Yes, and from the pictures I can see they also block the view quite well.For room ambiance/flutter the curtains are probably effective enough.
Extremely effective of blocking out light, though.
But, at night, may be.. And other rooms can be different, different situation, perhaps curtains are already in place. Then it is very useful to know before buying additional layers of thick curtains, how this will change acoustics. This thread, and information provided with measurements, is useful for someone.