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


1 – Fun Science: Sound – @charlieissocoollike –


Where Was I 14 Years Ago Today?

This morning was like most other mornings for me.   I woke up and got ready, my wife had just finished feeding our youngest daughter when I was getting ready to leave.   This is a little out of the norm as they are typically still sleeping, since she was in the kitchen when I was going to leave I gave her a kiss and a hug and it was one that just felt like it was really needed.   I hadn’t put much more thought into it, and headed on in to the office.   On my way in I stopped to pick up some morning snacks for the crew here and came on in to the office.   Still, nothing really struck me about today.

In a meeting this morning Bryan Peters mentioned that it was in a meeting just like the one we were in at pretty close to the same time when the first plane hit 14 years ago.  It is a memory that everyone with EXAIR 14 years ago remembers because someone brought a TV in from home and they placed it in the center of the office to try and learn what was happening. A very familiar setting as all of us throughout the country.

3322 Jefferson Ave.
3322 Jefferson Ave.

That made me think of where I was on this day 14 years ago.   I was Sophomore at University of Cincinnati and had just left a class, I was heading back to the fraternity house that I was living in. On the walk back I got a message from a good friend asking if I was okay and if I had seen what was happening.  Once I got to the house I went straight to the loft and turned on the TV. I sat and watched the news coverage with the few of us that were there at that time. t more messages and calls from friends on my phone asking if I had heard.   It still was something I couldn’t wrap my head around.

On that day I will always remember the first person who contacted me and not knowing what was going on.  I have been to the 9/11 site since then but it was before the memorial opened.   Even though it was years after that horrific day there were still memorials surrounding the construction site.
When 9/11 was mentioned this morning I got to see each person I was surrounded by begin to relive that day in their own minds and think of where they were.   Even though I wasn’t at the same place they where and I didn’t even know any of them, we all shared the same thoughts.

My thoughts and prayers still go out to the people that lost their lives on that day, and their families.  And I continue to honor and respect the brave service men and women that choose to protect our freedom as we go about our daily routines.

Never Forget!

Brian Farno
Application Engineer Manager