As opposed to the noise immission describing the noise exposure at a place, the noise emission describes the airborne noise emission of a machine, determined under standardised installation and operating conditions and without noise influences from other sources, as well as without reflected noise. Thus, emission is a source-internal feature. Parameters of the noise emission include the sound power level L_WA and the emission sound pressure level L_pA at the workstation.

• What does sound power level L_WA mean?

The sound power level L_WA of a machine identifies the noise the machine emits in total - i.e. in all directions. From a physics point of view, the sound power is the airborne noise energy emitted into the environment on average by an acoustic source. The sound power level is expressed in dB(A) and sometimes has an attached "re 1 pW" in order to avoid confusion with the sound pressure level. The sound power level is determined pursuant to the standard under defined installation, measurement, and operating conditions. As a value for the noise emitted in total, the sound power level is best suited for a comparing assessment of machines. Furthermore, it is an important input variable for performing noise forecasts in workplaces.

• What does emission sound pressure level L_pA mean?

The second variable for assessing the noise emission of a machine is the emission sound pressure level at the workstation L_pA. It is measured for the same operating conditions defined in the standard and expressed similarly to the sound power level. The emission sound pressure level at the workstation, expressed in dB(A), indicates how loud it would be at the workstation directly assigned to the machine if only the noise of this one machine would be present there, without any further background noise or reflected noise from walls and ceilings. One needs this emission value, since the sound power level alone cannot be used to assess the level of loudness at the workstation assigned directly to the machine.

There are measurement methods in internationally valid basic standards for the two acoustic parameters of emission. For example, the standards of the series DIN EN ISO 3740 describe different methods for determining the sound power level by measuring the sound pressure. Additionally, there are DIN EN ISO 9614 parts 1-3 where the sound intensity measurement method is used in order to determine the sound power level.

The emission sound pressure level may be determined according to the specifications made in the series DIN EN ISO 11200.

In order to be able to properly determine the noise emissions of machines, noise testing methods are defined in machine safety standards that, along with the application of the above-mentioned basic standards for describing the noise emission measurement methods, define the operating and installation conditions and the method to be used for declaring and verifying noise emission values. DIN EN ISO 4871 is available as the basic standard for noise emission declaration and verification.

Pursuant to the EC Machinery Directive 2006/42/EC, the machine manufacturer is obliged:

• to keep the noise emission as low as technically possible and

• to specify the noise emission

  • in the operating instructions and
  • in the sales literature describing the machine through technical data.
    

Here the noise emission is normally declared using the definitions in the noise testing sections of machine safety standards.
Normally, the two-number declaration specified in the DIN EN ISO 4871 will be used for the EC machinery directive, i.e. the measured value and the related uncertainty are filed separately, as requested in the machinery directive.

Along with the machinery directive, the "Outdoor" Directive 2000/14/EC is applicable to a selection of machines operated mainly outdoors (construction machines, gardening tools, high-pressure cleaners, etc.). It does not only differ from the machinery directive by the form of the noise emission declaration being a different one, but also by the fact that thresholds for the sound power level are defined for 22 different types of machines. These must be observed. Noise emission specifications according to the Outdoor directive are then also performed as a single-number declaration (measured value including inaccuracy) of the so-called guaranteed sound power level as a label on the housing of the machine and in the operating instructions. However, the emission sound pressure level and the related inaccuracy must then be specified in the operating instructions additionally, pursuant to the machine directive.

The noise emission declarations serve for selecting quieter machines by comparing the noise emission values and for the noise forecast and thereby also for a risk assessment, as requested of the employer pursuant to the German Ordinance on Occupational Safety concerning Noise and Vibration Protection (LärmVibrationsArbSchV).
Please note: Standards for determining, declaring and verifying noise emission values are available from the Beuth-Verlag.