Originally Posted by
reVintage
The 40Hz peak is not a room-resonant, itīs the ports resonance. By changing port-area it can be moved around a little, but also affects low-end drop. The dip at ca 70Hz is also due to 4560īs design. One can expect acceptable frequency-responce(for hajfaj) from 100-125Hz. So go for a sub from just over 100Hz. If the 4560 is corner-placed it can be used a little lower though.
If one reduces the chambervolume to ca 100dm3 instead of the original 220dm3, things begin to look really nice as the response gets straighter with the big dip and peaks smoothened out. We will be able to x/o against the sub at 60-70Hz.