An acoustic attenuation assembly includes a low frequency sound attenuation device having at least one sound attenuation chamber containing a volume and mass of air. First and second openings are associated with each low frequency chamber through which excited air resonates. The first and second openings extend through the first sheet into each low frequency chamber. Each chamber has an open side. A high frequency sound attenuation device is secured to the low frequency attenuation device and closes the open side of each chamber. The high frequency sound attenuation device includes a plurality of projections formed from a sound absorbing material that absorbs excited air.
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