How do you absorb low-frequency sound?

Effectively absorbing low-frequency sound requires special knowledge because low tones, below 200 Hz, have significantly longer wavelengths compared to high-frequency sounds. These long sound waves can easily pass through ordinary, thin absorbers that are effective against higher tones. Therefore, specific, thicker, and more specialized solutions are required to reduce low-frequency sound waves.

Common examples of disruptive low-frequency noise include traffic noise from heavy vehicles, rumbling ventilation systems, muffled bass from music or nightclubs, noise from heat pumps, motors in refrigerators and household appliances, and structure-borne noise from vibrations transmitted through the building's structure. These sounds are particularly disturbing because they are not only audible but can also often be felt as vibrations in the body, which can cause irritation, fatigue, and discomfort in both home and work environments.

To effectively absorb low-frequency sounds, thicker, high-density absorbers, often called broadband absorbers, with a thickness of at least 100–200 mm are needed. For even better results, it is recommended to install these absorbers with an air gap behind them, which enhances their ability to capture and absorb low-frequency sound waves. This is particularly effective in the frequency range around 125–500 Hz, where many low-frequency problems occur.

One of the most effective methods for dealing with low-frequency resonances is to install so-called bass traps in the corners of the room. The corners of a room are often the places where low-frequency sound waves accumulate and are amplified. Bass traps installed in the corners take advantage of this phenomenon and absorb the sound waves before they are reflected back into the room. The optimal thickness of these corner absorbers is often between 300 and 600 mm, depending on the room's acoustic properties and sound levels.

Another effective solution is membrane absorbers, also known as panel absorbers, which are constructed with a dense front panel and an air pocket behind it. These are specially tuned to absorb sound at a specific low frequency, often between 50 and 150 Hz. Membrane absorbers can be tailored to the specific needs of the room and placed where the problems are most noticeable, making them extremely effective at certain difficult frequencies.

Helmholtz resonators are another specialized solution for low-frequency sound problems. These resonance boxes are carefully dimensioned to capture a specific frequency and can be strategically placed where the sound level is most disturbing. Although they require careful design and dimensioning, they are very effective and take up relatively little space.

For the best possible results, we recommend a combination of these methods: start by installing corner-mounted bass traps, supplement with thicker absorbers on walls and ceilings, and adapt with membrane absorbers or Helmholtz resonators for specific frequency problems. By measuring and analyzing the room's acoustics with professional sound meters, you can identify exactly which frequencies need to be attenuated and thus choose the right solutions.

The benefits of absorbing low-frequency sound

Low-frequency noise is a common and often difficult acoustic problem in both residential and public environments. These low-frequency sounds, which are often perceived as rumbling or humming, have long wavelengths and spread easily through the building structure. Examples of common sources of low-frequency noise include heavy vehicle traffic, ventilation, heat pumps, music with strong bass, and vibrations from machinery and household appliances. Effectively absorbing low-frequency noise requires special solutions and materials with higher density and thickness compared to traditional sound absorbers. By carefully selecting and placing the right type of absorbers, low-frequency noise can be significantly reduced, providing many important benefits for both residential environments and workplaces.

Reduced disturbance from low-frequency noise and vibrations
Low-frequency sounds are often perceived as particularly disturbing because they are not only heard but also felt as vibrations. This can cause irritation, headaches, and difficulty concentrating. By placing broadband absorbers, bass traps, and membrane absorbers in the room, you can reduce both the sound level and the vibrations. These absorbent solutions prevent sound from spreading through the building's structure, thereby creating a quieter and more harmonious environment.

Improved sound quality and acoustic balance in the room
By dampening low-frequency sounds, a more even sound image is created in the room. Low-frequency sound waves often accumulate in the corners of the room, causing standing waves that result in an uneven bass response. When the bass is uneven, it becomes difficult to enjoy music, movies, or speech because some tones are greatly amplified while others disappear completely. Strategically placed bass traps and broadband absorbers can make the sound more balanced, resulting in a more natural and pleasant listening experience.

Better concentration and less stress
Low-frequency sounds can be subtle but very distracting. Constant background noise can negatively affect your ability to concentrate, which is particularly noticeable in office environments and in homes near traffic or machine rooms. By absorbing these low frequencies, you create a calmer atmosphere where you can concentrate more easily and feel less stress and irritation.

Increased comfort and well-being in homes and offices
Being in an environment with low, humming noises can affect your well-being and comfort. By effectively absorbing low-frequency sounds, you improve the comfort of your home or office. This makes residents, employees, and visitors experience the environment as more pleasant and attractive to stay in for longer periods of time.

Improved sleep and rest through effective sound absorption
Sleep quality can be negatively affected by low-frequency noise, especially from ventilation, heat pumps, or traffic noise. By installing suitable sound absorbers and bass traps, you can create a quieter sleeping environment where sleep is deeper and more undisturbed. This has a positive long-term effect on both your physical and mental health.

Professionally optimized sound environment for music and media
In recording studios, cinemas, and home theater systems, low-frequency control is crucial for sound quality. Without the right sound absorption, the bass can become uncontrolled and create problems when mixing or listening. By using specific low-frequency absorbers, such as bass traps, broadband absorbers, or membrane absorbers, you can ensure accurate and controlled bass reproduction. This makes the final product sound good in all listening environments.

Increased property value and attractiveness
Properties with effective sound absorption of low-frequency sounds become more attractive to both tenants and potential buyers. A room with an optimal sound environment signals quality and care, which can increase the value of the property in the long term. This applies to both residential properties, office environments, and public spaces where acoustics play a central role.

Typical examples of low-frequency sounds

Absorbing low-frequency sound requires specific measures, as low frequencies (below approx. 200 Hz) have longer wavelengths that are more difficult to dampen than higher frequencies. Standard, thin absorbers work well for higher tones but are insufficient for deeper, more disruptive sounds.

Here is a complete guide showing how you can effectively reduce disturbing low-frequency sound using the right methods and materials.

Typical examples of low-frequency sounds (20–200 Hz):

Before choosing measures, it is important to identify common low-frequency sound sources. Examples of such sounds are:

Traffic noise
Especially from heavier vehicles such as buses, trucks, and trains.

Ventilation and fan systems
A rumbling or dull humming sound.

Bass sounds from music
Bass lines from music systems or nearby nightclubs.

Heat pumps and cooling systems
A low humming sound that is often heard through walls.

Motors and machines
For example, refrigerators, pumps, washing machines, and other household appliances.

Impact noise and structure-borne noise
Vibrations that are transmitted through the building's structure.

These sounds are often perceived as particularly disturbing because they are not only heard but also felt, which can cause discomfort and irritation in homes or work environments.

1. Thicker absorbers (broadband absorbers)

The thicker the absorber, the better the absorption of low frequencies. Choose absorbers with a thickness of at least 100–200 mm, for example:

- SilentDirect PES Wall or PES Ceiling.

- Install with an air gap behind the absorber for further improved effect.

Advantages:

- Effective sound reduction in the 125–500 Hz frequency range.

- Easy installation with concealed keyhole fasteners.

2. Corner-mounted bass traps

Sound collects in corners and creates resonance. Corner absorbers (bass traps) are therefore one of the most effective solutions:

- SilentDirect PES Corner or diagonally mounted absorbers are recommended.

- The optimal thickness of bass traps is at least 300–600 mm for best effect.

Advantages:

- High efficiency at low-frequency resonances (30–250 Hz).

- Takes up little space by utilizing the unused space in corners.

3. Membrane absorbers (panel absorbers)

Membrane absorbers consist of a dense front panel with an airtight cavity behind it. These absorbers are tuned for specific low-frequency resonances:

- Placed on the wall where the resonances are strongest.

- Can be adapted precisely to problem frequencies (usually between 50 and 150 Hz).

Advantages:

- Tailored to specific low-frequency problems.

- Extremely effective absorption at the selected frequency.

4. Helmholtz resonators

Helmholtz resonators are specially designed resonance chambers that absorb a specific low frequency through a carefully balanced opening and air volume:

- Requires careful dimensioning for maximum effect.

- Installed in locations where the problem frequency is most noticeable.

Advantages:

- Very effective at specific frequencies.

- Takes up relatively little space.

5. Complementary diffusers

Diffusers do not absorb sound, but spread it more evenly throughout the room, complementing sound absorption:

- Used together with absorbers to provide a more even sound image.

- Well suited for studios or music rooms for better sound quality.

Advantages:

- Provides a more even sound distribution in the room.

- Contributes to higher sound quality.

Practical tips for optimal results:

Combine several methods
Use broadband absorbers together with corner absorbers for the best effect.

Prioritize corners
Always start with corner-mounted bass traps and then supplement with wall and ceiling absorbers.

Use a sound level meter
Identify problem frequencies with a sound meter and choose solutions that match the frequency.

Did you know that..

Low-frequency sound can travel through walls as if they weren't even there? Many people believe that bass sound is absorbed in the same way as high-frequency sound, but in reality, standard sound absorbers are virtually ineffective against low frequencies. Because bass sounds have long wavelengths, they can bend around obstacles, bounce around the room, and amplify in corners, making them difficult to control.

The thicker a sound absorber is, the better it captures bass frequencies. Thin sheets of foam or fabric are of little help, while deep porous materials, bass traps, and membrane absorbers can handle low frequencies much more effectively. A wall-mounted sound absorber often needs to be at least 100 mm thick to affect the bass, but a strategically placed bass trap in a corner can give even better results.

The corners of a room act as sound traps – but in the wrong direction! Because low-frequency sound waves accumulate and amplify where two or three walls meet, a poorly designed sound environment can actually make bass noise worse instead of dampening it. By placing bass traps in the corners and combining porous materials with membrane absorbers, you can effectively reduce the bass problem without having to fill the entire room with damping material.

So if you find that the bass is uncontrolled and muddy, keep in mind that low-frequency sounds require more than standard absorbers. The right thickness, the right placement, and the right type of material can be the difference between chaos and clarity!