of detail. As I recall, there's a link to a Woodworking Club in Oz that has a very detailed breakdown of how they made theirs

I was heavily involved in this including supplying the Clearvue. It is the single best installation I have ever seen and the noise reduction is to the point where a conversation can be had standing next to the cyclone enclosure.

http://mastslav.weebly.com

[Staffan Hamala]

Thanks for all suggestions! Today, I made an extension downwards. I lined it with "egg crate" foam. I also made a couple of extra walls, as a sort of labyrinth for the sound. These walls were also lined with foam. The air has no straight path out, and is forced to hit the foam a few times before exiting. New drawing:
dust_collector_outlet3.png

It made a huge difference! Now I can even listen under the outlet without wearing hearing protection. It was really loud before. Uncomfortably loud directly under the outlet. Now it sounds like a fan, not a jet engine. I even think the noise in my shop is louder than the noise outside! :-)

[andy bessette]

That's the way.

[Mike Bigfoot]

I have the solution and it worked for me. I search every where online and couldn't find what I was looking for, than I had an IDEA!
I recently installed a full diy dust collection system...I installed a large dust collector venting outside. My exhaust pipe was solid 7" metal pipe. It also sounded like a screaming jet turbine engine, Ouch, I have neighbors. Had to do something, I was ready to make a baffle, had the design & materials but had an idea that I just had to try. I purchased a 25' roll of flex 8" ducting with the pink insulation. I unhooked the 17' of metal 7" exhaust that I recently installed and replaced it with 20' of the flex. I shaped the flex into a few (S) shapes just for fun. This has completely eliminated 100% of the jet turbine noise going outside. I only hear the swoop of the air , no noise Period. Hope this helps the op AND FUTURE lurkers. I can once again work all night long with out disturbing the peace.
The third-fourth image is the wall vent I used, Has a magnetized flapper door.
Not sure if Im the originator of this idea but you heard it from me first.