Question about following a DIY bass trap video

[Audacity]

I decided to follow this tutorial:

 

 

My question is, why does he tell you to get 4 pieces of each length of wood and 2 pieces of each fabric? It seems like he only uses 2 pieces for each wood length and 1 piece of each fabric...am I missing something?

[astech13]

because he made two. one for each corner of the room. in the video he just made one but if you do it over again you would need twice as much wood and fabric. so the list tells you how much you need to do the room, not just the one in the video.