illustrated in fig6 here the dotted line represents the decibels of sound absorbed by the tuned acoustical chamber the curve formed by this dotted line peaks in the vicinity of 60 cycles per second which is the fundamental or first harmonic of the system resonance frequency note also how the tuned acoustical chamber continues to absorb sound at 120 and 180 cycles per second in the fig1 a and 2a b embodiments the bottom edge 22b of the partioning means 21 forms a gap with the bottom wall 7 of the enclosure 1 to form a rectangular sound entrance port 27 to the tuned acoustical chamber 23 in the fig3 embodiment the sound entrance port 27 to the tuned acoustical chamber 23 is formed by the bottom edge 22b of the partitioning means 21 and the edge 36 of the bottom wall 30 of the tuned acoustical chamber 23 as shown rather than being at right angles edge 36 is preferably cut so that it is parallel to the bottom surface of the partioning means 21 the cross sectional area 34 y 34 of the entrance port 27 of the acoustical chamber 23 varies between the three embodiments in the fig1 a embodiment this cross sectional area is preferably 23 square inches in the fig2 a b embodiment the cross sectional area of the sound entrance port 27 is preferably 21 square inches in the fig3 embodiment this area is a little less than 11 square inches each of the three embodiments also includes an acoustical coupling 34 for acoustically coupling together the compression chamber 25 the tuned acoustical chamber 23 and the transmission port 20 of enclosure 1.