Understanding Reverberation in Architectural Acoustics

Have you ever acknowledged the crystal-clear acoustics in a grand theatre yet found yourself straining to hear in a noisy office or restaurant? This phenomenon is largely attributed to reverberation, a key component of our auditory experience.

Rooms with many hard, sound-reflecting surfaces have more audible reverberations, and the opposite is true for rooms with many soft, sound-absorbing finishes.

But, of course, it can be much more complex than that. Read on to learn more about reverberation and its role in building acoustically optimised spaces.

Reverberation 101: definition and causes

Reverberation is the phenomenon where a sound persists after the initial noise due to reflections.

When sound waves hit surfaces (walls, floors, ceilings, etc., but also large surfaces like the side of a hill or mountain), some portion of the sound energy is absorbed by the surfaces, while the rest is reflected back into the space.

These reflected sound waves bounce around, reflecting and dispersing before fading away.

Rooms or spaces with many hard, sound-reflecting surfaces will typically have more audible reverberations that persist for longer, while a space with lots of sound-absorbing finishes will have shorter reverberation times.

Components of an echo

Reverberation is made up of several distinct parts, including:

• Direct Sound: Direct sounds travel in a straight line from the source to your ears. It’s the first sound you hear.
• Early Reflections: These are the initial echoes that bounce off surfaces like walls, ceilings, and floors and reach your ears shortly after the direct sound. They help give a sense of the space’s size and shape.
• Late Reflections (Reverberant Tail): After the early reflections, the sound waves continue to bounce around the space, creating a series of diminishing echoes that merge into a continuous, decaying sound. This is what most people commonly associate with reverberation. It adds ambience but can also blur clarity if prolonged.

Demystifying reverberation time (RT60)

One of the key measures of reverberation is reverberation time (RT60). RT60 quantifies how quickly sound decays in a given space after the original sound source has stopped.

Specifically, RT60 is defined as the time it takes for the sound pressure level to decrease by 60 decibels after the source has ceased.
For example, consider a loud clap in a concert hall that initially registers at 90 decibels. If it takes 2 seconds for the sound of that clap to diminish by 60 decibels down to 30 decibels, then the RT60 for that hall is 2 seconds.

A short RT60 generally indicates that a space is more acoustically damped and doesn’t reverberate sound as much. This dampening can be achieved with acoustic wall panels and acoustic ceiling rafts.

A long RT60 means sound persists for longer in a space, which may be desirable for venues like concert halls and opera houses.

The advantages of well-managed reverberation

Reverberation can both enhance and degrade audio experiences depending on the room design.

In thoughtfully engineered concert halls, for example, some reverberation is essential for full-bodied musical dynamics. The hall’s geometry reflects soundwaves to audiences with ideal timing and clarity.

However, uncontrolled reverberation can overwhelm listeners. Rooms with expansive hard surfaces and high ceilings, like churches or restaurants, create excessive reflections. These echoes create an uncomfortable environment and make speech difficult to understand.

In these cases, you’ll need to clamp down on reverberation. Here are some key advantages of doing so:

• Speech intelligibility: In educational and business settings, reduced reverberation ensures that speech is easily understood, improving learning and collaboration.
• Enhanced privacy: In offices and conference rooms, controlling reverberation helps keep conversations quieter and the need to raise volumes.
• Acoustic comfort: Balanced reverberation in homes and public spaces contributes to a comfortable and pleasing auditory environment.
• Increased productivity: In work environments, minimising distracting echoes and background noise can significantly boost concentration and efficiency.
• Efficient functioning of AV equipment: Controlling reverberation is crucial for the quality of recorded and amplified sound in spaces like theatres and recording studios.
• Improved focus: In general, a well-balanced acoustic environment helps people focus better on work, studying, or enjoying music.

Strategies for effective sound management

So, how can you practically manage reverberation?

While every room is different, there are a few rules of thumb that should help you control the reverberation in your space.

We call these the “ABCs” of acoustic design.

Absorb

• Sound absorption is the process of reducing the energy of sound waves as they hit surfaces. This is achieved by converting the sound energy into a miniscule amount of heat using materials that trap and dissipate these waves.
• Installing acoustic panels on walls and ceilings is a common and effective way to absorb sound. These panels are designed to trap sound waves and prevent them from bouncing back into the room.
• Consider covering the entire ceiling or at least 50% of the surface area with high-quality (Class A) absorbers for optimal sound absorption. The goal is to balance absorbing enough sound to reduce excessive reverberation while maintaining a level of liveliness in the room.

Block

• Blocking sound prevents travel or transmission from one area to another. This is typically about controlling the direct path of sound waves.
• Utilising acoustic screens, partitions, and strategically placed furniture can minimise sound travel, especially in open spaces like offices.
• The placement of these elements is key. For example, placing acoustic screens at the right height and position can intercept and block direct sound paths, thereby enhancing privacy and reducing distractions.

Cover

• Paradoxically, introducing a controlled level of background noise can improve the acoustic environment. This technique, known as sound masking, makes unwanted noise less perceptible.
• Implementing non-repetitive sound sources like white noise machines or ambient soundscapes can effectively mask distracting noises. This is particularly useful in too-quiet environments, where even minor sounds can be disruptive.
• The space should already offer good absorption; otherwise, adding background noise can exacerbate the problem. The goal is to create a subtle, unobtrusive sound background that improves privacy without becoming a distraction itself.

Wrapping up

Depending on what you’re using a space for, controlling reverberation can transform comfort and productivity. This is particularly true for modern minimalist rooms with sharp angles and reflective surfaces.

Use the ABCs of acoustic design – absorb, block, and cover – to improve the acoustics in your space, whether that is an office, restaurant, classroom or your new home cinema.

Investing in acoustic panels or “soundproofing” is crucial to keeping troublesome reverb at bay.

We have a great range of cost-effective products that offer the high levels of absorption you need to control troublesome reverb.

If you need help improving the acoustics of your space, call one of our consultants for a friendly, no-obligation chat.