Thread: Clearvue CVMax Install

One thing I would like to reduce is the high pitched whine that is still going through the silencer that vents outside.

The silencer box made from MDF and lined with sticky backed foam. It has about 5 changes in direction in the box, but I am wondering if the foam I used to line it is not good at removing high frequency noise. One option I am pondering is adding a longer flexible insulated ducting (e.g. Fiberglass Acoustic Noise Reducing Ducting 5m | Aqua Gardening) piece between the blower outlet and the silencer box (currently I only have a 500mm length of Ø250 flex hose connecting the blower to silencer box). I could make this insulated ducting a couple of metres long and put a bend in it to assist with sound damping. If I used Ø300 ducting it probably wouldn't add too much back pressure. Any idea if this would help get rid of the high pitch noise venting to outside? I'm not sure this type of ducting will absorb any sound from the inside - I suspect it is just to stop the sound being transmitted to the air surrounding the ducting. Other ideas welcome...

This is my silencer box;-
Capture.JPG IMG_20210209_194324479.jpg

Cheers

Mike

Can you measure some sound pressure levels (SPLs) with a mobile phone to give us some idea of what your SPLs are.
eg Outside 1m from vent, inside 1m from open door enclosure etc.
Some people are much more sensitive to certain frequencies and it may be to some extent your perception of the noise.

Is the noise definitely coming from the external vent and not just through the external wall?

What sort of foam is the lining inside the baffle box, soft furniture foam dense doesn't do all that much - better is heavy/dense mattress latex type foam.

Nice implementation BTW but you will need some sort of window on that drum to see the dust level inside.

Noise Reduction - CV1800

The link shows how I did it with a reduction from 92d to 68db. Sound is very directional so a vertical exhaust is more efficient than a horizontal one. A problem I have encountered just in the last few days was a cyclone which was much louder than it used to be after some work was done on it and the direction of rotation was wrong which in a CV produces an odd sound and it loses efficiency but still works at a reduced level.

PS. If you would like to have a chat about the noise problem PM me your phone number.

Bob - here are some sound levels I recorded yesterday at a distance of 1m from the open dust extractor room door and also 1m from the outside vent discharge location. As you can see my silencer box is not doing a lot to reduce the noise through the air venting outside (cutting only 1-2 dBA). For reference, the sound level inside the workshop with the dust room door shut when operating at 60 Hz is around 71 dBA (compared to 86 with the door open) so the dust room single stud wall is cutting about 15 dBA to the inside. The wall on the outside of the shed (that the silencer vents through) is even better with a double stud wall with air gap, insulation and 13mm gyprock on each stud wall. It looks to me like my silencer box needs to be revised.

Location	Hz	Dust Ports	dBA	Amps
1m from open extractor room door	50	Closed	83	4.1
	50	Open	84	5
	60	Closed	86	4.4
	60	Open	85	10.7
1m from outside exit vent	50	Closed	82
	50	Open	83
	60	Closed	85
	60	Open	85

I like the idea of Chris Parks' silencer box - I may redesign mine and make it with acoustic insulation/bird wire walls for the sound to absorb into...

Mike

Thanks for the detailed numbers.

The acoustic insulation and bird wire muffler is what we used at the mens shed and seems to be working well.
I think you night find n all round improvement using this method.
It will be interesting to see the numbers one you have done this.

I think the exit baffle is the real secret with mine.

Originally Posted by Stanger

One thing I would like to reduce is the high pitched whine that is still going through the silencer that vents outside.
This is my silencer box;-
Capture.JPG

Cheers

Mike

Hi Mike,

The speaker designer in me took one look at the drawing a few days ago and thought speaker cabinet design first, despite changes in direction etc it will transmit sound pretty good even with foam lining.

For that to work un-equal length vertical dividers both in length and spacing will help to break up the sound waves and stop resonant soundwaves being generated.

Flat non dense foam works inside sealed cabinets to deaden the sound but will do far less in this role, egg crate style foam would be far better.

The idea in all cases is to break up the actual sound wave before it exits.

To me if it's possible from the first direction change up to the top create a chicken wire based foam baffle and let the air come straight out.

Cheers
Phil

Finally finished the silencer box 2.0 on the weekend and tested it. I used polyester insulation and bird mesh similar to Chris Parks design. Got the sound power level (at 1m from discharge point) down to 60 dBA @ 50 Hz (was 83 dBA) and 66 dBA @ 60 Hz (was 85 dBA). Pretty happy with the results. Thanks for all the suggestions.

It was a bit hard to photograph due to the confined space, but here are some pics...

Flow path.JPG IMG_20210313_160312598.jpg IMG_20210313_160412858.jpg IMG_20210313_160419702.jpg

Mike

Mike, that looks good, I used acoustic batts in mine and they cost a lot of money and some time after I became aware of an acoustic batt that was available from Bradford and was a very good price. Recently a Men's Shed I have have been helping and equipping with automatic blast gates had a neighbour who up until now was happy with the amount of noise change his mind and ask then to do something about it because he had gone onto night shift. They made up a simple straight through muffler which met the approval of the neighbour and all it had was a perforated inner sleeve surrounded by insulation and everyone was very happy with the result. Others I can recall have tried the same approach with less than stellar results.

Originally Posted by Stanger

Finally finished the silencer box 2.0 on the weekend and tested it. I used polyester insulation and bird mesh similar to Chris Parks design. Got the sound power level (at 1m from discharge point) down to 60 dBA @ 50 Hz (was 83 dBA) and 66 dBA @ 60 Hz (was 85 dBA). Pretty happy with the results. Thanks for all the suggestions.

It was a bit hard to photograph due to the confined space, but here are some pics...

Looks good.

We used Chris's approach - chicken wire tube (200mm diam) with the isolation wrapped around it at the mens shed and it worked fine.

For my home DC with baffle box similar to yours with large flat surfaces of insulation I just glued the insulation to the baffle box walls. I was a bit worried that with air constantly rushing past the insulation that the Bernoulli effect would drag it off the walls but its been there for 10 years and last time I checked out was still stuck fast.