My outside-exhausting DC w/ baffle

[Myk Rian]

I'm not going to get into an argument over this, like there happens to be in another thread on motor capacitors. I'm just telling you that a collection box will muffle the sound. It has nothing to do with how a car engine makes noise. Make it look like an air conditioner unit if there's an issue with aesthetics. And, as I previously stated, I have 35+ years experience with ducting. If that means nothing to you, then don't bother asking for advise on a forum.

No, that's what I meant - I would not get away with setting a collection box outside. The HOA would declare that it didn't match the decor



How does a collection box muffle sound? I think you're thinking of this like a car muffler, but it's entirely different. In a car, noise is created by the expansion of the air, thus the muffler acts as a place for the noise to be produced and absorbed prior to leaving the system. Here, the noise is not generated by the same means.

As the noise energy is transmitted through the tube/duct/whatever, the more barriers it encounters, the more energy from it is absorbed.

What you're suggesting is that if I place a speaker at the end of a straight piece of PVC pipe and measure the volume, then repeat with a pipe with several bends in it, I'll hear the same volume with both. Again, I'm no expert on this, but that seems intuitively wrong.

[Dan Friedrichs]

I'm not going to get into an argument over this, like there happens to be in another thread on motor capacitors. I'm just telling you that a collection box will muffle the sound. .....If that means nothing to you, then don't bother asking for advise on a forum.

Myk - I didn't ask the question, I was just making a suggestion to someone else. I'm also not trying to argue with you, I just don't understand what you're saying, so I'm trying to draw on your extensive experience to learn something.

What I don't understand is: What mechanism causes the use of a chip box to decrease the noise? The box needs to have some way for exhaust air to exit, right? Is it just holes in the sides? If so, how is that functionally different from just blowing all the exhaust (chips included) directly outside? Either way, you'd seem to have very nearly the same amount of noise damping.

Without baffles, I don't understand how any sound is absorbed. For instance, if we're in a room talking to each other, and I hold up a piece of MDF in front of my face, the same air flow occurs (roughly), but now I seem quieter to you because the MDF is interrupting and absorbing the sound energy. Without something to interrupt or absorb, what causes the volume to decrease?

[Keith Outten]

I have two shops that both use exterior chip boxes. One at CNU and my personal shop at home. Both shops have the DC inside (no filters or bags) and nothing but a 4" PVC pipe exiting the building directly into a chip box. The chip box at CNU is only about 20 feet from an asphalt sidewalk that is heavily traveled by students all day long and they don't even pay it any attention.

There is very little noise outside if all you are doing is exhausting the DC discharge, the chip box will definitely drop the noise level due to some acoustic filtering and don't forget that sound attenuates naturally...loses its volume as it moves away from the source. On the other hand don't think that a chip box can reduce the sound coming from your planner.

The noise level (very low level hum) at both chip boxes is low enough that you could hear someone next to you whisper.

I wouldn't recommend a 55 gallon drum, metal doesn't absorb sound nearly as efficiently as wood. I recommend a plywood box, make your chip box at least 6 foot long, 3 foot wide and about 2 foot tall which is the size of the chip box I have at CNU....it is the plywood shipping box that the ShopBot CNC router shipped in. All i did was paint it white and install a 6" dryer vent in the right side at the far end of the box. I use air conditioning filter material over the end of the vent, inside the box for a filter. The pipe from the DC pump is a straight piece about 6 feet long and runs through the wall directly into the box. I expect there are at least a hundred ways to disguise your chip box and make it look like a toy box, deck storage, etc.

If you search our Forums you will find pictures of this setup in another thread.

Let me remind everyone that The Creek is a friendly place, if you cannot be friendly your privileges here will be removed without warning. We are all here trying to help each other and some will disagree or prefer to take a different option than others recommend. Trying different methods is often how we learn new things. Failure has been one of my best teachers
.

[Prashun Patel]

Dan-
I'm curious. Have you noticed a noise reduction simply by venting outside vis-a-vis collecting inside? I can't tell from the exchanges above whether that's been the case.

Also, I'm probably just going to vent outside directly into a catch basin. Myk, and others, how to keep the splatter to a minimum?

[Dan Friedrichs]

Keith - Thanks for clarifying how your chip boxes work. The ones I've seen other people use have been much lower-tech (like a 55gal drum or a shipping crate without a lid, etc). I can see how a design like yours would reduce noise much more than a metal 55gal drum does

Shawn - I located my blower in a crawlspace, so that significantly reduced the motor noise. In the shop, the noise from the suction alone is quite a bit louder than I expected, but obviously much less than with the motor in the shop.

If you're concerned about noise, you might do some searching through this forum. IIRC, Mr. Becker posted some pics of his cyclone closet where he used a Z-shaped return baffle to successfully dampen the loudness of the return air. I can't seem to find the link to that thread, though...

[Prashun Patel]

Thanks for this, Ken (on many levels )

So, how do you empty your dust "coffin" (or should I say "caughin'") when it fills? Is it on wheels?

I hate having my bag inside, but I gotta admit, once I pop it out (and wipe all the spray from myself and sweep up all the dust that settles sinisterly [sic] at the bottom of the top bag waiting to fall on me at precisely this time) the lower bag is quite convenient to change vis a vis a plywood box.

Also, Keith, how did you make up the connection to the pump exhaust such that it can be removed easily.

[Prashun Patel]

Dan-
I'm nervous about drilling a 6" hole through my rim joist. Are you sure that's safe?

[Dan Friedrichs]

Dan-
I'm nervous about drilling a 6" hole through my rim joist. Are you sure that's safe?

No But once the subfloor is assembled and has flooring above it, I doubt the rim joist is actually bearing much load. I did my best to center the hole, but didn't worry about it beyond that.

[Nick Abbott]

I mounted my DC unit outside in a small shed attached to the back of my shop. A 4" pipe runs through the shop wall into a 55 gallon drum. The 4" exhaust extends out of the side of the shed about 12" above the ground with a 90 pointing at the ground. Around the exhaust port I built a plywood box that is about 24" square and 30" tall. The exhaust dumps inside this box and flows out under the 36"X58" platform that is the shed floor. The box around the exhaust air dump cuts the sound way down.

I have about a dozen sheets of Celotex sound board left over from a previous job. I lined the shed and the exhaust port box with a couple of sheets. This helps quite a bit. My exterior DC unit went from sounding about as loud as a running lawnmower (before the shed and exhaust box were built) to being a nice quiet muffled unit that bothers no one in the neighborhood.

[Charles Robertson]

I'm with Myk. Use 6" where you can, to your vac and as your exhaust pipe away from your vac. I used 6" thin wall sewer pipe as my exhaust line, 6" steel duct for my interior runs. as close to the equipment as possible. Yes, this will suck heat and/or cooling out of your shop, but who runs their vac continuously. A thought, small trailer- build a box on it to collect dust and shavings-6 sides with exhaust holes as needed, cover with towels to act as cheap filters, get rid of bags. This will also act as a muffler. My vac is out side in an attached closet, my exhaust runs 30 plus feet to a sawdust pile. I'm in the country, no noise problem. Use blast gates to select equipment. My shop is quiet and clean. This works for me, hope you can use some of this for your shop. Al Robertson