In lower SS there are singers in 114 / 115 / 116 / 117, you also get 2 blocks in kippax corner singing. This is around 4,500 fans give or take. If even 70% of these sing it will create a lot of noise and we would all be buzzing. At times there is that many singing and it is loud, it then spreads for more to sing in the stadium. A loy of noise can come from SS3 when it is spreading.
When you think about the games when PSG / Bayern / Pozanan / Celtic can create more noise with just 2,800 fans and i mean they created enough noise for us to think it was loud for those games, it really doesnt take a lot.
If the blocks mentioned sang it would be enough, also other parts of the stadium would naturally join n then.
The problem is we get the low periods in the game where in lower SS about 50 - 100 of us sing, the rest watch the game or on phones are up and down. It really needs the singers to sing and if they dont want to then move out and other people wanting a good atmosphere can move in.