With the five blades and small diameter (high frequency for n/rev) as well as the narrow, stiff fuselage with two strong keel beams, the Comanche had no vibe absorbers, and needed none!
This illustrates something that is counter to another of those helo pilot myths, that vibration is not normal, and it indicates "something wrong" with the rotor.
N/rev vibration is a part of every helicopter. It is created by the rotor is a natural function of the way each blade chops up the amount of lift that is needed by the aircraft. The amount of natural vibration at the rotor head is almost purely due to rotor head hinge offset, number of blades and their stiffness, and the speed range of the helicopter. How much vibration the pilots and passengers feel is almost purely due to the way the fuselage responds to the vibration the rotor is providing. A wide, long, soft cabin will respond worse to vibration and have hot spots and cold spots where people feel more and less vibration. A narrow, stiff fuselage will prevent the vibration from creating hot and cold spots and generally provides a more comfortable ride. In reality the amount of vibration the pilots feel is driven by many factors it's quite possible to change a helicopter in some way (by cutting a door or moving the seats around) and discover that the perceived vibration is made vastly better or vastly worse.
I should also point out that in fact the vibration felt at the seat is often due to the way the seat itself responds to the vibration. It is quite possible for some pilot seats to multiply the N Per Rev vibration of the rotor by a factor of two or three! Often an aircraft vibration "gets worse" and all you have to do is tighten down the seat mounting bolts.
The inventor of that patent, Bill Welsh, is a great vibration engineer at Sikorsky, I worked with him on two projects.