One of the persisting problems of modern life is the noise pollution. The unwanted sounds like that of machinery, engines, etc., when released into the environment causes adverse effects on mental and psychological well being. Although, insulating the windows against sound is a solution to this issue, but this procedure is difficult and also very expensive. However, there is another solution to it – soundproofing, which transfers sound from the air into some other medium that absorbs and attenuates it. But, it also involves blockage of air. A team of two South Korean material scientists has come up with a way out of separating sound from the air and then attenuate it. They have created a double glazed window that stops sound but lets the air pass.
Sang-Hoon Kima at the Mokpo National Maritime University in South Korea and Seong-Hyun Lee at the Korea Institute of Machinery and Materials designed a sound resonance chamber by making use of material with a negative bulk modulus as only such a material can attenuate sound that passes through it. Since there is no solid material with a negative bulk modulus so they made the chamber with two parallel plates of transparent acrylic plastic about 150 millimeters square with a gap of 40 millimeters between them. Therefore any sound that resonates inside this chamber acts in an opposite way the same sound would have compressed the chamber and thus resulting out into a negative bulk modulus.
In order to maximize the efficiency of sound getting into the chamber, the scientists drilled a 50mm hole on each acrylic plate. This way any range of sound could be diffracted strongly inside the chamber, while allowing a free flow of air providing excessive ventilation.
This double glazed window was used as a building block to create bigger windows, which could reduce sound levels by 20-35 decibels over a sound range of 700 Hz to 2,200 Hz. What’s more, these double glazed windows are also tunable just by altering the size of the penetrations to stop the sounds of certain frequencies. This redesigned window is definitely a wise solution to the issue of everyday increasing noise pollution.