I've been looking at getting some 3.5 mm audio jacks for a project I'm working on and these seem to be the best: http://www.switchcraft.com/productsummary.aspx?Parent=529 The problem I'm having is that I don't know which is better for my application. I'm looking at 35RASMT2BHNTRX which is a dual open jack v.s. 35RASMT4BHNTRX which is a dual closed jack. If I use the dual closed jack can I use those switches to detect that an audio cable is present?
Unless you need to detect if a connector is plugged in (such as to select or connect something else like an internal speaker/mic instead) the difference is essentially irrelevant.
If you do need to do so, consider which will be most convenient for your circuit. You may find it clearer to look at the schematic symbols on the mechanical drawings than to try to interpet the written description.
As seen on The schematic option 12 and option 4 are the dual closed and dual open. Same exact thing, except the dual closed has two extra terminals that short to the tip and ring terminals when no plug is connected. Commonly used, the dual closed allows a passthrough only when no plug is connected.