Guide to electric air compressors for home shops

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log 2 = .3 (the definition of a decibel is the 10 x log of acoustical energy, iirc).
The decibel is not "hard" physics, like energy, absolute temp, etc, but rather a description of how we perceive acoustical energy. And is only approximate at that, with freq, loudness itself, spatial considerations, etc.
Play one trumpet at 60 db. Play second trumpet at 60 db. Play both trumpets together, you "hear" 63 db. The acoustical energy has indeed doubled, but not the perceived loudness. Or so I lernt.
The point being, "loudness" is best achieved by modifying the original source, not adding original sources. Which works to a shop's advantage, in this case.
Not saying that a smaller compressor is necessarily quieter than a larger compressor -- I have a Sam's Club 10 gal Alton (an unusual direct drive WITH OIL!) that is so effingly loud, I use it as an alarm for low pressure!!!
The point was, that IF you have a quiet small compressor, you won't greatly add to the noise factor by adding more quiet small compressors.
And, to the other points, indeed, you would not want them coming on all at once, or even operating all at once (unless necessary), as that defeats the purpose of staging. And yeah, circuitry is always an issue, which is why God invented breaker panels.
And, not saying that the three operating together would be more efficient than one big one -- just more efficient if the air load varies widely.
Note that there are probably a few ways to stage smaller compressors. The obvious way is via pressure -- set each pressure switch successively lower pressure, indicating demand. Another way is to use timed relays to sense when one compressor has been operating beyond a preset time, also indicating demand.
I'm a big fan of using volume to compensate for a small-ish compressor head. Can really help if electricity is limited.
Also, a compressor that is a little too large for the electrical service can be helped by changing pulley sizes, which if changed to reduce motor load will also reduce cfm. otoh, you could reverse this strategy to bump up cfm, if nec.
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"Proctologically Violated©®" wrote:

Only if both are exactly in phase. Anything less, and the increase is under 3 dB. If they are exactly 180 degrees out of phase and at the same level, they cancel each other.
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There ya go! So just get two identical compressors, delay the start of the second one by 1/2 wavelength, and you will have zero db air!!
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What that is how noise canceling head-phones work, it's not how two noise sources work. But the above is very much spot on (yws I actually make my living dealing with sound and noise, in the water but it still works the same)
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Ralph E Lindberg wrote:

I made mine with RF. Everything from microwave receivers that recovered data from the noise floor, to 5 MW EIRP UHF transmitters. At one time I owned a commercial sound business. My record was clear audio five miles away from some pole mounted music grade horns, driven with a 65 watt amplifier. It was at a high school football stadium, with open bleachers. The custom speaker mounts were made of heavy aluminum 'U" channel. 8" wide, 18 inches long, and three inches deep. The thinnest part was 5/8"
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Michael A. Terrell wrote:

When I was a kid, I found a screw in driver for a stadium horn. I taped it to a washing machine rotor which was horn shaped and made a pretty good loud speaker. I then took a carbon microphone from an old telephone, put in series with some D cells and the home made speaker and that sucker was loud. The feedback from dropping the microphone into the horn was horrid and being a kid, I just had to use it to chase the dogs all over the farm. Ah, the life of a young mad scientist.
TDD
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"Proctologically Violated©®" wrote:

Only if they are exactly identical, to the last atom, and you are positioned at the exact spot where full cancellation takes place. Otherwise, you would get some reduction. Try it with speakers some time. If they are in phase and facing each other you can find dead spots where you can't hear either speaker. I did this for a football stadium. The players couldn't hear the announcer over the speakers, and you could use a live microphone anywhere between the goal posts.
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On Sat, 13 Dec 2008 12:59:52 -0500, "Proctologically Violated©®"

My compressor is an extreme duty Campbell Hausfeld, 30 gallon tank on wheels. I don't use it often, does a great job, but wow, the noise. I don't have a sprayer...yet.
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