Mandrake, really good question! I take glass and water. Then I moisten glass and put TWO future diaphragms on wet glass. Here is photo of future left and right channels on dry glass. Then I take credit card ( I recommend Visa Infinite or at least Platinum ) and start removing air bubbles under the film. They are clearly visible. Once no single air bubble under the diaphragm I glue spacers on both channels and then cut off excess film. After assembling to be sure everything is right I measure resonance frequency of both channel. Difference is about 3 Hz only.