doing it in english rather than dutch for convenience (international audience)
So let me begin with saying they're huge (a folded horn subwoofer trait), the wheels are a must!
Hooking them up at home (25m2) resulted in a poor response under 40hz, another trait of horn loaded subwoofers when put in a small room
in a big (ball)room they are awesome, you will get chest thumping tight dry bass in the 40-80hz range, you really don't want them to run above 80hz and not under 35hz, so an audio processor comes in handy
i put them on a 35hz-75hz crossover and for the 0-35 hz a steep cutoff, these boxes really don't want to run 30hz or lower without nasty unloading symptoms and port noise when running high load.
actual db/SPL rating with above crossover setting is 127db/SPL 1 meter MEASURED, very respectable for the price, listed db/SPL is not reachable without blowing them up.
so in short, very good, needs an Audio processor and i must say the handles are not satisfactory, that's why 4 stars