Folded plenum to tame cyclone noise?

[Mike Desch]

Here we go again--another cyclone question.

Since there has been some excellent advice on SMC regarding what many of you have done with taming the noise of a cyclone, I thought I would throw this out for discussion.

Somewhere recently I read a thread about using a folded plenum on the return air to the shop. reminded me of some old work-related issues that my feeble mind had already forgotten.

Should the folded plenum have only one 180 degree turn or should there be at least two 180 degree bends to mostly eliminate the sound path?

Should the plenum insides be lined with something to reduce noise?
Maybe old pile carpet (cheaper than "titty foam" or the expensive real foam stuff).

What has worked for those of you who have gone this route?

I was thinking of using a return air plenum that was about 5 times larger than the size of the inlet air (to reduce the air velocity back into the shop).

Ok guys and gals, come forth and expound on your experiences and preferences ...

[Brad Gobble]

from what I can tell from my clearvue the sound comes from the impeller and radiates out through the housing around it.

My own plenum is 6" flexible ducting wrapped in insulation then enclosed in 3/4" mdf. Still noisy as hell. If you could wrap / attach something like a blanket directly to the cyclone and the impeller housing you might have a chance.

I built an insulated closet around mine.

[Bartee Lamar]

I built my return plenum inside a wall of the enclosure.

Here is link to ALL the pics

This is how the majority of the air be routed out of the enclosure. I will be putting up 1/2" ply on the outside of the wall. This will extend up to the ceiling on the top. I am going to leave a 2' opening at the bottom of the wall for the air to escape. I am really not sure this is necessary since I will have MANY air leaks that will just have to remain.



This is the exhaust for the enclosure. This allowed me to baffle the noise. Just a note, different materials will kill different frequency of sound. so I used MDF on one side of the wall and plywood on the other. ( It is also what I happened to have around)

[Dan Friedrichs]

Very nice looking installation, Bartee. I saw in the album that you measured the sound level before - did you take a measurement after building the closet?

[Bartee Lamar]

After building closet and doing everything db level is about 70. It is much more low end noise which is not bothersome. I really do not realize it is running after a while.

As you can see I tend to over engineer everything, but this time I think it really paid off.

The amazing thing is this is directly under the master bedroom. My wife takes naps while I work !!!

My cyclone DC has been one of the best investments in my shop.

[Mike Desch]

Thanks to all who have replied.
I already have the cyclone in an enclosed closet, but not sure I did the right "construction."
I put the beast in a 36x42" closet framed with 2x4s. used 1/2 inch drywall both inside and outside including the ceiling, but then added 1/2" sound board to the inside.

From some of the posts I have read here and on another Forum, I'm not sure that I should have added the inside drywall or the soundboard.

Thanks for your comments?

[Doug Shepard]

Not a folded plenum but I just went with a 6" thick filter through the closet wall with my ClearVue and dont have any noise concerns. I really hear more air rushing through the ducts than noise coming from the cyclone.
ClosetVent2.jpgClosetFilter1.jpg

[Ken Deckelman]

Jim Becker posted a great picture of this in post #18 here: http://www.sawmillcreek.org/showthre...g-Myself-Again

I also asked a question about if it was OK to use the 1/2" foam board I already had to make it but I never got an answer

[Phil Maddox]

The more turns the better for sound - 2 is usually plenty. Line the plenum with rigid insulation (fiberglass duct board, not foam) to REALLY cut down on the noise. Carpet will help to some degree but not as much as the insulation. My SDG is a low pitched sound which is hard to control but not as irritating. Is your noise high pitched? Is it mostly air related noise?

PM

[Alan Schaffter]

Not to be a downer, but I hope everyone realizes that the more ducting, fittings, filters, plenums, bends, sound absorbing material, etc., etc. no matter where, end-to-end, in a DC system the more static pressure resistance. The higher the static pressure resistance, the lower the CFM. The lower CFM, the less dust you collect at the source. Its just physics.

[Phil Maddox]

If the return is kept at 5x intake as Mike stated - that would mean a 16x16 opening or an 18" round duct. Should be short enough to not cause a lot of loss. Lots of other areas causing more problems that this will.

[Mike Desch]

Hi Al:

Maybe I misread your post and maybe you misread mine. I am talking about the "return" air after the cycle is through sucking it all in. The only fittings are the return air plenum from the DC closet thru a heavy door--no piping at all.

- - - - -

Phil:

Thank for the double check on the "turns" in the plenum, and especially the advice to use rigid insulation!

[Alan Schaffter]

Hi Al:

Maybe I misread your post and maybe you misread mine. I am talking about the "return" air after the cycle is through sucking it all in. The only fittings are the return air plenum from the DC closet thru a heavy door--no piping at all.

It doesn't matter- EVERYTHING after the blower just like everything before the blower MUST be considered part of an end-to-end system! The "return" air is still in the system and the cycle is not through sucking, until the air exhausts into the room at ambient pressure. In a simple (most extreme) example - if you cover the exhaust, suction stops as well. Every thing you add (pipe, plenums, filters, etc.) to the outlet side of the blower also affects CFM at the intake- CFM IS/MUST be (physics) the same at the inlet as it is at the outlet.

[Dan Hintz]

Alan,

In principle I agree, but we're talking diminishing returns here (no pun intended). If my return is 4" in diameter, then I have a huge amount of restriction. If it's 6", I'm much better. 8", a bit better, but the increase in efficiency from 6" is getting somewhat small. The move from 8" to 10" is going to be kinda titchy. Jumping to 18", I doubt I could measure much difference in restriction between it and a 10" return with even decent quality measurement tools, and even so, would I care? If I had to hazard a complete guess, I imagine that 18" pipe is reducing efficiency in the sub-1% range compared to an open room leading to the collector's 5" inlet.

[Aaron Rowland]

Mass is the best sound killer. If I had to have a cyclone in my shop I would build a concrete block enclosure around it. Mine is out side of our Brick house in a wood enclosure. It's right next to a garage type roll up door but very little noise comes back in. None from the duct work except moving air noise. Power tools drown it out so I have a light thingey to tell me it's status. If you have a wood enclosure your best bet is heavy carpet glued or stapled to particle board on all 6 sides. For air inlet use a labyrinth lined with carpet.

I made a small diy shop vac with a small cyclone. To kill the noise of the vac motor I used Helmholtz resonators and carpet. Very effective compared to my Ridgid vac.

The noise on all seem to come off the impellers and radiate from the metal blower housing. If the manufacturers would cut serrated slots in the impellers tips it would reduce noise . Note, please no patents rip off on this idea. It's been done.