Sound Pressure, Sound Power, and Sound Intensity Explained

We are all familiar with sounds in everyday life.  Some sounds are pleasant, and some sounds can be destructive.   Sound has exponents of pressure, power, and intensity.  In this blog, I will go over each one to see how we perceive sound and are affected by it. 

Sound pressure is what our ears pick up.  The small bones in our ears detect pressure changes with our eardrums to convert to noise signals.  In looking at a single source, sound pressure is created by sound waves. .  In looking at a single source, sound pressure is created by sound waves.  The units are measured in Pascals.  The lowest pressure perceived by human ears is 0.00002 Pa, and we can use this value as a reference point.  Depending on the frequency, pain can occur at 65 Pa.  We can arrive at a sound pressure level which is measured in decibels, dB.  This correlation between sound pressures and sound pressure levels is calculated by Equation 1.

Equation 1:

L = 20 * Log10 (P / Pref)

L – Sound Pressure Level, dB

P – Sound pressure, Pa

Pref – reference sound pressure, 0.00002 Pa

Sound pressure has to be measured at a certain distance.  Like a wave in a pond, the farther the distance, the smaller the waves.  Most standards are set at 1 meter away.  As an example, the sound pressure from a passenger car as heard from the roadside is 0.1 Pa.  With Equation 1, we can get the following decibel level:

L = 20 * Log10 (0.1Pa / 0.00002Pa) = 74 dB

Sound power deals with the amount of energy that is generated at the source, which is independent of distance.  There is an old saying, “if a tree falls in the forest and no one is nearby, does it make a sound?”.  Well, it does.  Even though you may be too far away from the source to detect the sound pressure waves, it still creates a sound.  Sound power is important to measure noise in different locations around the source.  This will help to ensure proper protection for the workers in the different areas.  The unit of measure for sound power is watts (W).  Equation 2 shows the formula to calculate sound power levels.  This equation also uses a reference point which was determined by a standard to be 1 pW or 1 * 10-12 Watts. 

Equation 2:

LN = 10 * Log10 (p / pref)

LN – Sound Power Level, dB

p – Sound power, W

pref – reference sound power, 1 * 10-12 W

As an example, a jet engine can generate roughly 1 watt of sound power.  From Equation 2, we get a sound power level of

L = 10 * Log10 (1 W / 1 * 10-12 W) = 120 dB

To avoid confusion with sound pressure levels, we usually use the unit of bel (B) rather than decibel (dB).  So, the jet engine would produce a sound power level of 12 Bel.

Sound intensity is defined as sound power per unit area; it is commonly measured in Watts per square meter, W/m2.  The formula is shown in Equation 3.

Equation 3:

I = p / A

I – Sound Intensity W/m2

p – Source power, W

A – Area from source, m2

From the sound source, the sound intensity is developed by the direction the sound “flows” through a particular area.  If you have ever seen a band trying to setup their sound system, they take into account walls, the size of the room, open areas, speaker angles, etc., to enhance the sound.  The sound pressure, or loudness, will travel through a median at a distance, which could encounter walls, machines, ceilings, etc.  Let’s look at the sound power of the jet engine above at 1 Watt.  If a plane was flying 1,000 meters (3,300 feet) above your head, you could find the sound intensity.  First, sound travels in all directions; so, we will use the surface area of a sphere, 4πr2 to calculate the area.  Since the source is at the center, the distance to the person will be the radius.  So, at 1,000 meters, the area will be 4 * 3.14 * (1,000 m)2 = 12,560,000 m2.  We can deduce from Equation 3 that

I = p / A = 1 W / 12,560,000 m2 = 7.96 * 10-8 W/m2

To correlate this to the sound intensity level, which your ears perceive, it is measured in decibels, dB, and is represented by Equation 4.    

Equation 4:

Li = 10 * Log10 (I / Iref)

Li – Sound Power Intensity, dB

I – Sound intensity, W/m2

Iref – reference sound intensity, 1 * 10-12 W/m2

With the example above of the jet engine that is 1,000 meters above our head, we can calculate the sound level that our ears can hear.  From Equation 4, we have

Li = 10 * Log10 (7.96 * 10-8 W/m2 / 1 * 10-12 W/m2) = 49 dB

Hearing loss is permanent; and it is the most recorded occupational illness in manufacturing plants.  The Occupational Safety and Health Administration (OSHA) is the enforcement agency responsible for determining and fining companies that violate this directive; 29 CFR 1910.95(a).  To keep your operators safe, it is important to measure the sound level of your pneumatic equipment.  NIOSH, or the National Institute for Occupational Safety and Health, uses a Hierarchy of Controls for dealing with safety issues.  And the Engineering Controls is more prevalent on this chart than purchasing personal protective equipment or PPE (reference diagram above).  EXAIR manufactures these engineered products for safety, noise reduction, and cost savings.  They are known as the Intelligent Compressed Air Products®.  To minimize any hearing loss with personnel, EXAIR has a variety of Super Air Nozzles, Safety Air Guns, Super Air Amplifiers, and Super Air Knives that can reduce the sound levels to a safe level.  And as a bonus, it will save you money by reducing your compressed air usage.  You can talk with one of our Application Engineers if you wish to reduce the surrounding sound levels with your pneumatic blow-offs.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo of Ear auricle Listen by geralt Pixabay License

Sound Levels in Your Facility

One of the most common and dangerous hazards that occur within a manufacturing and production facility is the noise level within the plant. Noise is measured in units known as decibels. Decibels are a ratio of the power level of the sound compared to a logarithmic scale. If an employee is an exposed for too long to high levels of noise, they can begin to lose their hearing. That is where the OSHA 29 CFR 1910.95 regulation comes into play.

Hearing loss is the best known, but not the only, ill effect of harmful noise exposure. It can also cause physical and psychological stress, impair concentration, and contribute to workplace accidents or injuries.

This OSHA standard doesn’t just provide the protection against noise in the work place but monitoring as well. Companies shall provide at no cost audiometric tests for all employees to ensure that no damage is being to the hearing of all personnel. This program is to be repeated every six months and the results are to be made accessible to all personnel.                

Hearing is very important to our everyday lives and must be protected due to the fact that once it is damaged hearing loss cannot be lost be repaired. The OHSA 29 CFR 1910.95 is there to protect and monitor this dangerous hazard in the workplace so that all employees can go home safe and sound.

Here at EXAIR we design all of our products to safe and quite. Weather it is using one of our mufflers for vortex tubes or E-vac’s or one of our Super air nozzles we strive to meet and exceed the OSHA standard. One could also purchase EXAIR’s Digital Sound Level Meter which can give a accurate and responsive reading of how loud your compressed air sources are.

For more information on EXAIR’s Digital Sound Level Meter and any of EXAIR‘s Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer

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Efficiency Lab Leads To Big Savings

EXAIR Corporation manufactures quiet, safe, and efficient compressed air products for industry. We want our customers to get the most out of our products, and, in turn, their compressed air systems. To do that, we offer a unique service called the EXAIR Efficiency Lab. Here’s how it works:

  • An Application Engineer can arrange to have your existing compressed air device(s) sent in to our facility.
  • We’ll use our calibrated test equipment to measure the compressed air consumption, sound level, and force applied of those devices.
  • You’ll receive a detailed test report, along with our recommendations to implement an efficient, quiet, and safety compliant solution.
  • We’ll even send your tested device(s) back to you, at no charge, if you wish.

I recently had the pleasure of conducting just such a test on some air guns.  The caller was the Environmental Health & Safety Director for a plastics manufacturer.  The main concern was safety compliance…a recent audit had shown that some workstations were using handheld blowoff devices that did not comply with OSHA standard 1910.242(b), which limits dead end pressure of compressed air products used for cleaning to 30psi.

After discussing their typical uses for these (and other) air guns, they sent in a couple for testing.  Here’s what we found out:

“Thumb guns” are especially popular for blowoff because of their compact size, ergonomic design. and low price.

The air gun with the 7″ straight extension (top) is a “textbook” example of non-compliance with OSHA standard 1910.242(b).  Because it has an open-end discharge with no relief path, this one could cause an air embolism if it were inadvertently dead-ended into the operator’s skin – a potentially fatal condition.  It also uses a considerable amount of compressed air, and is quite loud.  At 80psig supply pressure:

  • Compressed air consumption is 40.7 SCFM
  • Noise level is 95.5dBA
  • Force applied, at a distance of 12″, is 13oz

For comparison’s sake, EXAIR Model 1210-6 Soft Grip Safety Air Gun is fitted with our Super Air Nozzle, on the end of a 6″ rigid extension:

  • Compressed air consumption is 14 SCFM
  • Sound level is 74dBA
  • Force applied, at a distance of 12″, is 13oz…same as theirs.
Model 1210 Soft Grip Safety Air is fitted with an EXAIR Super Air Nozzle. We can also supply it with a Rigid Extension and Chip Shield (right).

The other one is OSHA compliant (it can’t be dead-ended…the cross-drilled hole provides a relief path, but it was still pretty inefficient and loud.  At our standard test pressure of 80psig:

  • Compressed air consumption is 30.8 SCFM
  • Noise level is 94.8dBA
  • Force applied, at a distance of 12″, is 16.9oz

Although the force generated by the Model 1210 Soft Grip Safety Air Gun isn’t quite as high as theirs, it’s still our recommendation here.  Oftentimes, the flow and velocity generated by the engineered Super Air Nozzle is more than capable of meeting the needs of the typical blow off applications these types of air guns are used in.

EXAIR Efficiency Lab testing proves that replacing these air guns with our Soft Grip Safety Air Guns (or at least replacing the tips with EXAIR Super Air Nozzles…we also have adapters for that) will result in compressed air savings of 66% and 55%, respectively, and lower sound levels to within OSHA standard 1910.95(a) limits:

All EXAIR Soft Grip Safety Air Guns comply with these limits for 8 hour exposure.

If you’d like to know more about the efficiency & safety (or lack thereof) of your current air blow off devices, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Managing Pneumatic Sound

I recently took my daughter to a basketball game to watch Xavier University’s Lady Musketeers play. Due to Covid the arena felt empty and we could hear the players on the court and also the the coaches from the opposite side. If this was a regular season game we could barely hear ourselves let alone the teams and coaches. The obvious reason why there was not much noise is that there wasn’t much of a crowd and the crowd makes a lot of sound. So, what is sound?

Sound can be defined as “vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear”. Sounds hit our ears at different pressure levels depending on its strength (“loudness” or volume) and is measured in decibels (dB).

When sound travels and comes into contact with a surface, a portion will be absorbed and another portion will be reflected. Manufacturing environments obviously can be the source of a lot of sound and personnel near the sources should be protected as much as possible. One extremely effective way to do this is to substitute a loud noise source with a quieter one or remove the source all together. PPE can be effective but is much less reliable due to people forgetting to use PPE, using PPE improperly or even deciding for themselves they do not need it.

To substitute or eliminate means something like the strategic placement of air compressor which is not near personnel or recognizing the type of product you choose to use is vital to sound management and the health and safety of people working near the point of use. Many EXAIR products can help you reduce the sound level of your current point-of-use compressed air by replacing commercial air nozzles, open pipes and homemade blowoff solutions with our Engineered Air Nozzles, Safety Air Guns, Air Amplifiers, or Super Air Knives. These products are all designed to minimize compressed air noise and can contribute to lowering the overall noise exposure of your personnel. The additional benefit is that you customers will also typically see a reduction in air consumption which saves money on generating compressed air.

EXAIR’s Digital Sound Level Meter is a tool used to identify and quantify the particular noise levels within an area. The source of loud noises can be quickly identified and isolated so corrective measures can be implemented.

Compressed air noise levels often exceed OSHA (Occupational Safety and Health Administration) noise level exposure requirements. EXAIR pneumatic products meet or exceed the OSHA Standard 29 CFR-1910.95(a) and can be used to reduce sound levels in your compressed air environment.

EXAIR has has many engineered compressed air products that can help reduce your sound levels. Our Application Engineers are ready and eager to help assist your sound level decrease projects. Please contact us at www.EXAIR.com so we can be a vital part of your successful sound reduction program.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: Twitter: @EXAIR_EK