The ideal cut off for hybrid models
There is no such a thing as the ideal crossover point between flat panels and dynamic woofers. Speaking of hybrid loudspeakers in general, the crossover frequency between the woofer and the flat panel is usually found in a range between 30 Hertz and 500 Hertz, depending on the characteristics of the drivers.
Some hybrids with ribbon drivers can even reach crossover points around 1200 Hertz between the often combined bass/midrange driver and the ribbon. The Final Model 3, Model 5 and Model 7 are available in a hybrid version. The crossover points for the panels starts approximately from 90 Hertz and upwards. So, the woofer has to tune in around these points. The crossover point depends on the panel’s size. A larger size means a lower crossover point and less ‘woofer influence’.
The crossover point will lead to implications on a soundwise level. As good as the match between the woofer and the panel is for the Final hybrids, from a technological perspective it’s always a compromise. Flat panels are very fast, directive and neutral. Woofers are radiating omnidirectional and you have to work hard to get the sound as neutral as possible. You have to cope with an enclosure that might give some coloration.
Hybrid basically stands for combining two drivers with very different architectural principles and resulting sound. Choosing the crossover point between the two depends on the driver’s specifications but does have impact on the sound. It works on the spatial level, but a larger woofer also stands for more low frequency power and a frequency range reaching subsonic territory. A larger panel (and mostly smaller woofer) will usually bring more focus, detail, a larger soundstage and less acoustic problems. In the real world you can find several variations. Sometimes very large electrostatic panels with separate woofer towers, scattered with 15-inch low frequency drivers. The Final hybrid models make sense and are optimized for a setting where people are in their domestic environment.