I found the best method is mechanically tensioning the diaphragm in both axes, and then using minimal heat just to remove any remaining wrinkles. A hair drier is useless, better to use a heat gun set to the lowest heat and air flow, and use some attachment to spread the air flow. It should be from 5"...8" distance and keep moving, never stop at one spot. To be honest, heat tensioning is not very important, IMO.