2.2       Noise, sound emission and sound immission

Interfering sound or interfering noises are termed "noise". This shows that the term "noise" includes a negative assessment of neutral physical terms. According to DIN 1320, noise is audible sound, which disturbs silence or a desired sound perception or which causes annoyances or adverse health effects. What we have to consider is the subjective character of the term "noise", which is revealed by the fact that the negative impacts of noise on a person are associated with their current situation.

In order to guard against misunderstandings, the differentiation between emitted sound and incoming sound has proved necessary depending on the situation and is common practice in the field of environmental protection. There is in fact a major difference between the statement that a machine for example emits too much noise (emission) and the statement that this noise exceeds defined noise limit values in the affected neighbourhood as an environmental impact (immission).

A systematic differentiation between the terms "emission" and "immission" is regulated by the "Act on the prevention of harmful effects on the environment caused by air pollution, noise, vibration and similar phenomena", in short "Federal Immission Control Act" (Gesetz zum Schutz vor schädlichen Umwelteinwirkungen durch Luftverunreinigungen, Geräusche, Erschütterungen und ähnliche Vorgänge, Bundes-Immissionsschutzgesetz) (available in German). § 3 of this Act gives the following definitions:

(1) Harmful effects on the environment as used in this act shall mean any immissions which, because of their nature, extent or duration, are likely to cause any hazards, significant
disadvantages or significant nuisances to the general public or the neighbourhood.

(2) Immissions as used in this act shall mean any air pollution, noise, vibration, light, heat, radiation and similar effects on the environment which affect human beings, animals and plants, soil, water, the atmosphere as well as cultural objects and other material goods.

(3) Emissions as used in this act shall mean any air pollution, noise, vibration, light, heat, radiation and similar phenomena originating from an installation.

Exceeding a particular acceptable extent, they are called "harmful effects on the environment". Immissions require emissions, which are in the present work sound or noise emissions coming from a sound source. The term "emission" also designates the process of the emission of sound waves from a source and their entering the environment.

An immission is therefore at the end of a causal chain with an emission at the beginning. The link between emission and immission is "transmission" (propagation), which usually weakens the environmental effects on the propagation path from the source of the emission to the place of reception (point of immission) due to the distance and local conditions.

The official use of the terms "emission" and "immission" requires the context of human actions with the consequence that the associated effects on the environment are man-made. This means that the  twittering of birds, the breaking of waves and the howling of a storm for example are not noise within the meaning of the Federal Immission Control Act. In principle, this circumstance is easy to understand but it can cause certain problems in real life when it comes to sound measurements and the assessment of complaints as the question of where nature ends and a causer (emitter) comes into play can sometimes be controversial. These disputes range from the keeping of animals (e.g. cock-crow, the croaking of frogs from a garden pond) to the noise of running waters (in the context of hydraulic-engineering measures) or to the sound of wind (in the context of tower blocks and overhead lines). It therefore proves necessary at this point to refer to the term "installations" used within the Federal Immission Control Act and described below in section 2.3.1.

The causal chain of emission - transmission - immission plays an important role in the context of noise reduction as each of the three components can be the subject of noise reduction measures. The voluminous set of technical regulations developed for this purpose can be classified according to these three subject areas as illustrated in figure 2/2 using the examples of fundamental technical directives and standards. This figure comprises the most important "technical rules" for the description and solution of noise problems:

In the following chapter, we will go into more details about these and other directives and regulations, especially about DIN 18005 (Noise abatement in town planning) which covers the whole problem, as far as it is necessary in the context of the Noise Manual for Urban Development.