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Thread: Moving the DC outside
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15th January 2018, 09:00 PM #61Intermediate Member
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Ah, ok that makes sense.
I've only ever had the one DC so if there was something unusual with the noise or vibration then I might not be aware of it.
I just tried starting it up and pressing in various places around the case to see if I could significantly reduce the sound, no real benefit there. (I presume you were referring to the casing rather than the actual spinning impeller there.)
It does vibrate quite a bit when first starting up but settles down when its up to speed.
I've attached a short video clip, if that helps at all (was taken with the DC connected by 4" flexi to the TS - haven't started work on the infeed ducting yet.)
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17th January 2018, 07:50 PM #62.
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Ian - I finally got to watch the vid - the noise made by your impeller does not sound right to me and the start up noise it makes is I think a hint as to what might be going on.
It could be that one of the impellers is bent, or a tad longer than the others and this was corrected for by balancing but that means it will produce a different noise than an impeller that has all even length blades. Unless it is something that is clearly visible then fixing this is not easy and it is often just easier to replace the impeller.
You will need much more force than hand force to make a difference.
Try carefully clamping bricks either side of the impeller exit.
It could be the orientation of the impeller/motor.
Try removing the exit ducting and standing the impeller back up on its base and compare that to the SPL with it hanging from the side.
A bracket between the impeller exit and the base of the stand might help.
inside.jpg
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20th January 2018, 04:31 PM #63Intermediate Member
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Ok. Another set of test. This time I rebuilt the whole DC in the shed, and ducted the input back through into the workshop. As I currently have 6" ducting between the shed and workshop, and a 4" intake to the DC, I did this by running my 3 metres of 4" flexi internally up the 6" ducting. So airflow is definitely restricted but the intake noise is moved out of the DC shed.
73db with the DC on and the door closed
75db with the door open a couple of inches to allow exhaust
81db with the door open fully
Also I measured the intake noise in the workshop at 75db, I imagine its going to be significantly higher with a full 6" duct and unrestricted air flow.
So with the door fully closed, 73db vs my original 77db with the naked input. But with the door open a crack, 75db vs the original 85db measurement, a significant reduction.
After all that, with the door closed and the full DC in the shed (73db) vs only the filter/bag in the shed (68db) is still a significant difference (I am presuming with a proper baffle the end result will be much closer to these figures than with having the door open a crack.
I am going to pick up some freebie carpet offcuts and line the walls, then measure again. If I can get down to 70db at 1m from the shed, then I'll put the whole DC into the shed which will keep the garage quieter!
Also regarding motor noise, I turned it back upright and it doesn't change the vibration significantly. As Bob points out, I may well have a slightly unbalanced impeller or a noisy motor bearing. I don't know how to fix those short of replacing them, and I don't really want to buy another 2hp DC knowing how poor they are at actually collecting all the fine dust. Unfortunately a 3hp unit won't fit in my shed space so I will make the best with what I currently have.
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20th January 2018, 04:54 PM #64
IMHO a 6" pipe with a bell mouth intake will likely be quieter than a 4" intake, usually the smaller the intake for a "given flow rate from a DE" the louder the intake air noise - forcing XX flow rate through smaller and smaller intakes creates higher intake air speed and noise- up to the point - then it drops off as flow rate chokes down.
(1) Our small workshop layout __ (2) Bandsaw circle cutting jig __ (3) Spindle sander modifications __ (4) Dust Sensor
(5) Router table redesigned ____ (6) DC and where it all began __ (7) Bandsaw dust extraction build
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25th January 2018, 12:30 PM #65Intermediate Member
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I got some old rubber-backed carpet tiles and lined the shed with it, including the roof. (Note double stick carpet tape doesn't hold on roof and walls, I will have to get myself a tube of construction adhesive and try again.)
That brought the noise level outside the closed shed down to 70db.
Then I realised that my free download sound meter app has been measuring unweighted decibels and most of the noise is low frequency rumble. So I upgraded it to measure weighted dbA (weighted for human hearing perception), and measured the noise level as 62dbA outside the closed shed. That seems intuitively correct, I don't perceive the noise as overly loud myself.
Ok, I'm now comfortable with finishing the full DC 6" mod and keeping the motor/impeller in the shed too.
Next step is to make a MDF exhaust baffle and a frame to mount the motor/impeller unit.
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25th January 2018, 01:57 PM #66
That's better, I just assumed that the app would be dbA. Thanks for the update.
(1) Our small workshop layout __ (2) Bandsaw circle cutting jig __ (3) Spindle sander modifications __ (4) Dust Sensor
(5) Router table redesigned ____ (6) DC and where it all began __ (7) Bandsaw dust extraction build
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27th January 2018, 07:52 PM #67Intermediate Member
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I've revised my plan with the DC configuration. Rather than building a frame to lift the motor up to the same height as the bag unit input, I'm now going to keep the motor section lower down and connect the two pieces together with 6" ducting.
This works better with my shed configuration as it was going to be a very tight squeeze with the way I've mounted the baffle box internally
I have turned the motor 90 degrees so that the input can come in directly from the side wall of the shed, this saves a 90 degree elbow.
Also I turned the bag mounts 90 degrees so the section facing the shed door doesn't have a mounting pole on it, that will make bag changes much easier. By doing this, I am also cutting out and enlarging the original bag inlet area.
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27th January 2018, 08:30 PM #68.
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Looks very tidy.
Not a biggie because you save a 90º elbow which probably cancels out the following. Usually this arrangement will have some small flow losses because the rotational flow of the air in the impeller is not in the same plane as the bag housing.
It will be interesting to see what SPL you get with this setup.
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29th January 2018, 08:37 PM #69Intermediate Member
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29th January 2018, 09:03 PM #70.
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29th January 2018, 10:26 PM #71Intermediate Member
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Thanks Bob, silly me, you were talking about flow loss in the previous paragraph then mentioned SPL and I misinterpreted that as referring to static pressure level, i.e. WC"
I will need to get new 6" shed inlet ducting in place before I can measure the noise level again. The new entry point needs to be much lower down so I enlarged the old inlet cutout into a long rectangle and made that the output vent from the baffle box.
Also I need to convert the impeller input over to 6". Not sure how to do the reverse BMH at present ... my largest roundover bit is 1/2" and I haven't turned anything on a lathe in 30 years. I am thinking of a long session with rasps or a sanding drum, but hard to get a consistent profile all around.
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29th January 2018, 10:42 PM #72.
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4th February 2018, 06:32 PM #73Intermediate Member
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The 6" input to the impeller is now installed. I'll fabricate a manometer and take some hard measurements plus redo the noise level check after I get it back into the shed. It certainly seems to be moving a lot more air now.
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4th February 2018, 06:38 PM #74Woodworking mechanic
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The next problem maybe that is in fact moving too much air for a single filter to cope with. I’ve added another filter to my modified 2hp and my flow has increased somewhat over the single filter.
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4th February 2018, 07:57 PM #75Intermediate Member
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No room for a second bag in my shed, but I could swap the bag for a PF if that decreases the back pressure?
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