Thread: enclosure sound baffles...

[QUOTE=Kuffy;1837491]How do i vent the air from the cupboard without the sound escaping as well? aka...how do i design the baffle?
Is it simply a case of just building a Z type maze so the air can escape, but also making the sound waves bounce around so much that they eventually run out energy?[QUOTE]

Pretty much. Mine is a more of an "M" than a "Z" but have a look here.
https://www.woodworkforums.com/f245/b...70/index9.html

Mine is lined on one side with foam

also...if i have a 6inch inlet to the dusty, that means the vent should be atleast double the cross-sectional correct?

Mine is 4 times the area so the resistance is even lower. Bear in mind that this will release more sound and take up more space.

thanx bob

I guess im on the right track. ill just make my baffle area about 50,000sq/mm which is about 2.5 times the intake and ill line it with something, some foam, some fatbatts, old plush carpet...something that will absorb the waves.

How about egg cartons? That way the sound waves will reflect off randomly and theoretical have less chance of escaping.

Originally Posted by johnredl

How about egg cartons? That way the sound waves will reflect off randomly and theoretical have less chance of escaping.

It beats me why egg cartons get so much airplay in this regard.
To reflect sound the material must be dense ,e.g., concrete, steel or lead, while to absorb sound the material should be thick and and full of still air, neither of which are properties of egg cartons.

Right...disregard me

well i built the enclosure...and eagerly got out my android decibel meter. I was very disappointed with the results. the dust extractor as is outside the enclosure is about 103db on my app. inside the enclosure it is still 103db, and to the ear it sounds about as loud. inside the enclosure you cant hear any of the air moving around in the bags...so thats slightly better

what have i done wrong?

I built a cupboard 1700 wide x 700deep and 2200high all out of 18mm MDF. I used a 70x35 merch pine inner frame. inside the box there is no light coming thru so i suspect all airgaps are gone. I also have a M shaped baffle which vents the air back out of the box with foam lining. On the inside of the cupboard I lined all interior walls with 100mm earthwool. I put the cupboard on castors so I can move it, because since there is about 5 sheets of MDF in it, it weighs about 200kg without the dust extractor inside. The castors have nylon wheels.

Here are some pics.

IMG_20150126_160819_nopm_[1].jpg20150127_152755[1].jpg20150127_152822[1].jpg

hmm....they r all upside down...but u get the idea.

That's quite disappointing.

One problem I can see is because the DC wheels sit hard on the floor of the enclosure, and then the enclosure itself is on wheels means the whole enclosure has been turned into a resonator.
I would work on this aspect first.

Making the enclosure mobile means that the whole enclosure can easily flex - this is a major problem and there's nothing you can really do about this short of making the hard and soft components thicker/heavier.

Fixing the enclosure to a wall and floor is an easier way to do this. The floor of mine is paving bricks and the walls are Colorbond, 32 mm melamine/chipboard, 50 mm of insulation and the 16 mm of MDF on top of that. The whole thing is bolted to the shed wall which is a 600 mm spaced 75 x 50 Jarrah stud wall so it is very rigid. of the enclosure

One thing you could try is to add some angular bracing on the outside. You say you used a 70 x 30 mm frame but your pictures show a distinct lack of framing under the floor (the MDF floor even looks like its bending under the weights of the DC) and none of the doors have framing around them of any kind let alone any framing across their middle. The same applies to the walls - this will turn them very easily into resonators. My doors are framed in 30 x 70 pine and then lined with 32 mm melamine. At 18 mm I would be using framing across the middle of some kind.
The whole frame should probably have been be built as sections of a stud wall with 450 mm spaced uprights. This will prevent the walls and doors resonating.

The other thing that would be needed is to decouple the DC from the enclosure floor. I would use some thick (100 mm) dense foam that support the DC frame (not the wheels). 3-4 layers of rock wool might work

The next thing that I can see is the way the light weight insulation is nailed down. It more effective to make large pockets so the rock wool can sit neatly/firmly inside these pockets. My pockets are covered with 16 mm MDF

Just because the cupboard appears light tight is no guarantee that it is air tight. Some foam on the door edges and multiple door fixtures around the door edge to force the door into these will help. Provided the door is well framed this will reduce the resonating effect.

BTW where are you measuring the SPL. The defector standard we use here is 1m away at waist height and another measurement at 3m away (also waist height)

Hmm, so things aren't looking too good, but thats ok, I can fix..I hope.

I measured the sound all around the garage from 1meter away to 7meters away. it fluctuated between 103db and 101db.

First thing ill try is to remove the castors from the cupboard as well as the castors from the dust extractor base. and then ill sit the unit hard down on the concrete slab. This I hope will prevent/absorb the resonance. If that doesnt help enough, ill screw the cupboard back against the wall which divides the garage and home theater, it is 10mm gyprock either side with acoustic batts inside, it is a load bearing wall.

so long as I can get the sound down to about 85-93db, that will be good enough, my panel saw runs at 90db and I dunno about the jet combo buzzer/thicky with helix..thats probably around the 82-84db range.

well i quickly removed the castors from the cupboard...and leaving only one major ding in the wall when the thing nearly fell over.../shrug

the noise is now only 96db, so just by putting it on the concrete it removed 7db without any hoses connected..this will reduce it further i believe.

its late now, tomorrow ill remove the castors from the dust extractor, and line the base with enough earthwool so it jacks the outlet height high enough to to compensate for the inch or so i lose from removing the castors.

I also noticed I hadnt put any insulation around the baffle thing and the center front panel /doh!

I reckon after these couple of mods, it will achieve no more than 90db..that will have to be good enough since its 90db inside the garage..by the time it passes thru the brick veneer build to boundary wall, it will have reduced heaps and there is a 35meter strip of parkland out the front of the house. so good enough

Originally Posted by Kuffy

Hmm, so things aren't looking too good, but thats ok, I can fix..I hope.

I measured the sound all around the garage from 1meter away to 7meters away. it fluctuated between 103db and 101db..

That's awfully loud, especially for a DC7. I wonder how accurate your app is?
The sound variation with distance will only work outside. Inside a shed there is too much for the sound to bounce off.

First thing ill try is to remove the castors from the cupboard as well as the castors from the dust extractor base. and then ill sit the unit hard down on the concrete slab. This I hope will prevent/absorb the resonance. If that doesnt help enough, ill screw the cupboard back against the wall which divides the garage and home theater, it is 10mm gyprock either side with acoustic batts inside, it is a load bearing wall.

I reckon you will also need to stiffen the panels that make up the back and front of the enclosure.

so long as I can get the sound down to about 85-93db, that will be good enough, my panel saw runs at 90db and I dunno about the jet combo buzzer/thicky with helix..thats probably around the 82-84db range.

.

I doubt you will get that sort of reduction (103 -> 85) without increasing the thickness of heavy material being used and making the framing a lot stiffer.

i am only using the app as a reference. Im sure it isnt 103db, because i know roughly how loud each machine is, for example circular saw with bushes are about 105-110db and those things make my ears bleed. the dust extractor noise isnt making my ears bleed so its probably more like about 90-93 in real terms.

Originally Posted by Kuffy

i am only using the app as a reference. Im sure it isnt 103db, because i know roughly how loud each machine is, for example circular saw with bushes are about 105-110db and those things make my ears bleed. the dust extractor noise isnt making my ears bleed so its probably more like about 90-93 in real terms.

When you get a chance see if you can compare it to another phone running an SPL app or better still an SPL meter.

So after running around all day looking for stuff I started working on the enclosure a bit more.

I added the insulation behind the center front panel, added some insulation and plush carpet beneath the dust extractor (which is still sitting on its own castors).
Messed around with the two doors so they fit slightly better and added a couple of latches top and bottom of the doors.
quickly plumbed in some 6inch flexi 3600mm long, running to that 3way 4" splitter that comes with the dusty and ran 2 @ 3m 4" flexi of that into my panelsaw (which sadly only has 4 inch ports above and below the table...my review of the LEDA Prima 2500 panelsaw to come later on...short version is, it aint bad, aint fantastic)

So after starting with 103dB with the dusty out in the open garagewithout enclosure. Im now down to 92dB with the doors open and 86dB with the doors closed. Inside the theater which is the wall directly adjoining the dusty you can hear it running, but my app says about 46dB. outside the garage standing next to the brick veneer boundary wall, you can't hear the dusty at all, the wind from outside was much louder. You can only hear the dusty outside the garage standing next to any of the three roller doors I have which are about 2400wide/2200high.

A different app, same samsung galaxy note device, says it is 82dBwith dusty inside the enclosure.

i'm pretty happy with it at this point in time. at the very least I have taken out much of the bite of the low frequency noise from the dusty, and it is now quieter than the panelsaw which is 90-91dB, its probably on par with the combo buzzer/thicky.

Thanks BobL and everyone else.

Good to hear about the improvement.

It's interesting to see/hear that just a small amount of decoupling of the DC from the enclosure made such a difference.
I reckon if the enclosure itself (especially the large areas of unsupported MDF) was a lot stiffer this would also reduce this effect.

Your experience is worth noting by newbies.
It is really important to consider flexibility/stiffness as well as mass of material used.
A 30 x 70 pine stud wall clad both sides with only 6 mm MDF and loose filled with 70 mm of insulation may work better than an unsupported 16 mm thick sheet with 100 mm of insulation nailed to it.