four responses of an 18" driver in a baffle hole cutout.
first is no hole. just mounted on the wall flush.
next is hole that is 25cm deep and area equal to the cone.
next is hole that is 25cm deep and area equal to half the cone.
last is hole that is 50cm deep and area equal to half the cone.
so, the smaller the hole, the higher the peak, the deeper the hole, the lower in frequency where it occurs.
hornresp overshoots the resonant peaks, but it provides some sense for what is going on.