Reducing noise by room acoustic measures

Noise exposure in workrooms is composed of the sound directly emitted by machines and equipment and of the sound reflected by the walls and ceiling. By giving ceiling and/or wall surfaces a sound-absorbing design, it is possible to reduce the share of reflected sound and thus reduce the noise exposure at the workplaces concerned. These room acoustic modifications make sense in many firms. When planning new workplaces, it is important to take the room acoustics into account, as a sound-attenuation retrofit in an existing room is usually much more elaborate and expensive.

According to the Noise and Vibration OSH Ordinance, workrooms are to be designed so that the sound propagation conditions conform to the state of technology. In the noise section, the Technical Rules for this ordinance (TRLV) lend concrete expression to these requirements by stating certain room acoustics parameters. The state of technology can be considered complied with if

• the mean sound attenuation coefficient α in the octave bands with centre frequencies of 500 to 4000 Hz is at least 0.3
  or
• the decrease in the noise level with double the distance Δ L in the distance range of 0.75 to 6 m in the octave bands with centre frequencies of 500 to 4000 Hz is at least 4 dB.

The relevant experience has shown that it is advisable to design smaller workrooms on the basis of the demanded mean sound attenuation coefficient and larger rooms on the basis of the demanded decrease in sound level per doubling of distance [1]. Because room acoustics modifications and the attenuation materials employed can be extremely costly, the materials should be used with great deliberation and only in the actually required quantities. Forecast calculations are necessary for different room acoustics configurations so that the ordinance’s specifications can be gradually satisfied by approximation. For this, the IFA uses software conforming to Guideline VDI 3760 (see [2], for example).

Since the results achievable with modifications of the acoustics of existing workrooms also depend essentially on the initial situation, a precise analysis of the original room acoustics is necessary. Depending on the initial situation, noise reductions of roughly 1 to 6 dB(A) can be achieved in the proximity of machines, and even 10 dB(A) and more at greater distance from the noise sources. In workrooms in which noise nuisance is the result of talking among the room’s occupants, as in call centres and classrooms, noise reduction rates of the order of 8 dB(A) can be achieved in many cases. The room acoustic modifications improve not only the comprehensibility of the spoken word, but employees no longer have to raise their voices in order to make themselves understood.

Further information on designing the acoustics of workrooms is contained in the noise protection worksheets LSA 01-234 to LSA 03-234 “Geräuschminderung in Fertigungshallen” (noise reduction in production shops) (BGI  674, BGI  678, BGI  797) and LSA 01-391 “Geräuschminderung im Büro” (noise reduction in offices) (BGI/GUV-I 792-310).