You can get purpose made curtains that have a vinyl liner.
Vinyl - i.e. the flexible variety, is extremely good as absorbing sound
I had a window behind the listening postion at my last house and a simple vinyl roller blind instlled at ceiling height cured most issues.
What surprised me is it only needed to be extended about 18" from the ceiling.
I also tried one behind the speakers, but it made no improvement
The effectvieness was later confirmed when I assisted a friend with echo issues at his condo - it was all concrete and had 12 ft ceilings.
We found that in his case a curtain 24" high, placed at ceiling height remedied most issues - in his case he reqired 2-3 curtains at different locations.
see
http://www.allnoisecontrol.com/products/Acoustic-Curtains.cfm
https://www.acousticalsurfaces.com/acoustical_drapery/acoustical_curtains.htm
http://soundblackout.com/best-types-of-heavy-curtains-for-soundproofing-home/
https://www.lowes.ca/home-decor/curtains-drapes-hardware/curtains-drapes/special-features/noise-redu...
Be aware - they are heavier than normal drapes and reqire a more sunstantial support system
Hope that helps - Steve
Vinyl - i.e. the flexible variety, is extremely good as absorbing sound
I had a window behind the listening postion at my last house and a simple vinyl roller blind instlled at ceiling height cured most issues.
What surprised me is it only needed to be extended about 18" from the ceiling.
I also tried one behind the speakers, but it made no improvement
The effectvieness was later confirmed when I assisted a friend with echo issues at his condo - it was all concrete and had 12 ft ceilings.
We found that in his case a curtain 24" high, placed at ceiling height remedied most issues - in his case he reqired 2-3 curtains at different locations.
see
http://www.allnoisecontrol.com/products/Acoustic-Curtains.cfm
https://www.acousticalsurfaces.com/acoustical_drapery/acoustical_curtains.htm
http://soundblackout.com/best-types-of-heavy-curtains-for-soundproofing-home/
https://www.lowes.ca/home-decor/curtains-drapes-hardware/curtains-drapes/special-features/noise-redu...
Be aware - they are heavier than normal drapes and reqire a more sunstantial support system
Hope that helps - Steve