A friend of mine has a studio and he put cellular window shades up to deaden the sound.  He put them in the windows but also hung them from the ceiling in various places.  That deadened the sound considerably.  He got them at YourBlinds.com www.yourblinds.com Good Luck!

I have heard that using cellular window shades works wonders.  A friend of mine has a recording studio.  He put them on his windows, but also hung some from the ceiling throughout the studio.  It worked great!  It deadened the echo.  He got his from YourBlinds.com.  Here's the link to their noise page  www.yourblinds.com Good Luck!