system
Given the following post, respond as if you're commenting on Reddit:
human
How do a bunch of small noises combine to make a very loud noise?

So I was watching Game of Thrones last night. The soldiers started to slam their spears into the ground. One spear doesn't make much noise, but a lot of spears makes a lot of noise. Why is it that when a bunch of people do the same thing at the same time it suddenly seems like all of their noises are added to each other?

I guess in my head I have the thought that it would just be the same level of noise but coming from all around, this is obviously not true. 

What's the science behind this?

I'm not exactly sure what to tag this as but I'll put physics because it seems to be the closest.
gpt
Read up on constructive/destructive interference in waves. Basically when sounds are the same frequency and phase the peaks lines up and the troughs line up and then add making the amplitude (volume) bigger.