There seems to be a mistake with polarity, if I read the graphs right. To get monopole or bipole operation in low freq, both woofers must be pumping air in/out of the box at same time. In the graph they are in opposite polarity, which means cancelling!
I have some JBL PD5322s that use the left configuration above and they work well to 300hz or so. They're mounted about 14" apart.
I also have IB loaded PPSL similar to Weltersys. They go goofy above 100hz. I cross them at 90 for very good results.
The longest manifold dimension and\or driver distance difference are important and can't be ignored.
another interesting configuration, depending on the venue, if there are useable corners and the sub can be positioned right in the corner with opposing woofers firing on either side could be very affective and simple design.
Ignore the +/-. The woofers are purposely left unconnected. The symbols are left overs from what i started with. Drivers need to be acoustically in phase but mechanically opposed.
dave
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