Thread: Sound Insulation

John concerning the flexible HAVAC duct....um problay no benifit...the insulation on air con duct is primarily intended to be thermal.

There should not be much noise on the discharge pipe and most of that will come out the end of it.

There are greater benifits to running PVC pipe which has a smooth interiour, that will produce less backpressure, turbulance and resutant noise than any flexible.

Remember you need to isloate the blower from both the incommin and outgoing duct if you are getting fussy about controlling vibration and resulatant noise.

Scott.
Remember one thing about all upspec plaster products, mostly they are marketed in response to a desire rather than significant improvements in engineering performance.....and usually in comparison to other down spec plaster products.

I have not looked at the specs recently, but go have a look and compare the soundcheck to other upspec heavy plasters or even just thicker down spec product and tell me if there realy is any justification to a seperate product other than marketing reasons.

When it comes down to noise transmission the predominating factor is mass.

If you want plaster and are comfortable with it, go ahead, but dont think that using an up spec board is going to make large differences in transmission.

15mm MDF or chip or even 15mm ply will make a far better interiour surface for a workshop than plaster.......if you anchor it well, you can then more or less attach stuff like shelves and brackets anywhere you like on the walls.

What will make a large difference...especially if it is a tin shed...is packing the cavity with insulation material so that it is in firm contact with the metal sheeting...or gluing the insulation to the metal sheeting.

I have had very good sucess with spray gluing the bats to the insides of the metal cladding......this does two things, it increases the mass of the metal sheet and deadens it...and it make throwing the interiour sheets soooo much easier, especially on the roof.

cheers

The cyclone is in and running. No ductwork yet, but like most hobbyists that will get done a bit at a time.

I hung the cyclone, blower and motor unit on a wall shelf with the rubber isolators provided. Happily, I am able to report that so far I am not detecting any low frequency rumbling travelling along walls and into the house (workshop is part of the house structure).

My first noise readings, taken 3M away at a height of 1.5M are:
* With the VSD set to 50 Hz ... 86dB
* With the VSD set to 60 Hz ... 97dB

These things are noisy, so now it is easy to see why so many are keen to suppress this noise.

Next comes ducting ... then noise suppression.

Originally Posted by John Samuel

The cyclone is in and running. No ductwork yet, but like most hobbyists that will get done a bit at a time.

I hung the cyclone, blower and motor unit on a wall shelf with the rubber isolators provided. Happily, I am able to report that so far I am not detecting any low frequency rumbling travelling along walls and into the house (workshop is part of the house structure).

My first noise readings, taken 3M away at a height of 1.5M are:
* With the VSD set to 50 Hz ... 86dB
* With the VSD set to 60 Hz ... 97dB

Good to hear there is no rumbling but thats still pretty loud.
How far away are the neighbours?

My naked 3HP DC is 80dB at 1 m (1.5 m height).
When it is inside the enclosure it's 64 dB at 3 m.
Inside the shed it's 68 dB with the noise being all hissing from the ducting.

Bob,

64 dB is a pretty good outcome. You must be pleased.

You will not be surprised that doing a quick check to gauge the impact on neighbours was an early priority. It is not at all bad.

By my estimation the worst the closest neighbours will hear is about the same as inside my laundry, with the door open, and that is forty something dB. However, I plan to ask them if I can take measurements inside their place.

Just tested it at 1M, and it rises from 86 to 88 dB (compared to 3M) at 50 Hz. If I hold it 2M high, it rises another dB or two (brings the instrument closer to the blower and exhaust. Currently there is no ducting, including the exhaust, and Getting about 10 feet of 8 inch insulated HVAC duct out of an adjacent high window will help. Then I'll need to check the noise outside that window where the cyclone will exhaust to determine whether I need a baffle.

So, sound suppression is an issue I need to deal with, but when I put my hand close to the intake and feel that rush of air, it all seems worth the effort. My only real bitch is the nonsense that must be negotiated to modify machine ports. Some are going to be tough.

Originally Posted by John Samuel

Bob,
64 dB is a pretty good outcome. You must be pleased.

Yes, it took a while but is worth it. The nearest neighbour is on the "difficult" side and I did not want to give him a reason to complain. That's also why I put a bit off effort into making it look reasonable. I spoke to an acoustics researcher at work and he said I should write a paper on my enclosure because getting a real 16 dB reduction in such a situation is not that easy to achieve.

You will not be surprised that doing a quick check to gauge the impact on neighbours was an early priority. It is not at all bad.
By my estimation the worst the closest neighbours will hear is about the same as inside my laundry, with the door open, and that is forty something dB. However, I plan to ask them if I can take measurements inside their place.

That should be fine.

Just tested it at 1M, and it rises from 86 to 88 dB (compared to 3M) at 50 Hz. If I hold it 2M high, it rises another dB or two (brings the instrument closer to the blower and exhaust. Currently there is no ducting, including the exhaust, and Getting about 10 feet of 8 inch insulated HVAC duct out of an adjacent high window will help. Then I'll need to check the noise outside that window where the cyclone will exhaust to determine whether I need a baffle.

Adding ducting should make a difference.

Hell that's pretty noisy.......where is all that noise comming from.........when you say no ducting. do you mean nothing on the inlet of the blower?...are you also takling no ducting on the outlet?


I assume you ar talking a blown cyclone rather than a sucked one.

You may not seem to heay the coupling into the wall....but it will be there.

With my com pressor it was not obvious that the sound was comming from the slab, but the difference between the compressor standing direct on the floor and on its isolation board is considerable.

If you are expecting to surpress arround 50 to 100Hz or below you need pretty soft mounts.

Remember also if you are finding noise in the air stream, mufflers can be made out of PVC tube.

cheers

Soundman,

Its a Clear Vue cyclone, so it sucks air from the centre of the cyclone and blows it through the outlet. There is no ducting on either inlet or outlet at this stage. Chris warned me it would be noisy, and all my reading showed that a bigger more powerful motor was required for a cyclone to move a similar amount of air as a DC, but when I see and feel how much air is being moved noise suppression becomes a labour of love. And you have already given me a bunch of good ideas on sound suppression ... thanks.

Also, the literature suggests a lot of the noise comes from the blower and the exhaust, so the HVAC vent duct should help.

I chose the Clear Vue because it has a very small footprint, moved plenty of air, had a bin rather than a collector bag and because I have a series of high windows that are ideal to vent the exhaust. A Clear Vue just fell together nicely in my shop. It fits, and is very effective in terms of air moved and particle size in the exhaust. The other cyclones I looked at were more expensive and had a much bigger footprint. By comparison, the 3 HP DC's are considerably larger such that I would have needed to build a shed outside ... a lot more work and even more expense as it would have been necessary to buy everything for the shed. I discarded that idea because it made a 3 HP DC at least as expensive as a Clear Vue and it added more ducting and fittings to the design ... so ... less air volume and velocity.

You may well be correct about the wall coupling. Once I reduce the other noise we will soon know. The plan is to enclose it. if rumbling is found through the wall, I'll disconnect it from the wall ... not a big job at all when the cupboard is built.

The intake ducting gets picked up today and a start will be made on assembly this weekend (hopefully). I'll also start looking around for some 8 inch insulated HVAC duct for the outlet.

I found this site a month or two ago. Please allow me to thank everyone here for their generosity. As someone relatively new to woodworking, you have all been a great help. Almost without fail, a question soon brings several considered responses from people who know their stuff, and I appreciate it greatly.

John,
RE: Comparing sound levels.
if you are measuring the sound levels of the cyclone inside your shed, sound reflections may give several dB higher readings than the sound source really is.
Good luck with the suppression.

I just fitted a length of 200mm insulated HVAC ducting to the exhaust, and dropped it out of a high window.

The sound reduction is good. Here are the results before and after the exhaust duct was fitted.

At 50 Hz ... without duct ... 86dB ... with duct ... 70-76dB.
At 60 Hz ... without duct ... 97 dB ...with duct ... 72-78dB.

The range for the "with duct" reading is because it is clear some of the noise is directional. Moving laterally creates this range of values at a constant distance to the blower of 3M. As we might expect, the louder readings are towards the back of the "L" shaped shop which is closed off and smaller; the lower readings occur when I stand towards the bigger, more open area of the shop between the cyclone and the garage door. My principal work area is near that door, so the fan can blow over me and out through the big opening.

In any event, I now have the noise down to 72-78dB running at 60Hz. Given that a reduction of 10dB about halves the noise this is a great start! At 60 Hz I now have about one quarter of the noise that used to be present before the exhaust duct was fitted. At 50Hz it has halved. Clearly the frequency/harmonic/power/pressure produced by the higher speed is different to that produced at lower speeds, and the HVAC duct does a better job of suppressing the noise frequency/harmonic/power/pressure produced at the higher speed. With the duct on, the two noise levels are quite close.

Put my ear to the wall. Sure enough, a very low rumbling is now detected. However, when I step inside the house to the ensuite (house and shop are the same brick veneer building) and close the hollow core door the noise drops to 45dB 1.5M behind that door. The next room is our bedroom, and the noise there drops to 40dB with the door open and to 25dB with it closed.

The very good news is that the neighbours should not be bothered by this at all. Standing beside the fence near the neighbour's house produces about 40db. At the back of the house where the exhaust duct exits the reading is less than 40dB. It varies a bit depending on where I stand, but stays under 40dB. It looks like I'll not need a baffle. Bill Pentz did say that most of the noise came from the exhaust and that he had been told by an associate that 8-10 feet of insulated HVAC duct would make a big difference ... and it did. So much so that I am considering wrapping some more insulation around the 1M or so of the existing duct that is inside the shop. The duct only has a fairly thin layer of polyester (I think R1). Might also put a wrap around the blower before I enclose it.

Soundman was right. A big part of the trick is to maximise absorption.

You were absolutely right. I took a series of readings at different places in my shop and the numbers can vary considerably.

At 3M from the cyclone is a spot where I initially chose to take my readings. I got 72dB this morning, but moving the instrument as little as a foot changed the reading to 75dB. Stand 3M away from the cyclone on the other side of the shed (more enclosed) and the reading rises to 78dB. The noise is bouncing around, just as you suggested.

But generally, as I back out towards the garage door the readings continually drop, so I have some faith in them.

Picked up my PVC ducting and fittings this afternoon. They wanted about $18.00 for a hose clamp. Carba Tech charges $6.00, but I have found a supplier that will sell me 133-170mm hose clamps for $4.00. So this weekend should see a start made on the ducting.

I am still grizzling about the amount of work involved in some of the machine porting, but it needs to be done.

IMAG0015.jpg
I was so impressed with the sound reduction the HVAC insulated vent provided, I decided to do it again.

About 1.5M of the vent is inside the shop (see pic). Bought 3M of 300MM HVAC insulated duct, and pulled the smaller duct through it so the 3M of the bigger duct is concertinaed to 1.5M. Took the sound readings, and they fell again. Here are the results so far, all at 60 Hz:

1. Nothing on at all ... 5dB ... its a quiet shed.
2. Turn on the VSD (it hums) ... 10 dB
3. Turn on the Clear Vue:

• Naked ... no ductwork in and no exhaust ... 97 dB (ouch).
• 200mm HVAC duct to exhaust (about ten feet long) ... 78dB
• Add 300mm duct to the 1.5 M inside shop ... 66 dB.
• Wrap three layers of thin polyester insulation (off-cuts) around blower ... 62dB

When Bill said that the bulk of the noise comes from the exhaust and the blower he got it right. So too did the guy who recommended HVAC duct to the exhaust.

Right now I have mentally parked up the notion of building an enclosure. I will do a proper job of insulating the blower, hook up the ductwork and take matters from there. But if I can keep it below 65dB in my main work area, I cannot see the purpose of building a cupboard.

The total cost of the HVAC duct was $40.89 including GST. $16.50 for 3M of the 200mm duct and $24.39 for 3M of the 300mm duct. Much cheaper than an enclosure; and I have a huge bag of polyester insulation off-cuts that the duct making guy gives away to get rid of it. If anyone in Brisbane wants it, they are welcome to it.

That's excellent - well done
What you will find is that when you set up the ducting and air inlets inside the shed their shape/size will become the limiting factor for noise generation. For some machines like saws and thicknessers it doesn't matter because they will be much louder, but for quieter machines like lathes that tend to run for a longer time you will appreciate a quieter operation.

BTW that is a very quiet shed. Depending on which way the wind is blowing my shed (with everything off) can be as high as ~40 dB in the day time - two major roads about 200 and 500 m away.

By my reckoning, you are right.

Don't own a lathe ... maybe I just like noisy machines.

Most of my machines get used for short, regular periods. This is true of the table saw, the vertical/horizontal sander and many other quieter machines. The only machine that gets used for reasonably long periods non-stop is the planer thicknesser, at the beginning of every job. As you said, it is a noisy beast anyway so having the cyclone running the whole time is no big deal.

Bob, if last week you'd have suggested that the two layers of exhaust duct and the little bit of polyester wrapping on my cyclone would drop the noise from 97 to 62Db I'd likely have told you that you had taken leave of your senses ... but that's what has happened. I am a very happy chappie indeed.

I recon any sort of enclosed duct on the output would have dropped the noise level significantly.

As mentioned before..my main concern with the HAVC duct is the flow resistance particularly withe the bends i see in the picture.

When ya start putting up barriers and absorption...it is surprising hw much difference can be made.

One thing that will reduce the noise comming out of the blower is increasing the mass of the walls.....gluing heavy rubber or the like will do this...of course the absorbent material over that.

Another...option would be to enclose only the bower in some sort of cabinet.

cheers