Reverberation 101: Understanding Reverb

Every space has reverberation (or “reverb”), but we don’t pay attention to it most of the time. Our ears are used to hearing sound in the context of a space. Very few spaces are truly “dry” (i.e. no reverb), and dry sound can be unpleasant to the human ear. On the other hand, too much reverberation can obscure a sound and make it difficult to comprehend. This is especially true when hosting a conference call, where it’s important to hear every word as clearly as possible.

Below, we’ve shared the basics of reverberation, including how to calculate reverberation time, how hard surfaces can increase reflections, and why the inverse square law is a useful tool in this concept.

What is Reverberation?

When you speak in a room with reflective surfaces (think glass windows, blank walls, etc.), you can hear the sound bouncing off the walls and coming back to your ears. On the other hand, when you speak in an open field without anything nearby to reflect the sound, you don’t hear any reflections. When a sound keeps bouncing off surfaces and continues traveling around a space, that’s reverberation. Depending on the shape and material construction of a room, the reverberation can last a long time, or it can fade out quickly.
Ideally, your conference room should be designed with just enough reverberation for voices to sound natural, without reflecting too much at the microphones and creating feedback. The audio entering the microphone should mostly be coming from the person speaking so that the other parties hear a clean, direct signal.   
There are some cases where reverberation can be a good thing. Reverberation is sometimes added to a voice or musical instrument to create depth in the context of a mix or live show. This is typically done with a digital or analog effects unit called a reverb. Finding the balance of the right amount of reverberation is an important factor based on your use case. 

How Do I Calculate Reverberation Time?

In a reflective room, reverberations take longer to die out. Conversely, an absorbent room has minimal reflections and the reverb dies out more quickly. The initial volume of a sound also has an impact on the reverberation time.  
To calculate the total reverberation time in a space, we recommend using the RT 60 measurement. Essentially, you measure the time between when a sound source ends and the reverb reaches a level of 60 decibels below the initial volume. Many level recorders and digital sound level meters can measure RT 60 automatically. Ideally, you should test the room’s reverberation time with a fairly loud sound that has a defined cut-off point. This will provide a better reading for the meter so that it can distinguish between the original sound and its reverberation.

Measuring Room Criteria

Another important factor that affects our conference rooms is ambient noise. Ambient noise is essentially the standard background noise that any room may have. For example, this could be city sounds coming from outside or even an HVAC system.

To measure this background sound in a room, audio engineers developed the Room Criteria (RC) standard as a baseline for ambient noise. The scale of Room Criteria measures anything between 16 Hz and 4000 Hz on the frequency spectrum. Hz stands for Hertz, which basically means how loud noise is. For instance, an office conference room has an RC of 25-30Hz, while an open-plan office has an RC of 35-40Hz.
There are tools available to help you easily determine the RC in your space. A few of our Sales Engineers use apps on their phones to help customers when they are out in the field. 
If your conference room has a lot of hard surfaces, the ambient noise may be louder than the RC standard. Many rooms exceed the Neutral (N) level described in the Room Criteria chart, but it’s a good baseline to shoot for. 

If your room is not performing well after these two measurements, there are things you can do to help! Adding sound absorbing materials to the room, like acoustic panels, rugs, or artwork can all help to help the room’s reverberance.

What is the Inverse Square Law?

When measuring how sound travels and reverberates in a room, the inverse square law can be useful for optimizing a conference room. Essentially, this law states that as an object (such as a microphone) is moved farther away from a sound source, the sound level goes down in inverse proportion to the distance squared. The opposite is true when you move closer to a sound source.  
For instance, if a microphone is 1 foot away from your mouth, and you move it to 2 feet away, the sound will go down by about 6 dB. Then, if you move the mic to 4 feet away, the sound will drop -12 dB from the original level. 

Why is this so important? It helps us understand that placing conferencing microphones at an optimal distance from speakers is critical so that the sound is clear and intelligible. If a mic is too far away from the speaker, you’ll start to pick up more room reverberation than the original sound source, and the voice will sound muddy and obscured.

Now that you understand reverberation, check out our guide on conference room set up for more info.

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