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)

where:

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

Sound – It Adds Up! How to Calculate Decibel Levels

Keeping noise levels in check and at safe levels is very important to ensure employee safety and well being.  OSHA (the Occupational Safety and Health Administration) through standard 29 CFR-1910.95(a) has studied the situation and set Maximum Allowable Noise Exposure limits in Hours per Day based on the Sound Level, in dBA, of exposure.

For existing processes, a Digital Sound Meter is a valuable tool to measure the sound level to ensure that the source of loud noises can be quickly identified and isolated for immediate corrective action.

For new processes, or changes to an existing process, it is important to estimate the sound level prior to installation and start-up, so that precautions can be taken as needed.

For example, let’s say we are going to add a blow off station to clean off a part on a conveyor to improve the process and increase the throughput.  A typical set-up might be a 12″ Super Air Knife (model 110012) blowing off the top and a pair of Super Air Nozzles (model 1100) to blow off the sides.

SAK and ASAN
12″ Super Air Knife and Super Air Nozzle

If we look at the performance data for the (2) different blow off devices, we find that the Super Air Knife is rated at 69 dBA and the nozzles at 74 dBA, when operated at 80 PSIG of compressed air supply.

SAK and ASAN

When asked, “what is the sound level for (1) of the knives, and (2) of the nozzles” a little Acoustic Engineering is in order. The decibel scale is logarithmic, and determining the total sound level when all (3) devices are in operation is not as easy as adding up the three sound level values (which would equal 218 dBA, way off the charts!).  Thankfully, both the actual sound level and the numerical value are determined another way.  I’ll spare you a lot of the math but the equation is as below.

Capture

… where SL1, SL2, SL3, … are the sound levels in dBA of the each sound makers, for as many that are being combined (in our example SL1 = 69, SL2 = 74 and SL3 = 74)

Plugging in the numbers into the equation, the combined sound level works out to be a quiet 77.65 dBA — well within the OSHA limit for exposure for a full 8 hour period.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can make your process better and quieter, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Small, Precise Blowoff at Your Fingertips

For many blowoff applications, stronger isn’t necessarily better.  For applications and processes where a light, but effective blast of air is needed for cleaning and drying, the VariBlast Compact Safety Air Gun with the Atto, Pico, or Nano nozzle fits the bill. The smallest of the EXAIR engineered Super Air Nozzle family, the Atto, Pico, and Nano have been designed to provide the smallest, most precise blowoff possible. The focused airflow pattern allows for very accurate control and placement of the air stream.  The nozzles are available in both Type 316 Stainless Steel and PEEK plastic (useful for harsh environments, and is non-marring)

img_7480.jpg
The Atto, Pico, and Nano Super Air Nozzles (Scale is in Inches)

The new VariBlast Compact Safety Air Gun is a great choice for putting the power and performance of the nozzle into a small and lightweight air gun. Designed with a variable flow trigger, the airflow can be throttled from a whisper to full force, simply by varying the trigger pull distance.

1698SS
VariBlast Model 1698SS, with Stainless Steel Nano Super Air Nozzle

The Atto, Pico, and Nano nozzles use very little compressed air and are extremely quiet, easily meeting OSHA Standard 29 CFR 1910.95(a) for Noise Exposure.  The design incorporates engineered solutions for safety and can be supplied with higher pressure compressed air and meet OSHA Standard 29 CFR 1910.242(b), relating to dead end pressure requirements.

The table below provides performance data, including the compressed air consumption, force, and sound level for the various configurations.

VariBlast With Small Nozzles

Note that the VariBlast air guns can be had with extensions from 6″ to 72″ and chip shields to meet the performance and safety needs of any application.

The Atto, Pico and Nano Nozzles can also be configured to work with the Soft Grip style of Safety Air Gun.  Consult an Application Engineer for assistance in choosing.

If you have any questions about the Atto, Pico, or Nano nozzles, the VariBlast Compact Safety Air Gun, or any EXAIR compressed air product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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The Decibel

The decibel is a unit of measurement that relates the ratio of a physical value to another value and is expressed on a logarithmic scale.  The common symbol for decibel is dB.  The decibel is used as a measure for many parameters in science and engineering such as acoustics (sound), electronics (power levels) and control theory.

The decibel originates from methods used to express performance and loss in telegraph and telephone circuits.  The term ‘bel’ was coined in honor of Alexander Graham Bell, and the decibel, being 1/10th of a bel was established.

For most of us, the decibel is the familiar term relating to how loud a sound is.

With sound, the sound pressure is typically what is measured and is the local pressure deviation from the base or equilibrium atmospheric pressure, caused by a sound wave. In air, the sound pressure can be measured by a standard microphone, and is measured in pascals (Pa.)

To get to the common decibel reading we are familiar with, a little mathematics comes into play.

Capture

  • where Lp is the Sound Level in dB, prms is the measured sound pressure, and pref is the standard sound reference pressure of 20 micropascals.
  • The prms is what is measured by a microphone

Below are some representative sounds and the decibel rating – Note that sounds that are above 85 dB can cause hearing issues, and proper protection should be taken.Decibel Scale Still Photo

Some other interesting blogs about sound for you take a look at-

Measuring and Adding Sounds

Sound Power Level and Sound Pressure

Super Air Knife Math – When 72  + 72 = 75

If you would like to talk about sound or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Digital Sound Level Meter Identifies Harmful Noise in the Workplace

slm-newlabel EXAIR offers the model 9104 Digital Sound Level Meter.  It is an easy to use instrument for measuring and monitoring the sound level pressures in and around equipment and other manufacturing processes.

Sound meters convert the movement of a thin membrane due to the pressure waves of sound into an electric signal that is processed and turned into a readable output, typically in dBA.  The dBA scale is the weighted scale that most closely matches the human ear in terms of the sounds and frequencies that can be detected.

 

To protect workers in the workplace from suffering hearing loss OSHA has set limits to the time of exposure based on the sound level.  The information in the OSHA Standard 29 CFR – 1910.95(a) is summarized below.

OSHA Noise Level

The Digital Sound Meter can be used to monitor and measure sound levels of manufacturing processed such as blowoffs for cooling or drying.  Many blowoffs, especially open or drilled pipes are very inefficient and can be identified as a source of excessive noise, outside the OSHA exposure ranges.  Once the noise violators are identified, a review can be done and the implementation of engineered solutions such as Super air Nozzles or Super Air Knives can be investigated. Keeping harmful noise levels in check benefits everyone involved.

The EXAIR Digital Sound Level Meter is an accurate and responsive instrument that measures the decibel level of the sound and displays the result on the large optionally back-lit LCD display. There is an “F/S” option to provide measurement in either ‘slow’ or ‘fast’ modes for stable or quickly varying noises. The ‘Max Hold’ function will capture and hold the maximum sound level, and update if a louder sound occurs.

Certification of accuracy and calibration traceable to NIST (National Institute of Standards and Technology) is included.

There is an informative Video Blog, presented by @EXAIR_LE that can be found here.

If you have questions about the Digital Sound Level Meter, or would like to talk about any of the quiet EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Calibration – Keep Your Meters True

EXAIR offers meters to measure the level of physical parameters such as sound and static. Each meter has sensitive electrical circuitry and a periodic calibration is recommended to ensure the meter readings are tried and true.

The model 9104 Digital Sound Level Meter is an easy to use instrument that measures and monitors the sound level pressure in a wide variety of industrial environments. The source of loud noises can be quickly identified so that corrective measures can be taken to keep sound levels at or below OSHA maximum allowable exposure limits.

The sound meter comes from the factory with an NIST (National Institute of Standards and Technology) certificate of accuracy and calibration.  As a good practice, EXAIR recommends a yearly calibration of the instrument, and we offer a service that calibrates the unit to the same NIST standards and provide a written report of the calibration.

The model 7905 Static Meter allows easy one-hand static measurements.  It is useful in both locating sources of high static charge and checking the reduction of static after treatment with an EXAIR Static Elimination product.  The unit is sensitive and responsive, and indicates the the surface polarity of objects up to +/- 20 kV when measured from 1″ away.

It is also recommended that the Static Meter be calibrated on a yearly basis.  EXAIR offers (3) levels of calibration service.  The first two provide calibration in accordance with MIL Standards using accepted procedures and standards traceable to NIST.  The third calibration service conforms to the same Mil Standard, as well as ISO/IEC standards.

Annual calibration service of your EXAIR Digital Sound and Static Meter, along with proper care and storage, will keep your meter performing tried and true for many years, providing accurate and useful measurements.

To initiate a calibration service, give us a call and an Application Engineer will issue an Returned Good number, and provide instructions on how to ship the meter to EXAIR.

If you have questions regarding calibration services for your meters or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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