Air sound emission

Professional Definition

the occurrence of sound in a certain area or at a point being under the influence of a specific source(s) of sound;

In acoustic engineering, it is crucial to distinguish between emission and immission. Emission refers to the acoustic energy radiated directly by the source (e.g., an industrial fan) and is constant for a given device. Immission, on the other hand, describes the sound level that reaches a specific point in space (e.g., the window of a residential building). The value of immission results from the sound power level of the source, but reduced by losses resulting from wave propagation – that is, distance, absorption by air, reflections from the ground, and the use of acoustic screens.

Acoustics in Simple Words

To understand this phenomenon, imagine a campfire in the forest. Emission is the total amount of heat and light generated by the fire – this value does not change, regardless of whether someone is standing next to it or not. Immission is the heat you feel on your face when sitting two meters away. If you move back to ten meters or place a screen between yourself and the fire, the heat that reaches you (immission) will drastically decrease, even though the campfire (source of emission) burns just as fiercely. In acoustics, we strive to ensure that despite high noise emissions from the road or factory, the immission in your home is as low as possible.

Summary

Airborne sound immission is a measure of the noise “received” at a specific observation point. It is the values of immission, not emission, that are the basis for determining exceedances of environmental standards and determine the acoustic comfort of residents.