Rue D’Avron is one of many side streets in central Paris, a stone’s throw from the famous Père Lachaise Cemetery, where Édith Piaf and Jim Morrison are buried. Unlike there, there is a lot of hustle and bustle along the street: people are chattering in front of the cafés, and loud haggling is going on in front of the fruit stalls, while mopeds weave their way through the traffic and suppliers honk their horns in annoyed footsteps.
The street may be nondescript, but it’s one of the noisiest streets in the French capital. The residents here have to endure an average of 75 decibels day and night. That’s as loud as a washing machine on the spin cycle. This is shown by interactive maps on which Parisian noise researchers have drawn the loudest routes through the city as a colored mesh. To create the noise maps and keep them up-to-date, they use a whole network of sensors distributed throughout the city.
Noise radar against traffic hooligans
Their latest prototype recently hung from a lamppost in front of a fruit stand on Rue D’Avron. From there, the world’s first noise radar monitors particularly noisy road users. Four microphones protrude like tentacles from the sensor, which the researchers have dubbed “Medusa”. The microphones record noise peaks, analyze their origin and assign the noise sources to 360-degree images with pinpoint accuracy. These are from a camera in the center of Medusa. Thanks to artificial intelligence (AI), she can evaluate the images directly on the road. Nothing is saved for data protection reasons.
So far, Medusa has only recorded the noise for study purposes. But since the beginning of 2023, anyone who hits the gas hard in their vicinity and generates more than 85 decibels will receive a letter from the police. Then a fine of 135 euros will be due. This will not cover the costs of the pilot project, as initial projections by Bruitparif, the operator of the Medusa system, show. But that’s not the goal at all. Rather, the city administration of the Seine metropolis wants to improve the quality of life of its residents.
Paris is not only the city of love, but also of noise. This can be seen in a ranking from the end of 2021, in which Paris, as the loudest city in Europe, is ahead of London and Rome. The ranking is based on data from the European Environment Agency. According to this, 5.5 million people in Paris suffer from night-time noise of more than 55 decibels. The World Health Organization (WHO) recommends a maximum of 40 decibels at night, which corresponds to light rain splashing on the window.
Roaring motorcycles
The lion’s share of noise in Europe comes from road traffic, followed only by planes and trains. Bored-out motorcycles are the biggest rioters in Paris at night, as the Bruitparif researchers have found. To do this, they simulated a moped driving through the city center at night on the computer. The result: In its original state, it would have woken up 300 sleeping people, while a souped-up moped would have woken up perhaps 10,000 people. This not only causes trouble, but is also bad for your health.
Scientists link city dwellers to hearing disorders, stress, high blood pressure and cardiovascular diseases. Noise costs Parisians almost a whole year of life alone. The WHO estimates that a total of 1.6 million years of life are lost in the countries of Western Europe. Every fourth resident there is permanently exposed to excessive volume.
Anti-noise poles at the rock festival
Some do it voluntarily: at the Roskilde Festival in Denmark it gets really loud for four days once a year. Then bass and electric guitars smash from the stages when headliners like Cardi B and Bob Dylan perform. In the midst of the 130,000 festival visitors, a team of acoustics researchers pitched their tents for a unique open-air experiment in 2019: Finn Agerkvist and his team from the Technical University of Denmark in Lyngby near Copenhagen set up a so-called Sonic Crystal here.
The sound barrier looks like a bare forest of about 100 wooden poles, each three meters high, arranged very regularly. The piles are lined up in a grid-like layout.
The name of the arrangement refers to the similarity with the regular arrangement of atoms in a crystal. When sound waves hit such a forest of poles, they are reflected and scattered from one pole to the next. The incident and reflected sound waves partially cancel each other out.
The construction looks quite simple, but is planned exactly. The scientists used a mathematical model to calculate the thickness of the piles, their cross-section and, in particular, their distances from one another. As a rule of thumb, the distance between the posts must be less than half the wavelength of the sound that a Sonic Crystal is designed to block. Therefore, each individual Sonic Crystal can only filter out very specific pitches. Visitors to Roskilde were able to try it out for themselves on a meadow next to the stages.
A Sonic Crystals consisted of thick square-section piles spaced 30 centimeters apart. Above all, they swallowed up bass and let high tones pass through without any problems. These were then swallowed up by the neighboring crystal’s round posts, which were screwed onto plates close together.