Improve Room Acoustics in the Living Room

Reverberation in the Living Room

The TV sound doesn’t just reach the sofa directly. The larger part travels to the listener via walls, ceiling, floor, and windows, arriving slightly later and from different directions. The impact of this varies depending on the size of the room and how many hard surfaces it contains.

Direct Sound and Reflections

Direct sound is the part of the sound that travels directly from the speaker to the ear. Shortly after, the first reflections arrive, usually from the side walls, floor, and ceiling. These are followed by many more, which overlap and slowly become quieter. Together, they are heard as reverberation.

The further the seating position is from the speakers, the more the room’s reflections mix with the direct TV sound. In a reverberant room, this is noticeable even at a short distance. In a well-furnished room, it only becomes apparent at a greater distance.

Reverberation Time

How reverberant a room is can be determined by its reverberation time. This indicates how long it takes for a sound to decrease by 60 decibels after being turned off. At that point, it is practically inaudible.

In furnished living rooms, the reverberation time is often around half a second. In the deep bass, it can be significantly longer because furniture and textiles hardly absorb low frequencies. Larger rooms also reverberate longer. An empty room reverberates much more strongly, as is known from a freshly renovated apartment before moving in.

Flutter Echo and Boom

If two smooth surfaces are parallel to each other, such as two bare walls or a tiled floor and a smooth ceiling, sound can bounce back and forth between them. After a clap or a loud word, a fast, slightly metallic flutter is heard.

In the bass range, standing waves, known as room modes, form between the walls at certain low frequencies. At some points in the room, individual bass notes boom, while at others, they are barely audible. How the bass sounds therefore strongly depends on where you are sitting.

Assessing Your Own Room

You can usually tell if a living room is too reverberant by clapping your hands or speaking loudly. Music can also be used to check if individual bass notes boom on the sofa. A smartphone app provides a rough value that can be used to compare the room before and after a change.

Listen Carefully

Clap your hands loudly once or speak loudly and pay attention to how the sound fades. If a flutter is heard, it is usually due to two parallel, hard surfaces. Walking through the room will quickly reveal between which walls it is strongest.

For bass, play a piece of music with a consistent bass line at normal volume. If the bass sounds significantly different on the sofa than a meter away, it’s due to room modes. This has less to do with reverberation than with the position in the room.

Measuring with a Smartphone

There are apps that measure reverberation time using the smartphone’s microphone. You start the measurement, clap your hands or make another short, loud sound, and get an approximate value. This is usually sufficient to compare the room before and after a change.

However, you should not expect precise values from this. Smartphone microphones are designed for speech and only inaccurately record low frequencies. Therefore, such measurements are of little use for bass.

Typical Weaknesses

Reverberation occurs primarily where hard surfaces like exposed concrete, large glass fronts, or smooth floors without carpets make up a large part of the room. A living room with little furniture and a lot of bare wall can therefore sound significantly more reverberant than a fully furnished room of the same size.

Open-plan kitchens are larger than a separate living room and therefore reverberate longer with the same furnishings. In addition, kitchen fronts, countertops, and tiled backsplashes are almost always made of hard materials that absorb little sound. The same applies to high ceilings. They make the room larger without adding soft surfaces.

Improve Room Acoustics with Furniture

The first steps usually cost little because you use things that already belong in the living room. How much this helps depends on where they are placed and how much area they cover. Textiles primarily absorb high and mid frequencies. Shelves tend to distribute sound throughout the room.

Textiles and furniture primarily remove the bright, sharp reverberation from the room. They do little against booming bass.

Carpet and Floor

In many living rooms, the floor accounts for a large portion of the hard surfaces. A large rug in front of the sofa dampens reflections precisely along the path the sound takes from the TV. A thin runner, however, does little. Thick, dense rugs also absorb mid frequencies, but hardly any bass.

Using Curtains Correctly

Curtains absorb more sound the heavier the fabric and the more pleats it has. Light, smoothly hanging fabrics, however, do little. If the curtain hangs with some distance from the window or wall, it also works for slightly lower frequencies. However, this only applies as long as it is drawn.

Upholstered Furniture and Shelves

A fabric-covered sofa is a large, soft surface that absorbs a lot of sound. Smooth leather, on the other hand, reflects more sound. Open shelves with books, plants, or decor absorb less sound but distribute it in many directions. This makes the room sound more even. A flutter echo between two walls is also weakened this way. Diffusers made of wood or plastic work on the same principle but are rather rare in living rooms.

Sound Absorbers on Walls and Ceiling

If furniture and textiles are not enough, sound absorbers can help. These are panels, pictures, or ceiling elements made of porous material specifically designed to absorb sound. How effective they are depends primarily on their thickness and where they are placed.

How Porous Absorbers Work

Porous absorbers consist, for example, of mineral wool, polyester fibers, or open-cell foam. When sound penetrates the material, the air rubs against the fibers. A portion of the sound energy is thereby converted into heat. Thin absorbers are primarily effective for high frequencies. For mid and low frequencies, the material must be thicker or hung with a distance from the wall.

Many data sheets show a weighted sound absorption coefficient between 0 and 1. The higher the value, the more sound the material absorbs. Often, an absorber class from A to E is also given, with A representing the strongest absorption. However, both specifications are based only on frequencies from 250 to 4,000 Hertz. How well an absorber works for lower frequencies cannot be determined from this.

The Right Spots

There is plenty of space on the ceiling in most living rooms. One or more ceiling clouds between the TV and the sofa dampen reflections there without having to change the furniture. On the walls, absorbers are most effective where the sound first hits the wall on its way from the TV to the sofa.

These spots can be found with a mirror. One person sits on the sofa, a second holds a mirror flat against the side wall and slowly slides it along. If you can see the TV or soundbar in the mirror from the sofa, you have found such a spot. Do the same on the second side wall and, if the sofa is close to the wall, also on the wall behind it.

Acoustic Panels and Acoustic Slatted Panels

Acoustic panels are absorbers covered with printed fabric and hung on the wall like a picture. Inside, there is usually a panel made of mineral wool, polyester, or foam. How effective they are depends primarily on the thickness of this panel and the distance from the wall.

Wood slatted panels consist of narrow wooden slats on a felt layer. Only the felt and, if present, insulation behind it absorb sound. The slats themselves reflect some of the sound. Without insulation behind them, such panels often appear less effective than one would expect.

If you build absorbers yourself, you should use flame-retardant material. This applies to both the filling and the fabric used to cover them.

Amount and Distribution of Damping

How long a room reverberates depends on its size and how much sound is absorbed in total. The more sound-absorbing surfaces there are in the room, the shorter the reverberation. Therefore, carpets, curtains, furniture, and absorbers together usually achieve more than a single measure.

However, you can also over-dampen. If only the high frequencies are strongly absorbed, the room sounds dull, while the bass reverberates as long as before. It is better to distribute several measures throughout the room and listen again after each step.

Bass and Corners

Low frequencies have wavelengths of several meters. Therefore, carpets and curtains have little effect on them. In a room, they also behave differently than voices or music in the mid-range. It is usually more effective to rearrange the sofa, speakers, and subwoofer.

Room Modes

Room modes occur between parallel walls and between the floor and ceiling. At certain frequencies, sound is amplified at one point and almost canceled out at another. Which frequencies these are depends on the dimensions of the room. Bass is usually strongest at the walls and especially in the corners.

If the sofa is directly against the back wall, individual bass notes can be particularly prominent. If you move the sofa a bit away from the wall, the bass often changes audibly. You have to experiment to find which position sounds most even. Exactly in the center of the room, however, some bass notes are almost completely missing. Therefore, it’s not a good place to sit either.

Subwoofer and Seating Position

A subwoofer in the corner sounds more powerful but also amplifies room modes. The bass then booms more easily. During explosions or loud music, the rest of the sound gets lost in it. It often helps to place the subwoofer at different spots along the wall and listen from the sofa each time.

The quicker way is usually the reverse, where you temporarily place the subwoofer on the sofa. Then, play a piece of music with a consistent bass line. Then, sit on the floor at the spots where the subwoofer could later be placed. Where the bass sounds most even is the right place for the subwoofer. This works because sound travels the same path in both directions between two points in a room.

Limits of Simple Solutions

Room modes can only be dampened with very thick absorbers or special bass traps, which are usually placed in the corners. They are large and quite noticeable in the living room. Many AV receivers and some soundbars also have automatic calibration that measures the room with a microphone. This can reduce booming bass notes. However, it cannot bring back sounds that are canceled out at the seating position.

Limits of Room Acoustics

With better room acoustics, the sound in the room becomes clearer. However, it is not a substitute for sound insulation. Absorbers reduce reflections in the room but do not prevent TV sound from traveling through walls and ceilings into other rooms. It also does not change the distance between the speaker and the sofa.

Room Acoustics is Not Sound Insulation

To reduce sound transmission to the neighboring apartment, structural measures are needed, such as heavier walls or coverings that are not firmly attached to the wall. A room with less reverberation seems quieter and often is a little, because less sound reflects off the walls. However, little usually changes for the apartment next door.

Distance Between Speaker and Seating Position

Even in a well-furnished living room, some of the sound reaches the sofa indirectly. This proportion increases the further the sofa is from the speakers. Acoustic measures reduce these reflections, but they do not change the distance itself.

A TV speech amplifier like OSKAR shortens this distance because the TV sound is reproduced closer to the listening position.