Home Theater Curtain Ideas

So I'm still working on finishing up my home theater. I've got a combination of absorption panels and diffusers on the way from Auralex, but I still have a pretty notable gap in my room's acoustics. I have a fairly large window (~5'W x 3'H) just to the left of my TV which will be right behind my left front speaker.

When I submitted my room diagram to Auralex for analysis, my engineer suggested putting a heavy curtain over the window. I've done some looking online and haven't come up with anything great. I'm definitely not above putting something together myself, but I don't have a great idea of where to start.

Anyone have any success using any sort of curtains for sound absorption? Or any thoughts on what might work well?

Yeah, I found that site as well. I sent them an email to try to get a quote, but looking quickly it seemed like they're probably out of my price range. I'll post what kind of pricing the respond with.

I was looking for something cheaper. Pre-made's great, but I'm definitely not opposed to spending some time with a sewing machine.

Reply from quietcurtains.com:
"Curtain with .5NRC costs $280; .7NRC $330 [for a] 4'w x 2'h pleated curtain"

That's a little much...