Reflection, Refraction & Reverberation

Do you have an open space that is noisier than you can tolerate? Gymnasiums, lobbies, atriums, meeting halls, conference rooms, factory production areas, and many more are examples of the types of spaces where noise can be an issue for those who work in or use those spaces on a regular basis.

How does one mitigate this noise problem where “reflective noise” is generally the culprit? First, let’s understand what we are dealing with. When sound travels in a given medium, it strikes the surface of another medium and bounces back in some other direction, this phenomenon is called the reflection of sound. The waves are called reflected sound waves.

Hard, reflective, nonporous interior building surfaces such as glass, wood, plaster, brick and concrete absorb only 2% to 5% of the sounds striking their surfaces. Accordingly, they generally reflect 95% or more of the sound that strikes their surfaces.

As the sound waves bounce, they frequently change direction as they pass from one medium to another. This change of direction is called refraction. Refraction, or the bending of sound waves is generally accompanied by a change in speed and/or wavelength of the waves.

When reflected or refracted sound waves hit a surface such as a wall or a floor, two things happen. A proportion of the sound is continually reflected into the room (energy is preserved) OR some much smaller proportion is transmitted through the surface and escapes from the space (energy is lost).

Let’s talk about the sound that is reflected into the space. It is now reverberating. A reverberation is perceived when the reflected sound wave reaches your ear in less than 0.1 second after the original sound wave was created. Since the original sound wave is still held in your memory, there is no time delay between the perception of the reflected sound wave and the original sound wave. The two sound waves tend to combine as one very prolonged sound wave. This means the sound still exists even after the source of the sound has been cut off.

So………………now you have an open space, and you have reflective noise with refracting sound waves that is causing reverberation and your space is just plain LOUD!!!!!! How do we stop it?


Remember this? Hard, reflective, nonporous interior building surfaces such as glass, wood, plaster, brick and concrete absorb only 2% to 5% of the sounds striking their surfaces.

We need to get absorption materials into the space that are much more effective at absorbing sound than the existing surfaces in the space. Thankfully, we have many options to consider but how do we know which material is correct and how much of the material to use? To answer those questions, we need to understand one more technical term. SABINS.

A Sabin is a scientific term for a unit of measurement of sound absorption. It is calculated by using one square foot and assigning a maximum value of 1.00 if the material tested has 100 % absorption of the sound or frequency. If you are using the metric system, you would use one square meter as your reference size and it would yield a value of 1.00 also if 100 % absorption occurred at any chosen test frequency.

Any material tested will produce so many Sabins per square foot (or per square meter) depending on your standard of reference. If a square foot of any given material had a Sabin count of 30, you would know that it is equal to 30 sq. ft. of 100 % absorption at that frequency of that test sample.

To quiet your space, we need to “add Sabins” and to figure out how many we need to add, we need to visit with you to get some details about your space. Contact us or fill out the form to the right and one of our acoustic specialists will contact you to work up a specific solution for your impacted space!