What is Sound and Interesting Facts About Sound

In physics, sound is a wave of pressure. It occurs in a medium, which can be a solid, liquid or gas. Sound cannot travel through a vacuum, such as in space. The wave of pressure reaches our ears and causes the ear drum to vibrate, which then goes through a complex process to ultimately be perceived as audible sound.

There are several characteristics of sound waves that can be measured and help define the sound. A sound wave can be visualized as a repeating sinusoidal wave (see below), and can be described by these properties – frequency and wavelength, amplitude, and speed.

Sound Wave
Sound Wave
  • Frequency is the number of cycles in 1 second, and is measured in Hertz (Hz)
  • Wavelength is the distance over which 1 cycle occurs, and for audible sound is  between 17 m and 17 mm long
  • Amplitude is the measure of its change over a single period, and normally a measure of sound loudness
  • Speed is the distance traveled per unit time

The speed of sound in air can be found using the equation:  a = Sqrt (γ•R•T)

where for air:
γ = ratio of specific heats = 1.4,
R = gas constant = 286 m²/s²/K
T = absolute temperature in °K (273.15 + °C)

At room temperature, 22°C (71.6°F), the speed of sound is 343.8 m/s (760 mph)

Some interesting facts about sound:

  • Sounds generally travels faster in solids and liquids than in gases.
  • You can estimate the distance from a lightning strike by counting the seconds that pass between seeing the lightning flash and hearing the thunder.  Take this duration an divide by 5 to get the distance away, in miles.
  • Humans normally hear sound frequencies between 20 Hz and 20,000 Hz.
  • Sound waves above 20,000 Hz are known as ultrasound, and sound waves below 20 Hz are known as infrasound.
  • Sound travel through water close to 4 times faster then through air.
  • The sound of a cracking whip occurs because the speed of the tip has exceeded the speed of sound.

Sound that is too loud can be a problem. The Occupational Safety and Health Administration (OSHA) has set limits on the noise exposure that an employee can be subjected. Exceeding these values can cause permanent damage to your ears and cause noise induced hearing loss. So, knowing and reducing the sound levels within a manufacturing operation is important.

OSHA Chart

EXAIR has many products that can help reduce the sound levels in your processes.  With products such Air Knives, Air Wipes, Air Amplifiers, Air Nozzles and Jets, and Safety Air Guns, strong, quiet and efficient blowoff, drying, and cooling can be performed.

Quiet Products

If you have questions about sound and keeping your sound levels in check or any of the 15 different EXAIR 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.

Brian Bergmann
Application Engineer
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Understanding Decibels & Why OSHA Pays Attention to Your Noise Exposure

In the simplest of metric terms, a decibel is one-tenth of a bel.  But, historically, bel was a unit created to honor Alexander Graham Bell who invented the telephone.  In the early days with telephone wires, they noticed that the signal strength would decay over a long distance.  In order to determine power requirements to connect people for communications, they determined that they could use the ratio of power levels.  As a start, it had to be based on a minimum amount of power required for a person to hear on the telephone.  They found that the signal power level to generate an angular frequency of 5000 radians per second would be that minimum value as determined by an average number of people.  They used this mark as a reference point in the ratio of power levels.  Because of the large variations in values, they simplified the equation on a base-10 log scale and dividing the bel unit by 10.  Thus, creating the measurement of decibel.

Today, this same method is used to measure sound.  Like frequency waves that travel through the telephone wires, pressure waves travel through the air as sound.  This sound pressure is what our ears can detect as loudness, and it has a pressure unit of Pascals (Pa).  As an example, a small sound pressure would be like a whisper while a large sound pressure would be like a jet engine.  This is very important to know as high sound pressures, or loudness, can permanently damage our ears.

With sound pressures, we can determine the Sound Pressure Level (SPL) which is measured in decibels (dB).  Similar to the equation for the telephone power signals above, the SPL also uses a ratio of sound pressures in a base-10 logarithmic scale.  For a minimum reference point, an average human can just start to hear a sound pressure at 0.00002 Pa.  So, the equation for measuring sound levels will use this minimum reference point as shown in 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

Why is this important to know the decibels?  OSHA created a chart in 29CFR-1910.95(a) that shows the different noise levels with exposure times.  This chart was created to protect the operators from hearing loss in work environments.  If the noise level exceeds the limit, then the operators will have to wear Personal Protection Equipment (PPE), or suffer hearing damage.  EXAIR offers a Sound Level Meter, model 9104, to measure sound levels in decibels.  It comes calibrated to accurately measure the sound to determine if you have a safe work environment.

Sound Level Meter

There is a term that is used when it comes to loud noises, NIHL.  This stands for Noise Induced Hearing Loss.  Once hearing is damaged, it will not come back.  To keep your operators safe and reduce NIHL, EXAIR offers many different types of blow-off products that are designed to decrease noise to a safe level.  So, here’s to Alexander Graham Bell for creating the telephone which can be used to contact EXAIR if you have any questions.

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


Photo of Telephone by Alexas_FotosCC0 Create Commons

Video Blog: EXAIR’s Efficiency Lab

If you’d like to know how efficient (or not,) quiet (or not,) and effective (or not) your current compressed air devices are, the EXAIR Efficiency Lab can help.  For more details, we hope you’ll enjoy this short video.

If you’d like to talk about getting the most out of your compressed air system, we’d love to hear from you.

Russ Bowman
Application Engineer
EXAIR Corporation
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Calculating Static Friction To Eject Parts with Air

2″ Flat Super Air Nozzle

In today’s fast-paced world, companies are always looking for ways to do things faster, cheaper, more efficiently without sacrificing safety.

A cereal company had a high-speed system to check the quality of each box of cereal.  When a box did not meet the quality criteria for visual and/or weight, the box would be rejected.  The rejection system that they used was a quick blast of compressed air to remove the box from the conveyor line into a non-conforming bin.  For their first attempt, they tried to use a ¼” copper tube with a solenoid valve attached to a reservoir tank.  When a “bad” box was detected, the solenoid would be triggered, and compressed air would “shoot” the box off the rubber conveyor belt.  The ¼” copper tube can be an inexpensive, common, and easy-to-use device; but they found that the copper tube was very loud (above OSHA limits for noise exposure) and not very effective.  As a note, this company had a safety committee, and they wanted to keep all blowing devices below 80 dBA in this department.  The ¼” copper tube was around 100 dBA.  So, they contacted EXAIR to get our expertise on this type of application.

The cereal company gave me some additional details of the operation.  The box weighed 26 oz. (740 grams) with a dimension of 7.5″  wide by  11″ tall by  2 3/4″ deep (19 cm X 28 cm X 7 cm respectively).  The issue with the ¼” copper tube was the small target area compared to the area of the box.  With any slight variation in the timing sequence, the force would miss the center of mass of the box.  The box could then spin and remain on the conveyor belt.  This would cause stoppage and disruption in the system.  They asked if EXAIR had a better way to remove the defective boxes.

I recommended a model 1122, 2” Flat Super Air Nozzle.  The reason for this style of nozzle was for a variety of reasons.  First, we needed a larger area to “hit” the box.  This Flat Super Air Nozzle has a width of 2” versus the ¼” copper tube.  This increased the target area by 8 times.  So, any small variations in time, we could still hit the center of mass and remove the box.  The second reason was the force rating.  The model 1122 has a force of 22 oz. (624 grams) at 80 PSIG (5.5 bar).  This is slightly under the 26 oz. (740 grams) weight of the cereal box, but we are just sliding the box and not lifting it.  If we can overcome the static friction, then the box can be easily removed.  With Equation 1, we can calculate the required force.

Equation 1:

Fs = ms * W

Fs – Static Force (grams)

m– Static Friction

W – Weight (grams)

From the “Engineering Toolbox”, the static friction between rubber and cardboard is between 0.5 to 0.8.  If I take the worse case condition, I can calculate the static force between the belt and cereal box using Equation 1:

Fs = 0.8 * 740 grams

Fs = 592 grams

The model 1122 has a force of 22 oz. (624 grams), so plenty enough force to move the box from the rubber conveyor belt.

The third reason for this nozzle is the noise level.  The noise level of the model 1122 is 77 dBA, well below the safety requirement for this company.  Noise levels are very important in industries to protect operators from hearing loss, and the model 1122 was able to easily meet that requirement.  I added an additional reason for recommending the 2” Flat Super Air Nozzle; compressed air savings.  Companies sometimes overlook the cost when using compressed air for blow-off devices.  In this comparison, the ¼” copper tube will use 33 SCFM (934 SLPM) at 80 PSIG (5.5 bar) while the model 1122 will only use 21.8 SCFM (622 SLPM).  This is a 33% reduction in compressed air; saving them money.

At the intro, I mentioned that companies are looking to do things faster, cheaper, more effective without sacrificing safety.  For this company, we were able to increase production rates by removing every cereal box from the conveyor belt.  We also saved them money by reducing the compressed air requirement as well as keeping it safe by reducing noise.

If you have an application that needs products to be moved by air, you can contact an Application Engineer at EXAIR to help you with a solution.

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

“Go Green” in 2019 With EXAIR’s Super Air Nozzles & Jets!

If one of your New Year’s resolutions for 2019 is to help improve your impact on the environment, look no further than EXAIR’s Engineered Air Nozzles & Jets. By upgrading your blowoff, cooling, and drying operations to use one of our Super Air Nozzles or Jets you can save as much as 80% of your compressed air usage when compared with an inefficient solution.

open tubes
Example of a manifold of open pipes

An open copper pipe or tube, even if “flattened” as we’ll commonly see, wastes an excessive amount of compressed air. This wasted compressed air can create problems in the facility due to unnecessarily high energy costs and the pressure drop that can be experienced affecting other processes. In addition to simply using too much compressed air, an open pipe or tube will often produce sound levels in excess of 100 dBA. At these sound levels, according to OSHA, permanent hearing damage will occur in just 2 hours of exposure.

OSHA Chart

By simply replacing the open tubes and pipe with an EXAIR Super Air Nozzle, you can quickly reduce air consumption AND reduce the sound level. Sound level isn’t the only thing an OSHA inspector is going to be concerned about regarding an open pipe blowoff, in addition OSHA 1910.242(b) states that a compressed air nozzle used for blowoff or cleaning purposes cannot be dead-ended when using with pressures in excess of 30 psig. I don’t know if you’ve ever tried to use an air gun with 30 psig fed to it, but the effectiveness of it is dramatically reduced. This is why there needs to be a device installed that’ll prevent it from being dead-ended so that you can operate at a higher pressure.

EXAIR Super Air Nozzle entrainment

EXAIR’s Super Air Nozzles are designed with fins that serve two purposes. They help to entrain ambient air from the environment, allowing us to maximize the force and flow from the nozzle but keeping the compressed air consumption minimal. In addition, these fins are what prevents the nozzle openings from being completely blocked off. Using an OSHA compliant compressed air nozzle for all points where a blowoff operation is being performed should be a priority. Each individual infraction will result in a fine if you’re subject to an OSHA inspection. Inspections are typically unannounced, so it’s important to take a look around your shop and make sure you’re using approved products.

The fins along the outside of the Super Air Nozzle prevent it from being dead-ended

So, go ahead and make 2019 the year of energy savings, increased efficiency, and improving worker safety. You’ll find all of the tools you need in EXAIR’s 32nd edition of the catalog. Click here if you’d like a hard copy sent directly to you! Or, get in touch with us today to find out how you can get saving with an Intelligent Compressed Air Product.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD


General Good Ideas For The Compressor Room

When considering your compressor room all too often the phrase applies “out of sight and out of mind”.  Of course, we all know that is not a good approach to the compressor room or really anything in life.  Unfortunately, many of us take for granted that very system that delivers the power to keep our machines, equipment and tools operating.

Air Compressor
Compressor Room Located Outdoors

So, what can we do keep the ‘lungs” of our plants performing reliably and efficiently?  Since this Blog is about “General Good Ideas For The Compressor Room”, I have some points below for your consideration.

  • Ideally the compressor room should be centrally located to minimize the length of the pipes and allows for easier noise control. With long piping runs leaks become more likely and frictional losses are increased.
  • The compressor room should be sized to allow for easy maintenance and future expansion.
  • For efficient operation air compressors need clean intake air. Intake air that is dusty, dirty or contains gaseous contamination will reduce the efficiency and possibly the longevity of your equipment.
  • The compressor room needs adequate ventilation since air compressors generate significant heat. If excessive heat is allowed to build up it reduces the efficiency of the air compressor raising utility costs, causes compressor lubricant to break down prematurely that could possibly result in increased maintenance and compressor failure.
  • What is the velocity of the air through the main headers? If the speed is above 1200 FPM many dryers have reduced efficiency and speeds greater than this can also carry moisture past the drainage drop legs.
  • Excess friction caused by too small of a diameter piping creates pressure loss, which reduces efficiency and if the compressor is ran above its pressure rating to overcome the frictional losses increases energy consumption, maintenance costs and down time.

Now that your compressor room is shipshape in Bristol fashion, you might think that all is well.  While that may be true, chances are there are other significant additional savings to be had.  EXAIR specializes in point of use compressed air products that are highly efficient and quiet!  If you have any blow-offs that are open tube or howl as loud as the ghost of Christmas yet to come, check out EXAIR’s Super Air Nozzles.  They are highly efficient and quiet, in fact they meet OSHA Standard 29 CFR – 1941.95 for maximum allowable noise and OSHA Standard 29 CFR 1910.242 (b) for higher than 30 PSIG blow-off pressure.  All of EXAIR’s compressed air products are engineered to minimize compressed air consumption and take advantage of the Coanda effect.  Simply stated EXAIR’s highly engineered, intelligent designs entrain (combine) ambient air with the compressed air supply which saves you money!

EXAIR Super Air Nozzle entrainment

EXAIR also offers the Ultra Sonic Leak Detector.  Simply point the device at a suspected leak which are typically found at unions, pipes, valves and fittings from up to 20’ away.   Plants that are not maintaining their plumbing can waste up to 30% of their compressors output through undetected leaks.

EXAIR Ultra Sonic Leak Detector

EXAIR has a complete optimization product line that the Ultra Sonic Leak Detector is in that includes the Electronic Flow Control, Digital Flowmeter’s and a Digital Sound Level Meter.  All designed to either increase the safety or efficiency of your compressed air usage.

EXAIR has 15 other product lines all designed to increase your process efficiency and save you money by using you compressed air supply efficiently.  Why not visit the EXAIR website or call and request a free catalog?

When you are looking for expert advice on safe, quiet and efficient point of use compressed air products give us a call.   We would enjoy hearing from you!

Steve Harrison
Application Engineer
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Image taken from the Best Practices for Compressed Air Systems Handbook, 2nd Edition

Back Blow Nozzles Clean Inside Metal Tubes

A manufacturing plant EXAIR worked with made cast aluminum tubes for the automotive industry.  After the parts were cast, a machining operation would clean the ends.  This left coolant and metal shavings inside the tube.  Before going to assembly, they had to clean the part.  They created a two-tube fixture (reference picture above) to fit the 25mm tubes in place.

Two home-made nozzles were used to fit inside the tubes to blow compressed air.  The nozzles were attached to the ends of two 17mm pipes which supplied the compressed air.  A cylinder was used to push the nozzles from the top of the aluminum tube to the bottom then back up again.  The liquid emulsion and debris would be pushed downward into a collection drum.  When they started operating their system, the inside of the tubes still had contamination inside.  They wanted to improve their process, so they looked for an expert in nozzle designs, EXAIR.

Back Blow Air Nozzle Family

EXAIR designed and manufactures a nozzle for just this type of operation, the Back Blow Air Nozzles.  We offer three different sizes to fit inside a wide variety of diameters from ¼” (6.3mm) to 16” (406mm).  They are designed to clean tubing, pipes, hoses, and channels.  The 360o rear airflow pattern can “wipe” the entire internal surface from coolant, chips, and debris.  For the application above, I recommended the model 1006SS Back Blow Air Nozzle.  This 316SS robust design would fit inside the tubes above.  The range for this Back Blow Air Nozzle is from 7/8” (22mm) to 4” (102mm) diameters.  The customer did have to modify the function of the equipment by placing the cylinder and the rods under the aluminum tubes.  The reverse airflow would still push the contamination into the collection drum that was placed underneath the tubes.

After installing the model 1006SS onto the rods, the cleaning operation became more efficient.  Not only was the entire internal diameter getting clean, they were able to turn off the compressed air until they reached the top of the tube.  With the model 1006SS, they only needed one pass to clean.  This cut the air consumption in half, saving them much money by using less compressed air.  In addition, they were able to speed up their operation by 20%.  Cleaner tubes, less time, cost savings; they were happy that they contacted EXAIR for our expertise.

Reverse Air Flow

If you need to clean the inside of tubes, hoses, pipes, etc., EXAIR has the perfect nozzle for you, the Back Blow Air Nozzles.  EXAIR can also offer these nozzles on our VariBlast, Soft Grip and Heavy Duty Air Guns for manual operations.  They come with Chip Shields and extensions that can reach as far as 72” (1829mm).  Or like the customer above, automate the system to get a great non-contact cleaning.

If you require any more details, you can contact an Application Engineer at EXAIR.  We will be happy to help.

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