Room acoustics

Fundamentals of room acoustics: Understanding and controlling sound

To optimize the acoustics of a room, it is necessary to understand the physical propagation of sound. Low and high frequencies behave fundamentally differently. The boundary between these ranges is called the cutoff frequency .

This cutoff frequency is not fixed, but depends significantly on the room volume. While it is around 400 Hz in a car, it drops to approximately 180 Hz in a living room and to around 30 Hz in a concert hall. The transition between these acoustic environments is gradual.

High frequencies: The ray model (Geometric acoustics)

Far above the cutoff frequency, the wavelength of the sound is small in relation to the room dimensions. In this range, the model of geometric acoustics applies: sound propagates in straight lines like light rays and is reflected by the walls.

• Reverberation time: The best-known criterion for the "reverberation" of a room.
• Sound level: The longer the reverberation time, the higher the overall noise level in the room.

With each reflection off a wall, the sound beam loses energy. This is where classic absorbers come into play, to regulate the reverberation time.

Low frequencies: The wave model (wave-theoretical acoustics)

The ray model no longer applies well below the cutoff frequency. Here, spatial eigenmodes dominate – three-dimensional standing waves that occur at specific frequencies.

This leads to an uneven sound pressure distribution in the room: In some places, the bass is perceived as extremely loud and booming, while in others it is barely audible. Controlling these low frequencies is usually significantly more complex from a structural point of view than damping high frequencies.

Technological comparison: Where the HSA3 comes into play

Conventional acoustic solutions are often based on porous materials (such as mineral wool or foams) or solid panel resonators. The HSA3 , as a microperforated absorber, offers technological advantages in areas where standard systems reach their limits:

• Fiber-free hygiene: Unlike mineral wool or open-cell foams, HSA3 is completely fiber-free. No particles are released into the air, making it ideal for allergy sufferers and sensitive environments.
• Shallow installation depth with high efficiency: Thanks to precise micro-perforation, air friction is used directly at the material surface for absorption. This allows the HSA3 to achieve efficiencies that would often require significantly thicker material layers for conventional absorbers.
• Material independence: While porous absorbers rely on their soft structure, the HSA3 principle can be applied to solid, durable surfaces that are more robust and easier to clean.
• Broadband effect: By adjusting the hole geometry, the HSA3 can be more precisely targeted to specific frequency ranges than conventional standard absorber panels.