What is the difference between sound-absorbing materials and sound diffusers?

Sound absorbers and sound diffusers are both used to improve room acoustics, but their functions should not be confused. A sound absorber converts part of the incident sound energy into heat within the material, thereby reducing the intensity of reflections. This makes it particularly useful when a room has a long reverberation time, annoying echoes, or poor speech intelligibility. A sound diffuser typically absorbs significantly less sound. Instead, its shape breaks up a concentrated reflection and disperses the sound energy in multiple directions and at different times.

The difference is clearly noticeable in how these solutions affect the character of the room. With sufficient absorption, the acoustic environment becomes calmer, conversations clearer, and the sound level often more manageable. With well-balanced diffusion, the room can retain more liveliness and spaciousness while strong individual reflections become less prominent. Therefore, absorbers are usually the first choice in ordinary rooms with hard surfaces, while diffusers are more often used as a later addition in music rooms, listening rooms, and studios where placement can be carefully planned.

SilentDirect generally recommends starting with sound absorbers on the ceiling when the goal is to improve the acoustics overall. The ceiling often provides a large available surface area and can influence the reverberation throughout the entire room. If the acoustics then need to be fine-tuned, absorbers on the walls and—in the right environment—diffusers on selected reflective surfaces can provide a better balance. A diffuser, however, should not be used as a shortcut to compensate for insufficient absorptive surface area.

Always start with the problem. A distinct echo after clapping your hands, a tiring buzz of background noise, and difficulty understanding speech all point to a need for absorption. A disruptive directional reflection or an uneven sound field in an already controlled listening environment may indicate a need for diffusion. Neither absorbers nor diffusers primarily stop sound traveling between rooms; that is a separate issue of sound insulation.

Here's how sound absorbers and sound diffusers differ.

The absorber absorbs some of the energy and produces a weaker reflection. The diffuser, on the other hand, redistributes a larger portion of the reflection in multiple directions.

What problem does this solution address?

Absorption is primarily used to combat echoes, long reverberation, and poor speech intelligibility. Diffusion is primarily used to avoid harsh, directional reflections and create a more even sound field.

What does the surface look like?

An absorber often has a porous core and a flat or slightly textured surface. A diffuser typically has a clearly varied depth, such as ribs, blocks, or calculated recesses.

How does this affect the character of the room?

High absorption makes the room feel drier and calmer. Diffusion can preserve more energy and a sense of space while making the reflections less concentrated.

Which rooms are suitable?

Absorbers are suitable for most rooms with disruptive reverberation, from homes and offices to schools and restaurants. Diffusers are more common in dedicated listening rooms, music rooms, and studios.

How critical is placement?

Absorbers need to be placed over a sufficiently large area to have a noticeable effect. Diffusers also require the correct distance, orientation, and geometry relative to the listening position.

What should be prioritized first?

For general room acoustics issues, we typically recommend ceiling absorbers first. Diffusion becomes relevant when the reverberation time is already reasonable and the sound field needs fine-tuning.

Can the solutions be combined?

Yes. Absorbers can reduce excess energy while diffusers disperse remaining reflections. The balance should be adjusted according to the room’s volume, use, and acoustic goals.

When should you use sound absorbers and sound diffusers?

Don’t start with the shape or appearance of the acoustic product. Start by determining what you actually hear in the room. An absorber and a diffuser can both improve the listening experience, but only if they’re used to address the right issues and placed with a clear purpose in mind.

1. Listen for reverberation and echoes

Clap your hands once and listen to how long the sound lingers. Try this in several locations, since a room can behave differently near corners, glass surfaces, and large parallel surfaces. If the clap is followed by a distinct ringing echo, if voices blend together, or if the background noise quickly becomes tiring, the room usually needs more absorption. Sound absorbers reduce the energy of reflections and are therefore the most direct solution to the problem.

2. Assess the room’s use

A classroom, office, kitchen, or restaurant primarily needs good speech intelligibility and a controlled sound level. In these spaces, absorbers are usually more important than diffusers. In a music room, studio, or critical listening room, the goal may also be to maintain a natural sense of space. Diffusion can then become relevant, but only once the basic reverberation is at a reasonable level.

3. Prioritize the large open surface

For general sound absorption, we typically recommend starting with the ceiling. The ceiling surface is often large and unobstructed, making it possible to distribute absorption throughout the room without interfering with furniture or movement. PES Ceiling is a flexible ceiling absorber for a wide range of applications, while PES Ceiling Deep Absorb provides a deeper absorption option for rooms with more significant acoustic issues or higher ceilings.

4. Add Absorbers Where Reflections Are Pronounced

Once the ceiling has been treated, wall absorbers can be used to dampen remaining wall reflections and improve the balance. Don’t just place a few panels at random. Start by identifying where people speak, work, or listen, and which hard surfaces are located near these zones. PES Wall serves as a flexible standard solution, while PES Wall Deep Absorb provides greater depth when more damping is needed.

5. Try diffusion only after absorption is sufficient

If the reverberation is under control but a listening position still experiences a harsh reflection or an uneven sound field, a diffuser can serve as a complement. A properly designed diffuser has varying depths that affect a specific frequency range. It needs to be placed at a sufficient distance from the listener so that the scattered reflections have time to blend. A simple decorative slatted wall is therefore not automatically an effective broadband diffuser.

6. Avoid over-damping the room

More absorption isn’t always better. If nearly all reflections are removed, music and speech can sound unnaturally dry. Instead, distribute sufficient absorption across relevant surfaces and listen for any significant changes. In rooms where a lively character is important, a combination can work well: absorbers reduce excess sound, and diffusers scatter portions of the remaining energy.

7. Check the results in the same way

Repeat the clapping test and listen to speech or music from the locations that are actually used. For more demanding rooms, reverberation time and reflection patterns should be measured before and after the treatment. A successful absorption treatment should result in shorter and more even reverberation. A successful diffuser placement should reduce the distinct, directional reflections without making the room noticeably duller.

8. Distinguish Between Room Acoustics and Sound Insulation

If the disturbance is coming through a building component, neither absorbers nor diffusers are sufficient as the primary solution. They alter the sound inside the room but do not normally stop sound transmission between rooms. In such cases, the structure’s mass, density, decoupling, and connections must be investigated as a separate sound insulation issue.

In short: choose absorbers when the sound needs to decay faster and become clearer. Choose diffusers when a room that’s already reasonably controlled needs more even, less directional reflections. Combine them when the room’s function requires both control and a preserved sense of space.

Did you know that…

Did you know that a room can feel unnaturally quiet and “dead” if you only use sound absorbers? Sound absorbers capture sound waves and reduce reverberation, but if too much sound is absorbed, it can create an uncomfortable and confined acoustic environment. Sound diffusers, on the other hand, scatter and distribute sound waves instead of blocking them, allowing the room to retain a natural resonance without disruptive echoes.

In studios and concert halls, both solutions are often combined to achieve balanced acoustics—absorbers are placed where sound is reflected most strongly, while diffusers are used to create a fuller soundscape. By understanding the difference between these two, you can create acoustics that are both pleasant and natural, instead of making the room feel like an echoing cathedral or a muffled sound trap!

Products for reducing reverberation using sound absorbers.

The following products are sound-absorbing solutions for rooms where reverberation, echoes, and harsh reflections need to be reduced. They are appropriate when an analysis indicates that absorption is the right solution and include options for both ceilings and walls. The choice should be tailored to the room’s size, available surface areas, and the amount of sound attenuation required. Diffusers serve a different purpose and are therefore not included in this product overview.

PES ceiling is a flexible 50 mm ceiling absorber for homes, offices, schools, and other environments where the ceiling can be used for broad reverberation control.

PES Ceiling Deep Absorb is a 100-mm ceiling absorber for larger or more demanding rooms where a deeper absorptive layer is needed.

PES Allergy Ceiling reduces echoes from the ceiling and is ideal when you want an allergy-friendly solution without a fabric surface.

PES Wall is a 50 mm wall absorber for a wide range of applications where speech, echoes, and pronounced wall reflections need to be attenuated.

PES Wall Deep Absorb provides 100 mm of absorption depth for walls in rooms where standard panels do not provide sufficient sound absorption.

PES Circle Ceiling combines ceiling absorption with a circular shape when the acoustic solution is also intended to enhance the room’s aesthetic.

PES Hexagon Wall reduces wall reflections and can be arranged in patterns where multiple smaller absorbers fit the room’s layout.

SilentDirect PET Rectangle is a thin, 9 mm PET absorber designed for simple acoustic improvement on walls where thicker panels are not suitable.