In order to reduce noise exposure at workplaces, one of the requirements of the German Ordinance on noise and vibration protection is that sound-absorbing measures must be taken during the design of working areas.
Since conventional, porous sound absorbers cannot be used in working areas in which particular requirements are placed upon hygiene, new absorbers featuring a closed membrane surface and which are therefore hygienically safe, and which also exhibit high absorption of low-frequency sound, were to be developed in a generic project. Closed membrane surfaces (such as high-grade steel foil) can impair sound absorption. The efficacy of the absorbers therefore had to be tested in the laboratory.
The echo chamber at the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) was adapted to the test conditions by minor incremental structural changes. Various absorber concepts were installed in the echo chamber and the sound absorption measured in accordance with EN ISO 354, "Acoustics - Measurement of sound absorption in a reverberation room" (12/2003) beyond the usual frequency range also to include low frequencies (<100 Hz).
The measurements performed showed that a concentration of sound-absorption material in the corners of the room (corner bass traps) had a substantially better absorption effect at low frequencies than when the same quantity of material was distributed over the surfaces.
The studies showed this effect to be attained only when the corner bass traps had a thickness/depth of at least 400 mm. Covering the corner bass traps with a hygienically safe surface in the form of very thin, high-grade steel foil led to a substantial reduction in the absorption at frequencies above approximately 500 Hz, whereas this material was not seen to produce any notable reduction in the absorption at frequencies below approximately 200 Hz. Conversely, when aluminium foil of the same thicknesses was used, no notable reduction in absorption was observed in the entire frequency range.
-cross sectoral-Type of hazard:
noiseDescription, key words:
room acoustics, intelligibility of speech, noise stress, low-frequency noise, noise abatement, sound-level reduction, hygiene