The role of sound absorption and diffusion in acoustic design

Much like the ball in a pinball machine, sound bounces around a room until it loses momentum; either slowed by an absorber, scattered by a diffuser, or gradually dissipating on its own.

In rooms without acoustic treatment, this ‘bouncing’ can continue for a long time, causing strain on the ears and, ultimately, making it very difficult to concentrate and hear. By treating a space with acoustics, the energy of the sound wave is either absorbed (stopping the bounce) or diffused (scattering the bounce) to reduce noise and create a more comfortable, functional environment.

Why absorption and diffusion matter

“Sound absorption and diffusion are both critical factors to consider when designing a space. Absorption and diffusion impact how sound behaves within an area, affecting everything from speech clarity to overall comfort,” says Autex Acoustics® technical advisor, Jack Soffe.

Absorption and diffusion work best in tandem—and for a space to feel natural, both should be thoughtfully balanced.

“Ignoring the impact of either absorption or diffusion will result in a space that is too “live” (echoey, like inside a bathroom) or too “dead” (flat and unnatural),” Jack explains. “To achieve great room acoustics you need to use a combination of sound absorbers and sound diffusers.”

How absorption and diffusion work

Sound moves through space in waves. The length of each wave depends on the sound’s frequency, which can range on a spectrum from low (bass) to high (treble). For a material to absorb sound effectively, it needs to be thicker than the length of the wave to stop the wave from continuing its journey. Low frequency sounds have a longer wave cycle than high frequency sounds, which is why sound absorption materials designed to absorb bass are so thick. By absorbing sound, you reduce reflections—those repeated bounces, known as echo and reverberation—which helps keep the original sound source clear and intelligible.

Diffusers, on the other hand, don’t stop the sound—they scatter it in multiple directions. This softens the reflections and leads to a more balanced and nuanced distribution.

In performance venues such as auditoriums and concert halls, acoustic design often focuses on preserving the ‘liveliness’ of sound to ensure a good listening experience; other spaces, like classrooms and meeting rooms, prioritise speech clarity, minimising background noise and echo. Both types of environments rely on a mix of absorption and diffusion—the exact balance is tailored to the needs of each space.

Always consult an expert

If you want to get acoustic design right, it’s essential to bring in the right expertise.

“With years of knowledge and experience, an acoustic design expert knows when and where to place absorbers and diffusers to achieve the right level of sound control for the needs of your space,” Jack says. “Acoustic design should always be considered early in the project so any acoustic issues can be tackled at the beginning, avoiding costly retrofits.”

If your space could benefit from improved sound performance, our team of acoustic specialists are here to help. Get in touch for solutions tailored to meet the unique requirements of your project.