This seems to be about ribbon speakers ... but ribbon speakers don't have a planar field coming from below the ribbon, it wouldn't work. Ribbon speakers need the magnetic field lines to be parallel to the ribbon, Lorentz force and right hand rule and all.
I know the Apogee ribbon speaker has a massive "ribbon" which makes it impossible to achieve that with magnets just on the side of the ribbon (like ribbon tweeters have) but they can't cheat physics ... if the force has to move the ribbon front to back, then the magnetic field lines have to come from the side (on average).
What you could do is have the ribbon metallized in sections, and run the current up and down on alternating sections. Then have alternating strips of N/S magnets below, along the insulated parts of the ribbon. It won't be an even field, but on average the magnetic field will have a component running parallel to the ribbon and at a right angle to the current and thus create a force front to back. The forces on all the sections will point the same way too.