All of the tube calls that I have seen have been a single sheet of flexible diaphragm material like latex or rubber of varying thicknesses
.. Has anyone had any success in stacking and/or cutting the diaphragm material similar to what is usually done with mouth calls? Does the different direction of air flow across the reeds of the two calls make any difference in the sounds that they generate?
I make a tube call with a slanted mouthpiece, and I've stacked latex and used it successfully. With the regular flat mouth tube, it was more difficult to position and layer the latex, but it worked....although, for me, I had more success with the slanted mouthpiece tube call.
I have used multiple reeds successfully but have never tried making cuts in them.