From fundamentals: A loudspeaker in a box is a spring-mass-damper
situation. The mass is the mass of the diaphragms, voice coils, and
part of the surround and spider. The spring is the air in the
enclosure, which provides a restoring force to the diaphragms. This
gives a certain fundamental resonance, which is the low frequency
corner that the speaker can reproduce.
Now, if you put a partition in the middle, you halve the moving mass,
but you also halve the air volume. Intuitively the fundamental
resonance should not change, because the two factors cancel out. I
would verify this by finding the resonance with and without the
partition using an oscillator, AC voltmenter, and resistor.