The amount of noise exposure depends on several factors:

• amount of the noise emission of the acoustic sources, i.e. the machines and devices used, procedures, as well as additional equipment, e.g. extraction systems
• amount of the sound pressure level reduction from the source to the workstation
• distance of the source(s) to the workstation concerned
• number of acoustic sources and the actual operating hours during the daily working time

The amount of noise exposure is characterised by the assessment level L_r in the field of the non-ear-damaging noise exposures. In the field of the ear-damaging exposures, it is in turn characterised by the daily noise exposure level L_EX,8h and expressed in dB(A) (DIN 45645-2, ISO 9612, ISO 1999).

Noise reduction of machines

Machines constitute the main noise source at the workstation. Hence, the requirement of the EC Machine Directive regarding noise reduction at source is an essential factor in the noise reduction concept. In order to support the machine manufacturer and particularly for the engineers working there, DIN EN ISO 11688 was developed. It is intended to ensure that the machines developed are as low-noise as possible.
Within the framework of this standard, the basic principles of machine acoustics are presented systematically. That is across the entire functional chain, starting at the excitation of the noise and the noise transmission through the machine to the emission through machine surfaces. This is covered entirely in the first part of the standard without using any formula representations. On the contrary, the underlying physics is represented by formulae in part 2 as well.
This is intended to motivate engineers to also be aware of the noise emission when developing machines. Thus, they are to reduce the noise emission at source, pursuant to the requirements in the Machine Directive, i.e. they are to incorporate machine-acoustic noise reduction principles in the design work.
Furthermore, the following measures should be taken into consideration regarding the noise reduction at the workstation (according to DIN EN ISO 11690-1, -2):

• Low-noise machines must be selected with the help of the noise emission specification when procuring new or replacement machines
• low-noise procedures must be observed
• a sufficient noise level reduction per doubling of the distance in the installation space of machines can be achieved by means of noise-absorbing ceilings in connection with baffle collectors
• noise insulation products, such as capsules, screens, silencers, etc. must be attached near or on the machine; if required, the workstation must be screened off

Only if all these measures do not lead to the desired result, the proper use of hearing protection must be taken into consideration.