Soundproofing attempt! Enclosure for a noisy dust extractor

[OscarG]

Inspired by a really great thread by Erik the viking and SunnyBob's dust extraction silencer I thought I'd have a go at taming my stupidly noisy Rutlands dust extractor.

My plan was to copy most of Bob's design (cheers Bob by the way!) but with the silencing exhaust baffle box on the back as I'm a bit short of vertical space (my extractor sits underneath my router table).

This isn't going to be a pretty so hope this "project" is allowed here?!

So rough box made out of 18mm MDF scraps , I've got a lid and removable front panel that I need to drill a big hole in for the hose and maybe some quick release connection.

I've left a 440 x 100mm space in the back for the exhaust air, that's a bit tricky to see in this pic.

Here's my plan for the baffle box (80mm deep) which will get screwed on the back. I thought I'd make it a separate box so if this goes wrong, I can try it in another position. I'd like to line it with acoustic foam but as I'm tight, probably some old towels!

I'm not sure why but something tells me to make that first baffle (orange one) a bit shorter to encourage more air to enter the chamber.

I'm hoping to test the noise before and after using a sophisticated decibel meter (free iphone app!).

If anyone can see anything horribly wrong can you let me know?!

 

[clanger]

My thoughts are that apart from the elephants trunk, you will also need to allow air to enter the cabinet for motor cooling purposes. Also, if you are putting in baffles that will slow down the dispersal of the air inside, and also wrapping in towels, I suspect that you will have heat and thermal cutout issues.
I am by no means a specialist, so I expect to be told that I'm wrong - don't worry, I'm thick enough skinned to take it.

HTH

 

[OscarG]

My understanding (I could be wrong!) is that the noise comes from 2 sources, a) the motor and b) the speed of the exiting air.

The idea is for the baffles to slow down (and force the soundwaves to change direction and lose intensity) that exiting air and hopefully reduce noise.

Proof's in the pudding though, if it doesn't get any quieter, I'll take this mdf hunk of crap and burn it!

 

[Bucks woodshop]

Im struggling with noise too interested to see how this goes

Sent from my SM-G935F using Tapatalk

 

[Chris152]

I built mine following Bob's guidance and it works a treat. One thing I'd suggest on your design would be trying less baffling pieces - When I built mine, I tried it with the lid not clipped down and the lid started to hover around on account of the air getting out through the top rather than leaving via the baffle. I figured if I just clipped the lid down it'd be putting extra load on the motor, so I reduced the baffle to just a few sections and it still works well but with less added load on the motor. At least, that's how I figured it.

 

[AES]

I'm very interested in this too. my Kaercher shop vac makes a noise roughly akin to standing alongside the runway when Concorde's taking off! So far I've only "established" (by "empirical means" - i.e. try it n see) that most of the noise seems to be produced by the "exhaust air" exiting the vac body. Whether or not that's a mixture of air that's been cooling the motor plus air that's been doing the sucking, or simply just one or the other I'm not sure.

Watching with great interest, please keep us updated.

 

[OscarG]

I built mine following Bob's guidance and it works a treat. One thing I'd suggest on your design would be trying less baffling pieces - When I built mine, I tried it with the lid not clipped down and the lid started to hover around on account of the air getting out through the top rather than leaving via the baffle. I figured if I just clipped the lid down it'd be putting extra load on the motor, so I reduced the baffle to just a few sections and it still works well but with less added load on the motor. At least, that's how I figured it.

Cheers Chris, I'll do that! Less is more.

 

[Chris152]

Cheers Chris, I'll do that! Less is more.

That said, my baffle space was only 50mm deep - I notice yours is 80mm, so less of an issue I'd think.

 

[sunnybob]

points raised;
ALL motor cooling air comes THROUGH the pipes and the through the canister. There is NO cooling from surrounding air. The air around the motor can not possibly overcome the force of the air being thrown out.

Oscar, I agree with chris (seeing as how he used my basic design) You have too many baffles.
you have to slow the air down, but not create a restriction so great that the air backs up. That WILL cause the motor to get hot.
Once you have all the sound deadening on those baffles, what is the actual gap between them? Not very much from your drawing.
Its the high pitched whine that is most annoying, and high frequency noise hitting soft baffles dies almost instantly. deeper notes can be allowed to get through as they are not very noticeable over the equipment noise. remember, we do not need SILENCE, its a workshop. we need a low enough noise that will blend in.

material; old towels and blankets over every flat hard surface, even duvet if you can cram it around the lower canister to fill up the space inside. Fit them loosely, but just tight enough that they do not sag and block the air way, and make sure you are NOT blocking the exit trunking.

 

[OscarG]

Cheers Bob!

I'll take out some of those baffles, might shorten that first one too.

Do you think 8cm clearance inside is a bit shallow? Wonder if I should bump it up to 10?

 

[sunnybob]

I would consider 80 mm to be ok, but measure AFTER you have draped all surfaces with baggy blankets. Dont forget to do the sides of the run as well. No point having soft fences if the walls are hard.

 

[OscarG]

Managed to steal a couple of hours in the workshop last night. As per advice, revised the design a little. Made the inside of the baffle box 10 cm to give a bit more space for the towelling.

Ripped a load of 10cm strips and finally got to do something useful with my new (but still unfinished!) crosscut sled.

So with the baffles losely placed, this is what it looks like

and from underneath with the baffle lid (please ignore piss-poor job of glueing those 2 panels together!) on you can see the final exit port where hopefully nice quiet civilized air will emerge

Next job to stick the towels on everything. Not sure how I'm gonna do that or what glue, any suggestions? Tempted to staple it but wonder if that's a crap idea?

 

[sunnybob]

I used furniture seat webbing, stapled very 6 inches or so.
stapling is fine, just put something to reinforce it other wise the weight of the towels will pull the staples out, or pull it off the staples.
Cant see any of your pics though.

 

[OscarG]

Update... (hope the pics show up, I changed hosting site)

So baffle box inside lined with towels, glued with PVA and stapled.

Inside of box, you can see baffle box screwed on back.

With dust extractor inside.

Finshed, ain't it pretty?!

Ok, so first test, wanted to make it realistic so hooked up end of hose to my table saw. From about 4-5 feet away took a reading using a Decibel measuring app. Measured with DX outside then inside the box.

Outside. 87 dB

Inside box. 77 dB

Test 2, with box in final position. I'm probably 6-7 feet away now with my phone.

With front door open... 81 dB

All sealed up, box closed. 70 dB

So both tests showed approx 10 dB drop. I'm a little disappointed if I'm honest, was hoping for more than that. It's not amazing but even without iphone decibel meter the difference is immediately obvious. It's gone from a horrendous screaching piercing banshee to sounding like someone hoovering next door (albeit loudly!). It's certainly taken the edge off.

As the box currently sits on floor, I'm wondering if adding casters and raising base off floor might help in some small way with the noise?

If I started again I'd have made the box bigger and maybe doubled up the 18mm MDF alround. I'd have gone for proper soundproofing foam too. The towels when glued seem to go a bit smoother and lose some of their fluffyness. I think I may have added extra baffles too as I can really feel the air rushing out of the exhaust at the bottom, I'm not sure it was slowed down that much. I'd also made the removable panel on the side, having the front removable with the hose attached makes it too complicated, I wasted ages faffing about with pipes and fittings, even so, it feels like a bit of a bodge and makes it hard to get that front door on.

I might make a mini version for my little Wickes shopvac that's also bloody noisy.

It wasn't a great success but I may tinker further with it (the base is chipboard as I run out of MDF, might replace that) . Anyway hope this proves useful to someone!

 

[AES]

Thanks for posting that Oscar. Interesting, especially as I'm still just "thinking about it" for my own Kaercher shop vac.

Please note that I'm NOT a noise expert (far from it, I'm sure someone who is will be along soon) but don't forget the decibel scale is logarithmic, meaning that a reduction of 10 Db HALVES the noise you hear (I THINK that's right)! Also, noise is very subjective, and a lot of the "aggravation" you get from any noise depends more on the frequency of the noise (high-pitched, or low?) than on the outright "volume" number on the Db scale.

In other words, with the door closed, does the resulting noise still bother you enough to do something more? If so, at a guess (rpt GUESS) doubling the thickness of the towelling MAY help to get it down to the level you find acceptable. Worth a try?

Do please keep us informed, I for one find this thread very useful, thanks.

P.S. Does anyone know how to bookmark a thread in the new Forum software please? I've looked but (as usual) can't find it?

 

[sunnybob]

thats not a bad result, but those towels are too tight and too thin. You could lay yet another set over them and not glue but just staple.

Because you glued them to the back boards there is no flex. Imagine shouting at a solid wall (as you have it now) and then shouting at a thick wooly blanket hanging loose from the ceiling (what youre trying to achieve).Have you covered ALL the internal surfaces? doors and flaps?

If you can find any of the old papier mache egg trays they are best cheap (free) material.
Egg foam as used in camera cases is very good, but usually pricey.
Go buy a duvet (brownie points!) and then re cycle the old bed blankets.

 

[OscarG]

Please note that I'm NOT a noise expert (far from it, I'm sure someone who is will be along soon) but don't forget the decibel scale is logarithmic, meaning that a reduction of 10 Db HALVES the noise you hear (I THINK that's right)! Also, noise is very subjective, and a lot of the "aggravation" you get from any noise depends more on the frequency of the noise (high-pitched, or low?) than on the outright "volume" number on the Db scale.

I think from what I've read 3 dB is doubling your perceived volume, so in that sense 10 dB is a good result but I've seen youtube vids where people have achieved 20 dB using acoustic foam.

I've been bit obsessed with noise recently, using my app to gauge the world around me, on the tube it can be 70-80dB in the station, 90-100 between stations and 110+ when really screeching (very unpleasant and actually painful), in that sense 10 dB makes a huge difference.

It has reduced the volume of the DX, you could have a conversation with someone in room whereas before you couldn't but it's still uncomfortable enough you'd want to use ear-protection.

It seems to have changed the pitch, it almost sounds like a car that's changed gear.

I think it's worth having a go, I invested a bit too much time as I was mean, trying to recycle scraps and towels! I think get a few nice clean sheets of MDF and acoustic foam and this could be built pretty quick.

 

[sunnybob]

Found a pic of mine, see how the blanket is hanging loose from the top webbing straps.

 

[AES]

Another "little gem" I picked up somewhere (and only HALF understood, as usual!) is that the position of, and distance from the source, of your noise meter when measuring Db, AND the surfaces surrounding the noise source, all make a big difference to the reading on the meter.

 

[OscarG]

thats not a bad result, but those towels are too tight and too thin. You could lay yet another set over them and not glue but just staple.

Because you glued them to the back boards there is no flex. Imagine shouting at a solid wall (as you have it now) and then shouting at a thick wooly blanket hanging loose from the ceiling (what youre trying to achieve).Have you covered ALL the internal surfaces? doors and flaps?

If you can find any of the old papier mache egg trays they are best cheap (free) material.
Egg foam as used in camera cases is very good, but usually pricey.
Go buy a duvet (brownie points!) and then re cycle the old bed blankets.

I'm pretty confident I covered every area, I was very careful with that, but take your points about the towels. They started off nice and fluffy, but once the glue seeps through they did seem to lose it.

Do you think something like this would work, cutting it overlong, pinching the towels and stapling so it looks like pic on the right?

It is Prime day on amazon, maybe could do with a new duvet ;-)