If Xmax shouldn't be exceeded, why have a Xlim?

Ok, again got your point Elliot. Intertechnik just called to confirm that a Dayton DATS will arrive at my doorstep in 8 weeks. So I'll be back on here in august, hopefully with some gained knowledge! Thanks for the replies again. Keep up the good work.
Regards,
Robert

For those interested, some kind of 'rectification': after a day of swapping and testing it has turned out that there was a tiny little air gap between basket and baffle. Only at 165 Hz, this leak would make an agressive, loud rattling sound. At all other frequencies it was silent. So on techno, it sounded very much like if the coil were hitting the plate on every beat. The Nd9300 that I got don't have a back gasket. So that's why the problem never arose with PD186, which has a back gasket. Without an air leak, there's hardly any difference noticable, which is what I'd expect with two similar drivers in horns.

So the 18sound was not reaching it's Xlim at all.

Another problem discovered in the process: the chassis holes on the 18sound driver are just about big enough to pass the head of a DIN912 M6 allen screw, if you don't use washers!

The original cardboard box contains a sheet of air tight plastic foam that looks just perfect for cutting out some gaskets ;-).

Conversely, this is entirely possible if you’re very smart about designing the cabinet and the driver together for a desired non-linear response. However, it requires the use of a very accurate lumped element model of the entire loudspeaker, including non-linear and linear distortions plus thermal compression and such.

You also have to be willing to use ‘wrong’ drivers and work with the non-linearities. For example, you can use over-damped suspension or even very low Bl motors to ensure there’s a large resonant peak at your desired cutoff frequency.

It works better for sealed and bandpass enclosures due to the nature of those cabinets’ effect on loading.

The model can then be used alongside measurements of a prototype to develop mirror filter sets which can be applied in real-time via DSP and relatively inexpensive current or pressure sensors to dynamically correct the response of the cabinet. It’s possible to work towards a pre-configured target, while reducing distortion and having an adaptable filter set as level increases.

You might be surprised how many consumer and automotive audio products use a variation of this method, obviously some better than others. Although since Klippel has been publishing papers on how to do it for over 20 years, maybe not. Plenty of those are available to read on the Klippel site, but be warned there’s a lot of equations ahead.

Typically it’s a method applied to small speakers. IPAL and M-Force use a similar method for large drivers and higher output.

Andre, a friend of mine has a pair of  Beyma loaded 18" DIY subs, they must be close to 30 years old by now. They are very compact CB, with a roughly 50x 50 cm baffle and about 30 cm depth if memory serves me well. 

Please keep Us Reconers busy by grossly overdriving  Your woofers.......Thanx, Troy Bernard  VECTORSONICS