Originally Posted by zheka
it looks like drivers may unload while the output at 20Hz is still way short of the max level. in the few models i tried for the new SI drivers, it's possible to get them beyond Xmex with as little as 200-300W. the DEQ would have to kick in early to protect the drivers which defeats the point imo.
In post #18 LTD02 describes a brilliant idea for moving the corner of the hpf lower down, so that you get full level to 20Hz, may be that can be used.
Then the ordinary hpf can be used, might be better because it has the option of steeper slope, the dynamic is only 12dB/oct.
I was about to say you can use the dynamic filter, but, of course, then you would have a level-dependent eq down low, and that may not be desirable.
If you have a model of the sub in some simulator software, this can be simulated, to some extent.
Just add the filters, and observe the excursion.
The problem is that it is difficult to model the exact behavior of the driver, as the Bl is very nonlinear at high excursions and high power, and this has a very significant effect on what excursion you actually will get.
Reduced Bl may actually lead to significantly larger excursion when you operate relatively close to the tuning frequency of the system.
Just try to simulate with a lower Bl, and (typically) you will see lower spl, but higher excursion.
Assuming that we here deal with some kind of ported design - a ported box or some variation of horn.
Far below tuning the only thing that limits excursion is the stiffness of the suspension, and the driving force is the Bl and the current that flows through the voice coil.
Low-fs drivers can reach xmax (or xmech) with say quite less than 100W when unloaded.