Patent attributes
An acoustic absorber includes a chamber formed from walls with a resistive portion providing the only communication between the chamber volume and ambient air. In some examples chamber walls enable selection or adjustment of chamber volume or resistive area, thereby altering the acoustic absorption spectrum below 250 Hz. In some examples the chamber volume contains fibrous filler material exhibiting no airflow resistance or acoustic absorption. Density and heat capacity of the fibrous filler material results in the chamber volume exhibiting compressibility of air within the chamber, for at least acoustic frequencies up to about 50 Hz, that is larger than adiabatic compressibility of air. That larger compressibility results in an increased acoustic absorption coefficient, for at least acoustic frequencies up to about 50 Hz, 50% to 100% larger than that of an identical chamber entirely characterized by the adiabatic compressibility of air.
