Many hunters rely heavily on diaphragm calls to entice mature gobblers to the gun, and these are great tools. However, as veteran hunter Charles Hudson points out, it is difficult to call softly with a diaphragm call. He suggests using a trumpet call or a scratch box for extremely soft calling. 

“With the scratch box, I can whisper to him and get him excited,” he said.

The same is true of most friction calls; it is much easier to call softly with a friction call than with an air-driven call. These calls allow for a lot of versatility and volume control. Scratch box calls are harder to find, and these legendary calls are fading away with time. But as many seasoned turkey hunters will tell you, few calls can mimic the turkey as well as the scratch box. 

Thankfully a few manufacturers still make scratch boxes; a quick internet search can find them. With a little practice, these calls can make a huge difference in killing mature, pressured toms.