What does the Spine Line do?

What does the spine line on the drumhead actually do? Well that simple question opens up a TON of answers. Information presented come from my old notes in chat with Seamus O'Kane, Christian Hedwitschak and Rob Forkner of Metloef. Lastly I pull information from Brent Cuyler from Finnegan Hill bodhrans whom I interviewed about this topic. Also here are the links I mentioned in the video. Scanamara's ronan O' Snodaigh "Belly vs Back".    • 13. Belly vs Back: Rónán Ó Snodaigh - Bodh...   Circular membrane modes and maths calculator: http://hyperphysics.phy-astr.gsu.edu/... **Just a note, I barely understand any of the math and physics aspect so all I'm talking about in the video is stuff that a buyer would want to know.