All response graphs I’ve seen are based on a 0dB centre line upon which is drawn the relative gain as the frequency increases - e.g.
That’s pretty self-explanatory.
I’m now looking at the graph in the data sheet for another mic (actually Thomann’s SM58 clone), and I don’t understand it.
What is the y-axis scale and why are there two lines in the graph?
Can anyone help explain the second graph to me please ?