# Soundproofing attempt! Enclosure for a noisy dust extractor



## OscarG (3 Jul 2018)

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?!


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## clanger (3 Jul 2018)

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


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## OscarG (3 Jul 2018)

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 rubbish and burn it!


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## Bucks woodshop (3 Jul 2018)

Im struggling with noise too interested to see how this goes 

Sent from my SM-G935F using Tapatalk


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## Chris152 (3 Jul 2018)

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.


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## AES (3 Jul 2018)

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.


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## OscarG (3 Jul 2018)

Chris152":3h06whpf said:


> 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.


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## Chris152 (3 Jul 2018)

OscarG":2sosw1n4 said:


> 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.


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## sunnybob (3 Jul 2018)

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.


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## OscarG (4 Jul 2018)

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?


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## sunnybob (4 Jul 2018)

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.


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## OscarG (6 Jul 2018)

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 water-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 rubbish idea?


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## sunnybob (6 Jul 2018)

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.


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## OscarG (16 Jul 2018)

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!


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## AES (16 Jul 2018)

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?


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## sunnybob (16 Jul 2018)

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.


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## OscarG (16 Jul 2018)

AES":21p6xs19 said:


> 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.


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## sunnybob (16 Jul 2018)

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


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## AES (16 Jul 2018)

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.


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## OscarG (16 Jul 2018)

sunnybob":3vgpz95i said:


> 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?
> 
> ...



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 ;-)


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## sunnybob (16 Jul 2018)

If you did that over the existing, I'm sure you would notice the difference.
Decibel scale is logarithmic. every decimal place is ten times the difference. 1 whole number is a hundred times difference.
you can see on the scale below you have gone from hearing damage after 8 hours to loud traffic. If you can get another 5 reduction you should be happy.
As far as distance from noise source, remember you have a phone app. Its nowhere near as accurate as a calibrated laboratory meter (which is what the manufacturers will have used), so in this instance you are just looking for a reduction, so take all your reading at the same distance and you will get an accurate reduction value.

The Decibel Scale
From rustling leaves to jet engines, here's a quick guide to some everyday sounds...
Level in decibels	Everyday example	Times more intense	Times louder
10dB	Rustling or falling leaves.	
20dB	Watch ticking.	
30dB	Birds flying by.	
40dB	Quiet conversation.	
50dB	Louder conversation.	
60dB	Quiet traffic noise.	
70dB+	Louder traffic	
80dB+	Loud highway noise at close range	
85dB	Hearing damage after about 8 hours. 
100dB	Jackhammer (pneumatic drill) at close range	
100dB	Hearing damage after about 15 minutes. 
110dB+	Jet engine at about 100m	
120dB	Threshold of pain. Hearing damage after very brief exposure.


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## Fidget (16 Jul 2018)

AES Wrote:
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?[/quote]

Top of the page under the page number there are 4 icons

email
Print
Subscribe
Bookmark

HTH


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## MountainMan (16 Jul 2018)

Close but not quite right. It is a base 10 logarithm and "decibel" is 0.1 of Bel but no one uses Bels.
Where you were wrong is saying each 0.1 was and order of magnitude, it isn't. It's the other way around.

So change of 1 Bel is x10 in power. That means 10 dB is x 10. So the "sound power" you measure when you drop from 87dB to 77 dB is 90% reduction. Good work! In terms of damage to your ears you've improved the situation.

Unfortunately human perception more fits the logarithmic scale so 77 compared to 87 feels more like 10% than 90% reduction. But to compare with standard noises you've just gone from the high 80s where you would worry about damage in 8 hours to 70s where you might be annoyed listening to music that loud all the time.

Personally - I'm going to house my extractor externally for just this reason. I think it will be easier to direct the noise away than simply muffle.


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## AES (16 Jul 2018)

Thanks for that fidget. Thread now bookmarked!

And thanks to sunnybob and mountainman for the noise "chart" info. Copied n printed out.


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## TopCat 32 (16 Jul 2018)

i got a record power 1000 dust extractor, i want to build a sound proof box for, anyone point me to the original posts from sunnybob and Eric projects, so i can study


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## sunnybob (16 Jul 2018)

Topcat; the pics on this thread alone get you almost all the way there. Its just a box shrouded in soft layers of material with an exit channel also likewise covered.
I cant find my original, it was a couple years ago and I'm not scrolling through 3000 plus posts :roll: 

But to put you straight. It WILL NOT be SOUNDPROOF. Taking it down from hearing damage to a slightly noisy background can be done quite cheaply.
If you want soundproof, youre into hundreds of pounds on materials alone

22mm mdf is the most sound deadening material for this job.


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## will1983 (17 Jul 2018)

Shamelessly copied from another UK woodworking forum;



> I finished a project last night that I've been working on for a few weeks now.
> 
> I bought a Bosch GSM10s mitre saw from Axminster but was not impressed with the built in dust collection so designed a dust collecting hood to fit behind the existing fence to capture as much saw dust as possible yet maintain the full use of the saws mitring functions.
> 
> ...


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## AES (17 Jul 2018)

Neat job. How did the EP sheet do as a noise reducer please (as opposed to the OP's bits of old towel on baffles)?


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## will1983 (17 Jul 2018)

Well I haven't done any scientific testing but it is definitely quieter.

The main reasons for doing this were;
Connect extraction to the MS because I was sick of hovering up after using it.
Make use of the noisy extractor.
Make the dust separation better because I didn't want to be breathing in the muck that it was throwing out.
Make something for the MS to sit on because its really really heavy!
Make something mobile that I can shift when I need the space in the workshop.

I'd say it has done pretty much all that and the sound deadening is a nice little extra.

Will


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## TopCat 32 (18 Jul 2018)

sunnybob":4bhiwj3u said:


> Topcat; the pics on this thread alone get you almost all the way there. Its just a box shrouded in soft layers of material with an exit channel also likewise covered.
> I cant find my original, it was a couple years ago and I'm not scrolling through 3000 plus posts :roll:
> 
> But to put you straight. It WILL NOT be SOUNDPROOF. Taking it down from hearing damage to a slightly noisy background can be done quite cheaply.
> ...



cheers, Bob, if i could reduce the noise that would be great, and thanks for the heads up re 22mm mdf, i was heading for about for about 12mm , so thanks again


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## sunnybob (18 Jul 2018)

22 mm is a good compromise. Thicker is always better, but the price and the weight of anything thicker gets a bit silly.
Remember LOOSE padding in the container and ducting. Hanging curtains absorb a lot more sound than ones glued to a wall.

As long as you can get it down to a volume that you can talk normally standing next to it, your hearing is safe. Quieter than that starts to eat into your bank account very quickly.


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## Chris152 (18 Jul 2018)

I used this in mine as I had some left from doing the van and garage door. Easy to fit and works well, I think.
https://www.kiravans.co.uk/thermo-acous ... r-surface/


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## lurker (19 Jul 2018)

If you have truely reduced the sound pressure by 10dB then it is 90% quieter.
3dB less is half the noise.
So even assuming your measuring device is poor I think you can assume you have done a good job there.


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## lurker (19 Jul 2018)

AES":19wfy6sa said:


> 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.



Inverse square rule 8)


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## OscarG (23 Jul 2018)

*Update time*.

Thought I'd try improving it, and bearing in mind comments about towels being too tight I thought I'd try lining the inside with an extra layer, stapling it to get a concertinaed look. I didn't have any more donor towels so thought I'd try a blanket .

So one day, one butchered blanket and an entire box of staples (all 1000 of them) later I have a box, baffle box, lids and doors looking like this.




















Did the same before and after to compare. With door open, 78 dB. 
With door closed on new green blanket lined effort....... 73 dB. 

73 dB  

I did several readings to verify but it's definitely got worse!! 

Even without looking at meter I knew with just my ears soon as I switched it on something had gone wrong. Before adding green blanket, with box closed it sounded like a different pitch, like a hoover in another room. Now the pitch is same as with the box open. It's a bit quieter than with door open but still has that unpleasant shrill high pitched whine which I eliminated before I added that green blanket.

I'm annoyed I wasted a day doing this but really puzzled, how can adding a blanket make it worse?! Do you think it's too tight around the machine and maybe a little more empty space is needed to make it breathe? The air is still flowing out of the exhaust port so I know that's not blocked.

Really fed up with this thing now, tempted to start again with bigger box lined with proper acoustic foam.


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## thick_mike (23 Jul 2018)

That’s Science! 

I had three years doing a PhD that was exactly like that. Come up with a good idea, design an experiment, look at results...come up with a new idea.

Could be turbulent flow, or restriction of air flow due to narrower exhaust making the motor work harder. That could be what the screaming noise is?

One way to investigate is to take the vac out of the box and put your hand over the exhaust. Does the screaming noise get worse?


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## giantbeat (23 Jul 2018)

im a bit late to this thread, been an interesting read... i have done a far bit of sound treatment in my life, i have built 3 recording /rehersal studios in the past 10 years.

what i was going to say when i saw your first attempt is what Bob was saying re the lining, make it loose, make it completely random... essentially with sound treatment you have 3 tools to fight how the sound travels....

mass (thick dense walls to block & shield)
absorption (soft layers to muffle) 
random surface treatment via baffles (odd shapes to break up the waves) 

the first attempt was certainly missing the latter, so randomizing the inside with loose material would as Bob said would be the way to go.

im slightly confused as to how you have made it worse with your latest attempt, if anything i would have expected it to be about the same... however you do seem to be going for consistency on your work & that goes against you in sound treatment, the air & sound will just roll over it.

i would have placed my baffles at varying spacing (keeping in mind not to restrict airflow but allow areas that let it pool before moving on & i would have also suck off cuts & random shapes to them before i then lined them with a material & foam, but the messier & more inconstant the better. 

this is exactly how we build ventilation ducts for studios where we needed reasonable sound proofing but still want fresh air.


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## sunnybob (23 Jul 2018)

If the pitch is higher, then there is a hard surface leak.
Low frequency notes are like long waves, they bounce around very slowly and those blankets are absorbing them without a doubt.
High frequency notes bounce around like a swarm of bees on speed, bouncing again and again with their energy and escaping through any sized hole.

looking at your cabinet, the finger of suspicion points directly to that hose connection. It appears to be a HARD plastic tube that the plastic hose slides through. I suggest you reassemble the cabinet and wrap another blanket or even a thick woolly jumper around that port hole and see what happens (oops, HEAR what happens).

Dont get too hung up on decibels. The digital meter age has a lot to answer for through being just too damn accurate. Its your hearing that counts, nothing else (unless youre writing your thesis on it). Once you have an acceptable level, the job is done.


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## OscarG (23 Jul 2018)

thick_mike":wnr8nhkf said:


> One way to investigate is to take the vac out of the box and put your hand over the exhaust. Does the screaming noise get worse?



Kind of hard to cover exhaust, there's no one single exhaust point, it comes out around the perimeter of the motor like this...






I'm wondering if those loose folds are maybe moving in the breeze of the exhausted air and their movement creating some speaker type effect?


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## OscarG (23 Jul 2018)

sunnybob":nidpfphi said:


> If the pitch is higher, then there is a hard surface leak.
> Low frequency notes are like long waves, they bounce around very slowly and those blankets are absorbing them without a doubt.
> High frequency notes bounce around like a swarm of bees on speed, bouncing again and again with their energy and escaping through any sized hole.
> 
> ...



I initially thought (and hoped!) leak too, especially as front door is bit tight and maybe forcing it shut had opened up some gaps in the top. I went round with extra screws closing up any gaps, even the removable door is now screwed in place. Sadly it didn't help.

I take your point about the plastic pipe but it's the same as it was before when it had lower pitch. 

I suppose I could simply rip all that blanket out, go back to what I had before. Just amazed how adding a soft, rippled layer could actually make it worse!

The motor's always been a little warm after use but after feeling it after a couple of mins in the blanket box it was really bloody hot! Don't know if that's a factor, maybe a sign the exhausted air isn't being removed quick enough?


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## OscarG (23 Jul 2018)

giantbeat":3t2epcf6 said:


> im a bit late to this thread, been an interesting read... i have done a far bit of sound treatment in my life, i have built 3 recording /rehersal studios in the past 10 years.
> 
> what i was going to say when i saw your first attempt is what Bob was saying re the lining, make it loose, make it completely random... essentially with sound treatment you have 3 tools to fight how the sound travels....
> 
> ...



Thanks for your post!

I'm due to pick these up tonight...







I was thinking I could cut them down and fit them inside cabinet. Do you think these would work or would I be better off getting that spikey acoustic foam type stuff?


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## MikeK (23 Jul 2018)

I'm also coming to this dance late, but I think you might be chasing unicorns by trying to build a sound enclosure for your vacuum that is not much larger than your vacuum. I test a lot of rooms for work to make sure the sound doesn't go where it's not supposed to go, and mass is definitely your friend when trying to block sound.

I never saw much success with acoustic foam as a sound absorbing material, but it does well for reducing resonance and reflection. From my experience, most foam and fabric materials are transparent to sound. For a quick treatment of walls, we used mass loaded vinyl sheets or MDF panels glued directly to the surface with acoustic sealant.

I notice you don't have any gasket material on the joints where the panel meets the enclosure. Sound flanking can be difficult to correct, and not having a good rubber gasket to seal the gaps makes it easier for the sound to pass. This could be the source of some of the whistling you hear. Doors and panels are especially difficult, but good astragal seals help.

Another point to consider is the exhaust port, where size, shape, and path are everything. A Z-duct is good at reducing the sound amplitude by absorbing the energy at each change in direction. However, the ducting must be appropriately sized so it is not restricting the airflow and contributing to the sound. Your vacuum is pulling in air at a high pressure, but your exhaust port must be much larger in order to allow the exiting air to leave at a lower pressure. Using a smaller than required port size for the exhaust will contribute greatly to the apparent sound. Increasing the area of the exhaust port will lower the velocity of air while attempting to retain the same volume of air passing through the system.


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## sunnybob (23 Jul 2018)

sound frequencies are all around at the same time. if the base note is loud it will overpower the treble notes. remove the base and suddenly the treble is very annoying.
i dont think you made it worse, i think you altered it and you now hear different things that have been there all the time but just covered up. Its just like a detective story, you have to hunt one clue at a time. Thats the part I actually enjoy.
I never used any form of measuring on mine. Its was loud and annoying, i built a cabinet, its now a lot quieter and no longer annoying, I have no idea of decibels involved, but the job is done.

One extra thought, are you sure your intake is not blocked? harsh increase in noise and hot motor suggests to me that it is.

keep us informed.


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## Brandlin (23 Jul 2018)

The logarithmic scale of decibels and the inverse square law that dictates the wave energy as a function of distance combine to make any measurement with a meter very sensitive. Add into this mix the inaccuracies in a cheap meter/phone app and differences in air pressure and temperature and you are in a position where your meter reading comparisons are going to be next to meaningless. 

Sound measurement is a VERY sophisticated science. not helped by the fact that the human ear and brain is actually total carp at judging volume. Trying to resolve this down to a single Db number is futile and counter productive.

I strongly doubt you made it worse. What happened is the material you added removed a lot of the lower frequency and you can now hear the higher frequency notes that were already there.

I agree with what giant beat has said. In general terms your work is far too regular. You need to break up the waves by being random. There is nothing wrong with the cheap materials you are using and I strongly doubt you will see any improvement in spending money on commercial foams.

The last thing you want is a square box that encourages regular reflections of waves. And even though you have made a long 'baffle tunnel' you made it a regular size with 90 degree corners, you need to break up ANY regularity as much as possible. You also need enough space around the vac to allow air movement and deflect, break up and absorb it, a bigger box means you can get more irregularity in there.

A smaller issue is that you might want to insulate the box from the surface it sits on. One option would be to suspend it on short bungy chords under your bench. Though i doubt this is a significant contributor.


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## OscarG (23 Jul 2018)

Thanks for input, will take the time to read everyone's comments.

My head's buzzing at the moment, thought I'd quicky make this. Do you think the design on the right would be better?






I'm wondering if currently I'm wasting the lower half of the box and the air is exhausted before it's "tamed" if that makes sense?

I'm thinking in the 2nd design there's more of an enclosed wall around that noisy motor and the exhausted air will be forced to travel further and hopefully lose some intensity before it enters that baffle box.


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## sunnybob (23 Jul 2018)

I'm not all fancy pants drawings like you (lol) so I have very quickly sketched out my system.
One point, because the thing is fully enclosed inside the box, I removed the top motor cover to allow air to move more freely. There was a foam cover over the motor as a very poor attempt at sound deadening, that went as well.


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## OscarG (23 Jul 2018)

sunnybob":yuoj5rs0 said:


> sound frequencies are all around at the same time. if the base note is loud it will overpower the treble notes. remove the base and suddenly the treble is very annoying.



ah! So the green blanket (now known as the stupid green blanket) might have acted like a graphics equalizer, turning down the bass so I notice the treble more!?

That actually makes sense and provides an answer as to why it seems "whinier" now!


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## sunnybob (23 Jul 2018)

Speaking as a hi-fi audiophile from the 60's....and paraphrasing the original quote....
By george, He's got it.
=D> =D> =D>


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## OscarG (23 Jul 2018)

Brandlin":ns5ovwn6 said:


> The logarithmic scale of decibels and the inverse square law that dictates the wave energy as a function of distance combine to make any measurement with a meter very sensitive. Add into this mix the inaccuracies in a cheap meter/phone app and differences in air pressure and temperature and you are in a position where your meter reading comparisons are going to be next to meaningless.
> 
> Sound measurement is a VERY sophisticated science. not helped by the fact that the human ear and brain is actually total carp at judging volume. Trying to resolve this down to a single Db number is futile and counter productive.
> 
> ...



Thanks for post!

Maybe I should just ignore the towels/foam and just use MDF as thick as possible, make the walls 36mm thick.

To combat the regularity, do you think something like this would work?

Inside walls of a (much bigger) box, with glued/screwed on bits of MDF random shaped nonsense.








I've learned so much from this thread and you guys, thanks so much!


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## sunnybob (23 Jul 2018)

I think youre ready for the big time now,
go surf for an "anechoic chamber"

:shock: :shock: =D> =D> =D> =D> =D>


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## OscarG (23 Jul 2018)

sunnybob":qav4mvkf said:


> I think youre ready for the big time now,
> go surf for an "anechoic chamber"
> 
> :shock: :shock: =D> =D> =D> =D> =D>



Holy moly!





Got my work cut out!

I have to say and I know this terms seems to be dirty with regards to sound reduction, but doesn't it seem a little ahem..."regular", repeated patterns? Doesn't seem that random?!

Do you think If I buy a load of Stealth Bomber models and glue them to inside of box it'll work?


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## sunnybob (23 Jul 2018)

I thought you might like that. :twisted: :roll: 

Its all about the angle of the dangle. If you can reflect EVERY frequency before it reaches your ears, you have absolute silence.

Sound waves is even more complicated than tropical fish keeping (but only just)
Dont give up the fight. 8) 8) 8)


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## OscarG (23 Jul 2018)

ha... just been reading about how the Stealth Bomber works, seems it the same principle, all odd angles and curved surfaces so nothing gets reflected back to the radar.


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## Lazurus (23 Jul 2018)

Blimey this all seems a lot of work and expense chasing a holy grail. How about a weatherproof box outside the workshop feeding the inlet through the wall, cheap and easy fix?


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## Brandlin (23 Jul 2018)

OscarG":3njnnygp said:


> Maybe I should just ignore the towels/foam and just use MDF as thick as possible, make the walls 36mm thick.
> 
> To combat the regularity, do you think something like this would work?



Extra mass helps. But if you ONLY use increased mass to damp then you need LOTS of it. Going to 36mm MDF may help, but its a lot more expensive than putting in additional wadding to absorb sound.

I would:

1. Stick to 18mm MDF but make the box bigger to give greater airflow, allow for more dampening material inside.
2. dont mount the vac in the dead centre and make the inside of the box have varying corner angles (mitre off three corners say) so you try to reduce any way you can get a standing wave.
3. build a 'Z' baffle as you have but make each tunnel section a different dimension and don't make every turn 90 degrees.
4. *Roughly *cover the insides with the kinds of material you already have done but bunch them up randomly.
5.Insulate the Vac from the box on soft rubber feet or hung on bungees. Use thick rubber seals on any openings like doors.
6. Accept you simply wont make it silent and ANY improvement is great.


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## OscarG (24 Jul 2018)

Thanks Brandlin, I'll try that.

I went on a bit of an anechoic chamber and diy sound baffle youtube journey last night. Interesting, apparently staying in an enechoic chamber too long can make you go a bit loopy!

They had some people making DIY sound absorption baffles using Rockwool sound insulation. Seen I could get some for £25 from Wickes, do you think that would work better than towels for this dust extraction silencer application?

I discovered people talking about reverb rooms and how none of the walls are parallel to stop standing waves. That worried me a little as I thought the effects of a reverb room are what I'm trying to avoid? Sorry if I've misunderstood that.


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