The Sounding Board

Reverberation time and speech intelligibility (Part I)

By June 7, 2019 No Comments

Reverberation time and speech intelligibility (Part I).

Everyone has at some point experienced a room or space with a particularly long reverberation time, more commonly known as an echo. Many places exhibit this type of acoustic behavior; sports halls, churches, music venues, meeting rooms… the list goes on. But what is actually happening in these spaces? Well, it’s all down to reflection.

When we speak, the vibration of our vocal chords excites local air particles, this in turn causes the vibration of neighboring air particles, which in turn vibrates more neighboring air particles and so on and so forth until all the energy is spent. This process continues, creating a sound wave which spreads out; just like the surface waves you can observe when stone is dropped into a pond.

Reverberation (or echo) is formed when this sound wave encounters a solid object – which, based on the examples above, is usually a wall. At this intersection, depending on the material properties, a portion of the wave will be absorbed into the object, another portion will pass through the object and the remaining acoustic energy will be reflected.

This reflection, multiplied thousands of times, is what we refer to as reverberation.

Reverberation can be a good or bad quality, depending upon the situation. For example, most concert halls are designed to provide a certain amount of reverberation as it nicely compliments orchestral and vocal music performances, providing a natural tail-off to the end of notes rather than an abrupt stop.

Negative situations include meeting rooms (which we will look at further in the next blog post). In this situation, spoken words can become difficult to understand, reducing what we refer to as speech intelligibility.

If you have any questions regarding reverberation time, or would like any help in optimising your space, feel free to get in touch.

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