Diaphragms calls get to be a very personal thing, what works for one won't do well for another. Every body has a different shape to there mouth and not all calls fit well. If it doesn't fit you won't use it well. The number of reeds makes a huge difference also. 1,2,2.5,3,3.5,4. The thickness of each reed makes a difference in the pitch a reed can make, the 2 standards are .003, .004 although some are making .0035. The other issue is how the latex is stretched, they stretch from side to side and front to back. This is known as tinsel strength and plays into pitch and volume. The tighter the reeds the more pitch and volume is possible. But the other things that play into this is air speed and tongue pressure. As Elknut stated[HI Paul] this is an art form and requires great amounts of practice to have great control of the reeds vibration against the tongue. To be good you must be able to control pitch going up and down, also volume. This is no easy trick, time and effort are the key to success. As others have already stated Elknut is the one to teach when and what to say, HE IS VERY GOOD! A small piece of info, there is one call on the market that is not made from latex, High Plains Call, it is made from dental rubber. This call is made by John Sarkisian and comes in doubles and triples and youth reeds. I have watched John bend the frame to fit peoples mouth and have them making sound in less than 3 minutes, pretty good trick.
Back to calls I use, HS 3.5 in .004 reed thickness and a double High Plains call. With these two calls I can cover the gambit of elk calling. I will use and do carry other reeds in my pack of calls, but these are my go to reeds. I also carry external calls one given to me by my friend Wayne Carlton and a couple sent to me from Will Primos. These should not be over looked they are very fine calls and do have a purpose in elk calling. For a field tube I have used a Carlton tube wrapped with polar fleecefor the last 20yrs. But for being big and bad, a 4" wiffle ball bat cut at 24" long.
Gselkhunter