What is an acoustic filter?

In simple terms, the attenuating filter is a “plastic” tube with a length and a diameter. The greater the length and the smaller the diameter, the more pronounced the attenuation will be.

COTRAL International has a range of 8 filters for the COTRAL PREMIUM model and 3 filters for the COTRAL ULTRA MINI model.

All the filters are tested and EC certified by the National Institute for Research and Safety - INRS and provide selective attenuation according to the frequency bands in order to adapt to the sound environments encountered in all industrial, agricultural fields etc....

The filters from COTRAL International are made of “charged” polypropylene. Each filter is derived from a moulding with precise lengths and diameters. It is these technical characteristics that make it possible to obtain the desired attenuation.

The attenuation is inversely proportional to the diameter of the central stricture and proportional to the length of this stricture.

Furthermore, it is attributable to the following three mechanisms:

• the deadening related to the viscosity of the air in a small cavity,
• the changes in sections, manifesting themselves in a high reflection coefficient,
• the nature of the material.

It is possible to “charge” the filter material to render it more or less absorbent in order to obtain, within the context of acoustic filters, an ability to reduce frequencies of 0 - 1 000 Hz to a lesser degree than frequencies of 4 000 - 8 000 Hz in order to promote better intelligibility of the voice.