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What makes a quiet air compressor quiet?

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edpalmer42:
Has anyone seen a teardown and analysis that explains what design features are responsible for the reduced noise level of the new 'quiet' air compressors?

I recently bought one of the newer types of air compressors that is advertised as 'quiet', 'ultra quiet', 'silent' or other similar marketing babble.  There are endless videos about how quiet they are.  Instead of being so loud that you can barely shout over them, the quiet(er) ones make claims of < 60 dBA for small portable units (typically 1 gallon tanks) up to < 80 dBA for larger units with 20 gallon tanks.  These numbers are almost worthless because they rarely describe the measurement environment i.e. distance between compressor and microphone or indoors/outdoors, etc.  Even so, these compressors are a lot quieter than older designs.  The 2 gallon / 2.5cfm@90psi unit that I bought claims 62 dBA with no more details.  My old Radio Shack sound level meter reads about 65 - 66 dBA at 1 meter in my living room with wall-to-wall carpeting and typical furniture.  Move it outside and the level will drop significantly from that.

But what design features accomplish this magic?  AFAIK, the first company to produce these was California Air Tools.  The air pumps on all of these units, regardless of brand, share an obvious family resemblence to this brand.  Licensed copies?  Outright design theft?  No idea.  But there's something about that design that results in a significant reduction in noise.

Any thoughts?

Ed

GLouie:
When I saw these on the market, I got a Lowe's Kobalt unit with wheels. And yes, all such units seem to use the same 2 cylinder design. I don't know much more, but figured that the RPM is halved but gets the same air moved with 2 cylinders, and some attention to other details quiets them to a reasonable level.

Stray Electron:
  I don't know what they're calling "a Quiet air compressor" but I expect that it's nothing more than a sales slogan.  But the quietest air compressors that I have seen are the ones that use an 1800 (or less)  RPM motor instead of a 3600 RPM one. AND the compressors are belt driven to run significantly slower than the motor.  The old industrial built Ingersol-Rand (IIRC) only run their compressors at 180 RPM.  Not only are the motors and the compressors much quieter but they also last MUCH longer.  The down side is that for a given size compressor, the slower driven ones take much longer to deliver any given volume of compressed air.

  A two cylinder compressor may not be running both cylinders in parallel but may be operating them in series.  A so called "two stage compressor".  Most true industrial compressors are two stage since it lets the compressor develop higher pressures.  160 PSI instead of 90 to a MAX of about 110 PSI.

thm_w:
https://www.eevblog.com/forum/reviews/quiet-electric-compressor-like-an-aerosol/
https://www.eevblog.com/forum/projects/small-quiet-compressor-to-exclusively-run-a-syringe-dispenser/
https://www.californiaairtools.com/ultra-quiet-series-of-air-compressor-contractor-grade/

BlackICE:
I was intrigued by Cal air compressor so looked more. I found this review and from the tilting piston/rod design would never buy one unless I considered the purchased a non-repairable throwaway like many cheap Harbor Freight compressors that new can't buy parts for.

https://youtu.be/sG9Hl5iaL3M?t=352

Makita has a similar compressor design with proper pistons that stay aligned with the cylinder bore. Of course they cost a lot more.

https://www.ereplacementparts.com/makita-ac310h-25hp-high-pressure-air-compressor-parts-c-97_1547_39919.html

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