Soundproofing attempt! Enclosure for a noisy dust extractor

[sunnybob]

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.

 

[Fidget]

AES Wrote:
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HTH

 

[MountainMan]

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.

 

[AES]

Thanks for that fidget. Thread now bookmarked!

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

 

[TopCat 32]

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

 

[sunnybob]

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.

 

[will1983]

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.

Made from 1/8" ply

This has two 68mm ports, one each end, built in to receive plastic guttering down pipe.

I wanted the saw mounted on a mobile unit that contained a Draper extractor. I bought the Draper unit about 3 years ago but despite having lots of suck it was very noisy and didn't have the best filtration. I raided my scraps pile and built a cabinet and fitted some locking castors from amazon. I found some 30mm polystyrene sheeting on Freecycle so 2 layers of this lined the cabinet to soundproof it to some extent. To provide the necessary extra filtration I bought some of these panel filters off eBay.

The door of the cabinet was designed around the filter units and allows them to be removed for cleaning or replacement as required. As the cabinet is sealed it forces the air expelled from the dust collector to pass through the filter.

The pipework runs down the back of the mobile cabinet to a 110mm soil pipe straight connector which I butchered to make a bulkhead fitting. To combine the two 68mm pipes I made a custom Y connector. I also drilled the Y connector to take a 30mm flexible hose fitting from the saws factory dust outlet.

To power both the extractor unit and the saw I installed a double socket on the side of the cabinet and tidied up all the cables with clips. The lead to power the socket is about 2m long and can be coiled up on the side of the unit when not in use.

I did some preliminary testing, I cleaned up everywhere around the saw with the hoover until it was spotless and then turned a 3" length of 2x2" softwood to dust. I'd say it collected 90-95% of the saw dust which is a massive improvement over the original arrangement.

For some videos showing the system in more detail look up my Instagram account in my signature.

Will

 

[AES]

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)?

 

[will1983]

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

 

[TopCat 32]

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.

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

 

[sunnybob]

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.

 

[Chris152]

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/

 

[lurker]

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.

 

[lurker]

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)

 

[OscarG]

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.

 

[thick_mike]

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?

 

[giantbeat]

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.

 

[sunnybob]

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.

 

[OscarG]

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?

 

[OscarG]

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.

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?