Windows in a listening room

A couple of years ago, I changed the four curtains in my room because they let in too much light. The new blackout curtains were made of much heavier materials. It did not occur to me that the new curtains would have an effect on the sound system, but they did. The imaging became more focused and detailed. I thought that the acoustics in this room was damped well. I was very wrong, and it shows that you could never let your guard down. There is always something to upgrade. Damn this hobby.