Octave Bands

Let’s talk about octave bands. You hear that term a lot in acoustics. Let’s break it down into its separate components. See if we can get an understanding of it. Octave bands is composed of individual frequencies.

So we have our standard groupings here: 63, 125, 250, 500. Those are the standard octave bands that we see. A lot of our test results are based upon those particular octave bands. A lot of your sound transmission ratings that we get STC ratings on materials and barriers are based on just those particular groupings. So it’s a group of frequencies into bands that have upper and lower limits. So we’ll talk about that. So it has a lower and an upper limit to it.

And what do octave bands do? They allow for a definition of loudness across the frequency spectrum. So when you look at your RTA and you’re doing a 3rd octave, a 6th octave, a 12th octave, a resolution then you can kind of see how each group reacts in terms of strength and amplitude. So it’s a way to measure the loudness across the frequency that really contains these elements. So these frequencies. So that’s what we have to look at.

So we have 125 if we choose 125 as our octave band. We know that our next octave band is two times that or 250. Two times 250 is 500. Two times 500, it’s a 1000 and so forth. So it’s a doubling of that. Now, we have to realize that each octave band has an upper and lower limit, okay? So the 250 has a lower limit of 177 and an upper limit of 354 and then the 250 is right in the middle.

So it gives you an idea of how they break down these octave bands. But it’s just a simpler way to look at frequencies that kind of are related and act at the same situations, act the same way in terms of loudness. So it’s really a simplified way. Those of you that have used our apps that you download for your iPhone to do noise measurement, know that we have an FFT function on those apps and that function allows you to see individual frequencies within the octave band. So it’s another higher resolution format so to speak to look at the frequencies within the octave band.

So octave bands individual, it is a grouping of individual frequencies that have upper and lower limits. It’s all about loudness, amplitude, strength into those groupings and there’s the upper and lower limits that we went through.

Let’s look at some examples of bass, tenor, alto and soprano because I think this will help us clarify octave bands a little bit and the ranges, with which they operate. So we have bass, a real low bass voice that people have, 250 to 300 Hz range. Tenor voice 125 to 500. Alto is 150 to 750 and soprano is 250 to 1000. So you can see that there’s ranges to the octave bands and that’s what we talked about originally.

So I hope this helps. Remember, octave bands is just a way to group a bunch of frequencies together so we can look at groupings instead of individual frequencies.

—

This is an unedited transcript from our video series from Acoustic Fields. There will be some errors in grammar and sentence structure that occur during this translation process.

For complete understanding and comprehension, please view the video which is included in this text. For any additional information regarding this topic or others relating to room acoustics, please contact us directly at:

P: 520 – 392 – 9486

info@acousticfields.com