Originally Posted by Brian Carlton

A six bladed prop would put you right in the frequency that you have specified if the primary driver for vibration is the blades. This would be 6X engine speed for a six bladed prop. However, I'd be somewhat curious as to whether the 1X engine frequency is your primary driver for the vibration that you seek to eliminate.

I don't see how the Dynamat is going to eliminate this vibration. Rubber mounts..........or fluid filled mounts............to the airframe that are tuned to the desired frequency are definitely the way to go. Naturally, the problems associated with modifying the airframe for such mounts are extensive.