sound level

Sound level in the room: direct sound, diffuse sound and the reverberation radius

The sound level is the key measure of the perceived loudness of a sound source. In enclosed spaces, this level is composed of two physically distinct sound fields, the interaction of which determines the acoustic quality.

The two components of the sound field

1. The direct sound field: This is the sound that reaches the listener directly from the source. In a free field without obstacles, the level decreases continuously with increasing distance – for a spherical source, this decrease is physically due to 6 dB per doubling of distance .

2. The diffuse sound field: This component is created by reflections from walls, ceilings, and floors. The sound waves spread out in all directions, so that in an ideal diffuse field, the sound level is almost identical throughout the entire room.

The reverberation radius ($r_h$): At a specific point, the level of the direct sound is exactly the same as that of the diffuse sound. This distance from the source is called the reverberation radius. The more absorption present in the room, the larger the reverberation radius and the clearer the sound event is perceived.

Assessment of noise reduction: Standards and key figures

To ensure that rooms do not become too noisy, DIN 18041 and ÖNORM B 8115-3 use specific characteristic values:

• A/V ratio (DIN 18041): This ratio relates the equivalent sound absorption area $A$ to the room volume $V$. A higher value indicates an acoustically "drier" and quieter room.
• Average absorption coefficient ($\alpha_m$): The Austrian standard ÖNORM assesses the average effectiveness of all room boundary surfaces, including furnishings.

Application areas and technological solutions

Offices and call centers: The challenge of thermal activation

Modern office buildings often use thermally activated building systems (TABS). Since the concrete ceilings are used for heating and cooling, they must not be covered by large, heat-insulating acoustic ceilings.

The HSA3 advantage: As a microperforated absorber, the HSA3 requires no conventional fiber material or thick foams. It can be designed as a slim, metallic element that barely impedes the thermal convection of the ceiling, while simultaneously reducing sound energy in the diffuse field with high efficiency.

Medical areas: Hygiene and acoustics

In operating rooms or treatment rooms, hygiene standards often prohibit the use of conventional, porous absorbers, as these could bind dust or release fibers.

The HSA3 advantage: HSA3 technology is completely fiber-free and has a smooth, closed surface that is easy to clean and disinfect. Acoustic optimization and the highest clinical purity are no longer mutually exclusive.

Restaurants and public halls

In canteens, restaurants, or train stations, hard surfaces (glass, stone, metal) encounter high foot traffic. The goal is to dampen the diffuse sound field to such an extent that conversations are possible without strain.

The HSA3 advantage: Micro-perforation allows absorbers to be discreetly integrated into the architecture. Whether as a transparent solution in front of glass surfaces or as unobtrusive wall elements – the HSA3 controls the sound level without disrupting the visual concept of the room with "heavy" acoustic elements.

Traffic routes: Stairwells and corridors

Often neglected, corridors and foyers are critical zones for noise transmission to adjacent rooms. Targeted, highly effective sound absorption is necessary here.

The HSA3 advantage: Due to the high mechanical stability of the micro-perforated surfaces, the HSA3 is significantly more robust against mechanical impacts in high-frequency areas than conventional soft fiberboards.