**Understanding frequency bands**

In fundamental concepts of sound, we covered some basic concepts like** wavelengths** and **frequencies**.

**Acoustic experts** often use **frequency bands** in their studies.

For **non-experts**, understanding concepts like **third-octave** and **octave frequency bands** can be tricky.

If you find this concept challenging, **worry not!** Atelier Crescendo has crafted this post** just** **for you**.

Enjoy the read!

*(See at the end the references used to confirm these concepts)*

**Acoustic analysis **

Studying the **acoustic performance** of materials or the **acoustic characteristics** of sources/signals comes in** different ways**.

Frequently, **acoustic experts** use f**requency bands** for** measurements** or **calculations**.

Essentially, it is a method to **reveal acoustic information** across **different frequency ranges**.

Most commonly, frequency analysis occurs in:

**octave**bands**third-octave**bands

In **third-octave** bands, the **precision/resolution** is about **three times higher** than in octave bands.

The **formula** to obtain **octave band values** from **third octave values** depends on the acoustic metric you want to study.

**What is an octave ?**

An octave is an (key musical) **interval**, corresponding to **doubling** or **halving frequency**.

** Example: **from

**125 Hz**to

**250 Hz**is an octave, as is

**20,000 Hz**to

**10,000 Hz**.

**Musicians** often use the **A note** as the reference for **tuning**. The frequency of this note is **440 Hz**. The A note at the **next octave **is **880 Hz**.

**Upper & higher frequency band limits **

**and band centre frequency **

When talking about **bands**, we must set their * upper* and

*.*

**lower frequency limits**Also, in each band, there is a **center**, known as the ** band center frequency**. It is the

**mean**of the upper and lower limits.

** Example: ** in the

**250 Hz**center frequency octave band:

- the
**lower**limit is**178 Hz** - the
**upper limit**is**355 Hz**

Setting limits for **third-octave bands** is a **little more complex**.

**Preferred (and standardised) frequency bands**

Frequency band analysis has even been **standardised**.

**International Standards Organisations** have agreed on ** preferred frequency bands** for the

**analysis of sound or vibrations**.

Typically, in **acoustic building projects**, the** frequency range** under consideration spans **from 63 Hz to 8000 Hz**.

In the case of **vibrations**, exploration can extend to frequencies **as low as 2 Hz**.

** Note: **If you want to know about the standards, here they are:

*ANSI/ASA S1.6 (2020) – Preferred Frequencies And Filter Band Center Frequencies For Acoustical Measurements**ANSI/ASA 51.11 (2004) – Octave-Band And Fractional-Octave-Band Analog And Digital Filters**IEC 61260 -1 (2014) – Electroacoustics – Octave-band and fractional-octave-band filters – Part 1: Specifications**TS0 266 (1997) – Acoustics – Preferred frequencies*

**References**

See below the references used to confirm the above concepts:

*Noise Control in Building Services*– Sound Research Laboratories Ltd – Pergamon Press*Sound Materials, A Compendium of Sound Absorbing Materials for Architecture and Design*– Tyler Adams – Frame Publishers*Acoustic Absorbers and Diffusers – Theory, Design and Application –*Third Edition – Trevor Cox, Peter Dâ€™Antonio*Engineering Noise Control*– Sixth Edition – CRC Press – David A. Bies, Colin H. Hansen, Carl Q. Howard, Kristy L. Hansen