soundproofing enclosures?

discussion of design changes / improvements / suggestions
Woodworker
Posts: 639
Joined: Tue Mar 11, 2014 1:37 am
Location: 5 miles north of Benson, NC

Re: soundproofing enclosures?

Post by Woodworker » Sat May 03, 2014 11:47 am

Another source of material might be anti fatigue mats. I have 2 in my shop and they are heavy rubberized foam. I am sure they would contribute to the mass and I am pretty sure they would deaden the sound. I got mine on sale at Woodcraft.
BRuce - SO2 #4798 - IC's Z axis upgrade, customized Z rail and Z motor mount, spindle Dewalt 611

Philip
Posts: 16
Joined: Wed Apr 30, 2014 9:08 am

Re: soundproofing enclosures?

Post by Philip » Sat May 03, 2014 12:46 pm

Llamas wrote:I found a few examples out there of people building enclosures for air compressors, which generate a fair amount of waste heat. They all resorted to the use of fan-driven ventilation through baffles lined with sound deadening/diffusing material.

It will be interesting to see what the sound levels are like when using different enclosures. What does it take to hit certain levels of sound reduction, and to what lengths do you need to go in order to get to that next noticeable level?

I started out with a cabinet inside a cabinet design, but I'm building a single cabinet first. If it's good enough, I'm not going to the extra effort to go from good to better. I'm not sure the sand and concrete aspects of your design lend themselves to half-measures, so I can't suggest the same approach here. How quiet do you need to make things?

--Mike
Perfect is the enemy of Good.
Making holes in a no-compromise solution as I sketched seems counter intuitive, but running jobs for several hours will need some solution to dust and heat I guess. And I like the two-stage approach. Hmmm. BTW, changed from my earlier setup I now dropped the concrete slap as a base and changed to a torsion box filled with sand; that should be easier removable.


If everything I dreamt up doing with the eShapeOko works out (which is not sure at all) I want to use it on a daily basis. I'll be working to finish earlier produced objects while new objects are being milled in the same room. The good news is that finishing will take quite a while so I won't need a very powerful spindle, but I don't want to work hours a day in a noisy environment. Plus the family (lower floor) and neighbors should not be bothered. So I want to go the extra mile in sound reduction, but obviously overdoing it is a no go.

Therefore I'm dedicated to do some testing before I even think of actually building something so I'm interested in thoughts on how to reliably measure the sound level. Looking at the results of FattyMatty earlier in the thread with the iPad, that can't be accurate. He measured just the running spindle without enclosure @95 db (100db is a jack hammer at 1 meter), then closed the cover, started milling and measured 58 db where 60 db is a TV set using home volume at 1 meter (http://en.wikipedia.org/wiki/Sound_pressure).

I do have a reasonably good microphone and home-studio recording software.

Nigel K Tolley
Posts: 226
Joined: Sat Feb 08, 2014 4:06 pm

Re: soundproofing enclosures?

Post by Nigel K Tolley » Sat May 03, 2014 9:14 pm

It is possible, 58dB isn't exactly whisper quiet. 95dB to 58dB is a 37dB reduction, which isn't outside what a set of cans (Ear defenders) will do with a decent seal and a bit of foam.

However, I'd like to see a couple of like-for-like readings.

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FattyMatty
Posts: 9
Joined: Fri Jan 17, 2014 7:41 pm

Re: soundproofing enclosures?

Post by FattyMatty » Sun May 04, 2014 6:18 am

In my opinion with the lid down it does take it below TV at home volume (although that in itself is fairly open to interpretation) and as the picture shows I'm a lot closer to the spindle than 1 meter which is already inside the box (not sure if taking the reading inside the box would cause a false increase in noise due to the sound bouncing back off the walls, which could explain the rather high db reading).

Unfortunately I don't have anything else that can easily take audio readings to record the noise. If anyone has any suggestions on getting more accurate reading I'd be more than happy to try them out.

Nigel K Tolley
Posts: 226
Joined: Sat Feb 08, 2014 4:06 pm

Re: soundproofing enclosures?

Post by Nigel K Tolley » Sun May 04, 2014 10:49 am

I was thinking just do a level reading from infront ofthe door with the door open cutting then with it down.

That would tell us how well it cuts the sound level like-for-like.

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Philip
Posts: 16
Joined: Wed Apr 30, 2014 9:08 am

Re: soundproofing enclosures?

Post by Philip » Mon May 05, 2014 11:33 am

I started a topic on a local 'noise control' forum where I got the following advice for a box without windows but with air ducts:

Starting from the outside, make a frame and screw 18mm plywood or underlayment to it to form the box. Glue 25mm or 50mm rockwool to it. Then add a layer of thin PE plastic foil. Lastly a layer of perforated board or, on the cheap, mesh wire (chicken fence). The mass of the 18mm plywood should be enough to handle the high frequencies. To make sure the high frequencies do not escape use rubber or kit (the sticky stuff from a tube, do not know the English name) to close any tiny gaps.

To bring cables and air into and out of the box create a labyrinth which is completely covered with rockwool on all internal surfaces, better not use the thin PE foil there to prevent the high frequencies leaking out.

My no compromise solution using two layers of thick mass is overkill for these high frequencies and is more suited to low frequencies like bass drums from a rehearsing band (which is where I got the idea from). It pays to ask a question sometimes :D

Nigel K Tolley
Posts: 226
Joined: Sat Feb 08, 2014 4:06 pm

Re: soundproofing enclosures?

Post by Nigel K Tolley » Mon May 05, 2014 7:34 pm

As an (hopefully) interesting aside, the low frequency materials used in the latest helicopters and the like, where mass is kept as low as possible, uses what can be best likened to ball bearings in a rubber matrix. The massive balls take up the low frequency vibrations/noise and they oscillate, & the rubber then absorbs the energy. Using this system you can stop fairly precise frequencies with tuning of the ball mass and elastic material, & do it well with a material that is thinner than the wavelength of the vibrations/noise, which was previously impossible to do effectively.

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Llamas
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Re: soundproofing enclosures?

Post by Llamas » Mon May 05, 2014 10:07 pm

Philip wrote: Looking at the results of FattyMatty earlier in the thread with the iPad, that can't be accurate. He measured just the running spindle without enclosure @95 db (100db is a jack hammer at 1 meter), then closed the cover, started milling and measured 58 db where 60 db is a TV set using home volume at 1 meter (http://en.wikipedia.org/wiki/Sound_pressure).
From an earlier post:
Llamas wrote:I've measured 100 dB standing next to the machine during operation (DW660 + a shopvac ... didn't measure with the aircompressor running), and 60 dB standing in the hall on the other side of the closed (and weatherstripped) garage door.
I was using an analog meter that I usually use to set levels on my surround sound system. I [/i]may have been closer to a meter (but not much) for the first measurement, and I was on the other side of a door for the second (that difference being the point of the experiment), but the absolute 100 dB and 60 dB values are still relevant for reference purposes.

Also, my ShapeOko was sitting on a tabletop, with no walls around it (though it was inside of a one-car garage). It's going to be interesting to see if it measures louder when in an enclosure with the doors open, since there will be reflections off of the enclosure walls.

Philip
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Joined: Wed Apr 30, 2014 9:08 am

Re: soundproofing enclosures?

Post by Philip » Wed May 07, 2014 1:07 pm

I since learned/realized that different frequencies are damped differently. It seems the 2000Hz frequency is absorbed quite well so that makes the high reduction measured more understandable.

FattyMatty
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Joined: Fri Jan 17, 2014 7:41 pm

Re: soundproofing enclosures?

Post by FattyMatty » Wed May 07, 2014 10:24 pm

Unfortunately My spindle stopped working so I'm not going to be able to repeat a noise measurement with the default shapeoko spindle, but I did splash out on one of those 400w chinese spindles off of ebay.

http://www.ebay.com/itm/CNC-400W-Spindl ... 3f35450b64

I haven't made any official readings but this thing is very quiet, I kinda wish I had of purchased this before attempting to make a soundproof box.

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