Thread: Seeking Advice on ClearVue System Layout/noise attenuation

Originally Posted by Flindersia

An 8" trunk run is extremely challenging to route so I intend to run 6” PVC duct from the extractor inlet into the workshop which will then split into 2 x 6" duct runs to service the machines.

The only reason to run 8" main is if you want to run 2 x 6" ducts to one machine (EG a large sander) or use more than one machine at the same time. Other wise a 6" duct will give you more than enough airflow and dust collection over 7-8 m.

By running a single 6” duct I assume that running the machine at 50Hz would provide the best noise attenuation whilst still providing adequate suction

Yes

I will construct a basic stud wall enclosure around the unit lined externally with 6mm fibro sheeting (Villaboard) but would welcome some advice on what to line the internals of the enclosure with? I could possibly line the enclosure internally with 18mm plywood and carpet offcuts but I’m sure there are better options.

You could use Acoustic Rockwool between the Villaboard and the ply.

FWIW I have
- on the walls and ceiling of my pine frame enclosure there is, Colorbond sheeting, 32 mm thick melamine, 50 mm ordinary rock wool, 16 mm ply and 50 mm mattress foam.
- the doors have Colorbond sheeting, 32 mm thick melamine, 100 mm mattress foam.

My clearvue has the rectangular transition section on the exhaust opening to an 8" circular duct. I have seen one of the Mens shed muffler designs on the web but this looked quite complicated and I was hoping insulated HVAC duct might provide adequate attenuation for the exhaust.

It might and you could always try it. If it doesn work then encase the HVAC in an MDF box with more acoustic or even regular rock wool in between the HVAC dust and the box housing.

Can I ask why you are going the CVMax? Sounds like a CV1800 would be ample.

I have run my CV1800 at 50hz & 60hz without too much noticeable rise in volume - 3rd party confirmed with the mistress of finance. Running at 70hz on the other hand (for purely scientific reasons of course *insert maniacal laugh here*) will ensure neighbors put hit contracts on you within minutes. Your millage may vary.

My enclosure is Villaboard with acoustic batts and 12mm MDF/chipboard with conveyor belt rubber on the wall on the neighbors side. I found it reduces the perceivable sound dramatically. I am still looking to install a muffler on the exhaust to try and reduce the noise further in the coming weeks.

I was surprised by how much the noise drops with distance. If I am around 3 meters away from the enclosure, it sounds like a large A/C condenser. But around 1 meter from the enclosure, the lower sound frequencies are much more noticeable.

You're possibly right about the CV1800 but I was lucky enough to pick up a second hand CVMax a couple of years ago at 1/2 new price that had been installed but never run. It's been sitting in my garage ever since as it became one of those project that seemed to thwart me at every turn. I've worked a solution not that makes sense, extractor location, machinery layout, ducting routes etc etc so i'm keen to press on at last.

One of the problems I have with attenuation is the outer diameter of the impellor housing on the neighbours side will be very close to right up against the villaboard. Hence, in this one (small) location a secondary lining and good application of instulation will be impossible to install. The limitation comes about due to the existing depth of the eave above and I don't want to go tacking on extensions to the house when the unit can be adequately (and neatly) enclosed as is. Everywhere else on the enclosure there will be adequate size for lining and insulation as the unit tapers in diameter or width. One way to overcome this problem may be to put a wrap around the impellor housing of insulating material. If I was to wrap the impellor housing what would be the best product to use. Perhaps some of the sound deadening material made for vehicles?? Any thoughts?

Originally Posted by maxxsinner

I was surprised by how much the noise drops with distance. If I am around 3 meters away from the enclosure, it sounds like a large A/C condenser. But around 1 meter from the enclosure, the lower sound frequencies are much more noticeable.

Reflections/scattering can make a big difference both with perceived and actual sound levels and this of course also applies to your neighbour. It's interesting to walk around a noise source at the same distance from the source and measure/listen to the variations. I found locating the exhaust outlet at ground level helped reduced the noise. Since installing my external enclosure setup in 2011 between my shed and back fence, significant vegetation has grown up and across the fence and this has knocked a further 1-2dB off the noise levels at the back fence line. I think the vegetation reduces the reflections channeling up between the shed and the back fence. Assuming visual pollution was not a problem hanging old carpet on the back fence would help.

Originally Posted by Flindersia

I was lucky enough to pick up a second hand CVMax a couple of years ago at 1/2 new price

Nice find there!

Originally Posted by Flindersia

One way to overcome this problem may be to put a wrap around the impellor housing of insulating material. If I was to wrap the impellor housing what would be the best product to use. Perhaps some of the sound deadening material made for vehicles?? Any thoughts?

After seeing the incident on the Corrimal Mens shed website - https://mastslav.weebly.com/ (around 3/4 the way down the page. The rest is a good read also) where a small block went through the blower housing, I have been tempted to install some conveyor belt rubber around it just for the safety aspect, but no doubt it would absorb some of the noise also. As for a primary noise reducer, I don't think it would be enough personally as nothing that I know of can absorb all noise except the vacuum of space.

Wait... there is an idea. Hey Bob - Think I have come up with the perfect sound proof enclosure method!

Originally Posted by maxxsinner

After seeing the incident on the Corrimal Mens shed website - https://mastslav.weebly.com/ (around 3/4 the way down the page. The rest is a good read also) where a small block went through the blower housing, I have been tempted to install some conveyor belt rubber around it just for the safety aspect, but no doubt it would absorb some of the noise also.

I've had blocks of wood up to about a pack of cigarettes going through my impeller from time for the last 7 years. The housing outer is made of steel and just now I have the impeller out of its housing and had a look on the inside and can't see anything other than few small dimples and nothing significant on the impeller itself.

As for a primary noise reducer, I don't think it would be enough personally as nothing that I know of can absorb all noise except the vacuum of space.

Technically a vacuum it does not absorb noise, sound just cannot pass through it. To absorb sound the sound has to be travelling through the material so it would need an infinitely large block of any material will eventually absorb the sound.

Remember for a DC acoustic enclosure you don't need to absorb the sound you just need it to stop escaping so the sound can either be absorbed, or continually reflected back into the enclosure . Every time the sound is reflected by one wall across to an other a small amount is absorbed by the air in between so it might take several dozen reflections to absorb the initial sound and by then there is new sound made to reflect and absorb, but that does not matter because hopefully no one is inside the enclosure. This is why a concrete bunker alone would work well as an acoustic enclosure although it would be somewhat expensive and impractical.

Originally Posted by BobL

Technically a vacuum it does not absorb noise, sound just cannot pass through it.

Damn you and your facts Bob. My concept was sound (no pun intended)

Could you wrap the impeller (housing) with lead sheet?
I'm just building my enclosure now. Hopefully ply and multiple layers of carpet will do the trick..

Russ

Just a thought on the exhaust. I have a 3m (approx) length of 8" galvanised ducting here that was gifted to me long ago. Instead of the insulated HVAC duct would it be better to use this and wrap it externally with insulation material. I notice on the Corrimal Mens shed website that they placed additional insulation on the inside as well but I can't understand why they choked the muffler down to 6"?? I would have thought it best to avoid any additional back pressure on the exhaust side of the impellor? This ducting run will be under cover but it's open to the side and therefore will be exposed to wind blown rain. With this in mind if I were to go with the galv ducting then what material would be effective to use as an insulation wrap? Should it be insulated on the inside or outside or both? I notice some 75mm thick polystyrene pipe insulation on Gumtree pre formed into strap on pipe segments and also some polyethylene foam sheets. These should both take the weather ok but not sure of their effectiveness. Welcome any thoughts on HVAC duct Vs insulated Galv.

Originally Posted by Flindersia

Just a thought on the exhaust. I have a 3m (approx) length of 8" galvanised ducting here that was gifted to me long ago. Instead of the insulated HVAC duct would it be better to use this and wrap it externally with insulation material. I notice on the Corrimal Mens shed website that they placed additional insulation on the inside as well but I can't understand why they choked the muffler down to 6"?? I would have thought it best to avoid any additional back pressure on the exhaust side of the impellor? This ducting run will be under cover but it's open to the side and therefore will be exposed to wind blown rain. With this in mind if I were to go with the galv ducting then what material would be effective to use as an insulation wrap? Should it be insulated on the inside or outside or both? I notice some 75mm thick polystyrene pipe insulation on Gumtree pre formed into strap on pipe segments and also some polyethylene foam sheets. These should both take the weather ok but not sure of their effectiveness. Welcome any thoughts on HVAC duct Vs insulated Galv.

Locating the sound absorber on the inside of any ducting will be just as effective as putting the insulation on the outside to prevent noise escaping from the walls of the muffler itself. However, to reduce sound coming out of the end of the muffler, having the absorber on the inside should be more effective.

Galv duct consists of only a hard surface so sound will be reflected internally down and out of the duct and any sort of external insulation won't have much of an effect because of the internal reflections never get to the absorber. This will in fact act like a straight through car muffler. What is required is a soft internal inner lining that soaks up the sound and a hard eternal shell that reflects the sound back into the inside of muffler. At our mens shed we used a 1.8m long 400 x 400 mm MDF box lined internally with rockwool insulation and held in place by an 200 mm diameter cylinder of chicken wire. there are other ways to do this - a thick carpet or foam lined piece of 9" PVC ducting would be one possibility.

Yo could use the galv ducting in place of the chicken wire inner by drilling a bunch of holes in it but it would be quicker to use chicken wire.

HVAC has a thin flexible inner and outer skin with insulation in between which soaks up some of the sound.

Originally Posted by Flindersia

You're possibly right about the CV1800 but I was lucky enough to pick up a second hand CVMax a couple of years ago at 1/2 new price that had been installed but never run.

The one from Mackay? He was going to use it for a soda blasting operation.

The only reason I used to recommend a 235mm main line was that a 150mm port can be left open in the 235 if only one machine was being used as the Max could handle that amount of inlet area at 60hz. This has the effect of scrubbing at least some of the air that has the smallest particles in it while the cyclone is working.

Just laying out the exhaust on the Clearvue now and as luck would have it i’ve picked up an offcut of 225mm PVC which I intend to try per your note Bob. A few quick questions I have are:

1. Any recommendations for attaching it to the strange circular duct size on the end of the CVMax outlet transition. Which measures up and around 220mm OD. I found an earthenware to PVC Furnco that goes very close but these things are pretty expensive. Any thoughts?
2 The PVC offcut I acquired is just over 4m in length. I can actually fit that in as a straight run under the eaves without any trouble straight off the Clearvue outlet but is there any noise attenuation benefit in the long length or will a section of say 1.5-2m be just as effective?
3 Thinking of what acoustic insulation material is best to line it with I have some 40mm mattress foam here and also have access to used carpet. Is one any better than the other? I need to think through how to “attach” it internal to the PVC to prevent it dropping down inside. Maybe some pieces of spring steel or chicken wire which may be naturally springy enough to push the foam out onto the inner wall of the pipe?

Thanks in advance for your help.

Originally Posted by Flindersia

1. Any recommendations for attaching it to the strange circular duct size on the end of the CVMax outlet transition. Which measures up and around 220mm OD. I found an earthenware to PVC Furnco that goes very close but these things are pretty expensive. Any thoughts?

The ClearViue Impeller outlet is rectangular. Are you using their supplied outlet Elbow? If so this is a restriction to flow as it is too tight a radius. You would be better off making your own larger radius elbow like this Mens Shed Dust Collection
These are dead easy to make, and while you are at it make the outlet the size to fit the 225mm PVC pipe (NB it's not 225 but more like 240mm)

2 The PVC offcut I acquired is just over 4m in length. I can actually fit that in as a straight run under the eaves without any trouble straight off the Clearvue outlet but is there any noise attenuation benefit in the long length or will a section of say 1.5-2m be just as effective?

The improvement will be marginal, probably logmarithic, most of your reduction happens in the first metre, less in the second metre etc.

3 Thinking of what acoustic insulation material is best to line it with I have some 40mm mattress foam here and also have access to used carpet. Is one any better than the other?

Why not use both - cut and roll the carpet to size so that when it it is rolled up and pops out inside the tube it sits up against the inside wall of the pipe and then wrap the foam around a chicken wire tubular frame and shove that into the pipe.

I need to think through how to “attach” it internal to the PVC to prevent it dropping down inside. Maybe some pieces of spring steel or chicken wire which may be naturally springy enough to push the foam out onto the inner wall of the pipe?

Chicken wire works fine.

Thanks Bob. I don’t have the right angle transition that is usually used for filters. Mine has the 8” straight transition (closer to 220mm OD) and the 225 PVC will run straight off that along the eaves in a continued horizontal run aligned with the elevation of the Clearvue outlet. It should present a very clean run with little backpressure. If you think the extra attenuation will be marginal I’ll probably run with a 2m length as this will make it much easier to fit the carpet and foam internally. Any ideas on how to make the connection between the Clearvue round 8” outlet and 225PVC? The PVC slides over easily and perhaps I just need to fill the void with foam and then use duct tape to hold it all together? Better ideas most welcome.