Low frequency requires large cabinets. Each Driver will require a certain volume to approach its Fs (resonant frequency in free air). When you add multiple Drivers, you need to increase the volume of the cabinet accordingly (related to the parameter known as Vas).
Now to complicate things more, number of Drivers will improve power handling, and if done properly will increase Sensitivity, however this does not improve extension of the FR.
Also, being ported or sealed will have an impact on size, too. A sealed cabinet will be smaller, and have a much higher F3 than a ported cabinet will assuming it is optimized smartly.
As I’m sure you are aware, modern Centers are mostly designed with limited size in mind. Large Centers are only minimally marketable. Add to this that most HT users will be adding a Sub or 2, thus crossing the Speaker over to a Sub, then hopefully you begin to see the tradeoff a manufacturer might make.
Some quick math will reveal that the internal volume of that Speaker is less than 2cu.ft. total. Assuming the Mids are separated from the woofers, that removes more internal volume from the woofers: by how much I won’t guess. But taken into consideration, that will be far less than even .4 cu.ft per driver after other volume losses.
Realistically, I’m not surprised at all to see such FR on that Speaker.
Based on other designs I’ve seen that place two Mids side by side like that, I also wouldn’t be surprised to see poor dispersion with some cancelations and lobing associated with such designs.
I know you aren’t asking, but I’ll give it anyway: unless you can find a good set of measurements for this Speaker, I would keep shopping.
