Sound: What Is It … More Importantly, Weighted Scales of Frequencies

We’ve blogged about sound and what exactly it is before, see the link. Understanding that sound is vibration traveling through the air which it is utilizing as an elastic medium.  Well, rather than me continue to write this out, I found a great video to share that is written in song to better recap how sound is created.

Now that we have that recap and understand better what sound is let’s dig a little deeper to better understand why some sounds may appear louder to a person when they may not appear different on a sound scale that is shown by something like a Digital Sound Level Meter.

Loudness is how a person perceives sound and this is correlated to the sound pressure of the frequency of the sound in question.  The loudness is broken into three different weighing scales that are internationally standardized. Each of these scales, A, C, and Z apply a weight to different frequency levels.

  1. The most commonly observed scale here in the USA is the A scale. A is the OSHA selected scale for industrial environments and discriminates against low frequencies greatly.
  2. Z is the zero weighting scale to keep all frequencies equal, this scale was introduced in 2003 as the international standard.
  3. C scale does not attenuate these lower frequencies as they are carrying the ability to cause vibrations within structures or buildings and carry their own set of risks.

To further the explanation on the A-weighted scale, the range of frequencies correlates to the common human hearing spectrum which is 20 Hz to 20kHz. This is the range of frequencies that are most harmful to a person’s hearing and thus were adopted by OSHA. The OSHA standard, 29 CFR 191.95(a), that corresponds to noise level exposure permissible can be read about here on our blog as well.

When using a handy tool such as the Digital Sound Level Meter to measure sound levels you will select whether to use the dBA or dBC scale.  This is the decibel reading according to the scale selected. Again, for here in the USA you would want to focus your measurements on the dBA scale. It is suggested to use this tool at a 3′ distance or at the known distance an operator’s ears would be from the noise generation point.

Many of EXAIR’s engineered compressed air products have the ability to decrease sound levels in your plant. If you would like to discuss how to best reduce sound levels being produced within your facility, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

1 – Fun Science: Sound – @charlieissocoollike – https://youtu.be/xH8mT2IQz7Y

 

Sound: Explaining Power and Pressure

Sound Power…  When I hear that term all I can think of is the classic commercial Maxell®Sound made in 1983.  I was only a year old when that commercial graced the presence of everyone’s TV.  I did see it throughout the years and recall recording Casey Kasem’s Top 40 on Maxell cassettes.  Then, in college it was a classic poster you would see around the dorms.

1(Maxell / Retrontario, 2009)

Needless to say, this does show sound power and sound pressure which is the point of this blog. This video however is not an industrial environment that most of us are accustomed to when worrying about the sound power / sound pressure within an environment.

If you observe the video above the speakers and the driver of the speakers is the generator of sound power.  That is the energy rate emitted by a source.  This power then begins to fill a space which is equivalent to the sound intensity.  This is because the sound energy has a direction that is given to it, think of the speaker.  The speaker gives the sound energy a vector to travel.  Then when the vector hits surfaces that is the sound intensity.

This sound intensity can then be interpreted as the sound power transfer per unit of surrounding surface at a distance.  This will then give the information needed to convert the information to the Sound Pressure level.  This is the force of a sound on a surface area perpendicular to the direction of the sound.

With this information we can then observe the logarithmic unit (or value) used to describe the ratio of sound power, pressure, and intensity, the decibel.  The decibel is what all industrial hygienists and safety personnel are concerned with.   In the end, all of this is started at the point of power generation, when observing compressed air blowoffs, this is the exit point of air from the device.  If you optimize the point of use device to use the least amount of compressed air and be the most efficient then the amount of sound power being generated and eventually being measured as decibels at an operator’s work station, then the result will be lower ambient noise levels.

If you would like to see any of the math behind these conversions (an amazing blog by our own Russ Bowman), click the link. If you want to discuss optimizing your compressed air operations and lower the noise level of the compressed air products in your plant, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

 

 

Video Source: Classic Maxell Cassette commercial – Retrontario – https://www.youtube.com/watch?v=Zk71h2CQ_xM

 

Safety – When You Least Expect It You Need it Most

The cold weather kept me indoors this weekend and I conceded to being a couch potato in front of the TV. One of the shows I watched was the lumberjack competitions – and let me tell you, those guys are crazy. Standing on a board wedged into a notch in the side of a tree, up 40 feet in the air and swinging an ax is just not safe. But, that was the way it was done in the early days before mandated safety rules.

Afterward, I watched a little news only to see hundreds of motorists stranded in their cars due to inclement weather. Folks were on their way home from work and ended up sleeping in their cars. I know it is recommended that you carry an emergency kit in your car but I never gave it any thought it would be needed it in the city. Then I was jolted from my couch when the smoke alarms went off. I forgot about my buffalo wings in the oven. Wow! What if I had left the house?

In the workplace, compressed air safety should be a top priority. Open compressed air lines are extremely noisy and can cause permanent hearing loss which is addressed  OSHA Standard 29 CFR – 1910.95 (a) regarding the allowable noise exposure. High pressure compressed air can pierce the skin and enter the blood stream, causing a dangerous blood embolism – this is why OSHA has standard CFR 1910.242(b), 30 PSI maximum dead end pressure for compressed air blow off.

One of the main issues with regulating all of your compressed air lines to less than thirty psig is, thirty psig does not provide a very effective blow off.  With EXAIR’s  engineered nozzles the air can be kept at higher line pressure and still meet or exceed the OSHA standard. Higher pressure equate to higher velocity and more force upon your application. Because of this, we can solve the application, keep compressed air to a minimum, and keep safety a top priority.

Air Nozzle and Safety Air Gun

EXAIR nozzles are safe, provide very effective blow off, and reduce compressed air consumption. By design they produce output flow up to 25 times the compressed air consumed. For more information or help with your application call our application engineers at 1-800-903-9247

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