Thread: Sound insulation for garden shed setup

You will find the info needed to make a muffler for your DC, in a thread started by BobL on 31st March 2015. The thread title is BAFFLE BOX/MUFFLER FOR DC ENCLOSURE. You can use 2nd hand materials or offcuts for most of it, to keep cost down.

BobL is very knowledgeable on noise control and dust collection. You can learn a lot by reading his posts.

You might like to post a picture of your muffler when completed and comment on its effectiveness.

Good luck, Rob

It would have been better to ask your question before installing the DC inside a garden shed because retrofitting sound insulation is usually more difficult than building it into the shed to start with.

From what I can see of your shed it does not appear to have a dedicated air outlet although there may be one around the back.
Relying on the gaps in the shed construction usually still generates too much "back pressure" and will restrict the flow so some sort of sound insulated baffle box will be needed.
The gaps may not let much air out but they will let a lot of the sound out so these have to be blocked up
Baffle boxes themselves also generate "back pressure" so to reduce that they need to be made large but of course that take up space.
I recommend the cross sectional area of a baffle box be around 4x that of the ducting you are using.


There absolutely no getting around sound insulation without using
1) As thick and stiff as possible a layer of dense material on the outside - this reflects sound back into the enclosure. Sheet metal is dense but generally too thin and flexes so it does not work so well.
Wood like chipboard works provided it is thick i.e. 20 mm or more. I used 38 mm melamine/chipboard on mine. This material needs to be mounted on a stiff frame to be at its best but could be screwed or bolted to the sheet metal of a garden shed provided the shed can support it.
and
2) as thick as possible a layer of low density material - something that contains small pockets of air - this absorbs the sound as it bounces around back and forth inside the enclosure. Material like foam, cardboard or even most thermal insulating material usually work. It needs to be reasonably thick to be effective, at least 50 mm and preferably 100 mm. I use 100 and 75 mm foam rubber mattresses I picked up during kerbside collection week on my doors and rock wool insulation on the sides. Mine abuts onto my shed, the inside of which is insulated and lined with gyprock and then a large cupboard is located up against the wall. Cardboard sounds easy until you realise how much is needed to create a 50 mm layer of it.

The acoustic materials need to cover the ceiling as well as the walls.

Now you can see that the acoustic materials take up a lot of space which means your shed may not be large enough.

Specific details about my DC enclosure are here
BobL's shed fit.

Get your self a Sound Pressure Level App. These fellow you to measure the SPL before and after you do something so you can tell if what you are doing makes a difference.
I recommend measuring SPL at 1m above the ground and 1 and 3m away from the sound source. That way you can compare against what other people are measuring on the forum.

I'm little confused. Am I building a muffler inside the DC? Or sound insulation in the shed? Also what is a baffle box? Is that a box outside of the entire shed ? Or just a small box inside the DC?

Originally Posted by wwf9984

I'm little confused. Am I building a muffler inside the DC? Or sound insulation in the shed? Also what is a baffle box? Is that a box outside of the entire shed ? Or just a small box inside the DC?

A baffle box is essentially the same as a muffler.

A muffler usually refers to a tube of moving air like a car muffler and a baffle box usually refers to a volume of noisy air that needs to be allowed to escape quietly.

Either can be built inside the shed with a large opening to the outside, or outside the shed with the same opening between the shed and the external box/muffler
It's easier to build it inside the shed because then it does not need to be made out of waterproof materials e.g. chip board

I thought the muffler was actually fitted inside the hose. So it's essentially a wooden box which the hose feeds into?

Originally Posted by wwf9984

I thought the muffler was actually fitted inside the hose. So it's essentially a wooden box which the hose feeds into?

If the box is smaller than the pipe (i.e. fits inside the pipe) it will severely restrict the flow.
Look at car mufflers - these are always larger than the pipe that is carrying the escaping exhaust.
eg
ToyotaExhaust.jpg

Even this design using small internal piping is too tortuous for a dust extractor muffler and will suppress flow.
A car engine can afford to use such small pipe because its exhaust has a large pressure behind it,
Mufflers for dust extractors are used mainly on cyclones where the exhaust air is already contained into a 6" or 8" duct.
Baffle boxes are more suited to a large volume of noisy air like the inside of a shed containing a DC.

So I would have a short hose feeding into a baffled box. Then the other side will also hook up a hose which goes to my machines.

Originally Posted by wwf9984

So I would have a short hose feeding into a baffled box. Then the other side will also hook up a hose which goes to my machines.

No hose needed that will just restrict the flow - the air from inside of the shed goes straight into the baffle box

Like this - the beige/orange colour inside the box represents some foam or similar material .


As I said before mufflers suit cyclones where the air coming out of the impeller is already inside a tube
At the mens shed we have a cyclone and the muffler we made for it was very simple.

Muffler.jpg
A 400 x 400 x 1800 mm Chipboard box lined with 100 mm of thermo/acousktic insulation held up against the insides of the box by a 200 mm diameter chicken wire (the dashed lines) tube.
Unlike a DC te muffler connects direct to the outlet of the impeller
This muffler takes up lot of space but that is no problem as the cyclone has a footprint that is smaller than most large DCs and the enclosure we have constructed is 3 x 1 x 3.3m (i.e. huge) although it also has to hold a large compressor.

so the muffler is simply to vent air out but through a baffled box?

I've actually tried to close the entire door on the shed, due to material of the shed(thin metal sheets), the noise is still quite loud.

To be honest, unless I wrap the entire shed with insulation and have a baffled box, I don't think the baffled box does anything. Am I right?

The baffle box or muffler is simply the final part of sound insulating - it's there to make sure that there is no back pressure on the dust extractor by providing a large, low resistance outlet for the air that the dust extractor is pulling out of your garage at the same time as minimising sound transmission through this outlet.

You'll need to see if you have around 100mm or more clearance on all the walls, roof and door of your dust collector shed, as to sound proof them (cheaply) you'll need to line them with both more mass (for example 30mm MDF or three sheets of gyprock) and a sound diffusing material like rockwool.

If that sort of clearance is not available then you'll have to work around the clearance you have, using bulky and massy materials where possible, and seeing what else you can do where you don't have the room (such as using some of the proprietary sound deadening materials like mass loaded vinyl - the stuff sold in car audio shops).

Master Splinter has pretty well nailed it but to answer your questions specifically.

QUOTE=wwf9984;1918950]so the muffler is simply to vent air out but through a baffled box?[/QUOTE]

No, either use a muffler OR a baffle box.

Muffler makes more sense for a cyclone, Baffle box for DC enclosure/shed.

I've actually tried to close the entire door on the shed, due to material of the shed(thin metal sheets), the noise is still quite loud.

That's exactly why I said you should have asked your questions BEFORE building the shed out of just sheet metal.

To be honest, unless I wrap the entire shed with insulation and have a baffled box, I don't think the baffled box does anything. Am I right?

Correct. if it was me I would start again and take all the things in this and other threads into consideration.