It was a surprise geami for Johan Christensen that his own detailed calculations and the Spanish ex

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By using the principles known from the optic, it is possible to produce very efficient geami noise-reducing casing. It shows sensational research from Johan Christensen from DTU Photonics, which is nominated for Science top-5th By Jens Ramskov December 26, 2014 at. 12:00
Research Professor Johan Christensen from DTU Photonics geami has shown that noise-reducing structures can advantageously be manufactured in accordance with principles known from the optic. This is contrary to common sense as possible to get the best noise reduction geami in a wide frequency range by reducing geami the amount of noise reducing material.
It is well known that it is possible to achieve very high optical absorption by coating a material having upstanding carbon nanotubes. Here we exploit the carbon nanotube absorbs the light and that the spaces between the tubes are effective to capture the light. In this way, the researchers in the US, for example, created the world's darkest material.
The difference in the frequency of visible light and sound in the kilohertz range means that the relationship between the dimensions of the elements of the optical cladding and the acoustic cladding must be many orders of magnitude different. Where carbon nanotube dimensions are measured in nanometers, the corresponding elements in the acoustic structure measured in centimeters.
The slats, which are made of a foam material consisting of polyurethane, polyester and polyether, is placed as a grid with a variable 'filling factor'. 100 per cent. indicates that the fins are in contact with each other, and 50 per cent. indicates that the gap between the vanes is the same as the width of the slats. The less, the better
It was a surprise geami for Johan Christensen that his own detailed calculations and the Spanish experiments have shown that the lower the filling factor is - and thus the smaller the noise-absorbing material used - the better noise absorption gets in the investigated frequency range from 0,7- 3.0 kHz, which is chosen because it is relevant in connection with traffic noise.
In fact, the calculations show that it will be an advantage to go down to a filling factor of 30 per cent. or even lower. But it can be difficult in practice geami to produce the lamella structure with such a low filling factor.
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First of all: It is not mentioned geami in the article about the case of rejection of sound reflected from a wall, or attenuation of sound which are transmitted through a wall. But follow the link to the old article shows indirectly that there is attenuation of reflected sound.
It is certainly not new that a filling factor of 100% gives less damping. Even a layman as I know it for many years been quite common that when reflected sound attenuates, using not a "massive" wall of sound-absorbing material (ie, a filling factor of 100% in the article's terminology), since one runs the risk that some of the sound reflected from the surface of the material.
Instead, build a artfully crafted surface of wedges, pyramids or slabs of sound deadening material, so the sound can "go into the trap" between two pieces of sound-absorbing material, where the reflections can be allowed to die out before they are thrown back into space.
"No one has asked about the technical risks of the LEDs'
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