[Henry Schmidt]

The problem seems to be definition not function.
A harmonic balancer is a vibration damper.
A dual mass flywheel is a vibration damper.
Can we call a dual mass flywheel a harmonic balancer?
I believe we can , but opinions will vary. It seems that before the DMF, harmonic balancers were only mounted on the front. This was done for convieniece not because that was the only place it would function. Now we know it will work at either end.

The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.

When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.

A dual mass flywheel, or DMF, is made up of a primary and secondary flywheel with a series of torsion springs and cushions. There is a friction ring located between the inner and outer flywheel that allows the 2 flywheels to slip. This feature saves the transmission from damage when torque loads exceed the vehicle rating of the transmission.

The function of the DMF is to isolate the torsional crankshaft spikes created by high compression ratios. The DMF isolates the frequency below the normal engine operating rpm's during startup, acceleration and shutdown.