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  #1  
Old Thu 23 February 2012, 15:04
Axel1966
Just call me: Axel
 
Paris
France
Quieting a Vacuum system

Hi all,

As i'm graduated in sound engineering and achitectural acoustics, I've been asked to post solutions to quiet a vacuuming system.
Sorry if this post is in the wrong place, feel free to dispace it.

First, what is sound ?

Noise is some sound. A sound is a vibration propagated into air, like a weave can propagated into water. You can hear or feel sound. Apreciate, all the vibrations surrounding us may not be heared. A standard people can hear frequencies in a range between 22 to 20.000 hz. Most of peoble can feel low frequecies from 16 to 40 hz. 16hz is the sound produced by the tallest pipe of a classical church organ. Audition is the only sense which is never disconnected. You can rest your vision by closing your eyes, but you can't turn off your ears. You wake up not by a smell or a touch, but by the sound of your alarm clock.

Noise is a public and personal enemy

Human brain acts as a filter. It helps to focus on important sounds (talks) but noise still exists and have a real influence on you hearing capacity. The more noise you will stand during your life, the more, the fast, you will lose your hearing ability. You can easily understand you see or read with difficulties, but you'll never understand by yourself you have hearing problems, because human brain still manage the sounds to help you analyse your acoustic environment, much better than you hear in reality. Ears never regenerate. You must preserve your hearing capital. Apreciate, humans have ears adapted to a quiet tropical forest, nothing else.

Otherhand, sound pollution is a disaster. Noise can turn anybody mad easily. If you can stand heavy noises (maybe because of a lack of hearing ability), your neighborhood may not. A noise may be standable in a close location, while it can be louder several meters or rooms away.

You'll get tired more, and more quickly, in a noisy environment. A noisy workshop can even disturb outside of the workshop, creating conflits inside and outside. It's good to kill noise wherever it is.

Sound propagation

Sound have two ways of propagation. First, direct or air propagation. Second, propagation through solids. (See fig. 1)

Air propagation don't need to be explained. Propagation through solids can be considered as chain reactions. A vibration can progress inside an object, then progress into another one in contact with the first one, and so on. Each object can resitute the vibration by vibrating itself. As example, when you talk to someone through a simple window, the sound of your voice vibrates in the air, then the air hit the window, then the window vibrate and transmit your voice through the outside air, which will be recieved by your listener. He hears your indirect voice.

Sound insulation

Sound insulation is not the same than heat insulation. The second is quite simple, and may have questionable results on sound. Otherhand, a good sound insulation is always an excellent heat insulation. A total sound insulation needs heavy implementation, very expensive most of the time, pervection is close to be impossible. Let's rather talk about sound reduction, which is much more reachable.

A good sound insulation is focused on three axis :
  • Prevent propagation through solids
  • Limit air propagation
  • Sound absorbtion (quieting)

1/ as sound may travel through solids, the goal is to lock the vibrations inside the solid. The method is simple : isolate the solid from others objects, with an antivibratory base or an antivibratory suspension.

2/ now we may limit air propagation. Another simple method : create an antivibratory environment within sound will be trapped. Generaly soft surfaces.

3/ Absorbant surfaces, like foam or mineral whool, can absorb vibrations by division. If the surface and path is large enough, a spectacular sound reduction can be conducted.

Note it's easy to reduce medium to high frequencies. Low frequencies needs more mass and surface to be reduced. If you have to manage low frequecies, better look at a way to limitate their early propagation/generation.

This are general principles, not a sound insulation bible.

Quieting a Vacuum system

At last, we're ready to give an application of the above.

First, the best way to manage noise is to avoid creating some. So, a simple electric relay will make the vacuum start simultaneously as the MM spindle. No vacuuming needed ? No vacuum noise...


Second, think "box in a box", open space, means propagation (dust, smell, noise...). The best way to manage propagation is to manage environment.
It is right for a vacuum system, right for a MM, even if it takes more place and you may think about comfortable access to the machines. Think you don't have to access the vaacum tray frequently, and the MM can cut for a long time within your close presence.

Note the care needed to isolate in/outs (tubes, cables). Through, the noise trapp's path needs to be as long as possible for a better noise reduction.

About 's'.
'S' is a surface value in mē, needed for a good air flow.
Air flow can make noise by itself. It would be pittyfull to add noise while reducing some...
'S' is calculated from air speed (must be inferior than 20km/h to avoid grid whistling) and air flow.
The calculation is :
Air flow (m3/h) / 20 (km/h) / 1000 = grid surface and noise trapp section (mē)

I wish my english was good enough to make this topic helpfull for members.
I'll try to awnser any question.

Regards.
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  #2  
Old Thu 23 February 2012, 15:27
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Great explanation on transmission of noise.
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  #3  
Old Thu 23 February 2012, 20:30
KenC
Just call me: Ken
 
Klang
Malaysia
Thanks for the lesson in noise transmission.
I now know we can design to kill whisling sound.
How do we go about designing an exhaust silencer for a shopvac?
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  #4  
Old Fri 24 February 2012, 02:24
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Make the outlet pipe look like a birdcage (use wire mesh), then wrap glasswool around the cage. Cage length 5x to 10x diameter.
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  #5  
Old Fri 24 February 2012, 03:56
Axel1966
Just call me: Axel
 
Paris
France
Ken, do you mean "mobile vacuum" ?
You can do the same, just adapt dimensions to your shopvac's shape and specs.
Plan about an easy door access and plugging, to extract yout vacuum for mobile purpose.
An ventilated air circulation might be added (double insulated tunel, one for air contribution, the second one for air extraction), until a mobile vacuum don't generate enough air flow to scatter heat by itself.
A bench shape may be an idea :



I'ts an utopy to silent a mobile vacuum itself.
It has structural defaults generating the noise, from the engine lack of suspension, to small air entrance/exit, among many other reasons.

Last edited by Axel1966; Fri 24 February 2012 at 04:00..
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  #6  
Old Sat 25 February 2012, 07:03
digger
Just call me: Milosh #113
 
Toronto
Canada
Alex,

is there any way that we can do something about reducing a noise from a main source - blower? When you analyze the noise from blower you may notice that there is a dominant frequency, so instead of dealing with wide spectrum we have to deal with one. Is it possible to make some sort of acoustic tank circuit (parallel connection of acoustic capacitor and acoustic inductor) for that particular frequency?

Milosh
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  #7  
Old Sun 26 February 2012, 00:02
KenC
Just call me: Ken
 
Klang
Malaysia
Alex,
I totally agree with Milosh. Blanketing the equipment isn't a practical solution... especially when there are heat... Add a fan to remove heat again is not a good solution...

Is there anything which we can do acoustically to cancel a certain band of frequency.

Some time ago, a friend suggested recording the noise with a microphone & amplify it with an inverted amplifier & crank up the volume that in theory should cancel out the noise.... It sounds logical.... Procrastination is holding me back in this experiment.
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  #8  
Old Sun 26 February 2012, 04:24
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
play it back inverted, thats how they deal with car side mirrors noise in high speed. you record a sound and play it back in real-time just phase inverted and the waves should cancel each other. Its just like when you invert the wires on a speaker and the low frequency bass disappears
Not a practical ideal but it ran trough my head
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  #9  
Old Sun 26 February 2012, 09:55
Axel1966
Just call me: Axel
 
Paris
France
Dear all,
Well, I wish this would be so simple. Unfortunately this is not.

Just a try with your stereo.
Invert phase of one of your speaker and hear what's happens.
You'll notice, if you're an aware listener, a pumping effect, especialy on low frequencies, but the accoustic pressure might be close as it was before,
while the sound of L/R channels are very similar.
You may record and broadcast the vacuum sound with professionnal quality equipment,
to get a reasonabily similar noise. Note you may record the sound of the vacuum and the sound of the vacuum in the room...

Otherhand, phase shift are a realy sensible factor. The phase may change depending of distance of the noise source and the position of the speaker reproducing the phase inverted sound.
If you move one step ahead or left, inverted phase might perfectly regular. Contrary of low frequencies, high frequencies phase may change in shortest distances.

I'm affraid there's no other way (I means easy way) to quiet a noise,
than insulating the source into an insulated box.

One other method might be to create an accoustic environment in the room itself.
With absorbant walls, a soft floor, a large sound trapp on the ceiling.
This would reduce dramaticaly the reverberation in the workshop.
But the direct sound of equipments might be the same.
Otherhand the workshop might be more comfortable and less tiring.
Please note this might be also a much more expensive method,
and this will not reduce significantly the noises.

I apreciate there's good and bad in insulating equipment in a box.
Anyway I do not know how to make better, simpler and cheaper.
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  #10  
Old Sun 26 February 2012, 14:36
servant74
Just call me: Jack
 
Nashville (Tennessee)
United States of America
There are web sites that talk about acoustically quieting a room or two, typically used for studios, or for helping your kids 'garage band' be better neighbours to the rest of the family and neighbourhood. These sites use similar points about the insulation, transmission, and deflection of sound. ( www.acoustics101.com is one such site).

I have thought doing that for a shop, might make it a better neighbour if you want to work late in the suburbs, but it doesn't do a lot for your hearing if you just 'keep the sound in' and are in there yourself.

I have used 'sound cancelling headphones' in the past (using the 'negative sound energy'), but it does seem to be most easily used with headphones rather than making large areas quiet. ( They seem to work best to keep down the drone of airplane engines rather than the kids rock bands, mainly, so I am told, because it is more easily reproduced in a negative sound rather than constantly rapidly changing sounds (like the rock bands)).

If making a separate shop building (helps due to distance between buildings and you can make the building insulated with heavier material and air spaces and sound absorbing material) than refitting a basement room! Also consider directing openings away from normally occupied spaces (open garage doors toward an open field, rather than toward a homes bedroom area) will let the sound more readily dissipate before it gets to others ears.

I like the idea of sound dampening enclosures for dust collectors. I assume the majority of the noise pollution comes from the blowers rather than the breeze through the collection pipes, even though there is some there too. I have seen pictures of shops where the dust collection equipment is put in insulated closets (all around) with access door on the outside of the building (to keep from pulling chips through the work space).

Just a few random thoughts.

All this talk makes me think an inexpensive dB meter to measure sound levels might be a health investment before I loose the rest of my hearing!
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  #11  
Old Wed 29 February 2012, 21:36
rayditutto
Just call me: Robin
 
Victoria
Canada
Send a message via MSN to rayditutto
check out http://www.floweringelbow.co.uk/2011...st-sniper-vid/ which includes a pair of Bill Pentz mini cyclones powered by a double boxed & bafffled shop vac style vacuum all on wheels.

Instructable found at: http://www.instructables.com/id/Dust...ractor-system/
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  #12  
Old Thu 01 March 2012, 03:03
KenC
Just call me: Ken
 
Klang
Malaysia
Housing the dust collector & vacuum hold-down vacuum blower in an outdoor enclosure is high on my preferred list. but as Jack mention, its not a friendly gesture to my neighbour.
Axcel, you enclosure design is fine. Questions, I see raw motor noise will get through the ventilation hole. Is there anything we can do to lower the noise without restricting the ventilation inlet & outlet?
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  #13  
Old Thu 01 March 2012, 04:08
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ken, when I said . . . .

Quote:
Originally Posted by Gerald D View Post
Make the outlet pipe look like a birdcage (use wire mesh), then wrap glasswool around the cage. Cage length 5x to 10x diameter.
. . . I was being serious. This is standard practice for restaurant extractor fans and many other applications. Also, you can aim your noise straight up, away from the neighbours.
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  #14  
Old Thu 01 March 2012, 04:47
KenC
Just call me: Ken
 
Klang
Malaysia
Hi Gerald,
Firing the exhaust upward... hmmm... why didn't I think of that...
I never doubt your words
As a matter of fact, I'd already got hold of some wire mesh & fashioned the bird case as you described. what I need now are some insulation mats; As the suppliers only sell 2" thick x 2'x4' packs 10pcs pack, which is way too much for my consumption... hence, I'm waiting patiently for some scrap glass-wool or rock-wool insulation mats for insulating autoclaves & massive sterilisers...
I read that your suggested method will reduce some -10db easily but I think the twin a vacuum blowers are producing over 110db... & 86db is what I'm working toward keeping my sanity & hearing.

If I can get the noise down to 86db, plus wearing a pair of ear plugs, I'll have internal peace...

Or I'm asking too much with 86dB...
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  #15  
Old Thu 01 March 2012, 05:57
Axel1966
Just call me: Axel
 
Paris
France
Well, quitening over than 50db generaly means expensive purposes.
It ain't necessarary to supress the whole noise.
- 30db produces a good result at low cost.
With -30db you'll quiet more than half the noise, it will be very comfortable.
Remember decibels are a logarithmic scale. db are not %.
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  #16  
Old Wed 07 March 2012, 17:16
digger
Just call me: Milosh #113
 
Toronto
Canada
Some ideas regarding quieting blower:
http://www.clearvuecyclones.com/Bull...?t=1067&page=2
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  #17  
Old Wed 07 March 2012, 20:09
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The whole forum at Clearvuecyclones Noise Control
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  #18  
Old Tue 03 July 2012, 20:55
litemover
Just call me: Chris
 
Auckland
New Zealand
Been looking at noise dampening in computer fan applications. Usually, the fan blade design has a lot to do with it in that application. Blade notches, and even non-uniform blade sizes help to spread the frequency. Check out noctua's products. Also the new Macbook pro ad shows this on apple's site.
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  #19  
Old Tue 03 July 2012, 21:45
servant74
Just call me: Jack
 
Nashville (Tennessee)
United States of America
Just staw a video where folks from JPL I think it was developed a fan that is a lot quieter and doesn't clog with dust, and uses less power.

There are some companies vieing to license the tech.

Basics are, has an air-bearing, and new design of radial fan that keeps laminar air speeds going fast enough so dust can't settle on blades, so lowers drag. Generates about half the CFM but at much lower power requirements.

Still, not ready to help us NOW!
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