Measuring And Adding Sound Levels Together

What sound level do you get when you feed an EXAIR Super Air Nozzle at 80psig? What if there are two of them?  Or three?  Grab your scientific calculators, folks…we’re gonna ‘math’ today!

But first, a little explanation of sound power & sound pressure:

Strictly speaking, power is defined as energy per unit time, and is used to measure energy generation or consumption.  In acoustics, though, sound power is applicable to the generation of the sound…how much sound is being MADE by a noisy operation.

Sound pressure is the way acoustics professionals quantify the intensity of the sound power at the target.  For the purposes of most noise reduction discussions, the target is “your ears.”

The sound levels that we publish are measured at a distance of 3 feet from the product, to the side.  The units we use are decibels, corrected for “A” weighting (which accounts for how the human ear perceives the intensity of the sound, which varies for different frequencies,) or dBA.  Also, decibels follow a logarithmic scale, which means two important things:

  • A few decibels’ worth of change result in a “twice as loud” perception to your ears.
  • Adding sources of sound doesn’t double the decibel level.

If you want to know how the sound level from a single source is calculated, those calculations are found here.  For the purposes of this blog, though, we’re going to assume a user wants to know what the resultant sound level is going to be if they add a sound generating device to their current (known) situation.

Combined Sound Level (dBA) = 10 x log10[10SL1/10 + 10SL2/10 + 10SL3/10 …]

Let’s use an EXAIR Model 1100 Super Air Nozzle (rated at 74dBA) as an example, and let’s say we have one in operation, and want to add another.  What will be the increase in dBA?

10 x log10[1074/10 + 1074/10] = 77.65 dBA

Now, there are two reasons I picked the Model 1100 as an example:

  • It’s one of our most versatile products, with a wide range of applications, and a proven track record of efficiency, safety, and sound level reduction.
  • We proved out the math in a real live experiment:

Why do I care about all of this?  My Dad experienced dramatic hearing loss from industrial exposure at a relatively young age…he got his first hearing aids in his early 40’s…so I saw, literally up close and very personal, what a quality of life issue that can be.  The fact that I get to use my technical aptitude to help others lower industrial noise exposure is more than just making a living.  It’s something I’m passionate about.  If you want to talk about sound level reduction in regard to your use of compressed air, talk to me.  Please.

Russ Bowman
Application Engineer
EXAIR Corporation
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Video Demonstration of Compounding Sound Levels

In industrial settings, having a single air nozzle or other blowoff product is often not the scenario that is seen.  Many applications require multiple points of blowoff, even if not in the same direction or for the same position within the machine.  In the scenario where multiple nozzles are used, sound levels can get tricky to calculate and is often thought of as a mystery.  If you follow our blog then you may have seen this excellent blog that shows all the math behind calculating the total decibels when multiple sources of noise will be present. The video below gives a demonstration of utilizing two of the EXAIR model 1100 – 1/4″ FNPT Super Air Nozzle.

In the video you see a model 1100 being operated and producing a sound level of 74 dBA from 3′ away from the nozzle point.  When the second nozzle is turned on (also producing 74 dBA individually), the pressure is adjusted back up to the same input pressure and the sound level meter registers 78 dBA from 3′ away.  Following the math laid out in the “excellent blog” link above, the sound level calculated comes out to be the same 78 dBA that is shown in the video using EXAIR’s Digital Sound Level Meter.

If you would like help determining the sound levels within your facility, check out the EXAIR Digital Sound Level Meter as well as reach out to an Application Engineer.

Brian Farno
Application Engineer


Image of Ear auricle Listen by geraitCC0 Create Commons.

Big TV’s and Big Compressed Air Savings

My great big TV bit the dust recently. It was a 65” rear projection, high definition…quite an upgrade over the 32” tube set that it replaced, a decade ago. One thing I remember from the day I bought it: the seller said to me as we were loading it up, “A warning: you’ll never be able to watch anything smaller.” The other thing I remember from that day was getting it back to the house and set up before my wife got home. She walked in, looked at its huge awesomeness in our modestly sized living room and said, “That’s almost embarrassing!” To which I replied, “I KNOW!!!”  Now, it WAS a little big for the room, but we acclimated quickly.

Until last month, when the display started to malfunction. I looked it up, and it was a fatal flaw: the parts would cost almost as much as a new 65” flat screen. Which we’re saving our money for…for now, though, we’re “getting by” with a 42” plasma TV that we “repurposed” from the back room. And the seller’s warning proved mostly true, although I’ve almost adjusted to the smaller screen. First world problems; I know.

One benefit of the smaller screen and advanced technology (plasma vs. those three big light bulbs in the rear projection) was decreased operating cost. Turns out, the 42” plasma uses less than 1/3 the power of the 65” rear projection (91 Watts vs. 283 Watts, respectively.) When my next electric bill comes, I’m wondering if I’m going to be pleased with the reduction, or if it’s going to put into perspective just how much TV I really watch. Stay tuned for more on that…

I recently had the pleasure of helping a customer realize a similar “a-ha” moment, with the amount of compressed air they were using throughout their plant. They were running (40) production machines, turning out custom plastic parts. Each machine had a ¼” crimped-end copper tube, which blows off the part as it’s being machined.

Each of the crimped copper lines uses approximately 30 SCFM when supplied at 80psig. These are being replaced with our Model 1100 Super Air Nozzles. They were able to quickly and easily adapt these by simply cutting off the crimped end, and installing a compression adapter fitting:

EXAIR Model 1100 Super Air Nozzle installs easily on copper lines, with a simple compression adapter.
EXAIR Model 1100 Super Air Nozzle installs easily on copper lines, with a simple compression adapter.

The Super Air Nozzle consumes just 14 SCFM @80psig, so we should be looking at around a 50% reduction in their compressed air usage in the operation, across their (40) machines. While all the data is still not compiled to determine their actual savings, the noise reduction alone has made a noticeable difference in the plant, which they’re getting used to a LOT quicker (and more agreeably) than I am to the smaller TV screen. But enough about that…I’ll be all right; really.

So that’s two of us, waiting for the next electric bill to see just how happy we can be with our energy savings. I don’t know what they’re going to do with their savings, but mine’s going into the 65” (energy efficient) TV fund.

Russ Bowman
Application Engineer
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