Thread: Sound Insulation

Originally Posted by John Samuel

In the near future a cyclone to extract dust will make an appearance in my workshop.

The current plan is to enclose it in a cupboard, but it seems that there is a lot of conflicting advice on forums such as this one. Some say cupboards don't work, others say they do if you use the right material (the Americans seem to like rockwool).

Did a bit of hunting around for products specifically manufactured for the purpose, but the prices quoted soon brought on a sharp intake of breath.

And ideas or advice gratefully received.

Well Soundman is around and he is a sound man, well maybe he's not that sound , but he knows sound. He should be able to explain this in succinct terms for you.
Have you seen my setup? It would apply equally well inside as out and it generates a decent dB sound reduction.

Originally Posted by BobL

Well Soundman is around and he is a sound man, well maybe he's not that sound , but he knows sound. He should be able to explain this in succinct terms for you.
Have you seen my setup? It would apply equally well inside as out and it generates a decent dB sound reduction.

Anticon roofing blanket | Bradford Insulation works really well as an sound insulator, I can run my 15" thicknesser anytime of the day or night and it can just be heard from about 2 metres away through the roller door that has no insulation but once you go over that, it is barely heard and on the sides where there is no doors or windows, I cannot hear it from 2 metres. My neighbour who hangs her washing about 10 to 15 metres says she has never heard it, even with the door open which faces away from her.

Insulation like the bradford batts will help with higher frequencies but DCs also put out a low frequency rumble and for that you will need some "mass" in the sound barrier. Lead sheeting is effective but expensive and alternative is something like thick chipboard.

For cheap insulating mat'l you could use old carpet/underlay or layers of cardboard, polystyrene is good as well, as Bob says, a layer of something with some mass for the lower frequencies.



Pete

Green Glue looks like a good approach. http://www.ultrafonic.com.au/images/...20Brochure.pdf especially if combined with glasswool or rockwool insulation.

The data look impressive, especially for low frequency sound ... but it is not cheap. They also make sealants (for around vents etc) and tape.

Does anyone have any experience with this stuff?

I know the local agent for green glue and am familiar with the product......it is a material that has a particular function and in this case I do not believe it is appropriate.

It is an isolation and deadning material designed to go between sheets of material to reduce transmission.
It is effective...well I believe so, but so are many other methods.

In acoustic treatment we have two issues, absorbtion and transmission.
Employing both yeilds best results, using either on their own gives limited results.

Certain groups of "professionals" are very pro transmission, in that they try to block sound with big heavy things.....and they fail to employ absorbtion....and certain others the opposite.

So if I build a pool filter shed (as so many do) and work only on preventing transmission without the use of absorbtion......in short a block bunker.... we cant completly seal the bunker because we need ventilation and there are practical limitations........the sound will bounce arround until it finds a hole to come out, it will then come out in a focused and directional manner, the noise may be reduced in some directions but may be incresed in others.

This is why so many say, enclosures do not work.

If however we enclose the offending machine as best as we practicaly can and apply as much absorbtion as we practicaly can to the interiour we can very very effectivly reduce noise....and often without complete enclosure.

So we want to shut something up.
We need, dense, heavy dead material for the walls.....15mm+ MDF is good and we need soft stuff for the absorbtion...soft & heavy is an advantage.....the lower the frequencies we what to deal with the thicker and heavier everything needs to be.

Fiberglass, rock wool and all of the bulk thermal insulations will work well, carpet, carpet underlay, rubber and the like is not so flash on the absorbtion (they absorb but arent real flash) but adds weight & deadness to to the barrier....forget egg cartons.

To deal with low frequencies (rumbles in the 100Hz region) we need absorbent material in the 100mm thickness range, sharp high frequencies like routers 25 to 50mm can be effictive

By far the best absorber is purpose made acoustic foam.....but it costs

One thing I have had good sucess with is a 35 x70 stud frame with 15mm MDF on the back filled with thermal insulation of choice and some sort of material (carpet, cloth, hesian even sizalation or PVC sheet) stretched over the noisy side to seal it for practical reasons.

Anticon blanket can be good for the front face...but for good absorbtion more thickness is needed and the will be some lack in high frequency performance because of tha hard reflective surface of the anticon.

Peg board works as a surface but it compromises the absorbtion and is about 60%+ reflective.

If you have a good barrier and good absorbtion you may not need to completly enclose whatever machine it is.

If you have a U shaped barrier, with the open side facing an absorbent wall you can leave a surprisingly large gap between the wall and the barrier and still get considerable reductions in noise levels.

One thing to be sure not to neglect, is isolating the machine from the slab......My compressor sits on a braced 15mm plywood board that sits ontop of strips of 25 x 50mm high density foam.....the amount of low frequency this has removed is considerable...all that throbbing is gone.

We can achieve very good noise control of our machines quite cheaply...if we think about it and don't believe all the folk law.

Thick, dense and heavy to stop sound transmission, thick, soft and heavy for absorbtion.
Sound travels mostly in straight lines like light...view hard surfaces as a mirror and soft surfaces as mat black will help to visualise.

cheers

That helps a lot. It is the medium to low frequency sound from the cyclone I am installing that I am concerned about most. Fortunately, it is not connected to the slab but hangs off the wall using rubber isolators.

I was thinking of MDF or chipboard for the interior walls, insulation in the walls and plasterboard on the outside walls.

Thanks again,

Put the MDF on the exteriour walls, and ditch the plaster...use something on the interiour that will allow the absorment material to work.

cheers

Originally Posted by John Samuel

Green Glue looks like a good approach. http://www.ultrafonic.com.au/images/...20Brochure.pdf especially if combined with glasswool or rockwool insulation.

The data look impressive, especially for low frequency sound ... but it is not cheap. They also make sealants (for around vents etc) and tape.

Does anyone have any experience with this stuff?

we are uisng this for a job currenlty its being used between multi layers of plasterbaord and also in the construction of soild doors, can not comment on how effective it is but takes a while to get used to using it.

Looks like I had that all backwards.

I am installing the cyclone now. Will take some sound readings, build the cupboard (one day) and take new sound readings.

How about I install carpet over the insulation on the interior walls?

i would use CSR bradford ultrcael glass wool 50mm thick 48kg/m2 then cover with perforated sheet metal to conceal it that will asorb a lot of sound its often used for sheet metal duct work

I would avoid hanging or attaching any noise making device to a wall even using rubber isolators. The noise can still be transmitted a long way to other surfaces attached to that wall. I had this problem with my DC and despite using all manner of rubber isolators it still made the whole enclosure rumble at a low frequency so much so that it could be easily felt on the walls. When I detached the DC from the wall and made it free standing it dropped the noise levels by 3 dB. It doesn't sound like much but it was noticeable enough.

Originally Posted by John Samuel

Looks like I had that all backwards.

I am installing the cyclone now. Will take some sound readings, build the cupboard (one day) and take new sound readings.

How about I install carpet over the insulation on the interior walls?

carpet over the insulation will work fine.

as for fiberglass......I've sworn off the stuff.....AND iff you are going to use it sheet it over in plastic sheet before putting any mesh, grid or perforated material over it.

as for the perforated sheet metal........yeh that stuff aint cheap.

As for hanging things off walls......yeh I agree with bob........unless the wall is realy heavy......like tilt slab it will just act like a sounding board and amplify the noise form anything connected to it.

people consistently underestimate what is required to isolate a vibrating item.

Think on this....the cyclone is not the noisy part.........if its noisy it will be inefficient......it is the blower.........isolate and treat that.

Even partly enclosing the blower with 4 or 5 absorbent pannels with big wide ( like 2 inch) gaps between, Y cooling air has to get in and out........will knock a heap of noise out of it

cheers

I have done a bit of reading on this subject and had figured out that the blower was the nosiest part ... and the exhaust. The current plan is to use about 8 feet of insulated 8 inch HVAC flexible ducting for the exhaust, which will exit the shop through a 71/2 feet high window which is right beside the unit.

That should help.

I'll run the blower once it gets wired up (hopefully this afternoon) and start making some decisions about what and how to undertake any noise reduction.

Again, thanks to everyone for their advice, especially BobL and Soundman.