Acoustic Treatment

In this article, we assume a typical living room environment — not a dedicated room or recording studio, a basic living room that is usually very reverberant.

We will avoid creating coupled volumes; closed doors are always preferable to prevent this effect.

Rear and Front Walls

The ideal place for absorption is the wall behind the speakers, as this accounts for about 80% of the reduction needed in room reverberation time (RT).

Use melamine foam (e.g., BASF Basotect G+) or rockwool (e.g., Rockfeu REI, bi-density — place the low-density side facing outward) over a large portion of the wall, prioritizing exposed surfaces near corners.
The treatment should be substantial, at least 8–10 cm thick, covering at least 50% of the wall, focusing exclusively on absorption.

To better control lower frequencies, this treatment can be extended to the wall behind the listening position, while some reverberant components can be preserved to maintain a deep soundstage.

Avoid placing your listening position directly against the wall — maintain at least 1 m distance.

Side Walls

Their effect depends on the loudspeaker directivity: When the directivity is adapted to the listening distance — typically around 90° in a regular living room — the lateral energy is already close to an ideal balance, so we can focus on the quality of these primary reflections. Without this adaptation, lateral energy may be excessive, requiring heavy absorption.

Consider treating the side walls using a combination of diffusive and absorptive elements placed side by side. If the loudspeaker directivity is already adapted to listening distance, the absorptive component can be reduced, and in some cases, removed in favor of the diffusive element.
Avoid products that combine both diffusion and absorption in one material, as they tend to produce a “V”-shaped absorption curve, which is undesirable.

Early reflections are the first sounds that bounce off nearby surfaces, such as side walls, floors, and ceilings, before reaching the listener.
These reflections arrive within the first 20–30 ms (the Integration Time (IT) window) and are perceived as part of the direct sound rather than separate echoes. Their characteristics—dependent on frequency, distance, sound complexity, room geometry, and listener factors such as age—affect imaging, stereo perception, and listener envelopment. For more details about soundstage, see our Listener Envelopment and Early Reflections article.

Sidewall treatments should be chosen according to loudspeaker directivity and room conditions. Diffuse absorption helps prevent mirror-like, or specular, reflections that degrade imaging and the horizontal soundstage, while in some cases, lateral absorption near the speaker corners is required, particularly in dedicated rooms, to absorb the very first reflections arriving within the initial 10–15 ms of the direct sound.

Untreated early reflections can cause phantom image shifts or soundstage asymmetry, especially in asymmetrical spaces or when speakers are placed close to walls.

In studio environments, where only the direct sound field is desired, absorption is generally applied everywhere.

Over-damping the lateral walls can create a nearly dead room and collapse the horizontal soundstage.
When horizontal directivity is well matched to the room and listening position — typically around 90° in a domestic living room — lateral absorption can be minimized or even omitted in living room.
This allows the focus to shift, if needed, to quadratic diffusers, which redistribute reflections without producing specular effects, preserving the lateral energy needed for listener envelopment and a wide, coherent soundstage.

In a regular living room, furnishings and furniture can provide a naturally diffuse reflection regime so when the loudspeaker directivity is adapted to the listening distance (around 90° in a typical living room), sidewall treatment may be unnecessary, with little or no need for either absorptive or diffusive elements. This is one of the advantages of adapting loudspeaker directivity to the listening distance.

Some early reflections are still desirable to support the soundstage, but they must be controlled: not too intense, and not too close in time to the direct sound.
If they arrive too early, or if the speakers are placed too close to the side walls, tonal degradation and comb-filtering effects can occur in the mid and high frequencies.

Toeing-in the speakers and using horns with directivity matched to the listening distance will help reduce the level of these early reflections.

The auditory system integrates early sound within a specific time window, known as the Time Period of Integration (TPI).
You can find more information about TPI here.