Sound dampening

I'm helping a friend with his theater and one thing he is doing with a 7" high platform for second row seats is lining the platform with insulation and adding port cut-outs that turn the whole platform into a giant bass trap.

You want to break up the sound that travels along flat surfaces. Port the platforms as you described but fill with random stone and not fiberfill. Bass waves will still pass thru the fiberglass. The stone will diffuse and reduce the chance of standing wave resonance. Tom

Bass frequencies will not be damped or absorbed by curtains if that's what you're looking for. And they won't do much to keep the sound from leaking to the rest of your house either if that's a concern (you don't specify if you're looking for sound isolation or optimization or both). If you're looking to just absorb higher frequencies I suppose the curtains would help but could even prove to be too much. If you construct the walls and ceiling the right way the need for additional damping will be reduced. I'd highly recommend reading the book Premium Home Theater by Earl Geddes as it will give you good theoretical and practical guidelines that could help you decide how far you ultimately might want to go with this. Best of luck in building your theater.