Reducing noise by room acoustic measures

Ceiling with vertically fixed elements for noise-absorption

Noise-absorbing baffle ceiling in a stamping shop
Source: IFA

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 absorption coefficient ᾱ in the octave bands with centre frequencies of 500 to 4000 Hz is at least 0.3
  • the decrease in the noise level with double the distance DL2 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.

It is advisable to design smaller workrooms on the basis of the sound absorption coefficient and larger rooms on the basis of the decrease in sound level. 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.

Since the results achievable with modifications of the acoustics of existing workrooms 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.

Further information on the acoustic design of industrial workrooms can be found in noise protection information leaflet IFA-LSA 01-234, which describes requirements, principles, measurement methods, measures, and the efficacy of noise abatement by room acoustic measures.

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Dr Florian Schelle

Division 4: Ergonomics, Physical environmental factors

Tel: +49 30 13001-3410
Fax: +49 30 13001-38001

Jan Selzer