??? explain please ......
Sure - one of the main reasons that OB speakers (planars or cone based) don't blend well with sealed woofers/subs is that they load the room in different ways. The OB upper portion (mids/highs) loads the room in a figure 8 pattern, most energy going forward and backward and nulls at the side. A sealed woofer does NOT radiate in a figure 8 pattern, it acts as a pulsing sphere. This loads the room in a very, very different manner than the OB top section. Hence, they never, ever sound seamless. Even with a nicely built sealed box. Even with servo control. Box bass just physically propagates differently than the top part of the speaker.
On the other hand, OB bass radiates in a figure 8 pattern, matching exactly the pattern of the top section. So you get a much better match because of, you know, physics.
A nice side benefit - if you're using the woofers for mid bass or upper bass, it's a lot easier to keep the drivers physically close to the mids/highs drivers, whereas with sealed woofers, they tend to sound best in the corners or along the side walls due to how they load the room.
Ah, and I'll also stipulate that this applies less to very deep bass like 20hz-40hz. For that range, a sealed sub works wonders. Anything above 40hz though and you really should be using OB bass to match the OB mids/highs.