The Knock Down Triple uses three layers of super thin prophylactic and latex making this diaphragm an excellent choice for producing the deep, guttural sounds of older bulls. Its raspy bugles can easily pierce thick, dark stands of timber. Cow elk like big bulls! Call in the cows, and the bull will follow. The Knock Down Triple uses three layers of super thin prophylactic and latex making this diaphragm an excellent choice for producing the deep, guttural sounds of older bulls. Its raspy bugles can easily pierce thick, dark stands of timber. Cow elk like big bulls! Call in the cows, and the bull will follow.