Understanding Noise: Sound Power Vs. Sound Pressure

Sound Power and Sound Pressure have been covered a few other times here on the EXAIR Blog. Once here by Brian who made the visual correlation in regards to a speaker and a musical instrument. And here by Russ who breaks down how you calculate sound power level with the below equation!
Sound Power Equation
too lou Sound Power Level Equation
All machines generate sound when they are in operation. The propagated sound waves cause small changes in the ambient air pressure while traveling. A sound source produces sound power and this generates a sound pressure fluctuation in the air. Sound power is the cause of this, whereas sound pressure is the effect. To put it more simply, what we hear is sound pressure, but this sound pressure is caused by the sound power of the emitting sound source. To make a comparison, imagine for example a simple light bulb. The bulb’s power wattage (in W) represents the sound power, whereas the bulb’s light intensity represents the sound pressure.
Light Bulb
Sound power does not generally depend on the environment. On the contrary, the sound pressure depends on the distance from the source and also on the acoustic environment where the sound wave is produced. In the case of indoor installations for example, sound pressure depends on the size of the room and on the sound absorption capacity of the surfaces. For instance, say the room walls don’t absorb all the sound but reflect parts of it, then the sound pressure will increase due to the so called reverberation effect. (reverberation time is broadly defined as the time it takes for the sound pressure to reduce by 60 dB after the sound emitting source has been shut off). OSHA puts the following limits on personnel exposure to certain noise levels:
Working in areas that exceed these levels will require hearing protection.
EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind.  If you’d like to talk about how we can help protect you and your folks’ hearing, call us. Jordan Shouse Application Engineer Send me an email Find us on the Web  Like us on Facebook Twitter: @EXAIR_JS Light Bulb image courtesy of  josh LightWork  Creative Commons License

Sound Power Level and Sound Pressure

Energy…all day (and night) long, we humans are surrounded by – and bombarded by – all kinds of energy. Sometimes, the effects are pleasant; even beneficial: the warmth of the sun’s rays (solar energy) on a nice spring day is the sure-fire cure for Seasonal Affective Disorder, and is also the catalyst your body needs to produce vitamin D. Good things, both. And great reasons to get outside a little more often.

Sometimes, the effects aren’t so pleasant, and they can even be harmful. Lengthy, unprotected exposure to that same wonderful sun’s rays will give you a nasty sunburn. Which can lead to skin cancer. Not good things, either. And great reasons to regularly apply sunblock, and/or limit exposure if you can.

Sound is another constant source of energy that we’re exposed to, and one we can’t simply escape by going inside. Especially if “inside” is a factory, machine shop, or a concert arena. This brings me to the first point of today’s blog: sound power.

Strictly speaking, power is energy per unit time, and can be applied to energy generation (like how much HP an engine generates as it runs) or energy consumption (like how much HP a motor uses as it turns its shaft) For discussions of sound, though, sound power level is applied to the generation end. This is what we mean when we talk about how much sound is made by a punch press, a machine tool, or a rock band’s sound system.

Sound pressure, in contrast, is a measure of the sound power’s intensity at the target’s (e.g., your ear’s) distance from the source. The farther away you get from the sound’s generation, the lower the sound pressure will be. But the sound power didn’t change.

Just like the power made by an engine and used by a motor are both defined in the same units – usually horsepower or watts – sound power level (e.g. generation) and sound pressure (e.g. “use” by your ears) use the same unit of measure: the decibel.  The big difference, though, is that while power levels of machinery in motion are linear in scale, sound power level and pressure scales are logarithmic.  And that’s where the math can get kind of challenging.  But if you’re up for it, let’s look at how you calculate sound power level:

Sound Power Level Equation


Wis reference power (in Watts,) normally considered to be 10-12 W, which is the lowest sound perceptible to the human ear under ideal conditions, and

W is the published sound power of the device (in Watts.)

That’s going to give you the sound power level, in decibels, being generated by the sound source.  To calculate the sound pressure level:

Sound Power Level to Sound Pressure Equation


Lis the sound power level…see above, and

A is the surface area at a given distance.  If the sound is emitted equally in all directions, we can use the formula for hemispheric area, 2πrwhere r=distance from source to calculate the area.

These formulas ignore any effects from the acoustic qualities of the space in which the sound is occurring.  Many factors will affect this, such as how much sound energy the walls and ceiling will absorb or reflect.  This is determined by the material(s) of construction, the height of the ceiling, etc.

These formulas may help you get a “big picture” idea of the sound levels you might expect in applications where the input data is available.  Aside from that, they certainly put into perspective the importance of hearing protection when an analysis reveals higher levels.  OSHA puts the following limits on personnel exposure to certain noise levels:

Working in areas that exceed these levels will require hearing protection.

EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind.  If you’d like to talk about how we can help protect you and your folks’ hearing, call us.


Can Fish Hear & Other Noise Exposure Facts?

When I was visiting a supplier in Japan, our host was extremely proud of their koi pond and wanted to demonstrate something. He took us to the pond’s edge and clapped his hands. From the murky depths of the pond emerged huge koi breaking the surface with open mouths. As their reward, he tossed them a handful of fish food.

While everyone else was enamored with his ability to have trained the fish, I was awestruck with the fact that they could hear the sound of clapping deep down into the pond. No wonder dad kept telling me to be quiet or you will scare the fish away.

According to the National Wildlife Federation fish don’t have ears that we can see, but they do have ear parts inside their heads. They pick up sounds in the water through the lateral lines that runs down each side of its body and transmitted to their internal ear.

While human auditory abilities may not be as sensitive as the rest of the animal kingdom, the inner workings of our ears are very sensitive easily damaged. Listening to loud noise for long periods of time can damage the hair cells in the inner ear. Noise-induced hearing loss usually develops gradually and painlessly. We live in a noisy world and hearing loss among Americans is significant. According to the Center for Hearing and Communications, approximately 12% of the U.S. population or 38 million Americans have a significant hearing loss.

For 30 years EXAIR has been designing and manufacturing compressed Super Air Nozzles, jets, knives, and amplifiers that significantly reduce sound levels and compressed air costs. Protect your hearing as well as your employee’s and save money by contacting our application engineers and they will show you how.

Joe Panfalone
Application Engineer
Phone (513) 671-3322
Fax   (513) 671-3363
Web: www.exair.com
Twitter: EXAIR_JP


If It Doesn’t Seem Completely Safe, It Probably Isn’t

I like quips and quotes. I keep a few funny ones tucked away for special moments. I don’t golf a lot (or well), but when friends talk about it, I always feel the need to tell them that Mark Twain called the game “a fine walk, ruined.” Even though I rarely fly, and don’t drink, if the topic of an airplane trip arises, I’m quick to recall the words of my favorite author Lewis Grizzard, who said: “Given a choice, I will not fly. Given no choice, I will not fly sober.”

Recently, I stumbled across a list of safety-related quotes. With apologies to the various authors, I don’t see myself looking for opportunities to insert them into conversations with the same zeal that I use my Twain and Grizzard. A few of them, however, reminded me of the folly of one of my all-time overused quips, attributed to baseball player Lefty Gomez: “I’d rather be lucky than good.”

Hearing protection is a sound investment. ~Author Unknown

A few years ago, I took a routine hearing test as part of a job-related physical exam. I hear just fine, so it was nothing I’d thought about having done on purpose in years. The results were well within specifications, but the technician noted a slight dip among certain frequencies, and asked if I’d ever had long-term exposure to heavy machinery. Turns out, I did indeed spend a majority of my waking hours, for months at a time, in the engine room of a Trident submarine, during my six years as a sailor. Hearing protection was actually abundantly available, and honestly, I considered my use of it to be “frequent” if not “fastidious.” Again, my hearing’s fine, and I don’t lie awake at night worrying about going deaf, but, since that test, I do have a higher appreciation for my sense of hearing, and a greater sense of urgency to protect it. Ask around; you won’t find me in the Efficiency Lab without a set of foam ear plugs, correctly inserted.

To learn about eye protection, ask someone who has one. ~Author Unknown

I once suffered a scratched cornea. It wasn’t industrial accident; in fact, it happened at home, in my bedroom. It was early morning, and I’d hit the “snooze” button to capture just a few more blessed moments of pillow time. Just as I rolled back over, my wife adjusted one of those sacred pillows, and her fingernail found my eye socket. It’s especially curious that such a freak accident would happen to me, because I’ve always been very keen on eye protection.  I always keep my safety glasses handy, and I don’t sleep on that side of the bed anymore.

Of course, workplace safety encompasses way more than just sight & hearing protection, but this is a blog, not a book. So if your job, or current task that may just be a small part of your job, calls for it, wear the ear plugs, and/or the safety glasses, long sleeves, steel-toed boots, respirators, or whatever.  If your job/task(s) involves the use of compressed air, you can limit your noise exposure by using engineered products – for instance, EXAIR’s Super Air Knives (running at 80psig) generate only 69 dBA, versus drilled pipe blowoffs, flat air nozzles, or blower air knives, which can run over 100 dBA.  But even if you forego the earplugs around a Super Air Knife (OSHA says you can, but I still don’t), you’ll definitely need the safety glasses – when the air (and any particles entrained in it) is moving at up to 11,800 feet per minute, you just can’t blink that fast.

In closing, I leave you with the words of the venerable philosopher Red Green, who said, “We’re all in this together, and I’m pulling for you.”

Working safely may get old, but so do those who practice it. ~Author Unknown

Russ Bowman
Application Engineer
EXAIR Corporation
Web: www.exair.com
Blog: http://blog.exair.com/
Twitter: twitter.com/exair_rb
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