Thread: Noise Reduction - CV1800

Some pics of what we did. Sadly I did not take all the pics intended. This is the internal of the exhaust box after we pulled the MDF lining to reveal insulation batts



Then we put some 12mm square wire to hold it in place. This is one piece folded top and bottom edge at 90° to hold it stiff and straightish and then folded the corners to all 3 sides from one piece



At the top corner above you see the inlet into the box. The outlet is in the bottom piece on the LHS.

There was an iternal shute double lined with 3 mm MDF that ran almost full height to the outlet. Now this shute is made from 12mm wire. Below you see the internal wire



Then we folded a ling piece to contain the insulation batts as below



No more pics sadly but what we did was lay a bat on the outer wire and and sat the inner wire on top. Then we wrapoed the outer wire around the bat continually putting more bats in till it was completele enclosed.

While there are no pics to show this shute stood about 60mm clear of the overhead batts in the too of the box.

Dave TTC
Turning Wood Into Art

Wow!

68dB is an outstanding result. Mine is a bit over 80 dB with a couple of lengths of HVAC duct.

Could you post a pic of the finished installation, both from the inside and outside? My poor feeble brain is having difficulty sorting out the design.

I am very interested too Chris. I have got my CV down to about 82db by building a muffler similar to the mens shed up your way but it seems you have done much better.
I am moving house in about three months so as I will be starting from scratch again it would be nice to get the sound down to your levels.

Originally Posted by Chris Parks

I always warned anyone enquiring on buying a CV cyclone that noise is the issue and the figure I used was 92db out of the open exhaust. .

Chris is that at 50 or 60Hz?

Bob,

My CV 1800 went off the 100 dB scale at 60 Hertz, but my sound meter was a phone, and not terribly reliable. After the HVAC exhaust went on my measurements said that the noise levels drop by about 10 dB when reduced from 60 to 50 hertz. A big difference, but you also lose about 20% of air flow. Be interesting to see what others discovered.

This is at 60hz Bob. I checked it all again a short while ago, when I posted yesterday it was from memory so thought I had better go back and check things as Dimentia is rapidly setting in. Directly under the exhaust up against the bottom panel of the cabinet but out of the air stream I get 78db which I am fairly impressed with and 68 at the point I have always measured at and that is down from 92db at the same point. Some of the difference can be attributed to the exhaust now pointing down to the ground whereas before it blasted horizontally straight out from the wall. Just measuring randomly within a few meters of the enclosure averages about 70db in the carport. In the shed with one gate open on the saw it is 71 if the enclosure is closed and 74 if the enclosure door is open. It is now so quite that we have been using it at night while Dave is here with no problems. I mentioned before that I am sure I could get it down further if I could be bothered but other projects are getting in the way.

Don't under estimate the expense involved as I reckon it cost me close to $500 to get this far and I did not follow any set plan, it was guesswork and intuition all the way. The box is lined with 50mm acoustic batting and the is built with 12mm plywood. The internal vertical duct sits directly on the floor of the box and the air entry into it is close to the top panel. It took me a while to figure out that I had made a mistake by using 3mm MDF to hold the batts in but a lesson was learned. My thinking was that the MDF would stop the batts being eroded by the air stream but changing to the wire has not caused any problems so far and that alone dropped the noise level considerably. I think the wire mesh actually attenuates the noise but I may be wrong there. I was tempted to put some mesh cylinders in the enclosure standing full height but that got lost in the construction. It would be interesting to see what effect the mesh would have on the noise levels as it used to work in car mufflers when i was a broke teenager.

I must express my thanks to Dave TTC who helped me pull it all apart and get the wire lining in as trying to do it on my own was just not going to happen for all sorts or reasons. If I get a chance later this week I will pull the front off and post some photos of the duct. Thanks for the interest.

I assume you have quite a short run from the clearvue to the exhaust in your wall? I ask, because I exhaust through the roof after about 2.5 m of HVAC ducting and at the actual exhaust point on the roof all I hear is a lot of air rushing but it's very quiet. No drone at all and I'd expect around 50-55 dBA or maybe less. Noise inside the workshop was something I worked to reduce (I'm at less than 75 dBA at 3m) but the actual exhaust outside never even entered my mind as a possible issue as it was so quiet.

Originally Posted by DomAU

I assume you have quite a short run from the clearvue to the exhaust in your wall? I ask, because I exhaust through the roof after about 2.5 m of HVAC ducting and at the actual exhaust point on the roof all I hear is a lot of air rushing but it's very quiet. No drone at all and I'd expect around 50-55 dBA or maybe less. Noise inside the workshop was something I worked to reduce (I'm at less than 75 dBA at 3m) but the actual exhaust outside never even entered my mind as a possible issue as it was so quiet.

Yes, very short and unable to extend it. John Samuel's use of a similar duct (if I am not mistaken) does not seem to reflect your experience at all from what I can gather. People's perception of what constitutes excessive noise is fascinating, I have had customers tell me that a CV with an open exhaust is not noisy at all and does not worry them which I find astounding. How can anyone truly say that 92db or greater is not an issue? Venting the exhaust vertically is a good option and one I suggested to a lot of customers as the noise is very directional.

Yes, it can definitely be subjective. My measurements were done using calibrated high-end equipment so I'm confident of my numbers. With no exhaust ducting on the noise was completely unbearable! (for the brief few seconds before I shut it down!). I assume people who don't mind that noise are already clinically deaf .

All my measurements were done using a $25 Jaycar instrument from exactly the same spots at the same height unheld. I doubt they are exactly accurate but they are comparative to what each other and that is what to me is important. This is not a science experiment and comparing anyone's reading to anyone else's is a bit of a stretch for me. Relating a true comparative reading with a datum figure is what I have aimed for using the same instrument.

Well done! I think you have acheived a remarkable result. I agree with Chris though that sound is very directional so a vertical outlet may help in that regard.

I would also appreciate being able to forward any pictures to anyone interested. Once I get my shed finished and my own installation set up I want to experiment with a baffle box combined with some sound absorbent materials.

Guys, I'd love to see pics of anyones solutions (including roof vents etc) as a CV is next on my list for the shed, but I've delayed getting one purely because of the noise issue. My only difficult neighbours just happen to be right on the other side of the fence where the CV will be mounted.


A CV is definitely going to happen, but before I jump in, I need to be confident I can manage the exhaust noise issue. I have the option of building an external room/box/cupboard bit on the outside of the shed to exhaust into, that I had planned on baffling somehow. I can also put a chimney hat thingy on the roof and exhaust upwards.

So any pics of solutions that work I'd love to see.

After working with in Chris's workshop I think the dc is louder in the workshop than outside.

I ponder if the ducting was lagged if it might reduce some noise inside.

His motor is not particularly insulated and I believe some running noise is traveling through the steel roof structure and into the carport area.

It is very tollerable outside and especially during the day unlikely to draw a complaint from any neighbours in my opinion

Dave TTC
Turning Wood Into Art