Tunable acoustic attenuation

An acoustic attenuation device extending from a first end to a second end comprising:

• first and second sheets;
• a plurality of webs positioned between the first and second sheets and cooperating with the first and second sheets to form a series of sound attenuation chambers containing a volume and mass of fluid;
• a first panel secured to the sheets and closing the chambers at the first end of the device;
• a second panel secured to the sheets and closing the chambers at the second end of the device;
• at least one partition for dividing at least one of the chambers into chamber sections, each partition including an outer wall and an inner wall spaced from the inner wall by an annular space;
• first and second openings associated with each chamber and through which excited fluid resonates, the first and second openings extending through the first sheet into each chamber, the first openings having an invariable cross-section and at least one of the second openings having an adjustable cross-section for varying a resonant frequency of the chamber;
• and
• a frequency tuning mechanism associated with each second opening for adjusting the cross-section of each second opening, the frequency tuning mechanism having a plurality of leaves and a controller for changing the spacing between the leaves to adjust the cross-section of each second opening for varying the resonant frequency of the chamber.