The complaints in Darmstadt have been piling up for some time.
Because they were disturbed by a deep humming noise, especially at night, many citizens could no longer sleep properly.
In 2020, the complaints increased significantly because it was quieter than usual at night due to the lockdown and the background noise was therefore perceived as particularly loud.
Noise is diverse – and is perceived in just as many ways.
Anyone who dances in a discotheque is happy if the music is as loud as possible, but the local residents are annoyed.
Anyone who drives around in a souped-up car likes the special sound of the engine, which upsets the residents along the street.
Some people are already bothered by the fly on the wall, others are sitting at the bathing lake directly under the flight path of Frankfurt Airport and think it's great.
But there are noises that apparently have a much higher potential for disturbance than others and that are perceived as very annoying on hot days, but especially at night.
It is a deep hum with a frequency of less than 90 Hertz, which is mainly emitted by cooling devices such as air conditioning.
These noises are everywhere in everyday life: in the car, for example, on the train or on the plane.
But nowhere are they perceived as strongly as in one's own home.
Especially if you want to sleep and it's quiet in the area.
Five sound sources
The Federal Environment Agency reports that low-frequency noise has increased in recent years, which is why more and more people are complaining about humming noises not only in Darmstadt but throughout Germany.
In everyday life, the low-frequency noises are usually lost in the ambient noise, but the quieter it gets, the more annoying they are.
In Darmstadt, employees of the Environmental Agency, supported by employees of the Hessian State Agency for Nature Conservation, Environment and Geology, went in search of the sources because of the many complaints and, after extensive measurements, found what they were looking for.
As the administration announced, five sound sources were localized, including at the university, the technical university, the building association and a private building.
The noises could be heard very clearly there.
Cooling units, heating pumps, heat exchangers and air conditioning systems were the sources of the annoying humming noise, which according to doctors' findings not only disturbs but can also make you ill.
In the previously known cases, the administration contacted the perpetrators to remedy the situation.
The noise was largely eliminated by small structural changes or changes to the setting of the devices.
Covered up by other noises
That is also the strategy for the future, says Daniel Klose from the Darmstadt city administration.
As soon as there are complaints, the environmental agency goes in search of the source of the noise.
Measurements are taken not only in the vicinity of the apartments, but also in the apartments themselves, where the noise is perceived as particularly annoying.
Because it cannot be ruled out that such noises are caused by the appliances in the household or your own heating system.
In Darmstadt, the complaints came mainly from the Martinsviertel and from the area around the Bürgerpark.
According to Klose, the complaints have now subsided significantly, probably also because after the lockdown, the humming noises were masked by other noises again.
In southern Hesse, it's not just the Darmstadt residents who complain about low-frequency humming.
Complaints also come from other municipalities, the causes are likely to be similar.
Already in the early 1990s, after Opel opened its new company headquarters, the residents of a neighboring residential area were disturbed by noise at night.
After complaints, the air conditioning system installed on the roof of the building was also identified as the cause in this case, and structural changes quickly eliminated the noise.
As with almost every problem, there is advice on the Internet on what annoyed people can do about annoying noises at night.
Yoga, autogenic training or tai chi are recommended, as are small electrical devices that cause so-called counter-noise.
These then stand on the bedside table and imitate, for example, the sound of waves or a waterfall, which is perceived as pleasant and drown out the annoying noises.
Some even get holiday feelings.
Studies by the Federal Environment Agency have shown that around five percent of residential buildings nationwide are in the vicinity of low-frequency noise sources.
The number is expected to double by 2030.
So the problem will remain - not only in Darmstadt.