# Noise reduction for air compressor



## deeferdog (Jun 29, 2017)

I have a small direct drive air compressor in my shed that generates an astonishing noise level. It is impossible to think when it operates and as a consequence I mainly leave it turned off and only use it when I'm desperate for compressed air. The other day I finally had had enough and decided to do something about it. My first thought was to put the whole thing in a box, but my space is severely limited so I decided to box just the compressor. The budget didn't stretch to much so I just used what was at hand. The interior foam is purple because that was my wife's old yoga mat. I generally only use the air once or twice a day so I made no allowance for compressor cooling. The MDF is 16mm. The project was a limited success, at least the harshness of the noise has gone and it doesn't impinge too much on my concentration. The compressor cools quite rapidly, even quicker if I lift the lid. For prolonged use I would leave the lid off completely. To be honest, if I need a constant supply of air I would get a better machine, certainly go for a belt drive slow RPM style the way air compressors used to be made. Cheers, Peter.


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## Hopper (Jun 29, 2017)

It looks like you have the main noise-generator sticking out the side of the box: the compressor fresh air intake. Most of the noise comes from that. The actual moving parts of the compressor make  very little noise. 

You might try building a smaller box over the intake, lined with solid lightweight foam for the air to pass through while the noise is dampened. Or put a large air filter off a car on there to provide a large-volume chamber to dampen the noise. You could even run an intake hose to outside the workshop so the noise is out there.


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## Blogwitch (Jun 29, 2017)

Peter,

You won't be able to get a quieter compressor unless you go for a 'silent' type, expensive and not much airflow or a Hydrovane type, which are again expensive.

I have a belt driven V-twin unit, and I had to bury it in a back room with a door so that I could think while it was working in the main shop. My only other course of action would be outside, then it would annoy the neighbours, which it even does now if I forget to turn it off before going to bed..








John


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## XD351 (Jun 29, 2017)

Has anyone ever considered using a larger air tank or two or more smaller ones linked together then using a large pump running very slowly  say 60 - 100 rpm via a worm drive gearbox ? 
It may take a few minutes to reach full pressure and if you are only using  low flow tools or tools that get used intermittently like a air duster / blow gun the extra tank volume will keep up with it .
I had a home made compressor that used the air tank and compressor of a truck , it was only spinning at 500 or so rpm and the grumbly bearing in the electric motor made more noise than the pump .
Maybe the old bodged up fridge compressor set up will do for most of your needs ?
These days i have one of those small buzz box units that i stuck in the cabinet under my small mill and it shut it up enough to make it bearable ,  it is only for my blower guns on my machines so its duty cycle is low and it comes on with the main power so by the time i get my bearings it is ready to go .
I have a 15 cfm unit that gets me by with spray painting , die grinders and just keeps up with my little sandblasting unit , none of these get used very often so every few months i start the bigger unit up just to keep the internals lubricated .


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## ShopShoe (Jun 29, 2017)

Has anyone tried retrofitting a Solberg air filter to these compressors?  I have one of these small ones and my new 5HP-60Gal vertical big comprressor only has the very noisy accordion-folded single-layer paper filter. That is one thing I noticed the more expensive shop compressors all seem to have.

--ShopShoe


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## deeferdog (Jun 29, 2017)

Thanks for all the interest, I'll try Hopper's solution and make a sound box for the intake. If it works I'll post the result, to be honest I feel like I'm spending a lot of time polishing a **** and not getting much lustre. Regards, Peter.


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## MRA (Jun 29, 2017)

Noise control used to be my job, so maybe I can help.  

An intake muffler will be useful, as has been pointed out.  Silencer design is tricky, but try a volume of air with pipe constrictions on either side (one to fresh air, one to the intake).  Line the volume with absorbent - open cell foam is easier than fibreglass or rockwool as you don't have to worry about fibres getting pulled into the air stream and blown out into the shop.  Open cell foam - you can blow through it.  Closed cell (furniture) foam is stiffer and much less acoustically absorbent - you can't blow though it.  You can increase the area of absorbent by dividing the volume with absorbent 'splitters', as well as lining the walls.

Make sure there are no unintended air gaps in your box at all - go for a good seal.  And make it as heavy as you can - more mass, more low (-er) frequency noise attenuation.  I'd use scaffold pole or something for the pipe I mention - noise will piss through a lightweight plastic pipe.  

Your box will vibrate since it is mounted on the same structure as the compressor, and this will radiate LF noise off the box itself.  So for best performance you'd mount the tank and compressor on small spring isolators and put the box around the outside, not touching and bolted down hard to the floor.  This might not suit you, but maybe it would work for someone else's set up.  

It's never convenient and always space-consuming!


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## Wizard69 (Jun 30, 2017)

One solution many forget is to put the compressor outside.   Then it only bothers the neighbors.


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## dnalot (Jun 30, 2017)

Hi

I hoisted my compressor up into the attic. Helped with the noise a lot without bothering the neighbors (much). 

Mark T


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## Wizard69 (Jul 1, 2017)

dnalot said:


> Hi
> 
> I hoisted my compressor up into the attic. Helped with the noise a lot without bothering the neighbors (much).
> 
> Mark T



That is another idea.   Anything that results in it being in another room, hopefully isolated, helps a great deal.


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## Philipintexas (Jul 4, 2017)

I made the mistake of buying one of those direct drive types. Dangerous noise level, I had to go outside when it ran. I sold it to a neighbor and bought a belt drive. Much quieter and I installed it as far from my shop as I could and piped air to my shop with PVC. Cheaper than a hearing-aid!


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## deeferdog (Jul 6, 2017)

Amen to that!


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## Nick Hulme (Sep 3, 2017)

Hopper said:


> It looks like you have the main noise-generator sticking out the side of the box: the compressor fresh air intake. .



+1 
I ran plastic Hep2o pipe outside to an old car air filter for my V-twin compressor air intake and my garage was instantly more civilised, I use refrigeration compressors in the workshop, you can only hear them when they reach pressure, cut out and dump.


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