There are acoustic penels. That you can buy it on ebay, some internet shops and specializing audio-shops with Hi-End Audio. Difference in sound is considerable, but It depends also from place and amounts of panels, Depending on your acoustic specificity of accommodation. In My case the bass has become much better ( Softest and bigger-greatest )
The huge correction of sound we get Suppressing Interior the subwoofer.
Subwoofer of altec is factory exactly suppresing.
I advice suppress interior Klipsch iFi subwoofer, becouse it's empty.