Home Engineering Building Acoustics
The basic idea is to prevent the equipment from generating noise levels that may be harmful to the user (or to people in the vicinity).
EU Directive 89-391 and later on EU Directive 2006/42/EC  requires equipment to display the value of the noise level at the operator’s position when it is greater than 70 dB(A) as measured under the relevant applicable measurement standard. In addition, when this value is greater than 80 dB(A), it must display the sound power level as measured under the relevant applicable measurement standard.
Community Noise Control Regulations
Typical community noise control regulations will typically state a schedule of operation for noisy operations (e.g., forbidding operations before 10:00 a.m. and after 4:00 p.m. on weekends, as well as before 8:00 a.m. and after 7:00 p.m. on weekdays).
In addition, there will be a noise limit (typically to be assessed according to the type of area and the period of the day; the early version of standard ISO 1996 provided guidance on the sound level values and gave examples of such values  to be complied with at the edge of the property). This is no longer the case, as this is the task of regulations (that may rely on the standard for assessment and verification purposes though); as befits a standard, ISO 1996-1 does not provide examples of such values .
Some countries also use a quantity that describes the excess of particular noise over the background noise level. This quantity is defined as the difference between the ambient noise level when the equipment is operating and the background noise level measured when it is not.
It is called emergence in the recent (2014) FDIS ISO 1996  (please refer to Section 2.8.5 for more information on this topic). For example, in France a recommendation by the Health Ministry states that a noise from an equipment or activity can be considered potentially annoying when its emergence value is greater than 5 dB(A) in daytime and 3 dB(A) in nighttime . The local authorities can give precise information regarding those restrictions and their eventual mitigating circumstances (e.g., limited duration or emergency operation).
Contractual requirements will typically cover requirements that are in excess of the legal requirements, or simply not covered by legal aspects. For example, this may concern the noise from pieces of equipment inside a performance hall or in a room not covered by regulations (e.g., director’s office).
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