CamVac noise reduction with a baffle tube

[Moonsafari69]

Hi,

A few weeks ago I made a Baffle Tube to reduce the noise from my CamVac 286W. This is the single motor type wall-mounting machine. As you all likely know these have quite a screech when in operation. The easy and simple approach is to install a 2 1/2" hose from the extract port at the top of the unit down to floor level preferably a few meters away. This does have good results.

That wasn't quite what I was looking for in terms of noise reduction though. A bit of searching led to the possibility of enclosing the CamVac in a MDF enclosure with sound proofing material on the inside. Again this was no use to me as it would take away the 'easy bag change' benefits of the wall-mounting version. Plus I'd question the heat gains if the unit were inside another enclosure.

So, I've come up with is a more simple acoustic approach. I mocked this us a couple of months ago using cardboard (very Blue Peter!) and it worked better than I expected. Two weeks ago I made a more robust and permanent solution using a section of new soil waste pipe and some 20mm deep convoluted acoustic foam. The process I used is detailed below and the results are nothing short of staggering:

In the photo below you can see I've used a new piece of waste soil pipe straight from B&Q, at 1100mm long and 110mm in diameter.

I used convoluted (egg box style) acoustic foam panels for the inside of the baffle tube. The panels are 400mm x 300mm x 20mm thickness and are rated up to 70'C continuous use. The thickness ranged from 10 to 20mm as it is convoluted. Three panels were made into a tube shape and put inside the waste pipe lengthways and the excess was trimmed off the bottom. When the 300mm edge is rolled up inside the waste pipe the fit is perfect and so tight it doesn't need gluing.

This is the view inside the Baffle Tube taken from one end. You can see the acoustic foam panels fit very uniformly. Note this is a photo that was taken today, so after 2 weeks (10+ hours of use of the CamVac). They are very stable with no change to how I originally fitted them.

This CamVac is designed to be used with a 2 1/2" or 63mm hose connection on the inlet and the outlet. To ensure there was no detriment to the airflow I made the narrowest points inside the Baffle Tube to be greater than the 2 1/2" or 63mm. The widest points actually go just over 80mm in diameter.

The top connection point is a rubber connector I found at B&Q too (same section as the waste pipe). This fits snugly into the waste pipe and creates a solid seal around the piece of 2 1/2" plastic duct. I fixed the length of duct so that it was maybe 100mm into the waste pipe. A length of flexible 2 1/2" hose was then connected to the duct and a black CamVac connector added to the end of that for fitting into the extract port. The bit of paracord is used to hang the tube up in the corner behind the CamCav.

As I've said, the difference this has made was a surprise to me. Bearing in mind the Baffle Tube is simply an open tube and wider than a traditional 2 1/2" hose. I've used this nearly every day for the last two weeks with 10 individual sessions lasting over one hour in duration. The CamVac itself does not get any warmer and the extract air is the same temperature after the hour as it was without the Baffle Tube fitted. I don't have a calibrated way of measuring the air pressures, however with the Baffle Tube fitted there is no difference in motor speed and the few simple experiments I've done suggest there's no difference in suction either.

The big difference though is in the sound levels produced:

Without using the baffle and the exhaust air venting directly upwards, the dB reading is between 81 and 82dB.

When the baffle is connected the sound level instantly drops by 15dB down to between 66 and 67dB. In the real world this is a huge difference, it's more than 50% quieter than it was before. I can now easily hold a conversation in the workshop with the dust extraction running, this was simply impossible before without very raised voices.

There will of course be the purist opinion that a baffle of any kind must have an impact on not just the sound levels but also the pressures and air velocities too. I'm an engineer, but not a scientist, so I can't say either way for certainly. What I can say though, is that after two weeks of use I have no fears of this having an adverse affect on my CamVac and will continue to use it. The benefit is beyond words for a small workshop situation where there is no possibility to have the dust extractor located in a different room.

There's enough info here should anyone else wish to make one. I'd imagine this idea would suit any type of HPLV dust extractor.

Hope this will be of interest to somebody.

 

[Duncan A]

An excellent idea, beautifully presented. All noted for the future.
Many thanks
Duncan

 

[Moonsafari69]

An excellent idea, beautifully presented. All noted for the future.

Thanks Duncan. The all in cost for parts was £20, a decent return for the price.

 

[Mike-W]

I found a similar solution a few years ago, while visiting Tool Post in Didcot I could not help to notice how much more quite there Camvac was than my wall mounted 286, closer examination showed they had installed a pipe similar to the OP.
My Camvac is mounted in my workshop that was once an integral garage with the ceiling lined with plaster board and a loft hatch very close to the top of my Camvac, its very simple to put a short piece of 'Stayput' flexible hose (sold by Axminster) up into the loft space, its amazing just how much more quite this is, the other benefit (for the summer at least) is that the heat produced when running the Camvac is vented out of my small workshop.

 

[MattRoberts]

Great solution - thanks for sharing the details

 

[Moonsafari69]

...the other benefit (for the summer at least) is that the heat produced when running the Camvac is vented out of my small workshop.

I'm guessing you divert the exhaust back into the workshop for the winter Mike? CamVac's do make good heaters too :wink:

Great solution - thanks for sharing the details

You're very welcome Matt!

 

[Mike-W]

...the other benefit (for the summer at least) is that the heat produced when running the Camvac is vented out of my small workshop.

I'm guessing you divert the exhaust back into the workshop for the winter Mike? CamVac's do make good heaters too :wink:

I tend to put up with the noise in the winter as I don't like leaving the hatch ajar through the winter, I do have a radiator in the workshop but most of the time its turned off, if I leave the loft hatch open it can get mighty cold in there!

 

[Fitzroy]

I'm sure I'm preaching to the choir but there is also the risk of moist air in to a cold space.

 

[Moonsafari69]

Another potential risk to consider if the exhaust air is being blown out of the workshop space is the question of what air is being sucked back in to replace it. If the workshop is close to a room with a gas boiler (e.g. central heating boiler) then be careful as it will be very easy for the monixides in the flue gases to be sucked back inside. If the workshop is standalone this is unlikely be a problem though.

 

[Eric The Viking]

You've actually achieved a nominal 30:1 reduction in emitted sound power!*

There are a few caveats to that statement, for example over what frequency spread the sound is measured and how that has changed, but the expression "phenomenally good" springs to mind - jolly well done.

E.

PS: I've suggested for some time that you can use a very similar idea to reduce workshop noise to the outside world - air vents of the Victorian style, but lined. Rockwool is good as it's fireproof and thus building-regs friendly.

*15dB is approx 32:1, 3dB being roughly a halving or doubling each time. The ear doesn't hear in a linear way, which is why we use a log scale in the first place, so it only seems like a halving of the noise.

 

[Moonsafari69]

You've actually achieved a nominal 30:1 reduction in emitted sound power!*

There are a few caveats to that statement, for example over what frequency spread the sound is measured and how that has changed, but the expression "phenomenally good" springs to mind - jolly well done.

Thanks very much Eric, when I first mocked up the cardboard trial version it worked so well I was pretty sure I was on to a winner. I may even still have that cardboard 'version-1' n the workshop, will see if I can find it later and post a pic. It looks a tad less engineered than the new one. As you point out there's a few different ways to measure sound (power, air pressure, subjective loudness etc). It's been too long since my physics days, but can happily say that the result speaks for itself. Really chuffed with how well it works. I think, for high air volumes, the trick is finding the sweet spot for the size of the baffle, not too wide where the effect is dulled and not too narrow so as to induce choking down and potential motor overheating.

Thanks again!

 

[woodpig]

This one is very quiet. :wink:

camvac-silencer-t99639.html

 

[Moonsafari69]

This one is very quiet. :wink:

camvac-silencer-t99639.html

Hi, yes this should be even quitter than mine with using the additional deflectors. The exhaust air comes out at 45'C so is worth checking that with the foam specs. It would be interesting to know the sound level with and without the internal 90 degree deflectors, the less interference with airflow the better? Looks like a well made piece of kit! Also good to know it's not just my mind that's wired this way.

 

[Inoffthered]

I had been thinking about just venting mine outside and not bothering with baffles and sound insulation merely a pipe from exhaust port out of a window.

 

[Moonsafari69]

I had been thinking about just venting mine outside and not bothering with baffles and sound insulation merely a pipe from exhaust port out of a window.

Certainly a possibility (and it will be a quiet option), like I said before though just be cautious about any other gasses or exhaust fumes that could be sucked back into your workshop space.

 

[bigbob1]

This is very helpful I have a 2.5" CamVac with two motors and at first when switched on with one motor the noise is not to bad but after a while it becomes annoying. I noticed that if you put a pipe on the exhaust port and pointed it away from you this did quite things a bit and was going to have 2 pipes fitted and exhaust to the outside but realized that after spending money on insulation and heat all this would do is take my nice warm air and transfer it to outside of the shed so your solution will be tried in my workshop soon.
I did see a video on u tube where the guy had used plastic sewer pipe with a smaller pipes internally built just like a baffle system that you would find in a car exhaust system but he never gave details or dimensions to build this and I can not find the video anywhere today altough I am sure its there somewhere.

 

[Moonsafari69]

This is very helpful I have a 2.5" CamVac with two motors and at first when switched on with one motor the noise is not to bad but after a while it becomes annoying.

Thanks bigbob1, this is exactly the reason I started looking into this too. If you have the 2 motor version you will need to use two baffles as connecting both exhausts into one pipe (even a larger pipe) will be problematic for the system when you consider potential back pressures. I would be very interested to hear how it works if you get round to making one for yourself. The 110mm diameter waste pipe is just the right size for the sheets of 300mm x 400mm (20mm thick) acoustic foam as they fit perfectly without any cutting. I would not use thicker than 20mm foam for this size of pipe as the inner core for free airflow would be restricted.

Glad you find this useful. I'm certain you will be very happy with how much more comfortable this will make your workshop.

 

[Moonsafari69]

For those interested, this was the first mock-up so see if the concept worked, a bit of a cardboard, foam and sticky tape special. The tube was about 30cm long but still quite effective. Not as tidy as the more permanent solution:

 

[Eric The Viking]

The box one is interesting: I was thinking that, if you wanted to finesse yours, you might put a slow 90 bend on the end, with a foam strip running round the larger radius, say 1/3 of the diameter. It shouldn't need much more than that, Then there's no straight path.

That eggbox foam is pretty handy stuff, We used to pack hard disks in it years ago, and I've collected a reasonable amount for that sort of job, but not yet had cause (or at least a reasonably dust-free application). It is a pig to clean though.

 

[Moonsafari69]

The box one is interesting: I was thinking that, if you wanted to finesse yours, you might put a slow 90 bend on the end, with a foam strip running round the larger radius, say 1/3 of the diameter. It shouldn't need much more than that, Then there's no straight path.

Hi Eric, having the uninterrupted straight path for the air-flow I think is really important and ultimately a benefit. This has the least impact on the overall system and produces the lowest additional stress on the motor. The sound levels are supressed significantly in the straight tube and I don't think they will go much lower without impacting the airflow/efficiency of the CamVac. This is a permanent solution now and I am conscious that I don't want to affect the motor in the unit.