Tag: sound pressure

Measuring and Adding Sounds

Published on by John BallLeave a comment

My colleague, Russ Bowman, wrote a blog about “Sound Power vs Sound Pressure vs Sound Pressure Level”.  He discussed the logarithmic equations around sound.  I will be discussing what happens when you have more than one sound source, as often heard within manufacturing plants.  Sounds can be added together to determine the overall sound level that you hear.  This is very important when it comes to minimizing hearing loss.

In looking at a single source of sound, sound pressure is created by the loudness of a noise.  The units are measured in Pascals.  The lowest pressure perceived by human hearing is 0.00002 Pa, and we can use this value as a reference point.  From sound pressures, we can arrive at a sound pressure level which is measured in decibel, dB.  This correlation between sound pressures and sound pressure levels are calculated by Equation 1:

L = 20 * Log10 (P / Pref)

L – Sound Pressure Level, dB

P – Sound pressure, Pa

Pref – reference sound pressure, 0.00002 Pa

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

Because human ears are sensitive to different frequencies, the sound pressure levels can be modified, or weighted, to indicate an effective loudness level for humans.  This adjustment is done in two different ways; A-weighting and C-weighting.  The C-weighting is for very loud noises with high peaks or sharp impacts like gunfire. The A-weighting is the most used value as the sound pressure levels are adjusted by the frequency level.  For higher and lower frequencies, the change in the sound value is much greater than the mid-level frequencies that are within our hearing range.  Sound measurements for safety are measured on an A-weighted scale.  OSHA created a chart in the standard 29CFR-1910.95(a).  It shows the noise levels over exposure times for an operator.  To use the OSHA chart accurately, the total noise level in dBA should be calculated.

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.

To determine the total sound level, we can add all the sound pressure levels together by Equation 2:

Equation 2:

Where L1, L2… represents the sound pressure level in dBA for each sound source.

As an example, a manufacturing plant had an operator using a machine that had four copper tubes to blow off a cutting operation (reference photo below).

Blow off station

The decibel level for a copper tube was measured at 98 dBA.  The total amount of sound that the operator was exposed to was determined by Equation 2 with four values.

L = 10 * log10 (109.8 + 109.8 + 109.8 + 109.8)

L = 104 dBA

In looking at the OSHA chart above, the operator would only be allowed to operate the machine only a little over one hour without hearing protection.  In this same example, we replaced the copper tubes with an EXAIR Super Air Nozzle, model 1100SS.  The noise level for each nozzle is 74 dBA at 80 PSIG (5.5 bar).  By replacing all four copper tubes with Super Air Nozzles, Equation 2 becomes:

L = 10 * log10 (107.4 + 107.4+ 107.4 + 107.4)

L = 80 dBA

The total sound level is now in accordance with OSHA regulations for the operator to work all 8 hours at the machine without hearing protection.

A commonly used acronym for hearing safety is NIHL, or Noise Induced Hearing Loss.  To keep your operators safe and reduce NIHL, it is important to measure the total sound level in that area.  As a protocol in safety, it is a requirement to use engineering standards before purchasing personal protective equipment or PPE.  For the customer above, they followed that protocol with our Super Air Nozzles.  If you need to reduce noise levels in your facility, EXAIR offers a large line of blow-off products that can meet the safety requirements.  You can contact an Application Engineer for more information. 

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

Photo: Ear by PublicDomainPictures  Pixabay License

The Story Behind Decibels

Published on by Russ BowmanLeave a comment

While ‘sound’ has been around (almost quite literally) forever, our units of quantifying it are relatively new. Most of us are familiar with the word ‘decibel’ and know that it has something to do with how ‘loud’ a sound is. The word ‘decibel’ originated, however, as a unit to quantify the loss of the strength of a signal as it traveled through telephone and telegraph wires. From the invention of the telegraph in the 1840’s, miles and miles (and miles) of cable started crisscrossing the country, and eventually the world. The unit they used to quantify signal loss back then was known as a “mile of standard cable” or “MSC”. And it was just that: the loss of signal energy as it traveled through one mile of standard (approximately 19 gauge wire back then) cable.

In 1924, Bell Telephone Laboratories introduced a new unit: the Transmission Unit (TU) which changed the math from linear to logarithmic. One TU was defined such that the number of TUs was ten times the base-10 logarithm of the ratio of measured power to a reference power. In 1928, the Bell folks proposed using a new word they’d coined: ‘decibels’, instead of TU’s, in honor of the founder of their technology and namesake of their company, Alexander Graham Bell.

While the decibel is still the commonly accepted unit of measure for signal loss in cable, it also became popularized as a unit to quantify sound pressure level, since that’s a logarithmic measurement as well, of the ratio of actual sound pressure being applied (determined by the frequency & amplitude of the sound waves hitting your eardrum) to a base level of sound pressure (the low threshold of hearing for a typical person…what we might informally call “complete silence”.)

There are two ways to determine sound pressure level: you can do the math, or you can use a device that measures it, like the EXAIR Model 9104 Digital Sound Level Meter. These will tell us how ‘loud’ a sound (or the overall sound in a given space) is.

In contrast to the 98dBA sound level from this array of nozzles, the sound pressure level from an EXAIR Super Air Knife is only 69dBA.

This is important because too much of ANYTHING is likely to be detrimental, and sound pressure level is absolutely in that category. Exposure to extraordinarily loud sounds, even momentarily, can irreversibly damage your hearing. And constant exposure to moderately loud sound levels can do it too.

In the United States, the Occupational Safety and Health Administration (OSHA) published Standard 1910.95(a) to identify the maximum allowable noise exposure by hours, and sound level. The proper use of hearing protection is mandated if personnel are exposed to levels in excess of these limits for a given period of time:

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

When I was little, my Dad had to get hearing aids as a result of occupational noise exposure, so I know first-hand what an impact has on one’s quality of life – and that of the people they spend a lot of time around. It’s one of the big reasons that I always talk about how quiet EXAIR engineered compressed air products are, compared with air blowoffs that aren’t designed to attenuate sound pressure levels.

The ability to hear well is a wonderful gift, and one worth preserving. If you have to work in a loud environment, get some good ear plugs or ear muffs. They make them now with noise-canceling features, so you can still hear people talk while wearing them. If you have questions about whether the environment is “too loud”, it very well might be. Take measurements. If they’re higher than the OSHA limits above, consider the source and whether it can be mitigated, or even eliminated. And if the source is from compressed air blow offs, EXAIR can definitely help – give me a call.

Russ Bowman, CCASS

Application Engineer
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Sound Power vs Sound Pressure vs Sound Pressure Level

Published on by Russ BowmanLeave a comment

A long time ago, in this galaxy right here, a movie called “Star Wars” was released. It was 1977, and, as a 10-year-old boy, the previews (that’s what we called “trailers” back then) grabbed my complete attention. I was fascinated by sound effects like the evil roar of the Empire’s TIE fighters, the sleek whistling hum of the Rebel’s X Wings, the terrifying explosion of Alderaan, and the victorious one of the Death Star. Imagine my surprise when, later that year, in 6th grade science class, we learned that SOUND DOESN’T TRAVEL IN A VACUUM!

Turns out, though, that sound DOES travel quite well through air. You’re almost certainly experiencing some right now – it’s actually quite difficult to eliminate ALL the sounds from any given area. Like anything that travels, it’s got a start and an end point, and we can measure parameters at both to quantify levels of sound power (at the starting point) and sound pressure (at the end point.)

Power is defined as the amount of energy transferred or converted per unit time, and applies to any form of energy…sound included. Philosopher types can debate the question “If a tree falls in the forest and nobody’s there to hear it, does it make a sound?” all day long, but engineers know the answer is “Of course it does!” Whether the sound comes from a hammer hitting a nail, a stereo’s speakers, a tree falling in a deserted forest or whatever, we can quantify the power generated in watts, just like any other generation of power.

Pressure is defined as the amount of force applied to a specified area. When we hear a sound, it’s because a sound wave created by the energy transfer at the source – perhaps by a tree hitting the ground in a forest – causes changes in the relatively low pressure being applied to our eardrums by the low power of the sound being generated in the quiet forest. This is measured in pascals – the SI unit of measure for pressure.

These units of sound power & sound pressure are used all the time by professionals who are calculating acoustic levels. For example, they’ll be used to determine how powerful a PA system has to be in a room of a certain size to hear a lecturer, or a singer, or a symphony. Each of those setups will need different sound power generation values for listeners to get the desired effect of what they’re hearing.

For those of us who are keen on preventing hearing loss, we’re going to concern ourselves with the sound pressure level. This is a logarithmic measure of the ratio of the sound pressure being applied to a reference, or base level, sound pressure. Most of the time, that reference level is the hearing threshold of a typical person without any hearing impairments, and it’s measured in decibels…a unit that most of us are at least somewhat familiar with. There are two ways to determine the sound pressure level: you can do the math, or you can use a measurement device, like EXAIR’s Model 9104 Digital Sound Level Meter.

Identify -and quantify – high noise levels quickly & easily with EXAIR Model 9104 Digital Sound Level Meter.

Compressed air use is LOUD. EXAIR has solutions for that, though. If you’d like to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
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What is Sound, and How Can You Reduce It?

Published on by John BallLeave a comment

Many manufacturing plants have a strong focus on safety for their workers.  One major safety concern that is commonly overlooked is noise.   Occupational Safety and Health Administration, or OSHA, has a directive that defines the noise exposure over a time-weighted average; 29CFR 1910.95(a).   For an eight-hour day, the maximum noise level is 90 dBA.  The Center for Disease Control, CDC, reports that “approximately 18% of all manufacturing workers have hearing difficulty”1.

What is sound?  In the simplest of terms, a decibel is one-tenth of a bel.  Historically, bel was a unit created to honor Alexander Graham Bell, who invented the telephone.  Like the frequency waves that travel through telephone wires, pressure waves travel through the air as sound.  This sound pressure is what our ears can detect as loudness.  EXAIR offers a Digital Sound Level Meter, model 9104, that is calibrated and can measure sound in decibels.  It is very important to know the sound level, as it can permanently damage your ears.

Here is a test for you.  If you go and stand in your plant, you can probably hear loud noises coming from your compressed air system.  EXAIR has an engineered product to solve most of them.  On the Hierarchy of Controls for NIOSH, Personal Protection Equipment, PPE, is the least effective.  A better control would be to isolate your operators from the hazard with an engineered product.  EXAIR can offer that solution for many of your blow-offs and pneumatic discharges to reduce noise levels.  This would include; but not be limited to; Super Air Nozzles, Safety Air Guns, Super Air Knives, and Super Air Amplifiers. 

Let’s look at a ¼” open copper tube.  It can create a sound level of over 100 dBA.  They are commonly used because they are readily available and inexpensive to make.  But they waste a lot of compressed air, as well as creating a hazard for your operators.  Just by adding a model 1100 Super Air Nozzle to the end of the copper tube, we can reduce the noise level to 74 dBA at 80 PSIG (5.5 bar).  Wow!  Not only will it remove the hazard, but it will reduce the amount of compressed air usage; saving you money.  Here is a quick video to show the importance of the EXAIR Super Air Nozzles.

At EXAIR, we have a statement, “Safety is everyone’s responsibility.”  EXAIR manufactures engineered products with high quality, safety, and efficiency in mind.  To keep your operators safe, 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 you can use to contact an Application Engineer at EXAIR.  We will be happy to help to reduce your sound levels. 

John Ball
Application Engineer


Email: johnball@exair.com
Twitter: @EXAIR_jb

Note 1: https://www.cdc.gov/niosh/topics/ohl/manufacturing.html