“Raum der Stille”, the room of silence. Since 1993, those who go on holiday to Berlin have found in various parts of the city, such as the Brandenburg Gate, a small room with free admission, in which words are not needed. You can pray, think, reflect, rest or observe, write or read, breathe… the only rule: in silence! The room is poorly soundproofed, but effectively. Thick glass, pillows, curtains.
I guarantee you the passage from the crowded and noisy Plaz des 18 März, this little paradise that is nearby is an experience not to be missed, pleasant but at the same time painful due to the lack of aptitude of our ear to complete silence.
Raum der Stille at the Brandenburg Gate in Berlin - The room of silence
There is often an attraction between opposites or at least one extreme makes one appreciate the other better. The days would not be bearable without the stillness of the night, the music would not be the same without the breaks and some have even marched somewhat accomplishing in-questionable masterpieces with only the use of silence (see the rumored John Cage "4.33"
).
But there is silence e Ssilence. Those who work in a recording studio, those who study a “noisy” instrument in an apartment building, those who are tormented by the noises of their neighbors know it! Often a chimera is chasing and there is no panel that holds!
Silence is never completely silent due to echoes, waves bouncing off surfaces, background noises and basses that propagate for miles.
Various chambers have been built anechoic, without echo, environments that are a kind of black holes in sound, with an absorption of around 99%. Obviously their unnaturalness soon makes them rather unbearable to hearing and inconceivable to the human mind, which loses the link between action and noise and becomes disoriented.
The quieter the room, the more things you hear.
Anechoic chamber
The company of the Minnesota Orfield Laboratories has created the most sound-absorbing anechoic chamber in the world, 99,99%, so quiet that it earned a mention in the Guinness Book of World Records.
It is said that right here, in this surreal silence, Bob Dylan recorded the album Blood on the Tracks.
If it is true that one cannot stay more than 45 minutes in such an environment without showing signs of imbalance, I strongly doubt that Great Bob he succeeded, but oh well, the anecdote adds an aura of mystery to the already successful album (ed. deepening the sources there are versions of the Dylan type "... he recorded in the same building… ”Or“… recorded some parts of Blood on the Tracks ..." etc. - we also add that the room is "The most silent in the world" only from 2004 while the aforementioned album is from the 70s).
But let's get to the point. Building an anechoic chamber requires space to absorb sound and is not within everyone's reach. The one in Minnesota is made of fiberglass, steel and one foot of concrete.
In Hong Hong, a group of researchers has changed their approach to the problem. Instead of looking for ultra-absorbent materials, he focused his work on a solution that was able to actively counteract sound waves rather than passively absorb them.
The solution - published on Applied Physics Letters of September 2015 - is simple but ingenious, based on an element called DSR (decorated membranes resonators), membrane resonator, able on the one hand to absorb sound and on the other to reflect it in the opposite direction.
Just for those who ended up in this article without knowing how ... equal waves traveling in the opposite direction cancel each other out. Once this is understood, that's it! The sound wave arrives, hits the material and is reflected in the opposite direction with a sound reduction of 99,7%!
The DSR element consists of a small, slightly absorbent part followed by a highly reflective surface. In between a very thin portion of air sufficient to make the sound travel in both directions and cancel it. We are obviously talking about thousands and thousands of cells of this type capable of interfering with sound waves coming from any direction.
It is the new frontier of soundproofing, reducing the bulk of materials and maximizing results.
We will have to talk about this silence!
The structure of the membrane resonator (DSR)
The functioning of the DSR system as a whole.
