Helmet antibruits

A helmet antibruits is a helmet of which the essential goal is the reduction of the intensity of the perceived Bruit, mainly in a situation of Travail.

The active helmets antibruits

To reduce the noise by the wearing of helmet, the first solution was to use the acoustic properties fibrous or porous materials such as the Glass wool. Unfortunately, these materials are effective only against the acute ones, from approximately 600 Hz.

However, in front of the evolution of the analogical filters and the numerical systems, one could make profitable the idea stated by Paul Lueg in 1933, a German engineer who deposited a patent of it: it is a question of adding to the noise exactly the same sound, but in opposition of phase. Thus was born the active helmet.

Indeed, the noise can be regarded as a sum of its S pure, with Fréquence fixed. The Air oscillates under the impulse of these sound waves, i.e. its Pression increases then decreases regularly. In the active helmet, one adds to the noise a second signal so that the overpressure of the air due to the noise coincides with the depression due to its addition: the signal is then in opposition of phase, and the pressure is brought back to a constant of time.

The active helmet must thus comprise a Microphone to analyze the noise, a Haut-parleur to emit the correct Signal, in addition to the filter which treats the data and of its food.

Random links: