The four π loads the driver with a bass-reflex cabinet and the seven π cornerhorn is very large conical horn, with the motor chamber incorporating a Helmholtz resonator. But the ten π is not large compared to the wavelengths it reproduces, and this is what makes it more sensitive. This is true of all portable basshorns - They're really somewhat undersized, so placement and choice of drivers becomes more important than otherwise would be the case.

Anyway, the point is that the Selenium 1505 has been used in the Professional Series four π and seven π cabinets with success, but I'm not sure whether it has been used in a ten π cabinet. It may be perfectly suited for this design, but performance in a seven π isn't complete assurance that it will work as well in a ten π, unless it is used in eighth-space. Maybe someone here has used the Selenium 1505 in a ten π horn and can confirm its suitability for this particular purpose.