The Ohm A's used two different sections of cone and the F's used three different sections of cone, all seemed together mechanically. The Ohm A's had a larger cone with a non-linear flare rate whereas the F's had a smaller diameter cone that maintained the same flare rate for the length of the driver. The differences in materials, cone mass and driver geometry all add up to differences in radiation pattern, transient response, etc... As such, even though the A's and F's are TRUE "Walsh drivers", even they differ from one another in design and performance.
As a side note, the Ohm G used a smaller version of the Walsh. Due to the cabinet design, the radiation pattern was not nearly as omni as the A or F. This not only changes the sound that one hears, but also negates many of the spatial properties that make the Walsh design special.
Due to using a smaller cone with the reduction in piston area, Ohm was looking for a way to augment the bottom end of this driver. They did this via the use of a passive radiator. Passive radiators have the slowest transient response of any vented design*. As such, the bass on such a design typically sounds very "heavy" i.e. thick and powerful, but lacking in definition due to slower rise times and a lack of damping i.e. excessive "ringing" once excited.
While passives are great for HT use where "earth shaking" bottom end is more desirable, they really have limited use in a "hi-fi" system. Passives are, once again, another form of venting that achieves "quantity" over "quality". Sean
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