Silencing an air compressor

[wxn]

Hello everyone.

My problem is not directly audio related but acoustics are the same nevertheless so I ask DiyAudio gurus for an advice.



I have recently started airbrushing and acquired an oil-less air compressor. 500W, 6l receiver - compact and gets the job done. The problem is it's quite noisy. I have to raise my voice to have a conversation near it.

Goal - to quiet the thing enough to be able to work at night (okay probably not, but evening definitely) and not upset the neighbors, which means pretty damn quiet operation. I am not limited by the final weight - I can use it as a table if needed.

I got rid of most of high frequency noise from valves by putting a muffler on intake. Doesn't seem to affect operation but did wonders to that "plack plack plack" noise.

Now, the motor is standard emulated three-phase electric motor. I guess there's nothing I can do to make it run slower than mains frequency. The whole thing vibrates and the 50Hz fundamental is very prominent and while not very annoying, it is powerful enough to shake the floor. Oh and the whole thing vibrates like hell.

I am thinking about enclosing the compressor in a MDF box, lined internally with fibrous material and thick foam at the bottom to physically decouple compressor from the box (which is probably easier to do than trying to damp vibration with mass - I'd need a block of concrete for that..). And the box itself should be as heavy as possible I guess. This should bring SPL to levels acceptable even at nightime.

The problem is that the compressor heats up quite a bit in operation (that's about 2min for empty tank (should last at least 15min of painting), bout 40s if auto switching but naturally much more often). So making a sealed box is not an option.

Simple solution - to make a door of sorts and periodically open it to let hot air out. Easy to forget - dangerous.

Sophisticated solution - built in ventilation system. That's what I am aiming for. The only sources of information on the subject I managed to find are these two projects:

Picture Framer's Blog: Part 2 of 5 - Building the sound proof enclosure for my air compressor

Sound Suppressing Compressor Enclosure

The question is how to estimate the shape, number of bends, materials of the labyrinth to attenuate low frequency noise (and all harmonics, naturally) efficiently while allowing (forced) ventilation? I realise that up to a point the more - the better. But after some number of bends airflow will start to suffer.

Also, what is better - thick walls of 25mm MDF for mass or several thin layers, smth like that:



Any input is welcome.
kipsus

[infinia]

Have you considered more air storage? Say two 15 gal portable tanks at 130psi. That sould give at least 4 hours of airbrush time. You could run a compressor on a daily timer to automatically charge them up at times when the neighbors arent home.

[imix500]

The silencer box idea is probably your best bet. Though you will be surprised what 2" of insulation will do- it may be all you need. You will need ventalation no question. I'd do what they do for entertainment generators and baffle the input and output. You will probably need some forced cooling as the box will be VERY good at keeping heat in. Also, a set of good isolation feet will decouple the vibration.

[wxn]

infinia:
Very neat idea. But the keyword here is *compact*. I don't have a workshop (yet) so huge receivers are not really an option for the moment.

imix500:
Perhaps you have some plans/photos of internals of working systems?

[woody]

I wonder if active noise cancelling would work like is used in noise cancelling headphones?

[imix500]

Here's a bad Apple Works drawing via word via pdf to give an idea. You could build it so the vents are vertical or horizontal. Though you will have to help cool it much more horizontally. I wouldn't use plywood for the enclosure if possible. Plywood is not a good sound insulator. There's this stuff called Homasote that would work much better. It's fantastic. You could also use really thin plywood as the outer panels and attach the homasote to that.

[jemswillam]

I have a 3 gallon air compressor that is loud as CRAP when it is filling. I wanted to know, is there a way that I can muffle the sound of the compressor, or do I have to get 100 feet of hose and run the thing from my backyard? Another alternative I was thinking of was to use it as one of my scares...I went to a haunted house in California that had a metal pad that, when stepped on, vibrated and made a loud noise...almost like the noise of a compressor...So if anyone can help out...it would be greatly appreciated..

[Conrad Hoffman]

It looks like one of those direct drive monstrosities everybody's making now. The first time I heard one I couldn't believe it, compared to my belt drive. Even that's too noisy for what you want. It's hard to build a quiet compressor because even if the mechanical stuff is balanced perfectly, the load isn't. Two cylinders probably help, but the answer for your problem is simple. Save your pennies and find a new or used Jun-Air. We use those at work for vibration isolation tables and I believe they're what many people use for air-brushing. Not silent, but darn close. The enclosure idea isn't simple to do well, and is probably a fire hazard no matter what.

CH

[chris661]

Here's an idea instead of ventilation - get a heatsink. You see them on active subwoofers all the time, so they must be widely available... If you then damped it with foam, the heatsink would vibrate a little, but the rest of the box should be Ok.
How about a passive water cooling system? I'd say convection alone would move the water around enough - I've seen it gain a metre (meter) in height before now, but that was nearer 60 degrees. Surely, some kind of scaled down version may work?
HTH
Chris

[infinia]

Originally Posted by Conrad Hoffman

It looks like one of those direct drive monstrosities everybody's making now.

Yup and oil less too. Quite nice for painting. Unlike the old cast iron/belt drive ultra monstrosities. Probably less operating life as well as a bit noiser as you pointed out.